Optical fiber

Optical fiberFrom Wikipedia, the free encyclopedia Jump to: navigation, search A bundle of optical fibers A TOSLINK fiber optic audio cable being illuminated at one end An optical fiber or optical fibre is a thin, flexible, transparent fiber that acts as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communication. Fibers are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference. Fibers are also used for illumination, and are wrapped in bundles so they can be used to carry images, thus allowing viewing in tight spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers. Optical fiber typically consists of a transparent core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by total internal reflection. This causes the fiber to act as a waveguide. Fibers which support many propagation paths or transverse modes are called multi-mode fibers (MMF), while those which can only support a single mode are called single-mode fibers (SMF). Multi-mode fibers generally have a larger core diameter, and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 1,050 meters (3,440 ft). Joining lengths of optical fiber is more complex than joining electrical wire or cable. The ends of the fibers must be carefully cleaved, and then spliced together either mechanically or by fusing them together with heat. Special optical fiber connectors are used to make removable connections. Contents [hide] • • 1 History 2 Applications ○ ○ ○ 2.1 Optical fiber communication 2.2 Fiber optic sensors 2.3 Other uses of optical fibers 3.1 Index of refraction 3.2 Total internal reflection 3.3 Multi-mode fiber 3.4 Single-mode fiber 3.5 Special-purpose fiber 4.1 Light scattering 4.2 UV-Vis-IR absorption 5.1 Materials     • 3 Principle of operation ○ ○ ○ ○ ○ • 4 Mechanisms of attenuation ○ ○ • 5 Manufacturing ○ 5.1.1 Silica 5.1.2 Fluorides 5.1.3 Phosphates 5.1.4 Chalcogenides ○ ○ • ○ ○ ○ 5.2 Process 5.3 Coatings 6.1 Optical fiber cables 6.2 Termination and splicing 6.3 Free-space coupling 6 Practical issues ○ • • • • • • 6.4 Fiber fuse 7 Example 8 Electric power transmission 9 See also 10 References 11 Further reading 12 External links [edit] History Daniel Colladon first described this "light fountain" or "light pipe" in an 1842 article titled On the reflections of a ray of light inside a parabolic liquid stream. This particular illustration comes from a later article by Colladon, in 1884. Fiber optics, though used extensively in the modern world, is a fairly simple and old technology. Guiding of light by refraction, the principle that makes fiber optics possible, was first demonstrated by Daniel Colladon and Jacques Babinet in Paris in the early 1840s. John Tyndall included a demonstration of it in his public lectures in London a dozen years later.[1] Tyndall also wrote about the property of total internal reflection in an introductory book about the nature of light in 1870: "When the light passes from air into water, the refracted ray is bent towards the perpendicular... When the ray passes from water to air it is bent from the perpendicular... If the angle which the ray in water encloses with the perpendicular to the surface be greater than 48 degrees, the ray will not quit the water at all: it will be totally reflected at the surface.... The angle which marks the limit where total reflection begins is called the limiting angle of the medium. For water this angle is 48°27', for flint glass it is 38°41', while for diamond it is 23°42'."[2][3] Practical applications, such as close internal illumination during dentistry, appeared early in the twentieth century. Image transmission through tubes was demonstrated independently by the radio experimenter Clarence Hansell and the television pioneer John Logie Baird in the 1920s. The principle was first used for internal medical examinations by Heinrich Lamm in the following decade. In 1952, physicist Narinder Singh Kapany conducted experiments that led to the invention of optical fiber. Modern optical fibers, where the glass fiber is coated with a transparent cladding to offer a more suitable refractive index, appeared later in the decade.[1] Development then focused on fiber bundles for image transmission. The first fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Wilbur Peters, and Lawrence E. Curtiss, researchers at the University of Michigan, in 1956. In the process of developing the gastroscope, Curtiss produced the first glass-clad fibers; previous optical fibers had relied on air or impractical oils and waxes as the low-index cladding material. A variety of other image transmission applications soon followed. In the late 19th and early 20th centuries, light was guided through bent glass rods to illuminate body cavities. Alexander Graham Bell invented a 'Photophone' to transmit voice signals over an optical beam.[4] Jun-ichi Nishizawa, a Japanese scientist at Tohoku University, also proposed the use of optical fibers for communications in 1963, as stated in his book published in 2004 in India.[5] Nishizawa invented other technologies which contributed to the development of optical fiber communications, such as the graded-index optical fiber as a channel for transmitting light from semiconductor lasers.[6][7] Charles K. Kao and George A. Hockham of the British company Standard Telephones and Cables (STC) were the first to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer (dB/km), allowing fibers to be a practical medium for communication.[8] They proposed that the attenuation in fibers available at the time was caused by impurities, which could be removed, rather than fundamental physical effects such as scattering. They correctly and systematically theorized the light-loss properties for optical fiber, and pointed out the right material to manufacture such fibers — silica glass with high purity. This discovery led to Kao being awarded the Nobel Prize in Physics in 2009.[9] NASA used fiber optics in the television cameras sent to the moon. At the time such use in the cameras was 'classified confidential' and only those with the right security clearance or those accompanied by someone with the right security clearance were permitted to handle the cameras.[10] The crucial attenuation limit of 20 dB/km was first achieved in 1970, by researchers Robert D. Maurer, Donald Keck, Peter C. Schultz, and Frank Zimar working for American glass maker Corning Glass Works, now Corning Incorporated. They demonstrated a fiber with 17 dB/km attenuation by doping silica glass with titanium. A few years later they produced a fiber with only 4 dB/km attenuation using germanium dioxide as the core dopant. Such low attenuation ushered in optical fiber telecommunication. In 1981, General Electric produced fused quartz ingots that could be drawn into fiber optic strands 25 miles (40 km) long.[11] Attenuation in modern optical cables is far less than in electrical copper cables, leading to long-haul fiber connections with repeater distances of 70–150 kilometers (43–93 mi). The erbium-doped fiber amplifier, which reduced the cost of long-distance fiber systems by reducing or eliminating optical-electrical-optical repeaters, was co-developed by teams led by David N. Payne of the University of Southampton and Emmanuel Desurvire at Bell Labs in 1986. Robust modern optical fiber uses glass for both core and sheath and is therefore less prone to aging processes. It was invented by Gerhard Bernsee of Schott Glass in Germany in 1973.[12] The emerging field of photonic crystals led to the development in 1991 of photonic-crystal fiber[13] which guides light by diffraction from a periodic structure, rather than by total internal reflection. The first photonic crystal fibers became commercially available in 2000. such as 4 pair Cat-5 Ethernet cabling. or because many sensors can be multiplexed along the length of a fiber by using different wavelengths of light for each sensor. Sensors that vary the intensity of light are the simplest. fiber is used to connect a non-fiberoptic sensor to a measurement system. each using a different wavelength of light (wavelength-division multiplexing (WDM)).[20] Bell Labs also broke a 100 Petabit per second kilometer barrier (15. or by sensing the time delay as light passes along the fiber through each sensor. there is no cross-talk between signals in different cables and no pickup of environmental noise. wavelength or transit time of light in the fiber. temperature. They can also be used in environments where explosive fumes are present. [edit] Applications [edit] Optical fiber communication Main article: Fiber-optic communication Optical fiber can be used as a medium for telecommunication and networking because it is flexible and can be bundled as cables. or the fact that no electrical power is needed at the remote location. The current laboratory fiber optic data rate record.1 Tbit/s over a single 240 km fiber (multiplexing 432 channels. if required. polarization. The net data rate (data rate without overhead bytes) per fiber is the per-channel data rate reduced by the FEC overhead. is multiplexing 155 channels. equating to 171 Gbit/s per channel). fiber may be used because of its small size. fiberoptic cabling can be used to save space in cable ducts.[15][16] although 10 or 40 Gbit/s is typical in deployed systems. provide distributed sensing over distances of up to one meter.5 Tbit/s over a single 7000 km fiber). which makes fiber a good solution for protecting communications equipment located in high voltage environments such as power generation facilities. and there are concentric dual core fibers that are said to be tap-proof. In other cases. held by Bell Labs in Villarceaux. It is especially advantageous for long-distance communications. This allows long distances to be spanned with few repeaters.[vague] Fiber is also immune to electrical interference.[21] For short distance applications. Optical fibers can be used as sensors to measure strain. phase. or metal communication structures prone to lightning strikes. because light propagates through the fiber with little attenuation compared to electrical cables. Additionally. A particularly useful feature of such fiber optic sensors is that they can. This is because a single fiber can often carry much more data than many electrical cables. France. multiplied by the number of channels (usually up to eighty in commercial dense WDM systems as of 2008[update]). Depending on the application.[17][18] Each fiber can carry many independent channels. Wiretapping is more difficult compared to electrical connections.[14] Photonic crystal fibers can carry higher power than conventional fibers and their wavelength-dependent properties can be manipulated to improve performance. such as creating a network within an office building.[22] [edit] Fiber optic sensors Main article: Fiber optic sensor Fibers have many uses in remote sensing. each carrying 100 Gbit/s over a 7000 km fiber. pressure and other quantities by modifying a fiber so that the quantity to be measured modulates the intensity. Time delay can be determined using a device such as an optical time-domain reflectometer. In some applications.[19] Nippon Telegraph and Telephone Corporation have also managed 69. without danger of ignition. . the sensor is itself an optical fiber. since only a simple source and detector are required. Non-armored fiber cables do not conduct electricity. the per-channel light signals propagating in the fiber have been modulated at rates as high as 111 gigabits per second by NTT. where the extreme electromagnetic fields present make other measurement techniques impossible. An example is the measurement of temperature inside aircraft jet engines by using a fiber to transmit radiation into a radiation pyrometer located outside the engine. velocity.Extrinsic fiber optic sensors use an optical fiber cable. to transmit modulated light from either a non-fiber optical sensor. The fiber optic gyroscope (FOG) has no moving parts and exploits the Sagnac effect to detect mechanical rotation. A solid state version of the gyroscope using the interference of light has been developed. A common use for fiber optic sensors are in advanced intrusion detection security systems. Extrinsic sensors are used to measure vibration. displacement. and if an intrusion has occurred an alarm is triggered by the fiber optic security system. where the light is transmitted along the fiber optic sensor cable. Extrinsic sensors can also be used in the same way to measure the internal temperature of electrical transformers. normally a multi-mode one. which is placed on a fence. acceleration. pipeline or communication cabling. rotation. torque. and twisting. [edit] Other uses of optical fibers A frisbee illuminated by fiber optics Light reflected from optical fiber illuminates exhibited model . This return signal is digitally processed to identify if there is a disturbance. and the returned signal is monitored and analysed for disturbances. A major benefit of extrinsic sensors is their ability to reach places which are otherwise inaccessible. or an electronic sensor connected to an optical transmitter. Swarovski boutiques use optical fibers to illuminate their crystal showcases from many different angles while only employing one light source. Optical fibers doped with a wavelength shifter are used to collect scintillation light in physics experiments. In spectroscopy. art. making the dots slightly brighter than the surroundings. and shotguns. The doped fiber is optically pumped with a second laser wavelength that is coupled into the line in addition to the signal wave. made in such a way that ambient light falling on the length of the fiber is concentrated at the tip. The process that causes the amplification is stimulated emission. optical fibers are used to route sunlight from the roof to other parts of the building (see non-imaging optics). is the use of short pieces of optical fiber for contrast enhancement dots. Fiber optic sights can now be found on handguns. Optical fiber is an intrinsic part of the lighttransmitting concrete building product. Optical fiber illumination is also used for decorative applications. both as aftermarket accessories and a growing number of factory guns. Optical fiber is also used in imaging optics. A growing trend in iron sights for arms. or gasses. sometimes along with lenses. In some buildings. A coherent bundle of fibers is used. and artificial Christmas trees. a spectrometer can be used to study objects that are too large to fit inside. but many makers offer sights that use fiber optics on front and rear sights. thin imaging device called an endoscope. A spectrometer analyzes substances by bouncing light off of and through them. They are used as light guides in medical and other applications where bright light needs to be shone on a target without a clear line-ofsight path. LiTraCon. rifles. including signs. Examples of this are electronics in highpowered antenna elements and measurement devices used in high voltage transmission equipment. optical fiber bundles are used to transmit light from a spectrometer to a substance which cannot be placed inside the spectrometer itself. which is used to view objects through a small hole. By using fibers.[26] .Fiber optic front sight on a hand gun Fibers are widely used in illumination applications. Medical endoscopes are used for minimally invasive exploratory or surgical procedures (endoscopy). for a long. Optical fiber can be used to supply a low level of power (around one watt) to electronics situated in a difficult electrical environment. Rare-earth doped optical fibers can be used to provide signal amplification by splicing a short section of doped fiber into a regular (undoped) optical fiber line.[23][24][25] An optical fiber doped with certain rare earth elements such as erbium can be used as the gain medium of a laser or optical amplifier. in order to analyze its composition. Both wavelengths of light are transmitted through the doped fiber. This method is most commonly used in front sights. such as jet engine interiors. Industrial endoscopes (see fiberscope or borescope) are used for inspecting anything hard to reach. which transfers energy from the second pump wavelength to the signal wave. or reactions which occur in pressure vessels. To confine the optical signal in the core. means that there is an absolute minimum delay of 60 milliseconds (or around 1/16 of a second) between when one caller speaks to when the other hears.000 kilometres (186 thousand miles) per second. The typical value for the cladding of an optical fiber is 1. the refractive index of the core must be greater than that of the cladding. The core value is typically 1. (Of course the fiber in this case will probably travel a longer route. The index of refraction of a vacuum is therefore 1.[edit] Principle of operation An optical fiber is a cylindrical dielectric waveguide (nonconducting waveguide) that transmits light along its axis. and there will be additional delays due to communication equipment switching and the process of encoding and decoding the voice onto the fiber). to travel 1000 kilometers in fiber. Thus a phone call carried by fiber between Sydney and New York. Single-mode fiber has a small NA. The speed of light in a vacuum is about 300. in the core of the fiber. the signal will take 5 milliseconds to propagate. This range of angles is called the acceptance cone of the fiber. both of which are made of dielectric materials. Fiber with a larger NA requires less precision to splice and work with than fiber with a smaller NA. The larger the index of refraction. only light that enters the fiber within a certain range of angles can travel down the fiber without leaking out. The boundary between the core and cladding may either be abrupt. Index of refraction is calculated by dividing the speed of light in a vacuum by the speed of light in some other medium.46[citation needed]. The fiber consists of a core surrounded by a cladding layer. the light will be completely reflected. In simpler terms. The size of this acceptance cone is a function of the refractive index difference between the fiber's core and cladding. or gradual. the slower light travels in that medium. by definition. in graded-index fiber. The sine of this maximum angle is the numerical aperture (NA) of the fiber. [edit] Multi-mode fiber . such as outer space. [edit] Total internal reflection Main article: Total internal reflection When light traveling in a dense medium hits a boundary at a steep angle (larger than the "critical angle" for the boundary). Light travels along the fiber bouncing back and forth off of the boundary.48[citation needed]. or travel. Because the light must strike the boundary with an angle greater than the critical angle. Or to put it another way. This effect is used in optical fibers to confine light in the core. [edit] Index of refraction Main article: Refractive index The index of refraction is a way of measuring the speed of light in a material. a 12000 kilometer distance. there is a maximum angle from the fiber axis at which light may enter the fiber so that it will propagate. From this information. in stepindex fiber. by the process of total internal reflection. a good rule of thumb is that signal using optical fiber for communication will travel at around 200 million meters per second. Light travels fastest in a vacuum. In graded-index fiber. The critical angle (minimum angle for total internal reflection) is determined by the difference in index of refraction between the core and cladding materials. In a step-index multi-mode fiber. Rays that meet the core-cladding boundary at a high angle (measured relative to a line normal to the boundary). However. the index of refraction in the core decreases continuously between the axis and the cladding. rays of light are guided along the fiber core by total internal reflection. often reported as a numerical aperture. The resulting curved paths reduce multi-path dispersion because high angle rays pass more through the lower-index periphery of the core. A laser bouncing down an acrylic rod. and do not convey light and hence information along the fiber. This ideal index profile is very close to a parabolic relationship between the index and the distance from the axis.The propagation of light through a multi-mode optical fiber. are completely reflected. Optical fiber types. illustrating the total internal reflection of light in a multi-mode optical fiber. allowing efficient coupling of light into the fiber. This causes light rays to bend smoothly as they approach the cladding. this high numerical aperture increases the amount of dispersion as rays at different angles have different path lengths and therefore take different times to traverse the fiber. rather than reflecting abruptly from the core-cladding boundary. Rays that meet the boundary at a low angle are refracted from the core into the cladding. . A high numerical aperture allows light to propagate down the fiber in rays both close to the axis and at various angles. Such fiber is called multi-mode fiber. rather than the high-index center. Main article: Multi-mode optical fiber Fiber with large core diameter (greater than 10 micrometers) may be analyzed by geometrical optics. The critical angle determines the acceptance angle of the fiber. greater than the critical angle for this boundary. The index profile is chosen to minimize the difference in axial propagation speeds of the various rays in the fiber. from the electromagnetic analysis (see below). The normalized frequency V for this fiber should be less than the first zero of the Bessel function J0 (approximately 2. Photonic-crystal fiber is made with a regular pattern of index variation (often in the form of cylindrical holes that run along the length of the fiber). 3.405). is manufactured with core diameters as small as 50 micrometers and as large as hundreds of micrometers. Such fiber uses diffraction effects instead of or in addition to total internal reflection. The results of such modeling of multi-mode fiber approximately agree with the predictions of geometric optics. which shows that such fiber supports more than one mode of propagation (hence the name). the fiber supports one or more confined transverse modes by which light can propagate along the fiber. to confine light to the fiber's core. The electromagnetic analysis may also be required to understand behaviors such as speckle that occur when coherent light propagates in multi-mode fiber. The waveguide analysis shows that the light energy in the fiber is not completely confined in the core. especially in single-mode fibers. so that this fiber actually supports a small number of additional modes at visible wavelengths. Instead. Jacket: 400 µm dia. The properties of the fiber can be tailored to a wide variety of applications. Core: 8 µm diameter 2. 4. The mode structure depends on the wavelength of the light used.[edit] Single-mode fiber The structure of a typical single-mode fiber. Instead. [edit] Special-purpose fiber Some special-purpose optical fiber is constructed with a non-cylindrical core and/or cladding layer. . Multi-mode fiber. Main article: Single-mode optical fiber Fiber with a core diameter less than about ten times the wavelength of the propagating light cannot be modeled using geometric optics. usually with an elliptical or rectangular cross-section. The behavior of larger-core multi-mode fiber can also be modeled using the wave equation. 1. by solution of Maxwell's equations as reduced to the electromagnetic wave equation. if the fiber core is large enough to support more than a few modes. Fiber supporting only one mode is called single-mode or monomode fiber. it must be analyzed as an electromagnetic structure. by comparison. Cladding: 125 µm dia. Buffer: 250 µm dia. These include polarizationmaintaining fiber and fiber designed to suppress whispering gallery mode propagation. a significant fraction of the energy in the bound mode travels in the cladding as an evanescent wave. As an optical waveguide. The most common type of single-mode fiber has a core diameter of 8–10 micrometers and is designed for use in the near infrared. much research has gone into both limiting the attenuation and maximizing the amplification of the optical signal. Attenuation coefficients in fiber optics usually use units of dB/km through the medium due to the relatively high quality of transparency of modern optical transmission media. The medium is usually a fiber of silica glass that confines the incident light beam to the inside.[edit] Mechanisms of attenuation Light attenuation by ZBLAN and silica fibers Main article: Transparent materials Attenuation in fiber optics. Thus. [edit] Light scattering Specular reflection . is the reduction in intensity of the light beam (or signal) with respect to distance traveled through a transmission medium. Attenuation is an important factor limiting the transmission of a digital signal across large distances. Empirical research has shown that attenuation in optical fiber is caused primarily by both scattering and absorption. also known as transmission loss. as well as glasses and ceramics. can cause light rays to be reflected in random directions. in addition to pores. Light scattering depends on the wavelength of the light being scattered.[27] At high optical powers. In (poly)crystalline materials such as metals and ceramics. one emerging school of thought is that a glass is simply the limiting case of a polycrystalline solid. This phenomenon has given rise to the production of transparent ceramic materials. Indeed. Similarly.Diffuse reflection The propagation of light through the core of an optical fiber is based on total internal reflection of the lightwave. Within this framework. This same phenomenon is seen as one of the limiting factors in the transparency of IR missile domes. it depends on whether the electron orbitals are spaced (or "quantized") such that they can absorb a quantum of light (or photon) of a specific wavelength or frequency in the ultraviolet (UV) or visible ranges. and it is typically characterized by wide variety of reflection angles. Thus. in a manner similar to that responsible for the appearance of color. "domains" exhibiting various degrees of short-range order become the building blocks of both metals and alloys. limits to spatial scales of visibility arise. Rough and irregular surfaces. depending on the frequency of the incident light-wave and the physical dimension (or spatial scale) of the scattering center. Primary material considerations include both electrons and molecules as follows: 1) At the electronic level. most of the internal surfaces or interfaces are in the form of grain boundaries that separate tiny regions of crystalline order. attenuation results from the incoherent scattering of light at internal surfaces and interfaces. the scattering of light in optical quality glass fiber is caused by molecular level irregularities (compositional fluctuations) in the glass structure. . attenuation or signal loss can also occur due to selective absorption of specific wavelengths. Distributed both between and within these domains are micro-structural defects which will provide the most ideal locations for the occurrence of light scattering.[28][29] [edit] UV-Vis-IR absorption In addition to light scattering. which is typically in the form of some specific micro-structural feature. This is what gives rise to color. This is called diffuse reflection or scattering. Thus. even at the molecular level. the scattering no longer occurs to any significant extent. It has recently been shown that when the size of the scattering center (or grain boundary) is reduced below the size of the wavelength of the light being scattered. Since visible light has a wavelength of the order of one micrometre (one millionth of a meter) scattering centers will have dimensions on a similar spatial scale. scattering can also be caused by nonlinear optical processes in the fiber. A high transparency in the 1. and this high attenuation limits the range of POF-based systems. particularly around 1. fluoroaluminate. [edit] Silica Silica exhibits fairly good optical transmission over a wide range of wavelengths. or one of its harmonics. Reflection and transmission of light waves occur because the frequencies of the light waves do not match the natural resonant frequencies of vibration of the objects.5. radio and microwave ranges. it depends on the frequencies of atomic or molecular vibrations or chemical bonds.5 μm. they will selectively absorb different frequencies (or portions of the spectrum) of infrared (IR) light. Plastic optical fibers (POF) are commonly step-index multi-mode fibers with a core diameter of 0. Alternatively. such as fluorozirconate. 1 dB/m or higher. a high OH concentration is better for transmission in the ultraviolet (UV) region. Silica and fluoride glasses usually have refractive indices of about 1. The design of any optically transparent device requires the selection of materials based upon knowledge of its properties and limitations. all materials are bounded by limiting regions of absorption caused by atomic and molecular vibrations (bond-stretching)in the far-infrared (>10 µm). Typically the index difference between core and cladding is less than one percent. Since different atoms and molecules have different natural frequencies of vibration.g. but some other materials.4-μm region is achieved by maintaining a low concentration of hydroxyl groups (OH). far IR. When IR light of these frequencies strikes an object. The selective absorption of infrared (IR) light by a particular material occurs because the selected frequency of the light wave matches the frequency (or an integer multiple of the frequency) at which the particles of that material vibrate. the energy is either reflected or transmitted. and has a fairly broad glass transformation range. [edit] Manufacturing [edit] Materials Glass optical fibers are almost always made from silica. These factors will determine the capacity of the material transmitting longer wavelengths in the infrared (IR). POF typically have higher attenuation coefficients than glass fibers.2) At the atomic or molecular level. are used for longer-wavelength infrared or other specialized applications.5 millimeters or larger. multi-phonon absorption occurs when two or more phonons simultaneously interact to produce electric dipole moments with which the incident radiation may couple. One other advantage is that fusion splicing and cleaving of silica fibers is relatively effective. and whether or not the atoms or molecules exhibit long-range order. Thus. These dipoles can absorb energy from the incident radiation. Si-O bond) in the far-infrared. Hence. In the nearinfrared (near IR) portion of the spectrum. silica can have extremely low absorption and scattering losses of the order of 0. They are the result of the interactive coupling between the motions of thermally induced vibrations of the constituent atoms and molecules of the solid lattice and the incident light wave radiation. how close-packed its atoms or molecules are. but some materials such as the chalcogenides can have indices as high as 3. reaching a maximum coupling with the radiation when the frequency is equal to the fundamental vibrational mode of the molecular dipole (e. and chalcogenide glasses as well as crystalline materials like sapphire. Silica can be drawn into fibers at reasonably high temperatures. Silica fiber also has high mechanical strength against both pulling and . The lattice [disambiguation needed] absorption characteristics observed at the lower frequency regions (mid IR to far-infrared wavelength range) define the long-wavelength transparency limit of the material.2 dB/km. Their best attribute is that they lack the absorption band associated with the hydroxyl (OH) group (3200–3600 cm−1).g. which are transparent only up to about 2 μm. They are advantageous especially in the mid-infrared (2000–5000 nm) range. Particularly for active fibers. Their main technological application is as optical waveguides in both planar and fiber form. Both the fiber core and cladding are typically doped. Doping is also possible with laseractive ions (for example. Later. fiber amplifiers. HMFGs were initially slated for optical fiber applications. as required for medical applications (e. they are not only difficult to manufacture. ophthalmology and dentistry). provided that the fiber is not too thick and that the surfaces have been well prepared during processing. These include mid-IR spectroscopy. fluoride fibers can be used for guided lightwave transmission in media such as YAG (yttria-alumina garnet) lasers at 2. Because of these properties silica fibers are the material of choice in many optical applications. Even simple cleaving (breaking) of the ends of the fiber can provide nicely flat surfaces with acceptable optical quality. Silica glass can be doped with various materials. fiber lasers. but are quite fragile. In particular. Silica fiber also exhibits a high threshold for optical damage. the utility of fluoride fibers for various other applications was discovered.[30][31][32][33][34][35][36][37] [edit] Fluorides Fluoride glass is a class of non-oxide optical quality glasses composed of fluorides of various metals. which is present in nearly all oxide-based glasses. because it exhibits a low solubility for rare earth ions. This can lead to quenching effects due to clustering of dopant ions. This property ensures a low tendency for laser-induced breakdown. rare earth-doped fibers) in order to obtain active fibers to be used. Also.g. However. for example.9 μm. and have poor resistance to moisture and other environmental attacks. and imaging. with Germanium dioxide (GeO2) or Aluminium oxide (Al2O3)) or to lower it (e. composed of zirconium. lanthanum. aluminium. and sodium fluorides. This is important for fiber amplifiers when utilized for the amplification of short pulses. Because of their low viscosity. Thus. pure silica is usually not a very suitable host glass. such low losses were never realized in practice. Silica is also relatively chemically inert. germanosilicate.g.even bending.[38][39] [edit] Phosphates . The large efforts which have been put forth in the development of various types of silica fibers have further increased the performance of such fibers over other materials. an aluminosilicate. it is very difficult to completely avoid crystallization while processing it through the glass transition (or drawing the fiber from the melt).g. and the fragility and high cost of fluoride fibers made them less than ideal as primary candidates. An example of a heavy metal fluoride glass is the ZBLAN glass group. so that the entire assembly (core and cladding) is effectively the same compound (e. phosphosilicate or borosilicate glass). fiber optic sensors. and fiber-optic sensors. Aluminosilicates are much more effective in this respect. such as communications (except for very short distances with plastic optical fiber). in fiber amplifiers or laser applications. with fluorine or Boron trioxide (B2O3)). although heavy metal fluoride glasses (HMFG) exhibit very low optical attenuation. thermometry. because the intrinsic losses of a mid-IR fiber could in principle be lower than those of silica fibers. barium. it is not hygroscopic (does not absorb water). One purpose of doping is to raise the refractive index (e. Phosphate glasses can be advantageous over silica glasses for optical fibers with a high concentration of doping rare earth ions. [edit] Process . metallic or semiconducting. which crystallizes in at least four different forms. The most familiar polymorph (see figure) comprises molecules of P4O10.[40][41] [edit] Chalcogenides The chalcogens—the elements in group 16 of the periodic table—particularly sulfur (S). in that they can be crystalline or amorphous. Instead of the SiO4 tetrahedra observed in silicate glasses. A mix of fluoride glass and phosphate glass is fluorophosphate glass. and conductors of ions or electrons. such as silver.The P4O10 cagelike structure—the basic building block for phosphate glass. selenium (Se) and tellurium (Te)—react with more electropositive elements. the building block for this glass former is Phosphorus pentoxide (P2O5). to form chalcogenides. Phosphate glass constitutes a class of optical glasses composed of metaphosphates of various metals. These are extremely versatile compounds. proof testing. the preform starts as a hollow glass tube approximately 40 centimeters (16 in) long. this technique is called modified chemical vapor deposition (MCVD). is built up on its end. in contrast to earlier techniques where the reaction occurred only on the glass surface. resulting in precise control of the finished fiber's optical properties. An outer secondary coating protects the primary coating against mechanical damage and acts as a barrier to lateral forces. solid preform by heating to about 1800 K (1500 °C. is then placed in a device known as a drawing tower. however constructed. 3000 °F). bringing the temperature of the gas up to 1900 K (1600 °C. The preform is commonly made by three chemical vapor deposition methods: inside vapor deposition. An inner primary coating is designed to act as a shock absorber to minimize attenuation caused by microbending. where the preform tip is heated and the optic fiber is pulled out as a string. which is removed before further processing. whose length is not limited by the size of the source rod. Gases such as silicon tetrachloride (SiCl4) or germanium tetrachloride (GeCl4) are injected with oxygen in the end of the tube." The cladding is coated by a "buffer" that protects it from moisture and physical damage. Sometimes a metallic armour layer is added to provide extra protection. which subsequently deposit on the walls of the tube as soot. Today’s glass optical fiber draw processes employ a dual-layer coating approach. The preform. In outside vapor deposition or vapor axial deposition. After the torch has reached the end of the tube. the tension on the fiber can be controlled to maintain the fiber thickness. In outside vapor deposition the glass is deposited onto a solid rod. The porous preform is consolidated into a transparent. The coatings protect the very delicate strands of glass fiber—about the size of a human hair—and allow it to survive the rigors of manufacturing. For each layer the composition can be modified by varying the gas composition. the glass is formed by flame hydrolysis. and then pulling the preform to form the long. The deposition is due to the large difference in temperature between the gas core and the wall causing the gas to push the particles outwards (this is known as thermophoresis). The oxide particles then agglomerate to form large particle chains. cabling and installation. This process is repeated until a sufficient amount of material has been deposited. outside vapor deposition. which is placed horizontally and rotated slowly on a lathe. thin optical fiber. The gases are then heated by means of an external hydrogen burner. it is then brought back to the beginning of the tube and the deposited particles are then melted to form a solid layer. The buffer is what gets stripped off the fiber for termination or splicing.[42] With inside vapor deposition. a reaction in which silicon tetrachloride and germanium tetrachloride are oxidized by reaction with water (H2O) in an oxyhydrogen flame. 2800 °F). . The torch is then traversed up and down the length of the tube to deposit the material evenly.Illustration of the modified chemical vapor deposition (inside) process Standard optical fibers are made by first constructing a large-diameter preform. and vapor axial deposition. a short seed rod is used. and a porous preform. In vapor axial deposition. where the tetrachlorides react with oxygen to produce silica or germania (germanium dioxide) particles. [edit] Coatings The light is "guided" down the core of the fiber by an optical "cladding" with a lower refractive index that traps light in the core through "total internal reflection. By measuring the resultant fiber width. When the reaction conditions are chosen to allow this reaction to occur in the gas phase throughout the tube volume. with a carefully controlled refractive index profile. These coatings are UVcured urethane acrylate composite materials applied to the outside of the fiber during the drawing process. fiber fatigue can occur. Fiber optic coatings protect the glass fibers from scratches that could lead to strength degradation. dual use as power lines. which is then UV cured. which can ultimately result in fiber failure. Rigid fiber assemblies sometimes put light-absorbing ("dark") glass between the fibers. making FTTX installations more complicated.[43][44] Modern cables come in a wide variety of sheathings and armor. [edit] Practical issues [edit] Optical fiber cables An optical fiber cable Main article: Optical fiber cable In practical fibers. and wet-on-wet. External fiber optic coatings protect glass optical fiber from environmental conditions that can affect the fiber’s performance and long-term durability. high voltage isolation. designed for applications such as direct burial in trenches. The cost of small fiber-count pole-mounted cables has greatly decreased due to the high demand for fiber to the home (FTTH) installations in Japan and South Korea. attenuation and resistance to losses caused by microbending. On the inside. and is susceptible to greater signal attenuation. This reduces cross-talk between the fibers. Over time or in extreme conditions. Under proper drawing and coating processes. these factors combine to cause microscopic flaws in the glass fiber to propagate. at speeds approaching 100 kilometers per hour (60 mph). . in which the fiber passes through a primary coating application. to prevent light that leaks out of one fiber from entering another. Three key characteristics of fiber optic waveguides can be affected by environmental conditions: strength. Fiber optic coatings are applied using one of two methods: wet-on-dry. coatings ensure the reliability of the signal being carried and help minimize attenuation due to microbending.[45][not in citation given] installation in conduit.These fiber optic coating layers are applied during the fiber draw. Unevenly coated fiber will experience non-uniform forces when the coating expands or contracts. which may be further surrounded by a jacket layer. the cladding is usually coated with a tough resin buffer layer. and insertion in paved streets. When fiber is subjected to low stresses over a long period. continuous over the length of the application and have constant thickness. usually glass. Fiber cable can be very flexible. This creates a problem when the cable is bent around corners or wound around a spool. but traditional fiber's loss increases greatly if the fiber is bent with a radius smaller than around 30 mm. Fiber optic coatings are applied in concentric layers to prevent damage to the fiber during the drawing application and to maximize fiber strength and microbend resistance. The combination of moisture and scratches accelerates the aging and deterioration of fiber strength. in which the fiber passes through both the primary and secondary coating applications and then goes to UV curing. the coatings are concentric around the fiber. or reduces flare in fiber bundle imaging applications. then through the secondary coating application which is subsequently cured. These layers add strength to the fiber but do not contribute to its optical wave guide properties. submarine installation. lashing to aerial telephone poles. In commercial terms. Then the splicer generates a larger spark that raises the . and emits a small spark between electrodes at the gap to burn off dust and moisture. LC. It is technically called max tensile strength defining how much force can applied to the cable during the installation period. [edit] Termination and splicing ST connectors on multi-mode fiber."Bendable fibers". joining two fibers together to form a continuous optical waveguide. SC.5 mm without adverse impact. which melts the fiber ends together with an electric arc. Optical fibers may be connected to each other by connectors or by splicing.[47] Another important feature of cable is cable withstanding against the horizontally applied force. that is. and the fiber ends are stripped of their protective polymer coating (as well as the more sturdy outer jacket. This type of fiber can be bent with a radius as low as 7. or MTRJ. Telecom Anatolia fiber optic cable versions are reinforced with aramid yarns or glass yarns as intermediary strength member. Optical fibers are connected to terminal equipment by optical fiber connectors. The splicer uses small motors to align the end faces together.657. and are placed into special holders in the splicer. Glass yarns also protect the cable core against rodents and termites. The generally accepted splicing method is arc fusion splicing. have been standardized as ITU-T G. if present). a "mechanical splice" is used.[46] Bendable fiber may also be resistant to fiber hacking. For quicker fastening jobs. Fusion splicing is done with a specialized instrument that typically operates as follows: The two cable ends are fastened inside a splice enclosure that will protect the splices. usage of the glass yarns are more cost effective while no loss in mechanical durability of the cable. in which the signal in a fiber is surreptitiously monitored by bending the fiber and detecting the leakage. Even more bendable fibers have been developed. The ends are cleaved (cut) with a precision cleaver to make them perpendicular. ST. targeted towards easier installation in home environments. The splice is usually inspected via a magnified viewing screen to check the cleaves before and after the splice. These connectors are usually of a standard type such as FC. fusing the ends together permanently. Once the adhesive has set. a laser diode. with the gel surrounding the point where the two piece meet inside the connector very little light loss is exposed. terminating fiber optic cables was very labor intensive. The mating mechanism can be "push and click". and this minimizes optical loss. The location and energy of the spark is carefully controlled so that the molten core and cladding do not mix. Fibers are terminated in connectors so that the fiber end is held at the end face precisely and securely. to make an "angled physical contact" (APC) connection. by directing light through the cladding on one side and measuring the light leaking from the cladding on the other side. The curved surface may be polished at an angle. A fiber-optic connector is basically a rigid cylindrical barrel surrounded by a sleeve that holds the barrel in its mating socket. less labor intensive way of terminating the cables. A splice loss under 0. The complexity of this process makes fiber splicing much more difficult than splicing copper wire. or device to allow the coupling efficiency to be optimized. or can use a lens to allow coupling over an air gap. especially if the gel is used. A typical connector is installed by preparing the fiber end and inserting it into the rear of the connector body. size . many different connectors are on the market and offer an easier. the direction. or screw-in (threaded). To achieve the best injection efficiency into single-mode fiber. the fiber ends are typically polished with a slight curvature. Quick-set adhesive is usually used so the fiber is held securely. In the 1990s. because light that reflects from the angled surface leaks out of the fiber core. For single-mode fiber. which contains a lens that is either accurately positioned with respect to the fiber. which uses a microscope objective lens to focus the light down to a fine point. Mechanical fiber splices are designed to be quicker and easier to install. This is known as a "physical contact" (PC) polish. or is adjustable. Some of the most popular connectors have already been polished from the factory and include a gel inside the connector and those two steps help save money on labor especially on large projects. Such connections have higher loss than PC connections. but greatly reduced back reflection. but there is still the need for stripping. the fiber's end is polished to a mirror finish. or with an optoelectronic device such as a light-emitting diode. The number of parts per connector. a bare fiber end is coupled using a fiber launch system. the resulting loss in signal strength is known as gap loss. Such joints typically have higher optical loss and are less robust than fusion splices. A cleave is made at a required length in order to get as close to the polished piece already inside the connector. In some cases the end of the fiber is polished into a curved form that is designed to allow it to act as a lens. often using a clear index-matching gel that enhances the transmission of light across the joint.temperature above the melting point of the glass. A splice loss estimate is measured by the splicer. All splicing techniques involve the use of an enclosure into which the splice is placed for protection afterward. or a modulator. "turn and latch" ("bayonet").[citation needed] [edit] Free-space coupling It is often necessary to align an optical fiber with another optical fiber. In a laboratory environment. such that when the connectors are mated the fibers touch only at their cores. fiber.1 dB is typical. This can involve either carefully aligning the fiber and placing it in contact with the device. The fiber ends are aligned and held together by a precision-made sleeve. depending on the type of fiber and the application. careful cleaning and precision cleaving. polishing of the fibers. and a strain relief is secured to the rear. APC fiber ends have low back reflection even when disconnected. Fibers with a connector on the end make this process much simpler: the connector is simply plugged into a pre-aligned fiberoptic collimator. A precision translation stage (micro-positioning table) is used to move the lens. Today. position. and the need to oven-bake the epoxy in each connector made terminating fiber optic cables very difficult. Various polish profiles are used. it is especially useful in situations where it is desirable to not have a metallic conductor as in the case of use near MRI machines which produce strong magnetic currents. and this new defect remains reflective so that the damage propagates back toward the transmitter at 1–3 meters per second (4−11 km/h. Aspheric lenses are typically used. [edit] Example Fiber connections can be used for various types of connections. such as undersea cables. can also effectively halt propagation of the fiber fuse. most high definition televisions offer a digital audio optical connection. above 2 megawatts per square centimeter. which ensures laser eye safety in the event of a broken fiber. With properly polished single-mode fibers. 2–8 mph). a "fiber fuse" protection device at the transmitter can break the circuit to prevent any damage. a fiber fuse can occur. 70 to 90% coupling efficiency can be achieved. where high power levels might be used without the need for open fiber control.[50] In situations. The reflection from the damage vaporizes the fiber immediately before the break.and divergence of the beam must all be optimized. when a fiber is subjected to a shock or is otherwise suddenly damaged. This allows the streaming of audio over light. With good beams. using the TOSLink protocol.[52] [edit] See also • • • • • • • • • • • • • • • Cable jetting Data cable Fiber Bragg grating Fibre channel Fiber pigtail Fiber laser Gradient-index optics Interconnect bottleneck Leaky mode Light Peak Modal bandwidth Optical cable Optical communication Optical fiber connector Optical interconnect . The lens needs to be large enough to support the full numerical aperture of the fiber. and must not introduce aberrations in the beam. [edit] Fiber fuse At high optical intensities.[48][49] The open fiber control system.[51] While the efficiency is not nearly that of traditional copper wire. [edit] Electric power transmission Optical fiber can be used to transmit electricity. For example. the emitted beam has an almost perfect Gaussian shape—even in the far field—if a good lens is used. gov/alsj/MSC-SESD-28-105. Ken (2004)..1079280. ISBN 0195108183.130a3558587d56e8fb2275875bac26c8/index.nishizawa .org/portal/site/tionline/menuitem.html. GE Innovation Timeline. 3. "Six Lectures on Light". Philip (2003). ^ Tyndall. ^ "Press Release — Nobel Prize in Physics 2009". The Story of Fiber Optics. p. City of Light. New Delhi. Jeff (1999). ^ http://history.google. ^ "Optical Fiber".sendai. . ^ "New Medal Honors Japanese Microelectrics Industry Leader". http://nobelprize. p. ISBN 007137356X. Regis J (2001). Retrieved 2009-10-07. India: Narosa Publishing House. 4. 10.• • • • • • • • • • Optical mesh network Optical power meter Optical time-domain reflectometer Optoelectronics Parallel optical interface Photonic-crystal fiber Small form-factor pluggable transceiver Soliton. In Bhat.crystal-fiber.966. DasGupta. Notes about Light.nasa. ISBN 8173195676. 27.com/. 114. Retrieved 2008-10-22. 10. 8. 14. http://www. John (1873). "Total Reflexion". http://www. http://www.com/innovation/timeline/index. ^ a b Bates. ^ Hecht. ^ "The History of Crystal fiber A/S". Retrieved April 5. Patent 3. ^ Russell.html. The Nobel Foundation.org/details/notesofcourseofn00tyndrich. Sendai New.google. http://books. Science 299 (5605): 358–62. N. ^ Tyndall. PMID 12532007. Institute of Electrical and Electronics Engineers.jp/soumu/kouhou/s-new-e6/page01.com/?id=4oMu7RbGpqUC&pg=PA114.pdf 11. Amitava.com/? id=2NTpSnfhResC&pg=PA27&lpg=PA27&dq=Junichi+Nishizawa+proposal+on+use+of+optical+fiber. Physics of semiconductor devices. K.archive.1126/science.html. 12. John (1870). Optical Switching and Networking Handbook.org/details/sixlecturesonlig00tynduoft. doi:10. Suto. Crystal Fiber A/S.S. http://www.ge. General Electric Company. 6. Jun-ichi. p. ^ U.archive. http://books.300 "Light conducting fibers of quartz glass" 13.city.org/nobel_prizes/physics/laureates/2009/press. 2009. ^ The Birth of Fiber Optics 5. 7. New York: McGraw-Hill. "Photonic Crystal Fibers". New York: Oxford University Press.ieee. 2. http://www. 9. ^ Nishizawa. Vector soliton Submarine communications cables XENPAK Electronics portal [edit] References 1.xml&.jsp? &pName=institute_level1_article&TheCat=1003&article=tionline/legacy/inst2003/jun03/6w. http://www. Retrieved 2008-10-22. "Terahertz wave generation and light amplification using Raman effect". ^ "1971-1985 Continuing the Tradition". C (1988). Mary (2002). Journal of Non-Crystalline Solids 102: 71. Wiley. Retrieved 18 Dec 2009. p. Mo. http://www... SPIE CR73: 1. Thomson. Peter R. 26.647 (1978) 28.pdf.com/pdfs/SP5619. and Coating of Silica Lightguides". http://www.50715. Spectroscopy. Krause. ^ Bartenev. S. "Strength and fatigue of silica optical fibers". Charles R.1117/12.tb03727. 18. "In situ real-time monitoring of a fermentation reaction using a fiber-optic FT-IR probe" (pdf). Peter J. "Strength. Sep.15. ^ 14 Tbps over a Single Optical Fiber: Successful Demonstration of World's Largest Capacity . M. 2009 20. Daryl (1993). "Mechanical stability of oxide glasses". ^ Proctor. . RP Photonics. doi:10.) (pdf).0085. 36. Matthewson.pdf.1111/j.E. 19. ^ Glasesmenn.11512916. Rüdiger. ^ Siemen's claim to a fiber optic line that can not be tapped. doi:10. JANET Delivers Europe’s First 40 Gbps Wavelength Service 07/09/2007 Retrieved 29 Oct 2009. Zaid. 17. Yao.rp-photonics. ^ Kurkjian. 2008. and by NSN 16. W. ^ Melling. http://www. ”Polarization in Fiber Systems: Squeezing Out More Bandwidth”. and Bennett. ^ Paschotta.com/WorkArea/downloadasset. Proceedings ECOC 2008: pp.com/pdfs/2703_o.11. Arne (2000). Encyclopedia of Laser Physics and Technology. Series A. Strength variations in silica fibers. Proc. Thomson. Peter G. Nonlinear mechanical properties of silica-based optical fibers.1993.R.1016/0022-3093(88)90114-7. I. doi:10. Scattering from infrared missile domes.. pp.corning.140 digital high-definition movies transmitted in one second. "The structure and strength of glass fibers".1364/AO. 2003.002489. 37. 28.. Simpkins.. 23. (1967).372757. http://www. Vol. 31. John M. ^ S.1109/50. G (1968). "Advancements in Mechanical Strength and Reliability of Optical Fibers". ^ Kurkjian.1967. The Photonics Handbook.7 Gb/s NRZ-OOK Neighbours".. 278. ^ Melling.remspec. A. Mathematical and Physical Sciences (1934-1990) 297: 534. ^ "Novak Fiber Optic Sights" Novak Sights Web site.. Applied Optics 11 (11): 2489–94. (1972). Peter J.com/brillouin_scattering. 24. Johnson. 29. P. Stacey Higginbotham. (1999). "Reaction monitoring in small reactors and tight spaces" (pdf). (1989).x. 34. J. "111 Gb/s POLMUX-RZ-DQPSK Transmission over 1140 km of SSMF with 10. ^ Smith. Proceedings of the Royal Society of London.remspec.1098/rspa.pdf. G. (1999).T. Whitney. 33. J.remspec. ^ Kurkjian. 27. R.com/pdfs/amlab1002. "Optical Power Handling Capacity of Low Loss Optical Fibers as Determined by Stimulated Raman and Brillouin Scattering". September 29. Griffiths. ^ Bell Labs breaks optical transmission record. "The Strength of Fused Silica".396408. ^ Ciena. (eds.. Handbook of Vibrational Spectroscopy. B. ^ Kurkjian. doi:10. 100 Petabit per second kilometer barrier 22.html. Journal of Lightwave Technology 7: 1360. ^ M. doi:10. PMID 20119362. ^ Al Mosheky. Charles R.1.aspx?id=7783. 17.2. Mary (October 2002). Journal of the American Ceramic Society 76: 1106. Opt. Mary A.1117/12. Retrieved July 29. Thomson.1016/0022-3093(68)90007-0. . ^ !!!x-in-lab/ Alcatel Boosts Fiber Speed to 100 Petabits in Lab. Degradation. Peter. doi:10. 77. "Brillouin Scattering". (2008). American Laboratory News. 30. In Chalmers. C.. G.. (June 2001). et al. S. pp. 2006. Inniss. 25. [1].S. 32. ^ Archibald. p. http://www.4. Laurin Publishing. Alfiad. doi:10.J. H. doi:10. ^ Skontorp. 35. Melling. Journal of Non-Crystalline Solids 1: 69.E. ^ World Record 69-Terabit Capacity for Optical Transmission over a Single Optical Fiber 21. Engr. "Fiber-optic probes for mid-infrared spectrometry". NTT Press Release. 47.archive. (July 2008) This articleimprove this article bycitations for verification.ak. related reading or citations. but article includes a list of references.aspx. Alaska Division of Community and Regional Affairs. Archived from the original on May 8. Retrieved 2007-03-19. 43. "Protect your network against fiber hacks". ^ Corning Incorporated (2007-07-23). C (2000). ^ Gowar. http://www. "Mechanical properties of phosphate glasses".state. Retrieved April 11. Understanding Fiber Optics (4th ed. Press release. (2000). ^ Karabulut.us/dca/AEIS/PDF_Files/AIDE A_Energy_Screening. J. 41. UK: Prentice-Hall. "Heavy metal fluoride glasses and fibers: A review". 44. ISBN 0136387276.1984. http://web. John (1993) (2d ed. M (2001). et al. 209.pdf.). "Corning announces breakthrough optical fiber technology". Hempstead.com. ^ "Light collection and propagation". Journal of Non-Crystalline Solids 263-264: 207. doi:10. National Instruments' Developer Zone.corning. 2008-0705. http://blogs.405276. Optical and surface properties of oxyfluoride glass. 2006. Unsourced material may be challenged and adding (July 2008) . D. 39. ^ Nee. 42. "Mechanical and structural properties of phosphate glasses". Journal of NonCrystalline Solids 288: 8. http://zone.1109/JLT.com/security/?p=222. 46. the free encyclopedia Jump to: navigation. Tom (2007-05-03). ^ Hecht. ^ "Screening report for Alaska rural energy plan" (pdf). 2006. reliable references. ^ Kurkjian.1117/12. Top of Form Special:Search Gradient-index optics From Wikipedia.ieee. search Thisits sources remain unclear because it lacks inlineexternal links. doi:10. Prentice Hall.com/devzone/cda/ph/p/id/129#toc2.38.org/xpl/freeabs_all. Jeff (2002).. Lightwave Technology 2: 566. Soe-Mie F. 45. ^ Tran. Techrepublic.1016/S0022-3093(01)00615-9. p. ^ Olzak. (1984).ni. Retrieved 2007-12-09.org/web/20060508191931/http://www. http://ieeexplore. doi:10.dced. 40. Please improve this article by introducing more precise citations where appropriate. Retrieved 2007-12-10. ISBN 0-13-027828-9.). 2011-01-23. National Instruments Corporation.1073661. doi:10.com/media_center/press_releases/2007/2007072301.techrepublic. .1016/S0022-3093(99)00637-7. 122. CNET.jsp? arnumber=1073661. pp. Please help needs additionalremoved. is impractical to make and has little usefulness since. only points on the surface and within the lens are sharply imaged and extended objects suffer from extreme aberrations. thus giving them a misconception of the object’s spatial displacement. in a desert. R W Wood used a dipping technique creating a gelatin cylinder with a refractive index gradient that varied symmetrically with the radial distance from the axis. Known as the Maxwell Fisheye Lens. This lens.A gradient-index lens with a parabolicthe same way as a conventional with radial distance (x). 2006). Gradient-index optics is the branch of materials science dealing with the production and characterization of gradually changing refractive index lenses. 1854). axial. or radial. Nature progressively varies the refractive index of the lens in order to optimise the optics required for survival. Since refractive index generally increases with density of the material. In humans. i. Gradient index lenses may have a refraction gradient that is spherical. however. it is seen that cool air has a higher refractive index than hot air. Contents [hide] • 1 Gradient-Index Lenses in Nature • • • • • 2 History 3 Theory 4 Design and Manufacture of GRIN Lenses 5 Applications 6 References [edit] Gradient-Index Lenses in Nature A variety of inhomogeneous lenses exists in nature that allow for different functions. Eagles have the ability to maintain focus and high resolution at large distances. The eyes of an antelope have a broad field of view. deteriorate with age with noticeable effects usually occurring after the age of 40 in humans. it involves a spherical index function and would be expected to be spherical in shape as well (Maxwell. Disk shaped slices of the cylinder were later shown to have plane faces with radial index . however. The most obvious lens in nature is the lens present in the eye. In 1905. These lenses are able to eliminate the aberrations caused by traditional spherical lenses without requiring variation to the shape of the lens. The quality of the lens does. light passes from the cool air to the warm air causing the path of the light ray reaching an observer to bend. Therefore. the lens is able to highly resolve and reduce aberration for both short and long distances (Shirk et al.e. which allows them to detect predators. J C Maxwell suggested a lens whose refractive index distribution would allow for every region of space to be sharply imaged. [edit] History In 1854. The lens focuses light in variation of refractive index (n) lens. Another phenomenon related to the varying refractive indexes of materials in nature is the Mirage. The object may appear closer to the observer than it actually is. If Cartesian coordinates are used. Figure 2: How a Two Dimensional Gradient Index Lens Works. According to Fermat’s principle. it was thought to have had some usefulness in microwave applications. in that it is difficult to be used to focus visual light. [edit] Theory Yet to upload images and equations. Point P’ is the point at which the light rays would ideally converge if an aberration free lens was used. Figure 1: Cartesian Interpretation of Aberrations. and pass through point A. and Δx and Δy are the deviations from P’. then Δx and Δy are measures of the aberration for the rays perceived (Figure 1) (Marchand. they acted like converging and diverging lens depending on whether the index was a decreasing or increasing relative to the radial distance (Wood. however. such that the lens may be easily reproduced in the future.y. Gradient index lens converge all light rays onto a common point. to each physical dimension: where prime corresponds to d/ds (Marchand. Luneburg where he discovered a lens that converge all rays of light onto a point which is located on the opposite surface of the lens (Luneburg. 1905). the light path integral (L). K. 2006). He showed that even though the faces of the lens were flat. nr the refractive index at a distance. If a ray is emitted from point P. and passes near point P’. Inhomogeneous GRIN lenses attempt to reduce the aberrations Δx and Δy to zero (See Figure 2). r. In 1964. This also limits the applications of the lens. 1964). Point A and point P’ differ by the values Δx and Δy. The refractive index gradient of GRIN lenses can be mathematically modelled according to its method of production. 1976). For example. it is necessary to interpret the projections of light in terms of Gaussian Principles. express a refractive index that varies according to: Where. is the design index on the optical axis and A is a positive constant. from the optical axis. this equation is modified to incorporate the change in arc length for a spherical gradient. The light path integral is able to characterize the path of light through the lens in a qualitative manner.distribution. GRIN lenses made from a radial gradient index material. by refracting light through a changing refractive index (many different refractive indices). was published a posthumous book of R.z) of the coordinates of the region of interest in the medium. is stationary relative to its value for any nearby curve joining the two points. such as SELFOC® (Flores-Arias et al. taken along a ray of light joining any two points of a medium. An inhomogeneous gradient-index lens possesses a refractive index whose change follows the function: n=f(x. [edit] Design and Manufacture of GRIN Lenses . The light path integral is given by the equation: Where n is the refractive index and S is the arc length of the curve. Rays of light leaving point P are refracted at the lens plane. When considering aberrations. 1978). Recently. which can later be filled using a variety of salts or concentration of salts to give a varying gradient. plastics. When considering the manufacturing of GRIN lenses.904. When this technique is modulated spatially. preventing the ray from touching the walls. 1980). In telecommunications. Opt. germanium. 1980). Partial Polymerisation (Moore. with refractive index decreasing as distance from the centre increases. • • • • [edit] Applications The main uses of GRIN lenses involve applications in telecommunications and optical imaging. “Mathematical Theory of Optics. Gomez-Reino C.. in that all modes of the GRIN fibres propagate at the same velocity. Imaging using GRIN lenses is used to mainly reduce the aberrations and increase focus. the lens is evaluated by analytical techniques. "Optical Waveguide Having Optimal Index Gradient. Chemical Vapour Deposition (Keck et al. optical glasses. Soc. 1975) – Ions. and sodium chloride. This allows for a sinusoidal height distribution of the ray within the fibre. of California Press.873." U. onto a surface to produce a cumulative refractive change. 490-494 Hensler J R. 66.The GRIN lens is designed in two separate phases. Amer.S. zinc selenide.” Univ. such as. 1975) – Involving the deposition of different glass with varying refractive indexes. (2006). Bao C. 1975). a number of different methods of gradient production have been implemented.S. [edit] References Flores-Arias M T. 8. 188 . 1979) – Phase separation of a specific glass causes pores to form.C. J. there are two important features of any technique: the depth of the gradient.268 (9 Sept. (1854). Cambridge and Dublin Math. In the first phase. "Method of Producing a Refractive Index Gradient in Glass. Maxwell. a gradient index lens is formed. Marchand E W (1978). Keck D B and Olshansky R. This involves detailed calculations of aberrations as well as the efficient manufacture of the lenses. New York Academic Press. such as lithium replace sodium ions already present in a glass substrate. Δn. Berkeley. Production techniques involve: • Neutron Irradiation (Sinai. Luneberg R K. “Optics Communicaitons”266. thus allowing for a higher temporal bandwidth for the fibre (Moore. Marchand E W (1976). and thus the refractive index of the lens. Perez M V. (1964). Ion Stuffing (Mohr. Castelo A.408 (25 Mar. a long fibre many kilometres in length but only a 20-100µm diameter have refractive gradients engineered to vary radially from the centre. 1326. Patent 3. 1975). 1973) – Organic monomer is partially polymerized using UV light at varying intensities in order to give a refractive gradient. throughout the lens (Moore. Patent 3. 1971) – Boron-rich glass is bombarded with neutrons in order to cause a change in the boron concentration. The second phase involves the design of the lens. J. “Gradient Index Optics”. and the magnitude of the change in index-of-refraction." U. Ion Exchange (Hensler. J. This differs from the traditional optical fibres which rely on total internal reflection. 1973). Sandrock M. Wilder J A. Shirk J.index Optical Imaging Systems (Optical Society of America. Baer E. Scribner D. Hilter A. Applied Optics.S. Fleet E. Applied Optics. New York.W.Mohr R K. paper WAL. Moore. (2006) NRL Review pp 53-61 Sinai P. 1035-1038 Moore R S. “Physical Optics. 10. and Gupta P K. Macedo P B. (1980). 19. "Plastic Optical Element Having Refractive Index Gradient.383 (Feb. Stroman R. Macmillan.T.C. [hide]v · d · eGlass science topics Basics Glass · Glass transition · Supercooling AgInSbTe · Bioglass · Borophosphosilicate glass · Borosilicate glass · Ceramic glaze · Chalcogenide glass · Cobalt glass · Cranberry glass · Crown glass · Flint glass · Fluorosilicate glass · Fused quartz · Glass GeSbTe · Gold ruby glass · Lead glass · Milk glass · Phosphosilicate formulation glass · Photochromic lens glass · Silicate glass · Soda-lime glass · Sodium hexametaphosphate · Soluble glass · Tellurite glass · Ultra low expansion glass · Uranium glass · Vitreous enamel · Wood's glass · ZBLAN Glass-ceramics Bioactive glass · CorningWare · Glass-ceramic-to-metal seals · Macor · Zerodur Glass preparation Annealing · Chemical vapor deposition · Glass batch calculation · Glass forming · Glass melting · Glass modeling · Ion implantation · Liquidus temperature · Sol-gel technique · Viscosity · Vitrification Achromat · Dispersion · Gradient index optics · Hydrogen Optics darkening · Optical amplifier · Optical fiber · Optical lens design · Photochromic lens · Photosensitive glass · Refraction · Transparent materials Anti-reflective coating · Chemically strengthened glass · Corrosion · Surface Dealkalization · DNA microarray · Hydrogen darkening · Insulated modification glazing · Porous glass · Self-cleaning glass · Sol-gel technique · Toughened glass . 1979). (1970).” p. (1905).S. 99-104 Wood. Patent 3. R. Washington. in Digest of Topical Meeting on Gradient. 71. D.." U. D.718. wikipedia.Glass-coated wire · Glass databases · Glass electrode · Glass fiber reinforced concrete · Glass ionomer cement · Glass microspheres · Diverse topics Glass-reinforced plastic · Glass science institutes · Glass-to-metal seal · Porous glass · Prince Rupert's Drops · Radioactive waste vitrification · Windshield Retrieved from "http://en.org/wiki/Gradient-index_optics" Categories: Optics | Fiber optics | Glass engineering and science Hidden in-text citations | Articles needing citations from July 2008 | All articles lacking categories: Articles lacking in-text additional references from July 2008 | All articles needing additional references Personal tools • • • Views Log in / create account Article Discussion Namespaces Variants • • • Actions Search Read Edit View history Top of Form Special:Search Search Bottom of Form Navigation • • • • • • • • • • • Toolbox Main page Contents Featured content Current events Random article Donate to Wikipedia Help About Wikipedia Community portal Recent changes Contact Wikipedia What links here Interaction • . Inc. a non-profit organization. additional terms may apply. See Terms of Use for details. the free encyclopedia Jump to: navigation. Text is available under the Creative Commons Attribution-ShareAlike License.. .• • • • • • • • • • • • • Related changes Upload file Special pages Permanent link Cite this page Create a book Download as PDF Printable version Deutsch Polski Русский This page was last modified on 7 March 2011 at 05:38. search A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. Contact us Privacy policy About Wikipedia Disclaimers Print/export Languages • • • • • • Bottom of Form Fiber Bragg grating From Wikipedia. Wikipedia® is a registered trademark of the Wikimedia Foundation. 2 Chirped fiber Bragg gratings 5. or as a wavelength-specific reflector.1 Standard gratings or Type I gratings 4.2 Type IA gratings 4.4 Production 3 Theory 4 Types of gratings ○ ○ ○ ○ ○ 4. A fiber Bragg grating can therefore be used as an inline optical filter to block certain wavelengths.1 Interference 2. Figure 1:response spectral A Fiber Bragg Grating structure.This is achieved by adding a periodic variation to the refractive index of the fiber core.5 Type II gratings 5.4 Regenerated gratings 4.1 Communications 6.2 Fiber Bragg grating sensors • 5 Grating structure ○ ○ ○ ○ • 6 Applications ○ ○ • • • 7 See also 8 References 9 External links . which generates a wavelength specific dielectric mirror. with refractive index profile and Contents [hide] • 1 History • 2 Manufacture ○ ○ ○ ○ • • 2.3 Tilted fiber Bragg gratings 5.3 Point-by-point 2.2 Photomask 2.1 Apodized gratings 5.4 Long-period gratings 6.3 Type In (commonly known as Type IIA gratings) 4. the laser has a narrow beam that is equal to the grating period. Gerald Meltz and colleagues demonstrated the much more flexible transverse holographic technique where the laser illumination came from the side of the fiber. Here the UV laser is split into two beams which interfere with each other creating a periodic intensity distribution along the interference pattern. all in a single stage.[edit] History The first in-fiber Bragg grating was demonstrated by Ken Hill in 1978. [edit] Interference The first manufacturing method. which is directly related to the interference period and a function of the incident angle of the laser light. The shadow of the photomask then determines the grating structure based on the transmitted intensity of light striking the fiber. A special germanium-doped silica fiber is used in the manufacture of fiber Bragg gratings. Here. This method allows for quick and easy changes to the Bragg wavelength.[1] Initially. [edit] Theory . the manufacture of the photosensitive optical fiber and the 'writing' of the fiber Bragg grating were done separately. This method is specifically applicable to the fabrication of long period fiber gratings. The refractive index of the photosensitive fiber changes according to the intensity of light that it is exposed to. In 1989. [edit] Production Originally. is the use of twobeam interference. [edit] Point-by-point A single UV laser beam may also be used to 'write' the grating into the fiber point-by-point. Point-by-point is also used in the fabrication of tilted gratings. [edit] Photomask A photomask having the intended grating features may also be used in the manufacture of fiber Bragg gratings. The photomask is placed between the UV light source and the photosensitive fiber. in that the refractive index of the core changes with exposure to UV light. [edit] Manufacture Fiber Bragg gratings are created by "inscribing" or "writing" systematic (periodic or aperiodic) variation of refractive index into the core of a special type of optical fiber using an intense ultraviolet (UV) source such as a UV laser. The germanium-doped fiber is photosensitive. This technique uses the interference pattern of ultraviolet laser light[2] to create the periodic structure of the Bragg grating. specifically used for uniform gratings. production lines typically draw the fiber from the preform and 'write' the grating. As well as reducing associated costs and time. Today. Mass production is in particular facilitating applications in smart structures utilizing large numbers (3000) of embedded fiber Bragg gratings along a single length of fiber. the gratings were fabricated using a visible laser propagating along the fiber core. The method that is preferable depends on the type of grating to be manufactured. with the amount of the change a function of the intensity and duration of the exposure. this also enables the mass production of fiber Bragg gratings. which cannot be manufactured using an interference pattern. Photomasks are specifically used in the manufacture of chirped Fiber Bragg gratings. Two main processes are used: interference and masking. [edit] Types of gratings . called the Bragg wavelength.Figure 2: FBGs reflected power as a function of wavelength The fundamental principle behind the operation of a FBG. 2). see Fig. The wavelength spacing between the first minima (nulls. The grating will typically have a sinusoidal refractive index variation over a defined length. . . For this reason. particularly the temperature . . where ne is the effective refractive index of the grating in the fiber core and Λ is the grating period. where N is the number of periodic variations. − n2). is defined by the relationship. The reflected wavelength (λB). where δn0 is the variation in the refractive index (n3 the core. where. and η is the fraction of power in The peak reflection (PB(λB)) is approximately given by. The effective refractive index quantifies the velocity of propagating light as compared to its velocity in vacuum. The different methods of creating these fringes have a significant effect on physical attributes of the produced grating. or the bandwidth (Δλ). is given by. ne depends not only on the wavelength but also (for multimode waveguides) on the mode in which the light propagates. The full equation for the reflected power (PB(λ)). it is also called modal index. Where light traveling between media of different refractive indices may both reflect and refract at the interface. is given by. . is Fresnel reflection. The term “type” in this context refers to the underlying photosensitivity mechanism by which grating fringes are produced in the fiber. though not always.[8][9] [edit] Regenerated gratings These are gratings that are reborn at higher temperatures after erasure of gratings. Type I gratings are the most commonly used of all grating types. This type IA grating appeared once the conventional type I FBG had reached saturation followed by subsequent complete or partial erasure.[10] These are extremely attractive for ultra high temperature applications. It was also noted that the temperature coefficient of the regenerated grating was lower than a standard grating written under similar conditions. Typically.response and ability to withstand elevated temperatures. Type II label is reserved for those that are distinctly made above the damage threshold of the glass). outperforming even Type II femtosecond gratings. It is usually associated with gradual relaxation of induced stress along the axis and/or at the interface. in the presence of hydrogen. Thus far. These gratings have recently been relabeled Type In (for Type 1 gratings with a negative index change. There is a clear relationship between type IA and IIA gratings insomuch as their fabrication conditions are identical in all but one aspect: they both form in B/Ge co-doped fiber but IAs form only in hydrogenated fibers and IIAs form only in non-hydrogenated fibers. Recent work has shown that there exists a regeneration regime beyond diffusion where gratings can be made to operate at temperatures in excess of 1295C.[7] Later research by Xie et al. a large positive wavelength shift was measured. usually Type I gratings and usually.[4][5][6] [edit] Type In (commonly known as Type IIA gratings) • These are gratings that form as the negative part of the induced index change overtakes the positive part. The gratings were formed in germanosilicate fibers with pulses from a frequency doubled XeCl pumped dye laser. Further exposure showed that a grating reformed which underwent a steady blue shift whilst growing in strength. [edit] Type IA gratings • Regenerated grating written after erasure of a type I grating in hydrogenated germanosilicate fiber of all types Type IA gratings were first published in 2001[4] during experiments designed to determine the effects of hydrogen loading on the formation of IIA gratings in germanosilicate fiber. five (or six) types of FBG have been reported with different underlying photosensitivity mechanisms. and the only types of grating available off-the-shelf at the time of writing. This means that the reflection and transmission spectra are complementary and there is negligible loss of light by reflection into the cladding or by absorption. the reflection spectra of a type I grating is equal to 1-T where T is the transmission spectra. They have been interpreted in different ways including dopant diffusion (oxygen being the most popular current interpretation) and glass structural change. [edit] Type II gratings . In contrast to the anticipated blue shift of the peak Bragg wavelength. It was shown that initial exposure formed a standard (type I) grating within the fiber which underwent a small red shift before being erased. showed the existence of another type of grating with similar thermal stability properties to the type II grating. This grating exhibited a negative change in the mean index of the fiber and was termed type IIA. and was therefore labeled as regenerated.[3] These are summarized below: [edit] Standard gratings or Type I gratings Written in both hydrogenated and non-hydrogenated fiber of all types Type I gratings are usually known as standard gratings and are manufactured in fibers of all types under all hydrogenation conditions. They include recent developments in multiphoton excitation using femtosecond pulses where the short timescales (commensurate on a timescale similar to local relaxation times) offer unprecedented spatial localization of the induced change. and higher with femtosecond laser inscription). a chirped FBG (2). It was further shown that a sharp threshold was evident at ~30mJ. Lasers employed are usually pulsed in order to reach these intensities. these cracks can be very localized so as to not play a major role in scattering loss if properly prepared [11][12] [edit] Grating structure Figure 3:a tilted FBG (3). 1) a uniform positive-only FBG. and 4) a discrete phase shift a raised-cosine-apodized FBG with zero-dc change.• Damage written gratings inscribed by multiphoton excitation with higher intensity lasers that exceed the damage threshold of the glass. they labeled gratings fabricated below the threshold as type I gratings and above the threshold as type II gratings.8%) reflectance with a single UV pulse in fibers on the draw tower. . and a superstructure FBG (4).uniform FBG (1). Structure of the refractive index change in a Figure 4: Refractive index profile in the core of. Microscopic examination of these gratings showed a periodic damage track at the grating’s site within the fiber [10]. 3) FBG. and in recognition of the distinct differences in thermal stability. The gratings were inscribed using a single 40mJ pulse from an excimer laser at 248 nm. Archambault et al. The amorphous network of the glass is usually transformed via a different ionization and melting pathway to give either higher index changes or create. hence type II gratings are also known as damage gratings. The resulting gratings were shown to be stable at temperatures as high as 800˚C (up to 1000C in some cases. For ease of identification. However. above this level the index modulation increased by more than two orders of magnitude. whereas below 30mJ the index modulation grew linearly with pulse energy. voids surrounded by more dense glass. showed that it was possible to inscribe gratings of ~100% (>99. through micro-explosions. 2) a Gaussian-apodized FBG. In a tilted FBG (TFBG). uniform positive-only index change. and the offset. the refractive index profile can be uniform or apodized. There are.[13] 1. A grating possessing a chirp has the property of adding dispersion—namely. The reflected wavelength changes with the grating period. This means the grating strength can be used to set the bandwidth. and the refractive index offset is positive or zero.The structure of the FBG can vary via the refractive index.[14][citation needed] This supported the development of the first distributed feedback (DFB) fiber lasers. different wavelengths reflected from the grating will be subject to different delays. These are the grating length. The first complex grating was made by J. effectively N. Typically. The grating length. chirped. The term apodization refers to the grading of the refractive index to approach zero at the end of the grating. as well. the bandwidth depends on the grating strength. Gaussian apodized. Canning in 1994. and is typically uniform across the width of the fiber. and not the grating length.[citation needed] [edit] Apodized gratings There are basically two quantities that control the properties of the FBG. however. including the sampled gratings first made by Peter Hill and colleagues in Australia. and either localised or distributed in a superstructure. There are six common structures for FBGs. and 6. This is apodization of the refractive index change. . raised-cosine apodized. and also laid the groundwork for most complex gratings that followed. This property has been used in the development of phasedarray antenna systems and polarization mode dispersion compensation. the grading or variation of the refractive index is along the length of the fiber (the optical axis). the bandwidth. Lg. which depends on both the grating strength and the grating length. The result of this is that the side-lobe strength cannot be controlled. The grating period can be uniform or graded. 5. 3. called a chirp. δn0 η. The two functions typically used to apodize a FBG are Gaussian and raised-cosine. broadening the reflected spectrum. and this simple optimisation results in significant side-lobes. A third quantity can be varied to help with side-lobe suppression. Apodized gratings offer significant improvement in side-lobe suppression while maintaining reflectivity and a narrow bandwidth. or the grating period. As shown above. [edit] Chirped fiber Bragg gratings The refractive index profile of the grating may be modified to add other features. three properties that need to be controlled in a FBG. [edit] Tilted fiber Bragg gratings In standard FBGs. . 2. superstructure. and the side-lobe strength. the variation of the refractive index is at an angle to the optical axis. and bandwidth. discrete phase shift. given as and the grating strength. the refractive index profile. The refractive index has two primary characteristics. The angle of tilt in a TFBG has an effect on the reflected wavelength. These are the reflectivity. such as a linear variation in the grating period. 4. can then be used to set the peak reflectivity. [edit] Applications [edit] Communications Figure 5: Optical add-drop multiplexer. another signal on that channel can be added at the same point in the network. CT is the coefficient of temperature. They are also used in optical multiplexers and demultiplexers with an optical circulator. the grating period is 500 nm. depicted as 4 colours. The primary application of fiber Bragg gratings is in optical communications systems. here channel 4. the Bragg wavelength is also sensitive to temperature. αΛ. CS is the coefficient of strain. which is related to. Since the channel has been dropped. These gratings are called long-period fiber grating. Also. This means that fiber Bragg gratings can be used as sensing elements in optical fiber sensors. the strain optic coefficient pe. The sensitivity of a FBG to strain is discussed below in fiber Bragg grating sensors. ΔλB / λB. using a refractive index of 1. The relative shift in the Bragg wavelength. They are specifically used as notch filters. or. . [edit] Fiber Bragg grating sensors As well as being sensitive to strain. where each drop element uses a FBG set to the wavelength to be demultiplexed. and the thermo-optic coefficient. For a grating that reflects at 1500 nm. The signal is reflected back to the circulator where it is directed down and dropped out of the system.5. ΔλB. the Bragg wavelength of the FBG can be tuned by strain applied by a piezoelectric transducer.[edit] Long-period gratings Typically the grating period is the same size as the Bragg wavelength. Here. A demultiplexer can be achieved by cascading multiple drop sections of the OADM. Figure 5 shows 4 channels. αn. FBG demultiplexers and OADMs can also be tunable. to a millimeter. Longer periods can be used to achieve much broader responses than are possible with a standard FBG. In a FBG sensor. a multiplexer can be achieved by cascading multiple add sections of the OADM. and are therefore much easier to manufacture. In a tunable demultiplexer or OADM. which is made up of the thermal expansion coefficient of the optical fiber. The FBG is set to reflect one of the channels. Conversely. as shown above.[15] . due to an applied strain (ε) and a change in temperature (ΔT) is approximately given by. impinging onto a FBG via an optical circulator. the measurand causes a shift in the Bragg wavelength. or Optical Add-Drop Multiplexer (OADM). They typically have grating periods on the order of 100 micrometers. 5. Advanced fiber gratings and their application. Johnson.embedding FBGs in flexible skins [edit] References 1. converting the amount of gas to a strain. G.1364/OL. As such they offer a significant advantage over traditional electronic gauges used for these applications in that they are less sensitive to vibration or heat and consequently are far more reliable. Optical Fibre Sensors and Their Interrogationdv. "Photosensitivity in optical fiber waveguides: application to reflection fiber fabrication". ^ Hill. Canning. Aston University. G. PMID 19752980.. "An ideal method for the fabrication of temperature compensating IA-I strain sensors". and as downhole sensors in oil and gas wells for measurement of the effects of external pressure. D. "Formation of Bragg gratings in optical fibers by a transverse holographic method". Lett. A. Nara.. which generates a strain or temperature change from the measurand. OFS16.D. Wiley. Appl.. I. B. seismic vibrations and inline flow measurement. 3. (1978). Lasers and Photonics Reviews. (2003). doi:10. Fiber Gratings and Devices for Sensors and Lasers. Kalli. K.1063/1. Ph. Thesis. ^ Simpson. postdeadline paper PD4. 32: 647.D. C. 2 (4). ^ Meltz. Thesis. ^ Simpson.. Opt. Japan. K.. USA (2008) 4. doi:10. Kawasaki. Phys.O. ^ a b Liu. G.. pp. Ph.. They can also be used as transduction elements. 6. 14 (15): 823.14. for example fiber Bragg grating gas sensors use an absorbent coating. the absorbent material is the sensing element. Aston University. which in the presence of a gas expands generating a strain. temperature. The Bragg grating then transduces the strain to the change in wavelength.[16] pressure sensors for extremely harsh environments. converting the output of another sensor. (2005). S. In the 1990s. 275-289. which is measurable by the grating.[17][18] [edit] See also • • • • • • • • • Bragg's law Bragg diffraction Diffraction ○ Diffraction grating Dielectric mirror Hydrogen sensor Long-period fiber grating Photonic crystal fiber Distributed temperature sensing by fiber optics PHOSFOS project . et al. Specifically. (1989).. Technically. Fujii. . K.Fiber Bragg gratings can then be used as direct sensing elements for strain and temperature. Y. 2. A. Y. Bennion. L. Zhang. (2001).000823. Zhou. fiber Bragg gratings are finding uses in instrumentation applications such as seismology.89881. investigations were conducted for measuring strain and temperature in composite materials for aircraft and helicopter structures. ^ J. Lett. Fibre Optic Sensing Network Europe Development Platforms • TFT .ieee. D. M. http://ieeexplore. "On the possible use of optical fiber Bragg gratings as strain sensors for geodynamical monitoring". Artech House. M. 20. Dunphy & et al.Technobis Fibre Technologies Other . Kalli. M.^ J. 10.1109/50. Canning. J. issued Feb. Turan (August 1997).R. Electronics Letters 29 (17): 1577–1578. Fiber Gratings and Devices for Sensors and Lasers. USA (2008) 8. 30. De Natale (2002). S. P.. P. Georges.^ J. Georges. ISBN 0890063443.1049/el:19930303.^ Archambault. Journal of Lightwave Technology 15 (8): 1277–1294. M.^ US patent 5399854. Kyriacos (1999). "Integrated optical instrumentation for the diagnostics of parts by embedded or surface attached optical sensors".. W. "Single-Pulse Bragg Gratings Written During Fibre Drawing". (1993). N. (1993). X. "100-Percent Reflectivity Bragg Reflectors Produced in Optical Fibres By Single ExcimerLaser Pulses". Bandyopadhyay. 12. Optics Communications 113 (1-3): 176–192. F. 1995 [edit] External links International Optical Sensor Societies • FOSNE . Poumellec. Optics Communications 104 (13): 185–195. L. P. doi:10. K.. T. ^ Niay. Bernage. S. L. T. Fiber Bragg Gratings: Fundamentals and Applications in Telecommunications and Sensing. G. (1994) 15. 2 (4). 275-289. 1996 18. “Extreme silica optical fibre gratings”.. Poumellec.. ^ For a contemporary review.jsp? tp=&arnumber=618322&isnumber=13456. "p-phase-shifted periodic distributed structures in germanosilicate fibre by UV post-processing". (16).. L. (1994). see J. Bernage. Monerie. Lett.. Sceats.^ Dong. "Experimental-Evidence of 2 Types of Photorefractive Effects Occurring During Photo inscriptions of Bragg Gratings Within Germanosilicate Fibres". W.. Andreas. S. B. Lasers and Photonics Reviews.. Electron.. J.618322. P. Sensors. Wiley. J.. B. "Embedded optical sensor capable of strain and temperature measurement using a single diffraction grating". 8. J. Douay.. Stevenson. F.^ US patent 5493390. "Fiber Grating Spectra". Monerie. 14. 13. P..^ P. issued March 21. Legoubin. Electronics Letters 29 (5): 453–455.^ Erdogan.^ Othonos. doi:10. X. 17. doi:10. Reekie. Canning.. Canning. L. Ferraro. Xie. 16.. Bayon.org/xpl/freeabs_all. pp. Archambault..1016/S0143-8166(01)00141-5..7. P. M. Russell. ^ Xie.. "Behaviour of Spectral Transmissions of Bragg Gratings Written in Germania-Doped Fibres Writing and Erasing Experiments Using Pulsed or CW UV Exposure".1016/0030-4018(93)90127-Q.. doi:10. Cook. (2008) 11. Payne. M. Douay.1049/el:19931051. G. J. doi:10. J.. 1344-1345. doi:10. 9. Russell. Niay.1-5.1016/0030-4018(94)906068. Reekie. S. Optics and Lasers in Engineering 37: 115–130. Bayon.. (1993). J... L. Optic filter with tunable grating Retrieved from "http://en.• • Bragg grating as hydrogen detector http://www.org/wiki/Fiber_Bragg_grating" Categories: Optical fiber | Diffraction Hidden categories: All articles with unsourced statements | Articles with unsourced statements from May 2009 Personal tools • • • Views Log in / create account Article Discussion Namespaces Variants • • • Actions Search Read Edit View history Top of Form Special:Search Search Bottom of Form Navigation • • • • • • • • • • • Toolbox Main page Contents Featured content Current events Random article Donate to Wikipedia Help About Wikipedia Community portal Recent changes Contact Wikipedia What links here Related changes Upload file Special pages Permanent link Interaction • • • • • .wikipedia.patentgenius.com/patent/7133582.Fiber .html . Inc. a non-profit organization. the free encyclopedia Jump to: navigation. In order for a leaky mode to be definable as a mode. Contact us Privacy policy About Wikipedia Disclaimers Print/export Languages • • • • • • Leaky mode From Wikipedia. additional terms may apply. [edit] References . the relative amplitude of the oscillatory part (the leakage rate) must be sufficiently small that the mode substantially maintains its shape as it decays. Such a mode gradually "leaks" out of the waveguide as it travels down it.• • • • • • • • • • Cite this page Create a book Download as PDF Printable version Deutsch Norsk (bokmål) Polski Svenska This page was last modified on 15 January 2011 at 08:25. Text is available under the Creative Commons Attribution-ShareAlike License. Wikipedia® is a registered trademark of the Wikimedia Foundation. See Terms of Use for details. Leaky modes correspond to leaky rays in the terminology of geometric optics. producing attenuation even if the waveguide is perfect in every respect.. search A leaky mode or tunneling mode in an optical fiber or other waveguide is a mode having an electric field that decays monotonically for a finite distance in the transverse direction but becomes oscillatory everywhere beyond that finite distance. wikipedia.v · article Retrieved from "http://en. This optics-related d · e is a stub.This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C" (in support of MIL-STD-188).org/wiki/Leaky_mode" Categories: Optics stubs | Fiber optics Hidden categories: Wikipedia articles incorporating text from the Federal Standard 1037C | Wikipedia articles incorporating text from MIL-STD-188 Personal tools • • • Views Log in / create account Article Discussion Namespaces Variants • • • Actions Search Read Edit View history Top of Form Special:Search Search Bottom of Form Navigation • • • • • • • • • • • Toolbox Main page Contents Featured content Current events Random article Donate to Wikipedia Help About Wikipedia Community portal Recent changes Contact Wikipedia What links here Related changes Upload file Interaction • • • . You can help Wikipedia by expanding it. Wikipedia® is a registered trademark of the Wikimedia Foundation. and a medium by which the basic transmission systems: A transmitter. Figure illustrates these elements. case. a non-profit organization.info Transmission| Basics | Performance | Applying Fiber Optic Technology System Components Parts of a Transmission Link Fiber optic transmission uses the same receiver.info Fiber Optic History Fiber Optic Articles Fiber Optic Glossary Fiber Optic Community Fiber-Optics. Text is available under the Creative Commons Attribution-ShareAlike License.1310 nm. a in this elements as copper-based1 signal is passed from one to the other. The transmitter uses an electricallaser diode or an the use the encoding to allowAM. A interface to encode information through an FM or output of 850 nm. See Terms of Use for details. Inc.. Contact us Privacy policy About Wikipedia Disclaimers Print/export • • • • • • • • • • • fiber-optics. optical fiber.• • • • • • • • Special pages Permanent link Cite this page Create a book Download as PDF Printable version This page was last modified on 5 April 2010 at 05:06. or 1550 nm LED do (typically). . opticaldigital modulation. additional terms may apply. These elements comprise the simplest link. A coating or the light. further system complexity.three main regions. provides to be confined in receiver it back into an electrical signal. further addsignal fanouts. long-haul transmission systems require quality. The buffer. The fiber of the fiber. dispersion management multiplexers. A data demodulator converts the data convert its original electrical form. Long distance fiber optic transmission leads tosignal regenerators. and error-correction components. Manyor optical amplifiers such as EDFAs in order to maintain signal signal repeaters. System drop/repeat/add to the fiber optic system. couplers/splitters.Cross-section of an Optical Fiber The optical fiber connects the transmitter and the receiver. typically uses either a PIN photodiode or an APD to receive the optical signal and plastic. These are discussed in separate articles as linked in this paragraph.interfaces. allowing the light core the center the fiber core. remote monitoring information on these components. the cladding surround thestrength and protection to the optical fiber. as consists of actually carries illustrated in Figure 2.Elements of a Fiber Optic Link Figure 2 .in a glass with a different refractive index than The core. The core. a composite signal for transmission. the linked articles for additional . such as those in multichannel broadcast networks.Figure 1 . incorporating add-drop requirements. Other wavelength-division multiplexing their original techniques allow up to eight signals (CWDM) or more (DWDM) to be combined onto a single fiber. back into elements may also appear in a fiber optic transmission system. and then can be separated into joined into signals at the receive end. This fiber may be either single-mode or multimode. For but other the addition of WDM components allows two separate signals to be example. See equipment.