In addition to being used to transmit information, what else can optical fibers be used for?

With the technological progress of optical fiber, optical fiber family has also formed a series. In this paper, we intend to develop and apply the family of optical fiber series of products to make a brief introduction.1 Classification of optical fiber optical fiber is an optical fiber (OF: OpticalFiber) abbreviation. But the optical communication system is often OpticalFibe (optical fiber) and simplified for Fiber, for example: fiber amplifier (FiberAmplifier) or fiber trunk (FiberBackbone) and so on. Some people ignore that Fiber has the meaning of fiber, but in the optical system is to refer to the optical fiber. Therefore, some optical products in the description, the fiber directly translated into "fiber", obviously is not desirable. Optical fiber actually refers to the core made of transparent materials and cladding made of materials with slightly lower refractive index than the core around it is covered, and will be shot into the core of the optical signal, through the cladding interface reflection, so that the optical signal propagation in the core of the media forward. There are many types of optical fibers, depending on the use, the functions and performance required also vary. But for cable television and communications with optical fiber, its design and manufacturing principles are basically the same, such as: ① loss is small; ② a certain bandwidth and dispersion is small; ③ wiring is easy; ④ easy to become a system; ⑤ high reliability; ⑥ manufacturing is relatively simple; ⑦ inexpensive and so on. Classification of optical fibers is mainly from the working wavelength, refractive index distribution, transmission mode, raw materials and manufacturing methods for a summary of the various classifications are listed below. (1) operating wavelength: ultraviolet fiber, visible fiber, near-infrared fiber, infrared fiber (0.85pm, 1.3pm, 1.55pm). (2) Refractive index distribution: step (SI) type, near-step, gradient (GI) type, others (e.g., triangular, W-type, concave, etc.). (3) Transmission modes: single-mode fiber (including polarization-holding fiber, non-polarization-holding fiber), multi-mode fiber. (4) Raw materials: quartz glass, multi-component glass, plastics, composite materials (such as plastic cladding, liquid core, etc.), infrared materials. According to the cladding material can also be divided into inorganic materials (carbon, etc.), metal materials (copper, nickel, etc.) and plastics. (5) manufacturing methods: pre-shape with vapor-phase axial deposition (VAD), chemical vapor deposition (CVD), etc., drawing method has a tube law (Rodintube) and double crucible method, etc. 2 quartz optical fiber is based on silicon dioxide (SiO2) as the main raw material, and according to the amount of different doping to control the refractive index of the core and cladding of the optical fiber distribution. Quartz (glass) series of optical fibers, with low consumption, broadband characteristics, is now widely used in cable television and communication systems. Fluorine doped fiber (FluorineDopedFiber) is one of the typical products of quartz fiber. Usually, as a 1.3Pm wavelength communication fiber, the control core dopant for the dioxide (GeO2), cladding is made of SiO fried. However, the core of the fluorine-connected fiber is mostly made of SiO2, and the cladding is doped with fluorine. Rayleigh scattering loss is a light scattering phenomenon caused by the change of refractive index. Therefore, it is desirable to minimize the amount of dopant that contributes to the change in refractive index. Fluorine is mainly used to reduce the refractive index of SIO2. Therefore, it is often used in the doping of the cladding. As in fluorine doped fiber, the core does not contain fluorine dopants that affect the refractive index. Because of its Rayleigh scattering is very small, and the loss is close to the theoretical minimum. Therefore, it is mostly used for long-distance optical signal transmission. Quartz fiber (SilicaFiber), compared with other raw materials, also has a broad spectrum of light transmission from ultraviolet to near-infrared light, in addition to communications applications, can also be used in the field of light conduction and image conduction.3 Infrared fiber as the field of optical communications developed in the quartz series of optical fibers operating wavelengths, although used for a shorter transmission distance, can only be used for the 2pm. In order to work in the field of longer infrared wavelengths, the optical fibers developed are called infrared optical fibers. Infrared optical fiber (InfraredOpticalFiber) is mainly used for optical energy transmission. For example: temperature measurement, thermal image transmission, laser scalpel medical treatment, thermal processing, etc., the popularity rate is still low.4 CompoundFiber Compound fiber (CompoundFiber) in the SiO2 raw materials, and then mixed appropriately, such as sodium oxide (Na2O), boron oxide (B2O2), potassium oxide (K2O2) and other oxides such as multi-component glass optical fiber, characterized by multi-component glass than quartz softening point is lower and the softening point of quartz is lower. The softening point of multi-component glass is lower than that of quartz, and the refractive index difference between the core and the cladding is very large. Mainly used in the medical business of fiber-optic endoscopy.5 Fluoride Fiber Chloride fiber (FluorideFiber) is made of fluoride glass optical fiber. This fiber material is also referred to as ZBLAN (i.e., aluminum fluoride (ZrF4), barium cyanide (BaF2), lanthanum fluoride (LaF3), aluminum fluoride (A1F2), sodium cyanide (NaF), and other chloride glass raw materials into a simplified acronym. It mainly works in the optical transmission business of 2 to 10pm wavelength. Because ZBLAN has the possibility of ultra-low-loss fiber, is being used for long-distance communication fiber feasibility development, for example: its theoretical minimum loss, in the 3pm wavelength up to 10-2 ~ 10-3dB / km, while the quartz fiber in the 1.55pm but between 0.15 ~ 0.16dB / Km. Currently, ZBLAN fiber is only used for temperature sensors and thermal image transmission at 2.4 to 2.7 pm due to the difficulty in reducing scattering loss, and has not yet been widely used. Recently, in order to use ZBLAN for long-distance transmission, is developing 1.3pm fault-doped fiber amplifier (PDFA).6 Plastic Clad FiberPlastic Clad Fiber (PlasticCladFiber) is a high-purity quartz glass for the core, and will be slightly lower than the refractive index of quartz, such as silica and other plastics as the cladding of the step-type optical fiber. Compared with quartz fiber, it has the characteristics of core rent and high numerical aperture (NA). Therefore, it is easy to combine with light-emitting diode LED light source, and the loss is also smaller. Therefore, it is very suitable for local area networks (LAN) and short-distance communication.7 Plastic Optical FiberThis is an optical fiber whose core and cladding are made of plastic (polymer). Early products are mainly used for decorative and light-guided lighting and short-distance optical bonding optical communications. The raw materials are mainly plexiglass (PMMA), polystyrene (PS) and polycarbonate (PC). Losses are constrained by the inherent C-H bonding structure of the plastic, generally up to tens of dB per kilometer, in order to reduce losses are being developed and applied to fluorosol series plastics. As plastic optical fiber (PlasticOpticalfiber) core diameter of 1000pm, 100 times larger than single-mode quartz fiber, simple splicing, and easy to bend the construction is easy. In recent years, coupled with the progress of broadbandization, the development of multi-mode plastic optical fiber as a gradual change (GI) refractive index has been emphasized by society. Recently, it has been applied more rapidly in LANs inside automobiles, and may be used in home LANs in the future.8 Single-mode fiber This is an optical fiber that transmits only one propagation mode in the operating wavelength, often abbreviated as single-mode fiber (SMF: SingleModeFiber). Currently, it is the most widely used fiber in cable television and optical communications. Since the core of an optical fiber is very thin (about 10 pm) and the refractive index is distributed in a step-like manner, when the normalized frequency V parameter <2.4, theoretically, only single-mode transmission can be formed. In addition, SMF does not have multimode dispersion, not only the transmission band is wider than multimode fiber, coupled with the SMF material dispersion and structural dispersion of the sum of the offset, the synthetic characteristics of the formation of zero-dispersion characteristics, so that the transmission band is even more broadened.SMF, due to the dopant different and the difference in manufacturing methods, there are many types of SMF. DePr-essed Clad Fiber (DePr-essedCladFiber), its cladding to form a twofold structure, adjacent to the core of the cladding, the outer inverted cladding than the refractive index is also low. In addition, there are matched cladding fiber, its cladding refractive index is uniformly distributed.9 Multi-mode fiber will work according to the optical fiber to its propagation of the possible modes for more than one mode of the optical fiber is called multi-mode fiber (MMF: MUltiModeFiber). The core diameter is 50 pm, and the transmission bandwidth is dominated by mode dispersion compared to SMF due to the transmission of up to several hundred modes. Historically, it has been used for short distance transmission in cable television and communication systems. Since the emergence of SMF fiber, it seems to form a historical product. However, in reality, MMF is more advantageous in many LANs due to its larger core diameter than SMF and the ease of combining it with light sources such as LEDs. Therefore, MMF is still being re-appreciated in the field of short-distance communication.When MMF is classified according to the refractive index distribution, there are two types: gradient (GI) type and step (SI) type.The refractive index of the GI type is highest at the center of the fiber core, and decreases gradually along the cladding. From a geometrical optics point of view, the light beam advancing in the core appears to propagate in a serpentine fashion. Since the time required for each path of light is approximately the same, the transmission capacity is higher than that of the SI type. Therefore, the transmission capacity is larger than that of SI-type.The refractive index distribution of SI-type MMF fiber is the same as that of the core, but the interface with the cladding is stepped. Due to the SI-type light wave reflection in the fiber forward process, resulting in the time difference between the various optical paths, resulting in a distortion of the ejected light wave, the color excitation is larger. The result is a narrower transmission bandwidth, the current SI-type MMF applications are less.10 dispersion shift fiber single-mode fiber operating wavelength at 1.3Pm, the mode field diameter of about 9Pm, the transmission loss of about 0.3dB / km. At this time, the zero-dispersion wavelength is exactly at 1.3pm. Quartz fiber, from the raw material of the 1.55pm section of the transmission loss is the smallest (about 0.2dB / km). Since the erbium-doped fiber amplifier (EDFA), which is now practical, operates in the 1.55pm band, if zero dispersion can also be achieved in this band, it will be more conducive to the application of long-distance transmission in the 1.55Pm band. Thus, by cleverly using the quartz material dispersion in the fiber material and the core structure dispersion of the synthetic offset characteristics, the original zero dispersion in the 1.3Pm band can be shifted to the 1.55pm band also constitutes zero dispersion. Therefore, it is named Dispersion Shifted Fiber (DSF: DispersionShiftedFiber). The method to increase the structural dispersion is mainly to improve the refractive index distribution performance in the fiber core. In long-distance transmission for optical communications, zero fiber dispersion is important, but not unique. Other properties are low loss, easy splicing, cable formation, or small changes in the characteristics of the work (including bending, stretching and environmental changes affect).DSF is in the design, a combination of these factors.11 Dispersion Flat Fiber Dispersion Shifted Fiber (DSF) is a single-mode optical fiber will be designed zero dispersion is located in the 1.55pm band of the optical fiber. Dispersion Flattened Fiber (DFF: DispersionFlattenedFiber) is the dispersion from 1.3Pm to 1.55pm of a wider band of dispersion, can be made to a very low, almost zero dispersion of the optical fiber called DFF. due to the DFF to be made to the range of 1.3pm ~ 1.55pm dispersion are reduced. The refractive index distribution of the fiber needs to be designed in a complex way. However, this type of fiber is very suitable for wavelength division multiplexing (WDM) lines. Due to the complexity of the DFF fiber process, it is more expensive. In the future, as production volume increases, the price will decrease.12 Dispersion-compensated fiber For trunk systems using single-mode fibers, most of them are composed of fibers with zero dispersion in the 1.3 pm band. However, nowadays, 1.55pm, which has the smallest loss, will be very beneficial if 1.55pm wavelength can be operated even on 1.3pm zero dispersion fiber due to the practical use of EDFA. Because, in the 1.3Pm zero-dispersion fiber, the dispersion of the 1.55Pm wavelength is about as much as 16ps/km/nm. If in this fiber line, insert a section of fiber with the opposite sign of this dispersion, the dispersion of the entire optical line can be zero. The fiber used for this purpose is called Dispersion Compensation Fiber (DCF: DisPersionCompe-nsationFiber). DCF and the standard 1.3pm zero-dispersion fiber compared to the core diameter is finer, and the refractive index difference is also larger. DCF is also an important part of the WDM optical line.13 The bias maintains the optical fiber in the optical fiber propagation of the light wave because of the has the nature of electromagnetic waves, so, in addition to the basic single mode of light waves, there are essentially two orthogonal modes of electromagnetic field (TE, TM) distribution. Usually, due to the structure of the fiber cross-section is circularly symmetric, the propagation constants of the two polarization modes are equal, and the two beams of polarized light do not interfere with each other. However, in reality, the fiber is not completely circularly symmetric, for example, with a curved section, there will be a combination of the two polarization modes between the factors, in the optical axis is irregularly distributed. The dispersion caused by this change in polarized light is called polarization mode dispersion (PMD). For cable television, which now focuses on distributing images, the impact is not yet significant. But for some future ultra-wideband business with special requirements, such as: ① coherent communications using differential detection, requiring more stable polarization of the light wave; ② optical machines, such as input and output characteristics of the input and output requirements related to polarization; ③ in the production of polarization to maintain the optical coupler and polarizer or de-polarizer, etc.; ④ the production of the use of optical interference of the fiber optic sensitivity, etc., wherever required to keep the polarization wave constant, the optical fiber is improved to make the polarization state constant. Polarization state of the fiber is called polarization maintaining fiber (PMF: Polarization Maintaining fiber), also known as fixed polarization fiber.14 Birefringent Fiber Birefringent fiber refers to a single-mode optical fiber that can transmit two intrinsic polarization modes orthogonal to each other. Because, the phenomenon in which the refractive index varies with the direction of polarization is called birefringence. In the method of causing birefringence. It is also known as PANDA fiber, Polarization-maintaining and absorption-reducing fiber (Polarization-maintai-ningANDAbsorption-reducingfiber). It consists of a glass portion with a large coefficient of thermal expansion and a circular cross-section on both lateral sides of the fiber core. In the high-temperature fiber drawing process, these parts of the contraction, the result in the core y-direction produces tensile, and at the same time in the x-direction presents compressive stress. This results in a photoelastic effect in the fiber, causing a difference in the refractive index in the x-direction and y-direction. According to this principle to achieve polarization to maintain a constant.15 Resistant to harsh environments Fiber optic communications fiber optics can usually work in the ambient temperature of -40 ~ +60 ℃ between the design is not subject to a large number of radiation as a prerequisite. In contrast, for lower or higher temperatures and can be subjected to high pressure or external influences, exposure to radiation lines of the harsh environment, can also work in the optical fiber is called a harsh environment resistant fiber (HardConditionResistantFiber). Generally, in order to protect the surface of the fiber mechanically, a layer of plastic is coated. However, as the temperature rises, the protective function of plastic decreases, which limits the operating temperature. If you change to heat-resistant plastics, such as polytetrafluoroethylene (Teflon) and other resins, you can work at 300 ℃ environment. There are also in the quartz glass surface coating nickel (Ni) and aluminum (A1) and other metals. This kind of fiber is called heat-resistant fiber (HeatResistantFib-er). In addition, when an optical fiber is exposed to radiation, the optical loss increases. This is because when the quartz glass is irradiated by radiation, structural defects appear in the glass (also called color center: ColourCenter), especially at 0.4 to 0.7 pm wavelength when the loss increases. The way to prevent this is to switch to quartz glass doped with OH or F elements, which can suppress the loss defects caused by radiation. This kind of fiber is called radiation-resistant fiber (RadiationResista-ntFiber), mostly used in nuclear power stations to monitor the use of optical fibers, such as mirrors.16 Seal-coated optical fiber in order to maintain the mechanical strength of the optical fiber and the loss of a long period of time stable, and in the glass surface coating silicon carbide (SiC), titanium carbide (TiC), carbon (C), and other inorganic materials, used to prevent water and hydrogen diffusion from the outside. The optical fiber (HCF: Hermetically Coated Fiber) is made by coating inorganic materials such as silicon carbide (SiC), titanium carbide (TiC), and carbon (C) on the surface of glass to prevent the diffusion of water and hydrogen from outside. Currently, it is common to achieve a full sealing effect by building up carbon layers at high speed in the chemical vapor deposition (CVD) production process. This Carbon Coated Fiber (CCF) effectively cuts off the fiber from the intrusion of external hydrogen molecules. It has been reported to last up to 20 years without increasing loss in a hydrogen environment at room temperature. Of course, it prevents the intrusion of moisture to delay the fatigue process of mechanical strength, and its fatigue coefficient (FatigueParameter) can reach more than 200. Therefore, HCF is used in harsh environments requiring high reliability systems, such as undersea fiber optic cables is an example.17 Carbon Coated Fiber Optic fiber coated with a carbon film on the surface of the quartz optical fiber, called Carbon Coated Fiber (CCF: CarbonCoatedFiber). The mechanism is the use of carbon dense film layer, so that the surface of the fiber and the outside world to isolate, in order to improve the mechanical fatigue loss of the fiber and hydrogen molecules increase the loss of the CCF is a kind of sealing coated optical fiber (HCF).18 Metal Coated Optical FiberMetal Coated Optical Fiber (MetalCoatedFiber) is the surface of the optical fiber coated with a metal layer of Ni, Cu, A1 and other optical fibers. There are also coated with plastic outside the metal layer, the purpose is to improve heat resistance and can be energized and welded. It is one of the optical fibers that are resistant to harsh environments and can also be used as a component of electronic circuits. Early products were made by coating molten metal during the wire drawing process. Since the difference between the expansion coefficient of the glass and the metal is too large, it will increase the bending loss, and the practicalization rate is not high. Recently, due to the success of the low-loss non-electrolytic coating method on the surface of the glass optical fiber, so that the performance has been greatly improved.19 Doped rare-earth optical fiber in the core of the optical fiber, doped with how (Er), Chin (Nd), spectral (Pr) and other rare-earth elements such as optical fibers.1985, the United Kingdom's Sourthampton (Sourthampton) University of the Pace (Payne) and others were the first to find that doped Rare earth elements of optical fiber (RareEarthDoPedFiber) has the phenomenon of laser oscillation and light amplification. Thus, from then on, unveiled the tragic bait and other light amplification, and now has been practical 1.55pm EDFA is the use of bait-doped single-mode optical fiber, the use of 1.47pm laser excitation, to get 1.55pm light signal amplification. In addition, the error-doped fluoride fiber amplifier (PDFA) is under development.20 Raman fiber Raman effect refers to a substance in the shot frequency f monochromatic light, in the scattered light will appear outside the frequency f f ± fR, f ± 2fR and other frequencies of the scattered light, the phenomenon known as the Raman effect. This phenomenon is called the Raman effect, because it is produced by the energy exchange between the molecular motion and the lattice motion of matter. When a substance absorbs energy, the number of vibrations of light becomes smaller, and this scattered light is called Stokes (stokes) line. On the contrary, from the matter to get energy, and the vibration number becomes larger scattered light, is called anti-Stokes line. Thus, the vibration number of the deviation FR, reflecting the energy level, can show the inherent value of matter. The optical fiber made from this nonlinear media is called Raman fiber (RF: RamanFiber). In order to enclose light in a tiny core for long-distance propagation, an interaction effect between light and matter occurs, which enables long-distance transmission without distortion of the signal waveform. Coherent induced scattered light is obtained when the input light is enhanced. The application of induced Raman scattered light devices are Raman fiber lasers, which can be used as power supplies for spectroscopic measurements and fiber dispersion tests. In addition, induced Raman scattering, long-distance communication in optical fibers, is studying the application of optical amplifiers.21 Eccentric fiber standard optical fiber core is set in the center of the cladding, the core and cladding cross-section shape of concentric circles. However, due to different uses, there will be the core position and core shape, cladding shape, made into different states or perforated cladding to form a heterogeneous structure. Compared with standard optical fiber, these optical fibers are called exotic optical fibers. Eccentric fiber (Excentric Core Fiber), which is a type of shaped fiber. Its core is set in the off-center and close to the outer line of the cladding of the eccentric position. Because the core is close to the exterior, part of the light field will spread out of the cladding (called EvanescentWave). Therefore, when a substance is attached to the surface of an optical fiber, the light waves propagating through the fiber are affected by the optical properties of the substance. If the refractive index of the attached material is higher than that of the fiber, the light wave is radiated out of the fiber. If the refractive index of the attached material is lower than the refractive index of the optical fiber, the light wave cannot be radiated outward, but will be subject to the loss of light wave absorption by the material. Using this phenomenon, it is possible to detect the presence or absence of an attached substance and changes in the refractive index. Eccentric fiber (ECF) is mainly used as a fiber optic sensor to detect substances. Combined with the optical time domain reflectometer (OTDR) test method, it can also be used as a distribution sensor.22 Luminescent optical fiber is an optical fiber made with a fluorescent substance. It is an optical fiber that transmits a portion of the fluorescence generated when irradiated by light waves such as radiation and ultraviolet rays, and can be closed by the optical fiber. Luminescent fiber (LuminescentFiber) can be used for detecting radiation and ultraviolet rays, as well as for wavelength conversion, or as a temperature sensor or chemical sensor. It is also called ScintillationFiber for the detection of radiation. Luminescent fibers are being developed from the point of view of fluorescent materials and doping for plastic fibers.23 Multi-core FibersThe usual optical fiber consists of a core region and a cladding region around it. However, a multi-core fiber (MultiCoreFiber) is one where multiple cores are present in the same cladding zone. Due to the proximity of the cores to each other, there can be two functions. One is the fiber core spacing is large, that is, does not produce optical coupling will be the structure. This type of fiber, due to the ability to increase the integrated density per unit area of the transmission line. In optical communication, it can be made into a ribbon cable with multiple cores, and in the field of non-communication, as a fiber optic transmission beam, there are thousands of cores. The second is to make the distance between the cores close enough to produce light-wave coupling. The use of this principle is being developed dual-core sensitive or optical loop devices.24 Hollow fiber will be made into a hollow fiber, forming a cylindrical space, used for optical transmission of optical fiber, called hollow fiber (HollowFiber). Hollow fibers are mainly used for energy transmission for X-ray, ultraviolet and far-infrared light energy transmission. There are two kinds of hollow fiber structure: one is to make the glass into a cylinder, its core and cladding principle and step type. The use of light in the air and glass between the total reflection propagation. As a result, most of the light can be propagated in the lossless air, with a certain distance propagation function. Secondly, the reflectivity of the inner surface of the cylinder is made close to 1 to reduce the reflection loss. In order to improve the reflectivity, there is a dielectric set in the simple, so that the working wavelength band loss is reduced. For example, it can be made to wavelength 10.6pm loss of a few dB/m.