Optical fiber (optical fiber) is an abbreviation for optical fiber (a fiber that can conduct light) . It is a fiber made of glass or plastic that can be used as a light transmission tool. The transmission principle is "total reflection of light".
In 2022, single-crystal organometallic perovskite optical fibers will be made for the first time.
In May 2023, Chinese scientists realized quantum key distribution over thousands of kilometers of unrepeated fiber optics. In June, Chinese scientists successfully achieved 508 kilometers of optical fiber quantum communication.
Development History
invention
One day in 1870, British physicist Tyndall went to the lecture hall of the Royal Society to talk about the principle of total reflection of light. He did a simple experiment: he drilled a hole in a wooden barrel filled with water, and then used a lamp to pour light from the barrel. The water illuminates. The results took the audience by surprise. People saw that the shining water flowed out from the small hole in the bucket, the water flow was bent, and the light was also bent, and the light was actually captured by the curved water.
It has been found that light energy travels along fine streams of wine spewing from wine barrels; it has also been found that light energy travels along curved glass rods. Why is this? Doesn't the light go straight any more? These phenomena attracted Tyndall's attention. After his research, he found that this is the effect of total reflection of light. Since the density of water and other media is greater than that of surrounding substances (such as air), that is, when light shoots from water to air, when the incident angle Above a certain angle, the refracted light disappears and all light is reflected back into the water. On the surface, it appears that light is bending forward in a stream of water.
Later, people created a glass fiber with high transparency and thickness like spider silk—glass fiber. When light hits the glass fiber at a suitable angle, the light will advance along the curved glass fiber. Because this fiber can be used to transmit light, it is called an optical fiber.
Memorabilia
1880 Alexandra Graham Bell invents light beam telephony transmission
1960 The transmission loss of glass fiber is greater than 1000dB/km, and other materials include aperture waveguide, gas lens waveguide, hollow metal waveguide, etc.
In July 1966, Dr. KKao, a British and Chinese scholar, published a paper "Dielectric Fiber Surface Waveguide for Optical Frequency" in PIEE magazine, which theoretically proved the possibility of using optical fiber as a transmission medium to realize optical communication. And predicted the possibility of manufacturing ultra-low loss optical fiber for communication.
In 1970, three researchers from Corning Corporation of the United States, Marel, Capron, and Keck, successfully developed a low-loss silica optical fiber with a transmission loss of only 20dB/km by using the modified chemical phase deposition method (MCVD method).
1970 Bell Laboratories of the United States developed the world's first gallium aluminum arsenide semiconductor laser that works in continuous wave at room temperature.
1972 The transmission loss was reduced to 4dB/km.
In 1974, the Bell Research Institute of the United States invented the low-loss optical fiber manufacturing method - CVD method (chemical vapor deposition method), which reduced the optical fiber transmission loss to 1.1dB/km.
In 1976, the United States opened the world's first test line of optical fiber communication system in the underground pipeline of Bell Laboratories in Atlanta. A cable with 144 optical fibers is used to transmit signals at a rate of 44.736Mbps, and the relay distance is 10 km. What adopted is the multi-mode optical fiber, what the light source used was the light-emitting tube LED, the wavelength is the infrared light of 0.85 microns.
1976 The transmission loss was reduced to 0.5dB/km.
1977 Bell Research Institute and Nippon Telegraph and Telephone Corporation almost simultaneously successfully developed a semiconductor laser with a service life of 1 million hours (about 10 years in practical use).
1977 The world's first optical fiber communication system was put into commercial use in Chicago, USA, with a rate of 45Mb/s.
1977 First actual installation of fiber optic telephone network.
1978 FORT installed its fiber optic cables for the first time in France.
In 1979, Zhao Zisen drew the first practical optical fiber independently developed by my country, and was known as "the father of Chinese optical fiber".
1979 The transmission loss was reduced to 0.2dB/km.
1980 The multi-mode optical fiber communication system was commercialized (140Mb/s), and the field test of the single-mode optical fiber communication system was started.
1990 The single-mode optical fiber communication system entered the commercialization stage (565Mb/s), and started to conduct field tests of zero dispersion shift optical fiber, wavelength division multiplexing and coherent communication, and successively formulated technical standards for digital synchronization system (SDH).
In 1990, the transmission loss was reduced to 0.14dB/km, which was already close to the theoretical attenuation limit of 0.1dB/km for silica fiber.
1990 Optical fiber for LAN and other short-distance transmission applications.
In 1992, Bell Labs and its Japanese partners successfully tested an optical amplifier that could transmit 9,000 kilometers without errors. The initial rate was 5Gbps, and then increased to 10Gbps.
1993 SDH products began to be commercialized (below 622Mb/s).
1995 2.5Gb/s SDH products entered the commercial stage.
1996 10Gb/s SDH products entered the commercial stage.
1997 A major breakthrough was achieved in 20Gb/s and 40Gb/s SDH product tests using wavelength division multiplexing technology (WDM).
2000 Fiber to the house => Fiber to the table.
2005 3.2Tbps ultra-large-capacity optical fiber communication system was opened from Shanghai to Hangzhou.
2005 FTTH (Fiber To The Home) fiber optic direct to the home.
The 2021 Distributed Optical Fiber Sensing Technology Application Exhibition was held in Beijing. Optical fibers are not just "vessels" that transmit signals, but now also become "nerves" that monitor signals.
In May 2023, it was learned from the National Key Laboratory of Optical Communication Technology and Networks of China Xinke Group (hereinafter referred to as Optical Quanzhong), that after the world's first 3.03Pbit/s single-mode 19-core optical fiber transmission system experiment was realized in October 2022, The laboratory has also achieved a single-mode 19-core optical fiber transmission system experiment with a total transmission capacity of 4.1Pbit/s and a net transmission capacity of 3.61Pbit/s. Compared with last year's record, the transmission capacity has increased by nearly 40%.
In May 2023, Chinese scientists realized quantum key distribution over thousands of kilometers of unrepeated fiber optics. Not only has it set a world record for the distance of quantum key distribution without relays in optical fiber, but it also provides a solution for high-speed backbone links of intercity quantum communication.
definition
optical fiber
The tiny fiber is encapsulated in a plastic sheath that allows it to be bent without breaking. Usually, the transmitting device at one end of the fiber uses a light emitting diode (LED) or a laser beam to transmit light pulses to the fiber, and the receiving device at the other end of the fiber uses a photosensitive element to detect the pulse.
In daily life, optical fiber is used for long-distance information transmission because the transmission loss of light in optical fibers is much lower than that of electricity in wires.
Usually the terms optical fiber and optical cable are confused. Most optical fibers must be covered by several layers of protective structures before use, and the coated cables are called optical cables. The protective layer and insulating layer on the outer layer of the optical fiber can prevent the surrounding environment from harming the optical fiber, such as water, fire, electric shock, etc.
Optical cables are divided into: cable sheath, aramid yarn, buffer layer and optical fiber. Fiber optics are similar to coaxial cables, except without the mesh shield. In the center is the glass core for light propagation.
In the multimode optical fiber, the diameter of the core is two kinds of 50 μm and 62.5 μm, which are roughly equivalent to the thickness of a human hair. The diameter of the single-mode fiber core is 8 μm to 10 μm, and the commonly used one is 9/125 μm . The core is surrounded by a glass envelope with a lower refractive index than the core, commonly known as the cladding, which keeps the light inside the core . Beyond that is a thin plastic coat, the coating, that protects the cladding. Optical fibers are usually bundled and protected by a jacket. The fiber core is usually a double-layer concentric cylinder with a small cross-sectional area made of quartz glass. It is brittle and easy to break, so an additional protective layer is required.
Explanation: 9/125μm means that the core of the fiber is 9μm, and the cladding is 125μm. 9/125μm is an important feature of single-mode fiber. It is an important feature of multimode fiber.
Among them, the BRICS optical cable project is a submarine optical cable project that directly connects five BRICS countries. The total length of the project is 34,000 kilometers, including about 24,000 kilometers of submarine optical cables directly connecting the five BRICS countries.
In 2013, global 100G optical fiber revenue is expected to exceed $1 billion for the first time. The company analyzed the financial results of the global optical network market in the first quarter of 2013 and found some trends, including a disappointing trend, that is, the overall growth of the market is still difficult, and only Japan's Fuji Corporation has increased its profits year by year.
While it's not uncommon for the fiber optic market to experience a recession in the first quarter, the decline is concerning because it marks the fifth straight quarter of declines and the lowest quarterly revenue in six years.
The situation of 100G optical fiber is relatively optimistic, showing strong growth both on a quarter-on-quarter basis and year-on-year basis. In the first quarter of 2013, the shipment of 100G optical fiber increased by 41% compared with the fourth quarter of 2012, and the revenue increased by 24% compared with the fourth quarter of 2012. On this basis, annual revenue is expected to exceed $1 billion for the first time. In the first quarter of 2013, 20 suppliers sold 100G optical fiber, and more manufacturers will join the market competition. Suppliers are cautiously optimistic, short-term order volume is bullish, but long-term order volume is not optimistic.
Principle type
Light and its properties:
1. Light is an electromagnetic wave
The wavelength range of visible light is: 390~760nm (nanometer). The part greater than 760nm is infrared light, and the part less than 390nm is ultraviolet light. There are three types of optical fibers: 850nm, 1310nm, and 1550nm .
2. Refraction, reflection and total reflection of light.
Because light travels at different speeds in different substances, when light travels from one substance to another, refraction and reflection will occur at the interface between the two substances . Also, the angle of refracted light varies with the angle of incident light. When the angle of the incident light reaches or exceeds a certain angle, the refracted light will disappear, and all the incident light will be reflected back, which is the total reflection of light. Different substances have different refraction angles for the same wavelength of light (that is, different substances have different light refraction indices), and the same substance has different refraction angles for different wavelengths of light. Optical fiber communication is formed based on the above principles.
1. Bare optical fiber is generally divided into three layers: the central high refractive index glass core (core diameter is generally 50 or 62.5 μm), the middle is low refractive index silica glass cladding (diameter is generally 125 μm), and the outermost is for strengthening Resin coating . The light is transmitted in the core. When the angle between the fiber and the interface between the core and the outer layer is greater than the critical angle for total reflection, the light cannot pass through the interface and will be completely reflected back and continue to transmit forward in the core, while the cladding mainly acts to the protective effect.
optical fiber
2. Numerical aperture:
Not all the light incident on the end face of the fiber can be transmitted by the fiber, but only the incident light within a certain angle range. This angle is called the numerical aperture of the fiber. The larger numerical aperture of the fiber is beneficial for the butt joint of the fiber. Optical fibers produced by different manufacturers have different numerical apertures (AT&T CORNING).
3. Types of optical fibers:
There are many types of optical fibers, and the required functions and performances vary depending on the application. But for cable TV and communication optical fiber, its design and manufacturing principles are basically the same, such as:
① small loss;
②There is a certain bandwidth and small dispersion;
③Easy wiring;
④Easy to form;
⑤ High reliability;
⑥ manufacturing is relatively simple;
⑦ Cheap and so on. The classification of optical fibers is mainly summarized from the working wavelength, refractive index distribution, transmission mode, raw materials and manufacturing methods. Here are examples of various classifications.
(1) Working wavelength: ultraviolet fiber, observable fiber, near-infrared fiber, infrared fiber (0.85μm, 1.3μm, 1.55μm).
(2) Refractive index distribution: step (SI) fiber, near-step fiber, graded (GI) fiber, others (such as triangular, W, concave, etc.).
(3) Transmission mode: single-mode fiber (including polarization-maintaining fiber and non-polarization-maintaining fiber), multimode fiber.
(4) Raw materials: quartz optical fiber, multi-component glass optical fiber, plastic optical fiber, composite optical fiber (such as plastic cladding, liquid core, etc.), infrared materials, etc. According to the coating material, it can also be divided into inorganic materials (carbon, etc.), metal materials (copper, nickel, etc.) and plastics.
(5) Manufacturing methods: pre-molding includes vapor phase axial deposition (VAD), chemical vapor deposition (CVD), etc., wire drawing methods include tube law (Rod intube) and double crucible method, etc.
Silica fiber
Silica Fiber is an optical fiber that uses silicon dioxide (SiO2) as the main raw material and controls the refractive index distribution of the core and cladding according to different doping amounts. Quartz (glass) series optical fibers have the characteristics of low consumption and broadband, and have been widely used in cable TV and communication systems.
The advantage of quartz glass optical fiber is low loss. When the light wavelength is 1.0-1.7μm (about 1.4μm), the loss is only 1dB/km, and the lowest at 1.55μm is only 0.2dB/km.
Fluorine doped fiber
Fluorine Doped Fiber is one of the typical products of silica fiber. Usually, as a communication optical fiber in the 1.3μm wave domain, the dopant for controlling the core is germanium dioxide (GeO2), and the cladding is made of SiO2. However, the core of the fluorine-connected optical fiber mostly uses SiO2, but the cladding is doped with fluorine. Because the Rayleigh scattering loss is the light scattering phenomenon caused by the change of the refractive index. Therefore, it is desirable to have less dopant that forms a refractive index variation factor. The main function of fluorine is to reduce the refractive index of SIO2. Therefore, it is often used for cladding doping.
Compared with optical fibers made of other materials, quartz optical fiber also has a broad spectrum of light transmission from ultraviolet light to near-infrared light. In addition to communication applications, it can also be used in light guide and image transmission.
Infrared Fiber
As the working wavelength of the quartz series optical fiber developed in the field of optical communication, it can only be used for 2 μm even though it is used for a short transmission distance. For this reason, it is possible to work in the longer infrared wavelength field, and the developed optical fiber is called infrared optical fiber. Infrared Optical Fiber (Infrared Optical Fiber) is mainly used for light energy transmission. For example: temperature measurement, thermal image transmission, laser scalpel medical treatment, thermal energy processing, etc., the penetration rate is still low.
composite fiber
Compound Fiber (Compound Fiber) is made of SiO2 raw materials, and then properly mixed with oxides such as sodium oxide (Na2O), boron oxide (B2O3), potassium oxide (K2O) and other oxides to make multi-component glass optical fiber, which is characterized by multi-component glass The softening point is lower than that of quartz glass and the refractive index difference between the core and the cladding is large. Fiber optic endoscopes mainly used in medical business.
Fluoride Fiber
Fluoride Fiber is an optical fiber made of fluoride glass. The representative of fluoride optical fiber is ZBLAN optical fiber, its raw material is zirconium fluoride (ZrF2), barium fluoride (BaF2), lanthanum fluoride (LaF3), aluminum fluoride (AlF3), sodium fluoride (NaF) and other fluoride combined in certain proportions. Optical transmission is mainly realized at a wavelength of 2 to 10 μm. Because ZBLAN fiber has the possibility of ultra-low loss fiber, it is being developed for the feasibility of long-distance communication fiber, for example: its theoretical minimum loss can reach 10^-2~10^-3 dB at a wavelength of 3 μm /km, while the silica fiber is between 0.15~0.16dB/Km at 1.55μm. Due to the difficulty in reducing the scattering loss, ZBLAN fiber can only be used in temperature sensors and thermal image transmission of 2.4-2.7 μm, and has not been widely used. Recently, in order to use ZBLAN for long-distance transmission, 1.3 μm praseodymium-doped fiber amplifier (PDFA) is being developed.
plastic clad fiber
Plastic clad fiber (Plastic Clad Fiber) is a step-type optical fiber that uses high-purity silica glass as the core and plastics such as silica gel with a slightly lower refractive index than silica as the cladding. Compared with silica fiber, it has the characteristics of thick core and high numerical aperture (NA). Therefore, it is easy to combine with light-emitting diodes and LED light sources, and the loss is also small. Therefore, it is very suitable for local area network (LAN) and short-range communication.
plastic optical fiber
This is an optical fiber in which both the core and the cladding are made of plastic (polymer). The early products are mainly used for decoration, light guide lighting and optical communication of short-distance optical key paths. The raw materials are mainly plexiglass (PMMA), polystyrene (PS) and polycarbonate (PC). The loss is limited by the inherent C-H combination structure of plastics, and generally can reach tens of dB per km. In order to reduce the loss, the application of Fluoro series plastics is being developed. Since the core diameter of plastic optical fiber is 1000μm, which is 100 times larger than that of single-mode silica fiber, the connection is simple, and it is easy to bend and easy to construct. In recent years, coupled with the progress of broadband, the development of multimode plastic optical fiber as a graded (GI) refractive index has attracted the attention of the society. Recently, it has been applied rapidly in the interior LAN of the car, and it may also be applied in the home LAN in the future.
single mode fiber
Single-mode fiber refers to the fiber that can only transmit one propagation mode in the working wavelength, usually referred to as single-mode fiber (SMF: Single Mode Fiber) . In cable TV and optical communication, it is the most widely used optical fiber. Since the fiber core is very thin (about 10 μm) and the refractive index is distributed in a step shape, when the normalized frequency V parameter is <2.4, theoretically, only single-mode transmission can be formed. In addition, SMF has no multi-mode dispersion, not only the transmission frequency band is wider than that of mode fibers, but also the addition and cancellation of SMF's material dispersion and structural dispersion, and its synthetic characteristics just form the characteristics of zero dispersion, which makes the transmission frequency band wider. In SMF, there are many types due to differences in dopants and manufacturing methods. Depressed cladding fiber (DePr-essed Clad Fiber), its cladding forms a double structure, the cladding adjacent to the core has a lower refractive index than the outer cladding.
multimode fiber
Multimode fiber refers to an optical fiber in which the optical fiber is multi-mode according to the working wavelength and its possible modes of propagation are called multimode optical fiber (MMF: MUlti ModeFiber). The fiber core diameter is 50 μm, and since the transmission mode can reach several hundred, the transmission bandwidth is mainly dominated by the mode dispersion compared with SMF. Historically used for short-distance transmission in cable TV and communication systems. Since the appearance of SMF optical fiber, it seems to form a historical product. But in fact, because MMF has a larger core diameter than SMF and is easy to combine with light sources such as LEDs, it has more advantages in many LANs. Therefore, MMF is still receiving renewed attention in the field of short-distance communication. When MMF is classified according to the distribution of refractive index, there are two types: gradual (GI) type and step (SI) type. The refractive index of the GI type is the highest at the center of the fiber core, and gradually decreases along the cladding. Due to the time difference of each optical path during the reflection and progress of SI-type light waves in the optical fiber, the emitted light waves are distorted and the color shock is large. As a result, the transmission bandwidth is narrowed, and SI-type MMF is less used.
dispersion shifted fiber
When the operating wavelength of the single-mode fiber is 1.3Pm, the mode field diameter is about 9Pm, and its transmission loss is about 0.3dB/km. At this time, the zero dispersion wavelength is exactly at 1.3pm. Among the silica optical fibers, the transmission loss of the 1.55pm section is the smallest (about 0.2dB/km) from the raw material. Since the already practical erbium-doped fiber amplifier (EDFA) works in the 1.55pm band, if zero dispersion can also be achieved in this band, it will be more conducive to the long-distance transmission of the 1.55pm band. Therefore, by cleverly using the synthetic and offset characteristics of the dispersion of the quartz material in the fiber material and the dispersion of the fiber core structure, the original zero dispersion in the 1.3pm section can be shifted to the 1.55pm section to form zero dispersion. Therefore, it is named dispersion shifted fiber (DSF: DispersionShifted Fiber). The method of increasing structural dispersion is mainly to improve the refractive index distribution performance of the fiber core. In the long-distance transmission of optical communication, it is important, but not the only one, to have zero fiber dispersion. Other performances include low loss, easy splicing, small changes in characteristics during cabling or work (including bending, stretching and environmental changes). DSF takes these factors into consideration in the design.
Dispersion Flattened Fiber
Dispersion-shifted fiber (DSF) is a single-mode fiber designed to have zero dispersion in the 1.55pm band. Dispersion Flattened Fiber (DFF: Dispersion Flattened Fiber) is called DFF, which can achieve very low dispersion in a wide band from 1.3pm to 1.55pm, and almost achieve zero dispersion. Since the DFF needs to reduce the dispersion in the range of 1.3pm to 1.55pm. A complex design of the refractive index profile of the fiber is required. However, this fiber is very suitable for wavelength division multiplexing (WDM) lines. Because the process of DFF optical fiber is more complicated, the cost is more expensive. In the future, as production increases, prices will also decrease.
Dispersion Compensating Fiber
As for the trunk line system using single-mode optical fiber, most of them are formed by using optical fiber with zero dispersion in the 1.3pm band. However, for the 1.55pm with the smallest loss, due to the practical use of EDFA, it will be very beneficial if the 1.55pm wavelength can also work on the 1.3pm zero-dispersion optical fiber. Because, in the 1.3Pm zero-dispersion optical fiber, the dispersion in the 1.55Pm band is about 16ps/km/nm. If a section of optical fiber with the opposite sign of the dispersion is inserted in this optical fiber line, the dispersion of the entire optical line can be made zero. The optical fiber used for this purpose is called dispersion compensating fiber (DCF: DisPersion Compe-nsation Fiber). Compared with the standard 1.3pm zero-dispersion fiber, DCF has a thinner core diameter and a larger refractive index difference. DCF is also an important part of WDM optical line.
polarization maintaining fiber
The light wave propagating in the optical fiber has the property of electromagnetic wave, therefore, in addition to the basic single mode of light wave, there are actually two orthogonal modes of electromagnetic field (TE, TM) distribution. Usually, since the cross-sectional structure of the fiber is circularly symmetric, the propagation constants of the two polarization modes are equal, and the two polarized lights do not interfere with each other. The combination factor between two polarization modes is irregularly distributed on the optical axis. The dispersion caused by this change in polarized light is called polarization mode dispersion (PMD). For cable television, which mainly distributes images, the impact is not too great, but for some services with special requirements for future ultra-broadband, such as:
① When heterodyne detection is used in coherent communication, when the polarization of light waves is required to be more stable;
② When the input and output characteristics of optical machines are required to be related to polarization;
③When making polarization-maintaining optical couplers and polarizers or depolarizers, etc.;
④ Manufacture of optical fiber sensors using light interference, etc.,
Where the polarization is required to remain constant, the fiber that has been improved to keep the polarization state constant is called a polarization maintaining fiber (PMF: Polarization Maintaining fiber), or it is called a fixed polarization fiber.
birefringent fiber
A birefringent fiber refers to a fiber that can transmit two intrinsic polarization modes that are orthogonal to each other in a single-mode fiber. The variation of the refractive index with the direction of polarization is called birefringence. It is also called PANDA fiber, that is, Polarization-maintai-ning AND Absorption-reducing fiber (Polarization-maintai-ning AND Absorption-reducing fiber). It is in the transverse direction of the fiber core, and the glass part with a large thermal expansion coefficient and a circular cross section is set. During fiber drawing at high temperatures, these portions shrink, resulting in tension in the y-direction of the core and compressive stress in the x-direction. As a result, the photoelastic effect appears in the fiber material, and the refractive index differs in the X direction and the Y direction. According to this principle, the effect of maintaining constant polarization is achieved.
Anti-bad environment optical fiber
The usual working environment temperature of optical fiber for communication can be between -40 and +60°C, and the design is also based on the premise that it will not be exposed to a large amount of radiation. In contrast, optical fibers that can work at lower or higher temperatures and in harsh environments that are subjected to high pressure or external forces and exposed to radiation are called Hard Condition Resistant Fibers. Generally, in order to mechanically protect the surface of the optical fiber, an additional layer of plastic is coated. However, as the temperature rises, the protective function of the plastic decreases, resulting in a limitation of the use temperature. If you use heat-resistant plastics, such as polytetrafluoroethylene (Teflon) and other resins, you can work in an environment of 300 ° C. There are also metals such as nickel (Ni) and aluminum (Al) coated on the surface of quartz glass. This kind of fiber is called Heat Resistant Fiber. In addition, when the optical fiber is irradiated with radiation, the optical loss will increase. This is because when quartz glass is irradiated by radiation, structural defects (also called color center: Color Center) will appear in the glass, and the loss increases especially at the wavelength of 0.4-0.7pm. The way to prevent it is to use quartz glass doped with OH or F, which can suppress the loss defects caused by radiation. This kind of fiber is called radiation resistant fiber (Radiation Resistant Fiber), and it is mostly used in fiber optic mirrors for monitoring nuclear power plants.
Hermetic Coated Fiber
In order to keep the mechanical strength and loss of the optical fiber stable for a long time, inorganic materials such as silicon carbide (SiC), titanium carbide (TiC), and carbon (C) are coated on the glass surface to prevent water and hydrogen from the outside. Fiber produced by diffusion (HCFHermeticallyCoated Fiber). It is common to use high-speed accumulation of carbon layers to achieve sufficient sealing effect during the production process of chemical vapor deposition (CVD). This carbon-coated fiber (CCF) can effectively cut off the intrusion of the fiber and external hydrogen molecules. It is reported that it can be maintained for 20 years in a hydrogen environment at room temperature without increasing loss. Of course, it prevents moisture intrusion and delays the fatigue process of mechanical strength, and its fatigue coefficient (Fatigue Parameter) can reach more than 200. Therefore, HCF is applied to systems that require high reliability in harsh environments, such as submarine optical cables.
carbon coated fiber
A fiber coated with a carbon film on the surface of a silica fiber is called a carbon-coated fiber (CCF: Carbon Coated Fiber). The mechanism is to use the dense film layer of carbon to isolate the surface of the optical fiber from the outside world, so as to improve the mechanical fatigue loss of the optical fiber and the increase in the loss of hydrogen molecules. CCF is a type of Hermetic Coated Fiber (HCF).
Metal Coated Optical Fiber
Metal coated fiber (Metal Coated Fiber) is an optical fiber coated with metal layers such as Ni, Cu, Al, etc. on the surface of the optical fiber. There are also those covered with plastic on the outside of the metal layer, the purpose is to improve heat resistance and allow for electrification and welding. It is one of the anti-environment optical fibers and can also be used as a component of electronic circuits. Early products were made by coating molten metal during the drawing process. Due to the large difference in expansion coefficient between glass and metal, this method will increase micro-bending loss, and the practical rate is not high. Recently, the performance has been greatly improved due to the success of low-loss electroless coating on the surface of glass optical fiber.
rare earth doped fiber
In the core of the optical fiber, the optical fiber is doped with rare earth elements such as erbium (Er), chromium (Nd), praseodymium (Pr), etc. In 1985, Payne of the University of Southampton in the United Kingdom first discovered that the optical fiber doped with rare earth elements (Rare Earth DoPed Fiber) has the phenomenon of laser oscillation and optical amplification. Thus, since then, the veil of light amplification such as bait has been lifted, and the practical 1.55pm EDFA uses bait-doped single-mode fiber to excite with 1.47pm laser to obtain 1.55pm optical signal amplification. Additionally, praseodymium-doped fluoride fiber amplifiers (PDFAs) are under development.
Raman fiber
The Raman effect means that when a monochromatic light of frequency f is shot into a certain substance, f±fR, f±2fR and other frequencies of scattered light other than f will appear in the scattered light. This phenomenon is called the Raman effect. . Because it is produced by the energy exchange between the molecular motion of the substance and the lattice motion. When a substance absorbs energy, the vibration number of light becomes smaller, and the scattered light is called Stokes line. Conversely, when energy is obtained from matter, the scattered light whose vibration number becomes larger is called anti-Stokes line. Therefore, the deviation FR of the vibration number reflects the energy level and can show the inherent value in the substance. Optical fibers made of this nonlinear medium are called Raman optical fibers (RF: Raman Fiber). In order to confine the light in the tiny fiber core for long-distance transmission, there will be an interaction effect between light and matter, which can make the signal waveform undistorted and realize long-distance transmission. When the input light is enhanced, coherent inductively scattered light is obtained. Raman fiber lasers are used to induce Raman scattered light, which can be used as power supply for spectroscopic measurement and fiber dispersion test. In addition, inductive Raman scattering is being studied as an optical amplifier in long-distance optical fiber communication.
Eccentric Fiber
The core of the standard optical fiber is set at the center of the cladding, and the cross-sectional shape of the core and the cladding is concentric. However, due to different uses, there are also cases where the position of the core, the shape of the core, and the shape of the cladding are made into different states, or the cladding is perforated to form a special-shaped structure. Compared with standard optical fibers, these optical fibers are called special-shaped optical fibers . Eccentric fiber (Excentric Core Fiber), which is a kind of special-shaped fiber. Its core is set at an eccentric position off-center and close to the outer line of the cladding. Since the core is close to the outer surface, part of the optical field will overflow the cladding propagation (called this, Evanescent Wave). Utilizing this phenomenon, it is possible to detect the presence or absence of attached substances and changes in the refractive index. Eccentric Fiber Optics (ECF) are mainly used as fiber optic sensors for detecting substances. Combined with the test method of optical time domain reflectometer (OTDR), it can also be used as a distribution sensor.
Luminous Fiber
Optical fibers made of fluorescent substances are used. It is a part of the fluorescence generated when it is irradiated by light waves such as radiation and ultraviolet rays, and it can be transmitted through the optical fiber closure. Luminescent Fiber (Luminescent Fiber) can be used to detect radiation and ultraviolet rays, and perform wavelength conversion, or as a temperature sensor, chemical sensor. It is also called Scintillation Fiber in the detection of radiation. Luminescent optical fibers are developing plastic optical fibers from the perspective of fluorescent materials and doping.
multi-core fiber
A typical optical fiber consists of a core region and a cladding region surrounding it. But multi-core fiber (Multi Core Fiber) has multiple cores in a common cladding region. Due to the mutual proximity of the cores, two functions are possible. One is that the distance between the fiber cores is large, that is, there is no structure for optocouplers. This optical fiber can increase the integration density per unit area of the transmission line. In optical communication, ribbon cables with multiple cores can be manufactured, while in non-communication fields, tens of thousands of cores are used as optical fiber image bundles. The second is to make the distance between the fiber cores close to produce light wave coupling. Using this principle, dual-core sensors or optical circuit devices are being developed.
hollow fiber
The optical fiber is made hollow to form a cylindrical space, and the optical fiber used for light transmission is called hollow fiber (Hollow Fiber). Hollow-core optical fibers are mainly used for energy transmission, and can be used for X-ray, ultraviolet and far-infrared light energy transmission.
There are two types of hollow fiber structures:
One is to make the glass into a cylindrical shape, and the principle of the core and cladding is the same as that of the step type. Use the total reflection of light between air and glass to propagate. Because most of the light can be transmitted in the air without loss, it has a certain distance propagation function.
The second is to make the reflectivity of the inner surface of the cylinder close to 1 to reduce the reflection loss. In order to improve the reflectivity, there is a dielectric in the Jane to reduce the loss in the working wavelength band. For example, a loss of several dB/m at a wavelength of 10.6pm can be achieved.
polymer light guide
According to the material, there are inorganic optical fibers and polymer optical fibers, and the former is widely used in industry. Inorganic optical fiber materials are further divided into single-component and multi-component. The single component is quartz, and the main raw materials are silicon tetrachloride, phosphorus oxychloride and boron tribromide. Its purity requires that the impurity content of transition metal ions such as copper, iron, cobalt, nickel, manganese, chromium, and vanadium be less than 10ppb. In addition, OH ions are required to be less than 10ppb. Quartz fibers have been widely used. There are many multi-component raw materials, mainly silicon dioxide, boron trioxide, sodium nitrate, thallium oxide, etc. This material is not yet widely available. Polymer optical fiber is an optical fiber made of transparent polymer, which is composed of fiber core material and sheath material. The core material is high-purity and high-transparency polymethyl methacrylate or polystyrene fiber, and the outer layer is fluorine-containing polymer or silicone polymer.
The optical loss of polymer optical fiber is relatively high. In 1982, Nippon Telegraph and Telegraph Co., Ltd. used deuterated methyl methacrylate polymerized spinning as the core material, and the optical loss rate was reduced to 20dB/km. However, the characteristics of polymer optical fibers are that they can be made into optical fibers with large size and large numerical aperture, high light source coupling efficiency, good flexibility, micro bending does not affect light guiding ability, easy arrangement and bonding, easy to use, and low cost. However, the optical loss is large, so it can only be used in short distances. An optical fiber with an optical loss of 10-100dB/km can transmit hundreds of meters.
PM fiber
Polarization-maintaining optical fiber: Polarization-maintaining optical fiber transmits linearly polarized light, and is widely used in various fields of the national economy such as aerospace, aviation, navigation, industrial manufacturing technology, and communications. In the interferometric optical fiber sensor based on optical coherent detection, the use of polarization-maintaining optical fiber can ensure that the linear polarization direction remains unchanged, improve the coherent signal-to-noise ratio, and achieve high-precision measurement of physical quantities. As a special optical fiber, polarization maintaining optical fiber is mainly used in optical fiber gyroscopes, optical fiber hydrophones and other sensors and optical fiber communication systems such as DWDM and EDFA. Because fiber optic gyroscopes and fiber optic hydrophones can be used in military inertial navigation and sonar, they are new technological products, and polarization-maintaining optical fibers are their core components. Therefore, polarization-maintaining optical fibers have been included in the embargo list by Western developed countries. During the drawing process of the polarization maintaining fiber, the structural defects generated inside the fiber will cause the degradation of the polarization maintaining performance, that is, when the linearly polarized light is transmitted along one characteristic axis of the fiber, part of the optical signal will be coupled into another perpendicular to it. The characteristic axis will eventually cause a decrease in the polarization extinction ratio of the outgoing polarized light signal. This defect is the birefringence effect that affects the fiber. In polarization-maintaining fiber, the stronger the birefringence effect, the shorter the wavelength, and the better the polarization state of the transmitted light is maintained.
Application and Future Development Direction of Polarization Maintaining Optical Fiber
Polarization-maintaining fiber will have greater market demand in the next few years. With the rapid development of new technologies in the world and the continuous development of new products, polarization maintaining optical fiber will develop along the following directions:
(1) Adopt the new technology of photonic crystal fiber to manufacture new high-performance polarization-maintaining fiber;
(2) Develop temperature-adaptive polarization-maintaining optical fibers to meet the environmental requirements of aerospace and other fields;
(3) Develop various rare earth-doped polarization-maintaining fibers to meet the needs of optical amplifiers and other device applications;
(4) Develop fluoride polarization-maintaining optical fibers to promote the development of fiber optical interference technology in the field of infrared astronomy;
(5) Low-attenuation polarization-maintaining fiber: With the continuous improvement of single-mode fiber technology, loss, material dispersion and waveguide dispersion are no longer the main factors affecting optical fiber communication, and the polarization mode dispersion (PMD) of single-mode fiber has gradually become a limitation The most serious bottleneck of optical fiber communication quality, especially in high-speed optical fiber communication systems of 10 Gbit/s and above.
(6) Make polarized light devices by using Kerr effect and Faraday rotation effect.
In addition, depending on the fiber optic head, there are: C-Lens. G-Lens. Green lens
4. Commonly used optical fiber specifications:
Single mode: 8/125μm, 9/125μm, 10/125μm
Multimode: 50/125μm, European standard
62.5/125μm, American standard
Industrial, medical and low-speed network: 100/140μm, 200/230μm
Plastic: 98/1000μm for automotive controls
Transmission advantages
Until 1960, after American scientist Maiman invented the world's first laser, it provided a good light source for optical communication. Over the next two decades, people made breakthroughs in optical transmission media, and finally made low-loss optical fibers , thus laying the foundation of optical communication. Since then, optical communication has entered a stage of rapid development.
Optical fiber transmission has many outstanding advantages:
Bandwidth
The width of the frequency band represents the size of the transmission capacity. The higher the frequency of the carrier, the wider the frequency bandwidth over which the signal can be transmitted. In the VHF frequency band, the carrier frequency is 48.5MHz ~ 300Mhz. The bandwidth is about 250MHz, and it can only transmit 27 sets of TV sets and dozens of sets of FM radio. The frequency of visible light reaches 100,000 GHz, which is more than one million times higher than the VHF frequency band. Although the optical fiber has different losses for different frequencies of light, the frequency bandwidth is affected, but the frequency bandwidth in the lowest loss region can reach 30000 GHz. The bandwidth of a single light source only accounts for a small part of it ( the frequency band of multimode fiber is about several hundred megahertz, and a good single-mode fiber can reach more than 10GHz ), and advanced coherent optical communication can arrange 2000 optical carriers in the range of 30000GHz , for wavelength division multiplexing, which can accommodate millions of channels .
low loss
In a system composed of coaxial cables, the best cables have a loss of more than 40dB per kilometer when transmitting 800MHz signals. In contrast, the loss of optical fiber is much smaller. When transmitting 1.31um light, the loss per kilometer is less than 0.35dB. That's 100 million times less power loss than coaxial cable, allowing it to travel much farther.
In addition, there are two characteristics of optical fiber transmission loss,
One is that it has the same loss in all cable TV channels, and there is no need to introduce an equalizer for equalization like a cable trunk;
The second is that its loss hardly changes with the temperature, so there is no need to worry about the fluctuation of the mains level due to the change of the ambient temperature.
light weight
Because the optical fiber is very thin, the diameter of the single-mode optical fiber core wire is generally 4um to 10um, and the outer diameter is only 125um. With the addition of waterproof layer, reinforcing rib, sheath, etc., the diameter of the optical cable composed of 4 to 48 optical fibers is less than 13mm. It is much smaller than the 47mm diameter of the standard coaxial cable, and the optical fiber is glass fiber with a small specific gravity, which makes it have the characteristics of small diameter and light weight, and it is very convenient to install.
Strong anti-interference ability
Because the basic component of optical fiber is quartz, it only transmits light, does not conduct electricity, and is not affected by electromagnetic fields. The optical signal transmitted in it is not affected by electromagnetic fields, so optical fiber transmission has strong resistance to electromagnetic interference and industrial interference. Also because of this, the signal transmitted in the optical fiber is not easy to be eavesdropped, which is conducive to confidentiality.
High degree of integrity
Because optical fiber transmission generally does not require relay amplification, new nonlinear distortion will not be introduced due to amplification. As long as the linearity of the laser is good, TV signals can be transmitted with high fidelity. Actual tests show that the triple beat ratio C/CTB of a good AM fiber optic system is above 70dB, and the intermodulation index cM is also above 60dB, which is much higher than the nonlinear distortion index of a general cable trunk system.
Reliable performance
We know that the reliability of a system is related to the number of devices that make up the system. The more equipment there is, the greater the chance of failure. Because the fiber optic system contains a small number of devices (not dozens of amplifiers like the cable system), the reliability is naturally high, and the life of the fiber optic equipment is very long, with a trouble-free working time of 500,000 to 750,000 hours. Among them, the laser in the optical transmitter has the shortest life span, and the minimum life span is more than 100,000 hours. Therefore, the working performance of a well-designed, correctly installed and debugged optical fiber system is very reliable.
falling costs
Someone proposed a new Moore's Law, also known as the Optical Law (Optical Law). This law states that the bandwidth of optical fiber to transmit information doubles every six months, while the price doubles. The development of optical communication technology has laid a very good foundation for the development of Internet broadband technology. This clears the last obstacle for the large cable TV system to use optical fiber transmission. Due to the abundant sources of materials (quartz) for making optical fibers, the cost will be further reduced with the advancement of technology; while the copper raw materials required for cables are limited, and the price will become higher and higher. Obviously, optical fiber transmission will have an absolute advantage in the future and become the most important transmission means for establishing the province's and even the whole country's cable television network.
transfer speed
In 2023, an international team set a new record for transmission speed over industry-standard fiber optics: up to 1.7 petabytes per second of data transmission over 67 kilometers of fiber.
Structural principle
Optical fibers are composed of two layers of glass with different refractive indices. The inner layer is an optical core with a diameter of several microns to tens of microns, and the outer layer has a diameter of 0.1-0.2 mm. Generally, the refractive index of the inner core glass is 1% larger than that of the outer glass. According to the principle of refraction and total reflection of light, when the angle at which the light hits the interface between the inner core and the outer layer is greater than the critical angle for total reflection, the light cannot pass through the interface and is fully reflected.
fiber attenuation
The main factors that cause fiber attenuation are: intrinsic, bending, extrusion, impurities, unevenness and butt joint, etc.
Intrinsic
Is the inherent loss of the fiber, including: Rayleigh scattering, intrinsic absorption, etc.
bending
When the fiber is bent, part of the light in the fiber will be lost due to scattering, resulting in loss.
extrusion
The loss caused by the slight bending of the optical fiber when it is squeezed.
Impurities
Impurities in the fiber absorb and scatter the light propagating in the fiber, resulting in loss.
uneven
The loss caused by the uneven refractive index of the fiber material.
docking
Losses caused when optical fibers are connected, such as: out-of-axis (single-mode fiber coaxiality requirement is less than 0.8 μm), end faces not perpendicular to the axis, uneven end faces, mismatched butt core diameters, and poor splicing quality, etc.
artificial attenuation
In actual work, it is sometimes necessary to perform artificial fiber attenuation, such as optical fiber attenuators used for debugging optical power performance in optical communication systems, debugging fiber optic instrument calibration, and fiber optic signal attenuation.
production method
Optical fibers used in communication are generally silica optical fibers . The chemical name of quartz is silicon dioxide (SiO2), and it has the same main component as the sand we use to build our houses every day. But optical fibers made of ordinary quartz materials cannot be used for communication. Communication optical fibers must be composed of extremely pure materials; however, doping trace amounts of dopants in the host material can make the refractive index of the core and cladding slightly different, which is beneficial to communication.
Optical fiber preform made by VAD method
There are many methods for manufacturing optical fibers, mainly including: in-tube CVD (chemical vapor deposition) method, in-rod CVD method, PCVD (plasma chemical vapor deposition) method and VAD (axial vapor deposition) method. But no matter which method is used, it must first be made into a preform at a high temperature, then heated and softened in a high-temperature furnace, drawn into a filament, and then coated and overmolded to become an optical fiber core wire. The manufacture of optical fiber requires that each process should be quite precise and controlled by a computer. In the process of manufacturing optical fiber, pay attention to:
① The purity of optical fiber raw materials must be very high.
② It is necessary to prevent impurity contamination and air bubbles from mixing into the optical fiber.
③ It is necessary to accurately control the distribution of the refractive index;
④ Correctly control the structural size of the optical fiber;
⑤ Minimize the scar damage on the surface of the optical fiber and improve the mechanical strength of the optical fiber.
Tube and stick method
Insert the inner glass rod into the outer glass tube (as tight as possible), melt and draw;
double crucible method
In two concentric platinum crucibles, put the inner core and outer glass frit into the inner and outer crucibles respectively;
Molecular packing
The microporous quartz glass rod is immersed in the high refractive index additive solution to obtain the cross-sectional structure of the desired refractive index distribution, and then the wire drawing operation is relatively complicated. In the optical fiber communication, the internal and external vapor deposition method can also be used to ensure that the optical fiber with low light loss rate can be manufactured.
| vapor deposition |
||||||||
| object |
mandrel |
Outer cladding |
||||||
| method |
External Chemical Vapor Deposition （OVD） |
Improved Chemical Vapor Deposition/In-Tube Chemical Vapor Deposition （MCVD） |
axial chemical vapor deposition (WHAT) |
Plasma Chemical Vapor Deposition （PCVD） |
casing method |
powder method |
plasma spraying method |
Sol-gel |
| reaction mechanism |
flame hydrolysis |
high temperature oxidation |
flame hydrolysis |
low temperature oxidation |
VAD mandrel OVD deposited outer cladding |
|||
| heat source |
methane or oxyhydrogen flame |
oxyhydrogen flame |
oxyhydrogen flame |
plasma |
||||
| deposition direction |
Outer diameter of target rod |
Tube inner surface |
Target coaxial |
Tube inner surface |
||||
| deposition rate |
big |
middle |
big |
Small |
||||
| deposition craft |
Intermittent |
Intermittent |
continuous |
Intermittent |
||||
| Preform size |
big |
Small |
big |
Small |
||||
| Refractive index distributed control |
easy |
easy |
Singlemode: easy Multimode: Difficult |
extremely easy |
||||
| raw material purity Require |
Not strict |
strict |
Not strict |
strict |
||||
| research and development enterprise |
Developed by Corning Corporation in 1974 Fully operational in 1980 |
Developed by Alcatel in 1974 |
Developed by NTT Corporation of Japan in 1977 |
Developed by Philips of the Netherlands |
Developed by American Spectram in 1995 |
|||
| use factory (represent) |
Corning Corporation Japan Nishitani Co., Ltd. China Fortis |
Alcatel of America Tianjin 46 |
Japan's Sumitomo, Furukawa and other companies |
Netherlands Philips, China Wuhan Changfei Company |
||||
When the optical fiber is applied, it is also made into an optical cable. It is composed of several optical fibers combined to form an optical fiber core, which is covered with a plastic skin, and then the optical fiber core is combined into an optical cable. The number of optical fibers can range from dozens to Several hundred, the largest reaches 4000.
Schematic diagram of VAD process
space fusion
Putting the drawing device of optical fiber in the microgravity environment of space to draw it can obtain ultra-long and high-quality optical fiber that cannot be obtained on the earth.
Construction method
In practical applications, the connection between optical fiber and optical fiber is generally carried out by two methods of thermal fusion and cold splicing.
heat welding
使用光纤熔接机的高压电弧将两根光纤熔化后连接起来，这种方法早期一般用于长距离通讯施工，不过随着国民对网速需求的提高和光纤入户的兴起，热熔接法也用于短距离光纤铺设施工（如小区宽带网和光纤入户等），已成为国际上主流的光纤施工方法。
冷接法
冷接法是相对于热熔接法而言的，指不需要高压电弧放电来融化光纤，而使用光纤冷接子来将光纤连接起来或将光纤接入到光通讯设备中。
光纤分类
根据不同光纤的分类标准的分类方法，同一根光纤将会有不同的名称。
按光纤的材料分类
按照光纤的材料，可以将光纤的种类分为石英光纤和全塑光纤。
石英光纤一般是指由掺杂石英芯和掺杂石英包层组成的光纤。这种光纤有很低的损耗和中等程度的色散。通信用光纤绝大多数是石英光纤。
全塑光纤是一种通信用新型光纤，尚在研制、试用阶段。全塑光纤具有损耗大、纤芯粗（直径100～600μm）、数值孔径（NA）大（一般为0.3～0.5，可与光斑较大的光源耦合使用）及制造成本较低等特点。目全塑光纤适合于较短长度的应用，如室内计算机联网和船舶内的通信等。
按光纤剖面折射率分布分类
按照光纤剖面折射率分布的不同，可以将光纤的种类分为阶跃型光纤和渐变型光纤。
按传输模式分类
按照光纤传输的模式数量，可以将光纤的种类分为多模光纤和单模光纤。
单模光纤是只能传输一种模式的光纤。单模光纤只能传输基模（最低阶模），不存在模间时延差，具有比多模光纤大得多的带宽，这对于高码速传输是非常重要的。单模光纤的模场直径仅几微米（μm），其带宽一般比渐变型多模光纤的带宽高一两个数量级。因此，它适用于大容量、长距离通信。
按照国际标准规定分类（按照ITU-T 建议分类）
为了使光纤具有统一的国际标准，国际电信联盟（ITU-T）制定了统一的光纤标准（G 标准）。按照ITU-T 关于光纤的建议，可以将光纤的种类分为：
G.651 光纤（50/125μm 多模渐变型折射率光纤）
G.652 光纤（非色散位移光纤）
G.653 光纤（色散位移光纤DSF）
G.654 光纤（截止波长位移光纤）
G.655 光纤（非零色散位移光纤）。
为了适应新技术的发展需要，G.652 类光纤已进一步分为了G.652A、G.652B、G.652C 三个子类，G.655 类光纤也进一步分为了G.655A、G.655B 两个子类。
按照IEC 标准分类，IEC 标准将光纤的种类分为
A 类多模光纤：
A1a 多模光纤（50/125μm 型多模光纤）
A1b 多模光纤（62.5/125μm 型多模光纤）
A1d 多模光纤（100/140μm 型多模光纤）
B 类单模光纤：
B1.1 对应于G652 光纤，增加了B1.3 光纤以对应于G652C 光纤
B1.2 对应于G654 光纤
B2 光纤对应于G.653 光纤
系统运用
高分子光导纤维开发之初，仅用于汽车照明灯的控制和装饰。主要用于医学、装饰、汽车、船舶等方面，以显示元件为主。在通信和图像传输方面，高分子光导纤维的应用日益增多，工业上用于光导向器、显示盘、标识、开关类照明调节、光学传感器等。
通信应用
光导纤维可以用在通信技术里。1979年9月，一条3．3公里的120路光缆通信系统在北京建成，几年后上海、天津、武汉等地也相继铺设了光缆线路，利用光导纤维进行通信。
多模光导纤维做成的光缆可用于通信，它的传导性能良好，传输信息容量大，一条通路可同时容纳数十人通话。可以同时传送数十套电视节目，供自由选看。
利用光导纤维进行的通信叫光纤通信。一对金属电话线至多只能同时传送一千多路电话，而根据理论计算，一对细如蛛丝的光导纤维可以同时通一百亿路电话！铺设1000公里的同轴电缆大约需要500吨铜，改用光纤通信只需几公斤石英就可以了。沙石中就含有石英，几乎是取之不尽的。
医学应用
光导纤维内窥镜可导入心脏和脑室，测量心脏中的血压、血液中氧的饱和度、体温等。用光导纤维连接的激光手术刀已在临床应用，并可用作光敏法治癌。
另外，利用光导纤维制成的内窥镜，可以帮助医生检查胃、食道、十二指肠等的疾病。光导纤维胃镜是由上千根玻璃纤维组成的软管，它有输送光线、传导图像的本领，又有柔软、灵活，可以任意弯曲等优点，可以通过食道插入胃里。光导纤维把胃里的图像传出来，医生就可以窥见胃里的情形，然后根据情况进行诊断和治疗。
传感器应用
光导纤维可以把阳光送到各个角落，还可以进行机械加工。计算机、机器人、汽车配电盘等也已成功地用光导纤维传输光源或图像。如与敏感元件组合或利用本身的特性，则可以做成各种传感器,测量压力、流量、温度、位移、光泽和颜色等。在能量传输和信息传输方面也获得广泛的应用。
艺术应用
由于光纤的良好的物理特性，光纤照明和LED照明已越来越成为艺术装修美化的用途。
应用如下：
门头店名（标设）和LOGO采用粗光纤制作光晕照明。
门头的局部轮廓采用Φ18（Φ14）的侧光纤进行照明。
场所外立面局部采用光纤三维镜。
采用艺术分布的光纤点阵，配置光纤照明YY-S150光纤扫描机。
在草坪上布置光纤地灯。
光纤瀑布、光纤立体球等艺术造型。
同时也用在装饰显示、广告显示。
光纤也可以用作各种视觉艺术的展示等，光纤的特性得到充分的应用，如图所示：
光纤成为装饰品：利用光纤发光的特性，可以做成各种色彩的荧光光纤、满天星光纤花瓶、做礼品晚会用，还是室内装饰都很漂亮：如下图:
井下探测技术
过去，石油工业只能利用现有的技术开采油气储量，常常无法满足快速投资回收和最大化油气采收率的需求，并导致原油采收率平均只有35%左右。井下系统供应商预测，通过利用智能井技术可以使原油采收率提高到50%~60%。
在开发井中传感器之前，收集井下信息的唯一方法是测井。测井方法虽然能提供有价值的数据，但作业成本高，并有可能对井产生损害。因此，需要更好的井下技术提高无干扰流动监测和控制。
可以共同提高采收率的技术有：
·电子井下传感器，提供定点温度和压力监测；
·流量和含水量传感器；
·井下电-液压操控流动控制系统；
·基于实时油藏动态数据；
·优化油藏模拟；
·高温光纤井下传感器；
·电子与光纤井口湿式连接系统。
过去几年，传感器技术愈来愈多地从其它行业转向海上和井下，特别是光纤传感器技术，光纤传感器极大地提高了高温系统的可靠性。近期，大型井下设备供应商经常与光纤探测技术专业公司合作或收购这类公司，充分证实了这项技术的潜力。
光纤传感器系列包括3项被证实的核心技术和1项待开发的技术：
·分布式温度探测（DTS）。该项技术凭借一定长度的光纤监测不同位置上温度的变化。其温度分辨率为0.1oC，位置分辨率为1m（光纤长度大于10000m）。
·光纤还可以作为直接读值的机械点源传感器。最简单的形式，可能只是一个空腔，随外部压力改变长度，入射到空腔的光信号强度随空腔长度而下降。光纤传送设备允许在一根光纤上组合多个传感器，测量不同物理变量。
·化学探测。专业光纤的开发与工业应用正在增长，它们对化学物质的存在和丰度比较敏感。这种技术还不太先进，但很有发展潜力。
光纤收发器
光纤收发器是一种将短距离的双绞线电信号和长距离的光信号进行互换的以太网传输媒体转换单元，在很多地方也被称之为光电转换器。产品一般应用在以太网电缆无法覆盖、必须使用光纤来延长传输距离的实际网络环境中，且通常定位于宽带城域网的接入层应用；同时在帮助把光纤最后一公里线路连接到城域网和更外层的网络上也发挥了巨大的作用。
企业在进行信息化基础建设时，通常更多地关注路由器、交换机乃至网卡等用于节点数据交换的网络设备，却往往忽略介质转换这种非网络核心必不可少的设备。特别是在一些要求信息化程度高、数据流量较大的政府机构和企业，网络建设时需要直接上连到以光纤为传输介质的骨干网，而企业内部局域网的传输介质一般为铜线，确保数据包在不同网络间顺畅传输的介质转换设备成为必需品。
收发器分类
国外和国内生产光纤收发器的厂商很多，产品线也极为丰富。为了保证与其他厂家的网卡、中继器、集线器和交换机等网络设备的完全兼容，光纤收发器产品必须严格符合10Base-T、100Base-TX、100Base-FX、IEEE802.3和IEEE802.3u等以太网标准，除此之外，在EMC防电磁辐射方面应符合FCC Part15。时下由于国内各大运营商正在大力建设小区网、校园网和企业网，因此光纤收发器产品的用量也在不断提高，以更好地满足接入网的建设需要。
随着光纤收发器产品的多样化发展，其分类方法也各异，但各种分类方法之间又有着一定的关联。
按光纤性质分类
单模光纤收发器：传输距离20公里至120公里
多模光纤收发器：传输距离2公里到5公里
按光纤来分，可以分为多模光纤收发器和单模光纤收发器。由于使用的光纤不同，收发器所能传输的距离也不一样，多模收发器一般的传输距离在2公里到5公里之间，而单模收发器覆盖的范围可以从20公里至120公里。需要指出的是因传输距离的不同，光纤收发器本身的发射功率、接收灵敏度和使用波长也会不一样。
如5公里光纤收发器的发射功率一般在-20～-14db之间，接收灵敏度为-30db，使用1310nm的波长；而120公里光纤收发器的发射功率多在-5～0dB之间，接收灵敏度为-38dB，使用1550nm的波长。
按所需光纤分类：
单纤光纤收发器：接收发送的数据在一根光纤上传输
双纤光纤收发器：接收发送的数据在一对光纤上传输
顾名思义，单纤设备可以节省一半的光纤，即在一根光纤上实现数据的接收和发送，在光纤资源紧张的地方十分适用。这类产品采用了波分复用的技术，使用的波长多为1310nm和1550nm。但由于单纤收发器产品没有统一国际标准，因此不同厂商产品在互联互通时可能会存在不兼容的情况。另外由于使用了波分复用，单纤收发器产品普遍存在信号衰耗大的特点。市面上的光纤收发器多为双纤产品，此类产品较为成熟和稳定，但需要更多的光纤。
按工作层次/速率分类
100M以太网光纤收发器：工作在物理层
10/100M以太网光纤收发器：工作在数据链路层
按工作层次/速率来分，可以分为单10M、100M的光纤收发器、10/100M自适应的光纤收发器和1000M光纤收发器。其中单10M和100M的收发器产品工作在物理层，在这一层工作的收发器产品是按位来转发数据。该转发方式具有转发速度快、通透率高、时延低等方面的优势，适合应用于速率固定的链路上，同时由于此类设备在正常通信前没有一个自协商的过程，因此在兼容性和稳定性方面做得更好。
而10/100M光纤收发器是工作在数据链路层，在这一层光纤收发器使用存储转发的机制，这样转发机制对接收到的每一个数据包都要读取它的源MAC地址、目的MAC地址和数据净荷，并在完成CRC循环冗余校验以后才将该数据包转发出去。存储转发的好处一来可以防止一些错误的帧在网络中传播，占用宝贵的网络资源，同时还可以很好地防止由于网络拥塞造成的数据包丢失，当数据链路饱和时存储转发可以将无法转发的数据先放在收发器的缓存中，等待网络空闲时再进行转发。这样既减少了数据冲突的可能又保证了数据传输的可靠性，因此10/100M的光纤收发器适合于工作在速率不固定的链路上。
C-LENS
G-LENS
格林透镜
按结构分类
桌面式（独立式）光纤收发器：独立式用户端设备
机架式（模块化）光纤收发器：安装于十六槽机箱，采用集中供电方式
按结构来分，可以分为桌面式（独立式）光纤收发器和机架式光纤收发器。桌面式光纤收发器适合于单个用户使用，如满足楼道中单台交换机的上联。机架式（模块化）光纤收发器适用于多用户的汇聚，如小区的中心机房必须满足小区内所有交换机的上联，使用机架便于实现对所有模块型光纤收发器的统一管理和统一供电，国内的机架多为16槽产品，即一个机架中最多可加插16个模块式光纤收发器。
按管理类型分类
非网管型收发器：即插即用，通过硬件拨码开关设置电口工作模式
网管型收发器：支持电信级网络管理
按网管来分，可以分为网管型光纤收发器和非网管型光纤收发器。随着网络向着可运营可管理的方向发展，大多数运营商都希望自己网络中的所有设备均能做到可远程网管的程度，光纤收发器产品与交换机、路由器一样也逐步向这个方向发展。对于可网管的光纤收发器还可以细分为局端可网管和用户端可网管。局端可网管的光纤收发器主要是机架式产品，多采用主从式的管理结构，即一个主网管模块可串联N个从网管模块，每个从网管模块定期轮询它所在子架上所有光纤收发器的状态信息，向主网管模块提交。主网管模块一方面需要轮询自己机架上的网管信息，另一方面还需收集所有从子架上的信息，然后汇总并提交给网管服务器。如武汉烽火网络所提供的OL200系列网管型光纤收发器产品支持1（主） 9（从）的网管结构，一次性最多可管理150个光纤收发器。
按电源分类
内置电源：内置开关电源为电信级电源
外置电源：外置变压器电源多使用在民用设备上
按电源来分，可以分为内置电源和外置电源两种。其中内置开关电源为电信级电源，而外置变压器电源多使用在民用设备上。前者的优势在于能支持超宽的电源电压，更好地实现稳压、滤波和设备电源保护，减少机械式接触造成的外置故障点；后者的优势在于设备体积小巧和价格便宜。
按工作方式分类
全双工方式（full duplex）是指当数据的发送和接收分流，分别由两根不同的传输线传送时，通信双方都能在同一时刻进行发送和接收操作，这样的传送方式就是全双工制，如图1所示。在全双工方式下，通信系统的每一端都设置了发送器和接收器，因此，能控制数据同时在两个方向上传送。全双工方式无需进行方向的切换，因此，没有切换操作所产生的时间延迟。
半双式方式（half duplex）是指使用同一根传输线既作接收又作发送，虽然数据可以在两个方向上传送，但通信双方不能同时收发数据，这样的传送方式就是半双工制。采用半双工方式时，通信系统每一端的发送器和接收器，通过收/发开关转接到通信线上，进行方向的切换，因此，会产生时间延迟。 市面上有些晶片，只能使用全双工环境，无法支持半双工，若接至其他品牌的交换机（N-Way Switch）或集线器（HUB），其又使用半双工模式，则一定会造成严重的冲撞及丢包。
辨别方法
颜色辨别
黄色的代表单模
外套标识辨别
50/125, 62.5/125为多模，并且可能标有mm
光纤磨制端头
在放大镜下可辨别，多模呈同心圆
熔接机熔接时从屏上可辨别
多模纤中间没白条
单模中间有一白条
同时，熔接机对多模光缆不做熔接损耗计算。再，单模与多模光纤熔接机不能熔接。
单模收发器可以用于多模光缆链路，但注意跳线要用多模的。
依据信号在光纤中传输的模式，主要分两大类：单模和多模。模式通常是指光信号在光纤内的传输路径，单模的传输路径就是中心轴线；将光纤沿中轴线切出一个刨面，光信号在刨面上利用全反射进行传输。光纤可以拥有这种刨面无限多个，所以光信号的传输路径就会有无限多条，即有无限多种模式，如此传输的光纤就被称作多模光纤。
单模的纤芯尺寸一般是8~10um，在单模中信号沿直线进行传播，也就是一种模式。多模的纤芯比较大，50um或是62.5um，可以同时进行多种模式的传输。
单模的传输带宽高，传输距离远，主要用于中长距离的信号传输系统，如光纤到户、地铁和道路等长距离网络。但是，因为单模的纤芯比较小，与发射机连接时需要精确对接，从而耦合到较高的光源。这使得单模光纤网络系统的其他配件价格升高，单模光发射机的价格比多模的就贵不少。使用单模连接器进行端接时，要注意精确对接，不然会产生数值较高的插入损耗，降低光纤传输性能。
而多模能主要用于满足短距离网络的传输。事实上，多模光纤能够支持万兆以太网550米内的垂直子系统布线和短距离建筑群子系统布线，以及40G/100G网络150米内的数据中心布线。并且，多模光纤系统的光电转换元件比单模更便宜，现场安装和端接也更简单。
国际发展
2022年，英国伦敦玛丽女王大学的一个研究团队发明了一种利用钙钛矿制备光纤的全新应用。他们通过使用一种新的温度生长方法，能在非常便宜的液体溶液中生长并精确控制单晶有机金属钙钛矿纤维的长度和直径。研究成果9月23日发表在《科学进展》杂志上。
国内发展
光纤作为宽带接入一种主流的方式，有着通信容量大、中继距离长、保密性能好、适应能力强、体积小重量轻、原材料来源广价格低廉等的优点，未来在宽带互联网接入的应用可预料会非常广泛。
根据市场研究与预测公司IDC预计2012年中国光纤接入用户数将超过2660万户，未来5年保持56.4%的年复合增长率，而且中国已成为全球最大的光网络设备市场之一。截至2011年底，中国光纤接入端口数已超过1亿个，同比增长超过100%；中国光纤接入用户数已达1556万户，同比增长超过370%。比起中国1.58亿的宽带用户数，光纤接入用户数还将会有非常广阔的上升空间。根据我国光纤宽带发展计划，到2015年全国互联网出口带宽达到5T，城市家庭带宽接入能力基本达到20M以上，农村家庭带宽能力基本达到4M以上；家庭光纤接入覆盖超过500万户；无线局域网的公共运营热点规模将超过15万个；届时将实现全市公益性机构光纤到达率100%，实现全部科技园区、工业园区、商务楼宇、宾馆酒店等商务类场所的光纤到楼、到办公室。
这些数据都表明，中国的宽带市场蕴藏着巨大的潜力，必将是未来宽带运营商对抗的主战场之一。而光纤宽带的普及也是大势所趋。所以未来宽带市场的斗争很大程度上是光纤宽带的斗争。
中国电信集团副总工程师靳东滨表示，中国电信光纤宽带用户数量三年后将超过1亿，达到世界领先水平。中国联通也明确了2012年新增光纤到户家庭1000万。中国移动在2010年在三大运营商光纤光缆招标量达40%~50%。可以看出各大运营商对于光纤宽带这项前景看好的业务都给予了很大的重视。
2023年6月，北京量子信息科学研究院袁之良团队与南京大学尹华磊合作，首次在实验上实现打破安全码率-距离界限的异步测量设备无关量子密钥分发（也称模式匹配量子密钥分发），成功实现508公里光纤量子通信。
光纤之父
光纤之父——高锟
前香港中文大学校长高锟和George A. Hockham首先提出光纤可以用于通讯传输的设想，高锟因此获得2009年诺贝尔物理学奖。高锟从理论上分析证明了用光纤作为传输媒体以实现光通信的可能性，并预言了制造通信用的超低耗光纤的可能性。被誉为“光纤之父”。
转自：百度百科-验证