Optical fiber is an optical fiber (OF: Optical Fiber) for short. But the optical communication system is often Optical Fibe (optical fiber) and simplified to Fiber, for example: Fiber Amplifier (FiberAmplifier) or Fiber Backbone (Fiber Backbone) 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, the description of the fiber directly translated into "fiber", is clearly not desirable.
Fiber actually refers to the core made of transparent materials and cladding around it than the core of the refractive index of the material is slightly lower than the core of the cladding is covered, and will be injected into the core of the light signal, through the cladding interface reflections, so that the light signal propagation in the core of the media forward.
There are many types of optical fibers, according to the different uses, 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.
The classification of optical fiber is mainly from the working wavelength, refractive index distribution, transmission mode, raw materials and manufacturing methods for a generalization of the classification of the following examples.
(1) working 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 fiber core, etc.), infrared materials. According to the coated material can also be divided into inorganic materials (carbon, etc.), metal materials (copper, nickel, etc.) and plastics.
(5) manufacturing methods: pre-molding with vapor-phase axial deposition (VAD), chemical vapor deposition (CVD), etc., drawing method has a tube law (Rod intube) and double crucible method.
Two, quartz optical fiber
Silicon dioxide (SiO2) as the main raw material, and according to different doping, to control the core and cladding of the refractive index distribution of the optical fiber. Quartz (glass) series of optical fiber, with low consumption, broadband characteristics, is now widely used in cable television and communication systems.
Fluorine Doped Fiber (Fluorine Doped Fiber) 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 better to have fewer dopants to cause refractive index variation.
Fluorocarbon is mainly used to reduce the refractive index of SIO2. Therefore, it is commonly used in the doping of the cladding. As 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. So more for long-distance optical signal transmission.
Quartz fiber (Silica Fiber) and other raw materials compared to the optical fiber, but also from the ultraviolet light to the near-infrared light transmittance broad spectrum, in addition to communications purposes, but also can be used for light conduction and conduction of images and other fields.
Three, infrared optical fiber
The quartz series of optical fibers developed in the field of optical communication can only be used for 2 pm as the operating wavelength for a short transmission distance, and the optical fiber developed to work in the field of longer infrared wavelengths is called an 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, thermal processing, etc., the popularity rate is still low.
Four, compound optical fiber
Compound fiber (Compound Fiber) in the SiO2 raw materials, and then mixed appropriately, such as sodium oxide (Na2O), boron oxide (B2O2), potassium oxide (K2O2), and other oxides of the multi-component glass made of optical fiber, featuring a multi-component glass than the softening point of the quartz is lower than that of the refractive index of the core and the cladding of the refractive index of the core is very large difference. Mainly used in the medical business of fiber optic endoscopy.
V, fluoride fiber
Chloride fiber (Fluoride Fiber) is made of fluoride glass fiber. This fiber optic material is also referred to as ZBLAN (that is, 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. Mainly work in 2 ~ 10pm wavelength optical transmission business.
As ZBLAN has the possibility of ultra-low-loss optical fiber, is being used for long-distance communication fiber feasibility development, for example: its theoretical minimum loss, in the 3pm wavelength when up to 10-2 ~ 10-3dB / km, while the quartz fiber in 1.55pm but in the 0.15 ~ 0.16dB / Km between.
At present, ZBLAN fiber can only be used for temperature sensors and thermal
image transmission at 2.4 to 2.7pm due to the difficulty of reducing scattering loss, and is not yet widely practical.
Recently, a 1.3pm fault-doped fiber amplifier (PDFA) is being developed to utilize ZBLAN for long-distance transmission.
Six, Plastic Clad Fiber
Plastic Clad Fiber (Plastic Clad Fiber) is a high-purity quartz glass as the core, and the refractive index is slightly lower than quartz, such as silicone and other plastics as a cladding 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.
VII, plastic optical fiber
This is the core and cladding are made of plastic (polymer) optical fiber. 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 km. In order to reduce losses are being developed and applied to fluorosol series of plastics. As plastic optical fiber (Plastic Optical fiber) core diameter of 1000pm, 100 times larger than single mode quartz fiber, simple splicing, and easy to bend 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 received attention from society. Recently, it has been rapidly used in LAN inside automobiles, and may be used in home LAN in the future.
VIII, Single Mode Fiber
This refers to the working wavelength, can only transmit a propagation mode of the optical fiber, usually referred to as single mode fiber
(SMF: Single ModeFiber). Currently, it is the most widely used fiber in cable television and optical communications.
Because the core of the fiber is very thin (about 10 pm) and the refractive index is step-like distribution, when the normalized frequency V parameter <2.4, theoretically, can only form a single mode transmission. In addition, SMF does not have multimode dispersion, not only the transmission band is wider than multimode fiber, plus the SMF material dispersion and structural dispersion of the additive offset, the synthetic characteristics of the formation of zero-dispersion characteristics, so that the transmission band is more broadened.
There are many types of SMFs, depending on the dopant and manufacturing method. DePr-essed Clad Fiber (DePr-essed Clad Fiber), 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.
Nine, multi-mode fiber
The optical fiber according to the work of the length of its propagation of the possible modes for a number of modes of optical fiber called multi-mode fiber (MMF: MUlti ModeFiber). The core diameter is 50pm, and because the transmission modes can be up to several hundred, the transmission bandwidth is dominated by mode dispersion compared to SMF. 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 regaining importance in the field of short-distance communication.
When MMFs are 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 core, and decreases slowly along the cladding. From a geometric optics point of view, the light beam advancing in the core appears to propagate in a serpentine fashion. Since each path of light takes approximately the same amount of time, the transmission capacity is higher than that of the SI type. Therefore, the transmission capacity is larger than SI type.
The refractive index distribution of SI-type MMF fiber, the core refractive index distribution is the same, 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 the ejection of light wave distortion, color excitation is larger. As a result, the transmission bandwidth becomes narrower, and SI-type MMFs are less used at present.
Ten, dispersion shift fiber
Single-mode fiber operating wavelength in 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 to see the 1.55pm section of the transmission loss is the smallest (about 0.2dB/km). Since now has been practical erbium-doped fiber amplifier (EDFA) is working in the 1.55pm band, if in this band can also achieve zero dispersion, it is more conducive to the application of 1.55Pm band long-distance transmission.
So, the clever use of optical fiber materials in the quartz material dispersion and core structure dispersion of the synthetic offset characteristics of the original in the 1.3Pm section of the zero dispersion, shifted to the 1.55pm section also constitutes zero dispersion. Therefore, it is named Dispersion Shifted Fiber (DSF: DispersionShifted Fiber).
The method to increase the structural dispersion is mainly to improve the refractive index distribution performance in the fiber core.
Zero fiber dispersion is important, but not unique, in long-distance transmission for optical communications. Other properties are low loss, easy splicing, cable formation or work with little change in characteristics (including bending, stretching and environmental changes affect).DSF is in the design, a combination of these factors.
XI dispersion flat fiber
Dispersion-shifted fiber (DSF) is a single-mode fiber design zero dispersion is located in the 1.55pm band of the fiber. Dispersion Flattened Fiber (DFF: Dispersion Flattened Fiber) 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. It requires a complex design of the refractive index distribution of the fiber. 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, with the increase in production, the price will be reduced.
Twelve dispersion-compensated fiber
For the use of single-mode fiber trunk system, because most of the use of 1.3pm band dispersion is zero fiber composition. However, nowadays, the loss of 1.55pm is the smallest, and due to the practical use of EDFA, it would be very beneficial if the 1.3pm zero dispersion fiber can also be made to work at 1.55pm wavelength.
Because, in 1.3Pm zero-dispersion fiber, the dispersion in the 1.55Pm band is as much as about 16ps/km/nm.
If in this fiber optic line, insert a section of fiber with the opposite sign of this dispersion, you can make the entire optical line
dispersion is zero. The fiber used for this purpose is called a Dispersion Compensation Fiber (DCF: DisPersion Compensation Fiber).
DCF has a finer core diameter and a larger refractive index difference than standard 1.3pm zero-dispersion fiber.
DCF is also an important component of WDM optical circuits.
Thirteen Polarization Holding Fibers
Light waves propagating in optical fibers, because of the nature of electromagnetic waves, there are essentially two orthogonal modes of the electromagnetic field (TE, TM) distribution in addition to the basic single
mode of light waves. Normally, because the structure of
the cross-section of an optical fiber is circularly symmetric, the propagation constants of these two polarized 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 is a binding factor between the two polarization modes
, which is irregularly distributed on the optical axis. The dispersion caused by this change in polarized light is called polarization mode dispersion (PMD). For the current distribution of image-based cable television, the impact is not yet too great. 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.
XIV birefringent fiber
Birefringent fiber refers to a single-mode fiber, can be transmitted orthogonal to each other in the two intrinsic polarization modes of light
Fiber. Because, the phenomenon that 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, that is, Polarization-maintai-ning AND Absorption- reducing fiber. It is a glass part with a large coefficient of thermal expansion and a circular cross-section in the transverse direction of the fiber core. In the high-temperature fiber drawing process, these parts shrink, 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.
Fifteen anti-hazardous environment fiber
Communication fiber is usually working in the ambient temperature can be between -40 ~ +60 ℃, the design is not subject to a large number of radiation as a prerequisite. In contrast, optical fibers that can operate at lower or higher temperatures and in harsh environments where they can be subjected to high pressures or external forces and exposed to radiation are called Hard
Condition Resistant Fibers (HRF).
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 the plastic decreases, which limits the temperature at which the fiber can be used. If you switch to heat-resistant plastics, such as poly
Tetrafluoroethylene (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. These fibers are called Heat Resistant Fibers (Heat Resistant Fib-
er).
Additionally, when optical fibers are exposed to radiant rays, the light loss increases. This is because when quartz glass is exposed to
radiation, structural defects (also called color centers: Colour Center) appear in the glass, 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
Suppression of loss defects caused by radiation lines. This fiber is called radiation-resistant fiber (Radiation Resista-
nt Fiber), mostly used in nuclear power stations to monitor the use of optical fiber mirrors.
XVI Sealed Coated Fiber
In order to maintain the mechanical strength of the optical fiber and the loss of long-term stability, and the glass surface coating silicon carbide
(SiC), titanium carbide (TiC), carbon (C) and other inorganic materials, used to prevent the diffusion of water and hydrogen from the outside
manufactured by the optical fiber (HCF): Hermetically Coated Fiber (HCF: Hermetically Coated Fiber). 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 in a room-temperature
hydrogen environment without increasing losses. Of course, it prevents the intrusion of moisture to delay the mechanical strength of the fatigue
labor process, its fatigue coefficient (Fatigue Parameter) can reach more than 200. Therefore, HCF is used in
harsh environment requires high reliability of the system, such as undersea fiber optic cable is an example.
XVII Carbon Coated Optical Fiber
In the quartz optical fiber surface coated with a carbon film of optical fiber, known as carbon coated fiber (CCF: Carbon Coated
Fiber).
xviii Metal Coated Fiber
Metal Coated Fiber (Metal Coated Fiber) is an optical fiber coated with Ni, Cu, A1 and other
metal layers on the surface of the optical fiber. There are also coated with plastic on the outside of the metal layer, aiming to improve heat resistance and be available for pass
electricity and welding. It is one of the anti-viral environment fiber, can also be used as a component of electronic circuits.
Early products were made by coating molten metal during the drawing process. Due to this method because of the difference between the expansion coefficient of the glass and
metal is too large, will increase the small bending loss, the rate of commercialization is not high. Recently, due to the success of the low-loss non-electrolytic coating method on the surface of the
glass fiber, the performance has been greatly improved.
XIX doped rare earth optical fiber
In the core of the fiber, doped with how (Er), Chin (Nd), spectrum (Pr) and other rare earth elements
fiber. 1985, the United Kingdom's Sourthampton (Sourthampton) University of the Pace (Payne) and other first
first found that the doped rare earth elements of optical fiber (). Rare Earth DoPed Fiber) has the phenomenon of laser oscillation and light amplification
. Thus, from then on unveiled the veil of tragic bait and other light amplification, has now 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 optical signal amplification
large. In addition, the fault-doped fluoride fiber amplifier (PDFA) is under development.
Twenty LaMan fiber
LaMan effect refers to a substance in the shot frequency f monochromatic light, in the scattered light there will be a frequency f
outside the frequency f ± fR, f ± 2fR and other frequencies of the scattered light, the phenomenon known as the LaMan effect. This phenomenon is called the Raman effect because it is produced by the exchange of energy between the molecular motion and lattice motion of matter
. When matter absorbs energy, the vibration
momentum of light becomes smaller, and this scattered light is called a Stokes line. On the contrary, from the matter to get energy, and
vibrational number becomes larger scattered light, is called anti-Stokes lines. Thus the deviation FR of the vibrational number, which reflects the energy level,
can show the value inherent in the matter.
The optical fiber made from this nonlinear media is called Raman fiber (RF: Raman Fiber).
In order to enclose the light in a tiny core for long-distance propagation, there is a light-matter interaction
effect that enables the signal waveform to be undistorted, enabling long-distance transmission.
Coherent induced scattered light is obtained when the input light is enhanced. A device that applies induced Raman scattered light
is equipped with a Raman fiber laser, which can be used as a power source for spectroscopic measurements and for fiber dispersion testing. In addition, the induction
Raman scattering, long-distance communication in the fiber, is being discussed as an optical amplifier applications.
XXI Eccentric fiber
The core of the standard optical fiber is set in the center of the cladding, the core and the cladding of the cross-sectional shape of concentric circles.
But due to different uses, there will be the core location and core shape, cladding shape, made into different states or cladding
Layer perforation to form a heterogeneous structure. Relative to the standard optical fiber, these fibers are called shaped optical fiber.
Eccentric Core Fiber (Excentric Core Fiber), which is a type of shaped fiber. The core is set
in an eccentric position off-center and close to the outer line of the cladding. Because of the core's proximity to the exterior, some of the light field propagates out of the cladding (called the Evanescent Wave).
Therefore, when there is a substance attached to the surface of the 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 radiates out of the fiber. If the refractive index of the attached material
texture is lower than the refractive index of the optical fiber, light waves can not be radiated out, but will be subject to material absorption of light waves
loss. Using this phenomenon, it is possible to detect the presence or absence of attached substances and changes in the refractive index.
Eccentricity 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.
Twenty-two luminescent optical fiber
Optical fiber manufactured using fluorescent substances. It is irradiated by radiation, ultraviolet light and other light waves,
a portion of the fluorescence generated by the optical fiber can be closed by the optical fiber for transmission of the optical fiber.
Luminescent fiber (Luminescent Fiber) can be used for the detection of radiation and ultraviolet light, as well as for wavelength conversion, or used as a temperature sensitive device, chemical sensitive device. It is also known as Scintillation Fiber in the detection of radiation.
Luminescent fiber from the perspective of fluorescent materials and doping, is being developed in plastic fibers.
XXIII Multi-core fiber
The usual optical fiber is composed of a core area and the cladding area around it. But Multi
Core Fiber (Multi
Core Fiber) is a **** the same cladding area in the presence of multiple cores. Because of the proximity of the cores to each other
, there are two functions.
One is a structure with a large core spacing, i.e., no optical coupling. This kind of fiber, as it can improve the integrated density per unit area of the transmission
line. In optical communications, can be made into a ribbon cable with multiple cores,
and in the field of non-communication, as a fiber optic imaging beam, there will be made into thousands of cores.
The second is to make the distance between the core close, can produce light wave coupling. The use of this principle is developing
Double core sensitizer or optical loop device.
Twenty-four Hollow Fiber
The optical fiber is made hollow, forming a cylindrical space, used for optical transmission of optical fiber, called hollow fiber
(Hollow Fiber).
Hollow fibers are mainly used for energy transmission for X-ray, ultraviolet, and far-infrared light energy transmission. Hollow
There are two types of hollow fiber structure: one is to make the glass into a cylinder, and its core and cladding principle is the same as the step-type.
The use of light in the air and glass between the total reflection propagation. As a result, most of the light can propagate 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
radiation loss. In order to improve the reflectivity, there is a dielectric inside the Jane, so that the operating wavelength band loss is reduced.
For example, it can be made to the wavelength of 10.6pm loss of a few dB / m.
This is the first time in the world that a dielectric is used.