Optical fiber is the abbreviation of optical fiber. But Opti is usually used in optical communication systems.

Calfib is also simplified as optical fiber, such as fiber amplifier or light.

Fiber skeleton, etc. Some people ignore the significance of fiber, but in the optical system,

But in terms of optical fiber. So in the description of some optical products, fiber is literally translated as "fiber", obviously.

Is not desirable.

Optical fiber actually refers to the core made of transparent material and the surrounding material with slightly lower refractive index.

The cladding made of material is covered, and the optical signal injected into the fiber core is reflected by the cladding interface, so that the optical signal is in the fiber core.

The media that spread forward.

There are many kinds of optical fibers, and the required functions and performances are different according to different uses. But for those who

The design and manufacturing principles of optical fiber for CATV and communication are basically the same, such as: ① low loss; ② There is one.

Fixed bandwidth and small dispersion; ③ Easy wiring; (4) easy to unify; ⑤ High reliability; ⑥ The manufacturing is relatively simple; All landowners valence

Lian et al.

The classification of optical fibers mainly depends on the working wavelength, refractive index distribution, transmission mode, raw materials and manufacturing methods.

To sum up, the following are some examples of various classifications.

(1) working wavelength: ultraviolet fiber, observable fiber, near-infrared fiber, infrared fiber (0.85pm, 1.3pm,

1.55pm).

(2) refractive index distribution: step (SI) type, nearly step type, gradient (GI) type, others (such as triangle, W type,

Concave type, etc. ).

(3) Transmission mode: single-mode fiber (including polarization-maintaining fiber and non-polarization-maintaining fiber) and multimode fiber.

(4) Raw materials: timely glass, multielement glass, plastic and composite materials (such as plastic cladding, liquid fiber 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 plastic.

Wait a minute.

(5) Manufacturing method: Preforming includes vapor axial deposition (VAD), chemical vapor deposition (CVD), etc. And the wire drawing method comprises the following steps

Rod intubation method and double crucible method.

Second, the timely optical fiber

Silicon dioxide (SiO2) is used as the main raw material, and the core and cladding are controlled according to different doping amounts.

Optical fiber with refractive index distribution. Timing (glass) series optical fibers have the characteristics of low loss and wide frequency band, and have been widely used.

Used in cable TV and communication systems.

Fluorine-doped optical fiber is one of the typical products of timely optical fiber. Usually, as

In the optical fiber for 1.3 μm wave domain communication, the dopant controlling the core is GeO2 _ 2 and the cladding is SiO _ 2.

It's fried. However, silica is mostly used in the core of fluorine-doped optical fiber, while fluorine is doped in the cladding. Because,

Rayleigh scattering loss is a light scattering phenomenon caused by the change of refractive index. Therefore, it is desirable to form a refractive index change.

The doping of factors, the less the better.

The main function of fluorine is to reduce the refractive index of silicon dioxide. So it is often used for cladding doping. Due to doping

In fluorine fiber, the core does not contain fluorine dopant which affects the refractive index. Because its Rayleigh scattering is very small, and

The loss is also close to the theoretical minimum. So it is mostly used for long-distance optical signal transmission.

Compared with optical fibers of other materials, the optical fiber also has the characteristics from ultraviolet light to near infrared light.

External light has a broad spectrum of light transmission, which can be used to guide light and conduct images in addition to communication purposes.

Third, infrared fiber.

As the working wavelength of timely series optical fiber developed in the field of optical communication, although it is used for short transmission distance,

Can only be used at 2 pm. Therefore, it can work in the field of longer infrared wavelength, and the developed optical fiber is called infrared fiber.

Infrared optical fiber is mainly used for light energy transmission. Such as temperature measurement,

Thermal image transmission, laser scalpel medical treatment, thermal energy treatment, etc., the penetration rate is still low.

Fourth, multiple optical fibers

Composite fiber in silicon dioxide raw material, and then properly mixed with sodium oxide (Na2O),

Optical fibers made of multicomponent oxide glasses such as boron oxide (B2O2) and potassium oxide (K2O2) are characterized by multicomponent.

The softening point of the divided glass is lower than the corresponding softening point, and the refractive index difference between the core and cladding is very large. Optical fiber is mainly used in medical services.

Endoscope.

Fluoride fiber

Fluoride fiber is an optical fiber made of fluoride glass. This optical fiber raw material

ZBLAN (namely aluminum fluoride (ZrF4), barium cyanide (BaF2), lanthanum fluoride (LaF3) and aluminum fluoride) for short.

(A 1F2), sodium cyanide (NaF) and other chloride glass raw materials. The main work is at 2 ~ 10 in the afternoon.

Wavelength optical transmission service.

Because ZBLAN has the possibility of ultra-low loss optical fiber, the possibility of long-distance communication optical fiber is under way

Taking linear development as an example, its theoretical minimum loss can reach 10-2 ~ 10-3dB/km at 3pm wavelength, while

The optical fiber in time is between 0. 15 ~ 0. 16 dB/km at1.55pm.

At present, ZBLAN fiber can only be used for 2.4 ~ 2.7 pm temperature sensors and heaters because it is difficult to reduce the scattering loss.

Image transmission has not been widely used.

Recently, in order to use ZBLAN for long-distance transmission, 1.3pm doped fiber amplifier (PD

FA).

6. Plastic coated optical fiber

Plastic Clad Fiber is made of high-purity timely glass, which will be refracted.

Step-type optical fiber, the cladding of which is made of plastics such as silica gel, has a slightly slower speed. Compared with the timely fiber, it has

Core rent and high numerical aperture (NA). Therefore, it is easy to be combined with a light emitting diode (LED) light source, and the loss is also low.

Small. Therefore, it is very suitable for LAN and short-distance communication.

Seven. Plastic optical fiber

This is an optical fiber whose core and cladding are made of plastic (polymer). Early products were mainly used for decoration and

Light-guiding illumination and optical communication of short-distance optical key road.

The main raw materials are PMMA, PS and PC. wear

The inherent C-H bonding structure of plastics can generally reach tens of dB/km. Applications to reduce losses are being developed.

Fluorosol series plastics. Because the core diameter of plastic optical fiber is 1000 μm,

It is 100 times larger than single-mode optical fiber, which is simple to connect and easy to bend and construct. In recent years, coupled with broadband

The development of graded index multimode plastic optical fiber has attracted social attention. Recently,

It is widely used in automobile internal LAN and may also be used in home LAN in the future.

Eight, single-mode fiber

This refers to the optical fiber that can only transmit one propagation mode within the working wavelength, usually referred to as single-mode optical fiber.

(SMF: Single Mode Optical Fiber). At present, it is the most widely used optical fiber in cable TV and optical communication.

Because the core of the optical fiber is very thin (about 10pm) and the refractive index is distributed in a stepped manner, when the normalized frequency v is a parameter,

When the number is less than 2.4, only single-mode transmission can be formed theoretically. In addition, SMF has no multimode dispersion, it not only transmits frequency bands.

Compared with multimode fiber, it is wider, and its synthetic characteristics are just right with and without the material dispersion and structural dispersion of SMF.

The characteristic of zero dispersion makes the transmission band wider.

In SMF, there are many kinds because of different dopants and different manufacturing methods. Recessed clad fiber

Cladding fiber), its cladding forms a double structure, and the cladding adjacent to the core is more refractive than the cladding.

This ratio is still very low. In addition, the cladding refractive index distribution of matched cladding fiber is uniform.

Nine, multimode fiber

According to its possible propagation modes, optical fibers with multiple modes are called multimode fibers (MMF:

Multimode fiber). The core diameter is 50pm, and the transmission modes can reach hundreds, which is better than SMF.

Bandwidth is mainly determined by mode dispersion. Historically, it has been used for short-distance transmission in cable TV and communication systems. oneself

Since SMF fiber appeared, it seems to be a historical product. But in fact, because the core diameter of MMF is larger than that of SMF, it is similar to that of LED.

Equal light sources are easy to combine and have advantages in many local area networks. Therefore, MMF is still constantly updated in the field of short-distance communication.

Be valued.

When MMF is classified according to refractive index distribution, there are two types: gradient (GI) type and step (SI) type. GI type

The refractive index is the highest in the center of the core and decreases gradually along the cladding. From the point of view of geometrical optics, in the core part,

The advancing beam propagates in a snake shape. Because each path of light takes about the same time. So, by

The transmission capacity is larger than that of SI type.

The refractive index distribution of silicon MMF fiber is the same as that of the core, but the interface with the cladding is the same.

Step. Due to the reflection of SI-type light wave in optical fiber, the time difference of each optical path is generated, which leads to

The emitted light wave is distorted and the color excitation is large. Therefore, the transmission bandwidth becomes narrower, and the application of silicon MMF is less at present.

Dispersion-shifted fiber

When the working wavelength of single-mode fiber is 1.3Pm, the mode field diameter is about 9Pm, and its transmission loss is about 0.3 dB/km.

At this time, the zero dispersion wavelength is just at1.3pm..

In the timely optical fiber, the transmission loss of 1.55pm section is the smallest (about 0.2 dB/km) from the perspective of raw materials. because

The erbium-doped fiber amplifier (EDFA), which has been put into practical use now, works in the band of1.55pm. If it is also in this band,

It can achieve zero dispersion, which is more conducive to the application of long-distance transmission in 1.55Pm band.

Therefore, the comprehensive cancellation characteristics of timely material dispersion and core structure dispersion in optical fiber materials are skillfully used.

The original zero dispersion in the 1.3Pm segment can be moved to the 1.55pm segment to form zero dispersion. Therefore, it is named color.

DSF: dispersion shifted fiber (DSF).

The main way to increase the structural dispersion is to improve the refractive index distribution performance of the core.

In the long-distance transmission of optical communication, it is important, but not unique, that the fiber dispersion is zero. Other attributes

There are also small losses, easy connection, wiring or small changes in working characteristics (including bending, stretching and environmental changes)

Influence). These factors should be considered comprehensively in the design of DSF.

Eleven-dispersion flat fiber

Dispersion-shifted fiber (DSF) is a single-mode fiber with zero dispersion in 1.55 μm band. Scottish guy whispers

DFF (Dispersive Flat Fiber) is an optical fiber that will change from 1.3Pm to1.55pm.

Optical fiber with low dispersion and almost zero dispersion in broadband is called DFF. Because DFF has to do this.

The dispersion decreases in the range of 1.3 pm ~ 1.55 pm. It is necessary to design the refractive index distribution of optical fiber in a complicated way.

However, this kind of fiber is very suitable for wavelength division multiplexing (WDM) lines. Due to the process comparison of DFF fiber

Complicated and expensive. In the future, with the increase of output, the price will also decrease.

Twelve-dispersion compensation fiber

For trunk systems using single-mode optical fiber, most of them adopt 1.3pm band zero dispersion optical fiber structure.

It's over. But at present, the lowest loss is1.55pm. Because of the practicability of EDFA, if the dispersion energy is zero at 1.3pm,

It will be very beneficial to make the wavelength of 1.55pm work on optical fiber.

Because, in the fiber with zero dispersion of 1.3Pm, the dispersion of 1.55Pm band is about 16 ps/km/nm.

If a section of optical fiber with opposite dispersion sign is inserted into the optical fiber line, the entire optical fiber line can be made.

The deviation is zero. The optical fiber used for this purpose is called dispersion compensation fiber (DCF).

Synthetic fiber).

Compared with the standard 1.3pm zero dispersion fiber, DCF has smaller core diameter and larger refractive index difference.

DCF is also an important part of WDM optical lines.

Thirteen-bias maintaining fiber

The light wave propagating in optical fiber has the nature of electromagnetic wave, so it is single except the basic light wave.

In addition to modes, there are basically two orthogonal modes of electromagnetic field (TE, TM) distribution. Usually, due to

The cross-sectional structure of optical fiber is circularly symmetric, the propagation constants of these two polarization modes are equal, and the two polarized lights are different from each other.

Interference. But in fact, optical fiber is not completely circularly symmetric. For example, if it has a curved part, there will be two deflections.

The combination factors between vibration modes are irregularly distributed on the optical axis. Dispersion caused by this change of polarized light,

It is called polarization mode dispersion (PMD). For cable TV, which mainly distributes images now, the impact is not too great.

However, for some future UWB services with special requirements, such as: ① heterodyne detection in coherent communication, it is necessary to

When the polarization of light waves is more stable; (2) When the input and output characteristics of the optical machine are related to polarization; 3 production.

Polarization-maintaining optical coupler and polarizer or depolarizer, etc. (4) Making optical fiber sensors by optical interference.

Where the polarization wave is required to remain unchanged, the fiber whose polarization state remains unchanged by improving it is called polarization.

PMF (polarization maintaining fiber) is also called fixed polarization.

Optical fiber.

Fourteen birefringent optical fibers

Birefringent fiber refers to single-mode fiber, which can transmit light with two inherent polarization modes orthogonal to each other.

As far as fibers are concerned. Because the phenomenon that the refractive index changes with the bias direction is called birefringence. In the method of inducing birefringence

Medium. It is also called panda fiber, which is polarization maintaining fiber.

Ning and absorption-reducing fibers). It is characterized in that heat is distributed in two transverse directions of the core.

Glass parts with large expansion coefficient and circular cross section. During the drawing process of high-temperature fibers, these parts shrink,

As a result, tensile stress is generated in the Y direction of the core, while compressive stress is generated in the X direction. Resulting in the fiber exhibiting photoelasticity.

Sex effect, so that the refractive index is different in X direction and Y direction. According to this principle, polarization remains unchanged.

Fifteen-resistant optical fiber for harsh environment

The normal working environment temperature of optical fiber for communication can be between -40℃ and +60℃, and the design is not limited.

On the premise of radiation exposure. In contrast, it can withstand high pressure or external force at lower or higher temperatures.

Optical fibers that can work in harsh environments that affect and expose radiation are called hard.

Conditioned fiber).

Usually, in order to mechanically protect the optical fiber surface, it is necessary to coat an extra layer of plastic. However, with the increase of temperature,

The protective function of plastics decreases, which limits the use temperature. If you use heat-resistant plastics, such as polyethylene,

PTFE and other resins can work at 300℃. It is also coated on the surface of timely glass.

Nickel and aluminum (A 1). This kind of optical fiber is called heat-resistant fiber (heat-resistant fiber B-

Er).

In addition, when the optical fiber is irradiated, the optical loss will increase. This is because timely glass met.

When exposed to radiation, structural defects (also known as color centers) will appear in glass, especially in

When the wavelength is 0.4 ~ 0.7 pm, the loss increases. The preventive method is to use the timely glass doped with OH or F, which can inhibit it.

Make up for the loss caused by radiation. This kind of fiber is called radiation-resistant fiber (radiation-resistant)

Nt optical fiber), which is mostly used to monitor the optical fiber mirror of nuclear power plant.

Sixteen hermetically coated optical fibers

In order to keep the mechanical strength and loss of optical fiber stable for a long time, silicon carbide was coated on the glass surface.

Inorganic materials such as (SiC), titanium carbide (TiC) and carbon (C) are used to prevent water and hydrogen from entering from the outside.

The manufactured optical fiber (HCF) is diffused. At present, the general is in progress.

In the production process of chemical vapor deposition (CVD), carbon layers are piled up at high speed to achieve the effect of complete sealing. such

Carbon coated optical fiber (CCF) can effectively block the invasion of optical fiber and external hydrogen molecules. It is reported that it is at room temperature.

It can last for 20 years in hydrogen environment without increasing loss. Of course, it is to prevent moisture from invading and delay the fatigue of mechanical strength.

The fatigue parameters in the fatigue process can reach more than 200. Therefore, HCF is suitable for

Systems that require high reliability in harsh environments, such as submarine optical cables, are an example.

Seventeen-carbon coated optical fiber

The optical fiber whose surface is coated with carbon film is called CCF: carbon coated optical fiber (CCF).

Fiber). Its mechanism is to use dense carbon film to isolate the fiber surface from the outside world, thus improving the fiber.

Mechanical fatigue loss and hydrogen molecular loss increase. CCF is a hermetically coated optical fiber (HCF).

Eighteen-layer coated optical fiber

Metal coated optical fiber is an optical fiber coated with Ni, Cu, A 1 etc.

Optical fiber with metal layer. There are also those that are coated with plastic on the outside of the metal layer to improve heat resistance and provide ventilation.

Electricity and welding. It is one of the anti-environmental optical fibers and can also be used as an element of electronic circuits.

Early products were made by coating molten metal during wire drawing. Because this method is made of glass and

The difference of expansion coefficients of metals is too large, which will increase the slight bending loss and the utility rate is not high. Recently, due to

The success of low-loss electroless plating on the surface of glass fiber greatly improves its properties.

XIX rare earth doped fiber

What rare earth elements, such as erbium, neodymium and praseodymium, are doped in the core of optical fiber?

Optical fiber. Payne 1985, Sourthampton University, UK.

Firstly, it is found that rare earth doped fiber has laser oscillation and optical amplification.

Phenomenon. Thus, the veil of optical amplification such as miserable bait was unveiled, and it has been applied to 1.55pmEDFA.

That is, the doped single-mode fiber is excited by the laser of 1.47pm, and the optical signal amplifier of 1.55pm is obtained.

The big one. In addition, wrongly doped fluoride fiber amplifier (PDFA) is under development.

Twenty Raman fibers

Raman effect means that when monochromatic light with human frequency f is emitted into matter, the monochromatic light with frequency f will appear in scattered light.

Scattered light with frequencies other than f fR and f 2fR is called Raman effect. Because it is a substance.

Because of the energy exchange between molecular motion and lattice motion. When matter absorbs energy, light vibrates.

The number of shifts becomes smaller, and the scattered light is called Stokes line. On the other hand, getting energy from matter.

Scattered light with large vibration number is called anti-Stokes line. So the deviation FR of the vibration number reflects the energy level,

It can show the intrinsic value of matter.

The optical fiber made of this nonlinear medium is called radio frequency: Raman fiber (RF).

In order to enclose light in tiny fiber cores for long-distance propagation, there will be interaction between light and matter.

The effect can make the signal waveform undistorted and realize long-distance transmission.

When the input light is enhanced, coherent induced scattered light will be obtained. Application of induced Raman scattering light

Equipped with Raman fiber laser, it can be used as power supply for spectrum measurement and fiber dispersion test. In addition, I feel

Raman scattering is being studied as an optical amplifier in long-distance optical fiber communication.

2 1 eccentric fiber

The core of standard optical fiber is located in the center of cladding, and the cross-sectional shapes of the core and cladding are concentric circles.

However, due to different uses, the position of the fiber core, the shape of the fiber core and the shape of the cladding are also made into different States or wrapped.

The perforated layer forms a special-shaped structure. Compared with standard optical fibers, these optical fibers are called profiled optical fibers.

Eccentric core fiber is a kind of fiber with special shape. Its fiber core arrangement

In an eccentric position off the center, close to the outer line of the cladding. Because the core is close to the outer surface, some light fields will overflow.

Cladding propagation (called evanescent wave).

Therefore, when the substance is attached to the surface of the optical fiber, the light wave propagating in the optical fiber is affected due to the optical characteristics of the substance.

To the impact. If the refractive index of the attached substance is higher than that of the optical fiber, light waves are radiated to the outside of the optical fiber. If the attachment

When the refractive index of mass is lower than that of optical fiber, light waves cannot radiate outward, but will be absorbed by matter.

Loss. Using this phenomenon, we can detect whether there are attached substances and the change of refractive index.

ECF is mainly used as an optical fiber sensor to detect substances. And optical time domain reflectometer (OTDR)

Combined with the test method, it can also be used as a distributed sensor.

Twenty-two luminescent fibers

Optical fiber made of fluorescent substance. When it is irradiated by light waves such as radiation and ultraviolet rays,

Part of the generated fluorescence can be transmitted through a closed optical fiber.

Luminous fibers can be used to detect radiation and ultraviolet rays, as well as to enter.

Line wavelength conversion, or used as temperature sensor and chemical sensor. It is also called flash in radiation detection.

Optical fiber (scintillation fiber).

Luminous fiber is a plastic fiber developed from the perspective of fluorescent materials and doping.

Twenty-three multi-core optical fibers

An ordinary optical fiber consists of a core region and a cladding region surrounding it. But Multi-core optical fiber (multi)

A core optical fiber) is a cladding region having a plurality of cores. Because the fiber cores are close to each other

Degree, can have two functions.

One is that the fiber core spacing is large, that is, there is no optical coupling structure. This kind of optical fiber can improve transmission

Integral density per unit area of a line. In optical communication, multi-core ribbon optical cable can be made.

In the non-communication field, there are thousands of fiber cores as optical fiber image bundles.

The second is to make the fiber core spacing close, which can produce light wave coupling. Using this principle, it is open.

Double fiber core sensor or optical path device.

24 hollow fibers

Optical fiber is hollow and forms a cylindrical space for light transmission, which is called hollow optical fiber.

Hollow fiber.

Hollow optical fiber is mainly used for energy transmission, which can be used for X-ray, ultraviolet and far infrared light energy transmission. empty

There are two kinds of core optical fiber structures: one is to make glass cylindrical, and its core and cladding principles are the same as those of ladder type.

Using the total reflection of light between air and glass. Because most of the light can be in lossless air.

Communication has the function of communication at a certain distance. The second is to make the reflectivity of the inner surface of the cylinder close to 1 to reduce the reflection.

Radiation loss. In order to improve the reflectivity, a dielectric is arranged in Jane, which reduces the loss in the working wavelength band.

For example, the loss of wavelength 10.6pm can reach several db/m. ..

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