Optical fibers are divided into single-mode and multi-mode
Types and scope of application of optical fiber jumper interfaces
The classification and overview of optical fiber jumpers are as follows:
Fiber optic jumpers (also known as fiber optic connectors), which are fiber optic connectors that connect to optical modules, come in many types, and they are not interoperable with each other. The SFP module is connected to the LC fiber optic connector, while the GBIC is connected to the SC fiber optic connector. The following is a detailed description of several commonly used optical fiber connectors in network engineering:
①FC type optical fiber jumper: The external reinforcement method is a metal sleeve, and the fastening method is a turnbuckle. Generally used on the ODF side (most commonly used on patch panels)
②SC type optical fiber jumper: a connector connected to the GBIC optical module. Its shell is rectangular and the fastening method is a plug-and-pull latch. formula, no rotation required. (Most used on router switches)
③ST-type optical fiber jumper: commonly used in optical fiber distribution frames, the shell is round, and the fastening method is a screw buckle. (For 10Base-F connections, the connector is usually ST type. Commonly used in fiber optic patch panels)
④LC type fiber optic patch cord: Connects to the SFP module connector, which adopts a modular and easy-to-operate Jack (RJ) latch mechanism is made. (Commonly used in routers)
⑤MT-RJ type optical fiber jumper: a square optical fiber connector with integrated transceiver and integrated dual-fiber transceiver at one end
ST and SC connectors are commonly used in general networks. The ST connector is fixed with a bayonet after half a turn after being inserted. The disadvantage is that it is easy to break. The SC connector is directly plugged in and out, which is very convenient to use. The disadvantage is that it is easy to fall out. The FC connector is generally used in telecommunications networks and has a nut screwed to the adapter. The advantage is that it is easy to break. It is reliable and dust-proof, but the disadvantage is that it takes a little longer to install. The MTRJ fiber optic jumper consists of two high-precision plastic molded connectors and an optical cable. The outer parts of the connector are precision plastic parts, including a push-pull plug-in clamping mechanism. Suitable for indoor applications in telecommunications and data network systems.
Optical fiber module: generally supports hot swapping. The optical fiber interface used by GBIC is mostly SC or ST type; SFP, that is, small package GBIC, uses LC type optical fiber.
Fiber used:
Single-mode: L wavelength 1310 Single-mode long-distance LH wavelength 1310, 1550
Multi-mode: SM wavelength 850
SX/LH means that single-mode or multi-mode optical fiber can be used
In the labels indicating pigtail connectors, we often see "FC/PC", "SC/PC", etc. The meaning is as follows
1 The front part of "/" indicates the connector model of the pigtail
The "SC" connector is a standard square connector, made of engineering plastics, with high temperature resistance and not easy to oxidize advantage. The optical interface on the transmission equipment side generally uses SC connectors
The "LC" connector has a similar shape to the SC connector and is smaller than the SC connector.
The "FC" connector is a metal connector, generally used on the ODF side. Metal connectors can be plugged and unplugged more times than plastic ones.
There are many types of connectors with signals. In addition to the three types introduced above, there are also MTRJ, ST, MU, etc.
2.'/'The following indicates the fiber connector cross-section process , that is, the grinding method
"PC" is the most widely used in telecom operators' equipment, and its joint cross-section is flat.
The attenuation of "UPC" is smaller than that of "PC". It is generally used for equipment with special needs. Some foreign manufacturers use FC/UPC for internal fiber jumpers in ODF racks, mainly to improve ODF equipment. own indicators.
In addition, the "APC" model is widely used in radio and television and early CATV. Its pigtail head adopts an inclined end face, which can improve the quality of the TV signal. The main reason is that the TV signal is Simulating light modulation, when the connector coupling surface is vertical, the reflected light returns along the original path.
Since the uneven refractive index distribution of the fiber will return to the coupling surface again, although the energy is very small at this time, the analog signal cannot completely eliminate the noise, so it is equivalent to superimposing a signal on the original clear signal. Weak signals with time delays appear as ghost images on the screen. The inclination of the pigtail headband prevents the reflected light from returning along the original path. Generally, digital signals generally do not have this problem.
Scope of use:
A: Optical fiber communication system
B: Optical fiber broadband access network
C: Optical fiber CATV
D: Local area network LAN
E: Fiber optic instrument meter
F: Fiber optic sensor
G: Fiber optic data transmission system
H: Test equipment
The classification of optical fibers is mainly based on working wavelength, refractive index distribution, transmission mode, raw materials and manufacturing methods
We will summarize various Classification examples are as follows.
(1) Working wavelength: UV fiber, visible 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, other (such as triangular type, W type,
Concave type wait).
(3) Transmission mode: single-mode fiber (including polarization-maintaining fiber, non-polarization-maintaining fiber), multi-mode fiber.
(4) Raw materials: quartz glass, multi-component glass, plastic, composite materials (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
etc.
(5) Manufacturing methods: Pre-molding includes vapor axial deposition (VAD), chemical vapor deposition (CVD), etc., and drawing methods include
Rod intube ) and the double crucible method, etc.
2. Quartz optical fiber
Uses silica (SiO2) as the main raw material, and controls the fiber core and cladding according to different doping amounts
Fibers with refractive index profiles. Quartz (glass) series optical fibers have the characteristics of low consumption and broadband, and are now widely used in cable TV and communication systems.
Fluorine Doped Fiber is one of the typical products of quartz optical fiber. Usually, as a communication optical fiber in the 1.3Pm wave domain, the dopant controlling the core is dioxide (GeO2), and the cladding is made of SiO
. However, most of the cores of fluorine-connected optical fibers use SiO2, while fluorine is incorporated into the cladding. Because,
Rayleigh scattering loss is a light scattering phenomenon caused by changes in the refractive index. Therefore, it is desirable to have as few dopants as possible that cause a refractive index change
factor.
The main function of fluorine is to reduce the refractive index of SIO2. Therefore, it is often used for doping of cladding. Because in
fluorine-doped optical fiber, the core does not contain fluorine dopants that affect the refractive index. Because its Rayleigh scattering is very small and the loss is close to the theoretical minimum. Therefore, it is mostly used for long-distance optical signal transmission.
Compared with optical fibers made of other raw materials, quartz optical fiber (Silica Fiber) also has a broad spectrum of light transmission from ultraviolet light to near-red
External light. In addition to communication purposes, It can also be used in fields such as light guidance and image transmission.
3. Infrared optical fiber
As the working wavelength of the quartz series optical fiber developed in the field of optical communication, although it is used in shorter transmission distances,
it is only Available for 2pm. For this reason, the optical fiber developed can work in the longer infrared wavelength field and 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., but the penetration rate is still low.
Four. Compound Fiber
Compound Fiber is mixed with SiO2 raw materials, such as sodium oxide (Na2O),
boron oxide ( Optical fiber made of multi-component glass of oxides such as B2O2) and potassium oxide (K2O2). The characteristic of the multi-component glass is that the softening point of the multi-component glass is lower than that of quartz and the refractive index difference between the core and the cladding is very large. . Optical fiber endoscopes mainly used in the medical business.
5. Fluoride optical fiber
Chloride optical fiber (Fluoride Fiber) is an optical fiber made of fluoride glass. This optical fiber raw material is also referred to as ZBLAN (i.e. aluminum fluoride (ZrF4), barium cyanide (BaF2), lanthanum fluoride (LaF3), aluminum fluoride
(A1F2) , sodium cyanide (NaF) and other chloride glass raw materials are simplified as an abbreviation. It mainly works in the optical transmission business of 2 ~ 10pm
Because ZBLAN has ultra-low loss. The possibility of optical fiber is being developed for the feasibility of long-distance communication optical fiber. For example, its theoretical minimum loss can reach 10-2~10-3dB/km at 3pm wavelength. , while
Quartz fiber is between 0.15~0.16dB/Km at 1.55pm.
Currently, ZBLAN fiber can only be used at 2.4~2.7 due to difficulty in reducing scattering loss. pm thermosensors and thermal image transmission have not yet been widely used.
Recently, in order to use ZBLAN for long-distance transmission, 1.3pm doped fiber amplifiers (PD
FA).
6. Plastic Clad Fiber
Plastic Clad Fiber is made of high-purity quartz glass into a fiber core that refracts
A step-type optical fiber with a slightly lower efficiency than quartz, such as silica gel, as a cladding. Compared with quartz optical fiber, it has a core diameter and a numerical aperture (NA). High characteristics. Therefore, it is easy to combine with light-emitting diode LED light sources, and the loss is also small. Therefore, it is very suitable for local area network (LAN) and short-range communication. 7. Plastic. Optical fiber
This is an optical fiber whose core and cladding are made of plastic (polymer). Early products are mainly used for decoration and
light guide lighting and short-distance optical bonding. In optical communications.
The raw materials are mainly organic glass (PMMA), polystyrene (PS) and polycarbonate (PC). The loss is affected by the inherent C- of plastic. H combined with structural constraints, generally can reach tens of dB per km. In order to reduce the loss, fluorocarbon series plastics are being developed and applied. Since the core diameter of plastic optical fiber is 1000pm,
100 times larger than single-mode silica fiber, easy to connect, easy to bend and easy to construct. In recent years, with the progress of broadband
, it is a multi-mode graded index (GI) refractive index. The development of plastic optical fibers has attracted social attention.
It has been rapidly used in automotive internal LANs and may also be used in home LANs in the future.
8. Single-mode optical fibers.
This refers to an optical fiber that can only transmit one propagation mode in the operating wavelength, usually referred to as single-mode fiber (SMF: Single ModeFiber). Currently, it is the most widely used optical fiber in cable TV and optical communications.
Since the core of the optical fiber is very thin (about 10pm) and the refractive index is distributed in a step-like manner, when the normalized frequency V parameter
is <2.4, theoretically, only Can form single-mode transmission.
In addition, SMF has no multi-mode dispersion. Not only does the transmission frequency band
are wider than that of multi-mode optical fiber, but also the additive cancellation of SMF's material dispersion and structural dispersion makes its synthetic characteristics just right
has zero dispersion characteristics, which further broadens the transmission frequency band.
There are many types of SMF due to differences in dopants and manufacturing methods. DePr-essed Clad Fiber (DePr-
essed Clad Fiber), its cladding forms a double structure, the cladding adjacent to the core has a higher refractive index than the outer cladding
Still low. In addition, there are matched cladding fibers whose cladding refractive index is evenly distributed.
9. Multimode optical fiber
An optical fiber that has multiple propagation modes according to its working length is called multimode optical fiber (MMF:
MUlti ModeFiber). The core diameter is 50pm. Since the transmission modes can reach hundreds, compared with SMF, the transmission bandwidth is mainly dominated by mode dispersion. Historically used for short-distance transmission in cable television and communications systems. Since the emergence of SMF optical fiber, it seems to have formed a historical product. But in fact, because MMF has a larger core diameter than SMF and is easier to combine with light sources such as LED, it has more advantages in many LANs. Therefore, MMF is still receiving renewed attention in the field of short-distance communications.
When MMF is classified according to the refractive index distribution, there are two types: gradient (GI) type and step (SI) type. GI type
The refractive index is highest at the core center and gradually decreases along the cladding. From the perspective of geometric optics, the forward light beam propagates in a serpentine shape in the fiber core. Because each path of light takes approximately the same time. Therefore, the transmission capacity is larger than that of SI type.
The refractive index distribution of SI type MMF fiber and the core refractive index distribution are the same, but the interface with the cladding is
step-shaped. Due to the reflection and progression of SI-type light waves in the optical fiber, time differences occur in each light path, resulting in
distortion of the emitted light wave and large color excitation. As a result, the transmission bandwidth becomes narrower, and currently SI type MMF is rarely used.
10. Dispersion-shifting fiber
When the operating wavelength of 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 quartz optical fibers, the 1.55pm segment has the smallest transmission loss (about 0.2dB/km) from the perspective of raw materials. Since
the now practical Erbium-doped Fiber Amplifier (EDFA) operates in the 1.55pm band, if zero dispersion can also
be achieved in this band, it will be more conducive to the application of 1.55 Long distance transmission in Pm band.
Thus, by cleverly utilizing the synthetic cancellation characteristics of the quartz material dispersion in the optical fiber material and the core structure dispersion,
the original zero dispersion in the 1.3Pm segment can be shifted. The segment up to 1.55pm also constitutes 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 long-distance transmission of optical communications, zero fiber dispersion is important, but not the only one. Other properties include low loss, easy splicing, and little change in characteristics during cabling or operation (including the effects of bending, stretching, and environmental changes). DSF takes these factors into consideration in design.
11 Dispersion Flat Fiber
Dispersion-shifted fiber (DSF) is a single-mode fiber designed with zero dispersion in the 1.55pm band.
Dispersion Flattened Fiber (DFF: Dispersion Flattened Fiber) has a wider dispersion from 1.3Pm to 1.55pm and can achieve very low dispersion, almost Optical fibers that achieve zero dispersion are called DFF. Because DFF needs to reduce dispersion in the range of 1.3pm to 1.55pm. This requires complex design of the refractive index distribution of the optical fiber.
However, this kind of optical fiber is very suitable for wavelength division multiplexing (WDM) lines. Because the process of DFF optical fiber is more complex and more expensive. As production increases in the future, prices will also decrease.
Twelve-dispersion compensating optical fiber
For trunk systems using single-mode optical fiber, most of them are composed of optical fibers with zero dispersion in the 1.3pm band
. However, 1.55pm, which has the smallest loss now, will be very beneficial if the 1.55pm wavelength can also be operated on the 1.3pm zero-dispersion optical fiber due to the practical use of EDFA.
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 dispersion sign is inserted into this optical fiber line, the
dispersion of the entire optical line can be zero. The optical fiber used for this purpose is called dispersion compensating fiber (DCF: DisPersion Compe-
nsation Fiber).
Compared with 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 lines.
The Thirteen Partial Sect maintains the optical fiber
The light waves propagating in the optical fiber have the properties of electromagnetic waves, so in addition to the basic single light wave mode
, essentially there are two orthogonal modes of electromagnetic field (TE, TM) distribution. Usually, since the structure of the optical fiber cross-section is circularly symmetrical, the propagation constants of the two polarization modes are equal, and the two polarized lights do not interfere with each other. But in fact, the optical fiber is not completely circularly symmetrical. For example, if it has a curved part, there will be a combination of two polarization modes, which will be irregularly distributed on the optical axis. The dispersion caused by this change in polarized light is called polarization mode dispersion (PMD). For cable TV, which currently focuses on distributing images, the impact is not too great.
However, for some future ultra-wideband services that have special requirements, such as: ①Heterodyne detection is used in coherent communications, when the light wave polarization is required to be more stable; ②Optical machines, etc. When the input and output characteristic requirements are related to polarization; ③ When making
polarization-maintaining optical couplers, polarizers or depolarizers, etc.; ④ When making optical fiber sensors that utilize optical interference, etc.
When the polarization wave is required to remain constant, an optical fiber that has been modified to keep the polarization state unchanged is called a polarization maintaining fiber (PMF: Polarization Maintaining fiber), which is also called fixed polarization.
Fiber optic.
Fourteen birefringent optical fibers
Birefringent optical fibers refer to single-mode optical fibers that can transmit light of two mutually orthogonal intrinsic polarization modes
In terms of fiber. Because the phenomenon of the refractive index varying with the deflection direction is called birefringence. In methods of causing birefringence
. It is also called PANDA fiber, which is polarization-maintai-
ning AND Absorption- reducing fiber. It is a glass part with a large thermal expansion coefficient and a circular cross-section on both sides of the fiber core.
During the high-temperature fiber drawing process, these parts shrink, resulting in tension in the y-direction of the fiber core and compressive stress in the x-direction. This causes a photoelastic effect in the fiber material, causing a difference in refractive index between the X and y directions. According to this principle, the polarization remains constant.
Fifteen harsh-environment-resistant optical fibers
The normal working environment temperature of communication optical fibers can be between -40 and +60°C, and they are also designed to be resistant to severe environmental conditions
Amount of radiation exposure is the premise. In contrast, optical fibers that can work in harsh environments with lower or higher temperatures, as well as those that can be subjected to high pressure or external force
, or exposed to radiation are called harsh environment optical fibers (Hard
p>
Condition Resistant Fiber).
Generally, in order to mechanically protect the optical fiber surface, an extra layer of plastic is coated. However, as the temperature rises,
the protective function of plastic decreases, resulting in restrictions on the use temperature. If you switch to heat-resistant plastics, such as polytetrafluoroethylene (Teflon) and other resins, you can work in an environment of 300°C. There are also quartz glass surfaces coated with metals such as nickel (Ni) and aluminum (A1). This kind of optical fiber is called Heat Resistant Fiber-
er.
In addition, when the optical fiber is illuminated by radiation, the optical loss will increase. This is because when quartz glass is exposed to radiation, structural defects (also called color centers) will appear in the glass, especially at wavelengths of 0.4 to 0.7pm. time loss increases. The preventive method is to use quartz glass doped with OH or F, which can suppress the loss defects caused by radiation. This kind of optical fiber is called radiation resistant optical fiber (Radiation Resista-
nt Fiber), which is mostly used in optical fiber mirrors for monitoring nuclear power plants.
Sixteen-sealed coated optical fiber
In order to maintain the mechanical strength of the optical fiber and the long-term stability of the loss, silicon carbide is coated on the glass surface
(SiC ), titanium carbide (TiC), carbon (C) and other inorganic materials to prevent the diffusion of water and hydrogen from the outside (HCF: Hermetically Coated Fiber). At present, it is common to use high-speed deposition of carbon layers in the chemical vapor deposition (CVD) production process to achieve a sufficient sealing effect. This kind of
Carbon-coated optical fiber (CCF) can effectively cut off the intrusion of optical fiber and external hydrogen molecules. It is reported that it can last 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. Its fatigue coefficient (Fatigue Parameter) can reach more than 200. Therefore, HCF is used in systems that require high reliability in harsh environments, such as submarine optical cables.
Seventeen-carbon coated optical fiber
An optical fiber that is coated with a carbon film on the surface of a quartz optical fiber is called a carbon-coated optical fiber (CCF: Carbon Coated)
Fiber). The mechanism is to use a dense film layer of carbon to isolate the optical fiber surface from the outside world to improve the mechanical fatigue loss of the optical fiber and the increase in the loss of hydrogen molecules. CCF is a type of hermetically coated fiber (HCF).
Eighteen metal-coated optical fibers
Metal-coated optical fibers (Metal Coated Fiber) are coated with Ni, Cu, A1, etc. metals on the surface of the optical fiber
layer of optical fiber. There are also those that are coated with plastic outside the metal layer in order to improve heat resistance and provide for electrical connection and welding. It is one of the optical fibers that are resistant to harsh environments and can also be used as a component of electronic circuits.
Early products were made by coating molten metal during the drawing process. Since the expansion coefficients of this method are too different between glass and
metal, which will increase the micro-bending loss, the practical application rate is not high. Recently, due to the success of using low-loss electrolytic coating method on the surface of
glass optical fiber, the performance has been greatly improved.
Nineteen rare earth-doped optical fibers
In the core of the optical fiber, rare earth elements such as Er (Er), Nd (Nd), and Pr (Pr) are doped.
Fiber optics. In 1985, Payne and others from the University of Southampton in the UK first discovered that rare earth doped optical fiber (Rare Earth DoPed Fiber) has laser oscillation and light amplification
>phenomenon. As a result, the veil of optical amplification such as bait has been unveiled. The now practical 1.55pm EDFA
uses bait-doped single-mode fiber and uses a 1.47pm laser for excitation to obtain a 1.55pm optical signal amplifier.
Big. Additionally, doped fluoride fiber amplifiers (PDFA) are under development.
Twenty Raman optical fiber
The Raman effect means that when monochromatic light of frequency f is emitted into a substance, frequency f will appear in the scattered light
Scattered light with frequencies other than f±fR and f±2fR is called the Raman effect. Because it is produced by the energy exchange between the molecular motion and the lattice motion of matter
. When a substance absorbs energy, the vibration number of light
becomes smaller, and the scattered light is called a Stokes line. On the contrary, when energy is obtained from matter and the scattered light becomes larger in vibration number, it 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.
The optical fiber made of this nonlinear media is called Raman fiber (RF: Raman Fiber).
In order to confine light in a small fiber core and propagate it over long distances, there will be an interaction effect between light and matter.
The signal waveform will not be distorted and the signal waveform will not be distorted. Long distance transmission.
When the input light is enhanced, coherent induced scattered light is obtained. Equipment that uses induced Raman scattered light
It is equipped with Raman fiber laser, which can be used as a power supply for spectroscopic measurement and fiber dispersion testing. In addition, the application of induced Raman scattering as an optical amplifier in long-distance optical fiber communications is being studied.
Twenty-one Eccentric Optical Fiber
The core of a standard optical fiber is set in the center of the cladding, and the cross-sectional shapes of the core and the cladding are concentric circles.
However, due to different uses, the core position, core shape, and cladding shape can also be made into different states or the cladding
perforated to form a special-shaped structure. Compared with standard optical fibers, these optical fibers are called special-shaped optical fibers.
Excentric Core Fiber is a type of special-shaped optical fiber. Its core is set
in an eccentric position off-center and close to the outer line of the cladding. Since the fiber core is close to the surface, part of the light field will overflow
and propagate through the cladding (this is called the Evanescent Wave).
Therefore, when a substance is attached to the surface of the optical fiber, the light waves propagating in the optical fiber are affected
due to the optical properties of the substance. If the refractive index of the attached material is higher than that of the optical fiber, the light waves will radiate out of the optical fiber. If the refractive index of the attached material is lower than the refractive index of the optical fiber, the light wave cannot be radiated outward, but will be lost by the material absorbing the light wave. Using this phenomenon, the presence or absence of attached substances and changes in refractive index can be detected.
Eccentric optical fiber (ECF) is mainly used as an optical fiber sensor for detecting substances.
Combined with the optical time domain reflectometer (OTDR) test method, it can also be used as a distributed sensor.
Twenty-two Luminous Optical Fibers
Using optical fibers made of fluorescent substances. It is an optical fiber that can transmit part of the fluorescence produced when it is illuminated by radiation, ultraviolet and other light waves.
It can be transmitted through the optical fiber closure.
Luminescent Fiber can be used to detect radiation and ultraviolet rays,
convert wavelength, or be used as a temperature sensor or chemical sensor. In the detection of radiation, it is also called scintillation fiber.
Fiber (Scintillation Fiber).
Light-emitting optical fiber Plastic optical fiber is being developed from the perspective of fluorescent materials and doping.
Twenty-three multi-core optical fiber
Usually an optical fiber is composed of a core area and a cladding area surrounding it. However, multi-core fiber (Multi
Core Fiber) has multiple cores in the same cladding area. Due to the close proximity of the cores to each other, they can have two functions.
One is that the fiber core spacing is large, that is, the structure does not produce optical coupling. This kind of optical fiber can increase the integration density per unit area of ??transmission lines. In optical communications, ribbon cables with multiple fiber cores can be made.
In non-communication fields, as optical fiber imaging bundles, tens of thousands of fiber cores can be made.
The second is to bring the distance between the fiber cores closer, which can produce light wave coupling. Using this principle, dual-fiber core sensors or optical circuit devices are being developed.
Twenty-four hollow optical fibers
The optical fiber is made hollow to form a cylindrical space for light transmission, which is called hollow optical fiber
（Hollow Fiber).
Hollow-core optical fiber is mainly used for energy transmission and can transmit X-ray, ultraviolet and far-infrared light energy.
There are two types of hollow core optical fiber structures: one is to make glass into a cylindrical shape, and the core and cladding principles are the same as the step type.
Use the total reflection propagation of light between air and glass. Because most of the light can propagate in lossless air
it has the propagation function of a certain distance. The second is to make the reflectivity of the inner surface of the cylinder close to 1 to reduce reflection loss. In order to improve the reflectivity, a dielectric is installed inside the module to reduce the loss in the working wavelength range.
For example, the loss at wavelength 10.6pm can reach several dB/m.