Optical fiber, optical cable

Optical fiber, optical cable

1. Fiber
1 Overview

Optical fiber is similar to coaxial cable, except that it does not have a mesh shield. At the center is a glass core for light propagation. In multimode fiber, the diameter of the core is 15mm ~ 50mm, which is roughly equivalent to the thickness of human hair. The diameter of single-mode fiber core is 8mm ~ 10mm. The outside of the core is surrounded by a glass envelope with a lower refractive index than the core to keep the optical fiber in the core. Outside is a thin layer of plastic jacket to protect the envelope. Fibers are usually bundled into bundles and protected by an outer shell. The fiber core is usually a double-layer concentric cylinder made of quartz glass with a small cross-sectional area. It is brittle and easy to break, so it needs an additional protective layer. Its structure is shown in Figure 1.

Figure 1 Schematic diagram of optical fiber planing

The optical fiber on land is usually buried 1 meter underground, and sometimes it will be damaged by small animals underground. Near the coast, the transoceanic fiber jacket was buried in the trench. In deep water, they are at the bottom and are most likely to be bitten by fish or hit by a fishing boat.

2. Classification

Optical fiber is mainly divided into the following two categories:

1) Transmission point modulus

The transmission point modulus is divided into single mode fiber (Single Mode Fiber) and multimode fiber (MulTI Mode Fiber). The single-mode fiber has a very small core diameter and can only be transmitted in a single mode at a given operating wavelength, with a transmission frequency bandwidth and large transmission capacity. Multimode fiber is an optical fiber that can be transmitted in multiple modes simultaneously at a given operating wavelength. Compared with single-mode fiber, the transmission performance of multi-mode fiber is worse.

2) Refractive index distribution

The optical fibers with refractive index distribution can be divided into hopping optical fibers and graded optical fibers. The refractive index of the core of the hopping fiber and the refractive index of the protective layer are both constant. At the interface between the core and the protective layer, the refractive index changes stepwise. The refractive index of the graded fiber core decreases with a certain rule as the radius increases, and it decreases to the refractive index of the protective layer at the junction of the core and the protective layer. The change in the refractive index of the core is approximately parabolic. The optical fiber beam transmission of refractive index distribution is shown in Figure 2.

Fig. 2 Light transmission process in the optical fiber with refractive index profile

3. Connection method

There are three connection methods for optical fiber. First, they can be plugged into connectors and plugged into fiber optic sockets. The connector consumes 10% to 20% of the light, but it makes it easy to reconfigure the system.

Second, it can be joined mechanically. The method is to put the ends of two carefully cut optical fibers in a ferrule and then clamp them. The fiber can be adjusted through the junction to maximize the signal. It takes about 5 minutes for the trained personnel to complete the mechanical bonding, and the loss of light is about 10%.

Third, two optical fibers can be fused together to form a solid connection. The fiber formed by the fusion method is almost the same as a single fiber, but it also has a little attenuation. For these three connection methods, there is reflection at the junction, and the reflected energy will interact with the signal.

4. Send and receive

There are two kinds of light sources that can be used as signal sources: light-emitting diode LED (light-emit TIng diode) and semiconductor laser ILD (injecTIon laser diode). They have different characteristics, as shown in the table below.

The receiving end of the fiber is composed of a photodiode, which gives a point pulse when it encounters light. The response time of the photodiode is generally 1ns, which is why the data transmission rate is limited to 1Gb / s. Thermal noise is also a problem, so light pulses must have enough energy to be detected. If the pulse energy is strong enough, the error rate can be reduced to a very low level.

5. Interface

There are two types of interfaces currently in use. The passive interface is formed by two streets fused to the main fiber. One end of the connector has a light-emitting diode or laser diode (for sending). At the other end there is a photodiode (for receiving). The joint itself is completely passive and therefore very reliable.

The other interface is called an active repeater (acTIve repeater). The input light is converted into an electrical signal in the repeater. If the signal has weakened, it is re-amplified to the maximum intensity, and then converted into light before being sent out. Connected to the computer is a common copper wire that enters the signal regenerator. There are now pure optical repeaters. This device does not require photoelectric conversion and can therefore operate with very high bandwidth.

Second, the optical cable

Optical fiber is a fine and flexible medium that transmits light beam. Optical fiber cable is composed of a bundle of fibers, referred to as optical cable. Optical cable is the most effective transmission medium in data transmission.It has the following advantages:

(1) The frequency band is wider.
(2) Good electromagnetic insulation performance. The optical fiber cable transmits a light beam. Because the light beam is not affected by external electromagnetic interference and does not radiate the signal itself, it is suitable for long-distance information transmission and occasions requiring high security. Of course, the difficulty of tapping is its inherent problem, because the cut optical cable needs to be regenerated and retransmitted.
(3) The attenuation is small. It can be said that the signal is a constant over a longer distance and range.
(4) The interval between the repeaters is large, so the number of repeaters in the entire channel can be reduced and the cost can be reduced. According to Bell Labs tests, when the data transmission rate is 420 Mbps and the distance is 119 kilometers without a repeater, the bit error rate is 10-8, which shows that the transmission quality is very good. The coaxial cable and twisted pair need to connect a repeater every few kilometers.

In applications that use optical cables to interconnect multiple minicomputers, the unidirectional nature of the fiber must be considered. If bidirectional communication is to be used, then dual-strand fiber should be used. Due to the multiplexing and multiplexing of light of different frequencies, optical multiplexers have appeared in the communications device market.

The installation of optical cables in ordinary computer networks starts with user equipment. Because the optical cable can only be transmitted in one direction. In order to achieve two-way communication, optical cables must appear in pairs, one for input and one for output. The optical cable is connected to the optical interface at both ends.

Extra care must be taken when installing optical cables. When connecting each optical cable, polish the end, and connect it with the optical interface through the electric barbecue or chemical ring chlorine process to ensure that the optical channel is not blocked. The fiber cannot be pulled too tightly, nor can it form a right angle.

The type of optical fiber is determined by the mold material (glass or plastic fiber) and the size of the core and the outer layer. The size of the core determines the quality of light transmission. Commonly used fiber optic cables are:

· 8.3μm core, 125μm outer layer, single mode.
· 62.5μm core, 125μm outer layer, multi-mode.
· 50μm core, 125μm outer layer, multi-mode.
· 100μm core, 140μm outer layer, multi-mode.

3. Optical fiber communication system and its composition
1. Optical fiber communication system

The optical fiber communication system is a communication method using light waves as carriers and optical fibers as transmission media. The light source, optical fiber, optical transmitter and optical receiver play a leading role.

· The light source is the source of light waves.
· Optical fiber is a conductor that transmits light waves.
· The function of the optical transmitter is to generate a light beam, convert the electrical signal into an optical signal, and then introduce the optical signal into the optical fiber.
The function of the optical receiver is responsible for receiving the optical signal transmitted from the optical fiber and converting it into an electrical signal, which is then processed after decoding.

2. Composition

The basic composition of the optical fiber communication system is shown in Figure 3:

Figure 3 Basic composition of optical fiber communication system

The main advantages of fiber optic communication systems are:

(1) Transmission frequency bandwidth and large communication capacity.
(2) Low line loss and long transmission distance.
(3) Strong anti-interference ability and wide application range.
(4) Thin wire diameter and light weight.
(5) Strong resistance to chemical corrosion.
(6) Rich optical fiber manufacturing resources.

In network engineering, 62.5μm / 125μm specifications are generally used for multimode fiber, and sometimes 100μm / 125μm and 100μm / 140μm specifications are used. Single-mode fiber can be used when outdoor wiring is greater than 2 kilometers. Some basic characteristics of optical fiber that need to be understood when carrying out comprehensive wiring, now take AMP's optical fiber cable products as an example. Table 1 and Table 2 are the optical fiber performance indicators and operating temperature range, respectively.

Table 1 Characteristics of AMP fiber cable

Table 2 Temperature application range of AMP fiber

In order to facilitate reading the following table, first explain the diameter, weight, tensile force and bending radius as follows:

· Diameter: The unit is expressed in mm.
· Weight: expressed in kg / km.
Rally: N (Newton) is used for the rally unit. There are two cases of tension: the maximum is 2700N during installation; the long-term after installation is 440N;
· Bending radius: refers to the bending radius of the optical cable during installation and turning.

4. Types and mechanical properties of optical cables
1. Single-core interconnected optical cable (1) Scope of application

· Jumper.
· Internal device connection.
· Communication cabinet wiring panel.
· Connection from the wall outlet to the workstation.
· The horizontal cable is directly terminated.
· Suitable for termination with epoxy resin or LIGHTCRIMP connector.

(2) Performance advantages

· High-performance single-mode and multi-mode optical fibers meet all industry standards.
· 900μm tight buffer coat is easy to connect and strip.
· Aramid anti-pull wire strengthens the organization and improves the protection of optical fiber.
· UL / CSA verification meets OFNR and OFNP performance requirements.
· Design and testing are based on Bellcore GR-409-CORE and IEC793-1 / 794-1 standards.
· Extended level 62.5 / 125 conforms to ISO / IEC 11801: 1995 standard.

The single-core physical structure of the interconnected optical cable is shown in Figure 4.

Figure 4 Single-core optical cable

2. Dual-core interconnected optical cable (1) Application range

· Crossover jumper.
· The horizontal wiring is directly terminated.
· Fiber to the table.
· Communication cabinet wiring panel.
· Connection from the wall outlet to the workstation.
· Suitable for termination with epoxy resin or LIGHTCRIMP connector.

(2) Performance and characteristics

· Easily distinguish between optical fibers.
· High-performance single-mode and multi-mode optical fibers meet all industry standards.
· 900μm tight buffer coat is easy to connect and strip.
Aramid anti-pull wire reinforced organization improves the protection of optical fiber.
· UL / CSA verification meets OFNR and OFNP performance requirements.
· Design and testing are based on Bellcore GR-409-CORE and IEC793-1 / 794-1 standards.
· Extended level 62.5 / 125 conforms to ISO / IEC 11801: 1995 standard.

The physical structure of the dual-core interconnected optical cable is shown in Figure 5. The physical structure of the 4-core optical cable is shown in Figure 6. The mechanical properties of the interconnected optical cable are shown in Table 3.

Figure 5 Dual-core dual-set optical cable


Figure 6 Four-core optical cable


Table 3 Mechanical properties of interconnected optical cables
3. Distributed optical cable (1) Application range

· Multi-point information port horizontal wiring.
· Vertical wiring.
· Backbone wiring in the building.
· Connection from equipment to passive jumper.
· Application from the main branch to each floor.
· Suitable for glue type optical fiber connector and LIGHTCRIMP optical fiber terminal termination.

(2) Performance and characteristics

· High-performance single-mode and multi-mode optical fibers meet all industry standards.
· 900μm tight buffer coat is easy to connect and strip.
· Marked according to EZA standard color code.
· UL / CSA verification meets OFNR and OFNP performance requirements.
· Design and testing are based on Bellcore GR-409-CORE and IEC793-1 / 794-1 standards.
· Extended level 62.5 / 125 conforms to ISO / IEC 11801: 1995 standard.
· The protective net can resist the damage of sharp objects.

Distributed optical cable is divided into multi-unit decentralized 12-core optical cable and multi-unit decentralized 24- to 72-core optical cable. Its physical structure is shown in Figure 7.

Figure 7 Distributed optical cable

The mechanical properties of the distributed optical cable are shown in Table 4.

Table 4 Mechanical properties of distributed optical cables
4. Decentralized optical cable (1) Scope of application

· Disperse optical cable combination.
· Multiple optical fibers are interleaved and connected, the structure is solid.

· Horizontal optical fiber to multi-site exit, simple and direct termination. · Suitable for epoxy fiber optic connector and LIGHTCRIMP fiber optic connector for direct termination.

(2) Performance and characteristics

· High-performance single-mode and multi-mode optical fibers meet all industry standards.
· 900μm tight buffer coat is easy to connect and strip.
· 2.4mm independent optical fiber auxiliary unit, which allows the sleeve connector to terminate.
· UL / CSA verification meets OFNR and OFNP performance requirements.
· Design and testing are based on Bellcore GR-409-CORE and IEC793-1 / 794-1 standards.
· Extended level 62.5 / 125 conforms to ISO / IEC 11801: 1995 standard.
· The wiring method is highly flexible.
Aramid anti-pull wire reinforced organization improves the protection of optical fiber.

The decentralized optical cable has 4 cores, 6 cores, 8 cores, and 12 cores. Its physical structure is shown in Figure 8, and its mechanical properties are shown in Table 5.

Fig. 8 4-12 cores of distributed optical cable


Table 5 Mechanical properties of decentralized optical cable
5. Outdoor optical cable 4 ～ 12 core armored type and fully insulated type (1) Application range

· Connection between buildings in the park.
· Long-distance network.
· Trunk line system.
· Local loops and tributary networks.
· Severely humid environment with large temperature changes.
· Overhead connection (used with suspension cable), underground pipeline or directly buried, suspension cable / service cable.

(2) Performance and characteristics

· High-performance single-mode and multi-mode optical fibers meet all industry standards.
· 900μm tight buffer coat is easy to connect and strip.
· Independent optical fiber with TIA color coding in the sleeve.
· Lightweight single-channel structure saves space in the tube, filled with waterproof gel to prevent water from seeping in.
· Design and testing are based on Bellcore GR-20-CORE standard.
· Extended level 62.5 / 125 conforms to ISO / IEC 11801: 1995 standard.
Aramid anti-pull wire reinforced organization improves the protection of optical fiber.
· Polyethylene outerwear has a protective effect against ultraviolet rays or harsh outdoor environment.
· The low-friction skin makes it easy to pass through the pipeline, fully insulated or armored structure, and the peeling rope makes it easier to peel the surface.

The outdoor optical cable has 4 cores, 6 cores, 8 cores, and 12 cores, which are divided into armored and fully insulated types.

Figure 9 outdoor optical cable


Table 6 Mechanical properties of outdoor optical cables
6. Outdoor optical cable 24 ～ 144 core armor type and full insulation type (1) Application range

· Connection between buildings in the park.
· Long-distance network.
· Trunk line system.
· Local loops and tributary networks.
· Severely humid environment with large temperature changes.
· Overhead connection (used with suspension cable), underground pipeline or directly buried.

(2) Performance and characteristics

· High-performance single-mode and multi-mode optical fibers meet all industry standards.
· Insulation structure can avoid lightning strike.
· Independent optical fiber with TIA color coding in the sleeve.
Lightweight single-channel structure saves space in the tube. The tube is filled with waterproof gel to prevent water from seeping in. The rubber injection core is completely wrapped by polyester tape.
· Design and testing are based on Bellcore GR-20-CORE standard.
· Extended level 62.5 / 125 conforms to ISO / IEC 11801: 1995 standard.
· Aramid anti-pull wire enhances tissue performance and improves the protection of optical fiber.
· Polyethylene outerwear has a protective effect under ultraviolet light or harsh outdoor environment.
· The low-friction skin makes it easy to pass through the pipeline, fully insulated or armored structure, and the peeling rope makes it easier to peel the surface.

Outdoor optical cable 24- to 144-core optical cable is divided into full insulation and armor. There are 7 specifications of 24, 36, 48, 60, 72, 96, 144 core. Its physical structure is shown in Figure 10, and its mechanical properties are shown in Table 7. .

Figure 10 Outdoor 24-144 core optical cable

Table 7 Mechanical properties of outdoor optical cables with 24 to 144 cores
7. Single tube fully insulated indoor / outdoor optical cable (1) Application range

· Without the need for any interconnected equipment, extending from outdoor to indoor, the cable has flame retardant properties.
· Interconnection between buildings in the park.
· Local lines and tributary networks.
· Severely humid environment with extreme temperature changes.
· Overhead connection (when used with suspension cable).
· Underground pipeline or direct burial.
· Suspension cable / service cable.

(2) Performance and characteristics

· High-performance single-mode and multi-mode optical fibers meet all industry standards.
· The design of LSZH meets the requirements of low toxicity and no smoke.
· Independent optical fiber with TIA color coding in the sleeve.
Lightweight single-channel structure saves space in the tube. The tube is filled with waterproof gel to prevent water from seeping in. The rubber injection core is completely wrapped by polyester tape.
· Design and testing are based on Bellcore GR-20-CORE standard.
· Extended level 62.5 / 125 conforms to ISO / IEC 11801: 1995 standard.
· Aramid anti-pull cable strengthens the organization and improves the protection of optical fiber.
· Polyethylene outerwear has a protective effect under ultraviolet light or harsh outdoor environment.
· The low-friction skin makes it easy to pass through the pipeline, fully insulated or armored structure, and the peeling rope makes it easier to peel the surface.

The indoor / outdoor optical cable has 4 cores, 6 cores, 8 cores, 12 cores, 24 cores, and 32 cores. Its physical structure is shown in Figure 11, and its mechanical properties are shown in Table 8.

Figure 11 Indoor / outdoor optical cable


Table 8 Mechanical Performance of Urban / Outdoor Optical Cable

When conducting comprehensive wiring, according to the actual application situation, refer to the application range and mechanical performance indicators of the optical cable, and select the appropriate optical cable product.

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