Principle and application of optical cable (history)

1976, Bell Research Institute of the United States built the first optical fiber communication experimental system in Atlanta, using the 144 optical fiber cable manufactured by Western Electric Company. 1980, commercial optical cables made of multimode optical fibers began to be used in local inter-office trunk lines and a few long-distance lines. 1983 commercial optical cables made of single-mode optical fibers began to be used on long-distance lines. 1988, the first transatlantic submarine cable connecting the United States, Britain and France was successfully laid, and soon the first transatlantic submarine cable was built. 1978, China developed its own communication optical cable, which adopts multimode optical fiber and has a stranded core structure. Field tests were carried out in Shanghai, Beijing, Wuhan and other places. Soon after, it was tried as an inter-office relay in the local telephone network. After 1984, it was gradually used for long-distance lines, and single-mode optical fibers began to be used. Compared with copper cable, communication optical cable has larger transmission capacity, long relay distance, small volume, light weight and no electromagnetic interference. Since 1976, it has developed into the backbone of wired transmission lines for long-distance trunk lines, local trunk lines, maritime and transoceanic submarine communications, local area networks and private networks, and has begun to develop into the field of local subscriber loop distribution networks, providing transmission lines for fiber-to-the-home and broadband integrated services digital networks.

Principle and application of optical fiber and optical cable Optical cable is the cornerstone of information expressway)

Optical fiber cable is the main transmission tool of various information networks in today's information society. If the Internet is called information expressway, then the optical cable network is the cornerstone of information expressway-the optical cable network is the physical route of the Internet. Once an optical cable is damaged or blocked, the "information expressway" in this direction will be destroyed. In addition to the usual telephone, telegraph and fax, information transmitted through optical cables is also transmitted in large quantities, such as TV signals, bank remittances, stock market information and so on. At present, the transmission mode of long-distance communication optical cable has developed from PDH to SDH, and the transmission rate has also developed from the original 140MB/S to 2.5GB/S, 4×2.5GB/S, 16×2.5GB/S or even higher, that is to say, a pair of fiber cores can open 30,000 pieces and120,000 pieces. With such a large transmission capacity, once the optical cable is blocked, it will not only cause huge losses to the telecommunications department, but also bring a lot of inconvenience to the masses because of poor communication, such as computer users can't access the Internet, the stock market can't know, bank remittance can't be carried out, remote access becomes a bubble, and all kinds of information can't be transmitted. In remote mountainous areas, once the optical cable is interrupted, the whole county and even several counties along the optical cable will be isolated from the world in communication and become isolated islands. The losses caused to the party, government, military organs and the people are incalculable.

The first part is the principle and application (theory and structure) of optical cable.

Light and its characteristics 1. Light is an electromagnetic wave.

The wavelength range of visible light is 390~760nm (nanometer). The part above 760nm is infrared light and the part below 390nm is ultraviolet light. At present, there are three kinds of optical fiber applications: 850,13,10 and 1550.

2. Refraction, reflection and total reflection of light.

Because the propagation speed of light in different substances is different, when light is emitted from one substance to another, it will be refracted and reflected at the interface between the two substances. Moreover, the angle of refracted light will change with the angle of incident light. When the angle of incident light reaches or exceeds a certain angle, the refracted light will disappear and all the incident light will be reflected back, which is the total reflection of light. Different substances have different refraction angles for light with the same wavelength (that is, different substances have different refractive indexes), and the same substance has different refraction angles for light with different wavelengths. Optical fiber communication is based on the above principle. Optical fiber structure and type 1, optical fiber structure:

Bare optical fiber is generally divided into three layers: the middle high refractive index glass core (core diameter is generally 50 or 62.5μm), the middle low refractive index Shi Ying glass cladding (diameter is generally 125μm), and the outermost resin cladding is used for reinforcement.

2. Numerical aperture:

The light incident on the end face of the optical fiber can not be completely transmitted by the optical fiber, but only the incident light within a certain angle range. This angle is called the numerical aperture of the optical fiber. The larger numerical aperture of optical fiber is beneficial to the docking of optical fiber. Optical fibers produced by different manufacturers have different numerical apertures (at & amp； T turn).

3. Type of optical fiber:

A. According to the transmission mode of light in optical fiber, it can be divided into single-mode fiber and multimode fiber.

Multimode optical fiber: The central glass core is thick (50 or 62.5μm), which can transmit multiple modes of light. However, its large intermodal dispersion limits the frequency of transmitting digital signals, and it will become more serious with the increase of distance. For example, a 600MB/KM optical fiber has only 300MB bandwidth at 2KM. Therefore, the transmission distance of multimode fiber is relatively short, generally only a few kilometers. Single-mode fiber: The glass core in the center is thin (the core diameter is generally 9 or 10μm) and can only transmit one mode of light. Therefore, its intermodal dispersion is very small, which is suitable for long-distance communication, but its dispersion plays a major role. Therefore, single-mode fiber requires high spectral width and stability of light source, that is, narrow spectral width and good stability.

B, according to the optimal transmission frequency window: conventional single-mode fiber and dispersion-shifted single-mode fiber.

Conventional type: optical fiber manufacturers optimize the transmission frequency of optical fiber at a single wavelength, such as 13 10nm.

Dispersion shift type: optical fiber manufacturers optimize the transmission frequency of optical fiber at two wavelengths, such as 13 10nm and 1550nm.

C, according to refractive index distribution: abrupt fiber and graded fiber.

Abrupt type: The refractive index from the central core of the optical fiber to the glass cladding is abrupt. It has low cost and high dispersion between modules. Suitable for short-distance low-speed communication,

Such as industrial control. However, due to the small dispersion between modes, single-mode fibers are all abrupt.

Graded fiber: the refractive index decreases gradually from the central core of the fiber to the glass cladding, which can make the high-mode light propagate in sinusoidal form, reduce the intermodal dispersion, increase the bandwidth of the fiber and increase the transmission distance, but the cost is higher. Nowadays, multimode fibers are mostly graded fibers.

4, commonly used optical fiber specifications:

Single mode: 8/ 125μm, 9/ 125μm,10/125μ m.

Multimode: 50/ 125μm, European standard.

62.5/ 125μm, American standard

Industrial, medical and low-speed networks: 100/ 140μm, 200/230μ m.

Plastics: 98/ 1000μm, used for manufacturing and attenuation of automobile control optical fiber 1, optical fiber manufacturing;

At present, the main manufacturing methods of optical fiber are: in-tube CVD (chemical vapor deposition), in-rod CVD, PCVD (plasma chemical vapor deposition) and VAD (axial vapor deposition).

2. Attenuation of optical fiber:

The main factors causing optical fiber attenuation are intrinsic, bending, extrusion, impurity, unevenness and butt joint.

Inherent: it is the inherent loss of optical fiber, including Rayleigh scattering and inherent absorption.

Bending: when the optical fiber is bent, some light in the optical fiber will be lost due to scattering, resulting in loss.

Squeeze: Loss caused by slight bending of optical fiber when squeezed.

Impurity: Loss caused by absorption and scattering of light propagating in optical fiber by impurities in optical fiber.

Non-uniformity: Loss caused by non-uniform refractive index of optical fiber materials.

Butt joint: Losses caused by fiber butt joint, such as: different axes (the coaxiality of single-mode fiber is required to be less than 0.8μm), the end face is not perpendicular to the axis, the end face is uneven, the butt joint diameter is not matched, and the welding quality is poor. The advantage of optical fiber is 1, and the passband of optical fiber is very wide. Theoretically it can reach 3 billion MHz.

2. The road section without relay is long, tens to 100 kilometers, and the copper wire is only a few hundred meters.

3, not affected by electromagnetic fields and electromagnetic radiation.

4. Light weight and small size. For example, 900 pairs of twisted-pair 2 1 thousand telephone lines have a diameter of 3 inches and a weight of 8 tons/km. Optical cable with ten times the traffic, with a diameter of 0.5 inch and a weight of 450P/KM.

5, optical fiber communication is not charged, safe to use, and can be used in flammable and explosive places.

6, the use of a wide range of environmental temperatures.

7, chemical corrosion, long service life. Part II Principle and Application of Optical Fiber and Cable (Knowledge of Optical Fiber and Cable) The manufacturing process of optical fiber and cable is generally divided into the following procedures:

1. Optical fiber screening: Select optical fibers with excellent transmission characteristics and qualified tension.

2. Optical fiber dyeing: standard full chromatography should be used for identification, and it is required not to fade or migrate at high temperature.

3. Secondary extrusion: select plastics with high elastic modulus and low linear expansion coefficient, extrude them into pipes with certain size, add moisture-proof and waterproof gel into the optical fiber, and finally store them for several days (not less than two days).

4. Stranding of optical cable: A plurality of extruded optical fibers are stranded with the reinforcement unit.

5. Squeeze the outer sheath of the optical cable: add a sheath to the stranded optical cable. The type of optical cable is 1. According to the laying mode, there are self-supporting overhead cables, pipeline cables, armored buried cables and submarine cables.

2. According to the structure of optical cables, there are bundled optical cables, stranded optical cables, tight optical cables, ribbon optical cables, nonmetallic optical cables and branched optical cables.

3. According to the use, there are: long-distance communication optical cable, short-distance outdoor optical cable, hybrid optical cable and building optical cable. The third part is the principle and application of optical fiber cable (cable construction)

Outdoor construction of optical cable;

The most important thing for long-distance optical cable laying is to choose the appropriate path. The shortest path here is not necessarily the best, but also the right to use the land, the possibility of erection or burial and so on.

Must have a very complete design and construction drawings, so that the construction and subsequent inspection is convenient and reliable. During the construction process, always be careful not to make the optical cable bear heavy pressure or be stabbed by hard objects.

When the optical cable turns, its turning radius is 20 times larger than the diameter of the optical cable itself.

1, outdoor overhead cable construction:

First, the hanging wire hanging overhead way, this way is simple and cheap, and it is widely used in China, but it is time-consuming to hook, hang and arrange.

B, hanging wire winding overhead way, this way is more stable, less maintenance workload. But you need a special binding machine.

C, self-supporting overhead mode, which has high requirements for trunk lines, great difficulty in construction and maintenance and high cost, is rarely used in China at present.

D, overhead, optical cable guide line dry place must add guide device, and avoid optical cable mopping the floor. Pay attention to reducing friction when pulling optical cables. Each trunk should have a section of optical cable for expansion and contraction.

E, pay attention to the reliable grounding of metal objects in optical cable. Especially in mountainous areas, high-voltage power grid areas and many areas, there are generally three grounding points per kilometer, and even non-metallic optical cables are selected.

2, outdoor pipeline optical cable construction:

A. Before construction, check the pipeline occupancy, clean and place the plastic sub-pipes, and put in the traction line at the same time.

B, calculate the laying length, be sure to have enough reserved length.

C, a cloth length should not be too long (generally 2KM), wiring should start from the middle to both sides of the traction.

D, optical cable traction is generally not more than 120kg, and the reinforced core of optical fiber should be pulled, and the waterproof strengthening treatment of optical cable head should be done well.

E, the introduction and exit of optical cables should be equipped with downstream devices, and it is not allowed to mop the floor directly.

F, pipeline optical cable should also pay attention to reliable grounding.

3. Laying of directly buried optical cable:

A, the depth of directly buried optical cable trench shall be excavated according to the standard, and the standard is shown in the table below:

B, can't dig pipe trench buried pipeline in overhead or drilling place.

C, the bottom of the ditch should be smooth and solid, and a part of sand, cement or support can be pre-filled when necessary.

D, manual or mechanical traction can be used when laying, but attention should be paid to guidance and lubrication.

E, after the completion of laying, backfill soil should be covered and compacted as soon as possible.

4. Laying of optical cables in buildings:

A, when laying vertically, pay special attention to the bearing problem of optical cable. Generally, optical cables are fixed once every two layers.

B, optical cable through the wall or floor, to add protection plastic tube with mouth protection, and to fill the tube with flame retardant filler.

C, you can also lay a certain number of plastic pipes in the building in advance, and then use traction or vacuum Fabry optical cable when you want to apply optical cable in the future. The fourth part is the principle and application of optical fiber cable (selection). The choice of optical cable should be based not only on the number of optical fiber cores and optical fiber types, but also on the use environment of optical cable.

1. When outdoor optical cables are directly buried, armored optical cables should be selected. When overhead, you can choose black plastic outer sheath and optical cable with two or more reinforcing ribs.

2. Attention should be paid to the characteristics of flame retardancy, toxicity and smoke when selecting building optical cables. Generally, the flame retardant but smoky type can be selected in the pipeline or forced ventilation place, and the flame retardant, nontoxic and smokeless type should be selected in the exposed environment.

3. When laying cables vertically in buildings, you can choose stranded optical cables; Branchable optical cables can be used for horizontal wiring.

4. If the transmission distance is less than 2km, you can choose multimode optical cable; If it is more than 2km, trunk or single-mode optical cable can be used.

Buried depth standard of directly buried optical cable

Paved area or soil depth (m) Remarks

Ordinary soil (hard soil) ≥ 1.2

Semi-stony (sandy soil, aeolian fossils) ≥ 1.0

The whole stone is more than or equal to 0.8, and the bottom of the ditch is padded with 10cm of fine soil or sandy soil.

Quicksand ≥0.8

Suburbs, villages and towns ≥ 1.2

Urban sidewalk ≥ 1.0

Crossing railways and highways from the bottom of ballast or from the pavement ≥ 1.2.

Gully, canal and pond ≥ 1.2

Farmland drainage ditch ≥0.8

The fifth part is the principle and application of optical cable (connection and detection)

Connection of optical cable

Methods mainly include permanent connection, emergency connection and active connection.

1, permanent optical fiber connection (also called hot melt):

This connection is to melt and connect the connection points of two optical fibers by discharging. Generally used for long-distance connection, permanent or semi-permanent fixed connection. Its main feature is that the connection attenuation is the lowest among all connection modes, with a typical value of 0.0 1~0.03dB/ point. However, special equipment (welding machine) and professionals are needed to operate the connection, and the connection point also needs special container protection.

2, emergency connection (also known as cold melt):

Emergency connection mainly adopts mechanical and chemical methods to fix and bond two optical fibers together. The main feature of this method is fast and reliable connection, and the typical connection attenuation is 0. 1~0.3dB/ point. However, the long-term use of the connection point will be unstable and the attenuation will increase greatly, so it can only be used in a short time.

3. Active connection:

Mobile connection is a method of connecting stations or stations with optical cables by using various optical fiber connectors (plugs and sockets). This method is flexible, simple, convenient and reliable, and is often used for computer network wiring in buildings. Its typical attenuation is 1dB/ joint. Optical fiber detection The main purpose of optical fiber detection is to ensure the quality of system connection, reduce the failure factors and find out the failure point when the optical fiber fails. There are many detection methods, mainly divided into manual simple measurement and precision instrument measurement.

1, simple manual measurement:

This method is generally used to quickly detect the on-off of optical fibers and distinguish optical fibers in construction. It is realized by injecting visible light from one end of an optical fiber with a simple light source and observing which one emits light from the other end. Although this method is simple and convenient, it cannot quantitatively measure the attenuation and breakpoint of optical fiber.

2, precision instrument measurement:

Using optical power meter or optical time domain reflectometer (OTDR) to quantitatively measure optical fiber, we can measure the attenuation of optical fiber, the attenuation of joint, and even the breakpoint position of optical fiber. This measurement can be used to quantitatively analyze the causes of optical fiber network failures and evaluate optical fiber network products. Part VI Principle and Application of Optical Fiber Cable (Application and System Design) The application of optical fiber has now developed into an information society, and the exchange of information such as sound, image and data is very large. The previous means of communication can no longer meet the current requirements, but optical fiber communication is widely used for its advantages of large information capacity, good confidentiality, light weight, small size and long distance without relay. Its application fields cover communication, transportation, industry, medical care, education, aerospace, computer and other industries, and it is developing to a wider and deeper level. The application of light and optical fiber is bringing profound influence and change to human life. The design of optical fiber network system generally follows the following steps:

1. Make clear what kind of network to design, its present situation and why to use optical fiber.

2, according to the actual situation, choose the appropriate optical fiber network equipment, optical cable, jumper and other items to connect. Selection should be based on availability, and then determined according to performance, price, service, origin and brand.

3. Determine the route according to the customer's requirements and network type, and draw the wiring diagram.

4. When the line is long, it is necessary to calculate the attenuation margin of the system, which can be carried out according to the following formula:

Attenuation margin = transmitted optical power-receiving sensitivity-line attenuation-connection attenuation (dB), where line attenuation = cable length × unit attenuation;

The unit attenuation is closely related to the fiber quality, and the average single mode is 0.4 ~ 0.5 dB/km. The multimode is 2 ~ 4dB/km.

Connection attenuation includes welding attenuation and joint attenuation, which is related to welding means and personnel quality. General hot melt is 0.0 1~0.3dB/ point. Cold melting 0. 1~0.3dB/ point; The joint attenuation has a great relationship with the joint quality, which is generally 1dB/ point. The attenuation margin of the system is generally not less than 4dB.

5. If the accounting is unqualified, the design shall be modified as appropriate before the accounting. This situation may sometimes be repeated several times. Part VII Principle and Application of Optical Fiber and Cable (Pattern Recognition Method)

Classification code

GY communication room (field) optical cable GS communication equipment optical cable

GH communication submarine optical cable GT communication special optical cable

GJ Communication Room (Office) Optical Cable Metal-free Optical Cable for GW Communication

Flexible optical cable for GR communication and mobile optical cable for GM communication.

Note: between the first part and the second part: rebar code (rebar core)

Reinforcing member refers to the member located in the sheath or embedded in the sheath to enhance the tensile strength of optical cable;

Unsigned metal reinforcing member; G- metal heavy-duty reinforcing member

F- nonmetallic reinforcing member; H-type nonmetallic heavy-duty reinforcing member

(For example: GYTA: metal reinforced core; GYFTA: specification for structural characteristics of cable cores and optical cables.

The structural characteristics of optical cable should indicate the main types of cable core and the derivative structure of optical cable. When several structural features of optical cable types need to be represented, they can be represented by combination codes. B flat c self-supporting structure

D optical fiber ribbon structure e elliptical shape

G skeleton groove structure j optical fiber tight sleeve coating structure

Test the filling structure or inflating structure of ointment.

X- cable bundle tubular (coated) structure Z flame retardant

Code name of sheath

Aluminum-polyethylene bonded sheath G steel sheath

L aluminum sheath q lead sheath

U-shaped polyurethane sheath bonded with stainless steel and polyethylene for magnetic protection

V PVC sheath y PE sheath

Parallel steel wire w steel-polyethylene bonded sheath

Note: Between Part IV and Part V:

Its code name is represented by two groups of numbers, the first group represents the armor layer, which can be one or two digits; The second group represents the coating and is a number.

Armor layer code

Code armor layer

5 corrugated steel strip

44 double thick round steel wire

4 single thick round steel wire

33 Double thin round steel wire

3 single thin round steel wires

2 wound double-layer steel belts

0 no armor layer

Coating code coating code or coating code

1 fiber outer quilt

2 polyethylene protective tube

3 polyethylene casing

4 Polyethylene casing covered with nylon casing

5 PVC sleeve

Specification and model of optical cable

Multimode fiber

B single-mode fiber

B 1. 1(B 1) non-dispersive displacement fiber G652

B 1.2 cut-off wavelength shifted fiber G654

B2 dispersion-shifted optical cable G653

B4 non-zero dispersion shifted fiber G655

Note: Multimode optical fiber is almost eliminated because it can't carry out long-distance optical transmission due to multimode dispersion.

Part VIII Principle and Application of Optical Fiber and Cable (Judgment and Maintenance of Obstacles)

Common obstacles of optical cable lines and reasons for finding obstacles The methods and steps for judging optical cable line obstacles by OTDR test at endpoints or relay stations are roughly as follows:

1) Use OTDR to test the maximum distance from the obstacle point to the test end.

2) When the optical cable is blocked due to external forces such as natural disasters or external construction, the searcher should find out the position of the obstacle provided by the maintenance personnel. If this is not the case, it is not easy for inspectors to find the location of obstacles from the road. At this time, it is necessary to check the distance from the obstacle point measured by OTDR with the original test data to find out which landmark (or which two joints) the obstacle point is located between, and then accurately measure the ground length after necessary conversion, so as to determine the specific position of the obstacle.

3) If the broken fiber is caused by the structural defect of the optical cable or the aging of the optical fiber, it is difficult to accurately measure its breakpoint with OTDR, and only the obstacle section can be detected, then a section of optical cable should be replaced. Obstacle repair When there is an obstacle in the optical cable line, it is necessary to race against time, temporarily connect the circuit or deploy the emergency optical cable to temporarily grab the circuit, and organize forces to repair it as soon as possible.

1, emergency repair

(1) All optical cable lines in one direction are blocked.

According to the predetermined circuit scheduling scheme, all circuits or some main circuits are turned on immediately and temporarily.

(2) Individual optical fibers of optical cable lines in a certain direction are blocked.

If there is a spare optical fiber in the optical fiber, or there is another circuitous circuit, immediately use the spare optical fiber or circuitous circuit to temporarily connect the obstacle circuit; If there is spare optical fiber in the optical cable and there is no circuitous circuit, it should be handled according to the prescribed scheduling principle to ensure the smooth flow of important circuits and suspend the secondary circuit.

(3) Some optical fibers of the optical cable line are blocked in a certain direction.

If there are spare optical fibers in the optical cable, in addition to using the spare optical fibers to temporarily connect the circuit, you can also choose non-blocking optical fibers to temporarily connect the circuit according to the specified scheduling principle and order. If there are still not enough optical fibers for temporary pairing and there is no circuitous circuit, the secondary circuit will be suspended.

2. Precautions:

The temporary scheduling of optical fibers above (1) must be completed with the close cooperation of both parties after the scheduling scheme is reported to the superior of both parties for approval.

(2) As long as the optical fibers are paired in the original line order, the circuit can be switched by the maintenance stations at both ends according to the system scheduling; If the optical fiber is used for temporary pairing, it should be adjusted on the connectors of the optical fiber distribution frame (or junction box) in the relay station on both sides of the obstacle point.

(3) If the main optical fiber is connected with an optical attenuator and the standby optical fiber is not pre-connected with an attenuator, the corresponding optical attenuator should also be connected when calling the standby optical fiber. Pay attention to this problem when using temporary optical fiber pairing.

3. Laying emergency optical cable

(1) Conditions for laying emergency optical cables

When all the optical cable lines in a certain direction are blocked, consider repairing the optical cable once after all the circuits or main switches are turned on, and it is not necessary to use the emergency rush circuit. When there is no condition to temporarily connect the circuit, or some circuits cannot meet the needs of large-capacity communication, emergency optical cables should be deployed, and the circuits should be rushed through according to the scheduling principle and sequence specified by the circuit scheduling system to temporarily restore communication, and then new optical cables should be rerouted and deployed for formal emergency repair.

(2) Determination of the scope of emergency optical cable.

When the optical cable is blocked by natural disasters or external forces, it is easier to find the obstacle point according to the unfamiliar road surface after determining the approximate position of the obstacle point, and then determine the laying scope of the emergency optical cable. However, when OTDR is only used to measure the obstacle point of the terminal station or relay station, which two joints appear and the specific position of the obstacle cannot be determined, it is difficult to determine the deployment scope of the emergency optical cable. At this time, if conditions permit, OTDR can be used to enter the test at the opposite relay station, and the test results on both sides can be comprehensively analyzed, so that the breakpoint of the optical cable can be roughly and accurately judged. If there is no condition to use OTDR to test from two directions, two situations can be sent for processing:

A, the obstacle point is close to a joint, and the emergency optical cable is planned to be laid from this joint. Just open this joint and use OTDR to test the direction of obstacles at the joint. At this time, the test distance is short, and the specific position of obstacles can be accurately measured, so as to determine the laying position of emergency optical cables.

B, obstacles in the middle of the two joints, it is not appropriate to start laying emergency optical cable at a joint, it is necessary to further determine the location of obstacles, and lay a section of emergency optical cable on both sides of obstacles. In this case, the step-by-step trial and error method can be used to find out the specific position of the obstacle, that is, the obstacle point is initially detected by OTDR at the terminal station or relay station, and the optical cable is dug out before the obstacle point, and one optical fiber is cut off for retest. If it is found that the obstacle point is not within the cut-off range, it is necessary to determine the approximate distance, then dig out the optical cable from the front, then cut off an optical fiber and retest until the obstacle point is within the cut-off range, so that the layout of the emergency optical cable can be determined. Generally, the specific position of the obstacle point can be determined by repeating the measurement twice.

C, the same type of optical cable accelerated connector emergency maintenance.

Another emergency repair method of optical cable is to use the optical cable with the same model as the obstacle optical cable as the emergency repair optical cable, and use the connector (movable joint) for temporary connection and the matching liquid grab circuit.

4. Formal repair

When formally repairing optical cable line obstacles, communication must be maintained as much as possible, especially the communication of important circuits cannot be interrupted, and the construction quality must meet the requirements of optical cable line construction quality standards and maintenance quality standards.

When formally repairing the total resistance obstacle of optical cable line, the following problems should be paid attention to:

(1) Obstacles near junction boxes or connectors should be repaired by using optical fibers reserved in junction boxes or in connector pits, and no additional connectors are needed. When there is a reserved optical cable near the obstacle point, the connection should be adopted and only one connector should be added.

(2) When it is necessary to formally repair the optical cable obstacle by intervening or replacing the optical cable, the optical cable of the same manufacturer and model should be adopted.

(3) The following three factors can be considered when intervening or replacing the length of optical cable:

A, considering that it is necessary for the terminal station or relay station to use OTDR to monitor the formal repair of the optical cable connecting optical fibers, or it is convenient to distinguish the obstacles between two adjacent connection points in daily maintenance work; The minimum length of intervening or replacing optical cable must meet the requirements of OTDR instrument response resolution (two-point resolution), which should generally be greater than 100m.

B, considering that it will not affect the communication quality of single-mode optical fiber under single-mode steady-state conditions, the minimum length of intervening or replacing optical fiber should be more than 22 meters.

C, intervention or replacement of the length of optical cable, can refer to the principle requirements of (1) and (2), combined with the actual situation, comprehensive consideration, flexible grasp. For example, if there is an existing connector near the inserted or replaced optical cable, the optical cable should extend as far as possible to the connector and only one connector should be added.

5. The general sequence of intervention or replacement of optical cables and optical fibers:

(1) First of all, according to the scheduling principle and order stipulated by the circuit scheduling system, both parties agree on the optical fiber cut-over scheme and report it to the superior competent department for approval.

(2) Try not to interrupt circuits (especially important circuits) during fiber splicing. When the original newly laid optical fiber is cut off by emergency optical cable, the standby optical cable should be connected first, and the standby optical fiber is used as a replacement pair. According to the original cutting sequence, cut the recovery circuits one by one, temporarily pair the intact optical fibers in the original barrier optical cable to adjust the circuits, or suspend the secondary circuit if there is no spare optical cable in the original optical cable. First, the optical fiber of this system should be cut as a replacement pair, and then the circuits should be cut one by one according to the original cutting order.