[Abstract] Communication optical cable lines are an important part of communication, and their safe and stable operation is the key to ensuring the quality of communication. Therefore, communication enterprises need to pay more attention to communication optical cable lines and do a good job in the operation and maintenance management of communication optical cable lines. In the operation and maintenance management of communication optical cable lines, the location of fault points is a difficult link. The accurate positioning of fault points can effectively improve the efficiency of fault maintenance and reduce the economic losses of communication enterprises.
[Keywords] Communication optical cable; line fault point; accurate positioning; effective detection
1.Analysis of common causes of communication optical cable line failure
First of all, the defects in the communication optical cable itself lead to the failure of the optical cable. The communication optical cable is composed of optical fiber and the outer protective layer. The quality of the optical fiber directly affects the transmission performance of the optical cable. If the optical fiber itself is defective, when the optical cable is used for a period of time, the the clading diameter and concentricity of the optical fiber are wrong, or if the mechanical performance of the optical fiber is wrong, the communication optical cable will fail. In addition, if the outer protective material of the optical cable is defective, it will also lead to accelerated aging, which will ultimately affect the service life and performance of the communication optical cable. Secondly, human factors lead to optical cable communication failure. There are two kinds of human factors in the operation of communication optical cable lines. One is that external personnel cause the operation safety failure of communication optical cable, such as theft of optical cable lines, vehicle safety accidents and damage to optical cable lines, and the construction process of communication optical cable lines. Damage, etc. Another reason is the communication optical cable operation failure caused by the staff at work. Generally, in the process of troubleshooting, the staff believe too much in their work experience and fail to form a scientific and reasonable fault solution. Finally, natural environmental factors lead to optical cable failure. Natural environmental factors include extreme climatic conditions such as wind, rain, thunder, electricity, earthquakes, high temperature, ice and snow. When the optical cable works in an extremely high temperature or cold natural environment, the outer protective layer of the optical cable will be damaged due to large or frequent temperature changes. Nowadays, communication optical cables in many areas adopt direct buried laying methods. Soil humidity and pH are also one of the factors affecting the normal operation of optical cables.
2.Factors affecting the location judgment of the fault point of the communication optical cable line
2.1 The location of the fault point is affected by the test error
The location of the fault point of the communication optical cable line is generally realized through OTDR test equipment, and there is a certain degree of error between the test data and the actual situation. In the OTDR test, in view of the existence of the sampling interval, the error is generated, especially in the distance resolution, which is very obvious, which is proportional to the sampling frequency.
2.2 The use of fault test equipment is not scientific, and operating errors occur from time to time.
First of all, there is an error in the refractive index. The refractive index is closely related to many factors, and the difference between the manufacturer and the product model will cause different refractive indexes. When using OTDR, the refractive index should be set reasonably to avoid inaccurate positioning due to this factor. Secondly, the range selection is unreasonable. When using OTDR instruments, the appropriate selection of measuring range is very critical. Once the selection is not scientific, it is difficult to ensure the accuracy of fault location. Different measurement ranges of OTDR instruments will cause differences in data. Once the selection of measurement ranges is unreasonable, it will inevitably lead to inaccurate measurement results. Thirdly, the pulse width is improper. If the pulse amplitude can be consistent, then its width is proportional to the energy. That is to say, the greater the pulse width, the greater the degree of error. Finally, the time is handled inappropriately. The sampling of pulse reflection signals of OTDR instruments needs to achieve balanced processing, reduce the occurrence of random events, and reduce the adverse effects of random events. The test accuracy is closely related to the average time. After reaching a certain time, the accuracy is invariant. In order to effectively shorten the test time, the time is generally set in the range of 0.5-3 minutes.
3.Key points of the location of fault points of optical fiber lines
3.1 Familiar with instrument operation
Only by mastering the correct operation method of the instrument and ensuring the scientific reliability of its work can we ensure the accuracy of positioning. In the maintenance work, the most commonly used is the OTDR instrument. In use, it is necessary to ensure that the parameters are correct, and then the test range is selected. On this basis, the amplification function of the instrument itself is utilized. Only by ensuring the correct application of the instrument can it facilitate the positioning and maintenance work.
3.2 Understand the line information
In specific work, it is also necessary to actively collect information on optical fiber lines and keep them properly. It is also necessary to check its accuracy at work, and only the correct information can provide reference for the maintenance work. Specifically, it includes the age, material, construction unit and design of the line construction, etc.
3.3 Flexible testing methods combined with the characteristics of the fault
For the test work of the fault point, it is necessary to flexibly select the test method in combination with the line and the fault situation. For example, for the fault points, it is necessary to form a corresponding response idea. On the one hand, it is necessary to integrate the original data of the optical cable line, carry out on-site measurement at the same time, and compare the two aspects of data and data, so as to analyze the fault points more accurately and objectively and provide necessary support for the follow-up maintenance work.
4.Optical time domain reflector and detection method
The working principle of OTDR is to use the Rayly scattering and Fresnel reflection principles of light. After OTDR is connected to the detected optical fiber, the laser pulse used for testing is emitted to the detected optical fiber. Among them, OTDR uses the principle of Fresnel reflection: according to the principle of Fresnel reflection, if the back reflection light is detected at the sending end, the echo pulse of the front and back end can be seen. The time interval between these signals is twice the length of the light, so as to detect the length of the optical fiber. Similarly, if there is a fracture or defect inside the optical fiber, it is also necessary to detect the echo pulse at the input end of the optical fiber, and accurately locate the fault according to the condition of the echo pulse. OTDR uses the Rayley scattering principle, which is to inject a narrow pulse into the input end of the optical fiber. If the optical pulse is transmitted along the optical fiber, the different points of Raylly scattering part will continue to return to the optical fiber input. The optical fiber receives the return light detected by the circuit, and improves the signal-to-noise ratio through digital processing. The electrical signal corresponding to the reflected power is connected to the oscilloscope. Through proper processing, the corresponding logarithmic attenuation curve can be displayed on the screen. Due to the influence of optical fiber’s own factors, the laser will scatter, and the scattering is not directional, and a scattered light will return to OTDR. Because the returned and transmitted optical power show a positive relationship, through in-depth analysis of the returned optical power, the transmitted optical power can be displayed, so as to measure the attenuation of the optical fiber. When the optical transmission path is completely interrupted, the back-scattering light power at the breakpoint is reduced to zero, resulting in Fresnel reflection.
5.Simulation analysis of fault point positioning and detection in communication optical cable lines
In order to further clarify the positioning accuracy of the optical time domain reflector, the author’s simulation software analyzes the application effect of the optical time domain reflector. In the room simulation analysis, the threshold B is specified by the maximum and minimum criterion and compared with the wavelet coefficient at different scales. If the modulus is less than the threshold B, the wavelet coefficient is set to 0; if the modulus is greater than the threshold B, the wavelet coefficient value is subtracted from B to obtain a relatively smooth wavelet coefficient. The sampling frequency set by the simulation test is 2000kHz, and a total of 19,600 sampling points are sampled; the wavelet decomposition of the optical signal is carried out through dB3 wavelet, so as to obtain the wavelet coefficient modulus at different scales. According to the denoising processing method mentioned above, the light signal obtained after noise reduction is similar to the original signal. It can be seen that when using the optical time domain reflector for fault point positioning and detection, technicians can use the wavelet transform coefficient to effectively calculate, remove the noise in the optical signal, improve the accuracy of the optical time domain reflector positioning, and provide assistance for operation and maintenance personnel to carry out fault maintenance work.
6.Optical cable line fault handling method
Line maintenance management personnel should skillfully master and use relevant fault repair technology, find faults in time, find out the root cause of faults, and ensure the quality of line maintenance. When a fault occurs, the technician on duty in the computer room must judge the location and type of the fault in time. In order to reduce the probability of failure, the line maintenance unit needs to ensure sufficient repair force, complete maintenance equipment and well-equipped personnel. The line inspection and repair work needs to be carried out every day. Regardless of the weather, the line information should be obtained in time, so as to take effective measures to carry out emergency repair in a timely manner, and strive to restore the line in a short time. After the fault is solved, it is necessary to make relevant records, comprehensively analyze the fault problem, and formulate effective solutions. For example, before jumping to optical fiber detection, the first step is to test the spare fiber core to meet the relevant requirements. When dealing with the failure. We usually encounter the requirement to resume the fiber-jumping business first. Once you encounter this problem, you must keep in touch with the transmission center and seek its consent before you can jump the fiber. In addition, you can only pull and insert the fiber core by core. For each core jump, you need to wait until the transmission room is confirmed to be correct before starting the jump of the next core.
7.Concluding remarks
Through the analysis of this article, it can be seen that in the actual application of the optical time domain reflector, the operation and maintenance personnel of communication enterprises need to reasonably set the parameters of the optical time domain reflector, and carry out the denoising processing of the optical signal through the wavelet change modulus max method, so as to realize the non-distortion reconstruction of the optical pulse signal, and improve the accuracy of fault point positioning and Eliminate efficiency and promote the sustainable development of communication enterprises.
