The birth of optical fiber communication technology is a revolutionary advancement in the telecommunications industry. In 1966, Dr. Charles K. Gao, a British Chinese, published an epoch-making essay (Grandin, 1966). He proposed using quartz glass optical fiber with a cladding material as a communication medium. Since then, research work in the field of optical fiber communication has been initiated. The current optical fiber fourth-generation communication technology has the advantages of light weight, high speed, low loss, small volume and can stably cope with the magnetic interference environment and has a large transmission bandwidth. It is widely used in many fields, especially in the production and service industries. Such as Local communication, media industry and the development of fiber sensors are widely used for measurement of small gauge length on civil engineering.
1.Technical principle of optical fiber communication
Optical fiber communication refers to a communication method in which a light wave is used as a carrier wave, and a signal to be transmitted is transmitted from one place to another by using an optical fiber as a transmission medium. Among them, the optical fiber is composed of a core, a cladding and a coating. The core is a glass material, measured in micrometres, usually a few micrometres thick, thinner than the hair (Hecht, understanding fiber optics, 2015). The middle layer is called a cladding layer, and according to the different refractive indices of the core and the cladding layer, total reflection in the core during optical signal transmission is realized, and signal transmission is realized. The coating is a protective layer that increases the toughness of the cable to protect the fiber. The basic components of the optical fiber communication system are optical transmitters, optical lines, optical receivers, repeaters and passive components. The function of the transmitter is to convert the signal to be transmitted into an optical signal that can be transmitted on the optical fiber, and then realize the long-distance transmission of the signal through the optical fiber line, and the optical fiber line couples the signal to the photodetector of the receiving end at the terminal, and passes the light. The receiving end converts the changed optical signal into an electrical signal and amplifies the weak electrical signal to a sufficient level through an optical amplifier, and finally sends the signal to the receiving end to complete the signal transmission. (keiser, 2003, p. 50) The role of the repeater in this process is to compensate for the attenuation of the optical signal during fiber transmission and to correct the waveform distortion pulse. The function of the passive device is to complete the connection and coupling between the fibers. Through the transmission process of the signal, it can be seen that the form of the signal mainly realizes two conversions during the transmission process, the first time the electric signal becomes the optical signal that can be transmitted in the optical fiber, and the second time the optical signal is taken to restore an electrical signal at the receiving end. (Hecht, 2015, pp. 227-249). In addition, at the transmitting end, it is also necessary to first convert a signal to be transmitted, such as a voice signal, into a transmittable electrical signal. (Wang, 2006)
Application Analysis of Distributed Optical Fiber Sensing Technology
(1) For civil engineering
Fiber optic sensors can be used in civil engineering (Chang, 2010), especially in the construction industry, where the frequency of applications is higher. In the course of the building, the relevant data of the bridge can be detected, and the rock can be measured, which plays an important role in determining the foundation and determining the relevant construction technology and can improve the quality and efficiency of the building. Therefore, in civil engineering, the application of fiber optic sensors is very extensive. It can provide important data for relevant departments as the basis for later research, and on the motorway, real-time monitoring of road conditions can be carried out, to avoid failures and ensure the safety of the vehicle counterparts.
(2) For Aerospace
In the aerospace industry, fiber optic sensors are also needed. (Chang, 2010) This is because the fiber optic sensors can be used to more accurately understand the specific situation of the space shuttle. Because the fiber optic sensor is relatively small in size, it can form an intelligent network structure that facilitates the propagation of relevant data and signals, and can perform real-time monitoring of the aerospace aircraft internally and externally, thus ensuring problems in aircraft can be found in time, and take appropriate solutions and methods to ensure the safety of the flight crew and the aircraft. At present, the fiber optic sensor can be used in the aircraft’s wing, as well as the stable axis and other important positions, and can monitor the specific situation of the aircraft at any time. Therefore, the application of fiber optic sensors in aerospace is also very extensive.
(3) For power industry
The power industry is also one of the industries in which fiber optic sensing technology is widely used. The main reason is that the use of light sensors can detect the condition of cables and wires, which can ensure the normal operation of power companies and power systems. At the same time, the use of optical fiber sensing technology can predict and analyze the cable temperature, avoid high temperature, damage the cable, maintain the normal operation of the power system, and ensure a safe preventive measures and means of the power system. Therefore, in high voltage power systems, fiber optic sensors are required. (Liu, 2010)
The development trend of optical fiber communication technology
Soliton communication It is recognized as the most promising and most pioneering frontier in optical fiber communication. It is an all-optical nonlinear communication scheme. The basic principle is that the (Agrawal, 2000)nonlinear (self-phase modulation) effect of the refractive index of the fiber causes the compression of the optical pulse to be balanced with the broadening of the optical pulse caused by the group velocity dispersion. (Ablowitz, 2000)Optical solitons can be transported in the fiber over long distances without deformation. It eliminates the limitation of fiber dispersion on transmission rate and communication capacity, and its transmission capacity is 1~2 orders of magnitude higher than today’s best communication systems. Optical soliton communication and linear fiber communication have three significant advantages:
(1) Transmission capacity is one to two orders of magnitude larger than the best linear communication system.
(2) All-optical relay can be performed. Due to the special nature of the soliton pulse, the relay process is simplified to an adiabatic amplification process, which greatly simplifies the relay device, which is efficient, simple and economical.
(3) Compare to linear optical fiber communication, soliton communication has obvious advantages in both technology and economy. it is superior to light intensity modulation/direct detection mode and coherent optical communication in high fidelity and long-distance transmission.
Due to these advantages and potential development prospects of optical soliton communication technology, this technology has been vigorously researched and developed in the international and domestic markets. The research to nowaday has laid a theoretical, technical and material basis for the realization of ultra-high-speed, ultra-long-distance non-relay optical soliton communication systems:
(1) The invariance of soliton pulses determines the need for no relay
(2) Fiber amplifiers, especially erbium-doped fiber amplifiers pumped with laser diodes will compensate the losses
(3) The stability of soliton collision separation provides convenience for designing wavelength division multiplexin
(4) Using pre-emphasis technology, and using dispersion-shifted fiber transmission, the erbium-doped fiber lumped signal is amplified (Taylor, 2005), which weakens the influence of ASE and expands the relay distance at low gain
The future of optical soliton technology is: In the transmission speed, ultra-long-distance high-speed communication, ultra-short pulse control technology in the time domain and frequency domain, and ultra-short pulse generation and application technology increase the current rate of 10~20 Gbit/s to more than 100 Gbit/s; Optical filtering increases the transmission distance to over 100,000 km; In terms of high performance EDFA, low noise and high output EDFA is obtained.
Communication technology has a great impact on people’s lives. As one of its technical fields, optical fiber communication has developed rapidly since its inception in the 1970s with its unique convenience, security, and large amount of information transmission. It has become one of the main communications means. In the future development process, along with the continuous development of science and technology and the increasingly strict requirements of communication technology, optical fiber communication technology will inevitably develop into new areas such as intelligence while breaking through the existing technical limitations. The scope is wider, the technology update is more difficult, the influence and influence are wider, and it will inevitably have a far-reaching impact on the entire telecommunications network and information industry. As soliton communication still has many technical problems. But the breakthrough progress that has been made today makes us believe that optical soliton communication has bright prospects in ultra-long-distance, high-speed, large-capacity all-optical communication, especially in the seabed optical communication system, there is a bright future. Its evolution and development results will largely determine the future of the telecommunications network and the information industry and will have a huge impact on the future national economy. (Haus, 1996)
- Ablowitz, M. j. (2000). Optical solitons: perspective and application. American institute of Physics.
- Agrawal, G. p. (2000). Nonliner Fiber Optics. (pp. 3-11). Springer.
- Chang, T. (2010). Optical fiber sensing technology and its application in smart cities and smart oil fields. Innovation of information technology , 111-113.
- Grandin, K. (1966). Retrieved from nobleprize: https://www.nobelprize.org/prizes/physics/2009/kao/lecture/
- Haus, H. (1996). Amplifier Noise . Solitons in optical communication, (pp431).
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- Hecht, J. (2015). In J. Hecht, Understanding Fiber Optics (pp. 227-249).
- keiser, g. ( 2003). Optical Fiber Communications.
- Liu, D. (2010). Distributed optical fiber sensing technology and its application. Progress in laser and optoelectronics, 122-124.
- Taylor, J. R. (2005). soliton amplification in erbium doped fiber amplifiers and its application to soliton communication. In optical solitons thery and experiements (pp. 152-160). Cambridge university.
- Wang, L. (2006). The development and future of optical fiber communication. China Science and Technology Information.