Principles and Development of Optical Fiber Communication

1 Development of Optical Fiber Communication

In 1966, the Chinese Scholar Gao was a Chinese scholar. k. KA) and hawkhaamu C. k. HOCKHAM) published a paper on the new concept of transmission media, pointed out the possibility and technical path of using optical fiber OpticalFiber for information transmission, and laid the foundation for modern optical communication-optical fiber communication. In 1970, the development of optical fiber has made significant breakthroughs, and substantial progress has also been made as a light source for optical fiber communication. The technological advances in optical fiber and semiconductor lasers have become an important milestone in the development of optical fiber communication in 1970. In 1976, the United States in ATLANTA, ATLANTA) conducted the world's first practical optical fiber communication system field experiment, the system uses GAALAS laser as the light source, multimode optical fiber as the transmission medium, the rate is 44.7 Mb/s, the transmission distance is about 10 km.

The field experiment conducted in Atlanta, USA in 1976 marks the development of optical fiber communication from basic to commercial application. Since then, the optical fiber communication technology has continued to develop: from multi-mode to single-mode, and from 0.85um to 1.31 and 1.55um, the transmission rate has increased from dozens to dozens. On the other hand, with the development of technology and the formation of a large-scale industry, the price of optical fiber is constantly decreasing and the application scope is constantly expanding: from the early stage of inter-city telephone relay to long-distance trunk lines to the user access network, from a digital phone to a cable TV CATV), from the transmission of a single type of information to the transmission of a variety of services. At present, optical fiber has become the main medium for information broadband, and the optical fiber communication system will become the pillar of national infrastructure in the future.

2 Optical Fiber Communication System

The birth and development of optical fiber communication is an important revolution in the history of China Telecom. It was listed as a technology in 1990s with satellite communication and mobile communication. After the 21st century, with the rapid development of Internet services and the growth of audio, video, data, and multimedia applications, light wave transmission systems and networks with large capacity, ultra-high speed, and ultra-long distance have more urgent needs.

Optical Fiber Communication is the latest communication technology that uses optical waves as carriers to transmit information and uses optical fiber as transmission media to achieve communication purposes.

The development process of communication is to continuously increase the carrier frequency to expand the communication capacity. As the carrier frequency, the optical frequency has reached the upper limit of the communication carrier because it is an extremely high frequency electromagnetic wave, therefore, light as the carrier for communication capacity is huge, times the past communication methods, has a great attraction, optical communication is a long-pursued goal, but also the inevitable direction of communication development.

Compared with the previous electrical communication, optical fiber communication has many advantages: its transmission bandwidth and communication capacity are large, its transmission loss is low, and its relay distance is long. Its wire diameter is fine and its weight is light, the raw materials are Z, which saves metal materials and facilitates the rational use of resources; strong insulation and electromagnetic resistance; it also has the advantages of strong corrosion resistance, strong anti-radiation ability, good bypassing ability, no spark, small leakage, and strong confidentiality. It can be used in special environments or military scenarios.

Fiber-optic communication is widely used in many fields, and is mainly used for local telephone relay. The advantages of fiber-optic communication can be used to replace cables gradually and be widely used. In the past, long-distance trunk lines were mainly used for cable, microwave, and satellite communications. Now, fiber-optic communication is gradually used to form a bit transmission method that is dominant in the world; it is used for global communication networks and public telecommunication networks of various countries, such as China's National Level 1 trunk lines, Provincial Level 2 trunk lines and regional branches below the county level ); it is also used for high-quality color television transmission, on-site monitoring and scheduling of Industrial Production, Traffic Monitoring and Control Command, urban cable TV network, and shared antenna CATV system, it is used in optical fiber LAN and other applications, such as aircraft, spacecraft, ships, underground mines, power sectors, military and corrosive and radiation.

The optical fiber transmission system consists of the optical transmitter, the optical receiver, the optical fiber transmission line, the optical repeater, and various passive optical devices. To achieve communication, the baseband signal must also be processed by the electrical terminal and then sent to the optical fiber transmission system for communication. It is shown as a diagram of the optical fiber communication system.

Structure of optical communication system

It is suitable for optical fiber analog communication systems, and also for optical fiber digital communication systems and data communication systems. In optical fiber analog communication systems, electrical signal processing refers to the amplification, pre-modulation, and other processing of baseband signals, while electrical signal reverse processing is the inverse process of initial processing, demodulated and amplified. In an optical fiber digital communication system, Electrical Signal Processing refers to amplification, sampling, and quantification of baseband signals, that is, pulse encoding modulated PCM) and line code encoding processing, the reverse processing of electrical signals is also the initial inverse process. For data Optical Fiber Communication, electrical signal processing mainly involves amplifying the signal. Unlike the digital communication system, it does not require code conversion.

3. Role of the optical terminal and current status of the optical terminal

In optical fiber communication systems, optical transmitters are an important part of optical transceiver and Optical Repeater. Their most basic function is to modulated the electrical signals to be transmitted on Optical Waves, and inject it into the optical fiber line. The main function of the optical receiver is to convert the received optical signal into the original electrical signal and use the automatic gain control circuit (AGC) to ensure stable output. The main component of the optical receiver is the optical detector, its main task is to perform photoelectric conversion. It is very weak to transmit the attenuation optical signal from the optical transmitting end to the receiving end. In order to effectively implement the photoelectric conversion, the system requires the optical detector to have high response and low noise, fast response, stable and reliable operation.

At present, the data optical terminal has a history of development. It is neither a simple one nor a simple interface, and has reached hundreds of, such as 120, 240, etc.), a variety of different interface RS-232, RS-485, USB, etc.) is quite mature, such as Wuhan boshi electronics, Beijing xunfeng communications, Hangzhou yibang communications and other companies are the main products of the optical terminal, which boshi electronic RS-232 single-mode and multimode optical terminal can also do not need power. This article describes the Reuse Principle in eight ways.

4. Purpose, functions, and significance of Data optical terminal design

This design for multi-channel RS-232C interface standard is a widely used universal standard. It applies to the applicable general standards. It covers a wide range and far exceeds the communication and computer fields. In the 1960s s, there was almost no exception in using the telephone exchange network for remote access, so RS-232C interfaces were used for local communications, so it was more widely used. This design is based on RS-232 serial port through optical fiber transmission.

With the establishment of distributed computers, the cost of communication equipment has gradually become a major concern for users. to reduce these costs, by studying a large number of network structures, we can determine to use dedicated equipment as much as possible. Many networks are geographically distributed users who access public computing devices and build central areas as service centers linking these users to computers. Although the dedicated leased line cost is not reasonable when the terminal business volume is small, if the structure of many terminals sharing communication equipment can be used, in general, it can reduce the accumulated communication costs for a group of users, and the use of multipleaders may use a high-speed line to assume the business volume transmitted separately by a group of vulgar lines, therefore, when a large number of data terminals in the same geographic region communicate with each other, or when many lease lines at any distance are concurrently transmitted, you should consider using multiplets.

This data optical terminal adopts a multi-channel design, which not only greatly utilizes the line, but also makes full use of the huge bandwidth resources of the optical fiber. In addition, it can be widely used in various fields. The eight-way multiplexing technology designed in this paper can transmit different information through eight-way channels and reuse different information to one light for transmission, saving equipment, in the field application can be in the same system, a variety of control information and data information with a single optical terminal for transmission, can be connected to the computer and other terminals that comply with the RS-232 standards at the same time, convenient control and operation. This is the significance of the design of multi-channel multiplexing optical terminal. This article focuses on eight-channel multiplexing.

5 Overall Design Description of Data OPTICAL TERMINAL

The principle of the overall circuit is shown in the box: It connects several terminals to a high-speed data link, the transmission process is sent by the computer or terminal to the RS-232C standard signal first level conversion, the RS-232C level to TTL level, in order to be compatible with the subsequent circuit, and then through the MOTOROLA MC145428 Asynchronous Synchronous conversion chip in the RS-232C frame structure of the Start bit, stop bit removed, converted to synchronous output. After a multiplexing circuit is used to drive the unique path of multiplexing signals, the light source is modulated to convert the electrical signals into optical signals and send them to the optical fiber for transmission.

System principle diagram

Similar to the receiving process, the optical receiving module converts the received optical signal into an electrical signal, and then sends the signal to a multiplexing circuit through an ECL/TTL level converter after a line receiver, through the control of the time series circuit in the multiplexing circuit, the received signals are separated and sent to each channel. After the synchronous asynchronous MC145428 chip conversion, the start bit and stop bit are added, and then converted to the RS-232C level, enables it to comply with RS-232C interface standards and can be transferred in a computer or terminal. This is how the entire circuit works.

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