Application of Optical Communication Technology in Submarine Weapon System
Optical fiber guidance technology has the characteristics of large information transmission capacity, high guidance accuracy and good concealment. Due to light weight, small size and low cost, optical fiber guidance weapons have become an important way to extend and improve the wired guidance distance and the probability of weapon hit.
With the development of submarine weapon systems and the increase in the content of communication between various devices in the system, traditional communication forms and communication media are difficult to meet the requirements. Therefore, optical communication has received widespread attention because of its large capacity, short delay, and high reliability . The submarine weapon communication system includes the communication between the various devices in the system and the communication between the submarine weapon system and the weapon. With the development of technology, the speed and range of weapons have far exceeded the original range, and the high speed and large range have brought more information traffic, and the communication form based on traditional metal wires is difficult to meet Because of the large amount of information exchange requirements, optical fiber communication technology has gradually attracted people's attention due to its many advantages.
1 Application of optical fiber communication technology in submarine weapon systems is inevitable
Before talking about submarine weapon systems, let ’s first talk about the classification of communication systems:
1) Classification according to the physical characteristics of the message: According to the different physical characteristics of the message, the communication system can be divided into a telegraph communication system, a telephone communication system, a data communication system, and an image communication system.
2) Classification by modulation method: according to whether modulation is used, the communication system can be divided into baseband transmission and frequency band (modulation) transmission.
3) Classification according to signal characteristics: it can be divided into analog communication system and digital communication system.
4) Classification by transmission media: divided into wired and wireless categories.
5) Classification according to signal multiplexing mode: there are 3 multiplexing modes for transmitting multiple signals, namely frequency division multiplexing, time division multiplexing and code division multiplexing. Frequency division multiplexing uses the method of spectrum shift to make different signals occupy different frequency ranges; time division multiplexing uses sampling or pulse modulation to make different signals occupy different time intervals; code division multiplexing uses a group of The interleaved code group carries multiple signals.
According to the above classification standards, submarine weapon systems belong to time division multiplexing, cable, digital, frequency band transmission, and data communication systems. The use of optical fiber communication technology in submarine weapon systems has the following advantages:
1) Large communication capacity: the use of optical fiber communication is much larger than the traditional communication capacity using metal wires;
2) Reliable communication;
3) Small fiber density and light weight: The fiber composition is silica, so its density is less than that of copper wires, and it has zero or positive buoyancy in seawater, so no matter how long the communication distance is, there is no need to consider its own gravity to the entire communication system. Impact;
4) The optical fiber is cheap and good: the physical composition of the optical fiber is silica, which is very high in nature, and the civilian optical fiber has been developed very mature, so the cost is low;
5) Enhanced anti-electromagnetic interference capability: As we all know, electromagnetic interference is a big problem in the communication of submarine weapon systems, but optical fiber communication naturally gets rid of the problem of electromagnetic interference due to the use of optical signal form;
6) Civil technology is mature and easy to transplant: fiber optic communication technology has been widely and deeply researched, and has been widely used in telecommunications and other fields, so the application of fiber optic communication in submarine weapon systems can be based on civil technology The transplantation shortens the development cycle and cost.
2 Realization of optical fiber communication system
2.1 Composition of optical fiber communication system
The optical communication system is generally composed of a light transmitting part, a light receiving part, a light source, a photodetector, an optical wavelength division multiplexer, and an optical connector. The following is a brief introduction to some of them:
1) Optical transmitter and receiver
To realize information transmission, optical modulation and demodulation must be realized. The modulation of the information signal to the light signal emitted by the light source is light modulation. The modulated optical signal is transmitted to the photodetector through the optical fiber, and the original information is recovered after processing. This process is called demodulation. The modulation of the optical signal is done by the optical transmitter, and the demodulation is done by the optical receiver. The amplitude, frequency, phase and light intensity of the optical signal can be modulated. For digital modulation, the first three modulation methods correspond to the ASK, FSK, and PSK electrical signals. Optical intensity modulation (IM) is currently the most important modulation method in optical fiber communications. The light intensity system uses the "1" and "0" of the electrical signal to control the on and off of the light source, so it is also called the OOK (On-Off-Key) mode, which can directly modulate the light source. An external modulator can also be used. The direct modulation is convenient and the price is low; the external modulation technology is complex and the price is high, but the performance is superior.
2) Photoelectric detector
The photoelectric detector is a core device of the optical fiber communication system, which mainly completes the conversion function of the optical signal to the electrical signal, and requires the advantages of high sensitivity, short response time, low noise, low consumption, and high reliability. At present, photodetectors made of semiconductor materials can better meet these requirements. There are two types of photodetectors in practical use. One is the PIN photodiode (PIN-PD); the other is the avalanche photodiode (APD). PIN photodiodes are mainly used in short-distance, small-capacity optical fiber communication systems; APD is mainly used in long-distance, large-capacity optical fiber communication systems.
3) Optical wavelength division multiplexer
The function of the optical wavelength division multiplexer is to combine multiple different optical signals together and inject them into a fiber for transmission. The quality of the body characteristics largely determines the performance of the entire system. According to different manufacturing methods, the optical wavelength division multiplexer can be divided into four types: angular dispersion type, dielectric film interference type, fiber coupling type and integrated optical waveguide type.
4) Fiber optic connector
Optical fiber connection method: fusion splicing method, V-groove mechanical connection and elastic tube connection.
Connection loss is divided into internal loss and external loss. External loss is also called mechanical alignment error or connection dislocation loss. As the name implies, it is due to the loss caused by the connection dislocation between optical fibers. The internal loss is also called the loss related to the optical fiber, which is mainly due to the loss caused by the difference between the waveguide characteristics and the geometric characteristics of the optical fiber. There are several cases of connection misalignment: axial displacement, connection interval, tilt displacement, and uneven cross-section.
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