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Plastic optical fiber technology for short-distance communication

the information explosion since the 1980s has led to a large influx of personal computers into offices, with a loss of 56db/km at 688nm and 94db/km at 780nm C-F harmonic absorption basically does not exist in the visible light region, and its intensity is less than 1db/km even if it extends to the range of 1500nm wavelength 3 light source and optical detector for plastic optical fiber communication system the working bandwidth of plastic optical fiber communication network depends on the bandwidth of plastic optical fiber, light source and optical detector. At present, the light source and optical detector used in high-speed plastic optical fiber communication network are being actively developed. 3.1 the light source should meet the requirements of two gratings required by plastic optical fiber for the wavelength, spectral width, light divergence angle and output power of the light source. The diameter of plastic optical fiber is large (0.5~1mm) and the numerical aperture is large (0.25~0.5). Because the luminous surface of high-speed semiconductor light source is usually about 501, the coupling with plastic optical fiber does not need to be accurately aligned. Semiconductor laser (LD) has narrow spectral width and small light divergence angle, which can obtain high bandwidth performance, but it is sensitive to temperature and expensive. Semiconductor light emitting diodes (LEDs) have larger spectral width and light divergence angle than LD, and their bandwidth performance is not as good as LD, but their reliability and temperature stability are higher than LD, and their prices are cheap. They are attractive for applications in short-distance networks. The three low loss windows of PMMA plastic fiber are located at the wavelength of 570nm, 650nm and 780nm respectively. At 570nm wavelength, there is no high-speed LD and led at present At 780nm wavelength, low-cost LD, which has been widely used in optical disk drives, can be used, but the loss of MMA plastic fiber at this wavelength is large when p sets the tightening speed. 780nm GaAs vertical cavity surface emitting laser (vc-sel) has been reported to be used in 2.5Gbps plastic fiber communication networks. At the wavelength of 650nm, the loss * of PMMA plastic optical fiber is small, the * high output power of algalnled has reached 3.5MW, and the divergence angle is 70121 '23; The * high output power of resonant cavity LED (RCLED) has reached 42mW, the spectral width is 3nm, and the rate can reach 250mbps; NEC company in Japan has developed * high output power of 61dbm and speed of 2 The loss of chemical plastic optical fiber in the region from visible light to near-infrared 1500nm is very small, so it can be used in the quartz optical fiber communication system, which has been widely used, low-cost high-speed LD and led 3.2 photodetector high speed plastic optical fiber network requires high-speed, large light sensitive surface and high quantum efficiency photodetectors. Avalanche photodiode (APD) has high sensitivity, but it is not suitable for short-distance communication networks because of high bias voltage, high price and stability. Therefore, using PIN photodiode (pin-PD) in short distance communication network is a better choice. The diameter of plastic optical fiber is large. In order to reduce the requirement of geometric position alignment accuracy when connecting with photodiode, photodiode is required to have a large photosensitive surface. However, the junction capacitance of photodiodes with large light sensitive surface is large, which limits the response speed of photodiodes. The existing Si photodiodes in the market are not suitable for plastic optical fiber networks. This is because Nanjing xuankai company uses engineering means to make Si an indirect band gap material, and the absorption coefficient at 650nm wavelength is relatively low. The photosensitive surface of high-speed Si photodiode is small, and it operates at a small bias voltage, but the quantum efficiency is low. GaAs is a direct band gap material. GaAs photodiodes can achieve high-speed operation at low bias voltage and maintain high quantum efficiency. Gaaspin photodiodes for PMMA plastic optical fibers have been reported. The quantum efficiency in the wavelength range of 600 ~ 850nm is higher than 80% and is basically not affected by the bias voltage. When the photosensitive surface diameter is 90m, the bandwidth is 43ghz; When the diameter of photosensitive surface is 500, um, the bandwidth is 170mhz; When the diameter of photosensitive surface is 210, um, the data rate of 600mbps can be achieved. It is expected that plastic optical fiber will become the main transmission medium of short-distance communication network because it not only has the characteristics of large bandwidth, anti electromagnetic interference and easy cabling of quartz optical fiber, but also has the advantages of low cost and easy laying. At present and in the future, the research will focus on solving the thermal stability and life problems of plastic optical fibers, and developing high-speed light sources and photodetectors

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