Light Modulator For Atmospheric Optical Communications And Optical Amplification Technology Research

Free space optical communication(FSO)is integrated with fiber communication and wireless communication. It is a new method of network with wireless optical access. It is now widely applied in free space communication and some special situations, for its exclusive advantage compared with fiber and wireless communication, cost declining of laser diode and developing of high sensitivity receiver and communication equipment, free space optical communication has become one choice of next generation of optical communication. So the dissertation researches the key technology of optical transmitter that could be suitable for FSO.Based on the Analysis of structure of OOK, PPM, DPIM, which are typical FSO modulations, the dissertation compares the three modulations in bandwidth demand, transmission capacity, power demand and error performance. Theoretical analysis and simulation results show that: OOK is easy to get, does not need symbol synchronization, has the minimum bandwidth demand, but low-power utilization; PPM greatly improves the power utilization, but has the lowest bandwidth utilization, also needs symbol synchronization; DPIM has higher power utilization compared to OOK, higher bandwidth utilization compared to DPIM, and does not need symbol synchronization. So DPIM has significant advantage in free space optical communication.To take EDFA for example, the dissertation introduces the principle and structure of fiber amplifier, and analyzes its property: gain and bandwidth, gain saturation, amplifier noise and gain spectra. It also discusses the factors that affect the gain and noise characteristics, such as the length of fiber, pump power, the input signal optical power, signal wavelength, etc. And it gives methods and directions that could improve the property of EDFA, which is good for the fiber amplifier design and optimization.For the requirement of China Electronics Technology Group Corporation for the 34th Research Institute, the standardizing EDFA that could be used in practical application is designed and made: with cascade amplifying, the gain of optical power could reach 30dBm; and the micro control module could reasonably and intelligently judge and control the pump switch and warning signals. The design and optimization of fiber amplifier in the internal arrangement, dimension, fa?ade, and interface are also necessary, so the fiber amplifier could steadily and properly run in the practical working environment.The experiment tests the major functional indicators of the amplifier. The signal output at 1552nm is about 826mW, when pump wavelength is 975nm, pump power is 3×3W. It basically achieves the request of 30dBm. And the micro control module could automatically control the pump laser diode according to the signal input, output and other warning signals.