Research Of Mid And Short Distance Free-space Optical Communication System Based On The Circle Polarization Modulation

In modern society, with people’s increasing demand for the communicationperformance, the optical fiber communication and microwave communication technologyhas become unable to adapt to the development of modern science and technology,because of the limition of these problems like high cost, difficult to build, limitedbandwidth. So we must find some new ways to develop new communicationtechnologies. As an important part of the optical communication, Free-space opticalcommunication technology is very important. It is a kind of technology that use of laseras a carrier of information in the free space transmission. This technique has a lot ofadvantages, such as large information capacity, easy to build, high confidentiality,enough bandwidth, etc. It has good prospects for development.In free space optical communication technology, modulation technique is one of themost important parts. With appropriate modulation, the information can be loaded intothe various physical parameters on the laser, for example, amplitude, frequency, phase,polarization state. These methods can improve the performance of the communicationsystem. Because in the air channel, the polarization state of the laser is less affected bythe environment. Therefore, the polarization modulation can effectively improve thecommunication quality of the free-space optical communication system.Now, the widely used method in the world is intensity modulatiom, this articlemainly studies the circular polarization shift keying modulation, and use of the relatedexperiments equipment to finish the buliting of the free-space optical communicationsystem based on the circle polarization shift keying modulation, then carried out relatedresearch and comparative experiment.This paper mainly used optisystem software for the simulation of the experimentalsystem, by observing the received signal simulation experiments, we confirmed thefeasibility of the method and analysised of the various components of the system. So wecould determine each of the devices used in this issue. After completing this experimentsystem, our group has changed the transmit power of the transmitter, and thetransmission distance between the transmitter and the receiver. In this case, we canobserve which kind of change of the received signal waveforms, eye diagrams, bit errorrate of system will generate.We also carried out the comparative experiments between single-channel receiversystem and dual differential receiver system, and the comparative experiments betweenCPolSK systems and OOK system. Our group has observed the difference of someparameters such as bit error rate between the two systems in the same case. We determinethe system using of dual differential receiver system CPolSK system can obtain moreexcellent signal quality. It is more suitable for optical communication system in the real world.In order to verify whether the system is able to complete the transmission ofinformation when receiver occurs displacement deviation. This research group continuedto study the bit error rate changes of the received signal, when the light spot and apertureof receiver is not aligned. We found that until the light spot is completely removed out ofthe receive aperture, the system is able to tolerate the deviation of the receiver andtransmitter. But bit error rate of system will be significantly reduced. It also verify thatthe confidentiality of the communication system.The experiments show that the free-space optical communication system based onthe circle polarization shift keying modulation is preferable to complete the process ofinformation transfer, and it has a distinct advantage relative to OOK method.