Research Of Coherent Optical Communication System

With the development of Internet and Internet of things technologies,requirements for wireless communication bandwidth are getting higher,while the wireless spectrum resources are increasingly scarce.Optical communication has large capacity,high speed and good compatibility with optical fiber,while the coherent optical communication has higher spectral efficiency and wider channel bandwidth than visible light in IM/DD(Intensity modulation with direct detection)mode.It causes industry and academic concerns in recent years.In this paper,we discuss coherent optical communication technology,and design and implement an indoor coherent optical communication system based on near infrared laser.Firstly,we investigate the key devices in coherent optical communication and derive the system performance based on the mathematical model of the key devices of the transceiver.Theoretically,we have proved the feasibility of the indoor coherent optical wireless communication via generating an optical spot near the receiver by a diffuser.Secondly,based on the existing optical fiber communication and wireless communication technology,this paper designs and implements a set of DSP(Digital Signal Processing)algorithm flow for indoor coherent optical wireless communication system.Using all-digital operations,signal imbalance,timing error,frequency shift and phase noise are compensated.Thirdly,this paper designs and realizes the coherent optical wireless communication platform.The suitable equipment and devices are selected by analyzing the parameters of the platform and devices.The peripheral circuits of the devices such as the laser control interface and the PD(Photodiodes)signal amplifying circuit are designed and realized independently.Finally,this article debugs the system and analyzes the performance of hardware platform.The performance test includes the optical power of each node in the optical path and the spectrum,the time domain signal waveform of the receiver,the system transmission rate and the bit error rate.The relationship between bit error rate and optical signal-to-noise ratio is obtained by using the experimental data of the system at different transmission rates.The test results show that with 20Gbps in 1m distance,the system bit error rate is lower than 10-5 when the optical signal to noise ratio is greater than 13dB,and the system can realize the error free transmission by using the forward error correction code when the optical signal to noise ratio is greater than 9dB.