Research On Digital Photoelectric Heterodyne Detection Technology Based On QD

The space laser communication system has the advantages of high transmission rate,large channel capacity,strong confidentiality and strong anti-interference ability,and is a hot research object today.Coherent laser communication is mainly applied to inter-satellite laser communication links.Because the communication link is far away,the detected signal is very weak.Aiming at the application requirements of long-range inter-satellite laser communication,this paper studies the digital photoelectric heterodyne detection technology based on QD?quadrant detector?.This technology can improve the detection sensitivity of the optical communication receiver and the tracking accuracy of the signal light.In this paper,QD is used for heterodyne detection to receive weak optical signals,and BPSK?binary phase shift keying?modulation is used for communication.At the same time,QD is used to realize the spot position detection and the aiming of the signal light when there is no off-target output.It is based on QD to realize the communication and tracking combination in heterodyne detection.This paper first introduces the application status of QD in space laser communication,and then discusses the principle of QD heterodyne detection and communication,and proposes the realization scheme of digital photoelectric heterodyne detection system based on QD,and completes the hardware design.Hardware systems include QD,TIA?transimpedance amplifier?,ADC?analog-to-digital converter?,FPGA,and ARM.In terms of software,this paper uses FPGA digital algorithm to perform signal processing,including communication modulation and demodulation of heterodyne detection,spot miss amount calculation and spot capture algorithm,which realizes the digitization of heterodyne detection.Through theoretical analysis,when the bit error rate is 10^-6 and the communication rate is 10Mbps,the direct detection sensitivity of the QD heterodyne detection system is-37.4dBm,the heterodyne detection sensitivity is-73.8dBm,and the detection sensitivity is improved by 36dB.When the signal light power is-37.4dBm and the spot radius is 1/2photosurface radius?500?m?,the direct detection position resolution is 8.29?m,achieving a subdivision capability of 1/250.The heterodyne detection position resolution is 0.01?m,achieving a 1/200,000 subdivision capability,and the spot position detection performance is improved by 29dB.Finally,the experimental system was built,and the direct detection method was adopted.When the communication light wave wavelength was 1550 nm and the optical power was-15 dBm,the communication rate was the highest.When the bit error rate is the communication rate,the detection sensitivity is.Secondly,the simulation experiment of heterodyne detection communication demodulation is carried out to verify the communication demodulation capability of heterodyne detection.In terms of spot position detection,the spot position detection error of different optical powers and different spot sizes is calibrated,and the aiming of the signal light is achieved when there is no off-target output.This paper preliminarily demonstrates the feasibility of using QD to realize digital photoelectric heterodyne detection.The comparison between direct detection and heterodyne detection confirms the performance improvement of QD digital heterodyne detection system,which is the application of QD based digital heterodyne detection optical communication system.Lay the foundation with design.