Research On Detection Sensitivity Of Coherent Detection In Optical In Optical Wireless Communication

Compared with traditional radio frequency communication,wireless optical communication has advantages such as higher communication bandwidth,smaller spatial beams,smaller receiving antennas,no need for spectrum allocation,and higher security.It has broad application prospects in many fields such as island communication,military,special terrain communication,and secure communication.In order to achieve long-distance space communication,the coherence detection sensitivity of the coherent detection system is a very important research direction.This dissertation focuses on the sensitivity of coherent detection systems,and explores in depth the factors that affect the detection sensitivity of the system.A series of feasible schemes are proposed and the feasibility and effectiveness of multiple optimization schemes are verified.These schemes provide important guidance and reference for the design and implementation of high-sensitivity coherent detection systems.The main contents of this work are as follows:1.The system introduces the basic principles of direct detection of spatially coherent optical beams,coherent detection,partially coherent optical beams,and coherent detection sensitivity,providing the necessary theoretical foundation for the subsequent research work.2.The factors affecting the detection sensitivity were discussed,and the impact of local oscillator beam power,thermal noise,intensity noise,photodiode quantum efficiency,and splitter splitting ratio on detection sensitivity were studied.By optimizing the design parameters of the detection system,a highly sensitive coherent detection scheme was achieved.In addition,how to reduce the additional loss of the signal beam,achieve efficient mixing and coupling,and achieve long-distance,high-rate data transmission for wireless optical communication were also discussed.3.The sensitivity expression of the heterodyne detection system is derived when the partial coherent electromagnetic Gaussian-Schell model(EGSM)beam travels obliquely under the nonKolmogorov turbulence spectrum,and the relationship between the degree of polarization and the sensitivity is established.The influence of the power spectrum power law,turbulence scale,transmission distance,receiving height and detector photosensitive area diameter on the system sensitivity is analyzed when the EGSM beam is transmitted through the uplink and downlink under different polarization states under non-Kolmogorov atmospheric turbulence.4.An experimental platform for the influence of the polarization state of partially coherent EGSM beams on system performance was built,and the influence of EGSM beams on the system performance in completely polarized,partially polarized,and non-polarized states was studied.Experimental results show that the partially polarized EGSM beam exhibits an intermediate performance in a coherent detection system compared to completely polarized and unpolarized states.The research in this dissertation provides a theoretical basis for analyzing the sensitivity of coherent detection.In order to realize a coherent detection system with longer distance and higher sensitivity,it comprehensively analyzes the influence of the detector performance of the coherent detection system and the influence of external factors on the sensitivity of the coherent detection system.The existing optical influencing factors provide important technical support and theoretical guidance for the development of coherent detection technology.