Effects Of Factors On The Performance Of Heterodyne Detection And Experimental Investigation In Wireless Optical Communication

Along with the improvement of laser performance and the in-depth research of high-speed digital signal processing technology,in order to overcome the shortcomings of single modulation mode and low channel capacity utilization of Free Space Optics(FSO)system with intensity modulation/direct detection,coherent detection has been ref-ocused attention in recent years.In this dissertation,the performance influencing factors and applications of FSO heterodyne detection system are deeply investigated,the main results as follows(1)Based on the principle of coherent detection,the FSO heterodyne detection communication system was developed.The key modules involved in the system were analyzed and experimentally verified.The performance of the heterodyne coherent detection system under the ideal condition and the effects o f alignment error on the performance of the heterodyne detection system were analyzed numerically.(2)Under the weak atmospheric turbulence condition,we use classical analytical and numerical methods of optical wave propagation in turbulent random medium,the average varian ce of the angle-of-arrival fluctuation and the log-amplitude variance on the circular receiving aperture for a slant path under the modified Von Karman refraction power spectrum were derived,respectively.Based on th e obtained results,the mathematical model of the effect of random pointing errors and amplitude and phase random fluctuations on the performance of heterodyne detection were established,respectively.The effects of angle-of-arrival fluctuation and irradiance and phase fluctuations on the performance of heterodyne detection were investigated through theoretical analysis,respectively.(3)Considering the propagation problem of the beam in the turbulent atmosphere,based on the modified Hill refraction power spectrum,the mathematical model of heterodyne detection system with the partially coherent Gauss Schell Model(GSM)beam as signal beam was established.The closed-loop expression of the weighting factor of the partially coherent GSM beam at the receiving plane was derived using non-coherent mode decomposition method.Based on the obtained results,the effect of beam mode and turbulence parameters on the performance of the partially coherent GSM beam heterodyne detection system under atmospheric turbulence condition was investigated through numerical analysis and experimental verification.(4)The developed FSO heterodyne detection communication system was operated on the 1.3km communication link between buildings.The experimental data in different weathers were collected and processed.It verifies the stability performance of the developed heterodyne detection system proposed in Chapter 2,and provides powerful experimental support for real-time communication at a longer distance and at a higher rate.The work of this dissertation lays a theoretical foundation for analyzing the effect of factors on the performance of FSO heterodyne detection system,and provides an experimental basis for the FSO heterodyne detection system to achieve longer-distance communication.