Research On Influencing Factors Of Free Space Optical Hybrid Performance

Compared with the traditional space laser communication system,the space coherent optical communication system has more advantages such as high sensitivity,long transmission distance and large transmission capacity.It has been developed very fast in recent years.The space optical hybrid is one of main components of space coherent optical communication system.It can precisely hybrid optical wavefront of optical signal and local oscillator,and utilize optical field interference phenomenon to provide gain for optical signal.Heterodyne efficiency is an important performance criteria of optical hybrid.It depends on the intermediate frequency signal component which is contained in optical hybrid field.The performance of coherent optical communication system can be reflected by the heterodyne efficiency.In practical applications,the hybrid optical field is often affected by internal errors and external disturbances,and that can cause the reduction of heterodyne efficiency.Therefore,it is necessary to analyze the relationship between various influencing factors and heterodyne efficiency for high performance system.Most of the existing the research of heterodyne efficiency regularities are based on the model that hybrid optical field is directly transmitted to detector.Actually,the detector structure and package are difficult to interface with various types space optical hybrid directly.A reasonable way to solve this problem is to couple the output optical field into fiber.But on the other hand,existing research conclusions are no longer suitable for this new model.In order to obtain the law of the heterodyne efficiency under influence of various factors and to compare the space optical hybrid of fiber output model with traditional optical hybrid model.We analyzed the influence of intensity mode,spot size,tilt angle and signal wavefront distortion on heterodyne efficiency based on traditional model.Then we established the heterodyne efficiency model of space optical hybrid of fiber output type,and the relationship between heterodyne efficiency and fiber parameters.Furthermore,the effect of hybrid optical power ratio on the heterodyne efficiency were obtained.We tested the effect of incident light tilt on the heterodyne efficiency of fiber output type hybrid.The space optical hybrid performances of single-mode output and multi-mode output are compared.At last,the insertion loss and output signal beat waveform of fiber output type hybrid were tested in different incident optical beam angles.The presented theoretical model was confirm partially.The established model and analysis results can be used as a reference for spatial optical hybrid design.It will promote system theoretical design to transform to practical application.