Study Of Inter-Satellites Laser Communication Terminals And Its Laboratory Testing Platform’s Optical System

Laser communication Terminals(LCT) have got widespread attention now, duesto its advantages such as huge capacity of information, high optical gain and highanti-interception ability. The optical system of LCT has the characteristics of highimaging quality requirement and multi-channel used, which give a great pressure onoptical manufacture and alignment. As to direct optical design, manufacture andalignment, studying on the relationship between aberration and communicationproperty and developing more reasonable optical structure are very significative.Besides, it’s difficult to promote effective experiment on ground because of the fardistance among the communication LCTs, therefore, developing test platform for LCTand designing the space link models to evaluation LCT in laboratory is veryindispensable.Based on different detection model and the function peculiarity of differentchannels, the relationship between primary monochrome aberrations of transmitantenna and far field laser intensity distribution, primary monochrome aberrations ofreceiving terminals and tracking accuracy, receiving power, and bit error rate(BER)were established. The relationship between pointing error, tracking accuracy, BER andaberration were analyzed by numerical method. The results indicate that tilt and comahave a great effect on pointing error and tracking accuracy, liner and cubic curve can stand its relationship, respectively. The effects of aberration to BER were determinedby the ideal BER, the lower BER needs higher requirements of the optical system.Coherent heterodyne detection based on BPSK modulation have rigid requirement onaberration, compared to uncoherent detection based on IM/DD modulation. Theanalysis of heterodyne efficiency with different coherent beam shows that theparameters of the beam rest with the detector parameters and coherent beam styles soas to obtain high heterodyne efficiency.On the basis of the GEO-Ground LCT’s working mode and application feature,optical index of GEO LCT based on BPSK modulation were presented. In order todevelop a suitable antenna optical structure, transmission, reflection of off-axis,classical cassegrain and developed cassegrain types were compared upon manufacture,alignment and test. The results states developed cassegrain have the advantages ofsmaller size, easier manufacture and looser tolerance, and is propitious to be used foroptical antenna of inter-satellite communication. Using Zemax software, the opticalsystem was designed with developed cassegrain structure, and its performance werealso discussed.According to the analysis of the function and characteristic about laboratory testequipment of LCT at home and aboard, principle and optical requirement of LCT’slab test and link model system were brought forward, and also designed the opticalsystem upon the requirement with reflection structure, the beam splitter’s reflectionand transmission were used to compensated the polarization diverse. The system canbe used to test different LCT that not only different communication wavelength, butdifferent types of modulation. Because of the manufacture levels and highly imagequality demand, the alignment results were not satisfied for the optical requirementsproposed. After analyzed the wavefront’s features, method using mask phase plate tocorrect the wavefront was discussed. The result indicated that mask phase plate canimprove the wavefront to its requirments with practicable process. The space linkmodel was also designed based on the test equipment, the theoretical analysis of thespace link model shows its can model10~3km~10~5km communication link, which can satisfied the most LCT payload used in inter-satellite communication.