Design For FSO System And Experiment Of Optical Subsystem

Atmospheric free space optical system(FSO) is a new-style wireless communication device which transmits information in atmosphere by laser.The system has wide applying field and good economic benefit because of the advantage of low costs, high secrecy and convenient setting. The objective of this project is designing a high bandwidth with low cost laser communicating device, which is consist of optical system, transmittal and receiver module and pointing,acquiring and tracking system.The function of optical system is transferring data in atmosphere and it. include transmitting aerial and receiving antenna. The function of transmitting is compressing divergence angle with Galileo telescope. The receiving antenna is used to collect the weak laser signature as much as possible and couple to APD.The transmittal module choose the newest style of VCSEL laser and the driving chip to complete optical/electric transformation. The perfected circuit can inspect and adjust the laser power so that VCSEL can keep unvarying power output. The APD is chosen as the optical receiver. And the control circuit is designed basing on the analysis of the relation between signal-to-noise ratio (SNR) and optimal multiplication gain of APD and the relation among the temperature of APD,and reverse voltage and the gain.The pointing,acquiring and tracking system is the key equipment of FSO which can assure the communication security during working period. It can reduce the possibility of communication intermitting because of building swinging and excursion of optical flat. The PSD is main part of an apparatus to measure excursion information and supply the FSM which has high response speed and resolving power to change the direction of laser transmitting ,ensuring communication continuity.In addition, the optical system is adjusted and the experiment data is listed and analyzed. So the feasibility of optical system is approved.