Research of fine tracking and signal detection system based on QD without beacon

In this paper, we propose a simultaneous fine tracking and signal detection subsystem based on QD (Quadrant Detector) for FSO (Free Space Optical communication) system in 1550nm without beacon. Then we test the sensitivity, resolution, SNR characteristics and the influence the size of light spot on QD by building an indoor experiment. We select 1550nm waveband which suffers relatively less from background radicalization and atmospheric channel as the waveband of transmitter and receiver, also our selection catered for the trend of FSO system. We use the same QD for both fine tracking and signal detection for FSO in our design. Besides we use the scheme without beacon beam, for which we reduce the use of a beacon laser source, so we can obtain weight reduction and size decrease which is very important for FSO system.