Broadband Laser Doppler Frequency Shift Emulator for Satellite Laser Communication

A novel emulator of laser Doppler frequency shift (DFS) for satellite laser communication based on microwave photonics technology is proposed and experimentally demonstrated. In order to overcome the bottleneck that the optical frequency shift signal with a wide frequency offset from near zero can hardly be obtained using traditional electro-optic or acousto-optic frequency shifting, the frequency of laser signal is first moved to a lower/higher fixed frequency and then shifted back to a higher/lower tunable frequency. The signal after cascaded frequency shifting in the opposite direction is equivalent to the original laser signal with DFS. In the experiment, the value and direction of DFS correspond to the magnitude and sign of the difference between the two frequency shifts. The DFS from -14 GHz to +14 GHz with a varying rate of 323 MHz/s is accurately implemented. In addition, the side mode suppression ratio (SMSR) of laser signals with DFS are all over 52.3 dB. The proposed scheme is significant to evaluate and test the DFS compensation capability of the satellite laser communication terminal.