Research On Optimal Bias Control System Of DSP-Based Electro-Optic Modulator

Optical intensity modulation is an important part for the remote and distortionless transmission in space optical communication. Mach-Zehnder optical modulator is the main device of optical intensity modulation system. However, because of the characteristics of modulator its own structure, the set work points will be offset when happen accidental disturb bring by surrounding environment, then the output optical signal is anamorphic.In order to solve this problem, this thesis mainly research on optimal bias automatic control system of DSP-Based electro-optic modulator, to make the bias point of the optical modulator is detected and adjusted in time, to avoid the output of the optical signal distortion.The proposed control scheme is to add a disturbance signal at the optical modulator bias voltage input terminal, and its amplitude is 60 mV, frequency is 1kHz. Detecting the disturbance signal at the output end of the optical modulator, then do the 2FFT harmonic analysis base on DSP from the feedback disturbance signal, calculate the first harmonic and the second harmonic amplitude, the calculated harmonic amplitude is used as the feedback signal to the digital PID control system based on DSP, after setting, the control system output compensates bias voltage, and then the bias point is corrected.Based on the above theory, finished the development and design of the optimum bias point control system of the optical modulator. According to the proposed index, complete the verification test of the system, the extinction ratio of the output light signal of the optical modulator is promoted, the intensity of the transmitted signal is stable, achieved the expected target.