Effect of dither tone-based electro-optic modulator bias control on radio-frequency signal

Bias control of Mach-Zehnder electro-optic modulators( EOM) is of great importance in radio over fiber links. In order to study the impact of dither tone-based modulator bias control on radio frequency( RF) signal,the output signal component of the system was theoretically analyzed by means of spectrum analysis after it was turned into the Bessel series,a system for arbitrary bias point was designed to confirm the analysis experimentally. The results of MATLAB simulation show that when the input RF power is 18dBm,only when the amplitude of dither tone is smaller than 45mV,the suppression ratio of the second harmonic of RF signal to signal caused by dither tone can be greater than 20dB. When the input RF power is 10dBm,the amplitude should be smaller than 19mV accordingly. When the amplitude of dither tone changes,the error between the experimental data of the suppression ratio of the second harmonic of RF signal to signal caused by dither tone and the simulation results is maintained at about from 3dB to 3. 2dB. The results demonstrate that when Mach-Zehnder EOM works at linear bias-point,frequency components caused by dither tone can be ignored,however,when Mach-Zehnder EOM works at smallest bias-point,the impact of dither tone cannot be ignored.