As one of the core devices for an electro-optic analog-to-digital converter (ADC), the\nMachâ??Zehnder (MZ) modulator plays an important role, and the output stability of the MZ\nmodulator has a decisive influence on the conversion accuracy of the ADC. This paper proposed a\npilot tone-based method to stabilize the bias point of the modulator. This method could obtain the\ncorresponding control voltage of the MZ modulator by adding a KHz-level dither tone to the bias\nend of the modulator and calculating the ratio of the first and second harmonic components. The\nexperimental results showed that the output optical power of the modulator was stable at 3.2 dB\nwhen the bias point of the modulator was set at the orthogonal point. Moreover, the fluctuation\nrange was not more than 0.15 dB, the first harmonic of the output signal was stable at 50.5 dB, and\nthe fluctuation range was not more than 0.6 dB. The proposed bias controller based on the field\nprogrammable gate array (FPGA) and digital signal processing (DSP) can stabilize the modulator\nbias point at the orthogonal point and with a relatively high locking accuracy.
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