Optical sampling analog-to-digital converter based on two asynchronous mode-locked fiber lasers

Using a mode-locked fiber laser in an electronic analog-to-digital converter (ADC) system has attracted increasing attention because an optical pulse train, generated by an optical mode-locked fiber laser, has an ultrashort pulse width and ultralow timing jitter compared with an electronic pulse train. An optical sampling ADC system based on a mode-locked fiber laser has made great progress in high-speed microwave signal ADC systems with high resolution. In this paper, we report an optical sampling ADC system based on two mode-locked fiber lasers with a slight difference in repetition frequency. Working with the Chinese remainder theorem, we can determine the microwave whose frequency is far greater than the sampling rate. We can precisely measure carrier frequency with a subsampling method. The optical ADC system can digitize a narrow bandwidth at high carrier frequency. In our system, the repetition rate of one mode-locked fiber laser is 100 MHz, and the other is (100  M+1  k) Hz. We digitize a narrow bandwidth (<50  MHz) microwave signal on a 10 GHz carrier frequency with greater than 7 effective-number-of-bit (ENOB) resolution.