Ultrawide-band photonic time-stretch a/D converter employing phase diversity

The performance of analog-to-digital converters can be greatly enhanced by preprocessing the analog signal using the photonic time-stretch technique. The analog bandwidth of a time-stretch preprocessor is limited by dispersion-induced frequency fading. In this paper, we propose and demonstrate a new implementation of the time-stretch analog-to-digital (A/D) conversion system that overcomes the bandwidth limitation. It is shown that the fading phenomenon can be mitigated by using phase diversity, and the maximum ratio combining algorithm is identified as a potential technique for maximizing the signal-to-noise-ratio. Real-time A/D conversion at 480 Gsample/s is demonstrated.