Theoretical study and demonstration of photonic asynchronous first-order delta-sigma modulator for converting analog input to NRZ binary output

Abstract

A novel photonic analog-to-digital converter based on asynchronous first-order delta-sigma modulation (ADSM) has been theoretically investigated and experimentally demonstrated. The architecture uses an optical leaky integrator, an optoelectronic bistable quantizer, and positive corrective feedback for a noninterferometric optical implementation of the ADSM. The principles of the proposed first-order ADSM are mathematically modeled and simulated. A prototype fiberoptic system is constructed, producing nonreturn-to-zero type binary output for frequencies in the MHz range. For an analog input of 3 MHz and oversampling rate of 13.8 MHz, the system achieves a signal-tonoise ratio of about 38 dB, spurious-free dynamic range of 23 dB, and effective-number-of-bits of 6 within the 7 MHz band of interest.