Photonic analog-to-digital conversion based on time-to-frequency mapping

A novel photonic analog-to-digital conversion (ADC) scheme based on time-to-frequency mapping is proposed and experimentally demonstrated. In the approach, the amplitude of the input analog signal is firstly converted into a time-varying signal by pulse position modulation, then the time variation is mapped into the optical spectrum with the help of time-to-frequency mapping offered by the chirped optical pulse. The optical spectral information can be directly encoded by using interleaving filters and a binary receiver array, which outputs the digital records of the input analog signal. Compared with the existing photonic ADC schemes, the proposed approach greatly simplifies the system configuration and uses only one modulator with a dispersive element to achieve 2(N) quantization levels. Meanwhile, it also avoids the limitation of optical nonlinearity and realizes the linear mapping between the analog voltage and optical spectrum. A proof-of-concept experiment of the proposed approach based on time-to-frequency mapping is successfully carried out to verify the feasibility of the scheme. In addition, we also discuss the performance limitations induced by the frequency ambiguity in chirped spectra and the timing jitter in sampling.