Distortion compensation in continuous-time photonic time-stretched ADC based on redundancy detection.

Abstract

In continuous-time photonic time-stretched analog-to-digital conversion (PTS-ADC), a wavelength-division multiplexer (WDM) is widely used to separate the overlapped stretched signal segments in both the wavelength and time domains. However, the spectrum shape of the WDM is not an ideal rectangle, and signal distortion occurs when we reconstruct the stretched signal by connecting the segments carried by the rising or falling edges of the spectrum. A signal distortion compensation scheme based on redundancy detection is proposed in this paper. Two WDMs with complementary spectrum division are employed; if we properly set the central wavelength of each channel of both WDMs, the signal segments that might be distorted by inter-channel mismatch can be redundantly detected and the distortion can be completely avoided. Moreover, by adjusting the dispersion amount of the first dispersive medium, the optical carrier obtained by connecting the stretched chirped pulses is partly overlapped, which guarantees the redundant modulation of signal segments that might be distorted by inter-pulse mismatch. Accordingly, the signal distortion induced by inter-pulse mismatch can be perfectly removed. In addition, the effective bandwidth of each chirped optical pulse is given. The maximum system stretch factor is also derived in this paper, and experiments based on the proposed signal distortion compensation scheme are carried out. The results obtained provide instructive guidelines for the design of a continuous-time PTS-ADC with the desired performance.