Mitigation of Group-Delay-Ripple Distortions for Use of Chirped Fiber-Bragg Gratings in Photonic Time-Stretch ADCs

Low-loss dispersive components are critical to photonic time-stretch analog-to-digital converters (TS-ADCs) for attaining high resolutions. Chirped fiber-Bragg gratings (CFBGs) provide low losses plus high nonlinear thresholds but introduce time-warp and intensity-modulation distortions from group-delay ripple (GDR). Practical signal processing routines to mitigate GDR distortions are assessed for the two fundamental TS-ADC differential architectures. For differential TS-ADCs that use a common time-stretching element, differential RF extraction together with time-stretch linearization provides effective GDR mitigation. For differential TS-ADCs that use separate time-stretching elements, intensity scale factors proportional to the reciprocal of the GDR-induced intensity modulation are first applied, or alternatively DC-offset subtraction can provide effective mitigation when the separate path losses are sufficiently balanced. Using pulse propagation simulations with actual CFBG GDR data, these routines are projected to mitigate CFBG GDR distortions to levels commensurate with >;11 effective resolution bits for input RF bandwidths of at least 0-to-10 GHz and time-stretch factors >; 10.