Distortion Cancellation in Time-Stretch Analog-to-Digital Converter

We show that the symmetry properties of the two outputs from a push-pull Mach-Zehnder modulator can be exploited to reject dispersion-induced second-order distortions in the time-stretch analog-to-digital converter (TS-ADC). Using differential operation and signal processing in the digital domain, we experimentally demonstrate suppression of the signal harmonics generated due to system nonlinearities. Simulations predict that distortion-limited dynamic range improves from 34 to 57 dB. In addition, differential signaling improves the signal-to-noise ratio (SNR) by 3 dB and rejects an even-order nonlinear distortion added by an electronic digitizer in the TS-ADC. It is also shown that this approach is robust even in the presence of mismatches in the differential signal paths. In general, the approach can also be applied to any ultrawideband (multioctave) optical link to obtain a high dynamic-range system.