  Optical communication systems, which operate at very high rates, are often
limited by the sampling rate bottleneck. The optical wideband regime may exceed
analog to digital converters (ADCs) front-end bandwidth. Multi-channel sampling
approaches, such as multicoset or interleaved ADCs, have been proposed to
sample the wideband signal using several channels. Each channel samples below
the Nyquist rate such that the overall sampling rate is preserved. However,
this scheme suffers from two practical limitations that make its implementation
difficult. First, the inherent anti-aliasing filter of the samplers distorts
the wideband signal. Second, it requires accurate time shifts on the order of
the signal's Nyquist rate, which are challenging to maintain. In this work, we
propose an alternative multi-channel sampling scheme, the wideband demodulator
for optical waveforms (WINDOW), based on analog RF demodulation, where each
channel aliases the spectrum using a periodic mixing function before
integration and sampling. We show that intentionally using the inherent ADC
filter to perform integration increases the signal to noise ratio (SNR). We
demonstrate both theoretically and through numerical experiments that our
system outperforms multicoset in terms of signal recovery and symbol estimation
in the presence of both thermal and quantization noise but is slightly less
robust to timing jitter.
