  We experimentally demonstrate an all-optical programmable thresholder on a
silicon photonic circuit. By exploiting the nonlinearities in a
resonator-enhanced Mach-Zehnder interferometer (MZI), the proposed optical
thresholder can discriminate two optical signals with very similar amplitudes.
We experimentally achieve a signal contrast enhancement of 40, which leads to a
bit error rate (BER) improvement by 5 orders of magnitude and a receiver
sensitivity improvement of 11 dB. We present the thresholding function of our
device and validate the function with experimental data. Furthermore, we
investigate potential device speed improvement by reducing the carrier
lifetime.
