On-chip auto-correlator using counter-propagating slow light in photonic crystal with two-photon absorption photodiodes

We propose an ultra-compact solid-state auto-correlator fabricated using Si photonics technology that obtains correlation by detecting the overlap of two slow light pulses counter-propagating in a photonic crystal waveguide integrated with a two-photon absorption photodiode array. As the device does not require a mechanical delay scanner, it can be easily integrated onto a chip and operated without alignment. Using the correlator, we successfully acquired the auto-correlation of pico-second pulses. The device’s nonlinear enhancement of slow light improves sensitivity, resulting in an evaluated detection limit in terms of the product of the peak and average power on the order of 10−7 W2, which is equal to or even better than that of commercial scanning auto-correlators and 107 times better than conventional single-shot auto-correlators’.