On-Chip Photon Pair Source with Pump Rejection Filter

Abstract

Integrated photon-pair sources are fundamental building blocks of any quantum circuit. Spontaneous four-wave mixing in Si micro-resonators has already shown efficient on-chip generation of entangled photon pairs [1,2]. However, owing to the substantially higher pump intensity, compared to that of the photon-pair signal, suppression of the pump requires rejection levels exceeding 100 dB [3]. Besides strong pump suppression, narrow rejection bandwidth (<10 nm) is particularly important to allow short wavelength separation of the paired photons, thereby minimizing dispersion effects in the micro-ring that may reduce the efficiency of the nonlinear process. Implementing such pump-rejection filter on chip remains a challenge. Indeed, the only demonstration of photon-pair generation with on-chip pump rejection required cascading two identical chips [3], compromising the feasibility of the solution. The main reason for this is the limited rejection achieved by state-of-the-art on-chip Bragg filters. Ultra-high rejection has been demonstrated in actively controlled filters [4,5] at the expense of increased insertion loss and a high complexity, due to the control of all the filters. Nevertheless, photon-pair generation with effective pump rejection in a single chip has not been demonstrated yet.