Optimization of AlGaAs-based Bragg-reflection waveguides for entangled photon sources

AlGaAs Bragg-reflection waveguides offer the potential for on-chip entangled photon sources which integrate the entangled photon source and the pump source in the same chip. We designed and experimentally realized an AlGaAs Bragg-reflection waveguide structure in which the effective refractive indices for TE and TM polarized down converted photons are the same to improve the degree of entanglement without external compensation. This was realized by appropriate choice of the ridge width of 1.8 μm, which offers lateral optical confinement. The difference in effective refractive indices has been reduced by more than a factor of 10 compared to waveguides of several micron width. Photon generation rates of 9,200,000 cps (single rates) and 1,700,000 cps (coincidence rate) and a coincidence accidence ratio of about 60 were determined for these waveguides for 5 mW pump power.