Dispersion engineered SiON ring resonators for integrated photon sources

The interest in integrated photonic processors is growing rapidly, with the perspective of the realization of devices capable to provide single photon qubits for efficient and scalable quantum computation. While the on-chip single photon manipulation is well developed in quantum photonics circuits, the integration of photon generation and photon detection stages on the same chip is currently far from being established. In this work we present a potentially scalable, integrated source of near-infrared photon pairs based on ring resonators, realized with dispersion-engineered silicon oxynitride waveguides. The use of high-index silicon oxynitride as core material gives the possibility to engineer the optical properties of waveguides by adapting the ratio between oxygen and nitrogen gases in the deposition chamber and allows the realization of films with thicknesses over 500nm without the formation of cracks. An efficient photon generation process via nonlinear Four-Wave-Mixing (FWM) in a ring resonator requires a zero group-velocity-dispersion in order to have energy equidistant resonances. Here we show that, while it is almost impossible to achieve such a condition with oxide-cladded SiON waveguides, the zero-dispersion-point in the red and near-infrared wavelengths can be engineered if the waveguides are in direct contact with air. This can be achieved through a selective removal of the top oxide cladding from the ring resonators by the means of wet chemical etching and a silicon nitride etch-stop layer. We show that the realized devices are characterized by a constant Free Spectral Range at the engineered wavelengths and are thus feasible devices for nonlinear photon generation via FWM.