Ultra-low power Four Wave Mixing wavelength conversion in silicon micro-ring resonators with tunable Q-factor

The development of highly non-linear silicon devices is a fundamental step towards the realization of low power optical signal processing devices. In order to achieve this final goal several constraints have to be overcome. In particular, the next generation of opto-electronic integrated devices must be ultra-compact, compatible with foundry model fabrication processing and exhibit low power consumption. In recent years, many non-linear photonic devices have been demonstrated based on the Silicon On Insulator (SOI) technology platform allowing for an unprecedented level of integration. Many research groups have demonstrated non-linear devices that can perform wavelength conversion, demultiplexing operations and all-optical switching. In particular, in order to perform wavelength conversion, Four Wave Mixing (FWM) effects are typically used in silicon, showing conversion efficiencies that have ranged from -40 dB to -8 dB. The latter figure was demonstrated on a 8-cm long waveguide with a very high pump peak power (P_p=5 W) and a lateral pin junction to reduce the free carrier losses due to two photon absorption. In order to decrease the pump power, resonant devices have been considered and demonstrated in the past few years. In such structures the non-linear response is substantially improved due to the field enhancement of the cavity, which is proportional to the cavity Q-factor.