Ultra-low loss waveguide platform in silicon photonics

Silicon photonics is the most promising technology for applications ranging from large-bandwidth, low power consumption datacom transceivers, to wearable health monitoring devices, or optical data-bus for quantum processors. To bring silicon PIC based products to the market, ultra-low loss waveguides would be preferred. In the conventional submicron silicon platforms, higher propagation loss (in the order of ∼1 dB/cm) induced by the roughness of the etched sidewalls, as well as higher fiber-to-waveguide coupling loss due to its sub-micron dimensions impose challenges for its deployment in many products. VTT's thick-SOI technology offers a promising alternative, owing to its lower propagation loss (∼0.1 dB/cm), reduced polarization sensitivity, and capacity to handle higher optical power without exciting nonlinear losses. Its micron-scale cross-section enables efficient edge coupling. Exploiting its ultra-low loss, we have demonstrated unprecedented level of integration such as, a 40-channel array waveguide grating (AWG) based mux/de-mux, or a Faraday rotator based on silicon spirals, without employing any magneto-optic material. Now we reduced the propagation loss further, down to record-low 4 dB/m, by controlled annealing of waveguides in 100% pure H2 environment. In our optimized, MPW-compatible annealing process, the atomic mobility of Si smoothens the scallops from etching, without causing any structural deformation of the waveguides. This substantially reduced loss enabled us to develop ultra-high Q ring resonators on our thick-SOI platform, as well as sidewall smoothening for the active components, thereby making our platform a bedrock for the emerging applications such as, quantum computing, biosensors, and 3D imaging.