Strip Waveguide Enabling Low Loss for Silicon on Silica Technology in the MIR

Mid-infrared silicon photonics is attracting academic and industrial interest due to the potential applications in chip-scale sensors, free-space optical communications in addition to others. This work offers a technique to push the limit of silicon photonics using the traditional silicon on silica technology deeper into the mid-infrared region, up to a wavelength of 4.28 μm, despite the extensive silica absorption losses. It is demonstrated that a waveguide of 400 nm height and 1600 nm width requires a buried oxide buffer of 3.5 μm so that the leakage loss is below 0.01 dB/cm. The silica absorption loss in this case is only 3.4 dB/cm. In this approach, the silicon on silica platform can be employed for photonic devices, such as gas sensors, in that range of wavelength.