Sub-wavelength cladding mid-infrared devices

Suspended structures enable low loss propagation in silicon waveguides for mid-infrared wavelengths by removing the lossy buried oxide (BOX) layer. We previously demonstrated suspended waveguides with a silicon core and a sub-wavelength grating (SWG) lateral cladding, which allows access to the buried oxide layer for under-etching with hydrofluoric acid. Here we show that bends, multimode interference couplers (MMI) and Mach-Zehnder interferometers (MZI) can be successfully implemented in this platform. Specifically, we report waveguides with propagation losses of 1.2 dB/cm, 90° bends with 0.03 dB/bend loss, compact MMI couplers with imbalances of 0.5 dB, and MZI structures with extinction ratios in excess of 24 dB.