Fig. 1. Schematic of the monolithically integrated on-chip MIR germanium device that contains a high-Q nanocavity, two suspended-membrane waveguides, and two focusing subwavelength grating couplers. The inset to the bottom left shows the design of the high-Q nanocavity. The inset to the bottom right shows a cross-sectional view of a suspended-membrane waveguide.

Fig. 2. SEM images of the MIR germanium device, including the high-Q nanocavity. (a) Top view of the device. Scale bar: 10 μm. (b) Top view of the high-Q nanocavity. Scale bar: 500 nm.

Fig. 3. Experimental characterization of the MIR germanium device, including the high-Q nanocavity. (a) Measured transmission spectrum of the device (blue) and measured coupling efficiency of the focusing subwavelength grating couplers (red). (b) Lorentzian fitting of the measured nanocavity resonant mode. The inset shows the electric field magnitude distribution of the resonant mode.