Our paper "Focusing subwavelength grating coupler for mid-infrared suspended membrane germanium waveguides" is published online in Optics Letters.

https://www.osapublishing.org/ol/abstract.cfm?URI=ol-42-11-2094

In this paper, we present a focusing subwavelength grating for efficient coupling of mid-infrared light into suspended membrane Ge photonic integrated circuits that enable mid-infrared applications in the entire fingerprint region. By virtue of their wide spectral transparency window and air-cladding device configuration, the suspended membrane Ge photonic integrated circuits are expected to be effective for mid-IR applications over the spectral region covering from 2 μmto 15 μm. Specifically, we demonstrate the maximum coupling efficiency of −11dB with a 1-dB bandwidth of ~58 nm at the subwavelength grating’s center wavelength of 2.37 μm.Our focusing subwavelength grating is expected to advance the development of on-chip long-wavelength mid-IR applications such as biochemical sensing, thermal imaging, and nonlinear optics in the fingerprint region.