Suspended germanium waveguides with subwavelength-grating metamaterial cladding for the mid-infrared band

In recent years, sensing and communication applications have fueled important developments of group-IV photonics in the mid-infrared band. In the long-wave range, most platforms are based on germanium, which is transparent up to similar to 15-mu m wavelength. However, those platforms are limited by the intrinsic losses of complementary materials or require complex fabrication processes. To overcome these limitations, we propose suspended germanium waveguides with a subwavelength metamaterial lateral cladding that simultaneously provides optical confinement and allows structural suspension. These all-germanium waveguides can be fabricated in one dry and one wet etch step. A propagation loss of 5.3 dB/cm is measured at a wavelength of 7.7 mu m. These results open the door for the development of integrated devices that can be fabricated in a simple manner and can potentially cover the mid-infrared band up to similar to 15 mu m. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Automated summary

A suspended germanium waveguide design with a subwavelength metamaterial cladding has been proposed to overcome the limitations of traditional platforms in terms of intrinsic losses and complex fabrication processes. These waveguides can be fabricated in a simple dry and wet etch step, with a measured propagation loss of 5.3 dB/cm at a wavelength of 7.7 μm, opening the door for the development of integrated devices covering the mid-infrared band up to approximately 15 μm.