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Suspended low-loss germanium waveguides for the longwave infrared
A. Osman, M. Nedeljkovic, J. Soler Penades, Y. Wu, Z. Qu, A. Z. Khokhar, K. Debnath, G. Z. Mashanovich
Optoelectronics Research Centre, University of Southampton, Southampton SO17 1BJ, UK

Published: 07 December 2018 by The Optical Society in Optics Letters
The Optical Society, Volume 43; 10.1364/ol.43.005997
Abstract: Germanium is a material of high interest for mid-infrared (MIR) integrated photonics due to its complementary metal–oxide–semiconductor (CMOS) compatibility and its wide transparency window covering the 2–15 μm spectral region exceeding the 4 and 8 μm limit of the silicon-on-insulator platform and Si material, respectively. In this Letter, we report suspended germanium waveguides operating at a wavelength of 7.67 μm with a propagation loss of 2.6±0.3 dB/cm. To the best of our knowledge, this is the first demonstration of low-loss suspended germanium waveguides at such a long wavelength. Suspension of the waveguide is achieved by defining holes alongside the core providing access to the buried oxide layer and the underlying Si layer so that they can be wet etched using hydrofluoric acid and tetramethylammonium hydroxide, respectively. Our MIR waveguides create a new path toward long wavelength sensing in the fingerprint region.
Keywords: SCANNING ELECTRON MICROSCOPY, chemical vapor deposition, waveguide gratings, slot waveguides, Waveguide Cores, Quantum cascade semiconductor lasers
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