High aspect ratio Ge-on-Si waveguide platform for miniaturized mid-infrared applications

Andrew Whye Keong Fong; Rachel Chen Fang Ang; Leh Woon Lim; Lennon Yao Ting Lee; Qingxin Zhang; Doris Keh Ting Ng; Xianshu Luo; Landobasa Y. M. Tobing

doi:10.1117/12.3000110

12 March 2024 High aspect ratio Ge-on-Si waveguide platform for miniaturized mid-infrared applications

Andrew Whye Keong Fong, Rachel Chen Fang Ang, Leh Woon Lim, Lennon Yao Ting Lee, Qingxin Zhang, Doris Keh Ting Ng, Xianshu Luo, Landobasa Y. M. Tobing

Author Affiliations +

Proceedings Volume 12889, Integrated Optics: Devices, Materials, and Technologies XXVIII; 128890I (2024) https://doi.org/10.1117/12.3000110
Event: SPIE OPTO, 2024, San Francisco, California, United States

Abstract

On-chip spectrometer operating in the mid-infrared (MIR) regime (λ = 2 – 14 μm) enables the miniaturization of a chemical sensing platform that identifies compounds based on their unique molecular fingerprints. Germanium-on-Silicon (Ge-on- Si) material system is a suitable candidate for its transparency in the MIR spectrum and compatibility with silicon processing. As chemical sensing is conducted by having the mode evanescent field interacting with the analyte, the design of Ge-on-Si waveguide for a compact footprint (small bending radius) and large evanescent field coverage is necessary. However, the bending radius of the Ge-on-Si waveguide is limited to hundreds of micrometers due to the low refractive index contrast between germanium and silicon. In this work, we demonstrate a 3 μm thick Ge-on-Si waveguide, with ~89° sidewall angles and a high gap aspect ratio of 10 (resolvable gaps of 300 nm). Different types of Ge-on-Si devices are fabricated including in-plane distributed Bragg grating (DBR) structures, cascaded Fabry-Perot resonators, and polarization splitters. We show that over-etching the Si lower cladding is able to reduce bending loss by ~10x, allowing us to decrease the bending radius to ~50 μm. Designs of 32 waveguide geometries for single mode propagation from 5.5 μm to 11 μm are presented, each of which is integrated with grating couplers operating at specific peak wavelengths. Our measurements show high consistency between the simulated and measured peak wavelengths of the grating couplers, with an inter-chip standard deviation of σ_λ⁄ λ_peak<1%

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(2024) Published by SPIE. Downloading of the abstract is permitted for personal use only.

Citation Download Citation

Andrew Whye Keong Fong, Rachel Chen Fang Ang, Leh Woon Lim, Lennon Yao Ting Lee, Qingxin Zhang, Doris Keh Ting Ng, Xianshu Luo, and Landobasa Y. M. Tobing "High aspect ratio Ge-on-Si waveguide platform for miniaturized mid-infrared applications", Proc. SPIE 12889, Integrated Optics: Devices, Materials, and Technologies XXVIII, 128890I (12 March 2024); https://doi.org/10.1117/12.3000110

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