Fong, A. W. K., Ang, R. C. F., Lim, L. W., Lee, L. Y. T., Zhang, Q., Ng, D. K. T., Luo, X., & Tobing, L. Y. M. (2024). High aspect ratio Ge-on-Si waveguide platform for miniaturized mid-infrared applications. In S. M. García-Blanco P. Cheben (Eds.), Integrated Optics: Devices, Materials, and Technologies XXVIII. SPIE. https://doi.org/10.1117/12.3000110
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 σλ ⁄ λpeak <1%
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Funding Info:
This research / project is supported by the National Research Foundation, Singapore and Agency for Science, Technology and Research - Low-Carbon Energy Research (LCER) Funding Initiative (FI)
Grant Reference no. : U2102d2012
This research / project is supported by the Agency for Science, Technology and Research - N/A
Grant Reference no. : C220415015
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