Mid-infrared Fourier-transform spectrometer based on metamaterial lateral cladding suspended silicon waveguides

Integrated mid-infrared micro-spectrometers have a great potential for applications in environmental monitoring and space exploration. Silicon-on-insulator (SOI) is a promising platform to tackle this integration challenge, owing to its unique capability for large volume and low-cost production of ultra-compact photonic circuits. However, the use of SOI in the mid-infrared is restricted by the strong absorption of the buried oxide layer for wavelengths beyond 4 mu m. Here, we overcome this limitation by utilizing metamaterialcladded suspended siliconwaveguides to implement a spatial heterodyne Fourier-transform (SHFT) spectrometer operating atwavelengths near 5.5 mu m. The metamaterial-cladded geometry allows removal of the buried oxide layer, yielding measured propagation loss below 2 dB/cm at wavelengths between 5.3 and 5.7 mu m. The SHFT spectrometer comprises 19 Mach-Zehnder interferometers with a maximum arm length imbalance of 200 mu m, achieving a measured spectral resolution of 13 cm(-1) and a free spectral range of 100 cm(-1) at wavelengths near 5.5 mu m. (C) 2022 Optica Publishing Group