Mid-Infrared Silicon-on-Insulator Fourier-Transform Spectrometer Chip

Mid-infrared absorption spectroscopy is highly relevant for a wide range of sensing applications. In this letter, we demonstrate a Fourier-transform spectrometer chip based on the principle of spatial heterodyning implemented in the silicon-on-insulator waveguide platform, and operating near 3.75-μm wavelength. The spectrometer comprises a waveguide splitting tree feeding to an array of 42 Mach-Zehnder interferometers with linearly increasing optical path length differences. A spectral retrieval algorithm based on calibration matrices is applied to the stationary output pattern of the array, compensating for any phase and amplitude errors arising from fabrication imperfections. A spectral resolution below 3 nm is experimentally demonstrated.