Compact on-chip spectrometer with high spectral channel density using cascaded filters

Chip-scale spectrometers play important roles in spectroscopy applications. Existing on-chip components face fundamental challenges for achieving compact footprints and large number of spectral channels. We propose and demonstrate an ultra-compact computational spectrometer on a silicon-on-insulator platform. The device cascades eight micro-ring resonators and a waveguide Bragg grating for spectral filtering. The device occupies compact chip area with a single heater for thermo-tuning. A spectral resolution of 0.17 nm and an operating bandwidth of 60 nm are experimentally achieved. It corresponds to a high spectral-channel-to-footprint ratio of 88000 ch/mm2, providing a possible solution for a highly integrated spectrometer.