Tandem Configuration of Microrings and Arrayed Waveguide Gratings for a High-Resolution and Broadband Stationary Optical Spectrometer at 860 nm

Abstract

Stationary optical spectrometers with both high spectral resolution and broad bandwidth at 800 nm −900 nm are needed in the high speed biosensing and bioimaging systems. Here we present an integrated spectrometer which uses a pair of fixed wavelength microring resonators (MRR) integrated in tandem with a pair of identical arrayed waveguide gratings (AWG). The use of narrow-line-width MRRs in the primary stage offers high-spectral resolution with an ultracompact footprint. The broadband AWG in the secondary stage provides a wide free spectral range (FSR). The AWG is designed to have channel spacing equal to the FSR of the MRR, so that the cyclically dropped wavelengths that cannot be distinguished by the MRR can be well separated by the secondary-stage AWG. By interleaving the resonances of the MRRs, high spectral resolution and wide optical bandwidth are attained. The proof-of-concept demonstration was implemented on a silicon nitride platform for 860 nm center wavelength. We interleaved two MRRs and integrated them with two 35-channel AWGs. The spectrometer has 70 wavelength channels within an overall size of 1.15 mm × 1.25 mm. The channel spacing is 0.75 nm, and the optical bandwidth is 57.5 nm.