Imaging spectrometers based on waveguide echelle diffraction gratings

Abstract

A method to integrate the spectroscopic system of the push-broom scanning imaging spectrometer onto a single chip is proposed using echelle diffraction grating to split the light in the near infrared range according to different wavelengths. The on-chip spectrometer consists of an optical on-off switch array, a multi-input echelle diffraction grating (EDG) and a detector array. The designed EDG has a channel spacing of about 4nm and up to 129 channels corresponding to wavelengths from 1.25 µm to 1.75 µm with channel uniformity less than 2 dB. Based on the 3 µm SOI platform the device is polarization insensitive. The switch array is integrated on the single mode ridge input waveguides, allowing the 129 input waveguides to be selected one-by-one in a time division multiplexed fashion. Since the switch can be scanned very fast (less than 10 microseconds), the imaging spectrometer can be operated in push-broom mode. Due to the CMOS compatibility, the waveguide EDG based imaging spectrometer can provide a low-cost solution for remote sensing on unmanned aerial vehicles, with advantages of small size, light weight vibration-proof, and high scalability.