Integrated Silicon-on-Insulator Spectrometer With Single Pixel Readout for Mid-Infrared Spectroscopy

Abstract

Mid-infrared spectroscopy in the 2–4 $\mu$ m wavelength range is of cardinal value for many sensing applications. Current solutions involve bulky and expensive systems to operate. Silicon-on-Insulator (SOI) waveguide technology offers means to miniaturize the different parts of the spectrometer. However, the development of on-chip detectors for the mid-infrared wavelength range is in its infancy and the characteristics are not on par with their discrete (cooled) counterparts. In this work, a compact and cheap mid-infrared spectrometer is realized by integrating a SOI arrayed waveguide grating (AWG) spectrometer operating in the 2.3 $\mu$ m wavelength range with a high performance mid-infrared photodiode. The AWG has 12 output channels with a spacing of 225 GHz (4 nm) and a free spectral range of 3150 GHz (56 nm), which are simultaneously collected by a single, transistor outline (TO)-packaged extended InGaAs PIN photodiode. The response of each AWG channel is discerned by time-sequentially modulating the optical power in each output channel using integrated Mach-Zehnder based thermo-optic modulators with a $\pi$ -phase shift power consumption of $\approx$ 50 mW. As an example, the absorption spectrum of a 0.5 mm thick polydimethylsiloxane sheet is sampled and compared to a benchtop spectrometer to good agreement.