Modelling of a miniature mid-IR thermo-optic spectrometer on chip based on a GaAs/In[formula omitted]Ga[formula omitted]P waveguide platform

Abstract

Spectrometers based on integrated optical waveguides, as opposed to free space optics, provide many advantages including robustness, compactness, and low cost, combined with alignment-free and low-power operation. Interest in such a chip-based approach for integrated spectrometers is growing, but the integrated spectrometers demonstrated so far have largely been limited to operation at wavelengths up to about 5μm due to intrinsic material absorption. In this work, we design and model an on-chip thermo-optically tuneable spectrometer based on a novel waveguide material platform consisting of GaAs (core) on InGaP (cladding), with potential to operate in the wavelength range between 1 and 17μm to fully cover the Mid-IR molecular fingerprint region. The strong thermo-optic effect exhibited by both of these materials makes the platform a very promising candidate for on-chip spectroscopy. A series of simulations were performed to predict the optical and thermal properties of the device. We show that with the proper optical and thermal optimisation of the platform and by using an interferometer with spiralled waveguides of 60 mm length, the device can effectively achieve a resolution of 10 cm−1 with a maximum temperature excursion of about 83 K and at the cost of a few tens of Watts of power.