Fourier transform spectrometer on silicon with thermo-optic non-linearity and dispersion correction

TL;DR

This paper demonstrates a silicon photonics Fourier transform spectrometer (Si-FTS) with integrated microheaters, modeling and correcting for dispersion and thermo-optic effects to achieve high-resolution on-chip broadband spectroscopy.

Contribution

It introduces a comprehensive model and experimental validation of a silicon-on-insulator FTS that accounts for dispersion and non-linearity, enabling accurate spectral measurements.

Findings

Successfully calibrated the Si-FTS using a tunable laser source.

Correcting for dispersion and thermo-optic effects enhances resolution.

The Si-FTS shows robustness against fabrication variations.

Abstract

The integration of miniaturized optical spectrometers into mobile platforms will have an unprecedented impact on applications ranging from unmanned aerial vehicles (UAVs) to mobile phones. To address this demand, silicon photonics stands out as a platform capable of delivering compact and cost-effective devices. The Fourier transform spectrometer (FTS) is largely used in free-space spectroscopy, and its implementation in silicon photonics will contribute to bringing broadband operation and fine resolution to the chip scale. The implementation of an integrated silicon photonics FTS (Si-FTS) must nonetheless take into account effects such as waveguide dispersion and non-linearity of refractive index tuning mechanisms. Here we present the modeling and experimental demonstration of a silicon-on-insulator (SOI) Si-FTS with integrated microheaters. We show how the power spectral density (PSD) of a light source and the interferogram measured with the Si-FTS can be related through a simple Fourier transform (FT), provided the optical frequency and time delay are corrected to account for dispersion, thermo-optic non-linearity and thermal expansion. We calibrate the Si-FTS, including the correction parameters, using a tunable laser source and we successfully retrieve the PSD of a broadband source. The aforementioned effects are shown to effectively enhance the Si-FTS resolution when properly accounted for. Finally, we discuss the Si-FTS resilience to chip-scale fabrication variations, a major advantage for large-scale manufacturing. Providing design flexibility and robustness, the Si-FTS is poised to become a fundamental building-block for on-chip spectroscopy