New photonic architectures for mid-infrared gas sensors integrated on silicon

TL;DR

This paper presents new integrated photonic architectures for mid-infrared gas sensors on silicon, including design, analysis, and experimental validation of diffraction grating-based multiplexers with temperature stability considerations.

Contribution

It introduces a semi-analytical tool for evaluating diffraction grating responses and analyzes phase errors and crosstalk in mid-IR integrated photonic multiplexers.

Findings

FTIR measurements agree with theoretical models

Spectral shift with temperature is linear and predictable

AWG responses are stable up to 41°C

Abstract

This work focuses on optical multiplexers for mid-IR broadband source in gas sensing application. The design of multiplexer configurations based on two types of diffraction gratings is discussed. Owing to utility of Gaussian approximation of the field and Fourier Optics, we developed a semi-analytical tool allowing to evaluate the responses of array waveguide grating (AWG) and planar concave grating (PCG). This approach also opened the way to implement numerical phase error analysis by introducing normal distribution of errors and to study the correlation between standard deviation of phase errors and the level of crosstalk. FTIR spectroscopy measurement results of 5.65 micrometer AWGs, built with SiGe graded index core encapsulated in a thick Si cladding on standard silicon substrate, are compared with the theoretical expectations. We have also performed evaluation of AWG response at elevated temperatures, in the range between 20oC and 41oC. The spectral shift showed linear dependence with the temperature, which is in a good agreement with simulation predictions.