Mid-infrared sensing between 52 and 66 µm wavelengths using Ge-rich SiGe waveguides [Invited

Qiankun Liu,Joan Manel Ramirez,David Bouville,Carlos Alonso Ramos,Jacopo Frigerio,Daniel Chrastina,Giovanni Isella,Laurent Vivien,Delphine Marris-Morini,Andrea Ballabio,Xavier Le Roux,Vladyslav Vakarin

doi:10.1364/ome.8.001305

Abstract

Mid-infrared (mid-IR) integrated photonics are expected to provide key advances for the demonstration of chip-scale spectroscopic systems. It has been recently reported that Ge-rich SiGe alloy-based photonic structures can provide broadband operation for a wavelength range spanning from 5.5 to 8.5 µm, thus holding great potential for mid-IR applications. In this paper, the Ge-rich SiGe platform is considered for a mid-IR photonic chip-scale sensor, based on the use of the evanescent component of the guided optical mode to probe specific molecular absorption features of the surrounding cladding environment. As a proof of concept, we monitored the absorption spectral patterns of a standalone photoresist spin-coated onto spiral Ge-rich SiGe waveguides. A significant increase of the waveguide optical loss at the spectral window of 5.8-6.2 µm is identified and correlated with the inherent photoresist absorption. The ability of this platform to sense small concentrations of methane gas is also discussed. These results pave the way towards the demonstration of compact, portable, label-free and highly sensitive photonic integrated sensors based on Ge-rich SiGe circuits.

Highlights

In the recent years, key advances towards the development of on-chip photonic platforms exploiting the mid-Infrared wavelength range have been made [1,2,3,4,5]
We demonstrated the potential of Ge-rich SiGe waveguides as a mid-IR photonic chip-scale sensor
We investigated evanescent-field absorption of the optical mode using a photoresist deposited on top of the waveguide

Summary

Introduction

Key advances towards the development of on-chip photonic platforms exploiting the mid-Infrared (mid-IR) wavelength range have been made [1,2,3,4,5]. Silicon photonics solutions have already been successfully implemented at near-IR wavelengths, providing a reliable and high volume platform that leverages from a standalone and mature technology that has been largely employed to develop microelectronic integrated circuits [3]. The use of silicon as a waveguide core limits the largest available wavelength for low-loss operation at values below 8 μm, in accordance with the Si mid-IR transparency window. This fact prevents Si photonic platforms from accessing to an important family of biological and chemical substances that present absorption patterns within the λ = 8-13 μm spectral window. Different solutions have been explored including Ge on Si [5, 16], Ge on insulator (GeOI) [17], SiGe on Si [18], or graded SiGe/Si waveguides [19]

Methods

Results

Discussion

Conclusion