Design and Simulation Investigation of Si3N4 Photonics Circuits for Wideband On-Chip Optical Gas Sensing around 2 µm Optical Wavelength.

Natnicha Koompai,Laurent Vivien,Xavier Le Roux,Papichaya Chaisakul,Delphine Marris-Morini,Pichet Limsuwan

doi:10.3390/s21072513

Abstract

We theoretically explore the potential of Si3N4 on SiO2 waveguide platform toward a wideband spectroscopic detection around the optical wavelength of 2 μm. The design of Si3N4 on SiO2 waveguide architectures consisting of a Si3N4 slot waveguide for a wideband on-chip spectroscopic sensing around 2 μm, and a Si3N4 multi-mode interferometer (MMI)-based coupler for light coupling from classical strip waveguide into the identified Si3N4 slot waveguides over a wide spectral range are investigated. We found that a Si3N4 on SiO2 slot waveguide structure can be designed for using as optical interaction part over a spectral range of interest, and the MMI structure can be used to enable broadband optical coupling from a strip to the slot waveguide for wideband multi-gas on-chip spectroscopic sensing. Reasons for the operating spectral range of the system are discussed.

Highlights

Photonic integration on silicon (Si) offers a unique opportunity in optical communication, sensing, and spectroscopic applications [1,2,3,4]
To explore the potential of Si3 N4 on SiO2 waveguide platform toward a wideband and simultaneous detection around 2 μm wavelength range, we report on the design of a Si3 N4 on SiO2 waveguide architecture that can be simultaneously employed for a wideband on-chip spectroscopic sensing around the 2 μm wavelength region using finite difference eigenmode (FDE) analysis [39] and eigenmode expansion (EME) method (Lumerical Inc.) [40,41]
We focus on employing Si3 N4 multi-mode interferometer (MMI) and tapering slot structures for wideband optical coupling from the Si3 N4 strip entrance waveguide into the Si3 N4 slot waveguide (Figure 1a) for spectroscopic sensing using absorption of gas molecules over the spectral range of interest

Summary

Introduction

Photonic integration on silicon (Si) offers a unique opportunity in optical communication, sensing, and spectroscopic applications [1,2,3,4] For the latter, interaction between evanescent field around Si-based optical waveguide and gas molecules enables the absorption spectrum of sensed gas molecules to be measured in millimeter-sized chips [5,6,7]. From the EME analysis, a Si3 N4 multi-mode interferometer (MMI) with tapering slot waveguide is interestingly shown to enable simultaneous coupling of light over a spectral range into the identified Si3 N4 slot waveguide for wideband onchip optical gas sensing, coinciding with the absorption bands of several important gas molecules. We found that over a certain wavelength of interest, a particular slot waveguide structure can be designed for using as optical interaction part, and MMI structure can be employed to enable broadband optical coupling from strip to the slot waveguide for wideband multi-gas on-chip spectroscopic sensing

Structure under Investigation

Slot Waveguides

Si3 N4 Multi-Mode Interferometer and Slot Waveguide for Wideband On-Chip

N4Sislot between

Findings

Conclusions