InGaAs Membrane Waveguide: A Promising Platform for Monolithic Integrated Mid-Infrared Optical Gas Sensor

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Chemical Sensing

Background:

• Integrated photonic circuits are promising for trace-gas sensing via mid-infrared (mid-IR) absorption spectroscopy.
• Quantum cascade lasers (QCLs) and detectors (QCDs) are key components in mid-IR sensing systems.

Purpose of the Study:

• To design and fabricate suspended InGaAs waveguide devices for mid-IR gas sensing on the InGaAs-InP platform.
• To compare the performance of holey photonic crystal waveguides (HPCWs) and subwavelength grating waveguides (SWWs) for gas sensing at 6.15 μm.

Main Methods:

• Fabrication of fully suspended InGaAs waveguide devices, including HPCWs and SWWs.
• Experimental detection of ammonia gas using these waveguide structures.
• Estimation of minimum detectable gas concentration based on Beer-Lambert law and experimental data.

Main Results:

• Experimental detection of 5 ppm ammonia using a 1 mm HPCW and a 3 mm SWW.
• Propagation losses of 39.1 dB/cm for HPCW and 4.1 dB/cm for SWW.
• Estimated minimum detectable ammonia concentration of 84 ppb for a QCL/QCD integrated SWW sensor.

Conclusions:

• This work demonstrates the first suspended InGaAs membrane waveguides on the InGaAs-InP platform for gas sensing at long wavelengths.
• SWWs show significant advantages over HPCWs in terms of reduced propagation loss and device footprint.
• The study paves the way for monolithic integration of QCLs/QCDs with passive waveguide sensors for on-chip mid-IR absorption spectroscopy.