1：Experimental Design and Method Selection

The study involved designing and fabricating fully suspended InGaAs waveguide devices with holey photonic crystal waveguides (HPCWs) and sub-wavelength grating cladding waveguides (SWWs) for mid-infrared sensing at λ=6.15μm. The methodology included mode profile and photonic band structure simulation, fabrication of suspended InGaAs HPCW and SWW, and measurements and instrumentation.

2：Sample Selection and Data Sources

The samples were fabricated using the InGaAs-InP platform, chosen for its transparency across the entire molecular fingerprint region (λ = 3-15 μm) and its compatibility with monolithic epitaxial growth of QCL/QCDs.

3：List of Experimental Equipment and Materials

The fabrication process involved epitaxial growth of InP/InGaAs/InP/InGaAs layers on InP substrate wafers, contact photolithography with AZ 5214-E photoresist, e-beam lithography using Jeol FSE 6000, reactive ion etching, and inductively coupled plasma etching. Measurement setup included a single-mode continuous-wave distributed-feedback QCL, black diamond-2 lenses, wire-grid polarizer, half wave plate, chopper wheel, lock-in-amplifier, multi-mode As2Se3 fiber, and a liquid-nitrogen-cooled HgCdTe detector.

4：Experimental Procedures and Operational Workflow

The fabrication process included defining suspending area, etching away the top layers, depositing gold alignment markers, depositing SiO2 hard mask layer, patterning waveguides using e-beam lithography, etching SiO2 and III-V layers, removing remaining PR and oxide, and suspending the HPCWs and SWWs structures. Measurements were conducted using an end-fire coupling setup with ammonia gas delivered via tubing directly to the surface of the chip.

5：Data Analysis Methods

The data analysis involved measuring the output power versus time in the presence and absence of ammonia flow, evaluating the HPCW’s and SWW’s ammonia sensing performances, and measuring the propagation losses by the cut-back method.