研究目的
To design, fabricate, and characterize a compact wavelength-flattened directional coupler based chemical sensor for the mid-infrared (MIR) that achieves broadband performance and high sensitivity to refractive index change.
研究成果
The compact wavelength-flattened directional coupler based chemical sensor for the mid-infrared (MIR) demonstrates broadband performance and high sensitivity to refractive index change. It achieves around fivefold enhancement in the operation bandwidth compared to conventional directional couplers and shows potential for tertiary mixture sensing and applications requiring broadband operation such as spectroscopic sensing systems.
研究不足
The study is limited by the fabrication precision of the subwavelength grating structure and the operational wavelength range of the experimental setup. The sensitivity and detection limit may be affected by the quality of the fabricated devices and the environmental conditions during testing.
1：Experimental Design and Method Selection:
The study involves the design and fabrication of a wavelength-flattened directional coupler (WFDC) incorporating a subwavelength grating (SWG) structure for mid-infrared (MIR) sensing. The dispersion in the directional coupler (DC) is engineered to allow broadband operation. The Bragg reflection introduced by the SWG structure is utilized for high sensitivity sensing.
2：Sample Selection and Data Sources:
The sensing capability is investigated for dichloromethane (CH2Cl2) detection in ethanol (C2H5OH) using a SWG-based WFDC sensor 136.8 μm long. The complex refractive indices of CH2Cl2 and C2H5OH are adopted from literature.
3：8 μm long. The complex refractive indices of CH2Cl2 and C2H5OH are adopted from literature.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: The fabrication starts from a commercially available 8-inch silicon-on-insulator (SOI) wafer. Devices are patterned by deep ultra-violet (DUV) photolithography followed by silicon reactive ion etching (RIE). Cladding oxide is deposited by plasma enhanced chemical vapour deposition (PECVD).
4：Experimental Procedures and Operational Workflow:
The experimental setup includes a MIR laser, half-wave plate for polarization control, chopper for modulation, ZrF4 MIR fiber for light coupling, and a MIR detector for capturing output light. The devices are tested for coupling efficiency and sensing performance.
5：Data Analysis Methods:
Sensing performance is studied by 3D finite-difference time domain (FDTD) simulation. Sensitivity is derived by computation. Both refractive index (RI) sensing and absorption sensing are examined.
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