Volume detection based on porous silicon waveguide for CO₂ mid-infrared spectroscopy

Area of Science:

• Materials Science
• Optical Engineering
• Chemical Sensing

Background:

• Porous silicon (PSi) offers unique optical and structural properties for sensor applications.
• Mid-infrared (mid-IR) spectroscopy is a powerful technique for gas detection.
• Waveguide-based sensors enhance light-matter interaction for improved sensitivity.

Purpose of the Study:

• To fabricate and characterize a mid-infrared porous silicon waveguide gas sensor.
• To investigate the light propagation characteristics and losses in the PSi waveguide.
• To determine the sensor's performance for carbon dioxide (CO2) detection.

Main Methods:

• Fabrication of PSi guiding and confinement layers via electrochemical anodization.
• Patterning of ridge waveguides using photolithography and reactive ion etching.
• Measurement of propagation losses in the mid-IR range (3.9–4.55 µm).

Main Results:

• Successful fabrication of a mid-IR PSi waveguide gas sensor.
• Propagation losses measured at 11.4 dB/cm at 4.28 µm.
• A limit of detection (LoD) of 1000 ppm for CO2 was achieved at its absorption peak.

Conclusions:

• The developed PSi waveguide sensor enables efficient light-gas interaction for sensing.
• The sensor demonstrates good performance for mid-IR CO2 detection.
• Further studies on oxidation and aging effects are warranted to optimize sensor stability.