Mid-infrared planar silver halide waveguides with integrated grating couplers

Area of Science:

• Optoelectronics
• Materials Science
• Nanotechnology

Background:

• Planar waveguides are crucial for optical integrated circuits.
• Efficiently coupling light into these waveguides, especially mid-infrared radiation, remains a challenge.
• Silver halide materials offer unique optical properties for mid-infrared applications.

Purpose of the Study:

• To design and fabricate efficient grating couplers for silver halide waveguides.
• To enable the coupling of mid-infrared radiation from quantum cascade lasers into thin-film waveguide structures.
• To demonstrate the functionality of these couplers for sensing applications.

Main Methods:

• Focused ion beam (FIB) milling technology was employed for precise grating fabrication.
• An optimized rectangular grating structure with a 16.4 μm grating constant was designed for a 10.4 μm wavelength.
• The grating coupler was integrated into a silver halide waveguide substrate.

Main Results:

• Efficient incoupling of mid-infrared radiation into the waveguide was achieved.
• Waveguide propagation of the coupled radiation was confirmed.
• Evanescent field absorption spectroscopy was used to analyze acetic acid droplets, demonstrating sensing capabilities.

Conclusions:

• The developed FIB-fabricated grating couplers are effective for mid-infrared light coupling into silver halide waveguides.
• This technology facilitates the integration of quantum cascade lasers with waveguide structures.
• The system shows potential for highly sensitive chemical sensing applications.