Graded-index mid-infrared planar optical waveguides made from silver halides

Area of Science:

• Materials Science
• Optics
• Photonics

Background:

• Silver halides, such as silver chloride (AgCl) and silver bromide (AgBr), are known for their transparency in the mid-infrared (mid-IR) spectrum.
• Controlling the refractive index of materials is crucial for fabricating optical waveguides.
• Planar waveguides are essential components in integrated optics and optical communication systems.

Purpose of the Study:

• To develop and characterize novel planar waveguides using silver chlorobromide (AgClBr) on an AgCl substrate.
• To investigate the feasibility of controlling the refractive index of AgCl by incorporating bromide ions.
• To assess the optical properties, specifically transmission and propagation loss, of the fabricated AgClBr waveguides in the mid-IR.

Main Methods:

• Fabrication of AgClBr planar waveguides by diffusing bromide (Br-) ions into an AgCl substrate.
• Characterization of the waveguides using transmission measurements of 10.6-micrometer CO2 laser radiation.
• Optical measurement of waveguide thickness.
• Experimental determination of output-beam profile distribution.
• Numerical analysis and simulation using a ray-tracing model of the eikonal equation.

Main Results:

• Successfully fabricated AgClBr planar waveguides with a controlled refractive index by diffusing Br- ions into AgCl.
• Demonstrated mid-IR transparency of the waveguides, enabling characterization with 10.6-micrometer CO2 laser radiation.
• Measured a typical waveguide thickness of 65 micrometers and a propagation loss of 16 dB/cm.
• Experimental output-beam profile distribution showed good correlation with numerical analysis based on a ray-tracing model.

Conclusions:

• Silver chlorobromide (AgClBr) planar waveguides can be fabricated with tunable refractive indices, offering a new material platform for mid-IR optics.
• The developed waveguides exhibit promising optical characteristics, including mid-IR transparency and measurable propagation losses.
• The study validates the use of ray-tracing models for simulating waveguide behavior, aiding in future design and optimization.
• These mid-IR transparent planar waveguides hold significant potential for numerous applications in optical devices and systems.