Characterization of a 3D optrode array for infrared neural stimulation.

Area of Science:

• Biomedical Engineering
• Optical Engineering
• Materials Science

Background:

• Deep tissue optical delivery is crucial for various medical applications.
• Silicon optrodes offer a potential platform for precise light delivery.
• Characterizing light transmission losses is essential for optimizing optrode performance.

Purpose of the Study:

• To characterize the Utah Slant Optrode Array (USOA) for deep tissue infrared light delivery.
• To identify and quantify light loss mechanisms within silicon optrodes.
• To optimize optrode design and fiber coupling for maximum light transmittance.

Main Methods:

• Fabrication of 10x10 silicon optrode arrays with varying lengths (0.5-1.5 mm) on a 400-μm pitch.
• Characterization of light delivery from optical fibers, including loss mechanisms (Fresnel reflection, coupling, radiation, total internal reflection).
• Investigation of transmission efficiency using different optical fiber core diameters and coupling interfaces at λ = 1.55 μm.

Main Results:

• Primary loss mechanisms identified as Fresnel reflection, coupling, radiation, and total internal reflection.
• Highest optrode transmittance of 34.7% achieved with a 50-μm multi-mode fiber and a 1.66 refractive index coupling medium.
• Optimal fiber core diameters for maximum power delivery were 200 μm or less.
• Longer, less tapered optrodes demonstrated higher light transmission efficiency.

Conclusions:

• The USOA is a viable platform for deep tissue light delivery.
• Optimized fiber coupling and optrode geometry significantly enhance light transmittance.
• Further improvements are expected to exceed 64% efficiency in future iterations.