Spatial Resolution and Refractive Index Contrast of Resonant Photonic Crystal Surfaces for Biosensing

Area of Science:

• Photonics
• Nanotechnology
• Optical Engineering

Background:

• Photonic crystals offer unique light manipulation properties.
• Spatial resolution is a critical performance metric for optical devices.
• Refractive index contrast (Δn) influences resonant mode behavior.

Purpose of the Study:

• To investigate the impact of refractive index contrast on the spatial resolution of Si3N4 photonic crystal resonant surfaces.
• To compare the performance of 1-D and 2-D gratings under varying conditions.
• To understand the relationship between Δn, resonant mode propagation, and spatial resolution for biosensing applications.

Main Methods:

• Fabrication of Si3N4 photonic crystal resonant surfaces with integrated resolution test patterns.
• Experimental measurements of spatial resolution at different refractive index contrasts (Δn).
• Finite-difference time-domain (FDTD) simulations to model optical behavior.

Main Results:

• Spatial resolution decreases as refractive index contrast (Δn) is reduced.
• At Δn = 0.077, resolutions of 2 µm (parallel) and 6 µm (perpendicular) were observed for 1-D gratings.
• Resolution dramatically worsens for Δn < 0.01, exceeding 10 µm.
• Resonance linewidth narrows with decreasing Δn, indicating longer mode propagation.

Conclusions:

• Refractive index contrast is a key factor determining spatial resolution in photonic crystal devices.
• Reduced Δn, common in biosensing, significantly compromises device resolution.
• Understanding Δn effects is vital for designing high-resolution photonic crystal sensors.