All-Dielectric Transreflective Angle-Insensitive Near-Infrared (NIR) Filter.

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Thin-Film Technology

Background:

• Spectral imaging requires precise optical filters for specific wavelength ranges.
• All-dielectric multilayer filters offer advantages in performance and durability over traditional metallic filters.
• Existing filters may face limitations in efficiency, angular dependence, or polarization sensitivity.

Purpose of the Study:

• To design and demonstrate an all-dielectric, cascaded, multilayered thin-film filter for near-infrared (NIR) spectral imaging.
• To achieve high transmission efficiency and broad angular/polarization tolerance.
• To validate simulation results with experimental measurements.

Main Methods:

• Utilized amorphous silicon (A-Si) and silicon nitride (Si3N4) layers for filter fabrication.
• Employed Finite Difference Time Domain (FDTD) simulations for theoretical analysis.
• Conducted experimental validation using spectroscopic ellipsometry (SE).

Main Results:

• Achieved a distinct transmission peak in the NIR region with up to 70% efficiency.
• Observed a narrow full-width-at-half-maximum (FWHM) of 77 nm.
• Demonstrated theoretical angle insensitivity up to 60° and polarization insensitivity (TM/TE modes).
• Experimental results confirmed theoretical predictions for angle invariance (up to 50°) and polarization insensitivity.

Conclusions:

• The proposed eight-layer A-Si/Si3N4 filter is a viable solution for NIR spectral imaging applications.
• The filter exhibits excellent performance characteristics, including high efficiency and robustness against angle and polarization variations.
• The good agreement between theoretical and experimental data validates the design and simulation methodologies.