Thin-film thickness-modulated designs for optical minus filter

Area of Science:

• Optics
• Materials Science
• Thin-film Technology

Background:

• Optical filters are crucial components in various photonic applications.
• Designing filters with narrow rejection bands and suppressed sidelobes presents a significant challenge.
• Existing methods may lack precision or ease of monitoring during fabrication.

Purpose of the Study:

• To propose a novel analytical method for designing optical minus filters.
• To demonstrate the effectiveness of thickness modulation in homogeneous thin-film layers.
• To enable precise filter design with improved performance characteristics.

Main Methods:

• Utilizing a two-material multilayer coating with discrete, homogeneous thin-film layers.
• Employing thickness modulation of individual layers to control optical properties.
• Designing a main stack for the narrow, second-order rejection band.
• Incorporating apodization and match layers to suppress passband sidelobes.

Main Results:

• Successfully designed optical minus filters through analytical thickness modulation.
• Achieved narrow, second-order rejection bands.
• Effectively suppressed passband sidelobes using apodization and match layers.
• Demonstrated that layer thicknesses are close to half-wave of the rejection wavelength.

Conclusions:

• The proposed analytical method provides an effective approach for designing optical minus filters.
• The method allows for precise control over filter performance, including rejection band and sidelobe suppression.
• The design's proximity to half-wave thicknesses facilitates accurate monitoring during thin-film deposition.