Two-dimensional guided-mode resonance gratings with an etch-stop layer and high tolerance to fabrication errors

Area of Science:

• Photonics and optical engineering
• Nanotechnology and materials science

Background:

• Guided-mode resonance (GMR) bandpass filters are crucial optical devices.
• Fabrication error tolerance is well-studied for 1D GMR gratings but underexplored for 2D designs.
• Existing 2D GMR designs lack robustness against fabrication imperfections, hindering unpolarized applications.

Purpose of the Study:

• Investigate fabrication tolerance of 2D zero-contrast gratings (ZCGs) in GMR filters.
• Compare the error sensitivity of 2D ZCGs with 1D gratings.
• Propose and validate a method to enhance the fabrication tolerance of 2D GMR filters.

Main Methods:

• Theoretical analysis of GMR filter designs, focusing on 2D ZCGs.
• Electromagnetic field analysis to understand mode interactions.
• Introduction of an etch-stop (ES) layer in the 2D ZCG architecture.
• Experimental fabrication and testing of the proposed ES-ZCG GMR filters.

Main Results:

• 2D ZCGs exhibit higher sensitivity to grating linewidth errors than 1D gratings.
• Linewidth errors orthogonal to polarization have a greater impact on 2D ZCGs.
• Field enhancement within gratings strongly influences waveguide modes.
• The proposed etch-stop layer suppresses grating-mode interaction, increasing linewidth tolerance by 4-fold.

Conclusions:

• 2D ZCGs require careful design considerations for fabrication tolerance.
• The etch-stop layer is an effective strategy to improve the robustness of 2D GMR filters.
• The developed etch-stop ZCGs (ES-ZCGs) demonstrate enhanced error robustness, paving the way for reliable unpolarized GMR filter designs.