Resonant Brewster filters with absentee layers

Area of Science:

• Photonics and Optical Engineering
• Materials Science

Background:

• Resonant waveguide-grating filters are crucial optical components.
• Unwanted spectral sidebands can degrade filter performance and limit applications.
• Existing methods for sideband suppression often compromise other filter characteristics.

Purpose of the Study:

• To present a novel method for suppressing sideband levels in resonant waveguide-grating filters.
• To demonstrate control over filter linewidth without impacting sideband suppression.
• To experimentally validate the proposed theoretical predictions.

Main Methods:

• Utilizing a TM-polarized incident wave near the Brewster angle.
• Incorporating a half-wavelength absentee waveguide layer.
• Employing an arbitrary-thickness grating layer for tunable linewidth control.

Main Results:

• Achieved significant suppression of filter sidebands to below 0.6%.
• Demonstrated precise control over filter linewidth by adjusting grating layer thickness.
• Fabricated and tested a double-layer waveguide-grating filter with a peak efficiency of 82.4% over a 95-nm spectral range.

Conclusions:

• The proposed method effectively lowers sideband levels in waveguide-grating filters.
• The technique offers independent control over sideband suppression and filter linewidth.
• Experimental results confirm the theoretical predictions and highlight the practical viability of the method.