Ultra-narrowband absorption filter based on a multilayer waveguide structure.

Area of Science:

• Photonics and optical engineering
• Nanophotonics
• Waveguide and grating structures

Background:

• Guided-mode resonance (GMR) offers a pathway to high-performance optical filters.
• Tunable narrowband filters are crucial for optical information processing and sensing applications.
• Existing GMR structures often face limitations in achieving ultra-narrow bandwidths and high tunability.

Purpose of the Study:

• To propose and analyze a novel six-layer waveguide structure embedded in a single-layer grating for ultra-narrowband filtering.
• To investigate the tunability of resonance wavelength and absorption characteristics.
• To evaluate the sensing capabilities, including sensitivity and figure of merit (FOM), for refractive index sensing.

Main Methods:

• Rigorous coupled-wave analysis (RCWA) for optical simulation.
• COMSOL Multiphysics for detailed structural analysis.
• Systematic variation of geometric and physical parameters (grating period, width, layer thickness, materials) to tune filtering properties.

Main Results:

• Achieved ultra-narrowband filtering with tunable resonance wavelength.
• Obtained absorption full width at half maximum (FWHM) as low as 8.51e-5 nm (TE mode) and 0.023 nm (TM mode).
• Demonstrated absorption coefficients exceeding 99.2% for both polarization states.
• Exhibited high sensitivity and figure of merit (FOM) for refractive index sensing, with a peak FOM of 17782.6/RIU for TM incidence.

Conclusions:

• The proposed six-layer GMR structure enables ultra-narrowband filtering with high absorption.
• The structure's performance is tunable by adjusting its geometric and material parameters.
• The GMR filter demonstrates significant potential for applications in optical information devices and highly sensitive refractive index sensors.