Micro-electromechanical-system-tuned resonant filters spanning the 8-12  µm band

Area of Science:

• Optics and Photonics
• Materials Science
• Spectroscopy

Background:

• The 8-12µm spectral band is crucial for terrestrial imaging and situational awareness due to atmospheric transparency.
• Existing tunable filters lack coverage across this entire important spectral range.
• Guided-mode resonance (GMR) offers a promising physical mechanism for filter development.

Purpose of the Study:

• To propose and demonstrate a novel tunable filter method for the 8-12µm spectral band.
• To utilize the guided-mode resonance (GMR) effect with a non-periodic lattice for filter design.
• To achieve a wide spectral tuning range for enhanced spectroscopic and imaging applications.

Main Methods:

• Designed a polarization-dependent tunable filter using a one-dimensional Germanium (Ge) grating on a Zinc Selenide (ZnSe) substrate.
• Employed the guided-mode resonance (GMR) effect with a non-periodic lattice structure.
• Optimized device parameters for sequential operation in transverse magnetic (TM) and transverse electric (TE) polarization states.

Main Results:

• Demonstrated clear transmittance nulls using a Gaussian beam centered at 1.5µm.
• Theoretical modeling predicted a tunable range exceeding 4µm, fully covering the 8-12µm band.
• Experimental results showed a spectral range of 8.6-10.0µm (TM) and 9.9-11.7µm (TE), totaling over 3µm.

Conclusions:

• The proposed GMR-based tunable filter effectively operates within the atmospherically transparent 8-12µm spectral band.
• The device demonstrates significant spectral tunability across TM and TE polarizations.
• Further fabrication advancements are expected to achieve the full 4µm theoretical tuning range.