Electrically tunable infrared filter based on the liquid crystal Fabry-Perot structure for spectral imaging detection

Area of Science:

• Optoelectronics and Photonics
• Infrared (IR) Spectroscopy
• Liquid Crystal (LC) Devices

Background:

• Traditional spectral imaging methods often face limitations in tunability, size, and power consumption.
• Liquid crystal (LC) materials offer unique electro-optic properties suitable for tunable optical devices.
• Fabry-Perot (FP) cavities are well-established structures for wavelength filtering applications.

Purpose of the Study:

• To design and fabricate an electrically tunable infrared (IR) filter.
• To achieve wavelength selectivity in the 5.5 to 12 μm range using a liquid crystal Fabry-Perot (LC-FP) structure.
• To demonstrate the potential for smart spectral imaging and integration with IR focal plane arrays.

Main Methods:

• Fabrication of a dual-mirror FP cavity using aluminum (Al) film on zinc selenide wafers.
• Filling the cavity with liquid crystal (LC) materials to form the LC-FP filter.
• Utilizing an alignment layer with V-grooves for effective LC molecule anchoring and applying voltage signals for tuning.

Main Results:

• The LC-FP filter operates in the 5.5–12 μm IR range with three transmission peaks.
• Achieved a minimum full width at half-maximum (FWHM) of ~120 nm and a tunable imaging wavelength range of ~500 nm.
• Demonstrated high structural and photoelectronic response stability, small size, low power consumption, and >95% filling factor.

Conclusions:

• The developed electrically tunable LC-FP filter successfully operates in the long-wavelength IR range.
• The device exhibits significant advantages over MEMS-FP spectral imaging approaches, including electrical tunability and stability.
• The LC-FP filter shows strong potential for advanced smart spectral imaging and integration with IR detector arrays.