title: Electrically tunable infrared filter based on the liquid crystal Fabry-Perot structure for spectral imaging detection.
abstract: An electrically tunable infrared (IR) filter based on the liquid crystal (LC) Fabry-Perot (FP) key structure, which works in the wavelength range from 5.5 to 12 μm, is designed and fabricated successfully. Both planar reflective mirrors with a very high reflectivity of ∼95%, which are shaped by depositing a layer of aluminum (Al) film over one side of a double-sided polished zinc selenide wafer, are coupled into a dual-mirror FP cavity. The LC materials are filled into the FP cavity with a thickness of ∼7.5  μm for constructing the LC-FP filter, which is a typical type of sandwich architecture. The top and bottom mirrors of the FP cavity are further coated by an alignment layer with a thickness of ∼100  nm over Al film. The formed alignment layer is rubbed strongly to shape relatively deep V-grooves to anchor LC molecules effectively. Common optical tests show some particular properties; for instance, the existing three transmission peaks in the measured wavelength range, the minimum full width at half-maximum being ∼120  nm, and the maximum adjustment extent of the imaging wavelength being ∼500  nm through applying the voltage driving signal with a root mean square (RMS) value ranging from 0 to ∼19.8  V. The experiment results are consistent with the simulation, according to our model setup. The spectral images obtained in the long-wavelength IR range, through the LC-FP device driven by the voltage signal with a different RMS value, demonstrates the prospect of the realization of smart spectral imaging and further integrating the LC-FP filter with IR focal plane arrays. The developed LC-FP filters show some advantages, such as electrically tunable imaging wavelength, very high structural and photoelectronic response stability, small size and low power consumption, and a very high filling factor of more than 95% compared with common MEMS-FP spectral imaging approaches.
authors.forename: Huaidong
authors.initials: H
authors.lastname: Zhang
authors.forename: Afzal
authors.initials: A
authors.lastname: Muhammmad
authors.forename: Jun
authors.initials: J
authors.lastname: Luo
authors.forename: Qing
authors.initials: Q
authors.lastname: Tong
authors.forename: Yu
authors.initials: Y
authors.lastname: Lei
authors.forename: Xinyu
authors.initials: X
authors.lastname: Zhang
authors.forename: Hongshi
authors.initials: H
authors.lastname: Sang
authors.forename: Changsheng
authors.initials: C
authors.lastname: Xie
mesh_terms: D004574:Electromagnetic Fields; D004867:Equipment Design; D019544:Equipment Failure Analysis; D007089:Image Enhancement / Q000295:instrumentation; D007259:Infrared Rays; D007368:Interferometry / Q000295:instrumentation*; D007909:Lenses; D050866:Liquid Crystals / Q000737:chemistry* / Q000528:radiation effects*; D012031:Refractometry / Q000295:instrumentation*; D013055:Spectrophotometry, Infrared / Q000295:instrumentation*