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.

MWIR/LWIR filter based on Liquid–Crystal Fabry–Perot structure for tunable spectral imaging detection

“…The transmission spectrum in LWIR wavelength shows in Ref. [15]. The results demonstrate that the resonant wavelength decreases with the increase of the RMS value of voltage signal when V RMS > 5.3 V, which shows a similar variance trend corresponding to the simulation.…”

“…In Eq. (2), h is the statistic twist angle of LC molecules anchored under a certain driving-voltage, and a [15] is the angle between statistical initial director of LC molecules and the incident wave vector, and n e and n o are the extraordinary and ordinary refractive indices of LC layer. Because the V-shaped grooves are relatively deep ($90 nm at average) and nonuniform, a relatively large angle between the surface of PI layer and the initial director of LC molecules will be formed.…”

Snapshot Multispectral Light‐Field Imaging Based on Nematic Liquid‐Crystal Microlens Array via Deep Learning

“…In contrast, LC elements have also been applied in spectral imaging, particularly Fabry-Pérot (F-P) cavity-type interference spectral imaging. [36][37][38] Research on LC elements combined with deep learning has also become a trend. Sigaki applied CNN to the prediction of the physical properties of LC elements.…”

Research on a Dual-Mode Infrared Liquid-Crystal Device for Simultaneous Electrically Adjusted Filtering and Zooming

“…According to the MEMS architecture developed, the depth of the FP micro-cavity could be altered through moving mechanical parts, which supported the mirrors to achieve the spectral choice or further spectral adjustment. At the same time, the liquid-crystal (LC)-FP filters [23,24,25,26] composed of the similar FP micro-cavity filled by LC materials had also attracted much attention. As shown, the depth of the FP micro-cavity was fixed, which indicated that the choice or adjustment of the spectral component needed could be conducted by only varying the equivalent index of refraction of the LC layer without any mechanical movement.…”