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We experimentally demonstrated an electrically controlled variable focus optical system based on cascading polymer dispersed liquid crystal (PDLC) lens. Through adjusting external electric field applied on the hole-type electrode of PDLC lens to change the spatial distribution of refractive index of PDLC, the plane PDLC cell can be functioned as a focusing lens with the variable focus length. In this article, we simulate the electromagnetic field distribution of the external electrical field, as well as analysis the corresponding principle and mathematic equation of its electrically controlled focusing length. The experimental results show that as external alternate current (AC) voltage is increased from 0 to 80 V, the focal length of single lens decreases from ∞ to 1.073 m, and that of the double lens from ∞ to 0.484 m. These experimental results are in good accordance with the simulation results. The experimental response time of PDLC tunable lens is less than 1 ms, which will bring benefits for the applications especially for the fast imaging system. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2830–2835, 2013

This paper reports on the investigation of the electrically controlled multifocus, multi-imaging characteristics of an on-axis holographic polymer-dispersed liquid-crystal (H-PDLC) Fresnel lens. The Fresnel lens is examined within a PDLC cell through the analysis of interference fringes generated by on-axis plane and spherical waves. Experiments are conducted to investigate the multifocus and multi-imaging phenomena of the H-PDLC Fresnel lens, and a corresponding geometrical optical analysis is also provided. It is then demonstrated that the H-PDLC Fresnel lens is a plane-surface diffractive optical device which modulates the phase of incident light through a periodic change of refractive index and forms multiple symmetrical images. Its diffraction properties, which can be controlled electrically, have further potential applications in this field.

Photonic crystals (PCs) with infiltrating liquid crystals (LCs) have many potential applications because of their ability to continuously modulate the band-gaps. Using the plane-wave expansion method (PWM), we simulate the band-gap distribution of 2D honeycomb lattice PC with different pillar structures (circle, hexagonal and square pillar) and with different filling ratios, considering both when the LC is used as filling pillar material and semiconductors ( Si , Ge ) are used in the substrate, and when the semiconductors ( Si , Ge ) are pillar material and the LC is the substrate. Results show that unlike LC-based triangle lattice PC, optimized honeycomb lattice PC has the ability to generate absolute photonic band-gaps for fabricating optical switches. We provide optimization parameters for LC infiltrating honeycomb lattice PC structure based on simulation results and analysis.

We report on the synthesis and characteristics of a holographic polymer dispersed liquid crystal (H-PDLC) switchable grating based on nano-Ag particles. The influence of doping different concentrations of nano-Ag on the diffraction efficiency, driving voltage, and response time of the H-PDLC grating is investigated. The best grating characteristics were achieved with 0.05% nano-Ag doping. Calculated and experimental results reveal that the improvement of the characteristics is likely due to the surface plasmon effect of nano-Ag.

We used a polymer dispersed liquid crystal material holographic lens in a fingerprint sensor, which reduced the total size of the sensor and improved image quality. The beam carrying fingerprint information was diffracted by the holographic lens and converged onto the complementary metal-oxide semiconductor image sensor directly, which omitted the traditional lens or fiber taper. The phenomenon that the image quality is poor when the finger is too dry or wet was explained based on the evanescent wave theory. The total size of the device was 50 mm x 25 mm x 30 mm. The fingerprint image had a contrast of 250:1 and a resolution of 800 dots/in.

A holographic polymer dispersed liquid crystal （H-PDLC） switchable lens is reported. The diffraction efficiency was analyzed at different phase separation coefficients within the visible band （400—800 nm） with the coupled wave theory for a phase-type H-PDLC switchable lens. In our experiments, the maximum efficency of 70% was achieved. The H-PDLC switchable lens shows excellent imaging performance and fast response.It is potentially useful in many applications, such as optical communications, optical imaging,e.g.,in digital cameras.