Light-focusing phenomena of field-tuned micro-lens made of polymer-stabilized blue phase liquid crystals (original) (raw)
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Electro-optical characteristics of a liquid crystal lens with polymer network
Ukrainian Journal of Physics
We study a tunable-focus lens in which the key element is a gradientpolymer-stabilized liquid crystal (G-PSLC) structure. In this paper, we further develop the theoretical model [1, 2] that describes the dependence of the G-PSLC lens' focal length on the applied voltage and presents a theoretical study of lens aberrations. According to Fermat's principle, we minimize the optical path of a test light beam and calculate the angles of a ray exiting from the cell. Using these results, the lateral and longitudinal aberrations are estimated. The obtained results can be used to optimize the G-PSLC lenses.
Dynamic focusing microlens array using liquid crystalline polymer and a liquid crystal
Optoelectronic Materials and Devices, 2006
An active microlens device is demonstrated by using a stacked layer structure of UV curable polymer, liquid crystalline polymer (LCP) and a liquid crystal (LC). The incident linearly polarized light is focused after passing through the combined refractive type microlens array system of UV curable polymer and LCP. Because used LCP shows highly birefringent macroscopic property from the well-ordered molecular structure, the additional polarization state control layer was inserted to modulate the dynamic focusing characteristics of the device. From the additional twisted LC layer's electro-optic response, we obtained good focal switching characteristics of microlens array with a small operation voltage application. This enhanced dynamic focusing characteristic of device was originated from the separate operation of polymer lens structure's beam focusing and twisted LC layer's polarization control ability. The measured focal length was well matched to the calculated one. This proposed LC microlens array is expected to play a critical role in the various real photonic components such as highly reliable optical switch, beam modulator and key device for 3-D imaging system.
All-optical controlling of the focal intensity of a liquid crystal polymer microlens array
Applied Optics, 2011
The current work demonstrates a liquid crystalline polymer microlens array (LCP MLA) with an alloptically tunable and multistable focal intensity through photochemical phase transition. The operational mechanism of the optical tuning is associated with the photoisomerization effect. The proposed LCP MLA device has a focusing unit based on a birefringence LCP and a tuning unit with a light responsive material to control the polarization state of the incident probe beam. The optically variable refractive indices of LCP enable a positive or negative MLA that can control the polarization of incident light to be realized.
Applied Physics Letters, 2007
We propose a focal intensity tunable microlens array by using a birefringent liquid crystalline polymer for lensing action. Due to the difference of effective refractive indices, it acts as a positive or negative microlens with respect to the polarization state. As we control the incident polarization by adding a liquid crystal layer, the focal intensity can be tuned by an applied voltage. Twisted nematic and bistable ferroelectric liquid crystal modes were applied to demonstrate the possibility of various driving features such as a continuously tunable focal intensity or fast switching with memory effect.
Polymer-stabilized liquid crystal for tunable microlens applications
Optics Express, 2002
We investigate the electro-optical properties of polymer stabilized nematic liquid crystals produced by in situ photopolymerization technique using Gaussian laser beam. The distribution of refractive index in such structure under the action of a homogeneous electric field reveals a non-homogeneous lens-like character, approximately reproducing the intensity transverse distribution in the photopolymerizing beam.
Electro-optic response of polymer-stabilized blue phase liquid crystals
The dynamic response of a polymer-stabilized blue phase liquid crystal (BPLC) is comprised of two distinct processes: Kerr effect-induced local reorientation and electrostriction-induced lattice distortion. A double exponential rise/decay model is proposed to analyze the underlying physical mechanisms. If the electric field is below a critical field (E c ), Kerr effect dominates and the response time is fast. However, when E > E c electrostriction effect manifests, leading to an increased response time and a noticeable hysteresis. A higher polymer concentration helps suppress electrostriction, but the tradeoff is increased operation voltage. These results provide useful guidelines for future BPLC material and device optimizations. V C 2014 AIP Publishing LLC.
Molecular Crystals and Liquid Crystals, 2006
In this paper we study the process of network formation, director reorientation upon applied voltage and electro-optical properties of the gradient polymer stabilized liquid crystal (G-PSLC) lens. Using classical scheme of radical photopolymerization the profile of the polymer network concentration is obtained. Minimizing the total free energy functional we find the director profile in the cell subject to externally applied electric field. We suppose that polymer network creates additional torque onto LC director forcing it to preserve planar orientation competing with applied voltage. Thus, inhomogeneous director reorientation profile arises despite the use of uniform electrodes. As a result inhomogeneous refractive index is obtained, which generates the lens with focal length dependant from applied voltage. Obtained results can be applied to develop G-PSLC lenses that have no moving parts and allow the electro-optical zooming.
Extended Kerr effect of polymer-stabilized blue-phase liquid crystals
Applied Physics Letters, 2010
Electric-field-induced birefringence of a polymer-stabilized blue-phase liquid crystal ͑BPLC͒ is investigated. In the low field region, conventional Kerr effect holds. As the electric field increases, the induced birefringence gradually saturates and deviates from Kerr effect. An exponential convergence model, called extended Kerr effect, is proposed to fit the experimental data. Good agreement between experiment and model is obtained. This extended Kerr effect will make a significant impact to the optimization of emerging BPLC display devices.