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We propose a method to improve the wavelength-sensitivity of a volume holographic grating by mixing dual-photoinitiation dopants, namely, rose bengal (RB)/N-phenylglycine (NPG) system and methylene blue (MB)/p-toluenesulfonic acid (PTSA) system, which enable the fabrication of gratings upon both green and red light illumination. The RB/NPG green light photoinitiation system is chosen in combination with the red-active MB/PTSA system because RB and MB absorb light near 567 and 665 nm independently. In this case, the holographic gratings, recorded in polymer-dispersed liquid crystal, can be fabricated simultaneously by two different visible laser lights with an output wavelength of 532 and 632.8 nm. The electro-optical performances of the gratings exposed upon 532 and 632.8 nm have been implemented: the diffraction efficiencies (DE) are 75% and 57% respectively when the exposure time is optimised to 2 min and 17 min; the threshold voltage is approximately 2.9 V/μm. The enhanced wavelength-sensitivity of holographic gratings allows for the storage of three-dimensional (3D) images on the same hologram plate, and these 3D images are easily reconstructed by both red and green light. [ABSTRACT FROM AUTHOR]

We propose the use of a varied-line-spacing (VLS) holographic polymer-dispersed liquid crystal (H-PDLC) Bragg grating as a switchable image splitter to generate a compatible three-dimensional (3D) stereogram and to increase the viewing angle of the observer. To fabricate the VLS grating, a cylindrical lens is adopted to form a cylindrical wave, which interferes with a plane wave, generating an H-PDLC grating with a continuously varying period. The proposed holographic optical element (HOE)-based image splitter comprises two VLS H-PDLC gratings. It can be attached on a designed pattern, with two rectangles taking the place of conventional liquid crystal display panel pixels, and can separate them into right and left viewing fields with a wider range. Experimental results show that the movement of the eyes of the observer can reach 37.6 mm. A theoretical simulation indicates that a shorter focal length of the cylindrical lens can yield a larger movement range. Switching between two-dimensional and 3D modes can be performed by applying an external alternating-current voltage at ~80 V. The contrast ratio of the diffracted images induced by crosstalk is greater than 60%, which indicates the feasibility of the proposed HOE for 3D image splitting. [ABSTRACT FROM AUTHOR]

An electrically tunable two-dimensional (2D) holographic polymer-dispersed liquid crystal (H-PDLC) grating with variable period was fabricated by inserting a cylindrical lens in a conventional holographic interference beam. The interference between the plane wave and cylindrical wave resulting in varying intersection angles on the sample, combined with dual exposure along directions perpendicular to each other, generates a 2D H-PDLC grating with varied period. We have identified periods varying from 3.109 to 5.158 µm across a 16 mm width, with supporting theoretical equations for the period. The period exhibits a symmetrical square lattice in a diagonal direction, with an asymmetrical rectangular lattice in off-diagonal locations. With the first exposure at 2 s and the second exposure at 60 s, the phase separation between the prepolymer and liquid crystal was most evident. The diffraction properties and optic-electric characteristics were also studied. The diffraction efficiency of first-order light was observed to be 13.5% without external voltage, and the transmission efficiency of non-diffracted light was 78% with an applied voltage of 100 V. The proposed method provides the capability of generating period variation to the conventional holographic interference path, with potential application in diffractive optics such as tunable multi-wavelength organic lasing from a dye-doped 2D H-PDLC grating. [ABSTRACT FROM AUTHOR]

A four-channel frequency division multiplexed fluorescent microscope (FDMFM) modulated by holographic polymer dispersed liquid crystal (H-PDLC) grating array is presented in this paper. The four-channel H-PDLC grating array is developed and employed to generate frequency modulation. Fluorescent signals at four different locations on a rat neural cell have been successfully modulated with four different frequencies, collected by a single high-sensitivity photodetector, such as photomultiplier tubes, and distinguished by taking the Fourier transform of the detected sum signal. The experimental and simulation results agree well. The new system offers the advantages of (1) multiple channel modulation capability, (2) no mechanical noise and (3) flexible and controllable modulation profile (e.g. square wave, triangular wave, etc.). Thus this four-channel FDMFM system can be very helpful for studying fast-changing transient events in biological samples. [ABSTRACT FROM AUTHOR]

Influence of CuO nanorods on the dielectric properties of polymer dispersed liquid crystal (PDLC) is studied in the 4 Hz–8 MHz frequency range. PDLC films doped with different concentrations of CuO nanorods were prepared by photopolymerization-induced phase separation. The scanning electron microscopy (SEM) images reveal that, the size of liquid crystal (LC) droplets in a polymer matrix is at the nanometer level. Besides, with the increasing of the concentration of CuO nanorods, the size of droplet can approach about 1 μm. The result indicates the doping of the CuO nanorods slows the polymerization rate of the PDLC and the size of the LC droplets becomes larger. Further analysis of the Cole-Cole plot fitted by the Havriliak-Negami (HN) equation shows that there are two relaxation processes in the low frequency and high frequency region of the PDLC doped with nanorods. With the nanorods concentration of 0.1 wt%, the electric conductivity of PDLC is increased >20 times and there is a saturation effect. Unlabelled Image • PDLC films doped with CuO nanorods were prepared by PIPS. • The surface morphology of PDLC doped with CuO nanorods was studied. • Dielectric relaxation spectroscopic studies of PDLC films doped with CuO nanorods. • Doping CuO nanorods into PDLC, the conductivity is increased by >20 times. [ABSTRACT FROM AUTHOR]

Through the preparation of free radicals and nanocomposite materials technology, this article introduces the Cerium oxide (CeO 2) nanorods doped trimethylpropane triacrylate and epoxy resin to solve the poor performance of holographic photopolymer. Dielectric analysis and spectrum data show that the incorporation of CeO 2 nanorod can serve as an inhibitor to interfacial interaction with Irgacure 784, and it prolong polymerization time, inhibit the molecular weight of the polymer, and promote monomer conversion and diffusion. Further experiments of aging show that the optimized photopolymer material has anti-aging (∼2.8% decreased) properties. The mechanism of initiator photodegradation and polymer chain formation under different concentrations of CeO 2 are elucidated, which can affect the diffusion and chain formation of photopolymerization. CeO 2 nanorods can effectively improve monomer double bond conversion of photosensitive polymers and the diffusion of epoxy resin, which improve the diffraction efficiency (30% increased), the refractive index modulation and the polarization holography, achieve high sensitivity and low volume shrinkage (∼0.186%). By combining the types of initiators and the role of electron donor, CeO 2 nanorod can manipulate the decomposition of initiators and polymerization process, thereby affecting the generated optical modulation characteristics and the manufacturing of optical information storage devices. • The addition of CeO 2 nanorod can improve the holographic properties and monomer conversion of photopolymers. • Dielectric, FTIR and GPC analysis show that the effect of CeO 2 nanorods delay curing of the cross-linked network. • CeO 2 nanorods can serve as inhibitors to improve the index modulation and polarization properties. • The optimized photopolymer nanocomposite has anti-aging, high temperature resistance properties, and low volume shrinkage. [ABSTRACT FROM AUTHOR]

Abstract: The dynamic gain equalizer consisting of gratings made of holographic polymer dispersed liquid crystal is explored and the structure and principle presented. The properties of the holographic polymer dispersed liquid crystal grating are analyzed in light of the rigorous coupled-wave theory. Experimental study is also conducted in which a beam of infrared laser was incident to the grating sample and an alternating current electric field applied. The electro-optical properties of the grating and the influence of the applied field were observed. The results of the experiment agree with that of the theory quite well. The design method of the dynamic gain equalizer with the help of numerical simulation is presented too. The study shows that holographic polymer dispersed liquid crystal gratings have great potential to play a role in fiber optics communication. [Copyright &y& Elsevier]