Light Valve Research Articles

Ultrafast laser spatial beam shaping based on Zernike polynomials for surface processing

In femtosecond laser machining, spatial beam shaping can be achieved with wavefront modulators. The wavefront modulator displays a pre-calculated phase mask that modulates the laser wavefront to generate a target intensity distribution in the processing plane. Due to the non-perfect optical response of wavefront modulators, the experimental distribution may significantly differ from the target, especially for continuous shapes. We propose an alternative phase mask calculation method that can be adapted to the phase modulator optical performance. From an adjustable number of Zernike polynomials according to this performance, a least square fitting algorithm numerically determines their coefficients to obtain the desired wavefront modulation. We illustrate the technique with an optically addressed liquid-crystal light valve to produce continuous intensity distributions matching a desired ablation profile, without the need of a wavefront sensor. The projection of the experimental laser distribution shows a 5% RMS error compared to the calculated one. Ablation of steel is achieved following user-defined micro-dimples and micro-grooves targets on mold surfaces. The profiles of the microgrooves and the injected polycarbonate closely match the target (RMS below 4%).

Fiber Optic Excitation of Silicon Microspheres in Amorphous and Crystalline Fluids

ABSTRACTThis study investigates the optical resonance spectra of free-standing monolithic single crystal silicon microspheres immersed in various amorphous fluids, such as air, water, ethylene glycol, and 4-Cyano-4’-pentylbiphenyl nematic liquid crystal. For the various amorphous fluids, morphology-dependent resonances with quality factors on the order of 105 are observed at 1428 nm. The mode spacing is always on the order of 0.23 nm. The immersion in various amorphous fluids affects the spectral response of the silicon microsphere and heralds this technique for use in novel optofluidics applications. Even though the nematic liquid crystal is a highly birefringent, scattering, and high-index optical medium, morphology-dependent resonances with quality factors on the order of 105 are observed at 1300 nm in the elastic scattering spectra of the silicon microsphere, realizing a liquid-crystal-on-silicon geometry. The relative refractive index and the size parameter of the silicon microsphere are the parameters that affect the resonance structure. The more 4-Cyano-4’-pentylbiphenyl interacting with the silicon microsphere, the lower the quality factor of the resonances is. The more 4-Cyano-4’-pentylbiphenyl is interacting with the silicon microsphere, the lower the mode spacing Δλ of the resonances is. The silicon microspheres wetted with nematic liquid crystal can be used for optically addressed liquid-crystal-on-silicon displays, light valve applications, or reconfigurable optical networks.

Infrared sensitive liquid crystal light valve with semiconductor substrate.

A liquid crystal light valve (LCLV) is an optically controlled spatial light modulator that allows recording of dynamic holograms. Almost all known LCLVs operate in the visible range of the spectrum. In the present work we demonstrate a LCLV operating in the infrared. The interaction of signal and pump waves is studied for different applied voltages, grating spacings, and intensities of the recording beams. A fourfold amplification of the weak signal beam is achieved. The amplitude of the refractive index modulation Δn=0.007 and nonlinear coupling constant n₂=-1 cm²/W are estimated from the experimental results. External phase modulation of one of the recording beams is used for a further transient increase of the signal beam gain.

Liquid crystal cells based on photovoltaic substrates

Liquid crystal cells with LiNbO3:Fe crystals as substrates, are described. The photovoltaic field generated by the substrates is able to reorient the liquid crystal director thus giving rise to a phase shift on the light propagating through the cell, as in liquid crystal light valves. The process does not require the application of an external electric field, thus being potentially useful for applications requiring a high degree of compactness. An efficient optical switch with a high transmission contrast, based on the described optically-induced electric field, is also proposed.

Analysis and model of the photorefractive-like effect in non-conductive asymmetric liquid crystal hybrid cell

In this paper we describe a non-conductive liquid crystal hybrid cell with the photoconductive polymer (PP) layer. The orientation of the liquid crystal (LC) molecules in the described optical device is controlled by an external electric field and proper illumination. Method to calculate photoinduced refractive index distribution in liquid crystal layer has been presented. We propose model of the space charge formation in photoconductive polymer layer in the presence of light. We assumed that the carriers generated by the light in the PP diffuse into unlighted area and drift in external field and local field of the generated charge. In determining the distribution of the space charge field, we take into account the field-induced charges on the borders of the individual layers. After calculation of the final distribution of space charge and proper field distribution, we determine the director field distribution and refractive index distribution in LC layer. Full Text: PDF References A. Walczak, E. Nowinowski-Kruszelnicki, "Waveguide couplers induced optically over organic junction", Opt. Eng. 47(3), 035402 (2008). CrossRef A. Walczak, "Electromagnetic wave beam self - guidance in liquid crystal - semiconductor cell", Phot. Lett. Poland 2(2), 73 (2010). CrossRef A. Brignon, I. Bongrand, B. Loiseaux, J.P. Huignard, "Signal-beam amplification by two-wave mixing in a liquid-crystal light valve", Opt. Lett. 22(24), 1855 (1997). CrossRef G. Cook, C.A. Wyres, M.J. Deer, D.C. Jones, "Hybrid organic-inorganic photorefractives", Liquid Crystals VII, SPIE Annual Meeting (2003). CrossRef F. Kajzar, S. Bartkiewicz, A. Miniewicz, "Optical amplification with high gain in hybrid-polymer–liquid-crystal structures", Appl. Phys. Lett. 74(20), 2924 (1999) CrossRef S. Bartkiewicz, K. Matczyszyn, A. Miniewicz, F. Kajzar, "High gain of light in photoconducting polymer–nematic liquid crystal hybrid structures", Opt. Commun. 187, 257 (2001). CrossRef M. Kaczmarek, A. Dyadyusha, S. Slussarenko, I.C. Khoo, "The role of surface charge field in two-beam coupling in liquid crystal cells with photoconducting polymer layers", J. Appl. Phys. 96, 2616 (2004). CrossRef P. Moszczyński, A. Walczak, P. Marciniak, "Model for simulation of photo-induced charges inside the hybrid LC cells", Phot. Lett. Poland 5(1), 11 (2013). CrossRef N. Kukhtarev, V. Markov, S. Odulov, M. Soskin, V. Vinetskii, "Holographic storage in electrooptic crystals. i. steady state", Ferroelectrics 22, 949 (1979). CrossRef N. Kukhtarev, T. Kukhtareva, "A unified treatment of radiation-induced photorefractive, thermal, and neutron transmutation gratings", IEEE Proceedings 87(11), 1857 (1999). CrossRef J.S. Schildkraut, Y. Cui, "Zero-order and first-order theory of the formation of space?charge gratings in photoconductive polymers", J. Appl. Phys. 72(11), 5055 (1992). CrossRef J.S. Schildkraut, A.V. Buettner, "Theory and simulation of the formation and erasure of space-charge gratings in photoconductive polymers", J. Appl. Phys. 72(5), 1888 (1992). CrossRef A. Twarowski, "Geminate recombination in photorefractive crystals", J. Appl. Phys. 65(7), 2833 (1989). CrossRef W.D. Gill, "Drift mobilities in amorphous charge-transfer complexes of trinitrofluorenone and poly-n-vinylcarbazole", J. Appl. Phys. 43(12), 5033 (1972). CrossRef A. Walczak, P. Moszczyński, E. Nowinowski-Kruszelnicki, "Semiconductor–LC Layer Boundary and Photonic Structures", Mol. Cryst. Liq. Cryst. 559(1), 186 (2012). CrossRef

Proposed high-speed micron-scale spatial light valve based on a silicon-graphene hybrid structure.

We propose a new ultracompact CMOS-compatible variable-transmission spatial light valve based on a silicon-graphene hybrid structure. Normally incident ∼1560 nm light can be coupled to a silicon-graphene-based 1D photonic crystal cavity through a perturbation-based diffractive coupling scheme. The lightwave modulation is achieved by tuning the Fermi level of the graphene, which can change both the loss and the resonant wavelength of the cavity. Based on finite-difference time-domain simulation, the modulation depth is larger than 10 dB with driving voltage of about 4.8 V(pp) while the modulation speed is estimated to be higher than 45 GHz.

Optical vortex induction via light–matter interaction in liquid-crystal media

Optical vortices are attracting much attention because of their applications in various fields of optical processing, communications, enhanced imaging systems, and bio-inspired devices. Different methods to generate optical vortices have been devised to date. Among them, several are based on the exploitation of light–matter interaction in liquid-crystal media. This review focuses on the main mechanisms of vortex generation in liquid crystals, in particular on vortex generation induced by umbilics, that is, defects arising in homeotropically aligned nematic cells, which act as topological matter templates able to realize the conversion from spin to orbital angular momentum of an incoming Gaussian beam. Optical vortex induction in a photosensitive light valve is presented as a self-stabilizing mechanism leading to reconfigurable and programmable vortex arrays. On each lattice site, every matter vortex acts as a photonic spin-to-orbital momentum coupler, converting input arrays of circularly polarized beams into output arrays of vortex beams with topological charges consistent with the matter lattice symmetry.

Safety Testing of Left Ventricular Vent Valves

Vent vacuum relief valves (VRVs) are used to limit the negative pressure at the ventricular vent catheter tip as well as prevent reversal of blood flow and prevention of air embolism. The purpose of this study was to evaluate the performance of three commercially available ventricular vent valves. The negative pressure at which the vent valve opened was measured at the valve inlet using high-fidelity pressure transducers. Also, the flow rate at which air entrainment occurred due to valve opening was recorded. Using a 51.5 cm column of saline, the resistance for each valve was calculated. The mean ± SD opening negative pressures were −231.3 ± 35.2 mmHg for the Quest Medical valve, −219.8 mmHg ± 17.2 for the Sorin valve, and −329.6 ± 38.0 mmHg for the Terumo valve. The red Quest Medical valve opened at a lower flow (1.44 ± .03 L/min) than the dark blue Sorin valve (2.93 ± .01 L/min) and light blue LH130 Terumo valve (2.36 ± .02 L/min). The Sorin valve had the least resistance of 34.1 dyn·s/cm5, followed by the Terumo LH130 valve resistance of 58.1 dyn·s/cm5, and the Quest Medical VRV-II valve with a resistance of 66.5 dyn·s/cm5. We found that the valves are significantly different in the negative pressure generated. Understanding the limitations of these devices is important to reduce the occurrence of adverse events associated with venting and to select the best device for a specific clinical application.

Development of an x-ray detector based on polymer- dispersed liquid crystal

The applications of active matrix flat-panel imagers (AMFPIs) in large-area x-ray imaging systems have increased over time but are still severely limited owing to its pixel resolution, complex fabrication processes, and high cost. As a solution, x-ray light valve (XLV) technology was introduced and expected to have a better resolution and contrast ratio than those of AMFPI, owing to its micrometer level of the LC cells and signal amplification by an external light source. The twisting angle of the LC cells was changed by charge carrier signals created in a photoconductor layer against x-rays, and the diagnostic images from XLV were acquired from the transmittance of the external light source. However, there was a possibility that the photoconductor layer may be crystallized or degenerated due to the application of high temperatures for sealing the LC layer during the fabrication process. To solve such problems, polymer-dispersed liquid crystals (PDLCs), which do not need high temperature for the sealing process of the LC layer, are used in this study instead of typical LC cells. A photoconductor and PDLC are combined to develop an x-ray detector. An external light source and optical sensor are used to investigate the light transmission of the PDLC . The PDLCs used in this paper do not need polarizers and are self-adhesive. Hence, the transmittance is very high in the transparent state, which allows for a linear x-ray response and sufficient dynamic range in digital radiography.

Video optical encryption technology based on liquid crystal light valve

Video optical encryption technology based on liquid crystal light valve

固态体积式真三维立体显示器显示体驱动电路设计

The display-body used in Solid Volumetric True 3D Display contains 20 pieces of Liquid Crystal Light Valve(LCLV).The high-speed video projector projects a sequence of pictures into different pieces of liquid crystal light valve so that people can see a true 3Dimage.It's necessary to syn-chronize the display body with the high-speed video projector.First,a circuit driver for large-size liquid crystal light valve is needed.The driver should have the strong capability of fast response and can realize bipolar drive.After solving the problem caused by the oscillation happened on the gate of MOSFET,the circuit driver for the display-body is designed.Finally,after analyzing the reasons of flicker happened when the body refresh rate is 60 Hz,a new method based on current hardware is given to solve the problem of flicker.Experiments show that the driver can realize the true 3D display without flicker.To one piece of liquid crystal light valve 48cm(19 in),the sum of rising time and falling time is 0.5ms when the drive voltage is 100 V.The circuit driver can realize the function and provides a method for driving the liquid crystal light valve in large size.

Imaging Characteristics Analysis of GLV-Based Thermal CTP System

The Grating Light Valve (GLV) is a spatial light modulator based on Micro Electro Mechanical Systems (MEMS), and it has been successfully applied in the computer-to-plate (CTP) system by modulating laser beams. Fast modulation rate, a mass of pixels, and high power handling capability of the GLV device increase imaging speed. Digital working states, combine of two GLV pixels and exact beam shape improve imaging quality. Numerical calculation and graph analysis using MATLAB software show that imaging quality of GLV-based thermal CTP system is higher than that of traditional acousto-optic modulator scanning system.

Isothermal electrically and optically induced phase separation of liquid crystal and poly(N-vinylcarbazole) films

This paper reports the electro- and photo-isomerization-induced isothermal phase separation of liquid crystals (LCs) and poly(N-vinylcarbazole) (PVK). The proposed phase separation process determines reformed PVK films on substrates to obtain switchable LC light valves. UV illumination induces simultaneous isothermal phase transition of the mixture and dissolution of PVK into the LCs. Phase separation of PVK and LCs occurs by the reversed phase transition via rapid electro-isomerization and slow dark-relaxation. During rapid phase separation, micron-sized LC domains (branch-like PVK structures) are generated to develop stable light scattering; during slow dark-relaxation, a uniform PVK film is obtained, thereby providing stable transparency.

Principle, design and fabrication of a passive binary micro-mirror array (BMMA) for speckle reduction in grating light valve (GLV) based laser projection displays

A binary micro-mirror array (BMMA) is proposed for speckle reduction in grating light valve based laser projectors. The mirrors are driven by the electrostatic force, and have two states, i.e., ‘1’ state (or ‘static/off’ state) corresponding to motionless mirrors or mirrors that are released to their zero-bias voltage position and ‘-1’ state (or ‘on’ state) in accordance to the fully deflected mirrors. The phase modulation depth between the two working states of the mirror is π radian. The control electronics of the BMMA is designed by a passive driving scheme derived from a hadamard matrix or a two-level orthogonal array, thus we can avoid using the memory transistors, and number of the control electrodes could be significantly reduced. Performances of the mirrors are analyzed by the analytical model. A proof-of-concept 32μm pitch BMMA fabricated using aluminum as the mechanical layer is presented, and the proper function of the BMMA is demonstrated with speckle reduction. About 5% speckle contrast ratio can be achieved after compounding the BMMA and a laser diode array.

Magnetophotonic intensity effects in hybrid metal-dielectric structures

The magneto-optical properties of a hybrid metal-dielectric structure consisting of a one-dimensional gold grating on top of a magnetic waveguide layer are studied experimentally and theoretically. It is demonstrated that a magnetic field applied in the longitudinal configuration (in the plane of the magnetic film and perpendicular to the slits in the gold grating) to the metal-dielectric structure modifies the field distribution of the optical modes and thus changes the mode excitation conditions. In the optical far field, this manifests in the alteration of the optical transmittance or reflectance when the structure becomes magnetized. This magneto-optical effect is shown to represent a novel class of effects related to the magnetic-field-induced modification of the Bloch modes of the periodic hybrid structure. That is why we define this effect as ``longitudinal magnetophotonic intensity effect'' (LMPIE). The LMPIE has two contributions, odd and even in magnetization. While the even LMPIE is maximal for the light polarized perpendicular to the grating slits (TM) and minimal for the orthogonal polarization (TE), the odd LMPIE takes maximum values at some intermediate polarization and vanishes for pure TM and TE polarizations. Two principal modes of the magnetic layer---TM and TE---acquire in the longitudinal magnetic field additional field components and thus turn into quasi-TM and quasi-TE modes, respectively. The largest LMPIE is observed for excitation of the antisymmetrical quasi-TE mode by TM-polarized light. The value of the LMPIE measured for the plasmonic structure with a magnetic film of Bi${}_{2}$Dy${}_{1}$Fe${}_{4}$Ga${}_{1}$O${}_{12}$ composition is about 1% for the even effect and 2% for the odd one. However, the plasmonic structure with a magnetic film with a higher concentration of bismuth (Bi${}_{2.97}$Er${}_{0.03}$Fe${}_{4}$Al${}_{0.5}$Ga${}_{0.5}$O${}_{12}$) gives significantly larger LMPIE: even LMPIE reaches 24% and odd LMPIE is 9%. Enhancement of the magneto-optical figure of merit (defined as the ratio of the specific Faraday angle of a magnetic film to its absorption coefficient) of the magnetic films potentially causes the even LMPIE to exceed 100% as is predicted by calculations. Thus, the nanostructured material described here may be considered as an ultrafast magnetophotonic light valve.

电控液晶光阀中的指向矢分布特性

Liquid crystals with dielectric and optical anisotropy have the ability of optical phase efficient modulation.When the liquid crystal system is placed in external electric field,the director of liquid crystal system will be redistributed.In this paper,the optical modulated effect of electronically controlled liquid crystal light valve was studied experimentally and theoretically.The result shows that threshold voltage of light valve is about 4volts.And when external voltage is higher than the threshold voltage, the transmitted intensity of liquid crystal light valve will present the aperiodic properties.According to the continuum elasticity theory model,the liquid crystal director distributions in the electric field were studied by numerical methods,and found that the aperiodic modulation of transmitted intensity is depending on the distribution of the liquid crystal directors critically.It is the theoretical and experimental basis for the study of polarization-modulation characteristics.

光栅光阀光学特性分析及其在热敏CTP中的应用

The grating light valve(GLV)is a diffractive MOEMS spatial light modulator,and it has been successfully applied in the computer-to-plate(CTP)system by modulating laser beams.A simplified grating light valve optical model is put forward,and the optical characteristics of GLV is analyzed according to Fraunhofer single-slit diffraction theory and multiple beam interference theory.The application of grating light valve in thermal CTP system is described,and the structure and imaging principle of GLV optical write engine are analyzed.The digital imaging process of the GLV-based thermal CTP system is concluded,which provides the theory basis for the domestic printing enterprise to use the thermal imaging technology.

Harnessing Optical Vortex Lattices in Nematic Liquid Crystals

By creating self-induced vortexlike defects in the nematic liquid crystal layer of a light valve, we demonstrate the realization of programable lattices of optical vortices with arbitrary distribution in space. On each lattice site, every matter vortex acts as a photonic spin-to-orbital momentum coupler and an array of circularly polarized input beams is converted into an output array of vortex beams with topological charges consistent with the matter lattice. The vortex arrangements are explained on the basis of light-induced matter defects of both signs and consistent topological rules.

P.66: An Electrowetting Light Valve using ODF Assembly Process

AbstractODF assembly process is difficult to implement in electrowetting display manufacturing. We have demonstrated an electrowetting light valve with both iris‐like pixel structure and nanoparticle ink by using similar ODF assembly process. In addition, the electrowetting light valve has three major characteristics, better aperture ratio, response time possibly and working on lower frequency, which can be applied e‐reader and video display.

Reversible Sliding in Networks of Nanowires

This work demonstrates that metal nanowires in a percolating network can reversibly slide across one another. Reversible sliding allows networks of metal nanowires to maintain electrical contact while being stretched to strains greater than the fracture strain for individual nanowires. This phenomenon was demonstrated by using networks of nanowires as compliant electrodes for a dielectric elastomer actuator. Reversible nanowire sliding enabled actuation to a maximum area strain of 200% and repetitive cycling of the actuator to an area strain of 25% over 150 times. During actuation, the transmittance of the network increased 4.5 times, from 13% to 58%. Compared to carbon-based compliant electrodes, networks of metal nanowires can actuate across a broader range of optical transmittance. The widely tunable transmittance of nanowire-based actuators allows for their use as a light valve.