Liquid Crystal Phase Modulator Research Articles

Adaptive optics scanning system with two-zone phase filters

ABSTRACTAn adaptive confocal system employing pupil filters and two light sources has been designed, providing improved transverse resolution. Coherent transfer functions are studied to show the transfer capability at different frequencies and the limitations of the filters in obtaining clear improvements in the focal plane. Then, intensity point spread functions are analysed to reveal the dependence of the resolution on the size of the pinhole and the inner radius of the filter. An experiment has been carried out using a liquid crystal phase modulator and an artificial eye to validate the simulation results. It proves that the system with two light sources can correct the aberrations, with the basic effect of the phase modulation being to decrease the low spatial frequencies and increase the high spatial frequencies. Improvement of the transverse resolution can be achieved by sacrificing light intensity and contrast.

44‐3: Large Area Multi‐Layer Liquid Crystal Phase Modulators Enabled by Two‐Photon Polymerization

We demonstrate multi‐fold speed enhancement of liquid crystal phase modulators through laser written sub‐micron scaffolds. The versatile fabrication process allows devices with arbitrary liquid crystal alignment and, therefore, polarization dependence. We lastly discuss the prospects of the technology for large area (>0.5 in2) spatial light modulators.

Papers] Dielectric Walls with Slits for Pixel Driving and Fabrication of Holographic Liquid Crystal Phase Modulators

Papers] Dielectric Walls with Slits for Pixel Driving and Fabrication of Holographic Liquid Crystal Phase Modulators

Polarization-independent phase modulators enabled by two-photon polymerization

A double-layer polarization-independent liquid crystal (LC) phase modulator is demonstrated and characterized. Using two-photon polymerization process, an ultra-thin partition polymeric film to separate the LC cell into two layers with orthogonal alignment directions is fabricated. Such a thin partition film also helps to reduce the voltage shielding effect. Using a high birefringence and low viscosity LC mixture, 2π phase change at merely 10 V for a He-Ne laser beam is achieved, while keeping a fast response time. Simulation result agrees reasonably well with experimental data.

Two-photon polymerization enabled multi-layer liquid crystal phase modulator

The performance of liquid crystal (LC) spatial light modulators depends critically on the amount of cumulative phase change. However, for regular phase modulators, a large phase change comes with a slow time response penalty. A multi-layer liquid crystal (LC) spatial light modulator offers a large phase change while keeping fast response time due to the decoupling between phase change and time response through engineered sub-micron scaffold. Here, we demonstrate specially designed 2- and 3-layer LC cells which can achieve 4 times and 7 times faster response time than that of conventional single-layer LC phase modulator of equivalent thickness, respectively. A versatile two-photon laser lithography is employed for LC cell scaffolding to accurately verify theoretical predictions with experimental measurements.

Holographic polymer networks formed in liquid crystal phase modulators via a He-Ne laser to achieve ultra-fast optical response.

The holographic polymer network formed in liquid crystal (LC) phase modulators via a He-Ne laser in this study demonstrates ultra-fast optically response and low light scattering. These advantages are mainly caused by the small LC domains and uniform polymer network when processing LC cells via holographic exposure to a He-Ne laser. The use of this method to fabricate LC cells as phase modulators results in a decay time of 49 μs under 2π phase modulation at room temperature. The predicted fast optical response can be achieved when operating devices at high temperatures.

Adaptive modulation system for liquid crystal phase modulator

An adaptive modulation system for a liquid crystal (LC) phase modulator is demonstrated. The phase retardation may be modulated by resetting the driving voltage automatically by matching the measured and ideal transmittance of an LC cell sandwiched by crossed polarizers. By using this system, an LC phase modulator can get a low error function of 0.25% in a short modulation time, which is less than the 10% obtained using a conventional modulation method.

Low voltage and high resolution phase modulator based on blue phase liquid crystals with external compact optical system.

Liquid crystal phase modulators are emerging as a new technological advancement, since they can be used for a wide range of applications. To improve their performance, polymer stabilized blue phase liquid crystal (PS-BPLC) phase modulators with fast response time and accurate phase profile become a necessary. Here, we proposed a facile PS-BPLC phase modulator to achieve particularly low voltage and high resolution. By employing a specific external compact optical system setup, the driving voltage is reduced to 26.09V to obtain 2π phase change at the wavelength of 532 nm. An accurate numerical modeling is also conducted to provide a systematic investigation of the fringing electric field effect to the performance of high resolution PS-BPLC phase modulator. The wavefront distortion caused by the fringing electric field can be automatically compensated to generate accurate phase profile for fast response liquid crystal phase modulator. This work provides a new protocol to realize liquid crystal on silicon based fast response and high resolution phase modulator.

Fast-response infrared phase modulator based on polymer network liquid crystal

We report a high birefringence terphenyl liquid crystal mixture, designated as M3, for infrared phase modulation with special emphasis on mid-wave infrared (MWIR). In addition to high birefringence, M3 exhibits excellent UV stability, modest dielectric anisotropy, and a very broad nematic range. The high birefringence enables a thin cell gap to be used for achieving a 2π phase change while maintaining a high transmittance (T>98%) in the MWIR region. To achieve fast response time, we employed a polymer network liquid crystal using M3 with 2π phase change at λ = 4μm and 3.6-ms response time. This response time is about 100X faster than that of a nematic LC phase modulator.

Holographic display based on liquid crystal spatial light modulator

In conventional phase-only holographic display, the phase-only computer generated hologram is usually calculated based on the fast Fourier transform (FFT) algorithm, in which the Nyquist theory should be satisfied. However, due to the pixel structure of the liquid crystal spatial light modulator and a fixed spatial sampling rate, the size of the reconstructed image is limited by the space-bandwidth product of the liquid crystal phase modulator. The traditional solution is to use convolution algorithm or double-step Fresnel diffraction algorithm to calculate the Fresnel hologram, but FFT has to be calculated many times in both of the methods, thereby increasing the burden of hologram computation. Therefore, in this paper we propose a method to calculate the phase-only hologram based on setting a virtual hologram plane. This virtual hologram plane is set based on the principle of lens imaging. So the calculation of the hologram can be divided into two steps: the first step is to calculate the Fresnel diffraction from the object plane to the virtual hologram plane, and the second step is to calculate the hologram from the virtual hologram plane by being multiplied with a quadratic phase term. In this way, the hologram can be calculated from the original object with any sampling rate we need by adjusting the corresponding parameters of distance. By this method one can calculate the Fresnel diffraction between hologram plane and object plane with variable sampling rates, without considering the space-bandwidth product of the liquid crystal phase modulator, and this algorithm uses only one FFT calculation, which can speed up the calculation of hologram compared with the convolution based method (using three FFTs in calculation) and the double-step Fresnel method (using two FFTs in calculation). Both the computer simulation and the optical experiments demonstrate that the object can be reconstructed with different sizes in the holographic display system. In the optical experiment, the zero-order diffraction can be removed by placing a filter on the back focal plane of the imaging lens and the speckle noise can also be eliminated in order to improve the reconstruction quality by displaying multiple phase-only holograms at a high speed. The proposed method in this paper shows a potential application in zoom-able liquid crystal spatial light modulator based holographic display system.

Morphology effect on the light scattering and dynamic response of polymer network liquid crystal phase modulator.

Polymer network liquid crystal (PNLC) was one of the most potential liquid crystal for submillisecond response phase modulation, which was possible to be applied in submillisecond response phase only spatial light modulator. But until now the light scattering when liquid crystal director was reoriented by external electric field limited its phase modulation application. Dynamic response of phase change when high voltage was applied was also not elucidated. The mechanism that determines the light scattering was studied by analyzing the polymer network morphology by SEM method. Samples were prepared by varying the polymerization temperature, UV curing intensity and polymerization time. The morphology effect on the dynamic response of phase change was studied, in which high voltage was usually applied and electro-striction effect was often induced. The experimental results indicate that the polymer network morphology was mainly characterized by cross linked single fibrils, cross linked fibril bundles or even both. Although the formation of fibril bundle usually induced large light scattering, such a polymer network could endure higher voltage. In contrast, although the formation of cross linked single fibrils induced small light scattering, such a polymer network cannot endure higher voltage. There is a tradeoff between the light scattering and high voltage endurance. The electro-optical properties such as threshold voltage and response time were taken to verify our conclusion. For future application, the monomer molecular structure, the liquid crystal solvent and the polymerization conditions should be optimized to generate optimal polymer network morphology.

分光ミュラー行列偏光計

Polarization tool as ellipsometry is a classic but still new technology. It is used in various fields : from materials science, such as the newest nanotechnology and optical function material, to biotechnology in recent years. It has been developing into the new areas, called polarization science and polarization technology. This paper reviews a measurement method for spectroscopic Mueller matrix such as a dual rotating retarder type polarimeter, a liquid crystal phase modulation type polarimeter, and a channeled spectrum polarimeter. In addition, the important analysis is introduced for equipment calibration and a decomposition method from obtained Mueller matrix.

48.1: Research on the Fringing Electric Field Effect of Liquid Crystal Phase Modulator for Digital Holography

AbstractThe fringing electric field effect in a high resolution liquid crystal phase modulator is studied by simulation. A new method to evaluate the phase shift properties of the device is proposed. The influence from adjacent pixel, driving voltage and pre‐tilt angle is investigated. A high driving voltage and 0° pre‐tilt angle is useful to reduce the fringing electric field effect.

Cardiomyocyte Imaging Using Real-Time Spatial Light Interference Microscopy (SLIM)

Spatial light interference microscopy (SLIM) is a highly sensitive quantitative phase imaging method, which is capable of unprecedented structure studies in biology and beyond. In addition to the π/2 shift introduced in phase contrast between the scattered and unscattered light from the sample, 4 phase shifts are generated in SLIM, by increments of π/2 using a reflective liquid crystal phase modulator (LCPM). As 4 phase shifted images are required to produce a quantitative phase image, the switching speed of the LCPM and the acquisition rate of the camera limit the acquisition rate and, thus, SLIM's applicability to highly dynamic samples. In this paper we present a fast SLIM setup which can image at a maximum rate of 50 frames per second and provide in real-time quantitative phase images at 50/4 = 12.5 frames per second. We use a fast LCPM for phase shifting and a fast scientific-grade complementary metal oxide semiconductor (sCMOS) camera (Andor) for imaging. We present the dispersion relation, i.e. decay rate vs. spatial mode, associated with dynamic beating cardiomyocyte cells from the quantitative phase images obtained with the real-time SLIM system.

A polarization-independent liquid crystal phase modulation using polymer-network liquid crystals in a 90° twisted cell

A polarization-independent liquid crystal phase modulation using polymer-network liquid crystals in a 90° twisted cell (T-PNLC) is demonstrated. T-PNLC consists of three layers. Liquid crystal (LC) directors in the two layers near glass substrates are orthogonal to each other and those two layers modulate two eigen-polarizations of an incident light. As a result, two eigen-polarizations of an incident light experience the same phase shift. In the middle layer, LC directors are perpendicular to the glass substrate and contribute no phase shift. The phase shift of T-PNLC is electrically tunable and polarization-independent. T-PNLC does not require any bias voltage for operation. The phase shift is 0.28 π rad for the voltage of 30 Vrms. By measuring and analyzing the optical phase shift of T-PNLC at the oblique incidence of transverse magnetic wave, the pretilt angle of LC directors and the effective thickness of three layers are obtained and discussed. The potential applications are spatial light modulators, laser beam steering, and micro-lens arrays.

P‐25: 3‐D Surface Profilometry for Accurate Extraction of Depth Profile with LC Phase Modulator

AbstractWe proposed a 3‐D surface profilometry with a liquid crystal (LC) phase modulator for accurate extraction of the position and depth profile. The LC phase modulator was designed to develop the dynamic fringe patterns to be operated with multi‐spatial frequencies, which were determined by changing the gap between micro‐pinholes. The amount of phase shift was controlled by changing the applied voltage. In addition, the fictitious pattern scanning method and geometrical parameters were used to reconstruct position and depth profile of an object. As a result, the depth profile of object could be computed accurately with profilometry. Also, 3‐D surface profilometry showed that integrated compact system could be constructed with the proposed scheme.

Multi-spatial-frequency and phase-shifting profilometry using a liquid crystal phase modulator

Optical profilometry is widely applied for measuring the morphology of objects by projecting predetermined patterns on them. In this technique, the compact size is one of the interesting issues for practical applications. The generation of pattern by the interference of coherent light sources has a potential to reduce the dimension of the illumination part. Moreover, this method can make fine patterns without projection optics, and the illumination part is free of restriction from the numerical aperture of the projection optics. In this paper, a phase-shifting profilometry is implemented by using a single liquid crystal (LC) cell. The LC phase modulator is designed to generate the interference patterns with several different spatial frequencies by changing selection of the spacing between the micro-pinholes. We manufactured the LC phase modulator and calibrated it by measuring the phase modulation amount depending on an applied voltage. Our optical profilometry using the single LC cell can generate multi-spatial frequency patterns as well as four steps of the phase-shifted patterns. This method can be implemented compactly, and the reconstructed depth profile is obtained without a phase-unwrapping algorithm.

Dynamic wavefront correction with a fast liquid-crystal on silicon device of pure phase

In order to increase the response speed of the liquid crystal phase modulator (LCPM), a new kind of fast liquid crystal material is designed and synthesized, and a corresponding LCPM, called liquid crystal on silicon (LCOS), is fabricated. We test the phase modulation of the LCOS and examine its wavefront correction ability on static and disturbed wavefront. First, the electro-optical response is tested. The response time to a phase modulation quantity of 780 nm is 2 ms. Second, the phase modulation of the LCOS is tested and linearized. Third, the 3 dB closed-loop and open-loop disturbance rejection bandwidths of the adaptive optics system (AOS) are measured to be 16 and 18 Hz, respectively. Finally, the simulated correction of 26 Hz turbulence with the open-loop AOS is conducted. After correction, the Strehl ratio increases from 0.026 to 0.225. Therefore, with our fabricated LCOS, the liquid crystal AOS is able to correct the turbulence below 30 Hz.

A polarization independent liquid crystal phase modulation adopting surface pinning effect of polymer dispersed liquid crystals

A polarization-independent liquid crystal (LC) phase modulation using the surface pinning effect of polymer dispersed liquid crystals (SP-PDLC) is demonstrated. In the bulk region of the SP-PDLC, the orientations of LC directors are randomly dispersed; thus, any polarization of incident light experiences the same averaged refractive index. In the regions near glass substrates, the LC droplets are pinned. The orientations of top and bottom droplets are orthogonal. Two eigen-polarizations of an incident light experience the same phase shift. As a result, the SP-PDLC is polarization independent. Polarizer-free microlens arrays of SP-PDLC are also demonstrated. The SP-PDLC has potential for application in spatial light modulators, laser beam steering, and electrically tunable microprisms.

Grating coupled optical waveguide interferometer for label-free biosensing

A phase shifting optical waveguide interferometer is demonstrated for label-free evanescent wave biosensing in aqueous solutions. In the proposed configuration, the reference and measurement arms of the interferometer are combined inside an integrated optical Ta 2O 5 waveguide using an ion implanted grating. Biomolecules adsorbing on the waveguide surface shift the phase in the measurement arm, which is modulated at the same time by a periodically relaxing liquid crystal phase modulator. It is demonstrated that by analyzing the periodic intensity response at the end facet of the waveguide, the phase shifts in the measurement arm can be monitored in real-time with a precision of 10 −4 rad. The high phase resolution allows the detection of surface adsorbed molecule densities below 1 pg/mm 2 without using any labeling or on-chip referencing. The instrument performance is demonstrated by monitoring in situ protein adsorption and affinity binding of low molecular weight pure biotin to an immobilized avidin layer.