Liquid Crystal Spatial Light Modulator Research Articles

Transmissive flexoelectro-optic liquid crystal optical phase modulator with 2π modulation

In this paper, we demonstrate analog phase modulation in a transmissive configuration using the flexoelectro-optic effect in short-pitch chiral nematic liquid crystal (LC) devices. Two different modes are considered, both of which are shown to generate full 2π phase modulation at 1 kHz switching frequency. The first configuration that is considered consists of a half-wave plate that is placed between two flexoelectro-optic LC devices that are subjected to electric fields that are applied in phase. Second, we demonstrate that a similar phase modulation response can be observed by removing the half-wave plate and subjecting the two flexoelectro-optic LC devices to electric fields whereby the polarities are out of phase. Both configurations demonstrated herein are promising for the development of next-generation LC spatial light modulators, particularly when reflective geometries are challenging or impractical.

Cylindrically polarized perfect optical vortex: Generation and focusing properties

In this paper we extend the concept of perfect optical vortex to the vector case and investigate its focusing properties in the high numerical aperture regime. We show that simultaneous phase encoding of orthogonal components can be realized by means of a 4f imaging system incorporating a phase only liquid-crystal spatial light modulator whose director axis is rotated 45° with respect to the horizontal axis. As an example of application, we demonstrate theoretically and experimentally that a ring-shaped field with inner radius of 0.15 λ can be obtained by focusing a radially polarized perfect vortex and a tight spot of 0.34 λ FWHM can be obtained by focusing an azimuthally polarized perfect vortex.

Simultaneous Measurement of In-Plane and Out-of-Plane Displacements Using Talbot Fringe Projection

The fringe projection technique has been widely used in optical measurements. In this paper, we demonstrate a scheme to measure the 3D displacement of a deformed sample using Talbot fringe projection. In this process, we designed a two-dimensional square Talbot hologram. In this approach, we used the basic principle of triangulation, and a computer-controlled liquid crystal spatial light modulator (LC-SLM) was placed in the optical path. The Talbot array hologram was displayed on the LC-SLM screen and projected onto the surface of a sample. Two patterns were recorded: one before and one after deformation. We simultaneously acquired the in-plane and out-of-plane displacements using the digital image correlation (DIC) method. This scheme is simple and easily implemented. Theoretical and experimental results are presented.

Characterization of a spatial light modulator using polarization-sensitive digital holography.

We show a digital holographic approach for polarimetric characterization of a twisted nematic liquid crystal spatial light modulator (TNLC-SLM). An experimental scheme is designed to perform polarization analysis of the SLM with gray levels. This is realized by simultaneous detection of the polarization states of the light from the SLM for a given gray level with the help of a specially designed spatial-frequency multiplex polarization interferometer. This provides amplitude and phase characteristics of the SLM in a single shot. In order to characterize the SLM, we perform Jones matrix imaging at its various gray values (driving voltages), and corresponding results are presented. These results are expected to be useful in designing and developing various SLM-based experiments in the scalar and vectorial domain.

Controlled formation of femtosecond laser-induced filaments in water

Controlled formation of femtosecond laser-induced filaments in water was introduced and demonstrated experimentally, based on the transverse spatial phase change in the initial femtosecond laser pulse. Single or multi-filament formations were controlled and organized by switching on and off through a computer-controlled transverse spatial phase mask on a liquid crystal Spatial Light Modulator (SLM). We introduced a π phase step on SLM, which distributed laser intensity non-uniformly and in certain locations peak intensity exceeded the critical threshold, and filaments were formed in the peaks of the intensity. The setup with controllable phase shift on SLM may have great flexibility and convenience in controls of filament formation.

3-DOF measurement method for non-diffracting Moiré fringes based on CGH

Aiming at the motion errors of the linear stage, a measurement method for the determination of three-degree-of-freedom (3-DOF) error motions is proposed based on non-diffracting Moire fringes produced by computer-generated holograms (CGHs). A liquid crystal spatial light modulator (SLM) is used to generate non-diffracting beams, and two non-diffracting beams form Moire fringes. A 3-DOF measuring optical path of non-diffracting Moire fringes is designed. Meanwhile, a 3-DOF mathematical model of motion errors is established, and three kinds of motion errors (yaw angle, roll angle and pitch angle) are separated by geometric analysis method. A rotary table is used to simulate the 3-DOF motion errors on different conditions. The NDB and non-diffracting Moire fringe patterns are obtained by CCD1 and CCD2 respectively. Experimental results show that the motion errors calculated by the positions of the central points agree well with the theoretical value with the error less than 0.0104°, which can verify the feasibility and correctness of the 3-DOF measurement system for non-diffracting Moire fringes.

Single atom movement with dynamic holographic optical tweezers

We report an experimental implementation of dynamical holographic tweezers for single trapped atoms. The tweezers are realized with dynamical phase holograms displayed on the liquid crystal spatial light modulator. We experimentally demonstrate the possibility to trap and move single rubidium atoms with such dynamic potentials, and study its limitations. Our results suggest that high probability transfer of single atoms in the tweezers may be performed in large steps, much larger then the trap waist. We discuss intensity-flicker in holographic traps and techniques for its suppression. Loss and heating rates in dynamic tweezers are measured and no excess loss or heating is observed in comparison with static traps.

Array detection in a holographic scanning microscope

In this paper we describe a simple experimental arrangement to implement array detection in a scanning optical microscope where both the beam shaping and beam scanning are done holographically. A ferroelectric liquid crystal spatial light modulator is used to implement dynamic and reconfigurable binary holograms and an ordinary camera is used as the array detector. We use a scanning scheme that enables array detection over 120 × 120 scan positions and 40 × 40 detector array data for each position with an acquisition time of 40 s using a 15 fps (frames per second) camera. We demonstrated the working of the microscope to implement image subtraction and image scanning microscopy in both reflected and fluorescence light.

Conversion of free-space optical path mode by spatial light modulator

The mode of spatial optical in wireless laser communication systems directly affects the coupling efficiency of spatial optics to single-mode fibers. The mode conversion model of a free-spatial optical path based on a liquid crystal spatial light modulator is studied to improve the content of fundamental modes. According to the spatial spectrum filtering relationship between the conversion mode and the target mode, the corresponding conversion transfer function (CTF) is obtained. Combined with the simulated annealing algorithm, the CTF is accelerated locally, and its optimal value is obtained. Therefore, the conversion efficiency from higher-order modes to fundamental mode is generally improved. In addition, an experimental platform is established to verify the rationality of the simulation results. Further, it is indicated that the coupling efficiency can be improved by mode conversion.

Wavefront-shaping-based correction of optically simulated cataracts

Cataracts is a common ocular pathology where the crystalline lens tends to become opaque, degrading the quality of the retinal images because of the increase of both aberrations and scattering. In this work, we simultaneously generated and optically corrected the effects of cataracts in an optical bench by using a liquid crystal device spatial light modulator. The correction was carried out by implementing a feedback-based wavefront shaping technique with different spatial resolutions of the corrector phase maps. Its benefits were evaluated through objective and subjective descriptors of the quality of vision. The analysis of the experimental results, in addition to numerical calculations of the uncorrected and corrected ocular point spread functions, allowed us to understand the limitations of the technique and to present a strategy to overcome it for future in vivo applications.

Control of supercontinuum generation from filamentation of shaped femtosecond laser pulses

Supercontinuum (SC), as one of the most spectacular phenomena occurring in the nonlinear process of intense femtosecond laser-material interaction, has attracted considerable interest. The broadband SC sources have a variety of applications including the spectroscopy, fluorescence microscopy, remote sensing, and generation of few-cycle pulses. Over the last few decades, the SC has been extensively investigated in various optical media, including liquid, gas, and solid. Especially, ultrabroadband SC sources have achieved remarkable development in the photonic crystal and micro-structured fibers. Even so, the generation of the SC with high brightness, high spatiotemporal coherence and good maneuverability, is still a challenging topic. The SC generation from femtosecond filamentation is a unique white light source with high pulse energy, high brightness and high spatiotemporal coherence, whose spectral range spans from ultraviolet to mid-infrared. In recent years, numerous studies have been conducted to optimize the filamentation and SC. The control of filamentation such as the filament length, number and position, as well as the generation of the ultra-broadband spectrum with high spectral energy density has been realized. To date, the optimal control of SC has been realized by the spatial modulation or time-domain shaping of the femtosecond laser pulse. However, there is no report on the control of SC generation and filamentation by spatiotemporally modulating the femtosecond laser pulses as far as we know. In this work, a spatiotemporal modulation for the femtosecond laser pulse is proposed, which combines the spatial modulation by using microlens array (MLA) and the laser pulse shaping based on liquid crystal spatial light modulator. We investigate the control of the SC generation from the filamentation of the spatiotemporally modulated femtosecond laser pulses in fused silica by using the feedback optimal control based on genetic algorithm. In our experiments, with the increase of the iterative generation, the cut-off wavelength in the blue-side extension of the SC becomes shorter gradually, and the spectral intensity of the SC increases significantly. After the eighth iteration, the increase of the spectral intensity slows. With the number of iterations increasing further, the intensity and broadening of SC spectrum will no longer apparently change. Hence, the feedback optimization control of spectral intensity of SC is realized, and the SC with controllable spectral intensity in a certain range is obtained. The maximum intensity variation of SC is more than three times. By integrating the spectral intensities of SC for different iterative generations, we characterize the increase trend of SC conversion efficiency. During the first few iterations, the conversion efficiency increases rapidly. Then it increases slowly after eighth generations and reaches its maximum after several generations (10th generation). The conversion efficiency has a similar evolution to the spectral intensity of the SC. To explain the physical mechanism, the initial envelope of the shaping pulse with typical iteration generation is calculated. It can be concluded that the spatial modulation of MLA allows for higher incident laser energy and for more filaments’ generation, which increases the energy of SC radiation directly. The peak intensity and envelope distribution of time domain pulse are the main factors affecting the spectral intensity and broadening the SC.

Paper] Evaluation of Holographic Reconstructed Image Quality considering Non-uniform Phase Distribution in Liquid Crystal Spatial Light Modulators

Paper] Evaluation of Holographic Reconstructed Image Quality considering Non-uniform Phase Distribution in Liquid Crystal Spatial Light Modulators

Projection of holographic images in volumetric fluorescent fluids for near-eye displays

The optical setup for holographic projection on the scatterings in fluorescent liquids is presented. Such media can be used as volumetric screens for near-eye holographic displays, solving the problem of speckle noise and very small exit pupils in existing setups. Three different oils (canola, olive and engine oil) with 532 nm laser and tonic water with 405 nm laser are used for projecting holographic fields, the quality of such images is investigated. The laser wavelength is cut out from acquisition on a camera and only filtered fluorescent light is observed. The best and brightest results are obtained with engine oil. Full Text: PDF ReferencesX. Li, C. P. Chen, H. Gao, et al. "Video-Rate Holographic Display Using Azo-Dye-Doped Liquid Crystal", Journal of display technology 10(6), 438-443 (2014). CrossRef X. Li, Z. Song, F. Li, X. Dong, W. Liu, "79‐3: Video‐rate Holographic Display in ZnSe layer‐assisted Quantum Dot Doped Liquid Crystal with High‐photorefractive Sensitivity", SID Symposium Digest of Technical Papers. Vol. 48. No. 1. 2017, CrossRef Sasaki, Takeo, et al. "Real-time dynamic hologram in photorefractive ferroelectric liquid crystal with two-beam coupling gain coefficient of over 800 cm–1 and response time of 8 ms", Applied Physics Letters 6(2) (2013) CrossRef N. Tsutsumi, K. Kinashi, A. Nomura, W. Sasaki, "Quickly Updatable Hologram Images Using Poly(N-vinyl Carbazole) (PVCz) Photorefractive Polymer Composite", Materials 5.8: 1477-1486 (2012) CrossRef M. Makowski, "Simple holographic projection in color", et al. Optics express 20.22: 25130-25136 (2012) CrossRef A. Yagi, M. Imura, Y, Kuroda, O. Oshiro, "360-degree fog projection interactive display", SIGGRAPH Asia 2011 Emerging Technologies. ACM, (2011) CrossRef C.H. Hsu, K. L. Hua, W. H. Cheng. "Omni-Tube: a low-cost portable omnidirectional interactive 3D display", SIGGRAPH Asia 2012 Posters. ACM, (2012) CrossRef Z. Zeng, H. Zheng, X. Lu, H. Gao, Y. Yu, "Dynamic holographic three-dimensional projection based on liquid crystal spatial light modulator and cylindrical fog screen", Opt Rev (2015) 22: 853 CrossRef I. Rakkolainen, "Feasible mid-air virtual reality with the immaterial projection screen technology", 3DTV-Conference, Tampere (2010) CrossRef S. Yanfeng, et al. "A multi-plane optical see-through holographic three-dimensional display for augmented reality applications", Optik 157: 190-196 (2018) CrossRef G. Li, D. Lee, Y. Jeong, J. Cho, B. Lee, "Holographic display for see-through augmented reality using mirror-lens holographic optical element", Opt. Lett. 41(11), 2486-2489 (2016) CrossRef C. L. Lin, Y. Z. Su, M. W. Hung, K. C. Huang "Augmented reality system", Proc. SPIE 7798, Applications of Digital Image Processing XXXIII, 779826 (2010) CrossRef A. Maimone, A. Georgiou, J. S. Kollin, "Holographic near-eye displays for virtual and augmented reality", ACM Trans. Graph. 36, 4, 1-16 (2017) CrossRef M. Quinten, Optical properties of nanoparticle systems: Mie and beyond (John Wiley & Sons 2010). CrossRef J.-W. Liaw, S.-W. Tsai, H.-H. Lin, T.-C. Yen, B.-R. Chen, "Wavelength-dependent Faraday–Tyndall effect on laser-induced microbubble in gold colloid", Journal of Quantitative Spectroscopy and Radiative Transfer 113(17), 2234-2242 (2012), CrossRef T. Mu et al. "Classification of edible oils using 532 nm laser-induced fluorescence combined with support vector machine", Anal. Methods 5, 6960 (2013) CrossRef T. Mu et al. "Classification of Motor Oil Using Laser-Induced Fluorescence and Phosphorescence", Analytical Letters 49:8, 1233-1239 (2015) CrossRef V. Rostampour, M. J. Lynch, "Quantitative Techniques To Discriminate Petroleum Oils Using LED-induced Fluorescence", WIT Transactions on Ecology and the Environment 95, 265 262 (2006) CrossRef F. Wyrowski and O. Bryngdahl, "Iterative Fourier-transform algorithm applied to computer holography", Opt. Soc. Am. A 5(7), 1058-1065 (1988) CrossRef

Calibration of phase liquid crystal spatial light modulators using high-order Taiji radial-shearing interferometry

The modulation characteristics of liquid crystal spatial light modulators (LC-SLMs) are related to the incident wavelength. In order to load the grayscale image correctly, LC-SLMs must be calibrated before using. We propose high-order Chinese Taiji radial-shearing interferometry to calibrate the phase modulation curve of an LC-SLM, which is different from the conventional calibration method. The new method is proposed to establish the mapping relationship between LC-SLM grayscale and phase modulation by rotating multiple Airy spots, which are derived from radial-shearing interference through a high-order Chinese Taiji lens. Compared with the traditional interference fringes, one of the greatest advantages is that the function between the grayscale and rotation angle of the two Airy spots is established more easily. Moreover, it eliminates the complex data processing steps and has a high enough signal-to-noise ratio. The experimental results show that high-order Chinese Taiji radial-shearing interferometry is a very effective calibration method for LC-SLM.

Simultaneous identification of the azimuthal and radial mode indices of Laguerre-Gaussian beams using a spiral phase grating

Transfer of information using optical vortex beams as signal carriers can extremely extend the capacity and spectral efficiency in optical communication systems. One of the key problems is to accurately measure the mode indices including radial mode p and topological charge l at the receiver side of an optical vortices transmission system. In this paper, we present a new scheme to determine the mode indices of optical vortices by using spiral phase gratings. Based on the Fresnel diffraction integral theory, the far-field diffraction intensity distributions of vortex beams through the gratings are numerically calculated. Simulation results show that the annular-shaped intensity profiles of incident vortex beams evolve to bright spot array diffraction patterns, which render the information of the mode indices. Specifically, the magnitude of topological charge l and radial index p can be easily determined by counting the number of the corresponding bright stripes. And the orientation of the diffraction optical fields reveals the sign of the topological charge. Experiments are implemented to demonstrate the feasibility and validity of the proposed detecting method by uploading such phase gratings on a reflective phase-only liquid crystal spatial light modulator. The experimental observations are in good agreement with the theoretical predictions.

Arbitrary vectorial state conversion using liquid crystal spatial light modulators

There is significant interest in the generation of complex vector beams, where the combined polarisation and phase profile is chosen to have particular properties. These beams have often been implemented in an adaptable manner using liquid crystal spatial light modulators (SLMs). Existing methods have concentrated mainly on the generation of these vector beams from a fixed polarisation state, but there are also applications were conversion between vectorial states is necessary. We discuss the limitations of existing SLM-based modulation systems for conversion between arbitrary vectorial states. Three degrees of freedom are required in principle for transition between two arbitrary states. We show that a three-SLM system can provide conversion between two arbitrary polarisation states, but cannot necessarily provide a full 2π radian phase modulation. Hence, we propose a design using four SLMs that removes these limitations on the phase modulation.

Active compensation of extrinsic polarization errors using adaptive optics.

We present a scheme for active compensation of complex extrinsic polarization perturbations introduced into an optical system. Imaging polarimeter is used to measure the polarization state across a beam profile and a liquid crystal spatial light modulator controls the polarization of the input beam. A sequence of measurements permits determination of the birefringence properties of a perturbing specimen. The necessary correction is calculated and fed back to the polarization modulator to compensate for the polarization perturbation. The system capabilities are demonstrated on a range of birefringent specimens.

Dual-beam cross-correlation spectrometer for radial velocity measurements.

Measuring the radial velocity of an object can be achieved by quantifying the Doppler shift of Fraunhofer lines. Measurements are typically made using high-resolution conventional spectroscopy, in which the Doppler shift is calculated numerically on a computer. An alternative technique includes cross-correlation spectroscopy, which performs an optical correlation of the incident spectrum against a reference spectrum embedded in the instrument. Many existing correlation spectrometers leverage a chrome mask and obtain a single beam measurement, making the sensors more sensitive to atmospheric turbulence without moving parts. In this paper, we present a static dual-beam polarization-based technique for acquiring cross-correlation spectra that is insensitive to atmospheric turbulence and contains no moving parts. The instrument is based on acquiring light both inside and outside of the solar Fraunhofer lines using a twisted nematic liquid-crystal spatial light modulator. Correlation spectra can be calculated as a ratio of these two components. A model of the dual-beam cross-correlation spectrometer is presented and subsequently validated with experimental observations of Venus. Radial velocity accuracies, as calculated against reference ephemerides, yielded an absolute error less than 0.24%.

Self-referenced multiple-beam interferometric method for robust phase calibration of spatial light modulator.

Phase-only liquid crystal spatial light modulator has wide ranging applications that require accurate phase retardance. The phase calibration of the spatial light modulator is therefore of vital importance. Available self-referenced calibration methods face the challenges of high time consumption, low efficiency, and low stability against the conditions. A self-referenced multiple-beam interferometric method is proposed to derive the global grayscale-phase response. As is presented theoretically and experimentally, the proposed method reduces the measuring time and improves the calibration efficiency by encoding multiple fringes in a single hologram. Results also show that the method is equally accurate when compared with traditional two-beam interferometric method, whereas providing a greater robustness against measuring errors since the standard deviation is only 56% of that of the traditional method.

Partially coherent Bessel vortex superposition with linear charge increase and aligned maxima

In this paper, the generation of a partially coherent optical vortex composed of the incoherent superposition of N coaxial Bessel vortex beams with linearly increasing topological charges and aligned intensity maxima is proposed. To generate this beam, concentric ring slits with increasing topological charges and random phase shifts are optically Fourier transformed. The radii of the ring slits are chosen in such a way that the maxima of their corresponding Bessel functions are coincident. It is demonstrated that the resulting beam radius is independent of the topological charges involved in the superposition and the beam is propagation invariant. The Bessel vortex addition is experimentally generated by means of a phase-only liquid crystal spatial light modulator.