Liquid Crystal Spatial Light Modulator Research Articles

Experimental study on phase conjecture based on two-dimensional image and carrying three-dimensional image with mist in electro-holographic reconstruction

A method is proposed for phase conjecture based on the intensity curve of a two-dimensional (2D) image by computing a polynomial equation. The intensity values of the 2D image, which represents the distance between the image detectors and the three-dimensional (3D) scene is converted to phase information by our method. The results of numerical calculation with phase conjecture are analyzed. And what’s more, the numerical reconstruction results with phase information obtained as initial phase factors of a complex object for Fresnel kinoform and dynamic pseudorandom-phase tomographic computer holography(DPP-TCH) are compared. The peak signal-to-noise ratio (PSNR) and correlation coefficient (CC) between the reconstructed images and original object are analyzed. An experimental system is designed for photoelectric holographic reconstruction based on phase-only liquid crystal spatial light modulator (LC-SLM) and mist screen. The electro-optical experimental results indicate that suppressed the speckle noise 3D images that can be observed with naked eye have been obtained.

Fast testing of partial camera lenses based on a liquid crystal spatial light modulator.

Today, there are strict requirements for the quality inspection of mobile phone cameras, as the design tolerance is getting critically tighter. In order to avoid unnecessary disposal of lens components when testing and assembling the complete cameras, testing the quality of each single lens group in advance before the final assembly is effective. However, as part of a whole camera, a single lens group cannot generate a sharp image independently; it needs to be combined with other elements in the testing system and assembled precisely. In order to address this challenge, we propose a fast testing method based on spatial light modulators (SLMs). By taking advantage of the programmable feature of the SLM, the assembly misalignments caused by fixing the lens group to be tested into the testing system are dynamically scanned and compensated at a fast speed. A design criterion of the phase map pattern to be loaded on the SLM is also verified by simulation and is applied on the testing system. In this way, the proposed method significantly reduces the positioning requirement of the lens under test, and thus improves efficiency. The passed yield of tested lens groups reaches 92.6%.

Holographic Tailoring of Structured Light Field with Digital Device

Structured light fields have attracted much attention due to rich spatial degrees of freedom. The tailoring of an arbitrary structured light field on demand is the precondition for the application of structured light. Therefore, the computer holography method used to reconstruct a coherent light field wavefront has been naturally applied for generating structured light. In this work, we comprehensively demonstrate the principles and procedures of pure-phase computer-generated holography (PP-CGH) and binary-amplitude computer-generated holography (BA-CGH) methods for tailoring structured light, realized by two digitally programmable devices: liquid-crystal spatial light modulators (Lc-SLM) and digital micromirror devices (DMD), respectively. Moreover, we first compare the two approaches in detail and clarify the recipe to obtain a high tailoring accuracy and efficiency, which will help researchers to better understand and utilize the holographic tailoring of structured optical fields.

Correction of Distorted Wavefront Using Dual Liquid Crystal Spatial Light Modulators

In space optical communication, owing to the influence of atmospheric turbulence, optical beams lose focus and become phase-distorted, which reduces the communication quality. Considering the polarization dependence of liquid crystal spatial light modulators and the dispersion effect of liquid crystal materials, the energy utilization rate of liquid crystal adaptive optics systems is low. In this study, a dual liquid crystal spatial light modulator adaptive optics system based on the GS algorithm is used to correct the wavefront distortion of a signal beam under different atmospheric turbulence intensities, and the Strehl ratio (SR) is used as the evaluation index. The simulation results show that the SR of the corrected system can be increased from 0.23, 0.41, and 0.72 to 0.77, 0.89, and 0.95, respectively. The corrected beam spot was more concentrated and the light intensity at the center of the beam spot was stronger. The experimental results show that, after the distortion wavefront is corrected by the dual liquid crystal spatial light modulator, the average gray value of the 10 × 10 pixels in the center of the spot increases from 159.3, 113.1, and 58.4 to 253.4, 247.7, and 198.3, respectively.

Sign-singularity solution in single-frame speckle interferometry with vortex-phase modulation

We propose a sign-singularity solution in single-shot digital speckle interferometry based on vortex-phase modulation. The vortex phase is introduced through the reference beam as variation information by a reflective liquid crystal spatial light modulator. The sign singularity is eliminated with the help of a single spiral speckle fringe pattern. To effectively obtain the deformation phase, the measurement process is specially designed on the consideration of the modulation principle of the vortex phase, which is discussed in terms of theoretical analysis and simulation results. Experiments on out-of-plane deformation measurement reveal the feasibility of the proposed method and suggest the potential in actual dynamic measurement applications.

Calibration of phase-only liquid-crystal spatial light modulators by diffractogram analysis

Phase-only spatial light modulator (SLM) is a key device for light manipulation. It is critical to calibrate the grayscale-phase response to the driving voltage of SLM, namely the look-up table (LUT), before use. The conventional calibration methods, which rely on interference, diffraction, or polarization to extract the phase, require extra optical devices and are sensitive to mechanical vibration, air turbulence, and systematic aberrations. To overcome these shortcomings, here we develop a novel method, which is based on the diffractogram analysis. By analyzing the intensity distribution of the diffractogram as a function of the specific SLM hologram, we identify both the global and the localized LUTs of SLM at high accuracy. Compared with the other ones, our method allows in-situ SLM calibration and is more tolerant to the exogenous factors.

Liquid crystal spatial light modulator based non-mechanical beam steering system fractional-order model.

The liquid crystal spatial light modulator (LCSLM) is an optical device that can realise non-mechanical beam scanning. However, the traditional integer-order model cannot adequately characterise the dynamic performance of LCSLM beam steering because of the viscoelasticity of liquid crystals. This paper uses the memory characteristics of fractional calculus to construct a fractional constitutive equation for liquid crystals. Combining this equation with the LCSLM beam steering principle, a fractional-order model of the beam steering system is established, and the Legendre wavelet integration operational matrix method is used to estimate the model parameters. In addition, we established a test platform for the dynamic characteristics of LCSLM beam steering system and verified the effectiveness of the established model through experiments. The fitting effects of the integer-order and fractional-order models are compared, and the influence of different model orders on the dynamic performance of beam steering is analysed. Experimental results show that the fractional-order model can accurately describe the dynamic process of beam steering, and this model can be applied to the study of LCSLM-based two-dimensional non-mechanical beam steering control strategies to achieve fast, accurate, and stable beam scanning.

Optical Drills by Dynamic High-Order Bessel Beam Mixing

One of the key trends in laser material processing is the usage of structured laser beams. Collimated and focused Gaussian beams are the most common tools; however, more exotic beams can be beneficial too. For instance, Bessel beams with elongated focal area and self-healing properties, or vortex beams with helical wave fronts and a dark area along the optical axis are being increasingly used. Here, we propose and experimentally demonstrate dynamical ``optical drill'' beams presenting nonstationary intensity distributions that resemble a spinning mechanical drill. Optical drills appear as the spatiotemporal interference of two Bessel-vortex beams of different topological charges and different carrier frequencies. By mixing a pair of high-order Bessel beams, synthesized using a liquid crystal spatial light modulator, optical drills of tuned helicities are experimentally observed, and the simplest cases of matter processing (fluorescence) with such beams are demonstrated. Optical drill beams are expected to be useful in material processing by light or in cell and particle manipulation in biomedical applications.

Combined Jones–Stokes Polarimetry and Its Decomposition into Associated Anisotropic Characteristics of Spatial Light Modulator

Jones–Stokes polarimetry is a robust in vitro polarimetric technique that can be used to investigate the anisotropic properties of a birefringent medium. The study of spatially resolved Jones matrix components of an object is a heuristic approach to extract its phase and polarization information. However, direct interpretation of Jones matrix elements and their decomposition into associated anisotropic properties of a sample is still a challenging research problem that needs to be investigated. In this paper, we experimentally demonstrate combined Jones–Stokes polarimetry to investigate the amplitude, phase, and polarization modulation characteristics of a twisted nematic liquid crystal spatial light modulator (TNLC-SLM). The anisotropic response of the SLM is calibrated for its entire grayscale range. We determine the inevitable anisotropic properties viz., diattenuation, retardance, isotropic absorption, birefringence, and dichroism, which are retrieved from the measured Jones matrices of the SLM using Jones polar decomposition and a novel algebraic approach for Jones matrix decomposition. The results of this study provide a complete polarimetric calibration of the SLM within the framework of its anisotropic characteristics.

Efficient wavefront sensorless adaptive optics based on large dynamic crosstalk-free holographic modal wavefront sensing.

The correction of wavefront sensorless adaptive optics (WFSless AO) can be significantly accelerated by using a holographic modal wavefront sensor (HMWFS). The HMWFS is realized by a computer-generated hologram (CGH) into which all aberration modes to be detected are encoded and only a single-shot image is required for simultaneous measurement of multiple modes. The conventional HMWFS suffers from a quite limited dynamic range and severe inter-modal crosstalk which deteriorates the sensing accuracy. We proposed a novel HMWFS with a large dynamic range and no crosstalk and validated its performance by simulation and experiment. In the improved HMWFS scheme, the aberration is represented by Lukosz modes whose gradients are orthogonal and the modal coefficients can be estimated independently. Instead of using a binary CGH in conventional HMWFS, a kinoform CGH with high diffraction efficiency is adopted in the improved HMWFS. The kinoform CGH is produced by a phase-only liquid-crystal spatial light modulator (LCSLM) which also serves as a wavefront corrector in our WFSless AO system.

Two-Wavelength Computational Holography for Aberration-Corrected Simultaneous Optogenetic Stimulation and Inhibition of In Vitro Biological Samples

Optogenetics is a versatile toolset for the functional investigation of excitable cells such as neurons and cardiomyocytes in vivo and in vitro. While monochromatic illumination of these cells for either stimulation or inhibition already enables a wide range of studies, the combination of activation and silencing in one setup facilitates new experimental interrogation protocols. In this work, we present a setup for the simultaneous holographic stimulation and inhibition of multiple cells in vitro. The system is based on two fast ferroelectric liquid crystal spatial light modulators with frame rates of up to 1.7 kHz. Thereby, we are able to illuminate up to about 50 single spots with better than cellular resolution and without crosstalk, perfectly suited for refined network analysis schemes. System-inherent aberrations are corrected by applying an iterative optimization scheme based on Zernike polynomials. These are superposed on the same spatial light modulators that display the pattern-generating holograms, hence no further adaptive optical elements are needed for aberration correction. A near-diffraction-limited spatial resolution is achieved over the whole field of view, enabling subcellular optogenetic experiments by just choosing an appropriate microscope objective. The setup can pave the way for a multitude of optogenetic experiments, in particular with cardiomyocytes and neural networks.

Single Beam Measurements of a Sony SVGA Liquid Crystal Spatial light modulator

In this work, non-linear optical properties of a Sony SVGA liquid crystal spatial light modulator sample are estimated by utilizing a single beam Z-scan technique with He-Ne laser at 632.8 nm. It was found that the magnitude of non-linear refractive index (NLR) is (0.694×10-7 cm2/mW) with a positive signal, demonstrates a self-focusing phenomenon, while the magnitude of non-linear absorption (NLA) for this sample is (0.0101×10-1 cm/mW), the pure magnitude of the NLR is (0.138×10-5 cm2/mW). These results are compared with past investigations in various liquid crystals types. The obtained results showed that the sample have a high ability of originating optical limiters, switches, and modulation gadgets.

Optimal trap velocity in a dynamic holographic optical trap using a nematic liquid crystal spatial light modulator

A dynamic holographic optical trap uses a dynamic diffractive optical element such as a liquid crystal spatial light modulator to realize one or more optical traps with independent controls. Such holographic optical traps provide a number of flexibilities and conveniences useful in various applications. One key requirement for such a trap is the ability to move the trapped microscopic object from one point to the other with the optimal velocity. In this paper we develop a nematic liquid crystal spatial light modulator based holographic optical trap and experimentally investigate the optimal velocity feasible for trapped beads of different sizes, in such a trap. Our results show that the achievable velocity of the trapped bead is a function of size of the bead, step size, interval between two steps and power carried by the laser beam. We observe that the refresh rate of a nematic liquid crystal spatial light modulator is sufficient to achieve an optimal velocity approaching the theoretical limit in the respective holographic trap for beads with radius larger than the wavelength of light.

High-Precision Calibration of Phase-Only Spatial Light Modulators

In the fields of optics and photonics, phase-only spatial light modulators (SLMs) play an increasingly important role in wave-front engineering. However, the SLMs are subject to wavefront distortion arising from the imperfection in the birefringence effect and physical structure of modulators. This paper presents a simple self-interference phase calibration method applicable to liquid-crystal SLM. We build an interferometric imaging system based on the Pancharatnam phase-shifting to measure the phase distribution of a light beam coming from SLMs. Two types of phase modulation errors of SLMs can be characterized in the measurement process: the erroneous gamma curve and shape aberration. The former belongs to dynamic phase distortion and is measured through a four-step Pancharatnam phase-shifting interference, which allows a one-shot recording of interference pattern via a polarization camera; the latter represents static phase distortion and is extracted from the interference between light waves coming from different regions of the SLM panel by using Zernike polynomial fitting. Our method has the advantages of high-precision pixel-wise phase correction and robustness against environmental disturbance and thus can facilitate the applications of SLM in optical field manipulation.

High laser damage threshold reflective optically addressed liquid crystal light valve based on gallium nitride conductive electrodes

Abstract In this paper, the feasibility of a high laser damage threshold liquid crystal spatial light modulator based on gallium nitride (GaN) transparent conductive electrodes is proved. The laser-induced damage threshold (LIDT) is measured, and a high LIDT reflective optically addressed liquid crystal light valve (OALCLV) based on GaN is designed and fabricated. The proper work mode of the OALCLV is determined; the OALCLV obtained a maximum reflectivity of about 55% and an on–off ratio of 55:1, and an image response is demonstrated.

Laser beam scatter angle control technology based on liquid crystal spatial light modulator

Laser beam scatter angle control technology based on liquid crystal spatial light modulator

Optimization method of diffraction efficiency of liquid crystal spatial light modulator based on spline interpolation

Optimization method of diffraction efficiency of liquid crystal spatial light modulator based on spline interpolation

Wave-front encoding method of computer-generated holography based on liquid-crystal spatial light modulator

Wave-front encoding method of computer-generated holography based on liquid-crystal spatial light modulator

LCOS Spatial Light Modulator for Digital Holography

Liquid crystal on silicon (LCOS) spatial light modulator (SLM) is the most widely used optical engine for digital holography. This paper aims to provide an overview of the applications of phase-only LCOS in two-dimensional (2D) holography. It begins with a brief introduction to the holography theory along with its development trajectory, followed by the fundamental operating principle of phase-only LCOS SLMs. Hardware performance of LCOS SLMs (in terms of frame rate, phase linearity and flicker) and related experimental results are presented. Finally, potential improvements and applications are discussed for futuristic holographic displays. Full Text: PDF ReferencesM. Wolfke, Physikalische Zeitschrift 21, 495 (1920). DirectLink D. Gabor, "A New Microscopic Principle", Nature 161, 777 (1948). CrossRef H. Haken, "Laser Theory", Light and Matter 5, 14 (1970). CrossRef S. Benton, "Selected Papers on Three-dimensional displays", SPIE Press (2001). DirectLink X. 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Enhancement of wavefront measurement sensitivity in a zonal wavefront sensor without curtailing the sensing speed

In this paper we propose a zonal wavefront sensing scheme that facilitates wavefront measurement with enhanced sensitivity at the standard video rate. We achieve this enhanced sensitivity by implementing a sequential display of binary holograms described over each zone sampling the incident wavefront with the help of a ferroelectric liquid crystal spatial light modulator. By keeping the number of active zones as 24 and using a camera with an imaging frame rate equal to the binary hologram display rate of the spatial light modulator, we are able to reach a sensing frame rate of 60 Hz. In addition to enhanced sensitivity, the proposed scheme facilitates zone-wise tuning of binary holograms and eliminates the possibility of any crosstalk between adjacent zones. We perform a proof-of-principle experiment that validates the proposed zonal wavefront sensing scheme and demonstrates its advantages.