Reflective Spatial Light Modulator Research Articles

Scanless multitarget-matching multiphoton excitation fluorescence microscopy

Using the combination of a reflective blazed grating and a reflective phase-only diffractive spatial light modulator (SLM), scanless multitarget-matching multiphoton excitation fluorescence microscopy (SMTM-MPM) was achieved. The SLM shaped an incoming mode-locked, near-infrared Ti:sapphire laser beam into an excitation pattern with addressable shapes and sizes that matched the samples of interest in the field of view. Temporal and spatial focusing were simultaneously realized by combining an objective lens and a blazed grating. The fluorescence signal from illuminated areas was recorded by a two-dimensional sCMOS camera. Compared with a conventional temporal focusing multiphoton microscope, our microscope achieved effective use of the laser power and decreased photodamage with higher axial resolution.

Flexible and high-efficiency generation of arbitrary vector vortex beams on hybrid-order Poincaré sphere

We propose theoretically and verify experimentally a compact optical configuration to directly generate arbitrary vector vortex beams on a hybrid-order Poincare sphere with good flexibility and high efficiency based on a reflective phase-only liquid crystal spatial light modulator (LC-SLM). The conversion system, consisting of an LC-SLM and a quarter-wave plate, can be considered a flexible dielectric metasurface to simultaneously modulate inhomogeneous polarization and helical phase-front. This approach has some advantages, including a simple experimental setup, good flexibility, and high efficiency. Orthogonally polarized modes alignment and an explicit superposition existing in the conventional method are not necessary in the proposed method, which exhibits potential applications in many advanced domains.

Fabrication of optical vortex lattices based on holographic polymer-dispersed liquid crystal films.

This Letter demonstrates optical vortex lattices based on holographic polymer-dispersed liquid crystal (HPDLC) films. The fabrication method uses a phase-only reflective spatial light modulator with numerically calculated phase profiles loaded on it to simplify multi-helical-wave interference. The beam profiles of the diffraction beams are simulated using the Fourier transform and compared with experimental results. The topological charges of the 1st-order diffraction beams reconstructed from the HPDLC films are examined using a Michelson interferometer.

Generation of elliptical and circular vector hollow beams with different polarizations by a Mach–Zehnder-type optical path

We present an experimental approach to convert linearly polarized Gaussian beams into elliptical and circular vector hollow beams (VHBs) with different polarization states. The scheme employed is based on a Mach–Zehnder-type optical path combined with a reflective spatial light modulator (SLM) in each path. The resulting VHBs have radial, azimuthal, and other polarization states. Our studies also show that the size of the generated VHBs remains constant during the propagation in free space over a certain distance, and can be controlled by the axial ratio of the SLM’s binary phase plate. These studies deliver great optical parameters and hold promising applications in the fields of optical trapping and manipulation of particles.

Nonsequential Speckle Reduction Method by Generating Uncorrelated Laser Subbeams With Equivalent Intensity Using a Reflective Spatial Light Modulator

Sequential speckle reduction methods demand the usage of fast modulators due to the short integration period of human eyes. Here, a nonsequential speckle reduction method by splitting one laser beam with short coherence length into uncorrelated laser subbeams (LSBs) is reported. In order to realize the most efficient speckle reduction, with the help of a polarization beam splitter, we have programmed a reflective spatial light modulator to make the LSBs intensities equivalent. Three uncorrelated LSBs with equivalent light intensity are designed to demonstrate this idea; the speckle contrast ratio is reduced to 0.55, which closes to the expected value of 0.58. This nonsequential speckle reduction method has no requirement of the modulators speed; thus, it has obvious merit comparing with the sequential speckle reduction methods.

High-efficiency and flexible generation of vector vortex optical fields by a reflective phase-only spatial light modulator.

The scheme for generating vector optical fields should have not only high efficiency but also flexibility for satisfying the requirements of various applications. However, in general, high efficiency and flexibility are not compatible. Here we present and experimentally demonstrate a solution to directly, flexibly, and efficiently generate vector vortex optical fields (VVOFs) with a reflective phase-only liquid crystal spatial light modulator (LC-SLM) based on optical birefringence of liquid crystal molecules. To generate the VVOFs, this approach needs in principle only a half-wave plate, an LC-SLM, and a quarter-wave plate. This approach has some advantages, including a simple experimental setup, good flexibility, and high efficiency, making the approach very promising in some applications when higher power is need. This approach has a generation efficiency of 44.0%, which is much higher than the 1.1% of the common path interferometric approach.

Full-color holographic 3D display using slice-based fractional Fourier transform combined with free-space Fresnel diffraction.

The fractional Fourier transform (FRT) has been used for computing holograms in holographic displays due to its continuity of describing wave diffraction in the near field and far field. In this study, we propose a method to realize a full-color holographic 3D display with combined use of the FRT and the free-space Fresnel diffraction. A slice-based optical configuration and the calculation algorithm of the FRT are proposed for generating phase-only holograms of full-color 3D objects. Sequential phase-only holograms are generated for reducing the speckle noise of reconstructed images by the time-averaging effect. Free-space Fresnel diffraction is used for 3D image reconstruction from the generated holograms. The relationship between the fractional orders of different color channels and the free-space Fresnel diffraction distance is analyzed. Chromatic aberrations caused by different wavelengths of RGB lasers are also compensated. A full-color holographic display system using a reflective phase-only spatial light modulator (SLM) is established. Both the numerical and optical reconstruction results demonstrate the feasibility of the proposed method.

Implementing focal-plane phase masks optimized for real telescope apertures with SLM-based digital adaptive coronagraphy.

Direct imaging of exoplanets or circumstellar disk material requires extreme contrast at the 10-6 to 10-12 levels at < 100 mas angular separation from the star. Focal-plane mask (FPM) coronagraphic imaging has played a key role in this field, taking advantage of progress in Adaptive Optics on ground-based 8 + m class telescopes. However, large telescope entrance pupils usually consist of complex, sometimes segmented, non-ideal apertures, which include a central obstruction for the secondary mirror and its support structure. In practice, this negatively impacts wavefront quality and coronagraphic performance, in terms of achievable contrast and inner working angle. Recent theoretical works on structured darkness have shown that solutions for FPM phase profiles, optimized for non-ideal apertures, can be numerically derived. Here we present and discuss a first experimental validation of this concept, using reflective liquid crystal spatial light modulators as adaptive FPM coronagraphs.

46‐1: Dual‐layer High Dynamic Range Head Mounted Display

In this paper, a high dynamic range (HDR) head mounted display system using a dual‐layer modulation configuration was proposed. By using two reflective spatial light modulators simultaneously, we demonstrated the ability to achieve an HDR head mounted display with a contrast ratio as high as 60000:1.

Experimental demonstration of square Fresnel zone plate with chiral side lobes.

In this study, we introduce what we believe is a novel holographic optical element called a chiral square Fresnel zone plate (CSFZP). The chirality is imposed on a square Fresnel zone plate (SFZP) using a nonclassical technique by rotating the half-period zones relative to one another. The rotation of the half-period zones, in turn, twists the side lobes of the diffraction pattern without altering the focusing properties inherent to a SFZP. As a consequence, the beam profile is hybrid, consisting of a strong central Gaussian focal spot with gradient force similar to that generated by a lens and twisted side lobes with orbital angular momentum. The optical fields at the focal plane were calculated and found to possess a whirlpool-phase profile and a twisted intensity profile. Analysis of the field variation along the direction of propagation revealed a spiraling phase and amplitude distribution. Poynting vector plot of the fields revealed the presence of angular momentum in the regions of chiral side lobes. The phase of the CSFZPs were displayed on a phase-only reflective spatial light modulator and illuminated using a laser. The intensity patterns recorded in the experiment match the calculated ones, with a strong central focal spot and twisted side lobes. The beam pattern was implemented in an optical trapping experiment and was found to possess particle trapping capabilities.

Design and demonstration of a foveated imaging system with reflective spatial light modulator

In this paper, a foveated imaging system using a reflective liquid crystal spatial light modulator (SLM) was designed. To demonstrate the concept of foveated imaging, we simulated with software Code V and established a laboratory prototype. The result of the experiment shows that an SLM can be used to correct the aberration of region of interest (ROI) while the resolution of other area was still very low. The vary-resolution system was relative simple compared to the traditional high resolution system and obviously can reduce the amount of data transmission. Such systems will have wide application prospect in various fields.

Engineering of cylindrical vector fields with a twisted nematic spatial light modulator

We demonstrate a technique for the generation of vectorial optical fields based on a single pass of light onto a reflective twisted nematic spatial light modulator (TN-SLM). Using a beam splitter and a quarter-wave plate, a polarization rotator is implemented. A curve of the behavior of this polarization rotator with the twisted nematic modulator in use proves a modulation up to 177 deg, making this setup suitable for engineering of cylindrical vector fields. A mathematical justification and an experimental demonstration of the generation of these beams and their quality are presented. The experimental results show that despite the presence of a small component of elliptical polarization, a twisted nematic modulator can be used to achieve local polarization control. A series of vector fields with variations of the parameters of topological charge, phase offset, and quadratic phase are engineered, analyzed with a linear polarizer, and captured. The proposed setup represents a simple approach for polarization manipulation using a TN-SLM and few optical elements, achieving polarization purity greater than 94%.

A Phase-coded Aperture Camera with Programmable Optics

We propose a novel computational imaging system that enables the generation of Point Spread Functions (PSFs) of userspecified geometry. Key ingredient of our system is a phase-coded aperture which manipulates the phase distribution of the pupil function by inserting a phase modulator. We use a reflective phaseonly liquid crystal-based Spatial Light Modulator (SLM) for phase modulation. Via encoding a grayscale image on the SLM, the refractive index of each cell can be altered. Phase patterns of PSFs with different shapes are optimized by the Gerchberg-Saxton algorithm. A number of non-trivial, complex shaped PSFs has been captured. We further demonstrate how such a system can realize refocusing through encoding a Fresnel lens phase pattern to shift the focal plane.

Compact and high-resolution optical orbital angular momentum sorter

A compact and high-resolution optical orbital angular momentum (OAM) sorter is proposed and demonstrated. The sorter comprises a quadratic fan-out mapper and a dual-phase corrector positioned in the pupil plane and the Fourier plane, respectively. The optical system is greatly simplified compared to previous demonstrations of OAM sorting, and the performance in resolution and efficiency is maintained. A folded configuration is set up using a single reflective spatial light modulator (SLM) to demonstrate the validity of the scheme. The two phase elements are implemented on the left and right halves of the SLM and connected by a right-angle prism. Experimental results demonstrate the high resolution of the compact OAM sorter, and the current limit in efficiency can be overcome by replacing with transmissive SLMs and removing the beam splitters. This novel scheme paves the way for the miniaturization and integration of high-resolution OAM sorters.

Creation of radially polarized optical fields with multiple controllable parameters using a vectorial optical field generator

A vectorial optical field generator (VOF-Gen) based on two reflective phase-only liquid crystal spatial light modulators enables the creation of an arbitrary optical complex field. In this work, the capabilities of the VOF-Gen in terms of manipulating the spatial distributions of phase, amplitude, and polarization are experimentally demonstrated by generating a radially polarized optical field consisted of five annular rings, the focusing properties of which are also numerically studied with vectorial diffraction theory. By carefully adjusting the relative amplitude and phase between the adjacent rings, an optical needle field with purely longitudinal polarization can be produced in the focal region of a high numerical aperture lens. The versatile method presented in this work can be easily extended to the generation of a vectorial optical field with any desired complex distributions.

Testing vision with angular and radial multifocal designs using Adaptive Optics

Multifocal vision corrections are increasingly used solutions for presbyopia. In the current study we have evaluated, optically and psychophysically, the quality provided by multizone radial and angular segmented phase designs. Optical and relative visual quality were evaluated using 8 subjects, testing 6 phase designs. Optical quality was evaluated by means of Visual Strehl-based-metrics (VS). The relative visual quality across designs was obtained through a psychophysical paradigm in which images viewed through 210 pairs of phase patterns were perceptually judged. A custom-developed Adaptive Optics (AO) system, including a Hartmann-Shack sensor and an electromagnetic deformable mirror, to measure and correct the eye’s aberrations, and a phase-only reflective Spatial Light Modulator, to simulate the phase designs, was developed for this study. The multizone segmented phase designs had 2–4 zones of progressive power (0 to +3D) in either radial or angular distributions. The response of an “ideal observer” purely responding on optical grounds to the same psychophysical test performed on subjects was calculated from the VS curves, and compared with the relative visual quality results. Optical and psychophysical pattern-comparison tests showed that while 2-zone segmented designs (angular & radial) provided better performance for far and near vision, 3- and 4-zone segmented angular designs performed better for intermediate vision. AO-correction of natural aberrations of the subjects modified the response for the different subjects but general trends remained. The differences in perceived quality across the different multifocal patterns are, in a large extent, explained by optical factors. AO is an excellent tool to simulate multifocal refractions before they are manufactured or delivered to the patient, and to assess the effects of the native optics to their performance.

Flatness parameter influence on scintillation reduction for multi-Gaussian Schell-model beams propagating in turbulent air.

Reduction in the scintillation index of multi-Gaussian Schell-model beams propagating in turbulent air is demonstrated as a function of two source parameters: the r.m.s. coherence width and the summation index. The beams were generated with the help of a nematic phase-only, reflective spatial light modulator at a cycling rate of 333 frames per second and recorded after propagating through a weakly turbulent air channel over a distance of 70m. Experimental results are in good agreement with theory.

Nonbulk motion system for simultaneously measuring the refractive index and thickness of a sample using tunable optics and spatial signal processing-based Gaussian beam imaging.

This paper presents a novel approach to simultaneously measuring the thickness and refractive index of a sample. The design uses an electronically controlled tunable lens (ECTL) and a microelectromechanical-system-based digital micromirror device (DMD). The method achieves the desired results by using the DMD to characterize the spatial profile of a Gaussian laser beam at different focal length settings of the ECTL. The ECTL achieves tunable lensing through minimal motion of liquid inside a transparent casing, whereas the DMD contains an array of movable micromirrors, which make it a reflective spatial light modulator. As the proposed system uses an ECTL, a DMD, and other fixed optical components, it measures the thickness and refractive index without requiring any motion of bulk components such as translational and rotational stages. A motion-free system improves measurement repeatability and reliability. Moreover, the measurement of sample thickness and refractive index can be completely automated because the ECTL and DMD are controlled through digital signals. We develop and discuss the theory in detail to explain the measurement methodology of the proposed system and present results from experiments performed to verify the working principle of the method. Refractive index measurement accuracies of 0.22% and 0.2% were achieved for two BK-7 glass samples used, and the thicknesses of the two samples were measured with a 0.1mm accuracy for each sample, corresponding to a 0.39% and 0.78% measurement error, respectively, for the aforementioned samples.

Electrically actuated phase-change pixels for transmissive and reflective spatial light modulators in the near and mid infrared.

Transmissive and reflective spatial light modulators have been designed and simulated for the 1.55 to 2.10 μm spectral region. An electrically actuated layer of phase-change material (PCM) was employed as the electro-optical medium for two-state self-holding "light-to-dark" intensity modulation of free-space light beams. The PCM was sandwiched between transparent conductive N-doped Si or indium tin oxide contact layers in a simple planar structure. A 100 to 500 nm PCM layer of Ge2Sb2Te5 (GST) was employed for optimum performance at 1.55 μm where the transmissive-modulator insertion loss was around 4.5 dB. The GST light-dark contrast was found to be 32 dB. For the GST reflection device, an included metal film (Ag) improved the 1.55 μm performance metrics to 0.7 dB of insertion loss with a contrast around 26 dB. The calculated performance for both types of spatial light modulators was robust to changes in the input incidence angle near normal incidence. Applications include infrared scene generation and signal processing.

Design of dually foveated imaging optical system

With the advances in technology, how to solve the problem of contradiction between the large field of view and high resolution of images becomes one of the research focus of many scientific researchers. In this paper we present the concept of dually foveated imaging optical system, based on the traditional singly foveated imaging system which simulates the human eye, by introducing a reflective liquid crystal spatial light modulator for modulating the aberrations of two fields of a view, so improving the corresponding aberrations and achieving high-resolution image of the two different fields of view, while the remaining fields of the view are of low-resolution image. In this way it can solve the contradiction between the large field of view and high resolution image. In this paper, we design a dually foveated imaging optical system with the following parameters: reference wavelength is 587 nm, the field of view is 60° (i.e., ± 30°), F/8, the focal length is 60 mm. Simulation is conducted by CODE V, achieving a 5° and 17° dual field high-resolution image, and the remaining field being of low-resolution image; and calculation shows the high diffraction efficiency of the system with sampling resolution of 32 × 32, verifying the scientificness and accuracy of the design method.