Showing papers on "Spatial light modulator published in 2000"

Two-dimensional polarization encoding with a phase-only liquid-crystal spatial light modulator

Abstract: We show how to two dimensionally encode the polarization state of an incident light beam using a parallel-aligned liquid-crystal spatial light modulator (LCSLM). Each pixel of the LCSLM acts as a voltage-controlled wave plate and can be programmed over a 2pi phase range at a wavelength of 514.5 nm. Techniques are reviewed for either rotating the major axis of elliptically polarized light or for converting an input linearly polarized beam into an arbitrary elliptically polarized beam. Experimental results are demonstrated in which we generate various two-dimensional spatial patterns of polarized light. Several potential applications are suggested. We also report an unexpected edge-enhancement effect that might be useful in image processing applications.

Holographic optical switching: the "ROSES" demonstrator

Abstract: The design, assembly, and performance of a prototype 1/spl times/8 free-space switch demonstrator using reconfigurable holograms are reported. Central to the switch fabric is a ferroelectric liquid crystal (FLC) on silicon spatial light modulator (SLM) deposited with a 540/spl times/1 array of highly reflective and planar mirror strips. The input and output ports of the switch are fabricated as a linear array of silica planar waveguides connected to single-mode fibers, and the holographic beam-steerer operates without the need for adjustment or dynamic alignment. The waveguide array and the single Fourier transform lens for the 2f holographic replay system are housed in an opto-mechanical mount to provide stability. The switch operates at 1.55 /spl mu/m wavelength and has a designed optical bandwidth of >60 nm. The first measured insertion loss and crosstalk figures are 16.9 dB and -19.1 dB, respectively. Improvements in SLM performance, the use of new addressing schemes and the introduction of better alignment techniques are expected to improve these figures considerably. The preliminary performance of a 3/spl times/3 optical crossconnect is also presented to show that this technology is scalable to N/spl times/N switching fabrics.

A low cost adaptive optics system using a membrane mirror

Abstract: A low cost adaptive optics system constructed almost entirely of commercially available components is presented. The system uses a 37 actuator membrane mirror and operates at frame rates up to 800Hz using a single processor. Numerical modelling of the membrane mirror is used to optimize parameters of the system. The dynamic performance of the system is investigated in detail using a diffractive wavefront generator based on a ferroelectric spatial light modulator. This is used to produce wavefronts with time-varying aberrations. The ability of the system to correct for Kolmogorov turbulence with different strengths and effective wind speeds is measured experimentally using the wavefront generator.

Spatial light modulator with conformal grating device

Abstract: A mechanical grating device for modulating an incident beam of light by diffraction includes an elongated element including a light reflective surface; a pair of end supports for supporting the elongated element at both ends over a substrate; at least one intermediate support between the end supports; and means for applying a force to the elongated element to cause the element to deform between first and second operating states

Method and apparatus for creating three-dimensional objects by cross-sectional lithography

Abstract: A method and apparatus for creating a three-dimensional object by generating a cross-sectional pattern of energy of an object to be formed at a selected surface of a medium capable of altering its physical state in response to the energy projected or transmitted onto the selected layer. By impinging radiation, particle bombardment, or chemical reaction by a method controlled by a spatial light modulator, successive adjacent cross-sections of the object are rapidly formed and integrated together to provide a step-wise laminar build-up of the desired object creating a three dimensional manifestation from bitmap images of a series of cross-sections of a computer generated model.

Optimal control of one- and two-photon transitions with shaped femtosecond pulses and feedback

Abstract: This paper reports two pump–probe experiments in sodium where dynamically tailored ultrashort pulses from a Ti:Sapphire-pumped optical parametric amplifier were employed The first study focuses on the one-photon Na(3s→3p) transition to derive sensitive criteria which judge the performance of a frequency-domain pulse shaper using a spatial light modulator On the basis of the interpretation, follow-up experiments are suggested to test their cogency The second experiment uses coherent quantum control by placing an appropriate phase distribution on the incident beam to enhance or cancel the transition probability in the nonresonant two-photon process Na(3s→→5s) Ignorant of the “ideal” phase function, an evolutionary algorithm which uses a feedback derived from the experiment performs the optimization and produces the desired bright or dark pulses within a few minutes Attention is given to the role of resonant 3s→3p transitions excited by the spectral wings of the pump pulse Different parametrizations of the phase distribution have been examined Two of these produced solutions which had not previously been predicted by theory still meet the objective of the experiment The study represents the first successful application of a feedback-organized self-learning algorithm to the design of dark pulses

Realization of the Hadamard Multiplex Advantage Using a Programmable Optical Mask in a Dispersive Flat-Field Near-Infrared Spectrometer:

Abstract: Spectrometry and hyperspectral imaging are finding numerous applications for micro-optoelectromechanical systems (MOEMS). A type of MOEMS device in the form of a digital micromirror array (DMA) has been made commercially available by Texas Instruments USA for projector display applications. We use this device as a spatial light modulator (SLM) in a new type of flat-field, near-infrared dispersive spectrometer (NIRDMAS). Attributes of the DMA used in this manner are presented for discussion. Features that make a DMA attractive for spectrometry and imaging are described. A brief introduction to Hadamard transform (HT) techniques is presented to show that the DMA may be the best Hadamard encoding mask yet developed. A comparison of a conventional raster scanning (CRS) scan and a Hadamard transform spectrometry (HTS) scan with respect to the Hadamard multiplex advantage using a nonphoton noise-limited, single-element detector is presented. A signal-to-noise ratio comparison using four spectral lines from a mercury-argon calibration lamp demonstrates that the theoretical noise reduction is approached for the HTS scan compared to the CRS scan. Some future applications of MOEMS in spectrometry and hyperspectral imaging are suggested.

Monochrome and color digital display systems and methods

Abstract: Methods and apparatus for producing a pulse-width-modulated (PWM) grayscale or color image using a binary spatial light modulator By staggering and re-quantizing the PWM intervals to a clock of a period based on the frame time divided by number of rows in the display, the system's peak bandwidth requirements are optimized for displays of arbitrary resolution and arbitrary choice of PWM waveform Additionally, a gating circuit increases the optical efficiency of a spatial light modulator using this PWM method in a field-sequential color system by reducing the duration of the blanking period between color fields

Methods and apparatus for imaging using a light guide bundle and a spatial light modulator

Abstract: Endoscopes and other viewing devices that control the light that contacts a sample and/or that is detected emanating from a sample. The viewing devices are particularly well suited for in vivo imaging, although other uses are also included. The viewing devices, and methods related thereto, comprise a spatial light modulator in the illumination and/or detection light path so that light transmitted to the target via a bundle of light guides or optical system is transmitted substantially only into the cores of the light guide bundle and not into the cladding surrounding the light guides, filler between the light guides in the bundle, or undesired light guides. Also, methods and apparatus for mapping the pixels of the spatial light modulator to the cores of the light guides in the bundle (preferably at least 3 pixels (e.g., at least 3 mirrors for a digital micromirror device) for each core), as well as for mapping the light guides of one light guide bundle to another.

Closed-loop aberration correction by use of a modal Zernike wave-front sensor

Abstract: We describe the practical implementation of a closed-loop adaptive-optics system incorporating a novel modal wave-front sensor. The sensor consists of a static binary-phase computer-generated holographic element, which generates a pattern of spots in a detector plane. Intensity differences between symmetric pairs of these spots give a direct measure of the Zernike mode amplitudes that are present in the input wave front. We use a ferroelectric liquid-crystal spatial light modulator in conjunction with a 4–f system and a spatial filter as a wave-front correction element. We present results showing a rapid increase in Strehl ratio and focal spot quality as the system corrects for deliberately introduced aberrations.

Authentication system and method

Abstract: An authentication system using a correlator that correlates an input with a reference wherein at least one of the input and reference comprises a phase volume mask having structures, preferably points, that are each less than about six microns in size and can have an aspect ratio (AR) greater than 1:1 so as to produce a phase encoded random pattern having millions of combinations in a mask that is as small as one square millimeter. The random pattern can be convolved with a second pattern, such as a biometric pattern, to produce a phase convolved mask. The correlator preferably is a nonlinear joint transform correlator that can use “chirp” encoding to permit the input to be located in a different plane than the reference. The correlator optically Fourier transforms images of the reference and input that are thereafter nonlinearly transformed and inverse Fourier transformed by a processor to determine the presence or absence of a correlation spike indicative of authenticity. A spatial light modulator (SLM) can be used as an input or reference and preferably is a liquid crystal panel having pixels or elements whose phase or grey scale intensity can be selectively controlled by a processor. The SLM can be used to display a biometric pattern, preferably scanned in real time from a person, that is correlated against an input or reference that can comprise a label on a card, a tag, or another object.

Fiber-optic confocal microscopy using a spatial light modulator.

Abstract: We present a novel fiber-optic confocal microscope in which the scanning operation is achieved by use of a spatial light modulator (SLM) to sequentially illuminate individual fibers or patterns of multiple fibers. Experimental images are presented, and the optical-sectioning capability of the device is demonstrated. The novel SLM-based system is more optically efficient, achieves higher contrast, and has improved optical-sectioning capabilities compared with those of other proposed instruments for confocal microendoscopy.

Dual-flexure light valve

Abstract: A spatial light modulator pixel includes a flexible reflective surface that is electrostatically actuated to control the surface shape and thereby phase-modulate reflected light. The reflected light is filtered by a projection aperture, wherein the phase modulation controls the amount of light from the pixel that is filtered through the aperture. The spatial light modulator includes and array of such pixels, which are imaged onto a conjugate image plane, and each pixel controls the image brightness at a corresponding conjugate image point. High image contrast is achieved by using a dual-flexure pixel design in which two flexure elements operate conjunctively to maintain well-defined diffraction nodes at or near the projection aperture edges over the full modulation range.

Optical encryption system with a binary key code

Abstract: A double-random-phase optical encryption system that uses a binary key code is proposed. The key code is generated as a binary computer-generated hologram. The binary key code can be displayed on a binary spatial light modulator (SLM) such as a ferroelectric liquid-crystal display. The use of a binary SLM enables us to renew the key at high speed. A joint transform correlator based on a photorefractive crystal in the Fourier domain is used to perform shift-invariant encryption and decryption. Computer simulations of the effects of using a binary encoded key code instead of a complex amplitude key code are shown. Preliminary optical experimental results are presented to demonstrate the effectiveness of the proposed system.

Laser printer utilizing a spatial light modulator

Abstract: A laser printer utilizes a total internal reflection spatial light modulator that is optimized to work with a partially coherent laser source. The laser source is a laser diode array having a plurality of multi-mode emitters. The spatial light modulator diffracts light from said laser source according to an applied electric field. A spatial filter having a slit passes designated diffracted light which corresponds to an applied electric field and the light is ultimately imaged onto an image plane by way of an imaging lens.

Adaptive wave-front correction by means of all-optical feedback interferometry.

Abstract: A novel adaptive wave-front correction system based on an all-optical feedback interferometer is described. In this system the two-dimensional output fringe intensity from a Mach-Zehnder interferometer with large radial shear is optically fed back to an optically addressed phase-only liquid-crystal spatial light modulator. Consequently, without a separate aberration-free reference wave, the modulator phase approximates the conjugate of the interferometer phase that is directly related to the phase of the input aberrated wave front, so this system is applicable in adaptive optics. We successfully achieved real-time correction of aberrated wave fronts: A diffraction pattern that was seriously distorted because of aberrations was transformed into a diffraction-limited spot immediately after the feedback loop was closed.

Programmable chirp compensation for 6-fs pulse generation with a prism-pair-formed pulse shaper

Abstract: We describe a TF5 prism-pair-formed pulse shaper for programmable pulse chirp compensation. The advantages of this kind of pulse shaper are: (1) very broad bandwidth of transmission; (2) smaller losses; and (3) no requirement for a large-size spatial light modulator (SLM) if the input spectrum is very broad. In our experiment, an ultrabroad spectral (500-1000 nm) pulse is produced by launching 1-kHz, 30-fs, 400-/spl mu/J pulses at 780 nm into an argon filled glass capillary fiber at the gas pressure of 2.0 bar. The fiber has an inner diameter of 140 /spl mu/m and a length of 60 cm. The chirped pulse is first precompressed by a pair of BK7 prisms with a separation length of 65 cm and then directed into the prism-pair-formed pulse-shaping apparatus with a 128-pixel SLM, which provides quadratic and cubic phase compensation. When the quadratic and cubic phases are -330 fs/sup 2/ and +2000 fs/sup 3/, respectively, at the wavelength of 760 nm, an ultrashort optical pulse of 6 fs (FWHM) is generated. This is, to the best of our knowledge, the shortest optical pulse ever compressed using the SLM pulse-shaping technique.

Optical device and projection display

Abstract: An optical device which is suitable for use in a projection display comprises a spatial light modulator, such as a liquid crystal device, with a microlens array disposed on its front surface The microlenses are of convergent type, such as lenticules The spatial light modulator is of the reflective type and comprises a plurality of rear reflectors, each of which has convergent optical power in at least one direction The reflectors are arranged such that, for a given direction of illumination, each reflector forms an image of the aperture A of a microlens on the aperture B of another microlens or at a different position on the same microlens When used in, for example, a projection display, light losses caused by vignetting are reduced

Programmable array microscopy with a ferroelectric liquid-crystal spatial light modulator

Abstract: We present a programmable array microscope that uses a ferroelectric liquid-crystal spatial light modulator (SLM) for dynamic generation of scanning apertures. A single SLM serves as both the source and the detector aperture array in a double-pass confocal system. Successive aperture frames scan the array across the viewing area for complete imaging of a sample while preserving depth discrimination. Integration of the microscope output across all aperture frames produces a confocal image.

Efficient modeling of volume holographic storage channels (VHSC)

Abstract: Equalizer design typically requires careful modeling of the underlying storage channel. The aim of this paper is to present an efficient ISI model for volume hololgraphic storage channels (VHSC) in which we consider the frequency plane aperture, spatial light modulator (SLM) and CCD fill factors, and SLM finite contrast ratio as the main sources of ISI.

Two-pixel computer-generated hologram with a zero-twist nematic liquid-crystal spatial light modulator

Abstract: We present a method of producing a computer-generated hologram by use of a zero-twist linear nematic liquid-crystal spatial light modulator. A 2×1 macro pixel method is used; one pixel represents the real data, and one, the imaginary. A method is shown that produces both positive and negative analog amplitude modulation.

Projection system comprising at least two light sources having a unique optical arrangement with respect to at least one spatial light modulator

Abstract: Projection system comprising at least two light sources, a projection lens and a spatial light modulator located between the light sources and the projection lens, which light modulator comprises a plurality of light-deflection devices each provided with an element which is tiltable about a tilt axis. The light sources are arranged with respect to the spatial light modulator in such a way that, in operation, the centers of the light beams coming from the light sources and projected on each element are located on a projection line which extends substantially parallel to the tilt axis of the element.

Optical system for producing a modulated color image

Abstract: An optical system divides a light source into its component color bands red, green and blue by making the light travel different physical paths, at least two of these paths use stack retardation films and a polarization beamsplitter. By creating distinct paths, each code can be independently processed and combined to form a single path using a polarization splitter and retarder stack. The system preferably includes an input retarder that aligns a first spectrum of a light from a light source, along a first polarization state, and aligns a second spectrum of the light from the light source, along a second polarization state different than the first polarization state, and a beam splitting unit, optically coupled to the input retarder, and including a first beamsplitter that transmits the first spectrum, as a transmitted spectrum, and that reflects the second spectrum, as a reflected spectrum. The system also includes a first spatial light modulator optically coupled to the beam splitting unit, that alters and reflects the transmitted spectrum, as a modulated transmitted spectrum, towards the beam splitting unit, and a second spatial light modulator optically coupled to the beam splitting unit, that alters and reflects the reflected spectrum, as a modulated reflected spectrum, towards the beam splitting unit. The beam splitting unit combines the modulated transmitted spectrum and the modulated reflected spectrum into a combined spectrum.

Enumeration of illumination and scanning modes from real-time spatial light modulators

Abstract: Using a phase-only spatial light modulator (SLM) in a Fourier transform setup together with fast diffractive optics design algorithms provides a way to automatically generate complex and rapidly changing laser illumination patterns in the far-field. We propose a hierarchical software structure for the adaptive, on-line design of far-field illumination patterns. Using the on-line design system together with camera feedback of the illuminated scene would make it possible to detect and actively laser designate multiple objects in parallel. Possibilities for multispot, arbitrary trajectory scanning and also broad-area speckle-reduced illumination are demonstrated with experimentally measured diffraction pattern sequences from a 120×128 pixel phase-only SLM.

Novel electro-optic modulator system for the production of dynamic images from giga-pixel computer-generated holograms

Abstract: A new electro-optic modulator system has been developed by the authors to replay dynamic holographic images. This Active TilingTM system offers a route to replay giga- pixel computer generated hologram images with video refresh rates. High speed, medium complexity electrically addressed spatial light modulators are combined with a high resolution optically addressed spatial light modulator to provide ultra-high complexity, video frame rate holographic data suitable for coherent readout.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.