Showing papers on "Spatial light modulator published in 1998"

Correction of the aberrations in the human eye with a liquid-crystal spatial light modulator: limits to performance

Abstract: We evaluated the performance of a liquid-crystal spatial light modulator for static correction of the aberrations in the human eye. By applying phase-retrieval techniques to pairs of double-pass images we first estimated the wave aberration of the eye to be corrected. Then we introduced the opposite phase map in the modulator, which was placed in a plane conjugated with the eye’s pupil, and we recorded double-pass images of a point source before and after correction of the aberrations. In a slightly aberrated artificial eye a clear improvement was obtained after correction, and, although diffraction-limited performance was not achieved, the results were close to the theoretical predictions. In the two living eyes that we studied some benefit also appeared in the correction, but the performance was worse than that expected. We evaluated possible explanations for the relatively poor performance that was obtained in the human eye: an incorrect estimate of the ocular aberration, the limited spatial resolution of the modulator, and the dynamic changes in the ocular aberrations. Based on the results in the artificial eye, the first problem was not considered to be a major source of error. However, we showed that the spatial resolution of the liquid-crystal spatial light modulator limits the maximum correction to be attained. In addition, the changes in the ocular optics over time also impose a limit in the performance of static corrections.

Theory of confocal fluorescence imaging in the programmable array microscope (PAM)

Abstract: The programmable array microscope (PAM) uses a spatial light modulator (SLM) to generate an arbitrary pattern of conjugate illumination and detection elements. The SLM dissects the fluorescent light imaged by the objective into a focal conjugate image, Ic, formed by the ‘in-focus’ light, and a nonconjugate image, Inc, formed by the ‘out-of-focus’ light. We discuss two different schemes for confocal imaging using the PAM. In the first, a grid of points is shifted to scan the complete image. The second, faster approach, uses a short tiled pseudorandom sequence of two-dimensional patterns. In the first case, Ic is analogous to a confocal image and Inc to a conventional image minus Ic. In the second case Ic and Inc are the sum and the difference, respectively, of a conventional and a confocal image. The pseudorandom sequence approach requires post-processing to retrieve the confocal part, but generates significantly higher signal levels for an equivalent integration time.

Dynamic wave-front generation for the characterization and testing of optical systems.

Abstract: We describe a simple method for generating known optical aberrations dynamically, using a ferroelectric liquid-crystal spatial light modulator. Aberrations inherent in the optical system are measured and corrected, and as an example Kolmogorov turbulence is simulated for aperture sizes D/r(0) from 0 to 30, varying at frame rates up to 2.5 kHz. A measure of wave-front generation efficiency is introduced and is shown to be better than 86% for Kolmogorov phase screens with D/r(0) in the range from 0 to 30.

Apparatus and method for production of three-dimensional models by spatial light modulator

Abstract: An apparatus and the method of its operation for rapid prototyping of a three-dimensional object which includes a radiant energy source of a wide beam of radiant energy of suitable intensity and wavelength for curing a layer of photo-curable resin contained in an open vat, a spatial light modulator (SLM) having an array of pixel elements which are individually digitally controllable by a computer, for modulating the radiant energy beam projected from the radiant energy source on a pixel by pixel basis, to form a series of time sequential images of the cross-sectional laminae of the object, an optical system for focusing each image formed by the SLM, one at a time, onto successive layers of photo-curable resin for predetermined exposure times to thereby form stacked laminae of cured resin, each lamina of cured resin being in the shape of a different one of the cross-sectional laminae, and a piston support for lowering each lamina of cured resin after it is formed by the SLM and for depositing a layer of resin corresponding to the thickness of one cross sectional lamina of the three-dimensional object before the step of projecting a new image by the SLM. The SLM, the piston support for lowering, and the optical system operate repeatedly and sequentially until a complete copy of the object is thereby produced.

A system for the production of a dynamic image for display

Abstract: A system for the production of a dynamic image for use in holography includes a light source (16) which travels via a liquid crystal modulator (18) placed in the path of the light source (16). The output of the LC modulator (18) passes modulated light through a lens array (22) which itself guides light to an optically addressed spatial light modulator (24). The resulting real image from the optically addressed spatial light modulator (24) may be used in holography. The addressing frame-rate of the liquid crystal modulator (18) is substantially greater than the frame-rate of the optically addressed spatial light modulator (24).

Anamorphic lens for providing wide-screen images generated by a spatial light modulator

Abstract: An anamorphic lens (11) for use in a display system (10) that has a spatial light modulator (12) and a projection lens (13) and that projects images to a screen (14). The anamorphic lens (11) is placed between the projection lens (13) and the screen (14). The spatial light modulator (12) generates an image that is anamorphically squeezed in the horizontal dimension, and the anamorphic lens (11) widens the image so that the viewer perceives a normal wide-screen image on the screen (14).

Programmable spatially light modulated microscope ND microscopy

Abstract: A confocal optical imaging system comprises light source means (110, 310, 410, 710), detector means (150, 160, 350, 360, 450, 750) with at least one two-dimensional detector camera, and spatial light modulator means (120, 320, 420, 720) with a first (121 a) and a second group (121 b) of modulator elements, wherein the first group of modulator elements is adapted to illuminate an object to be investigated according to a predetermined pattern sequence of illumination spots focused to conjugate locations (141, 341, 441) of the object from which detection light is directed to the detector means for forming a first image Ic, and the second group of elements is adapted to illuminate the object at non-conjugate locations and/or to direct detection light from non-conjugate locations of the object to the detector means for forming a second image Inc. In an optical imaging method using this system, the first and second images are collected simultaneously or subsequently.

Characterization of a digital micromirror device for use as an optical mask in imaging and spectroscopy

Abstract: The digital micromirror device (DMD) is a micro-optical- electro-mechanical structure consisting of an array of 16 micrometers X 16 micrometers square mirrors positioned on a 17 micrometers pitch. Each individual mirror can be tilted +/- 10 degrees relative to the DMD substrate; the tilt is along the diagonal direction of the micromirror. The device was invented and manufactured by Texas Instruments (TI), Inc. TI packages the DMD as an OEM product for use in projection displays. We are investigating the use of the DMD as a spatial light modulator for precision imaging and spectroscopy applications. This includes optical characterization of the device, as well as systems engineering to operate the device. Some of the performance metrics to be considered are the diffraction efficiency, optical-switching contrast, background scattering properties, mirror crosstalk, and the modulation transfer function.

UV microstereolithography system that uses spatial light modulator technology

Abstract: A new stereophotolithography technique utilizing a spatial light modulator ~SLM! to create threedimensional components with a planar, layer-by-layer process of exposure is described. With this procedure it is possible to build components with dimensions in the range of 50 mm–50 mm and feature sizes as small as 5 mm with a resolution of 1 mm. A polysilicon thin-film twisted nematic SVGA SLM is used as the dynamic photolithographic mask. The system consists of eight elements: a UV laser light source, an optical shutter, beam-conditioning optics, a SLM, a multielement reduction lens system, a high-resolution translation stage, a control system, and a computer-aided-design system. Each of these system components is briefly described. In addition, the optical characteristics of commercially available UV curable resins are investigated with nondegenerate four-wave mixing. Holographic gratings were written at a wavelength of 351.1 nm and read at 632.8 nm to compare the reactivity, curing speed, shrinkage, and resolution of the resins. These experiments were carried out to prove the suitability of these photopolymerization systems for microstereolithography.

Illumination system having an intensity calibration system

Abstract: An illumination system (10) having an automated calibration system (62) for adjusting the light intensity of individual elements (14) of an array of light emitting elements (12). An optical sensor (30) can be positioned in several locations (A,B,C) to sense incident light from a spatial light modulator (20) as the modulator is sequentially actuated one zone (50) at a time. The light output from each zone (50) of the spatial light modulator is characterized and compared to a golden standard, and the light emitting elements of the array associated with illuminating the zones that are deficient in light are ascertained. Adjustment circuitry (62) responsively adjusts and increases the drive current to the associated light emitting elements (14) that are deficient in light output. A look-up table is utilized to determine which LEDs (14) need adjustment to their drive currents to insure uniform illumination in the process and cross-process direction at an image plane. The present invention is ideally suitable for xerographic printers.

Balancing interpixel cross talk and detector noise to optimize areal density in holographic storage systems.

Abstract: We investigate the effects of interpixel cross talk and detector noise on the areal storage density of holographic data storage. A numerical simulation is used to obtain the bit-error rate (BER) as a function of hologram aperture, pixel fill factors, and additive Gaussian intensity noise. We consider the effect of interpixel cross talk at an output pixel from all possible configurations of its 12 closest-neighbor pixels. Experimental verification of this simulation procedure is shown for several fill-factor combinations. The simulation results show that areal density is maximized when the aperture coincides with the zero order of the spatial light modulator (SLM) (Nyquist sampling condition) and the CCD fill factor is large. Additional numerical analysis including finite SLM contrast and fixed-pattern noise show that, if the fixed-pattern noise reaches 6% of the mean signal level, the SLM contrast has to be larger than 6:1 to maintain high areal density. We also investigate the improvement of areal density when error-prone pixel combinations are forbidden by using coding schemes. A trade-off between an increase in areal density and the redundancy of a coding scheme that avoids isolated-on pixels occurs at a code rate of approximately 83%.

Rear-screen projection television with spatial light modulator and positionable anamorphic lens

Abstract: A television receiver ( 10 ) that has a spatial light modulator ( 15 ) and a projection lens ( 17 a ) and that projects images to a screen ( 18 ). If the aspect ratio of the image to be displayed does not match that of the spatial light modulator ( 15 ), an anamorphic lens ( 17 b ) is positioned in the optical path of the image, between the projection lens ( 17 b ) and the screen ( 18 ). In this case and in typical applications, the spatial light modulator ( 15 ) generates an image that is anamorphically squeezed in the horizontal dimension, and the anamorphic lens ( 17 b ) widens the image so that the viewer perceives a normal wide-screen image on the screen ( 18 ).

Optical Sectioning Fluorescence Spectroscopy in a Programmable Array Microscope

Abstract: We report the use of a programmable array microscope (PAM) for the acquisition of spectrally resolved and high-throughput optical sections. The microscope is based on the use of a spatial light modulator for defining patterns of excitation and/or detection of fluorescence. For obtaining optically sectioned spectral images, the entrance slit of an imaging spectrograph and a line illumination pattern defined with a spatial light modulator are placed in conjugate optical positions. Compared to wide-field illumination, optical sectioning led to greater than 3 X improvement in the rejection of outof-focus fluorescence emission and nearly 6 X greater peak-to-background ratios in biological specimens, yielding better contrast and spectral characterization. These effects resulted from a reduction in the artifacts arising from spectral contributions of structures outside the region of interest. We used the programmable illumination capability of the spectroscopic system to explore a variety of excitation/detection patterns for increasing the throughput of optical sectioning microscopes. A Sylvester-type Hadamard construction was particularly efficient, performing optical sectioning while maintaining a 50% optical throughput. These results demonstrate the feasibility of full-field highly multiplexed confocal spectral imaging.

Image displaying apparatus and method

Abstract: An image displaying apparatus and method is provided which can provide a satisfactory display with a gradation of intensity even with a spatial light modulator which provides a binary light modulation A light from a light source 1 is modulated by a spatial light modulator 3 which modulates a light at each pixel thereof correspondingly to a pixel data of an image to be displayed When the pixel state of the spatial light modulator 3 is being changed, the light source 1 is turned off When the pixel state of the spatial light modulator 3 is steady, a light pulse is irradiated from the light source 1 to the spatial light modulator 3 to display the image

Programmable phase control of femtosecond pulses by use of a nonpixelated spatial light modulator.

Abstract: Programmable spectral phase modulation of femtosecond pulses by use of a nonpixelated spatial light modulator is reported. This light valve, based on the optical addressing of a continuous layer of liquid crystal, allows the operation of spectral phase modulation when optical frequency components are spatially dispersed within a grating-and-lenses pulse-shaping apparatus. Characterization and feedback control of this device were determined by use of spectral interferometry. Demonstrations of the capabilities of this device are given in the spectral and the temporal domains, and recompression of chirped pulses was performed.

Dynamic digital holographic wavelength filtering

Abstract: This paper describes the theory and results of a new generic technology for use in optical telecommunications and wavelength division multiplexing (WDM): dynamic digital holographic wavelength filtering. The enabling component is a polarization-insensitive ferroelectric liquid crystal (FLC) spatial light modulator (SLM) in conjunction with a highly wavelength-dispersive fixed diffractive element. The technology has been used to perform demultiplexing of single or multiple WDM signals, dynamic erbium doped fiber amplifier (EDFA) gain equalization and channel management, and used to tune an erbium-doped fiber laser (EDFL) functioning as a high power, very narrow linewidth WDM source.

Single-panel field-sequential color display systems

Abstract: The present invention provides a single-panel field-sequential full color display systems that are less complex, smaller in size and less costly than prior additive split-path color systems, while exhibiting higher light output, greater flexibility and greater reliability than prior single-panel field-sequential systems. In the first preferred embodiment, the display system includes a “frame buffer” style spatial light modulator, in which a frame buffer pixel circuit is integrated into the spatial light modulator. The display system of the present invention also preferably includes on opto-electronic color sequencer which allows for the electronic control of the transmission of additive primary colors.

Apparatus for spatial light modulator registration and retention

Abstract: A method and apparatus for adjusting spatial light modulators in an imaging system. The apparatus includes several screws, plungers and pins connecting to a housing. When the screws and plungers are adjusted, the device held by the housing is manipulated along the x, y and z axes, allowing the device to be focused and aligned. If multiple modulators are involved, they can also be converged. The method includes the steps of mounting the devices in adjustable sockets, aligning each device, focusing each device and then positioning images from each device to converge with images from other devices.

Apparatus for holographic data storage

Abstract: A holographic data storage apparatus having no readout lens. The apparatus has a spatial light modulator (SLM), a focusing element such as a lens, a holographic data storage material and a spatial light detector such as a CCD. The lens is located between the SLM and CCD such that the SLM is imaged onto the CCD (i.e. the positions of the SLM, lens, and CCD satisfy the lens equation). The holographic storage material is located between the lens and CCD. Preferably, the storage material is located centered upon a Fourier plane of the lens. In this case, the apparatus also has a phase mask located adjacent to the SLM. Alternatively, the storage material is located a distance away from the Fourier plane or is not centered on the Fourier plane. In yet another embodiment, the holographic storage material is located in contact with the CCD.

Wavelength division multiplex transmitter

Abstract: A wavelength division multiplex transmitter for modulating light (12) from a broadband light source (14) and coupling modulated (26, 28, 30) to an optical waveguide (34) for digital optical communications. The wavelength division multiplex transmitter includes a diffraction grating (20) for receiving and diffracting light from a broadband light source (14). A first reflecting element (19) receives diffracted light from the diffraction grating (20). A spectrally programmable spatial light modulator (SLM) (24) receives reflected diffracted light (21, 22, 23) from the reflecting element (19) and selectively modulates a selected set of wavelengths of the reflected light. A lens (32) receives the selected set of wavelengths and directs them into an optical waveguide (34) for digital communication. This provides enhanced utilization of each wavelength within the broadband light source.

Modulated-amplitude illumination for spatial light modulator

Abstract: Methods of controlling the illumination source ( 18 ) of an SLM-based display system ( 10 ). It is assumed that the system ( 10 ) displays pixel data formatted into a bit-plane format so that all bits of the same bit-weight can be displayed simultaneously. To provide greyscale, the amplitude of the source ( 18 ) may be modulated so that bit-planes having greater bit-weights are displayed with more intense illumination than bit-planes having smaller bit-weights (FIGS. 2 and 3 ). To avoid visual artifacts, the duty cycle of the bit-plane display times may be shortened relative to the frame period. (FIG. 4 A). The latter method can be accompanied by a shortening of the duty time of the illumination on SLM ( 15 ). (FIG. 4 B). The short duty cycle method may be used together with illumination amplitude modulation, or it may be used with the PWM method of providing greyscale.

Light separation and recombination system for an off-axis projector

Abstract: A color separation and recombination system separates a beam of white light traveling along an optical axis into three differently colored light beams. The system then independently modulates each colored beam and recombines the colored beams to create a color image. The system includes a crossed pair of dichroic filters to separate the beam of white light and to recombine the modulated bundles. The system also includes a pair of aberration-compensating elements that equalize the optical thickness of glass through which each light bundle passes. This equalization of optical thickness equalizes the aberration induced into each bundle. In another embodiment the beam of white light is polarized before separation. The polarities of the colored light beams are then modulated using a spatial light modulator. An analyzer and half-wave plate are provided between the spatial light modulator and the crossed dichroic filters to pass only a portion of the modulated light. The half-wave plate ensures that the modulated light incident on the crossed dichroic filters is of the same polarity as was the polarized white light separated by the crossed dichroic filters.

Nearly diffraction-limited laser focal spot obtained by use of an optically addressed light valve in an adaptive-optics loop

Abstract: We demonstrate correction of laser wavefront distortions by use of an adaptive-optical technique based on a light valve. The setup consists of an achromatic and adjustable-sensitivity wavefront sensor and a wavefront corrector relying on an optically addressed liquid-crystal spatial light modulator. Experimental results with strongly aberrated beams focused close to the diffraction limit are presented for the cw regime. Additional experiments with pulses and measurement of damage thresholds show that this approach is relevant for spatial phase correction of ultraintense laser pulses.

Noise reduction of page-oriented data storage by inverse filtering during recording

Abstract: Two novel techniques for eliminating deterministic noise from a page-oriented memory are presented. The first technique equalizes the output response of ON pixels by adjustment of the exposure of each pixel during the recording of each data page. A test image transmitted through the system measures the spatial nonuniformities, and the appropriate inverse filter is imposed upon the data page and recorded in the storage material. On readout, the output signal values are then spatially uniform, perturbed only by random noise sources. Experimental results of using this predistortion technique in a pixel-matched holographic storage system are shown. Under conditions of high volumetric density, raw bit-error-rate (BER) improvements of 6–8??orders of magnitude are obtained (from 10-4 to <10-10). The second technique uses a phase shift during holographic storage to subtract from bright OFF pixels. Under conditions of low spatial light modulator contrast, BER improvements of 6??orders of magnitude (from 10-2 to 10-8) are demonstrated.

Compact optical crossbar switch

Abstract: A planar optical crossbar switch comprising two thin planar substrates, on each of which are recorded or attached two holographic lenses between which light propagates by means of total internal reflection. The first lens is a negative cylindrical lens, used to input the incident light signal to the substrate, and the second lens is a positive cylindrical lens. The two substrates are disposed at right angles to each other in such a way that the positive lenses are positioned one on top of the other with a spatial light modulator sandwiched between them or beneath them. A linear array of detectors collects the output signal from the negative lens on the second substrate. Light from an element in the linear array of sources is spread out, by means of the negative cylindrical holographic lens on the first substrate, across a row of the SLM, and light from a column of the SLM is focused by means of the cylindrical holographic lenses on the second substrate, onto a particular element of the linear array of output detectors. To connect a signal form the ith source in the input array to the jth detector in the output array, the value of the {i,j} pixel of the SLM matrix should be in the ON state.

Optical storage medium, optical storage method, optical storage apparatus, optical reading method, optical reading apparatus, optical retrieving method and optical retrieving apparatus

Abstract: An optical storage medium of the present invention enables storage of data with high precision at high speed, and rewriting of data at high speed without an erasing process. Optical storage, reading and retrieving methods and optical storage, reading, and retrieving apparatuses using the medium are also provided. The optical storage medium has at least a polarization-sensitive member having the photo-induced birefringence property, such as a member made of polyester polymer having cyanoazobenzene as a side chain. The above apparatuses have spatial light modulator capable of modulating polarization. The modulator provides information of bit of two-dimensional data to each corresponding pixel by application or non-application of a voltage, and modulates the polarization of the beam incident on each pixel. Thereby, a signal beam transmitted through the spatial light modulator having a spatial polarization modulation corresponding to the two-dimensional data is obtained. The signal beam illuminates the optical storage medium, and at the same time, a reference beam illuminates the same region in the medium where the signal beam illuminates. Thus a hologram of the polarization modulation of the signal beam corresponding to the two-dimensional data is stored in the optical storage medium.

Method for using a spatial light modulator

Abstract: Light is shined on an addressable spatial light modulator, and the light is also integrated. The data displayed on the spatial light modulator is changed when the integrated light reaches a predetermined value. The light may impinge on the spatial light modulator through a color wheel, which may be rotated faster than the frame repetition rate of video information that is being displayed. Alternatively, the light may be generated by different-colored lamps. The intensity of the light may be controlled in accordance with the bit rank or significance of the bits that are being displayed by the spatial light modulator. Several techniques for achieving different intensity levels are disclosed.

Real-time optical aberration correction with a ferroelectric liquid-crystal spatial light modulator.

Abstract: Real-time correction of an optically aberrated wave front by use of a 10 x 10 ferroelectric liquid-crystal spatial light modulator as the correction device and a point-diffraction interferometer as the wave-front sensor is demonstrated. This type of interferometer requires no reference arm and so can be used, in theory, in an astronomical adaptive-optics system. We discuss some of the unusual features of the point-diffraction interferometer for wave-front sensing.

Apparatus and method for creating and displaying planar virtual images

Abstract: A method and system for creating very thin displays producing virtual images (301, 312) based on extremely small 'pinpoint' light sources (302) In an embodiment, a pinpoint light source (301) is used in a manner analogous to a pinhole lens to magnify and view a displayed image up close In another embodiment, an array of pinpoint light sources with or without intervening lenses is used to illuminate a spatial light modulator (304) to produce an extremely thin virtual image display