Programmable Spatial Light Modulator Research Articles

Modelling of High Resolution Phase Spatial Light Modulators

A programmable LCOS reflective spatial light modulator using an array of liquid crystal pixels used as a phase modulating device is studied. Modelling has been performed to determine the pattern of electrode voltages required to achieve a blazed grating with a linear phase ramp and an abrupt phase transition. As two-dimensional steering of incoming wavefronts is required, oblique gratings are also considered and the effect of the angle of the pixel grid with respect to the phase front of the grating is also considered. Here we study this effect using two possible configurations of the director pre-twist.

Generation of nondiffracting Bessel beams by use of a spatial light modulator.

A laser beam with phase singularities is an interesting object to study in optics and may have important applications in guiding atoms and molecules. We explore the characteristics of a singularity in a nondiffracting Bessel beam experimentally by use of a programmable spatial light modulator with 64-level phase holograms. The diffraction efficiency with 64-level phase holograms is greatly improved in comparison with that obtained with a binary grating. The experiments show that the size and deflection angle of the beam can be controlled in real time. The observations are in agreement with scalar diffraction theory.

Multiwavelength mode-locked InGaAsP laser operating at 12 ch/spl times/2 GHz and 16 ch/spl times/10 GHz

In this letter, we report on the development and characterization of an InGaAsP semiconductor optical amplifier-(SOA) based ring cavity laser that emits up to 16 wavelengths in the 1550-nm region. The laser is loss modulation mode locked at up to 10 GHz with temporal pulses of /spl sim/25 ps. Spectral control of the emission is accomplished by an intracavity 4-f spectral pulse shaper with a programmable liquid crystal spatial light modulator (SLM) in the Fourier plane. Voltage control of the transmissibility of the pixels of the SLM defines the wavelength channels and allows flattening of channels to produce a uniform intensity of channel outputs.

Closed loop spectral control of multiwavelength 1550 laser

The spectral flatness of multiwavelength emission from an InGaAsP semiconductor optical amplifier based ring laser is controlled by a programmable liquid crystal spatial light modulator based on spectrally monitoring the individual wavelength intensities of the laser output. Spectrally equal amplified output is also shown by pre-distorting the laser to account for amplifier spectral gain dependence.

Continuous Image Writer with improved critical dimension performance for high-accuracy maskless optical patterning

We report on the development of a production tool for fast optical maskless patterning. The Continuous Image Writer (CIW) combines the advantages of direct writing by using a programmable mask with the advantages of conventional optical lithography by using the same lithographic process for image formation in photoresist. An electronically programmable spatial light modulator (SLM) is imaged onto the substrate by passing a demagnifying Fourier optics. The use of short pulses of a KrF excimer laser allows the imaging of the extended image field of the SLM without stopping the substrate carrying stage during exposure. This results in short writing times. Based on experience with a production-like prototype of the CIW [Proc. SPIE 4000 (2000) 866] we have investigated the various contributions to image quality such as address grid, stitching errors, and SLM quality. This paper describes a method for achieving a critical dimension performance well suited for the generation of photomask and wafer patterns for present and future technology nodes. The present configuration of the CIW makes it an ideal tool for the fabrication of photomasks as well as for direct-write applications for low volume production.

Image processing with the radial Hilbert transform: theory and experiments

The Hilbert transform is useful for image processing because it can select which edges of an input image are enhanced and to what degree the edge enhancement occurs. However, the transform operation is one dimensional and is not applicable for arbitrarily shaped two-dimensional objects. We introduce a radially symmetric Hilbert transform that permits two-dimensional edge enhancement. We implement one-dimensional, two-dimensional, and radial Hilbert transforms with a programmable phase-only liquid-crystal spatial light modulator. Experimental results are presented.

Programmable color liquid-crystal television spatial light modulator: transmittance properties and application to speckle-correlation displacement measurement

Drive electronics developed for a color liquid-crystal television (LCTV) display enable data to be written onto individual pixels. Display transmittance characteristics obtained with the new and the original TV drive electronics are compared. The enhanced performance obtained through this development has some potential for spatial light modulator applications in color, optical information processing based on the low-cost LCTV. As an example, we describe a novel, to our knowledge, speckle metrology technique used to display fringes and to output correlation peaks resulting from in-plane object displacement. This requires only a single LC display to encode, simultaneously in three pixel colors, speckle and fringe patterns for real-time measurements. Relative merits of this technique, including displacement range and temporal resolution, are discussed.

Programmable axial apodizing and hyperresolving amplitude filters with a liquid-crystal spatial light modulator

Amplitude-transmitting filters for apodizing and hyperresolving applications can be easily implemented by use of a two-dimensional programmable liquid-crystal spatial light modulator operating in a transmission-only mode. Experimental results are in excellent agreement with theoretical predictions. This approach can permit the analysis of various filter designs and can allow the filters to be changed rapidly to modify the response of an optical system.

Ambiguities in measuring the physical parameters for twisted-nematic liquid crystal spatial light modulators

There is great interest in using commercially available twisted-nematic liquid crystal displays as programmable spatial light modulators. Proper use of such displays, particularly as phase-only filters for optical correlators or as diffractive optical elements, requires knowledge of the physical parameters of the device including the twist angle, the birefringence, and the orientation of the director axes. A simple experimental technique was published for evaluation of these parameters. When we used this technique, however, we found a number of different sets of values that satisfied the experimental data. We demonstrate that additional measurements at different wavelengths can resolve these ambiguities and provide valuable information about the wavelength dependence ofthe birefringence.

Programmable dispersion compensation and pulse shaping in a 26-fs chirped-pulse amplifier

We have constructed a 26-fs chirped-pulse amplifier that incorporates a programmable liquid-crystal spatial light modulator in the pulse stretcher. The modulator serves a dual purpose. First, we apply frequency-dependent phase shifts to compensate for cubic, quartic, and nonlinear phase dispersion in the amplifier, which results in a reduction in pulse duration from 32 to 26 fs, in agreement with the transform limit of the amplified pulse spectrum. Second, we are able to produce high-fidelity compressed amplified shaped pulses by applying phase masks directly within the stretcher. Shaped pulse energies of greater than 1 mJ are routinely obtained.

Bessel function output from an optical correlator

We introduce a new filter for an optical correlator that produces a Bessel function correlation output. The advantage of this type of output is that the width of the central dark spot at the center of the correlator output is narrower than the width of the usual correlation spot. In addition, the dark spot is insensitive to changes in illumination intensity. We present experimental results with which we write the new filter onto a programmable magneto-optic spatial light modulator.

Adaptive computer-generated hologram using interpolation method

Kinoform synthesis by an electro-optic hybrid system using an interpolation method is proposed. A programmable liquid crystal spatial light modulator is used as a kinoform. The phase distribution of the kinoform is optimized using the simulated annealing. The cost function is represented by the mean square error between a desired image stored in a computer and a reconstructed image detected by a charge coupled device camera. The interpolation method enables one to reduce the random noise effect in the reconstructed image. Some experimental results are presented.

Range-finding by triangulation with nondiffracting beams

Nondiffracting beams are useful for alignment applications because the size of the beam does not change as the beam propagates. In this research we report a technique that allows for distance measurements with nondiffracting beams. With our approach a diffractive optical element is designed that generates two off-axis, tilted, nondiffracting Bessel function beams. These beams intersect at a desired distance from the input plane, producing interference. We generate these Bessel function arrays with a programmable spatial light modulator allowing external control over the intersection distance.

Nondiffracting interference patterns generated with programmable spatial light modulators

Nondiffracting beams are of interest for optical metrology applications because the size and shape of the beams do not change as the beams propagate. We have created a generating pattern consisting of a linear combination of two nondiffracting patterns. This pattern forms a nondiffracting interference pattern that appears as a circular array of nondiffracting spots. More complicated multiplexed arrays are also constructed that simultaneously yield two different nondiffracting patterns. We generate these Bessel function arrays with a programmable spatial light modulator. Such arrays would be useful for angular alignment and for optical interconnection applications.

Intensity and phase measurements of nondiffracting beams generated with a magneto-optic spatial light modulator

Nondiffracting beams are of interest for optical metrology applications because the size of the beam does not change as the beam propagates. However, accuracy can be increased if the diameter of the beam is smaller. One technique for accomplishing this is to use the dark axial intensity profile associated with a higher-order nondiffracting Bessel function beam. We generate these higher-order Bessel function beams with a programmable spatial light modulator. We study the intensity patterns and the phase dependence of these nondiffracting beams. In addition, we examine interference effects caused by recording these patterns onto a binary spatial light modulator.

Characterization of a liquid crystal television as a programmable spatial light modulator

The properties of a liquid crystal television to be used as a spatial modulator of the polarization of a laser beam are studied. It is found that the model most commonly used for the display description does not adequately reproduce the transmission through crossed polarizers. A new model is proposed that takes into account additional birefringence effects resulting from border effects near the television windows. With this correction, the anomalous behavior of the television is explained and the throughput for different configurations is properly predicted.

Differentiating optical correlator

We introduce a new filter for an optical correlator that produces the spatial derivative of the optical correlation between an input object and a reference object. The derivative signal has a dark spot at the center of the correlation output. The width of this dark spot is narrower than the width of the conventional correlator bright spot and provides more precise location of the input object as well as a higher signal-to-noise ratio. Experimental results are presented for the case in which the new filter is written onto a programmable magneto-optic spatial light modulator.

Programmable optical logic systems using free-space optical interconnections

A free-space optical logic technique is presented that utilizes a two-dimensional array of diffractive optical elements. Each optical element focuses light to multiple, separate positions in the output focal plane. The focal spots from different optical elements are allowed to overlap spatially, resulting in interference. By changing the phase shift between the optical elements, one can create different optical logic operations in the focal plane. The technique is demonstrated by the use of two input beams incident onto a multiplexed optical element written onto a programmable spatial light modulator. The optical element simultaneously creates both AND and XOR logic functions in the output plane.

Programmable liquid-crystal TV spatial light modulator: modified drive electronics to improve device performance for spatial-light-modulation operation

Liquid crystal television (LCTV) continues to play a useful role as a spatial light modulator in the development and evaluation of systems for optical image processing. We outline new addressing electronics developed for a commercially available LCTV that permit writing to individual pixels at an improved display up-date rate and allow the input video signal to cover a much greater transmittance range of the TV display for black and white pixels. We illustrate this by measuring the diffraction efficiency for gratings written onto the display. For vertical gratings written along the display columns the diffraction efficiency is increased significantly, but there is no improvement for horizontal gratings. Some merits of the modified LCTV modulator for optical processing applications are considered briefly.

Spatial image differentiation using programmable binary optical elements

Spatial differentiation can be performed by imaging an input pattern with a binary optical element consisting of Fresnel lenses having identical focal lengths but different center locations. Each of these lenses forms an image of the object at a different transverse location in the image plane. If the two lenses have a phase shift of pi rad, the two images will be subtracted, resulting in an image that is differentiated in the direction of the shifted lens positions. We show experimental results in which the optical element is written onto a programmable magneto-optic spatial light modulator.