Showing papers on "Spatial light modulator published in 2011"

Shaping the light transmission through a multimode optical fibre : complex transformation analysis and applications in biophotonics

Abstract: We present a powerful approach towards full understanding of laser light propagation through multimode optical fibres and control of the light at the fibre output. Transmission of light within a multimode fibre introduces randomization of laser beam amplitude, phase and polarization. We discuss the importance of each of these factors and introduce an experimental geometry allowing full analysis of the light transmission through the multimode fibre and subsequent beam-shaping using a single spatial light modulator. We show that using this approach one can generate an arbitrary output optical field within the accessible field of view and range of spatial frequencies given by fibre core diameter and numerical aperture, respectively, that contains over 80% of the total available power. We also show that this technology has applications in biophotonics. As an example, we demonstrate the manipulation of colloidal microparticles.

Controlling light through optical disordered media: transmission matrix approach

Abstract: We experimentally measure the monochromatic transmission matrix (TM) of an optical multiple scattering medium using a spatial light modulator together with a phase-shifting interferometry measurement method. The TM contains all the information needed to shape the scattered output field at will or to detect an image through the medium. We confront theory and experiment for these applications and study the effect of noise on the reconstruction method. We also extracted from the TM information about the statistical properties of the medium and the light transport within it. In particular, we are able to isolate the contributions of the memory effect and measure its attenuation length.

Hologram transmission through multi-mode optical fibers

Abstract: We demonstrate that a structured light intensity pattern can be produced at the output of a multi-mode optical fiber by shaping the wavefront of the input beam with a spatial light modulator. We also find the useful property that, as in the case for free space propagation, output intensities can be easily superimposed by taking the argument of the complex superposition of corresponding phase-only holograms. An analytical expression is derived relating output intensities ratios to hologram weights in the superposition.

Liquid-crystal photonic applications

Abstract: Liquid crystals are nowadays widely used in all types of display applications. However their unique electro-optic properties also make them a suitable material for nondisplay applications. We will focus on the use of liquid crystals in different photonic components: optical filters and switches, beam-steering devices, spatial light modulators, integrated devices based on optical waveguiding, lasers, and optical nonlinear components. Both the basic operating principles as well as the recent state-of-the art are discussed.

Display device, in particular a head-mounted display, based on temporal and spatial multiplexing of hologram tiles

Abstract: The invention relates to a display device, in particular a head-mounted display or hocular, having a spatial light modulator and a controllable light-deflecting device for generating a multiple image of the spatial light modulator, which consists of segments, the multiple image being produced at least with a predefinable number of segments which determines the size of a visible area within which a 3D-scene holographically encoded in the spatial light modulator can be reconstructed for observation by an eye of an observer.

Focusing light through random photonic media by binary amplitude modulation

Abstract: We study the focusing of light through random photonic materials using wavefront shaping. We explore a novel approach namely binary amplitude modulation. To this end, the light incident to a random photonic medium is spatially divided into a number of segments. We identify the segments that give rise to fields that are out of phase with the total field at the intended focus and assign these a zero amplitude, whereas the remaining segments maintain their original amplitude. Using 812 independently controlled segments of light, we find the intensity at the target to be 75±6 times enhanced over the average intensity behind the sample. We experimentally demonstrate focusing of light through random photonic media using both an amplitude only mode liquid crystal spatial light modulator and a MEMS-based spatial light modulator. Our use of Micro Electro-Mechanical System (MEMS)-based digital micromirror devices for the control of the incident light field opens an avenue to high speed implementations of wavefront shaping.

Metrology Method and Inspection Apparatus, Lithographic System and Device Manufacturing Method

Abstract: Methods are disclosed for measuring target structures formed by a lithographic process on a substrate. A grating structure within the target is smaller than an illumination spot and field of view of a measurement optical system. The optical system has a first branch leading to a pupil plane imaging sensor and a second branch leading to a substrate plane imaging sensor. A spatial light modulator is arranged in an intermediate pupil plane of the second branch of the optical system. The SLM imparts a programmable pattern of attenuation that may be used to correct for asymmetries between the first and second modes of illumination or imaging. By use of specific target designs and machine-learning processes, the attenuation patterns may also be programmed to act as filter functions, enhancing sensitivity to specific parameters of interest, such as focus.

Optical image encryption using a jigsaw transform for silhouette removal in interference-based methods and decryption with a single spatial light modulator

Abstract: Interference-based optical encryption schemes have an inherent silhouette problem due to the equipollent nature of the phase-only masks (POMs) generated using an analytical method. One of the earlier methods suggested that removing the problem by use of exchanging process between two masks increases the computational load. This shortcoming is overcome with a noniterative method using the jigsaw transformation (JT) in a single step, with improved security because the inverse JT of these masks, along with correct permutation keys that are necessary to decrypt the original image. The stringent alignment requirement of the POMs in two different arms during the experiment is removed with an alternative method using a single spatial light modulator. Experimental results are provided to demonstrate the decryption process with the proposed method.

Focusing Light through Random Photonic Media by Binary Amplitude Modulation

Abstract: We study the focusing of light through random photonic materials using wavefront shaping. We explore a novel approach namely binary amplitude modulation. To this end, the light incident to a random photonic medium is spatially divided into a number of segments. We identify the segments that give rise to fields that are out of phase with the total field at the intended focus and assign these a zero amplitude, whereas the remaining segments maintain their original amplitude. Using 812 independently controlled segments of light, we find the intensity at the target to be 75 +/- 6 times enhanced over the average intensity behind the sample. We experimentally demonstrate focusing of light through random photonic media using both an amplitude only mode liquid crystal spatial light modulator and a MEMS-based spatial light modulator. Our use of Micro Electro-Mechanical System (MEMS)-based digital micromirror devices for the control of the incident light field opens an avenue to high speed implementations of wavefront shaping.

Speckle-free and grayscale hologram reconstruction using time-multiplexing technique

Abstract: Speckle generation is an inherent problem of holography. A speckle-reduction technique employing a time-multiplexing method is proposed. Object points constituting a reconstructed image are divided into multiple object point groups consisting of sparse object points, and the object point groups are displayed time sequentially. The sparseness and temporal summation enable the suppression of speckle generation. The object point group is decomposed into multiple bit planes to represent the grayscale of object points, and binary holograms are generated from the bit plane patterns by using a half-zone plate technique. The binary holograms are displayed by a high-speed spatial light modulator.

Polarization fields: dynamic light field display using multi-layer LCDs

Abstract: We introduce polarization field displays as an optically-efficient design for dynamic light field display using multi-layered LCDs. Such displays consist of a stacked set of liquid crystal panels with a single pair of crossed linear polarizers. Each layer is modeled as a spatially-controllable polarization rotator, as opposed to a conventional spatial light modulator that directly attenuates light. Color display is achieved using field sequential color illumination with monochromatic LCDs, mitigating severe attenuation and moire occurring with layered color filter arrays. We demonstrate such displays can be controlled, at interactive refresh rates, by adopting the SART algorithm to tomographically solve for the optimal spatially-varying polarization state rotations applied by each layer. We validate our design by constructing a prototype using modified off-the-shelf panels. We demonstrate interactive display using a GPU-based SART implementation supporting both polarization-based and attenuation-based architectures. Experiments characterize the accuracy of our image formation model, verifying polarization field displays achieve increased brightness, higher resolution, and extended depth of field, as compared to existing automultiscopic display methods for dual-layer and multi-layer LCDs.

Optimal resolution in Fresnel incoherent correlation holographic fluorescence microscopy

Abstract: Fresnel Incoherent Correlation Holography (FINCH) enables holograms and 3D images to be created from incoherent light with just a camera and spatial light modulator (SLM). We previously described its application to microscopic incoherent fluorescence wherein one complex hologram contains all the 3D information in the microscope field, obviating the need for scanning or serial sectioning. We now report experiments which have led to the optimal optical, electro-optic, and computational conditions necessary to produce holograms which yield high quality 3D images from fluorescent microscopic specimens. An important improvement from our previous FINCH configurations capitalizes on the polarization sensitivity of the SLM so that the same SLM pixels which create the spherical wave simulating the microscope tube lens, also pass the plane waves from the infinity corrected microscope objective, so that interference between the two wave types at the camera creates a hologram. This advance dramatically improves the resolution of the FINCH system. Results from imaging a fluorescent USAF pattern and a pollen grain slide reveal resolution which approaches the Rayleigh limit by this simple method for 3D fluorescent microscopic imaging.

The holographic optical micro‐manipulation system based on counter‐propagating beams

Abstract: We present a system employing a dynamic diffrac- tive optical element to control properties of two counter- propagating beams overlapping within a sample chamber. This system allows us to eliminate optical aberrations along both beam pathways and arbitrarily switch between various num- bers of laser beams and their spatial profiles (i.e. Gaussian, Laguerre-Gaussian, Bessel beams, etc.). We successfully tested various counter-propagating dual-beam configurations includ- ing optical manipulation of both high and low index particles in water or air, particle delivery in an optical conveyor belt and the formation of colloidal solitons by optical binding. Furthermore, we realized a novel optical mixer created by particles spiraling in counter-propagating interfering optical vortices and a new tool for optical tomography or localized spectroscopy enabling sterile contactless rotation and reorientation of a trapped living cell. CP Bessel beams in a form of optical conveyor belt

Complex Fresnel hologram display using a single SLM

Abstract: We propose a novel optical method to display a complex Fresnel hologram using a single spatial light modulator (SLM). The method consists of a standard coherent image processing system with a sinusoidal grating at the Fourier plane. Two or three position-shifted amplitude holograms displayed at the input plane of the processing system can be coupled via the grating and will be precisely overlapped at the system's output plane. As a result, we can synthesize a complex hologram that is free of the twin image and the zero-order light using a single SLM. Because the twin image is not removed via filtering, the full bandwidth of the SLM can be utilized for displaying on-axis holograms. In addition, the degree of freedom of the synthesized complex hologram display can be extended by involving more than three amplitude holograms.

Exploiting sparsity in time-of-flight range acquisition using a single time-resolved sensor

Abstract: Range acquisition systems such as light detection and ranging (LIDAR) and time-of-flight (TOF) cameras operate by measuring the time difference of arrival between a transmitted pulse and the scene reflection. We introduce the design of a range acquisition system for acquiring depth maps of piecewise-planar scenes with high spatial resolution using a single, omnidirectional, time-resolved photodetector and no scanning components. In our experiment, we reconstructed 64 × 64-pixel depth maps of scenes comprising two to four planar shapes using only 205 spatially-patterned, femtosecond illuminations of the scene. The reconstruction uses parametric signal modeling to recover a set of depths present in the scene. Then, a convex optimization that exploits sparsity of the Laplacian of the depth map of a typical scene determines correspondences between spatial positions and depths. In contrast with 2D laser scanning used in LIDAR systems and low-resolution 2D sensor arrays used in TOF cameras, our experiment demonstrates that it is possible to build a non-scanning range acquisition system with high spatial resolution using only a standard, low-cost photodetector and a spatial light modulator.

Adaptive phase compensation for ultracompact laser scanning endomicroscopy

Abstract: We present an approach to laser scanning endomicroscopy that requires no moving parts and can be implemented with no distal scanners or optics, permitting extremely compact endoscopic probes to be developed. Our approach utilizes a spatial light modulator to correct for phase variations across a fiber imaging bundle and to encode for arbitrary wavefronts at the distal end of the fiber bundle. Thus, it is possible to realize both focusing and beam scanning at the output of the fiber bundle with no distal components. We present proof of principle results to illustrate three-dimensional scanning of the focal spot and exemplar images of a United States Air Force resolution test chart.

Point spread function and two-point resolution in Fresnel incoherent correlation holography.

Abstract: Fresnel Incoherent Correlation Holography (FINCH) allows digital reconstruction of incoherently illuminated objects from intensity records acquired by a Spatial Light Modulator (SLM) The article presents wave optics model of FINCH, which allows analytical calculation of the Point Spread Function (PSF) for both the optical and digital part of imaging and takes into account Gaussian aperture for a spatial bounding of light waves The 3D PSF is used to determine diffraction limits of the lateral and longitudinal size of a point image created in the FINCH set-up Lateral and longitudinal resolution is investigated both theoretically and experimentally using quantitative measures introduced for two-point imaging Dependence of the resolving power on the system parameters is studied and optimal geometry of the set-up is designed with regard to the best lateral and longitudinal resolution Theoretical results are confirmed by experiments in which the light emitting diode (LED) is used as a spatially incoherent source to create object holograms using the SLM

Far field subwavelength focusing using optical eigenmodes

Abstract: We report the focusing of light to generate a subdiffractive, subwavelength focal spot of full width half maximum 222 nm at an operating wavelength of 633 nm using an optical eigenmode approach. Crucially, the spot is created in the focal plane of a microscope objective thus yielding a practical working distance for applications. The optical eigenmode approach is implemented using an optimal superposition of Bessel beams on a spatial light modulator. The effects of partial coherence are also discussed. This far field method is a key advance toward the generation of subdiffractive optical features for imaging and lithographic purposes.

Holographic mode-selective launch for bandwidth enhancement in multimode fiber.

Abstract: With rapidly growing bandwidth demands in Local Area Networks, it is imperative to support next generation speeds beyond 40Gbit/s. Various holographic optimization techniques using spatial light modulators have recently been explored for adaptive channel impulse response improvement of MMF links. Most of these experiments are algorithmic-oriented. In this paper, a set of lenses and a spatial light modulator, acting as a binary amplitude filter, played the pivotal role in generating the input modal electric field into a graded-index MMF, rather than algorithms. By using a priori theoretical information to generate the incident modal electric field at the MMF, the bandwidth was increased by up to 3.4 times.

Laser forward transfer based on a spatial light modulator

Abstract: We report the first demonstration of laser forward transfer using a real-time reconfigurable mask based on a spatial light modulator. The ability to dynamically change the projected beam shape and size of a coherent light source, in this case a 355-nm pulsed UV laser, represents a significant technological advancement in laser direct-write processing. The application of laser transfer techniques with adaptive control of the laser beam pattern is unique and represents a paradigm shift in non-lithographic processing. This work describes how the size and shape of an incident laser beam can be dynamically controlled in real time with the use of a digital micromirror device (DMD), resulting in laser-printed functional nanomaterials with geometries identical to those of the projected beam. For applications requiring additive non-lithographic techniques, this novel combination, which relies on the laser forward transfer of variable, structured voxels, represents a dramatic improvement in the capabilities and throughput of laser direct-write processes.

Efficient generation of Bessel beam arrays by means of an SLM

Abstract: We use a Spatial Light Modulator (SLM) to produce arrays of Bessel beams by using multiple axicon phase-masks on the SLM. This approach utilises the whole of the SLM, rather than just a thin annular region (which is the case if the SLM is in the far-field of the generated Bessel beams). Using the whole SLM rather than just an annular region means that the required intensity on the SLM is an order of magnitude lower for a given power in the Bessel beams. Spreading the power over the whole SLM is important for high-power applications such as laser micromachining. We allow the axicons to overlap and interfere in the hologram, so the axial length of the Bessel beam core is maintained as we add more beams to the array.

Single-pass imaging apparatus with image data scrolling for improved resolution contrast and exposure extent

Abstract: An imaging (e.g., lithographic) apparatus for generating an elongated concentrated scan image on an imaging surface of a scan structure (e.g., a drum cylinder) that moves in a process (cross-scan) direction. The apparatus includes a spatial light modulator having a two-dimensional array of light modulating elements for modulating a two-dimensional light field in response to predetermined scan image data, and an anamorphic optical system is used to anamorphically image and concentrate the modulated light onto an elongated imaging region defined on the imaging surface. To avoid smearing, movement of the imaging surface is synchronized by an image position controller with the modulated states of the light modulating elements such that image features of the scan image are scrolled (moved in the cross-scan direction) at the same rate as the cross-scan movement of the imaging surface, whereby the features remain coincident with the same portion of the imaging surface.

Optical imaging with phase-coded aperture

Abstract: Experimental results are shown for an integrated computational imaging system with a phase-coded aperture. A spatial light modulator works as a phase screen that diffracts light from a point object into a uniformly redundant array (URA). Excellent imaging results are achieved after correlation processing. The system has the same depth of field as a diffraction-limited lens. Potential applications are discussed.

Temporally- And Spatially-Resolved Single Photon Counting Using Compressive Sensing For Debug Of Integrated Circuits, Lidar And Other Applications

Abstract: A method for photon counting including the steps of collecting light emitted or reflected/scattered from an object; imaging the object onto a spatial light modulator, applying a series of pseudo-random modulation patterns to the SLM according to standard compressive-sensing theory, collecting the modulated light onto a photon-counting detector, recording the number of photons received for each pattern (by photon counting) and optionally the time of arrival of the received photons, and recovering the spatial distribution of the received photons by the algorithms of compressive sensing (CS).

Holographic display with tilted spatial light modulator.

Abstract: In this paper, we analyze a holographic display system utilizing a phase-only spatial light modulator (SLM) based on liquid crystal on silicon (LCoS). An LCoS SLM works in reflection, and, in some applications, it is convenient to use with an inclined illumination. Even with a highly inclined illumination, the holographic display is capable of good-quality image generation. We show that the key to obtain high-quality reconstructions is the tilt-dependent calibration and algorithms. Typically, an LCoS SLM is illuminated with a plane wave with normal wave vector. We use inclined illumination, which requires development of new algorithms and display characterization. In this paper we introduce two algorithms. The first one is designed to process a digital hologram captured in CCD normal configuration, so it can be displayed in SLM tilted geometry, while the second one is capable of synthetic hologram generation for tilted SLM configuration. The inclined geometry asymmetrically changes the field of view of a holographic display. The presented theoretical analysis of the aliasing effect provides a formula for the field of view as a function of SLM tilt. The incidence angle affects SLM performance. Both elements of SLM calibration, i.e., pixel phase response and wavefront aberrations, strongly depend on SLM tilt angle. The effect is discussed in this paper. All of the discussions are accompanied with experimental results.

Controlling Light Through Optical Disordered Media : Transmission Matrix Approach

Abstract: We experimentally measure the monochromatic transmission matrix (TM) of an optical multiple scattering medium using a spatial light modulator together with a phase-shifting interferometry measurement method. The TM contains all information needed to shape the scattered output field at will or to detect an image through the medium. We confront theory and experiment for these applications and we study the effect of noise on the reconstruction method. We also extracted from the TM informations about the statistical properties of the medium and the light transport whitin it. In particular, we are able to isolate the contributions of the Memory Effect (ME) and measure its attenuation length.

Enhanced two-point resolution using optical eigenmode optimized pupil functions

Abstract: Pupil filters have the capability to arbitrarily narrow the central lobe of a focal spot. We decompose the focal field of a confocal-like imaging system into optical eigenmodes to determine optimized pupil functions, that deliver superresolving scanning spots. As a consequence of this process, intensity is redistributed from the central lobe into side lobes restricting the field of view (FOV). The optical eigenmode method offers a powerful way to determine optimized pupil functions. We carry out a comprehensive study to investigate the relationship between the size of the central lobe, its intensity, and the FOV with the use of a dual display spatial light modulator. The experiments show good agreement with theoretical predictions and numerical simulations. Utilizing an optimized sub-diffraction focal spot for confocal-like scanning imaging, we experimentally demonstrate an improvement of the two-point resolution of the imaging system.

Nondiffracting kagome lattice

Abstract: We introduce a generalized approach to generate an elementary nondiffracting beam, whose transverse intensity is distributed corresponding to a two-dimensional kagome structure. Furthermore, we present an effective experimental implementation via a computer controlled phase controlling spatial light modulator in combination with a specific Fourier filter system. Intensity and phase analysis of the kagome lattice beam accounts for an experimental wave field implementation. Altogether, the examined wave field may be a fundament for the fabrication of large two-dimensional photonic crystals or photonic lattices in kagome symmetry using miscellaneous holographic matter structuring techniques.

Binary encoded computer generated holograms for temporal phase shifting

Abstract: The trend towards real-time optical applications predicates the need for real-time interferometry. For real-time interferometric applications, rapid processing of computer generated holograms is crucial as the intractability of rapid phase changes may compromise the input to the system. This paper introduces the design of a set of binary encoded computer generated holograms (CGHs) for real-time five-frame temporal phase shifting interferometry using a binary amplitude spatial light modulator. It is suitable for portable devices with constraints in computational power. The new set of binary encoded CGHs is used for measuring the phase of the generated electric field for a real-time selective launch in multimode fiber. The processing time for the new set of CGHs was reduced by up to 65% relative to the original encoding scheme. The results obtained from the new interferometric technique are in good agreement with the results obtained by phase shifting by means of a piezo-driven flat mirror.