Reflective Spatial Light Modulator Research Articles

Recent results of medium wave infrared compressive sensing.

The application of compressive sensing (CS) for imaging has been extensively investigated and the underlying mathematical principles are well understood. The theory of CS is motivated by the sparse nature of real-world signals and images, and provides a framework in which high-resolution information can be recovered from low-resolution measurements. This, in turn, enables hardware concepts that require much fewer detectors than a conventional sensor. For infrared imagers there is a significant potential impact on the cost and footprint of the sensor. When smaller focal plane arrays (FPAs) to obtain large images are allowed, large formats FPAs are unnecessary. From a hardware standpoint, this benefit is independent of the actual level of compression and effective data rate reduction, which depend on the choice of codes and information recovery algorithm. Toward this end, we used a CS testbed for mid-wave infrared (MWIR) to experimentally show that information at high spatial resolution can be successfully recovered from measurements made with a small FPA. We describe the highly parallel and scalable CS architecture of the testbed, and its implementation using a reflective spatial light modulator and a focal plane array with variable pixel sizes. We also discuss the impact of real-world devices and the effect of sensor calibration that must be addressed in practice. Finally, we present preliminary results of image reconstruction, which demonstrate the testbed operation. These results experimentally confirm that high-resolution spatial information (for tasks such as imaging and target detection) can be successfully recovered from low-resolution measurements. We also discuss the potential system-level benefits of CS for infrared imaging, and some of the challenges that must be addressed in future infrared CS imagers designs.

Research on Characteristics of Reflective Liquid Crystal Spatial Light Modulator

According to the extended Jones matrix of reflective liquid crystal spatial light modulator, a method is proposed to determine the oblique incident angle range and the applied voltage range. According to the distribution of liquid crystal molecular director of each layer, extended Jones matrix of liquid crystal spatial light modulator for different incident angles and the equivalent refractive index of each layer are obtained. Then, amplitude and phase modulation characteristics are obtained based on extended Jones matrix and each layer of equivalent refractive index. Finally, the amplitude modulation characteristics are combined with the phase modulation characteristics, and the oblique incident angle range and the applied voltage range in phase-only modulation mode are obtained. The experimental results show that the proposed method is effective for reflective liquid crystal spatial light modulator to determine the incidence angle and the applied voltage in phase-only modulation mode.

In-line FINCH super resolution digital holographic fluorescence microscopy using a high efficiency transmission liquid crystal GRIN lens

We report a new optical arrangement that creates high-efficiency, high-quality Fresnel incoherent correlation holography (FINCH) holograms using polarization sensitive transmission liquid crystal gradient index (TLCGRIN) diffractive lenses. In contrast, current universal practice in the field employs a reflective spatial light modulator (SLM) to separate sample and reference beams. Polarization sensitive TLCGRIN lenses enable a straight optical path, have >90% transmission efficiency, are not pixilated, and are free of many limitations of reflective SLM devices. For each sample point, two spherical beams created by a glass lens in combination with a polarization sensitive TLCGRIN lens interfere and create a hologram and resultant super resolution image.

Vectorial optical field generator for the creation of arbitrarily complex fields

Generation of vectorial optical fields with complex spatial distribution in the cross section is of great interest in areas where exotic optical fields are desired, including particle manipulation, optical nanofabrication, beam shaping and optical imaging. In this work, a vectorial optical field generator capable of creating arbitrarily complex beam cross section is designed, built and tested. Based on two reflective phase-only liquid crystal spatial light modulators, this generator is capable of controlling all the parameters of the spatial distributions of an optical field, including the phase, amplitude and polarization (ellipticity and orientation) on a pixel-by-pixel basis. Various optical fields containing phase, amplitude and/or polarization modulations are successfully generated and tested using Stokes parameter measurement to demonstrate the capability and versatility of this optical field generator.

A digital laser for on-demand laser modes

Customizing the output beam shape from a laser invariably involves specialized optical elements in the form of apertures, diffractive optics and free-form mirrors. Such optics require considerable design and fabrication effort and suffer from the further disadvantage of being immutably connected to the selection of a particular spatial mode. Here we overcome these limitations with the first digital laser comprising an electrically addressed reflective phase-only spatial light modulator as an intra-cavity digitally addressed holographic mirror. The phase and amplitude of the holographic mirror may be controlled simply by writing a computer-generated hologram in the form of a grey-scale image to the device, for on-demand laser modes. We show that we can digitally control the laser modes with ease, and demonstrate real-time switching between spatial modes in an otherwise standard solid-state laser resonator. Our work opens new possibilities for the customizing of laser modes at source.

Polarization phase shifting interferometric technique for phase calibration of a reflective phase spatial light modulator

Calibration of phase in spatial light modulators is a prerequisite for applications where a prespecified phase distribution needs to be imple- mented over the surface of the modulator. The present work proposes a full-field polarization phase shifting interferometric technique, based on the Twyman-Green interferometer, for the purpose. © 2013 Society of Photo-Optical

Holographic superresolution using spatial light modulator

This paper describes a technique of superresolution using a reflective mode spatial light modulator, a coherent source of light, and a transmission mode object placed in the input plane of an imaging system, in particular we are using for the demonstration a 4f system. The spatial light modulator (SLM) enables for creating tilted plane wave illumination and it also permits adding constant phases of 0, π/2, 3π/2 and π. The angle of illumination created by the SLM is defined according to the dimension of aperture placed at the Fourier plane of 4f optical system. For each defined angle of illumination created by the SLM four holograms corresponding to the transmission mode object are recorded. This system is capable of retrieving phase and amplitude information of the images, corresponding to each impinging illumination. By simply adding these complex images a super resolved image is obtained.

Chalmers interferometric test using a reflective spatial light modulator

In this paper, we propose the use of a reflective spatial light modulator (RSLM) controlled by a PC, instead of a metal plate with holes, to produce the interference patterns in Chalmers interferometric test. The main advantage of the proposed method is that with an RSLM, it is possible to test and obtain an interference pattern for any zone of a surface or lens by opening two appropriate apertures. This increases the accuracy of the results and reduces the time required to obtain them.

Spatially resolved phase objects using Mach–Zehnder interferometry

Phase characterization with a good spatial resolution is crucial for focused beams in nonlinear media. The phase-shifting interferometry technique, using the least-squares error criterion for several interferograms, is implemented using a reflective spatial light modulator (SLM). The method provides a convenient calibration for any phase-shift steps. The reliability of the proposed method is checked by direct comparison with results obtained by the Fourier transform method as well as using a previously characterized circular phase object.

反射式液晶空间光调制器电控光束偏转

An electro-controllable spatial light modulator of 8 m spatial resolution was employed to deflect the 632 nm He-Ne laser beam to high steering angle. The phase shift characteristic of the modulator related to the applied gray level was measured by co-focal interferometry and the maximum phase shift is 3 . According to the principle of binary optics, Different phase models were designed to deflect the incident laser beam. The incident laser beam can be deflected by 10 mrad apart from the incident laser when the phase level is eight, and the diffraction efficiency is high as 46%. The experimental and numerical results indicate that beam deflection with large angle can be achieved by employing the reflective liquid crystal phase-mode spatial light modulator, and the diffraction efficiency is mainly limited by the fill factor and the fly-back region in the liquid crystal cell.

Advances in Ultra Short Pulse Laser based Parallel Processing using a Spatial Light Modulator

Abstract Presented here are latest advances in ultra short pulse laser based parallel processing using a spatial light modulator (SLM), which has the potential for use in high throughput precision patterning of photovoltaic and other device layers. Ultra short laser pulses allow selective material removal with minimal energy density, while here a computer- generated hologram driven reflective SLM is used to transform a single beam into multiple beamlets for increased process throughput. Based on this technique, the precision patterning of silicon, titanium, thin film ITO and metal on flexible and glass substrates is demonstrated and the benefits and current limitations discussed.

Geometrically superresolved lensless imaging using a spatial light modulator

In this paper we introduce an imaging system based on a reflective phase-only spatial light modulator (SLM) in order to perform imaging with improved geometric resolution. By using the SLM, we combine the realization of two main abilities: a lens with a tunable focus and a phase function that, after proper free-space propagation, is projected as an amplitude distribution on top of the inspected object. The first ability is related to the realization of a lens function combined with a tunable prism that yields a microscanning of the inspected object. This by itself improves the spatial sampling density. The second ability is related to a projection of a phase function that is computed using an iterative beam-shaping Gerchberg-Saxton algorithm. After the free-space propagation from the SLM toward the inspected object, an amplitude pattern is generated on top of the object. This projected pattern and a set of low-resolution images with relative shift are interlaced and, after applying the proper regularization method, a geometrically superresolved image is reconstructed.

Experimental verification of optical image encryption based on interference

We present experimental results to verify the optical image encryption based on interference. The optical experiment is performed by using a reflective phase-only spatial light modulator (SLM) to generate the desired phase retardations. A hologram plate is employed to record the modulated wavefronts in a double-step-holographic-exposure process. The experiment results are in good agreement with the numerical simulations of the encryption algorithm, which demonstrates the feasibility of the optical image encryption in actual optical systems.

Accurate optical wavefront reconstruction based on reciprocity of an optical path using low resolution spatial light modulators

A method for high precision optical wavefront reconstruction using low resolution spatial light modulators (SLMs) was proposed. It utilizes an adiabatic waveguide taper consisting of a plurality of single-mode waveguides to decompose an incident light field into simple fundamental modes of the single-mode waveguides. By digital generation of the conjugate fields of those simple fundamental modes a field proportional to the original incident light field might be reconstructed accurately based on reciprocity. Devices based on the method using transparent and reflective SLMs possess no aberration like that of a conventional optic lens and are able to achieve diffraction limited resolution. Specifically on the surface of the narrow end of a taper a resolution much higher than half of the wavelength is attainable. The device may work in linear mode and possesses unlimited theoretical 3D space-bandwidth product (SBP). The SBP of a real device is limited by the accuracy of SLMs. A pair of 8-bit SLMs with 1000 × 1000 = 10 6 pixels could provide a SBP of about 5 × 10 4. The SBP may expand by 16 times if 10-bit SLMs with the same number of pixels are employed or 16 successive frames are used to display one scene. The device might be used as high precision optical tweezers, or employed for continuous or discrete real-time 3D display, 3D measurement, machine vision, etc.

Adaptive Phase Modulation for Multiphoton Microscopy

Tissue structures present index mismatches at a variety of spatial scales that can aberrate the focal volume and thus blur cellularly resolved multiphoton images acquired within biological tissues and live animals. We are investigating the extent to which adaptive phase modulation can be used to reconstruct the point-spread-function (PSF) and enable deeper and clearer multiphoton imaging into biological tissues. To do this, a Ti:Sapphire beam is reflected off of a reflective spatial light modulator conjugate to the objective pupil plane.

Laser line shape recovery system based on a double pixelated axilens

We describe a scanning system for shape recovery that employs a pair of one-dimensional interlaced axilenses encoded onto a reflective liquid-crystal spatial light modulator. The design of these axilenses with opposite depth presets allows the generation of a high-quality laser line pattern with extended depth of focus, which is applied in the shape recovery. Other attributes of the system allow the scanning of objects whose lateral dimensions are larger that those of the spatial light modulator itself. The high performance of the scanning system is demonstrated by its application to the shape recovery of ceramic objects.

Control and measurement of spatially inhomogeneous polarization distributions in third-harmonic generation microscopy

We demonstrate in situ characterization of a spatially varying polarization state of an optical field at the focus of a scanning third-harmonic generation (THG) optical microscope. Polarization projections are measured by forming THG images of a polystyrene microsphere scanned through the focused beam and combined in a noniterative phase-retrieval algorithm. Controlled spatially varying polarization states are introduced by imaging spatially inhomogeneous polarization distributions constructed with reflective spatial light modulator to the focal plane of a microscope objective.

Compensation Of Tissue-induced PSF Aberrations Using Adaptive Phase Modulation

View Large Image | View Hi-Res Image | Download PowerPoint SlideTissue structures present index mismatches at a variety of spatial scales that can aberrate the focal volume and thus blur cellularly resolved multiphoton images acquired within biological tissues and live animals. We are surveying the types of aberrations that are caused by a variety of tissues to determine the best phase modulation strategies for adaptively correcting the excitation wavefront. A Ti:Sapphire beam is reflected off of a reflective spatial light modulator conjugate to the objective pupil plane. The excitation point-spread-function (PSF) is directly imaged with a separate objective mounted laterally to the optic axis. We find that the fluorescence signal increases with increasing size of the scattering structures. Resolution degradation, however, reaches a maximum with scatterer spatial frequencies at one tenth of the maximal frequency allowed by the focusing objective NA. PSF aberrations can be somewhat compensated by modulating the phase at the back aperture using Zernike polynomials as a basis set for increasing overall image brightness. (See figure for uncorrected vs corrected PSF's through mouse peritoneum.) Initial results show that spherical aberration is a problem, but not the only problem. (Research supported by NIH/NIBIB 41 RR04224 and NIH/NCI R01 CA116583.)

A novel three-dimensional holographic display system based on LC-R2500 spatial light modulator

A novel holographic display system is proposed in this paper. The system takes LC-R2500, a kind of reflective liquid crystal spatial light modulator, (LC-SLM) as the core display unit, which can meet the requirement of real-time reconstruction of three-dimensional (3D) objects from holograms in free space. The relationship between hologram recording and image reconstruction is discussed, and the parameters associated with the magnification of reconstructed image over original object are determined. Experimental results of holographic display using the system are also given in the end.

The Silicon Backplane Design for an LCOS Polarization-Insensitive Phase Hologram SLM

Polarization-insensitivity is achieved in a reflective spatial light modulator by laying a quarter-wave plate (QWP) at the incident wavelength directly over the mirror pixels of a silicon backplane, and forming a nematic Freedrickcz cell over the QWP to modulate the reflected phase. To achieve the highest drive voltage from the available silicon process, a switched voltage common front electrode design is described, with variable amplitude square wave drive to the pixels to maintain constant root-mean-square drive and minimize phase fluctuations during the dc balance refresh cycle. The silicon has been fabricated and liquid-crystal-on-silicon cells both with and without the QWP assembled; applications include optically transparent switches for optical networks, beam steering for add-drop multiplexers for wavelength-division-multiplexing telecommunications, television multicast, and holographic projection.