Four-phase holography for high-quality light field modulation with MEMS phase light modulators

Surface-stabilized antiferroelectric liquid crystals (AFLCs) and V-shape smectics share the spontaneous generation of intermediate transmission states, i.e. analogue grayscale. On the other hand, liquid crystal on silicon (LCOS) appears to be a promising alternative to thin-film transistors (TFTs) in the preparation of reflective microdisplays and spatial light modulators (SLMs). The feasibility of preparing LCOS SLMs using AFLC and V-shaped LCs has been analyzed. A comparative study of a number of AFLC and V-shape materials as candidates for LCOS SLMs has been carried out. Test cells below 1 µm have been prepared using an ITO-coated transparent glass plate and an aluminized silicon back plate mimicking the actual LCOS device. AFLC waveforms compatible to low-voltage operation of the silicon backplane have been demonstrated. V-shape waveforms have been designed and demonstrated as well. The results show that both LC families may be employed in this specific application. Dynamic behavior, with frame rates over 200 Hz, is especially remarkable.

A new holography display technology based on a phase-only spatial light modulator (SLM) is proposed. The normal use of laser diode (LD) light source led to the inevitable speckle noise introduced by the coherence of the laser beam. Algorithms and special diffractive optical elements have been proposed to reduce the speckle noise. In this paper, a selected light-emitted diode (LED) light source was used in the holographic display system to replace the LD light source. The temporal coherence and spatial coherence of the LED were studied. Though the temporal coherence of LED is short, the spatial coherence of the light field can be improved by optimizing the optical paths such as decreasing the emitting area of the light source and so on. A high-power LED with a narrow band-width was selected. An algorithm to generate computer-generated hologram for the SLM was proposed. The phase-only holograms for the display were computed using the coherent light algorithm. Then the phase holograms were uploaded to the SLM. LED was used as the light source to illuminate the SLM uniformly, and the reconstructions can be observed by naked eye. It is demonstrated that LED is an acceptable light source for holographic display. The reconstruction results showed that the speckle noise and multiple reflections were eliminated when LED was used as the light source.

Among known temporal-spatial light modulation methods, there is no realistic method that can precisely control a light pulse simultaneously in the temporal and spatial domains. By careful consideration of the symmetries and topological properties of electromagnetic waves, a novel spatial light modulator has been developed to create different far-field patterns for each wavelength of linearly polarized light composed of various wavelength components. The system consists of an optical rotatory dispersion device, which is like a Faraday rotator, and a spatial light modulator with parallel-alignment nematic liquid-crystal cells. Numerical simulation results show the effectiveness of this new spatial light modulation method.

Plasmonic modes within metal nanostructures play a pivotal role in various nanophotonic applications. However, a significant challenge arises from the fixed shapes of nanostructures post-fabrication, resulting in limited modes under ordinary illumination. A promising solution lies in far-field control facilitated by spatial light modulators (SLMs), which enable on-site, real-time, and non-destructive manipulation of plasmon excitation. Through the robust modulation of the incident light using SLMs, this approach enables the generation, optimization, and dynamic control of surface plasmon polariton (SPP) and localized surface plasmon (LSP) modes. The versatility of this technique introduces a rich array of tunable degrees of freedom to plasmon-enhanced spectroscopy, offering novel approaches for signal optimization and functional expansion in this field. This paper provides a comprehensive review of the generation and modulation of SPP and LSP modes through far-field control with SLMs and highlights the diverse applications of this optical technology in plasmon-enhanced spectroscopy.

Liquid crystal on silicon (LCoS) spatial light modulators (SLMs) are versatile scientific tools relevant to an increasingly wide variety of research and technological applications including digital holography, wavefront correction, optical tweezing, and non-mechanical beam steering to name a few. Since SLMs are used in a multitude of different ways, some aspects of device performance (e.g., response time) are crucial to certain applications while being irrelevant to others. In this work we couple our standard SLMs with a thermo-electric cooler, allowing for tunability of the device operating temperature from 0° to 75 °C. We show that there is an inherent tradeoff between the liquid crystal response time and the phase stability of an SLM, and that the operating temperature offers a means of controlling this tradeoff. Furthermore, this paper aims to provide the reader with a brief but thorough explanation of SLM operating principles and device structure, defines the performance metrics of the SLM, and provides a methodology for measuring the specifications. By allowing control over the SLM operating temperature and detailing how temperature affects device functionality, SLM users are afforded greater experimental flexibility and will be better able to tailor the performance of their device for the given project or application at hand.

Phase-only liquid crystal spatial light modulator (SLM) has been widely used for accurate phase-manipulation in holographic display, optical tweezers, lithography, etc. Due to the nonlinear optical response of liquid crystal and manufacturing defects, the grayscale-phase response could be different for every single SLM device. The calibration for phase modulation is needed for improving the performance of the SLM involved system. The principles of phase-only SLM are reviewed. The main phase calibration methods for SLM are discussed and compared.

A spatial light modulator (SLM) is a key element in several applications, but it is subject to surface deformation due to manufacturing imperfections or environmental factors. Therefore, the current study aims to analyze and compensate for such deformations in a phase-only SLM using a Michelson interferometer. The recorded interferogram represents the interference between the wavefront reflected from the SLM surface (object wave) and a reference wave. Noise in the recorded interferogram can degrade the accuracy of phase measurements. Various digital filtering techniques were applied to improve the signal-to-noise ratio (SNR) of the interferogram. The filtered interferogram enabled accurate phase extraction through Fourier transform processing and side peak selection using a spatial carrier frequency method. Additionally, phase errors caused by the tilt of the reference beam were corrected. Thereafter, the conjugate of the corrected phase distribution was used to calculate a phase-only computer-generated hologram (CGH), which was displayed on the SLM to compensate for surface deformations. The effectiveness of the proposed compensation procedure was confirmed by a second phase measurement, which demonstrated improved SLM performance. This study highlights the impact of combining the interferometric techniques with digital processing for precise surface deformation analysis.

Spatial light modulator (SLMs) based on liquid crystal displays as phase only modulators can be used as programmable, diffractive optics. The field of applications ranges from adaptive optics, beam shapers to beam splitters. The quality of the beam shapers, measured on basis of diffraction efficiency and beam uniformity are the main deficiencies of such optics.Over the years many improvement in the generation of the holographic phase mask could be accomplished, but in the application, deviations in the SLMs lead to a degradation of the optical quality. In this paper we present two methods, to measure and compensate for the inhomogeneity of the maximum phase range and the distortion of the wave front by distortions of the surface layer of the SLM. The presented method allows the calibration of the SLM inside the optical setup.We use an iterative algorithm to address sub-regions of the SLM and measure the diffraction efficiency depending of the phase difference in a binary grating. From this data we can create a spatial map for the phase calibration curve, thus improving the overall efficiency of the SLM.Spatial light modulator (SLMs) based on liquid crystal displays as phase only modulators can be used as programmable, diffractive optics. The field of applications ranges from adaptive optics, beam shapers to beam splitters. The quality of the beam shapers, measured on basis of diffraction efficiency and beam uniformity are the main deficiencies of such optics.Over the years many improvement in the generation of the holographic phase mask could be accomplished, but in the application, deviations in the SLMs lead to a degradation of the optical quality. In this paper we present two methods, to measure and compensate for the inhomogeneity of the maximum phase range and the distortion of the wave front by distortions of the surface layer of the SLM. The presented method allows the calibration of the SLM inside the optical setup.We use an iterative algorithm to address sub-regions of the SLM and measure the diffraction efficiency depending of the phase difference in a binary grating. From this data we can cre...

In this paper we present a method for topography measurement of high gradient reflective microstructures that overcomes the limited numerical aperture (NA) of a digital holographic (DH) system working in reflection. We consider a case when a DH system is unable to register the light reflected from the full sample area due to insufficient NA. To overcome this problem, we propose digital holography in a microscope configuration with an afocal imaging system and a modified object arm in the measurement setup. The proposed modification includes application of a spatial light modulator (SLM) based on liquid crystal on silicon (LCoS) technology for multidirectional plane wave illumination. The variable off-axis illumination enables characterization of the sample regions that cannot be imaged by the limited NA of a classical DH system utilizing on-axis illumination. In the proposed method, the final object topography is merged from a set of captured object waves corresponding to various illumination directions using a novel automatic algorithm. The proposed technique is experimentally validated by full-field measurement of a silicon mold with a high gradient of shape.

A liquid crystal panel for a video projector is often used for holographic television. However, its pixel size and pixel number are not enough for practical holographic 3-D display. Therefore, a multipanel configuration is generally used to increase the viewing window and displayed image size, and many spatial light modulators should be used in them. We propose a novel method to increase the viewing window of a holographic display system. The proposed method, which is implemented by using a mirror module and 4-f lens set, is to reconfigure the beam shape reflected by a spatial light modulator. The equipment is applied to a holographic display system, which has only a single spatial light modulator; a hologram could be displayed in a wider viewing window by the equipment than that of the conventional method. By the proposed method, the resolution of the reconfigured spatial light modulator has double resolution in the horizontal direction. Inversely, the vertical resolution is decreased. Even if the vertical resolution is decreased, a viewer could get 3-D effect because humans get more 3-D information in the horizontal direction. We have experimented using a liquid crystal on silicon (LcOS), whose resolution is 4096×2160 pixels. The reconfigured resolution by the mirror module is 8192×1080 pixels. From the experiments, the horizontal viewing window is almost two times wider than that without the mirror module. As a result, the hologram can be observed binocularly.

Diffractive optical element (DOE) design techniques can be applied to the generation of pattern recognition filters for optical correlators, in which case the spatial light modulator (SLM) in the filler plane is thought of as a real-time DOE. The designer must first select the desired complex pattern recognition filter and then apply DOE design techniques to map the fully complex function onto the limited dynamic range SLM. To illustrate the procedure, we apply the techniques to the problem of implementing a matched filter with limited dynamic range Fourier plane SLM’s. We use computer simulations to evaluate the effectiveness of the technique. We quantify the performance by measuring the mean squared error between the ideal matched output and output from quantized filters. Numerical simulations indicate that the DOE method yields a significant improvement over direct quantization. The improvement in mean squared error comes, however, at the expense of light efficiency. The DOE technique has been applied to design of matched filters with binary phase, ternary phase, and phase-only SLM’s for coherent as well as incoherent optical correlators. The additional phase freedom in the incoherent design results in improved performance, but incoherent systems are limited to correlation with real positive reference scenes. A proof-of-principle laboratory experiment has been constructed to complement the numerical simulations.

Holographic display system that uses six phase-only spatial light modulators (SLMs) performs holographic reconstructions from the phase-hologram of a point cloud that is extracted from 3D object. The SLMs are tiled as a three by two matrix on a virtual planar surface. The alignment is successful and the display system generates large holographic reconstructions. The proposed system can be used either to obtain reconstructions of large objects with a narrow field of view or reconstructions of smaller objects with a broader field of view. Therefore, since field of view is broader for smaller objects, observer has the flexibility to move around the reconstruction within a larger angle. This flexibility increases the motion parallax and as a consequence it increases the quality of 3D perception. Results show that even with three SLMs in horizontal direction the 3D perception is significantly increased. Experimental results are satisfactory.

For their capacity to shape optical wavefronts in real time into any desired illumination pattern, phase-only Spatial Light Modulators (SLM) have proven to be powerful tools for optical trapping and micromanipulation applications. SLMs are also becoming increasingly utilized in selective photo-stimulation of groups of neurons in the brain. However, conventional SLM based wavefront modulation introduces artifacts that are particularly detrimental for photo-stimulation applications. The primary issue is the unmodulated light that travels along the 0th order of diffraction. This portion of light is commonly blocked at the center of the object plane, which prevents photo-stimulation in the blocked region. We demonstrate a virtual lens configuration that moves the 1st order diffraction with the desired illumination pattern into the Fourier plane of the 0th order light. This virtual lens setup makes the whole field of view accessible for photo-stimulation and eliminates the need for removing the 0th order light in two-photon applications. Furthermore, in an example application to reconstruct a pattern consisting of an array of points, the virtual lens configuration increases the uniformity of the intensities these points. Moreover, diffraction-induced artifacts are also significantly reduced within the target plane. Therefore, our proposed high fidelity configuration yields target points with high signal to noise ratio.

A lensless Vanderlugt optical correlator using two phase-only spatial light modulators (SLMs) is proposed. The SLMs are used for displaying input and filter patterns respectively. The SLMs are also used as programmable lenses in order to realize the lensless construction. This lensless system is simple and its alignment adjustment is easy. The performance of the SLMs as programmable lenses is also described.

Three-dimensional light sculpting using a geometric analysis