Use Of Spatial Light Modulator Research Articles

Low-cost single-shot complex optical field imaging with a simplified aperture

We report a new computational imaging methodology for complex optical field based on a single-frame diffraction intensity pattern acquisition with a simplified aperture and an extremely low-cost industrial machine vision camera. The current design of the apertures for the recovery of complex optical field was suffering from specific coding associated with the use of spatial light modulator or digital micromirror device, where it is difficult to make the optical implementations compact and cost-effective. In this work, we demonstrate that a simplified aperture without any pattern-like coding is efficient to establish the physical constraint for computational reconstruction. The aperture attached to the object defines the imaging region of interest (ROI) with coherent trans-illumination, and only one snapshot of the diffraction intensity pattern is required for recovering the ROI's complex field. Proof-of-concept numerical simulations and optical experiments have been carried out to validate the feasibility, noise robustness, resolution, and potential biological imaging applications of the proposed computational method.

Evaluating the Speckle-SFDI for the Quantification of Optical Properties of Biotissues: Modeling and Validation on Optical Phantoms

The spatial frequency domain imaging (SFDI) method is rapidly emerging for quantitative mapping of the concentration of tissue chromophores and their scattering coefficients. This method analyzes the optical response of tissues to spatially inhomogeneous radiation with different spatial frequencies, which makes it possible to separate the contributions of absorption and scattering to the diffusely reflected light. However, the projection of spatially inhomogeneous radiation usually requires complex optical schemes, including the use of a spatial light modulator, which is difficult to implement in endoscopes. In this work, we evaluate an alternative approach, in which, instead of analyzing deterministic intensity patterns, the diffuse reflectance at different spatial frequencies can be reconstructed based on the information from random speckle patterns projected onto the surface of the studied tissue, which can be generated without the use of spatial light modulators. We evaluated the speckle-SFDI approach by simulating random speckle patterns and their interaction with turbid and absorptive media with tissue-like optical properties, as well as evaluated this approach experimentally using optical phantoms mimicking properties of real biotissues. The error of absorption and reduced scattering estimation on the number of projected speckles, speckle spatial properties, and optical properties of studied samples was assessed. The suggested approach provided an estimation error of ~10–15% for optical parameters. Given the ease of both experimental and analytical implementation of this technique, it can find applications for quantitative analysis of the optical properties of biological tissues, where “classical” SFDI is hard to implement. The major benefit is the possibility to implement the developed approach within endoscopes.

Advanced iterative algorithm for phase calibration of spatial light modulators integrated in optical instrumentation in a vibration environment.

We present a method to obtain the phase modulation characteristic curve of a spatial light modulator (SLM) under severe vibration conditions. The procedure is based on the well-known advanced iterative algorithm (AIA), which allows wavefront extraction from unknown phase-shifted interferograms. Generally, AIA is used to determine the wavefront and the determined phase shifts are of little interest. In contrast, in our method, the main goal of using AIA is to determine the unknown phase shifts induced by an SLM during the calibration procedure. Using a segmented approach to calibration, AIA enables successful calibration even in the presence of additional random phase shifts due to environmental changes. This method has the potential to calibrate SLMs integrated in complex optical instruments with little to no modifications to the optical setup, no matter the environmental conditions. We demonstrate our technique by calibrating an SLM under vacuum conditions (10-5mbar) in a common-path configuration compatible with usage of an SLM as a wavefront modulator at the pupil plane of an instrument. Our technique compensates for the vibrations produced by the vacuum pumps and reduces an order of magnitude the root-mean-squared error of the calibration curve evaluated with vibration errors. Our technique enhances the potential use of SLMs in complex optical systems, including aerospace optical instrumentation.

An All Optical Approach to Construct J-K Flip-Flop by Proper Exploitation of Nonlinear Material

Optical signal is the best suitable one for data processing and digital signal communication for its inherent parallelism and tremendous operational speed. Conventional electronic or optoelectronic devices are unable to fulfill this due to less speed and time delay. In the case of perfect electronic flip-flop, at the time of switching turned ON, there is noticeable propagation delay on the order of nanoseconds. In the case of an opto-electronic flip-flop, although the propagation delays time is much less than those of a pure electronic flip-flop about 10 to 100 times less, there are many disadvantages still have. Some of these disadvantages are delay of response time due to the use of spatial light modulators, an O/E converter that does not operate at all frequencies or wavelengths, and the unavailability of such materials. An optical input encoding methodology may be the alternative for the performance of two inputs all-optical flip-flop operations. These operations may be conducted in all-optical mode and will be parallel in nature. All the operations may be conducted with proper exploitation of some nonlinear materials. In this communication author reported an optical encoding technique for the construction of clocked J-K flip-flop with two inputs. All the operations are conducted by the proper exploitation of nonlinear materials.

Fast Calculation of Computer Generated Holograms for 3D Photostimulation through Compressive-Sensing Gerchberg-Saxton Algorithm.

The use of spatial light modulators to project computer generated holograms is a common strategy for optogenetic stimulation of multiple structures of interest within a three-dimensional volume. A common requirement when addressing multiple targets sparsely distributed in three dimensions is the generation of a points cloud, focusing excitation light in multiple diffraction-limited locations throughout the sample. Calculation of this type of holograms is most commonly performed with either the high-speed, low-performance random superposition algorithm, or the low-speed, high performance Gerchberg–Saxton algorithm. This paper presents a variation of the Gerchberg–Saxton algorithm that, by only performing iterations on a subset of the data, according to compressive sensing principles, is rendered significantly faster while maintaining high quality outputs. The algorithm is presented in high-efficiency and high-uniformity variants. All source code for the method implementation is available as Supplementary Materials and as open-source software. The method was tested computationally against existing algorithms, and the results were confirmed experimentally on a custom setup for in-vivo multiphoton optogenetics. The results clearly show that the proposed method can achieve computational speed performances close to the random superposition algorithm, while retaining the high performance of the Gerchberg–Saxton algorithm, with a minimal hologram quality loss.

Dynamic density shaping of photokinetic E. coli.

Many motile microorganisms react to environmental light cues with a variety of motility responses guiding cells towards better conditions for survival and growth. The use of spatial light modulators could help to elucidate the mechanisms of photo-movements while, at the same time, providing an efficient strategy to achieve spatial and temporal control of cell concentration. Here we demonstrate that millions of bacteria, genetically modified to swim smoothly with a light controllable speed, can be arranged into complex and reconfigurable density patterns using a digital light projector. We show that a homogeneous sea of freely swimming bacteria can be made to morph between complex shapes. We model non-local effects arising from memory in light response and show how these can be mitigated by a feedback control strategy resulting in the detailed reproduction of grayscale density images.

Coaxial superposition of Bessel beams by discretized spiral axicons

BackgroundA diffractive spiral axicon can be used for the generation of a vortex beam with orbital angular momentum. The coaxial superposition of multiple vortices can generate a complex field with off-axis optical vortices. These fields are known as optical vortex lattices. In general, this superposition is done by the use of spatial light modulators. Discretization of the continuous spiral in radial and azimuthal direction introduces additional degrees of freedom and thus, more complex fields are generated.Methods and ResultsHere, we discuss the basic theory for discretized spiral axicons. Then, as an example, we consider a discretized multi-pronged element where radial and azimuthal coordinates are discretized. Simulations of the near-field distribution show the occurrence of additional off-axis vortices with anisotropic character. The number of off-axis vortices depends on the number of discretization steps in azimuthal direction. Theory is confirmed by experiments. The diffractive element used in the experiments was fabricated lithographically. For instance, a Shack-Hartmann sensor was used to measure orbital momentum of on- and off-axis vortices.ConclusionOptical vortex fields can be achieved due to the discretization of the continuous spiral axicon. The resulting field distribution can be seen as superposition of different non-diffracting fundamental vortex modes.

Shaping of cylindrical and 3D ellipsoidal beams for electron photoinjector laser drivers.

With the use of spatial light modulators it became possible to implement in experiments the method of controlling the space-time intensity distribution of femtosecond laser pulses stretched to picosecond duration. Cylindrical and quasi-ellipsoidal intensity distributions were obtained and characterized by means of a 2D spectrograph and a cross-correlator.

Frequency division multiplex-based light spectroscopy.

Light spectrometers are highly versatile state-of-the-art measurement devices. However, using these systems, e.g., in semiconductor device characterization, creates challenging obstacles with respect to measurement time. We present a new, flexible and accurate approach to either characterize optical properties of arbitrary photosensitive devices or examine the spectral components of light reliably. Using a spatial light modulator (SLM) in combination with frequency division multiplexing methods, it is possible to significantly improve signal-to-noise ratios and decrease measurement times. Moreover, the use of SLM ensures a greater reliability of the setup because conventional moving parts are replaced. The feasibility and experimental setup are described in detail. The setup has been validated for various applications by comparative measurements.

Raman amplification of pure side-seeded higher-order modes in hydrogen-filled hollow-core PCF.

We use Raman amplification in hydrogen-filled hollow-core kagomé photonic crystal fiber to generate high energy pulses in pure single higher-order modes. The desired higher-order mode at the Stokes frequency is precisely seeded by injecting a pulse of light from the side, using a prism to select the required modal propagation constant. An intense pump pulse in the fundamental mode transfers its energy to the Stokes seed pulse with measured gains exceeding 60 dB and output pulse energies as high as 8 µJ. A pressure gradient is used to suppress stimulated Raman scattering into the fundamental mode at the Stokes frequency. The growth of the Stokes pulse energy is experimentally and theoretically investigated for six different higher-order modes. The technique has significant advantages over the use of spatial light modulators to synthesize higher-order mode patterns, since it is very difficult to perfectly match the actual eigenmode of the fiber core, especially for higher-order modes with complex multi-lobed transverse field profiles.

Spatial Light Modulator Microscopy

The use of spatial light modulators (SLMs) for two-photon laser microscopy is described. SLM phase modulation can be used to generate nearly any spatiotemporal pattern of light, enabling simultaneous illumination of any number of selected regions of interest. We take advantage of this flexibility to perform fast two-photon imaging or uncaging experiments on dendritic spines and neocortical neurons. By operating in the spatial Fourier plane, an SLM can effectively mimic any arbitrary optical transfer function and thus replace, in software, many of the functions provided by hardware in standard microscopes, such as focusing, magnification, and aberration correction.

Making and identifying optical superpositions of high orbital angular momenta

We report the experimental preparation of optical superpositions of high orbital angular momenta(OAM). Our method is based on the use of spatial light modulator to modify the standard Laguerre-Gaussian beams to bear excessive phase helices. We demonstrate the surprising performance of a traditional Mach-Zehnder interferometer with one inserted Dove prism to identify these superposed twisted lights, where the high OAM numbers as well as their possible superpositions can be inferred directly from the interfered bright multiring lattices. The possibility of present scheme working at photon-count level is also shown using an electron multiplier CCD camera. Our results hold promise in high-dimensional quantum information applications when high quanta are beneficial.

Optimal entanglement concentration for photonic qutrits encoded in path variables

We report on a technique that allows for the entanglement manipulation of qudit states encoded in the linear transverse momentum of photon pairs generated in the process of spontaneous parametric downconversion. It relies on the use of spatial light modulators and interferometric techniques for implementing the desired local measurements. As an application of our method we perform the optimal entanglement concentration of entangled qutrit states, where maximally entangled states are obtained with the maximal success probability. The procedure of entanglement concentration is fundamental for many quantum information tasks, thus showing the potential of our technique for future experimental investigations considering high-dimensional Hilbert spaces.

Robust Structured Light Pattern for Use with a Spatial Light Modulator in 3-D Endoscopy

This article introduces a novel structured light pattern designed to be compatible with the spatial light modulator (SLM) projection. The proposed pattern is a De Bruijn-based sequence applied to a combination of continuous and dashed lines for the pattern. The sequence is coded in the period and duty cycles of the dashed lines. It provides 16 different lines which limits to two the required number of dashed lines needed for identification. The segmentation has been made easier by alternating continuous and dashed lines. As required by the use of SLMs, the sequence has been adapted by making it symmetric. It has been improved by guaranteeing a hamming distance equal to two for two successive dashed lines. The implementation on a virtual model has shown that a subpixel accuracy has been achieved. This pattern has been developped for 3-D endoscopy.

New alternative approach to all-optical flip-flop with nonlinear material

Due to its inherent parallelism and tremendous operational speed, optical signal is the most suitable for data processing and digital communication in various fields. Conventional electronic and opto-electronic systems are unable to fulfill this arena, because of their low speed and time delay. In the case of pure electronic flip-flop, when a switch is turned ON, there is notable propagation delay on the order of nanoseconds. For an opto-electronic flip-flop although the propagation delay time is much less than that of an electronic flip-flop (about 10 to 100 times less), there are many disadvantages. Some of these disadvantages are delay of response time due to the use of spatial light modulators, an O/E converter that does not operate at all frequencies or wavelengths, and the unavailability of such materials. An optical input encoding methodology is proposed for the performance of all-optical flip-flop operations possible for two inputs. These operations were conducted in all-optical mode and are parallel in nature. All the operations are treated with proper exploitation of some nonlinear materials.

Optical mirror trap with a large field of view

Holographic optical tweezers typically require microscope objectives with high numerical aperture and thus usually suffer from the disadvantage of a small field of view and a small working distance. We experimentally investigate an optical mirror trap that is created after reflection of two holographically shaped collinear beams on a mirror. This approach combines a large field of view and a large working distance with the possibility to manipulate particles in a large size range, since it allows to use a microscope objective with a numerical aperture as low as 0.2. In this work we demonstrate robust optical three-dimensional trapping in a range of 1mm x 1mm x 2mm with particle sizes ranging from 1.4 mum up to 45 mum. The use of spatial light modulator based holographic methods to create the trapping beams allows to simultaneously trap many beads in complex, dynamic configurations. We present measurements that characterize the mirror traps in terms of trap stiffness, maximum trapping force and capture range.

Engineering the collected field for single-molecule orientation determination

We theoretically investigate the use of spatial light modulators (SLMs) for transformation of the collected fluorescence field in a high numerical aperture confocal microscope, for improved molecular orientation determination in single-molecule spectroscopy. The electric vector field in the back aperture of the microscope objective is calculated using the Weyl representation and taking into account components emitted at angles above the critical angle of the coverglass-immersion fluid interface. The coherently imaged fluorescence undergoes spatially-dependent phase and polarization transformation by the SLMs, before it passes to a polarization beamsplitter, and is subsequently focused onto two pinholes and single-photon detectors.

SLM microscopy: scanless two-photon imaging and photostimulation using spatial light modulators

Laser microscopy has generally poor temporal resolution, caused by the serial scanning of each pixel. This is a significant problem for imaging or optically manipulating neural circuits, since neuronal activity is fast. To help surmount this limitation, we have developed a “scanless” microscope that does not contain mechanically moving parts. This microscope uses a diffractive spatial light modulator (SLM) to shape an incoming two-photon laser beam into any arbitrary light pattern. This allows the simultaneous imaging or photostimulation of different regions of a sample with three-dimensional precision. To demonstrate the usefulness of this microscope, we perform two-photon uncaging of glutamate to activate dendritic spines and cortical neurons in brain slices. We also use it to carry out fast (60 Hz) two-photon calcium imaging of action potentials in neuronal populations. Thus, SLM microscopy appears to be a powerful tool for imaging and optically manipulating neurons and neuronal circuits. Moreover, the use of SLMs expands the flexibility of laser microscopy, as it can substitute traditional simple fixed lenses with any calculated lens function.

General approach of spatial input encoding for multiplexing and demultiplexing

In optical arithmetic, logic, and algebraic operations, spatial input encoding and decoding techniques have already been established as successful candidates for conducting parallel operations with optics. Many authors around the world proposed various schemes for successful conduction of the operations with different methodologies. We propose a new method of coding of any number input variables at a time with the use of spatial light modulators. In various places of information processing with optics, this method can be exploited successfully. We use this coding principle of any number of input variables in all optical multiplexing/demultiplexing processes.

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.