Phase Modulation Patterns Research Articles

An improved all-optical diffractive deep neural network with less parameters for gesture recognition

As a framework of optical machine learning, all-optical diffractive neural network (D2NN) has delivered an ideal outcome of feature detection and target classification, currently raising high interest in the optics and photonics community. In this paper, we applied an improved D2NN architecture to the field of gesture recognition, which features more complicated contour than the common MNIST handwriting recognition in the previous literature. The proposed network structure incorporates the wavelet-like phase modulation pattern technique and the highway network on the basis of all-optical neural network. Through modulating the phase of incident light, the wavelet-like pattern can substantially reduce the parameters in the network layer. In addition, a highway network is employed to address the vanishing gradient phenomenon in the training process. In the experiment, we numerically achieved blind testing accuracy of 95.6% for identifying ten different gestures, and the number of parameters is only 3% of the regular D2NN. Reliability test and analysis show that the proposed method is a high-efficiency solution with low-parameters expecting for implementation of various machine learning tasks.

Quantum Oscillator Noise Spectroscopy via Displaced Cat States.

Quantum harmonic oscillators are central to many modern quantum technologies. We introduce a method to determine the frequency noise spectrum of oscillator modes through coupling them to a qubit with continuously driven qubit-state-dependent displacements. We reconstruct the noise spectrum using a series of different drive phase and amplitude modulation patterns in conjunction with a data-fusion routine based on convex optimization. We apply the technique to the identification of intrinsic noise in the motional frequency of a single trapped ion with sensitivity to fluctuations at the sub-Hz level in a spectral range from quasi-dc up to 50kHz.

Characterization of Tiled Architecture for C-Band 1-Bit Beam-Steering Transmitarray.

A new implementation of a beam-steering transmitarray is proposed based on the tiled array architecture. Each pixel of the transmitarray is manufactured as a standalone unit which can be hard-wired for specific transmission characteristics. A set of complementary units, providing reciprocal phase-shifts, can be assembled in a prescribed spatial phase-modulation pattern to perform beam steering and beam forming in a broad spatial range. A compact circuit model of the tiled unit cell is proposed and characterized with full-wave electromagnetic simulations. Waveguide measurements of a prototype unit cell have been carried out. A design example of a tiled 10 × 10-element 1-bit beam-steering transmitarray is presented and its performance benchmarked against the conventional single-panel, i.e., unibody, counterpart. Prototypes of the tiled and single-panel C-band transmitarrays have been fabricated and tested, demonstrating their close performance, good agreement with simulations and a weak effect of fabrication tolerances. The proposed transmitarray antenna configuration has great potential for fifth-generation (5G) communication systems.

Continuous and long-term stabilization of degenerate optical parametric oscillators for large-scale optical hybrid computers.

The minimum requirements for an optical reservoir computer, a recent paradigm for computation using simple algorithms, are nonlinearity and internal interactions. A promising optical system satisfying these requirements is a platform based on coupled degenerate optical parametric oscillators (DOPOs) in a fiber ring cavity. We can expect advantages using DOPOs for reservoir computing with respect to scalability and reduction of excess noise; however, the continuous stabilization required for reservoir computing has not yet been demonstrated. Here, we report the continuous and long-term stabilization of an optical system by introducing periodical phase modulation patterns for DOPOs and a local oscillator. We observed that the Allan variance of the optical phase up to 100 ms was suppressed and that the homodyne measurement signal had a relative standard deviation of 1.4% over 62,500 round trips. The proposed methods represent important technical bases for realizing stable computation on large-scale optical hybrid computers.

Diffractive distortion of a pixelated computer-generated hologram with oblique illumination.

Computer-generated holograms (CGHs) have their phase and/or amplitude modulation pattern calculated rather than recorded as for traditional holograms. In practice, the CGH devices are normally pixelated, no matter if they are passive or active ones. In many cases, the reconstruction light illuminates on the CGH devices obliquely, and the pattern generated on the target plane will be distorted from the originally desired one, even if the modulation on the CGH devices has been calibrated for the corresponding illumination angle in CGH calculation and optimization. The distortion is purely related to the diffraction behavior resulting from the geometry of the pixel on the CGH, and therefore diffractive distortion has been coined for this specific phenomenon. In this paper, quantitative analysis of diffractive distortion and a corresponding scheme for correction have been given based on scalar diffraction theory. The proposed concept is that the distortion of the reconstructed image is proportional to the distortion of the signal window. An experiment has been conducted with a phase-type liquid crystal on silicon spatial light modulator (SLM). Both the distortion analysis and the correction scheme have been verified quantitatively for various illumination angles and the direction of the reconstruction light.

Energy adjustment pulse shaping algorithm part II: realization of a spectral intensity design

An accurately controlled arbitrary temporal waveform is required for many applications. To realize accurate pulse shaping, many optimization algorithms have been proposed to design spectral phase modulation patterns. However, as far as the authors know, no intensity optimization algorithm has been proposed. Therefore, in this paper, an algorithm is proposed to design an optimal spectral intensity modulation pattern for shaping short laser pulses. Consequently, it is numerically demonstrated that the proposed algorithm provides suitable spectral intensity modulation patterns, which create more accurate shapes of temporal waveform than those of spectral phase-only modulation.

Energy adjustment pulse shaping algorithm part I: accuracy improvement of phase retrieval IFTA.

Techniques to generate a targeted temporal waveform with high accuracy are desirable to extend the application range for pulse shapers. In this study, a target energy adjustment mechanism is applied to the input-output iterative Fourier transform algorithm (IFTA). It is numerically demonstrated that, considering multi-pulse temporal waveforms, the developed algorithm provides a suitable spectral phase modulation pattern and improves the shape of the temporal waveform compared to that of the input-output IFTA.

An Active Jamming Method Against ISAR Based on Periodic Binary Phase Modulation

Phase modulation technique is of great potential for generating jamming signal in electronic countermeasures. It is still a difficulty to devise a kind of jamming signal capable of generating both false targets deception jamming and barrage jamming. Attentions must be paid to phase modulation patterns and phase values. Inspired by scatter-wave jamming and phase modulation, an active jamming technique against inverse synthetic aperture radar (ISAR) is proposed based on periodic binary phase modulation in this paper. By imposing the periodic binary phase value (0 or π) onto the intercepted radar signal, the frequency properties of radar signal are changed, which result in the corresponding changes on the target echo. Accordingly, the imaging results are reformatted comparing with the target image. Radar pulses are sampled and phase-modulated in the fast time domain as well as the slow time domain, and then the jamming pulses are retransmitted to the target. After ISAR imaging, the false target images are induced. The principle and process of phase modulation are studied in detail. Then, the imaging model of jamming signal is established and the analysis of jamming effects are carried out. The simulation results with single scattering point and real data experiments with a ship show that both deception jamming and barrage jamming can be obtained. The theoretical analysis and simulation results prove the validity of the active jamming technique.

Large-scale spectral bandwidth compression by complex electro-optic temporal phase modulation.

Spectral-temporal shaping of quantum light has important applications in quantum communications and photonic quantum information processing. Electro-optic temporal lenses have recently been recognized as a tool for noise-free, efficient spectral bandwidth manipulation of single-photon wavepackets. However, standard electro-optic time lenses based on single-tone modulation exhibit, limited bandwidth modification factors due to material limitations on phase modulation amplitude. Here we numerically investigate the use of complex electro-optic temporal phase modulation patterns for bandwidth compression of light over multiple orders of magnitude and show the feasibility of their use in photonic interfaces for quantum network applications.

Optimization of Phase Modulation Formats for Suppression of Stimulated Brillouin Scattering in Optical Fibers

We theoretically investigate nonlinear optimization of periodic phase modulation for suppression of stimulated Brillouin scattering (SBS) in single-mode optical fibers. We use nonlinear multiparameter Pareto optimization to find modulations that represent the best tradeoff between SBS and optical linewidth, as measured by its rms value. The optimization uses a temporal-amplitude-domain finite-difference Brillouin solver with noise initiation to find the best phase modulation patterns in the presence of coherent so-called cross-interactions. These can be important in short fibers, when the period is large enough to make the frequency-domain separation of the modulated signal comparable to, or smaller than, the Brillouin gain linewidth. We calculate the SBS threshold for the optimized modulation patterns and find that smaller spectral line spacing improves the SBS threshold for the same linewidth. By contrast, whereas the maximum modulation depth and modulation frequency influence the range of accessible linewidths, they do not significantly alter the threshold for a given linewidth. We investigate the dependence on fiber length and find that while shorter fibers have a higher threshold, the increase is smaller than the often-assumed inverse dependence on length. Furthermore, we find that optimized formats are superior in terms of SBS threshold as well as in terms of linewidth control, compared to random modulation.

Quantitative EEG Signatures through Amplitude and Phase Modulation Patterns

Cortical spatiotemporal signal patterns based on object recognition can be discerned from visual stimulation. These are in the form of amplitude modulation (AM) and phase modulation (PM) patterns, which contain perceptual information gathered from sensory input. A high-density Electroencephalograph (EEG) device consisting of 48 electrodes with a spacing of 5 mm was utilized to measure frontal lobe activity in order to capture event-related potentials from visual stimuli. Four randomized stimuli representing different levels of salient responsiveness were measured to determine if mild stimuli can be discerned from more extreme stimuli. AM/PM response patterns were detected between mild and more salient stimuli across participants. AM patterns presented distinct signatures for each stimulus. AM patterns had the highest number of incidents detected in the middle of the frontal lobe. Through this work, we can expand our encyclopedia of neural signatures to object recognition, and provide a broader understanding of quantitative neural responses to external stimuli. The results provide a quantitative approach utilizing spatiotemporal patterns to analyze where distinct AM patterns can be linked to object perception.

Multilayer recording holographic data storage using a varifocal lens generated with a kinoform.

A multilayer recording method using a varifocal lens generated with a kinoform is presented. In this recording method, a focus position is axially displaced by adding a defocus phase to a phase modulation pattern, which consists of a random phase mask and a computer-generated reference pattern. Shift selectivity and multiplexed recording are experimentally investigated in coaxial holographic data storage. Experimental results show that the proposed method allows the recording of holograms along an optical axis without any mechanical movement.

Femtosecond laser pulse shaping at megahertz rate via a digital micromirror device.

In this Letter, we present a scanner and digital micromirror device (DMD)-based ultrafast pulse shaper, i.e., S-DUPS, for programmable ultrafast pulse modulation, achieving a shaping rate of 2 MHz. To our knowledge, the S-DUPS is the fastest programmable pulse shaper reported to date. In the S-DUPS, the frequency spectrum of the input pulsed laser is first spread horizontally, and then mapped to a thin stripe on the DMD programmed with phase modulation patterns. A galvanometric scanner, synchronized with the DMD, subsequently scans the spectrum vertically on the DMD to achieve a shaping rate up to 10 s MHz. A grating pair and a cylindrical lens in front of the DMD compensate for the temporal and spatial dispersion of the system. To verify the concept, experiments were conducted with the DMD and the galvanometric scanner operated at 2 kHz and 1 kHz, respectively, achieving a 2 MHz speed for continuous group velocity dispersion tuning, as well as 2% efficiency. Up to 5% efficiency of S-DUPS can be expected with high efficiency gratings and optical components of proper coatings.

Efficient freeform lens optimization for computational caustic displays.

Phase-only light modulation shows great promise for many imaging applications, including future projection displays. While images can be formed efficiently by avoiding per-pixel attenuation of light most projection efforts utilizing phase-only modulators are based on holographic principles which rely on interference of coherent laser light and a Fourier lens. Limitations of this type of an approach include scaling to higher power as well as visible artifacts such as speckle and image noise. We propose an alternative approach: operating the spatial phase modulator with broadband illumination by treating it as a programmable freeform lens. We describe a simple optimization approach for generating phase modulation patterns or freeform lenses that, when illuminated by a collimated, broadband light source, will project a pre-defined caustic image on a designated image plane. The optimization procedure is based on a simple geometric optics image formation model and can be implemented computationally efficient. We perform simulations and show early experimental results that suggest that the implementation on a phase-only modulator can create structured light fields suitable, for example, for efficient illumination of a spatial light modulator (SLM) within a traditional projector. In an alternative application, the algorithm provides a fast way to compute geometries for static, freeform lens manufacturing.

Ghost imaging using labyrinth-like phase modulation patterns for high-efficiency and high-security optical encryption

Ghost imaging has attracted more and more current attention due to its marked physical characteristics, and many physical applications, such as sensing and optical security, have been explored. In this letter, we propose ghost imaging using labyrinth-like phase modulation patterns for optical encryption. Since only one phase-only mask should be pre-set and the labyrinth patterns occupy only few spaces, high-efficiency storage or transmission of system keys can be implemented. In addition, each labyrinth pattern (i.e., phase modulation pattern) possesses high randomness and flexibility, hence high security can be guaranteed for the proposed optical encryption.

A new approach to detect and study spatial–temporal intracranial EEG frames

Studies on electroencephalography have revealed pointers for repetitive phase transitions in neocortex at frame rates in the theta and alpha bands. Phase transitions are the first step for frame emergence. Within the frame, brain activity is synchronized and amplitude and phase modulation pattern materialize. The phase patterns have radial symmetry resembling a cone. Cone fitting has been used to detect and study frames in different brain states, including task, awake, sleep and transition into epileptic seizure, revealing signs of disorganization before the seizure episode started. In this paper a new methodology to detect frames is presented. It is faster than the cone fitting previously used to study frames. The results are compared with frames obtained from cone fitting in awake, task, sleep and seizure states. The frames detected by cone fitting and the new method showed high levels of coincidence in time. The disorganization signs observed between pre-ictal period and normal brain state were also observed in the frames detected with the new method. Finally amplitude modulation patterns related to the different behavioral states were clearly distinguishable using the new method frames as time markers for pattern extraction.

Circadian KaiC Phosphorylation: A Multi-Layer Network

Circadian KaiC phosphorylation in cyanobacteria reconstituted in vitro recently initiates a series of studies experimentally and theoretically to explore its mechanism. In this paper, we report a dynamic diversity in hexameric KaiC phosphoforms using a multi-layer reaction network based on the nonequivalence of the dual phosphorylation sites (S431 and T432) in each KaiC subunit. These diverse oscillatory profiles can generate a kaleidoscopic phase modulation pattern probably responsible for the genome-wide transcription rhythms directly and/or indirectly in cyanobacteria. Particularly, our model reveals that a single KaiC hexamer is an energy-based, phosphorylation-dependent and self-regulated circadian oscillator modulated by KaiA and KaiB. We suggest that T432 is the main regulator for the oscillation amplitude, while S431 is the major phase regulator. S431 and T432 coordinately control the phosphorylation period. Robustness of the Kai network was examined by mixing samples in different phases, and varying protein concentrations and temperature. Similar results were obtained regardless of the deterministic or stochastic method employed. Therefore, the dynamic diversities and robustness of Kai oscillator make it a qualified core pacemaker that controls the cellular processes in cyanobacteria pervasively and accurately.

Structural changes induced by microalloying in Cu 46Zr 47−xAl 7Gd x metallic glasses

Circadian KaiC phosphorylation in cyanobacteria reconstituted in vitro recently initiates a series of studies experimentally and theoretically to explore its mechanism. In this paper, we report a dynamic diversity in hexameric KaiC phosphoforms using a multi-layer reaction network based on the nonequivalence of the dual phosphorylation sites (S431 and T432) in each KaiC subunit. These diverse oscillatory profiles can generate a kaleidoscopic phase modulation pattern probably responsible for the genome-wide transcription rhythms directly and/or indirectly in cyanobacteria. Particularly, our model reveals that a single KaiC hexamer is an energy-based, phosphorylation-dependent and self-regulated circadian oscillator modulated by KaiA and KaiB. We suggest that T432 is the main regulator for the oscillation amplitude, while S431 is the major phase regulator. S431 and T432 coordinately control the phosphorylation period. Robustness of the Kai network was examined by mixing samples in different phases, and varying protein concentrations and temperature. Similar results were obtained regardless of the deterministic or stochastic method employed. Therefore, the dynamic diversities and robustness of Kai oscillator make it a qualified core pacemaker that controls the cellular processes in cyanobacteria pervasively and accurately.

The Roles of CPG Phase Modulation and Reflexive Muscular Patterns in Balance Recovery During Walking—A Simulation Study

Most walking assist systems reported are not available for real world environments where frequent perturbations are caused by slips, uneven terrain, slopes and obstacles. It is evident that humans are able to cope with such perturbations with reflexes that cause unconscious, relatively fixed muscular response patterns to perturbations within a short period of time. In our previous study, we showed that artificial reflexes could improve the perturbation resistance for simulated walkers, though the roles of different reflexive mechanisms were not quantitatively clarified. In this study, we focused on the different roles of reflexive muscle responses and the CPG phase modulation mechanism. By proposing and evaluating two stability criteria through a series of simulation experiments, we revealed different roles for two mechanisms in the simulated walkers. These will not only further increase the possibility of realising artificial reflexes for paralysed individuals, but also bring new insights into the field of motor control.

One‐sided Achromatic Phase Apodization for Imaging of Extrasolar Planets

We propose a new approach to direct imaging of extrasolar planets: one-sided phase apodization. It is based on a discovery that an antisymmetric spatial phase modulation pattern imposed over a pupil or a relay plane causes diffracted starlight suppression sufficient for imaging of extrasolar planets. Calculations with specific square-pupil (side D) phase functions, such as demonstrate annulling in at least one quadrant of the diffraction plane to the contrast level of better than 10-12, with an inner working angle down to 3.5λ/D (with a = 3 and = 10-3). Furthermore, our computer experiments show that phase apodization remains effective throughout a broad spectrum (60% of the central wavelength) covering the entire visible-light range. Phase-only modulation has the additional appeal of potential implementation via active segmented or deformable mirrors, thereby combining compensation of random phase aberrations and diffraction halo removal in a single optical element.