Dynamic Holograms Research Articles

A holographic telementoring system depicting surgical instrument movements for real-time guidance in open surgeries

Background and ObjectiveDuring open surgeries, telementoring serves as a valuable tool for transferring surgical knowledge from a specialist surgeon (mentor) to an operating surgeon (mentee). Depicting the intended movements of the surgical instruments over the operative field improves the understanding of the required tool-tissue interaction. The objective of this work is to develop a telementoring system tailored for open surgeries, enabling the mentor to remotely demonstrate the necessary motions of surgical instruments to the mentee. MethodsA remote telementoring system for open surgery was implemented. The system generates visual cues in the form of virtual surgical instrument motion augmented onto the live view of the operative field. These cues can be rendered on both conventional screens in the operating room and as dynamic holograms on a head mounted display device worn by the mentee. The technical performance of the system was evaluated, where the operating room and remote location were geographically separated and connected via the Internet. Additionally, user studies were conducted to assess the effectiveness of the system as a mentoring tool. ResultsThe system took 307 ± 12 ms to transmit an operative field view of 1920 × 1080 resolution, along with depth information spanning 36 cm, from the operating room to the remote location. Conversely, it took 145 ± 14 ms to receive the motion of virtual surgical instruments from the remote location back to the operating room. Furthermore, the user studies demonstrated: (a) mentor's capability to annotate the operative field with an accuracy of 3.92 ± 2.1 mm, (b) mentee's ability to comprehend and replicate the motion of surgical instruments in real-time with an average deviation of 12.8 ± 3 mm, (c) efficacy of the rendered dynamic holograms in conveying information intended for surgical instrument motion. ConclusionsThe study demonstrates the feasibility of transmitting information over the Internet from the mentor to the mentee in the form of virtual surgical instruments’ motion and projecting it as holograms onto the live view of the operative field. This holds potential to enhance real-time collaborative capabilities between the mentor and the mentee during an open surgery.

Lithium niobate thin film electro-optic modulator

Abstract The linear electro-optic effect offers a valuable means to control light properties via an external electric field. Lithium niobate (LN), with its high electro-optic coefficients and broad optical transparency ranges, stands out as a prominent material for efficient electro-optic modulators. The recent advent of lithium niobate-on-insulator (LNOI) wafers has sparked renewed interest in LN for compact photonic devices. In this study, we present an electro-optic modulator utilizing a thin LN film sandwiched between top and bottom gold (Au) film electrodes, forming a Fabry–Pérot (F–P) resonator. This resonator exhibits spectral resonance shifts under an applied electric field, enabling efficient modulation of reflected light strength. The modulator achieved a 2.3 % modulation amplitude under ±10 V alternating voltage. Our approach not only presents a simpler fabrication process but also offers larger modulation amplitudes compared to previously reported metasurface based LN electro-optic modulators. Our results open up new opportunities for compact electro-optic modulators with applications in beam steering devices, dynamic holograms, and spatial light modulators, and more.

Features of application of adaptive interferometric fiber sensors of acoustic emission to monitor the condition of polymer composite materials

The results of an experimental study of the operation of fiber optic sensors (FOS) of acoustic emission introduced into the structure of polymer composite materials (PCM) are presented. The reliability and fault tolerance of FOS under critical mechanical loads on PCM was assessed, and the influence of the presence of FOS embedded into the structure of PCM on the mechanical characteristics of the material was investigated. For demodulation of FOS output signals, the principles of adaptive holographic interferometry based on two-wave mixing at dynamic hologram formed in a photorefractive crystal are used.

Complex RGB spatial light modulation with a dual-layer in-plane switching liquid crystal panel

Complex RGB spatial light modulators are required to produce full-color holographic displays. In particular, complex spatial light modulation, which modulates the amplitude and phase of incident light is essential for noiseless dynamic computer-generated hologram synthesis. The feasibility of full-color holographic image generation through the dual-layer in-plane switching liquid crystal plane is theoretically validated and experimentally demonstrated.

Controllable Deformation Modulated Multi‐Functionality for Phase‐Gradient Metamaterials

AbstractTunable metamaterials offer versatile approaches to achieve the dynamic manipulation of electromagnetic waves with various dimensionality. Recently, mechanical approaches have been extensively employed to construct reconfigurable metamaterials with simple composition and superior mechanical characteristics. Mechanical modulation methods in phase‐gradient metamaterials are even more worthy of being investigated to facilitate valuable applications. Here, an in‐plane rotational deformation principle is proposed to assist the structural design of reconfigurable phase‐gradient metamaterials by integrating split ring resonators (SRRs) on the hyperelastic kirigami substrate. The orientations and split angles of SRRs are explored to manipulate the amplitudes and phases of cross‐polarized transmittance under x‐polarized incidence, respectively. The tensile strains dramatically modulate the amplitudes yet not the gradient phase. As proof‐of‐concept, a reconfigurable metalens is elaborately designed to realize tunable focus location and number by regulating the transmittance amplitudes of meta‐atoms via stretching the kirigami substrate. Furthermore, a holographic metamaterial is developed to perform dynamic hologram on the imaging plane under the strain 0% and 40%. The proposed mechanical deformation principle offers a promising platform for dynamic manipulation of the wavefront and may promote the conformal and flexible designs in certain cases and enlarge the potential applications of meta‐devices in imaging and information encryption.

Isotropic Two-Dimensional Differentiation Based on Dual Dynamic Volume Holograms

We study the use of two dynamic thick holograms to realize isotropic two-dimensional (2D) differentiation under Bragg diffraction. Acousto-optic modulators (AOMs) are used as dynamic volume holograms. Using a single volume hologram, we can accomplish a first-order derivative operation, corresponding to selective edge extraction of an image. Since the AOM is a 1D spatial light modulator, filtering of the image only occurs along the direction of the sound propagation. To achieve 2D image processing, two AOMs are used within a Mach–Zehnder interferometer (MZI). By aligning one AOM along the x-direction on the upper arm of the interferometer and another AOM along the y-direction on the lower arm, we accomplish the sum of two first-derivative operations, leading to isotropic edge extraction. We have performed both computer simulations and optical experiments to verify the proposed idea. The system provides additional operations in optical computing using AOMs as dynamic holograms.

Experimental Synthesis and Demonstration of the Twisted Laguerre–Gaussian Schell-Mode Beam

The twisted Laguerre–Gaussian Schell-model (TLGSM) beam is a novel type of partially coherent beam embedded with both the second-order twist phase and the classical vortex phase. The intriguing properties induced by the interaction of the two types of phases have been demonstrated theoretically quite recently. In this work, we introduce a flexible way to experimentally synthesize a TLGSM beam with controllable twist strength. The protocol relies on the discrete pseudo-mode representation for the cross-spectral density of a TLGSM beam, in which the beam is viewed as an incoherent superposition of a finite number of spatially coherent modes. We show that all these pseudo modes endowed with random phases are mutually uncorrelated and can be encoded into a single frame of a dynamic computer-generated hologram. By sequentially displaying dynamic holograms on a single spatial-light modulator, the controllable TLGSM beam can be synthesized experimentally. The joint effect of the two phases on the propagation and self-reconstruction characteristics of the synthesized beam has also been studied in the experiment.

Pulse recording of dynamic holograms in bismuth silicate crystal in a broad wavelength range

The formation of dynamic holograms in a photorefractive bismuth silicate crystal by nanosecond laser pulses with a change in the radiation wavelength is studied. An original scheme for recording holograms is proposed to preserve the grating period when operating at different wavelengths. The method of pulsed recording of dynamic gratings based on the proposed optical scheme is applied, which ensures the fulfillment of the Bragg condition for probing radiation. The originality of the scheme lies in the use of the first orders of diffraction of a transmitting diffraction grating as the reference and signal waves, as well as a telescopic system used to fix the period of the recorded grating, regardless of the wavelength used. Kinetic dependences of the diffraction efficiency of dynamic holograms in a photorefractive bismuth silicate crystal are obtained with a change in the wavelength of recording radiation in the actual spectral range (from 450 nm to 600 nm). The effect of the manifestation of competing recording mechanisms of short-lived (hundreds of microseconds) and long-lived (seconds) gratings, the contribution of which depends on the wavelength of the radiation recording the hologram, has been established. The optimal wavelength for obtaining the highest diffraction efficiency of holograms is determined. It is shown that radiation in the blue-green region of the spectrum leads to the predominant recording of a short-lived grating, while long-lived gratings dominate in the red region of the spectrum. The need to study photorefractive crystals of the sillenite family is determined by their use for multiplex recording of dynamic holograms and the implementation of the adaptive interferometry method to track changes in objects in real time.

Dynamic complex opto-magnetic holography

Despite recent significant progress in real-time, large-area computer-generated holography, its memory requirements and computational loads will be hard to tackle for several decades to come with the current paradigm based on a priori calculations and bit-plane writing to a spatial light modulator. Here we experimentally demonstrate a holistic approach to serial computation and repeatable writing of computer-generated dynamic holograms without Fourier transform, using minimal amounts of computer memory. We use the ultrafast opto-magnetic recording of holographic patterns in a ferrimagnetic film with femtosecond laser pulses, driven by the on-the-fly hardware computation of a single holographic point. The intensity-threshold nature of the magnetic medium allows sub-diffraction-limited, point-by-point toggling of arbitrarily localized magnetic spots on the sample, according to the proposed circular detour-phase encoding, providing complex modulation and symmetrical suppression of upper diffractive orders and conjugated terms in holographically reconstructed 3-D images.

Near-infrared sensitive two-wave mixing adaptive interferometer based on a liquid crystal light valve with a semiconductor substrate.

Two-wave mixing adaptive interferometer based on a liquid crystal light valve with a semiconductor GaAs substrate is realized and studied at 1064 nm wavelength. The local response of the dynamic hologram recorded in the liquid crystal layer of the light valve allows for detection of small phase modulations of the object beam. The characteristics of the interferometer are estimated experimentally. The temporal adaptability lies in the subsecond range. The large optical nonlinearity of the cell is favorable for measurements of small displacements with high sensitivity.

Coherent beam amplification with dynamic holograms in glass-forming molecular azobenzene-based materials

Self-diffraction of two coherent light waves that record a holographic grating in thin films of azobenzene-containing molecular glass-forming materials is used for intensity enhancement of a weak beam in expense of the strong beam intensity. The intensity of a weak probe beam is doubled at interaction length of only 8 µm thus pointing to a very high specific coupling constant. The characteristic time of the intensity redistribution is relatively long, on the order of 200 s. Consequently, the underlying process of pronounced Kerr-type optical nonlinearity is related, most probably, to the photoinduced mass transfer.

PHOTOINDUCED GYROTROPY OF POLARIZATION-SENSITIVE LUMINESCENT HOLOGRAM MATERIALS BASED ON AQUEOUS MEDIA

The photoinduced gyrotropy (nonlinear optical activity) of polarization-sensitive luminescent recording materials based on various drinking and mineral waters are herein studied by the methods of polarizationluminescent holography. Photoluminescence spectra and spectra of the degree of circularity of (circular)polarization luminescence of the reconstructed phantom object are obtained. It is shown that during the transition between the racemic to chirally pure phases, a significant modification of the spectra of dynamic multiplex luminescent Denisyuk holograms is observed in the medium, in particular, a polarizationholographic memory of the gyrotropic properties is expressed in the considered water media. The polarization-holographic analysis of the optical polarization spectra of aqueous media makes it possible to obtain additional information about anisotropic-gyrotropic holographic materials, namely, the intrinsic chirality of the components of each compound present in the medium.

Fiber-optic vector acoustic receiver based on adaptive holographic interferometer

A mobile scalar–vector acoustic receiver is proposed, experimentally implemented and investigated. The key components of the receiver are (a) the six-channel fiber-optic coil-type sensor configured as to detect three projections of acoustic intensity vector, (b) the six-channel optical phase demodulator based on six-channel adaptive holographic interferometer configured with use of dynamic holograms multiplexed in a photorefractive crystal of cadmium telluride and (c) the signals recording ADC-based system combined with software package for data processing. Field tests of the developed receiver applied for obtaining scalar and vector parameters of acoustic waves generated by a stationary and moving acoustic source in open air and water area are carried out. Experimental results show perceptiveness of use of the fiber-optical adaptive interferometry system for bearing of weak acoustic sources in real conditions.

Holographic Display System to Suppress Speckle Noise Based on Beam Shaping

In this paper, a holographic system to suppress the speckle noise is proposed. Two spatial light modulators (SLMs) are used in the system, one of which is used for beam shaping, and the other is used for reproducing the image. By calculating the effective viewing angle of the reconstructed image, the effective hologram and the effective region of the SLM are calculated accordingly. Then, the size of the diffractive optical element (DOE) is calculated accordingly. The dynamic DOEs and effective hologram are loaded on the effective regions of the two SLMs, respectively, while the wasted areas of the two SLMs are performed with zero-padded operations. When the laser passes through the first SLM, the light can be modulated by the effective DOEs. When the modulated beam illuminates the second SLM which is loaded with the effective hologram, the image is reconstructed with better quality and lower speckle noise. Moreover, the calculation time of the hologram is reduced. Experiments indicate the validity of the proposed system.

Fresnel incoherent correlation hologram recording in real-time

Fresnel incoherent correlation holography (FINCH) showed its potential for three-dimensional images with super-resolution by using incoherent light sources. However, regular FINCH requires at least two times of holographic recording, and is not suitable for the instantaneous measurement of dynamic objects. Here, we propose the single-shot FINCH technology to realize real-time imaging. With three dual-lens patterns mixed regularly into a phase mask, the new system can capture a compound hologram, which contains three phase-shifted sub-holograms on different areas of image plane. We draw a comparison of both methods, and find it suitable for single-shot FINCH to realize holographic recording in real-time. A dice is used as a test object to record its dynamic rotational movement and holograms from different angles. We also clearly record the whole process of a drop of glue falling vertically under the force of gravity. Experimental results show the capability of single-shot FINCH system to record moving objects dynamically. This system provides a simple and flexible way to achieve real-time recording based on FINCH.

Realizing Colorful Holographic Mimicry by Metasurfaces.

Mimicry is a biological camouflage phenomenon whereby an organism can change its shape and color to resemble another object. Herein, the idea of biological mimicry and rich degrees of freedom in metasurface designs are combined to realize holographic mimicry devices. A general mathematical method, called phase matrix transformation, to accomplish the holographic mimicry process is proposed. Based on this method, a dynamic metasurface hologram is designed, which shows an image of a "bird" in the air, and a distinct image of a "fish" when the environment is changed to oil. Furthermore, to make the mimicry behavior more generic, holographic mimicry operating at dual wavelengths is also designed and experimentally demonstrated. Moreover, the fully independent phase modulation realized by phase matrix transformation makes the working efficiency of the device relatively higher than the conventional multiwavelength holographic devices with off-axis illumination or interleaved subarrays. The work potentially opens a new research paradigm interfacing bionics with nanophotonics, which may produce novel applications for optical information encryption, virtual/augmented reality (VR/AR), and military camouflage systems.

A deep learning approach for the fast generation of acoustic holograms.

Acoustic holographic techniques are crucial in diverse applications, such as three-dimensional holographic display and particle manipulation. However, conventional methods for computer-generated acoustics holography rely heavily on iterative optimization algorithms, which are time-consuming and particularly hinder their capacity of generating a dynamic hologram in real time. Here, a deep learning approach based on U-Net is proposed to rapidly generate an acoustic hologram with optimal amplitude and phase maps. It is demonstrated that, after being trained with adequate data that are numerically synthesized by the pseudo-inverse method, the proposed deep learning approach can generate both amplitude and phase maps for new target images with an improved overall reconstruction quality. Remarkably, after the offline cost is compensated by a lower online cost for the proposed DL approach, the hologram generation speed is significantly accelerated by the proposed deep learning approach as compared with the pseudo-inverse method, especially for complicated or dynamic images. With the hierarchical feature learning capability and the fast online computational speed, the proposed deep learning approach can serve as a smart platform for rapidly generating complete maps of holograms for the sophisticated or dynamical target images, leading to the new possibility of real-time acoustic-hologram-based applications.

Laser adaptive vector-phase hydroacoustic measuring system

We have developed and experimentally implemented an adaptive laser vector-phase hydroacoustic measuring system, which allows one to determine the total acoustic intensity vector. A receiving element of the measuring system comprises six spatially separated fibre-optic coil-type sensors. Signals from the sensors are phase demodulated by using a six-channel adaptive holographic interferometer based on dynamic holograms multiplexed in a photorefractive CdTe crystal. Performance of the developed measuring system has been experimentally tested by determining the bearing and localisation of a source of a weak hydroacoustic field.

Electrically switchable metasurface for beam steering using PEDOT polymers

Switchable and active metasurfaces allow for the realization of beam steering, zoomable metalenses, and dynamic holography. To achieve this goal, one has to combine high-performance metasurfaces with switchable materials that exhibit high refractive index contrast and high switching speeds. In this work, we present an electrochemically switchable metasurface for beam steering where we use the conducting polymer poly(3,4-ethylenedioxythiophene) as an active material. We show beam diffraction with angles up to 10° and a change of the intensities of the diffracted and primary beams employing an externally applied cyclic voltage between −1 V and +0.5 V. With this unique combination, we realize switching speeds in the range of 1 Hz, and the extension to typical display frequencies in the region of tens of hertz is possible. Our findings have immediate implications for the design and fabrication of future electronically switchable and display nanotechnologies, such as dynamic holograms.

Graphene-based active metasurface with more than 330° phase tunability operating at mid-infrared spectrum

Metasurfaces composed of subwavelength optical antennas offer fruitful functionalities to manipulate the amplitude, phase and polarization of light. Sufficient phase tunability of metasurfaces has significant potential for dynamic beam steering, hologram and flat optics exhibiting tunable focusing. Here, we demonstrate a graphene based metasurface that gives rise to more than 330° smooth and continuous phase modulation at mid-infrared spectrum. The phase modulator model introduces multiple resonances including Split-Ring-resonator (SRR) resonance and inductance-capacitance (LC) resonance, leading to the outstanding sensitivity of the metasurface to tiny change of surrounding electromagnetic environment. Through adjusting the Fermi level of the monolayer graphene beneath the resonators, both scattered amplitude and phase can be efficiently modulated, so that the electrically programmable metasurface enables nearly arbitrary manipulation of scattered wavefront. Electro-optically tunable focusing and beam steering are numerally realized by constructing one dimensional discrete array element. The phased array design achieves an average efficiency up to 22% within 60° steering range. The reflective focusing lens with focal lengths of 10 μm, 15 μm and 20 μm are successfully demonstrated, respectively. The proposed metasurface has promising potential in optoelectronic applications such as imaging, sensing and focusing.