Search

We propose a field of view (FOV) enlargement method using the line symmetric image input in the single layer volumetric holographic waveguide. We build a mathematical model and analyze the virtual image to be seen by the observer considering the interaction volume of the signal light ray within the volumetric hologram waveguide. It is found that the diffracted light intensity is varied with each ray angle due to the variation of the interaction volume, which results in a critical issue of poor uniformity of luminance on the virtual image in the volumetric hologram waveguide. Our proposed method compensates for the variation in the interaction volume by another ray coming from the line symmetric point within the input image. The proposed method achieves a 490-times improvement in uniformity of luminance over the FOV 60 (H) × 60 (V) degrees, which is twice the FOV compared with conventional waveguide.

In mode-division multiplexing systems, the transmission quality is restricted by the differential mode delay (DMD). We previously proposed a spatial mode exchange technique using volume holograms (VHET) to reduce the DMD. VHET can be used for the exchange of multiple spatial modes with different transmission speeds using a single device. However, in VHET, incidents of cross-talk (XT) caused by non-target holograms severely degrade the exchange performance. To address this issue, we propose a spatial mode exchange technique that uses volume holograms in combination with a random optical diffuser. By scattering the intensity distribution of the signal beam uniformly using a random optical diffuser, high exchange performance can be attained due to the reduction in the influence of non-targeted holograms. We confirmed the basic operation of the proposed scheme by considering the crosstalk component coupled to the few-mode fiber in a mode-division multiplexing system. The simulation results show that the maximum XTs are significantly suppressed to − 15.8 dB.

In this study, we reveal a novel aerial display system, to the best of our knowledge, that combines volume hologram mirrors with a dihedral corner reflector array (DCRA). The suggested aerial display has a see-through capability, which allows for a new design of aerial displays by combining with other types of displays. Furthermore, the virtual image, which frequently disrupts the observation of aerial images, can be suppressed by the Bragg condition of the volume hologram. The color dispersion in the holograms is efficiently compensated by employing features of the DCRA. The findings of preliminary experiments are demonstrated using a DCRA device and full-color hologram mirrors.

We propose a volume holographic optical element (VHOE) used as an objective turret in a lensless digital holographic microscope. It also served as a reference wave guide to reduce the volume of the system. For further optimization of resolution performance, it used a spherical wave in the object light of the VHOE, which served as the reference light of the microscope. Another sheared spherical wave was used to illuminate the sample. The optimized VHOE increased the spatial resolution of the record signal effectively. Furthermore, the change of spherical wave distance leads to the change of imaging magnification.

Advancements in 3D printing, specifically by 2-photon polymerization, enabled the fabrication of high resolution novel optical elements for various applications by engineering the topography of the structures. Recently, the ability to obtain a varying refractive index distribution by 2-photon polymerization also started to gain momentum to design and produce gradient-index (GRIN) micro-optics. Here, we demonstrate micro-scale volume holograms by 2-photon polymerization by tuning the exposure point by point in the 3D volume to obtain the necessary refractive index distribution. 3D printed micro-scale GRIN volume holograms lay an opportunity to open a complimentary dimension in various systems thanks to in-situ fabrication advantage, which can provide complex interconnections and beam shaping in micro-scale.

A new implementation of the weight vector in a classifier based on an optical system using a volume holographic filter with a vector decomposition algorithm is proposed for high-speed data classification. Using a volume holographic filter, the correlation between the input and the decomposed weight vector is calculated for the classification score, which is the output from the decision function in the optical classifier. The authors experimentally demonstrate the core concept and confirm the effectiveness of the proposed method by executing a two-class classification problem using a volume hologram medium.

The planar diffractive waveguide is widely adopted in optical see-through head-mounted displays in the field of augmented reality due to its distinguished trade-off among the form factor, optical character, and mass production process. The diffractive waveguides can be divided into surface relief grating waveguides and volume hologram grating waveguides. In this review, the state of the art of planar diffractive waveguides is described, including the physical principle, optical configuration, performance parameters, and manufacturing process. Typical commercial augmented reality head-mounted displays are also presented with a discussion on the advantages as well as disadvantages of surface relief grating and volume hologram grating waveguides. Finally, the bottleneck of planar diffractive waveguides and the future development trends are discussed.

We present a new type of filter that improves the SNR of systems where polychromatic signal and noise are located at different distances within the same line of sight. The filter is based on holographic technology that allows for the discrimination of wavefronts by range. In using a combination of two holographic elements, a pre-disperser and a thick volume hologram, we were able to significantly increase the spectral bandwidth of the filter, from 9nm without the pre-disperser to 70nm with both holographic elements. Laboratory proof of concept demonstrated that such a filter is capable of an SNR improvement of 15 dB for a monochromatic source, and up to 7.6 dB for a polychromatic source. This filter can find applications in astronomic observation, satellite or space debris tracking, and free-space optical communication.

The resolution of images is increasing year by year. High-definition images have a large amount of data so that high calculation cost is required for image processing. For example, when original data is restored from non-clear high-definition two dimensional coded images, it is necessary to improve the image quality. A volume holographic optical element works as a multiple lens for each pixel in an image so that spreading pixel patterns can be individually focused. Then, each pixel becomes clear and original data can be easily restored. However, it is difficult to analytically express the function of volume holographic optical elements. In our previous study, reconstructed images from a volume hologram, in which some data pages were recorded in multiple, were expressed by analytic function. The analytic function was called pixel amplitude function. In this study, the pixel amplitude function is used for an input image to a volume holographic optical element. Then, output image is analytically expressed.

In this study, we prepared a cylindrical wave diffractive optical element that diffracts color images using volume hologram technology to improve the performance and cost of HMDs.

A wavelength multiplexing procedure for color transmission volume holograms of diffusing objects recorded in Bayfol® HX200 photopolymer is proposed. For the recording, three lasers of 442 nm, 532 nm and 633 nm, and a Spectralon® diffusing object were used for monochromatic and polychromatic calibration. Monochromatic calibration shows that the maximum index modulation obtained for each wavelength was not enough to give 100% efficiency, although the efficiency values achieved in the case of monochromatic recordings with diffusing objects were high, at around 90% for 633 nm and 532 nm recordings, and 60% for 442 nm. The efficiency values obtained for multiplexed holograms were 19.1% for the 442 nm hologram, 25.9% for the 532 nm hologram and 15.2% for the 633 nm. This research was funded by the “Diputación General de Aragón-Fondo Social Europeo” (TOL research group, E44_17R), the “Generalitat de Catalunya” (2017FI_B2_00127 and 2017 SGR 1276) and the “Ministerio de Ciencia e Innovación” (PID2019-108598GB-I00, PID2019-111536RB-I00 and PID2021-114311RA-I00)

An optimized wavelength multiplexing procedure for color reflection holograms of diffusing objects recorded in Bayfol® HX photopolymer is proposed. It is based on simultaneous initial illumination of all the wavelengths and sequential shuttering down of the laser beams involved. Three lasers of 442 nm, 532 nm and 633 nm were selected, as a tradeoff solution between setup complexity and color reproduction accuracy. The obtained results prove that the presented method improves the simultaneous and sequential exposure methods by increasing the mean efficiency and reducing the standard deviation (increasing uniformity) of the involved wavelengths. For a Spectralon® diffusing object, the assessed method reports a mean efficiency of 25.0% with a standard deviation of 2.9%, while simultaneous and sequential iterative exposures result in mean efficiencies of 12.1% and 20.6% with standard deviations of 3.4% and 5.4%, respectively. The authors would like to thank Covestro Deutschland AG for supplying the recording photopolymer material. This research has been supported by the “Diputación General de Aragón-Fondo Social Europeo” (TOL research group, E44_17R), the “Generalitat de Catalunya” (2017FI_B2_00127 and 2017 SGR 1276) and the "Ministerio de Ciencia e Innovación" (PID2019-108598GB-I00). Daniel Chemisana thanks ICREA for the ICREA Academia award.

Radial polarization converters can convert an incident light into a radially polarized light, which is beneficial in a variety of applications. In this paper, a new design of holographic radial polarization converter is proposed which consists of eight space-variant polarization-selective volume hologram gratings. According to the coupled wave theory, a feasible design of the polarization-selective volume hologram gratings was described. The prism-hologram-prism sandwiched recording method was adopted for the recording. The s- and p-polarization diffraction efficiencies of the fabricated polarization-selective volume hologram gratings at 443.29 nm are 90.83% and 22.09%, respectively. The operation bandwidth is about 4.42 nm. A prototype of holographic radial polarization converter was successfully assembled and tested. Due to the introduction of volume hologram gratings, this design should have the advantages of high diffraction efficiency, narrow band, compactness, and planar configuration, meaning it is especially suitable for low-cost mass production and has high application potential in related fields.

The article describes the variants for using the relief phase diffraction gratings for a waveguide used as an optical input/output element for images in augmented reality systems. A characteristic feature of diffraction gratings with a surface relief, which, in this case, were recorded in the photoresist layer, is a relatively small relief depth (of the order of several tenths of a micrometer), while the diffraction efficiency of such gratings is quite high (up to 30%). The paper considers an implementation option for a waveguide with a common angular field of view close to 60°. The article presents the waveguide options used to output both monochrome images and display full-color images.

An approach for recording complex holograms using two beam interference setup incorporating a light modulating device in one of the arms of the holographic setup is proposed. This allows the intensity profile of the beam reflected by the DMD to be adjusted to a pre-determined profile. Using an UV laser, the created interference pattern is recorded into PTR glass plate. The variable light amplitude exposure of the glass is converted to a refractive index change after thermal treatment step. The DMD device makes possible the incorporation of zones in the hologram where there is no interference pattern and therefore there is no hologram. Such custom designed holograms can find applications in laser resonators or as spatially sensitive wavelength filters. In addition, the holograms recorded in the volume of the PTR glass are practically insusceptible to surface damage, changes in the environment and other factors from which holograms recorded in polymers suffer.

A see-through light-field 3D display that works in head-up configuration is being presented. The display system consists of only a commercial projector and a holographic screen and works on the principle of Integral Imaging. The holographic screen is a volume hologram that is digitally fabricated, which functions as a micro concave- mirror array. The screen also has other optical functions embedded that helps to eliminate the bulk of optical components needed otherwise. This significantly simplifies the system, there by taking it closer to the consumer market. A color 3D scene of size 20cm x 10cm x 5cm (depth) has been successfully reproduced and can be seen through naked eye for a viewing angle of 10-degrees.

In this research, we propose a mode selective switch (MSS) using volume holograms. MSS is a device that distributes the mode-division multiplexed (MDM) signal to different output ports for each spatial mode component contained in the signal. Using MSS, the function of reconfigurable optical add / drop multiplexer (ROADM) can be implemented, which can manipulate arbitrary spatial mode signal at any position in the next generation MDM network. In our proposed MSS, the incident signal is separated into spatial mode components by the volume hologram on the input side. The signal destination will be selected for each mode by diffracting independently. The spatial mode components are separated in direction of the plurality of volume holograms on the output side using a spatial light modulator (SLM). In the volume hologram on the output side, the multiple spatial mode components are recombined and emitted once again as an MDM signal. This method has the advantageous that one volume hologram can multiplex or de-multiplex multiple modes, allowing it to cope easily with the increase in the number of modes and ports to be multiplexed. In the experiment, the optical signal lights of three-mode are separated for each spatial mode by the volume hologram on the input side, and the switching to either of the two ports on the output side is successfully performed for each mode using the SLM.

In mode-division multiplexing (MDM) systems, transmission quality is restricted by differential mode delay (DMD). We have proposed and developed a spatial-mode exchange technique using volume holograms (VHET) as a leading technology to reduce DMD. VHET can equilibrate the transmission time of each spatial mode which has different transmission speeds in a few mode fiber using a volume hologram. This technology enables low signal distortion and high spectral efficiency, which are indispensable to the long-haul transmission for the MDM system. However, in this technology, modal cross-talks (MXTs), which are caused by inter-page cross-talks in the volume hologram, seriously degrade the performance of VHET. In this study, we proposed a method of combining a volume hologram and a random optical diffuser to reduce the MXTs. In our method, the intensity distribution of the input spatial mode is diffused uniformly by a random optical diffuser. The high exchange performance will be attained because the non-targeted holograms included in the multiplexed holograms do not affect most of the spatial mode. Moreover, our method can be applied to the communication wavelength bands using the dual wavelength method. We confirmed the basic operation of the proposed scheme using a linearly polarized mode group comprising LP0,1, LP1,1, and LP2,1. Compared with the conventional VHET, the simulation results show that the maximum MXTs are significantly suppressed from 0.4 to -15.8 dB.

International audience; We present a new version of a light scattering measurement setup, using a high-power supercontinuum laser source, two volume hologram filters, and two low-noise scientific grade cameras. This configuration enables spectral and angle resolved characterization of the light scattered by complex thin-film filters from 400 to 1650 nm. Measurements carried out on specific filters illustrate the performances of the setup.

Efficiency of optical frequency conversion in quadratic media critically depends on spatial modulation of the nonlinear optical response of the materials. This modulation ensures, via the quasi phase matching (QPM), an efficient energy exchange between optical waves at different frequencies. The QPM structures, also known as the nonlinear photonic crystals, offer a variety of novel properties and functionalities that cannot be obtained in uniform nonlinear crystals. In particular the 3-dimensional modulation of nonlinearity allows one to realize the so-called nonlinear volume holograms which extends the concept of volume holography to nonlinear optics. Nonlinear volume hologram represents the 3- dimensional distribution of the nonlinear polarization which arises from interaction between input fundamental beam and generated wave with complex wave front, in medium exhibiting quadratic nonlinearity (χ(2)). When illuminated by fundamental beam, the nonlinear hologram gives rise to a wave at different frequency (e.g. second harmonic of fundamental wave) having complex intensity distribution following the transverse structure of the hologram itself. In this way one can combine generation of waves at new frequencies with simultaneous shaping of their transverse and longitudinal intensity profiles. In this work we present formation of various types of nonlinear volume holograms in ferroelectric crystals by using unique all-optical domain inversion technique and demonstrate their application in optical wave-shaping.

We report on the null reconstruction effect (NRE) of an elliptical polarization volume hologram with orthogonal elliptically, circularly, and linearly polarized waves, respectively. The NRE is a special phenomenon in polarization holography, which means the diffraction efficiency declines to zero when the hologram is reconstructed by an orthogonally polarized reading wave. In our previous work [Opt. Express24, 1641 (2016)OPEXFF1094-408710.1364/OE.24.001641; Opt. Lett.42, 1377 (2017)OPLEDP0146-959210.1364/OL.42.001377; Opt. Express23, 8880 (2015)OPEXFF1094-408710.1364/OE.23.008880], the NRE of polarization holography recorded by linear and circular polarization waves has been investigated. Compared with linear and circular polarization holography, elliptical polarization holography represents a more general and unified recording hologram. However, no work on the NRE of elliptical polarization holography, as far as we know, has been reported until now. In this paper, the NRE of elliptical polarization holography is investigated and demonstrated theoretically and experimentally. First, the conditions of achieving NRE in elliptical polarization holography are studied based on vector holography theory. The results indicate that the NRE is a common phenomenon in polarization holography written by linear, circular, and elliptical polarization waves. Then, a series of experiments of NRE in a polarization hologram written by orthogonal elliptically, circularly, and linearly polarized waves is carried out. The NRE of elliptical polarization holography is experimentally observed, and the results are in nice agreement with the theoretical analysis. The NRE of elliptical polarization holography is expected to be applied in high-density optical data storage and polarization-controlled holographic elements.

In this paper, a comprehensive ray-tracing model for simulating volume holographic gratings is programmed and demonstrated in OpticStudio. The model integrates physical properties of the hologram, such as diffraction direction and efficiency based on incident rays’ direction and polarization state, into the standard ray-tracing model. The model also accounts for hologram emulsion shrinkage and refractive index shift. With integration of these physical effects, advanced modeling tools like image simulation and optimization become available and are demonstrated with a case study of a seethrough head-mounted display.