Research

18 pages, 4110 KiB

Open AccessEditor’s ChoiceArticle

Modelling and Design of Holographic Optical Elements for Beam-Coupling Applications for a Range of Incident Beam Angles

by Dipanjan Chakraborty, Rosen Georgiev, Sinead Aspell, Vincent Toal, Izabela Naydenova, Dervil Cody and Suzanne Martin

Photonics 2022, 9(12), 936; https://doi.org/10.3390/photonics9120936 - 03 Dec 2022

Cited by 4 | Viewed by 2113

Abstract

Theoretical modelling has been used to calculate the holographic recording beam angles required in air (at any recording wavelength) to produce a Volume Holographic Optical Element (VHOE) for any defined input and output beam angles. The approach is used to facilitate the design [...] Read more.

Theoretical modelling has been used to calculate the holographic recording beam angles required in air (at any recording wavelength) to produce a Volume Holographic Optical Element (VHOE) for any defined input and output beam angles. The approach is used to facilitate the design and fabrication of diffractive coupling elements through a holographic process that avoids the use of coupling prisms during recording and will help in the design of recording arrangements that better suit the mass production of low-cost elements, especially those designed for non-normal incidence. In this study, the recording angles needed for a range of recording wavelengths were explored for VHOE couplers designed for input angles (in air) ranging from 0° to −55°. Then, in order to validate the model, holographic recording in Bayfol HX 200 photopolymer at 532 nm was used to fabricate photopolymer VHOE couplers for 633 nm light (−45° input angle in air). Bragg curves obtained experimentally for different probe wavelengths (403 nm, 532 nm and 633 nm) confirm the recording of the desired grating structures to a precision of ±1°, and coupling is demonstrated at 633 nm with a diffraction efficiency of up to 72%. Furthermore, the model is used to identify the origins of some weaker spurious gratings observed alongside the expected ones. Full article

(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)

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10 pages, 2871 KiB

Open AccessCommunication

Analysis of Display Resolution of Volume Holographic Waveguide and High Resolution by Line-Symmetric Image Input

by Toshiteru Nakamura and Ryushi Fujimura

Photonics 2022, 9(9), 649; https://doi.org/10.3390/photonics9090649 - 12 Sep 2022

Viewed by 1937

Abstract

To reveal the fundamental characteristic of the volume holographic waveguide for a head-mounted display (HMD), we analyzed the resolution of a virtual image. We built a mathematical model considering the off-Bragg diffraction for each ray angle of the signal light ray. The display [...] Read more.

To reveal the fundamental characteristic of the volume holographic waveguide for a head-mounted display (HMD), we analyzed the resolution of a virtual image. We built a mathematical model considering the off-Bragg diffraction for each ray angle of the signal light ray. The display resolution performance of the HMD depended on the thickness of the waveguide and the ray angle. At the lowest-resolution ray angle, the input-point image was broadened more than 0.1° in a viewing angle for a 1-mm-thick waveguide. Conversely, our previously proposed line-symmetric image-input method, in which the input images were symmetrically arranged with respect to the center line, improved the resolution performance and luminance uniformity. We observed that the spread of the point image was suppressed to 0.01°, which was a sufficient resolution for a person with a visual acuity of 0.8. Full article

(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)

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16 pages, 4190 KiB

Open AccessArticle

Improving the Holographic Recording Characteristics of a Water-Resistant Photosensitive Sol–Gel for Use in Volume Holographic Optical Elements

by Brian Rogers, Tatsiana Mikulchyk, Mohamed Oubaha, Dervil Cody, Suzanne Martin and Izabela Naydenova

Photonics 2022, 9(9), 636; https://doi.org/10.3390/photonics9090636 - 04 Sep 2022

Cited by 8 | Viewed by 1967

Abstract

Continual improvements to holographic recording materials make the development of volume holographic optical elements increasingly more attainable for applications where highly efficient, lightweight diffractive optical elements can replace conventional optics. A fast-curing, water resistant photosensitive sol–gel capable of volume holographic recording has recently [...] Read more.

Continual improvements to holographic recording materials make the development of volume holographic optical elements increasingly more attainable for applications where highly efficient, lightweight diffractive optical elements can replace conventional optics. A fast-curing, water resistant photosensitive sol–gel capable of volume holographic recording has recently drawn attention for its extreme environmental and physical robustness, in particular its water/moisture and scratch resistance. However, to date, the refractive index modulation has been limited. While water-resistant properties are invaluable in the face of the weathering which many practical systems for outdoor applications will endure, high refractive index modulation is also important in order to facilitate high diffraction efficiency holograms recorded in relatively thin layers. Lower grating thickness ensures a large angular and wavelength range of operation-properties that are critical for many applications of holographic optical elements such as solar light harvesting, optical displays and illumination management. For any application where low-cost mass production is envisaged, sensitivity/writing speed is also a crucial factor. In this research, we studied the recording properties of these water-resistant photosensitive sol–gel layers at two different recording wavelengths (532 and 476 nm) and investigated methods for improving these properties. We report more than two-fold improvement of the refractive index modulation from

1.4 \times 10^{- 3}

to

3.3 \times 10^{- 3}

in layers of thickness ranging from 40–100 μm and more than an order of magnitude increase in photosensitivity/recording speed through better matching between recording wavelength and layer absorption, chemical alterations and thermal post-processing techniques. Full article

(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)

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10 pages, 5695 KiB

Open AccessCommunication

Flexible Image Reconstruction in the Orbital Angular Momentum Holography with Binarized Airy Lens

by Feili Wang, Xiangchao Zhang, Rui Xiong, Xinyang Ma, He Yuan, Leheng Li and Xiangqian Jiang

Photonics 2022, 9(7), 460; https://doi.org/10.3390/photonics9070460 - 29 Jun 2022

Cited by 2 | Viewed by 1382

Abstract

The orbital angular momentum (OAM) holography has been marked a path to achieving ultrahigh capacity holographic information systems. However, the practical applicability of the OAM holography is limited by the complicated optical setup and unadjustable image intensity and position. Here, a decoding method [...] Read more.

The orbital angular momentum (OAM) holography has been marked a path to achieving ultrahigh capacity holographic information systems. However, the practical applicability of the OAM holography is limited by the complicated optical setup and unadjustable image intensity and position. Here, a decoding method is proposed by using a binarized phase map derived from an autofocusing Airy beam. By adjusting the parameters of the phase map, the position and intensity distribution of the reconstructed image become flexibly adjustable. In addition, the cross-talk between different image channels can be effectively reduced thanks to the abruptly autofocusing capability of the Airy beams. As a result, the quality and practicability of the OAM holography can be greatly enhanced. Full article

(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)

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15 pages, 20304 KiB

Open AccessArticle

Multiplexed Holographic Combiner with Extended Eye Box Fabricated by Wave Front Printing

by Tobias Wilm, Jens Kibgies, Reinhold Fiess and Wilhelm Stork

Photonics 2022, 9(6), 419; https://doi.org/10.3390/photonics9060419 - 15 Jun 2022

Cited by 4 | Viewed by 2527

Abstract

We present an array-based volume holographic optical element (vHOE) recorded as an optical combiner for novel display applications such as smart glasses. The vHOE performs multiple, complex optical functions in the form of large off-axis to on-axis wave front transformations and an extended [...] Read more.

We present an array-based volume holographic optical element (vHOE) recorded as an optical combiner for novel display applications such as smart glasses. The vHOE performs multiple, complex optical functions in the form of large off-axis to on-axis wave front transformations and an extended eye box implemented in the form of two distinct vertex points with red and green chromatic functions. The holographic combiner is fabricated by our extended immersion-based wave front printing setup, which provides extensive prototyping capabilities due to independent wave front modulation and large possible off-axis recording angles, enabling vHOEs in reflection with a wide range of different recording configurations. The presented vHOE is build up as an array of sub-holograms, where each element is recorded with individual optical functions. We introduce a design and fabrication method to combine two angular and two spectral functions in the volume grating of individual sub-holograms, demonstrating complex holographic elements with four multiplexed optical functions comprised in a single layer of photopolymer film. The introduced design and fabrication process allows the precise tuning of the vHOE’s diffractive properties to achieve well-balanced diffraction efficiencies and angular distributions between individual multiplexed functions. Full article

(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)

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29 pages, 5984 KiB

Open AccessArticle

Thermal Fringe Formation during a Hologram Recording Using a Dry Photopolymer

by Friedrich-Karl Bruder, Thomas Fäcke and Thomas Rölle

Photonics 2021, 8(12), 589; https://doi.org/10.3390/photonics8120589 - 18 Dec 2021

Cited by 2 | Viewed by 2170

Abstract

In this study we investigated the undesired but possible fringe formation during the recording of large size holographic optical elements (HOE) using a dry photopolymer. We identified the deformation of the recording element during hologram exposure as the main source for this fringe [...] Read more.

In this study we investigated the undesired but possible fringe formation during the recording of large size holographic optical elements (HOE) using a dry photopolymer. We identified the deformation of the recording element during hologram exposure as the main source for this fringe formation. This deformation is caused mainly by the one-sided heating of the recording element, namely, the dry photopolymer–recording plate stack. It turned out that the main source for this heating was the heat of polymerization in the dry photopolymer released during the exposure interval. These insights were translated into a physical model with which quantitative predictions about thermal fringe formation can be made depending on the actual HOE recording geometry, recording conditions and characteristics of the dry photopolymer. Using this model, different types of large size HOEs, used as components to generate a steerable confined view box for a 23” diagonal size display demonstrator, could be recorded successfully without thermal fringe formation. Key strategies to avoid thermal fringe formation deduced from this model include balancing the ratio of lateral recording plate dimension R to its thickness h, recording the power density P or equivalently the exposure time t_exp at a fixed recording dosage E, and most importantly recording the the linear coefficient of thermal expansion (CTE) of the recording plate material. Suitable glass plates with extremely low CTE were identified and used for recording of the above-mentioned HOEs. Full article

(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)

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22 pages, 6551 KiB

Open AccessArticle

Holographic Optical Lenses Recorded on a Glassy Matrix-Based Photopolymer for Solar Concentrators

by Maria Antonietta Ferrara, Fabio Borbone and Giuseppe Coppola

Photonics 2021, 8(12), 585; https://doi.org/10.3390/photonics8120585 - 17 Dec 2021

Cited by 4 | Viewed by 2344

Abstract

Global warming is a very topical issue, therefore the search for new renewable energy sources is considered of fundamental importance. Among these, solar energy offers great possibilities considering that the amount of sunlight hitting the Earth ‘s surface in an hour and a [...] Read more.

Global warming is a very topical issue, therefore the search for new renewable energy sources is considered of fundamental importance. Among these, solar energy offers great possibilities considering that the amount of sunlight hitting the Earth ‘s surface in an hour and a half is enough to meet the world’s electricity consumption for a complete year. Generally, solar concentrators are used to collect the solar radiation and to concentrate it at a single focal point. These devices consist in a set of mirrors or mechanical structures to reduce the area of a photovoltaic cell, which is typically very expensive. Volume transmission phase holographic optical elements could be opportunely designed and realized to obtain a simple, lightweight, compact and inexpensive planar solar concentrator. With the aim of bringing scientific attention to this still developing topic, in this work we critically report a complete investigation on a new photopolymeric material obtained by sol-gel reactions used as possible recording material for volume holographic solar concentrators; as a proof of concept, both terrestrial and extreme environments, such as space, are considered as potential applications. Full article

(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)

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10 pages, 14305 KiB

Open AccessCommunication

Properties of Holographic Elements Based on Periodic Structures in a Wide Range of Angles of Incidence

by Nadezhda Vorzobova and Pavel Sokolov

Photonics 2021, 8(12), 562; https://doi.org/10.3390/photonics8120562 - 09 Dec 2021

Cited by 1 | Viewed by 1733

Abstract

An experimental study is carried out on the diffraction and angular selectivity properties of gratings for a wide range of angles of incidence in three-dimensional space. Results for three grating types are presented: nonslanted volume gratings, slanted volume gratings, and hybrid structures. The [...] Read more.

An experimental study is carried out on the diffraction and angular selectivity properties of gratings for a wide range of angles of incidence in three-dimensional space. Results for three grating types are presented: nonslanted volume gratings, slanted volume gratings, and hybrid structures. The study encompasses a wide range of directions of radiation incidence on structures and reveals grating orientations that can provide maximal diffraction efficiency for angles of incidence of more than 70°. Obtained data are used to assess the efficiency of diffractive deflectors on the basis of the considered structures, taking into account the trajectory of the Sun as applied to solar-energy problems. Full article

(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)

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9 pages, 3187 KiB

Open AccessArticle

Multi-Wavelength Optical Patterning for Multiscale Materials Design

by Biagio Audia, Pasquale Pagliusi, Alfredo Mazzulla and Gabriella Cipparrone

Photonics 2021, 8(11), 481; https://doi.org/10.3390/photonics8110481 - 28 Oct 2021

Cited by 5 | Viewed by 1899

Abstract

Laser interferometry is a consolidated technique for materials structuring, enabling single step and large area patterning. Here we report the investigation of the morphological modification encoded on a thin film of a photosensitive material by the light interference pattern obtained from a laser [...] Read more.

Laser interferometry is a consolidated technique for materials structuring, enabling single step and large area patterning. Here we report the investigation of the morphological modification encoded on a thin film of a photosensitive material by the light interference pattern obtained from a laser operating in multiline mode. Four lines with equal intensity are retained, with the same p linear polarization. An azopolymer is exploited as medium for the holographic recording. Optical microscopy and profilometer measurements analyze the modification induced in the bulk and on the surface of the irradiated area. We show that the intensity profile of the interference patterns of two laser beams is the one obtained assuming each line of the laser as an independent oscillator of given intensity and wavelength, and how these light structures are faithfully replicated in the material bulk and on the topography of the free surface. Patterns at different length scales are achievable in a single step, that can be traced back to both interference fringes and wave envelopes. The proposed multi-wavelength holographic patterning provides a simple tool to generate complex light structures, able to perform multiscale modifications of photoresponsive materials Full article

(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)

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16 pages, 4202 KiB

Open AccessArticle

Study of Full-Color Multiplexed Transmission Holograms of Diffusing Objects Recorded in Photopolymer Bayfol HX

by Marina Sevilla, Julia Marín-Sáez, Daniel Chemisana, María-Victoria Collados and Jesús Atencia

Photonics 2021, 8(11), 465; https://doi.org/10.3390/photonics8110465 - 22 Oct 2021

Cited by 5 | Viewed by 2334

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)

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12 pages, 3505 KiB

Open AccessArticle

Tunable Polarization and Surface Relief Holographic Gratings in Azopolymer Nanocomposites with Incorporated Goethite (α-FeOOH) Nanorods

by Lian Nedelchev, Georgi Mateev, Velichka Strijkova, Verónica Salgueiriño, David S. Schmool, Nataliya Berberova-Buhova, Elena Stoykova and Dimana Nazarova

Photonics 2021, 8(8), 306; https://doi.org/10.3390/photonics8080306 - 31 Jul 2021

Cited by 9 | Viewed by 2349

Abstract

We employ two approaches to tune the properties of concurrently inscribed volume polarization and surface relief gratings in nanocomposite thin films containing the azopolymer PAZO (poly[1-4-(3-carboxy-4-hydrophenylazo)benzensulfonamido]-1,2-ethanediyl, sodium salt]) and goethite (α-FeOOH) nanorods. The first one is applied on the stage of sample preparation [...] Read more.

We employ two approaches to tune the properties of concurrently inscribed volume polarization and surface relief gratings in nanocomposite thin films containing the azopolymer PAZO (poly[1-4-(3-carboxy-4-hydrophenylazo)benzensulfonamido]-1,2-ethanediyl, sodium salt]) and goethite (α-FeOOH) nanorods. The first one is applied on the stage of sample preparation by varying the concentration of the goethite nanorods from 0% to 15%. Then, different angles between the recording beams are set in the holographic scheme, which allow us to obtain gratings with spatial periods in the range from 0.86 to 2.51 µm. Surface relief modulation close to 300 nm is achieved as well as total diffraction efficiency in the ±1 diffracted orders of more than 50%. The influence of the incorporated goethite nanorods on the properties of both volume birefringence and the surface relief grating are discussed. Full article

(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)

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18 pages, 4144 KiB

Open AccessArticle

Crosstalk Reduction in Voxels for a See-Through Holographic Waveguide by Using Integral Imaging with Compensated Elemental Images

by Jiwoon Yeom, Yeseul Son and Kwangsoon Choi

Photonics 2021, 8(6), 217; https://doi.org/10.3390/photonics8060217 - 11 Jun 2021

Cited by 10 | Viewed by 2685

Abstract

The representation of three-dimensional volumetric pixels, voxels, is an important issue for the near-to-eye displays (NEDs) to solve the vergence-accommodation conflict problem. Although the holographic waveguides using holographic optical element (HOE) couplers are promising technologies for NEDs with the ultra-thin structure and high [...] Read more.

The representation of three-dimensional volumetric pixels, voxels, is an important issue for the near-to-eye displays (NEDs) to solve the vergence-accommodation conflict problem. Although the holographic waveguides using holographic optical element (HOE) couplers are promising technologies for NEDs with the ultra-thin structure and high transparency, most of them have presented only a single and fixed depth plane. In this paper, we analyze the imaging characteristics of holographic waveguides, particularly to represent the arbitrary voxels and investigate the voxel duplication problem arising from the non-collimated light from the voxels. In order to prevent the image crosstalk arising from the voxel duplication, we propose an adjustment method for the emission angle profile of voxels by using the integral imaging technique. In the proposed method, the sub-regions of elemental images, which correspond to the duplicated voxels, are masked in order to optimize the emission angle of integrated voxels. In the experimental verification, a see-through integral imaging system, based on the organic light-emitting diode display and a holographic waveguide with the thickness of 5 mm, was constructed. The fabricated HOE in the waveguide showed high diffraction efficiency of 72.8 %, 76.6%, and 72.5 % for 460 nm, 532 nm, and 640 nm lasers, respectively. By applying the masked elemental images, the proposed method resulted in a reduced crosstalk in the observed voxels by 2.35 times. The full-color experimental results of see-through holographic waveguide with integral imaging are provided, whereby the observed 3D images are presented clearly without the ghost images due to the voxel duplication problem. Full article

(This article belongs to the Special Issue Materials, Methods and Models for Holographic Optical Elements)

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