In this paper, we introduce an approach—multiplexing gratings plus drive signal management scheme implemented on a micro-display device within an optical engine—to precisely adjust the color uniformity of an Augmented Reality (AR) eyewear display. This display is based on Volume Holographic Optical Elements (VHOEs) and a waveguide. Our method simplifies the complexity of multiplexing, requiring only a single optical waveguide and three RGB gratings for primary colors to achieve a full-color eyewear display with an expansive horizontal field of view (FOV) of nearly 30° and less than 3% ΔELab color non-uniformity.
In this paper, we propose to fabricate the Geometric Phase (GP) optical device in a Nematic Liquid Crystal cell (NLC cell) by using photo-alignment technique with poly [1- [4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2- ethanediyl, sodium salt] azo-polymer (PAZO) as alignment layer. During fabrication, the necessary surface alignment pattern of GP modulations for the device is firstly created and written on the PAZO films of an empty cell by using polarization holographic method. With filling E7 LC molecule, GP grating and lens are formed. The design principle, fabrication and characterization of both GP diffractive grating and lens are presented. The results show that the device can appear as a polarization-selective transmission hologram with single diffractive order, although the thickness of cell is 5 μm. In addition, the polarization state and wavefront of diffracted wave can be converted simultaneously. Thus, the device can be named as the diffractive waveplate, which provides many unique photonic applications, becoming effective way for minimizing and integrating optical devices for a photonic modular.
In this paper, we present theoretic modelling of color breaking in a holographic-optical-element based Augmented Reality (AR) display. We first build up a theoretic optical model of the AR display system using scalar diffraction method. The discussions about the design parameters of holographic optical elements (HOE) for Augmented Reality (AR) glasses, focusing on color uniformity as a function of the waveguide thickness are conducted. It can be used to evaluate the color breaking of a displayed white image from user’s point of view. The simulation results show that color breaking occurs due to the limitations of pupil size and image shifting caused by the extended eye-box. Moreover, the thickness of the waveguide also causes uneven color distribution. Our model can also provide a way to analyze the relationship between waveguide thickness and color uniformity. In addition, based on those results, we propose a color correction algorithm by applying a pre-compensation scheme to the R/G/B values of each display pixel. Results show light display colors can be better corrected in the wider region of user’s field of view. It demonstrates the feasibility of compensation of color breaking in a holographic-optical-element based AR display.
Here we demonstrate the fabrication processes and working parameters of tunable phase retarders based on photoaligned Liquid Crystal (LCs) cells by combining the photo-pattering and self-assembly processes. The proposed LC devices were assembled by Indium Tin Oxide (ITO) transparent conductive layers deposited on a glass and quartz substrates and spin coated with thin polyamide (PI) layer as photo-alignment material. We study the voltagetransmittance and phase retardation behavior of assembled LC cells and demonstrate polarization sensitive spatial patterns, that open promising features for next generation optical elements as waveplates, lenses, phase retarders, etc.
In this paper, we present a space division technique to multiplex communication channels in a regular step-index multimode fiber using holographic correlator. We consider a multimode fiber with a large diameter of core as highly scattering medium. Thus, the focusing laser spot at different position on the incident plane of the fiber excites different sets of modes, which gives a different speckle pattern at the output of the fiber. Hence, each focusing spot can be considered as a communication channel for data transmission. By combining the volume holographic techniques to form channel multi/demultiplexer in a transmission system, we demonstrate conceptually transmission of multichannel optical information by using a regular step-index multimode fiber for data transmission application.
In this paper we demonstrate flexible polymer dispersed liquid crystal (PDLC) devices using graphene as transparent conductive electrodes on polyethylene terephthalate (PET) substrate. Graphene was grown by Low Pressure Chemical Vapor Deposition (LPCVD) technique and characterized by Raman analysis, optical and electrical measurements. Several graphene-based PDLC devices have been fabricated and their electro-optical characteristics, response time and bending ability were measured and discussed. The results support the graphene promising features for integration in flexible optoelectronics.
The continuing need of improvements governed by the development of all optically controlled devices providing wide broadband sensitivity, high spatial resolution and low energy consumption rapidly increase. In this paper, we review varieties of organic-inorganic hybrid structures that can be used as all optically driven high resolution spatial light modulators. In the proposed structures all optical processes are controlled by the surface activated photorefractive phenomena, typical for highly photoconductive substrates. The performed two-beam coupling measurements at Bragg match regime show prospective amplification values and sub-micron spatial resolution. The structures are easy to fabricate and their operation simple to control.
Polarization hologram provides some unique features over classical phase or amplitude hologram. One of the most important features is that the photo-induced anisotropy in those materials leads to the polarization-dependent diffraction from the hologram. This property is useful for many applications, such as optical interconnection, holographic data storage and bio-imaging …etc.
Recently, the 9, 10-phenanthrenequinone -doped poly(methyl methacrylate) (PQ/PMMA) photopolymer with cm thickness has attracted intense research interesting for the volume holographic applications because the experiments demonstrated that PQ/PMMA photopolymers possess not only high optical quality but also negligible shrinkage effect under light exposure [3-5]. Additionally, in terms of chemical formula, the PQ/PMMA consists of planar structures PQ molecules dispersed in amorphous PMMA polymer so that it is possible to be oriented if irradiated with polarized light, resulting in a photoinduced birefringence. This phenomenon makes it capable for permanent polarization holographic recording via photochemical reaction. Thus, combining these two properties may make PQ/PMMA photopolymer attractive for volume polarization holographic applications. In this paper, we particularly characterize polarization holographic recording in our materials for high-density data storage. Then, we will demonstrate a in-line polarization holographic memory system using PQ/PMMA photopolymer.
The paper reviews two types of organic-inorganic hybrid structures: electro-optically addressed and all optically addressed that can be used as spatial light modulator devices, operating in a transmission mode. Both hybrid devices are assembled by inorganic Bi12SiO20 (BSO) crystals and organic liquid crystals (LC). The electro-optically controlled device demonstrates very high beam-amplification values at Raman–Nath regime of diffraction whereas all optically controlled device operates at Bragg matched regime of diffraction allowing sub-micron spatial resolution. Phase modulation ability has been demonstrated supporting possibilities for applications in adaptive optics, information processing and display technologies.
We study the effect of graphene oxide (GrO) on the switching voltage of polymer dispersed liquid
crystal (PDLC). The threshold voltage decreases with addition of GrO nanoparticles. Scanning
electron microscopy (SEM) supported that the size of LC droplets in GrO-doped PDLC increase in
comparison with non-doped one. PDLC:GrO layer was combined with Bi12SiO20 (BSO) inorganic
substrate into a hybrid structure and based on the surface activated photorefractive phenomena
typical for BSO, it allows the opaque-transparent states to be all optically controlled,
operating faster and requiring less intensity due to the GrO addition in PDLC.
A light-valve device, assembled by Ru–doped Bi12SiO20 (BSO) photoconductive substrate and polymer dispersed liquid crystal layer is proposed, in which all the processes are controlled by the near infrared light. Laser beam illumination (Gaussian shape) on BSO:Ru crystal caused charge carriers generation, which migrate and form an inhomogeneous distribution and subsequent space charge field. This surface-localized electromagnetic field penetrates into the PDLC layer and modulate the orientation of the liquid crystals, that caused reverse of the device initial opaque state to the highly transparent one. The proposed structure is simple and easy to fabricate, without requirements of ITO contacts and alignment layers and opens further possibilities for near-infrared applications.
We report an improvement of the response time and near infrared sensitivity of sillenite crystals Bi12SiO20 (BSO), Bi12TiO20 (BTO) doped with transition metal ions as Ru and Rh. Real-time holographic recording is performed at 1064 nm at a diffusion regime. By using 532 nm light for pre-excitation, significant operation speed of 20 ms is achieved in case of Rh-doped BTO crystal. Further, a possibility to combine doped sillenite plates with liquid crystal into a organic/inorganic hybrid devices (Liquid Crystal Light Valves) is demonstrated, which opens many prospects for further near infrared photonic applications.
We report holographic recording in thick phenanthrenequinone-doped poly(methyl methacrylate) (PQ/PMMA) photopolymer material via the two-wavelength technique. By using gating light at 325 nm and writing light at 647 nm two-wavelength holographic recording is achieved. Non-volatile readout of a holographic image under 24 hours continuous reconstruction is demonstrated. A four-level modeling for the photochemical procedures of the two-wavelength holographic recording is proposed, and dynamic behaviors of the holograms are illustrated. A planar integrated optical correlator system is constructed by selective writing of holographic optical elements via two-wavelength holographic recording on a photopolymer disk.
In this paper, we report our investigations on real-time holographic recoding at 1064 nm in Ru-doped bismuth sillenite
crystal with a green gating light at 532 nm. By using gating light significant improvement of the response time to 80 ms
is achieved and the prolonged read-out process of the recorded hologram is observed. We also demonstrate quasipermanent
holographic recording of image with fast speed in Ru-doped BSO crystal using two-wavelength recording.
Bismuth germanate Bi4Ge3O12 (BGO) single crystals doped with ruthenium, manganese and ruthenium plus manganese are grown by Czohralski technique with automatically diameter-weight control method. The effect of doping on the
light-induced, magneto-optical and holographic properties of BGO single crystals is studied. It was found that the optical transmission spectrum of doped samples is modified strongly under thermal annealing and homogeneous illumination with UV light as well as the photochromic effect is fully reversible. The magneto-optical rotation was measured and Verdet constant was calculated at visible spectral range. Holographic grating are successfully recorded at 633 nm.
The effect of ruthenium doping on optical properites of Bi12TiO20 (BTO) single crystals is studied. A low concentration of ruthernium does not change absorption behavior of BTO, however higher ruthenium addition significantly shifts the optical absorption to the near infrared spectral region with an absorption shoulder appearing around 1.8 eV. The absorption coefficient increases with increasing the Ru concentration. Light-induced absorption changes are observed and the dynamics of build-up and dark decay processes are investigated. Results show that concentration of shallow levels increase with Ru content. Evolution of the build-up and dark decay of light induced absorption consists of fast and slow components: the first process occurs within few seconds, while the second one needs several hours (or days). It is established that light-induced absorption can be modified by preliminary illumination and thermal treatments thus multi-level lead to the transient and persistent parts of light-induced absorption. A model, assuming one deep and two shalow levels is proposed to explain the bi-exponential behavior of the build-up and the dark decay of light-induced absorption when the crystals are preliminary annealed in oxygen atmosphere.
Optically homogeneous bismuth germanate Bi4Ge3O12 single crystals doped with vanadium, cobalt and vanadium plus cobalt have been successfully grown by Czohralski technique with automatically diameter-weight control. The distribution coefficients for individual doping elements are determined. The effect of doping on the light-induced properties of BGO single crystals is studied. Optical absorption spectrum of annealed samples can be strongly modified under ultraviolet illumination. The photochromic effect is optically or thermally reversible from one state to another. Volt-amper charactersitcs show linear behavour and dark conductivity values are s ~ 10-13 (Ω.cm)-1. Holographic grating were successfully recorded in all investigated doped crystals at 514 nm.
Bi12TiO20 single crystals doped with Cd, Cu, P, Cr, Ag, Al were grown by the top-seeded solution growth method (TSSG). The electrical measurements were carried out on different BTO samples. The electrical conductivity followed the Arrhenius low, with an activation energy ranged from 0.38 to 0.63 eV. Mobility and transport properties of charge photo carriers were investigated by the time-of-flight technique. For non-doped BTO and doped with Cu, P, Al and Cd the obtained values for drift mobility of electrons varying between (mu) equals10-2 and 1 [cm2/V.s]. In the case of BTO doped with Al the dominant charge carriers were holes with mobility (mu) equals5x10-3 [cm2/V.s]. These key photorefractive parameters were used to calculate the lifetime of charge carriers using the period of the recorded holographic photorefractive space gratings.
Holographic characteristic of not-fixed and fixed holographic records in Bi12TiO20 crystal has been investigated. A long-term readout photorefractive memory, implemented in this crystal, has been proposed and demonstrated. The effect is achieved by reading the recorded and fixed hologram with a low-intensity light wave and by additionally amplifying the reconstructed image. Recording and amplification are performed in one and the same crystal. A good quality of the reconstructed image is demonstrated after 60 min of continuous readout of the photorefractive grating.
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