Reflection Volume Holographic Gratings Research Articles

Recording Reflection Volume Holographic Gratings with Enhanced Performance by Two‐Stage Photopolymers Containing Bifunctional Monomers

AbstractA holographic optical waveguide (HOW) is an optimal solution for augmented reality (AR) displays, in which reflection volume holographic gratings are core optical elements. In this study, five high‐refractive‐index (≈1.6) bifunctional acrylate monomers (TPBSAs) are designed and synthesized. A series of two‐stage photopolymers are prepared using TPBSAs as writing monomers. Among them, one containing 9 wt.% TPBSA‐3 shows the best holographic recording performance with a sensitivity as high as 26.59 cm mJ−1. Using it as the recording medium, a reflection VHG can be obtained with high spatial frequency (5634 lines per mm), diffraction efficiency (97.14%), refractive index modulation (0.029), and good transparency within 400−800 nm after photobleaching. Furthermore, a HOW capable of achieving virtual and real image fusion is fabricated.

3-3: Study on the Field of View Properties for a Holographic Waveguide Display System

The Field of View (FOV) properties and effects of the reflection Volume Holographic Grating (VHG) in conical mounting was studied when used in a see through Head Mounted Display in detail. Also, two methods for enlarging the FOV and improving the color uniformity for reflection VHG were analyzed and simulated.

非均匀膨胀与收缩下反射体全息光栅衍射特性分析

Diffraction characteristics of reflection volume holographic gratings at nonuniform swelling or shrinking by introducing a function between swelling factor and the thickness of the grating layer are investigated. By means of Kamiya's rigorous delamination-calculation method and Lorentz-Lorenz formula, the analytical expressions of the average refractive index and the modulation are derived. Accordingly, the diffraction efficiency curves of the 1st-order reflection are given when the swelling factors are constant, linear function and nonlinear function. The influences of the average refractive index and the modulation for an ideal grating or decay distribution for the nonideal grating on the angular and wavelength selectivity are analyzed. The diffraction characteristics of the grating are given when the swelling factors are unequal at the exposure area and the unexposed area, and the response degree of diffraction efficiency of the grating to the change of swelling factor is discussed. The results show that nonuniform distribution of the swelling factor causes a diffraction efficiency curve in the asymmetric profile; compared with the modulation of refractive index, the Bragg angle of grating is highly sensitive to the change of average refractive index; the swelling factors at the exposure area and the unexposed area affect the peak efficiency, the angular band range and the spectral bandwidth. The results have theoretical guiding sense for the swelling and shrinking process of the reflection volume holographic gratings.

Diffraction properties study of reflection volume holographic grating in dispersive photorefractive material under ultra-short pulse readout

Based on the modified Kogelnik diffraction efficiency equation, we study the diffraction intensity spectrum and the total diffraction efficiency of reflection volume holographic gratings in photorefractive media. Taking photorefractive LiNbO3 crystal as an example, the effect of the grating parameters and the pulse width on the diffraction properties is presented under the influence of crystal material dispersion. Under the combined effects, the diffraction pulse profiles and the total diffraction efficiency are compared with and without crystal material dispersion. The results show that the dispersion will decrease the diffraction intensity. Moreover, when pulse width is smaller or the grating spacing and the grating thickness are larger, the influence of dispersion on diffraction is large. The results of our paper can be used in pulse shaping applications.

Instantaneous characteristics study of the diffracted and transmitted light of a staticphotorefractive reflection volume holographic grating read by an ultrashort pulselaser

The time-domain diffraction and transmission of reflectionvolume holographic gratings (RVHGs) recorded in photorefractiveLiNbO3 crystals are theoretically studied and compared with transmission volume holographicgratings (TVHGs) when they are illuminated by ultrashort pulse laser light. The modifiedKogelnik’s coupled-wave theory, combining the dispersion effect in the crystal, is used.The results show that larger diffraction intensity can be obtained by choosing alarger grating period, grating thickness and modulation index for a given pulseduration. The RVHG has higher diffraction intensity than the TVHG with thesame grating parameters. Also, it is found that the diffracted pulse of the RVHGand the TVHG shift in opposite directions along the time-axis. The values ofthe shifts are functions of the readout pulse duration and grating parameters.The overmodulation phenomenon appears in the diffracted pulse of the TVHGat high values of the grating thickness and refractive index modulation, but itdoes not occur in the RVHG. The results of our study can be used in choosingproper grating parameters for pulse shaping and signal processing applications.

Diffraction properties of ultrashort pulsed beams with arbitrary temporal profiles by a reflection volume holographic grating

The diffraction properties of reflection volume holographic gratings are studied when the gratings are illuminated by an ultrashort beam with arbitrary temporal profiles. The modified Kogelnik's theory of coupled waves is used. Simple analytical expressions for spectral and temporal distribution of the transmitted and diffracted are obtained. The dependences of the diffraction bandwidth, the Bragg selectivity bandwidth and the total diffraction efficiency of the reflection volume grating on the temporal profiles of the input ultrashort pulse are investigated. Study shows that the bandwidth of the reflection volume holographic gratings varies with the grating parameters more slowly than the transmitting volume holographic gratings. For three different temporal profiles, numerical results about diffraction properties of the reflection volume holographic gratings are given and compared with the transmitting volume holographic gratings.

Pulse shaping and diffraction properties of multi-layers reflection volume holographic gratings

The multi-layers coupled-wave theory is extended to systematically investigate the pulse shaping and diffraction properties of a system of multi-layers reflection volume holographic gratings (MRVHG) under ultrashort laser pulse (ULP) readout. The combined effects that the grating parameters such as the number and thickness of layers and gaps between them and the pulse duration of the input ULP have on the pulse shaping properties are considered. The pulse profiles of the diffracted and transmitted beams, the diffraction bandwidth, and the total diffraction efficiency are presented. The calculated results we have derived permit an optimal choice of grating parameters for the pulse shaping and process applications.

Diffraction properties of volume holographic gratings for an ultrashort pulsed beam with different polarization states readout

The diffraction properties of volume holographic gratings are studied when the gratings are illuminated by an ultrashort pulsed beam with different polarization states. The developed coupled wave theory of Kogelnik is used. Considering the dispersion effect of the grating media, solutions for the diffracted and transmitted intensities, diffraction efficiencies and the bandwidths of the gratings are given in transmission volume holographic gratings and reflection volume holographic gratings. The bandwidths of the gratings are reduced by the dispersion effect of the grating media. They also have different influences on the diffraction of an ultrashort pulsed beam with different polarization states. For different values of the ratio of the spectral bandwidth of the input pulse to that of the grating, the changes of the spectral and temporal distributions of the diffracted intensities, as well as the diffraction efficiencies of the gratings are shown.

Analysis of polarization properties of reflection volume holographic grating

Polarization properties of reflection volume holographic grating were analyzed using characteristic matrix method. Computer simulation results showed the holographic grating's diffraction characteristics of P and S polarized components respectively. The angular selectivity and wavelength selectivity for P and S polarized components were analyzed in detail. Comparisons with some experimental results are given. The practical reference value of these results on the holographic component application is introduced.