Off-axis Holographic Lens Research Articles

Viewing angle enlargement in holographic augmented reality using an off-axis holographic lens

In this paper, a viewing angle enlargement method of holographic display using an off-axis holographic lens is proposed, and verification experiment of viewing angle enlargement is developed by using a single spatial light modulator (SLM) and an off-axis holographic lens fabricated by the holographic recording. The experimental results indicate that the viewing angle of holographic reconstructed image is increased to 11.2°, which is about 3.8 times as wide as the original viewing angle formed by the single SLM only. Furthermore, a see-through holographic display system for augmented reality (AR) is constructed, where virtual image is generated by holographic projection. The real scene and the virtual image will fuse together by using the off-axis holographic lens as the image combiner. The results prove that the proposed system can reconstruct virtual three-dimensional (3D) image with correct depth cues, solve the accommodation-vergence conflict problem effectively, and achieve the holographic AR 3D display effect without visual fatigue.

Off-axis holographic lens spectrum-splitting photovoltaic system for direct and diffuse solar energy conversion.

This paper describes a high-efficiency, spectrum-splitting photovoltaic module that uses an off-axis volume holographic lens to focus and disperse incident solar illumination to a rectangular shaped high-bandgap indium gallium phosphide cell surrounded by strips of silicon cells. The holographic lens design allows efficient collection of both direct and diffuse illumination to maximize energy yield. We modeled the volume diffraction characteristics using rigorous coupled-wave analysis, and simulated system performance using nonsequential ray tracing and PV cell data from the literature. Under AM 1.5 illumination conditions the simulated module obtained a 30.6% conversion efficiency. This efficiency is a 19.7% relative improvement compared to the more efficient cell in the system (silicon). The module was also simulated under a typical meteorological year of direct and diffuse irradiance in Tucson, Arizona, and Seattle, Washington. Compared to a flat panel silicon module, the holographic spectrum splitting module obtained a relative improvement in energy yield of 17.1% in Tucson and 14.0% in Seattle. An experimental proof-of-concept volume holographic lens was also fabricated in dichromated gelatin to verify the main characteristics of the system. The lens obtained an average first-order diffraction efficiency of 85.4% across the aperture at 532 nm.

基于低单色像差离轴全息透镜的解复用器

A novel scheme is proposed, in which the aberrations in the off-axis holographic lenses used as demultiplexers are reduced to a low enough level for relatively small channel spacing. The scheme includes optimizing the recording and reconstruction geometries and collimating the reconstruction wave with a gradient-index lens. A demultiplexer operated in the 1 550-nm band with 5-nm channel spacing and ?\infty-dB crosstalk is obtained using the scheme. The channel spacing can be decreased to 2 nm by etching the cladding of the output fibers to a smaller size.

Performance of an Off-axis Holographic Lens in the Presence of Aberrations Induced by Construction-reconstruction Wavelength Shift: Extended Object Imaging

In this paper investigations have been carried out on the imaging of extended objects by an off-axis holographic lens operating at a wavelength different from its recording. Aberration balancing and correction techniques have been applied to improve the quality of imaging coherent as well as incoherent bar and edge objects. The light intensity distribution in the Gaussian image plane has been computed numerically and the results have been presented in graphical form. The image quality of the aberration-balanced holo-lens has been found to be comparable to that of the ideal holo-lens.

Fourier transformation with a planar holographic doublet

The use of a single off-axis holographic lens for Fourier transformation results in phase errors that degrade its performance. A configuration of two identical off-axis holographic elements is proposed for performing Fourier transformation without phase errors. Such a configuration can be readily folded to form a compact and cascadable element that can be conveniently incorporated into optical correlators. The grating functions of the holographic elements needed for performing the desired transformation were used to record the planar configuration, which was then experimentally evaluated. The results reveal that phase errors were indeed eliminated, in close agreement with the calculations.

Imaging of extended objects using an off-axis holographic lens: effect of wavelength shift from construction to reconstruction

In this paper investigations on the imaging of extended objects by an off-axis holographic lens reconstructed at a wavelength different from its recording have been carried out. An aberration correction technique has been applied to minimise the aberrations introduced by the wavelength shift. The performance of a corrected holo-lens has been evaluated by computing the images of coherent as well as incoherent bar and edge objects and compared with that of the aberrated holo-lens. Light intensity distribution in the image plane has been evaluated numerically and the results have been presented in graphical form.

Two-step method for fabricating miniaperture on-axis holographic lenses with high numerical apertures

A two-step method for fabricating miniaperture on-axis holographic lenses with high numerical apertures is presented. The first step is to record a bifocus off-axis master holographic lens using a plane wave and a divergent spherical wave. The second step is to record the miniaperture on-axis holographic lens using the conjugate reconstructed wave of the master holographic lens. A holographic lens array is made in our experiments in which the numerical aperture of each lens in the array reached 0.31.

Imaging of Extended Objects Using an Off-axis Holographic Lens

Abstract The aim of this paper is to evaluate the performance of an off-axis holographic lens afflicted with third-order spherical aberration and coma using a numerical ray-tracing procedure. The light intensity distribution in the aberration spot observed at the Gaussian image plane has been evaluated for different amounts of coma and for a fixed value of spherical aberration. The images of both an extended coherent and an incoherent edge as well as bar objects have been computed and the results compared with the aberration-free case. All the results are illustrated in graphical form.

Evaluation of a technique for the design and manufacture of an off-axis holographic lens in dichromated gelatin

Variations in the intensities of the recording waves during the exposure of a holographic film cause fluctuations in the average intensity and the modulation depth of the resulting fringe pattern. The development process of the holographic layer stores these fluctuations and converts them into a variation of the diffraction efficiency and of the layer thickness if the exposure is in the linear range of the layer. A processing technique for dichromated gelatin layers is developed which results in a homogeneous distribution of the diffraction efficiency over the hologram aperture and restores the original layer thickness. Using this process technique, two different types of off-axis holographic lens have been developed. The resulting local Bragg angles, the diffraction efficiencies and the layer thickness were determined by fitting the angular sensitivity curve of the lenses using Kogelnik's coupled wave theory.

Holographic optical elements (HOE) for semiconductor lasers

A two step method is described to produce off-axis holographic lenses with high diffraction efficiency and without astigmatism for semiconductor lasers. The hologram is recorded in the visible (514 nm) and reconstructed in the infrared (800 nm). The principal parameters (recording and reconstruction angles, astigmatic focal lengths) for each hologram and wavelength are calculated analytically using second order approximation. Numerical methods, based on classical ray-tracing applied to holographic diffraction, have been developed to calculate spot diagrams and to investigate the effects of higher order aberrations.

Higher order aberrations in holographic lenses

Third-, fifth-, and seventh-order aberrations have been analyzed for in-line and off-axis holographic lenses of different f/No. The seventh-order wave aberrations and the corresponding aberration coefficients are reported here for the first time. It has been concluded that when the holograms are to be used as optical elements, fifth- and seventh-order aberrations should also be considered along with the third order to achieve ideal imagery as both the chromatic and nonchromatic aberrations are quite large even when only small deviations from the recording geometry are present in the reconstruction step.