Silviu Reinhorn

Visor-display design based on planar holographic optics.

A method for designing and recording visor displays based on planar holographic optics is presented. This method can deal with the problem of recording-readout wavelength shift. The display system is composed of two holographic optical elements that are recorded on the same substrate. One element collimates the waves from each data point in the display into a plane wave that is trapped inside the substrate by total internal reflection. The other diffracts the plane waves into the eye of an observer. Because the chromatic dispersion of the first element can be corrected by the dispersion of the second, this configuration is relatively insensitive to source wavelength shifts. The method is illustrated by the design, recording, and testing of a compact holographic doublet visor display. The recording was at a wavelength of 458 nm, and readout was at 633 nm. The results indicate that diffraction-limited performance and relatively low chromatic dispersion over a wide field of view can be obtained.

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.

Planar holographic elements with uniform diffraction efficiency

A planar holographic lens is investigated for imaging applications. The design and recording of the holographic lens are based on a transference of wavefronts method, where a desired grating function, with low aberrations, is transferred from a thin hologram to one recorded in thick recording materials. The resulting thick planar holographic lens fulfills the Bragg condition over a relatively large field of view. Experimental results, presented for planar holographic lenses recorded in photopolymers and dichromated gelatin materials, show that a high diffraction efficiency greater than 50% and uniform over a field of view of 16° can be obtained.

Compensation of the wavelength dependence in diffractive star couplers

Optical systems are described that compensate for the wavelength dispersion that arises in a diffractive fan-out star coupler. Two approaches are investigated, a space-variant one and a space-invariant one. In the space-variant approach an array of diffractive optical elements corrects the wave fronts. In the space-invariant approach a combination of refractive and diffractive lenses compensates for the chromatic focus shifts that are caused by the fan-out element. Examples for such compensating optical systems are presented, along with simulated results. The detailed design for an optimized space-invariant system is described.

White-light holographic display based on planar optics

A novel method for designing, recording, and reconstructing a planar-optics display holographic doublet, composed of two holograms on the same plate, is presented. The first hologram traps a light from a white-light source into the substrate by total internal reflection, whereas the second hologram couples out the trapped light from the plate to form the reconstructed three-dimensional image. The method is illustrated with a holographic doublet recorded at 488 nm and read out with a white-light source. A sharp image with high efficiency was reconstructed.

Planar Diffractive Elements for Compact Optics

Research in planar optics aims to develop a technology for designing and constructing compact optical systems. The basic planar multi-grating configuration is composed of cascaded gratings recorded on a single substrate. The first grating diffracts the incident light from the source so that it will be trapped inside the substrate by total internal reflection, while the last grating in the cascade diffracts the light out of the substrate to a detector (or into the eye of a viewer). The planar optical configurations are usually much more compact, more mechanically stable, less sensitive to illumination wavelength and more suitable for mass production than systems using free space optics. An example illustrating a planar optics configuration for head mounted display is presented.

Planar holographic configuration for efficient imaging

Abstract A planar holographic configuration that can be exploited for imaging with high light throughput efficiency is presented. The configuration is comprised of two elements — a linear grating and a corrected holographic lens. The design and recording of the holographic lens are based on a technique, where a desired-grating function, with low aberrations, is transferred from a thin hologram to on recorded in thick recording materials, so the Bragg condition is fulfilled over a broad range of incidence angles. As a result, it is possible to get a halographic lens having low aberrations and uniform high diffraction efficiency over a relatively large field of view. When combined with the linear grating, the overall planar optics configuration can be exploited for imaging information displayed with quasi monochromatic light source, as in a visor display application. Such a configuration was designed, recorded and evaluated experimentally, demonstrating a uniform, and relatively high diffraction efficiency over a field of view of 16 degrees.

Computer-originated planar holographic optical elements.

We present novel, to our knowledge, methods for the analytical design and recording of planar holographic optical elements in thick materials. The recording of each planar holographic element is done by interference of two aspherical waves that are derived from appropriately designed computer-generated holograms such that the element has the desired grating function for minimizing aberrations and closely fulfills the Bragg condition over its entire area. The design and recording methods are described, along with calculated results of representative elements.

Planar optical dynamic crossbar switch

A compact dynamic crossbar switch, based on a planar optics configuration, is presented. It consists of a pair of identical planar holographic cylindrical telescopes, each recorded on a single substrate, and a two-dimensional array (8x8) ferroelectric liquid crystal spatial light modulator. The crossbar switch can direct the light from any particular source in a one-dimensional array of 8 sources to a particular detector in a one-dimensional array of 8 detectors. The design of the overall configuration is presented along with experimental results.

Correcting asymmetric divergence from diode lasers with planar optical elements

A novel compact planar configuration for correcting the asymmetric divergence of light emanating from diode lasers is presented. It is comprised of two holographic lenses that are recorded on one transparent substrate, where the light propagates form one lens to the other by means of total internal reflections. The design of the overall planar configuration is presented along with experimental result. The results reveal that it is possible to focus a collimated asymmetric beam to a circular spot.