Three-dimensional see-through augmented-reality display system using a holographic micromirror array.

It is difficult to find the micromirror array with desired specifications for augmented-reality displays, and the custom fabricating methods are complicated and unstable. We propose a novel, to our knowledge, three-dimensional see-through augmented-reality display system using the holographic micromirror array. Unlike the conventional holographic waveguide-type augmented-reality displays, the proposed system utilizes the holographic micromirror array as an in-coupler, without any additional elements. The holographic micromirror array is fabricated through the simple, effective, and stable method of applying the total internal reflection-based hologram recording using a dual-prism. The optical mirror and microlens array are set as references, and the specifications can be customized. It reconstructs a three-dimensional image from a displayed elemental image set without using any additional device, and the user can observe a three-dimensional virtual image while viewing the real-world objects. Thus, the principal advantages of the existing holographic waveguide-type augmented-reality system are retained. An optical experiment confirmed that the proposed system displays three-dimensional images exploiting the augmented-reality system simply and effectively.

Diffraction efficiency enhancement and optimization in full-color HOE using the inhibition characteristics of the photopolymer.

A novel and effective simultaneous recording method, to the best of our knowledge, is proposed for improving the diffraction efficiency and uniformity of full-color holographic optical elements (HOE) using the Bayfol HX102 photopolymer. To improve the diffraction efficiency of a full-color HOE, it is important to find the optimal recording beam intensity taking into account the initial and late responses of the medium. The range of optimal beam intensity for recording full-color HOE can be found experimentally by analyzing the inhibition period and response characteristics of the recording medium for three wavelengths. Through this method, a full-color HOE with an average diffraction efficiency of about 56.81% and a standard deviation of about 1.7% was implemented in a single layer photopolymer.

Full-color holographic diffuser using time-scheduled iterative exposure.

A compact wavelength multiplexing technique is proposed and experimentally investigated to improve the efficiency of a full-color holographic diffuser using photopolymer. The exposure responses of a monochromatic hologram and a three wavelength multiplexed hologram recorded in photopolymer film are presented. The time-scheduled exposure energies at wavelengths of 633, 532, and 473 nm were chosen to optimize the uniform diffraction efficiency of the wavelength multiplexed hologram. These three wavelength iterative sequences of exposures are applied to achieve a specific color balance for a multicolor holographic diffuser. The experimental results confirm that the fabrication method is well suited to the manufacture of holographic diffusers for full-color display applications.

Holographic filter with cascaded volume Bragg gratings in photopolymer waveguide film.

A novel holographic filter using a photopolymer-based cascaded volume Bragg gratings (CVBGs) is proposed and experimentally demonstrated in this paper. The filter was designed to attain a narrow spectral bandwidth characteristic without increasing the thickness of photopolymer used, at 1550 nm operating wavelength region. The proposed filter is consisted of a 45° slanted grating working as a surface-normal input/output coupler and a non-slanted reflection grating acting as a narrow-band wavelength selective filter, and it was embedded in the photopolymer film as a waveguide mode. The fabricated filter showed that the bandwidth at the center wavelength of 1547.85 nm was about 0.45 nm.

Design of cascaded volume holographic gratings to increase the number of channels for an optical demultiplexer.

The design and demonstration of a holographic optical demultiplexer based on cascaded volume holographic gratings are presented. By serially adding a second holographic grating, which has a different grating period, slant angle, and center wavelength compared with those of the first grating, the operating wavelength range of the optical demultiplexer could be expanded, and, therefore, the number of channels of the holographic demultiplexer is doubled. As a result of the experiment, a 0.4 nm spaced 130- channel demultiplexer with a channel uniformity of 3.5 dB, a 3 dB bandwidth of 0.12 nm, and channel cross talk of -20 dB is experimentally achieved.

Effects of apodization on a holographic demultiplexer based on a photopolymer grating.

An investigation of the effects of apodization on a holographic demultiplexer that is based on a photopolymer grating is presented. Uniform and Gaussian apodized gratings are fabricated in a DuPont HRF-150-38 photopolymer. From the theoretical and experimental results, the spectral response of the apodized grating has a larger main lobe but lower sidelobes than those in the uniform-grating case. A 42-channel demultiplexer that is based on the Gaussian apodized grating with an 0.4-nm channel spacing is demonstrated. A cross-talk level of -30 dB and an interchannel uniformity of 1.5 dB are archived in the wavelength range of approximately 1550 nm.