We propose the coherent backlight unit (BLU) using Holographic Optical Element (HOE) for full-color flat-panel holographic display. The HOE BLU consists of two reflective type HOEs that change the optical beam path and shape by diffraction. The diverging incident beam is transformed to the collimated beam which has a very small diffraction angle (7.5°) by HOE 1 (H1) in order to illuminate the whole display. This collimated beam is converged to a point at a distance from the glass substrate by HOE 2 (H2). As a result, the diverging incident beam is converted to a point light by H1 and H2. When the high resolution Spatial Light Modulator (SLM) displaying Computer Generated Hologram (CGH) is illuminated by HOE BLU, the hologram image is displayed at a view point near focal point. Practically, we fabricated the full color HOE BLU for 5.5" flat panel holographic display by using the proposed design. At least 5.5" size of HOE is required to illuminate the whole panel. For this reason, we recorded 150 mm x 90 mm size HOE on the 10 mm thickness glass substrate. This HOE BLU exhibits a total efficiency of 8.0% at Red (660 nm), 7.7% at Green (532 nm), 3.2% at Blue (460 nm) using optimized recording conditions for each wavelength. Finally, a bright full color hologram image was achieved.
We propose slim coherent backlight unit for a mobile holographic display. This backlight unit consists of glass substrate for waveguide and two surface gratings produced by two-beam interference. The area of backlight illumination is 150 by 85 mm, and the thickness is 0.7 mm, which is thin compared to other conventional coherent backlight units. This backlight unit exhibits a total efficiency of 0.1%, preserving the collimation and a uniformity of 80% over the whole area. The proposed slim coherent backlight can be applied to a mobile holographic display.
We propose the effective viewing window enhancement method for a holographic display with an amplitude-only SLM by using algorithmic approach. The basic concept is the superposition principle of holography. The multiple computer generated holograms (CGH) can be displayed on the SLM, and multiple 3D images are reconstructed at different positions within a viewing window simultaneously. In the experiments, we have implemented the holographic display using an amplitude-only SLM, a field lens, and laser light sources. We can observe the holographic 3D image in the frustum formed by the field lens through the viewing window located in the Fourier plane of the hologram. To enhance the effective viewing window, we generate multiple CGHs with an observer’s eye positions, and then overlap them to make the final CGH. Multiple 3D images can be reconstructed in different positions within the theoretical viewing window from the CGH displayed on SLM. This makes the enlargement of viewing zone that can observe the holographic images. The multiple holograms can be also made for enlargement of the viewing window along both horizontal and vertical direction (2D enlargement viewing zone). We confirmed that the experimental results and the simulation based on Rayleigh-Sommerfeld theory match well.
We demonstrate a holographic image reconstructed by a FPD-based complex spatial light modulator (SLM) which is composed of a phase-only SLM and a sheet of beam combiner. A complex SLM which modulates both amplitude and phase independently is necessary for a better image quality with reducing conjugate images. The two-phase encoding method is one of the most practical candidates for the complex SLM. The proposed complex SLM is presented in a phase-only LCD panel which can be manufactured in a conventional LCD process and it was used for generating different phases. The PAL (Parallel-Aligned nematic Liquid crystal) mode is used to modulate the phase without the amplitude change. The film-type beam combiner consists of a prism array and a grating made by a conventional fabrication process. The beam combiner plays a vital role to merge two pixels and to adjust effective complex modulation. In this paper, the holographic image by the proposed complex SLM is verified by the experimental and simulation work in a monochromatic reconstruction. This complex SLM can be scaled up and it is a promising candidate SLM for a large-size holographic 3D display.
In this paper, an inversion-free subpixel rendering method that uses eye tracking in a multiview display is proposed. The
multiview display causes an inversion problem when one eye of the user is focused on the main region and the other eye
is focused on the side region. In the proposed method, the subpixel values are rendered adaptively depending on the eye
position of the user to solve the inversion problem. Also, to enhance the 3D resolution without the color artifact, the
subpixel rendering algorithm using subpixel area weighting is proposed instead of the pixel values. In the experiments,
36-view images were seen using active subpixel rendering with the eye tracking system in a four-view display.