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Since its discovery almost 70 years ago, the hologram has been considered to reproduce the most realistic three dimensional images without visual side effects. Holographic video has been extensively researched for commercialization, since Benton et al. at MIT Media Lab developed the first holographic video systems in 1990. However, commercially available holographic video displays have not been introduced yet for several reasons: narrow viewing angle, bulky optics and heavy computing power. Here we present an interactive slim-panel holographic video display using a steering-backlight unit and a holographic video processor to solve the above issues. The steering-backlight unit enables to expand the viewing angle by 30 times and its diffractive waveguide architecture makes a slim display form-factor. The holographic video processor computes high quality holograms in real-time on a single-chip. We suggest that the slim-panel holographic display can provide realistic three-dimensional video in office and household environments., Holographic displays that are both compact and produce realistic holograms without eyestrain are still difficult to realize. Here the authors implement a steering-backlight unit and a holographic video processor to produce a realistic holographic display in a slim panel.

Compact varifocal lenses are essential to various imaging and vision technologies. However, existing varifocal elements typically rely on mechanically-actuated systems with limited tuning speeds and scalability. Here, an ultrathin electrically controlled varifocal lens based on a liquid crystal (LC) encapsulated semiconductor metasurface is demonstrated. Enabled by the field-dependent LC anisotropy, applying a voltage bias across the LC cell modifies the local phase response of the silicon meta-atoms, in turn modifying the focal length of the metalens. In a numerical implementation, a voltage-actuated metalens with continuous zoom and up to 20% total focal shift is demonstrated. The concept of LC-based metalens is experimentally verified through the design and fabrication of a bifocal metalens that facilitates high-contrast switching between two discrete focal lengths upon application of a 3.2 V$_{\rm pp}$ voltage bias. Owing to their ultrathin thickness and adaptable design, LC-driven semiconductor metasurfaces open new opportunities for compact varifocal lensing in a diversity of modern imaging applications.

Holography has been considered as the ultimate technology for three-dimensional visual experience. Compared to the well-established static holographic technology, holographic video display is still in the research and development stage, before commercial products. This paper reviews various kinds of researches and related systems from the beginning of holographic video display to recent improvements, compares each specification, and describes their features. We discuss the key requirements for holographic display to be commercialized and widely used in everyday life.

A slim beam deflector that satisfies both a large steering angle and a large area can be very useful in various applications. However, a smaller electrode pitch for a large steering angle and enlargement of its area are trade-off relations due to the limited number of control channels in an electrically tunable beam deflector system. For a large steering angle in the active area where actual diffraction occurs, an indium tin oxide electrode of 2 µm pitch was implemented through a stepper lithography. The via-hole process was developed to expand the reduced active area due to the small electrode pitch. We developed a beam deflector with 7200 controllable channels in an active area of 14.4 m m × 14.4 m m . The maximum steering angle is 7.643° at a wavelength of 532 nm.

A hybrid liquid crystal and carbon nanotube-based device which shows the capacity to perform as a switchable diffraction grating is demonstrated. A liquid crystal layer was sandwiched between two electrodes (patterned into gratings). The bottom electrode consists of a two dimensional square array of carbon nanotubes, while the top electrode comprises an ITO-based in-plane switching electrode on glass. The carbon nanotubes, due to their high aspect ratios, produce defects within the liquid crystal layer, producing a two dimensional grating. The device displays distinct voltage-dependent diffraction patterns due to the two different electrodes. The diffraction patterns are studied both computationally and experimentally, with good agreement between the results obtained. Both the diffraction pattern and efficiency from the device could be switched by varying the applied voltage across the liquid crystal layer. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Highly efficient transmission-type beam deflectors that have high angular resolution have been widely used for various applications. Continuously tunable beam deflectors have also been needed for many purposes. An indium-tin-oxide (ITO), widely used for transparent electrodes, was placed on the upper and lower glass substrate. The ITO layer on the lower substrate was patterned by the contact mask aligner for relatively wide input and output pad compared to main grating ITO patterns in the active area. These input and output pads on the lower substrate are connected to each driving integrated circuit (IC), which has 360 channels for continuous control. A small pixel pitch of grating patterns of 6 μm (the electrode width is 3 μm with a 3 μm spacing) was developed, and the maximum diffraction angle is calculated and measured at 2.541° with a wavelength of 532 nm. A minimal cell gap of 2.5 μm was applied for the full 2π phase modulation by using a high-birefringence liquid crystal. A driving module for continuous beam steering is also developed and applied to the beam deflector system. A diffraction efficiency of about 50.9% is observed at an angle of diffraction about 2.541°.

The coherent backlight unit (BLU) using a holographic optical element (HOE) for full-color flat-panel holographic display is proposed. The HOE BLU consists of two reflection type HOEs that change the optical beam path and shape by diffraction. The illumination area of backlight is 150 mm x 90 mm and the thickness is 10 mm, which is slim compared to other conventional coherent backlight units for holographic display systems. This backlight unit exhibits a total efficiency of 8.0% at red (660 nm), 7.7% at green (532 nm), and 3.2% at blue (460 nm) using optimized recording conditions for each wavelength. As a result, we could get a bright full color hologram image.

The modulation efficiency of the double-phase hologram macro-pixel that is designed for complex modulation of light waves is defined and analyzed. The scale-down of the double-phase hologram macro-pixel associated with the construction of complex spatial light modulators is discussed. (C) 2014 Optical Society of America

We propose an optical system for synthesizing double-phase complex computer-generated holograms using a phase-only spatial light modulator and a phase grating filter. Two separated areas of the phase-only spatial light modulator are optically superposed by 4-f configuration with an optimally designed grating filter to synthesize arbitrary complex optical field distributions. The tolerances related to misalignment factors are analyzed, and the optimal synthesis method of double-phase computer-generated holograms is described. (C) 2013 Optical Society of America