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.
An arrayed beam steering device enables much simplified system architectures for high quality multiview 3D displays by adapting time multiplexing and eye tracking scheme. An array device consisting of microscale liquid prisms is presented, where the prism surface between two immiscible liquids is electrically controlled to steer light beams by the principle of electrowetting. An array prototype with 280×280μm pixels was fabricated and demonstrated of its full optical performances. The maximum tilting angle of each prism was measured to be 22.5° in average, with a tracking resolution of less than 0.04°. In this paper, we report a design and fabrication of eletrowetting based prism array, opto-fluidic simulations, optical characterizations, as well as applications to achieve low fatigue 3D displays.
Recently liquid-based optical devices are emerging as attractive components in three-dimensional (3D) display for its
compact structure and fast response time. Among them an electrowetting prism array is one of the promising 3D devices.
It steers a beam, which enables to provide corresponding perspectives to observer. For high quality autostereoscopic 3D
displays the important factors are the beam steering angle and the beam profile, the optical characteristics. In this paper,
we propose a method to measure the optical characteristics of the liquid prism and show experimental results on our
prototype electrowetting prism array, which consists of prisms with 200um by 200um size. A modified 4-f system is
adopted for the proposed method. It provides two kinds of information of the optical characteristics of the liquid prism at
the image plane and at the Fourier plane. First, the proposed measurement setup magnifies the image of the liquid micro
prism array so that we can observe the status of the each prism array directly with bare eye and align a mask easily for
selecting a prism to be examined at the image plane. Secondly, the steering angle can be calculated by measuring the
displacement of the beam at the Fourier plane, where the angular profiles that have important information on the oilwater
interface is observed precisely. The principle of the proposed method will be explained, and the measured optical
characteristics from experimental results on the liquid prism we fabricated will be provided, which proves the validity of
the measurement method.