A Low Cost Holographic Display
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A Low Cost Holographic Display Mark Green University of Ontario Institute of Technology Figure 1: (a) Prototype holographic display (left), (b) Image of wireframe truncated pyramid as displayed in the prototype display Abstract 1 Introduction Holography can be viewed as the ultimate display technology since In many ways holography is the ultimate display device capturing it correctly duplicates all the cues used by our visual system. In the all aspects of the light energy that is reflected or emitted by the graphics community this technology has largely been ignored in the environment. This includes all the cues that our visual system past due to its computational cost, but this is changing as more expects. This differs from other display technologies, such as head powerful parallel processors are becoming available. One of the mounted displays (HMDs) that present conflicting cues to the main challenges in this area is the lack of a commercially available viewer. In the case of an HMD the images are displayed on a fixed display device at a reasonable cost that can be used for testing and plane producing focus and accommodation cues suggesting that all evaluating algorithms. This paper describes a low cost holographic the objects are at the same depth, while the stereo and projection display device that can easily be constructed from standard parts as cues suggest they are at different depths. This causes fatigue and a solution to this problem. This paper discusses the design other visual problems. Light field displays are a step forward, but considerations for such a device, its construction and an overview only provide correct 3D cues over a limited depth range of how holograms can be computed for it. It is our hope that this [Yamaguchi 2011] device will stimulate further research on holography within the computer graphics community. Recently, holography has become a marketing term that has been associated with any type of 3D display. In this paper holography Keywords: 3D display, holography refers to the optical phenomena where an interference pattern is generated when a coherent light source (for example, a laser) Concepts: • Hardware~Displays and imagers illuminates both an object and the recording medium [Goodman • Computing methodologies~Virtual reality 2005, Saxby and Zacharovas 2016]. *e-mail: [email protected] There have been very few papers on holography in the graphics literature since it has been viewed as too computationally expensive Permission to make digital or hard copies of all or part of this to be a practical display medium. This is rapidly changing as work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or powerful parallel architectures are now becoming readily available even on consumer class devices. It is now possible to compute commercial advantage and that copies bear this notice and the full simple holograms on consumer devices in a matter of seconds citation on the first page. Copyrights for components of this work owned by others than the author(s) must be honored. Abstracting while in the past this would have taken many hours or days. with credit is permitted. To copy otherwise, or republish, to post Holography is based on the interference of two wave fronts that are on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from produced by a coherent light source, a light source with a single frequency. The most common source of coherent light is a laser. [email protected]. In its simplest form a single wave front from a laser is split into two SA '16 Technical Briefs , December 05 - 08, 2016, , Macao Copyright is held by the owner/author(s). Publication rights beams with one beam aimed at the object to be recorded and the other at the recording medium. The two beams meet at the surface licensed to ACM. of the recording medium and form an interference pattern. If the ACM 978-1-4503-4541-5/16/12…$15.00 DOI: http://dx.doi.org/10.1145/3005358.3005373 same light source illuminates the interference pattern the original wave front from the object is produced resulting in the same visual stimulus as the original object. Optical holograms have been produced for many decades and they One of the most important design consideration is the device that are typically recorded on film which then must be developed before is used to display the interference pattern. The size of the display the hologram can be viewed. Once the film has been developed a device’s pixels must be close to the wavelength of the light and the laser can then be used to reconstruct the hologram. The physics of pixel array must have a large fill factor. The fill factor is the holography is well known so it can be simulated numerically proportion of the device surface that is covered by pixels. This resulting in a computer generated hologram. In this case the pretty much eliminates LCD panels from consideration since they interference pattern for the hologram is stored as an image. To have a low fill factor and in most panels the pixels are considerably reconstruct the hologram this image must be displayed and larger than the wavelength of the light that we are using. illuminated by a laser. A large number of algorithms have been developed for computing holograms and digital holograms have a There are two display technologies that meet our requirements. wide range of applications [Goodman 2005]. The one that is the closest fit is LCOS (Liquid Crystal on Silicon), but unfortunately it is too expensive for our purposes with chips Figure 2 shows the interference pattern computed for a wire frame starting in the $4000 range in small quantities. The other truncated pyramid like the one shown in figure 1b. Clearly it is technology that fits our requirements is the Texas Instruments impossible to determine that this interference pattern represents a DMD display. These displays have larger pixels than LCOS, but truncated pyramid just by looking at it, so it is impossible to debug they are small enough to work. The cheapest DMD is the DLP3000 or evaluate computational holography algorithms without a which has a pixel size of 10.8 μm and a fill factor of 92%. A red holographic display device. Unfortunately, holographic display laser which has a wavelength of 650 nm, so the pixel size is roughly devices that can be used in computer graphics research are not an order of magnitude greater than this wavelength. Texas commercially available. Instruments has a LightCrafterTM evaluation module that includes the DLP3000 along with the electronics and microprocessor required to drive the DMD. This provided a good starting point for the development of our prototype. 3 Holographic Display Prototype The three main components of our prototype are the Texas Instruments LightCrafterTM evaluation module, a semiconductor laser and a lens for increasing the size of the laser beam so it completely covers the surface of the DMD. A bit of Meccano is used to assemble all of the components as shown in figure 1a. The LightCrafterTM comes with an optics system that allows the device to be used as a projector. This system consists of three LEDs plus a number of lens and half silvered mirrors. To get access to Figure 2 Interference pattern for truncated pyramid the DMD this optics system must first be removed. Instructions for doing this are on the Texas Instruments website. You should check This paper presents the design of a low cost holographic display that the LightCrafterTM works correctly before you remove the that can be used to test and evaluate holographic display algorithms. optics system, since this is hard test later. A good set of precision Our goal was to produce a display for under $1000 that can be screw drivers makes this a lot easier. constructed from readily available components. A graduate student should be able to construct the display in less than a day once the The next component is a laser. As shown in figure 1b the user looks components have been purchased. Since this is a research into the device to see the hologram, therefore, a low power laser prototype flexibility and cost are more important than image quality must be used to avoid eye damage. On the other hand, we want to be able to use the device in a room environment, so the laser cannot The next section of this paper describes the design considerations be too dim. A good compromise is a 10mw laser (Egismos that drove the design of our holographic display. The third section Technology model S8365010D) which is bright enough for the describes the construction of the holographic display and the fourth room environment. This laser requires 3V power which is supplied section briefly describes the software that can be used to compute by two AA batteries. interference patterns. The final section presents results and discusses possible extensions to the design. The beam produced by the laser is too narrow to illuminate the whole DMD; therefore a lens assembly is used to spread the beam. 2 Design Considerations In the prototype the 10x microscope objective (Edmund Optics part number 43905) is used for this purpose. Flexibility was one of our main design considerations, allowing us The final step is to assemble all of the components. This could be to rapidly explore different device configurations to determine the done on an optical bench, but then again this exceeds our budget ones that produce the best display. Better packaging can be for the project. Instead parts from a basic Meccano set were used considered once the final device configuration has been determined.