Dynamic Holography for scientific uses, military heads up display and even someday HoloTV Using TI's DMD
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    Our project to generate dynamic three dimensional views from two dimensional Holograms using Texas Instruments' Digital Light Processing (DLP) Digital Micromirror Device (DMD). Holograms are diffraction patterns encoding both amplitude and phase information of the light waves coming from a three dimensional object or scene. They are capable of reproducing these object light waves when illuminated with coherent light like lasers. High quality holograms have been produced for a number of years using photographic film emulsions and lasers. The virtual transmission images seen by looking into the film are known to be realistic 3-D reconstruction of the original scene. More recently, we have all seen the virtual reflection 3-D images in a film emulsion placed on our credit cards and illuminated by white light.

The concept of using a DMD is a direct application of these same holographic principles. The individual micromirrors (16 X 16 microns) on the DMD are like large grain film emulsion. All the physics applicable to large grain emulsion reflection holograms are applicable to DMD holograms, except the DMD alters the wave front by deflecting/oscillating the micromirrors (see related links below). The advantage of the DMD over film is the 60 Hz refresh rate for changing the hologram being viewed. This enables the possibility of real time display which is impossible for film emulsions. The Light Biology Applications Laboratory at UT Southwestern Medical Center has verified this concept through proof of principle (POP) demonstrations.

The following pictures show one of the 3-D scenes used in the POP experiments and the results obtained. The holograms used in the demonstration are computer generated. The concept assembles interferograms (2-D diffraction patterns of 2-D images) of two or more 2-D scenes or objects at various positions in the third dimension by the superposition principles. Our coordinate system uses the z-axis as the third dimension.

 

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Figure 1: Picture on the left shows the image-layout used to demonstrate 3-D Holograms with a DMD.In this spatial volume, an image is computationally placed at the rear plane and another at the front plane. The two interferograms of the front and rear plane are superimposed to produce a single hologram which will cause the two images to be simultaneously reproduced at different distances from the DMD.

 

 

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Figure 2: Reconstruction Setup

  

Figure 2 is a picture of the full optical system bench including magnifying mirrors and a 3-D real image reconstructor, an Agarose gel filled tank. The POP demonstration was conducted without the magnifying mirrors and, instead of the gel tank reconstructor, a frosted glass image reconstructor was used.


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Figure 3A

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Figure 3C
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Figure 3D

Figure 3: Photographs of reconstructed images captured with a Nikon Coolpix990 digital camera

 

Figure 3A is the photograph of the real 3-D image at 30 cm from the converging lens. Figure 3B is the photograph of the real 3-D image at 27.5 cm from converging lens. These pictures are taken with digital camera by moving the frosted plate to the best focus position of each image in the volume.

The more traditional way to visualize the reconstructed 3-D scene is to directly view the virtual image which appears in the DMD. Shown in Figure 3C is the virtual image of the reconstructed spatial volume as recorded on a 2-D focal plane of a digital camera. The helicopter appears in front of the fighter just as in the real image.

Next, like in the virtual image viewing mode, all objects in the 3-D real image can be seen simultaneously by projecting into a volume of translucent scattering bodies. Figure 3D is a photograph of the 3-D reconstruction of the jet and helicopter in a 7.5 cm thick gel volume made up of a 0.15 % Agarose concentration (gm-Agarose/ml-Buffer).

As noted above, to view the depth associated with these 3-D image reconstructions, photographs of the reconstructions on a frosted glass plate placed at different distances are captured and presented in the movie format below(3-D Holographic POP Demo). Since the size of the original reconstruction is small, the projections, for this movie, have been optically magnified before reconstructing the slices on the frosted glass plate. The z-axis location is shown in the movie for each position that a picture was taken. Notice the different focus on the helicopter or jet as the frosted glass plate approaches the focus point of one or the the other. The image focus position for the helicopter and jet, as magnified, are 15 cm and 22 cm, respectively.

Similarly, in order to appreciate the capability of DMD holograms to produce dynamic 3-D images, reconstructions at regular time intervals are recorded and presented below in Dynamic Holographic Projection. In this movie, one can observe two fighter jets flying in the background, while a helicopter is ready to take off in the foreground. The helicopter, its blades and the two jets are at different depth in the 3-D image. After the jets pass, take-off and landing of the helicopter follows. Thus, this movie is a demonstration of time dependent 3-D projection capability.

Recently, a solid state laser of wavelength 533nm was added to the system to demonstrate multi color capability. 3D scenes showing a red jet flying behind a green helicopter were pre-computed and transcribed to the projection system at video rate. DMD was illuminated by two lasers (wavelengths:633nm and 533nm) simultaneously in a novel way to obtain multicolor reconstruction. We observed reconstruction of dynamic 3D scene with moving objects in two colors, and with good image quality. The demonstration showing reconstruction on a frosted plate was recorded using a camcorder and presented as movie titled "Two Color". All the movies can be viewed using Windows Media Player or Real Player.

For a fully functional 3-D visualization projection system, major essential characteristics are robust capability for reliable data transmission and good resolution. The data lost in transmission or interference noise added to the transmission does not result in total loss of vital information during reconstruction (Figure 4). Figure 4A-4C show the photographs of the reconstructions and the corresponding holograms transcribed to DMD just below it. Figure 4A is the full hologram and its reconstruction. In Figure 4B, a number of adjacent rows and columns have been simulated as lost in transmission. In Figure 4C, it shows a discernable image when only a 300 X 300 block of hologram remains.

It can be easily inferred that missing blocks of data during transmission cause loss in intensity of the image but does not result in loosing the complete or partial image during reconstruction. A gauge of the robustness of interferometric images to random data loss or corruption is illustrated in the graph shown in Figure 4D.The data shows standard pixel-to-pixel correlation coefficient of grayscale values for each reconstructed image using interferograms of varying noise levels, to the reconstructed image uncompromised by random noise. Various approaches in terms of hardware and software are currently being explored to improve the resolution and develop a suitable 3-D display medium.

 

 

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Figure 4A

Figure 4B

Figure 4C
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Figure 4D

Figure 4: Resilience of projection to data noise

 

We believe near term, high payoff applications of this concept include: 1) a heads-up fighter aircraft displays which will require no headgear/goggles and provide target information (heading, elevation, range) with its real time positioning in a 3-D scene display; b) Air Traffic/Battle Management; and c) many others . Research is being undertaken to engineer a system with high resolution, multi-color and real time capabilities. This work is supported by the P.O'B Montgomery Distinguished Chair Account and Center for Translational Research (CTR) at UT Southwestern Medical Center.

Publications

Patents

  • Digital micro-mirror holographic projection
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    News Reviews

     
    Team Members
    • Evgeni Poliakov, Ph.D. - Post-doc physicist, University of Texas Southwestern Medical Center
    • Raj Munjuluri,BS- Student Intern, University of Texas Southwestern Medical Center
    • Erik Kildebeck, - Student Intern, University of Texas at Dallas

    Related Links

    Digital Light Microprocessor System by Texas Instruments

    Commercial potential for true 3D holo displays is substaintial. We have been studying, with SMU Cox School of Business Marketing students, two principle markets. One is for advanced medical displays and one is for advanced heads up displays for military applications. The working name for this commercial project is Holomedix and/or Holotactix.