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Researchers develop specialized hardware to render holographic projections at near real-time speeds. The framerate leaves a bit to be desired, however, so don't throw your 3D glasses away just yet.
To project the image, the process is reversed. Half the laser light is reflected off the interference pattern, and then recombined with the a beam that has not been modified. The combined beam is then projected towards the viewer using a lens system. Viewers perceive the 3D object rather than the interference pattern.
So, computing a hologram sounds pretty simple: just recreate the interference pattern. But there is a gotcha. For instance, if you cut a photograph in two, you get two partial images. Cutting a hologram in two, however, results in two complete images of lesser quality—every pixel encodes information about the entire image. And therein lies the rub: to display a computed hologram, the intensity of each pixel must be calculated from the entire interference pattern, not just the local contribution to the object.
Surely that can't be that difficult? Well, researchers in Japan have created a graphics card, called the HORN-6, that can do this for you. It consists of four Xilinx field programmable gate arrays (FPGA), each of which has about 7 million gates and a bit of memory (less than 1MB). Each FPGA is connected to 256MB of DDR RAM, while a fifth, smaller FPGA is used to manage the PCI bus.
These FPGAs divide the area of a 1,920 x 1,080 LCD and calculate the intensity of each pixel using a ray-tracing algorithm that also tracks the phase of the light—the phase allows the interference pattern to be calculated. In a nice bit of engineering, as the block size that each FPGA can process (e.g., the local storage limit) is completed in just under the time it takes to fetch the next block from memory. This allows the researchers to keep the FPGA load pretty much constant by prefetching data.
When the rendering is completed, the resulting interference pattern can be displayed on an LCD. This pattern can then be projected using a laser to render a hologram that is 1m along a dimension (the paper doesn't say which, so I suspect the diagonal) and has a five degree viewing angle.