Advances In Holographic Video

We discuss recent developments in the MIT electronic holography display. These include the use of multiple galvanometric scanners as the horizontal scanning element, two 18-channel acousto-optic modulators (AOMs) working in tandem, and a bank of custom-designed high-bandwidth framebuffers. We also describe some recent progress on computational issues. I ACOUSTO OPTIC MODULATORS The basic idea underlying the MIT electronic holography display is the use of an acousto-optic modulator (AOM) as a dynamic display medium1'2. The holographic information is first computed at suitable sampling intervals and then converted to a high bandwidth analog signal with a modified video display framebuffer. Those samples are then frequency shifted, amplified and fed to the AOM transducer. The fransducer converts the electrical signal into a phase modulation that propagates down the AOM crystal as shear waves. Laser light diffracted by the phase pattern is then scanned in a raster fashion by a combination of galvanometric X and Y scanners and the resulting hologram is imaged in front of an output lens. Because the AOM is a 1-dimensional device, the displayed holograms exhibit horizontal parallax only. The general direction of our recent research has been towards the parallelization of the computational and display processes. We believe that large displays can be implemented with available technologies if we take a massively parallel approach. The first logical step in that direction is to increase the number of available channels in the AOM since the space bandwidth product of the display scales linearly with the number of acoustic channels. Previous experiments with 3 channels AOMs3 met with success and convinced us of the feasibility of an 18-channel display. The design of that element was developed in conjunction with NEOS Corp. (Melbourne, FL). The two AOMs used in our newer design use shear mode Te02 as the acousto-optic material. Each acoustic channel is 2 mm wide and the intercharinel distance is 4 mm. The interchannel crosstalk is less than 30 dB and each channel has a spacebandwith product of 1000. The RF bandwidth of the AOM's ranges from 55 to 105 MHz. II OPTICAL SCANNING 2.1 Problem definition The limitations of the polygonal scanning approach described in a previous paper1 become evident if we describe how the design parameters scale with image size and horizontal view zone. We will consider here the case where the horizontal scanning element coincides with the Fourier transform of the AOM phase pattern, i.e., the focal point of lens L1 of Fig. 1. At the scanning plane, the size of this Fourier transform is given by: 188 / SPIE Vol. 1914 0-8194-1 147-7/93/$6.00 Downloaded From: http://proceedings.spiedigitallibrary.org/pdfaccess.ashx?url=/data/conferences/spiep/57580/ on 06/15/2017 Terms of Use: http://spiedigitallibrary.org/ss/termsofuse.aspx