While researchers around the globe have invested time and energy on holographic displays for years, the resulting tabletop setups have been too bulky and expensive to be practical for commercial applications. The MIT Media Laboratory (Cambridge, MA) has combined the latest generation of personal computers (PCs), lasers, and compact waveguides to undertake the construction of an affordable, user-ready holo-video display with standard television resolution.1
Targeted at a consumer price of a few hundred dollars or less, the most obvious application for such a device is virtual gaming for PCs and game consoles, which are already ripe with 3-D visual data crying out for holographic rendering-all that’s missing is the display. Another promising application is the medical field, in which 3-D magnetic-resonance images and computed-tomography scans used by doctors are now limited to 2-D viewing.
The MIT researchers designed their third-generation holo-video display, called the Mark III, around an inexpensive acousto-optic light modulator smaller than a postage stamp (see figure). Adapted from telecom applications, the novel lithium niobate modulator offers a bandwidth of up to 1 GHz. Used in conjunction with two holographic optical elements, the modulator diffracts 510 to 532 nm laser light along two axes to convert monochromatic light into holographic patterns, eliminating a horizontal scanning problem inherent in past architectures. Furthermore, it eliminates a rotating mirror that bulked up previous generations of the device; whereas past systems took up an entire optical table, the current design will measure approximately 1.5 m in total optical path length, folded to fit into a shallow box.
As part of the shortened optical design, a telephoto Fourier-transform system converts the linear motion of the diffraction fringes into rotational motion, which allows a reverse-rotation optical element to descan the fringes later. The Mark III will increase the number of scan lines by more than three times the Mark II system, offering 440 lines within a view volume of 80 × 60 × 80 mm (width × height × depth). The scan rate of 30 Hz and view angle of 24° are target specifications in line with previous generations.
The display is capable of being driven by a single PC video card. The major motivation behind the new smaller display system is its immediate widespread commercial potential. “Previous holo-video work was aimed at high-end users, employing expensive optoelectronic elements and specialized computing hardware,” says principal researcher Michael Bove, “We’re purposely trying to do the new work at a consumer price point, using off-the-shelf computing hardware and less expensive optoelectronics.”
The team is aiming for a monochrome version of the Mark III display that will display pictures by late this summer. Beyond that, plans for the fourth generation of the device are to add full color and focus on increasing the size of the image from the current size of a Rubik’s cube to that of a standard PC monitor.
1. D. Smalley et al., Proc. SPIE Photonics West, Practical Holography XXI, 6488 (2007).