Such a glasses-free 3D screen could also support content besides films – volumetric images might greet window shoppers, enhance sporting events, or even help improve driver safety. In this paper, Reitterer et al. move closer towards the realization of a large, glasses-free 3D screen with a clever type of dynamic optical actuation. Similar to large light emitting diode (LED) screens, their proposed design contains many small light-emitting elements. However, unlike an LED that can only change in brightness, each element of their screen can also vary the direction in which it emits light. By quickly “shooting” images in different directions, their single display turns into a multi-view display, which in turn can send 3D imagery to a viewer.
The key to Reitterer et al.’s large multi-view display lies within each of its many light-emitting elements, which they term a “trixel”. Unlike the traditional pixels that comprise conventional 2D displays (e.g., laptop and smartphone screens), each trixel contains three primary components – a set of colored laser diodes to generate light, a small cylindrical lens to collimate this light into a tight beam, and an electrically addressable (i.e., a micro-electro-mechanical system [MEMS]) mirror. When actuated, the MEMS mirror quickly tilts to a particular orientation to redirect each trixel beam to a particular distant spot, offering control over which direction an image is sent.
If a trixel is in an “on” state, its mirror will direct its beam towards a particular viewer’s eye, and if “off” it will direct the beam away from his or her eye. Together, all of the display’s “on” trixels will form into a unique two-dimensional image for this viewer. To show a 3D image, the trixel display must direct two unique images into slightly different directions: light from the first image must only enter the viewer’s right eye, and light from the second must only enter their left eye. If each image is displayed quickly enough in succession, then the trixel array achieves the same function as 3D movie glasses: a unique image will pass through each eye, which your visual system can interpret as a 3D scene.
Reitterer et al. demonstrate a prototype of their new display format using 15 trixels arranged into a 5 x 3 grid. They successfully deliver two unique images to a viewing distance of up to 5 meters with laser sources that are bright enough to function in sunlight. Currently, the primary limitation appears to be the slow divergence of each trixel’s beam as it travels far from the display, which sets a maximum viewing distance (otherwise, each enlarged beam will enter both eyes and mix the two images that must remain separate). While a perfectly flat MEMS mirror can keep each beam tight enough to create a 70 meter viewing distance, a realistic device may have to settle for less. This limitation withstanding, it appears that a full-resolution sign is within close reach. Future work might examine how to correctly direct images to multiple viewers, or even viewers on-the-move. It may not be long before this type of trixel display makes it into theatres to replace those funny glasses, or, better yet, shines a 3D image in front of you in a place that you’d least expect.
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