- Surface acoustic waves can be used to steer laser beams, in ways that could lead to glasses-free ‘3D’ displays
- The ‘3D’ display envisaged by Draper is not holographic but ‘autostereoscopic’. In this technology, it does not need any special glasses.
Screenless Display was an excellent thought that came into many experts in order to solve the major problems related to the device miniaturization. Lower space screen displays have made the need for screenless displays more than ever.
A new proof-of-concept device has been made for screenless 3D displays. The used fabrication techniques can be implied and scaled for production, According to Draper research engineer, Gregg Favalora talked about the prototype saying,
“We can report the first demonstration, to our knowledge, of a scalable, monolithic surface-emitting electronic holographic modulator – an element of a 3D display that is made using standard microfab techniques.”
Works on total internal reflection( TIR)
It consists of a strip of lithium niobate crystal with 1mm thickness. It resembles a microscope slide. A laser beam is fed into the crystal just below its surface, after which it continues to travel just below the surface. The surface acoustic waves are also launched in the opposite direction. It travels as parallel clusters of faint surface ripples.
Acts as diffraction grating
As the beam and ripple cluster passes one another, the surface waves act as a moving diffraction grating. It directs some of the laser energy downward into the thickness of the slide. The slide undergoes total internal reflection and captures the laser energy. A fixed diffraction grating on the back of the crystal is used to direct the beam out of the top surface.
Manually controlled exit angle and position
Both the exit angle and exit position of the laser can be controlled manually. The exit angle is set by the frequency of the SAW (280-320MHz, as well as the laser wavelength). It controls the initial downward deflection angle. The exit position is controlled by pulsing the laser and varying the position at which it encounters the SAW pulse.
Single laser pulse using an array of beams
The length available for SAW-laser interaction in the prototype is 8mm. The experiment targets a string of SAW pulses with similar frequencies and low intermittent time gap. It is quick enough for the pulses to reside in the 8mm surface at the same time. This results in a single laser pulse producing a row of exit beams.
The researchers talked about the experiment saying,
“ This is an early demonstration of an electro-holographic spatial light modulator device into which 8 mm of holographic fringes are loaded that can project a linear light field. This has many applications. For example: depending on the electronic signals applied to the modulator, light exits from programmable apertures, in programmable directions, with programmable luminance per direction. This is useful because the field of electronic holography, and digital print holography, has developed a variety of ways to use the surface of a hologram to project 3D imagery. ”
An autostereoscopic display
The ‘3D’ display envisaged by Draper is not holographic but ‘autostereoscopic’. In this technology, it does not need any special glasses. The display is effectively a pair of projectors. In this pair, one sends an image to a person’s left eye, and the other sends a slightly different image to the person’s right eye.
The images should differ in the correct way to add ‘depth’ to the overall perceived image. In practice, autostereoscopic displays send out a horizontal fan of different images, and the viewer’s eye picks up pairs of images from the fan.
Implies an easy fabrication process
According to Favalora, the Draper modulator fulfil these requirements because it can be designed into wafers that can be tiled. Also, the modulator consists of an easy fabrication process. This wavelength-based aiming exploits the effect the laser wavelength over exit angle.
In a real display, the device can be mounted so that it can create a horizontal fan. It would be surrounded by identical devices. If this device can be properly fabricated as a mini-module, it would be the generation of screenless displays.