Chip bends light to project images
1 min read
A chip that has the potential to turn any smartphone into a projector has been unveiled by a team of Caltech engineers.
The 1mm2 device uses an integrated optical phased array (OPA) to project images electronically, with only a single laser diode as the light source and no mechanically moving parts.
Lead researcher Ali Hajimiri and his colleagues discovered they could bypass traditional optics by manipulating the coherence of light.
They found that when two waves are coherent in the direction of propagation, they combine to achieve twice the amplitude and four times the energy.
"By changing the relative timing of the waves, you can change the direction of the light beam," Hajimiri explained. "For example, if 10 people kneeling in line by a swimming pool slap the water at the exact same instant, they will make one big wave that travels directly away from them.
"But if the 10 separate slaps are staggered – each person hitting the water a half a second after the last – there will still be one big, combined wave, but with the wave bending to travel at an angle."
Using a series of pipes for the light called phase shifters, the OPA chip similarly slows down or speeds up the timing of the waves, thus controlling the direction of the light beam.
To form an image, electronic data is converted into multiple electrical currents; by applying stronger or weaker currents to the light within the phase shifter, the number of electrons within each light path changes – which, in turn, changes the timing of the light wave in that path.
The timed light waves are then delivered to tiny array elements within a grid on the chip. The individual light beams combine to form a single light beam and a spot on the screen.
As the electronic signal rapidly steers the beam left, right, up, and down, the light acts as a very fast pen, drawing an image made of light on the projection surface.
"Because the direction of the light beam is controlled electronically and not mechanically, it can create a sort of line very quickly," said Hajimiri. "Since the light draws many times per second, the eye sees the process as a single image instead of a moving light beam."
So far, the researchers have only been able to project simple images, such as a triangle and a smiley face. However, they are currently experimenting with larger chips which they believe could improve the resolution and increase the complexity of the projected images.
