Caltech researchers develop silicon chip that can turn any cellphone into a projector

Researchers at California Institute of Technology (CalTech) have developed a new chip which acts as a lens-free projector. When used with a phone it could turn it into a projector.

The chip has been developed by Ali Hajimiri, Thomas G. Myers Professor of Electrical Engineering, and researchers in his laboratory (see image insert).


This is a light-bending silicon chip which uses integrated optical phased array (OPA) to project the image electronically with only a single laser diode as light source and no mechanically moving parts. This is unlike traditional projector that lets the beam of light pass through a tiny image, using lenses to map each point of the small picture to corresponding, yet expanded, points on a large screen.

The research team was able to bypass traditional optics by manipulating the coherence of light—a property that allows the researchers to "bend" the light waves on the surface of the chip without lenses or the use of any mechanical movement. If two waves are coherent in the direction of propagation—meaning that the peaks and troughs of one wave are exactly aligned with those of the second wave—the waves combine, resulting in one wave, a beam with twice the amplitude and four times the energy as the initial wave, moving in the direction of the coherent waves, says CalTech in a release.

The OPA chip uses a series of pipes for the light that are called phase shifters to slow down or speed up the timing of the waves passing through it. This controls the direction of the light beam. The electronic data from the computer or the cellphone are converted into multiple electrical currents to form an image. This is done by using stronger or weaker currents to the light within the phase shifter which changes the number of electrons within each light path. This also changes the timing of the light wave in that path.


These timed light waves are delivered to tiny array elements within a grid on the chip. The light is then projected from each array in the grid, the individual array beams combining coherently in the air to form a single light beam and a spot on the screen.


"In the future, this can be incorporated into a phone, and since there is no need for a lens, you can have a phone that acts as a projector all by itself," Hajimiri, of the research team says. He also clarifies that a tiny projection device can have many applications—including light-based radar systems (called "LIDAR"), which are used in positioning, robotics, geographical measurements, and mapmaking.


These results were described in a presentation titled "Electronic Two-Dimensional Beam Steering for Integrated Optical Phased Arrays" and were presented at the Optical Fiber Communication (OFC) conference in San Francisco on March 10.