A 3D image created by the NCI. Source: Caltech
Scanning technology has been around for many years. However, an inexpensive nanophotonic device that can accurately take scans is relatively new. The Caltech technology, called nanophotonic coherent imager (NCI), is made using a cost-effective silicon chip. The researchers say their tiny 3-D imaging technology boasts the highest depth-measurement accuracy of any such device.
The chip would essentially allow a smartphone camera to analyze both distance and intensity information. "Each pixel on the chip is an independent interferometer—an instrument that uses the interference of light waves to make precise measurements—which detects the phase and frequency of the signal in addition to the intensity," said Ali Hajimiri, an electrical engineering professor with Caltech.
Integrating LIDAR into the chip
Hajimiri and his team integrated LIDAR, a ranging technology, into the chip. "By having an array of tiny LIDARs on our coherent imager, we can simultaneously image different parts of an object or a scene without the need for any mechanical movements within the imager," Hajimiri added.
The NCI also counts with an optical concept known as coherence in order to offer high-resolution images. Two coherent waves have the same frequency and their peaks and troughs of light waves are perfectly aligned. The NCI uses coherent light to its advantage; on-chip detectors (also known as grating couplers) are utilized to pick up light reflected off of an object, which serve as “pixels” that form the 3D image.
Using coherent light
Coherent light is used as a reference to measure the difference in the reflected light, thanks to its consistent frequency and wavelength. An electrical current is created from the light, containing the crucial intensity and distance information for each and every pixel.
"By coupling, confining, and processing the reflected light in small pipes on a silicon chip, we were able to scale each LIDAR element down to just a couple of hundred microns in size—small enough that we can form an array of 16 of these coherent detectors on an active area of 300 microns by 300 microns," Hajimiri explained.
Scanning larger images
Using a proof of concept, the researchers successfully recreated a 3D image of the U.S. penny’s “hills and valleys” drawing. Hajimiri and his team are now working on creating a chip that can scan larger items (the current proof of concept has just 16 coherent pixels). He said his device could eventually serve various applications, including helping automated cars avoid collisions.
"The small size and high quality of this new chip-based imager will result in significant cost reductions, which will enable thousands of new uses for such systems by incorporating them into personal devices such as smartphones," he shared.
Source: Caltech