Better, Simpler Detection
New lidar-on-a-chip could make building autonomous cars much easier
By Liz Sheeley
When developing new technologies, engineers are constantly pushing the limits of currently available electronics—but progress can only get so far before new parts must be invented that create new, extended limits. Associate Professor Milos Popovic (ECE) and collaborators have built a new type of silicon chip that will help advance technologies such as sensors for self-driving cars and smartphone face recognition.
Technologies that need to detect remote objects with fine resolution rely on lidar, the optical version of radar, using laser beams rather than radio waves. Unlike radar systems, lidar is capable of generating high-resolution 3D images and can more accurately detect the shape of an object. Lidar systems are currently bulky components, but their performance, resolution, cost and complexity could all be improved if they could be realized on a silicon chip—creating lidar-on-a-chip.
To accomplish this task, a tiny silicon photonic chip will require additional electronic components to steer a laser beam emanating from the chip surface, detect its reflections from distant objects, and generate the 3D image. In order to detect an object with high resolution at even moderate distance, say 300 feet away, the electronics would need to be highly complex. That makes scaling up this type of system extremely difficult. There would be hundreds to thousands of electronic components required, just for forming and steering the beam to the correct location.
In a paper published in the journal Optica, Popovic’s team describes how they constructed a new chip with an all-optical, electronics-free steering capability in two dimensions without compromising the lidar performance.
The team included Popovic’s graduate students and co-lead authors Nathan Dostart and Bohan Zhang. Dostart is a National Science Foundation Graduate Fellow, and is continuing his career at NASA Langley Research Center. Zhang is a National Defense Science and Engineering Graduate Fellow. The group collaborated closely with Professor Kelvin Wagner and his lab at the University of Colorado Boulder.
Instead of using electronic control circuits that would be programmed to generate and steer an optical beam, the new silicon chip uses a serpentine structure, which was designed to distribute light, and form and steer the beam in two dimensions in response to the user’s manipulation of only the input laser wavelength. As the laser wavelength changes, the angle of the emitted light also changes, effectively steering the out-going laser beam to carry out a two-dimensional angular sweep. Instead of needing to control thousands of electronic circuits, this chip requires only the one control variable – the wavelength of light.
“There’s not really a technology that’s scalable up to large apertures,” says Popovic. “This paper is demonstrating a single optical tile that is the first step of an approach that breaks a lot of these barriers.”
“What’s unique about this thing is basically that it’s an ultra-low complexity, kind of a game changing design for an optical beam steering chip in the sense that it has basically zero controls,” he says.
The chip can be tiled, meaning the team can create many serpentine waveguides on a single chip, or use a series of chips, and guide light through all the waveguides simultaneously to provide enhanced capabilities, such as increasing the range and resolution of the detector. Sensors based on such chips could be placed in different spots around a car so that each array of on-chip serpentines can act as a detector in different directions.
The iPhone, for example, has an assembly of small parts, including a laser and lens that together can detect a face for its facial identification feature. Instead of a complex assembly of parts, Popovic’s team has shown a key component of such a system, the beam-steering device needed for high-resolution images, can be realized on a single chip—allowing future lidar systems to be much simpler, and potentially be entirely integrated in a single chip or chip package. This could significantly lower the cost of these technologies in many applications—phones, cars and satellites. These chips can also be made using the same manufacturing processes and factories currently in place – another benefit to rapid transition to application, and adoption.