Light detection and ranging technologies, commonly known as lidar, provide 3D information by measuring the time it takes reflected light to reach a receiver. This technology is used in systems such as self-driving vehicles to avoid collisions, but it is not available in more common, compact devices like smartphones and other cameras that use standard CMOS sensors. This is due to the relatively expensive, bulky and energy-intensive equipment typically needed to enable lidar capabilities, but a new breakthrough by Stanford engineers may enable new applications by bringing down the cost, size and energy requirements of the technology.
The Stanford team, a collaboration between the school’s Laboratory for Integrated Nano-Quantum Systems and ArbabianLab, came up with a new design that relies on acoustic resonance to modulate light using more lightweight and energy-efficient components than traditional systems. The acoustic modulator developed by the team uses a thin wafer of piezoelectric lithium niobate coated with two transparent electrodes; when electricity is introduced through the electrodes, the crystal lattice of the lithium niobate vibrates at very high, very predictable and highly controllable frequencies. Rapid modulation of light is necessary for lidar systems to measure variations in light reflectance and calculate distances between objects. With the addition of a couple polarizers, the team’s acoustic modulator turns light on and off several million times per second.
The engineers used their acoustic modulator concept to design a prototype lidar system using a commercially available digital camera as a receptor. The authors reported that the prototype could capture megapixel-resolution depth maps while requiring only small amounts of power to operate the new modulator. The new technology could potentially be used to develop a “standard CMOS lidar” that could be incorporated into compact devices such as smartphones or drones without major hardware changes. The design could further be used to enable megapixel-resolution lidar that can identify targets at a greater distance than currently possible. This research was published in Nature Communications.
“The geometry of the wafers and the electrodes defines the frequency of light modulation, so we can fine-tune the frequency. Change the geometry and you change the frequency of the modulation,” said first author Okan Atalar. “... While there are other ways to turn the light on and off, this acoustic approach is preferable because it is extremely energy efficient.”
Since building their first prototype, the team has already further refined the system to reduce the energy consumption by at least 10 times the amount reported in the paper, according to Atalar. Further development of the system could lower costs and energy consumption to the point where small-scale lidar would be readily available for 3D smartphone cameras, drones and lightweight robotics.
Photo: The lab-based prototype lidar system that the research team built, which successfully camptured megapixel-resolution depth maps using a commercially available digital camera. Credit: Andrew Brodhead