Integrated Optical Phased Array boost for LIDAR
French research group CEA-Leti has developed genetic algorithms to calibrate high-channel-count optical phased arrays (OPAs) to reduce the cost and size of LIDAR laser sensors.
OPAs are an emerging technology made of arrays of closely spaced (around 1µm) optical antennas and which radiate coherent light in a broad angular range. The produced interference pattern can then be changed by adjusting the relative phase of the light emitted by each antenna. For example, if the phase gradient between the antennas is linear, a directional beam will be formed. By changing the slope of the linear gradient, the direction of the beam can be controlled, which enables solid-state beam steering.
“The development of a high-performance OPA would pave the way to inexpensive LiDAR systems for autonomous vehicles, holographic displays, biomedical imaging and many other applications,” said researcher Sylvain Guerber. “But widespread adoption of LiDAR will hinge on lower system costs and smaller form factors.”
Resolving a 10cm object at 100m requires an OPA operating at a wavelength of 1µm with a circuit consisting of at least 1,000 antennas, each spaced 1µm apart. Therefore, the development of high-channel-count OPAs is necessary for a commercial OPA-based LiDAR system.
Using an OPA can improve performance in scanning speed, power efficiency and resolution compared to the heavy, power-hungry and expensive mechanical beam-steering systems used in current LiDARs. An additional feature of OPA-based LiDAR systems is that they have no moving parts, as the solid-state beam steering is achieved only by phase tuning the antennas, which significantly reduces the size and cost of these systems.
The researchers also developed an advanced measurement setup enabling wafer-scale OPA characterization that could further bring down the cost of the sensors.
Next: Integrated OPA LIDAR
An integrated chip-scale OPA with solid-state beam steering can be produced by leveraging the benefits of a mature silicon photonics platform, says Guerber. However, this is only the first step toward a fully functional OPA because beam scanning requires a preliminary calibration.
The high number of optical antennas means the calibration process can take a large amount of time, which is incompatible with massive deployment of a technology. The genetic algorithms is used to quickly and reliably calibrate high-channel-count OPAs. These allow up to 1,000x faster calibration than previously used algorithms.
However the use of OPAs is still several years away says Guerber.
“There are still a lot of challenges, especially at the system level,” he said. “A LiDAR is composed of many elements: a laser, an electronic driver, an OPA steering system, a detector and data-treatment capability. All of them must work together; the OPA is only a part of the system.”
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