“CEA-Leti has taken a critical step towards developing LiDAR systems suitable for a wide range of commercial applications, it has developed genetic algorithms for calibrating high channel count optical phased arrays (OPA), as well as a Advanced measuring device.
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CEA-Leti has taken a critical step towards developing LiDAR systems suitable for a wide range of commercial applications, it has developed genetic algorithms for calibrating high channel count optical phased arrays (OPA), as well as a Advanced measuring device.
OPA is an emerging technology consisting of an array of optical antennas that are closely arranged (about 108m) and emit coherent light over a wide angular range. The resulting interference pattern can then be altered 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, allowing solid-state beam steering.
This could improve performance in scan speed, power efficiency and resolution compared to the cumbersome, power-hungry and expensive mechanical beam steering systems used in current LiDARs. Another feature of OPA-based LiDAR systems is that they have no moving parts, as solid-state beam steering can be achieved simply by phasing the antenna, greatly reducing the size and cost of these systems.
In a paper titled “Development, Calibration and Characterization of Silicon Photonics-Based Optical Phased Arrays,” CEA-Leti reports calibration and characterization results at the Photonics West 2021 Digital Forum.
“The development of high-performance OPAs will pave the way for inexpensive LiDAR systems for autonomous vehicles, holographic displays, biomedical imaging and many other applications,” said Sylvain Guerber, lead author of the paper. “However, Widespread adoption of LiDAR will depend on lower system costs and smaller form factors. “
LiDAR, which stands for light detection and ranging, has become a key enabling technology for future sensing and vision systems. In addition to automotive and medical uses, they can enable autonomous movement of drones and robots, as well as industrial automation. Commercial LiDAR systems must meet stringent requirements, especially in automotive applications. In particular, high power and low divergence beams are required to accurately resolve the scene. For example, to resolve a 10cm object at 100m would require the OPA to operate in a circuit with a wavelength of 1-0.8m, which should contain at least 1,000 antennas, each spaced 1.00-8m apart. Therefore, for commercial OPA-based LiDAR systems, high-channel-count OPAs must be developed.
Integrated chip-scale OPAs with solid-state beam steering can be produced by taking advantage of well-established silicon photonics platforms, Guerber said. However, this is only the first step towards a fully functional OPA, as beam scanning requires preliminary calibration. This calibration process can be time-consuming due to the large number of optical antennas required, which is not compatible with large-scale deployment techniques. Therefore, the CEA-Leti team developed what may be the first wafer-level OPA characterization device, an important step towards the industrialization of OPA-based LiDAR. In addition, a Darwinian-based genetic algorithm has been developed to quickly and reliably calibrate high-channel-count OPAs. They can make calibration up to 1,000 times faster than previously used algorithms.
Widespread commercial use of LiDAR technology in the automotive industry and other markets is expected to continue for several years, Guerber noted. OPA is a crucial step and CEA-Leti will continue to work on it.
“There are still a lot of challenges, especially at the system level,” he explained. “LiDAR is made up of many elements: lasers, Electronic drivers, OPA steering systems, detectors and data processing capabilities. They all have to work together; OPA is just the system’s part.”
This work was partly funded by the French ANR through Carnot, the ECSEL Vizta European project and the French national program “Program d’investissement d’avenir of IRD Nanoelec” (n°ANR-10-AIRT-05).
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