42 Focus | Lidar For mid- to long-range implementations, 905nm EEL (edge emitting laser) can provide a more economical approach in cost and size. Triple-junction EEL devices are known for their temperature stability and have been combined with MEMS mirrors in first-generation hybrid Lidar systems. The range of 905nm Lidar has been significantly improved in recent years, thanks to the higher-efficiency, mainstream, single-photon avalanche detector (SPAD) devices. There are three types of commercial automotive Lidar based on the scanning method: mechanical Lidar (involving the movement of lasers, lenses and sensors); hybrid solid-state Lidar (in which only the scanning MEMS/mirror moves); and all-solid-state Lidar (with no mechanical movements, as the scanning beam is controlled electrically). Other scanning methods include optical phase arrays (OPA), focal plane switch array, acousto-optic beam steering, planar lens, MEMSintegrated metasurfaces, beam steering metasurfaces and liquid crystal metasurface (LCM) devices. OPA and LCM are commercially available, but have yet to achieve mass production, while others are still in the research phase. Metasurface potential One promising technology is the beam-steering metasurface. This is a programmable optical semiconductor technology, which can be used for automotive Lidar systems, AGVs with a 25 m range and a 10 Hz sensing frame rate, as well as for UAVs. One metasurface uses liquid crystals as those structures, which can be reconfigured to change the phase of the light beams to steer them. This beam steering allows the light to sweep the area in front of a vehicle. This technology was designed and optimised with a cloud-based simulation tool that provides an efficient method for predicting the anisotropic permittivity and the response of liquid crystal at the nanometre scale. The primary challenge when simulating performance was the requirement to model large-area optics while including the nanoscale features representing variations in the standard CMOS chip-making process. Specifically, the modelling needed to capture optical properties at a macro-scale length of over 100 µm with nanoscale precision of under 5 nm. This requirement created significant computational complexity, requiring a cloud-based tool that can provide the necessary compute power. The metasurface can be paired with the latest laser diodes. Recent discrete laser diodes have an optical power of 1 kW for detecting objects at greater distances with more accuracy. There is a need for laser diodes that serve as light sources to achieve high kW-level output while allowing multiple light sources to emit light at close intervals. A surface-mounted infrared laser diode can provide eight channels at 125 W each to provide 1 kW of power for Lidar applications that use 3D ToF systems for spatial recognition. Such an LED design uses eight emission areas per element, each 300 µm wide, which are installed on a submount fixed to a high heatdissipation substrate. With such high power, packaging is key to the Lidar design. The emitting surface can incorporate a clear glass cap to eliminate the risk of light scattering caused by scratches, which can happen during the dicing process when the LEDs are cut, which tends to occur with resin-encapsulated products. This will ensure a high beam quality, providing uniform emission intensity across the emission width, as well as a low wavelength temperature dependence of 0.1 nm/°C (vs 0.26 to 0.28 nm/°C for standard products). The eight-channel array is designed with a configuration that narrows the regions of reduced emission intensity between channels, while the bandpass filter minimises the effects of ambient light noise from the sun and other sources, contributing to long-distance detection and high-definition Lidar. The metasurface and LED laser can be combined with commercial SPAD detectors. This has the sensitivity to be used for long-range Lidar in a robotaxi or a self-driving truck. Hybrid solid-state Lidar manufacturers initially combined a point source such as a 1550nm fibre laser or 905nm EEL with a 2D MEMS or mirrors. One example of a hybrid system is a solid-state source April/May 2025 | Uncrewed Systems Technology A liquid crystal metasurface (Image courtesy of Lumotive)
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