As the core sensor of robots and unmanned driving, the importance of lidar is self-evident. At present, according to whether there are mechanical parts, lidar can be divided into mechanical lidar and solid-state lidar. Although solid-state lidar is considered to be The general trend of the future, but in the current lidar battlefield, mechanical lidar still occupies the mainstream position.
Mechanical lidars have rotating parts that control the laser emission angle, while solid-state lidars do not require mechanical rotating parts, and mainly rely on electronic components to control the laser emission angle.
The mechanical lidar is mainly composed of photodiodes, MEMS mirrors, laser emitting and receiving devices, etc. The mechanical rotating part refers to the MEMS emitting mirror that can control the laser emitting angle of 360°.
Solid-state lidar is different from mechanical lidar. It uses optical phased array (OpticalPhasedArray), photonic integrated circuit (PhotonicIC) and far-field radiation pattern (FarFieldRadiationPattern) and other electronic components instead of mechanical rotating components to adjust the angle of the emitted laser.
Due to the difference in internal structure, the sizes of the two types of lidars are not the same. Mechanical lidars are larger and more expensive overall, but the measurement accuracy is relatively high. The solid-state lidar is small in size and low in cost, but the measurement accuracy is relatively low.
In addition, compared to solid-state lidar, mechanical lidar has a more obvious advantage in that it has a 360° field of view. A lidar can be fixedly installed on the top of a robot or car to perceive the surrounding environment at 360°. In contrast, solid-state lidar , It needs to be fixed in some proper position, and the field of view is generally within 120°. Therefore, if it is used in unmanned vehicles, at least 4 units are required to achieve the same coverage as mechanical lidar. The more the number, It also means higher costs.
Solid-state lidar has another less obvious advantage. Eye safety regulations allow moving laser sources to emit higher power than fixed laser sources.
All level 1 safety systems must be designed to ensure that people do not blink and look directly at the laser device for a few seconds, and still not get hurt.
When using a solid-state scanning unit, if the human eye is within a few inches of the laser scanner, 100% of the laser light may enter the eye. However, if mechanical lidar is used, the laser is only concentrated in a specific direction, and only a small part of the 360° rotation. Therefore, mechanical lidar can provide higher power for each laser pulse without causing eye damage. This makes it easier to detect the reflected light, so in the foreseeable future, mechanical lidar may have a greater detection range advantage than solid-state lidar.
At the same time, most of the leading solid-state lidar designs face the significant challenge of "long-distance detection".
The amount of laser light that the micro scanning mirror in the MEMS system can project is limited. This makes it very difficult for distant objects to reflect the laser beam and be detected. Compared with other technologies, the optical phased array solution has greater beam divergence, so it is difficult to balance long distance, high resolution and wide field of view.
For flood imaging lidar, the light emitted each time will be scattered throughout the field of view, which means that only a small part of the laser will be projected to certain specific points. In addition, each pixel in the photodetector array must be very small, limiting the amount of reflected light it can capture.
In general, although solid-state lidar has the advantages of low cost, miniaturization, and easier mass production, there are still great challenges to popularize in large areas. Due to its unique advantages, mechanical lidar is expected to be in the next few years. Will continue to maintain a certain market position.