Pacala points out several advantages of traditional rotary mechanical LiDAR designs. Among them, the most obvious advantage is its 360 ° field of view. We can install a lidar fixed on the top of the car to sense the surroundings of the car 360 °. In contrast, solid-state LiDAR needs to be fixed in some appropriate positions (such as the front and rear of the vehicle or the four corners), and the field of view is generally 120 ° or less. Therefore, self-driving cars use solid-state LiDAR sensors, and at least four units are required to achieve the same coverage as rotary mechanical LiDAR.
Another less obvious advantage is that human eye safety regulations allow moving laser sources to emit higher power than fixed laser sources. According to Pacala, all Level 1 security systems must be designed to ensure that personnel do not stare directly at the laser device for a few seconds and remain harmless.
When using a solid-state scanning unit, if the human eye is located a few inches from the laser pointers scanner, it may cause 100% of the laser light to enter the eye. However, if a rotary LiDAR sensor is used, the laser is only focused in a specific direction, and only a small part of 360 ° rotation. Therefore, rotary LiDAR can provide higher power for each laser pulse without causing eye damage. This makes it easier to detect retroreflective light, so in the foreseeable future, rotary LiDAR units may have a larger detection range advantage than solid-state LiDAR units.
Solid-state LiDAR or mechanical LiDAR? Hear what the CEO of Ouster said. The picture above shows Google's early self-driving prototype. There is a huge rotating LiDAR sensor on the roof, a black radar (4 in total) on the front fender, a "wheel encoder" on the rear wheel, and a video camera in the car. The prototype is equipped with a variety of sensors that cost up to $ 150,000.
At the same time, most leading solid-state LiDAR designs face the significant challenge of “long-range detection”. Micro-scanning mirrors in MEMS systems can project a limited amount of laser pointer light. This makes it difficult for distant objects to reflect the laser beam and be detected. Compared with other technologies, the optical phased array scheme produces a larger beam divergence, so it is difficult to balance long distance, high resolution and wide field of view.