According to reports, the existing laser pointer radar system has been used in a variety of innovative applications from safety applications to mapping and industrial automation. Among them, the automotive market is particularly concerned about the development and application of LiDAR systems. The LiDAR scanner is a key component of the autonomous vehicle prototype system and is a key component in current traffic sign recognition, adaptive cruise control (ACC), blind spot detection, collision avoidance systems and lane departure warning systems.
Among all the LiDAR-based systems mentioned above, there is a core component that is indispensable, that is, the "eye of wisdom" of the LiDAR system - the detector.
Automotive LiDAR systems must be able to quickly and reliably sense the surroundings of the vehicle, creating 3D images of the surrounding environment and the road ahead as much as possible. LiDAR systems installed on fast-moving vehicles need to be able to “see” a distance of at least 150 m in front and detect obstacles as small as 10 cm in height.
LiDAR systems therefore require complementary but independent detector systems while ensuring environmental certification and functional safety. For example, to accommodate heat and ambient temperatures from other components of the system, the equipment must be rated for operating temperatures of -40 to 125 °C. Also, in order to be able to "see and recognize" the signal accurately in various background noises, the detector should have an ideal signal to noise ratio. In addition, optical detectors need to be prepared to handle ambient light of different intensities, so the laser pointer detector must have a wide dynamic range.
In addition to the basic laws of physics, LiDAR system designers need to consider economics. All components in the car need to be cost effective. For practical applications, the best price/performance ratio is the key to the successful application of advanced technology.
At present, almost all existing automotive systems using long-distance LiDAR use a "scanning" LiDAR device that can move the scanning laser beam throughout the scene. The effective detection range of the current technology is generally 30 to 300 m. Almost all LiDAR systems use 905 nm lasers (some companies on the market such as Blackmore, Neptec, Aeye, and Luminar are investigating lasers using 1550 nm wavelengths), which can be mass-produced at low cost and emit non-visible light. High power short pulse beams (for example, 75 W peak for 5 ns) provide the ideal power/cost ratio. These lasers have been widely used in advanced low cost silicon detectors.
As the industry evolves, design engineers can choose from a variety of different detector technologies for LiDAR systems, each with its own advantages and disadvantages. Such silicon-based detectors have a structure in which three types (P-type/intrinsic/N-type) semiconductors are laminated together.
They have the best dynamic range and can handle greatly varying light. For example, they are able to detect reflections from distant objects even in direct sunlight. Moreover, they are relatively economical.
However, they are not capable of providing the high level of signal-to-noise ratio and bandwidth required for most complex automotive LiDAR systems. In the end, they are neither fast nor sensitive enough. Silicon Photomultiplier (SiPM) and Single Photon Avalanche Diode (SPAD) detectors. These solid-state silicon-based detectors were originally built for professional small medical and scientific applications. Recently, they are actively trying to find applications in the larger LiDAR market.
While such laser pointer detectors are similar in functionality to APDs (Avalanche Photodiodes, discussed below), they are optimized for extremely high internal amplification or gain, enabling them to detect very weak light. And, they are very fast. Finally, they are compatible with commonly used CMOS technology and can therefore be coupled to related electronics on the same chip.
However, the sensitivity of single detectors for such detectors is quite low compared to the sensitivity of APDs. Therefore, they must rely on extremely high multi-level doubling. Unfortunately, during the multiplication process, noise is also increased, which typically significantly reduces the signal-to-noise ratio of the detector. In addition, their amplification mechanism suffers from false triggers caused by high temperatures.
It is speculated that the most critical drawback of such detectors is that their high gain is at the expense of saturation problems.