Firstly, in terms of scanning methods, laser radar is currently mainly classified into mechanical rotating, prism, rotating mirror, MEMS galvanometer, OPA, Flash, etc. Among them, OPA and FLASH are the two implementation routes for solid-state laser radar technology, while the mainstream hybrid solid-state laser radar currently uses several technologies such as prisms, rotating mirrors, MEMS galvanometers, etc.

Mechanical rotary type: By horizontally rotating the entire laser emitting module and receiving module 360 °, omnidirectional coverage is obtained. The laser beam is vertically arranged to form a surface, and the number of lines, such as 16 or 64, is the number of vertically arranged laser beams. The more lines there are, the higher the resolution and the greater the amount of information. Therefore, we can often see this type of laser radar in autonomous driving road testing vehicles. However, mechanical rotary LiDAR has a large volume, complex debugging, high cost, difficult mass production, and due to its mechanical structural characteristics, it is difficult to meet the requirements of automotive standards, resulting in a short lifespan.

Main manufacturers: Velodyne、 Hesai Technology, Sagitar Juchuang

Rotating mirrors: Rotating mirrors are divided into one-dimensional rotating mirrors and two-dimensional rotating mirrors. A one-dimensional rotating mirror reflects laser light in different directions through a rotating polyhedral reflector, thereby achieving a certain field of view; A two-dimensional rotating mirror, as the name suggests, integrates two rotating mirrors internally, one polygonal prism for lateral rotation and the other for longitudinal flipping. This enables scanning in two directions and dimensions with a single laser beam. Rotating mirror LiDAR has the advantages of small size, low cost, and the same effect as mechanical LiDAR, making it the mainstream route for hybrid solid-state radar at present. But after all, there are also mechanical structures, and the mechanical motion frequency is high, so the lifespan is also not ideal.

Main manufacturers: Valeo, Huawei Velodyne、 Laser God Intelligence

MEMS galvanometer: It uses a reflection mirror integrated on a silicon-based chip to vibrate with a certain harmonic between a pair of torsion bars on the front, back, left, and right sides, reflecting the laser beam to different angles and achieving scanning within a certain range. This technology eliminates the assembly of mechanical moving parts, improves reliability, and makes it easier to achieve mass production. At the same time, it can reduce the size of the LiDAR system, decrease the number of laser emitters and detectors, and significantly reduce costs. However, the limited optical aperture and scanning angle limit the distance measurement and field of view, and a large field of view requires stitching, which requires high algorithm requirements. In addition, there are also some issues with impact resistance and reliability.

Main manufacturers: Sagitar Juchuang Innoviz、 Valeo

Rotating mirror+MEMS galvanometer: Adding a galvanometer on the basis of a two-dimensional rotating mirror, the rotating mirror is responsible for the horizontal direction, and the galvanometer is responsible for the vertical direction, which can achieve a larger scanning area and higher frequency, but the price is also higher.

Main manufacturers: Innovusion TuDa Tong Luminar

Prism: By controlling the relative rotation speed of the two wedge-shaped prisms, the laser beam undergoes two refractions to achieve regional laser scanning coverage. The accumulated scanning pattern of prism lidar is shaped like petals, with dense scanning times at the center point and relatively sparse edges at the circle. Long scanning time is necessary to enrich the image, so multiple lidars need to work together to achieve higher results. Prism can achieve high-precision and long-distance detection by increasing laser beam and power, but its structure is complex, its volume is more difficult to control, and there is a higher risk of bearing and liner wear. At present, only Livox adopts this technology and has already achieved mass production on the Xiaopeng P5.

Main manufacturers: Livox

Flash: The structure of Flash is very simple and rough. The principle is to use a high-density laser source array to emit laser that can cover an area, and use a high-sensitivity receiver to construct images. This form of LiDAR has no mechanical moving parts, is small in size, high in accuracy, and has fast scanning speed. But it is easy to form sidelobe interference, disperse laser energy, and affect detection distance and resolution.

Main manufacturers: ibeo、LeddarTech、 Bright Way Intelligence

OPA: The principle of OPA LiDAR is to form an emission array through multiple laser emission units. By adjusting the phase difference of each unit in the emission array, the emission angle of the laser beam can be changed, and mutual interference can be generated in the set direction to achieve high-intensity pointing beam and complete scanning.

One important reason for the slow progress of OPA LiDAR has always been the difficulty in solving sidelobe effects. Side lobe effect is a proximity effect generated by optical diffraction. On OPA lidar, the beam synthesis after passing through OPA devices is actually formed by the mutual interference of light waves, which easily leads to array interference and disperses laser energy, resulting in optical artifacts and other problems. It is precisely for this reason that it is difficult to balance the OPA field of view and beam quality.

Main manufacturers: Quanergy、 Luowei Technology, Lice Technology

MMT (Micro Motion Technology): MMT is a unique imaging technology used in laser radar, which adopts a voice coil technology similar to a speaker. A proprietary optical array is connected to the voice coil, and when the voice coil is powered on, micro motion is generated. With the help of this micro motion laser radar, images can be scanned. This design has the simplest optical path, can produce the highest efficiency and the least number of components, is small in size, and has almost no loss of internal components.

In addition, compared to other laser radars, MMT technology's laser radar emphasizes resolution more, especially the vertical resolution can reach 4 to 5 times that of laser radars on the market. MMT technology was pioneered by Cepton, a laser radar manufacturer, and currently only Cepton adopts this technology.

Main manufacturers: Cepton

There are two main forms of ranging for LiDAR, namely ToF and FMCW. ToF stands for Time of Flight, which calculates distance information by directly measuring the time difference between the emitted laser and echo signals. It has high detection accuracy and fast response speed. ToF is currently the most widely used and mature distance measurement method in the market.

The FMCW coherent detection method linearly modulates the optical frequency of the emitted laser, and coherently correlates the echo signal with the reference light to obtain the frequency difference, thereby obtaining the flight time and inferring the distance of the target object. FMCW laser radar has the advantages of directly measuring speed information and resisting environmental light and other laser radar interference. The combination of FMCW and OPA laser radar is considered the "ultimate solution" for the future.