The Working Principle of LiDAR
ADDTIME:2025/5/23
1、The Working Principle of LiDAR
What is the working principle of LiDAR?
LiDAR (Light Detection and Ranging) is a radar system that emits laser beams to detect the position, velocity, and other characteristic quantities of a target. This system can also obtain the three-dimensional shape of a target object by scanning the emission and reception devices. By emitting and receiving laser pulses at different angles, it can construct the complete three-dimensional contour of an object. The working principle of LiDAR is based on the emission, propagation, and reception of light. Ultimately, it determines the distance by measuring the time it takes for a light pulse to travel from emission to reception.
Emitting laser pulses: The LiDAR device emits a laser pulse, which is usually in the infrared or near-infrared spectrum.
Light propagation: The laser pulse travels at the speed of light towards the target object.
Light reflection: When the laser pulse encounters the target object, part of the light is reflected back.
Receiving reflected light: The receiver in the LiDAR device captures the reflected laser. The receiver is typically aligned closely with the emitter to ensure that the received light is directly reflected from the target object.
Time measurement: A timer inside the device records the time interval between the emission and reception of the laser pulse. Since the speed of light is known, this time interval can be used to calculate the round-trip distance of the light pulse to the target object.
Distance calculation: The formula for calculating distance is: Distance = Speed of light × Time / 2, where time is the round-trip time of the light pulse.
Data processing: The measured distance data can be used to generate a point cloud. LiDAR can obtain a large amount of positional point information (also known as laser point cloud) in a short period of time. These point clouds can be further processed to generate three-dimensional models or terrain maps.
905nm: The receiver of a 905nm LiDAR can directly use the relatively inexpensive silicon material. Therefore, 905nm has become the most mainstream wavelength chosen by current LiDARs. However, the visible light wavelength that the human eye can recognize is between 390~780nm. Lasers in the 400~1400nm band can all pass through the vitreous body and focus on the retina without being absorbed by the lens and cornea. A temperature increase of 10℃ in the human eye's retina can cause damage to the photoreceptor cells. To avoid causing harm to the human eye, the emission power of a 905nm LiDAR must be within a harmless range. Consequently, the detection range of a 905nm laser is also limited.
1550nm: Compared to 905nm lasers, 1550nm lasers are absorbed by the human eye's lens and cornea and do not cause damage to the retina. Therefore, a 1550nm LiDAR can emit a higher power, allowing for a longer detection range. However, a 1550nm LiDAR cannot use the commonly needed more expensive indium gallium arsenide (InGaAs) material, so its price is higher than that of a 905nm LiDAR.
By measurement method:
ToF (Time of Flight): ToF LiDAR directly measures the time difference between the emitted laser and the echo signal, obtaining the distance information of the target object based on the speed of light in the air. It has the advantages of fast response and high detection accuracy. The ToF solution is highly mature in technology and relatively low in cost, making it the main scheme used by current LiDARs.
FMCW (Frequency Modulated Continuous Wave): FMCW LiDAR linearly modulates the frequency of the emitted laser. By obtaining the frequency difference through coherent beating between the echo signal and the reference light, it indirectly obtains the flight time and thus the target distance. FMCW has the advantages of being able to directly measure velocity information and strong anti-interference capability.
By scanning method:
Mechanical LiDAR: It rotates at a certain speed, using a mechanical structure to perform a 360° rotational scan in the horizontal direction and a directional distributed scan in the vertical direction. Both the emitter and receiver of a mechanical LiDAR rotate with the scanning components. As the earliest product installed on vehicles, mechanical LiDAR has relatively mature technology. Since it is controlled by a motor to rotate, it can maintain a stable rotational speed over a long period, and the scanning speed is linear each time.
Semi-solid-state LiDAR: The emitter and receiver are fixed, and only a few moving parts are used to achieve the scanning of the laser beam. Since semi-solid-state LiDAR has both fixed and moving parts, it is also called hybrid solid-state LiDAR. Depending on the type of moving part, semi-solid-state LiDAR can be further divided into rotating mirror semi-solid-state LiDAR, MEMS semi-solid-state LiDAR, and prism semi-solid-state LiDAR.
Solid-state LiDAR: There are no moving parts inside. Semiconductor technology is used to achieve the emission, scanning, and reception of the beam. Solid-state LiDAR can be further divided into Flash solid-state LiDAR and OPA solid-state LiDAR. Among them, OPA (Optical Phase Array) solid-state radar uses phased array technology. Phased array radar emits electromagnetic waves, while OPA LiDAR emits light. Since light, like electromagnetic waves, exhibits wave characteristics, the principle is the same. Waves can interfere with each other. By controlling the phase of the current in each element of the phased array radar's planar array, the phase difference can cause interference at different positions of the wave sources (similar to how two sets of water waves叠加后，有的方向会相互抵消，有的会相互增强), thus pointing in a specific direction. By repeatedly controlling it, a scanning effect can be achieved. Since light, like electromagnetic waves, exhibits wave characteristics, the same principle of using phase difference to control interference and direct the laser to a specific angle can be applied. Repeated control realizes the scanning effect.
Autonomous driving: In autonomous vehicles, LiDAR can accurately perceive the surrounding environment of the vehicle, including the position, velocity, and shape of vehicles, pedestrians, and obstacles, providing key information for the vehicle's path planning and decision-making.
Intelligent transportation: It is used for traffic flow monitoring, road condition assessment, and intelligent traffic signal control. It can detect the number, speed, and spacing of vehicles on the road in real time to optimize traffic flow.
Surveying and geographic information: It can quickly and accurately obtain the three-dimensional information of terrain, landforms, and buildings, which is used for map drawing, urban planning, and land surveying. For example, in large-scale terrain surveying projects, LiDAR can generate detailed digital elevation models.
Industrial automation: In factory automation, it is used for material handling, robot navigation, and quality inspection. For example, in warehousing and logistics, LiDAR can help automated guided vehicles (AGVs) accurately travel and load/unload goods in the warehouse.
Aerospace: It is used in aircraft collision avoidance systems, terrain following, and terrain avoidance. In satellite remote sensing, LiDAR can measure atmospheric parameters and surface features.
Military field: It is used for target reconnaissance, weapon guidance, and battlefield situation awareness. For example, in missile guidance systems, LiDAR can improve the accuracy of missiles.
What is the working principle of LiDAR?
LiDAR (Light Detection and Ranging) is a radar system that emits laser beams to detect the position, velocity, and other characteristic quantities of a target. This system can also obtain the three-dimensional shape of a target object by scanning the emission and reception devices. By emitting and receiving laser pulses at different angles, it can construct the complete three-dimensional contour of an object. The working principle of LiDAR is based on the emission, propagation, and reception of light. Ultimately, it determines the distance by measuring the time it takes for a light pulse to travel from emission to reception.
Emitting laser pulses: The LiDAR device emits a laser pulse, which is usually in the infrared or near-infrared spectrum.
Light propagation: The laser pulse travels at the speed of light towards the target object.
Light reflection: When the laser pulse encounters the target object, part of the light is reflected back.
Receiving reflected light: The receiver in the LiDAR device captures the reflected laser. The receiver is typically aligned closely with the emitter to ensure that the received light is directly reflected from the target object.
Time measurement: A timer inside the device records the time interval between the emission and reception of the laser pulse. Since the speed of light is known, this time interval can be used to calculate the round-trip distance of the light pulse to the target object.
Distance calculation: The formula for calculating distance is: Distance = Speed of light × Time / 2, where time is the round-trip time of the light pulse.
Data processing: The measured distance data can be used to generate a point cloud. LiDAR can obtain a large amount of positional point information (also known as laser point cloud) in a short period of time. These point clouds can be further processed to generate three-dimensional models or terrain maps.
2、Classification of LiDAR
LiDAR can be classified in many different ways:
By wavelength:905nm: The receiver of a 905nm LiDAR can directly use the relatively inexpensive silicon material. Therefore, 905nm has become the most mainstream wavelength chosen by current LiDARs. However, the visible light wavelength that the human eye can recognize is between 390~780nm. Lasers in the 400~1400nm band can all pass through the vitreous body and focus on the retina without being absorbed by the lens and cornea. A temperature increase of 10℃ in the human eye's retina can cause damage to the photoreceptor cells. To avoid causing harm to the human eye, the emission power of a 905nm LiDAR must be within a harmless range. Consequently, the detection range of a 905nm laser is also limited.
1550nm: Compared to 905nm lasers, 1550nm lasers are absorbed by the human eye's lens and cornea and do not cause damage to the retina. Therefore, a 1550nm LiDAR can emit a higher power, allowing for a longer detection range. However, a 1550nm LiDAR cannot use the commonly needed more expensive indium gallium arsenide (InGaAs) material, so its price is higher than that of a 905nm LiDAR.
By measurement method:
ToF (Time of Flight): ToF LiDAR directly measures the time difference between the emitted laser and the echo signal, obtaining the distance information of the target object based on the speed of light in the air. It has the advantages of fast response and high detection accuracy. The ToF solution is highly mature in technology and relatively low in cost, making it the main scheme used by current LiDARs.
FMCW (Frequency Modulated Continuous Wave): FMCW LiDAR linearly modulates the frequency of the emitted laser. By obtaining the frequency difference through coherent beating between the echo signal and the reference light, it indirectly obtains the flight time and thus the target distance. FMCW has the advantages of being able to directly measure velocity information and strong anti-interference capability.
By scanning method:
Mechanical LiDAR: It rotates at a certain speed, using a mechanical structure to perform a 360° rotational scan in the horizontal direction and a directional distributed scan in the vertical direction. Both the emitter and receiver of a mechanical LiDAR rotate with the scanning components. As the earliest product installed on vehicles, mechanical LiDAR has relatively mature technology. Since it is controlled by a motor to rotate, it can maintain a stable rotational speed over a long period, and the scanning speed is linear each time.
Semi-solid-state LiDAR: The emitter and receiver are fixed, and only a few moving parts are used to achieve the scanning of the laser beam. Since semi-solid-state LiDAR has both fixed and moving parts, it is also called hybrid solid-state LiDAR. Depending on the type of moving part, semi-solid-state LiDAR can be further divided into rotating mirror semi-solid-state LiDAR, MEMS semi-solid-state LiDAR, and prism semi-solid-state LiDAR.
Solid-state LiDAR: There are no moving parts inside. Semiconductor technology is used to achieve the emission, scanning, and reception of the beam. Solid-state LiDAR can be further divided into Flash solid-state LiDAR and OPA solid-state LiDAR. Among them, OPA (Optical Phase Array) solid-state radar uses phased array technology. Phased array radar emits electromagnetic waves, while OPA LiDAR emits light. Since light, like electromagnetic waves, exhibits wave characteristics, the principle is the same. Waves can interfere with each other. By controlling the phase of the current in each element of the phased array radar's planar array, the phase difference can cause interference at different positions of the wave sources (similar to how two sets of water waves叠加后，有的方向会相互抵消，有的会相互增强), thus pointing in a specific direction. By repeatedly controlling it, a scanning effect can be achieved. Since light, like electromagnetic waves, exhibits wave characteristics, the same principle of using phase difference to control interference and direct the laser to a specific angle can be applied. Repeated control realizes the scanning effect.
3、Application Scenarios of LiDAR
LiDAR plays an important role in many fields, and its application scope is continuously expanding with the development of technology.Autonomous driving: In autonomous vehicles, LiDAR can accurately perceive the surrounding environment of the vehicle, including the position, velocity, and shape of vehicles, pedestrians, and obstacles, providing key information for the vehicle's path planning and decision-making.
Intelligent transportation: It is used for traffic flow monitoring, road condition assessment, and intelligent traffic signal control. It can detect the number, speed, and spacing of vehicles on the road in real time to optimize traffic flow.
Surveying and geographic information: It can quickly and accurately obtain the three-dimensional information of terrain, landforms, and buildings, which is used for map drawing, urban planning, and land surveying. For example, in large-scale terrain surveying projects, LiDAR can generate detailed digital elevation models.
Industrial automation: In factory automation, it is used for material handling, robot navigation, and quality inspection. For example, in warehousing and logistics, LiDAR can help automated guided vehicles (AGVs) accurately travel and load/unload goods in the warehouse.
Aerospace: It is used in aircraft collision avoidance systems, terrain following, and terrain avoidance. In satellite remote sensing, LiDAR can measure atmospheric parameters and surface features.
Military field: It is used for target reconnaissance, weapon guidance, and battlefield situation awareness. For example, in missile guidance systems, LiDAR can improve the accuracy of missiles.
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