Principle of LiDAR Photodiode

Article Overview

LiDAR photodiodes detect reflected laser light and convert it into electrical signals, enabling precise distance measurement based on the time-of-flight principle.

Basic Operation

In a LiDAR system, a light source emits a laser pulse toward a target, and the photodiode detects the reflected light. The system calculates the distance using the time-of-flight (TOF) principle: the time taken for the light to travel to the target and back is measured, and the distance is determined by the formula d = (c × t) / 2, where c is the speed of light and t is the round-trip time . The photodiode converts incoming photons into an electrical current through the photoelectric effect, where absorbed photons generate electron-hole pairs in the semiconductor material .

Types of Photodiodes in LiDAR

PIN Photodiodes: These have a p-type, intrinsic, and n-type layer structure. They offer high quantum efficiency and fast response, making them suitable for short-range LiDAR applications without amplification .
Avalanche Photodiodes (APDs): Operated under high reverse bias, APDs provide internal gain through avalanche multiplication, enhancing sensitivity for low-light detection. They are ideal for medium to long-range LiDAR .
Single-Photon Avalanche Diodes (SPADs): These operate in Geiger mode, detecting single photons with extremely high gain. SPADs are used in high-resolution, long-range LiDAR systems, often integrated into arrays for multi-pixel detection .

Signal Considerations

The photodiode output current is proportional to the incident light intensity. In APDs, the signal-to-noise ratio (SNR) is critical and influenced by shot noise, dark current, and thermal noise. Proper design ensures accurate detection even under low-light or high-background conditions . SPADs require quenching circuits to prevent continuous avalanche after photon detection, allowing repeated measurements .

Role in LiDAR Systems

Photodiodes are essential for distance measurement, object detection, and mapping. By accurately converting reflected light into electrical signals, they enable LiDAR to generate high-resolution 3D point clouds, detect obstacles in autonomous vehicles, and perform environmental monitoring . The choice of photodiode type depends on range, resolution, and ambient light conditions. In summary, the principle of LiDAR photodiodes is based on photon detection and conversion to electrical signals, combined with TOF measurement, with different photodiode technologies (PIN, APD, SPAD) optimized for specific LiDAR performance requirements .

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Principle of LiDAR Photodiode [PDF]