Speckle Noise Reduction in FMCW LiDAR Using Intensity-Weighted Signal Acquisition With a Quadrant Photodiode Receiver

Frequency-modulated continuous-wave (FMCW) light detection and ranging (LiDAR) has gained attention for its robustness in harsh outdoor environments, leveraging an interferometry-based distance measurement principle. However, its accuracy is significantly degraded by speckle noise caused by surface roughness and optical instability. In this letter, we propose a speckle noise reduction method using a quadrant photodiode, which spatially separates the received beam and applies intensity-weighted averaging to suppress amplitude fluctuations. The proposed method is mathematically formulated and validated through experimental comparison with conventional interference signals. Experimental results show that the proposed approach effectively suppresses necking effects and reduces frequency measurement errors from 25 kHz to 5 kHz, achieving both the frequency and distance resolution limits of the developed FMCW LiDAR system. This confirms that the proposed method enhances the stability and reliability of interference signal acquisition, particularly in high-speed scanning environments.