Research background:
The advanced equipment manufacturing industry demands high-precision, versatile, and multi-dimensional geometric measurements. Multi-channel laser ranging technology offers a unified sensing approach, minimal error sources, and high measurement efficiency. Frequency modulated continuous wave (FMCW) laser measurement technology, with its high precision, wide dynamic range, strong anti-interference capability, and high signal-to-noise ratio, enables precise absolute distance measurements of large-scale, non-cooperative targets. It holds significant potential for industrial applications such as precision machining, equipment assembly positioning, and multi-dimensional surface scanning.
Traditional LiDAR systems are bulky and expensive. Photonic integration enables compact, chip-scale LiDAR, but most existing chip-based solutions rely on mechanical scanners to expand the imaging range, significantly limiting the efficiency of large time-bandwidth product (TBWP) FMCW LiDAR. Large-scale parallel coherent measurement architectures can greatly enhance measurement efficiency. By eliminating mechanical beam scanning, they enable high-speed, multi-channel data acquisition. However, the number of measurement channels directly determines the required circulators, photodetectors, and optical amplifiers, significantly increasing system complexity. Moreover, FMCW LiDAR systems based on current parallel coherent measurement architectures still have limited modulation bandwidth per channel. Non-mechanical beam scanners provide only a small, fixed imaging range, posing significant challenges for high-precision, multi-purpose measurements of large, non-cooperative targets in industrial applications.
To address these challenges, Professor Fumin Zhang's team at Tianjin University proposed a time-domain wavelength-division multiplexed (TWDM) multi-channel parallel FMCW LiDAR system incorporating optical switching. By leveraging the wide time-bandwidth modulation characteristics of FMCW lasers and the continuous time-domain band switching of optical switches, this approach enables TWDM technology for multi-channel parallel ranging. It unifies multi-length information transmission within a single channel, improving measurement efficiency while ensuring high-precision measurements for individual targets. This method offers a novel solution for large-scale 3D imaging and multi-dimensional geometric measurements. The related findings were published entitled "High-precision multichannel time-domain wavelength division multiplexing FMCW LiDAR ranging and 3D imaging" in Chinese Optics Letters, Vol. 23, No. 2, 2025.
Figure 1. Multichannel time-domain wavelength division multiplexing (TWDM) FMCW LiDAR
Research contents and results:
To meet the multi-dimensional measurement demands of advanced equipment manufacturing, this study proposes a TWDM multi-channel FMCW LiDAR system incorporating optical switches. By leveraging the wide time-bandwidth continuous modulation characteristics of FMCW lasers and the high-speed time-domain band switching of an optical switch array, the system enables multi-target parallel measurement and unified multi-length information transmission within a single channel. This approach provides geometric references for length, position, and orientation in large-scale complex environments and supports advanced 3D analysis strategies. The architecture and measurement principle of the TDM-WDM multi-channel FMCW LiDAR system are illustrated in Figure 1. This FMCW LiDAR system enhances measurement accuracy by averaging multi-channel measurements of the same target and supports multi-path distance measurements. For a non-cooperative target placed on a precision linear guide at a maximum distance of 1.3 m, the system achieved an overall absolute distance measurement accuracy better than 14 μm, with each channel maintaining an accuracy within 20 μm. The precision of the 3D point cloud data for spatial targets was better than 1 cm. Experimental results demonstrate that the TDM-WDM multi-channel FMCW LiDAR system exhibits high stability and precision in multi-purpose distance measurement and 3D imaging applications. Compared to traditional methods, it significantly improves measurement efficiency and performance.
Outlook:
Moving forward, integrating the TDM-WDM FMCW LiDAR system with advanced auxiliary scanning devices can enhance real-world environmental sensing. Combining this system with chip-scale arrayed waveguide gratings and lens-assisted beam steering technology can further miniaturize the system and expand its potential applications, including precision contour measurement, large-scale equipment assembly, and space exploration.
