## 3 FMCW LiDAR Research Progress
### Research Progress on Integration  
One of the primary challenges faced by FMCW LiDAR in its pursuit of technological breakthroughs is the complexity and cost of systems. The application of silicon-based optoelectronic integration technology offers a solution, combining two of the most important inventions of the 20 th century (i.e., integrated circuits and semiconductor lasers). Silicon photonics technology, which uses photons as information carriers and is compatible with CMOS processes, integrates optical and electronic devices on a single chip, significantly reducing costs and enhancing compatibility and integration. However, the challenges of developing this technology include high development costs, the increasing complexity of laser modulation, precise coupling alignment, and advanced signal processing techniques. Nonetheless, as silicon photonics chip technology develops, it is anticipated that future FMCW LiDAR systems will be more compact, consume less power, and be more cost-effective, providing a wide range of innovative applications for various industries. Silicon-based optoelectronic integration technology, as a cutting-edge solution, has demonstrated enormous potential in enhancing radar system performance and reducing costs. By integrating integrated circuit and semiconductor laser technologies, silicon photonics not only optimizes the performance of optoelectronic devices but also greatly enhances the integration and economic efficiency of radar systems. This technological advancement offers a viable path to address the high costs and issues with complexity faced by traditional FMCW LiDAR, while also driving the entire industry toward a higher technological level. In 2020, [PERSON] et al. [63] used a high-resolution remote detection method using uncompensated frequency-modulated continuous-wave sources to forge cost-effective FMCW LiDAR systems. Utilizing economical DFB laser diodes and VCSEL capable of nonlinear optical frequency scanning under conditions of high modulation frequency and integrating these with partial waveform techniques and the maximum power algorithm (MPA), they significantly enhanced the distance resolution of the system, achieving an accuracy of up to 1.93 mm. This work offers a pivotal reference for developing low-cost, high-precision LiDAR detection technologies. In 2023, the 55 th Research Institute of the China Electronics Technology Group Corporation (Nanjing, China) [64] made significant strides in FMCW LiDAR technology by developing and implementing an integrated module for single-channel FMCW LiDAR, aimed at multi-target ranging. This module, distinguished by its innovative integration of solid-state lasers, silicon-based optical phased arrays, and InP-based balanced photodetectors, showcased a core chip measuring just 1.65 cm \(\times\) 1.65 cm, demonstrating a leap forward in miniaturized design. Achieving a coupling efficiency of up to 62.8% from the laser to the silicon waveguide and a common-mode suppression ratio of 53.08 dB, these advancements not only improve system performance but also significantly enhance ranging accuracy to 8.82 cm. The development of this integrated module represents a new era in the integration and miniaturization of FMCW LiDAR technology, overcoming traditional radar system limitations such as speed, size, and stability. It realizes new prospects for high-speed scanning, low power consumption, and broad applicability in fields such as autonomous driving, robotic navigation, and environmental monitoring. In 2023, researchers from Korea National University [65] pioneered in enhancing distance recovery in FMCW LiDAR data processing through sweep-frequency heterodyning technology. This innovative approach, extracting beat frequency signals from FMCW LiDAR, exceeds the traditional Nyquist sampling limit, facilitating accurate distance measurements of objects. With sweep-frequency heterodyning, unambiguous measurements were achieved for distances ranging from 1.06 m to 6.34 m, using a sweep-frequency range of 1 MHz to 6 MHz.