Ziyu Hua

Multi-functional measurement of absolute distance, velocity, vibration, and imaging with one sensor is rare but important in industrial applications. In this article, a fusion light detection and ranging (LiDAR) system based on hybrid frequency modulation is reported for noncontact multi-functional measurement. The innovative frequency division multiplexing design of the proposed system facilitates rapid measurements of absolute distance, velocity, vibration, and imaging with only a single source. The unique common-path detection architecture allows for real-time compensation of environmental perturbations, ensuring high precision and stability despite the limited sweep bandwidth. The basic performances of the proposed system are evaluated experimentally, and extended applications in the motion tracking of quick vibration and the imaging of noncooperative targets are also demonstrated. With the advantages of multi-functional and noncontact measurement capability, anti-interference ability, high precision, and stability, the proposed system has potential applications in autonomous driving, intelligent robotics, and industrial manufacturing.

The Doppler effect can be divided into two types: the linear Doppler effect and the rotational Doppler effect. The rotational Doppler effect of a vortex beam has attracted extensive attention in rotational measurement due to its advantages, such as the ability to detect rotation perpendicular to the beam axis and a frequency shift independent of wavelength. In the application of rotational Doppler effect, the measurement of rotational direction, detection of weak scattered signals, and spectrum broadening pose several major challenges. This paper expounds on the theoretical and experimental basis of the rotational Doppler effect, summarizes the recent progress in signal detection methods, including advancements in rotational direction detection, weak signal detection, and signal subdivision. The spectrum broadening analysis method based on mode decomposition is introduced in this paper, and several common reasons leading to Doppler frequency spectrum broadening are provided, along with the introduction of the rotational shaft localization methods based on spectrum broadening. Finally, the existing challenges and promising future directions are discussed.

We demonstrate the direct generation of single-frequency switchable orbital angular momentum (OAM) modes in a 1 µm wavelength range using a Nd:YVO₄ microchip laser. The 808 nm laser diode pump beam is shaped into annular through an axicon associated with a lens. By adjusting the diameter and power of the annular pump beam, various OAM modes with different mode volumes can oscillate inside the Nd:YVO₄ microchip. Moreover, a single-frequency output is also available due to the short cavity of the microchip. In the proof-of-principle experiment, single-frequency twofold multiplexed OAM modes | ± 1> and | ± 2> are generated, with experimentally measured fidelity higher than 96%. This work presents a compact and versatile single-frequency OAM source and will inspire multiple advanced scenarios ranging from classical to quantum photonics.

We propose and demonstrate a novel light detection and ranging (LiDAR) system for 3D imaging, combined with laser feedback interferometry (LFI) and frequency-modulated continuous-wave (FMCW). Compared with the conventional FMCW method, the intra-cavity interference between the echo signal and local oscillator enhances the amplitude of the generated beat signal effectively, which improves the sensitivity in weak-signal detection with low photon consumption. The improvement is still effective even with frequency modulation nonlinearity. Besides, the system inherits the advantages of FMCW, possessing the capacity to measure position and velocity simultaneously. In experiments, the validity of distance and velocity measurement is demonstrated, and 3D imaging is realized by employing a pair of beam scanners. With a less than 200 μW probe beam, the system achieves imaging over 65 meters away in various scenes with good fidelity, and the distance resolution is better than 1 mm. A portable prototype is also designed and fabricated. Overall, the proposed system possesses high echo-signal sensitivity, simple structure, and dynamic information availability, which provides a new idea for FMCW-LiDAR optimization for practical applications.