Highly-time-resolved FMCW LiDAR with synchronously-nonlinearity-corrected acquisition for dynamic locomotion

FMCW laser ranging system based on equal-frequency resampling with direct injection current modulaton

This paper describes a laser ranging system based on modulation signal resampling to address the nonlinearity of Frequency-modulated in frequency-modulated continuous wave (FMCW) lidar. Using a 1550 nm DFB laser as a frequency-modulated light source, the modulation scheme adopts direct modulation of the injected current into the semiconductor laser. Based on the equal-frequency resampling method, the clock signal used for resampling undergoes data acquisition, data analysis, and data processing steps to identify and eliminate erroneous sampling points caused by laser frequency noise, mode hopping in frequency-modulated lasers, and sweep reversal points in the injection current. It solves the nonlinear error caused by the relaxation-oscillation effect of the prior art. Additionally, compared with the manual division of sampling points, the algorithm dividing the sampling area can retain as many correct sampling points as possible to improve the distance resolution and repeatability accuracy of the FMCW ranging system. Under the condition of approximately 20 GHz laser modulation bandwidth, the resolution of 10 m in free-space optical ranging is about 6.8 mm and the standard deviation (STD) of 1 m in free-space optical ranging is 0.19 mm.

Turbidity-tolerant underwater wireless optical communications using dense blue-green wavelength division multiplexing

Underwater wireless optical communication (UWOC) has demonstrated high-speed and low-latency properties in clear and coastal ocean water because of the relatively low attenuation 'window' for blue-green wavelengths from 450 nm to 550 nm. However, there are different attenuation coefficients for transmission in ocean water at different wavelengths, and the light transmission more seriously deteriorates with fluctuations in the water turbidity. Therefore, traditional UWOC using a single wavelength or coarse blue-green wavelengths has difficulty tolerating variations in water turbidity. Dense wavelength division multiplexing (WDM) technology provides sufficient communication channels with a narrow wavelength spacing and minimal channel crosstalk. Here, we improve the UWOC in clear and coastal ocean water using dense blue-green WDM. A cost-effective WDM emitter is proposed with directly modulated blue-green laser diodes. Dense wavelength beam combination and collimation are demonstrated in a 20-metre underwater channel from 490 nm to 520 nm. Demultiplexing with a minimum channel spacing of 2 nm is realized by an optical grating. Remarkably, our WDM results demonstrate an aggregate data rate exceeding 10 Gbit/s under diverse water turbidity conditions, with negligible crosstalk observed for each channel. This is the densest WDM implementation with a record channel spacing of 2 nm and the highest channel count for underwater blue-green light communications, providing turbidity-tolerant signal transmission in clear and coastal ocean water.

Robotics Perception and Control: Key Technologies and Applications

The integration of advanced sensor technologies has significantly propelled the dynamic development of robotics, thus inaugurating a new era in automation and artificial intelligence. Given the rapid advancements in robotics technology, its core area-robot control technology-has attracted increasing attention. Notably, sensors and sensor fusion technologies, which are considered essential for enhancing robot control technologies, have been widely and successfully applied in the field of robotics. Therefore, the integration of sensors and sensor fusion techniques with robot control technologies, which enables adaptation to various tasks in new situations, is emerging as a promising approach. This review seeks to delineate how sensors and sensor fusion technologies are combined with robot control technologies. It presents nine types of sensors used in robot control, discusses representative control methods, and summarizes their applications across various domains. Finally, this survey discusses existing challenges and potential future directions.

Pulse Accumulation Approach Based on Signal Phase Estimation for Doppler Wind Lidar

Coherent Doppler wind lidar (CDWL) uses transmitted laser pulses to measure wind velocity distribution. However, the echo signal of CDWL is easily affected by atmospheric turbulence, which can decrease the signal-to-noise ratio (SNR) of lidar. To improve the SNR, this paper proposes a pulse accumulation method based on the cross-correlation function to estimate the phase of the signal. Compared with incoherent pulse accumulation, the proposed method significantly enhances the correlation between signals from different periods to obtain high SNR gains that arise from pulse accumulation. Using simulation, the study evaluates the effectiveness of this phase estimation method and its robustness against noise in algorithms which analyze Doppler frequency shifts. Furthermore, a CDWL is developed for measuring the speed of an indoor motor turntable and the outdoor atmospheric wind field. The phase estimation method yielded SNR gains of 28.18 dB and 32.03 dB for accumulation numbers of 500 and 1500, respectively. The implementation of this method in motor turntable speed measurements demonstrated a significant reduction in speed error-averaging 9.18% lower than that of incoherent accumulation lidar systems. In experiments that measure atmospheric wind fields, the linear fit curve slope between the measured wind speed and the wind speed measured via a commercial wind-measuring lidar can be reduced from 1.146 to 1.093.