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Massively parallel coherent laser ranging using a soliton microcomb
摘要： Coherent ranging, also known as frequency-modulated continuous-wave (FMCW) laser-based light detection and ranging (lidar)1 is used for long-range three-dimensional distance and velocimetry in autonomous driving2,3. FMCW lidar maps distance to frequency4,5 using frequency-chirped waveforms and simultaneously measures the Doppler shift of the reflected laser light, similar to sonar or radar6,7 and coherent detection prevents interference from sunlight and other lidar systems. However, coherent ranging has a lower acquisition speed and requires precisely chirped8 and highly coherent5 laser sources, hindering widespread use of the lidar system and impeding parallelization, compared to modern time-of-flight ranging systems that use arrays of individual lasers. Here we demonstrate a massively parallel coherent lidar scheme using an ultra-low-loss photonic chip-based soliton microcomb9. By fast chirping of the pump laser in the soliton existence range10 of a microcomb with amplitudes of up to several gigahertz and a sweep rate of up to ten megahertz, a rapid frequency change occurs in the underlying carrier waveform of the soliton pulse stream, but the pulse-to-pulse repetition rate of the soliton pulse stream is retained. As a result, the chirp from a single narrow-linewidth pump laser is transferred to all spectral comb teeth of the soliton at once, thus enabling parallelism in the FMCW lidar. Using this approach we generate 30 distinct channels, demonstrating both parallel distance and velocity measurements at an equivalent rate of three megapixels per second, with the potential to improve sampling rates beyond 150 megapixels per second and to increase the image refresh rate of the FMCW lidar by up to two orders of magnitude without deterioration of eye safety. This approach, when combined with photonic phase arrays11 based on nanophotonic gratings12, provides a technological basis for compact, massively parallel and ultrahigh-frame-rate coherent lidar systems.
关键词： photonic chip,FMCW lidar,soliton microcomb,parallel distance and velocity measurements,coherent ranging
更新于2025-09-23 15:21:01
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Centroid tracking and velocity measurement of white blood cell in video
摘要： Automated blood cells tracking system has a vital role as the tracking process reflects the blood cell characteristics and indicates several diseases. Blood cells tracking is challenging due to the non-rigid shapes of the blood cells, and the variability in their videos along with the existence of different moving objects in the blood. To tackle such challenges, we proposed a green star based centroid (GSBC) moving white blood cell (WBC) tracking algorithm to measure its velocity and draw its trajectory. The proposed cell tracking system consists of two stages, namely WBC detection and blob analysis, and fine tuning the tracking process by determine the centroid of the WBC, and mark the centroid for further fine tracking and to exclude the bacteria from the bounding box. Furthermore, the speed and the trajectory of the WBC motion are recorded and plotted. In the experiments, an optical flow technique is compared with the proposed tracking system showing the superiority of the proposed system as the optical flow method failed to track the WBC. The proposed system identified the WBC accurately, while the optical flow identified all other objects lead to its disability to track the WBC.
关键词： Trajectory analysis,Video processing,Cell detection,Velocity measurements,Blob analysis,White blood cell,Tracking system
更新于2025-09-10 09:29:36
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The Analysis of Starlight (Two Centuries of Astronomical Spectroscopy) || The interpretation of stellar spectra and the birth of astrophysics
摘要： The interpretation of stellar spectra and the birth of astrophysics. At the end of the nineteenth century the two main branches of stellar spectroscopy were spectral classification and radial-velocity measurements. The latter department was still in its relative infancy, but classification, thanks mainly to the energy of Pickering at Harvard, was a major activity. Classification had become closely related to theories of stellar evolution and these two aspects could hardly be disentangled in, for example, the classification devised by Lockyer [1], which involved first rising and then falling temperatures of stars over their life cycles, and which had some theoretical support from the work of Jonathan Homer Lane (1819–80) and August Ritter on the gravitational collapse of gaseous spheres.
关键词： stellar evolution,spectral classification,stellar spectra,astrophysics,radial-velocity measurements
更新于2025-09-10 09:29:36