arXiv subjects

Z. Tu

Publications and source records attributed to Z. Tu.

6 recordsLinked to original sources

arXiv2026

Deterministic Control of Extreme Events in a semiconductor VCSEL via Polarization-Engineered Optical Feedback

Extreme events, or rogue waves, are high-amplitude, rare occurrences that emerge across diverse physical systems and often defy conventional statistical predictions. While optical systems provide a controlled setting for studying these phenomena, achieving deterministic control over their generation remains challenging. Here, we demonstrate a novel approach to induce and precisely modulate extreme events in a semiconductor VCSEL using polarization-controlled optical feedback. By integrating a $\lambda$/2-waveplate into a polarization-selective external cavity, we regulate the nonlinear interaction between TE and TM modes. This setup triggers high-intensity, heavy-tailed fluctuations in the TM mode, exhibiting clear signatures of extreme events. We show that these events arise from deterministic energy exchange between modes, as evidenced by strong bipolar correlations and long-range temporal memory. The waveplate angle serves as an effective external parameter, enabling non-monotonic tuning of the event rate, intensity, and temporal clustering. Our study establish a platform for exploring extreme events in dissipative systems, with implications for nonlinear photonics and optical technologies.

physics.optics↗

arXiv2025

Mode locking via delayed orthogonal-polarization reinjection in semiconductor VCSELs

We demonstrate harmonic mode-locking in a semiconductor VCSEL using polarization-controlled delayed feedback. By integrating a rotatable $\lambda$/2-plate within an external cavity, we achieve precise control over pulse multiplicity and repetition rates in TE and TM modes. For the TE mode, increasing the $\lambda$/2-plate angle ($\theta$) transitions the system from disordered quasi-periodic states to stable fundamental (single-pulse) and harmonic dual-pulse mode-locking. Polarization-resolved measurements and cross-correlation analyses reveal coherent pulse alignment at half the cavity roundtrip time, enabled by polarization-mediated nonlinear dynamics. This work establishes cross-polarization feedback as a fundamental mechanism for ultrafast pulse engineering, advancing the understanding of polarization-mediated nonlinear dynamics in laser physics.

physics.optics↗

arXiv2024

A Multi-station Meteor Monitoring (M$^3$) System. II. system upgrade and a pathfinder network

Meteors are important phenomenon reflecting many properties of interplanetary dust particles. The study of their origin, mass distribution, and orbit evolution all require large data volume, which can only be obtained using large meteor networks. After meteor networks in Europe and America, we present our designs and upgrades of a proposing network in China. The new designs are mainly aimed for facilitating data gathering process. Each of the newly designed meteor stations now can support up to 4 cameras to cover the full sky. Newer version of meteor station software now works as an integral system, which can streamline the process of detecting, measuring and uploading meteors. We have built a meteor data platform to store, process and display the meteor data automatically. The software and data platform are designed to be easy to learn and use, so it can attract more people to join and operate meteor stations. Four stations are installed as the first phase of the network, and during the operation in 10 months, the network detected 8,683 orbits, and we find that half of the orbits can be related to established meteoroid streams. The statistical analysis of sporadic meteoroids shows a bimodal distribution of the velocities, which coincides with previous studies. The distribution of Tisserand parameters, $T_j$, shows the two peaks at $T_j=0$ and 3, indicating the different orbits of parent bodies (isotropic and ecliptic), which are divided by $T_j=2$. The falling trajectory of a meteorite was also predicted using observational data of the network. We are currently expanding the network, and in the future we will carry out detailed analysis of the key parameters of the distribution of the meteoroids.

astro-ph.IM↗

arXiv2024

A Multi-station Meteor Monitoring (M$^3$) System. I. Design and Testing

Meteors carry important and indispensable information about the interplanetary environment, which can be used to understand the origin and evolution of our solar system. We have developed a Multi-station Meteor Monitoring ($\rm M^3$) system that can observe almost the entire sky and detect meteors automatically, and it determines their trajectories. They are highly extensible to construct a large-scale network. Each station consists of a waterproof casing, a wide field-of-view lens with a CMOS camera, and a supporting computer. The camera has a built-in GPS module for accurately timing the meteoroid entry into the atmosphere (accurate to 1 $\mu$s), which is the most prominent characteristic compared with other existing meteor monitoring devices. We have also developed a software package that can efficiently identify and measure meteors appearing in the real-time video stream and compute the orbits of meteoroids in the solar system via multi-station observations. During the Geminid meteor shower in 2021, the M$^3$ system was tested at two stations ($\sim$55 km apart) in the suburbs of Beijing. The test results show that the astrometric accuracy is about 0.3-0.4 arcmin. About 800 meteors were detected by these two stations. A total of 473 meteors have their orbits calculated by our software, and 377 of them belong to the Geminid meteoroid stream. Our M$^3$ system will be further tested and upgraded, and it will be used to construct a large monitoring network in China in the future.

astro-ph.IM↗

arXiv2022

Tunable nodal kagome superconductivity in charge ordered RbV3Sb5

Unconventional superconductors often feature competing orders, small superfluid density, and nodal electronic pairing. While unusual superconductivity has been proposed in the kagome metals AV3Sb5, key spectroscopic evidence has remained elusive. Here we utilize pressure-tuned (up to 1.85 GPa) and ultra-low temperature (down to 18 mK) muon spin spectroscopy to uncover the unconventional nature of superconductivity in RbV3Sb5. At ambient pressure, we detect an enhancement of the width of the internal magnetic field distribution sensed by the muon ensemble, indicative of time-reversal symmetry breaking charge order. Remarkably, the superconducting state displays nodal energy gap and a reduced superfluid density, which can be attributed to the competition with the novel charge order. Upon applying pressure, the charge-order transitions are suppressed, the superfluid density increases, and the superconducting state progressively evolves from nodal to nodeless. Once charge order is eliminated, we find a superconducting pairing state that is not only fully gapped, but also spontaneously breaks time-reversal symmetry. Our results point to unprecedented tunable nodal kagome superconductivity competing with time-reversal symmetry-breaking charge order and offer unique insights into the nature of the pairing state.

cond-mat.supr-con↗

arXiv2021

Observation of Unconventional Charge Density Wave without Acoustic Phonon Anomaly in Kagome Superconductors AV3Sb5 (A=Rb,Cs)

The combination of non-trivial band topology and symmetry breaking phases gives rise to novel quantum states and phenomena such as topological superconductivity, quantum anomalous Hall effect and axion electrodynamics. Evidence of intertwined charge density wave (CDW) and superconducting order parameters has recently been observed in a novel kagome material AV3Sb5 (A=K,Rb,Cs) that features a Z2 topological invariant in the electronic structure. However, the origin of the CDW and its intricate interplay with topological state has yet to be determined. Here, using hard x-ray scattering, we demonstrate a three-dimensional (3D) CDW with 2*2*2 superstructure in (Rb,Cs)V3Sb5. Unexpectedly, we find that the CDW fails to induce acoustic phonon anomalies at the CDW wavevector but yields a novel Raman mode which quickly damps into a broad continuum below the CDW transition temperature. Our observations exclude strong electron-phonon coupling driven CDW in AV3Sb5 and point to an unconventional and electronic-driven mechanism that couples the CDW and the topological band structure.

cond-mat.supr-con↗