Topological photonics has received extensive attention from researchers because it provides brand new physical principles to manipulate light. Band topolo

Topological photonics has received extensive attention from researchers because it provides brand new physical principles to manipulate light. Band topology is characterized using the Berry phase defined by Bloch states. Until now, the scheme for experimentally probing the topological phase transition of band topology has always been relatively lacking in topological physics. Moreover, radiation topology can be aroused by the far-field polarization singularities of Bloch states, which is described by the Stokes phase. Although such two types of topologies are both related to Bloch states on the band structures, it is rather surprising that their development is almost independent. Here, in optical analogs of the quantum spin Hall effects (QSHEs) and Su-Schrieffer-Heeger model, we reveal the correlation between the phase transition of band topology and radiation topology and then demonstrate that the radiation topology can be employed to study the band topological transition. We experimentally demonstrate such an intriguing phenomenon in optical analogs of QSHEs. Our findings not only provide an insightful understanding of band topology and radiation topology, but also can serve as a route to manipulate light.show less

The coexistence of a noise-like pulse (NLP) and a dark pulse was experimentally demonstrated in a net-anomalous dispersion Er/Yb co-doped fiber (EYDF) las

The coexistence of a noise-like pulse (NLP) and a dark pulse was experimentally demonstrated in a net-anomalous dispersion Er/Yb co-doped fiber (EYDF) laser, for the first time, to our knowledge. The cavity was mode-locked by nonlinear polarization rotation (NPR) technique. Meanwhile, a Sagnac loop with a section of polarization-maintaining fiber (PMF) was used as a comb filter to enable multiwavelength pulse operation. When the PMF length was 0.3 m, an asymmetric two-peak spectrum with central wavelengths of 1565.3 and 1594.2 nm was obtained by adjusting polarization controllers (PCs). It is a composite state of NLP and dark pulse due to the cross-phase modulation between the two different wavelength components along orthogonal polarization axes. The two pulses are synchronized with a repetition rate of 7.53 MHz. By adjusting the PC in the Sagnac loop, the spectral ranges of NLPs and dark pulses can be tuned from 1560 to 1577.8 nm and from 1581.8 to 1605.4 nm, respectively. In addition, the pulse characteristics were investigated by incorporating the PMF with different lengths, where the coexistence patterns can be generated when the PMF lengths were 0.2 and 0.3 m. A longer PMF can lead to a narrowband comb filtering, which causes a larger loss and is not favorable for stable operation of the coexistence regime. This fiber laser demonstrates an interesting operation regime and has significant potential for numerous practical applications.show less

The single-photon sensitivity and picosecond time resolution of single-photon light detection and ranging (LiDAR) can provide a full-waveform profile for

The single-photon sensitivity and picosecond time resolution of single-photon light detection and ranging (LiDAR) can provide a full-waveform profile for retrieving the three-dimentional (3D) profile of the target separated from foreground clutter. This capability has made single-photon LiDAR a solution for imaging through obscurant, camouflage nets, and semitransparent materials. However, the obstructive presence of the clutter and limited pixel numbers of single-photon detector arrays still pose challenges in achieving high-quality imaging. Here, we demonstrate a single-photon array LiDAR system combined with tailored computational algorithms for high-resolution 3D imaging through camouflage nets. For static targets, we develop a 3D sub-voxel scanning approach along with a photon-efficient deconvolution algorithm. Using this approach, we demonstrate 3D imaging through camouflage nets with a 3× improvement in spatial resolution and a 7.5× improvement in depth resolution compared with the inherent system resolution. For moving targets, we propose a motion compensation algorithm to mitigate the net’s obstructive effects, achieving video-rate imaging of camouflaged scenes at 20 frame/s. More importantly, we demonstrate 3D imaging for complex scenes in various outdoor scenarios and evaluate the advanced features of single-photon LiDAR over a visible-light camera and a mid-wave infrared (MWIR) camera. The results point a way forward for high-resolution real-time 3D imaging of multi-depth scenarios.show less

The Righi–Leduc heat flux generated by the self-generated magnetic field in the ablative Rayleigh–Taylor instability driven by a laser irradiating thin ta

The Righi–Leduc heat flux generated by the self-generated magnetic field in the ablative Rayleigh–Taylor instability driven by a laser irradiating thin targets is studied through two-dimensional extended-magnetohydrodynamic simulations. The perturbation structure gets into a low magnetization state though the peak strength of the self-generated magnetic field could reach hundreds of teslas. The Righi–Leduc effect plays an essential impact both in the linear and nonlinear stages, and it deflects the total heat flux towards the spike base. Compared to the case without the self-generated magnetic field included, less heat flux is concentrated at the spike tip, finally mitigating the ablative stabilization and leading to an increase in the velocity of the spike tip. It is shown that the linear growth rate is increased by about 10% and the amplitude during the nonlinear stage is increased by even more than 10% due to the feedback of the magnetic field, respectively. Our results reveal the importance of Righi–Leduc heat flux to the growth of the instability and promote deep understanding of the instability evolution together with the self-generated magnetic field, especially during the acceleration stage in inertial confinement fusion.show less