Hui Liu

The development of next-generation communication networks with integrated multifunctional capabilities across diverse environments—spanning space, air, land, and sea—requires efficient transduction between disparate information carriers. While substantial progress has been made in transducers for terrestrial applications, devices that unify sensing and communication in underwater environments remain in their infancy. We present an experimental demonstration of a dual-function acoustic-to-optical transducer, enabling simultaneous underwater encrypted communication and distance measurement. Specifically, the transducer efficiently converts underwater acoustic signals into single photons for transmission through optical fibers over distances of up to 50 kilometers. Concurrently, we achieve deep subwavelength precision in distance measurement, reaching an accuracy of 1/250 of the acoustic wavelength, while maintaining robust communication performance. Furthermore, we implement coincidence counting–based encryption to embed acoustic information within noisy optical fiber networks. This work represents a notable step toward next-generation network architectures that seamlessly integrate sensing and communication across heterogeneous media.

Exciton polaritons (EPs), hybrid light‐matter quasiparticles, enable deep subwavelength field confinement and strong intrinsic nonlinearities, making them highly promising for integrated nanophotonic devices. Realizing such applications, however, requires a thorough understanding of EPs properties, particularly their transport and loss mechanisms. Here, we employ scattering‐type scanning near‐field optical microscopy (s‐SNOM) to probe MoTe ₂ flakes on Si/SiO ₂ substrates, where the characteristic back‐bending EPs dispersion around 1.05 eV (1.2 µm) is clearly resolved. By combining excitation‐energy‐ and thickness‐dependent s‐SNOM measurements with rigorous simulations, two dominant loss channels are identified: excitonic absorption and radiation leakage into the underlying silicon. Furthermore, both loss pathways are substantially suppressed by replacing the Si/SiO ₂ substrate with LiNbO ₃ , enhancing the EPs propagation length from 2.7 to 7.6 µm for 120‐nm‐thick MoTe ₂ . Beyond eliminating silicon‐related radiation channels, the higher refractive index of LiNbO ₃ draws a larger portion of the EPs field into the substrate, thereby reducing exciton‐absorption‐induced losses. These findings not only provide crucial insights into EPs dispersion and propagation loss mechanisms in the technologically important near‐infrared communication band, but also demonstrate substrate engineering as an effective route toward low‐loss, tunable polaritonic devices.

Polarization vortices, crucial constituents of singular optics, manifest as vortices of polarization states around singularities. Recent progress has linked polarization vortices with bound states in the continuum (BICs) in optical waves. However, this association has not been explored in the realm of thermal emission, which holds the potential for generating arbitrary polarizations in a single thermal emitter. Here, we implement a polarization vortex thermal emitter (PVTE) based on BICs in a photonic crystal slab (PCS), allowing for the generation of various polarization states simultaneously along different directions. Using a custom-designed polarized angle-resolved thermal emission spectrometer (PARTES), we experimentally confirm polarization vortices of thermal emission originating from BICs with different charges and types. The proposed PVTEs present effective strategies for controlling thermal emission and show promising applications in infrared optical technology.

Efficient generation of high‐quality photon pairs is essential for modern quantum technologies. Micro‐ring resonator is an ideal platform for studying on‐chip photon sources due to strong nonlinear effect, resonant‐enhanced optical fields, and high integration. Thin‐film lithium niobate (TFLN) micro‐ring resonators with periodically poled quasi‐phase matching have shown high‐quality photon pair generation. However, periodic poling technology remains expensive and requires complex fabrication hindering its scalability and capability for practical application in nonlinear photonic devices. To address this, we propose a scalable approach using TFLN micro‐ring resonators based on modal phase matching to achieve cost‐effective, efficient high‐quality photon pair generation, significantly simplifying fabrication. We achieved pair generation rates up to 40.2 MHz/mW through spontaneous parametric down‐conversion, with coincidence‐to‐accidental ratios exceeding 1,200. By combining micro‐ring resonance enhancement with modal phase matching, our approach reduces device size and fabrication cost while maintaining high nonlinear efficiency. These results advance the development of compact, efficient on‐chip photon sources for next‐generation nonlinear and quantum photonic applications.

High frequency microwave, spanning up to terahertz frequency, is pivotal for next-generation communication, sensing and radar. However, it faces fundamental noise limitations when frequency is pushed towards such boundary of conventional electronic technologies. Photonic microwave generation, particularly Kerr-comb-based microwave source, benefits from high frequency operation but still suffers from phase noise constraints. Here we overcome this drawback by developing a compact, electrically-driven Kerr comb system that achieves near quantum-limited phase noise for microwave synthesis up to 384 GHz. Leveraging high-Q fiber Fabry-Perot resonators and optimized noise modeling under limited pump power, we demonstrate ultra-low phase noise performances of −133 dBc/Hz (10.1 GHz) and −95 dBc/Hz (300 GHz) at 10 kHz offset, approaching quantum noise limits. This breakthrough enables 64QAM modulation in terahertz wireless communication and record 240 Gbps data rate without need for carrier phase estimation. Our device can serve as a key building block for the future information technology.

In recent years, twisting has emerged as a new degree of freedom that plays an increasingly important role in Bloch bands of various physical systems. However, there is currently a lack of reports on the non-trivial physics of topological degeneracy in twisted systems. In this work, we investigated the intrinsic physical correlation between twisting and topological degeneracy. We found that twisting not only breaks the symmetry of the system but also introduces topological degeneracy that does not exist under the original symmetric system without twisting. Furthermore, the topological degeneracy can be easily tuned through twisting. This new twist-induced topological degeneracy gives rise to a unique polarization-degenerate birefringent medium, wherein the twist angle acts as a novel degree of freedom for dispersion and polarization management of interface states. Exhibiting fascinating properties and experimental feasibilities, our work points to new possibilities in the research of various topological physics in twisted photonics.

In recent years, twisting has emerged as a new degree of freedom that plays an increasingly important role in Bloch bands of various physical systems. However, there is currently a lack of reports on the nontrivial physics of topological degeneracy in twisted systems. In this Letter, we investigated the intrinsic physical correlation between twisting and topological degeneracy. We found that twisting not only breaks the symmetry of the system but also introduces topological degeneracy that does not exist under the original symmetric system without twisting. Furthermore, the topological degeneracy can be easily tuned through twisting. This new twist-induced topological degeneracy gives rise to a unique polarization-degenerate birefringent medium, wherein the twist angle acts as a novel degree of freedom for dispersion and polarization management of interface states. Exhibiting fascinating properties and experimental feasibilities, our Letter points to new possibilities in the research of various topological physics in twisted photonics.

Polarization singularities, crucial constituents of singular optics, manifest as vortices of polarization states. Recent progress has linked polarization vortices with bound states in the continuum (BICs) in optical waves. However, this association has not been explored in the realm of thermal emission, which holds the potential for generating arbitrary polarizations in a single thermal emitter. Here, we implement a polarization vortex thermal emitter (PVTE) based on BICs in a photonic crystal slab (PCS), allowing for the generation of various polarization states simultaneously along different directions. Using a custom-designed polarized angle-resolved thermal emission spectrometer (PARTES), we experimentally confirm polarization vortices of thermal emission originating from BICs with different charges and types. The proposed PVTEs present novel avenues for controlling thermal emission and show promising applications in infrared optical technology.

Entanglement entropy characterizes the correlation of multi-particles and unveils the crucial features of open quantum systems. However, the experimental realization of exploring entanglement in non-Hermitian systems remains a challenge. In parallel, quantum walks have offered the possibility of studying the underlying mechanisms of non-Hermitian physics, which includes exceptional points, the non-Hermitian skin effect, and non-Bloch phase transitions. Unfortunately, these studies have only involved and prevailingly focused on the behavior of a single particle. Here, we propose and experimentally realize quantum walks of two indistinguishable photons in engineered non-Hermitian photonic lattices. We have successfully observed the unidirectional behavior of quantum walks in the bulk far from the edges induced by the skin effect. Moreover, we experimentally reveal the suppression of entanglement that is caused by the skin effect in non-Hermitian systems. Our study may facilitate a deep understanding of entanglement in open quantum many-body systems that are far from thermal equilibrium.