Space-division multiplexing (SDM) systems based on few-mode multi-core fibers (FM-MCFs) utilize both spatial channels (fiber cores) and modes (optical modes per core) to maximize transmission capacity. Unlike laboratory FM-MCFs or field-deployed single-mode multi-core fibers (SM-MCFs), SDM transmissions over field-deployed FM-MCFs in outdoor settings have not been reported. Therefore, concerns remain that environmental interference and cabling stress could worsen inter-core and intra-core modal crosstalk and impact the performance of SDM systems over FM-MCFs. In this paper, we demonstrate successful bidirectional SDM transmission over a 5-km, field-deployed seven ring-core fiber (7-RCF) with a cladding diameter of 178 μm. Our measurements show no significant differences in attenuation and mode coupling compared to pre-cabling conditions, confirming the fiber’s resilience to environmental disturbances and adaptability to cable deployment. Using the field-deployed 7-RCF, bi-directional SDM transmission is implemented, achieving spectral efficiency (SE) of 2×201.6 bit/(s Hz) which sets a new record in field-deployed fiber cables that is a tenfold increase over previous systems. Furthermore, these results were achieved using a small-scale 4×4 multiple-input multiple-output (MIMO) scheme with a time-domain equalization (TDE) tap number not exceeding 15. These results demonstrate the substantial potential of using SDM techniques to significantly enhance SE and expand capacity in practical fiber-optic transmission applications.

Quantitative phase imaging (QPI) is an optical microscopy method that has been developed over nearly a century to rapidly visualize and analyze transparent or weakly scattering objects in view of biological, medical, or material science applications. The bulky nature of the most performant QPI techniques in terms of phase noise limits their large-scale deployment. In this context, the beam shaping properties of photonic chips, combined with their intrinsic compact size and low cost, could be beneficial. Here, we demonstrate the implementation of QPI with a photonic integrated circuit (PIC) used as an add-on to a standard wide-field microscope. Combining a 50 mm×50 mm footprint PIC as a secondary coherent illuminating light source with an imaging microscope objective of numerical aperture 0.45 and implementing a phase retrieval approach based on the Kramers–Kronig relations, we achieve a phase noise of 5.5 mrad and a diffraction limited spatial resolution of 400 nm. As a result, we retrieve quantitative phase images of Escherichia coli bacteria cells and monolayers of graphene patches from which we determine a graphene monolayer thickness of 0.45±0.15 nm. The current phase noise level is more than five times lower than that obtained with other state-of-the-art QPI techniques using coherent light sources and comparable to their counterparts based on incoherent light sources. The PIC-based QPI technique opens new avenues for low-phase noise, miniature, robust, and cost-effective quantitative phase microscopy.

This paper presents the design, fabrication, and characterization of a high-performance heterogeneous silicon on insulator (SOI)/thin film lithium niobate (TFLN) electro-optical modulator based on wafer-scale direct bonding followed by ion-cut technology. The SOI wafer has been processed by an 8 inch standard fabrication line and cut into 6 inch for direct bonding with TFLN. The hybrid SOI/LN electro-optical modulator operated at the wavelength of 1.55 μm is composed of couplers on the Si layer and a Mach–Zehnder interferometer (MZI) structure on the LN layer. The fabricated device exhibits a stable value of the product of half-wave voltage and length (VπL) of around 2.9 V·cm. It shows a good low-frequency electro-optic response flatness and supports 96 Gbit/s data transmission for the NRZ format and 192 Gbit/s data transmission for the PAM-4 format.

In pursuit of energy-efficient optical interconnect, the silicon microring modulator (Si-MRM) has emerged as a pivotal device offering an ultra-compact footprint and capability of on-chip wavelength division multiplexing (WDM). This paper presents a 1×4 metal-oxide-semiconductor capacitor (MOSCAP) Si-MRM array gated by high-mobility titanium-doped indium oxide (ITiO), which was fabricated by combining Intel’s high-volume manufacturing process and the transparent conductive oxide (TCO) patterning with the university facility. The 1×4 Si-MRM array exhibits a high electro-optic (E-O) efficiency with Vπ·L of 0.12 V·cm and achieves a modulation rate of (3×25+1×15) Gb/s with a measured bandwidth of 14 GHz. Additionally, it can perform on-chip WDM modulation at four equally spaced wavelengths without using thermal heaters. The process compatibility between silicon photonics and TCO materials is verified by such an industry-university co-fabrication approach for the MOSCAP Si-MRM array and demonstrated enhanced performance from heterogeneous integration.

Frequency-modulated continuous-wave (FMCW) light sources are essential components for coherent light detection and ranging (LiDAR), which is ubiquitously utilized in autonomous driving, industrial monitoring, and geological remote sensing. Traditional FMCW LiDAR systems often face challenges in achieving high frequency-sweep linearity and large excursion, which are critical for accurate distance and velocity measurements. Here, we propose a self-injection locked laser with frequency-shifted feedback to generate ultra-linear and wideband FMCW light. A record-low relative frequency nonlinearity of 6.4×10-7 is achieved when the frequency excursion is 100 GHz and the repetition frequency is 1 kHz. In the LiDAR test, a range resolution of 1.6 mm and a velocity accuracy of 3 mm/s at 300 m distance are demonstrated, and those of 8.1 mm and 6 mm/s at 1 km distance are also obtained. The reported FMCW light source provides not only enhanced performance in coherent LiDAR, but also utilization potential in various high-precision measurement scenarios.

Accurate positioning of nanoantennas is critical for their efficient excitation and integration. However, since nanoantennas are subwavelength nanoparticles, normally smaller than the diffraction limit, measuring their positions presents a significant challenge. This is particularly true for locating the nanoantenna along the z-direction, for which no suitable method currently exists. Here, we have theoretically developed and experimentally validated a novel light field capable of measuring the 3D positions of nanoantennas accurately. This field’s polarization chirality transitions from right-handed to left-handed along a predefined 3D direction at a subwavelength scale. For a spherical single-element nanoantenna, the polarization components of the scattering field change significantly as the nanoantenna moves, due to the rapid polarization transformation in the excitation light field. By analyzing the polarization components of the scattering field, we can achieve positional accuracy of the nanoantenna along the specified direction close to 20 pm. This work improves the accuracy of transversely distinguishing nanoantennas from 100 pm in conventional methods to 20 pm. Moreover, the positioning of the nanoantenna along three dimensions is all available as polarization transitions can be predefined along arbitrary 3D direction, which is significant for precision measurement and nanoscale optics.

Nanoscale light manipulation using plasmonic metasurfaces has emerged as a frontier in photonic research, offering strongly enhanced light–matter interactions with potential applications in sensing, communications, and quantum optics. Here, we unveil the realization and control of chiral quasi-bound states in the continuum (quasi-BICs) by judiciously rotating one of the paired plasmonic bricks and thereby influencing structural asymmetry. By precisely controlling the rotation angle, we enable continuous modulation of the radiation loss in quasi-BICs and transition from a perfect half-wave plate to a good absorber for the left-handed circularly polarized light. This transformation leverages the intrinsic chirality with moderately high circular dichroism of ∼0.35 in both simulation and experimental observations, manifesting unprecedented control over the chiral light within sub-wavelength scales. Theoretical modeling and numerical simulations complement our experimental findings, offering deep insights into underlying mechanisms and the role of symmetry breaking in realizing chiral quasi-BICs. The observed phenomena open new pathways for developing ultra-compact chiral photonic devices with tailored optical properties, including highly sensitive chiral biosensors, circular dichroism spectroscopy, and chiral flat optical components for information processing.

Laser diodes are widely used and play a crucial role in myriad modern applications including nonlinear optics and photonics. Here, we explore the four-wave mixing effect in a laser diode gain medium induced by the feedback from the high-Q microring resonator. This phenomenon can be observed at a laser frequency scan close to the microresonator eigenfrequency, prior to the transition of the laser diode from a free-running to a self-injection locking regime. The effect opens up the possibility for generation of remarkably low-noise, stable, and adjustable microwave signals. We provide a detailed numerical study of this phenomenon proven with experimental results and demonstrate the generation of the signals in the GHz range. The obtained results reveal the stability of such regime and disclose the parameter ranges enabling to achieve it. Cumulatively, our findings uncover, to our knowledge, a novel laser diode operation regime and pave the way for the creation of new types of chip-scale, low-noise microwave sources, which are highly demanded for diverse applications, including telecommunication, metrology, and sensing.

This paper describes a 3D-printed conformal reconfigurable spin-decoupled metasurface and supports both independent beam shaping and dual-channel reconfigurability. The increasing complexity of metasurface structures and reconfigurable spin-decoupling among conformal structures are rarely reported due to their challenging properties. In this paper, a reconfigurable metasurface based on 3D-printing technology is proposed for reconfigurable spin-decoupled curved structures at 13.5–14.5 GHz. Curved surface spin-decoupling is realized for the first time and verified by simulation and experiment. Beam deflection (20° and 35°) and near-field focusing (100 mm and 150 mm) were achieved at different circularly polarized wave incidences. Switching the beam between the two states was achieved by incorporating the water-based metasurface. As a proof of concept, metasurfaces that have anomalous reflections in both channels were fabricated and measured. Furthermore, reconfigurable spin-decoupling was achieved using a water-based metasurface. This work extends the phase engineering approach in metasurfaces and may have a wide range of applications in communications, sensing, imaging, and camouflage.

Optical resonators are a powerful platform to control the spontaneous emission dynamics of excitons in solid-state nanostructures. We study a MoSe2-WSe2 heterostructure that is integrated in a cryogenic open optical microcavity to gain insights into fundamental optical properties of the emergent interlayer excitons. First, we utilize a low-quality-factor planar open cavity and investigate the modification of the excitonic lifetime as on- and off-resonance conditions are met with consecutive longitudinal modes. Time-resolved photoluminescence measurements revealed a periodic tuning of the interlayer exciton lifetime by 220 ps, which allows us to extract a 0.5 ns free-space radiative lifetime and a quantum efficiency as high as 81.4%±1.4%. We subsequently engineer the local density of optical states by spatially confined and spectrally tunable Tamm-plasmon resonances. The dramatic redistribution of the local optical modes allows us to encounter a significant inhibition of the excitonic spontaneous emission rate by a factor of 3.2. Our open cavity is able to tune the cavity resonances accurately to the emitters to have a robust in situ control of the light-matter coupling. Such a powerful characterization approach can be universally applied to tune the exciton dynamics and measure the quantum efficiencies of more complex van der Waals heterostructures and devices.

Low-dimensional Ga2O3 monocrystalline micro/nanostructures show promising application prospects in large-area arrays, integrated circuits, and flexible optoelectronic devices, owing to their exceptional optoelectronic performance and scalability for mass production. Herein, we developed an 8×8 array of high-performance solar-blind ultraviolet photodetectors based on Pt nanoparticles-modified Ga2O3 (PtNPs@Ga2O3) nanorod film heterojunction with p-GaN substrate serving as the hole transporting layer. The PtNPs@Ga2O3/GaN heterojunction detector units exhibit outstanding photovoltaic performance at 0 V bias, demonstrating high responsivity (189.0 mA/W), specific detectivity (4.0×1012 Jones), external quantum efficiency (92.4%), and swift response time (674/692 µs) under an irradiance of 1 μW/cm2 at 254 nm. Their exceptional performance stands out among competitors of the same type. In addition, the detector array demonstrated satisfactory results in a conceptual demonstration of high-resolution imaging, benefiting from the excellent stability and uniformity exhibited by its array units. These findings provide a straightforward and viable method for developing a high-performance solar-blind ultraviolet detector array based on low-dimensional Ga2O3 nanorod monocrystalline, demonstrating their potential advancement in large-area, integrable, and flexible optoelectronic devices.

Metamaterials (MMs) have become increasingly prominent in terahertz flexible devices. However, bending deformation often alters the structure of the unit, which affects the response performance and stability of MMs. Here, a metal-aperture metamaterial (MA-MM) utilizing the strong coupling effect induced by two resonance modes is innovatively proposed to address the mentioned limitations. Specifically, it is found that the coupling state between multiple resonance modes remains consistent at different bending angles. Under these circumstances, the generated Rabi splitting peak presents stable response performance even under low resonance intensity caused by excessive deformation. The experimental results demonstrate that despite the amplitude of two resonant peaks decreasing significantly by 87.6%, the Q-factor of the Rabi splitting only reduced by 14.8%. Furthermore, armed with the response mode of the Rabi splitting being unaffected by plasma excitation range, the designed MA-MMs are able to maintain constant Q-factors and frequencies on curved surfaces of varying sizes. These findings exhibit the characteristics of electromagnetic response for multi-mode resonance-coupled MA-MMs on different curved surfaces, presenting a novel design approach for terahertz flexible functional devices.

Dynamic generation of multimode vortex waves carrying orbital angular momentum (OAM) utilizing programmable metasurfaces has attracted considerable attention. Yet, it is still a challenge to achieve multiplexed vortex waves with an arbitrary customized mode combination, stemming fundamentally from the discrete control over phase exhibited by current programmable metasurfaces, which are typically constrained to a limited 1-bit or 2-bit discrete resolution. In this paper, we propose, to our knowledge, a new strategy for dynamic generation of multiplexed vortex beams based on a space-time-coding metasurface, capable of quasi-continuous complex-amplitude modulation for harmonic waves. As a proof of concept, a metasurface prototype for generating multiplexed vortex beams with the customized mode composition and power allocation is established based on the transmissive space-time-coding meta-atoms regulated by the field programmable gate array controller. The mode purity of the vortex beams with a single OAM mode of +1, +2, and +3 generated by the metasurface is as high as over 0.93. The generated multiplexed vortex beams carrying (+1, +2, +3) OAM modes with a power ratio of 1:1:1, (+1, +2, +3) modes with a power ratio of 1:2:3, and (-2, -1, +1, +2) modes with a power ratio of 1:2:2:1 are further verified effectively. The proposed space-time-coding metasurface has great potential for OAM multiplexing communication systems.

Synthetic dimensions have emerged as promising methodologies for studying topological physics, offering great advantages in controllability and flexibility. Photonic orbital angular momentum (OAM), characterized by discrete yet unbounded properties, serves as a potent carrier for constructing synthetic dimensions. Despite the widespread utilization of synthetic OAM dimensions in the investigation of topological physics, the demonstration of an edge along such dimensions has remained challenging, significantly constraining the exploration of important topological edge effects. In this study, we establish an edge within a Floquet Su–Schrieffer–Heeger OAM lattice, creating approximate semi-infinite lattices by introducing a pinhole in the optical elements within a cavity. Leveraging the spectral detection capabilities of the cavity, we directly measure the phase transitions of zero (±π) energy edge states, elucidating the principle of bulk-edge correspondence. Furthermore, we dynamically observe the migration of edge modes from the gap to the bulk by varying the edge phase, and we reveal that interference near the surface results in the discretization of the spectrum. We offer, to our knowledge, a novel perspective for investigating edge effects and provide an important photonic toolbox in topological photonics.

Optical frequency combs in integrated photonics have widespread applications in high-dimensional optical computing, high-capacity communications, high-speed interconnects, and other paradigm-shifting technologies. However, quantum frequency combs with high-dimensional quantum states are vulnerable to decoherence, particularly in the presence of perturbations such as sharp bends. Here we experimentally demonstrate the robust on-chip topological transport of quantum frequency combs in valley photonic crystal waveguides. By measuring the time correlations and joint spectral intensity of the quantum frequency combs, we show that both quantum correlations and frequency entanglement remain robust against sharp bends, owing to the topological nature of the quantum valley Hall effect. We also demonstrate that dissipative Kerr soliton combs with a bandwidth of 20 THz maintain their spectral envelope and low-noise properties even in the presence of structure perturbations. These topologically protected optical frequency combs offer robust, complex, highly controllable, and scalable light sources, promising significant advances in high-dimensional photonic information processing.

Swept laser interferometry is an extremely powerful solution embedded in several recent technologies such as absolute distance measurement, light detection and ranging (LiDAR), optical frequency domain reflectometry, optical coherence tomography, microresonator characterization, and gas spectroscopy. Nonlinearity in the optical frequency sweeping of tunable lasers is a fatal drawback in gaining the expected outcome from these technologies. Here, we introduce an on-chip, millimeter-scale, 7 m spiral resonator that is made of ultralow-loss Si3N4 to act as a frequency ruler for correction of the tunable lasers sweeping nonlinearities. The sharp 2 MHz frequency lines of the 8.5×107 high-quality factor resonator and the narrow-spaced 25.566 MHz frequency ticks of the 7 m spiral allow unprecedented precision for an on-chip solution to correct the laser sweeping nonlinearity. Accurate measurements of the ruler’s frequency spacing, linewidth, and temperature and wavelength sensitivities of the frequency ticks are performed here to demonstrate the quality of the frequency ruler. In addition, the spiral resonator is implemented in an frequency-modulated continuous-wave LiDAR experiment to demonstrate a potential application of the proposed on-chip frequency ruler.

A hydrogen (H2)-enhanced light-induced thermoelastic spectroscopy (LITES) sensor is proposed for the first time, to our knowledge, in this paper. The enhancement with H2 significantly reduces the resonance damping of a quartz tuning fork (QTF), leading to a 2.5-fold improvement in the quality factor (Q-factor) to 30,000 without introducing additional noise into the LITES sensor system. Based on the H2-enhancement effect, a self-designed round-head QTF with a low resonance frequency (f0) of 9527 Hz and a fiber coupled multipass cell (MPC) with an optical length of 40 m were utilized to increase the energy accumulation time of QTF and the optical absorption of the target gas, respectively, to demonstrate an ultra-highly sensitive C2H2-LITES sensor. The long-term stability of the H2-enhanced C2H2-LITES sensor was investigated based on Allan deviation analysis. With an optimal integration time of 140 s, the minimum detection limit (MDL) was improved to 290 parts per trillion (ppt). Compared to other reported state-of-the-art C2H2-LITES techniques with similar parameters, this sensor shows a 241-fold improvement in the MDL. This H2-enhancement technique proves to be a highly effective method for achieving a high Q-factor QTF, characterized by its simplicity and efficiency. It offers substantial potential for applications in QTF-based gas sensing.

Time dilation constitutes a crucial aspect of Lorentz invariance within special relativity and undergoes constant scrutiny through numerous Ives-Stilwell-type experiments employing the Doppler effect. In our study, we employed optical Ramsey spectroscopy on a Li+ ion beam to enhance the precision of measuring the intrinsic transition frequency 23S1-23P2 to the level of four parts in 1010 with speed of 0.00035c. Our findings reconciled an existing 2 MHz disparity between collinear and perpendicular laser spectroscopy. Furthermore, in conjunction with previous studies on Li+ ion beams traveling at speeds of 0.064c and 0.338c [Nat. Phys.3, 861 (2007)NPAHAX1745-247310.1038/nphys778; Phys. Rev. Lett.113, 120405 (2014)PRLTAO0031-900710.1103/PhysRevLett.113.120405], we updated the Robertson-Mansouri-Sexl parameter α^ to be (-10.0±9.9)×10-8 and (-2.9±2.0)×10-8, respectively.

Recently organic-inorganic perovskite has been established as a promising platform for achieving room temperature exciton-polaritons, attributable to its superior optical coherence and robust exciton binding energies. However, when interfaced with metallic surfaces, the rapid degradation and quenching effect in perovskite have presented significant challenges, which critically hinders the exploration of light-matter interactions within metallic plasmonic structures. In this study, we report a quasi-two-dimensional lead halide perovskite that demonstrates a pronounced strong coupling phenomenon within an array of aluminum nanocones. The investigated quasi-two-dimensional perovskite structure exhibits high photoluminescence quantum efficiency and improved stability against metallic-induced degradation. Interestingly, the periodical arraying in honeycomb formation of plasmonic structure has advantages in angle-dependent dispersions and the loss neutralizing effectively. Besides, the plasmonic cone lattice characterized by its collective surface lattice resonance, features an exceptionally small mode volume and high quality, enhancing its interaction with the perovskite. A significant Rabi splitting of 243 meV is observed at an incident angle of 30°. The dynamics of the Rabi oscillation is revealed by transient absorption spectra and theoretically analyzed by cavity quantum electrodynamics. This advancement in polariton research paves the way for novel applications, including quantum sources, enhanced photon-electron conversion efficiencies, and low-threshold lasing.

Surface plasmons (SPs) are one of the most effective information carriers for on-chip systems due to their two-dimensional propagation properties. Benefitting from the highly flexible designability, metasurfaces have emerged as a promising route in realizing SP devices. However, related studies are mainly focused on passive devices. Here, by introducing nonvolatile phase-change material Ge2Sb2Te5 (GST) into the metasurface design, we experimentally demonstrate a dual-function switchable SP device in the terahertz regime. Specifically, the device works as a spin-dependent directional plane-wave SP coupler when GST is in the amorphous state, while it works as a spin-dependent directional SP Fresnel zone plate (FZP) when GST is in the crystalline state. The states of GST are switched back and forth using thermal excitation and nanosecond laser illumination, respectively. Our method is simple and robust, and can find broad applications in on-chip photonic devices.

Artificially designed hyperbolic metamaterials (HMMs) with extraordinary optical anisotropy can support highly sensitive plasmonic sensing detections, showcasing significant potential for advancements in medical research and clinical diagnostics. In this study, we develop a gold nanoridge HMM and disclose the plasmonic sensing physical mechanism based on this type of HMM through theoretical and experimental studies. We determine that the high modal group velocity of plasmonic guided modes stemming from a large transverse permittivity of HMMs directly results in high sensitivity. By combining electron-beam lithography, oxygen plasma etching, and electroplating, the fabricated gold nanoridge array possesses an extremely high structural filling ratio that is difficult to obtain through conventional processes. This leads to a large transverse permittivity and enables highly confined and ultra-sensitive bulk plasmon–polariton (BPP) guided modes. By exciting these modes in the visible to near-infrared region, we achieve a record sensitivity of 53,300 nm/RIU and a figure of merit of 533. Furthermore, the developed plasmonic nanoridge HMM sensor exhibits an enhanced sensitivity of two orders of magnitude compared to that of the same type of HMM sensor in label-free biomolecule detection. Our study not only offers a promising avenue for label-free biosensing but also holds great potential to enhance early disease detection and monitoring.

Through achieving high-spatial-frequency laser-induced periodic surface structures (HSFLs) on a gold/graphene hybrid film, we introduce a high-speed, high-resolution, and wide-gamut chromotropic color printing technique. This method effectively addresses the trade-off between throughput and resolution in laser coloring. To realize Au HSFL, disordered lattice structures and high transmittance of amorphous Au (a-Au) thin film are used to overcome the rapid hot-electron diffusion and loss of plasmonic coherence typically observed on low-loss metal surfaces, respectively. Coupled with crystallization in Au and modulated surface plasmon polaritons by artificial “seed” pre-structure growing in a SiO2/Si substrate, HSFL emerged with a period of 100 nm on crystalline Au after single and rapid femtosecond laser scanning. This equips the proposed color printing with high-resolution and high-speed features simultaneously. In addition, the crystallization process is demonstrated to initiate change in the complex refractive index of Au, which causes wide-gamut colors. The chromotropic capability, which facilitates the background color to be tailored in color as well as into desirable shapes independently, enables three-level anti-counterfeiting based on the proposed color printing. Therefore, the proposed color printing is amenable for practical implementation in diverse applications, including security marking and data storage, ranging from nanoscale to large-scale fabrication.