We give an introduction to the feature issue composed of twelve articles on Optical Microresonators.

Optical chaotic signals emitted from an external-cavity feedback or injected laser diode enable small-signal information concealment in a noise-like carrier for secure optical communications. Due to the chaotic bandwidth limitation resulting from intrinsic relaxation oscillation frequency of lasers, multiplexing of optical chaotic signal, such as wavelength division multiplexing in fiber, is a typical candidate for high-capacity secure applications. However, to our best knowledge, the utilization of the spatial dimension of optical chaos for free-space secure communication has not yet been reported. Here, we experimentally demonstrate a free-space all-optical chaotic communication system that simultaneously enhances transmission capacity and security by orbital angular momentum (OAM) multiplexing. Optical chaotic signals with two different OAM modes totally carrying 20 Gbps on–off keying signals are secretly transmitted over a 2 m free-space link, where the channel crosstalk of OAM modes is less than -20 dB, with the mode spacing no less than 3. The receiver can extract valid information only when capturing approximately 92.5% of the OAM beam and correctly demodulating the corresponding mode. Bit error rate below the 7% hard-decision forward error correction threshold of 3.8×10-3 can be achieved for the intended recipient. Moreover, a simulated weak turbulence is introduced to comprehensively analyze the influence on the system performance, including channel crosstalk, chaotic synchronization, and transmission performance. Our work may inspire structured light application in optical chaos and pave a new way for developing future high-capacity free-space chaotic secure communication systems.

Combining the synthetic aperture radar (SAR) with the optical phase recovery, Fourier ptychography (FP) can be a promising technique for high-resolution optical remote imaging. However, there are still two issues that need to be addressed. First, the multi-angle coherent model of FP would be destroyed by the diffuse object; whether it can improve the resolution or just suppress the speckle is unclear. Second, the imaging distance is in meter scale and the diameter of field of view (FOV) is around centimeter scale, which greatly limits the application. In this paper, the reasons for the limitation of distance and FOV are analyzed, which mainly lie in the illumination scheme. We report a spherical wave illumination scheme and its algorithm to obtain larger FOV and longer distance. A noise suppression algorithm is reported to improve the reconstruction quality. The theoretical interpretation of our system under random phase is given. It is confirmed that FP can improve the resolution to the theoretical limit of the virtual synthetic aperture rather than simply suppressing the speckle. A 10 m standoff distance experiment with a six-fold synthetic aperture up to 31 mm over an object of size ∼1 m×0.7 m is demonstrated.

Diffraction tomography is a promising, quantitative, and nondestructive three-dimensional (3D) imaging method that enables us to obtain the complex refractive index distribution of a sample. The acquisition of the scattered fields under the different illumination angles is a key issue, where the complex scattered fields need to be retrieved. Presently, in order to develop terahertz (THz) diffraction tomography, the advanced acquisition of the scattered fields is desired. In this paper, a THz in-line digital holographic diffraction tomography (THz-IDHDT) is proposed with an extremely compact optical configuration and implemented for the first time, to the best of our knowledge. A learning-based phase retrieval algorithm by combining the physical model and the convolution neural networks, named the physics-enhanced deep neural network (PhysenNet), is applied to reconstruct the THz in-line digital hologram, and obtain the complex amplitude distribution of the sample with high fidelity. The advantages of the PhysenNet are that there is no need for pretraining by using a large set of labeled data, and it can also work for thick samples. Experimentally with a continuous-wave THz laser, the PhysenNet is first demonstrated by using the thin samples and exhibits superiority in terms of imaging quality. More importantly, with regard to the thick samples, PhysenNet still works well, and can offer 2D complex scattered fields for diffraction tomography. Furthermore, the 3D refractive index maps of two types of foam sphere samples are successfully reconstructed by the proposed method. For a single foam sphere, the relative error of the average refractive index value is only 0.17%, compared to the commercial THz time-domain spectroscopy system. This demonstrates the feasibility and high accuracy of the THz-IDHDT, and the idea can be applied to other wavebands as well.

Fiber scanners are portable and miniaturized laser scanning devices used for a wide range of applications, such as endoscopic probes for biomedical imaging. However, in order to achieve different resonant frequencies for 2D actuation, existing fiber scanners have complex actuation mechanisms and structures, resulting in being an obstacle for endoscopic imaging. By exploiting the intrinsic difference in bending stiffness of non-symmetrical fibers, we present the most simplified fiber scanner to date, containing only a single piezoelectric bimorph and a single non-symmetrical fiber with a 1D actuator for 2D laser scanning. 5-fps (frames per second) Lissajous scan is achieved with a scanning range of >300 μm and a driving voltage of ≤10Vpp. The ultra simplified structure of the fiber scanner enables a miniaturized optical probe with a diameter of 1.9 mm, and image quality comparable to that of commercial microscopes. Taking advantage of its ease of manufacture and low cost, the fiber scanner offers a transformative way forward for disposable endoscopic probes that avoid the risk of cross infection during endoscopic inspections.

Optical-resolution photoacoustic microscopy (OR-PAM) is capable of observing the distribution of optical absorbers inside bio-tissues with a high spatial resolution of micrometers. Unfortunately, due to the employment of a tight optical focus, it suffers from a limited depth of field (DOF), making it challenging to achieve high-resolution imaging of targets with arbitrary surfaces. Here, we propose a high spatiotemporal adaptive photoacoustic focusing mechanism through integrating a high-speed optical focuser, a time-of-flight contour deriving algorithm, and the rotary-scanning photoacoustic microscopy. The developed system, named high-speed adaptive photoacoustic microscopy (HA-PAM), features an ultrashort focus-shifting time of 5 ms and an enlarged DOF of up to 5 mm. With the assistance of the proposed mechanism, we can achieve a homogeneous lateral resolution of 6 μm over a 10 mm circular imaging domain within 5 s. We demonstrate the advantages of HA-PAM through imaging phantoms with curved surfaces, subcutaneous tumor-bearing mice, resected rabbit kidneys, and pulsating mouse brains. The imaging results suggest that this approach provides a high and consistent spatial resolution for imaging bio-tissues with arbitrary surfaces without sacrificing the imaging speed, and has the potential to extend the fundamental and clinical applications of OR-PAM.

Polarimetric imaging provides valuable insights into the polarization state of light interacting with a sample. It can infer crucial birefringence properties of specimens without using labels, thereby facilitating the diagnosis of diseases such as cancer and osteoarthritis. In this study, we present a novel polarimetric coded ptychography (pol-CP) approach that enables high-resolution, high-throughput gigapixel birefringence imaging on a chip. Our platform deviates from traditional lens-based systems by employing an integrated polarimetric coded sensor for lensless coherent diffraction imaging. Utilizing Jones calculus, we quantitatively determine the birefringence retardance and orientation information of biospecimens from the recovered images. Our portable pol-CP prototype can resolve the 435 nm linewidth on the resolution target, and the imaging field of view for a single acquisition is limited only by the detector size of 41 mm2. The prototype allows for the acquisition of gigapixel birefringence images with a 180 mm2 field of view in ∼3.5 min, a performance that rivals high-end whole slide scanner but at a small fraction of the cost. To demonstrate its biomedical applications, we perform high-throughput imaging of malaria-infected blood smears, locating parasites using birefringence contrast. We also generate birefringence maps of label-free thyroid smears to identify thyroid follicles. Notably, the recovered birefringence maps emphasize the same regions as autofluorescence images, underscoring the potential for rapid on-site evaluation of label-free biopsies. Our approach provides a turnkey and portable solution for lensless polarimetric analysis on a chip, with promising applications in disease diagnosis, crystal screening, and label-free chemical imaging, particularly in resource-constrained environments.

To further advance nanomaterial applications and reduce waste production during synthesis, greener and sustainable production methods are necessary. Pulsed laser ablation in liquid (PLAL) is a green technique that enables the synthesis of nanoparticles. This study uses synchronous-double-pulse PLAL to understand bubble interaction effects on the nanoparticle size. By adjusting the lateral separation of the pulses relative to the maximum bubble size, an inter-pulse separation is identified where the nanoparticle size is fourfold. The cavitation bubble pair interaction is recorded using a unique coaxial diffuse shadowgraphy system. This system allows us to record the bubble pair interaction from the top and side, enabling the identification of the bubble’s morphology, lifetime, volumetric, and displacement velocity. It is found that the collision and collapse of the bubbles generated at a certain inter-pulse separation results in a larger nanoparticle size. These results mark a significant advancement by controlling the abundance of larger nanoparticles in PLAL, where previous efforts were primarily focused on reducing the average nanoparticle size. The experimentally observed trends are confirmed by numerical simulations with high spatial and temporal resolution. This study serves as a starting point to bridge the gap between upscaled multi-bubble practices and fundamental knowledge concerning the determinants that define the final nanoparticle size.

In this study, we present a method for free-space beam shaping and steering based on a silicon optical phased array, which addresses the theoretical limitation of traditional bulk optics. We theoretically analyze the beam propagation properties with changes in the applied phase. Different beam profiles can be shaped by varying the phase combination, while a high-order quasi-Bessel beam can be generated with a cubic change to the phase modulation. The simulated results are validated further experimentally, and they match one another well. Beam steering can be achieved with a field of view as large as 140°, which has potential benefits for practical applications. The presented method is expected to have broad application prospects for optical communications, free-space optical interconnects, and light detection and ranging.

Temporal dissipative solitons have been widely studied in optical systems, which exhibit various localized structures and rich dynamics, and have shown great potential in applications including optical encoding and sensing. Yet, most of the soliton states, as well as the switching dynamics amongst, were fractionally captured or via self-evolution of the system, lacking of control on the soliton motion. While soliton motion control has been widely investigated in coherently seeded optical cavities, such as microresonator-based dissipative solitons, its implementation in decoherently seeded systems, typically the soliton mode-locked lasers, remains an outstanding challenge. Here, we report the universal dynamics and deterministic motion control of temporal dissipative solitons in a mode-locked fibre laser by introducing a scanned spectral filtering effect. We investigate rich switching dynamics corresponding to both the assembly and the disassembly of solitons, revealing a complete and reversible motion from chaotic states to soliton and soliton-molecule states. Significant hysteresis has been recognized in between the redshift and blueshift scan of the motorized optical filter, unveiling the nature of having state bifurcations in dissipative and nonlinear systems. The active soliton motion control enabled by filter scanning highlights the potential prospects of encoding and sensing using soliton molecules.

Dendrites, branches of neurons that transmit signals between synapses and soma, play a vital role in spiking information processing, such as nonlinear integration of excitatory and inhibitory stimuli. However, the investigation of nonlinear integration of dendrites in photonic neurons and the fabrication of photonic neurons including dendritic nonlinear integration in photonic spiking neural networks (SNNs) remain open problems. Here, we fabricate and integrate two dendrites and one soma in a single Fabry–Perot laser with an embedded saturable absorber (FP-SA) neuron to achieve nonlinear integration of excitatory and inhibitory stimuli. Note that the two intrinsic electrodes of the gain section and saturable absorber (SA) section in the FP-SA neuron are defined as two dendrites for two ports of stimuli reception, with one electronic dendrite receiving excitatory stimulus and the other receiving inhibitory stimulus. The stimuli received by two electronic dendrites are integrated nonlinearly in a single FP-SA neuron, which generates spikes for photonic SNNs. The properties of frequency encoding and spatiotemporal encoding are investigated experimentally in a single FP-SA neuron with two electronic dendrites. For SNNs equipped with FP-SA neurons, the range of weights between presynaptic neurons and postsynaptic neurons is varied from negative to positive values by biasing the gain and SA sections of FP-SA neurons. Compared with SNN with all-positive weights realized by only biasing the gain section of photonic neurons, the recognition accuracy of Iris flower data is improved numerically in SNN consisting of FP-SA neurons. The results show great potential for multi-functional integrated photonic SNN chips.

To facilitate the development of on-chip integrated mid-infrared multi-channel gas sensing systems, we propose a high-power dual-mode (7.01 and 7.5 μm) distributed feedback quantum cascade laser based on stacked 3D monolithic integration. Longitudinal mode control is achieved by preparing longitudinal nested bi-periodic compound one-dimensional Bragg gratings along the direction of the cavity length in the confinement layer. Additionally, transverse coherent coupling ridges perpendicular to the cavity length direction are fabricated in the upper waveguide layer to promote the fundamental transverse mode output when all ridges are in phase. Stable dual-wavelength simultaneous emission with a side-mode suppression ratio of more than 20 dB was achieved by holographic exposure and wet etching. The entire spectral tuning range covers nearly 100 nm through joint tuning of the injection current and heat-sink temperature. High peak power and beam quality are guaranteed by the parallel coherent integration of seven-element ridge arrays. The device operates in a fundamental supermode with a single-lobed far-field pattern, and its peak output power reaches 3.36 W in pulsed mode at 20°C. This dual-mode laser chip has the potential for in-situ on-chip simultaneous detection of CH4 and C2H6 gases in leak monitoring.

Direct generation of visible frequency from a compact all-fiber laser while preserving high output characteristics has been a subject of research in laser technology. We investigated the high output performance of all-fiber lasers based on Ho3+-doped ZBLAN fluoride glass fiber especially operating in the deep-red band by pumping at 640 nm. Remarkably, we achieved a maximum continuous-wave output power of 271 mW at 750 nm with a slope efficiency of 45.1%, which represents, to our knowledge, the highest direct output power recorded in an all-fiber laser with a core diameter of less than 10 μm in the deep-red band. Additionally, we successfully developed a 1.2 μm all-fiber laser pumped by a 640 nm laser. We extensively investigated the correlation between these two-laser generation processes and their performances at 750 nm and 1.2 μm wavelengths. By increasing the pumping rate, we observed an efficient recycling of population through a highly excited state absorption process, which effectively returned the population to the upper laser level of the deep-red transition. Moreover, we determined the optimized conditions for such lasers, identified the processes responsible for populating the excited state energy levels, and established the corresponding spectroscopic parameters.

Strong coupling of mid-infrared (mid-IR) vibrational transitions to optical cavities provides a means to modify and control a material’s chemical reactivity and offers a foundation for novel chemical detection technology. Currently, the relatively large volumes of the mid-IR photonic cavities and weak oscillator strengths of vibrational transitions restrict vibrational strong coupling (VSC) studies and devices to large ensembles of molecules, thus representing a potential limitation of this nascent field. Here, we experimentally and theoretically investigate the mid-IR optical properties of 3D-printed multimode metal–insulator–metal (MIM) plasmonic nanoscale cavities for enabling strong light–matter interactions at a deep subwavelength regime. We observe strong vibration-plasmon coupling between the two dipolar modes of the L-shaped cavity and the carbonyl stretch vibrational transition of the polymer dielectric. The cavity mode volume is half the size of a typical square-shaped MIM geometry, thus enabling a reduction in the number of vibrational oscillators to achieve strong coupling. The resulting three polariton modes are well described by a fully coupled multimode oscillator model where all coupling potentials are non-zero. The 3D printing technique of the cavities is a highly accessible and versatile means of printing arbitrarily shaped submicron-sized mid-IR plasmonic cavities capable of producing strong light–matter interactions for a variety of photonic or photochemical applications. Specifically, similar MIM structures fabricated with nanoscopic voids within the insulator region could constitute a promising microfluidic plasmonic cavity device platform for applications in chemical sensing or photochemistry.

Lithium niobate’s substantial nonlinear optical and electro-optic coefficients have recently thrust it into the limelight. This study presents a thorough review of bound states in the continuum (BICs) in lithium niobate metasurfaces, also suggesting their potential for sensing applications. We propose an all-dielectric tunable metasurface that offers high Q factor resonances in the terahertz range, triggered by symmetry-protected BICs. With exceptional sensitivity to changes in the refractive index of the surrounding medium, the metasurface can reach a sensitivity as high as 947 GHz/RIU. This paves the way for ultrasensitive tunable terahertz sensors, offering an exciting path for further research.

Top-illuminated structure facilitates the integration of organic photodetectors (OPDs) into high-resolution flexible wearable light detection systems by allowing the OPDs to be deposited on the bottom readout circuit. However, constructing this structure poses a challenge as it demands metallic electrodes with both high optical transparency and high electrical conductivity. But to achieve practical sheet resistances, most semitransparent metallic electrodes tend to reflect a large portion of incident light instead of allowing it to be absorbed by the photoactive layer of the OPDs. This, in turn, results in reduced photocurrent generation. To address this issue, a semiconducting germanium (Ge) film is introduced into a sliver (Ag) film, effectively reducing its reflectivity by lessening scattering. The Ge film also changes how the Ag film grows, further reducing its absorption by lowering the critical thickness needed for forming a continuous film. This approach yields a 10 nm metallic electrode with a transmittance of 70%, a reflectivity of 12%, and a sheet resistance of 35.5 Ω/□. Using this metallic electrode, flexible OPDs exhibit a high photo-to-dark current ratio of 2.9×104 and improved mechanical properties. This finding highlights the benefits of the top-illuminated structure, which effectively reduces losses caused by waveguided modes of the incident light.

Superconducting nanowires enable the operation of outstanding single-photon detectors, which are required particularly for quantum information and weak-light measurement applications. However, the trade-off between detection speed and efficiency, which is related to the filling factors of superconducting nanowires, is still a challenge. Here, we propose a fast, efficient single-photon detector fabricated by integrating ultralow-filling-factor meandered superconducting nanowires atop a photonic crystal (PhC) resonator. This unique structure enables a fast photon response due to the low kinetic inductance of the short nanowires and ensures efficient photon absorption due to the resonant effect of the PhC structure. The proposed detector has a filling factor of only ∼12% while maintaining a high maximum absorption in our simulation of 90%. The fabricated device exhibits a maximum system detection efficiency of 60%, a maximum count rate of ∼80 MHz, and a recovery time of only ∼12 ns, which is three times faster than that of the conventional meandered structure at the same sensing diameter (18 μm). This work helps advance the movement toward high-efficiency, high-speed single-photon detectors and promotes their future application in quantum communication and imaging.

In this work, a Si/MoS2 heterojunction photodetector enhanced by hot electron injection through Fano resonance is developed. By preparing Au oligomers using capillary-assisted particle assembly (CAPA) on the silicon substrate with a nanohole array and covering few-layer MoS2 with Au electrodes on top of the oligomer structures, the Fano resonance couples with a Si/MoS2 heterojunction. With on-resonance excitation, Fano resonance generated many hot electrons on the surface of oligomers, and the hot electrons were injected into MoS2, providing an increased current in the photodetector under a bias voltage. The photodetectors exhibited a broadband photoresponse ranging from 450 to 1064 nm, and a large responsivity up to 52 A/W at a wavelength of 785 nm under a bias voltage of 3 V. The demonstrated Fano resonance-enhanced Si/MoS2 heterojunction photodetector provides a strategy to improve the photoresponsivity of two-dimensional materials-based photodetectors for optoelectronic applications in the field of visible and near-infrared detection.

The fabrication of different perovskite materials with superior properties into lateral heterostructures can greatly improve device performance and polarization sensitivity. However, the sensitivity of perovskites to solvents and environmental factors makes the fabrication of lateral heterojunctions difficult. Here, we realize high-quality perovskite microwire crystal heterojunction arrays using regioselective ion exchange. Photodetectors with responsivity and detectivity up to 748 A W-1 and 8.2×1012 Jones are fabricated. The photodetector exhibits responsivity as high as 13.5 A W-1 at 0 V bias. In addition, the device exhibits ultra-high polarization sensitivity with a dichroic ratio of 5.6, and 81% of its performance was maintained after 144 days of exposure to air.

The phenomenon of branched flow has attracted researchers since its inception, with recent observations of the light branching on soap bubbles. However, previous studies have primarily focused on the flat spacetime, overlooking the effect of surface curvature on branched flows. In this paper, we explore the branched flow phenomenon of light on a rough curved surface called constant Gaussian curvature surfaces (CGCSs). Compared with flat space, a CGCS demonstrates that the first branching point advances due to the focusing effect of the positive curvature of the surface. Furthermore, unlike on flat space, optical branches on curved surfaces do not consistently become chaotic during its transmission in a random potential field. On the contrary, the “entropy” decreases at specific positions, which reveals a sink flow phenomenon following the generation of branched flows. This result highlights the time inversion characteristics of CGCSs. Lastly, we demonstrated that the anomalous entropy reduction is related to the transverse and longitudinal coherence transformations of light. We suppose these efforts would fuel further investigation of the thermodynamic evolution and spatiotemporal inversion of random caustics, as well as their future application in the information transmission of random potentials in curved spacetime.

Optical skyrmions are quasiparticles with nontrivial topological textures that have significant potential in optical information processing, transmission, and storage. Here, we theoretically and experimentally achieve the conversion of optical skyrmions among Néel, Bloch, intermediate skyrmions, and bimerons by polarization devices, where the fusion and annihilation of optical skyrmions are demonstrated accordingly. By analyzing the polarization pattern in Poincaré beams, we reveal the skyrmion topology dependence on the device, which provides a pathway for the study of skyrmion interactions. A vectorial optical field generator is implemented to realize the conversion and superposition experimentally, and the results are in good agreement with the theoretical predictions. These results enhance our comprehension of optical topological quasiparticles, which could have a significant impact on the transfer, storage, and communication of optical information.

We report three orders of magnitude optical cooling of the fundamental torsional mode of a 5 mm long, 550 nm diameter optical nanofiber. The rotation of the nanofiber couples to the polarization of guided laser fields. We use a weak laser probe to monitor the rotation and use feedback to modulate the polarization of an auxiliary drive laser providing torque. Our results present a tool for the optomechanical control of large-scale torsional resonators, with metrological applications and potential implications for studying macroscopic objects in quantum states.

Optical frequency combs (OFCs) have great potential in communications, especially in dense wavelength-division multiplexing. However, the size of traditional OFCs based on conventional optical microcavities or dispersion fibers is at least tens of micrometers, far larger than that of nanoscale electronic chips. Therefore, reducing the size of OFCs to match electronic chips is of necessity. Here, for the first time to our knowledge, we introduce surface plasmon polaritons (SPPs) to the construction of OFCs to realize a miniature device. The thickness of our device is reduced below 1 μm. Though the presence of SPPs may induce ohmic and scattering loss, the threshold of the device is obtained as 9 μW, comparable to the conventional device. Interestingly, the response time is 13.2 ps, much faster than the optical counterparts. This work provides a feasible strategy for the miniaturization of OFCs.

Employing couplers to convert guided waves into free-space modes and flexibly control their wavefront is one of the key technologies in chip-integrated displays and communications. Traditional couplers are mainly composed of gratings, which have limitations in footprint, bandwidth, as well as controllability. Though the resonant/geometric metasurface newly emerges as a promising interface for bridging guided waves with free-space ones, it either relies on complex optimizations of multiple parameters, or is subject to the locked phase response of opposite spins, both of which hinder the functional diversity and practical multiplexing capability. Here, we propose and experimentally demonstrate an alternative with a spin-decoupled meta-coupler, simultaneously integrating triple functions of guided wave radiation, polarization demultiplexing, and dual-channel wavefront manipulation into a single device. By endowing polarization-dependent functionalities into a pure geometric metasurface, the out-coupled left-handed and right-handed circular polarization guided waves intelligently identify the predesigned phase modulation and reconstruct desired wavefronts, like bifocal focusing and holography multiplexing, with a polarization extinction ratio over 13.4 dB in experiments. We envision that the robust, broadband, and multifunctional meta-coupler could pave a way for the development of versatile multiplexed waveguide-based devices.

Surface lattice resonances (SLRs) with ultra-narrow linewidth (high quality factor) can enhance light–matter interactions at the nanoscale and modulate the propagating light from the emission wavelength direction to efficiency by photonic band engineering. Therefore, SLRs can serve as an excited candidate to enhance and, more importantly, modulate amplified spontaneous emission (ASE) with more optical parameters. Here, this work presents a system of two-dimensional Ag-coated Al nanocone array (Ag-NCA) packaged with Nile red, and a normal ASE with 15-fold enhancement is observed under external driving light. This enhancement fades away, obviously, in the case of the off-normal condition, as the optical feedback evolves from the band edge steady state to the propagating state. The ASE of this hybrid plasmonic system expands the possibilities of interaction between light and matter and has great promise for applications in nanolasing, super-resolution imaging, and photonic integration circuits.

Surface lattice resonance (SLR) is a pretty effective mechanism to realize ultranarrow linewidths in the spectrum. Herein, we propose and demonstrate reflection-type SLRs in all-metal metasurfaces experimentally, compared with the traditional transmission-type SLR, which can avoid the refractive index (RI) mismatch problem and are more suitable for high-efficiency RI sensing due to direct contact and strong light–matter interaction. The measured SLR linewidth is 13.5 nm influenced by the meta-atom size, which needs a compromise design to keep a balance between the narrow linewidth and noise immunity. Notably, the SLR sensitivity is determined by the lattice period along the polarization direction with regularity, which establishes an intuitive link between structures and optical responses and provides a theoretical guide for metasurface designs. Additionally, incident angle multiplexing will make the resonance wavelength red shift or blue shift in the case of orthogonal polarization. The rectangular array metasurface can realize dual SLRs with different sensing performances. Flexibly, the SLR can also be formed by the different meta-atoms and arrays. This research supports SLR multifarious applications involving not only RI sensing but also nonlinear optics, nano-lasers, etc.

The manipulation and detection of polarization states play a crucial role in the application of 6G terahertz communication. Nonetheless, the development of compact and versatile polarization detection devices capable of detecting arbitrary polarizations continues to be a challenging endeavor. Here, we demonstrate a terahertz polarization detection scheme by performing mode purity analysis and multidimensional analysis of the transmitted vortex field. The power of the proposed polarization recognition is verified by using three polarization trajectories, including linear polarizations, circular polarizations, and elliptical polarizations. Using the reconstructed complete polarization parameters, the detected polarization states are characterized using polarization ellipses, Poincaré sphere, and full-Stokes parameters. The experimental results validate the power of this scheme in polarization detection. This scheme holds promise for applications in polarization imaging and terahertz communication.

Launching, tracking, and controlling picosecond acoustic (PA) pulses are fundamentally important for the construction of ultrafast hypersonic wave sources, ultrafast manipulation of matter, and spatiotemporal imaging of interfaces. Here, we show that GHz PA pulses can be all-optically generated, detected, and manipulated in a 2D layered MoS2/glass heterostructure using femtosecond laser pump–probe. Based on an interferometric model, PA pulse signals in glass are successfully decoupled from the coexisting temperature and photocarrier relaxation and coherent acoustic phonon (CAP) oscillation signals of MoS2 lattice in both time and frequency domains. Under selective interface excitations, temperature-mediated interfacial phonon scatterings can compress PA pulse widths by about 50%. By increasing the pump fluences, anharmonic CAP oscillations of MoS2 lattice are initiated. As a result, the increased interatomic distance at the MoS2/glass interface that reduces interfacial energy couplings can markedly broaden the PA pulse widths by about 150%. Our results open new avenues to obtain controllable PA pulses in 2D semiconductor/dielectric heterostructures with femtosecond laser pump–probe, which will enable many investigations and applications.

High-precision time interval measurement is a fundamental technique in many advanced applications, including time and distance metrology, particle physics, and ultra-precision machining. However, many of these applications are confined by the imprecise time interval measurement of electrical signals, restricting the performance of the ultimate system to a few picoseconds, which limits ultrahigh precision applications. Here, we demonstrate an optical means for the time interval measurement of electrical signals that can successfully achieve femtosecond (fs) level precision. The setup is established using the optical frequency comb (OFC) based linear optical sampling (LOS) technique to realize timescale-stretched measurement. We achieve a measurement precision of 82 fs for a single LOS scan measurement and 3.05 fs for the 100-times average with post-processing, which is three orders of magnitude higher than the results of older electrical methods. The high-precision time interval measurement of electrical signals can substantially improve precision measurement technologies.