Semiconductor metal oxides with narrow bandgap have emerged as a promising platform for photoelectrochemical reactions, yet their photoelectron-induced photocorrosion effect has been a limitation for their wider applications. Understanding the conversion processes concomitant with photoelectrochemical reaction at the electrode–electrolyte interface plays a crucial role in revealing the corrosion mechanisms and advancing the development of efficient photocathodes. However, accurately and in situ tracking these dynamic chemical events remains a great challenge due to the fact that reaction processes occur at nanoscale interfaces. Here, we track the electrochemical growth and conversion of copper nanostructures at interface by the evanescent field of the surface plasmon wave by using a gold-coated optical fiber as an electrochemical electrode and light sensing probe. The results exhibit correlation between redox processes of copper species and plasmonic resonances. Furthermore, in situ fiber-optic detection reveals the photocorrosion dynamics under photoelectrochemical reaction, including photoelectron-induced self-reduction of copper oxide and self-oxidation of cuprous oxide. These demonstrations facilitate not only the diagnosis for the health condition of photocathode nanomaterial, but also the understanding of the underlying reaction mechanism, and thus are potentially crucial for advancing the development of highly efficient photocathodes in future energy applications.

The performance of an all-fiber-integrated photodetector (AFPD) depends on the integration of the active layer, where FA0.4MA0.6PbI3 emerges as a promising candidate due to its high absorbance, long carrier diffusion distance, and self-assembly. In this study, we report an AFPD based on FA0.4MA0.6PbI3 perovskite, along with thickness design for enhancement. The active layer of the AFPD is regarded as a thin-film waveguide for thickness design. Theoretical analysis and simulation results indicate the presence of resonance mode, enhancing and confining the light field even in a thinned active layer. An FA0.4MA0.6PbI3 based metal-semiconductor-metal (MSM) photodetector is directly deposited onto a side-polished multimode fiber (SP-MMF). The transmitted light in fiber leaks from the core to the MSM photodetector through the polished surface of SP-MMF, inducing a detection response. Experimental results demonstrate that the device achieves a responsivity of 3.2 A/W to 650 nm light, with both rising and falling edges of the response time reaching 8 ms. The proposed AFPD and method exhibit potential to simultaneously achieve high responsivity, fast response, and low insertion loss, providing a reliable solution for high-performance photodetection.

Holographic near-eye augmented reality (AR) displays featuring tilted inbound/outbound angles on compact optical combiners hold significant potential yet often struggle to deliver satisfying image quality. This is primarily attributed to two reasons: the lack of a robust off-axis-supported phase hologram generation algorithm; and the suboptimal performance of ill-tuned hardware parts such as imperfect holographic optical elements (HOEs). To address these issues, we incorporate a gradient descent-based phase retrieval algorithm with spectrum remapping, allowing for precise hologram generation with wave propagation between nonparallel planes. Further, we apply a camera-calibrated propagation scheme to iteratively optimize holograms, mitigating imperfections arising from the defects in the HOE fabrication process and other hardware parts, thereby significantly lifting the holographic image quality. We build an off-axis holographic near-eye display prototype using off-the-shelf light engine parts and a customized full-color HOE, demonstrating state-of-the-art virtual reality and AR display results.

Framing photography provides a high temporal resolution and minimizes crosstalk between adjacent frames, making it an indispensable tool for recording ultrafast phenomena. To date, various ultrafast framing photography techniques have been developed. However, simultaneously achieving large sequence depth, high image quality, ultrashort exposure time, and flexible frame interval remains a significant challenge. Herein, we present a spatiotemporal shearing-based ultrafast framing photography, termed STS-UFP, designed to address this challenge. STS-UFP employs an adjustable ultrashort laser pulse train with a spectrum shuttle to illuminate the dynamic scenes for extracting the transient information and records discrete frames using a streak camera via spatiotemporal shearing. Based on its unique design, STS-UFP achieves high-quality ultrafast imaging with a sequence depth of up to 16 frames and frame intervals ranging from hundreds of picoseconds to nanoseconds, while maintaining an extremely short (picosecond) exposure time. The exceptional performance of STS-UFP is demonstrated through experimental observations of femtosecond laser-induced plasma and shockwave in water, femtosecond laser ablation in biological tissue, and femtosecond laser-induced shockwave on a silicon surface. Given its remarkable imaging capabilities, STS-UFP serves as a powerful tool for precisely observing ultrafast dynamics and holds significant potential for advancing studies of ultrafast phenomena.

By exploiting the nonlinear responses of fluorescent probes, the spatial resolution of structured illumination microscopy (SIM) can be further increased. However, the traditional reconstruction method of nonlinear structured illumination microscopy (NL-SIM) is very slow due to its complex process, which poses a significant challenge to display super resolution results in real-time. Here, we describe an efficient and robust SIM algorithm that enables rapid and accurate full-process SIM reconstruction. First, we present a fast illumination parameters estimation algorithm based on discrete Fourier transforms that result in a more simplified workflow than that of classical methods. Second, an accelerated NL-SIM reconstruction algorithm is developed by extending a high-speed reconstruction framework, joint space and frequency reconstruction (JSFR), to the NL-SIM. In particular, we provide the open-source MATLAB toolbox of our JSFR-NL-SIM algorithm. The entire image reconstruction process is completed in the milliseconds range, representing a significant time saving for the user.

An exhaustive study of the noncontinuous-state laser dynamics associated with the transient optical process is significant because it reveals the complex physical mechanisms and characteristics in nonlinear laser systems. In this study, in-depth theoretical interpretation and experimental verification of the noncontinuous-state dynamics in laser system are presented, based on developed pulse-modulated frequency-shifted laser feedback interferometry (LFI). By introducing external pulse modulation, we investigate the nonlinear time-of-flight dynamics and related photon behaviors evolution of the pulsed LFI system by observing the changes in effective interference time sequences for interference realization and attainable minimum feedback photon number of the signal under various modulated noncontinuous states. Implementation of the pulse-modulated LFI scheme should exceed the pulse overlapping time window limit of 1.93 μs to effectively extract and preserve the extracavity feedback photon information. Experiments reveal that the minimum feedback photon number of signals successfully measured by the pulsed LFI sensor is 0.067 feedback photons per Doppler cycle, exhibiting high sensitivity for extremely weak signal detection. Further, simultaneous measurement for velocity and distance of the moving object is performed to validate the feasibility and applicability of the pulsed LFI. The system can successfully achieve large-range simultaneous measurements within the velocity range of 73.5-612.6 mm/s, over a distance of 25.5 km. This work opens the way to unexplored frontiers of pulsed LFI to fill the research gap in noncontinuous laser dynamics in this field, showcasing diverse and wide-ranging applications in the realm of integrated sensing, remote monitoring, and positioning and navigation.

Broadband polarization measurement plays a crucial role in numerous fields, spanning from fundamental physics to a wide range of practical applications. However, traditional approaches typically rely on combinations of various dispersive optical elements, requiring bulky systems and complicated time-consuming multiple procedures. Here we have achieved broadband spectropolarimetry based on single-shot images for spatial intensity distributions of polychromatic vector beams. A custom-designed diffractive optical element and a vortex retarder convert the incident polychromatic waves into structured vector beams: the former diffracts light of different wavelengths into concentric circles of different radii, while the latter codes their polarization information into intensity distributions along the azimuthal direction. The validation experiments verify our exceptional measurement accuracy (RMS errors<1%) for each Stokes component in the visible light range (400–700 nm), with good spectral (<0.8 nm) and temporal (an output rate of 100 Hz) resolutions. We have further employed our broadband polarimeter to study the mutarotation of glucose, making direct observations of temporal evolutions of chemical reactions accessible. Our work has significantly broadened the toolboxes of spectropolarimetry, which can potentially incubate various disruptive applications that depend on broadband polarization measurements.

This paper presents a wavelength-stepped swept laser based on a dispersion-tuned swept laser with the integration of a Mach–Zehnder interferometer, enabling a transition from continuous wavelength sweeping to wavelength-stepped sweeping. A comprehensive investigation of this laser is conducted, wherein different modulation schemes are employed to dynamically compare the switching mode, static-sweeping mode, and sweeping mode; the absence of mode hopping in the sweeping mode of the laser is verified. However, it is observed during experiments that the wavelength always remains stationary for a long time during the initiation of sweeping and change in sweeping direction, exhibiting latency compared to the modulation frequency variations. Through a simplistic modeling analysis of the composite cavity, it is revealed that the detuned state of the sub-cavity plays a critical role in the stable operation of the laser. Subsequently, simulation verification using the Ginzburg–Landau equation supports this observation. Additionally, compared to dispersion-tuned swept lasers, not only the linewidth significantly is narrowed in the proposed laser, but it also demonstrates enhanced stability during the sweeping process. This study provides, to our knowledge, a new laser source for ultra-fast optical imaging, ranging, and sensing applications, and presents novel methods and theoretical models for linewidth compression in swept lasers.

In a hollow-core fiber (HCF), light propagates through an air/vacuum core rather than a solid material, resulting in a low thermo-optic coefficient and ability to handle high powers. Here, we demonstrate a laser locked to a hollow-core fiber reference, which thanks to the low HCF thermal sensitivity, shows long-term stability an order of magnitude better than compact commercially available low-noise lasers. The laser frequency variation within ±600 kHz was measured over 50 h. The stability of our proof-of-concept laser is ensured via a strong self-injection ratio of -15 dB, enabled by the high-power handling and low loss of the hollow-core fiber’s resonator. Moreover, our results show appealing performance parameters, including a fractional frequency stability of 4×10-13 at 1 s averaging time and a Lorentzian component of the linewidth of 0.2 Hz.

Blood flow is essential for maintaining normal physiological functions of the human body. Endoscopic laser speckle contrast imaging (LSCI) can achieve rapid, high-resolution, label-free, and long-term blood flow perfusion velocity monitoring in minimally invasive surgery. However, conventional endoscopic LSCI uses a low-coherence laser illumination scheme, leading to restricted angles of illumination, compromised laser coherence, uneven laser illumination distribution, and low coupling efficiency, all of which degrade the quality of LSCI in the endoscope. In this paper, we propose that conical fiber (CF)-coupled high-coherence laser can be used to achieve large-angle, high-coherence, high-uniformity, and high coupling efficiency laser illumination in the endoscope. Additionally, we establish an effective model for calculating the divergence angle of CFs. Through phantom and animal experiments, we reveal that laser illumination based on CF markedly enhances endoscopic LSCI performance. This technology broadens the imaging field of view, enhances the signal-to-noise ratio, enables more sensitive detection of minute blood flow changes, expands the detectable flow range, and improves signal-to-background ratio of endoscopic LSCI. Our findings suggest that CF-based laser illumination stands as a highly promising advancement in endoscopic LSCI.

Bound states in the continuum (BICs) have gained considerable attention for their ability to strengthen light–matter interactions, enabling applications in lasing, sensing, and imaging. These properties also show great promise for intensifying free-electron radiation. Recently, researchers realized momentum-mismatch-driven quasi-BICs in compound grating waveguides. This category of quasi-BICs exhibits high Q factors over a broad frequency spectrum. In this paper, we explore the possibility of achieving multi-frequency terahertz Smith–Purcell radiation empowered by momentum-mismatch-driven quasi-BICs in silicon compound grating waveguides. By leveraging the low-loss properties of silicon in the terahertz range, quasi-BICs are achieved through guided-mode resonance, delivering exceptionally high Q factors over a broad frequency spectrum. The broadband nature of these quasi-BICs enables efficient energy extraction from electron beams across varying voltages, while their multimode characteristics support simultaneous interactions with multiple modes, further boosting radiation intensity. The findings demonstrate significant enhancement of free-electron radiation at multiple frequencies, addressing the limitations of narrowband methods and high-loss metallic systems. By integrating broadband performance with the advantages of low-loss dielectric platforms, this work advances the development of compact, tunable terahertz free-electron radiation sources and provides valuable insights into optimizing quasi-BIC systems for practical applications.

Point-of-care sensors are pivotal for early disease diagnosis, significantly advancing global health. Surface plasmons, the collective oscillations of free electrons under electromagnetic excitation, have been widely studied for biosensing due to their electromagnetic field enhancements at sub-wavelength scales. We introduce a plasmonic biosensor on a compact photonic integrated circuit (PIC) enhanced by exceptional points (EPs). EPs, singularities in non-Hermitian optical systems, provide extreme sensitivity to external perturbations. They emerge when two or more complex resonating modes merge into a single degenerate mode. We demonstrate an EP in a single coupled nanoantenna particle positioned in a uniquely designed silicon nitride slot-waveguide, which we call a junction-waveguide. By laterally shifting two optically coupled gold nanobars of different lengths, we achieve a single particle EP. The junction-waveguide enables efficient coupling of the plasmonic nanoantenna to the waveguide mode. The system integrates a four-port Mach–Zehnder interferometer (MZI), allowing for simultaneous measurements of the amplitude and phase of EP, facilitating highly accurate real-time eigenvalue extraction. For biosensing, we encapsulated the detection zone with a microchannel, enabling low-volume and simple sample handling. Our single particle integrated EP sensor demonstrates superior sensitivity compared to the corresponding linear diabolic point (DP) system under both local and bulk sensing schemes, even at large perturbations. Our studies revealed that the integrated EP sensor can detect a single molecule captured by the nanobars with the average size ranging from 10 to 100 nm. The proposed EP biosensor, with its extreme sensitivity, compact form, and real-time phase sensing capabilities, provides an approach for detecting and quantifying various biomarkers such as proteins and nucleic acids, offering a unique platform for early disease diagnosis.

High-index dielectric nanoparticles supporting strong Mie resonances, such as silicon (Si) nanoparticles, provide a platform for manipulating optical fields at the subwavelength scale. However, in general, the quality factors of Mie resonances supported by an isolated nanoparticle are not sufficient for realizing strong light-matter interaction. Here, we propose the use of dielectric-metal hybrid nanocavities composed of Si nanoparticles and silicon nitride/silver (Si3N4/Ag) heterostructures to improve light-matter interaction. First, we demonstrate that the nonlinear optical absorption of the Si nanoparticle in a Si/Si3N4/Ag hybrid nanocavity can be greatly enhanced at the magnetic dipole resonance. The Si/Si3N4/Ag nanocavity exhibits luminescence burst at substantially lower excitation energy (∼20.5 pJ) compared to a Si nanoparticle placed on a silica substrate (∼51.3 pJ). The luminescence intensity is also enhanced by an order of magnitude. Second, we show that strong exciton-photon coupling can be realized when a tungsten disulfide (WS2) monolayer is inserted into a Si/Si3N4/Ag nanocavity. When such a system is excited by using s-polarized light, the optical resonance supported by the nanocavity can be continuously tuned to sweep across the two exciton resonances of the WS2 monolayer by simply varying the incident angle. As a result, Rabi splitting energies as large as ∼146.4 meV and ∼110 meV are observed at the A- and B-exciton resonances of the WS2 monolayer, satisfying the criterion for strong exciton-photon coupling. The proposed nanocavities provide, to our knowledge, a new platform for enhancing light-matter interaction in multiple scenarios and imply potential applications in constructing nanoscale photonic devices.

Structural colors have always attracted much attention due to important applications in display devices, imaging security certification, optical data storage, and so on. The brightness of structure colors, as the carrier of chiaroscuro information, is the key to making images appear stronger in the spatial and three-dimensional sense. However, relatively little work has been done on the control of the color brightness, and the reported structures are complex and difficult to fabricate. Here, we demonstrate a low-aspect-ratio anisotropic metasurface consisting of a PMMA film patterned by arrays of elliptical-shaped holes clamped by two thin aluminum films. By utilizing localized surface plasmon resonances, we realize a three-dimensional (3D) HSB (hue, saturation, and brightness) structure color with independent brightness control and enhance the cross-polarization reflection, covering approximately 120% of the sRGB color gamut. It is shown that the ratio of the major and minor axes leads to the independent control of brightness of the structural colors. The nanoprinting of HSB images with smooth brightness transitions is demonstrated through elaborate design of the metasurface geometry parameters and CMOS-compatible micro–nano fabrication process. Our findings will facilitate the broad range of 3D nanoprinting and modern advanced display applications.

Phase change material is promising for a color-changing device owing to its substantial optical contrast between amorphous and crystalline states. However, current phase change material, such as Ge2Sb2Te5 thin film, has restrained the color-changing performance owing to its high optical absorption. Sb2S3 thin film, exhibiting large refractive index difference and low absorption between crystalline and amorphous states, is a promising alternative. Here, a color device with Al/Sb2S3/SiO2-stacking layer is prepared, and high-resolution, multilevel, reversible color printing is realized. Wide color gamut is successfully obtained by controlling either the Sb2S3 thickness or its crystallization degree. Furthermore, the proposed color device can be patterned by direct laser writing and erased by a picosecond laser system, possessing good reversible cycling stability. High-resolution pixel higher than 42,000 DPI is further implemented. Moreover, a flexible color device is also fabricated, which possesses superior angular insensitivity from 10° to 60° and is hardly faded after bending and folding 10 times. This work may have wide applications in the fields of color printing, flexible displays, wearable optoelectronic devices, and so forth.

Chaotic dynamics generated by vertical-cavity surface-emitting lasers (VCSELs) has stimulated a variety of applications in secure communication, random key distribution, and chaotic radar for its desirable characteristics. The application of machine learning has made great progress in the prediction of chaotic dynamics. However, the performance is constrained by the training datasets, tedious hyper-parameter optimization, and processing speed. Herein, we propose a heterogeneous forecasting scheme for chaotic dynamics in VCSELs with knowledge-based photonic reservoir computing. An additional imperfect physical model of a VCSEL is introduced into photonic reservoir computing to mitigate the deficiency of the purely data-based approach, which yields improved processing speed, increased accuracy, simplified parameter optimization, and reduced training data size. It is demonstrated that the performance of our proposed scheme is robust to the deficiency of the physical model. Moreover, we elucidate that the performance of knowledge-based photonic reservoir computing will fluctuate with the complexity of chaotic dynamics. Finally, the generality of our results is validated experimentally in parameter spaces of feedback strength and injection strength of reservoir computing. The proposed approach suggests new insights into the prediction of chaotic dynamics of semiconductor lasers.

With the rapid spread of Internet technology, e-commerce is gradually becoming an integral part of the modern business models. The e-commerce transactions should obey integrity, authentication, nonrepudiation, traceability, and impartiality. Here, we propose and demonstrate a complete continuous-variable quantum e-commerce scheme, which involves subscription, payment, transport, and reception protocols among five parties. To this end, a simple, efficient quantum digital payment scheme is proposed. Furthermore, we streamline the entire e-commerce process by eliminating the private amplification step in the pre-distribution of keys. We achieve a contract signing rate of 1.51×103 times per second for a 33 kilobits contract, and a payment rate of 2.70×103 times per second over 80 km of single-mode fiber. Our results can support 411 times complete transactions per second, including three contract signings and two separate monetary payments. The proposed scheme takes into account the compatibility with existing e-commerce platforms to ensure a smooth transition and provides a practical solution for quantum e-commerce at metropolitan distances.

We present hybrid tunable lasers at 2.0-μm wavelength, seamlessly integrated within silicon photonic circuits for advanced biomedical applications. Leveraging III/V semiconductor materials for gain and silicon ring resonators for tuning, the laser achieves a tuning range of 25 nm, precise adjustments below 0.1 nm, and a side-mode suppression ratio of 40 dB. This advancement contributes to the progress in photonic integrated circuits beyond the telecommunication wavelength range, offering scalable and cost-effective solutions for enhanced spectroscopic systems within the 2.0-μm wavelength range.

We demonstrate a dual-wavelength optical frequency standard based on the dual-optical-transition modulation transfer spectroscopy (DOT-MTS) between different quantum transitions of the rubidium D1 (795 nm) and D2 (780 nm) lines. In a single rubidium atomic ensemble, modulation frequency sidebands from the 780 nm pump beam are simultaneously transferred to both the 780 and 795 nm probe lasers. The DOT-MTS enables the simultaneous stabilization of 780 and 795 nm lasers on a single vapor cell. Both lasers exhibit a frequency instability in the low 10-14 range at 1 s of averaging, as estimated from the residual error signal. A theoretical model is developed based on the V-type atomic level structure to illustrate the dual-wavelength spectroscopy. This approach can be extended to develop a multi-wavelength optical frequency standard within a single atomic ensemble, broadening its applicability in fields such as precision metrology, Rydberg atoms, wavelength standards, optical networks, and beyond.

The ultralow limit of detection (LoD) and exceptional sensitivity of biosensors are a significant challenge currently faced in the field. To address this challenge, this work proposes a highly sensitive laser ring cavity biosensor capable of detecting low concentrations of des-γ-carboxy prothrombin (DCP). A tapered W-shaped fiber probe based on multi-mode fiber (MMF)-multi-core fiber (MCF)-MMF is developed to excite strong evanescent waves (EWs). By immobilizing gold nanorods (GNRs) on the fiber probe, localized surface plasmon resonance (LSPR) is generated at the near infrared wavelength to further enhance the sensitivity of the fiber probe. Moreover, an erbium-doped fiber (EDF) ring laser with a narrow full width at half maximum (FWHM) of 0.11 nm is employed as a light source. The spectrum with narrow FWHM has been demonstrated to obtain lower LoD. Compared to the ASE light source, the LoD of the laser ring cavity can be reduced by an order of magnitude. The developed biosensor is capable of detecting DCP within a concentration range of 0–1000 ng/mL, and the detection sensitivity of 0.265 nm/lg(ng/mL) and the LoD of 367.6 pg/mL are obtained. In addition, the proposed laser ring cavity biosensor demonstrates good specificity, reproducibility, and repeatability by corresponding tests. The study results indicate that the proposed biosensor has potential in the detection of hepatocellular carcinoma markers.

Transition metal dichalcogenides (TMDs) hold great promise as a platform for optoelectronic devices, thanks to their exceptional optical characteristics. Nonetheless, their intrinsic low radiative recombination rate results in diminished efficiency in light emission and absorption. Here, we report photoluminescence (PL) enhancement of monolayer MoS2 through the utilization of full-wavelength (λ) nanodipole antennas. It is revealed that λ antennas demonstrate more pronounced PL enhancement and enhanced directivity compared to the previously examined half-wavelength (λ/2) antennas, relaxing the fabrication difficulty for ultra-narrow antenna gap configurations. By geometry and dimension optimization, a maximum PL enhancement of 17-fold is achieved. Furthermore, dual-polarized cross-shaped nanoantennas are developed to mitigate the reliance of the nanoantenna’s performance on the polarization state. Our method charts an effective path for amplifying the PL intensity of monolayer TMDs, thereby accelerating their integration into high-performance optoelectronic technologies.

Combining high peak power and high average power has long been a key challenge of ultrafast laser technology, crucial for applications such as laser-plasma acceleration and strong-field physics. A promising solution lies in post-compressed ytterbium lasers, but scaling these to high pulse energies presents a major bottleneck. Post-compression techniques, particularly Herriott-type multi-pass cells (MPCs), have enabled large peak power boosts at high average powers but their pulse energy acceptance reaches practical limits defined by setup size and coating damage threshold. In this work, we address this challenge and demonstrate, to our knowledge, a novel type of compact, energy-scalable MPC (CMPC). By employing a novel MPC configuration and folding the beam path, the CMPC introduces a new degree of freedom for downsizing the setup length, enabling compact setups even for large pulse energies. We experimentally and numerically verify the CMPC approach, demonstrating post-compression of 8 mJ pulses from 1 ps down to 51 fs in atmospheric air using a cell roughly 45 cm in length at low fluence values. Additionally, we discuss the potential for energy scaling up to 200 mJ with a setup size reaching 2.5 m. Our work presents a new approach to high-energy post-compression, with up-scaling potential far beyond the demonstrated parameters. This opens new routes for achieving the high peak and average powers necessary for demanding applications of ultrafast lasers.