Optics express最新文献

The stability, linewidth, and noise of multi-wavelength laser sources are regarded as critical factors determining detection accuracy and sensitivity. A narrow-linewidth and switchable four-wavelength fiber laser is proposed and experimentally demonstrated. The laser is constructed with a triple-coupler dual-ring (TCDR) compound cavity filter and a 30 m self-injection locking polarization-maintaining delay fiber. Two cascaded polarization-maintaining fiber Bragg gratings (PM-FBGs) define four wavelength channels. Flexible switching among four single- and six dual-wavelength lasing states is achieved through polarization hole burning induced by intracavity polarization control. The TCDR filter is constructed from three 2 × 2 optical couplers. It effectively suppresses dense longitudinal modes and ensures stable single-longitudinal-mode operation. Optical signal-to-noise ratios (OSNRs) above 61 dB are obtained for all single-wavelength outputs, and values above 58 dB are achieved for dual-wavelength states. Maximum wavelength drift is restricted to 0.08 nm, and power fluctuation remains within 0.83 dB. Through self-injection locking with a 30 m polarization-maintaining delay fiber, the linewidth is compressed to below 585 Hz, accompanied by a 4.5 kHz reduction in relaxation oscillation frequency. Furthermore, each single-wavelength output exhibits a high degree of polarization above 97%, attributed to the polarization-selective nature of the PM-FBGs. This integrated design of multi-wavelength switching, ultranarrow linewidth, high OSNR, and polarization purity makes the laser highly suitable for advanced applications such as coherent LIDAR, high-resolution sensing, and precision metrology.

We present a long-range free-space photothermal spectroscopy (PTS) system based on a coherent light Fabry-Pérot (FP) demodulator employing a broadband mode-locked pulse laser with high coherence. By combining fast Fourier transform and Buneman frequency estimation, the PTS system achieves a sub-nanometer optical path difference of the FP interferometer with a refresh rate of 17 kHz, which can enable real-time sensing of photothermal-induced refractive index variations over an extended optical path of 1.8 m. The high-resolution demodulation of the FP interferometer makes it possible to detect trace acetylene with a minimum detection limit (MDL) of 3.6 ppm, corresponding to a normalized noise-equivalent absorption (NNEA) coefficient of 4.1 × 10^-7cm^-1·W·Hz^-1/2. The proposed approach offers significant sensitivity improvement compared with conventional white-light demodulators and provides a promising platform for high-precision, long-path PTS in trace sensing.

Electronic dynamics at relativistic laser intensities have aroused extensive attention, and meanwhile, the enhancement of extreme-ultraviolet high-order harmonic generation (XUV-HHG) intensities has also been pursued. Here we propose, for the first time, a new scheme that involves the construction of a transient electrostatic field induced by electron nanobunches from relativistic intensity laser-irradiated double nanofoils, which then results in robust enhancement of XUV radiation in the transmitted direction, and experimentally demonstrate it. This scheme does not require purposely optimizing the laser contrast and pulse duration, and significant enhancement of harmonic radiation by more than one order of magnitude can be achieved as long as the laser is focused between the two foils. Our work offers novel insights into plasma-induced electronic dynamics at relativistic laser intensities and also proposes a robust scheme to realize significant enhancement of XUV-HHG at relativistic laser intensities, which promotes the application of XUV-HHG in atomic physics, ultrafast dynamics, and other fields.

Unseen hologram synthesis enables the generation of phase-only holograms (POHs) directly from user-specified instructions, eliminating reliance on amplitude inputs and enabling unprecedented creative flexibility for immersive mixed reality applications. However, existing non-end-to-end methods rely on amplitude-domain generative models trained on massive but physically inconsistent datasets, introducing phase cumulative errors that degrade hologram quality with noise and artifacts. Although end-to-end methods based on autoencoders avoid phase error accumulation, their entangled latent representations hinder the manipulation of holographic attributes. This paper proposes holo-LDM, an end-to-end conditional diffusion model for unseen hologram synthesis directly from user provided semantic and physical constraints with only 2 KB parameters. Physical model-driven complex-valued UNets are employed to generate speckle-suppressed holographic datasets. For precise holographic attribute control, cross-attention transformers dynamically align labels with holographic features during the denoising process, which enables the synthesis of novel holograms with user-specified attributes during inference. Simulation and optical experiments confirm that holo-LDM is capable of synthesizing high-quality holograms across diverse semantic categories with accurate control of diffraction depth. Compared to existing diffusion-based non-end-to-end baselines, holo-LDM achieves over 30% improvement in terms of Fréchet inception distance (FID), while reducing training costs by an order of magnitude.

Strong field enhancement supported by metasurfaces at resonance can be used to control and enhance the spontaneous emission rate of emitters. This is particularly relevant for emitters with comparatively low quantum yield such as germanium. Here, we investigate the µ-photoluminescence response obtained from a hybrid metasurface comprising a square lattice of Al/Si/Ge pillars. We explore how variations in excitation energy, excitation intensity and number of excited meta-atoms affect the spectral dependence of the photoluminescence signal and, in particular, the contribution of the metasurface to it. Our metasurface exhibits a magnetic dipole collective lattice resonance, whose contribution to the photoluminescence signal increases with increasing number of excited meta-atoms. Measuring only one metasurface under different illumination conditions can potentially be an alternative approach to probe the transition between finite-size effects and collective effects.

We report heterogeneously integrated Si/III-V two-ring Vernier lasers featuring a 10-nm divinylsiloxane-bis-benzocyclobutene (BCB) bonding layer, which is the thinnest to our knowledge. The fabricated laser device demonstrates a double-facet output power of 13.6 mW, a linewidth of 2.6 kHz, a free spectral range (FSR) of 40 nm, and a side mode suppression ratio (SMSR) of 46 dB. These values are comparable to those of a directly bonded Vernier laser structure, which is thermally ideal. The comparability is attributed to a small thermal impedance value of 45.1 K/W, which was experimentally measured with what we believe to be a new method developed for lasers with extensive passive sections. A laser model calibrated with experimental inputs predicts that the output power of a 10-nm BCB bonded Vernier laser with a 4-µm current aperture differs from that of a directly bonded one by less than 10% even beyond a thermal rollover. It is also anticipated that the 10-nm BCB bonded laser can emit a few mW even at an ambient temperature of 120 °C. Such a high-temperature operation capability is desirable for light detection and ranging (LiDAR) chip applications. The investigated 10-nm BCB bonding approach can be an attractive alternative for cases where a relaxed surface roughness condition is beneficial.

Modern industrial production demands high-precision and efficient full-field functional surface measurements. Multi-wavelength digital holography (MWDH) addresses these measurement needs and has been applied in various measurement scenarios. However, the measurement precision of MWDH for rough surfaces is still evaluated experimentally, lacking a comprehensive theoretical model for guidance. In this work, we propose an MWDH precision model focused on rough surfaces, considering both decorrelation noise and acquisition noise. Besides, the model provides a more meaningful assessment of full-field noise under spatial inhomogeneity scattering from rough surfaces. For the first time, we introduce the concept of coherent stray light noise, which is considered a component of acquisition noise in this study. Experiments performed on a rough surface validate the proposed model. Our model not only enables the assessment of measurement precision in MWDH systems, but also allows for a preliminary determination of the measurability of target objects.

Energy backflow is an intriguing counterintuitive phenomenon, which has been reported in the focal region of light beams with phase or polarization singularities. Although the scenarios involving vector vortex beams with both polarization and phase singularities have been discussed, the impact of the light beam's initial phase on energy backflow remains not fully clear. Here, we theoretically prove and numerically demonstrate that the longitudinal component of the Poynting vector in the focal plane is independent of the initial phase of incident light beams. We further reveal the general condition for the emergence of on-axis energy backflow near the focus of such light beams with arbitrary initial phase: specifically, the polarization order l and the phase topological charge m need to satisfy l ± m = 2. And we unveil the existing Poynting vector singularities associated with on-axis energy backflow. More remarkably, the exceptional cases are uncovered, where l = 1 and m = ±1. And we find that it is possible to construct on-axis energy backflow by appropriately modulating the amplitude of the incident light beam. Furthermore, we propose a general method to achieve a strong longitudinal electric field on the optical axis by utilizing light beams satisfying the condition with l ± m = 1. The results enrich the toolkit for constructing and modulating light fields as well as energy flow distributions in the focal region.

We demonstrate the design and experimental verification of a programmable bit array antenna with reconfigurable characteristics of the operating frequency, polarization state, and radiating direction. To be more specific, an annular ring-structured radiator is equipped with continuous frequency adjustment functionality through four strategically placed varactor diodes across an annular gap. Additionally, the antenna is fed through an asymmetrically reconfigurable printed Wilkinson power divider, incorporating a Schiffman phase shifter to switch two distinct circular polarizations, while being capable of prescribing desired phases for each programmable radiating element to facilitate the two-dimensional scanning. The theoretical framework of such a design is validated through the fabrication and testing of the array over the 1.4∼2.3 GHz continuous tuning range (48.6%), while four representative operating frequencies are demonstrated. The experimental results are in good agreement with the simulation outcomes, affirming the reliability of multiple parameter reconfigurable performances of the proposed programmable bit array antenna and thus should offer the enhanced flexibility and versatility in advanced modern communication systems.

Vortex beams carrying orbital angular momentum (OAM) increase the channel capacity of underwater wireless optical communication (UWOC) systems but are susceptible to oceanic turbulence (OT), resulting in the degradation of communication quality. Therefore, the correction of distorted vortex beams and the identification of OAM modes are crucial for UWOC. In this work, a joint distortion correction and OAM mode identification approach is proposed and experimentally verified based on a Siamese network (SN). The SN performs feature extraction and feature fusion on the phase screen and intensity pattern. In addition, a classification network is integrated into the SN framework, thereby enabling both mode identification and prediction of Zernike polynomial coefficients with a limited number of samples. The results show that the improved SN can quickly and accurately identify four OAM modes and predict the Zernike polynomial coefficients of four OT levels. The phase screen reconstructed with the predicted Zernike polynomial coefficients enables high-quality correction of the distorted vortex beam. The proposed SN-based vortex beam correction and identification exhibits robust generalization performance under small-sample conditions, opening a new path for UWOC.