Optics letters最新文献

Fourier ptychography microscopy (FPM) is a powerful computational imaging technique; however, its performance is limited by the stringent matched-illumination requirement, especially when using high-numerical-aperture (NA) objective lenses. To address this challenge, we propose a phase-contrast modulation-based FPM (PCM-FPM). By introducing a 0.5π phase shift to the non-scattered components of object waves generated under unmatched illuminations from six LEDs, PCM-FPM encodes otherwise undetectable low-frequency phase information into measurable intensity variations. Then, a novel iterative reconstruction algorithm, to our knowledge, processes these six phase-contrast intensity images to recover full-spectrum phase details. Both simulations and experimental results, acquired with an illumination NA of 0.7 and a 100×/1.44 objective lens (OL), demonstrate the superior phase imaging performance of PCM-FPM. This approach represents a significant advancement in FPM with strong potential for broader application.

Solar Ground-Layer Adaptive Optics (GLAO) is the preferred solution for achieving wide-field, high-resolution imaging in ground-based solar telescopes. However, current GLAO guide-star (GS) arrangement optimization relies on extensive iterative simulations, which are time-consuming and resource-intensive, and do not provide a prior reference for system design. To address this issue, an analysis of GLAO wavefront sensing in the spatial frequency is conducted. A filter is constructed to optimize the detection of conformal aberrations, leading to the development of an analytical framework for GS arrangement optimization. This framework provides accurate prior optimization results for any GS configuration. The correctness of the theory is validated through comparison with Monte Carlo simulations, and the practical utility of this method in optimizing solar GLAO system performance is demonstrated.

This Letter demonstrates that non-paraxial 2D TE-polarized light fields form 2D optical vortices near intensity zeros, with the amplitude having the form x+iz, where x and z are the transverse and longitudinal Cartesian coordinates. Near the intensity zeros, the longitudinal projections of the wave vector have gigantic values of both signs. Negative values of the longitudinal projections of the wave vectors indicate that a reverse energy flow occurs near the intensity zeros. Around the intensity zeros, the energy flow circulates both clockwise (if the topological charge of the optical vortex is -1) and counterclockwise (if the topological charge of the optical vortex is +1). The gigantic values of the wave vectors near the intensity zeros indicate that the wavelength of the light is small, and therefore the phase velocity of rotation of light around the intensity zero is small, compared to the speed of light in a vacuum. A giant wave vector, energy flow circulation, and energy return flow are formed in a substantial subwavelength region around intensity zeros of fractions of a wavelength in size, demonstrating the presence of superoscillations.

Fiber-wireless systems offer a promising way to enhance high-capacity wireless services and extend transmission distances by leveraging the low loss and broad bandwidth of optical fiber. They depend on efficient electro-optic receivers in millimeter-wave (mmWave) and terahertz (THz) fiber-wireless systems to convert high-frequency wireless signals into the optical domain. However, traditional down-conversion relies on real-valued IF processing using a balanced mixer, which can generate conjugate spectra that appear as image interference during optical modulation. To address this, we introduce a hybrid electro-optic receiver design that directly connects an electrical I/Q mixer with an optical I/Q modulator, enabling direct electro-optic conversion of complex IF signals. By preserving the inherent I/Q orthogonality, the proposed approach allows optical single-sideband modulation without optical filtering and avoids image components associated with conjugate spectra. Building on this innovative hybrid optoelectronic communication system, we have successfully demonstrated the transmission of 16 Gbaud QPSK signals over a 2-m wireless link and a 5-kilometer single-mode fiber at 142.8 GHz with error-free performance.

In this work, we report our experimental studies on the start time of a passively mode-locked soliton fiber laser based on nonlinear polarization rotation (NPR), with a focus on the impact of different operation states. We found that given the same cavity configuration, the statistical distributions of the start time are strongly correlated with the operation states determined by the pump power and the NPR-induced loss of the laser. While the start time for the single-pulse state exhibits a long-tail distribution, for the multi-pulse state a much faster start time is observed at the same pump level. We also find that the start-time distribution of the multi-pulse state is dramatically sensitive to both the laser pump power and the NPR-induced loss. Numerical simulations have been performed to reproduce these statistical features, revealing their delicate dependence upon the intra-cavity balance between gain and loss. Our work sheds some light on the statistical self-starting dynamics of the mode-locked fiber laser and may provide valuable guidance to practical laser design.

Elliptically or circularly polarized terahertz (THz) radiation plays a crucial role in advanced applications such as chiral spectroscopy, spintronics, and polarization-sensitive imaging and communication. Here, we demonstrate an efficient method for generating elliptically polarized THz radiation from a single-color laser-driven water column. By tilting the water column along the laser propagation direction and displacing the laser axis from the column center, both vertical and horizontal THz components are produced with a nonzero relative phase. As a result, elliptically polarized THz radiation with an ellipticity up to 0.75±0.02 is achieved in our experiment. Furthermore, the ellipticity and handedness of the emitted THz waves can be flexibly controlled by adjusting the tilt angle and the horizontal offset of the water column. This work provides a simple and robust scheme for controllable generation of elliptically polarized THz radiation, opening new opportunities for THz-based spectroscopy, imaging, and information technologies.

Rapid and reliable target classification is essential in resource-constrained vision applications, yet conventional imaging-based approaches suffer from severe performance degradation under optical aberrations, defocus, and motion blur. Single-pixel detection has recently emerged as a promising solution for low-cost and high-speed sensing, but existing methods mainly address motion-induced degradation and still rely on image reconstruction or computationally intensive recognition pipelines. In this Letter, we present a fast and blur-resilient classification framework that directly extracts blur-invariant features from single-pixel measurements using only seven fixed DMD modulation masks. The proposed system bypasses the traditional "image-then-recognize" paradigm and instead enables a direct "measure-to-recognize" workflow without the need for image processing or neural network training. Extensive simulations and experiments demonstrate 98.96% recognition accuracy on the test dataset at an update rate of 2.551 kHz under various degraded imaging conditions. The proposed framework provides a simple and efficient solution for blur-robust recognition and opens a new, to the best of our knowledge, avenue for high-speed optical intelligence in challenging imaging environments.

The integration of low-loss phase-change materials (PCMs) with silicon photonics has attracted increasing interest for reconfigurable and non-volatile photonic devices. However, most existing approaches selectively pattern PCM regions through additional lithography and lift-off processes. Here, we propose a whole-circuit integration approach to simplify the fabrication of PCM-based silicon photonic devices, where a PCM thin film is deposited on a silicon-on-insulator (SOI) wafer and co-etched with a silicon layer. Using low-loss Sb₂Se₃, the additional propagation loss is limited to ∼0.78 dB/mm. Meanwhile, whole-circuit integration provides a modulation region far exceeding selective integration. A full 2π multi-level phase modulation is experimentally demonstrated in an unbalanced Mach-Zehnder interferometer (UMZI). These results establish whole-circuit PCM integration as a scalable and foundry-compatible route toward programmable silicon photonic circuits.

The elasticity of luminal tissues is closely associated with disease progression and functional status. Endoscopic optical coherence elastography (OCE) has emerged as a promising technique for assessing the mechanical properties of luminal tissues. However, previous endoscopic OCE approaches typically measure elasticity along only a single direction-either laterally or in depth-thereby potentially leading to an inaccurate estimation of anisotropic tissue mechanics. In this study, we propose a forward-scanning endoscopic OCE method that enables quantitative measurement of tissue elasticity in both the lateral and depth directions, allowing direct characterization of anisotropic mechanical properties in luminal tissues. An air-pulse excitation was applied to generate Rayleigh waves and longitudinal shear waves in agar phantoms and ex vivo gastric tissues. Elastic wave propagation was detected using phase-resolved Doppler optical coherence tomography. Experimental results demonstrate that the proposed method can quantitatively assess anisotropic elasticity with a forward-viewing configuration, highlighting its potential for clinical diagnosis and biomechanical characterization of luminal tissues.

This paper proposes a circularly polarized (CP) metasurface antenna array integrating absorbers with polarization conversion metasurfaces (PCMs). By synergistically deploying PCM units and absorber units, the antenna array combines the scattering control properties of PCM units with the electromagnetic energy absorption characteristics of absorber units and ultimately achieves broadband radar cross section (RCS) reduction. Simulation results indicate that the array exhibits an impedance bandwidth of 12% (11.8-13.3 GHz), a 3 dB axial ratio (AR) bandwidth of 12.9% (11.78-13.4 GHz), and a 3 dB gain bandwidth of 9.7% (11.64-13 GHz). Within the wideband range of 10.2-20.9 GHz (68.8%), the array achieves 10 dB RCS reduction both out-of-band and in-band, with a maximum reduction of 33.2 dB. A prototype of the antenna array was fabricated and tested, with measured results showing good agreement with simulations, validating the design effectiveness.