Optics express最新文献

Photonic generation of broadband linearly frequency modulated microwave waveforms based on ultra-short optical feedback in an optically injected semiconductor laser is proposed and numerically demonstrated. The optical injection is employed to induce period-one (P1) oscillation in the semiconductor laser for photonic microwave generation. An ultrashort feedback is introduced to further shift the laser's cavity-resonance frequency, enhancing the generated microwave frequency. By properly modulating the feedback light, the cavity-resonance frequency can be continuously shifted with the variation of the feedback strength, giving rise to a linearly frequency-modulated microwave signal. Because the injection strength remains constant, the proposed approach bypasses the limitations imposed by injection-locking and achieves more than 60 GHz of linearly frequency modulated microwave bandwidth. In addition, the microwave-comb contrast can be further optimized using a weaker long feedback loop whose time delay is equal to the modulation period of the ultrashort feedback. This approach provides a compact and flexible route for high-bandwidth photonic linearly frequency-modulated microwave signal generation.

We present a quantitative framework for inducing optical transparency in biological tissue samples by utilizing an absorbing dye to modulate the refractive index. Ou et al. found that loading a strongly absorbing dye into biological tissue enhances transparency via refractive-index modulation at wavelengths that are off-resonance to the dye's absorption peak [Science385, 6869 (2024)10.1126/science.adm6869]. In this study, we designed an optical platform that enables a precisely controlled manifold of the tissue thickness for repeatable transmission measurements. Chicken breast samples soaked in tartrazine-water solutions for a range of concentrations (1-400 mM) exhibited concentration- and thickness-dependent transparency enhancements. A threshold concentration (∼100 mM for thin and ∼400 mM for thick tissues) marked the transition from reduced to enhanced transmission, with enhancement factors of up to 26-fold when chicken breast tissue was soaked in a 200 mM tartrazine solution. These results agree with the Kramers-Kronig dispersion model, linking the narrow-band absorption peak of tartrazine at 428 nm with refractive-index modulation and scattering suppression in the near-IR region. Using our optical platform, we can determine the dye loading required to obtain a specific level of optical transparency for a given thickness of tissue sample.

Valley photonic crystals (VPCs) hold significant potential for electromagnetic (EM) device applications; however, their fixed structural parameters restrict practical versatility, highlighting a critical need for dynamic control. This research investigates a tunable valley topological photonic crystal (TPC) integrated with liquid crystals (LCs). By electrically modulating the permittivity of the LCs via applied bias voltages, we realize frequency-selective topological edge states (TESs) that exhibit robust and chiral propagation characteristics. Furthermore, by analyzing the correlation between the propagation directionality and the Stokes parameters of the eigenmodes, the excitation position of the chiral source is optimized to achieve polarization-directed chiral propagation. This approach demonstrates an electrically tunable TPC device, presenting an efficient and versatile strategy for active EM manipulation and polarization control in prospective topological photonic systems.

We propose an underwater multidimensional metrology approach in degraded environments utilizing augmented reality devices. The approach uses a risk-aware next-best-view (NBV) framework for metrology in degraded visual environments, introducing a conditional value-at-risk (CVaR) objective to guide viewpoint selection. Using anisotropy-aware geodesic metrics, local sensitivities, and a CVaR optimization, the approach prioritizes views that reduce worst-case geodesic-length uncertainty. We validated the performance of the proposed system experimentally on turbid scenes with augmented reality device imagery and five-dimensional WaterSplat reconstructions. The results across increasing turbidity demonstrate that CVaR achieves 2 - 3 × greater median error reduction compared to entropy-based NBV selection. We further conduct controlled synthetic experiments to analyze asymptotic error plateaus. To the best of our knowledge, this is the first report on an augmented reality-based NBV approach aimed at improving metrology in turbid environments.

Levitated optomechanics is opening new opportunities for quantum measurement in mesoscopic systems and for understanding the transition between quantum and classical mechanics. But loading microparticles into optical traps for measurements in vacuum remains an obstacle to the development of the field, in part because the process of launching particles so that they can be efficiently trapped remains poorly understood. We measure the dynamics of particle motion from vibrational excitation and launch from a surface to trapping in air. We demonstrate the direction of launch from a resonantly vibrating glass coverslip to be highly anisotropic and the measured escape velocity of tens to hundreds of millimeters per second to be insensitive to the amplitude of vibrational excitation. For a single particle launched repeatedly, escape velocities less than 50 mm per second are trapped with the highest probability. Trajectories from the launch point to the trap are found to follow a roughly two-step process in air: rapid deceleration due to drag, followed by drift into the trapping region that is accurately modeled by the Stokes-Einstein relation. These results illuminate the launch process in air, supporting the development of controlled launching of microparticles to enable application in a vacuum. This also enables selecting particles for trapping to optimize characteristics such as shape or Mie spectra, as well as repeated measurement of single particles to ensure reproducibility.

We propose and experimentally demonstrate a fully planar high-order frequency selective surface (FSS) based on multimode resonators (MMRs) with a quasi-elliptic bandpass response characterized by finite-frequency transmission zeros near the passband edges. In our design, these TZs are realized by implementing cross-coupling paths synthesized and guided by a coupling-matrix formulation. The proposed unit cell adopts a resonator-dual-mode-resonator configuration, functioning as a high-order filter low profile, and high selectivity. Coupling-matrix theory is further employed to elucidate the operating mechanism and to analyze the transmission and reflection characteristics, indicating that the filtering performance can be improved by increasing the resonator order and the number of coupling paths. A planar prototype is fabricated and measured, exhibiting four transmission poles and two transmission zeros in good agreement with simulations. The structure achieves a 3-dB fractional bandwidth (FBW) of 11.5% with an overall thickness of only 0.14λ₀, while maintaining low insertion loss and enabling simple, low-cost fabrication.

Mueller polarimetry is a powerful technique with broad applications in astronomy, remote sensing, advanced material analysis, and biomedical imaging. However, instrumental constraints frequently restrict the measurement to an incomplete Mueller matrix limited to its upper-left 3×3 submatrix. Simply padding the missing entries with zeros to form a 4×4 matrix can produce physically inconsistent results, for both nondepolarizing and depolarizing systems. To address this issue, we present a systematic procedure to complete 3×3 measured Mueller matrices into physically consistent 4×4 matrices. The method relies on the covariance matrix formalism and selects, among the infinitely many admissible completions, the one with maximal polarimetric purity. This criterion ensures that the synthesized matrix corresponds to the least random (most deterministic) two-component model compatible with the measurement. The procedure is fully general and can be applied to any 3×3 partial Mueller polarimetric data, providing a reliable and physically grounded reconstruction tool for polarimetric imaging and materials characterization.

Single-pixel imaging uses a single-pixel detector and sequential structured illumination to reconstruct images, offering remarkable flexibility across spectral bands. A longstanding challenge is that object or platform motion during acquisition is traditionally regarded as a source of blurring and degradation. Here, we present a paradigm in which object motion is reinterpreted as a beneficial source of sub-pixel sampling diversity rather than a detriment. By accurately tracking translational motion-accomplished via geometric moment illumination patterns fused with Hadamard patterns-we encode the known motion into the SPI forward model as structured perturbations. This approach converts motion from a blurring nuisance into a valuable imaging resource, effectively increasing the sampling density beyond the native grid. Incorporating the motion information directly into the inverse problem, we demonstrate that an enhanced-resolved reconstruction of the scene becomes achievable. The resulting linear measurement system, solved via total variation minimization, yields finer image details than SPI reconstructions acquired with a stationary target. Our work suggests that motion in SPI, far from being merely something to mitigate, can be harnessed to fundamentally improve SPI resolution and fidelity in dynamic scenes.

We propose III-V/Si hybrid plasmonic waveguide photodetector incorporating an InGaAs membrane. We confirmed that Ni-InGaAs alloy functions effectively as an electrode for a plasmonic waveguide. Utilizing Ni-InGaAs alloy enabled the integration of plasmonic waveguide photodetectors into the Si photonics platform through a simplified fabrication process. We achieved a responsivity of 0.13 A/W at 1 V with a dark current of 400 nA and confirmed a 32.1 Gbit/s clear eye diagram, demonstrating the potential for high speed InGaAs plasmonic photodetector in Si photonics.

Absorption imaging is a well-established method for determining both the atom number and spatial distribution of atomic ensembles, traditionally limited to a single focal plane and a fixed depth of field. However, as atom optics experiments grow more complex, atomic clouds can exceed the depth of field or leave the focal plane, as seen in large atomic arrays or bubble Bose-Einstein condensates (BECs). Here, we present an absorption imaging system that allows for tuning the object distance of 88.9 mm by ±5 mm and the depth of field from 26 µm to 203 µm. We determine performance metrics relevant for atomic experiments, such as the resolution and the optical distortion.