Optics express最新文献

Orbital angular momentum (OAM) vortex waves have become a prominent topic in scientific research and engineering applications. With the developments of metasurface-based OAM generation and manipulation technologies, Huygens' metasurfaces demonstrate the advantages of low profile and simple structure. In this paper, we propose a broadband Huygens' metasurface capable of polarization-independent OAM-multiplexed beam deflections. Firstly, a highly efficient polarization-independent Huygens' meta-atom is designed, and then the dual-polarized 3-bit phase profiles are constructed to generate the polarization-independent OAM-multiplexed beams. On this basis, dual-polarized phase sequences are incorporated into the 3-bit phase profiles, enabling the broadband polarization-independent OAM-multiplexed dual beam deflections in two orthogonal planes. We fabricated and measured three metasurface samples, and the experimental results are consistent with the simulations, confirming the feasibility and practicality of the proposed method. The proposed metasurface operated at 8.5 GHz-11.5 GHz, achieving a 30% relative bandwidth and 14.8% aperture efficiency. We believe this design demonstrates promising potential for applications in multi-target wireless communications and wide-range radar detections.

Single-pass second-harmonic generation (SHG) of a phase-modulated fiber laser is an effective scheme for high-power, continuous-wave, narrow-linewidth visible laser generation. However, this approach encounters difficulties in improving conversion efficiency. In this paper, we demonstrate enhanced single-pass SHG conversion efficiency via four-wave-mixing (FWM) broadened fundamental lasers. By co-amplifying two phase-modulated seeds in an ytterbium-doped fiber amplifier, the cascaded FWM redistributes power into multimode spectra, enabling 1.52 times higher efficiency than that of conventional phase-modulated laser schemes in sum-frequency generation (SFG). A green laser up to 76.9 W at 531.5 nm is achieved with a conversion efficiency of 24.2% while maintaining relative intensity noise (RIN) below -120 dBc/Hz above 2 kHz. This approach provides a robust route to high-power and low-noise visible lasers with straightforward phase modulation.

The performance of the current high-speed optical transmission system could be limited by the bandwidth of optical transceivers. Linear equalization is a feasible way to mitigate the inter-symbol interference (ISI) caused by the bandwidth limitation, but it enhances high-frequency noise, thereby degrading receiver performance. One effective way to cope with noise enhancement is based on the noise-whitening approaches at either the transmitter side or receiver side. However, conventional noise whitening requires a maximum likelihood sequence estimation (MLSE) equalizer to correct the ISI introduced intentionally, while its computation complexity is beyond the power of cost-sensitive applications. In this paper, we propose a novel selective noise decorrelation (SND) equalizer positioned after the linear equalizer to correct most of the errors in a feedforward manner. By leveraging the noise patterns to predict the likelihood of symbol errors and applying a weighted average of neighboring noise for decorrelation only when it is necessary, the SND equalizer provides an alternative approach to mitigate the noise enhancement issue without complicated MLSE equalization or noise whitening. We demonstrate its capability through proof-of-concept experiments at various bandwidth limitation ratios. The proposed SND equalizer outperforms the feedforward equalizer as well as the decision feedback equalizer in all cases. Moreover, it achieves comparable performance as the MLSE-based approach with a much lower computational complexity. Based on analysis, the proposed SND equalizer needs a mere 6.25% of the PF-MLSE equalizer's computational load.

High-fidelity super-resolution (SR) imaging is critical for probing subcellular structures and dynamics. While current SR techniques often require complex hardware, SR optical fluctuation imaging (SOFI) enables rapid SR reconstruction on conventional wide-field microscopes by leveraging fluorescence blinking. However, higher-order SOFI suffers from structural artifacts and discontinuities due to statistical errors in cumulant estimation. We propose frequency separation correlation (FSC), a computational method that decomposes pixel-wise blinking signals into single-frequency components via Fourier analysis. By accumulating auto-correlation cumulant of these components while eliminating cross-frequency correlations, FSC enhances statistical precision. FSC-enhanced SOFI outperformed conventional SOFI, balanced SOFI (bSOFI), and super-resolution auto-correlation with two-step deconvolution (SACD) across simulated and experimental datasets. It maintained structural continuity under challenging conditions (e.g., dense labeling, weak blinking, short sequences). Using only 20 frames, FSC-enhanced bSOFI (fs-bSOFI) and fs-SACD achieved lateral resolutions of 96 nm and 92 nm, respectively, while preserving image fidelity. Large-field fs-SACD imaging of microtubule networks (166 × 166 µm²) was accomplished within ∼2 seconds. FSC-enhanced SOFI provides a robust tool for high-speed, high-fidelity SR imaging, particularly for live-cell applications.

In this paper, we present a method for reconstructing video from event data alone captured by an event camera. We employ point-spread-function engineering in the imaging optics to compress spatiotemporal information into each event. Dynamic scenes are reconstructed solely from the sparse, signed-polarity event data using a compressive sensing algorithm. We numerically validate the concept and characterize the video-imaging performance of the compressive event camera. This method enhances event-to-video reconstruction while preserving the advantages of event cameras-high speed, high dynamic range, and high energy efficiency.

With the growing demand for high-performance imaging, freeform optical elements are increasingly used in optical systems. The computer generated hologram (CGH) designed for null interferometric testing often spans large areas and exhibits complex, high-density fringe patterns. In this context, the trade-offs between encoding accuracy, computation workload, and data size have become key constraints on the efficient and widespread adoption of freeform optics. This paper proposes a CGH encoding method that efficiently infers the phase values at the majority of sampling points by leveraging the structural characteristics of fringe patterns and the spatial continuity of the fringe phase. Theoretical analysis demonstrates that, whereas conventional methods exhibit quadratic growth in the number of explicit points with increasing encoding resolution or region size, our method reduces this to linear growth. In a representative case involving a 94mm-diameter CGH designed for testing an off-axis Bi-conic Zernike freeform mirror, while maintaining an encoding error below λ/200, the proposed method reduces runtime to only 1.32 hours and data size to 0.496 GB, corresponding to reductions of approximately 107.92 times and 99 times over conventional methods, demonstrating the method's high computational efficiency and low storage demand. Furthermore, the CGH encoded is applied in interferometric testing. The accuracy and effectiveness of the proposed CGH encoding method were verified through theoretical error modeling and analysis of interferometric measurement data. These results highlight the method's favorable trade-off among encoding accuracy, computational workload, and storage demand. This work offers a practical solution for high-precision CGH encoding in freeform optics null testing.

Enhancing imaging resolution is a crucial point in structured illumination microscopy (SIM). However, the high-frequency structured light fields required for super-resolution imaging are prone to introducing frequency gaps during the process, leading to reconstruction artifacts. Simultaneously achieving high-resolution imaging and minimizing reconstruction artifacts in SIM remains a critical challenge. In this manuscript, we overcome this challenge by introducing a method that generates a tunable structured light field with high spatial frequencies. The optical field is the bulk plasmon polaritons (BPPs) generated by an integrated structure comprising a metal grating, a hyperbolic metamaterial (HMM), and a reverse Kretschmann (RK) configuration. Its spatial frequency can be tuned by adjusting the thickness of the nanocavity between the RK configuration and the HMM, enabling the extraction of sample frequency information across an exceptionally wide and continuous range, thereby suppressing artifacts arising from missing frequency information. The BPPs exhibit a maximum spatial frequency reaching up to 6.6 times that of the incident light. Therefore, the tunable BPPs based SIM (T-BPPSIM) achieves a resolution enhancement of 7.6-fold compared to conventional fluorescence microscopy. By further applying the fluorescence emission difference (FED) technique to the surface plasmon-coupled emission (SPCE) signals coupled out by the RK configuration, the resolution is enhanced to exceed 8-fold, achieving a resolution below 30 nm. This method provides a technical foundation for high-fidelity imaging of nanoscale at cell membrane interfaces.

Thermal conductivity (κ) of Y₂O₃ ceramics, Y₃Al₅O₁₂ (YAG) ceramics, Y₃Sc₂Al₃O₁₂ (YSAG) ceramics, Y₃Ga₂Al₃O₁₂ (YGAG) ceramics, and sapphire compared to YAG single crystal from 160 K to 773 K was studied. κ of undoped Y₂O₃ ceramics, undoped YAG single crystal, 1at.% YAG single crystal, undoped YAG ceramics, 1at.% Nd:YAG ceramics, 1at.% Nd:YSAG ceramics, 1at.% Nd:YGAG ceramics, a-cut sapphire, and c-cut sapphire at 298 K were 10.7 W/mK, 10.4 W/mK, 9.85 W/mK, 9.75 W/mK, 9.28 W/mK, 6.41 W/mK, 6.74 W/mK, 33.8 W/mK, and 35.9 W/mK, respectively. κ of Y₂O₃ ceramics was found to be inferior to YAG single crystal below 252 K. We also investigated the linear thermal expansion coefficient (α) of YSAG and sapphire compared to YAG. α of 1at.% YAG ceramics, 1at.% Nd:YSAG ceramics, sapphire along a-axis, and sapphire along c-axis were 6.18×10^-6 /K, 6.46×10^-6 /K, 5.00×10^-6 /K, and 5.79×10^-6 /K, respectively.

Plasmonic metasurfaces supporting multiple resonances are highly desirable for enhancing optical fields at distinct wavelengths. Here, we demonstrate doubly stacked nanogap arrays that exhibit dual Fabry-Pérot resonances of the gap plasmons. Numerical simulations reveal that both resonances appear at different wavelengths due to the lateral length difference between the upper and lower nanogaps. Furthermore, we fabricated stacked nanogap arrays by alternating metal-insulator deposition, electron beam (e-beam) lithography, and ion milling. Due to the dual plasmon resonance, the photoluminescence spectra of spin-coated dyes (R6G and IR-820) show distinct modifications near the two reflection dips. These results highlight stacked nanogaps as a promising platform for co-localized multicolor dye excitation and multispectral photoluminescence engineering, with potential applications in multi-wavelength light sources and multicolor displays.

We systematically investigate the existence, stability, and propagation dynamics of multipole-mode (necklace-shaped) solitons in the two-dimensional model of an optical medium with the defocusing saturable nonlinearity and an annular potential trough. Various families of stable multipole solitons trapped in the trough, from dipole, quadrupole, and octupole ones to multi-lobe complexes, are found. The existence domain remains invariant with the increase of the potential's depth. Solitons with a large number N of lobes are stable in a wide parameter region, up to N = 48 and even farther. Actually, stable multipole solitons of an arbitrarily high order N can be found, provided that the trough's radius is big enough. The power of stable multipoles is essentially larger in comparison to previously studied models. It is demonstrated analytically and numerically that the application of a phase torque initiates stable rotation of the multipole complexes. Thus, we put forward an effective scheme for the stabilization of multipole solitons with an arbitrary high number of lobes, including rotating ones, which offers new possibilities for manipulating complex light beams.