Optics express最新文献

Deep-subwavelength, dilute, weakly nonlinear dielectric composites are widely assumed to obey the nonlinear Maxwell-Garnett effective medium theory (NMGT). Here, we demonstrate that evanescent fields can cause NMGT breakdown at deep-subwavelength scales. We show that strong evanescent fields near linear dielectric components, even at λ₀/100 scale, create local optical hotspots and zero-field regions. When nonlinear components are positioned within these regions, the composite's nonlinear response becomes highly sensitive to component placement, a behavior that conventional NMGT fails to capture due to its averaging approximation. We overcome this limitation by developing a semi-analytic corrected NMGT that incorporates evanescent-field effects in dilute, weakly nonlinear composites. By harnessing these evanescent fields, we further demonstrate a nonlinear quenching effect and design a metamaterial with extreme nonlinear anisotropy. Our findings unveil the mechanisms underlying NMGT breakdown at deep-subwavelength scales and enable new strategies for nonlinear optical engineering.

To overcome the insufficient long-term stability of conventional Raman lasers, we demonstrate a single-frequency diamond Raman laser enabled by a pump-wavelength locking strategy. A three-mirror V-shaped cavity pumped by a 1064 nm fiber laser (6 kHz linewidth) provides single-longitudinal-mode (SLM) output at 1240 nm using Pound-Drever-Hall (PDH) stabilization. We further find that eliminating active temperature control of the diamond crystal suppresses rapid thermal perturbations and improves short-term stability. To compensate thermally induced slow cavity-length drifts, we implement a dual-loop feedback architecture that employs a fast PID loop acting on the pump wavelength and a slow PID loop driving a cavity piezoelectric transducer (PZT). Specifically, the fast loop tunes the pump wavelength via laser-current modulation, while the slow loop stabilizes the cavity length by regulating the PZT voltage. With 22 W pump power, the system produces 2.5 W SLM output with a linewidth of ∼2.9 kHz. The locked Raman laser exhibits an output power instability below 1.59% and a wavelength drift below 87 MHz, demonstrating markedly improved long-term operational stability. Unlike mainstream cavity-length locking techniques, our approach exploits the PDH error signal to directly lock the pump wavelength, providing a high-performance and wavelength-scalable route to highly stable single-frequency laser sources.

This work presents a framework for modeling, measuring, and correcting position-dependent pupil aberrations in Fourier holography. Aberrations are characterized by six coefficients: four Seidel terms, tip, and tilt. Two efficient diffraction integral approximations are developed: a series expansion for defocus-like aberrations and a patch-based method for the general case. The coefficients are estimated by scanning over a range of values to optimize correction on a grid of target markers. Experiments on a compact Fourier holographic projector demonstrate substantial improvements in image sharpness across the entire field of view.

Single optical detection methods alone are insufficient to meet the requirements for detecting Jupiter's high-order oscillation modes. In this paper, we present an interferometric polarization spectral imager together with a systematic design methodology that combines material property databases, fringe visibility functions, and phase sensitivity modeling. This approach ensures optical path difference stability across a wide temperature range and optimizes system parameters through global optimization techniques. A prototype instrument has been designed and developed, capable of stably outputting four orthogonal phase images to suppress photometric variations on Jupiter's surface. Laboratory tests confirm the predicted phase sensitivity and validate the calibration procedure, while initial field observations with a 1.6-m telescope demonstrate the feasibility of the end-to-end phase demodulation and velocity retrieval procedure. Beyond planetary seismology, the proposed methodology provides a generalizable framework for designing interferometric velocimetry instruments with high sensitivity and robustness.

Vortex beams have attracted considerable interest due to their compatibility with orbital angular momentum (OAM) modes. Based on an OAM mode decomposition approach, this study systematically investigates the mode composition of Laguerre-Gaussian (LG) and perfect Laguerre-Gaussian (PLG) beams with lateral displacement. It is demonstrated that a laterally displaced beam relative to the detection axis can be described as a linear superposition of multiple coaxial beams. The lateral displacement broadens the topological charge (TC) spectrum. Notably, by modulating the radial index of the beam, directed TC transfer in the spectrum can be achieved. This behavior is confirmed in both single-mode and dual-mode LG beams. Furthermore, in specific superposed beam structures, the adjacent modes in the TC spectrum exhibit a constant spacing of 2, revealing a unique mode distribution feature. For comparison purposes, PLG beams exhibit significantly higher sensitivity to lateral displacement, with their TC spectrum broadening more prominently and showing less controllable transfer behavior despite the advantage of constant transverse size. This work provides a novel strategy to address beam misalignment issues in optical detection and communication, holding significant potential for advanced practical applications of OAM-based technologies.

InGaN/GaN systems are commonly employed for designing near-ultraviolet (UV) light-emitting diodes (LEDs) due to their excellent quantum efficiency and tunable emission wavelengths. However, existing studies predominantly focus on the emission-related functionalities of near-UV LEDs, such as photopolymerization and anti-counterfeiting. This work breaks through the conventional limitation of using these diodes solely as emitters by innovatively designing and demonstrating a 4 × 4 array integrated with 16 near-UV multiple quantum well (MQW) diodes operating at 395-405 nm, exhibiting multifunctional capabilities. When in emission mode, the array performs traditional anti-counterfeiting and UV curing tasks. When in detection mode, the array acts as a photodetector, detecting externally stimulated pixels and enabling optical image input and character recognition via a convolutional neural network (CNN) with an accuracy exceeding 96%. During content display, the non-emitting pixels are repurposed for multiple-input multiple-output (MIMO) near-UV wireless optical communication (WLC), achieving per-pixel data rates up to 40 kHz. Moreover, the array's robustness under strong ambient sunlight was experimentally validated. The integration of these functionalities offers new perspectives and technological solutions for near-UV MQW diode applications, not only in conventional roles, but also in advanced areas such as covert optical input and anti-interference WLC.

Threshold excitation intensity is a key parameter for characterizing triplet-triplet annihilation photon upconversion (TTA-UC) systems, expected for diverse applications, including management of the sunlight spectrum. However, its measurement is a laborious and time-consuming process. In this article, we propose a simple and quick method for determining the threshold intensity from a snapshot of the emission image. The proposed method significantly shortens the measurement time compared to that for the conventional, widely used intensity-by-intensity method; it can be within a second. Its accuracy was confirmed to be comparable to that of the conventional method.

We present a scalable software framework for synchronization and waveform reconstruction in asynchronous nonlinear optical sampling, designed to enable efficient processing of long, bandwidth-constrained measurement records. High-speed optical signals exceeding electronic baseband bandwidth are sampled using a nonlinear optical sampling gate based on four-wave mixing and a low-bandwidth photodetector, and are resynchronized entirely in software by estimating the sampling time step through spectral peak refinement using zero-padded Fourier transforms. Because the proposed framework relies primarily on Fourier analysis, peak estimation, and time-axis remapping, it avoids iterative optimization and is inherently well suited to parallel execution. We experimentally validate the framework using 10-GHz mode-locked laser pulses and 10-Gb/s pseudo-random bit sequence (PRBS) signals, and quantitatively assess reconstruction quality in terms of extinction ratio, Q-factor, pulse width, and timing jitter. A composite figure of merit is introduced to guide parameter selection under trade-offs between amplitude and timing fidelity. GPU-based parallelization of the proposed software framework yields an approximately tenfold reduction in processing time compared with a CPU implementation, demonstrating scalability to long datasets. The reconstructed waveforms with picosecond pulse width indicate picosecond-scale temporal resolution, highlighting the applicability of the framework to waveform-level diagnostics in future ultra-high-speed communication systems.

In fluid flow imaging, intensity gradients are a good measure of spatial variations in scalar properties, which play an important role in controlling transport processes. However, current flow imaging techniques exhibit system-limited spatial resolutions, thus inhibiting the ability to accurately detect intensity gradients. To address this challenge, we present a method and system, inspired by Structured Illumination Microscopy (SIM), which can be implemented in dynamic flow imaging to enhance pixel resolution and, thereby, the estimation of scalar gradients. We utilize sub-pixel-scale patterned light matching the system pixel scale and multi-frame imaging that creates quasi-static images over four frames, with scalability for high-speed imaging. These multi-frame images are then processed using a bespoke recombination algorithm that produces a new image with twice the pixel resolution compared to the original images. The sub-pixel spatial-resolution enhancement capabilities are shown with static images and dynamic fluid flow, for which enhancement in the flow gradient is demonstrated.

ZnS crystals are critical infrared optical materials for national defense development. However, their soft-brittle and polycrystalline nature poses significant challenges to achieving sub-nanometer precision machining. To address this issue, a hybrid process combining single-point diamond turning (SPDT) and vibration-assisted magnetorheological finishing (V-MRF) is proposed. SPDT enables rapid shaping but generates periodic tool marks, while V-MRF disturbs the polishing trajectory to eliminate these tool marks, ultimately realizing sub-nanometer precision polishing of ZnS. In this study, process parameters were optimized to suppress tool marks during both the SPDT and MRF stages. Under the optimal parameters, the SPDT-processed surface achieved a roughness of 1.327 nm RMS with a tool mark amplitude of < 2 nm, and V-MRF further improved the surface quality to a roughness of 0.887 nm RMS with a tool mark amplitude of < 0.9 nm. After V-MRF processing, the surface roughness of the turned surface and the amplitude of the tool marks were reduced by 33.15% and 55%, respectively, proving the correctness of this combined process.