Applied optics最新文献

The hybrid multiplexing technique is an essential way to satisfy the rapid growth of optical communication capacity. All-optical wavelength conversion (AOWC), a fundamental function to support the all-optical networks, becomes challenging for hybrid multiplexed signals involving wavelength-division multiplexing (WDM) and mode-division multiplexing (MDM). An AOWC method is presented for hybrid WDM-MDM signals based on a segmented thin-film periodically poled lithium niobate (STFPPLN) waveguide, which has the ability to deal with each mode in a separate segment. By considering three modes (TE₀, TE₁, and TE₂), the STFPPLN waveguide is designed and a difference-frequency generation (DFG) conversion efficiency of -9.67dB with a uniformity variation of 0.37 dB throughout the C band is achieved using a 100 mW pump in an 11 mm long waveguide. The conversion bandwidth is predicted as 87.5 nm, which enables 330 WDM-MDM channels (110 wavelengths × 3 modes), with the crosstalk suppressed below -50dB.

To address periodic phase jump errors caused by stripe misalignment, unstable phase truncation information, and order decoding errors in the Gray code phase-shifting method, a phase unwrapping method based on phase information partition correction is proposed. The core of this method lies in a partition governance strategy: First, based on the decoded fringe order K, we roughly determine the range of each period of the wrapped phase. Then, guided by the wrapped phase values within each period, the fringe order K is divided into three characteristic regions (K₁, K₂, and K₃). Subsequently, dedicated correction algorithms are designed for each region's unique error patterns-collapse-type errors in the K₁ region, discrete errors in the K₂ region, and jump-type errors in the K₃ region. Experimental results demonstrate that the proposed method can effectively eliminate jump errors without requiring additional projected patterns. It remains effective in eliminating jump errors even when processing highly discontinuous curved surfaces. Compared with pre-avoidance methods such as complementary Gray code and tripartite phase unwrapping, this method successfully solves jump errors caused by order decoding errors that those methods cannot handle. Compared with post-correction methods such as median filtering, this method eliminates jump errors without blurring genuine geometric details, demonstrating high robustness and edge preservation capability.

The pile-up effect inherent in the common synchronous gating mode of single-photon avalanche diodes (SPADs) limits detection accuracy under high photon flux. Traditional correction methods based on recursion insufficiently utilize full time-domain information, leading to significant errors under moderate to high noise intensity. To address this, this paper constructs a smooth photon detection probability distribution model for complex illumination conditions, based on the Gaussian waveform prior of the signal light and the Poisson distributed response model of the detector. Leveraging the differentiability of this model, we propose an iterative high-precision imaging parameter inversion algorithm by introducing adaptive moment estimation (Adam) and an adaptive parameter initialization mechanism. Extensive simulations and real-system testing demonstrate that the proposed method exhibits stronger noise robustness compared to existing algorithms. Specifically, under the conditions with the signal photon count of 0.1 and the noise photon count of 0.1, the proposed method reduces the root mean square error (RMSE) by 5.71 cm (from 12.766 to 7.056 cm).

The dust detection system (DDS), a subsystem of the dust multi-properties analyzer (DMA) onboard the Tianwen-2 mission, was designed for in situ measurement of the sizes and velocities of dust particles near asteroid 311P/PanSTARRS using the laser-scattering techniques. Ground calibrations with spherical particles enable the establishment of a polynomial retrieval function, which results in a satisfactory accuracy in size detection [Appl. Opt.64, 4851 (2025)APOPAI0003-693510.1364/AO.558537]. However, the irregular morphologies of natural dust particles introduce systematic deviations. As a companion piece of [Appl. Opt.64, 4851 (2025).APOPAI0003-693510.1364/AO.558537], this paper focuses on the analysis of the optical response of non-spherical dust analogs in the DDS, both experimentally and theoretically. Laboratory tests were conducted with apatite, anhydrite, and fluorite particles. Theoretical calculations of the scattered flux of particles, whose geometries were modeled as spheroids, are implemented using the T-matrix method to reveal the influence of elongation and orientation on scattering. By introducing elongation-dependent correction factors into the polynomial retrieval function, the size retrieval deviation for irregular anhydrite and apatite particles was reduced to below 18%. This work provides a practical correction strategy to enhance the reliability of in situ size measurements during Tianwen-2's rendezvous with 311P/PanSTARRS.

A silica waveguide three-mode (de)multiplexer based on an asymmetric 3×3 multimode interference (MMI) coupler is demonstrated. The phase-preset scheme allows the (de)multiplexing of TE₁₁/TM₁₁, TE₂₁/TM₂₁, and TE₃₁/TM₃₁ modes with the compact MMI coupler. The three-dimensional finite-difference beam propagation method is adopted in design optimization. Ultraviolet photolithography and plasma etching have been adopted in device fabrication. The fabricated (de)multiplexer exhibits an insertion loss (IL)<5.59dB and crosstalk (CT)<-16.29dB for all six modes at 1550 nm. Over the wavelength range of 1500-1600 nm, polarization-dependent loss (PDL)<0.94dB, IL<9.33dB, and CT<-11.84dB can be obtained for all supported modes. The demonstrated phase-preset scheme can be applied to integrated waveguide devices for compact mode processing.

Infrared polarization image fusion aims to generate a single image that integrates complementary information from both modalities to enhance scene perception. However, this task is hindered by significant modality gaps, high noise levels in polarization images, and the difficulty of preserving fine details from both sources. To address these challenges, we propose an end-to-end network, the feature-decoupled multi-scale Swin transformer (FDMSFuse). The proposed network uses a multi-scale architecture to capture rich shallow features. Its core component, the mix Swin transformer layer, employs a symmetric shared-key-value attention mechanism for efficient cross-modal interaction. Furthermore, a feature decoupling loss based on a channel-correlation matrix promotes feature complementarity while the DySample module ensures high-quality detail reconstruction. Experiments on the public LDDRS dataset demonstrate that FDMSFuse significantly outperforms nine state-of-the-art methods, ranking first on seven of nine key metrics. Crucially, it improves normalized mutual information (NMI) by nearly 25% over the runner-up, while also achieving top scores for visual fidelity (VIF) and perceived aesthetic quality (NIMA). Qualitative results further confirm its superior performance in noise suppression, texture preservation, and small-target enhancement.

Understanding the optical scattering properties of cirrus ice particles is crucial for optimizing atmospheric circulation models, improving radiative transfer simulations, and advancing our understanding of global climate change, including the assessment of cirrus cloud thinning geoengineering strategies. However, due to the limited understanding of cirrus microphysics and the enormous diversity of ice crystal geometries, the microphysical scattering characteristics of cirrus clouds remain an active and challenging topic of research. In this work, based on the convex hull construction algorithm, a new geometrical model of ice crystals, to our knowledge, is proposed to investigate the scattering properties of cirrus cloud particles. A program named Mueller matrix of convex polyhedron (MMCP) has been developed. Light scattering matrices involving complete polarization information are calculated in geometric optics approximation for randomly oriented large crystals with random and given convex polyhedron shapes. The proposed model construction method and computational scheme of the light scattering matrix work for any convex polyhedron within the scope of geometrical optics. To illustrate the broad applicability of the proposed ice crystal model, scattering matrices for three ice crystal examples with different geometrical shapes are calculated under a unified computational framework. Diffraction, interference, and absorption are not considered in this work. The calculated results for the classical hexagonal column model show the overall agreement with those reported by other authors. The crystal model and scattering matrix computational framework developed in this study are applicable to radiative transfer simulations and remote sensing data interpretation in terrestrial and planetary atmospheres.

A compact opto-mechanical setup has been developed for the precise characterization of optical filters with spatially varying spectral responses. Combining high spatial resolution and low-divergence illumination with high dynamic range detection, the instrument enables accurate and spatially resolved measurement of spectral transmission properties of butcher block filters in both their pass band and stop band.

Vortex beam-based interferometric measurement technology is widely utilized in high-precision displacement measurement. However, beam misalignment leads to interference pattern distortion, introducing significant measurement errors. To address this, we propose a vortex interferometer based on speckle-correlation feedback alignment and global Zernike polynomial fitting. First, a speckle-based automatic beam alignment system is implemented for real-time correction to ensure interference pattern quality. Second, aberrations are eliminated through global Zernike polynomial fitting, and the piston term is extracted for displacement calculation. In 10 nm step tests conducted under both misaligned and automatically aligned states, the residual standard deviation decreased from 3.85 to 0.517 nm. Experimental results demonstrate that the interference quality is restored, achieving sub-nanometer measurement precision.

Multiple plane light conversion (MPLC) has great potential in mode manipulation but is highly sensitive to misalignment. To cope with this challenge, this work proposes an image-processing-based phase mask localization method to realize high alignment accuracy between the phase mask and the optical beam. Sub-pixel precision in locating the beam center can be obtained by directly analyzing the interaction between the lateral shifts of the phase mask and the correlation coefficient of the beam mode, without requiring complex optical setups or advanced algorithms. The feasibility of the proposed scheme has been experimentally verified with several typical modes (LP₀₁,LP_11a, and LP_21a), where the phase mask localization time is all below 3 min, while maintaining a similarity >90% compared to the theoretical results. All results show that this method offers a practical and effective solution for enhancing the performance of multi-pass cavity systems with high efficiency and robustness.