Optics express最新文献

Optoelectronic tweezers (OET) offer a versatile, programmable, and contactless method for manipulating microscale objects. While factors like AC voltage and light intensity have been extensively studied, the role of light pattern curvature in the performance of OET manipulation remains underexplored. This study investigates how the curvature of light patterns affects the movement of polystyrene microparticles under negative dielectrophoretic (DEP) forces in an OET system. Experimental results show that as the curvature decreases, the maximum velocity of microparticles first increases to a peak and then gradually decreases. Numerical simulations reveal that light pattern curvature significantly influences the horizontal and vertical DEP forces, altering equilibrium positions and maximum velocities. By defining the optimal curvature (χ, the ratio of microparticle diameter to the inner diameter of the light pattern), we found that microparticles achieve maximum velocity and stability at this optimal ratio regardless of the sizes. These findings offer key insights into optimizing OET for improved manipulation performance, facilitating more precise and efficient applications in micromanipulation, micro-assembly, microfabrication, and beyond.

Type-II superlattice (T2SL) detectors are emerging as key technologies for next-generation long-wavelength infrared (LWIR) applications, particularly in the 8-14 µm range, offering advantages in space exploration, medical imaging, and defense. A major challenge in improving quantum efficiency (QE) lies in achieving sufficient light absorption without increasing the active layer (AL) thickness, which can elevate dark current and complicate manufacturing. Traditional methods, such as thickening the absorber, are limited by the short carrier lifetime in T2SLs, necessitating alternative solutions. In this study, we introduced a guided-mode resonance (GMR) structure into T2SL LWIR detectors to enhance QE while maintaining a thin AL for efficient carrier collection. The GMR structure was fabricated by introducing a grating array on the surface of the detector and an Au mirror beneath the absorber. This configuration enhanced light trapping, which introduced additional resonance modes. The optimized grating design, with a 5 µm period and a fill factor of 0.6, significantly increased absorption, as predicted by finite-difference time-domain (FDTD) simulations and confirmed experimentally. The GMR-enhanced T2SL detector demonstrated a 2.58-fold improvement in QE over conventional LWIR detectors and a 1.33-fold increase compared to Fabry-Pérot (FP) resonance-based detectors in the 6-11 µm range. Despite exhibiting an almost identical dark current density, the GMR LWIR detector demonstrated superior performance, featuring a broader cut-off wavelength of 9.3 µm and higher QE compared to FP LWIR detectors.

Rate equations and numerical simulations relying on complex mathematical and physical principles are typically used to model directly modulated lasers (DMLs) but have difficulty simulating dynamic DML behavior in real-time under varying conditions due to their high complexity. Here, we introduce a data-driven deep learning method to model DMLs, aiming to achieve high accuracy with reduced computational complexity. This approach employs bidirectional long short-term memory (BiLSTM) enhanced by advanced feature recalibration and nonlinear fitting techniques. The result is compared with LSTM, standard BiLSTM, and recurrent neural network (RNN) architectures. The proposed model obtains the best results for the evaluated metrics. The satisfactory output waveforms and acceptable spectra indicate that the proposed model offers an accurate and real-time method to model DMLs.

Directional emission sources are required in wide application scenarios such as 3D displays and optical communication. The integration of beam deflection metasurfaces on emission devices can construct a compact directional emission source. However, most reported metasurfaces and metagratings focus on the deflection of linear polarized light with relatively small angles(< 30 degrees), which limits their further application for unpolarized light sources. In this work, a nanorod-based two-dimensional metagrating is proposed for a polarization independent incident beam with a large deflection angle ranging from 30 degrees to 75 degrees, and a maximum beam deflection efficiency of 90.1%. An efficient global optimization method based on Bayesian optimization is developed for the design of metagrating and demonstrates a faster converge speed and a better beam deflection performance compared with traditional particle swarm optimization. The proposed metagrating and optimization method also provides useful guidance for the design of polarization independent functional meta-devices.

Lensless imaging offers a lightweight, compact alternative to traditional lens-based systems, ideal for exploration in space-constrained environments. However, the absence of a focusing lens and limited lighting in such environments often results in low-light conditions, where the measurements suffer from complex noise interference due to insufficient capture of photons. This study presents a robust reconstruction method for high-quality imaging in low-light scenarios, employing two complementary perspectives: model-driven and data-driven. First, we apply a physics-model-driven perspective to reconstruct the range space of the pseudo-inverse of the measurement model-as a first guidance to extract information in the noisy measurements. Then, we integrate a generative-model-based perspective to suppress residual noises-as the second guidance to suppress noises in the initial noisy results. Specifically, a learnable Wiener filter-based module generates an initial, noisy reconstruction. Then, for fast and, more importantly, stable generation of the clear image from the noisy version, we implement a modified conditional generative diffusion module. This module converts the raw image into the latent wavelet domain for efficiency and uses modified bidirectional training processes for stabilization. Simulations and real-world experiments demonstrate substantial improvements in overall visual quality, advancing lensless imaging in challenging low-light environments.

In living organisms, the natural motion caused by heartbeat, breathing, or muscle movements leads to the deformation of tissue caused by translation and stretching of the tissue structure. This effect results in the displacement or deformation of the plane of observation for intravital microscopy and causes motion-induced aberrations of the resulting image data. This, in turn, places severe limitations on the time during which specific events can be observed in intravital imaging experiments. These limitations can be overcome if the tissue motion can be compensated such that the plane of observation remains steady. We have developed a mathematical shape space model that can predict the periodic motion of a cylindrical tissue phantom resembling blood vessels. This model is then used to rapidly calculate the future position of the plane of observation of a two-photon laser scanning fluorescence microscope. The focal plane is continuously adjusted to the calculated position with a piezo-actuated objective lens holder. We demonstrate active motion compensation for non-harmonic axial displacements of the vessel phantom with a field of view up to 400 µm × 400 µm, vertical amplitudes of more than 100 µm, and at a rate of 0.5 Hz.

We designed silicon nanowire array cavities with high optical confinement (Γ) in the central nanowire and a high quality factor (Q) through an inverse design method that maximizes Γ×Q. Moreover, we fabricated an inversely designed cavity with inline input and output waveguides, which is a new configuration for such cavities. The experimental Q exceeded 50,000, which was consistent with a simulation. The cavity exhibited the thermal nonlinearity effect and optical bistability, which indicate that our cavity strongly confines the light in the nanowires.

This article conducts a comparative study of the complexity reduction of neural network (NN) models for nonlinearity compensation used in digital subcarrier multiplexing (DSCM)-based optical communication systems. We employ the NN model based on bi-directional long short-term memory (biLSTM) and 1D-convolutional NN (1D-CNN) layers. To reduce the computation complexity of the proposed solution, weight clustering is applied to the NN. We specifically compare the performance of our proposed NN-based equalizer with traditional methods such as chromatic dispersion compensation (CDC), digital back-propagation (DBP) and alternative NN, based on triplet coefficients in perturbation analysis, proposed in previous literature, evaluating both Q-factor performance and computational complexity. Our findings show that the NN-based equalizer offers competitive Q-factor improvements while significantly reducing computational complexity, particularly when weight clustering is used. We show that the complexity of the NN can be reduced by up to 91.1% compared to the NN based on the perturbation analysis proposed in previous literature and by 31.5% compared to the DBP with 1 step per span. The results underscore the potential of NN-based approaches to deliver high-performance nonlinear compensation with lower computational demands, positioning them as a promising solution for future optical nonlinear equalizers.

Metasurfaces consisting of subwavelength structures have shown unparalleled capability in light field manipulation. However, their functionalities are typically static after fabrication, limiting their practical applications. Though persistent efforts have led to dynamic wavefront control with various materials and mechanisms, most of them work in free space and require specialized materials or bulky configurations for external control. This deviates from the original intention of metasurface to realize compact and integrated devices. Here, we leverage the on-chip geometric metasurface associated with polarization reconfiguration of the guided wave, enabling three functions simultaneously: guided wave radiation, polarization multiplexing, and dynamic wavefront manipulation. We demonstrate proof-of-principle functionalities, including intensity-continuously tunable multifocal metalens, and dynamic zoom metalens as well as dynamic holography, based on a metasurface dressed lithium-niobate-on-insulator waveguide. Such an integrated platform for dynamic wavefront shaping implies the prospect of advancements in chip-integrated multifunctional meta-devices.

Film-coupled plasmonic resonators offer efficient platforms for light enhancement due to the excitation of gap surface plasmons (GSPs) at metal-insulator-metal interfaces, where electromagnetic energy is stored within the spacer. In applications like biosensing and spontaneous emission control, spatial overlap between the target molecule and plasmonic hotspots is essential. Here, we propose utilizing the controllable, efficient light enhancement capabilities of a specifically designed GSP disk resonator for biosensing and spontaneous emission enhancement. To create an external plasmonic hotspot and make the strong field stored in the spacer accessible to nearby molecules, we introduce a nanoslot in the top metallic disk with its long axis oriented perpendicular to the incident field polarization. This orientation ensures significant electric field enhancement due to boundary conditions, while the resonant modes of the GSP and nanoslot are further tailored to optimize the field distribution. Finite element method-based simulations reveal the simultaneous excitation of electric-dipole modes due to the nanoslot alongside GSP modes, resulting in a more than two-order magnitude increase in total electromagnetic energy. Additionally, varying the slot length allows precise control over resonances, revealing different modes of the system. The external hotspot in the nanoslot ensures direct interaction with nearby molecules, enhancing the radiative decay rate by nearly three orders of magnitude. The suggested configuration of a plasmonic disk combined with a rectangular nanoslot extends the degree of freedom for designing external electromagnetic hot spots.