Optics and Laser Technology最新文献

We have demonstrated a deformed octagonal microcavity semiconductor laser with manipulated lasing modes for bistable operation and direct modulation. There are two sets of degenerated four-bounced modes, S₀₁ and S₀₂, in the octagonal microcavity, and the degeneracy between them is broken by introducing a square hole into the center of the cavity. In the deformed octagonal microcavity laser, mode S₀₁ dominates the lasing process during the current rising process. However, mode S₀₂ also lases when the current decreases and interacts nonlinearly with S₀₁, which is caused by the non-uniform distribution of the refractive index induced by the square-ring-shaped current injection. We observe a counterclockwise bistable hysteresis loop with continuous injection current ranging from 31 to 13 mA at 288 K. We also study the small-signal modulation response of the laser at high and low states with different injection currents. By utilizing the photon-photon resonance effect between modes S₀₁ and S₀₂, we effectively increased the 3-dB bandwidth of the laser from 12 GHz to 16.2 GHz.

In silicon optical device design, traditional methods are often time-consuming and lack of efficient convergence when directly employing artificial neural networks for inverse design. To address this challenge, we propose an efficient inverse design approach rooted in migration learning for silicon interlayer coupled structures. This method employs Figure of Merit (FOM) screening to preprocess data, followed by training the first Backward Propagation (BP) neural network on the silicon interlayer coupled structure dataset. Subsequently, the learned hyperparameters from the first BP neural network are transferred to the second BP neural network, enhancing the neural network’s accuracy significantly. The results in the mean absolute percentage error (MAPE) for the single-layer and the two-layer coupled-structure neural network can be reduced to 1.2845 % and 7.3409 % in respectively. These findings demonstrate the practical utility of the method in the inverse design of silicon interlayer coupled structures and provide guidance for the design of silicon optical devices.

Accurate assessment of the conveyor belt wear state is a crucial part of measuring belt conveyor safety and reliability. Therefore, this paper proposes an accurate detection approach for conveyor belt wear based on multispectral imaging(MSI), and designs a lightweight network model, named depthwise shuffle coordinate attention network (DSCANet) to assess and classify conveyor belts in three wear states. The multispectral images of the conveyor belt in the Huainan mining area were collected by the MSI system, with a wavelength range of 675–975 nm. The multispectral data at the wavelength with the largest imaging differences was screened as the input to the assessment model DSCANet. Compared with other widely used neural network models, the proposed DSCANet demonstrated the best performance, achieving a classification accuracy of 98.78 %, with floating point operations(FLOPs) of only 136.53M. The findings indicate the great efficacy of the MSI and DSCANet combination in assessing the conveyor belt wear, holding importance in reducing the risk of sudden failures and enhancing production efficiency.

The direct inscription of fiber Bragg gratings (FBGs) in double-clad ytterbium-doped fiber (DCYDF) by fs-laser has the potential to reduce the fusion splices in fiber lasers, which is significant for developing a more compacted and stable monolithic laser system. This study demonstrates that the distinctive inner-cladding structure of DCYDF has a non-negligible influence on the focal position and intensity of the fs-laser. To realize accurate and efficient inscription of FBGs, the fs-laser is controlled to incident at a specific angle based on direct imaging of the DCYDF, and the focus of the fs-laser is determined for the first time using the 1 μm photoluminescence attributed to Yb³⁺ under fs-laser excitation, to the best of our knowledge. The results provide new insights into the influence of the cladding structure on the inscription process of FBGs and its influence on the characteristics of FBGs. This paper presents an accurate and efficient method for inscribing fiber Gragg gratings in DCYDF (YDFBGs), which is of great significance for the fabrication and application of FBGs.

The effect of nonlinearity on the topologically protected linear interface modes in photonic moiré lattice is theoretically investigated. The linear topological mode of moiré lattice is transformed into a set of topological gap solitons under the focusing nonlinearity. These solitons are stable up to a certain propagation constant in the lattice range. Stable symmetric and antisymmetric dipole solitons as well as quadrupole solitons can be formed in the continuously-periodic photon moiré lattice, however, they exhibit only low amplitudes, which indicates weak nonlinearities even when the band gap of the moiré lattice is wide. In addition, the propagation dynamics of metastable and unstable quadrupoles are discussed. Therefore, if the initial beam has a high amplitude, it will either evolve into an unstable soliton that is not a member of the topological gap soliton family, or delocalization.

Functionally graded materials directly bonded with various alloys may result in high internal stress and defects at the interface due to the mutation of the component elements, thus affecting the quality of the formed specimens. Compositionally graded alloys (CGA) based on the LPBF process can achieve uniform changes in elements to reduce the occurrence of defects. The microstructure, mechanical properties and thermal expansion properties of Invar36/Ni22Cr3 CGA alloy were investigated in this paper. The sample has a high relative density, with a density of about 99.78 % on the Ni22Cr3 side. As the Ni22Cr3 content (10 wt% Invar36) increases, the single fcc γ phase transforms into the fcc γ and bccα phases. The S5 sample is particularly unique, with a smaller grain size of 11.46 (±2.23) μm, and a larger KAM value. The S1 sample has the highest elongation of about 35.0 (±0.63) % compared to other representative samples. With the change in temperature, Invar36/Ni22Cr3 CGA represents a significant change in the thermal expansion displacement curve of the sample.

The quality of air significantly impacts both the quality of life and the health of individuals. Femtosecond laser filament-induced nonlinear spectroscopy effectively measures both aerosol concentration and composition. Specifically, the nonlinear refractive index coefficient of the atmosphere directly influences the nonlinear propagation of femtosecond lasers in the air. The presence of aerosol particles in the atmosphere, particularly water droplets, may affect this nonlinear refractive index coefficient. However, the measurement of the nonlinear refractive index coefficient of highly scattering aerosols has not yet been reported. In this paper, a method to obtain the nonlinear refractive index coefficients of aerosols based on spectral changes is presented. Experiment measured the n₂ coefficient of the air and water vapor aerosols respectively. Experimental results show that the n₂ coefficients are 2.5 × 10⁻¹⁹ cm²/W and 2.4 × 10⁻¹⁹ cm²/W respectively for air with incident energy of 48 μJ and 68 μJ, the n₂ coefficient are 2.5 × 10⁻¹⁹ cm²/W and 2.3 × 10⁻¹⁹ cm²/W respectively for aerosol with attenuation coefficients of 0.029 dB/cm. When the concentration of aerosols was increased to an attenuation coefficient of 0.045 dB/cm, the nonlinear refractive index coefficient of the aerosols was 3.1 × 10⁻¹⁹ cm²/W. The experimental results indicated that low concentrations of aerosols did not affect the nonlinear refractive index coefficient of air, but as the concentration increased to a certain level, the nonlinear refractive index coefficient of air increased. This work provides a simpler and faster technical route for measuring the n₂ coefficient of gaseous media, offers a new approach to the problem of measuring the nonlinear refractive index of thick, highly scattering media, and addresses the shortcomings of the z-scan.

Deposited photonics represents a promising avenue for monolithic back-end integration on CMOS, yet encounters challenges in simultaneously enhancing waveguide loss and modulation dynamics. In this paper, a novel amorphous/polycrystalline hybrid scheme for deposited silicon photonics on CMOS was proposed, which utilizes mask-assisted local laser annealing to crystallize the active region of low-loss amorphous silicon (α-Si) PICs only into high-mobility polycrystalline silicon (poly-Si). The feasibility of key techniques such as laser annealing of α-Si thin films, laser activation of doping ions, and mask-assisted local laser annealing of photonic devices is validated. A comparative study between excimer laser annealing and solid-state laser annealing of α-Si is conducted, examining the impacts of pre-dehydrogenation, doping, etching depth, laser pulse energy density, and pulse number. During mask-assisted laser annealing the necessity of a buffer layer between the mask and the α-Si to prevent metal contamination is highlighted. The mask-assisted local laser annealing technique effectively mitigates the optical loss increase by ∼140 dB/cm typically associated with laser crystallization in a α-Si racetrack resonator and reduces the coupling loss in grating couplers by ∼8 dB/pair. Mask-assisted laser annealing not only facilitates high-yield wafer-level active deposited photonics but also allows for leveraging the strengths of both α-Si and poly-Si within a single photonic integrated circuit. This work provides technological insights and valuable guidance for the development of high-performance deposited silicon photonics.

Laves/NbC phase formation due to Nb element segregation is detrimental to the mechanical properties of gradient materials fabricated using stainless steel and nickel-based superalloys. Here, a novel gradient design approach was employed by selecting Nb-free HA188 and SS316L as base materials, enabling uniform transition in element distribution and phase composition. The HA188/SS316L functionally graded material exhibited a heterogenous grain structure, which was also confirmed through the grain boundary distribution map and kernel average misorientation map. The deformation twins have been observed to significantly impede dislocation motion in the fracture region. Notably, the developed gradient material exhibited a yield strength of 392 MPa, an ultimate tensile strength of 608 MPa, and an elongation of 45.2 %, surpassing conventional gradient materials derived from nickel-based superalloys and stainless steels. This research provides valuable insights into the design of heterogeneous gradient materials, offering new perspectives for enhanced performance.

The outstanding mechanical properties of carbon fiber reinforced thermoplastic polymer (CFRTP) have led to its widespread application in many industrial sectors. In response to the engineering challenge of repairing large non-critical CFRTP structural components in situ, an infrared fiber laser surface cleaning technology is proposed to treat the bonding interface and enhance the tensile strength of polypropylene (PP)-based CFRTP single-lap bonded joints. Specifically, through single-factor and orthogonal experiments, the impact of different process parameters on the properties of the bonded joints was identified first. Then, online temperature monitoring was performed to elucidate the laser treatment mechanism of the CFRTP sample interface. Surface morphology of the laser-treated samples further indicates that when the temperature of the sample surface surpasses the resin decomposition temperature with extended holding time, the resin could be removed from the surface more thoroughly. Additionally, a novel three-dimensional woven finite element (FE) model, accounting for anisotropic heat transfer, was established to predict the surface temperature and cleaning quality of CFRTP. The FE model incorporates the anisotropic heat transfer characteristics of carbon fibers, thus accurately simulating the heat transfer behaviors between carbon fibers and the resin matrix. The laser ablation mechanism is elucidated by examining the surface ablation morphologies and peak surface temperatures. A comparison between experimental results and FE simulations demonstrated a notable coherence in the trend of surface morphology variations, with discrepancies in peak surface temperatures ranging from 3.29 % to 24.63 %. The experimental tests proved that the shear strength of single-lap bonded joints reaches its maximum value when the laser power is 35 W, the scanning speed is 2500 mm/s, and the number of scans is four. The enhancement of the mechanical properties of bonded joints can be attributed to the improved wettability and higher surface free energy of the laser-treated samples.