Applied optics最新文献

This study investigates a novel dual-band plasmonic refractive index (RI) sensor, to our knowledge, based on an air-silver metal-insulator-metal waveguide configuration, incorporating a circular cavity featuring a centrally embedded elliptical notch. The sensor design was modeled using COMSOL Multiphysics (version 6.2) and optimized through a two-dimensional finite element method analysis. The proposed sensor exhibits dual-band resonance behavior in the ranges of 800-1200 nm and 1300-1900 nm. It demonstrated remarkable sensitivities ranging from 1137 to 1970nm/RIU^-1 for lead nitrate [Pb(NO₃)₂] detection and from 682 to 1136.4 nm/RIU for thyroxine (T4) sensing, alongside a high figure of merit (FoM) reaching 76 and a quality factor (Q.factor) of approximately 83. The structure also achieved a maximum transmission of ∼88% and a narrow full-width at half-maximum of 24.8 nm, underscoring its suitability for high-resolution detection.

Artificial eyes that mimic the human eyes are used to develop humanoid robots and to evaluate the accuracy of eye trackers. However, conventional artificial eyes have issues in reproducing fast movements such as saccades. In this paper, we propose artificial eyes that can generate microsaccadic motion, have retroreflective bright pupils, and have an optical design that optically visualizes their gaze direction. The eye rotation is reproduced by a high-speed galvano motor, and the bright pupil is reproduced by a sand-surface plano-convex lens and retroreflective material, respectively. A laser light source and a prism mirror are placed on the rotational axis to enable optical gaze visualization while maintaining the light weight required for fast rotation. Evaluation experiments confirmed the appearance quality of the bright pupil and gaze visualization, quantitatively evaluated the responsiveness of the microsaccadic motion, and showed the performance of gaze measurement and microsaccade detection in a commercial eye tracker.

In order to improve the analytical sensitivity of surface-enhanced laser-induced breakdown spectroscopy (SENLIBS) for the elemental analysis of liquid samples, a 20 µm cylindrical hole periodic micro-structure was efficiently fabricated on the surface of copper foil substrates using an integrated method of electroplating and imprinting. The periodic micro-structured surface decreases the reflectance of the incident laser and changes the interaction of the laser with the substrate. Thus, the spectral intensity of both substrates' elements and samples' elements can be effectively enhanced by SENLIBS analysis. Boron (B) in aqueous solution was quantitatively analyzed by SENLIBS using the copper foil substrate with a periodic micro-structured surface. The limit of detection (LoD) of boron reached 0.22 µg/mL under the current experimental conditions, and 3.1-fold improvement factors on the analytical sensitivity were achieved when compared with a flat copper foil substrate. For boron analysis, the quantitative results analyzed by SENLIBS are in good agreement with those analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES). An efficient method for fabricating periodic micro-structure on metal surfaces was demonstrated. This approach is expected to extend the applications of SENLIBS and improve its analytical performance for elemental analysis of liquid samples.

This paper presents a magnetic field responsivity-enhancement sensing system, which comprises a magnetic field enhanced-responsivity fiber Bragg grating (FBG) sensing unit and a microwave photonic demodulation system utilizing an optoelectronic oscillator (OEO). The enhanced-responsivity structure integrates a mechanical stress coupling mechanism and a magnetic field bias, applying both prestress and pre-magnetization to a giant magnetostrictive material to improve its magnetostrictive coefficient. The FBG is mechanically bonded to this structure, forming a highly responsive magnetic field sensing unit. The OEO-based demodulating system consists of a feedback oscillation loop incorporating a broadband light source, an optical modulator, a dispersion medium, and a photodetector. It converts the wavelength shift of the FBG induced by the magnetic field into a corresponding oscillation frequency shift of the OEO, enabling precise magnetic field measurement through frequency monitoring. Experimental results demonstrate that the magnetic field responsivity of the enhanced sensor reaches 3920 Hz/mT, which is 16.3 times higher than that of the unenhanced configuration. A magnetic field resolution of 0.255 µT and an accuracy of 51 µT are achieved. The proposed magnetic field sensing system significantly enhances responsivity without increasing the complexity of the demodulation architecture. This work provides a novel, to our knowledge, and practical approach for high-accuracy magnetic field measurement in engineering applications.

Quality control is critical in cabinet panel manufacturing due to the complexity of the assembly process, which requires three-dimensional measurement methods for enhanced precision and efficiency compared to conventional two-dimensional techniques. Stereo vision offers an effective solution with high accuracy, efficiency, and cost-effectiveness, yet challenges like unclear edge disparities, occlusions, and weak textures persist. To overcome these, we propose a high-precision stereo reconstruction method combining guided image filtering with Markov random fields. Simulated and real-world experiments validate our approach, demonstrating significant improvements in challenging scenarios. This work aims to advance stereo vision's practical application in manufacturing.

This work presents the design and performance analysis of a high-performance optical 3 bit Gray-code counter that employs electro-optic modulation using GaAlAs directional couplers. The developed system comprises a mix of T-flip flops and directional couplers for optical logic operations and state transitions. The miniaturized layout design leverages the electro-optical concept to modulate signals with sufficient efficiency, resulting in an all-photonic synchronous counter. The functioning of the structure is fully explained using K-map-based Boolean logic synthesis to generate the required conditions for the flip flops used in the system. The suggested device configuration consists of GaAlAs material designed with a 3µm×3µm modulator. The coupling length (L_C) of the device is set at L_C=1cm. The EODC achieves optimal switching at a light wavelength of 900nm by inducing a refractive index shift (Δn) of approximately Δn≅1×10^-4. The required electric field magnitude of approximately 3×10⁴V/cm to perform optical switching is transformed into a voltage of 10 V placed across the electrodes of the EODC along the 3 µm channel. The counter operation is established using simulation results, including 3D MATLAB simulations and temporal simulations of counter state changes. This work presents a comprehensive analysis of the extinction ratio, contrast ratio, and amplitude modulation characteristics of the proposed optical 3 bit Gray-code converter circuit. These findings have gained wide appeal due to their low circuit complexity and faster circuit design compared to electrical circuits.

We propose an amplitude-signal-to-noise ratio (A-SNR) method to utilize the spectral leakage components in the depth profile using a sub-bin (SB) in spectral domain optical coherence tomography (SD-OCT). The conventional bin interval was divided by the SB, and a rectangular spectral density was used. The amplitude and SNR under SB conditions were derived theoretically, and the simulation results are presented. In experiments, using SD-OCT with a 0.8 µm SLD, for the conventional depth resolution of 19.1 µm, the displacements of 2-3 µm in depth were measured using the proposed method. The example of applications of the A-SNR method is also discussed.

As the demand for astronomical observations continues to grow, the aperture of telescopes is increasing, with segmented primary mirrors becoming a prevailing trend. However, segmented telescopes require a series of complex steps to ensure precise alignment between the individual segments, achieving diffraction-limited imaging performance. Among these steps, global alignment mainly focuses on placing the secondary mirror (SM) and primary mirror (PM) in the best possible positions, thus laying the foundation for subsequent alignments. This paper simulates the global alignment process using a stitched sensitivity matrix model for the segmented telescope to calculate the misalignments of optical elements. The specific formulation of the stitched sensitivity matrix model and the segment tilt misalignment calculation model has been explicitly derived in this paper. Furthermore, to the best of our knowledge, the sensitivity matrix is constructed based on the first nine fitted Zernike coefficients. Incorporating the piston and tip/tilt terms introduces additional constraints to the matrix, thereby improving the solution accuracy. During the alignment process, the segment tilt misalignment calculation model is employed to constrain the positions of the spots, ensuring their stability. These combined constraints collectively guarantee that the spot positions remain fixed throughout the global alignment, while enabling high-precision wavefront correction. The alignment process for global alignment is described in detail, and the correction results are analyzed under no error and measurement error conditions. Monte Carlo simulations indicate that the proposed method is effective in solving misalignments during global alignment. The research presented in this paper provides valuable insights for the development of large-aperture segmented telescopes.

Crosstalk errors induced by the coupling between rotational and translational motions in multi-degree-of-freedom measurement systems critically degrade system accuracy. This study proposes a crosstalk compensation model based on the optical symmetry of the corner cube retroreflector, aiming to decouple the interaction between the roll, pitch, yaw, and horizontal/vertical displacements. A mathematical framework was developed, integrating the coordinate transformation, vector analysis, and optical path equations. This model can precisely forecast the spot displacement of the detector by solving the incident plane equation under the condition of multi-degree-of-freedom motion. Experimental results demonstrate an 84.2% reduction in horizontal displacement error (from 17.1 to 2.7 µm) and a 94.3% reduction in vertical displacement error (from 73.5 to 4.2 µm) after compensation. The proposed model significantly reduces inaccuracies caused by crosstalk in multi-degree-of-freedom measurement systems, thereby enhancing the overall performance and reliability of the system.

This study investigates a method for fabricating hybrid periodic micro/nanostructures based on polarization-controlled two-beam holography using a femtosecond laser. By adjusting the polarization combination of the two laser beams, four types of hybrid micro/nanostructures were successfully fabricated on the ZnO surface. The evolution of surface structures with increasing pulse numbers and laser fluences was also discussed. Theoretical calculations revealed the crucial role of polarization distribution in determining the orientation of nanostructures, which is consistent with the experimental results. This method enables structural diversity through polarization adjustment without the need for optical path adjustments, offering new ideas for applications such as photonic crystals and polarization-sensitive optical devices, to our knowledge.