Applied optics最新文献

A deep learning-enhanced holographic wavefront sensor (DLHWS) is proposed to overcome the limitations of conventional holographic modal wavefront sensors (HMWS). Traditional HMWS, based on the second-moment-intensity (SMI-HMWS), suffers from measurement inaccuracies due to speckle noise from kinoform computer-generated holograms (CGHs) and restricted measurable modes. The DLHWS utilizes deep neural networks to process multiple biased images generated by a CGH, either a lightweight convolutional neural network (CNN) for modal coefficient estimation (DLHWS-c) or a UNet for direct phase map reconstruction (DLHWS-p). Simulations and experiments demonstrate that DLHWS significantly improves wavefront sensing accuracy and capability to detect high-order aberrations. DLHWS-c offers superior inference speed and high accuracy for low-order modes. In contrast, DLHWS-p delivers higher precision in capturing high-order aberrations comprising hundreds of modes induced by atmospheric turbulence but requires greater computational resources.

To improve the efficiency of wind turbine blade fatigue testing, a displacement measurement method for wind turbine blades based on LiDAR is proposed, which is suitable for biaxial fatigue testing of wind turbine blades. By utilizing the geometric characteristics of retroreflective targets captured by the LiDAR, the position of target points is determined, and the displacement of these points during testing is calculated. The feasibility of this method is verified through static and dynamic experiments, with experimental results showing that the distance measurement error is controlled within 5%. This method requires low point cloud density from the LiDAR and offers advantages such as minimal environmental impact and non-contact measurement. Additionally, an optimization-based vibration parameter calculation method is proposed, which can accurately compute vibration parameters such as frequency and phase. By decoupling the data using vibration parameters, this approach provides additional data support for the fatigue testing of wind turbine blades.

We designed a compact broadband mode converter based on metasurface technology, operating in the 180-210 GHz band (the effective bandwidth is approximately 22 GHz), which achieves high-efficiency conversion from the TE₁₀ mode in a standard WR-4 rectangular waveguide to the TE₀₁ mode in a circular waveguide. The mode converter consists of two sub-mode converters: the first, based on a magic-T waveguide, transforms the TE₁₀ mode into the TE₂₀ mode, and the second, based on a metasurface, converts the TE₂₀ mode into the TE₀₁ mode. Simulation results demonstrate that the conversion efficiency from the TE₁₀ mode to the TE₀₁ mode reaches a maximum of 88.3% (184.6 GHz), with a return loss 8.4%. This metasurface-based mode converter can replace traditional complex transitional waveguide structures, providing a solution for generating high-quality TE₀₁ mode in the terahertz band. Furthermore, the theoretical approach can be extended to the generation of other modes in the terahertz band.

In this paper, we present a novel method, to the best of our knowledge, for achieving high-power second-harmonic generation (SHG) of continuous-wave light. By employing lithium triborate-based resonant cavity with moderate finesse, we propose an approach for generating efficient SHG in the visible and ultraviolet spectral ranges without requiring an active electronic servo loop. As a proof of concept, we demonstrate frequency doubling of a high-power 1064 nm laser to 532 nm. To the best of our knowledge, this is the first implementation of such a cavity featuring a highly reflective coating on one end of this crystal. This quasi-monolithic design enables simultaneous control of phase matching and cavity resonance solely through temperature adjustment of the nonlinear crystal.

Range-selective digital holography (RSDH) is an advanced imaging technique that combines digital holography with the range-selective capabilities of frequency-modulated continuous-wave (FMCW) chirped lidar. Temporal heterodyne FMCW range-selective digital holography (TH FMCW RSDH) further extends this method by incorporating phase-shifting techniques to enable on-axis holographic imaging. In standard implementations, maximum hologram strength is achieved when the local oscillator (LO) frequency shift is set by the target distance, assuming that the hologram integration and chirp duration are aligned. However, in systems where hologram integration spans multiple chirps, this alignment is no longer guaranteed, and the optimal LO frequency shift may deviate from the nominal value. This work develops a theoretical framework to analyze the effects of LO detuning on range resolution and hologram strength in TH FMCW RSDH under multi-chirp integration. The model is experimentally validated using a time-of-flight (ToF) camera to perform phase-shifting and integration. Our results demonstrate that maximum hologram strength can occur at LO frequency shifts that differ from the nominal range-dependent value. These findings provide valuable insights for optimizing the performance of both TH and non-TH FMCW RSDH systems in scenarios where hologram integration spans multiple chirps.

We report on an all-fiber polarization-maintained (PM) erbium-based nonlinear amplifying loop mirror mode-locked laser (figure-9). Due to a hybrid optical element, the laser can be operated in a simple and compact configuration with a high repetition rate reaching up to 247 MHz. By balancing the length of the Er-doped active fiber and the PM-1550 passive fiber, the cavity dispersion was designed to be near zero to negative. The central wavelength was centered at 1567 nm with a 3 dB bandwidth of 26.3 nm. The pulse duration was measured to be 245 fs. Further, the fundamental repetition frequency was locked to a stable radio reference. The Allan deviation for frequency stability was calculated to be 3.146×10^-12 at 1 s' gate time. To our knowledge, this is the highest repetition rate for all-fiber figure-9 structure mode-locked lasers.

Bonnet polishing, a cost-effective and high-precision polishing technique with remarkable adaptability, is widely utilized in the precision machining of complex curved surfaces. However, mid-spatial frequency (MSF) error residuals significantly constrain its convergence efficiency in form error correction and ultimate machining accuracy. This paper investigates the influence of tool removal function characteristics on MSF errors during bonnet polishing. Initially, the theoretical removal functions under varying tool and process conditions were derived through finite element simulations, with the computational framework grounded in Preston's law, Hertzian contact mechanics, and kinematic analysis. Subsequently, a spectral-domain simulation model was developed to quantify MSF error residuals on optically finished surfaces based on the characterized removal functions. The simulation results indicate that under conditions of larger curvature bonnets and lower air pressure, the MSF error residuals are smaller. Finally, experiments were conducted on a high-precision flat fused silica element with a diameter of 100 mm to validate the MSF prediction model, and the experimental results showed good consistency with the simulation results. The findings of this study provide critical guidance for suppressing MSF errors in high-precision bonnet polishing applications.

Integrated photonics is increasingly widely applied in fields such as optical communication and optical micro-operation, especially demonstrating great potential in the dynamic regulation of light wave characteristics. The orbital angular momentum (OAM) carried by vortex beams offers abundant orthogonal channels for optical communication; however, existing generation approaches frequently encounter issues such as large volume, high cost, and complex structure. This paper successfully realizes an ultra-compact dynamic OAM generation device by integrating phase-change materials with a trench waveguide. The device can dynamically generate OAM modes with topological charges of ±1, without changing the physical structure by taking advantage of the refractive index difference between the crystalline and amorphous states of the phase change materials. This design not only reduces the device length to 9.5µm but also enhances its applicability to multiple wavelengths of light waves, presenting extensive possibilities for the development of new photonic devices and systems in fields such as optical communication, quantum information processing, and optical micro-operation.

In recent years, radar depth completion has made significant advances in developing backbone networks and high-quality datasets. However, less attention has been paid to optimizing the supervision manner. In this work, we propose a novel supervision method, to the best of our knowledge, using a relative-to-metric conversion (R2MC) module to leverage the generalization capability of the monocular depth large model (MDLM). The R2MC module employs sparse LiDAR data to obtain metric depth scales through pixelwise local mapping while preserving the generalization capability of the MDLM. The experimental results illustrate that our R2MC module can be combined with different backbones and improve their performance compared to their original supervision manners.

Scene contrast temperature (SCT) is a measurement of temperature and photon flux variation in an emissive scene used to calculate targeting task performance, a metric used to determine the ability of an observer to perform visual tasks. While previous research has compared the SCT of midwave infrared (MWIR) and longwave infrared (LWIR) systems in a hot, dry climate, little work has been done to compare the performance of these systems in different climates. This paper compares the SCT of a hot, dry climate and a cold, dry climate in MWIR and LWIR. The results indicate that SCT is higher in the LWIR in most conditions, except for cold, daylight environments.