Optics letters最新文献

In the working environment, machines without vibrations are non-existent. The abnormal operating conditions of machines can be discerned through characteristic patterns within vibration signals. Therefore, real-time, low-cost vibration sensing is essential for industrial applications to track the status of machines. Herein, we propose an optical vibration sensor that is self-powered, supporting on-demand visual readouts. Without external power, this prototype device can cover a broad frequency range from 50 to 800 Hz, fitting into most industrial machinery scenarios. Through finite element analysis and experimental validation, the device exhibits exceptional performance, with a predicted minimum detectable deformation as low as 0.19 µm. Notably, the device possesses vibration signal storage functionality and adopts near-infrared light to achieve on-demand readout, bringing a novel visual perspective to the fields of vibration sensing and equipment health diagnostics.

In this Letter, we investigate the binding mechanism and motion dynamics of the bound state consisting of two pure-quartic solitons (PQSs) with unequal intensities and find that their movement occurs as an entity under the Raman self-frequency shift. By calculating the forces that induce the relative motion between the unequal PQSs, we derive the balanced conditions for maintaining a near-constant separation and the constant phase profile between them. The predictions are validated by the numerical simulations. Our work provides insights into the intrinsic features of symmetry-broken localized structures in nonlinear-dispersive systems, stimulating interest in asymmetric multi-soliton states with intriguing dynamics.

In addition to laser frequency sweep nonlinearity, sensing point misalignment caused by a random laser frequency sweep range (LFSR) is a key factor limiting the sensing performance of the optical frequency domain reflectometer (OFDR). Here we propose a synchronous equal frequency resampling (SEFR) method for the first time to our knowledge to simultaneously compensate both the random LFSR and sweep nonlinearity. A new linear frequency sequence has been constructed to perform signal resampling of both the reference and measurement stages, which eliminates the sensing point misalignment and nonlinear frequency interval at the same time. Thus the sensing distance and accuracy of both phase demodulation (PD) and cross-correlation demodulation (CD)-based OFDR have been greatly improved in distributed strain measurement. For PD, with SEFR the sensing distance is extended to 70 m, and the strain root mean square error (RMSE) is reduced by 16 times under the worst LFSR difference of 579.4 MHz. For CD, the sensing distance is extended from 6.8 m to 70 m, and the RMSE is reduced by 41 times when using SEFR under the worst LFSR difference.

In this Letter, we propose a new method utilizing femtosecond laser direct writing technology to rapidly inscribe high-quality tilted fiber Bragg gratings (TFBGs) in multicore fibers (MCFs). A series of TFBGs with varying tilt angles were directly inscribed in MCFs using the Plane-by-Plane (Pl-by-Pl) method, and the writing time for a 4 mm long TFBG was only 3.60 s. The TFBGs couple the transmitted light from the cores of the MCF into the cladding, thereby increasing the cross talk between adjacent cores. By monitoring the wavelength and intensity changes of the core modes coupled back to the central core from the TFBGs inscribed in the edge cores, two-dimensional (2D) vector bending measurements were achieved.

Moiré metasurfaces exhibit high optical tuneabilities and versatile light manipulation capabilities. Both infinite quality factor (Q factor) and topological vortex configurations in momentum space (k-space) of the bound state in the continuum (BIC) have introduced new dimensions for light modulation. Herein, we propose a moiré metasurface comprising two identical square photonic lattices superimposed with a commensurate angle of 12.68°. By tuning the incidence angle, the symmetric-protected BICs, Friedrich-Wintgen BIC, and accidental BIC can be achieved simultaneously in our moiré metasurfaces. It is found that the quasi-BICs maintain an ultrahigh Q factor beyond 10⁷. The photonic band structures manifest that the three types of BICs are at the center of far-field polarization vortices in k-space, which have their own topological charges. We experimentally show that these BICs exhibit high sensitivity to subtle changes in analyte refractive index for thin-film sensor application. Our discovery predicts an approach to a highly sensitive multi-channel terahertz biosensor.

This publisher's note contains a correction to Opt. Lett.49, 6549 (2024)10.1364/OL.540053.

A single-exposure method for complex amplitude reconstruction in beam quality analysis is proposed, utilizing lens-free coherent amplitude modulation imaging (LF-CAMI). This approach leverages a partially saturated diffraction pattern to reconstruct the complex amplitude of a measured laser beam. The corresponding intensity images near the beam waist along the axial direction are determined directly via the Fresnel diffraction formula. Spatial beam parameters, including the beam quality factor M², are then calculated following the ISO 11146-1 standard. The feasibility of the proposed method is validated through theoretical analysis and experiments, targeting both static and dynamic laser beams. Experimental results demonstrate that this method yields results consistent with those obtained using commercial beam quality analysis instruments while reducing the total measurement time by approximately 80%. The proposed method is compact, cost-effective, and immune to aberrations and offers a fast and accurate measurement process, making it particularly suitable for beam quality analysis in various laser systems, especially pulsed laser systems.

The application of upconversion nanomaterials relies heavily on the ability to produce bright upconversion luminescence (UCL) or high upconversion quantum yields (UCQYs) at low power density excitation. Herein, we synthesized silica-coated NaYF₄:Yb³⁺@NaGdF₄:Tm³⁺@NaYF₄:Tb³⁺ upconversion nanoparticles (UCNPs) and CsPbI₃ perovskites quantum dots (PeQDs) nanocomposites by the slow hydrolysis of (3-aminopropyl)triethoxysilane. The energy transfer (ET) of Gd³⁺→Tb³⁺ accelerates the five-photon upconversion process of Yb³⁺-Tm³⁺ and the design of the core@shell@shell layer effectively mitigates the energy jumps between Gd³⁺ ions. Importantly, the involvement of multiple ET channels in the UCNPs@CsPbI₃ PeQDs nanocomposites increased the intensity of the UCL on the CsPbI₃ PeQDs by about six times. In addition, the stability of PeQDs encapsulated in a silica matrix under air and water conditions was greatly improved.

We address the development of efficient neural network (NN)-based post-equalizers in long-haul coherent-detection dense wavelength-division multiplexing (DWDM) optical transmission systems. To achieve a high level of generalization of the NN-based equalizers, we propose to employ multi-task learning (MTL). MTL refers to a single shared machine learning (NN) model that can perform multiple different (albeit related) tasks. We verify the good performance of the developed MTL equalizer model using experimental data as compared to the previously proposed approaches. Furthermore, we report how MTL can improve performance compared to single-task counterparts. We also demonstrate that reducing the complexity of the resulting MTL equalizer is possible without essential performance compromise.

To cope with the rapid preparation and tunable function of terahertz (THz) devices, a kind of THz beam meta-deflector (BMD) based on a bilayer metasurface doublet is proposed to implement tunable beam deflection with additional functions. By superimposing functional phases on one of the layers and sliding the other layer, the BMDs can achieve continuously beam deflection with beam splitting or beam focusing. It is possible to quickly switch between different functions by replacing the functional phase. As a demonstration, two devices are designed and fabricated by 3D printing, including a splitting BMD (s-BMD) and a focusing BMD (f-BMD). The experimental results show that the designed metasurfaces can achieve a deflection of ±26.96° while achieving a splitting angle of 38.94°-44.11° for the s-BMD and a focus deflection of ±30.76° for the f-BMD. The BMD is expected to be applied as a multifunctional and tunable device in THz communication and imaging.