Frontiers of Optoelectronics最新文献

In this paper, we report a coherent beam combining (CBC) system that involves two thulium-doped all-polarization maintaining (PM) fiber chirped pulse amplifiers. Through phase-locking the two channels via a fiber stretcher by using the stochastic parallel gradient descent (SPGD) algorithm, a maximum average power of 265 W is obtained, with a CBC efficiency of 81% and a residual phase error of λ/17. After de-chirping by a pair of diffraction gratings, the duration of the combined laser pulse is compressed to 690 fs. Taking into account the compression efficiency of 90% and the main peak energy proportion of 91%, the corresponding peak power is calculated to be 4 MW. The laser noise characteristics before and after CBC are examined, and the results indicate that the CBC would degrade the low frequency relative intensity noise (RIN), of which the integration is 1.74% in [100 Hz, 2 MHz] at the maximum combined output power. In addition, the effects of the nonlinear spectrum broadening during chirped pulse amplification on the CBC efficiency are also investigated, showing that a higher extent of pulse stretching is effective in alleviating the spectrum broadening and realizing a higher output power with decent combining efficiency.

The non-ionizing and penetrative characteristics of terahertz (THz) radiation have recently led to its adoption across a variety of applications. To effectively utilize THz radiation, modulators with precise control are imperative. While most recent THz modulators manipulate the amplitude, frequency, or phase of incident THz radiation, considerably less progress has been made toward THz polarization modulation. Conventional methods for polarization control suffer from high driving voltages, restricted modulation depth, and narrow band capabilities, which hinder device performance and broader applications. Consequently, an ideal THz modulator that offers high modulation depth along with ease of processing and operation is required. In this paper, we propose and realize a THz metamaterial comprised of microelectromechanical systems (MEMS) actuated by the phase-transition material vanadium dioxide (VO₂). Simulation and experimental results of the three-dimensional metamaterials show that by leveraging the unique phase-transition attributes of VO₂, our THz polarization modulator offers notable advancements over existing designs, including broad operation spectrum, high modulation depth, ease of fabrication, ease of operation condition, and continuous modulation capabilities. These enhanced features make the system a viable candidate for a range of THz applications, including telecommunications, imaging, and radar systems.

Since their inception, frequency combs generated in microresonators, known as microcombs, have sparked significant scientific interests. Among the various applications leveraging microcombs, soliton microcombs are often preferred due to their inherent mode-locking capability. However, this choice introduces additional system complexity because an initialization process is required. Meanwhile, despite the theoretical understanding of the dynamics of other comb states, their practical potential, particularly in applications like sensing where simplicity is valued, remains largely untapped. Here, we demonstrate controllable generation of sub-combs that bypasses the need for accessing bistable regime. And in a graphene-sensitized microresonator, the sub-comb heterodynes produce stable, accurate microwave signals for high-precision gas detection. By exploring the formation dynamics of sub-combs, we achieved 2 MHz harmonic comb-to-comb beat notes with a signal-to-noise ratio (SNR) greater than 50 dB and phase noise as low as - 82 dBc/Hz at 1 MHz offset. The graphene sensitization on the intracavity probes results in exceptional frequency responsiveness to the adsorption of gas molecules on the graphene of microcavity surface, enabling detect limits down to the parts per billion (ppb) level. This synergy between graphene and sub-comb formation dynamics in a microcavity structure showcases the feasibility of utilizing microcombs in an incoherent state prior to soliton locking. It may mark a significant step toward the development of easy-to-operate, systemically simple, compact, and high-performance photonic sensors.

The topological photonics plays an important role in the fields of fundamental physics and photonic devices. The traditional method of designing topological system is based on the momentum space, which is not a direct and convenient way to grasp the topological properties, especially for the perturbative structures or coupled systems. Here, we propose an interdisciplinary approach to study the topological systems in real space through combining the information entropy and topological photonics. As a proof of concept, the Kagome model has been analyzed with information entropy. We reveal that the bandgap closing does not correspond to the topological edge state disappearing. This method can be used to identify the topological phase conveniently and directly, even the systems with perturbations or couplings. As a promotional validation, Su-Schrieffer-Heeger model and the valley-Hall photonic crystal have also been studied based on the information entropy method. This work provides a method to study topological photonic phase based on information theory, and brings inspiration to analyze the physical properties by taking advantage of interdisciplinarity.

InGaN/GaN micro-light-emitting diodes (micro-LEDs) with a metal-insulator-semiconductor (MIS) structure on the sidewall are proposed to improve efficiency. In this MIS structure, a sidewall electrode is deposited on the insulating layer-coated sidewall of the device mesa between a cathode on the bottom and an anode on the top. Electroluminescence (EL) measurements of fabricated devices with a mesa diameter of 10 μm show that the application of negative biases on the sidewall electrode can increase the device external quantum efficiency (EQE). In contrast, the application of positive biases can decrease the EQE. The band structure analysis reveals that the EQE is impacted because the application of sidewall electric fields manipulates the local surface electron density along the mesa sidewall and thus controls surface Shockley-Read-Hall (SRH) recombination. Two suggested strategies, reducing insulator layer thickness and exploring alternative materials, can be implemented to further improve the EQE of MIS micro-LEDs in future fabrication.

Modulation of topological phase transition has been pursued by researchers in both condensed matter and optics research fields, and has been realized in Euclidean systems, such as topological photonic crystals, topological metamaterials, and coupled resonator arrays. However, the spin-controlled topological phase transition in non-Euclidean space has not yet been explored. Here, we propose a non-Euclidean configuration based on Möbius rings, and we demonstrate the spin-controlled transition between the topological edge state and the bulk state. The Möbius ring, which is designed to have an 8π period, has a square cross section at the twist beginning and the length/width evolves adiabatically along the loop, accompanied by conversion from transverse electric to transverse magnetic modes resulting from the spin-locked effect. The 8π period Möbius rings are used to construct Su-Schrieffer-Heeger configuration, and the configuration can support the topological edge states excited by circularly polarized light, and meanwhile a transition from the topological edge state to the bulk state can be realized by controlling circular polarization. In addition, the spin-controlled topological phase transition in non-Euclidean space is feasible for both Hermitian and non-Hermitian cases in 2D systems. This work provides a new degree of polarization to control topological photonic states based on the spin of Möbius rings and opens a way to tune the topological phase in non-Euclidean space.

With the rapid development of white LEDs, the research of new and efficient white light emitting materials has attracted increasing attention. Zero dimensional (0D) organic-inorganic hybrid metal halide perovskites with superior luminescent property are promising candidates for LED application, due to their abundant and tailorable structure. Herein, [(CH₃)₃S]₂SnCl₆·H₂O is synthesized as a host for dopant ions Bi³⁺ and Sb³⁺. The Sb³⁺ doped, or Bi³⁺/Sb³⁺ co-doped, [(CH₃)₃S]₂SnCl₆·H₂O has a tunable optical emission spectrum by means of varying dopant ratio and excitation wavelength. As a result, we can achieve single-phase materials suitable for emission ranging from cold white light to warm white light. The intrinsic mechanism is examined in this work, to clarify the dopant effect on the optical properties. The high stability of title crystalline material, against water, oxygen and heat, makes it promising for further application.

A highly sensitive temperature sensing array is prepared by all laser direct writing (LDW) method, using laser induced silver (LIS) as electrodes and laser induced graphene (LIG) as temperature sensing layer. A finite element analysis (FEA) photothermal model incorporating a phase transition mechanism is developed to investigate the relationship between laser parameters and LIG properties, providing guidance for laser processing parameters selection with laser power of 1-5 W and laser scanning speed (greater than 50 mm/s). The deviation of simulation and experimental data for widths and thickness of LIG are less than 5% and 9%, respectively. The electrical properties and temperature responsiveness of LIG are also studied. By changing the laser process parameters, the thickness of the LIG ablation grooves can be in the range of 30-120 μm and the resistivity of LIG can be regulated within the range of 0.031-67.2 Ω·m. The percentage temperature coefficient of resistance (TCR) is calculated as - 0.58%/°C. Furthermore, the FEA photothermal model is studied through experiments and simulations data regarding LIS, and the average deviation between experiment and simulation is less than 5%. The LIS sensing samples have a thickness of about 14 μm, an electrical resistivity of 0.0001-100 Ω·m is insensitive to temperature and pressure stimuli. Moreover, for a LIS-LIG based temperature sensing array, a correction factor is introduced to compensate for the LIG temperature sensing being disturbed by pressure stimuli, the temperature measurement difference is decreased from 11.2 to 2.6 °C, indicating good accuracy for temperature measurement.

Traditional inspection cameras determine targets and detect defects by capturing images of their light intensity, but in complex environments, the accuracy of inspection may decrease. Information based on polarization of light can characterize various features of a material, such as the roughness, texture, and refractive index, thus improving classification and recognition of targets. This paper uses a method based on noise template threshold matching to denoise and preprocess polarized images. It also reports on design of an image fusion algorithm, based on NSCT transform, to fuse light intensity images and polarized images. The results show that the fused image improves both subjective and objective evaluation indicators, relative to the source image, and can better preserve edge information and help to improve the accuracy of target recognition. This study provides a reference for the comprehensive application of multi-dimensional optical information in power inspection.

An ultrafast fiber laser system comprising two coherently combined amplifier channels is reported. Within this system, each channel incorporates a rod-type fiber power amplifier, with individual operations reaching approximately 233 W. The active-locking of these coherently combined channels, followed by compression using gratings, yields an output with a pulse energy of 504 μJ and an average power of 403 W. Exceptional stability is maintained, with a 0.3% root mean square (RMS) deviation and a beam quality factor M² < 1.2. Notably, precise dispersion management of the front-end seed light effectively compensates for the accumulated high-order dispersion in subsequent amplification stages. This strategic approach results in a significant reduction in the final output pulse duration for the coherently combined laser beam, reducing it from 488 to 260 fs after the gratings compressor, while concurrently enhancing the energy of the primary peak from 65% to 92%.