Advanced Photonics Research最新文献

Terahertz (THz) optical devices have emerged as critical tools across diverse applications, owing to the distinctive properties of THz radiation. The ability of THz waves to penetrate nonconductive materials enables numerous nondestructive testing applications, while their characteristic interaction with molecular vibrations produces unique spectral fingerprints, facilitating precise material identification and quantification. Moreover, the low photon energy of THz radiation makes it particularly suitable for biological inspection without sample damage. Despite these advantages, conventional THz devices, including emitters and detectors, remain bulky, impeding their miniaturization and integration. THz metalenses offer a promising solution by enabling wavefront control in compact, planar architectures. However, their reliance on electromagnetic diffraction introduces significant dispersion, presenting substantial challenges for implementation in the inherently broadband THz regime, which often spans multiple octaves. Herein, an advanced all-dielectric metalens operating at dual-frequency harmonics in the sub-THz regime is demonstrated. The lens, fabricated using commercial 3D printing technology, enables rapid prototyping and cost-effective manufacturing. This metalens achieves a numerical aperture of 0.86 (50 mm diameter, 15 mm focal length) at both 150 and 300 GHz. This development represents a significant advancement toward implementing higher-order metasurface elements in the THz regime.

A complementary metal oxide semiconductor-compatible transmission filter composed of subwavelength nanostructures is demonstrated through design, numerical modeling, and experimental verification. The tuning of the filters’ peak wavelength via lithographic means in a single dielectric layer, obviating the need for altering the device layer thickness to achieve different filter wavelengths is demonstrated. The Fabry–Perot function is achieved by sandwiching the nanostructures between a bottom distributed Bragg reflector and a top reflector composed of a layer of silver. A spectral resolution of 10 nm–30 nm full width at half maximum and peak transmission efficiency of ≈70% in the multispectral optical filters in both numerical simulations and experimental characterization is experimentally demonstrated. This approach provides a new paradigm in which to achieve color filters, eliminating the need for multiple mask steps for varied device layer thicknesses conventionally used to achieve Fabry–Perot filters, greatly reducing the manufacturing process cost and complexity.

This study introduces a reconfigurable metasurface that achieves transmission control across a broadband terahertz (THz) frequency range by leveraging the phase transition property of vanadium dioxide (VO₂) to enable precise beam steering. Designed with a single-layer metasurface composed of VO₂ split-ring resonator (SRR) unit structures, this device offers switchable THz beam steering upon actuation with a global temperature change. At high temperatures corresponding to the “ON” state, the metasurface exhibits frequency-dependent THz beam steering at large angles for crosspolarized THz transmission, as demonstrated both numerically and experimentally. At room temperature and in the “OFF” state, it achieves near-perfect ordinary transmission for the incident THz light, without distorting the incoming light. The reconfigurable metasurface demonstrates an average modulation depth of 95% with a maximum value of 99.8% at the designed deflection angles. This innovative approach indicates the potential advanced applications in THz technology, including communications, imaging, and sensing, which require high-performance, efficient, and reconfigurable THz deflectors.

Two-dimensional (2D) semiconductor materials are being explored for applications including photocatalysis and optoelectronic devices. This class of materials features high surface-to-volume ratio that imparts unique physical properties. Yet, this feature makes 2D semiconductor materials prone to chemical changes that translate to variations in their photophysical behavior. Large-scale application of these materials requires an understanding of degradation processes toward developing strategies to increase their stability. Here, the effect of air exposure on underexplored 2D semiconductor material γ-In₂S₃ is studied. This In₂S₃ polymorph is stabilized as nanoplatelets, which are then characterizes before and after exposure to air. A marked surface oxidation , accompanied by drastic variations in photoluminescence is observed. Temperature-dependent spectroscopic measurements show that the emission spectrum of fresh γ-In₂S₃ nanoplatelets is dominated by two defect-related bands, while oxidation enhances the contribution of a third band. An energy level scheme is proposed based on the analysis of the spectroscopic data. This study finally portrays how a postsynthesis treatment with an oxygen-containing molecule (oleic acid) changes the photoluminescence of γ-In₂S₃ nanoplatelets similarly to a prolonged air exposure. The work shines light on the optical properties of γ-In₂S₃, paving the way for their control and the use of this material in luminescence sensing.

Over the last decade, external seeded free-electron lasers (FELs) have achieved significant advancements across various disciplines, progressively establishing themselves as indispensable tools in fields ranging from fundamental science to industrial applications. The performance of seeded FELs is critically dependent on the quality of the frequency up-conversion process. Optimized conditions for seeded FELs are typically considered as the maximization of the bunching factor. This article discusses alternative perspectives on the optimization criteria for seeded FELs by analyzing the impact of dispersion strength on their overall performance. This study investigates the differences among the required dispersion strength for achieving the maximum bunching factor, maximum pulse energy, optimal energy stability through theoretical analysis, simulation calculations, and experimental explorations. The direct observation in experiments emphasizes the consideration of trade-off between pulse energy and energy stability in seeded FELs. These results provide valuable insights and practical guidance for controlling the pulse characteristics of seeded FELs, contributing to the tuning and optimization of FEL facilities.

In recent years, gigahertz (GHz)-burst-mode femtosecond lasers have revolutionized laser processing by significantly improving processing efficiency and quality. However, the underlying mechanisms are still unclear and experimentally optimizing the processing parameters is difficult due to their huge number. This study implements a theoretical approach based on simulations to investigate the underlying mechanisms of the Cu ablation efficiency enhancement by GHz-burst mode. The simulation results obtained using a two-temperature model suggest that the ablation efficiency is improved due to the interaction of subsequent intra-pulses in a GHz burst with Cu melted by the preceding intra-pulses. It is demonstrated that for GHz-burst mode, a 515 nm wavelength achieves higher Cu ablation performance than when using the infrared wavelength and demonstrates 2.8 times higher ablation efficiency than the single-pulse mode. The simulation results well agree with the experimental results. The approach used here represents a major advance not only in understanding the underlying mechanisms but also in determining the optimal processing conditions for practical applications.

Coherent anti-Stokes Raman spectroscopy (CARS) is a nonlinear optical technique widely utilized for vibrational imaging and molecular characterization in fields such as chemistry, biology, medicine, and materials science. Despite the high signal intensity provided by CARS, the nonresonant background (NRB) can obscure valuable molecular fingerprint information. Therefore, effective NRB removal and phase retrieval are essential for achieving precise spectral analysis and accurate material characterization. This review provides a comprehensive overview of the evolution of CARS-NRB removal and phase retrieval methods, tracing the transition from classical experimental techniques and numerical algorithms to cutting-edge deep learning models. The discussion evaluates the strengths and limitations of each approach and explores future directions for integrating deep learning to improve phase retrieval accuracy and NRB removal efficiency in CARS applications.

Thin-film coatings are a versatile option for creating color. These coatings can be made tunable by introducing phase-change materials (PCMs), whose optical response changes due to an external signal. However, commonly used PCMs such as Ge₂Sb₂Te₅ (GST) are limited in their applications for color coatings, due to high absorption of visible light. Here, the alternative PCM Sb₂S₃ is used, and a novel coating design is demonstrated, which incorporates the PCM layer into an asymmetric Fabry–Perot cavity with Ag, SiO₂ and Ti layers. Simulations are used to show that this design yields high-chroma colors in a wide range of hues, which exhibit a large tunable hue shift when the phase of the Sb₂S₃ layer changes. Three coatings are deposited to experimentally verify these results, which give good agreement with the simulations. The phase change of the Sb₂S₃ layer is demonstrated using direct heating using a hotplate, and also using laser annealing, which allows microscale image writing to be realized on the coatings.

Time-multiplexed laser projection is recognized as a promising projection technology owing to its broad color gamut and high energy efficiency. The escalating demands for enhanced laser safety and reduced space occupation necessitate the development of ultrashort throw ratio (UTR) projectors. However, the inherent mechanical deflection limitations and distortions of micro electro mechanical systems (MEMS) scanners pose significant challenges to achieving UTR projection. To address these constraints, trapezoidal distortion is first eliminated by ensuring vertical laser incidence on MEMS mirrors during the initial projection phase. Subsequently, a systematic design methodology for UTR laser MEMS projection systems is proposed, incorporating a miniaturized catadioptric projection objective that maintains uniformly optical étendue distribution. This configuration achieves a throw ratio of 0.27, reduces pillow distortion to 0.4%, and ensures consistent resolution across the entire screen. Segmentation and modular assembly of the catadioptric objective at telecentric intermediate image planes enhances the efficiency of initial structural design phase. The developed projection prototype experimentally validates the efficacy of the projection system designed through the proposed methodology in decreasing the projection ratio, correcting distortion, and maintaining uniform projection resolution across the full field of view.

Nonzero Berry curvature is central to the existence of topological edge states in electronic and photonic valley-Hall systems. While manipulating the Berry curvature in condensed matter systems is challenging, valley-Hall topological photonics offer unprecedented control, where the broken spatial inversion symmetry alters the Berry curvature. Herein, an all-silicon Berry antenna is presented, using a continuously varying geometry corresponding to a gradual change in Berry curvature. The on-chip topological edge mode with a tunable field extent is achieved to enhance effective antenna aperture, creating a high-gain on-chip photonic antenna with perfectly planar wavefronts. Experimentally, a maximum gain of 17 dBi that supports 20 Gbps chip-to-chip wireless communication is demonstrated, with active optical tunability of the antenna gain with modulation depths of 8 dBi. This Berry antenna paves the way for the development of complementary metal-oxide-semiconductor (CMOS) compatible topological Berry devices, with potential applications in integrated micro-/nano-photonics, next-generation wireless communications (6G to Xth generation), and terahertz detection and ranging.