Advanced Photonics Research最新文献

Topological boundary modes utilizing valley mode waveguides have opened opportunities in, for instance, the design of high transmission waveguides with tolerance to geometrical defects and sharp bends. Applications of these waveguides include linear computational processes and the emulation of logic gates using linear structures, among other scenarios. Herein, the design of a 6-port junction that exhibits equal power splitting to three other ports when excited at single port with no reflections is presented. In studying this structure, a scattering matrix is extracted at telecom wavelengths (around 1550 nm). The linearity of the system along with the scattering matrix is exploited to produce linear operations such as routing of information considering two incident signals or multiple signals applied from different ports. These results may be exploited to analytically design larger networks without the need of computationally expensive trial and error methods.

Many different approaches have been proposed or published in recent years on the measurement of small vibrations and/or large-amplitude displacements by interferometers, either traditional or self-mixing type. Most of them start from procuring a pair of orthogonal signals cos 2kΔs and sin 2kΔs, where k = 2π/λ and Δs is the variation of target distance, from which to proceed to calculate the measurand Δs with the atan of the ratio followed by an unfolding operation. These attempts are commented on, and it is shown that it is not really necessary to add phase modulators or other extra optical components nor to use elaborate signal processing to obtain the orthogonal pair, because simple hardware solutions readily supply, without the cosine and sine pair, a resolution close to the quantum limit together with excellent dynamic range, precision, linearity, and bandwidth. The examples reported in this article establish a benchmark of performances that must be referred to in developing new approaches that make sense, also considering that such performances have been offered by commercial instruments for several decades.

A W-type normal dispersion thulium-doped fiber (NDTDF) is utilized to generate high average power, high-energy femtosecond pulses at 1.7 μm region for bio-imaging applications. Net normal dispersion cavity fiber lasers are used to generate positively chirped soliton pulses, which are subsequently amplified through the NDTDF. Because of the normal dispersion of the Tm-doped silica fiber, the amplified pulses are able to be compressed using a conventional telecommunication fiber such as SMF-28. Hence, an all-fiber ultrafast laser source is constructed in the 1.7 μm wavelength region for deep tissue imaging applications. This paper reports ≈230 nJ, with its corresponding average power as high as 1.74 W. Further adjustment of dispersion in the all-fiber configuration allows the main pulse duration to be compressed to ≈200 fs. Core size scalability of the proposed W-type NDTDF has also been investigated.

Transition metal dichalcogenides (TMDC) are emerging as promising photonic platforms with favorable optical properties such as high refractive index, wide optical transparency window, and strong nonlinear optical susceptibilities. The electric field enhancement achievable within TMDC resonant subwavelength resonant structures can result in multifold enhancements in nonlinear optical processes. Herein, strong resonant enhancement in polarization anisotropy in third harmonic generation (THG) from isolated MoS₂ disk resonators is reported due to small structural ellipticity introduced during fabrication. The anisotropic optical response from the disks results in noticeable spectral shifts in the reflectance dip and THG peak for orthogonally polarized fundamental excitations. Polarization dependent THG response also reveals significant deviations from the expected isotropic behavior for circular disk with highly polarization selective double-lobed and fourlobed profiles. The observed polarization selectivity is quantified using a contrast metric, which is as high as 47% for the THG measurements, while linear reflectance yields only 2%–4%. These observations are corroborated by electromagnetic simulations of polarization-resolved linear and THG response considering the small structural ellipticity. Resonant tuning of nonlinear signal polarization properties through subwavelength structure perturbation can be leveraged for selective polarization state generation or detection with applications in classical and quantum photonics.

Combining in situ growth with sputtering deposition techniques, MAPbBr₃@Ag core–shell surface-enhanced Raman scattering (SERS) substrates are fabricated. The nanostructures of MAPbBr₃@Ag facilitate strong localized surface plasmon resonance responses, effectively enhancing the SERS performance. Furthermore, charge transfer between the MAPbBr₃@Ag core–shell structure and methylene blue (MB) leads to chemical enhancement—a key factor in boosting Raman scattering signals. The constructed MAPbBr₃@Ag core–shell SERS platform achieves a detection limit of 10⁻¹⁰ M for MB with an enhancement factor of 3.27×10⁷. Finite-difference time-domain simulations correlate well with experimental results.

This work presents a practical realization of a foundational approach for fabricating arrays of self-aligned micro- and nanopillar structures incorporating individual site-controlled quantum dots (QDs) for bright nonclassical light extraction. This method leverages the nonplanar surface morphology of pyramidal QD samples to define dielectric masks self-aligned to the QD positions. The mask size and consequently the lateral dimensions of the pillars, are precisely controlled through a chemical mechanical polishing (CMP) step, obviating the need for any additional lithography step for creating the pillar. This fabrication technique offers several key advantages, including precise control over the pillar sites, and fully deterministic embedding of QD structures. The functionality of the structures is validated by integrating single In_0.25Ga_0.75 As QDs—upon two-photon excitation (TPE) of the biexciton state, the emission of single and polarization-entangled photon pairs is observed. Additionally, an extra fabrication step to deposit dome-like structures atop the pillars was demonstrated, resulting in a total light extraction efficiency of 9.5% at the first lens—a record within the pyramidal QD family.

This review explores the potential of Raman spectroscopy and microscopy (RS) in clinical medicine, focusing on the diagnostic and therapeutic applications across multiple disciplines. For example, RS has proven effective in distinguishing between healthy and malignant cells or tissues, monitoring metabolic changes, and characterizing various biomolecular processes. Further applications include cancer detection and monitoring of neurodegenerative diseases, cardiovascular and gastrointestinal research, liquid biopsies, intraoperative guidance, and early disease diagnoses. Challenges such as signal interference, standardization issues, and limited clinical application are discussed. These show that better sensitivity, reproducibility further clinical validations, and standardization across different laboratories are needed in the future. In many areas, such as hematology, oncology, infectious diseases, neurology, gastroenterology, reproductive medicine, rheumatology, and cardiovascular research RS has contributed to early diagnoses, therapy monitoring, and intraoperative guidance. The development indicates that large-scale multicenter studies, harmonized protocols, reference databases, and close collaboration with regulatory agencies will be helpful to establish RS as a reliable clinical tool. Then RS may become a widely adopted method for diagnostics, patient stratification, and treatment monitoring across medicine.

Transmission Filters

In article number 2500057, Dawn T. H. Tan and co-workers develop a CMOS-compatible transmission structural color filter implemented using subwavelength nanostructures and validated through design, simulation, and experiments. Tunable peak wavelengths are achieved lithographically within a single dielectric layer, avoiding thickness variations. The proposed nanostructure yields 10–30 nm spectral resolution and ~70% efficiency, offering efficient, simplified, cost-effective multispectral filters.

The accurate estimation of propagation loss in microphotonic waveguides is a crucial factor in the performance optimization of photonic integrated circuits. This article presents a comprehensive review of both numerical and experimental methods used to estimate propagation loss. Numerical methods, including volume current, finite-difference time domain, finite element, and eigenmode expansion, offer high precision by modeling the intrinsic physical characteristics of waveguides, such as sidewall roughness, which significantly contributes to scattering loss. However, these methods are heavily dependent on detailed physical measurements, including roughness profiles. In contrast, experimental approaches like the cut-back method and interferometric techniques provide practical means for measuring propagation loss in real-world settings. These methods, while simpler and faster, are limited in their capacity to explain the origins of propagation loss. The synergy between numerical and experimental techniques is critical to developing effective strategies for minimizing loss in advanced photonic integrated circuits. The findings of this study highlight the necessity for continuous improvement in both computational and experimental methods to enhance the performance of microphotonic waveguides.

High-charge beams remain a key research focus in laser plasma acceleration, driven by the demands of extreme experimental conditions in nuclear physics, laboratory astrophysics, and fusion research. A distinct acceleration mechanism is presented in which the interaction between petawatt femtosecond laser pulses and the subcritical density (SCD) plasma produces electron beams with charges of hundreds of nanocoulomb (nC), far exceeding those typically achieved via conventional laser wakefield acceleration. The synergy between the multiwakefield structure in SCD plasma and the laser self-steepening effect significantly enhances the electron injection rate to 100 nC ps⁻¹, experimentally achieving the electron beam charge up to 245 nC. This mechanism operates by reducing the phase velocity of plasma waves and increasing electron momentum, allowing large numbers of electrons to exceed the wave-breaking threshold and undergo efficient injection. Experiments and simulations consistently confirm the dependence of charge on plasma density and laser energy, with charge reaching a maximum at a specific plasma density. Such high-charge, high-density electron beams offer promising applications in high-flux particle beam physics, large-field-of-view industrial imaging, advanced light sources, and radiation-hardness testing of electronic systems.