We demonstrate that a graphene-based guided-wave structure can realize an effective epsilon-and-mu-near-zero (EMNZ) medium over an exceptionally broad bandwidth. The proposed platform consists of a parallel-plate waveguide in which a graphene sheet is placed in deep subwavelength proximity to a PEC wall, forming a tunable reactive boundary that governs phase accumulation and modal dispersion. By exploiting this configuration, both the effective permittivity and permeability of the guided mode are simultaneously driven toward zero across a wide frequency range, yielding a robust EMNZ response that is not tied to narrow resonant phenomena. Closed-form dispersion relations reveal how the graphene conductivity and subwavelength spacing jointly control the effective material parameters. Full-wave simulations validate the analytical predictions and confirm the existence of a broadband regime characterized by extremely long guided wavelengths and negligible phase advance over electrically short sections. These results establish graphene-loaded waveguides as a simple, scalable, and physically transparent route to broadband EMNZ metamaterials, with direct relevance to integrated photonic and electromagnetic devices.
With high-power lasers widely used, protecting optical systems and human eyes from laser damage is crucial. In this work, using the high adhesive and low-melting-point polymer TPU as the matrix, we fabricated MAPbBr 3 PQD/TPU composite film. The film exhibits strong nonlinear absorption and optical limiting properties. The nonlinear absorption and nonlinear refraction coefficients are 1.2 × 10 −12 (m/W) and −6 × 10 −19 (m 2 /W), respectively. The optical limiting threshold is 0.11 J/cm 2 . Furthermore, the film demonstrates superior adhesion. These properties make the film highly promising for optical system laser protection applications.
This paper presented a spin-decoupled metasurface antenna that overcame the inherent spin-phase coupling limitation in conventional Pancharatnam-Berry (PB) phase designs. The intrinsic locking between spin states and phase responses in traditional approaches had significantly constrained their applications in dual-polarization communication and quantum information processing. By innovatively designing an S-shaped unit cell architecture that combines rotation-dependent geometric phase with arc-length modulation, independent wavefront control of left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) was achieved. Fabricated using cost-effective graphene assembled films (GAF), the design achieves high conductivity and scalable performance. Experimental results demonstrated that the 16 × 16 array simultaneously realized three breakthrough functionalities: wide-angle asymmetric beam deflection, high-purity (>79%) dual-mode vortex beam generation, and programmable orbital angular momentum (OAM) beam manipulation. This work provided crucial technical support for next-generation high-capacity polarization-multiplexed communication systems and integrated photonic devices.
Hyper-Rayleigh (HR) optical activity has attracted interest as a sensing method because it generates strong signals from extremely small sample volumes and exhibits high sensitivity to surface properties. Here, we investigate HR scattering from relatively large chiral scatterers: plasmonic silver nanohelices with characteristic dimensions of approximately one quarter of the excitation wavelength. The second-harmonic scattering intensity and nonlinear optical activity are measured in the forward, right-angled, and backward directions. The results confirm the expected geometric symmetry of HR scattering, with comparable forward and backward emission intensities. Notably, the backward detection geometry exhibits the strongest nonlinear chiroptical contrast. Statistical analysis of the intensity distributions yields a d′ value of 2.1 in the backward direction, compared with 1.5 for right-angle detection and 1.2 for forward detection. This enhanced separation between the responses to left- and right-circularly polarized excitation demonstrates that backward detection can provide improved discrimination of nonlinear chiral signals. These results establish backward hyper-Rayleigh scattering as a practical detection geometry for nonlinear chiroptical measurements, particularly in reflection-based configurations compatible with microscopy and high-throughput screening platforms.
Femtosecond laser direct writing enables rapid and flexible fabrication of optical waveguides for integrated photonics. We systematically examined the effects of laser energy, repetition rate, scanning speed, and slit insertion on the structural and optical properties of lithium niobate waveguides fabricated with 1031 nm, 420 fs pulses. End-face coupling was employed to characterize the near-field mode profiles, polarization-dependent behaviors, and propagation losses. The results show that Type I waveguides are preferentially formed at high repetition rates or with slit insertion, while Type II waveguides are favored at low repetition rates. These findings provide quantitative design rules for LiNbO 3 waveguides in specific photonic applications.
Valley edge states are commonly explained through bulk-edge correspondence between two valley Hall domains, yet their dispersion remains sensitive to interface geometry. At a glide-shifted interface, relative lattice translation opens a transport gap and suppresses continuous edge-state transmission. Here, we introduce a massless Dirac domain as a buffer into the glide-shifted valley interface to restore geometry-tolerant valley transport. The restoration requires spectral matching, including a Dirac cone at the same valley momentum and a Dirac frequency within the bandgap of the two gapped valley domains. It is tolerant to buffer domain position, with the strongest restoration near the half-shift position. The restoration is evidenced by the removal of the glide-induced transport gap, the recovery of continuous edge-state dispersion, and the preservation of valley transmission with an L3 defect. This work provides a practical route to reducing the sensitivity of valley edge states to interface termination and fabrication-induced misalignment.
We report a systematic investigation of the effect of lanthanum incorporation on the polarization-resolved spectroscopic and laser properties of Pr 3+ -doped Sr 1- x La x Mg x Al 12- x O 19 (ASL) hexaaluminate solid-solution crystals, with reference to the parent SrAl 12 O 19 (SRA) compound. The addition induces inhomogeneous broadening of absorption and emission bands, while only weakly affecting the phonon spectra and radiative transition probabilities. In the red spectral region (the 3 P J → 3 F 2 transition), Pr 3+ :SRA exhibits a stimulated-emission cross section σ SE as high as 16.4 × 10 −20 cm 2 at 643.6 nm, with an emission bandwidth of 1.0 nm. For the La 0.47 composition, σ SE decreases to 6.1 × 10 −20 cm 2 at 645.8 nm, while the bandwidth is broadened to 4.1 nm. The luminescence lifetime remains nearly unchanged across the compositions, in the range of 36–38 µs. Under 465 nm GaN diode pumping, the optimized Pr 3+ :ASL (La 0.26 ) crystal delivers 164 mW at 644 nm, with a slope efficiency of 13.2% and a laser threshold of 0.30 W. Laser action in the deep red is also demonstrated. These results highlight the potential of La-substituted, Pr 3+ -doped hexaaluminates as broadly emitting visible laser gain media.
We report the femtosecond laser inscription of mid-infrared waveguides in Pr3+-doped chalcogenide glasses with composition 90[0.8(GeS2) - 0.2(Ga2S3)] - 10[CsCl]. These glasses feature low phonon energies, high rare-earth solubility, and broad transparency, although impurity absorption emerges at higher doping levels. Pr3+ ions in the glass feature broadband luminescence spanning 3.5-5.5 & micro;m. Three hexagonal-cladding waveguides (27 & micro;m diameter) with varying channel separations were fabricated in a longitudinal writing geometry and characterized using mu-Raman and mu-luminescence spectroscopy, Nomarski microscopy, and confocal profilometry. The study revealed densification in the laser-modified regions and an anisotropic stress field surrounding the waveguides. The waveguides exhibited low propagation losses (<1 dB/cm) with no significant additional loss from Pr3+ doping, highlighting their potential for mid-infrared sensing and integrated photonic devices.
VO2/ZrO2 double- and triple-layer thin-film devices were fabricated by reactive magnetron sputtering on crystalline Si (100) and r-cut sapphire substrates. Structural and optical characterization showed that a ZrO2 buffer layer in VO2/ZrO2/sapphire enhanced transmittance while preserving a sharp phase transition. On sapphire, transmittance over 1500-2500 nm increased from single-layer VO2 to VO2/ZrO2 and to ZrO2/VO2/ZrO2, reaching 80% when the top ZrO2 was deposited at 500 degrees C. In contrast, ZrO2 capping at 650 degrees C partially overoxidized VO2 to VOx (x > 2), causing poorer transmittance and residual metallic-state transmission. Results indicate that layer placement and deposition temperature control switching performance and optical transmittance. (c) 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
Near-zero-index (NZI) metamaterials, characterized by an effective refractive index approaching zero, exhibit a near-zero propagation constant and an extremely large wavelength, resulting in fundamentally different wave dynamics. NZI media support nearly uniform phase and spatially coherent fields, enabling geometry-independent behavior and wave tunneling. These properties relax the coupling between geometry and electromagnetic response, offering a new way to overcome the limits of conventional electromagnetic devices. In antenna engineering, such decoupling challenges the conventional constraint that resonance and radiation characteristics are tied to structural dimensions, enabling new opportunities for antenna miniaturization and radiation control. In practice, NZI behavior is typically realized through zeroth-order modes (ZOMs), allowing antennas to achieve geometry-independent resonance with enhanced design flexibility. This review first outlines the fundamental electromagnetic properties of NZI metamaterials, then surveys the operating principles and representative designs of ZOM antennas across different platforms, including periodic structures, transmission-line loops, and waveguide-based configurations. Finally, we discuss key challenges such as loss, bandwidth, and system integration, and highlight future directions for NZI-enabled antenna engineering.
High-Q metasurfaces based on surface lattice resonances (SLRs) offer a viable route to mitigating the limited interaction volume of conventional near-field sensing by enabling stronger field confinement and enhancement within the sensing region. Here, we designed and fabricated a gold nanopillar array metasurface that simultaneously supports pronounced near-field enhancement and a high-Q resonance, with measured Q factors exceeding 200, and the refractive-index sensitivity reaches 319 nm/RIU. Moreover, in biomarker assays targeting BSA, S1001, and GFAP, the limits of detection were determined to be 8.46 fg/mL, 0.06 fg/mL, and 0.94 fg/mL, respectively. These results highlight the proposed SLR's gold metasurface as a robust and generalizable nanophotonic sensing platform that combines high-Q resonances with practical bioassay performance for ultrasensitive, multiplex-compatible biomarker detection.
Ho 3+ -doped disordered CaAlGdO 4 (CALGO) crystals have recently emerged as a promising gain material platform for next-generation high-power ultrafast 2.1-µm laser systems. This laser gain material offers a unique combination of high-gain, small quantum defect, inhomogeneously broadened spectra, and good thermal conductivity, enabling ultrashort pulse generation and amplification at high-average power and high pulse energy. Many systems, including mode-locked oscillators and amplifiers with state-of-the-art performance, have been demonstrated in the last few years that promise to meet growing application demands for efficient ultrafast laser technology in this wavelength region. In this review paper, we summarize recent achievements using this gain material both in oscillators and amplifiers and place these results in the state-of-the-art of 2-µm ultrafast laser technology, present detailed spectroscopic characterization of this material, and discuss future perspectives of further performance scaling of Ho:CALGO lasers.
Group-IV GeSn alloys have gained significant attention as an attractive material system for silicon photonics. Thermal annealing provides an efficient route to improve the crystalline quality and overall performance of GeSn layers. Here, we present a comparative study on the effects of rapid thermal annealing (RTA) and microwave annealing (MWA) on GeSn samples grown on Si via Ge buffer layers containing ∼6.3% Sn under a compressive strain of 0.793%. Structural analysis reveals that RTA at ∼380 °C yields a modest strain relaxation of ∼20% and enhanced crystallinity. However, RTA at higher temperatures results in defect generation and a decrease in photoluminescence (PL) emission intensity. In contrast, MWA at a moderate power of ∼900 W achieves a higher strain relaxation of ∼27–28% while preserving both material quality and PL emission. This advantage is attributed to the more localized energy delivery and reduced thermal budget of MWA, which mitigates Sn diffusion and maintains alloy integrity. In addition, theoretical analysis of the strain-dependent band structure and spontaneous emission in GeSn further confirms that increased strain relaxation enhances the direct-gap character and radiative recombination. These findings demonstrate that MWA offers a more robust and scalable post-growth annealing route for optimizing GeSn layers while balancing strain engineering, optical performance, and material stability, thereby advancing the development of high-performance, complementary metal oxide semiconductor-compatible GeSn-based photonic devices.
