Coupling Of Optical Modes Research Articles

Engineering Fano resonances in plasmonic metasurfaces for colorimetric sensing and structural colors

In this paper, we present the design and fabrication of a plasmonic metasurface based on titanium dioxide (TiO2) nanowire arrays integrated with plasmonic layers. The structure is engineered to produce Fano resonances within the visible spectrum, resulting from the coupling of localized surface plasmon resonances, lattice modes, and nanowire's optical modes. Experimentally, we show that by tuning the geometrical features of the metasurface, such as the length, diameter, and period of the nanowires, a high-quality factor single peak can be achieved in the reflection spectra, resulting in vivid structural colors in bright field. To our knowledge, this is the first demonstration of such vivid colors with nanowire arrays in bright field reflections. When characterized by refractive index fluids around the refractive index of water, the plasmonic metasurface also showed great potential for biochemical colorimetric sensing. The best design demonstrated a bulk sensitivity of 183 nm/RIU with high Q resonance features and linear changes in color values using image processing.

High thermoelectric performance in p-type ZnSb upon increasing Zn vacancies: an experimental and theoretical study

Zn-vacancy driven high power factor and strong coupling of acoustic and optical modes enhance the zT in p-type ZnSb.

Low-loss weak-coupling 6-mode hollow-core negative curvature fiber based on symmetric double-ring nested tube

Few-mode optical fibers have played an increasingly important role in breaking through the transmission capacity limitations of single-mode optical fiber and alleviating the bandwidth crisis in optic fiber communication systems in recent years. Nevertheless, traditional solid core few-mode optical fibers usually suffer optical fiber nonlinearity and mode coupling, leading to mode crosstalk between channels. Hollow core negative curvature fibers (HC-NCF) have attracted widespread attention due to their advantages, such as low latency, low nonlinearity, low dispersion, low transmission loss, and large operating bandwidth. In this work, a novel low-loss few-mode HC-NCF with symmetrically double ring nested tube structure is designed, which supports six core modes including LP<sub>01</sub>, LP<sub>11</sub>, LP<sub>21</sub>, LP<sub>02</sub>, LP<sub>31<i>a</i></sub>, and LP<sub>31<i>b</i></sub>. The designed optical fiber is based on silica dioxide substrate and adopts a unique symmetrical double ring nested cladding structure, which can effectively suppress the coupling between the core mode and the cladding mode. The finite element method (FDE) is used to numerically analyze the properties of the proposed few-mode HC-NCF and optimize the structural parameters of the few-mode HC-NCF. Moreover, the confinement loss and bending loss of all core modes are investigated. The simulation results show that the proposed few-mode HC-NCF can support the independent transmission of six weakly coupled core modes (with the effective refractive index difference greater than 1×10<sup>–4</sup> between the adjacent core modes, which greatly avoids the coupling between the adjacent modes in the fiber core). In the 400 nm bandwidth (1.23–1.63 μm, covering the O, E, S, C, and L bands), all six modes in the fiber core maintain low loss transmission. Moreover, in the range of 1.3–1.63 μm, the confinement loss (CL) of LP<sub>01</sub>, LP<sub>11</sub> and LP<sub>21</sub> mode are all less than 1×10<sup>–3</sup> dB/m, and the CL of LP<sub>02</sub> and LP<sub>31<i>b</i></sub> mode are both less than 3×10<sup>–3</sup> dB/m. The CL of each mode reaches the lowest value at 1.4 μm, and the LP<sub>01</sub> mode has the lowest CL of 4.3×10<sup>–7</sup> dB/m. In addition, for a bending radius of 7 cm, each mode maintains the low bending loss characteristic in a certain operating wavelength range. In the range of 1.23–1.61 μm, the BL of LP<sub>01</sub> is less than 4.5×10<sup>–4</sup> dB/m, and the BL of LP<sub>11</sub> is less than 1.3×10<sup>–3</sup> dB/m. The tolerance analysis shows that even with the deviation of structural parameters of ±1%, the few-mode HC-NCF can still maintain the characteristic of low-loss and weak coupling. The designed few-mode HC-NCF has ultra-low CL and bending-insensitive characteristics while supporting independent transmission of six modes, which will find huge potential applications in future high performance mode division multiplexing systems.

Strong anapole-plasmon coupling in dielectric-metallic hybrid nanostructures.

The nanoscale ampification of light-matter interactions exhibits profound potential in multiple scientific fields, such as physics, chemistry, surface science, materials science, and nanophotonics. Nonetheless, achieving robust optical mode coupling within cavities faces significant hurdles due to modal dispersion and weak optical field confinement. In this theoretical investigation, we demonstrate the viability of strong coupling between the anapole mode of a slotted silicon nanodisk and the plasmonic modes of an Ag nanodisk dimer at visible light frequencies. By introducing anapole modes, we successfully confine light to subwavelength volumes, suppressing radiative losses and achieving a remarkable Rabi splitting of 468 meV. This substantial coupling is facilitated by the large spatial overlap of intense optical fields. Capitalizing on this strong mode coupling, we generate novel hybrid energy states with significant electromagnetic field enhancement. Our study serves as a valuable blueprint for designing platforms based on strong anapole mode coupling at visible frequencies and paves the way for deeper explorations into nanoscale light-matter interactions.

Bose Condensation of Upper-Branch Exciton-Polaritons in a Transferable Microcavity.

Exciton-polaritons are composite quasiparticles that result from the coupling of excitonic transitions and optical modes. They have been extensively studied because of their quantum phenomena and potential applications in unconventional coherent light sources and all-optical control elements. In this work, we report the observation of Bose-Einstein condensation of the upper polariton branch in a transferable WS2 monolayer microcavity. Near the condensation threshold, we observe a nonlinear increase in upper polariton intensity accompanied by a decrease in line width and an increase in temporal coherence, all of which are hallmarks of Bose-Einstein condensation. Simulations show that this condensation occurs within a specific particle density range, depending on the excitonic properties and pumping conditions. The manifestation of upper polariton condensation unlocks new possibilities for studying the condensate competition while linking it to practical realizations in polaritonic lasers. Our findings contribute to the understanding of bosonic systems and offer potential for the development of polaritonic devices.

Magnetic Mode Coupling in Hyperbolic Bowtie Meta-Antennas.

Hyperbolic metaparticles have emerged as the next step in metamaterial applications, providing tunable electromagnetic properties on demand. However, coupling of optical modes in hyperbolic meta-antennas has not been explored. Here, we present in detail the magnetic and electric dipolar modes supported by a hyperbolic bowtie meta-antenna and clearly demonstrate the existence of two magnetic coupling regimes in such hyperbolic systems. The coupling nature is shown to depend on the interplay of the magnetic dipole moments, controlled by the meta-antenna effective permittivity and nanogap size. In parallel, the meta-antenna effective permittivity offers fine control over the electrical field spatial distribution. Our work highlights new coupling mechanisms between hyperbolic systems that have not been reported before, with a detailed study of the magnetic coupling nature, as a function of the structural parameters of the hyperbolic meta-antenna, which opens the route toward a range of applications from magnetic nanolight sources to chiral quantum optics and quantum interfaces.

Phase coupling of acoustic and optical modes in antiferromagnetic materials CrCl3

In layered antiferromagnetic material CrCl3, due to the antiferromagnetic coupling between two magnetic sublattices, there are two antiferromagnetic resonance modes, called acoustic mode with in-phase precession and optical mode with out-of-phase precession. By using Landau–Lifshitz–Gilbert equation, we study the magnetization dynamics of the two sublattices in CrCl3. A coupling resonance mode appears at the coupling point when the acoustic and optical magnon modes are tuned by an applied magnetic field, which is called ‘coupling mode’. In this paper, we present an explanation for the coupling of the acoustic and the optical mode. Our calculation shows that the coupling of the acoustic and optical mode is accomplished by change of the precession phase-difference between two magnetic sublattices.

Material- and shape-dependent optical modes of hyperbolic spheroidal nano-resonators.

Hyperbolic nanoresonators, composed of anisotropic materials with opposite signs of permittivity, have unique optical properties due to a large degree of freedom that hyperbolic dispersion provides in designing their response. Here, we focus on uniaxial hyperbolic nanoresonators composed of a model silver-silica multilayer in the form of spheroids with a broad aspect ratio encompassing both prolate and oblate particles. The origin and evolution of the optical response and mode coupling are investigated using both numerical (T-matrix and FDTD) and theoretical methods. We show the tunability of the optical resonances and the interplay of the shape and material anisotropy in determining the spectral response. Depending on the illumination conditions as well as shape and material anisotropy, a single hyperbolic spheroid can show a dominant electric resonance, behaving as a pure metallic nanoparticle, or a strong dipolar magnetic resonance even in the quasistatic regime. The quasistatic magnetic response of indicates a material-dependent origin of the mode, which is obtained due to coupling of the magnetic and electric multipoles. Such coupling characteristics can be employed in various modern applications based on metasurfaces.

Strong coupling of multiple optical interface modes with ultra-narrow linewidth in one-dimensional topological photonic heterostructures.

Coherent coupling of optical modes with a high Q-factor underpins realization of efficient light-matter interaction with multi-channels in resonant nanostructures. Here we theoretically studied the strong longitudinal coupling of three topological photonic states (TPSs) in a one-dimensional topological photonic crystal heterostructure embedded with a graphene monolayer in the visible frequencies. It is found that the three TPSs can strongly interplay with one another in the longitudinal direction, enabling a large Rabi splitting (∼ 48 meV) in spectral response. The triple-band perfect absorption and selective longitudinal field confinement have been demonstrated, where the linewidth of hybrid modes can reach 0.2 nm with Q-factor up to 2.6 × 103. Mode hybridization of dual- and triple-TPSs were investigated by calculation of the field profiles and Hopfield coefficients of the hybrid modes. Moreover, simulation results further show that resonant frequencies of the three hybrid TPSs can be actively controlled by simply changing the incident angle or structural parameters, which are nearly polarization independent in this strong coupling system. With the multichannel, narrow-band light trapping and selectively strong field localization in this simple multilayer regime, one can envision new possibilities for developing the practical topological photonic devices for on-chip optical detection, sensing, filtering, and light-emitting.

Design and Realization of Polymeric Waveguide/Microring Structures for Telecommunication Domain.

Polymer-based micro-optical components are very important for applications in optical communication. In this study, we theoretically investigated the coupling of polymeric waveguide and microring structures and experimentally demonstrated an efficient fabrication method to realize these structures on demand. First, the structures were designed and simulated using the FDTD method. The optical mode and loss in the coupling structures were calculated, thereby giving the optimal distance for optical mode coupling between two rib waveguide structures or for optical mode coupling in a microring resonance structure. Simulations results then guided us in the fabrication of the desired ring resonance microstructures using a robust and flexible direct laser writing technique. The entire optical system was thus designed and manufactured on a flat base plate so that it could be easily integrated in optical circuits.

Effects of propagation phase on the coupling of plasmonic optical modes

Effects of propagation phase on the coupling of plasmonic optical modes

Light Absorption Enhancement and Laser-Induced Damage Ability Improvement of Aluminum Alloy 6061 with Non-Porous Alumina/CdSe@Al2O3/SiO2 Functional Gradient Films.

Numerical calculations of ultraviolet to near-infrared absorption spectra by cadmium selenide quantum dots (CdSe QDs) doped in anodic aluminum oxide pores were performed using a finite-difference time-domain model. The height, diameter, and periodic spacing of the pores were optimized. Light absorption by the dots was enhanced by increasing the height and decreasing the diameter of the pores. When the height was less than 1 μm, visible light absorption was enhanced as the spacing was reduced from 400 nm to 100 nm. No enhancement was observed for heights greater than 6 μm. Finally, the optical mode coupling of the aluminum oxide and the quantum dots was enhanced by decreasing the pore diameter and periodic spacing and increasing the height. Laser ablation verified light absorption enhancement by the CdSe QDs. The experiments verified the improvement in the laser-induced damage ability with a nanosecond laser at a wavelength of 355 nm after aluminum alloy 6061 was coated with functional films and fabricated based on numerical calculations.

Phase Coupling of Acoustic and Optical Modes in Antiferromagnetic Materials Crcl3

Phase Coupling of Acoustic and Optical Modes in Antiferromagnetic Materials Crcl3

Combining Optical Strong Mode Coupling with Polaritonic Coupling in a λ/2 Fabry–Pérot Microresonator

Combining Optical Strong Mode Coupling with Polaritonic Coupling in a λ/2 Fabry–Pérot Microresonator

Frequency-multiplexed hybrid optical entangled source based on the Pockels effect

In the recent years important experimental advances in resonant electro-optic modulators as high-efficiency sources for coherent frequency combs and as devices for quantum information transfer have been realized, where strong optical and microwave mode coupling were achieved. These features suggest electro-optic-based devices as candidates for entangled optical frequency comb sources. In the present work, I study the generation of entangled optical frequency combs in millimeter-sized resonant electro-optic modulators. These devices profit from the experimentally proven advantages such as nearly constant optical free spectral ranges over several gigahertz, and high optical and microwave quality factors. The generation of frequency multiplexed quantum channels with spectral bandwidth in the MHz range for conservative parameter values paves the way towards novel uses in long-distance hybrid quantum networks, quantum key distribution, enhanced optical metrology, and quantum computing.

From Fano to Quasi-BIC Resonances in Individual Dielectric Nanoantennas.

Sharp optical resonances in high-index dielectric nanostructures have recently attracted significant attention for their promising applications in nanophotonics. Fano resonances, as well as resonances associated with bound states in the continuum (BIC), have independently shown a great potential for applications in nanoscale lasers, sensors, and nonlinear optical devices. Here, we demonstrate experimentally a close connection between Fano and quasi-BIC resonances excited in individual dielectric nanoantennas. We analyze systematically the resonant response of AlGaAs nanoantennas pumped with a structured light in the near-infrared range. We trace a variation of the scattering spectrum that fully agrees with an analytical expression governed by a Fano parameter and observe directly a transition to a quasi-BIC resonance. Our results suggest a unified approach toward the analysis of sharp resonances in subwavelength nanostructures originating from strong coupling of optical modes that can provide high energy localization for enhanced light-matter interactions.

Dynamical Characteristics of Twin-Microring Lasers With Mutual Optical Injection

Nonlinear dynamics of mutually injected twin-microring semiconductor lasers are studied numerically and experimentally. For the twin-microring laser, a bridge waveguide directly connecting two identical microrings is utilized to realize mutual optical injection or mode coupling. The coupling coefficient is related to the waveguide parameter and influences the mutual injection process dramatically. By adjusting the frequency offset between two microrings, four-wave mixing, injection locking, periodic, and multi-period oscillation states are observed from the experimental lasing spectra. The plentiful nonlinear dynamical states are induced by the mode interaction between the two microrings and can be well explained by the rate equations with mutual optical injection.

Design and characterization of a low-optical-loss UV-C laser diode

We present an optical modeling and characterization study of prototype ultraviolet laser diode (LD) structures grown on single-crystal AlN substrates, with focus on the reduction of modal loss caused by optical mode coupling to the absorptive layers on the p-side (i.e. p-contact and p-metal layers). The transparent AlN substrates enabled optical pumping for measuring modal loss without requiring functioning LDs. The modal loss measured in this way was in good agreement with electrically evaluated results of processed LDs, and both results were consistent with optical modeling predictions. By using 0.32 μm thick p-side cladding, we were able to suppress the modal loss of the designed LD structure to 8.4 cm−1, where the contribution from the absorptive p-contact layers was less than 3 cm−1.

Regimes of optical mode coupling: from core-shell single particle to dimer

We study a transformation of a core-shell dielectric rod into a dimer by pulling the core rod out of the shell. We present simulated scattering spectra of two infinite dielectric rods with dipole Mie resonances tailored to the same frequency by choice of the refractive indices ratio. We identify a transition between weak and strong coupling regimes by examining the peak splitting of the dipole Mie resonance. We find that the splitting increases as the distance between the rod centres decreases. This behaviour is kept for all configurations: core-shell, eccentrically embedded rod and dimer.

High figure of merit of monolayer Sb2Te2Se of ultra low lattice thermal conductivity

The electronic structure and thermoelectric properties of monolayer Sb2Te2Se are studied by density functional theory and semi-classical Boltzmann transport equation. The Seebeck coefficient for monolayer Sb2Te2Se is very high, comparing with other thermoelectric materials. The strong coupling of acoustic and optical modes enhanced phonon scattering, which will cause lower lattice thermal conductivity. The heavy elements and small band gap cause the low thermal conductivity of monolayer Sb2Te2Se, so the lattice thermal conductivity of monolayer Sb2Te2Se is much lower than other thermoelectric materials. The optimal value ZeT of monolayer Sb2Te2Se is so high, mainly due to the very low lattice thermal conductivity. For the better n-type, ZeT reaches 1.5 at a temperature of 1000 K, which proves that monolayer Sb2Te2Se is a good choice for thermoelectric materials.