Search Results (116)

Enhancing light absorption in two-dimensional (2D) materials, particularly few-layer structures, is critical for advancing optoelectronic devices such as light sources, photodetectors, and sensors. However, conventional absorption enhancement strategies often suffer from unstable resonant wavelengths and low-quality factors (Q-factors) due to the inherent weak light–matter interactions in 2D materials. To address these limitations, we propose an all-dielectric metasurface graphene-perfect absorber based on toroidal dipole bound state in the continuum (TD-BIC) with an ultra-narrow bandwidth and stable resonant wavelength. The proposed structure achieves tunable absorption linewidths spanning three orders of magnitude (6 nm to 0.0076 nm) through critical coupling modulation. Furthermore, the operational wavelength can be flexibly extended to any near-infrared region by adjusting the grating width. This work establishes a novel paradigm for enhancing the absorption of 2D materials in photonic device applications. Full article

Optical sensing technologies, particularly refractive index and temperature sensing, are pivotal in biomedical, environmental, and industrial applications. This study introduces a dual-parameter all-dielectric transmissive grating sensor leveraging symmetry-protected bound states in the continuum (BICs). A one-dimensional silicon grating on a silica substrate was designed and analyzed using finite element analysis software. The proposed grating structure enables the excitation of two distinct BICs, both exhibiting high quality factors (Q-factors) of $Q_{\mathrm{I}}=8.03\times {10}^4$ for Mode I and $Q_{\mathrm{I}\mathrm{I}}=4.48\times {10}^4$ for Mode II. These modes demonstrate significantly different sensing characteristics due to their unique field distributions: Mode I predominantly confines its electromagnetic field within the grating slits, achieving an outstanding refractive index (RI) sensitivity of ${S_{\mathrm{R}\mathrm{I}}}^{\mathrm{I}}=406 \mathrm{n}\mathrm{m}/\mathrm{R}\mathrm{I}\mathrm{U}$ with a minor thermal sensitivity of ${S_{\mathrm{T}}}^{\mathrm{I}}=0.052 \mathrm{n}\mathrm{m}/°\mathrm{C}$. In contrast, Mode II concentrates its field energy in the silicon substrate, resulting in enhanced thermal sensitivity of ${S_{\mathrm{T}}}^{\mathrm{I}\mathrm{I}}=0.078 \mathrm{n}\mathrm{m}/°\mathrm{C}$ while maintaining a refractive index sensitivity of ${S_{\mathrm{R}\mathrm{I}}}^{\mathrm{I}\mathrm{I}}=220 \mathrm{n}\mathrm{m}/\mathrm{R}\mathrm{I}\mathrm{U}$. This complementary sensitivity profile between the two modes establishes an ideal platform for developing a dual-parameter sensing system capable of simultaneously monitoring both refractive index variations and temperature changes. These results highlight the correlation between mode field distribution characteristics and sensing sensitivity performance, and enabling high Q-factor dual-parameter sensing with potential applications in lab-on-a-chip systems and real-time biomolecular monitoring. Full article

This study proposes and numerically demonstrates a novel nonreciprocal electromagnetic metasurface by integrating a highly nonlinear liquid metamaterial (LMM) with a simple two-dimensional silicon dielectric grating. The transmission characteristics of the proposed structure were investigated using a full-vector finite-element method. We demonstrated that the proposed subwavelength-thickness metasurface achieves a transmission coefficient contrast of up to 0.96 between forward and backward propagation. Highly nonlinear LMMs, when employed as nonreciprocal media, significantly lower the radiation power needed to induce a nonlinear response compared to natural materials. Furthermore, we numerically analyzed the effects of the grating’s structural parameters, LMM thickness, and packing fraction on transmittance. The proposed design holds promise for applications in optical isolators. Full article

Silicon photonics is the leading platform in photonic integrated circuits (PICs), enabling dense integration and low-cost manufacturing for applications such as data communications, artificial intelligence, and quantum processing, to name a few. However, efficient and polarization-insensitive fiber-to-PIC coupling for multipoint wafer characterization remains a challenge due to the birefringence of silicon waveguides. Here, we address this issue by proposing polarization-insensitive grating couplers based on subwavelength dielectric metamaterials and metaheuristic optimization. Subwavelength periodic structures were engineered to act as uniaxial homogeneous linear (UHL) materials, enabling tailored anisotropy. On the other hand, particle swarm optimization (PSO) was employed to optimize the coupling efficiency, bandwidth, and polarization-dependent loss (PDL). Numerical simulations demonstrated that a pitch of 100 nm ensures UHL behavior while minimizing leaky waves. Optimized grating couplers achieved coupling efficiencies higher than −3 dB and a PDL of below 1 dB across the telecom C-band (1530–1565 nm). Three optimization strategies were explored, balancing efficiency, the bandwidth, and the PDL while considering the Pareto front. This work establishes a robust framework combining metamaterial engineering with computational optimization, paving the way for high-performance polarization-insensitive grating couplers with potential uses in advanced photonic applications. Full article

The dispersion relationship of plasmons can be modulated by changing the carrier density of the propagating medium, which provides a new degree of freedom for optical modulation. Traditional graphene plasmonic modulators based on carrier control mainly revolve around chemical doping or voltage control methods, but using a single method of modulation limits the optimization of modulation depth. Herein, we propose a hybrid substrate–dielectric–silicon–graphene structure, which can achieve periodic control of the carrier density in graphene through chemical doping of silicon gratings and overall control of the carrier density by applying an external voltage between the substrate and graphene. The numerical results show that the optical transmission can reach 54.6 dB when the grating length, width, period, and working wavelength are 54 nm, 30 nm, 60 nm, and 8 μm, respectively. The modulation depth of the modulator is significantly optimized by combining the above control mechanisms. This structure will have potential applications in optoelectronic sensing, optoelectronic detection, and optical modulation. Full article

Accurate real-time temperature measurement under extreme thermal-pressure conditions remains challenging in aerospace. Sapphire fiber Bragg gratings (FBGs), exhibiting temperature measurement capabilities up to 1900 °C, demonstrate suitability for such extreme environments. However, the development of a high-performance demodulation system capable of processing sapphire FBG signals over wide spectral ranges at elevated speeds remains a technical challenge. This study presents a real-time FBG signal demodulation system that incorporates an all-dielectric subwavelength grating edge filter. The designed grating, comprising a TiO₂/Si₃N₄ subwavelength unit array, modulates Mie-type electric and magnetic multipole resonances to achieve precisely tailored transmission and reflection spectra. Simulation results indicate that the grating exhibits low ohmic loss, excellent linearity, complementary transmission/reflection characteristics, a wide linear range, and angular-dependent tunability. The designed edge-filter-based demodulation system incorporates dual single-point detectors to simultaneously monitor the transmitted and reflected signals. Leveraging the functional relationship between the center wavelength of the FBG and the detected signals, this system enables high-speed, wide-range interrogation of the center wavelength, thus facilitating real-time demodulation for wide-range temperature sensing. The proposed method and system are validated through theoretical modeling, offering an innovative approach for sapphire FBG signal demodulation under extreme thermal-pressure conditions. Full article

Due to their high breakdown threshold and acceleration gradient, dielectric laser accelerators (DLAs) have become an important technical direction of accelerator miniaturization. In this study, an electron accelerator scheme based on graphene surface plasmon polaritons (SPPs) is proposed. The grating was designed to be etched on the silica surface in the simulation, and a layer of graphene was modeled to cover the surface of the medium. The incident laser light in the simulation was configured to be coupled by the grating to generate surface plasmon polaritons (SPPs) on the graphene surface. According to the simulation results, a relatively large acceleration channel aperture and long acceleration length could be formed on the graphene surface using a mid-infrared laser; this provides a technical solution for increasing the beam current of a DLA. A 53.375 THz laser was incident on the surface of the accelerating structure to carry out tracking calculations on a 10 MeV electron beam. For the 100 $\mu$m accelerating structure, an energy gain of 0.105 MeV was achieved, and the acceleration gradient reached 1.05 GeV/m. Full article

Ultrafast fiber lasers have shown exceptional performance across various domains, including material processing, medical applications, and optoelectronic communication. The semiconductor saturable absorber mirror (SESAM) is a key enabler of ultrafast laser operation. However, the narrow wavelength range and limited modulation depth of conventional SESAMs pose challenges to further advancing ultrafast fiber laser technology. To address these limitations, we explored the integration of guided mode resonance (GMR) effects to enhance light–matter interaction within the absorption layer. By incorporating subwavelength dielectric film gratings onto the cap layer of SESAMs, we excited GMR and formed a microcavity structure in conjunction with the distributed Bragg mirror (DBR). This design significantly improved the absorption efficiency of InAs quantum dots. The experimental results demonstrate that the modulation depth of the SESAM increased from 6.7% to 17.3%, while the pulse width was reduced by 2.41 times. These improvements facilitated the realization of a high-quality, stable ultrafast fiber laser. This study not only broadens the application potential of ultrafast lasers in diverse fields but also offers a practical pathway for advancing SESAM technology toward industrial-scale deployment. Full article

Terahertz radiation patterns can be registered using various detectors; however, in most cases, the scanning resolution is limited. Thus, we propose an alternative method for the detailed scanning of terahertz light field distributions after passing simple and complex structures. Our method relies on using a dielectric waveguide to achieve better sampling resolution. The optical properties of many materials were analyzed using time-domain spectroscopy. A cyclic olefin copolymer (COC) was chosen as one of the most transparent. This study contains a characterization of the losses introduced by the waveguide and a discussion of the setup’s geometry. As a structure introducing the radiation pattern, a 2D quasi-periodic amplitude grating was chosen to observe the Talbot effect (self-imaging). Moreover, some interesting physical phenomena were observed and discussed due to the possibility of detailed scanning, with subwavelength resolution, registering the terahertz wavefront changes behind the structure. Full article

A core dielectric cylindrical rod wrapped in a dielectric circular pipe whose outer surface is enclosed by a helical conducting strip grating that is skewed along the axial direction is herein analyzed using the asymptotic strip boundary conditions along with classical vector potential analysis. Targeted for use as a cylindrical holographic antenna, the resultant field solutions facilitate the aperture integration of the equivalent cylindrical surface currents to obtain the radiated far fields. As each rod section of a certain skew angle exhibits a distinct modal attribute; this topology allows for the distribution of the cylindrical surface impedance via the effective refractive index to be modulated, as in gradient-index (GRIN) materials. Beam steering can also be achieved by altering the skew angle via mechanical sliding motion while leaving the cylindrical structure itself unchanged, as opposed to impractically reconfiguring the geometrical and material parameters of the latter to attain each new beam direction. The results computed by the program code based on the proposed technique in terms of the modal dispersion and radiation patterns are compared with simulations by a software solver. Manufactured prototypes are measured, and experimentally acquired dispersion diagrams and radiation patterns are favorably compared with theoretical predictions. Full article

Quantum well infrared photodetectors (QWIPs) are popular due to their following advantages: low cost, maturity of manufacturing, high uniformity, ease of wavelength adjustment, resistance to heat, and resistance to ionizing radiation. However, their low absorption efficiency due to their unique anisotropic absorption properties and ohmic loss of the metal grating severely limit their further adoption. We cleverly used cascaded dielectric metasurfaces to replace the traditional single-layer metal grating, which increased the absorption efficiency to near the upper limit of 100%. By analyzing the near-field profile of the electric field of the miniaturized device, we found that the upper grating, QWIP, and lower grating formed a high-efficiency FP cavity with a strong photon localization capability, allowing the microdevice to effectively achieve 99.3% absorption. In addition, QWIPs with cascade gratings can be incorporated into a polarimeter, allowing for the comprehensive detection of linear polarization information at a wavelength of 14 $\mathsf{\mu }\mathrm{m}$ through rational rotations. Our proposed double-layer grating coupling method can be considered a technology that can effectively address the low-absorption problem associated with QWIPs. Full article

In this paper, we introduce a novel approach to model bending phenomena on holographic volume gratings based on Rigorous Coupled Wave Analysis (RCWA), in which the bending as a phase in the dielectric permittivity expansion is introduced, and the Shooting Method (SM) is employed to solve the resulting system of equations. Further validation of our model is conducted by comparing its predictions to those obtained from reference Finite-Difference Time-Domain (FDTD) simulations and Coupled Wave Theory (CWT, referring to Kubota’s model that includes the bending phenomenon). Furthermore, we propose a methodology for estimating the bending from the diffraction efficiency curves in transmission volume gratings based on deep learning models, with a subsequent study of their accuracy and applicability. Full article

Since surface relief transmission gratings have very strict requirements on operators and use environment, according to the semiconductor laser external cavity spectral beam combining system, this paper proposes a design scheme for a semiconductor laser array spectral beam combining system based on the grating-external cavity. The finite element approach was used to create a wideband, high-efficiency fill-in multilayer dielectric transmission grating structure for a high-power spectrum beam combining system. The incidence angle, ridge height, duty cycle, and sidewall inclination angle of the transmission grating were tuned and evaluated, and a link between the transmission grating’s diffraction efficiency and grating characteristics was discovered. The calculated design of the high-power fused silica transmission grating has a negative first-order peak diffraction efficiency of 99.5% in the 800 nm range. In the spectral region of 765–872 nm, the transmission grating’s diffraction effectiveness exceeds 92%. The filled ultra-high diffraction efficiency multilayer dielectric transmission grating design addresses the issue of resistance to high-power lasers under complicated operating settings. It is intended to maintain a high diffraction efficiency even after several cleaning cycles, and it is an ideal component for high-power spectrum beam combining systems. Full article

This article presents the results of a numerical analysis of a nitride-based vertical-cavity surface-emitting laser (VCSEL). The analyzed laser features an upper mirror composed of a monolithic high-contrast grating (MHCG) and a dielectric bottom mirror made of SiO₂ and Ta₂O₅ materials. The emitter was designed for light emission at a wavelength of 403 nm. We analyze the influence of the size of the dielectric bottom mirrors on the operation of the laser, including its power–current–voltage (LIV) characteristics. We also study the effect of changing the electrical aperture radius (active area dimensions). We demonstrate that the appropriate selection of these two parameters enables the temperature inside the laser to be reduced, lowering the laser threshold current and increasing its optical power output significantly. Full article

Retroreflective gratings serve as fundamental optical elements in nanophotonics, with polarization-independent diffraction efficiency being one of the critical parameters for assessing their performance. In the far-infrared spectral range, traditional retroreflective gratings typically refer to metal echelette gratings, but their diffraction efficiency cannot approach 100% due to metal absorption. In the visible and near-infrared spectral ranges, metal echelette gratings have gradually been replaced by all-dielectric metasurfaces because dielectric materials exhibit negligible absorption at specific wavelengths. However, there is still a lack of relevant research in the far-infrared range, mainly due to the weak control capability of the existing devices over the polarization-independent phase. Here, we propose a kind of all-dielectric retroreflective metasurface composed of asymmetric pillars and freely tunable aperiodic multilayer films. The pillar structure can achieve polarization insensitivity, and the insufficient modulation capability of the dielectric materials can be compensated for by aperiodic Ge/ZnS films. The designed metasurface achieves the diffraction efficiency by RCWA, with the maximum larger than 99% and the overall reaching 95% (9.3–9.6 µm). We have provided detailed explanations of the design methodology and fabrication process. Our work lays the groundwork for further exploration and application of far-infrared lasers. Full article