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Direct laser writing of birefringent photonic crystals for the infrared spectral range
摘要： Infrared optical photonic crystals fabricated using direct laser writing, which is based on the two-photon polymerization of suitable monomers, have received substantial interest since the emergence of this process. Two-photon polymerization could be a disruptive technology for the fabrication of all-dielectric photonic crystals in the infrared spectral range, as it allows the synthesis of large scale arrays of uniform structures with arbitrary geometries and arrangements. However, all-dielectric photonic crystals that provide birefringent optical responses in the infrared spectral range have not yet been demonstrated using direct laser writing techniques. Here, the authors explore the form birefringence observed in photonic crystals composed of arrays of subwavelength-sized slanted polymer microwires. The photonic crystals investigated here were fabricated in a single fabrication step using direct laser writing of an infrared transparent photoresist (IP-Dip). A strong contrast of the cross-polarized re?ectance of photonic crystals as a function of the in-plane orientation is observed in the mid-infrared spectral range at λ ≈ 6:5 μm. This observation is indicative of an anisotropic optical behavior. Finite element based techniques corroborate the experimentally observed responses qualitatively.
关键词： two-photon polymerization,direct laser writing,infrared spectral range,birefringent photonic crystals,all-dielectric photonic crystals
更新于2025-11-14 15:18:02
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Direct Imaging of Isofrequency Contours of Guided Modes in Extremely Anisotropic All-Dielectric Metasurface
摘要： In this work, we investigate an all-dielectric metasurface based on the silicon on insulator platform for manipulating of guided modes in the visible and near-infrared spectral ranges. We use the Fourier modal method to demonstrate numerically, that guided modes excited in the metasurface support both hyperbolic-like and elliptic dispersion regimes. We implement a back focal plane microscope combined with a high refractive index solid immersion lens to directly image the isofrequency contours of the guided modes (surface waves). Reconstruction of dispersion unambiguously reveals the transition between different dispersion regimes.
关键词： Fourier microscopy,All-dielectric metasurface,isofrequency contours,Fourier modal method,dispersion reconstruction,surface waves
更新于2025-09-23 15:23:52
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Generation of polarization-sensitive modulated optical vortices with all-dielectric metasurfaces
摘要： Optical vortices (OVs) created from helical modes of light have extensive applications in optical manipulation, imaging and optical communications. Moreover, modulated optical vortices (MOVs) with modified wavefronts could provide new opportunities for fractionating particles and actuating microelectromechanical systems. Traditional devices for generating MOVs include spatial light modulators, spiral phase plates etc. However, such bulky devices are difficult to be applied to high-level integrated optical systems. Besides, other MOV generators are typically static and polarization-insensitive. Here, we proposed an all-dielectric metasurface to generate polarization-sensitive MOVs. The intensity patterns of the OVs can be modulated by adding a tangential modulation factor in the phase profile. Independent manipulation of two orthogonal polarizations was adopted via tailoring the geometric parameters of silicon (Si) pillars. We experimentally demonstrated that the metasurface could generate a doughnut and an actinomorphic vortex beams for different polarization inputs. In addition, the intensity pattern of the MOVs can be dynamically tuned by adjusting the polarization angle. This work can benefit optical manipulation and can be further extended to visible and near-infrared bands.
关键词： propagation phase,all-dielectric metasurfaces,mid-infrared,polarizations,modulated optical vortices
更新于2025-09-23 15:22:29
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Extreme Huygens' metasurfaces based on quasi-bound states in the continuum
摘要： We introduce the concept and a generic approach to realize Extreme Huygens’ Metasurfaces by bridging the concepts of Huygens’ conditions and optical bound states in the continuum. This novel paradigm allows creating Huygens’ metasurfaces whose quality factors can be tuned over orders of magnitudes, generating extremely dispersive phase modulation. We validate this concept with a proof-of-concept experiment at the near-infrared wavelengths, demonstrating all-dielectric Huygens’ metasurfaces with different quality factors. Our study points out a practical route for controlling the radiative decay rate while maintaining the Huygens’ condition, complementing existing Huygens’ metasurfaces whose bandwidths are relatively broad and complicated to tune. This novel feature can provide new insight for various applications, including optical sensing, dispersion engineering and pulse-shaping, tunable metasurfaces, meta-devices with high spectral selectivity, and nonlinear meta-optics.
关键词： all-dielectric,dispersion,bound states in the continuum,Huygens’ condition,metasurfaces
更新于2025-09-23 15:21:21
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Electro-optical Amplitude and Phase Modulators Based on Tunable Guided-Mode Resonance Effect
摘要： Here, electrically tunable amplitude and phase modulators are designed by the hybridization of indium tin oxide (ITO) into a guided-mode resonance mirror (so-called GMRM) which consists of a high-index silicon (Si) nanograting placed on top of a Si guiding core followed by a silicon-dioxide optical buffer layer and a highly reflective substrate. The physical mechanism is based on the intriguing optical characteristics of GMRMs and integration of a dual-gated ITO with the capability of charge carrier modulation into the Si nanograting. A gate-tunable amplitude modulator with a modulation depth as high as ≈0.80 is realized by careful selection of structural parameters, excitation of a strongly coupled guided-mode resonance, and modifying the external bias voltage. This design can also be adjusted only by changing the thickness of its optical buffer layer and moderating the strength of the guided-mode resonance to serve as an efficient active phase modulator. The phase variation of ≈210° and relatively high reflection amplitude in 0.45-0.6 range are accomplished when the applied bias voltage alters from -15 V to +24 V. This reflection phase tuning mainly originates from the carrier depletion and accumulation inside the incorporated 5 nm-thick ITO layer. The accurate modeling and numerical calculation of optical response of the proposed unit cell for different applied external voltages are carried out through linking the electrostatics device physics model and rigorous coupled wave analysis (RCWA) optical simulation. The design rules and physical principles behind the dual-gated ITO-integrated GMRM unit cell are discussed in-depth by investigation of the structural parameters, the nature of supported resonances, and voltage-dependent effects of inhomogeneous carrier distributions in both ITO and Si layers. The electrical addressability and individual control over pixelated subwavelength unit cells provide the opportunity for realizing an actively reconfigurable metasurface with the desired gradient phase delay.
关键词： metasurfaces,phase and amplitude modulators,electro-optical materials,silicon,guided-mode resonance,indium tin oxide,All-dielectric
更新于2025-09-23 15:19:57
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Wide-range line shape control of Fano-like resonances in all-dielectric multilayer structures based on enhanced light absorption in photochromic waveguide layers
摘要： We have succeeded in controlling the line shape of Fano-like resonances in all-dielectric multilayer structures in a wide range by UV light irradiation. Multilayer structures consisting of a waveguide layer supporting a half-leaky guided mode, a spacer layer, and another waveguide layer supporting a planar waveguide mode are known to exhibit Fano-like line shapes in attenuated total reflection spectra due to coupling between the half-leaky guided mode and the planar waveguide mode. Using a photochromic layer, i.e., a layer doped with spiropyran molecules, as one of the waveguide layers, we controlled the amount of light absorption in the waveguide layer by varying the UV irradiation dose. We demonstrated that the line shape changes dramatically depending on the UV dose, from the electromagnetically induced transparency-like to electromagnetically induced absorption-like line shape (or vice versa) passing through the Fano-like line shape. We also demonstrated that the photochromic response induced by UV irradiation in the Fano-resonant multilayer structure is enhanced by a factor of ～100 relative to that in a single photochromic layer. Our analyses based on electromagnetic calculations suggest that the dramatic line shape change and the enhanced photochromic response are the consequences of enhanced local electric fields inside the photochromic waveguide layer combined with the photoinduced increase in the imaginary part of the dielectric constant.
关键词： electromagnetically induced transparency,all-dielectric multilayer structures,Fano-like resonances,UV light irradiation,electromagnetically induced absorption,photochromic waveguide layers
更新于2025-09-23 15:19:57
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Guided‐Mode Resonances in All‐Dielectric Terahertz Metasurfaces
摘要： Coupling of diffracted waves in gratings with the waveguide modes gives rise to the guided mode resonances (GMRs). The GMRs provide designer linewidth and resonance intensity amidst a broad background, and thus have been widely used for numerous applications in visible and infrared spectral regions. Here, terahertz GMRs are demonstrated in low-loss, all-dielectric metasurfaces, which are periodic square lattices of silicon cuboids on quartz substrates. The silicon cuboid lattice simultaneously acts as a diffraction grating and an in-plane slab waveguide, thereby resulting in the formation of terahertz GMRs. At oblique incidence, two distinct frequency detuned GMRs are observed. The frequency difference between these two GMRs increases at larger angle of incidence. However, extremely small angle of incidence causes destructive interference between these counter-propagating GMRs that leads to a nonradiative symmetry-protected bound state in the continuum. GMRs in all-dielectric silicon metasurfaces can have potential applications in the realization of efficient terahertz devices such as high-Q transmission filters with angular spectral selectivity, ultrafast modulators, and free-space couplers.
关键词： guided-mode resonance,bound states in the continuum,all-dielectric metasurface,terahertz
更新于2025-09-19 17:13:59
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Bound States in the Continuum in Magnetophotonic Metasurfaces
摘要： We analyze the enhancement mechanisms of magneto-optical effects in all-dielectric metasurfaces caused by the bound state in the continuum resonance. In a structure under study, a square lattice of bismuth substituted yttrium iron garnet nanodisks with an air hole displaced away from the disk axis, magneto-optical polarization and intensity effects reach 0.7° and 22%, respectively.
关键词： bound state in the continuum,magneto-optical effects,all-dielectric metasurfaces,bismuth substituted yttrium iron garnet
更新于2025-09-19 17:13:59
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All-Dielectric Nanoresonators for ??(2) Nonlinear Optics
摘要： Metal-less nanophotonics offers new opportunities for non-linear optics with respect to optical waveguides and microresonators, taking advantage of the progress within nanofabrication to boost the development of subwavelength Mie-type structures. Here, we review recent results on second harmonic generation with semiconductor nanoresonators, focusing on their scattering features in terms of efficiency and control over radiation patterns. First, two theoretical models are comparatively discussed with a view to possible improvements in analysis and design. Then, some relevant experiments are reported, and the origin of the χ(2) generation is discussed, outlining the main open topics to investigate in the near future and the advantages offered by these nanostructures to the development of novel photonic devices.
关键词： Mie resonances,second harmonic generation,AlGaAs nanoresonators,all-dielectric resonators,nanophotonics
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - All-Optical Ultrafast Control of Second Harmonic Generation in AlGaAs Nanopillars
摘要： All-dielectric nanophotonics has recently raised an increasing interest because the optical response of high-permittivity dielectric nanoparticles exhibits negligible dissipative losses and strong magnetic multipole resonances [1-4] in the visible and near-IR. We recently reported a second harmonic generation (SHG) conversion efficiency higher than 10-5 at (cid:79)= 1554 nm (pump intensity (cid:124) 1.6 GW/cm2; pulse width (cid:124) 150 fs; repetition rate = 80 MHz) in all-dielectric Al0.18Ga0.82As-on-AlOx nanodisks [5-7]. Such a remarkable efficiency is achieved thanks to the exploitation of magnetic and electric resonances emerging at coincidence with both the pump and SHG wavelength. In addition, the choice of both the pump and, consequently, the SHG ((cid:124) 777 nm) wavelength, set below the energy of the material bandgap, allow minimizing the two-photon absorption of the pump and the re-absorption of the SHG. Here, we demonstrate the potential for the all-optical modulation of the SHG. First, we study the behavior of the emitted SHG signal when the nanoantennas are concurrently illuminated with a low-power (< 300 (cid:80)W) continuous wave (CW) laser with energy above the bandgap ((cid:124) 3.2 eV, 405 nm wavelength). We observe variations in the SHG yield of the nanoantennas up to 60%. Figure 1a shows the SHG differential map acquired on an array of nanopillars with variable radius (r). Figure 1b shows the overall SHG intensity (dashed line) as well as the SHG modulation (solid blue line) as a function of r. While SHG from the smaller nanopillar (r = 205 nm) is decreased by about 60% under a 300 (cid:80)W CW pump beam, the 220-nm-radius nanopillar show a 30% SHG enhancement. We also investigated the ultrafast modulation of the SHG in a pump-probe experiment, where the pump is an ultrashort pulse at (cid:79)= 510 nm (above material bandgap), while the probe is a time-delayed pulse at (cid:79)= 1550 nm generating the SHG, to study the SHG dynamics when the pillars are brought out of equilibrium and a transient plasma is photoinjected in the dielectric. Time-traces of the SHG as a function of the pump-probe delay are shown in Figure 1c. We measured an ultrafast SHG quenching (< 0.5 ps) and slower (10 to 100 ps) recovery times, which strongly depend on the nanopillars, hence on the resonances involved. Our results allow gaining further insight into the photophysics of the nonlinear emission in these nanoscale systems and pave the way to the all-optical control of nanoscale nonlinear photonic devices for data storage with AlGaAs-on-insulator all-dielectric platforms.
关键词： Second harmonic generation,All-optical modulation,Nanopillars,All-dielectric nanophotonics,AlGaAs,SHG
更新于2025-09-12 10:27:22