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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) - Genetically Optimized Photonic Crystal for Spatial Filtering of Reinjection into Broad-Area Diode Lasers
摘要： Modern high-power broad-area semiconductor laser diodes (BASLDs) deliver optical output powers of several ten Watts at high electro-optical conversion efficiencies, which makes them highly relevant for numerous industrial, medical and scientific applications. However, lateral multimode behavior in BASLDs due to thermal lensing turns out highly detrimental, as it results in poor focusability and decreased laser beam brightness. Approaches to overcome this issue include improved epitaxial layer design, the optimization of evanescent spatial filtering by tailoring the emitter geometry and facet reflectivity, or Fourier spatially filtered reinjection from an external resonator. Here, we consider the usage of longitudinally chirped photonic crystals (PhC) within the external cavity (EC) for tailoring the spatial filter properties. The corresponding EC setup, consisting of a slow-axis collimating lense, a 2D photonic crystal, and the external mirror (R=4%), is shown in Fig. 1a). While free space propagation in the EC is modeled by Fresnel diffraction integrals, optical propagation through the PhC requires accurate treatment of lateral angular dispersion. For the sake of efficiency of the time-domain BASLD simulator, we use a beam propagation method (BPM) based on Rayleigh-Sommerfeld diffraction theory. The chirp of the longitudinal PhC periods is optimized with a genetic algorithm. The transmission amplitude of the optimized structure suppresses lateral propagation angles between 2° and 4°, cf. Fig. 1b), and shows excellent agreement with an exact rigorous coupled wave analysis (RCWA) for calculating PhC transmission and almost vanishing reflection amplitudes. In a next step, we performed numerical simulations of a 1mm long and 100μm broad BASLD subject to PhC spatially filtered reinjection. We found a significant improvement of the lateral far-field profile and increase of beam brightness by a factor 1.5, cf. Fig. 1c). However, for BASLDs with a longer emitter length, lateral waveguide dispersion considerably limits the effectiveness of our scheme. In summary, we demonstrated theoretically that spatial filtering with photonic crystals is a viable alternative to Fourier slit spatial filtering schemes, and offers increased flexibility for designing tailored angular transmission profiles by suitably optimized longitudinal PhC chirp.
关键词： genetic algorithm,beam propagation method,photonic crystals,spatial filtering,broad-area semiconductor laser diodes
更新于2025-09-16 10:30:52
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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) - Magic Crossing Points of Temperature Dependent Cascaded Frequency Conversions in Nonlinear Photonic Crystals
摘要： In this study, we investigated the temperature dependence of cascaded parametric generations in nonlinear photonic crystals based on 2D periodically poled LiTaO3 (2D-PPLT) of square lattice structure. After establishing simultaneous multi-groups of frequency conversion from optical parametric generation (OPG) [1], it was found that the interaction of the signal ((cid:79)s), the idler ((cid:79)i) and the pump can further lead to several cascaded nonlinear processes such as SHG, SFG and DFG. The latter suggest existence of what can be called “magic” crossing points when mapping the nonlinear interactions vs temperature. We used a square lattice of 2D-PPLT with a period of 8.52μm and a filling factor of 38%. The crystal length was 2cm with a thickness of 0.5mm and pumped with a pulse 532nm green laser with a peak power of 80kW and a pulse width of 0.5ns. The measured spectra of the cascaded frequency conversion processes reveal 10 wavelength peaks at 393nm, 402nm,518nm, 532nm, 548nm, 787nm, 820nm, 1518nm, 1576nm and 1642nm at a crystal temperature of T= 110°C. More importantly, when the parametrically generated wavelengths were mapped as a function of the sample temperature (Fig. 1.a), an interesting phenomenon was observed at T = 64°C where four groups of wavelengths crossing at (cid:79) = 399nm ((cid:95)1(cid:178)), 532nm ((cid:95)2(cid:178)), 798nm ((cid:95)3(cid:178)), and 1596nm ((cid:95)4(cid:178)) concurred. By changing the crystal temperature, it would be possible to switch the involved nonlinear optical processes from degenerated to non- degenerated states. In addition to that, it implied a novel approach to generate entangled photons with controlled spectral features by parametric down conversion in a 2D nonlinear crystal [2]. We, then, took advantage of the Sellmeier equation for the crystal refractive index to evaluate the temperature effect on the QPM-parametric processes. Our study indicates that it is essential to carefully exert the parameters of Sellmeier equation reported in literature. Little changes of Sellmerier coefficients might induce an important misunderstanding of experimental data as well as erroneous design of efficient QPM frequency-conversion devices. The weight of this effect is more important when considering cascaded nonlinear interactions.
关键词： temperature dependence,nonlinear photonic crystals,magic crossing points,cascaded parametric generations,Sellmeier equation
更新于2025-09-16 10:30:52
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Micropatterning and defect engineering of colloidal photonic crystals <i>via</i> laser direct writing
摘要： Micropatterning and defect engineering of colloidal photonic crystals (CPCs) play a significant role in the functionality of photonic crystals as they are crucial for optical chip integration, microcavity lasing, chemical sensing, etc. However, obstacles have arisen in recent years especially due to the lack of a general, cost-effective and versatile strategy to make these functional structures in one step. Traditional micro-/nanofabrication techniques may work for one structure but fail for another and the fabrication process is mostly complicated, which potentially incurs reproducibility issues. Here, point defects, waveguides and micropatterns with variable feature sizes (4B500 nm) can be easily created in polystyrene (PS)/SiO2 CPC films via laser direct writing, which is based on selective photodegradation of PS beads. By applying different laser powers or irradiation times, different coloured micropatterns and images with high resolution can be generated, which has great implications for image displays and anti-counterfeiting.
关键词： photodegradation,Micropatterning,colloidal photonic crystals,anti-counterfeiting,defect engineering,laser direct writing,image displays
更新于2025-09-16 10:30:52
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Effect of a thin Au and ZnO layer on optical properties of 1D PhC structures patterned in LED surface
摘要： 1D patterns with different periods were fabricated by Electron Beam Direct Write (EBDW) lithography with the aim to improve the Light Emitting Diode (LED) efficiency, i.e. the light out coupling. Three sets of 1D PhC LED samples with bare PhC, thin Au, and ZnO layers were prepared. The highest Light Extraction Enhancement (LEE) was achieved for 600 nm Photonic Crystals (PhC) period in the case of bare and Au deposited PhC, and for 500 nm PhC period in the case of ZnO deposited PhC, respectively. LEE was studied by measuring L-I characteristics of untreated reference LEDs compared to patterned LEDs.
关键词： LED efficiency,Light extraction enhancement,Photonic crystals,1D structures,EBDW lithography,HSQ XR 1541 resist
更新于2025-09-16 10:30:52
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Theory for polaritons in graphene photonic crystals in an applied magnetic field
摘要： The dispersion relations for bulk and surface plasmon-polaritons in a semi-infinite 1D photonic crystal interlayered with graphene are calculated in the presence of an applied magnetic field. The results are applied to SiO2 as the constituent material in a geometry where the layers are arranged in a periodic array with the same layer thickness. The static magnetic field is applied perpendicular to the plane of layers. Numerical results are presented for the modes in THz range, up to 10 THz, to illustrate the important role of the applied magnetic field on the graphene sheets in modifying the polariton dispersion curves, especially for magnetic fields of the order of 1 T. It is found that the polariton frequencies and band gaps have a sensitive dependence on the electron scattering rate parameter (and hence the applied magnetic field strength) in the graphene sheets. Electromagnetic retardation effects are fully taken into account for the bulk bands, while for the surface modes (which are shown to have a novel non-reciprocal propagation characteristics) it is convenient to focus on the regime where retardation is small.
关键词： Magnetic field effects,Photonic crystals,Graphene,Transfer-matrix methods,Plasmon-polaritons
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - To the Treatment of Anterior Uveitis
摘要： We investigate terahertz quantum cascade lasers with a dense array of active micropillars forming the gain medium. Depending on the size of these pillars relative to the emission wavelength different optical regimes are identified. For pillar dimensions on the order of the emission wavelength, a photonic crystal resonator is created. Single mode emission is observed at high symmetry points of the photonic band structure. The selection mechanism of the favored laser mode is studied by analyzing the gain enhancement effect for eigenmodes with a low group velocity and a large mode confinement of the electric field energy in the micropillars. Subwavelength micropillar arrays constitute a photonic metamaterial, which can be described using an effective medium approximation. Similar to a bulk laser ridge, the array forms a Fabry–Pérot resonator that is defined by the boundaries of the array. From the longitudinal mode spacing, we derive an effective group index of the pillar medium. Limitations in terms of minimum filling factors and waveguide losses for the realization of subwavelength micropillar and nanowire array terahertz quantum cascade lasers are investigated.
关键词： Photonic crystals,terahertz,optical waveguides,optical metamaterials,quantum cascade lasers
更新于2025-09-16 10:30:52
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Hybrid External Cavity Laser with an Amorphous Silicon-Based Photonic Crystal Cavity Mirror
摘要： The authors present results on the performance of a hybrid external cavity photonic crystal laser-comprising semiconductor optical ampli?er, and a 2D photonic crystal cavity fabricated in low-temperature amorphous silicon. The authors demonstrate that lithographic control over amorphous silicon photonic crystal cavity-resonant wavelengths is possible, and that single-mode lasing at optical telecommunications wavelengths is possible on an amorphous silicon platform.
关键词： nanophotonics,silicon photonics,amorphous silicon,CMOS processing,photonic crystals,telecommunications,lasers
更新于2025-09-16 10:30:52
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High Refractive Index Inverse Vulcanized Polymers for Organic Photonic Crystals
摘要： Photonic technologies are nowadays dominated by highly performing inorganic structures that are commonly fabricated via lithography or epitaxial growths. Unfortunately, the fabrication of these systems is costly, time consuming, and does not allow for the growth of large photonic structures. All-polymer photonic crystals could overcome this limitation thanks to easy solubility and melt processing. On the other hand, macromolecules often do not offer a dielectric contrast large enough to approach the performances of their inorganic counterparts. In this work, we demonstrate a new approach to achieve high dielectric contrast distributed Bragg reflectors with a photonic band gap that is tunable in a very broad spectral region. A highly transparent medium was developed through a blend of a commercial polymer with a high refractive index inverse vulcanized polymer that is rich in sulfur, where the large polarizability of the S–S bond provides refractive index values that are unconceivable with common non-conjugated polymers. This approach paves the way to the recycling of sulfur byproducts for new high added-value nano-structures.
关键词： distributed Bragg reflectors,inverse vulcanization,refractive index,polymer photonic crystals
更新于2025-09-16 10:30:52
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Ultrafast Response of a Hybrid Device Based on Strongly Coupled Monolayer WS <sub/>2</sub> and Photonic Crystals: The Effect of Photoinduced Coulombic Screening
摘要： Quantum interactions between transition metal dichalcogenides (TMDs) and optical cavities are rapidly becoming an appealing research topic since these interactions underly a broad spectrum of optical phenomena. Here, we fabricate a simple device in which coherent strong coupling interactions occur between a photonic crystal (PhC) slab and monolayer tungsten disulfide (WS2). Both steady-state angle-resolved spectroscopy and transient absorption microscopy (TAM) are employed to explore the coupling behavior of this device. Specifically, anticrossing dispersions are observed in the hybrid device, indicating a Rabi splitting of 40.2 meV. A newly formed spectral feature emerges in the transient absorption (TA) spectrum of this polariton device under near-resonant excitation, which is subsequently evidenced to be a signature of the upper hybrid exciton–polariton state. Moreover, by carefully analyzing the ultrafast responses of both bare WS2 and the WS2-PhC polariton device excited both off resonance and near resonance, it is found that nonequilibrium thermal decay induces Coulombic screening in the monolayer WS2, which has a major impact on the formation of exciton–polariton. The results of this work could not only improve the current understanding of photophysics in the strong light–matter coupling regime but also lay the foundation for tailoring the development of TMD-based coherent devices.
关键词： strong coupling,transition metal dichalcogenides,photonic crystals,Rabi splitting,transient absorption microscopy,Coulombic screening
更新于2025-09-16 10:30:52
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Magneto-Optical Isolator Based on Ultra-Wideband Photonic Crystals Waveguide for 5G Communication System
摘要： This paper presents a novel magneto-optical isolator based on an ultra-wideband and high efficiency photonic crystals (PCs) waveguide and gyromagnetic ferrites. The three-dimensional numerical simulation finds that the photonic crystals waveguide’s (PCW) transmission efficiency rises with its height and width. The corresponding experiments are performed by using a triangular lattice Al2O3 dielectric posts array in 5G millimeter wave band. The measured transmission efficiency is up to 90.78% for the optimal PCs waveguide structure, which has ultra-wide operating bandwidth from 23.45 to 31.25 GHz. The magneto-optical isolator is designed by inserting two rectangular gyromagnetic ferrites into the PCs waveguide. Due to the contrast between the effective permeability of the left and right circular polarization waves passing through the magnetized ferrite sheets, the ferromagnetic resonance absorption of the forward and reverse waves is different. By using finite element method, the isolation is optimized to be 49.49 dB for the isolator and its relative bandwidth reaches 8.85%. The high isolation, broadband, and easy integration indicate that our designed magneto-optical isolator has significant advantage in 5G communication systems.
关键词： photonic crystals waveguides,magneto-photonic isolator,wideband,5G communication,photonic band gap
更新于2025-09-12 10:27:22