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Electromagnetic Wave Absorbers (Detailed Theories and Applications) || Basic Theory of Computer Analysis
摘要： One of the reasons that a wide variety of EM-wave absorber analyses came to be possible recently is the remarkable progress of modeling and computer simulation technologies. In addition, in actual computer simulation technologies, a number of theoretical analysis methods and means are compounded and systemized. In this chapter, in order to deepen the basic understanding of computer simulation analysis of EM-wave absorbers, the finite-difference time-domain (FDTD) method and finite element (FE) method are explained in detail, including their fundamental principles.
关键词： EM-wave absorbers,FDTD method,Maxwell's equations,Finite element method,Computer simulation
更新于2025-09-19 17:13:59
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Electromagnetic Wave Absorbers (Detailed Theories and Applications) || Fundamental EM‐Wave Absorber Materials
摘要： In this chapter, in order to obtain basic knowledge of carbon materials and ferrite materials, which are typical EM-wave-absorbing materials, their respective characteristics are examined, especially from the viewpoint of molecular and crystal structures. The Jaumann absorber in early stage of the EM-wave absorber was composed of overlaying the material dispersed carbonyl iron to rubber, the resistive sheet, and the dielectric plate, as described in Chapter 1. In this way, since the absorber was invented, carbon-based materials have been mainly used as EM-wave-absorbing materials. On the other hand, copper–zinc-based soft ferrite was invented in 1930 in Japan. However, the nature of this kind of soft ferrite as an EM-wave absorber was unknown for a long time. Magnetic materials typi?ed by ferrite, metallic resistors, and carbon materials used as resistive ?lms are applied to EM-wave absorbers, and they have changed little to this day.
关键词： molecular and crystal structures,EM-wave absorbers,ferrite materials,carbon materials
更新于2025-09-19 17:13:59
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Electromagnetic Wave Absorbers (Detailed Theories and Applications) || Absorber Characteristic Control by Equivalent Transformation Method of Material Constants
摘要： As mentioned in the previous chapters, demands for various EM-wave absorbers are rapidly increasing along with the trends toward complicated electromagnetic environments and the development of higher frequency communication equipment. Generally, it has been considered highly difficult to produce new EM-wave absorbers having a desired absorbing frequency and an absorbing characteristic. One reason for this is that realizing an optimum material constant satisfying the required characteristics becomes difficult when manufacturing an EM-wave absorber. That is, in the conventional method, it often becomes difficult to freely control parameters such as the mixing ratio of the EM-wave absorber’s raw materials, the firing temperature, the pressure, and the material compositions to realize the appropriate absorber. Furthermore, the problems of accurately measuring material constants and maintaining the accuracy of component sizes become important to the EM-wave absorber in high-frequency use, particularly in the millimeter or terahertz band.
关键词： equivalent transformation method of material constants (ETMMC),EM-wave absorbers,millimeter wave,terahertz band,high-frequency communication
更新于2025-09-19 17:13:59
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[IEEE 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Rome, Italy (2019.6.17-2019.6.20)] 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Bismuth and Bismuth Telluride Thin Films Deposited by MOCVD upon Tapered Fiber Sections as Q-switches for Fiber Lasers
摘要： Lasing regimes of ring erbium ?ber lasers passively Q-switched by means of ?ber tapers coated with thin crystalline ?lms of either Bi2Te3 or Bi as saturable absorbers (SAs) are investigated. 10–15 μm in diameter and 5–10 mm long ?ber tapers are prepared by local chemical etching out of a silica light re?ecting cladding of the standard SMF-28 optical ?ber. Nanometer thick island ?lms of pure Bi and Bi2Te3 are synthesized on the surface of the ?ber tapers by applying the metalorganic chemical vapor deposition (MOCVD). The deposited ?lms are then covered with two di?erent polymers: either polyvinyl acetate (PVA) or polydimethylsiloxane elastomer (PDMSE). The ?ber section with polymer-coated SA ?ber is installed into the ring laser cavity in tandem with the section of an active ?ber. For all the samples a stable generation of microsecond pulses in the Q-switch mode at a wavelength of about 1560 nm is observed. To the best of our knowledge, a passively Q-switched ?ber laser with nanometer Bi ?lms as a saturable absorber is implemented for the ?rst time. It is established that even a small increase in the temperature of the surrounding medium leads to a signi?cant increase in the transmission coe?cient of polymer-coated tapers with deposited SA ?lms, which may be attributed to a decrease in the refractive index of the polymers. The most signi?cant increase in the transmission coe?cient with increasing temperature is observed in tapers coated with PVA, which has a refractive index larger than fused silica.
关键词： MOCVD,Q-switches,polymer coating,saturable absorbers,Bi2Te3,fiber lasers,Bi
更新于2025-09-19 17:13:59
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - The nonlinear optical properties of few-layer VSe <sub/>2</sub> nanosheets
摘要： Vanadium Diselenide (VSe2) has a high electrical conductivity owing to the electron delocalization of the vanadium lattice framework. Most of previous research has been focused on its electronic properties. The nonlinear optical properties of VSe2 have not been investigated yet. Herein, we prepared few-layer VSe2 nanoflakes by liquid phase exfoliation. Subsequently, we utilized Z-scan technique to study the nonlinear optical properties of few-layer VSe2 nanoflakes. And we prepared VSe2 based saturable absorbers (SA) and achieved passively mode-locked operation in Er-doped fiber laser. The results indicate that VSe2 nanosheets own remarkable nonlinear optical properties and could be employed as ideal saturable absorption materials in pulsed fiber lasers.
关键词： Mode-locked,Saturable absorbers,Vanadium Diselenide,Nonlinear optical materials
更新于2025-09-16 10:30:52
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Yttrium oxide as a Q-switcher for the near-infrared erbium-doped fiber laser
摘要： Yttrium oxide (Y2O3) has been widely used in metal-reinforced composites, microelectronics, waveguide lasers, and high-temperature protective coatings because of its good physical and photoelectric properties. However, few studies have been done on the nonlinear optical applications of Y2O3 as saturable absorbers (SAs) in fiber lasers so far. Here, a passively Q-switched near-infrared fiber laser using Y2O3 as a Q-switching device is demonstrated. The optical nonlinear properties of the Y2O3 SA prepared by the magnetron sputtering method were measured by the twin-detector measurement technique, and the modulation depth of the proposed Y2O3 SA was found to be 46.43%. The achieved Q-switched laser delivers an average output power of 26 mW at 1530 nm with a pulse duration of 592.7 ns. To the best of our knowledge, this is the first report on the optical nonlinearity of Y2O3 as a Q-switcher for the near-infrared fiber laser, which may deepen the understanding of the optical nonlinear properties of Y2O3 and make inroads into the potential market of optical modulation and optoelectronic devices.
关键词： Q-switched laser,saturable,fiber lasers,absorbers,nonlinear optical materials
更新于2025-09-16 10:30:52
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[IEEE 2019 IEEE 31st International Conference on Microelectronics (MIEL) - Nis, Serbia (2019.9.16-2019.9.18)] 2019 IEEE 31st International Conference on Microelectronics (MIEL) - Reviewing MXenes for Plasmonic Applications: Beyond Graphene
摘要： MXenes are an emerging class of two-dimensional (2D) materials consisting of carbides, nitrides or carbonitrides of early transition metals. Due to the metallic type of conductivity of MXenes and their 2D structure, they are an ideal candidate to replace the conductive materials currently used in plasmonics, especially graphene. However, the use of MXenes for plasmonics and metamaterials is in its embryonal stage and practically all relevant publications appeared in the last few years. In this contribution we first consider some methods of MXenes fabrication. We continue by analyzing the optical and electronic properties of MXenes of interest for plasmonics (especially spectral dispersion of complex relative dielectric permittivity). We proceed by reviewing some reported applications of MXenes in plasmonics, including among others conventionally designed chemical and biological sensors based on surface plasmon resonance (SPR), metasurface-based optical absorbers and MXene-based nanoantennas, as well as some possible applications in nonlinear optics. In addition to that, we propose some novel uses of MXenes in plasmonics, including chemical and biological nanosensors, superabsorbers with a variable widths of the nanoholes, etc. It is our opinion that the applications of MXenes in plasmonics introduced until now are only scratching the surface of a vast bulk of potential practical devices, structures and effects.
关键词： absorbers,sensors,dielectric permittivity,MXenes,plasmonics,2D materials
更新于2025-09-12 10:27:22
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Facile growth of SnS and SnS0.40Se0.60 thin films as an absorber layer in the solar cell structure
摘要： SnS (S1) and SnS0.4Se0.6 (S2) thin films were prepared using thermal evaporation on annealing at 523 K of the thermally deposited films. Compositional analysis of the films reveals the formation of SnS and SnS0.40Se0.60 phase. X-ray diffraction results demonstrate the formation of orthorhombic structure corresponding to SnS and SnS0.40Se0.60 phase. Moreover, a decrease in the intensity of SnS0.40Se0.60 peaks as compared to those of SnS was observed. Thus, causes insertion of selenium (Se) atoms in SnS lattice and results in the modification of lattice parameters. These structural modifications leads to variations in crystallite size, lattice strain and dislocation density, thus, confirms the formation of ternary SnS0.40Se0.60 phase. The changes corresponding to optical parameters are also observed in the films in the form of lower transmission, bandgap value and absorption coefficient on Se insertion. Moreover, both the films exhibit absorption coefficient >105 cm?1 with bandgap values of 1.44 and 1.23 eV and found suitable for absorption in solar cell.
关键词： Tin,Thermal evaporation,X-ray diffraction,Solar absorbers,Bandgap,SnS1?xSex
更新于2025-09-12 10:27:22
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All-Dielectric Terahertz Plasmonic Metamaterial Absorbers and High-Sensitivity Sensing
摘要： Two types of plasmonic metamaterial absorbers (PMAs) formed from patterned all-dielectric resonators are designed and demonstrated experimentally in the terahertz (THz) range. Both PMAs use a simple grating design on highly N-doped silicon. The first shows broadband absorption with near-perfect peak absorbance at 1.45 THz and a bandwidth of 1.05 THz for 90% absorbance, while the second is a dual-band absorber. Experiments show that the second absorber has two distinct absorption peaks at 0.96 and 1.92 THz with absorption rates of 99.7 and 99.9%, respectively. A fundamental cavity mode coupled to coaxial surface plasmon polaritons is responsible for the characteristics of both PMAs. Additionally, the optically tunable responses of these all-dielectric absorbers demonstrate that the absorption behavior can be modified. The quality factor (Q) values of the dual-band resonances are 4.6 and 7.8 times larger than those of the broadband PMAs, respectively, which leads to a better sensing performance. As an example, the two proposed PMAs act as high-sensitivity sensors and demonstrate considerable potential for chlorpyrifos detection. These results show that these PMAs can be used as sensors that can detect the presence of trace pesticides in adsorption analyses, among other practical applications.
关键词： broadband absorption,all-dielectric resonators,plasmonic metamaterial absorbers,chlorpyrifos detection,dual-band absorber,terahertz,high-sensitivity sensors
更新于2025-09-12 10:27:22
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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) - Novel InN-Based SESAMs with Ultra-Short Time Response
摘要： Semiconductor saturable absorbers are becoming a matter of interest since they are keystone elements of pulsed lasers, leading to ultrashort pulses with high peak intensities and wide optical spectra. This kind of ultrafast lasers are empowering new applications in the fields of optical telecommunications and nonlinear optics. In order to improve the radiation source with regard to pulse energy and temporal duration, new saturable absorbers are still under development. In this work, we study semiconductor saturable absorbers (S1 and S2) consisting of an active InN layer grown by molecular beam epitaxy directly on a 10-μm-thick GaN-on-sapphire template. We compare structures with an InN thickness of 400 nm (S1) and 900 nm (S2). The energy band gap of the samples extracted from optical transmission measurements is Eg1 ～ 0.69 eV (1782 nm) and Eg2 ～ 0.70 eV (1767 nm) for samples S1 and S2, respectively. The nonlinear absorption of the samples at 1550 nm has been measured by the Z-scan method, using a radiation source which delivers 250 fs pulses with an average power of 35 mW and a repetition rate of 5.2 MHz. To increase the power density impinging the sample, the laser is focused with a lens with a focal length of 3 cm in the Z-scan scheme, attaining an energy fluence of E = 5.2 mJ/cm2. The nonlinear optical response of the samples is obtained by measuring the optical transmittance as a function of the incident peak intensity on the sample. In both samples, a huge nonlinear change is observed. The linear transmittance at 1550 nm has been estimated in Tlin = 17 % for S1 and Tlin = 2.6 % for S2, and the modulation depth is ΔT (S1) = 22.6 % and ΔT (S2) = 21.8 %, respectively. Thus, sample S1 exhibits a nonlinear transmittance change (Tnl/Tlin) above ～ 240% at the maximum peak intensity (optical bleaching), whereas for S2 the total change in transmittance reaches 815%. These results reveal that the thickness of S2 is particularly adapted for the fabrication of saturable absorbers at 1550 nm, since it is thick enough to get a low linear transmittance but keeping the maximum modulation depth. Semiconductor saturable mirrors (SESAMs) have been implemented by deposition of an aluminium mirror directly on the InN sample surface. Optical fiber mode-locked lasers have been developed with these SESAMs. The AC traces and optical spectra for lasers using samples S1 and S2 are plotted. The traces have been fitted to Gaussian curves with a temporal width of 210 fs for S1 and 150 fs for S2. In conclusion, we present a new SESAM technology based on InN thin films which displays huge nonlinear effects. Optimized InN layer thickness results in more than 800% change in transmittance, which makes it possible to generate ultrashort pulses with temporal duration as low as 150 fs.
关键词： Semiconductor saturable absorbers,InN,ultrafast lasers,SESAMs,nonlinear optics
更新于2025-09-12 10:27:22