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A Terahertz Traveling-Wave Tube Based on Defect Photonic Crystal Waveguide
摘要： A defect photonic crystal waveguide (DPCW) is presented as a slow-wave structure (SWS) for terahertz (THz) traveling-wave tube (TWT). Due to the characteristics of DPCW, the mode competition and backward wave are greatly depressed, improving the stability of TWT. The DPCW SWS has ?at dispersion characterization and high interaction impedance at 220 GHz. Simulation results show that saturated output power of 12.1 W, corresponding to a gain of 24.3 dB, and the 3-dB gain ripple within 20 GHz can be achieved at the center frequency of 220 GHz. The DPCW-TWT has a low working voltage at 9.52 kV compared to that of folded waveguide (FWG) SWS in this frequency band. The proposed DPCW for the THz regime is easy to fabricate and assemble using the modern fabrication processing technology.
关键词： terahertz,Defect photonic crystal waveguide (DPCW),traveling-wave tube (TWT),slow-wave structure (SWS)
更新于2025-09-23 15:21:01
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EXPRESS: Analysis of Natural Gas Using a Portable Hollow-Core Photonic-Crystal-Coupled Raman Spectrometer
摘要： The low accessibility of natural gas fields and transporting pipelines requires portable online analyzers of the composition of natural gas, ensuring nearly chromatographic precision and capable of in situ analysis of a wide range of gases, including infrared-inactive ones (hydrogen, oxygen, nitrogen, chlorine). We have developed an express method of gas analysis meeting all requirements for the analysis of natural gas and its derivative mixtures using a portable 532 nm Raman spectrometer rigidly connected to a hollow-core crystal photonic fiber.
关键词： hollow-core photonic crystal fiber,HC-PCF,Raman spectrometry,gas chromatography,natural gas,calibration gas mixture
更新于2025-09-23 15:21:01
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Luminescence relaxation dynamics for planar and rolled-up CdSe nanocrystals in a photonic-crystal matrix
摘要： Samples of inverted photonic-crystal films, containing planar and rolled-up (in the form of scrolls) CdSe nanocrystals, are studied. The transmission spectra of these structures are recorded. These spectra (along with the change in colour) confirm the incorporation of nanocrystals into the films. The photoluminescence decay dynamics is investigated. It is shown that the photonic-crystal matrix affects significantly the luminescence kinetics of nanostructures. The differences in the decay curves measured for nanocrystals in a photonic-crystal matrix and for their ensemble on a glass substrate are explained by the influence of the photonic-crystal stop band and the orientational effect of crystalline matrix, which orients anisotropic nanocrystals and prevents them from aggregation. The results obtained may be important for potential applications in optoelectronic devices.
关键词： nanoscrolls,luminescence kinetics,photonic crystal,nanoplates,CdSe
更新于2025-09-23 15:21:01
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Effect of nonlinear cap layer on TM-polarized surface waves in a graphene-based photonic crystal
摘要： In this paper, we investigated the effect of nonlinear cap layer and the chemical potential of the graphene on the p-polarized surface waves (SWs) in a one-dimensional graphene-based photonic crystal (GBPC). Three different cases were considered for the dielectric tensor of the nonlinear cap layer: (1) perpendicular uniaxial approximation, (2) parallel uniaxial approximation and (3) generic case. The results of the study indicated that the effect of nonlinear cap layer on TM SWs may be neglected due to the perpendicular approximation. On the other hand, in parallel approximation as well as generic form of dielectric function, the frequency of the TM SWs within the graphene-induced band gap (GIPBG) may be controlled by the nonlinear cap layer and the chemical potential of the graphene. Moreover, according to the results, in the GIPBG of GBPC with self-defocusing cap layer, enhancing chemical potential and optical nonlinearity shift the frequency of the SWs in the same direction. However, with respect to the self-focusing cap layer, enhancing chemical potential and optical nonlinearity shift the frequency of the SWs in the opposite direction. Consequently, by adjusting the chemical potential in the self-defocusing cap layer, the tunability range of the SW frequency may be extended and in the case of self-focusing, optical nonlinear effects may be eliminated.
关键词： Graphene,First integral,Nonlinear optics,Surface waves,Maxwell’s equations,Photonic crystal
更新于2025-09-23 15:21:01
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Superconducting one-dimensional photonic crystal with coupled semiconductor defects
摘要： We investigate the impact of the insertion of a semiconductor defect on the transmittance spectrum of a one-dimensional photonic crystal composed by alternating layers of superconducting materials. We report that the effect of the insertion of the semiconductor defect originates a defective mode in the photonic band gap that exhibits a shift towards long-wavelength regimes. Unexpectedly, for high values of temperatures, it is observed that the defective mode reduces its confinement as well as influences the optical response of the photonic crystal rather than the pressure. We also extend our analysis to the case of two coupled defects of GaAs, and it is studied the effect of the relative distance between these two defects. Our numerical results reveal that the defective mode has a significant reduction in its quality factor as well as it displays an asymmetry in the transmittance spectrum when the defects are close to each other.
关键词： Transfer matrix method,Defect mode,Semiconductor,Transmittance spectrum,One-dimensional photonic crystal,Superconductor
更新于2025-09-23 15:21:01
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Fiber temperature and humidity sensor based on photonic crystal fiber coated with graphene oxide
摘要： A temperature and humidity sensor based on photonic crystal fiber(PCF) coated with graphene oxide (GO) cascaded with two spherical structures is presented and demonstrated. The principle of this sensor is based on Mach–Zehnder interferometer (MZI), and the interference spectrum is sensitive to the change of temperature and humidity. Because of the hydrophilic property of GO, refractive index (RI) of the fiber surface changes significantly with the variation of humidity. Therefore, the GO film deposited on the PCF surface can improve the humidity sensitivity of the sensor. Experimental results show that the temperature sensitivities are 0.063 nm/?C and 0.086 nm/?C from 10?C to 70?C. The humidity sensitivities are 0.128 nm/%RH and 0.159 nm/%RH from 30% to 70%. Moreover, it also contains the following advantages: low cost, simple construction, and high sensitivity.
关键词： Photonic crystal fiber (PCF),Graphene Oxide (GO),Optical fiber sensor,Humidity,Temperature
更新于2025-09-23 15:21:01
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Double-sided Polished Ultra-stable and Ultra-sensitive Optical Fiber Sensor
摘要： A double-sided polished photonic crystal fiber (DP-PCF) for surface plasmon resonance(SPR) sensing is designed and analyzed by using the finite element analysis software COMSOL 5.5. The suggested design shows strong sensitivity stability in the low refractive index (RI) region (1.33 ～ 1.39) and ultra-high sensitivity in the high RI region (1.39 ～ 1.43), respectively. The structural parameters of the proposed sensor are studied to analyze the stability and high sensitivity of the fiber sensor. The introduced DP-PCF sensor offers high sensitivity of 32,434 nm/RIU in the RI range of 1.39 ～ 1.43 due to its special double-sided polishing design.
关键词： Photonic crystal fiber,Sensor,Surface plasmon resonance,Surface plasmon polariton
更新于2025-09-23 15:21:01
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A phase-change thin film-tuned photonic crystal device
摘要： This paper reports a tunable photonic device that incorporates a thin layer of phase-change material, Ge2Sb2Te5 (GST), in a photonic crystal (PC) structure. The PC structure is based on a one-dimensional grating waveguide with a metal cladding. The metal-cladded PC structure supports a guided-mode resonance (GMR) that selectively absorbs light at a particular wavelength. Inserting the GST material into the gating waveguide makes it possible to control the GMR mode. Here, the GST-PC device was numerically designed and optimized to obtain significant tuning of the GMR mode around 1550 nm. The tuning phenomena were experimentally demonstrated by the heat-induced phase change between crystalline and amorphous phases of the GST thin film. A spectral shift of the resonant wavelength from 1440 nm to 1610 nm was achieved via the crystallization process. The phase tuning of GST exhibits good repeatability as demonstrated by switching between amorphous and crystalline phases of GST for multiple cycles. The GST-PC device represents a new approach for tuning optical resonances with potential applications including but not limited to integrated photonic circuits, optical communications, and high-performance optical filters.
关键词： tunable filter,Photonic crystal,phase-change material
更新于2025-09-23 15:21:01
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THz cutoff frequency and multifunction Ti 2Ba2Ca2Cu3O10/GaAs photonic bandgap materials
摘要： By using the transfer matrix method (TMM), we theoretically explore the transmittance properties and cuto? frequency of one-dimensional photonic crystal (1DPCs) within the terahertz frequency region. The present structure consists of high-temperature superconductor and semiconductor layers. The results of the calculations represent the e?ects of various parameters on the cuto? frequency. We have used the two-?uid model as well as the Drude model to describe the permittivity of superconductor and semiconductor. Further, we consider that the permittivity of both the materials is depending on the hydrostatic pressure. The present results show that with the increasing of di?erent parameters as the operating temperature, the thickness of semiconductor, and the ?lling factor of semiconductor, then the cuto? frequency shift to lower frequencies regions. By the increasing of superconductor thickness, hydrostatic pressure, doping concentration and ?lling factor of the superconductor, we found the cuto? frequency shifts to higher frequency regions. These results indicate that cuto? frequency can be modi?ed through these di?erent parameters. Finally, the present design could be useful for many optical systems as the optical ?lter, re?ector and photoelectronic applications in the Terahertz regime.
关键词： Cuto? frequency,transfer matrix method,photonic crystal,doping concentration,hydrostatic pressure,two-?uid model,Drude model
更新于2025-09-23 15:21:01
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Higha??Performance Methanal Sensor Based on Metala??Organic Framework Based Onea??Dimensional Photonic Crystal
摘要： One-dimensional photonic crystal (1DPC) based on metal-organic framework (MOF) (MIL-101-NH2 (Cr) / TiO2)n was prepared by a spin coating method. The 1DPC structure was built to detect vapor gas. The optical properties of the 1DPC were investigated by varying the number of period, incident angles and thickness of MOF, and the results of the experiment are agreed with theoretical simulation. The 1DPC gas sensor shows good selectivity for vapor gas and allows for a reliable distinction between methanal and other investigated analytes with the maximal peak shift (43 nm). It was found that the response time and recovery time for the sensor are around 500 ms and 20 s, respectively. The relationship between the peak shift position and the methanal concentration was demonstrated to be linear. Moreover, the fabricated 1DPC exhibited high repeatability and long-term storage and thermal stability, which are beneficial for practical applications.
关键词： Sensors,Nanostructures,Metal-organic frameworks,Photonic Crystal
更新于2025-09-23 15:21:01