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Effect of Magnesium on Structural and Optical Properties of CaTiO3: A DFT Study
摘要： The electronic bandstructure, optical and structural properties of pure and Mg-doped CaTiO3 are calculated by using first-principle calculation which is based on the density functional theory. The effect of Mg-dopant on the properties of CaTiO3 perovskite explored by using ultra soft pseudo-potential (USP) and generalized gradient approximation (GGA). The incorporation of Mg at Ca site affected the electronic band structure of CaTiO3 meaningfully by introducing new gamma point. The incorporation of Mg increases the band gap from 1.84 eV to 1.92 eV. The partial density of states of pure CaTiO3 changed after doping cleared the effect of dopant on pure system. Optical properties of both the systems are examined which reveals that the absorption edge shifting from 2.1 eV to 2.5 eV indicates a blue shift whereas the refractive index also increases from 2 to 2.4 after doping. Thus Mg-doped CaTiO3 not only affect the optical properties of the system but also make it and appealing candidate for optical devices.
关键词： Refractive index,Doping,Density of states,Oxide Based Perovskite,Optical Properties,Band Gap
更新于2025-09-23 15:22:29
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Study of a large lateral core-offset in-line fiber modal interferometer for refractive index sensing
摘要： A large lateral core-offset in-line fiber modal interferometer was proposed in order to avoid the relative direction of the two core-offset joints affecting the interference performance. The RI sensing performances of the interferometers with different arm lengths were evaluated and compared with the small core-offset ones. The simulation and experimental results showed that the power remaining in the core mode decreased from 25 to 0.002% after the input light passing through the first core-offset joint as the core-offset displacement increased from 6 to 40 μm. Thus, the interference between the core mode and cladding mode within the enlarged core-offset interferometer was suppressed, and meanwhile the interference within the cladding modes was dominated. As the core-offset displacement was simply enlarged from 6 to 40 μm, the RI sensitivity was greatly improved from 43.97 to 123.40 nm/RIU. The proposed sensor is a cost-effective solution for RI sensing purpose, and exhibits the advantages of high sensitivity, simple structure and easy fabrication with only a fusion splicer.
关键词： Fiber modal interferometer,Core-offset,Optical fiber sensor,Refractive index measurement
更新于2025-09-23 15:22:29
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Optical absorption via intersubband transition of electrons in GaAs/Al <sub/>x</sub> Ga <sub/>1?x</sub> As multi-quantum wells in an electric field
摘要： Based on the effective mass approximation, the Schr?dinger equation and Poisson equation in GaAs/AlxGa1?xAs multi-quantum wells (MQWs) are self-consistently solved to obtain the wave functions and energy levels of electrons in the conduction band for the ground first excited state by considering a lateral electric field (LEF). Then, the effects of size, ternary mixed crystal, doping concentration, and temperature on linear and nonlinear intersubband optical absorption coefficients (IOACs), and refractive index changes (RICs) due to the transition between ground states and the first excited states of electrons are discussed based on Fermi’s golden rule. The results show that, under a fixed LEF, with increase of Al composition and doping concentration, the IOACs produce a red shift. With increases of both widths of the wells and barriers IOACs appear as blue shifts and their amplitudes increase, but the barrier width change is much more important to affect nonlinear IOACs, whereas increasing the temperature results in a blue shift first and then a red shift of IOACs. When the other parameters are fixed but there is an increase in the LEF, IOACs occur with a blue shift, and the RICs have similar properties.
关键词： multi-quantum wells,optical absorption of electronic intersubband transition,refractive index changes,lateral electric field
更新于2025-09-23 15:22:29
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Simulations of some physical parameters of homologous series of nBT and nCHBT at 0.3–20.0 THz
摘要： In this work, the terahertz (THz) absorption of homologous series of isothiocyanobiphenyls (nBT) and 4-(trans-4?-n-alkylcyclohexyl)isothiocyanato-benzene (nCHBT) are simulated by using the density functional theory (DFT) method. Numerical results show that absorption of the tested nematic liquid crystals (NLCs) varies up to 0.04 in the broad range of 0.3–20.0 THz and takes maximum value in the range of 9–14 THz. In addition, the values of molecular polarisabilities (αo, αe) increase with the increase in the number of carbon atoms in the alkyl chain, while refractive indices (no, ne) decreases. The calculated birefringence (Δn) values for nCHBT are approximately twice as large as the birefringence value for nBT. It is crucial to examine these series of nematic liquid crystals at THz frequencies due to the role of soft matter in various switchable THz components.
关键词： Numerical calculations,refractive index,terahertz radiation,birefringence,nematic liquid crystals
更新于2025-09-23 15:22:29
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[IEEE 2018 IEEE 15th International Conference on Group IV Photonics (GFP) - Cancun (2018.8.29-2018.8.31)] 2018 IEEE 15th International Conference on Group IV Photonics (GFP) - Phase-Shifted Multimode Bragg Gratings in Silicon-on-Insulator for Sensing Applications
摘要： In this paper, we experimentally characterize the sensitivity of different types of multimode Bragg gratings in Silicon-On-Insulator and demonstrate a high sensitivity of 120 nm per refractive index unit using Bragg gratings for TM polarized light.
关键词： Bragg gratings,refractive index sensing,multimode
更新于2025-09-23 15:22:29
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-shaped chiral metamaterials
摘要： A highly sensitive refractive index sensor based on the conjugated bilayer-shaped chiral metamaterial is proposed. It is composed of two-shaped structures and a microstrip connecting line. The strong conductive coupling between two-shaped structures can be realized by microstrip connecting line. The chiral metamaterial shows giant circular dichroism (CD) effect, and the CD effect can up to 93.8% and 96.2% at 1.767Thz and 3.008Thz, respectively. The physical origin of the observed CD effect is elucidated through distributions of magnetic and current at resonances. The designed conjugated bilayer-shaped chiral metamaterial as a refractive index sensor can achieve sensitivity of 1.065Thz/RIU and 1.777Thz/RIU, respectively. The effect of structural parameter on the sensitivity and CD spectra is investigated. Through this study we presented the giant CD metamaterial based on conductive coupling and its application potentials for low detection-limit physical and biochemical sensing applications.
关键词： chiral metamaterial,conductive coupling,circular dichroism,resonance,refractive index sensor,metamaterial
更新于2025-09-23 15:22:29
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Metal-insulator-metal nano square ring resonator for gas sensing applications
摘要： In this paper, three designs of Square Ring resonator (SRR) based on metal-insulator-metal (MIM) WG are reported. The transmission spectra and electric field distribution of the sensor structure are simulated using finite element method (FEM). The effect of structural parameters on the spectral characteristics and sensing performance are investigated comprehensively. The maximum achieved sensitivity and figure of merit of the sensor reached 1320 nm/RIU and 16.7, respectively. Due to the high performance and easy fabrication, this kind of plasmonic structures can find noteworthy applications in integrated optical circuits and on-chip nano-sensors.
关键词： refractive index sensor,square ring resonator,finite element method,Surface plasmon polariton,metal insulator metal waveguide
更新于2025-09-23 15:22:29
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Optical Properties of Energy-Dependent Effective Mass GaAs/GaxIn1?xAs and GaAs/AlxGa1?xAs Quantum Well Systems: A Shooting Method Study
摘要： In this paper, we study the effect of energy-dependent effective mass on optical properties of GaAs/GaxIn1?xAs and GaAs/AlxGa1?xAs quantum well systems through the compact density matrix approach. We solved the resulting non-linear Schro¨dinger equation by a simple shooting method and present the algorithm. We show that the energy-dependent effective mass effect is more important for systems with narrower quantum well systems. By an energy-dependent effective mass assumption, absorption coef?cient peak height increases with increasing the total system length L while in the constant effective mass limit, absorption coef?cient peak heights have not been in?uenced by changing L. In the GaAs/AlxGa1?xAs system, by increasing the number of wells, the linear absorption coef?cient amplitude at ?rst increases and then decreases in the ?xed effective mass approximation and monotonically decreases in the energy-dependent effective mass case. By increasing the number of wells, the linear absorption coef?cient peak position at ?rst shows a blue shift and then shows a redshift. In the GaAs/GaxIn1?xAs system, the situation is more complicated and it is described in more detail in the text. However, GaAs/GaxIn1?xAs quantum well systems have larger values of absorption coef?cient peak heights than GaAs/AlxGa1?xAs ones.
关键词： shooting method,GaAs/GaxIn1?xAs and GaAs/AlxGa1?xAs Quantum wells,refractive index changes,energy-dependent effective mass,absorption coef?cient
更新于2025-09-23 15:21:21
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Optimising porous silicon Bragg reflectors for narrow spectral resonances
摘要： Achieving sharp spectral resonances in porous silicon based photonic structures is of significant practical importance for improving the accuracy of refractive index-based sensing in chemical and biochemical applications. Here, we show that by compensating for depth related heterogeneities in the etching conditions, we are able to reduce the porosity modulation in Bragg reflectors to below 1% and achieve absorption limited spectral widths of 7 nm in the visible part of the spectrum. Such narrowband Bragg reflectors provide markedly improved sensing capability for real-time monitoring of refractive index changes compared with reflectors with broader spectral features.
关键词： optical sensing,porous silicon,Bragg reflectors,narrow spectral resonances,refractive index-based sensing
更新于2025-09-23 15:21:21
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Live E. coli bacteria label-free sensing using a microcavity in-line Mach-Zehnder interferometer
摘要： The paper presents the first study to date on selective label-free biosensing with a microcavity in-line Mach-Zehnder interferometer induced in an optical fiber. The sensing structures were fabricated in a single-mode fiber by femtosecond laser micromachining. In contrast to other studies of this sensing scheme, where only the sensitivity to refractive index changes in the cavity was investigated, this research used chemical surface treatment of the sensor to ensure detection specificity. Immobilized MS2 bacteriophages were applied as recognition elements specifically targeting live E. coli C3000 bacteria. It is shown that the sensor allows for real-time monitoring of biological phenomena taking place on the surface of the microcavity. The developed biosensor exhibits ultrahigh refractive index sensitivity of 15,000 nm/RIU and is capable of detecting live E. coli bacteria concentrations as low as 100 colony forming units (CFU)/mL in liquid volume as low as picoliters.
关键词： label-free biosensing,E. coli C3000 bacteria,refractive index sensitivity,MS2 bacteriophages,femtosecond laser micromachining,microcavity in-line Mach-Zehnder interferometer,optical fiber
更新于2025-09-23 15:21:21