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Methanol-Filled Hybrid Photonic Crystal Fiber with High Birefringent and Negative Dispersion
摘要： A unique hexagonal lattice structure of silica-based solid core photonic crystal fiber (PCF) surrounded by array of air holes is proposed. The cladding portion of the structure consists of five rings where core is made up of 11 small rings filled with methanol. Three different-shaped structures are used to analyze the effect on PCF parameters where the first structure uses circular air holes in cladding and core, the second structure consists of circular air holes in cladding and elliptical air holes in core, and the last structure was designed by using elliptical air holes in both cladding and core. Optical properties birefringence, confinement loss, and negative dispersion have been found theoretically and compared. A novel and relatively simple approach depicts the results that attain high birefringence, low confinement loss, and negative dispersion. It is found that the presence of elliptic air holes instead of circular air holes in the core region and the cladding brings higher birefringence, low confinement loss, and highly negative dispersion.
关键词： Photonic crystal fiber,Effective refractive index,Dispersion,Birefringence,Confinement loss
更新于2025-09-23 15:19:57
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Optical properties of ZnO thin films deposed by RF magnetron
摘要： We have grown ZnO thin films on glass substrate by RF magnetron sputtering using metallic zinc target. The influences of some parameters on thin film optical properties were assessed. They exhibited extremely high resistivity of 1012 ?.cm, an energy gap of 3.3 eV at room temperature. It was found that a RF power of 50 W, a target to substrate distance of 70 mm, very low gas pressures of 3.35 x 10-3 Torr of argon and oxygen mixed gas atmosphere gave ZnO thin films with a good homogeneity and a high crystallinity. All the films are transparent in the visible region (400 to 800 nm) with average transmittance above 80%. The optical transmittance and refractive index, calculated from the spectra of optical absorbance, show a significant dependence on the growth parameters. As for the sample grown at 100°C, the average transmittance is about 80% in the visible wavelength range and the refractive index is estimated to be 1.97.
关键词： X-ray diffraction,RF sputtering magnetron,refractive index,ZnO,transmittance
更新于2025-09-23 15:19:57
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Effect of applied electric field on the nonlinear optical properties of modulation-doped GaAs/Al Ga1-As double quantum well
摘要： In the present study, the effects of varying doping concentration and applied electric field on the intersubband-related optical absorption and relative refractive index change coefficients in modulation-doped GaAs/AlxGa1?xAs double quantum wells are theoretically investigated. The allowed energy levels and the corresponding wave-functions are calculated by solving the Schr?dinger and Poisson equations self-consistently within the framework of the effective-mass and parabolic band approximations. The optical coefficients are evaluated using the compact density matrix formalism within an iterative procedure. The numerical results are presented for two different doping concentration and several values of the electric field. They show that both the peak position and the magnitude of the calculated total optical absorption coefficients and refractive index changes are significantly affected by the applied electric field and the doping concentration. The treatment is suitable to consider the general problem with different wells and barrier sizes, although the barrier width should preferably be small enough as to allow for an effective inter-well coupling.
关键词： Relative refractive index change,Modulation-doped QW,Absorption coefficient,self-consistent method
更新于2025-09-23 15:19:57
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Polydopamine coating decreases longitudinal plasmon of Au nanorods: Experiment and simulations
摘要： Polydopamine (PDA) coated Au nanorods (AuNRs) have attracted great interest as a convenient platform to construct various multifunctional nanoparticles for theranostic applications. Typically, the formation of a dielectric shell on the surface of plasmonic particles results in an increase in the particle extinction and in a small red shift of the plasmonic peak. However, compared to the well-known coatings such as silica, biopolymers, and polyelectrolytes, polydopamine is light absorbing material in the visual and NIR spectral range. In this paper, we demonstrate, for the first time, unusual changes in plasmonic properties of AuNRs after PDA coating. Namely, the longitudinal plasmon resonance decreases while the transversal one increases compared to the corresponding initial values of bare AuNRs. Remarkably, the increasing and red shifting of the transversal plasmon is similar to the common changes in plasmonic properties of PDA-coated spheres. To confirm the experimental observations, we simulated the extinction, absorption and scattering spectra for AuNRs with different geometrical properties and PDA shell thicknesses by using two literature models for the refractive index of PDA. The decreasing of plasmonic peak intensity became higher with an increase in the AuNR aspect ratio and the imaginary part of PDA refractive index. Our experimental results and simulations provide a new insight into understanding the optical properties of composite plasmonic particles.
关键词： Plasmon resonance,Refractive index,Au nanorods,Polydopamine
更新于2025-09-19 17:15:36
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Spherical particle absorption over a broad range of imaginary refractive index
摘要： This paper presents studies of the optical absorption cross section for homogeneous spheres of radius R interacting with light of wavelength λ as calculated with the Mie equations. Four regimes of behavior are disclosed: the Rayleigh Regime, the Geometric Regime, the Re?ection Regime, and a Crossover Regime. Two parameters govern these regimes, the imaginary part of the refractive index, κ, and the product of κ with the sphere size parameter kR where k = 2 π / λ, i.e. κkR . Simple, approximate functionalities on κ, k , sphere volume and projected geometric cross section are derived for these regimes. Interesting aspects of our observations include: Rayleigh absorption can apply to all particle sizes, Fresnel re?ection can occur for sub-wavelength spheres, and while κ is the agent of absorption, large κ can increase scattering to the detriment of absorption.
关键词： Absorption,Complex refractive index,Rayleigh theory,Mie theory
更新于2025-09-19 17:15:36
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Tunable local surface plasmon resonance and refractive index sensitivity ability of three-layered dielectric-silver bimetallic nanoshells
摘要： Optical properties and refractive index sensitivity abilities of three-layered silver/gold-dielectric-silver bimetallic nanoshells are investigated based on quasi-static theory. The results show that absorption spectra of silver/gold-dielectric-silver bimetallic nanoshells can be well tuned by changing the inner core radius, middle dielectric radius and outer shell layer thickness. Local surface plasmon resonance (LSPR) shifts of |ω? ?? mode show a red-shift with increasing the inner core radius and the thickness of middle dielectric layer, while a blue-shift with increasing the thickness of outer shell. It is interesting to find that the shifts of |ω+ ?? mode are related to the ratio ε2∕ε4, the component of core and nanoshell. In addition, the refractive index sensitivity abilities of three-layered silver/gold-dielectric-silver bimetallic nanoshells are also reported. A higher refractive index sensitivity ability can be obtained by adjusting its geometric size and component. |ω? ?? mode gets more intensity with increasing the surrounding medium dielectric function, while |ω+ ?? mode fades down. The intensity difference between |ω? ?? mode and |ω+ ?? mode is mainly effected by the surrounding medium dielectric function, its geometric parameter, middle layer dielectric function, the component of core and nanoshell. Our study provides a way to analyze sensitivity application of nanoshells and broadens the application of nanoshells in sensor ability.
关键词： Plasmon hybridization theory,Local surface plasmon resonance (LSPR),Dielectric-silver bimetallic nanoshells,Refractive index sensitivity ability
更新于2025-09-19 17:15:36
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Ocean Salinity Sensing Using Long-Period Fiber Gratings Functionalized with Layer-by-Layer Hydrogels
摘要： Rapid, accurate, and real-time measurements of ocean salinity are of great importance for a host of scientific, commercial, and defense applications. We demonstrate a highly sensitive, fast-responding fiber-optic salinity sensor that integrates long-period fiber gratings (LPFGs) with ionic strength-responsive hydrogel. The submicron-thick hydrogel was synthesized via layer-by-layer electrostatic assembly of partially quaternized poly(4-vinylpyridine) (qP4VP) and poly(acrylic acid), followed by chemical cross-linking. Spectroscopic ellipsometry measurement of a hydrogel made of 37% quaternized qP4VP showed robust and reversible swelling/deswelling in solutions with salt concentrations ranging from 0.4 to 0.8 M (22.8?44.7 g/kg) around pH 8.1. The swelling/deswelling process induced large changes in the refractive index of the hydrogel, leading to resultant shift in the resonance wavelength (RW) of LPFGs. The salinity-dependent optical response of the hydrogel-coated LPFGs is in good agreement with ellipsometry measurement. LPFGs coated with the hydrogel exhibited a sensitivity of 7 nm RW shift/M (125.5 pm/‰) with a measurement time less than 5 s. The shift in the resonance wavelength correlated linearly with salt concentration, making quantification of measured salinity straightforward.
关键词： refractive index,layer-by-layer assembly,hydrogels,ocean salinity sensing,long-period fiber gratings,ionic strength
更新于2025-09-19 17:15:36
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Smartphone-based critical angle refractometer for real-time monitoring of Brix value
摘要： We demonstrate the first smartphone-based critical angle refractometer for monitoring refractive index and Brix value in real time. The principle design of an optical coupler is based on the total internal reflection of incident light from the phone screen. The images acquired from the front-facing camera are directly analyzed on smartphone using a custom developed application, to detect the shift of gradient peak position corresponding to the refractive index and Brix value. Calibrations are carried out using nine water-sucrose solutions providing a linear response in the refractive index range of 1.3330-1.3575 RIU (R2 = 0.9984) with the sensitivity and the resolution of 2778.1 pixel/RIU, and 3.6′10-4 RIU, and a linear response in the Brix value of 0-16.25 °Brix (R2 = 0.9968) with the sensitivity and the resolution of 4.239 pixel/°Brix and 0.24 °Brix. We also successfully determined the sugar content in six fruit juices with the absolute error from standard refractometer at less than 0.21 °Brix.
关键词： refractive index,Critical angle refractometer,Brix value,smartphone-based
更新于2025-09-19 17:15:36
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Performance of Arrayed Microring Resonator Sensors with the TriPleX Platform
摘要： Integrated-optical (bio) chemical sensors are more and more commercialized, mainly because of their high intrinsic sensitivity in combination with the possibilities they offer for integration in optofluidic devices. The microring resonator (MRR), for example, is a very feasible structure to be used as microarray sensor element for multiplex biosensing. Fabrication of MRRs has been described in the case of the TriPleX platform employing well-defined stacks of stoichiometric Si3N4 and SiO2 material. This platform allows for a wide variety of applications, due to its intrinsic low loss and its transparency for the VIS/NIR wavelength range. In the present paper, we describe the recent achievements in the characterization of arrays of these MRRs regarding temperature sensitivity, refractive index sensitivity and protein immobilization performance. Furthermore, the use of a reference channel/reference MRR is demonstrated in order to show the advantage of compensation of unintended change in temperature or sample composition. The refractive index sensitivity was determined to be 104 nm/RIU and the limit of detection was about 2 × 10-6 RIU. MRRs appeared to behave very comparable (expressed as the coefficient of (intra-array) variation (CV)) regarding the response to temperature (CV≈0.3%) as well as refractive index (CV<0.1%). Furthermore, it is shown that protein immobilization onto the different MRRs of the same arrays can be realized in a comparable way (CV<3%). A good comparability (i.e., a low variation) in these aspects allows for the use of internal referencing in order to compensate for unintended change in temperature or refractive index and also helps to attain a high assay precision in the ultimate biosensing application. Ongoing research is focused on the integration of more functionality on chip and further miniaturization in order to allow for fabrication of complex, though affordable, sensor devices.
关键词： Refractive index,Biosensor,MRR,Sensor array,Integrated optics,Microring resonator
更新于2025-09-19 17:15:36
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Cascaded tilted fiber Bragg grating for enhanced refractive index sensing
摘要： We proposed and experimentally demonstrated a cascaded tilted fiber Bragg grating (TFBG) for enhanced refractive index sensing. The TFBG is UV-inscribed in series in ordinary single-mode fiber (SMF) and reduced-diameter SMF with the same tilt angle, and then excites two sets of superposed spectral combs of cladding modes. The cascaded TFBG with total length of 18 mm has a much wider wavelength range over 100 nm and narrower wavelength separation than that of a TFBG only in the SMF, enabling an enlarged range and a higher accuracy of refractive index measurement. The fabricated TFBG with the merits of enhanced sensing capability and temperature self-calibration presents great potentials in the biochemical sensing applications.
关键词： refractive index measurement,tilted fiber Bragg grating,fiber optics sensors
更新于2025-09-19 17:15:36