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Athermalization of a self-assembled rolled-up TiO2 microtube ring resonator through incorporation of a positive thermo-optic coefficient material in planar bilayers
摘要： For the first time, this paper theoretically and experimentally investigates the thermal stability of optical filters based on self-assembled TiO2 rolled-up microtube ring resonators (RUMRs) by incorporating positive thermo-optic coefficient (TOC) materials (e.g., SiO2 and/or Si3N4). The influence of the TOC, refractive index, and thickness of the positive TOC materials on the filtering performance of the TiO2 RUMR is theoretically studied. The results illustrate that an increase in temperature leads to a blueshift in the resonant wavelength of the RUMR-based optical filter, which changes at a rate of ? 33.3 pm/K owing to the negative TOC of TiO2 (? 4.9 ± 0.5 × 10?5/K). By increasing the thickness of SiO2 or Si3N4 as a positive TOC material together with TiO2, the temperature-induced resonant shifts of TiO2/SiO2 and/or TiO2/Si3N4 RUMRs are theoretically obtained. The TIRS varies between ? 40 pm/K (? 22 pm/K) and about 30 pm/K (22 pm/K) for TiO2/SiO2 (TiO2/Si3N4) RUMRs. It is shown that thermal stability occurs when the thickness of the SiO2 (Si3N4) layer is ~ 16 nm (12 nm). At the end of this study, as a proof of concept, an experiment is demonstrated by fabricating an RUMR based on TiO2/SiO2 on the flat silicon wafer. The experimental results show that the athermalization of the system is experimentally achieved by selecting the appricated thickness ratio of TiO2/SiO2. This novel approach for athermalization of the resonators opens up interesting perspectives on the implementation of vertical and multi-routing coupling between photonic and optoelectronic layers and more specifically in a three-integration fashion.
关键词： TiO2,Rolled-up microtube ring resonators,SiO2,Athermalization,Si3N4,Thermo-optic coefficient
更新于2025-09-12 10:27:22
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Vacuum-annealed and oxygen plasma treated ellipsometric investigations on molybdenum bronzes and measurements of their thermo optic coefficients and electronic polarizability coefficients
摘要： In this investigation, we have measured the optical constants (n, k) of vacuum evaporated MoO3 thin films and of ZxMoO3 (Z = H+, Li+) bronze thin films being annealed at different temperatures and with different concentrations (x) over the range 298–453 K without and within an oxygen plasma environment using manual ellipsometry. We have also measured mass densities, thermo optic coefficients (TOCs), electronic polarizability coefficients (EPCs) and the coefficients of temperature dependence of density of MoO3 thin film and of its bronzes over the same temperature range. It was found that the change in density and porosity of MoO3 thin film (when annealed at 453 K for 36 h) was not more than 6.4% and 15% respectively from the room temperature data. In the case of bronzes, when the samples H0.203MoO3, Li0.076MoO3 and Li0.133MoO3 were annealed at 453 K within an oxygen plasma over different periods of times, it was found that the overall increase in mass density and decrease in the porosity was not more than 4% and 11%, respectively from the initial data at room temperature. Comparably, when the samples H0.211MoO3 and Li0.27MoO3 were annealed at 453 K within an oxygen plasma over different periods of time, the respective decrease in density and increase in porosity was found not more than 3.4% and 6% from the room temperature data. All these results are mostly due to evolution of H2O which causes diffusion of oxygen leading to shallow and deep localised states in the oxide bronze layers. TOCs and EPCs of samples HxMoO3 (x = 0.203) and LixMoO3(x = 0.076, 0.133) upon annealing at 453 K (without and within an oxygen plasma) over different periods of times have an increase in TOCs and in EPCs, and that increase is from 0.10 × 10?4 K?1 to 13.5 × 10?4 K?1 and 0.13 × 10?27 cm3 K?1 to 3.2 × 10?27 cm3 K?1, respectively. On the other hand, the thermo optic coefficient and the coefficient of temperature dependence of density of MoO3 thin films decrease from ? 1.2 × 10?4 K?1 to ? 8.86 × 10?4 K?1 and ? 1.86 × 10?4 g cm?3 K?1 to ? 15.13 × 10?4 g cm?3 K?1, respectively. In the case of H0.211MoO3 and Li0.27MoO3 when annealed at 453 K over different periods of time within oxygen plasma, the overall decrease in TOC is from ? 0.3 × 10?4 K?1 to ? 4.62 × 10?4 K?1, and the decrease in coefficient of temperature dependence of density is from ? 0.45 × 10?4 g cm?3 K?1 to ? 8.9 × 10?4 g cm?3 K?1. These results are due to linear thermal expansion effect.
关键词： ellipsometry,thermo optic coefficients,electronic polarizability coefficients,MoO3 thin films,molybdenum bronzes
更新于2025-09-11 14:15:04
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Investigation of Temperature Sensitivity of a Polymer-Overlaid Microfiber Mach-Zehnder Interferometer
摘要： The temperature sensitivity of the free spectral range (FSR) for a polymer-overlaid microfiber Mach-Zehnder interferometer (MZI) is investigated both theoretically and experimentally. The waist diameter of the optical microfiber can be controlled to alter the thermal expansion and optic properties of the polymer-coated MZI. Inserting an optical microfiber with a strong evanescent field into the MZI, a low index polymer with high thermal characteristics is deposited on the surface of the microfibers to realize a polymer-overlaid microfiber MZI. It was found that the thermal expansion factor in the proposed MZI plays an important role in the temperature sensitivity of the FSR. The temperature sensitivity of the polymer-overlaid microfiber MZI is improved, which is measured to be ?8.29 nm/?C at 25 ?C. The optical transmission spectrum of the polymer-overlaid microfiber MZI is converted to the spatial frequency spectrum via fast Fourier transform. The temperature sensitivity of the spatial frequency in the proposed polymer-overlaid MZI is estimated to be 18.31 pm?1 ?C?1, which is 17 times higher than that of the microfiber MZI without polymer coating (1.04 pm?1 ?C?1).
关键词： temperature sensors,thermo-optic effect,thermal expansion effect,microfibers,microfiber Mach-Zehnder interferometers
更新于2025-09-10 09:29:36
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Modeling the Temperature Dependent Material Dispersion of Imidazolium Based Ionic Liquids in the Vis-NIR
摘要： A thorough analysis of the refractive index of eleven 1-alkyl-3-methylimidazolium based ionic liquids with three different anions, tetrafluoroborate BF4, bis(trifluoromethylsulfonyl)imide NTf2 and trifluoromethanesulfonate OTf, is reported. Refractive indices were estimated, in the temperature interval from 298.15 K to 323.15 K, using an Abbe refractometer to determine the value at the sodium D line and white light spectral interferometry to obtain dispersion in the range of wavelengths from 400 to 1000 nm. The first part of the manuscript is focused on the dependence of refractive index with wavelength, temperature, cation alkyl chain length and anion nature. Once the main features are detailed, and in order to explain the experimental trends, a model for the refractive index is considered where its square is expressed by a single resonance Sellmeier dispersion formula. This formula has two coefficients, the first one identifies the position of the resonance in the spectral axis, and the second one specifies its strength. It was found that, for a given compound, the resonance's position is independent of temperature, while the strength varies linearly with it. This model reproduces successfully the experimental data within the refractive index uncertainty. Furthermore, the model allows calculating the thermo-optic coefficient and its wavelength dependence.
关键词： ionic liquids,refractive index,thermo-optic coefficient
更新于2025-09-10 09:29:36
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Highly c-axis oriented crystal growth induced giant unusual saturable absorption behavior in wet chemically grown ZnO thin films
摘要： Wet-chemical sol-gel spin coating technique was considered to fabricate ZnO thin films on bare glass substrates with different thickness values (30 nm, 90 nm, 110 nm, 150 nm). The XRD reflections showed a transition from semi-polar crystal growth orientation to polar crystal growth orientation when the thickness was reduced to 30 nm. The nonlinear characteristics of prepared nano-films were quantized by performing open aperture and closed aperture Z-scan measurements under a continuous wavelength regime. The open aperture Z-scan transmittance curves showed a remarkable transition from normalized valley to normalized peak in 30 nm thick ZnO film. The presence of normalized valley and peak were attributed to reverse saturable absorption (RSA) and saturable absorption (SA) behavior respectively. The RSA behavior was attributed to well known two-photon absorption (TPA) mechanisms and the SA behavior was due to the reduction in electron-hole wave function overlapping along c-axis. The closed aperture Z-scan measurement of 30 nm thick ZnO film revealed the violation of two parabolic band (TPB) and Kramer-Kronig relations by exhibiting self-focusing mechanism. The self-focusing mechanism was attributed to thermal effects due to the smaller thickness of ZnO. However, self-defocusing behavior was observed in 90 nm, 110 nm, and 150 nm thick ZnO films.
关键词： electron-hole wavefunction,saturable absorption,polar ZnO,thermo-optic effect,self-focusing
更新于2025-09-09 09:28:46
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Thermal Effects on Modal Properties of Dual-Core Yb-Doped Fibers
摘要： The impact of thermo-optic refractive-index changes arising from the core heat load in a dual-core fiber amplifier is studied through finite-element based numerical simulations. Trends in coupling lengths, effective area, core overlaps of fundamental and higher-order supermodes, effects of asymmetric heat loads, and thermo-optic mode coupling parameters are quantified. It is concluded that the coupling between cores is only moderately altered by the overall heat load, but can be strongly sensitive to asymmetric loads. The influence of the core coupling strength is demonstrated to be very important on the supermode effective area, besides the shrinking due to thermal effects. While the thermo-optic index perturbations can lead to guidance of higher-order supermodes, it seems realistic to maintain single-mode operation through gain suppression of the higher-order modes. On the other hand, thermo-optic couplings between fundamental supermodes are found to be quite strong.
关键词： dual-core fiber,fiber amplifier,supermodes,thermo-optic,thermal effects
更新于2025-09-04 15:30:14
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Investigation on the Thermo-Optic Coefficient of Silica Fiber Within a Wide Temperature Range
摘要： In this paper, the thermo-optic coef?cient of silica ?ber is analyzed and measured within a wide temperature range of 0–1200 °C for the ?rst time. To obtain the thermo-optic coef?cient, experiments were carried out by using ?ber optic extrinsic Fabry–Perot interferometers (EFPIs) embedded in silica ?ber. The optical cavity lengths of the EFPIs were measured with white-light interferometry. The experimental results show that the ?rst and second orders of the thermo-optic coef?cient are 1.090 × 10?5/°C and 1.611 × 10?9/°C2, respectively. The quadratic model for the temperature dependence of the basic optical parameter, the refractive index, is rigorous within a wide temperature range. Furthermore, this paper also provides a temperature calibration method for extrinsic Fabry–Perot interferometric temperature sensors. The temperatures measured by the sensors are in excellent agreement with those measured by the reference thermocouple. Hence, this calibration method is promising for temperature sensors with a wide working temperature range.
关键词： thermo-optic coef?cient,Fabry-Perot interferometers,silica ?ber
更新于2025-09-04 15:30:14