Mode characteristics of silver-coated inverted-wedge silica microdisks

The characteristics of whispering gallery modes(WGM) in silver-coated inverted-wedge silica microdisks are theoretically investigated by using finite element method. Dielectric TE mode always exists in silver-coated inverted-wedge resonators; dielectric TM mode tends to couple with SPP modes; only pure interior surface plasmonic polariton(SPP) mode but not pure exterior SPP mode is observed in contrast to the metal-coated cylindrical and toroidal resonators. The dependence of quality factor of different kinds of WGMs on the radius of the resonator and the thickness of the coated silver layer are systematically analyzed. We find that the quality factors of the hybrid WGMs associated with SPP mode can reach 104. The maximum light intensity enhancement in ambient for a hybrid mode consisting of a dielectric TM mode and an exterior SPP mode can be obtained when a silver film of thickness ~40 nm is deposited. The silver-coated inverted-wedge silica resonators may be widely applied in sensing and surface enhanced Raman scattering.     

High-pressure effects on nanometric hybrid xerogels, p-phenylenediamine/silica and p-anisidine/silica

The hybrid xerogels p-phenylenediamine/silica and p-anisidine/silica were prepared with different surface areas and porosities and they were processed at high pressure (7.7 GPa or ∼76000 atm) in a quasi-hydrostatic medium at room temperature. The morphologies of the materials were studied before and after the high-pressure treatment by using N₂ adsorption–desorption isotherms, scanning electron microscopy and infrared thermal analysis. The porous hybrid p-phenylenediamine /silica presented after the high-pressure treatment a surface-area reduction and an entrapment of organics in closed pores. However, the less porous hybrid p-anisidine /silica showed a surprising behavior, a pressure-induced increase in surface area with opening of pores. We propose a mechanism based on the inhibition of the cold sintering process by the organics to explain these results. PACS 81.20.-n; 81.40.Vw; 81.05.-t     

The 650-nm variable optical attenuator based on polymer/silica hybrid waveguide

Visible light variable optical attenuators(VOA) are essential devices in the application of channel power regulation and equalization in wavelength-division multiplexing cross-connect nodes in plastic optical fiber(POF) transmission systems.In this paper, a polymer/silica hybrid waveguide thermo–optic attenuator based on multimode interference(MMI) coupler is designed and fabricated to operate at 650 nm. The single-mode transmission condition, MMI coupler, and transition taper dimensions are optimized through the beam propagation method. Thermal analysis based on material properties provides the optimized heater placement angle. The fabricated VOA presents an attenuation of 26.5 dB with a 21-mW electrical input power at 650 nm. The rise time and fall time are 51.99 and 192 μs, respectively. The time–stability measurement results prove its working reliability.     

Hybrid polymer/silica thermo-optic vertical coupler switches

Thermo-optic 1×2 vertical coupler switches (VCSs) using a hybrid polymer/silica integration technology were designed using a finite element method and a coupled mode method for different refractive index contrasts. The multilayer structures were optimized by thermal analysis. Based on these designs and simulations, hybrid polymer/silica thermo-optic 1×2 VCSs exhibiting low insertion loss, low crosstalk, low switching power and polarisation independence were demonstrated. Based on this building block, a 1×8 VCS has been fabricated. Received: 21 May 2001 / Published online: 23 October 2001     

Thermal Stabilization of EDFA gain by hybrid concatenation of antimony-doped silica EDF

Sb-doped silica EDF showed an opposite temperature dependent gain profile compared to Al-doped silica EDF. Concatenation of those two EDFs showed a gain variation less than ± 0.4 dB over 40nm of C-band with the 15dB gain, in the temperature range of - 40 to + 80℃.     

Optical nonlinearity and structural phase-transition observation of organic dye-doped polymer silica hybrid material

The optical nonlinearity of organic dye-doped poly(methyl methacrylate) (PMMA)-silica-gel hybrid material was investigated by second-harmonic-generation measurement. We found that incorporation of in situ polymerized solgel precursors into the organic dye-doped PMMA significantly improved the nonlinear optical stability of the system. However, improvement of thermal stability occurred only when a sufficient amount of silica gel was incorporated. A structural phase transition from pure polymer to a hybrid system was found near a 10-mol.% silica-gel concentration. The optimum polymer/tetraethoxysilane molar ratio is 2:1 to 1:1.     

Difference frequency generation in GaAs microdisks

Semiconductor-based whispering-gallery-mode microcavities are very promising for nonlinear optics applications, thanks to the high optical quality factors attainable with today's technology. We propose to exploit this advantage to generate cw light through phase-matched difference frequency generation in a triply resonant GaAs microdisk. A proper choice of the microdisk radius and thickness allows one to select the generated wavelength in the band of 2.5-2.9 mum. Besides illustrating the design features, we numerically show that temperature can be effectively used to compensate for wavelength shifts induced on the generated field by fabrication errors.     

Optically S-polarized surface waves in symmetrical nonlinear sensors: Thermal effects

A surface wave in a planar nonlinear waveguide is a current problem that has several applications in modern electronics and optics such as optical sensors design. The effect of thermal stress on the optical performance of a nonlinear symmetrical sensor is studied. The mathematical forms of the dispersion equation and thermal-stress sensitivity are analytically derived and plotted numerically. It is found that the thermal sensitivity of the sensor can be controlled by tuning the core size, by changing the loading materials, and by carefully selecting the materials.     

共轭高分子链中电荷迁移的热效应

从理论上研究了共轭高聚物链中在电场作用下极化子运动的热效应.基于SSH模型以及通过绝热动力学演化的方法,模拟了共轭高聚物链中极化子在电场作用下从链左端向右端运动的过程.晶格受到的热扰动作用假设为通过局域的晶格范围内原子位移的随机涨落来实现.结果发现,晶格中的局域热涨落对于运动中的极化子而言等效于一个势垒.势垒高度由高分子中受到热扰动的区域的范围大小以及该区域与其周围环境的温差来决定.当分子中存在热吸收不均匀的现象时,链内极化子迁移率在低电场范围内随电场的变化遵循对数曲线变化规律.     

Characterization of photonic nanojets in dielectric microdisks

The direct imaging of photonic nanojets in different dielectric microdisks illuminated by a laser source is reported. The SiO₂ and Si₃N₄ microdisks are of height 650 nm with diameters ranging from 3 μm to 8 μm. The finite-difference time-domain calculation is used to execute the numerical simulation for the photonic nanojets in the dielectric microdisks. The photonic nanojet measurements are performed with a scanning optical microscope system. The photonic nanojets with high intensity spots and low divergence are observed in the dielectric microdisks illuminated from the side with laser source of wavelengths 405 nm, 532 nm and 671 nm. The experimental results of key parameters are compared to the simulations and in agreement with theoretical results. Our studies show that photonic nanojets can be efficiently created by a dielectric microdisk and straightforwardly applied to nano-photonics circuit.     

Quality-factor enhancement of supermodes in coupled microdisks

We investigate the optical modes in a coupled pair of semiconductor microdisks in symmetric and asymmetric configurations both experimentally and theoretically. While the quality factors of coupled first- and second-order whispering gallery modes (WGMs) show a conventional crossing, the quality factors of the same-order WGMs reveal an interesting splitting behavior, leading to the formation of high- and low-quality supermodes. Our results are reproduced by numerical simulations, and an explanation based on optical interference is suggested. Quality-factor splitting is a subtle phenomenon that might help to design microarchitectures for efficient optical coupling in cavity quantum electrodynamic experiments.     

Polyimide/hollow silica sphere hybrid films with low dielectric constant

Abstract

Polyimide (PI)/hollow silica (HS) sphere hybrid films with low dielectric constant values (low-k) were synthesized via thermal imidization process using pyromellitic dianhydride (PMDA)/4,4′-oxydianiline (ODA) as the polymer matrix and HS spheres as inorganic particles with the closed air voids. The monodispersed HS spheres were synthesized via a one-step process, which means that the formation of silica shells and dissolution of the core particles (polystyrene particles) occurs in the same medium. The HS particles have uniform size of ca. 1.5 μm in diameter and ca. 100 nm in shell thickness. PI/HS sphere hybrid films synthesized using mixture of polyamic acid (PAA) and HS spheres prepared via one-pot process, which means that the production of PAA and HS spheres mixture occurs with the polymerization of PMDA and ODA in the same bottle. HS spheres of two different kinds (pristine HS spheres (PHS spheres) and amine-modified HS spheres (AHS spheres)) were used for the preparation of the hybrid films. With the varying contents of AHS spheres in the range of 1–10 wt%, the dielectric constants of the PI/AHS sphere hybrid films were reduced from 3.1 of pure PI to 1.81 by incorporating 5 wt% AHS. The dielectric constants of the PI/PHS sphere hybrid films were reduced to 1.86 by incorporating 5 wt% PHS. Organic–inorganic hybrid porous polyimides may be expected as prime candidates for polymeric insulators due to their high thermal stability, good mechanical properties, solvent resistance, and low-k.     

Strong Purcell effect for InAs quantum boxes in high-Q wet-etched microdisks

We report on the fabrication of high-quality GaAs microdisks using a new two-step wet-etching fabrication process, and on their optical characterization, using the photoluminescence of InAs Quantum Boxes as an intracavity light source. We measure quality factors as high as 12 000 for the resonant whispering gallery modes, which highlights an excellent smoothness of the cavity sidewalls. Those small-volume/high-Q-confined modes are extremely attractive for performing CQED experiments on solid-state emitters. Using a novel experimental approach, we could in particular observe a record enhancement of the SE rate for emitters on-resonance with such modes (×18), in a cw PL experiment.     

Thermal effects vs. gain in femtosecond laser written waveguides in neodymium doped fused silica

The influence of thermal effects in gain measurements of fs laser-written waveguides in actively doped glass is reported for the first time. We show that these effects strongly contribute to the signal enhancement (up to 50% observed). Thus, a new measurement scheme to distinguish between thermal induced signal increase and real amplification is proposed. PACS 42.82.-m; 42.82.Et; 42.65.Re     

Thermal conductivity of neutron-irradiated silica

Low temperature thermal conductivity Λ(T) of vitreous silica has been measured after exposure to various neutron fluences. It has been observed that the increase in Λ(T) saturates for approximately the same fluence for which the change in mass density ? saturates. A correlation between Λ(T) and the fictive temperature has been found.     

Superconducting resonator in strong microwave fields: Thermal domain, nonlinear thermal effects

The thermal nonlinearity of superconducting films in an electromagnetic field is investigated theoretically. It is shown that the transition of the superconductor from the superconducting to the normal state as a result of Joule heating exhibits hysteresis, corresponding to the onset of a bistable state in the film. It is shown that as a result of the nonuniformity of the amplitude of the electromagnetic field along the surface of the superconducting film, above some threshold a normal-phase domain forms in the superconductor. It is ascertained that the temporal evolution of the domain walls exhibits the character of thermal autowaves of heating or cooling. The nonlinear radio-frequency characteristics (reflection and transmission coefficients and frequency responses) of a stripline resonator under conditions of thermal nonlinearity are calculated. Zh. Tekh. Fiz. 67, 81–89 (October 1997)     

Heater optimization for polymer in silica optical switch

An optimization process of specialized heater electrode design for a Multimode Interference (MMI) based polymer in silica thermo-optical switch is described. The switch is designed based on the waveguide structure of photodefinable BenzoCyclobutene (BCB 4024-40) polymer core, sandwiched by a 6 μm thickness of silica (SiO₂) upper clad layer and BK7 glass as a substrate. The upper clad thickness has been chosen such that to avoid any attenuation due to lossy behavior of the metal electrode. The light path is controlled by embedded thermal heater on top of the waveguide at specified location. Starting from a straight rectangular heater at pre-designed location, a migration technique and optimization toward a trapezoidal heater structure has been proposed which utterly claimed a significant improvement in terms of tuning power by more than 15%.     

Second order parametric processes in nonlinear silica microspheres

We analyze second order parametric processes in a silica microsphere coated with radially aligned nonlinear optical molecules. In a high-Q nonlinear microsphere, we discover that it is possible to achieve ultralow threshold parametric oscillation that obeys the rule of angular momentum conservation. Based on symmetry considerations, one can also implement parametric processes that naturally generate quantum entangled photon pairs. Practical issues regarding implementation of the nonlinear microsphere are also discussed.     

Lasing in microdisks with an active region based on lattice-matched InP/AlInAs nanostructures

The emissivity of unstrained quantum-dimensional InP/AlInAs nanostructures and their lasing properties in microdisk cavities prepared by wet etching have been studied. For as-prepared structures, it has been found that they radiate owing to quantum-dimensional InP islands 50–300 nm in diameter. At temperatures below 160 K, whispering gallery modes have been observed in the microdisks. Experimental data on the PL intensity for microcavity modes versus the pump power, which were obtained at liquid helium temperature, have made it possible to find the lasing threshold, 50 W/cm². The half-width of the laser line at above-threshold powers equals 0.06 nm, which corresponds to a Q factor of 15 000.