Multilayer Cavity Research Articles

Micromachined 38 GHz cavity resonator and filter with rectangular-coaxial feed-lines

Micromachined, multilayer cavity resonators and filters at 38 GHz are demonstrated. Each layer is made of gold-coated silicon, structured by deep reactive etching. Two external coupling structures by coaxial feed lines are proposed to suit the fabrication process. The measured resonator gives an unloaded Q-value of 343 at 38 GHz. Methods to further improve the resonator quality-factors are discussed. The measured insertion loss of the filter is 1.01 dB, the 3 dB bandwidth is from 36.53 to 39.13 GHz, and the return loss is better than −15 dB over the frequency range from 37.0 to 38.6 GHz.

Asymmetric temporal profile of optical Kerr signal from GaAs/AlAs multilayer with λ/2 phase shift layer

AbstractOptical Kerr response for a short‐input‐pulse of a GaAs/AlAs multilayer cavity which has a narrow cavity mode width was measured by an optical pump and probe technique. We observed a strong asymmetric temporal profile of the optical Kerr signal in the vicinity of Δt = 0. The initial rising time of the signal was 1.0 ps for Δt < 0, while the decay time was 0.25 ps for Δt > 0. The asymmetric profile of the Kerr signal was analyzed with the pulse shapes of the pump and probe pulses in the cavity. We found that the decay of the Kerr signal for Δt > 0 was faster than that of the profile explained by the pump and probe pulses. This suggests that the strong asymmetric profile of the Kerr signal was occurred by the strong phase shift due to the higher order term of the susceptibility. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A Receiver-Reactor for the Solar Thermal Dissociation of Zinc Oxide

An improved engineering design of a solar chemical reactor for the thermal dissociation of ZnO at above 2000K is presented. It features a rotating cavity receiver lined with ZnO particles that are held by centrifugal force. With this arrangement, ZnO is directly exposed to concentrated solar radiation and serves simultaneously the functions of radiant absorber, chemical reactant, and thermal insulator. The multilayer cylindrical cavity is made of sintered ZnO tiles placed on top of a porous 80%Al2O3–20%SiO2 insulation and reinforced by a 95%Al2O3–5%Y2O3 ceramic matrix composite, providing mechanical, chemical, and thermal stability and a diffusion barrier for product gases. 3D computational fluid dynamics was employed to determine the optimal flow configuration for an aerodynamic protection of the quartz window against condensable Zn(g). Experimentation was carried out at PSI’s high-flux solar simulator with a 10kW reactor prototype subjected to mean radiative heat fluxes over the aperture exceeding 3000suns (peak 5880suns). The reactor was operated in a transient ablation mode with semicontinuous feed cycles of ZnO particles, characterized by a rate of heat transfer—predominantly by radiation—to the layer of ZnO particles undergoing endothermic dissociation that proceeded faster than the rate of heat transfer—predominantly by conduction—through the cavity walls.

Resonance wavelength in planar multilayer waveguides: control and complete suppression of temperature sensitivity

We report the possibility of realizing complete thermal stabilization of the resonance transparency wavelength λchar in a planar multilayer tilted cavity waveguide. When the positive temperature coefficient of the refractive index dn/dT is a nonlinear function of the alloy composition, which is the case in most semiconductor alloys, there exists the possibility of achieving complete control of the resonance transparency wavelength. The thermal shift dλchar/dT can be positive, zero or negative. Our result applies quite generally to optical waveguides, etalons, filters, semiconductor lasers and optical amplifiers, potentially extending the performance of the devices and their application range.

Cholesteric liquid crystal laser in a dielectric mirror cavity upon band-edge excitation

Low threshold laser action of dye-doped cholesteric liquid crystals (CLCs) is demonstrated using an input circularly polarized light whose handedness is the same as the cholesteric helix of the sample at the high-energy band edge of the reflection band. The mechanism originates from the dramatic increase of the photon density of state at the band edges. We also demonstrate an enhanced laser action of a CLC in a dielectric multilayer cavity. In such a device configuration, the band-edge excitation at high-energy band edge improves the lasing performance not only for the same handedness circularly polarized pump beam as the cholesteric helix but also for the opposite one. It stems from the polarization independence of the dielectric multilayers.

Multiscaled polarization effects in Suneve coronata (Lepidoptera) and other insects: application to anti-counterfeiting of banknotes

The scales of many Lepidoptera and the elytra of quite a number of Coleoptera possess specialized micro- and nano-structures that produce special polarization effects. They are constituted by concave multilayered cavities. This leads to two different effects: (1) interferential non-polarized coloration by reflection near normal incidence in the middle of the cavities and (2) polarized interferential colouration at lower wavelength after double reflection near the Brewster incidence at the periphery of the cavities. The macroscopic appearance resembles the “pointillist effect” with one of the component polarized while the other one is not. The first one can be extinguished with linear polarizer so that the colour is modified. In most insects, the structure is locally symmetric; hence, no macroscopic effects can be seen. In certain species, this symmetry is partly broken, and a slight effect can be observed. In the wing dorsal surface of the fascinating neotropical butterflies genus Suneve, perpendicular structures of two different kinds in size polarize the reflected light. The larger one is constituted by the convex cover scales whose apex falls perpendicularly on the bases of the following scales, creating long polarized valley (50 μm width) transversally running across the wing. The smaller one is constituted by the ridges of the scales (2 μm apart) that polarize light in the perpendicular direction. Adapted multilayered structures can be deposited onto banknotes to create anti-counterfeiting patterns as a further development of protection and security. Different effects can be produced by the use of such structures. (1) Changes of luminosity: A specific pattern will be constituted by two different areas: one with horizontal concave multilayered structures, and the other one with vertical structures. Under unpolarized light, the reflected spectra of these different areas are identical and no pattern appears. Under polarized light, i.e., through a linear polarizer, one or the other area is partly extinguished, according to the orientation of the polarizer, and the pattern appears. (2) Changes in colours: a compound colour can be produced by the juxtaposition of planed and grooved surfaces. Due to the change of incidence of the incoming light, the colours of these two zones are different, but that produced by the first one is unpolarized while the second one is partly polarized and can be modified with a linear polarizer.

Distributed Bragg reflector resonators with cylindrical symmetry and extremely high Q-factors

A simple non-Maxwellian method is presented that allows the approximate solution of all the dimensions of a multilayered dielectric TE0qp mode cylindrical resonant cavity that constitutes a distributed Bragg reflection (DBR) resonator. The analysis considers an arbitrary number of alternating dielectric and free-space layers of cylindrical geometry enclosed by a metal cylinder. The layers may be arranged along the axial direction, the radial direction, or both. Given only the aspect ratio of the cavity, the desired frequency and the dielectric constants of the material layers, the relevant dimensions are determined from only a set of simultaneous equations, and iterative techniques are not required. The formulas were verified using rigorous method of lines (MoL) calculations and previously published experimental work. We show that the simple approximation gives dimensions close to the values of the optimum Bragg reflection condition determined by the rigorous analysis. The resulting solution is more compact with a higher Q-factor when compared to other reported cylindrical DBR structures. This is because it properly takes into account the effect of the aspect ratio on the Bragg antiresonance condition along the z-axis of the resonator. Previous analyses assumed the propagation in the z-direction was independent of the aspect ratio, and the layers of the Bragg reflector were a quarter of a wavelength thick along the z-direction. When the aspect ratio is properly taken into account, we show that the thickness of the Bragg reflectors are equivalent to the thickness of plane wave Bragg reflectors (or quarter wavelength plates). Thus it turns out that the sizes of the reflectors are related to the free-space propagation constant rather than the propagation constant in the z-direction.

Hankel transform-domain analysis of scattered fields in multilayer planar waveguides and lasers with circular gratings

Radiation patterns of scattered fields with arbitrary azimuthal orders in multilayer planar waveguides and laser cavities with circularly symmetric gratings are formulated based on the volume current method. Full-wave Green's function analysis based on the integral transform method lies at the heart of this approach. Unlike the conventional approach, the dyadic Green's function relates some auxiliary fields to some auxiliary sources in the spectral domain. These auxiliary functions are defined to facilitate the spectral domain formulation in the cylindrical coordinate system and the use of transfer matrix method for obtaining a closed-form solution of the spectral Green's function in multilayer planar structures. More importantly, it is shown that the far-field pattern of the scattered field can be expressed directly in terms of the auxiliary fields in the Hankel transform domain.

Vacuum fluctuation force on a rigid Casimir cavity in a gravitational field

We discuss the possibility of verifying the equivalence principle for the zero-point energy of quantum electrodynamics, by evaluating the force, produced by vacuum fluctuations, acting on a rigid Casimir cavity in a weak gravitational field. The resulting force has opposite direction with respect to the gravitational acceleration; the order of magnitude for a multi-layer cavity configuration is derived and experimental feasibility is discussed, taking into account current technological resources.

GRAVITATIONAL EFFECTS ON A RIGID CASIMIR CAVITY

Vacuum fluctuations produce a force acting on a rigid Casimir cavity in a weak gravitational field. Such a force is here evaluated and is found to have opposite direction with respect to the gravitational acceleration; the order of magnitude for a multi-layer cavity configuration is analyzed and experimental detection is discussed, bearing in mind the current technological resources.

Fabry–Perot multilayers for enhancing the diffraction efficiency of ion-implanted gratings

Enhancement of the free-space diffraction efficiency of gratings made by titanium-ion implantation is demonstrated both theoretically and experimentally. Indeed, by insertion of a grating into a multilayer dielectric Fabry-Perot cavity, the diffraction efficiency can be increased to as much as 24 times that of a single grating. The sensitivity of the diffraction efficiency to the optogeometrical parameters of the grating or of the Fabry-Perot cavity is discussed. Moreover, a process for performance of a phase grating inside a Fabry-Perot cavity is described, and experimental results concerning efficiency measurements are compared with computed values for various grating periods.

F210 IS0834に基づく積層型中空耐火壁の加熱シミュレーション(オーガナイズドセッション17 : 材料およびデバイス製造の熱工学)

The Building Standards Act designates fire zones and semi-fire zones for the purpose of decreasing the number of damages caused by serious city fires, and requires fireproof construction or fire protection for buildings. A fire resistance test is one of the methods of estimating the performance of fireproof construction, and is done by using the ISO method or the JIS method. However, these tests require large scale and expensive appliances, much preparation time, and the expenses for making specimens are huge. To cope with this issue, we have been developing numerical simulation codes for predicting mutual relation between the fireproof construction and the fire resistance test results. In this study the results of numerical simulation of the multi-layered cavity wall, which is one of the fundamental structures in building construction, is shown.

Optimized factor of merit of the magneto-optical Kerr effect of ferromagnetic thin films

This paper deals with the optimization of the factor of merit of the magneto-optical Kerr effect of a resonant multilayer cavity including a ferromagnetic film. This optimization is of interest in the context of optical storage technology. Using numerical simulations based on the Green's dyadic technique, we discuss a route to obtain magneto-optical multilayers with a vanishing ellipticity and factors of merit (with respect to the bulk magnetic material) larger than 3 on a broad range of wavelengths, significantly higher than the actual state of the art.

Enhanced diffraction efficiency of gratings in multilayers

Computations with the rigorous differential method show that single gratings made by ion implantation have a diffraction efficiency in the +1 transmitted order under TE illumination of only 0.78%. The insertion of such gratings into multilayer dielectric Fabry-Perot cavities leads to an enhancement of the free-space diffraction efficiency. Different designs for the multilayer are considered. An 18.8% efficiency is reached with 11-layer mirrors. This result is obtained by optimization of the thickness of the spacer of the Fabry-Perot cavity that contains the grating and centering of the wavelength of the mirrors. The dependence of optical properties of the structure on the various optogeometrical parameters of the structure is discussed.

Accurate three-dimensional modal solutions for optical resonators with periodic layered structure by using the finite element method

Accurate vector finite element solutions for three-dimensional (3-D) axisymmetric multilayered optical cavities are presented. Resonating wavelength and field profiles are shown for the fundamental and higher order modes for different types of optical cavities. The work has shown that for a narrow multilayered cylinder of diameter /spl les/0.5 /spl mu/m, for miniature vertical cavity surface emitting lasers (VCSEL), which is a popular class of laser showing favorable performance characteristics, the effect of waveguide dispersion is an important factor. This causes a blue shift of the output wavelength, requiring an adjustment to the layer thickness in the system design, to achieve the desired wavelength. The results of the simulation show close agreement with features obtained through experimental investigations.

Slow positron study on dielectric-coated mirror for free-electron-laser experiments

A positron lifetime study has been done on dielectric multilayer cavity mirrors for free-electron-laser experiments by the use of a variable-energy pulsed positron beam. A long-lived ortho-positronium component has been observed at low positron energy region, corresponding to the depth of the top amorphous SiO2 layer. The intensity of the positronium component correlates with the degradation and restoration of the mirrors. We discuss the relation between the positronium intensity and degradation mechanism of the mirrors. The present studies revealed that the slow positron lifetime technique is highly sensitive to the properties of the mirrors and is useful for the evaluation of the mirrors.

Dispersion of exciton polaritons in cavity-embedded quantum wells.

We study the interaction of quantum-well excitons with the electromagnetic normal modes of a multilayer dielectric cavity for finite in-plane wave vectors. In the strong-coupling regime we obtain the dispersion of the exciton polaritons by analyzing the exciton spectral function. We compare our numerical results with the recent angle-resolved photoluminescence data by Houdr\'e et al. [Phys. Rev. Lett. 73, 2043 (1994)]. We find a very good agreement for the lower polariton branch and a discrepancy between theory and experiment for the upper polariton branch that is probably due to an experimental inaccuracy.

Degradation and restoration of dielectric-coated cavity mirrors in the NIJI-IV FEL

In the NIJI-IV free-electron laser (FEL) system, the 6.3-m-long optical klystron generates very intense undulator radiation and its higher harmonics. As a result, the rapid degradation of dielectric multilayer cavity mirrors terminates the laser oscillation in a little while. We reported previously that the mirror degradation was mainly caused by the deposition and/or doping of carbon onto the mirror surface by the undulator radiation in case of the visible FEL and the degraded mirrors were restored to a considerable extent by surface treatment with RF-induced oxygen plasma. However, recent experiments have revealed that the volume degradation inside the dielectric cannot be ignored in the NIJI-IV FEL. Moreover, surface analysis by XPS (X-ray Photoelectron Spectroscopy) indicated that, in the UV FEL around 350 nm, the irradiation of the mirrors by undulator radiation can give rise to the ablation of the top dielectric layer for surface protection. We investigated the relation between the mirror degradation and the condition of both surface and inside of the dielectric for two types of mirrors (HfO2/SiO2 and Ta2O5/SiO2), by using XPS and slow positrons. The degradation mechanism is discussed. The method of restoring the surface- and volume-degraded mirrors are shown.

Thermal dependence of the refractive index of GaAs and AlAs measured using semiconductor multilayer optical cavities

The longitudinal optical mode shift with temperature was measured in two vertical cavity surface-emitting laser (VCSEL) type optical resonators with different GaAs and AlAs layer structures. The measurements show distinct differences in the behavior of the cavities. From the data the thermal dependencies of the indices of refraction of GaAs and AlAs for wavelengths near 1 μm were determined to be (2.67±0.07)×10−4/°C and (1.43±0.07)×10−4/°C, respectively.

Spontaneous emission of quantum well excitons in planar dielectric multilayer cavities

The spontaneous emission of quantum well excitons may be significantly altered by embedding the quantum well in a microcavity. We present theoretical results for the spontaneous emission based on the quantum field theory of interaction between excitons and electromagnetic eigenmodes of a multilayer dielectric cavity. Depending on the design of the cavity and the in-plane wavevector Q ‖ the emission can be enhanced or inhibited as compared to a QW not embedded in a cavity. We show that in the exciton-pole-approximation the enhancement/inhibition factor is given by the reciprocal normalization constant of the radiative electromagnetic modes.