Open Resonators with Conducting Cylindrical Inserts. 2. Resonators with Finite-Length Mirrors

We present the results of experimental studies of controlling the spectrum and Q-factors of modes in an open resonator with a conducting cylindrical insert. The phenomenon of an increase in the diffraction Q-factor is experimentally observed for the fundamental TEM_00q mode for two resonant diameters of the conducting cylindrical insert located inside the open resonator. The features of excitation of modes in an open resonator with smooth cylindrical finite-length mirrors and in an open resonator with cutoff bevels at the mirror edges are studied. Prospects for using open resonators with conducting inserts in quasi-optical devices in the millimeter-wave range are discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 8, pp. 684–691, August 2005.     

Noise suppression for micromechanical resonator via intrinsic dynamic feedback

We study a dynamic mechanism to passively suppress the thermal noise of a micromechanical resonator through an intrinsic self-feedback that is genuinely non-Markovian. We use two coupled resonators, one as the target resonator and the other as an ancillary resonator, to illustrate the mechanism and its noise reduction effect. The intrinsic feedback is realized through the dynamics of coupling between the two resonators: the motions of the target resonator and the ancillary resonator mutually inthence each other in a cyclic fashion. Specifically, the states that the target resonator has attained earlier will affect the state it attains later due to the presence of the ancillary resonator. We show that the feedback mechanism will bring forth the effect of noise suppression in the spectrum of displacement, but not in the spectrum of momentum.      

Noise suppression for micromechanical resonator via intrinsic dynamic feedback

We study a dynamic mechanism to passively suppress the thermal noise of a micromechanical resonator through an intrinsic self-feedback that is genuinely non-Markovian. We use two coupled resonators, one as the target resonator and the other as an ancillary resonator, to illustrate the mechanism and its noise reduction effect. The intrinsic feedback is realized through the dynamics of coupling between the two resonators: the motions of the target resonator and the ancillary resonator mutually influence each other in a cyclic fashion. Specifically, the states that the target resonator has attained earlier will affect the state it attains later due to the presence of the ancillary resonator. We show that the feedback mechanism will bring forth the effect of noise suppression in the spectrum of displacement, but not in the spectrum of momentum.     

Theory and design of a free-electron maser with two-dimensional feedback driven by a sheet electron beam

The use of two-dimensional Bragg resonators of planar geometry, realizing two-dimensional (2D) distributed feedback, is considered as a method of producing spatially coherent radiation from a large sheet electron beam. The spectrum of eigenmodes is found for a 2D Bragg resonator when the sides of the resonator are open and also when they are closed. The higher selectivity of the open resonator in comparison with the closed one is shown. A time-domain analysis of the excitation of an open 2D Bragg resonator by a sheet electron beam demonstrates that a single-mode steady-state oscillation regime may be obtained for a sheet electron beam of width 100-1000 wavelengths. Nevertheless, for a free-electron maser (FEM) with a closed 2D Bragg resonator, a steady-state regime can also be realized if the beam width does not exceed 50-100 wavelengths. The parameters for a FEM with a 2D planar Bragg resonator driven by a sheet electron beam based on the U-2 accelerator (INP RAS, Novosibirsk) are estimated and the project is described.     

General theory and design of microwave open resonators

Based on the analysis of wave propagation in a waveguide with slowly varying cross-section, a general theory is developed for microwave open resonators with rotational-symmetric waveguides; this geometry has been extensively used in the gyrotrons. The theoretical analysis is carried through under the most general conditions, that is the cross-section radius r(z) of the resonator is a slowly varying arbitrary function of z and the resonator is open. The general expressions for the resonant frequencies and the Q have been derived. A design method for this kind of open resonator has been proposed. Calculation results for two practical resonators are presented.     

缓变截面波导开放谐振腔的微波网络分析

本文利用微波网络理论分析了缓变截面波导开放谐振腔,给出了任意纵剖面形状开放腔的传输Q值的一般公式。估计了波导壁欧姆损耗对Q值的影响。简单讨论了谐振频率修正问题。并具体推导了双圆锥腔和圆柱形开放腔的传输Q值的计算公式。 关键词：     

Coherent interference induced transparency in self-coupled optical waveguide-based resonators

We propose a self-coupled optical waveguide (SCOW)-based resonator to generate an optical resonance analogous to electromagnetically induced transparency (EIT). The EIT-like effect is formed by the coherent interference between two resonance paths inherent to the SCOW resonator. For cascaded SCOW resonators, the spectrum they produce is significantly affected by the phase shift between them, with the EIT-like peak flattened or split as the two extreme cases. We also investigate the dispersion characteristics of an infinite array of SCOW resonators and show that the dispersion relation and group index in the EIT subband can be greatly changed by a small phase shift between the SCOW resonators.     

On classification of eigenmodes of an open resonator with spherical mirrors

A rigorous mathematical model describing eigenmodes of open resonators with spherical mirrors is proposed. Theoretical analysis of the spectral characteristics of an open resonator is performed for the case where the wavelength is comparable with the resonator size. Specification and significant generalization of eigenmode classification based on approximate open-resonator models are proposed. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 12, pp. 1051–1060, December 2008.     

Effect of diffraction on the electrodynamic characteristics of two-dimensional coaxial Bragg resonators

The electrodynamic properties of coaxial two-dimensional Bragg resonators with two-dimensional distributed feedback are analyzed. These resonators are made of coaxial waveguide sections with doubly periodic corrugation, which provides coupling and mutual scattering of four partial waves. Two of them propagate along the waveguide, while the other two propagate in the transverse (azimuthal) direction. It is shown that the high azimuthal index selectivity of two-dimensional Bragg resonators may be related to a qualitative difference in topology of the dispersion characteristics of azimuth-symmetric and asymmetric normal waves propagating in infinite waveguides of such a geometry. For the finite-length systems used as two-dimensional Bragg resonators, the eigenmode spectrum is found for two types of boundary conditions that correspond to the limiting cases of perfectly matched (open) systems and, conversely, of systems closed for the extraction of transverse electromagnetic fluxes. Perimeter-to-length ratios of the resonator at which the Q factor of the fundamental azimuth-symmetric mode is greater than those of the other modes are determined. The applicability domain of the geometrical approach, which was earlier applied to two-dimensional Bragg resonators, is discussed.     

Calculation of the resonance frequencies of an open dielectric axially symmetric resonator of piecewise constant radius

An algorithm is suggested for calculating the resonance frequencies of open dielectric axially symmetric resonators of piecewise constant radius suitable for an arbitrary layered axially symmetric dielectric filling. The resonator is placed into a case with ideally conducting walls of a sufficiently large radius. Cases are analyzed where the resonator structure is partly coated with a perfect conductor.     

串联双微环湿度传感器光谱特性研究

提出了一种基于串联双微环谐振器的新型聚酰亚胺(Polyimide,PI)湿度传感器,采用传输矩阵法和耦合模的理论计算微环谐振器的传递函数,并对比了传统单微环与串联不同半径的双微环的输出光谱特性。外界湿度变化使得聚酰亚胺SOI波导吸收水汽后折射率发生变化,从而引起微环输出光谱发生漂移,通过探测光谱漂移量来测湿度值,得到了串联双微环传感器的灵敏度和测量范围,并且分析了感湿部位不同时谐振器输出光谱特性。理论结果表明：串联不同半径的微环谐振器的自由光谱范围（FSR）要比单微环有所提高,而且串联双微环谐振器整体感湿比单个微环单独感湿的传感性能更优良,可作为最佳的湿敏元件。与传统的单微环传感器相比,串联不同半径的微环结构可提高系统的测量范围和灵敏度,半径为30和50 μm的串联微环谐振器的FSR可达到0.15 μm,传感器测量湿度范围为10%RH～80%RH,灵敏度可达到0.001 7 μm·(%RH)-1。因此串联不同半径的双微环谐振器为制备成本低、结构简单、高灵敏度、可集成的微型湿度传感器件提供一定理论基础。     

Losses in an open microwave resonator with an ultrathin cylinder

Two methods are used to calculate the losses introduced in an open resonator by an ultrathin cylindrical sample placed in the antinode of the electric field of the main oscillation mode. It is demonstrated that the dependence of the losses on the cylinder parameters for wires is ambiguous in character, which must be considered when developing methods for measuring and control of characteristics of such objects placed in open quasioptical resonators. In special cases, some parameters of the examined samples can be determined only from measurements of the losses introduced in the open resonator.     

Analysis about the effect of an on-chip all-optical analogue to electromagnetically induced transparency in the two resonators system

One theoretical model is provided for the design of an on-chip all-optical analogue to electromagnetically induced transparency (EIT) in the two resonators system. The design parameters (the perimeter and the separation of the resonators), the side-coupling efficiency and the resonator loss of the system have been investigated. The analysis shows, properly designed, the system exhibits an EIT-like transmission spectrum: a narrow high quality factor resonant mode (the line-width is about 0.1 nm).     

Self-radiation from arrays of niobium Josephson junctions embedded in the open resonator

This paper focuses on self-radiation from arrays of Josephson junctions embedded in a quasi-optical resonator. The mechanism of coupling this radiation to the principal mode of the open resonator is illustrated using experiments and simulations with CST microwave studio software. Comparing the microstrips and dielectric resonators used as the antennas of the series arrays of discrete Josephson junctions, we demonstrate that the dielectric resonator antennas are more effective than microstrips.     

Whispering-gallery modes in a barrel-shaped dielectric resonator

We experimentally study a new type of resonator, namely, a barrel-shaped dielectric resonator with whispering-gallery modes which is formed by the cutting dielectric hemisphere. Compared with a hemispherical dielectric resonator, the E type oscillation spectrum of such a resonator is rarefied with respect to the azimuthal index. Comparative analysis of the electromagnetic characteristics of the barrel-shaped dielectric resonator and half-disk dielectric resonators shows that the radiation losses of the mode energy from the spherical surface are smaller than those from the cylindrical surface. This fact stimulates the high values of the internal Q-factor of modes of the barrel-shaped dielectric resonator. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 12, pp. 1041–1048, December 2005.     

High-frequency EPR applications of open nonradiative resonators

A new class of open single-mode cavities, the nonradiative (NR) resonators, has recently been proposed in order to overcome the limitations of standard cylindrical cavities and Fabry-Perot resonators at millimeter wavelengths. This paper presents the first applications of a NR resonator in W-band pulsed electron paramagnetic resonance spectroscopy. It consists of a cylindrical cavity having a lateral aperture that represents about 35% of its total height. Electron-spin-echo measurements performed on different samples show that the signal-to-noise ratio and the optimal pulse length obtained with the proposed device are comparable to those obtained with the closed cavity used in the commercial W-band spectrometer, at both cryogenic and room temperature. Similar results have been obtained for paramagnetic species optically activated by means of an optical fiber inserted in the aperture of the resonator. The insertion losses estimated for the probe employed with the NR resonator are higher than those of the commercial probe, hence, demonstrating that the proposed cavity holds the promise of improved resonator performance.     

Experimental realization of an on-chip all-optical analogue to electromagnetically induced transparency

We provide the first experimental observation of structure tuning of the electromagnetically induced transparency-like spectrum in integrated on-chip optical resonator systems. The system consists of coupled silicon ring resonators with 10 microm diameter on silicon, where the coherent interference between the two coupled resonators is tuned. We measured a transparency-resonance mode with a quality factor of 11,800.     

Application of 150GHz quasi-optical EPR and endor systems to examination of materials for polarized nuclear targets

Some possibilities of mm and submm magnetic resonance spectrometers using a two-mirror open resonator as the sensor is demonstrated. A comparative analysis of sensitivity has been performed for spectrometer, with cavity and open resonators. Absorption spectra of the HMBA Cr^V complex in propylene glycol and ethylene glycol were investigated at 4.2 K.     

Acoustic instabilities control using Helmholtz resonators

The main focus of the present work is to evaluate the performance of the Helmholtz resonators to control acoustic instabilities inside combustion chambers. In the present stage of this work, some tests were conducted with non-reactive flow inside the combustion chamber. This paper presents a methodology to design the resonators and the calculations to theoretically determine the acoustic performance of damp instabilities, an experimental setup especially developed to study instabilities in reactive and non-reactive flows, and the experimental results for non-reactive situation with and without flow. The results show that the resonator has an exceptional capacity to damp the oscillations in the frequency of the design; but, it has a narrow range of actuation close to the design frequency. In addition, the experiments show that the resonator presence can modify the spectrum of frequencies, and in some cases it amplifies the oscillations, having the flow velocity inside the chamber some considerable influence in the performance attenuation.     

Prediction of the frequency spectrum of AT-cut contoured quartz resonators by means of X-ray diffraction topography

This paper presents some important relationships relating to frequencies in contoured AT-cut quartz resonators. It is shown that frequency interval relations are not affected by the piezoelement geometry but are functionally related solely to the indices of the Hermite functions. According to the analysis of trapped-energy resonators, an X-ray technique for predicting the frequency spectrum can be derived. It is based on the use of X-ray patterns of two wave motions and enables one to determine the whole frequency spectrum in the vicinity of any odd harmonic overtone of vibration. Two contoured resonator analyses show that the X-ray topography predictions are in good agreement with experimental data.