Laterally coupled buried heterostructure high-Q ring resonators

All-buried InP-InGaAsP ring resonators laterally coupled to bus waveguides are demonstrated. The buried configurations offer a lower built-in refractive index step along the resonator periphery, which affords enhanced optical coupling coefficients between the waveguides and reduced scattering losses caused by the resonator sidewall imperfections. Very low optical intensity attenuations of 0.4 cm/sup -1/ and coupling-limited quality factors of greater than 10/sup 5/ are observed from 200-/spl mu/m-radii ring resonators. The measured spectral linewidth is as narrow as 0.0145 nm.     

Irregular-waveguide elements coupling high-Q resonators with single-mode waveguides

A new type of element coupling a high-Q resonator with single-mode rectangular waveguides is proposed. The element is an irregular tapered section. A technique of electrodynamic calculation of such a coupling element is described. The element is experimentally investigated in the case of two-mirror open resonators. The high efficiency exhibited by the coupling element over a wide frequency band is confirmed by theoretical calculations and demonstrated experimentally.     

Provisional model technique in the FDTD analysis of high-Q resonators

We propose A technique for extracting Q-factors and resonant frequencies of resonators from signal models constructed using samples provided by a time-domain simulator. The method involves two models. The first model is a provisional one and serves one to generate additional samples that prevent the original sequence from being corrupted during signal processing. The second model is the final one and gives directly the quality factors and the resonant frequencies for the structures of interest. We show the application of the new technique to the fast time domain analysis of structures with the unloaded Q-factor exceeding 106.     

Polymer optical waveguide vertically coupled to high-Q whispering gallery resonators

We report on a novel implementation of a polymer optical waveguide vertically coupled to the whispering gallery modes of a fused silica resonator disc. This is the first step in bringing high-Q silica discs close to the integrated optics technology. We obtained near-critical coupling and a loaded Q/spl ap/3.4/spl times/10/sup 6/.     

Grating coupling elements for high-Q resonators and rectangular waveguides of the millimeter wave band

Techniques for electrodynamic-level calculation of slot-grating wideband coupling elements for single-mode waveguides are developed. New coupling devices that ensure the obtaining of a voltage standing-wave ratio of 1.6 in the entire tuning range of a resonator without readjustment of the coupling element are designed and tested experimentally. It is found that application of new coupling devices in resonators do not deteriorate the loaded Q factor of the resonator.     

Glass cavity resonators for low microwave frequencies

A series of experiments were undertaken to confirm the feasibility of the use of various glasses as walls in microwave cavity resonators with the objective of achieving low drift of resonant frequency with temperature     

High-Q microwave acoustic resonators and filters

The authors present recent experimental and modeling results for high-Q microwave acoustic resonators and filters for use in oscillators and other frequency control applications. Overmoded resonators have exhibited an FQ product greater than 1×10¹⁴ Hz (e.g., Q=68,000 at 1.6 GHz) with a strong inductive response suitable for one-port and two-port oscillator feedback circuits. Ladder filters fabricated with overmoded resonators have loaded Qs greater than 40,000 with 76-kHz bandwidth at 1.6 GHz. Aluminum nitride films were used for transduction on Z-cut sapphire and lithium niobate substrates     

Precision fabrication techniques and analysis on high-Q evanescent-mode resonators and filters of different geometries

High-Q evanescent-mode resonators and filters are realized by both silicon micromachining and layer-by-layer polymer processing. Capacitively loaded cavities can be reduced to a size much smaller than a wavelength, but still have a much higher unloaded Q than lumped elements. The loaded resonators are utilized for reduced-size filters with a low insertion loss enabled by the relatively high-Q factor. The small fabrication tolerances of silicon micromachining and polymer stereolithography processing enable the realization of highly loaded evanescent-mode resonators and filters. A 14-GHz resonator micromachined in silicon has a volume of 5 mm /spl times/ 5 mm /spl times/ 0.45 mm, representing a resonant frequency reduction of 66.8% compared to an empty cavity of the same dimensions. The polymer-based fabrication is used to create resonators of different three-dimensional geometries with Q's up to 1940 and frequency reductions up to 49.9%. An insertion loss of 0.83 dB is measured in a 1.69% bandwidth filter created by polymer processing with a frequency reduction of 47% compared to an unloaded cavity. The frequency sensitivity to fabrication tolerances of these structures is also analyzed.     

An improved theory of microwave open resonators

The analytic theory of microwave open resonators is improved here by means of solving the complex Airy equation, that the Q-value as well as the argument of field profile may be given accurately. The resonance conditions for open cavities with high and moderate Q-values are derived analytically. Theoreticl Q-values are well agreed with the measured ones from experiments.     

Stepped-impedance microwave resonators with combined frequency tuning

The results of the investigations of tunable stepped-impedance-impedance microwave resonators containing variable capacitive and inductive elements are presented. It is shown that these resonators provide a wider tuning range than the resonators based on uniform transmission-line sections. The specific features of the stepped-impedanceresonators tuned by capacitances and inductances are determined. In particular, it is shown that the resonance regions overlap in these resonators.     

Novel temperature-stable ceramics for microwave dielectric resonators and microstrip substrates

Ceramics comprising homogeneous single-phase zirconate solid solutions of suitable composition have very low temperature coefficients of permittivity, low-frequency permittivities of 30?40 and low losses. Dielectric resonators give Q values up to 4000 and permittivities of 28?35 at 4?5 GHz. The effective permittivity measured on a microstrip ring resonator on a calcium-zirconate substrate shows the dispersion predicted theoretically; the effective permittivity increases from 17 to 23 over the frequency range 1?12 GHz and gives 28.1 as the calculated real value of the permittivity of the substrate. The measured Q value of 200 indicates negligible dielectric losses compared with the I2R losses.     

Temperature-stable low-loss microwave filters using dielectric resonators

Recently developed high-permittivity low-loss temperature-stable dielectric materials have been used as resonators in microwave filters. The resulting low-loss filters possess extremely good temperature stability. Proper design and the use of metal-screw mode suppressors have eliminated the further problem in dielectric-resonator filters of spurious modes just above the passband.     

Capacitance-tunable microwave resonators with intersecting resonance regions

The effect of intersection of the resonance regions of neighboring oscillations in resonators formed of transmission-line sections with capacitive tuning is revealed. This effect takes place in stepped resonators with two capacitors. It makes possible a significant expansion of the continuous frequency tuning band by means of the use of several neighboring resonances. It is shown that, if the filter operates at the first three resonance frequencies and values of two capacitances vary in the interval 1:10, the continuous frequency tuning band can exceed two octaves.     

Comparison of current control techniques for active filterapplications

This paper presents the comparative evaluation of the performance of three state-of-the-art current control techniques for active filters. The linear rotating frame current controller, the fixed-frequency hysteresis controller, and the digital deadbeat controller are considered. The main control innovations, determined by industrial applications, are presented, suitable criteria for the comparison are identified, and the differences in the performance of the three controllers in a typical parallel active filter setup are investigated by simulations     

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.     

Dual-mode stepped-impedance ring resonator for bandpass filterapplications

It is well known that two orthogonal resonant modes exist within a one-wavelength ring resonator. In this paper, we focus on a ring resonator possessing an impedance step as a form of perturbation. A convenient analyzing method for obtaining the resonance characteristics of this resonator structure is presented. Furthermore, generation of attenuation poles obtained by the dual-mode ring resonator is discussed. In addition, a filter design method based on this resonator is explained, followed by experimental results, which prove the validity of the proposed design method     

A note on the Q-factor of microwave resonators

It is shown that the frequency variation of the resonator diaphragms has an effect of the order of 10 % on the calculated Q-factor of a waveguide resonator.     

Analysis of 3-D microwave resonators using covariant-projectionelements

Three-dimensional microwave resonators of arbitrary shape can be analyzed with the finite element method using covariant-projection elements, curvilinear bricks which impose only tangential field continuity. The method produces no spurious modes, and works well even when sharp metal edges are present. The matrices involved, though large, are sparse; an appropriate sparse eigenvalue algorithm allows the method to run using modest amounts of memory. Results are presented for a number of test cases, including a rectangular microstrip resonator     

Varactor-loaded split ring resonators for tunable notch filters at microwave frequencies

It is demonstrated that the resonant frequency of split ring resonators (SRRs) can be tuned using varactor diodes. The resulting particle, which is called a varactor-loaded split ring resonator (VLSRR), is applied to the design of a tunable notch filter at S-band. The device consists on a microstrip transmission line with VLSRRs placed at both sides of the conductor strip. Owing to the proximity of the particles to the line the rings are excited and a transmission notch arises. It is shown that simply using two VLSRRs pairs, rejection levels above 20 dB are achieved in a 0.5 GHz tuning interval centred at 2.85 GHz. The proposed device is the first tunable notch filter based on SRRs.     

A phase noise reduction technique in microwave oscillator using high-Q active filter

The authors present a 10 GHz oscillator that uses a high-Q active filter to reduce the phase noise. The loaded Q of active filter is obtained at about 500. This oscillator is compared with another oscillator which uses a passive filter. The difference of two oscillators' Q is estimated at 12.5 times the open-loop gain simulation. The measured result of phase noise at 100 kHz offset shows maximum 10 dB reduction with high-Q active filter.