Coupled Resonator Structure Research Articles

Design and development frequency reconfigurable microwave filter for wireless application

This paper presents a novel reconfigurable bandpass filter with three reconfigurable states used for C band wireless applications. The frequency reconfigurable is achieved using the combination of a different microstrip coupled resonator structure and switching device as PIN diodes. The open-loop filter structure provides three narrow band states at 5.1, 5.2, and 5.8 GHz. The frequency reconfiguration is obtained without compromising performances. The compact size of the proposed designed along with the targeted frequency bands at lower wireless local area network (WLAN) (5.1, 5.2 GHz), and worldwide interoperability for microwave access (WiMAX) (5.8 GHz) applications. The prototype is constructed on an RT duroid 5880 substrate and tested for validation in vector network analyzer (VNA). The designed filter provides excellent selectivity and good rejection at desired resonant frequencies.

Compact Waveguide Filters Using Novel Resonant Coupling Structures

In this article, new resonant coupling structures are proposed for designing miniaturized waveguide bandpass filters. The resonant coupling structure is constructed by adding one or two metal blocks in a relatively thick inductive iris, which can be considered as the integration of a resonator, the input, and output coupling structures. Positive or negative coupling can be realized by selecting a different number of metal blocks. The combination of different resonant coupling structures can be used to design higher-order filters with various transverse topologies, realizing different transmission zeros (TZs) distributions. In addition, the weak source–load coupling caused by the resonant coupling structures can introduce an additional TZ, which can further improve the out-of-band suppression level of the filter. For verification, two third-order waveguide bandpass filters based on all resonant coupling structures are designed and simulated to achieve different TZ distributions. Finally, a fifth-order waveguide bandpass filter employing both resonant coupling structures and classical rectangular cavities is designed and fabricated. The measured results verify the proposed method.

Broad band solar cell absorber based on double-ring coupled disk resonator structure: from visible to mid infrared

In this paper, a broad band absorber based on a double-ring coupled disk resonator periodic structure, which can work in the visible and mid infrared range, is proposed and investigated. Results show the absorbance is large than 92.4% in the range of 300 nm–4096 nm, and the average absorption is about 97.4% from the visible to mid-infrared bands. Besides, the proposed absorber is wide angle acceptance, background refractive index (RI), and polarization state insensitive. The absorption mechanisms are analyzed and found that it mainly originated from the dielectric lossy property in short-wavelength and gap plasmonic resonances in long-wavelength. It is believed the proposed absorber can find potential applications in the fields of solar cell devices, thermal emitters, and plasmonic imaging.

A 20 ns to 320 ns group delay controller and its application in long time delay self-interference cancellation system

A frequency tunable group delay controller (GDC) based on second-order reflective tunable resonant network and circulator is proposed. The GDC has continuous tunable group delay with allpass magnitude response. Trade-off between delay time and loss of general one-port lossy resonant circuit is studied, and a one-port second-order coupled-resonator structure is optimized. This proposed second-order reflective tunable resonant network is realized by microstrip resonators with optimized coupling location. A circulator is utilized to convert the reflection-type circuit to transmission type. The influence of the circulator isolation leakage upon the delay time is also analyzed. The GDC is designed, simulated and fabricated. Group delay can be tuned from 20 ns to 320 ns, and central frequency of the group delay response can be tuned from 940 MHz to 980 MHz. The insertion loss is less than 10 dB, 15 dB, 25 dB and 27 dB for 50 ns, 100 ns, 200 ns and 320 ns group delay, respectively. The figure-of-merit that the insertion loss per 1 ns delay of the GDC cell is the lowest among compared delay controllers. Two proposed GDC cells are then cascaded. The measurement demonstrates the bandwidth extension ability and the potential usage in full-duplex communication self-interference cancellation.

Design of a novel compact highly selective wideband bandstop RF filter using dual path lossy resonator for next generation applications.

This article presents the design of a wideband bandstop RF filter intending to improve selectivity and compactness. Conventional bandstop filter topology with finite unloaded quality factor produces degraded bandstop filter performance due to dissipation loss. In the proposed filter design, a novel dual path Capacitive Coupled Step Impedance Resonator (CCSIR) structure is used to obtain an infinite stopband attenuation. A uniform impedance resonator is used in Path 1, whereas Path 2 contains a resonator that is twice coupled to the transmission lines. The electrical length of both paths is chosen to be out of phase, resulting in a high rejection level at higher frequencies. It has been analyzed that the selectivity can be improved by increasing the order of the dual coupled step impedance resonator. The proposed design produces a wideband BSF centered at 5.25 GHz with a high rejection level of 104.3 dB and fractional bandwidth of 58.5%. The results have demonstrated that the resonant frequencies are regulated by varying the electrical length of CCSIR. Moreover, it has been realized that out of phase signal cancellation due to the dual path is involved in producing the finite frequency transmission poles, which further enhances the filter selectivity. However, the same electrical performance can only be achieved from coaxial cavities and waveguides due to the high-quality factor. The proposed topology is fabricated and measured on a high-frequency microstrip substrate having a low-quality factor with a compact output and better electrical performance compared to coaxial cavities or waveguides. Due to its high electrical performance and small size, the proposed BSF is appropriate for 4G and 5G (FR1) applications. The measurement shows good concurrence with the full-wave EM simulated results. The fabricated prototype of third order BSF has a compact size of (0.7 × 0.77)λg at 5.25 GHz.

Low-Frequency Wireless Power Transfer Via Rotating Permanent Magnets

The surging applications of low-power sensors and portable electronic devices require a safe, convenient and low-cost charging method which draws interests of the wireless power transfer research field. Conventional WPT techniques using resonant coupling structures are limited by complexity, safety concerns and hardware costs. Electromechanical wireless power transfer (EWPT) techniques provide a low-cost, easy-to-control and safe wireless charging method via moving magnets; but transmission failures may occur due to the position and orientation misalignments of loads from optimum conditions. This article proposes an EWPT system that is able to charge loads at different tilt angles via a low-frequency rotating magnetic field and a permanent magnet rotor. The magnetic field has a uniform distribution in a space volume over 125 000 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . A custom permanent magnet rotor embedded with six identical cylindrical magnets and an induction coil is employed to capture transmitted power. Theoretical analyses and experimental results are presented to prove the feasibility and output capability of the proposed system. The peak output power achieves 130 mW under a magnetic field strength around 1 mT and the system output maintains stable for loads at different tilt angles. Such EWPT method can be applied as a stable power supply for free-positioned and free-oriented sensors or other low-power devices in an enclosed or semienclosed area.

Pressure sensor based on multiple Fano resonance in metal–insulator–metal waveguide coupled resonator structure

This paper presents a plasmonic pressure sensor via an optical metal–insulator–metal (MIM) waveguide structure. The proposed pressure sensor is composed of a ring resonator, a stub, and a U-shaped resonator coupled to the bus waveguide. The finite-difference time-domain method (FDTD) is used to study the Fano resonance (FR) characteristics and magnetic field distributions. Results show that the Fano line shapes can be independently tuned by the geometrical parameters. When pressure is exerted on the U-shaped resonator layer, the deformation leads to the shift of the resonant wavelength. The calculated maximum pressure sensitivities are 10.96 and 10 .5 n m / M P a for FR 2, and FR 3, respectively ( M P a = 10 6 P a ). The good linear relationship between the pressure and resonance wavelength indicates that the proposed nano-scale structure can find potential applications in the fields of nano-biosensing and biomedical sensing.

A Filter Theory Approach to the Synthesis of Capacitive Power Transfer Systems

Resonant-coupled wireless power transfer (WPT) systems are typically modeled as circuits with inductively or capacitively coupled resonators. In a two-resonator system, the transmit and receive resonators are linked by a coupling coefficient, and the coupling can be adjusted for critical coupling, overcoupling, and undercoupling. In this work, we show that the coupled-resonator structure is equivalent to a filter structure and provide a demonstration of how filter theory can be used to design a capacitive WPT system. An advantage of this approach is that it provides access to a wide range of canonical structures and methods of impedance scaling to realize matched links. We show a maximally flat filter has a critically coupled response and an equiripple Chebychev filter has an overcoupled response. There is a relationship between frequency bandwidth in a filter design and spatial bandwidth in a WPT link. Therefore, the filter context can be used to synthesize wideband filters that are more robust to spatial variation than narrowband filters.

An In-Fiber Coupler for Whispering-Gallery-Mode Excitation in a Microsphere Resonator

An integrated in-fiber coupler for excitation of whispering-gallery modes (WGMs) of a microsphere resonator is proposed. The device is fabricated by embedding a microsphere into an optical fiber inner air-cavity through an open micro-channel to excite various WGMs via evanescent field coupling. The asymmetric Fano resonance line shape and the symmetrical Lorentzian line shape with a slope of −13.88 dB/nm and a quality (Q)-factor of $1.81\times 10^{3}$ are observed in the transmission spectrum of the device. Such an in-fiber WGM resonator coupling structure has the features of compactness, low-cost, robust and alignment-free.

A compact sept‐band bandpass filter utilising a single multi‐mode resonator

This study proposes a compact sept-band bandpass filter (BPF) with controllable centre frequencies and bandwidths. To achieve compact size and low insertion loss, the filter deploys a single multi-mode resonator and abandons conventional source–resonator coupling structure to reduce the order of coupling sections. The fabricated BPF demonstrates seven passbands located at 1.0, 1.6, 2.3, 2.8, 3.5, 4.2, and 5 GHz, which are targeted for global system for mobile communications (GSM), wireless local area network, WIFI, and 4G/5G communication. Within the seven passbands, the minimum insertion losses are 0.9, 1.5, 0.5, 1.2, 0.9, 1.9, and 1.6 dB, respectively. The overall size of the fabricated filter is 0.1λ g × 0.21λ g. This work provides a new approach to obtain the most passbands of BPF while achieving less insertion-loss and enhanced selectivity simultaneously.

Compact Tunable Balanced Bandpass Filter With Constant Bandwidth Based on Magnetically Coupled Resonators

In this letter, a compact high-selectivity and common-mode (CM) suppression tunable balanced microstrip bandpass filter (BPF) with constant bandwidth is designed by adopting the magnetically coupled resonators with step-impedance parallel coupling feedline (SIPCF) structure. The desired coupling coefficient $K_{12}$ and external quality factor $Q_{e}$ can be obtained by the mixed coupling between the two resonators and SIPCF structure, respectively. Two differential-mode (DM) transmission zeros (TZs) near the lower and upper passband edges are created by the mixed coupling and source–load coupling, respectively. Furthermore, intrinsic high CM suppression in the DM tunable operating passband can be maintained because of the magnetically coupled resonator structure. Finally, a compact tunable balanced BPF prototype with constant fractional bandwidth of 6.5% is implemented and fabricated. The measured results agree well with the simulated ones.

Wideband bright-soliton frequency-comb generation at optical telecommunication wavelength in a thin silicon nitride film

Bright-soliton frequency comb generation in a thin-film silicon nitride microresonator at optical telecommunication wavelengths is numerically demonstrated using our recently developed approach for dispersion engineering by virtue of coupling dispersion between two coupled microresonators. By coupling two identical resonators through an asymmetric Mach–Zehnder structure, sinusoidal splitting of the resonance frequencies can be achieved. This enables the engineering of the dispersion of the resulting modes of the coupled structure. Using this approach, anomalous dispersion of the resonant modes can be achieved at the pumping wavelength (which is selected to be the optical telecommunication wavelength, i.e., 1.55 μm) to enable Kerr-comb generation. In addition, by utilizing soliton-induced Cherenkov radiation in the coupled-resonator structure, we can increase the bandwidth of the resulting Kerr-comb signal.

Decoupling of Dual-band Closely Spaced MIMO Antennas Based on Novel Coupled Resonator Structure

Abstract A pair of dual-band closely spaced MIMO monopole antenna array working at WLAN 2.45/5.25GHz with a dual-band coupled resonator structure for decoupling is proposed, the edge-to-edge distance of which is 0.0735 ${^{\lambda _0}}$ at 2.45GHz and 0.1575 ${^{\lambda _0}}$ at 5.25GHz. Simulation and measurement on coupled antennas and decoupled antennas indicate that mutual coupling reductions of 24.52dB and 26.57dB at two frequencies are achieved. With good impedance matching, improved total efficiency and increased channel capacity, the proposed structure owns good applicability, compact size and effective decoupling capability, and is promising in the application of wireless terminal MIMO system.

Fabry–Pérot resonance coupling associated exceptional points in a composite grating structure**Project supported by the National Natural Science Foundation of China (Grant Nos. 61377054 and 61675140).

The exceptional point (EP) is a significant and attractive phenomenon in an open quantum system. The scattering properties of light are similar to those in the open quantum system, which makes it possible to achieve EP in the optic system. Here we investigate the EP in a Fabry–Pérot (F–P) resonant coupling structure. The coupling between different types of F–P resonances leads to a near zero reflection, which results in a degeneration of eigenstates and thus the appearing of EP. Furthermore, the multi-wavelength EPs and unidirectional invisibility can be achieved which may be used in integrated photonics systems.

Q-band cross-coupled dielectric resonator filter using TM mode for satellite application

AbstractA new structure of Q-band filter comprising rectangular high-permittivity dielectric resonators (DR) operating at TM11δ mode is introduced. The resonator shows high-quality factor (Q) and wide spurious free window compared with other technologies available at Q-band for realizing filters. Low permittivity ceramic material (quartz) is used as a support for holding DR at the center of the cavity. An eight-pole cross-coupled band-pass filter having a bandwidth of 225 MHz at 38.5 GHz was realized. Resonant coupling structure is introduced to realize cross-coupling in filter. The resonator assemblies were optimized precisely to achieve effective linear frequency drift over temperature of the order of 2 ppm/°C. The filter also survived severe sine and random vibration test for satellite application.

A single‐aperture duplex antenna with dual circular polarizations

AbstractThis article proposes a novel design of a compact single‐aperture dual circular polarization (CP) antenna with integrated duplexing functions using a phase controllable coupled resonator structure. To the best of the authors’ knowledge, this is the first report of a multifunctional CP antenna with integrated duplexing performance and dual polarizations. The two orthogonal CPs are realized for the two respective filtering channels. Each channel contains a phased filtering power divider forming the dual‐feed to a patch to achieve right‐hand or left‐hand CP (RHCP or LHCP). The required output phases of the dividers are realized by varied configurations of the coupled λ/2‐resonator pairs. A duplex‐CP‐antenna with RHCP/LHCP at the downlink/uplink (2.45/2.7 GHz) is designed, fabricated, and measured. It achieved a 3‐dB AR bandwidth of 3.2/7.7% at the downlink/uplink and an isolation better than 20 dB. Meanwhile, the antenna showed expected second‐order filtering characteristics at both channels.

In-fiber Mach-Zehnder interferometer and sphere whispering gallery mode resonator coupling structure.

An in-fiber Mach-Zehnder interferometer and sphere whispering gallery mode resonator coupling structure is demonstrated by femtosecond laser micromachining. Asymmetric spectra around the resonant wavelength of the whispering gallery cavities in different coupling states are experimentally observed. An extinction ratio of ∼7 dB and a slope of 117dB/nm can be achieved in the asymmetric spectrum of the overcoupled whispering gallery cavity, where an additional π phase shift at the resonant wavelength is introduced to the Mach-Zehnder interferometer.

Line shapes in a plasmonic waveguide system based on plasmon-induced transparency and its application in nanosensor

A compact plasmonic coupled-resonator structure is investigated using a finite element method, which consists of a ring resonator and a stub coupled with a metal-insulator-metal (MIM) waveguide. Simulation results show that due to the resonant enhancement effect in this system, the plasmon-induced transparency (PIT) occurs and a sharp asymmetric Fano line arise in the transmission spectra by adjusting the parameters of the structure. Meanwhile, the position of the transmission peak can be controlled in any resonance mode by changing the depth of the stub, which is different from the previous researches. The physical features provide a high refractive index sensing with a sensitivity of 1100nm/RIU and a figure of merit (FOM) of 42550. Moreover, dual resonance peaks are realized by adding an extra ring resonator placed on the stub. The proposed structures may have wide applications in photonic-integrated circuits and the on-chip nanosensors.

The Line Shape of Double-Sided Tooth-Disk Waveguide Filters Based on Plasmon-Induced Transparency**Supported by the National Natural Science Foundation of China under Grant Nos 11374041 and 11404030, and the Fund of State Key Laboratory of Information Photonics and Optical Communications of Beijing University of Posts and Telecommunications of China.

We numerically investigate a coupled-resonator structure consisting of a stub resonator and a nanodisk resonator using a two-dimensional finite element method. Simulation results show that plasmon-induced transparency (PIT) occurs in the transmission spectra, and the sharp asymmetric Fano lines increase the sensitivity to 1.4 × 103 nm/RIU. We also analyze the properties of the structure with different radii of the nanodisk and the length of the tooth cavity. Moreover, we find that the PIT only happens when the staggered system is around a fixed location with different separate distances, which is not similar to the previous researches. Our model may be important to photonic-integrated circuits and the sensitivity in sensors.

Design and optimization of integrated micro optical gyroscope based on a planar ring resonator

In order to optimize the performance of the coupled resonator optical waveguide (CROW) gyroscope, a well-designed structure by optimizing the ring number and the transmission coefficient of the coupler is used as the core component of the planar waveguide optical gyroscope. The structure with double coupled ring resonator may possess large effective group refractive index to enhance angular sensing sensitivity was proposed. The concept of the Sagnac effect in this new double coupled ring resonator structure with a large effective group refractive index is investigated, it’s found that the rotation-induced phase shift is proportional to the effective group refractive index. On the basis of this effect, we calculate the general relation expression of theoretical rotation sensitivity and the effective group refractive index for this two-ring bidirectional CROW gyroscope by numerically simulation. Based on the relation, the phase shift characteristics of double coupled ring resonator and single ring resonator was analyzed. And the changing characteristics of the transmission coefficient of the couplers and the effective group refractive index was discussed based on the double cascaded ring resonator coupling mode theory. In the case of R1=R2=100 μm and ring transmission loss coefficient t1=t2=0.95, the generating condition of the largest effective group refractive index was obtained, according to the different effects of the couplers between rings and waveguide on the effective group refractive index. By using the parameters of R=100 μm and t=0.95, the sensitivity of a single ring resonator gyroscope is (104-105) °/h, and the sensitivity of double coupled ring resonator gyroscope can reach to 10 °/h. In summary, we show that the theoretical sensitivity of the double coupled ring gyroscope and single ring gyroscope are comparable when both have the same parameters. Using numerical and analytical methods, we demonstrated that coupling multiple resonators together can enhance rotation sensitivity. This research is important for applications of coupled ring resonator in optical angular velocity detection, and a promising regime to realize highly compact optical gyroscope.