Showing papers on "Q factor published in 2018"

Bridging ultrahigh-Q devices and photonic circuits

Abstract: Optical microresonators are essential to a broad range of technologies and scientific disciplines. However, many of their applications rely on discrete devices to attain challenging combinations of ultra-low-loss performance (ultrahigh Q) and resonator design requirements. This prevents access to scalable fabrication methods for photonic integration and lithographic feature control. Indeed, finding a microfabrication bridge that connects ultrahigh-Q device functions with photonic circuits is a priority of the microcavity field. Here, an integrated resonator having a record Q factor over 200 million is presented. Its ultra-low-loss and flexible cavity design brings performance to integrated systems that has been the exclusive domain of discrete silica and crystalline microcavity devices. Two distinctly different devices are demonstrated: soliton sources with electronic repetition rates and high-coherence/low-threshold Brillouin lasers. This multi-device capability and performance from a single integrated cavity platform represents a critical advance for future photonic circuits and systems.

Optimization of photonic crystal nanocavities based on deep learning.

Abstract: An approach to optimizing the Q factors of two-dimensional photonic crystal (2D-PC) nanocavities based on deep learning is hereby proposed and demonstrated. We prepare a data set consisting of 1000 nanocavities generated by randomly displacing the positions of many air holes in a base nanocavity and calculate their Q factors using a first-principles method. We train a four-layer neural network including a convolutional layer to recognize the relationship between the air holes’ displacements and the Q factors using the prepared data set. After the training, the neural network is able to estimate the Q factors from the air holes’ displacements with an error of 13% in standard deviation. Crucially, the trained neural network can estimate the gradient of the Q factor with respect to the air holes’ displacements very quickly using back-propagation. A nanocavity structure with an extremely high Q factor of 1.58 × 109 was successfully obtained by optimizing the positions of 50 holes over ~106 iterations, taking advantage of the very fast evaluation of the gradient in high-dimensional parameter spaces. The obtained Q factor is more than one order of magnitude higher than that of the base cavity and more than twice that of the highest Q factors reported so far for cavities with similar modal volumes. This approach can optimize 2D-PC structures over a parameter space of a size unfeasibly large for previous optimization methods that were based solely on direct calculations. We believe that this approach is also useful for improving other optical characteristics.

Microwave Sensor for Liquid Dielectric Characterization Based on Metamaterial Complementary Split Ring Resonator

Abstract: A metamaterial-based microwave sensor with complementary split ring resonator (CSRR) is implemented for dielectric characterization of liquids. The novelty in the proposed contactless sensor is the use of liquid samples placed normal to the sensor surface. Placed inside of glass capillary tubes, it is quickly possible to analyze the dielectric properties of liquids simply by replacing the capillary tubes with new samples. The liquid samples inside the glass capillary tubes modify the resonant frequency and $Q$ -factor of the CSRR sensor. Thereby, a relation between the sensor resonant frequency, $Q$ -factor, and complex permittivity of the liquid samples can be estimated. A measurement setup was used to test the proposed sensor that exhibited successfully detection of 10% steps in binary mixtures of ethanol and water. The proposed sensor is compact, low cost, contactless, reusable, easily fabricated, and easy to work.

Orthogonally Polarized RF Optical Single Sideband Generation and Dual-Channel Equalization Based on an Integrated Microring Resonator

Abstract: We demonstrate narrowband orthogonally polarized optical radio frequency (RF) single sideband generation as well as dual-channel equalization based on an integrated dual-polarization-mode high- Q microring resonator. The device operates in the optical communications band and enables narrowband RF operation at either 16.6 or 32.2 GHz, determined by the free spectral range and TE/TM mode interval in the resonator. We achieve a very large dynamic tuning range of over 55 dB for both the optical carrier-to-sideband ratio and the dual-channel RF equalization.

Analysis and mitigation of interface losses in trenched superconducting coplanar waveguide resonators

Abstract: Improving the performance of superconducting qubits and resonators generally results from a combination of materials and fabrication process improvements and design modifications that reduce device sensitivity to residual losses. One instance of this approach is to use trenching into the device substrate in combination with superconductors and dielectrics with low intrinsic losses to improve quality factors and coherence times. Here, we demonstrate titanium nitride coplanar waveguide resonators with mean quality factors exceeding two million and controlled trenching reaching 2.2 μm in the silicon substrate. Additionally, we measure sets of resonators with a range of sizes and trench depths and compare these results with finite-element simulations to demonstrate quantitative agreement with a model of interface dielectric loss. We then apply this analysis to determine the extent to which trenching can improve resonator performance.

Broadband RF Channelizer Based on an Integrated Optical Frequency Kerr Comb Source

Abstract: We report a broadband RF channelizer based on an integrated optical frequency Kerr micro-comb source, with an RF channelizing bandwidth of 90 GHz, a high RF spectral slice resolution of 1.04 GHz, and experimentally verify the RF performance up to 19 GHz. This approach of realizing RF channelizers offers reduced complexity, size, and potential cost for a wide range of applications to microwave signal detection.

Parity-time-symmetric optoelectronic oscillator

Abstract: An optoelectronic oscillator (OEO) is a hybrid microwave and photonic system incorporating an amplified positive feedback loop to enable microwave oscillation to generate a high-frequency and low-phase noise microwave signal. The low phase noise is ensured by the high Q factor of the feedback loop enabled by the use of a long and low-loss optical fiber. However, an OEO with a long fiber loop would have a small free spectral range, leading to a large number of closely spaced oscillation modes. To ensure single-mode oscillation, an ultranarrowband optical filter must be used, but such an optical filter is hard to implement and the stability is poor. Here, we use a novel concept to achieve single-mode oscillation without using an ultranarrowband optical filter. The single-mode operation is achieved based on parity-time (PT) symmetry by using two identical feedback loops, with one having a gain and the other having a loss of the same magnitude. The operation is analyzed theoretically and verified by an experiment. Stable single-mode oscillation at an ultralow phase noise is achieved without the use of an ultranarrowband optical filter. The use of PT symmetry in an OEO overcomes the long-existing mode-selection challenge that would greatly simplify the implementation of OEOs for ultralow-phase noise microwave generation.

Dirac semimetals based tunable narrowband absorber at terahertz frequencies.

Abstract: In this paper, a bulk Dirac semimetals (BDSs) based tunable narrowband absorber at terahertz frequencies is proposed and it has the attractive property of being polarization-independent at normal incidence because of its 90° rotational symmetry. Numerical results show that the absorption bandwidth is about 1.469e-2 THz and the total quality factor Q, defined as Q = f0/Δf, reaches about 94.6, which can be attributed to the low power loss of the guided mode resonance in the dielectric layer. The simulation results are analyzed with coupled mode theory. Interestingly, on the premise of maintaining the absorbance at a level greater than 0.95, the absorption frequency can be tuned from 1.381 to 1.395 THz by varying the Fermi energy of BDSs from 50 to 80 meV. Our results may also provide potential applications in optical filter and bio-chemical sensing.

Antenna Miniaturization Techniques: A Review of Topology- and Material-Based Methods

Abstract: Antenna miniaturization has been the subject of numerous studies for almost 70 years [1]-[4]. Early studies showed that a decrease in the size of an antenna results in a direct reduction in its bandwidth and efficiency (hr) [1], [2]. The size limitation translates into a lower boundary on the achievable radiation quality factor (Q factor) and consequently on the maximum achievable impedance bandwidth. Recently, many new investigations have been conducted to reduce the form factor (or the overall size) of different types of antennas while trying to maintain acceptable matching properties and operating bandwidth. These miniaturization techniques are generally related to changing the electrical and physical properties of an antenna.

A Microwave Ring Resonator Sensor for Early Detection of Breaches in Pipeline Coatings

Abstract: A planar microwave resonator sensor is designed, customized, and fabricated to detect coating breaches in industrial steel pipelines. The sensor, which utilizes a ring-shaped resonator to maximize the sensitivity at its core, is tuned to 2.5 GHz with a quality factor of 280. In the setup, the sensor is grounded to a piece of steel pipeline with an Epoxy-100 coating, which provides the substrate beneath the microstrip structure. It is demonstrated that any change in the gap height between the substrate layer and the pipeline, from 0 to 3.5 mm, produces a significant resonant frequency variation and bandwidth change in the sensor's response. The sensor structure demonstrates sensitivity and selectivity to air and water penetration to the breach. The sensor structure described in this work is a compact, low-cost solution and has potential for further miniaturization in mobile applications which may serve as a method for pipeline breach detection.

A Continuously Tunable Sub-Gigahertz Microwave Photonic Bandpass Filter Based on an Ultra-High-Q Silicon Microring Resonator

Abstract: Microwave photonic filter (MPF) is one of the key fundamental subsystems in microwave photonics, and it shows great potentiality in numbers of applications such as optoelectronic oscillator, microwave frequency measurement, and so forth. A narrowband bandpass MPF is highly desirable with its high selectivity in microwave photonic applications. However, a resonator with a high quality factor (>106) is very difficult to fabricate on the mature silicon photonics platform without optimization, thus restraining the applications of the MPF. In this paper, we propose and experimentally demonstrate a tunable sub-gigahertz bandwidth MPF based on an ultrahigh quality factor silicon microring resonator. Most performance aspects of the MPF are well-balanced. A full width at half-maximum bandwidth of 170 MHz is achieved thanks to the ultrahigh total quality factor as 1.14 × 106 of the microring resonator, and the average waveguide loss and the intrinsic Q factor of the microring resonator are calculated as 0.25 dB/cm and 2.67 × 106, respectively. The corresponding rejection ratio of the bandpass filter is 26.5 dB. Besides, the central frequency of the filter could be continuously tuned from 2.0 to 18.4 GHz with a microheater fabricated upon the microring, and a 16.4 GHz tuning range is achieved with the maximum power consumption of 14.4 mW. The device area is ∼0.05 mm2.

Optimization of photonic crystal nanocavities based on deep learning

Abstract: An approach to optimizing the Q factors of two-dimensional photonic crystal (2D-PC) nanocavities based on deep learning is proposed and demonstrated. We prepare a dataset consisting of 1000 nanocavities generated by randomly displacing the positions of many air holes of a base nanocavity and their Q factors calculated by a first-principle method. We train a four-layer neural network including a convolutional layer to recognize the relationship between the air holes' displacements and the Q factors using the prepared dataset. After the training, the neural network becomes able to estimate the Q factors from the air holes' displacements with an error of 13% in standard deviation. Crucially, the trained neural network can estimate the gradient of the Q factor with respect to the air holes' displacements very quickly based on back-propagation. A nanocavity structure with an extremely high Q factor of 1.58 x 10^9 is successfully obtained by optimizing the positions of 50 air holes over ~10^6 iterations, having taken advantage of the very fast evaluation of the gradient in high-dimensional parameter space. The obtained Q factor is more than one order of magnitude higher than that of the base cavity and more than twice that of the highest Q factors reported so far for cavities with similar modal volumes. This approach can optimize 2D-PC structures over a parameter space of a size unfeasibly large for previous optimization methods based solely on direct calculations. We believe this approach is also useful for improving other optical characteristics.

Strong Mode Coupling and High-Q Supercavity Modes in Subwavelength Dielectric Resonators

Abstract: We reveal that isolated subwavelength dielectric resonators support states with giant Q-factors similar to bound states in the continuum formed via destructive interference between strongly coupled eigenmodes and characterized by singularities of the Fano parameters.

Advanced photonic filters based on cascaded Sagnac loop reflector resonators in silicon-on-insulator nanowires

Abstract: We demonstrate advanced integrated photonic filters in silicon-on-insulator (SOI) nanowires implemented by cascaded Sagnac loop reflector (CSLR) resonators. We investigate mode splitting in these standing-wave (SW) resonators and demonstrate its use for engineering the spectral profile of on-chip photonic filters. By changing the reflectivity of the Sagnac loop reflectors (SLRs) and the phase shifts along the connecting waveguides, we tailor mode splitting in the CSLR resonators to achieve a wide range of filter shapes for diverse applications including enhanced light trapping, flat-top filtering, Q factor enhancement, and signal reshaping. We present the theoretical designs and compare the CSLR resonators with three, four, and eight SLRs fabricated in SOI. We achieve versatile filter shapes in the measured transmission spectra via diverse mode splitting that agree well with theory. This work confirms the effectiveness of using CSLR resonators as integrated multi-functional SW filters for flexible spectral engineering.

Billion Q-factor in silicon WGM resonators

Abstract: Optical whispering gallery mode (WGM) resonators allow combination of small mode volume with high Q-factor. Silicon is a major material for modern microelectronics and photonics. However, relatively low Q-factors of optical Si microresonators demonstrated so far have limited some promising applications. We report what we believe is first time measurement of a Q-factor of 1.2×109 in millimeter scale crystalline silicon optical resonators at 1550 nm wavelength. A novel silicon hemispherical coupler allowed us to reach up to 35% of coupling efficiency.

Asymmetric Coil Structures for Highly Efficient Wireless Power Transfer Systems

Abstract: A transmitter coil (TX-coil) as well as a receiver coil (RX-coil) has been designed at 6.78 MHz for magnetic resonant wireless power transfer systems not only to have high efficiency at medium distances, which is comparable to the coil dimensions, but also to provide stable efficiency over the position variation of the RX-coil. For mobile devices, the coils should be compact and have low profile and asymmetric, meaning that TX- and RX-coils have different dimensions. In this paper, TX-coil is designed by adding a small coil in series to achieve high quality factor (Q-factor) as well as relatively uniform magnetic field distribution. On the other hand, the scaling factor is introduced for wire width to design RX-coil with higher Q-factor. As a result, the proposed asymmetric coils reveal improved efficiency and degree of freedom in terms of position variation. This has been verified by measuring the system performance, including a power amplifier, full-wave rectifier, regulator, and load. The proposed TX-coil has size of $200 \times 200 \times 1$ mm3, while the size of the RX-coil is $100\times 100\times0.4$ mm3. The power transfer efficiency is 96% and 39% at the transmission distances of 50 and 300 mm, respectively.

400%/W second harmonic conversion efficiency in 14 μm-diameter gallium phosphide-on-oxide resonators

Abstract: Second harmonic conversion from 1550 nm to 775 nm with an efficiency of 400% W−1 is demonstrated in a gallium phosphide (GaP) on oxide integrated photonic platform. The platform consists of doubly-resonant, phase-matched ring resonators with quality factors Q ∼ 104, low mode volumes V ∼ 30(λ/n)3, and high nonlinear mode overlaps. Measurements and simulations indicate that conversion efficiencies can be increased by a factor of 20 by improving the waveguide-cavity coupling to achieve critical coupling in current devices.

All-Optical Tunable Microlaser Based on an Ultrahigh-Q Erbium-Doped Hybrid Microbottle Cavity

Abstract: An all-optical tunable microlaser based on the ultrahigh-quality (Q)-factor erbium-doped hybrid microbottle cavity is proposed and experimentally demonstrated for the first time. All-optical wavelength tunability of the silica microcavity laser is a very attractive feature and has been rarely reported. By using an improved doping method, the erbium-doped silica microbottle cavity with a Q factor of 5.2 × 107 in the 1550 nm band is obtained, which is higher than the previous work based on the conventional sol–gel method. Through nonresonant pump in the 980 nm band, a lasing threshold of 1.65 mW is achieved, which is lower than all those realized through the same pump method. Besides, iron oxide nanoparticles are coated on the tapered area by doping them in the ultraviolet curing adhesive in order to precisely control the coating area, which enables the hybrid microcavity to maintain the ultrahigh Q factor and possess large tunability. By feeding the control light through the axial direction of the microbot...

Microwave Sensor for Detection of Solid Material Permittivity in Single/Multilayer Samples With High Quality Factor

Abstract: In this paper, a planar microstrip sensor based on a band-stop filter for determining relative permittivity of solid materials is presented. The proposed sensor has been composed of the structure of meandered microstrip line with a T-shaped resonator and an interdigital structure that is connected ground by via. Interaction between the T-shaped resonator and the interdigital structure is caused to increase electric field intensity and the high field increase the sensor sensitivity and resolution. The microwave sensor by using single layer technology is fabricated on the substrate RO4003. The samples of FR4 and RO4350 in single and double layer forms as multilayer are placed on the sensor, and the sensor is demonstrating different resonance frequencies. The relationship between changing the resonance frequency and variation of the relative permittivity is linear, and it determines unknown materials’ dielectric characterizations. The permittivity of samples changes from 3 to 11; therefore, the resonance frequency varies from 3.7 to 5.65 GHz linearly. The proposed sensor shows improvement relative to other similar works in the fields of sensitivity and quality factor.

Ultra-high Q terahertz whispering-gallery modes in a silicon resonator

Abstract: We report on the first experimental demonstration of terahertz (THz) whispering-gallery modes (WGMs) with an ultra-high quality factor of 1.5 × 104 at 0.62 THz. The WGMs are observed in a high resistivity float zone silicon spherical resonator coupled to a sub-wavelength silica waveguide. A detailed analysis of the coherent continuous wave THz spectroscopy measurements combined with a numerical model based on Mie-Debye-Aden-Kerker theory allows us to unambiguously identify the observed higher order radial THz WGMs.

High-Q chaotic lithium niobate microdisk cavity.

Abstract: Lithium niobate (LN) is the workhorse for modern optoelectronics industry and nonlinear optics. High quality (Q) factor LN microresonators are promising candidates for applications in optical communications, quantum photonics, and sensing. However, the phase-matching requirement of traditional evanescent coupling methods poses significant challenges to achieve high coupling efficiencies of the pump and signal light simultaneously, ultimately limiting the practical usefulness of these high Q factor LN resonators. Here, for the first time, to the best of our knowledge, we demonstrate deformed chaotic LN microcavities that feature directional emission patterns and high Q factors simultaneously. The chaotic LN microdisks are created using conventional semiconductor fabrication processes, with measured Q factors exceeding 106 in the telecommunication band. We show that our devices can be free-space-coupled with high efficiency by leveraging directional emission from the asymmetric cavity. Using this broadband approach, we demonstrate a 58-fold enhancement of free-space collection efficiency of a second harmonic generation signal, compared with a circular microdisk.

Generalized Parity-Time Symmetry Condition for Enhanced Sensor Telemetry

Abstract: Wireless sensors based on micro-machined tunable resonators are important in a variety of applications, ranging from medical diagnosis to industrial and environmental monitoring.The sensitivity of these devices is, however, often limited by their low quality (Q) factor.Here, we introduce the concept of isospectral party time reciprocal scaling (PTX) symmetry and show that it can be used to build a new family of radiofrequency wireless microsensors exhibiting ultrasensitive responses and ultrahigh resolution, which are well beyond the limitations of conventional passive sensors. We show theoretically, and demonstrate experimentally using microelectromechanical based wireless pressure sensors, that PTXsymmetric electronic systems share the same eigenfrequencies as their parity time (PT)-symmetric counterparts, but crucially have different circuit profiles and eigenmodes. This simplifies the electronic circuit design and enables further enhancements to the extrinsic Q factor of the sensors.

Design and demonstration of ultra-high-Q silicon microring resonator based on a multi-mode ridge waveguide

Abstract: We present the design and experimental demonstration of the ultra-high-Q-factor silicon microring resonator based on a multi-mode ridge waveguide. The multi-mode ridge waveguide is designed to decrease the propagation loss and to improve the Q factor. The ultra-high Q factor of 1.1×106 is experimentally demonstrated, with the free spectrum range of 0.208 nm. The single-mode ridge waveguide is used in the coupling region to reduce the dimension of the microring resonator, and the bend radius is only 20 μm. To precisely control the resonance wavelength, a small heater is implemented on the silicon microring resonator with the tuning efficiency of 7.1 pm/mW. The degenerate four-wave mixing of the silicon microring resonator is investigated, and the conversion efficiency is measured to be −15.5 dB without optimizing the dispersion of the microring resonator and carriers extraction.

An Implantable Circularly Polarized Patch Antenna Design for Pacemaker Monitoring Based on Quality Factor Analysis

Abstract: A design approach is presented in this paper to develop an implantable circularly polarized (CP) microstrip patch antenna (MPA) embedded in a lossy material by addressing its total quality factor ( $Q_{T}$ ). To achieve it, the effect of high-loss tissue on effective relative permittivity and loss tangent of MPA has been thoroughly investigated. To the authors’ best knowledge, it is the first time that the exact values of $Q_{T}$ with respect to the high-loss tissue and embedded depth are studied and applied to design an implantable MPA. As the calculated $Q_{T}$ is confirmed in simulation, one can understand that an implantable MPA is actually a lossy resonator with extremely low $Q_{T}$ . As such, CP radiation can be achieved by enlarging its truncated area to appropriately separate two degenerate modes in such high-loss environment. The designed implantable MPA is then exhibited to achieve a broad impedance bandwidth, wide 3 dB axial ratio bandwidth and beamwidth, and high realized gain at 2.4 GHz industrial, scientific, and medical band. After the studies of sensitivity, biocompatible materials, and model integrity are carried out, the designed implantable MPA is fabricated and tested. Simulations are accompanied by measurements with good agreement, thus underlying the importance of our approach.

Miniaturized Resonator and Bandpass Filter for Silicon-Based Monolithic Microwave and Millimeter-Wave Integrated Circuits

Abstract: This paper introduces a unique approach for the implementation of a miniaturized on-chip resonator and its application for the first-order bandpass filter (BPF) design. This approach utilizes a combination of a broadside-coupling technique and a split-ring structure. To fully understand the principle behind it, simplified LC equivalent-circuit models are provided. By analyzing these models, guidelines for implementation of an ultra-compact resonator and a BPF are given. To further demonstrate the feasibility of using this approach in practice, both the implemented resonator and the filter are fabricated in a standard 0.13- $\mu \text{m}$ (Bi)-CMOS technology. The measured results show that the resonator can generate a resonance at 66.75 GHz, while the BPF has a center frequency at 40 GHz and an insertion loss of 1.7 dB. The chip size of both the resonator and the BPF, excluding the pads, is only 0.012mm2 ( $0.08 \times 0.144 \,\text {mm}^{2}$ ).

Substrate-Integrated Waveguide Triple-Band Bandpass Filters Using Triple-Mode Cavities

Abstract: Substrate-integrated waveguide (SIW) triple-mode triple-band bandpass filters (BPFs) are synthesized, designed, and demonstrated for the first time based on a novel type of SIW triple-mode square cavities perturbed by centered cross-shaped metallized via holes. The resonant characteristics of the cavity are analyzed first to show the range of the realizable frequency ratios, and the design parameters corresponding to the specifications, i.e., the external quality factors and the internal coupling coefficients for the three passbands, can be specified flexibly within certain ranges by exploiting an advanced triple-mode coupling controlling technique. Two SIW triple-mode triple-band BPFs, including a third-order direct-coupled one operating at 13, 14, and 15 GHz and a fourth-order cross-coupled one operating at 11, 12, and 13 GHz, are synthesized, designed, fabricated, and measured for demonstration. Compact circuit sizes and excellent filtering performances have been achieved for the two prototypes.

Transverse Modes in I.H.P. SAW Resonator and Their Suppression Method

Abstract: We discuss transverse modes in a resonator on a multilayer substrate with a thin piezoelectric plate. A generation mechanism of the transverse mode response in I.H.P. SAW (Incredible High-Performance SAW)resonator with a LiTa03 plate is analyzed by using FEM simulations, and it is shown that a slowness curve of the I.H.P. SAW structure is changed significantly compared with a standard 42° Y-X LiTa03 substrate. A new tilted resonator structure is proposed to suppress the transverse mode spurious. It is found that the tilted resonator with a small tilted angle can suppress the spurious response successfully with maintaining a high-Q factor.

Gain-assisted ultra-high-Q spoof plasmonic resonator for the sensing of polar liquids

Abstract: By directly incorporating a sub-wavelength amplifier chip into the spoof plasmonic resonator, the quality (Q) factor of the original passive resonator has been significantly increased by several orders of magnitude. The spoof plasmonic resonator is composed of a corrugated ring with a slit whose optimized offset angle φ is 45°, aiming to achieve a better Q-factor. By tuning the bias voltage applied to the amplifier chip that is placed across the slit, the Q factor has been increased from 9.8 to 21000 for the quadrupole mode when a plastic pipe filled with polar liquids is placed upon the resonator. Experiments at the microwave frequencies verify that the amplifier chip could greatly compensate the loss introduced by the polar liquids under investigation, resulting in an ultra-high-Q sensor for the detection of polar liquids.

Silicon photonic filters based on cascaded Sagnac loop resonators

Abstract: We demonstrate advanced integrated photonic filters in silicon-on-insulator (SOI) nanowires implemented by cascaded Sagnac loop reflector (CSLR) resonators. We investigate mode splitting in these standing-wave (SW) resonators and demonstrate its use for engineering the spectral profile of on-chip photonic filters. By changing the reflectivity of the Sagnac loop reflectors (SLRs) and the phase shifts along the connecting waveguides, we tailor mode splitting in the CSLR resonators to achieve a wide range of filter shapes for diverse applications including enhanced light trapping, flat-top filtering, Q factor enhancement, and signal reshaping. We present the theoretical designs and compare the CSLR resonators with three, four, and eight SLRs fabricated in SOI. We achieve versatile filter shapes in the measured transmission spectra via diverse mode splitting that agree well with theory. This work confirms the effectiveness of using CSLR resonators as integrated multi-functional SW filters for flexible spectral engineering.

Generalized Multimode SIW Cavity-Based Sensor for Retrieval of Complex Permittivity of Materials

Abstract: In this paper, the generalized substrate integrated waveguide (SIW) cavity technique is presented for the retrieval of broadband complex permittivity of medium loss dielectrics using a number of higher order modes of the proposed cavity. The proposed SIW cavity design improves the coupling by implementing a novel feeding topology to achieve a better quality factor for the higher order TE $_{10n}$ modes as compared with the conventional SIW feeding arrangement. The conventional SIW cavity perturbation formula is modified to overcome various limitations of the SIW topology, such as the lower $Q$ -factor, lower sample to cavity volume ratio, and larger frequency shifts observed for the higher order modes. The applicability of the proposed technique is first numerically validated using independent data obtained with the help of full-wave electromagnetic solver, and then, the accuracy is compared with various cavity-based techniques available in the literature. Finally, the proposed SIW cavity sensor is fabricated on Rogers’ RT5880 substrate, where a number of standard RF substrates are tested using the network analyzer. The proposed generalized scheme based on the improved SIW cavity provides reasonably accurate values of the complex permittivity of the medium-loss dielectric substrates at multiband of microwave frequency in the range of 10–20 GHz.