Second-order Resonators Research Articles

Semi-self-similar fractal cellular structures with broadband sound absorption

Honeycomb core materials, recognized for their excellent sound absorption and load-bearing capabilities, are widely employed in engineering applications. The back cavity shape of honeycomb structure absorbers plays a crucial role in their sound absorption performance. In this study, the honeycomb structure absorbers are re-designed using fractal design principles, enabling a modification of the acoustic properties of traditional honeycomb-type absorbers and a significant enhancement in the sound absorption frequency band. The theoretical predictions of the semi-self-similar fractal honeycomb absorber structure are validated through finite element simulations and experimental studies, exhibiting remarkable consistency. The findings indicate that compared to single-layer first-order structures, the performance of dual-layer second-order fractal element Helmholtz resonators is significantly improved. Relative to conventional honeycomb panel structures, the fractal design approach markedly enhances the semi-absorption bandwidth of the absorbers, with an increase in the fractal order further broadening the sound absorption frequency band. The innovation of achieving broadband absorption through fractal resonators not only represents a new direction in the design of advanced honeycomb core materials but also holds substantial promise in the field of noise control.

A Demultiplexing Filter With Box-Like Response and Large FSR Based on LNOI Second-Order Micro-Ring Resonators

We propose and experimentally demonstrate a high-performance micro-ring resonator (MRR) with a large free-spectral range (FSR) on the lithium niobate-on-insulator (LNOI) platform. Mode crosstalk happens in LNOI waveguide bends because more than one mode is generated from the anisotropy of lithium niobate, which limits the minimum bending radius of MRRs. Mode properties of ridge waveguides on X-cut LNOI with different bend radii and wavelengths have been analyzed to remove the effect of mode hybridization and reduce the mode crosstalk. On this basis, a small radius MRR with large FSR and 3dB bandwidth is achieved. Further, to deal with the wavelength shift caused by fabrication error, a second-order micro-ring resonators (2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> -order MRRs) filter with a box-like response and a high out-of-band rejection ratio is realized. Besides, a multichannel demultiplexing filter is realized based on 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> -order MRRs with low crosstalk (<−13 dB) at a channel spacing of 1.16 nm. The demonstration of the demultiplexing filter with a box-like response paves an important step for high-density photonic integration on the LNOI platform.

Research and design of broadband muffler based on second-order Helmholtz resonators

Noise is always a serious factor affecting people's quality of life. The most common sound-absorbing materials are porous materials, which work based on the principle that sound waves entering into the pores inside the material are subjected to air friction and viscous resistance, thus converting sound energy into heat. Porous materials have excellent performance of absorbing medium-frequency and high-frequency sound , but they are required to be thick enough to control the low-frequency sound waves with large wavelengths, which limits the application of porous materials in low-frequency noise control. In recent years, acoustic artificial structures have become a research hotspot, which can realize exotic effective acoustic parameters based on periodical structure or local resonance. Acoustic artificial structure provides a new material basis for noise control, in which Helmholtz resonator plays an important role because of its simple geometry. In this study, a broadband muffler is designed based on the second-order neck embedded Helmholtz resonator. In order to achieve low-frequency and broadband sound insulation with a limited number of units and structure length, the second-order resonator is chosen as a basic structure unit, which has a stronger low-frequency noise reduction capability and has one high-frequency transmission loss peak more than a conventional Helmholtz resonator. The acoustic characteristics and insulation performance of second-order resonators are analyzed through theoretical calculation, simulation calculation and experimental test. Then, based on the theoretical model and empirical rules, a broadband muffler composed of nine second-order resonators is designed by carefully adjusting the geometry parameters of each resonator. The three-dimensional printed resonators are installed on the side wall of a square standing wave tube for experimental measurement. In the experiment, the transmission loss curve of the muffler is measured by the two-load method. The result shows that the designed muffler has good sound insulation performances in a frequency range of 267–927 Hz, with the whole transmission loss above 20 dB and the maximum sound insulation up to 60 dB. The experimental result is consistent with the calculation result and simulation result. The muffler has simple structure and high practicability, which will have a wide application prospect in noise control engineering.

Scalable multicast hybrid broadband-crossbar wavelength selective switch: proposal and analysis.

In this Letter, we present a new hybrid broadband-crossbar switching network that can switch multiple wavelengths on demand and can also multicast. This switch fabric is an improvement over our previous design in both switch footprint and power consumption, as it reduces the number of switching elements by approximately 50%. We compare the switch loss and crosstalk with that of a multiwavelength selective crossbar switch. We also comment on fabrication tolerance of second-order ring resonators based on experimental results of 64 second-order ring resonators, and more than 250 heaters.

Electronically tunable immittances with applications to LP, BP, HP filter and VCO implementation

ABSTRACT Electronically tunable synthesis of immittances viz., inductor (L) and FDNR (D), using the voltage tunable current conveyor transadmittance amplifier (VTCCTA) block is presented. Design of selective LC and DR type resonators are derived. Subsequently, based on these resonators new VCO implementations, underlying the concept of short-circuit natural-frequency is proposed. According to this concept, second-order resonators yield a pair of imaginary-axis pole-pair; if Q~∞ this is amenable to sinusoid oscillator implementation without necessitating a nominal input stimulus (Vi ~0: short-circuit) to the resonator whereby the oscillation frequency (fo ) is the natural pole-frequency. To this end, both the LC and DR resonators may be utilised for the VCO design using a multiplication mode current conveyor (MMCC) element, of which the LC type follows a linear tuning law variable by a control voltage (Vd.c.). Experimental results with simulation and hardware-circuit test had been satisfactorily verified using standard commercially available IC-modules. Linear range of f o-variation upto 10 MHz with satisfactory phase noise-margin had been measured.

Multi-channel silicon photonic receiver based on compact second-order microring resonators

A monolithically integrated multi-channel receiver fabricated on the Silicon-on-Insulator (SOI) platform is demonstrated experimentally. This receiver is composed of an eight-channel thermally tunable microring resonator (MRR) filter as the wavelength division multiplexing (WDM) demultiplexer and an array of high speed waveguide-integrated Ge-on-Si photodetectors (PDs) for light detection. Second-order MRRs were utilized in each channel to obtain steeper roll-off from passband to stopband and lower crosstalk. The receiver was fabricated by using CMOS-compatible fabrication process at IME A*STAR. With the thermal tunability, the channel spacing can be adjusted according to different channel grid. Lower than −30 dB crosstalk and higher than 50 GHz 3-dB bandwidth was obtained for the demultiplexer with a channel spacing of 150 GHz. Proof-of-principle demonstration shows that each channel is capable of operating at a data rate of 10 Gb/s, resulting in an aggregate data rate of 80 Gb/s.

Frequency-Adaptive Multiresonant LQG State-Feedback Current Controller for LCL-Filtered VSCs Under Distorted Grid Voltages

This paper combines the well-known linear quadratic Gaussian (LQG) control and frequency-adaptive resonators and presents a frequency-adaptive multiresonant LQG state-feedback current controller for LCL -filtered voltage-source converters connected to a distorted grid. The paper also provides a design guideline and procedure based on robust control criteria, which, in combination with the linear quadratic regulator technique, offers flexibility in the control structure and automatizes the design of the controller. The frequency-adaptive resonators, based on second-order IIR resonators and on an online tuning algorithm, and the robustness criteria considered for the design process offer robustness in the face of grid voltage disturbances. The controller is evaluated and validated in a 9-kVA voltage-source converter (VSC) setup configured as a rectifier.

Polarization-independent tunable optical filter with variable bandwidth based on silicon-on-insulator waveguides

Abstract We present a polarization-independent tunable optical filter with variable bandwidth based on silicon-on-insulator (SOI) waveguides. The polarization-independent operation is achieved through the use of a polarization splitter-rotator and a polarization rotator-combiner, which are based on a bilevel adiabatic taper and an asymmetric directional coupler. Two stages of second-order microring resonators (MRRs) with different radii are used to achieve wavelength filtering with variable bandwidth and large free spectral range (FSR). Each stage of the second-order MRRs has a flat-top spectrum. The central wavelength of the filter is tuned by synchronous tuning of the two stages. The 3 dB bandwidth is adjusted via intentional misalignment of the passbands of the two stages. We demonstrate a prototype of such an optical filter on the SOI platform. The FSR of the fabricated device is about 90 nm. We show the tuning of the central wavelength from 1460 to 1550 nm. We adjust the 3 dB bandwidth from 37.5 to 100 GHz with a step of 12.5 GHz, with the overall insertion loss varying from −5.4 to −7.9 dB.

Corrections to “Cascading Second-Order Microring Resonators for a Box-Like Filter Response” [Dec 15 2017 5347-5360

Corrections to “Cascading Second-Order Microring Resonators for a Box-Like Filter Response” [Dec 15 2017 5347-5360

Cascading Second-Order Microring Resonators for a Box-Like Filter Response

We demonstrate an optical filter using multistage of second-order microring resonators (2nd-order MRRs) for a box-like filter response. All stages have identical structure parameters elaborately designed to obtain a flat-top spectrum. The maximally flat condition is deduced in consideration of loss and compared with those reported in literature. We present the insertion loss, extinction ratio, bandwidth, and roll-off rate of the maximally flat response. We find that for the flat response of a 2nd-order MRR, the product of bandwidth and roll-off rate is constant. We compare the cascading 2nd-order MRRs with single-stage high-order filters with the same number of ring cavities. We find that the cascading structure has comparable performances in the aspects of insertion loss and roll-off rate for small radius. This cascading structure relaxes the fabrication tolerance and mitigates the difficulty of electrical wiring difficulty since there are only two ring cavities in each stage. As a proof of concept, we fabricate this kind of optical filter with ten stages on silicon-on-insulator platform, with each ring cavity tunable and each stage measurable. We obtain five flat-top responses corresponding to one to five cascading stages. The five-stage filter response has a 3 dB bandwidth of ∼17 GHz, a roll-off rate of ∼−5 dB/GHz at −3 dB point, and an on-chip insertion loss of ∼−6 dB.

Multistage second-order microring-resonator filters with box-like spectral responses and relaxed fabrication tolerances * * Project supported by the National High Technology Research and Development Program of China (Nos. 2015AA017001, 2015AA010103) and the Natural National Science Foundation of China (NSFC) (Nos. 61235001, 61575187, 61535002, 61204061, 6157031748, 61377067).

We demonstrate an optical filter based on multistage second-order microring resonators (MRs) with box-like spectral responses. Compared with single-stage high-order optical filters with the same number of MRs, the demonstrated structure has comparable performances in the aspects of passband flatness, rolling-off slope and insertion loss. Moreover, the architecture relaxes the fabrication tolerance, electrical wiring and tuning difficulty since there are only two MRs in each stage. We experimentally demonstrate this kind of optical filter with five stages, which shows a 3-dB bandwidth of ~17 GHz, a rolling-off slope of ~5 dB/GHz and an on-chip insertion loss of ~6 dB.

Across-formant integration and speech intelligibility: Effects of acoustic source properties in the presence and absence of a contralateral interferer.

The role of source properties in across-formant integration was explored using three-formant (F1+F2+F3) analogues of natural sentences (targets). In experiment 1, F1+F3 were harmonic analogues (H1+H3) generated using a monotonous buzz source and second-order resonators; in experiment 2, F1+F3 were tonal analogues (T1+T3). F2 could take either form (H2 or T2). Target formants were always presented monaurally; the receiving ear was assigned randomly on each trial. In some conditions, only the target was present; in others, a competitor for F2 (F2C) was presented contralaterally. Buzz-excited or tonal competitors were created using the time-reversed frequency and amplitude contours of F2. Listeners must reject F2C to optimize keyword recognition. Whether or not a competitor was present, there was no effect of source mismatch between F1+F3 and F2. The impact of adding F2C was modest when it was tonal but large when it was harmonic, irrespective of whether F2C matched F1+F3. This pattern was maintained when harmonic and tonal counterparts were loudness-matched (experiment 3). Source type and competition, rather than acoustic similarity, governed the phonetic contribution of a formant. Contrary to earlier research using dichotic targets, requiring across-ear integration to optimize intelligibility, H2C was an equally effective informational masker for H2 as for T2.

Acoustic source characteristics, across-formant integration, and speech intelligibility under competitive conditions.

An important aspect of speech perception is the ability to group or select formants using cues in the acoustic source characteristics—for example, fundamental frequency (F0) differences between formants promote their segregation. This study explored the role of more radical differences in source characteristics. Three-formant (F1+F2+F3) synthetic speech analogues were derived from natural sentences. In Experiment 1, F1+F3 were generated by passing a harmonic glottal source (F0 = 140 Hz) through second-order resonators (H1+H3); in Experiment 2, F1+F3 were tonal (sine-wave) analogues (T1+T3). F2 could take either form (H2 or T2). In some conditions, the target formants were presented alone, either monaurally or dichotically (left ear = F1+F3; right ear = F2). In others, they were accompanied by a competitor for F2 (F1+F2C+F3; F2), which listeners must reject to optimize recognition. Competitors (H2C or T2C) were created using the time-reversed frequency and amplitude contours of F2. Dichotic presentation of F2 and F2C ensured that the impact of the competitor arose primarily through informational masking. In the absence of F2C, the effect of a source mismatch between F1+F3 and F2 was relatively modest. When F2C was present, intelligibility was lowest when F2 was tonal and F2C was harmonic, irrespective of which type matched F1+F3. This finding suggests that source type and context, rather than similarity, govern the phonetic contribution of a formant. It is proposed that wideband harmonic analogues are more effective informational maskers than narrowband tonal analogues, and so become dominant in across-frequency integration of phonetic information when placed in competition.

Across-formant integration and speech intelligibility: Effects of acoustic source properties in the presence and absence of a contralateral interferer

Three experiments used three-formant (F1 + F2 + F3) analogues of natural sentences to explore the role of acoustic source properties in across-formant integration. In experiment 1, F1 + F3 were generated using a monotonous periodic source (F0 = 140 Hz) and second-order resonators (H1 + H3); in experiment 2, F1 + F3 were tonal analogues (T1 + T3). F2 could take either form (H2 or T2). Target formants were always presented monaurally; the target ear was assigned randomly on each trial. In some conditions, only the target was present; in others, a competitor for F2 (F2C) was added contralaterally. Listeners must reject F2C to optimize recognition. Competitors (H2C or T2C) were created using the time-reversed frequency and amplitude contours of F2. Without F2C, intelligibility was reasonably high and the effect of a source mismatch between F1 + F3 and F2 was negligible. For both shared- and hybrid-source targets, the impact of adding F2C was modest when it was tonal but large when it was harmonic, irrespective of whether F2C matched F1 + F3. Experiment 3 showed that this pattern was maintained when corresponding harmonic and tonal analogues were loudness-matched. These findings extend those from earlier research using dichotic targets. Source type and competition, rather than acoustic similarity, govern the phonetic contribution of a formant. [Work supported by ESRC.]

Acoustic surface structure, across-formant integration, and speech intelligibility

An important aspect of speech perception is the ability to group or select formants using cues in the acoustic surface structure—for example, fundamental frequency (F0) differences between formants promote their segregation. This study explored the role of more radical surface-structure differences. Three-formant (F1 + F2 + F3) synthetic speech analogues were derived from natural sentences. In one experiment, F1 + F3 were generated using second-order resonators (R1 + R3) and a monotonous glottal source (F0 = 140 Hz); in the other, F1 + F3 were tonal analogues (T1 + T3). F2 could take either form (R2 or T2). In some conditions, the target formants were presented alone, either monaurally or dichotically (left ear = F1 + F3; right ear = F2). In others, they were accompanied by a competitor for F2 (F1 + F2C + F3; F2), which listeners must reject to optimize recognition. Competitors (R2C or T2C) were created using the time-reversed frequency and amplitude contours of F2. In the absence of F2C, the effect of su...

Hitless wavelength-selective switch based on quantum well second-order series-coupled microring resonators

A hitless wavelength-selective switch (WSS) based on InGaAs/InAlAs multiple quantum well (MQW) second-order series-coupled microring resonators is proposed and fabricated. In the core layer, a five-layer asymmetric coupled quantum well (FACQW) structure is employed. The WSS is driven by the electrorefractive index change in the FACQW core layer caused by the quantum-confined Stark effect (QCSE). The wafer for the WSS is grown by molecular beam epitaxy and waveguide structures are formed by dry etching. Boxlike spectrum responses and hitless switching characteristics of the WSS are successfully demonstrated for the first time. The change in coupling efficiency at a coupler between a ring and a busline and between rings and its effect on the switching characteristics are also discussed.

Miniaturized substrate integrated waveguide symmetric filter with high selectivity

A compact substrate integrated waveguide symmetric filter with source–load coupling using low temperature cofired ceramic (LTCC) technology for high-selectivity application is presented. The proposed filter with second-order resonators has two transmission zeros which can be controlled flexibly by adjusting the coupling strength and modifying coupling style. With the assistance of the multilayer LTCC structure and refined coupling manner, the proposed filter has a more compact size while maintaining high selectivity. A demonstration filter is designed, fabricated, and measured to validate the proposed structure. Measured results are provided to show good performance and in agreement with the simulated results. Moreover, thanks to the vertical LTCC multilayer structure, the overall size of the proposed filter is only mm3.

Modeling of a violin input admittance by direct positioning of second-order resonators

When approaching violin sound synthesis, the theoretical advantage of body modeling by finite difference or finite element paradigms comes from parameterizing the model by geometry and material properties. However, difficulties in representing the complexity of physical phenomena taking place have kept such approaches from raising more success, due especially to limited modeling accuracy and high computational cost. Conversely, the design of digital filters from admittance measurements, although generally offering a less meaningful parameterization, represents a more affordable technique as it provides significant fidelity at lower computational cost. Within digital filter formulation applied to the violin, modal representations can be considered as among the most physically pertinent, since vibration modes defining the timbre signature are in general observable from admittance measurements. This work introduces a technique for designing violin passive admittances by direct, non-uniform positioning of second-order resonators. Starting from admittance measurements, second-order resonator parameters are designed so that desired modes are modeled from frequency-domain data. Positve real models providing significant accuracy at low order are obtained from second-order resonator parameter fits. As an example, a two-dimensional input admittance is designed from measurements, so that it can be used for a digital waveguide model to include a control for bowing angle.

GHz-bandwidth optical filters based on high-order silicon ring resonators

Previously demonstrated high-order silicon ring filters typically have bandwidths larger than 100 GHz. Here we demonstrate 1-2 GHz-bandwidth filters with very high extinction ratios (~50 dB). The silicon waveguides employed to construct these filters have propagation losses of ~0.5 dB/cm. Each ring of a filter is thermally controlled by metal heaters situated on the top of the ring. With a power dissipation of ~72 mW, the ring resonance can be tuned by one free spectral range, resulting in wavelength-tunable optical filters. Both second-order and fifth-order ring resonators are presented, which can find ready application in microwave/radio frequency signal processing.

Device Architecture and Precision Nanofabrication of Microring-Resonator Filter Banks for Integrated Photonic Systems

To achieve the maximum benefit of electronic-photonic integrated circuits wavelength-division multiplexing must be used. This requires the design and fabrication of a highly integratable photonic device, capable of performing multiplexing/demultiplexing operations with low loss and minimal crosstalk. A filter bank consisting of high-index-contrast microring-resonator filters, with accurately spaced resonant frequencies can meet these requirements. This paper describes the basic architecture of microring-resonator filter banks, and how to maximize performance while keeping fabrication challenges reasonable. The greatest challenge in fabricating such devices is achieving the dimensional precision, on the scale of tens of picometers, needed to attain accurately spaced resonant frequencies. To do this, a fabrication method based on varying the electron-beam dose during scanning-electron beam lithography is used. This approach is used to create a dual twenty-channel filter bank, comprised of second-order silicon-rich silicon nitride microring resonators. The average resonant frequency spacing is off from the target spacing by only 3 GHz, corresponding to a dimensional precision of 75 pm. This approach is also shown to be compatible with the fabrication process for silicon microring resonators. Furthermore, it is shown that any remaining resonant frequency errors can be corrected with postfabrication thermal tuning. Also, a method of using the contra-propagating mode of a microring-resonator filter is demonstrated, enabling a single filter bank to multiplex/demultiplex two signals at the same time.