Large Coupling Coefficient Research Articles

Tunable Monolithic DWDM Band-Selection Interleaver Filter Switch on Silicon-on-Insulator Substrate

A tunable band-selection interleaver filter switch formed on a silicon-on-insulator (SOI) substrate for dense wavelength-division-multiplexing (DWDM) system was fabricated, and its fundamental performances were experimentally demonstrated. The device consists of monolithic integration of a Michelson interferometer (MI) structure with two arm-waveguides with different lengths, appropriately designed for ITU-grid separation, a phase-modulation electrode on one arm and tunable wideband Bragg gratings reflectors. An SOI rib waveguide structure with a medium mode size was adopted for low loss and easy fabrication. A bandwidth of the grating, formed by electron beam (EB) lithography and deep reactive-ion etching (Deep-RIE), was rather large of 4 nm at -10 dB transmission level, from which a large coupling coefficient of the Bragg grating of 105 cm-1 was evaluated. A large tuning range of the Bragg grating of 17 nm was obtained. An extinction ratio of the interleaver filter was about 18 dB, and the interleaving switching was also attained with an applied electric power of 50 mW and a switching speed of about 1 ms.

Giant magnetoelectric coupling and E-field tunability in a laminated Ni2MnGa/lead-magnesium-niobate-lead titanate multiferroic heterostructure

The multiferroic properties of a laminated heterostructure consisting of magnetostrictive Ni2MnGa ribbon and piezoelectric lead-magnesium-niobate-lead titanate crystal are reported. A tunability of the electric field-induced magnetic field was measured by a shift in the ferromagnetic resonance (FMR) field by 230 Oe at X-band while applying an electric field of 6 kV/cm. Concomitantly, a frequency shift in the FMR of 370 MHz was observed. The sensitive tunability stems from a large linear magnetoelectric coupling coefficient, A=41 Oe cm/kV, measured in the heterostructure. This represents a new class of metallic multiferroic heterostructures that operate at microwave frequencies.

Optically induced lattice dynamics probed with ultrafast x-ray diffraction

We have studied the picosecond lattice dynamics of optically pumped hexagonal ${\text{LuMnO}}_{3}$ by using ultrafast x-ray diffraction. The results show a shift and broadening of the diffraction curve due to the stimulated lattice expansion. To understand the transient response of the lattice, the measured time- and angle-resolved diffraction curves are compared to a theoretical calculation based on the dynamical diffraction theory of coherent phonon propagation modified for the hexagonal crystal structure of ${\text{LuMnO}}_{3}$. Our simulations reveal that a large coupling coefficient $({c}_{13})$ between the $a\text{\ensuremath{-}}b$ plane and the $c$ axis is required to fit the data. Though we interpret the transient response within the framework of thermal coherent phonons, we do not exclude the possibility of strong nonthermal coupling of the electronic excitation to the atomic framework. We compare this result to our previous coherent phonon studies of ${\text{LuMnO}}_{3}$ in which we used optical pump-probe spectroscopy.

마이크로스트립 사각 개방 루프 공진기와 가변 부성 저항을 이용한 저위상 잡음 Push-Push 전압 제어 발진기

본 논문에서는 마이크로스트립 사각 개방 루프 공진기와 가변 부성 저항을 이용한 향상된 push-push 전압제어 발진기를 제시하였다. 마이크로스트립 사각 개방 루프 공진기는 큰 결합 계수 값을 갖는데, 이는 Q값을 크게 만들고, 전압 제어 발진기의 위상 잡음을 줄인다. 1.8V의 공급 전압을 사용한 전압 제어 발진기는 <TEX>$5.744{\sim}5.859GHz$</TEX>의 주파수 조절 범위에서 <TEX>$-124.67{\sim}-122.67dBc/Hz\;@\;100 kHz$</TEX>의 위상 잡음 특성을 갖는다. 이 전압 제어 발진기의 FOM은 같은 주파수 조절 범위에서 <TEX>$-202.83{\sim}-201dBc/Hz\;@\;100 kHz$</TEX>의 값을 갖는다. 마이크로 스트립 사각 개방 루프 공진기를 이용한 단일 종단 전압 제어 발진기와 마이크로스트립 공진기를 이용한 push-push 발진기와 비교했을 때 개선된 위상 잡음 특성은 각각 -8.51 dB와 -33.67 dB이다. In this paper, a novel push-push voltage-controlled oscillator(VCO) using microstrip square open loop resonator and tunable negative resistance is presented. The microstrip square open loop resonator has the large coupling coefficient value, which makes a high Q value, and has reduced phase noise of VCO. The VCO with 1.8V power supply has phase noise of <TEX>$-124.67{\sim}-122.67dBc/Hz\;@\;100 kHz$</TEX> in the tuning range, <TEX>$5.744{\sim}5.859 GHz$</TEX>. The FOM of this VCO is <TEX>$-202.83{\sim}-201dBc/Hz\;@\;100 kHz$</TEX> in the same tuning range. When it has been compared with single-ended VCO using microstrip square open loop resonator, and push-push oscillator using microstrip line resonator, the reduced phase noise has been -8.51dB, and -33.67dB, respectively.

Cross‐coupled Hilbert spiral resonator for bandpass filter design

AbstractThe modified cross‐coupled spiral resonators with Hilbert configuration are introduced for a large coupling coefficient in this article. For comparison, the conventional cross‐coupled spiral resonators are fabricated and measured herein. To obtain low insertion loss (−0.27 dB), high out‐of‐band rejection level (−19.5 dB) and wider FBW (50.9%), the filter of simplified CCSR‐H is proposed. Results included surface current distribution and frequency responses are presented and discussed. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1890–1894, 2007; Published online in Wiley Inter‐Science (www.interscience.wiley.com). DOI 10.1002/mop.22630

High-frequency surface acoustic waves excited on thin-oriented LiNbO/sub 3/ single-crystal layers transferred onto silicon

The need for high-frequency, wide-band filters has instigated many developments based on combining thin piezoelectric films and high acoustic velocity materials (sapphire, diamond-like carbon, silicon, etc.) to ease the manufacture of devices operating above 2 GHz. In the present work, a technological process has been developed to achieve thin-oriented, single-crystal lithium niobate (LiNbO3) layers deposited on (100) silicon wafers for the fabrication of radio-frequency (RF) surface acoustic wave (SAW) devices. The use of such oriented thin films is expected to favor large coupling coefficients together with a good control of the layer properties, enabling one to chose the best combination of layer orientation to optimize the device. A theoretical analysis of the elastic wave assumed to propagate on such a combination of material is first exposed. Technological aspects then are described briefly. Experimental results are presented and compared to the state of art.

Influence of strain on the magnetization and magnetoelectric effect inLa0.7A0.3MnO3∕PMN−PT(001)(A=Sr,Ca)

We investigate the influence of a well-defined reversible biaxial strain <=0.12 % on the magnetization (M) of epitaxial ferromagnetic manganite films. M has been recorded depending on temperature, strain and magnetic field in 20 - 50 nm thick films. This is accomplished by reversibly compressing the isotropic in-plane lattice parameter of the rhombohedral piezoelectric 0.72PMN-0.28PT (001) substrates by application of an electric field E <= 12 kV cm-1. The magnitude of the total variable in-plane strain has been derived. Strain-induced shifts of the ferromagnetic Curie temperature (Tc) of up to 19 K were found in La0.7Sr0.3MnO3 (LSMO) and La0.7Ca0.3MnO3 films and are quantitatively analysed for LSMO within a cubic model. The observed large magnetoelectric coupling coefficient alpha=mu0 dM/dE <= 6 10-8 s m-1 at ambient temperature results from the strain-induced M change in the magnetic-film-ferroelectric-substrate system. It corresponds to an enhancement of mu0 DeltaM <= 19 mT upon biaxial compression of 0.1 %. The extraordinary large alpha originates from the combination of three crucial properties: (i) the strong strain dependence of M in the ferromagnetic manganites, (ii) large piezo-strain of the PMN-PT substrates and (iii) effective elastic coupling at the film-substrate interface.

Large and stable thickness coupling coefficients of [001]C-oriented KNbO3 and Li-modified (K,Na)NbO3 single crystals

Large thickness coupling factors kT⩽0.7 are measured in both [001]C-oriented (45° cut in the orthorhombic ac plane), monodomain and [001]C-poled, domain-engineered single crystals of KNbO3. kT is extremely stable over a large temperature range, remaining high (⩾0.65) even upon heating and cooling through the orthorhombic-tetragonal phase transition. This is likely related to another finding that spontaneously high kT values (⩽0.68) are observed in as-grown (unpoled), [001]C-cut, polydomain KNbO3 crystals. kT is also stable upon thinning to thicknesses below 60μm, as required for high-frequency applications. Finally, large kT values (⩽0.7) are reported in [001]C-poled, polydomain, Li-doped (K0.5Na0.5)NbO3.

Monolithic Integrated Piezoelectric MEMS-Tunable VCSEL

A novel actuation mechanism that utilizes the inherent piezoelectric properties of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> As compounds is presented for short-wavelength microelectromechanical systems tunable vertical-cavity surface-emitting laser centered at 850 nm. Piezoelectric actuation can provide precise bidirectional displacements and linear tuning characteristics with respect to the applied voltage, does not suffer from travel limitations and catastrophic electrical damage, consumes low power (~1 muW), and has a relatively fast response compared to thermal actuation. In addition, piezoelectric actuation based on Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> As films offers a large piezoelectric coupling coefficient comparable to those of zinc oxide and quartz, and it can be integrated with high-speed electronic and optoelectronic devices. Single-mode emission with a linear continuous tuning range of 3 nm and low power consumption were experimentally obtained

Analysis of power output for piezoelectric energy harvesting systems

Power harvesting refers to the practice of acquiring energy from the environment whichwould be otherwise wasted and converting it into usable electric energy. Much work hasbeen done on studying the optimal AC power output, while little has considered theAC–DC output. This article investigates the optimal AC–DC power generation for arectified piezoelectric device. In contrast with estimates based on various degrees ofapproximation in the recent literature, an analytic expression for the AC–DC power outputis derived under steady-state operation. It shows that the harvested power depends on theinput vibration characteristics (frequency and acceleration), the mass of the generator,the electrical load, the natural frequency, the mechanical damping ratio and theelectromechanical coupling coefficient of the system. An effective power normalizationscheme is provided to compare the relative performance and efficiency of devices. Thetheoretical predictions are validated and found to be in good agreement withboth experimental observations and numerical simulations. Finally, several designguidelines are suggested for devices with large coupling coefficient and qualityfactor.

RF Filter using Boundary Acoustic Wave

In this paper, we report a new structure of a shear horizontal (SH) type boundary acoustic wave for cellular phone applications. Such a structure composed of electrodes with a low shear wave velocity between two materials, namely, the SiO2 film/Au-electrode/LiNbO3 substrate, is proposed. The ladder filter used in this paper had this structure. By changing the propagation angle of the acoustic wave, the electromechanical coupling factor k2 range from 0 to 16% was obtained, as well as a normalized bandwidth range 0.67 to 1.85 fold as large as that of a 36–46°Y–X LiTaO3 leaky surface acoustic wave (LT-LSAW) filter. In addition, an excellent temperature coefficient of delay time (TCD=25 ppm/°C) and a large mutual coupling coefficient κ12 (=0.15) were also obtained.

Plasma Generation at Atmospheric Pressure using a High Power Microwave Beam and its Application to Rocket Propulsion

Experiments on microwave plasma generation and its application to microwave beamed energy propulsion were conducted using a 1MW-class, 170GHz gyrotron. The microwave beam was focused using a parabola reflector and plasma was initiated near the focal point in the ambient air. Plasma propagated upstream in the microwave beam channel while absorbing microwave. Its propagation velocity was supersonic when the microwave power density was larger than 75kW/cm2. The propulsive impulse was measured using a cone-cylinder shaped thruster model. As a result, maximum momentum coupling coefficient was obtained at a certain plasma propagation distance. In addition, large momentum coupling coefficient was obtained when plasma was propagated at a supersonic velocity. It would be because supersonic plasma propagation forms a strong shock wave, resulting in an efficient pressure increase.

Theoretical calculation of the surface acoustic wave characteristics of GdCOB single crystals

Fabrication and crystalline characteristics for various piezoelectic materials have been studied. In particular, quartz, LiNbO 3, LiTaO 3 and LiB 4O 7 crystals have been investigated, and their piezoelectric properties for applications such as surface acoustic wave (SAW) devices have been evaluated in detail; however, there has been interest in new materials with improved properties. Recently, new rare earth crystalline materials, such as ReCa 4O(BO 3) 3 (Re: Y, Gd, La and others) have been grown, and excellent nonlinear optical properties have been reported. It is expected that these materials may also have good piezoelectric properties; however, few studies of the piezoelectricity of these materials have been performed. Of particular interest is that a large electric-mechanical coupling coefficient may be obtained in GdCa 4(BO 3) 3 (GdCOB). In this study, a theoretical analysis of the SAW characteristics, and investigation of the piezoelectric properties is reported in detail. The analysis was performed using material constants obtained from resonance–anti-resonance method by Wang et al. [J. Wang, X. Hu, X. Yin, R. Song, J. Wei, Z. Shao, Y. Liu, M. Jiang, J. Mater. Res. 16 (2001) 790–796]; SAW velocities and coupling constants were calculated at several crystalline cuts and propagation directions. In particular, the result calculated at the Z-cut of GdCOB was substantially in accordance with the measured results. Two SAW propagation modes (lower and higher) existed on the cut. From comparison between measured and calculated results, the lower and higher modes were identified as the Rayleigh mode and the leaky mode, respectively. From the theoretical analysis of Rayleigh SAW for all crystalline cuts and propagation directions, the maximum velocity and coupling coefficients were obtained for GdCOB Y-cuts, revealing that the Y-cut will be suitable for SAW device applications.

Synchronization of Discrete Time Dynamical Systems†

The synchronization of two discrete time dynamical systems is considered, where the systems are described in terms of first order difference equations, each of which satisfies a global dissipativity condition and hence has a global attractor. It is shown that the coupled trajectories converge to each other as time increases for sufficiently large coupling coefficient and that the global attractor of the coupled system converges upper semi continuously as the coupling parameter increases to the diagonal of the product of the global attractor of a discrete time dynamical system for which the defining function is the average of those of the original uncoupled systems.

Improvement on the photorefractive performance of a monolithic molecular material by introducing electron traps

The electron-injecting material, tris(8-hydroxyquinoline) aluminum (Alq3), was introduced into photorefractive (PR) samples containing the (9-ethyl-9H-carbazol-3-ylmethylent)-(4-nitrophenyl)-amine (ECYENPA) molecule, which has been proved to possess the fine functions of both electro-optic effect and hole transportation. A small amount of Alq3 forms quantum dots in ECYENPA, serving as electron traps and leading to a great enhancement of the PR effect. A large two-beam coupling coefficient of 424cm−1 (at 44.6V∕μm) was observed in a sample doped with 2wt% of Alq3, in contrast to a value of 232cm−1 for a sample without Alq3. Moreover, the measured response time was one order of magnitude shorter than that of the undoped sample.

Lead Free Piezoelectric Materials

Lead oxide based ferroelectrics, represented by lead zirconate titanate (Pb(Zr,Ti)O-3) or PZT) are the most widely used materials for piezoelectric actuators, sensors and transducers due to their excellent piezoelectric properties. Considering lead toxicity, there is interest in developing piezoelectric materials that are biocompatible and environmentally friendlier. The low density of non-lead based materials can also be an advantage in transducers for underwater and medical imaging due to expected lower acoustical impedance. Another impetus for seeking alternative to lead based compositions is the need for piezoelectric materials for operation at high temperatures. Several classes of materials are now being reconsidered as potentially attractive alternatives to PZT for special applications. The potassium niobate family, KNbO3, exhibits low dielectric constants, large thickness coupling coefficient along certain non-polar directions, and low density, all of which have advantages for high frequency transducer applications. Several compositions belonging to bismuth titanate family, Bi4Ti3O12, such as SrTi4Bi4O15, are promising candidates for high temperature applications. Lead free materials alone (eg. (Na0.5Bi0.5)TiO3) or in solution with PT (BiSCO3-PbTiO3) are also potentially interesting as they combine high piezoelectric activity and, in some cases, relatively high T-c. For these families of piezoelectric materials, the processing and piezoelectric response under different conditions of pressure, frequency, and temperature are presently much less understood than for the classical lead containing systems. In this presentation we review and discuss piezoelectric properties of selected lead free compositions (principally for members of the potassium niobate family and bismuth titanate layered compounds) in relation to structural and microstructural features as well as extrinsic contributions (domain walls displacement, conductivity) to their electromechanical properties. It is shown that it is possible to obtain remarkably stable piezoelectric response in some compositions, while others exhibit strong dependence of piezoelectric properties on driving field and frequency. Origins of these different behaviours are discussed.

Simulation of 1.55 μm distributed feedback semiconductor laser: investigation of dielectric grating yielding high coupling effect

A novel dielectric grating for semiconductor distributed feedback laser was proposed. A five-layer model was developed to examine the effect of the dielectric grating based on Coupled Mode Theory. The large refractive index difference between dielectric material and InP yields much larger coupling coefficient and provides greater spatial flexibility in grating design and fabrication, resulting in improved efficiency of the gratings.

Investigation of External Optical Feedback Resistance of IC-DFB and GC-DFBLasers Using a Very Simple Experimental set-up

We study the external optical feedback resistance of both index-coupled(IC) and gain-coupled distributed feedback (DFB) lasers using avery simple experimental set-up. Though IC-DFB lasers with largecoupling coefficients are found to be less sensitive to externalreflection, they suffer from mode instability at high injection level.On the other hand, the introduction of gain-coupling mechanism cansignificantly improve both the immunity to external optical feedbackand the single mode yield of the device.

Time-domain travelling-wave algorithms on the analysis of distributed feedback lasers

Simple and straightforward modifications are proposed to improve the performance of the existing time-domain travelling-wave algorithm in solving the coupled-wave equations. The conditions of convergence of the modified time-domain travelling-wave algorithms are also derived. It can be shown that the algorithm realised by a two-dimensional second-order approximation has the fastest computational speed. It is also accurate enough to model the static and dynamic behaviour of different types of distributed feedback semiconductor lasers with large coupling coefficient.

Nonlinear phase mismatch and optimal input combination in atomic four-wave mixing in Bose-Einstein condensates

This work treats four-wave mixing (4WM) in Bose-Einstein condensates (BEC), focusing on the nonlinear phase mismatch, maximum output, and optimal input combination. We show that the nonlinear phase mismatch decreases the 4WM efficiency. It was found that the 4WM efficiency depends on both the coupling coefficient (i.e., the product of the total number of atoms, the scattering length, and the overlap integral) and the ratios among the three initial input beams. The 4WM efficiency increases with the increase of the coupling coefficient when it is small, then saturates, and finally decreases at high coupling coefficient due to both pump depletion and phase-modulation effects. A maximum output efficiency of about 50% in our case is predicted. In order to get the maximum output, the two pump beams should have equal amplitude and the probe beam should be as small as possible. In addition, a large coupling coefficient (&gt;\ensuremath{\pi}/2), which is determined by the ratio of the probe beam to the total input, is required. On the other hand, when the coupling coefficient is fixed, a maximum output for this case can be obtained by optimizing the input ratios among the three input beams. Other ratio combinations will decrease the 4WM efficiency.