Tunable Waveguide Research Articles

Tunable acoustic waveguide based on vibro-acoustic metamaterials with shunted piezoelectric unit cells

We propose a new class of acoustic waveguides with tunable bandgaps (TBs) by using vibro-acoustic metamaterials with shunted periodic piezoelectric unit cells. The unit metamaterial cells that consist of a single crystal piezoelectric transducer and an electrical shunt circuit are designed to induce a strong vibro-acousto-electrical coupling, resulting in a tunable acoustic bandgap as well as local structural resonance and Bragg scattering bandgaps. The present results show that the TB frequency can be actively controlled and the transmission loss of the acoustic wave can be greatly improved by simply changing the inductance values in the shunt circuit.

One dimensional tunable Coupled Resonator Optical Waveguide based on Liquid-Crystal layers

The tunability of one-dimensional Coupled Resonator Optical Waveguides (CROWs) composed of periodic arrangement of Liquid Crystals (LCs) and Si slabs is investigated, theoretically. The anisotropy of LC slabs is fundamental to form the propagation modes within the Photonic Band Gap (PBG), known as the defect mode, and is considered into the calculations by exploiting the 4×4 matrix representation of transfer matrix proposed by Yeh. Moreover, varying the electric field applied to LCs is an essential real-time tool in order to change the frequency of defect mode and, hence, turning the device to a tunable one. Several CROW structures are introduced and characterized by means of their PBG.

Squeezing Light in Wires: Fundamental Optical Properties of Si Nanowire Waveguides

Single-mode Si-wire waveguides, fabricated in the Si-on-insulator platform, are the basis for a growing number of potential applications in linear and nonlinear integrated optical devices and systems. This paper reviews the fundamental optical physics and behavior of these waveguides and demonstrates how their reduced transverse dimensions and index contrast lead to a series of unique and distinct modal properties. These properties include readily tunable waveguide dispersion (including dispersion flattening), large longitudinal fields, a decrease in group velocity over those of the bulk materials, and anisotropic nonlinear optical properties. In turn, new devices and device structures are achievable as a result of these features and examples of new device structures are provided.

Tunable coplanar waveguide resonator with nanowires**Project supported by the National Basic Research Program of China (Grant Nos. 2011CB922104 and 2011CBA00200), the National Natural Science Foundation of China (Grant No. 11474154), the Jiangsu Natural Science Fund for Distinguished Young Scholars (Grant No. BK2012013), and a Doctoral Program (Grant No. 20120091110030).

A tunable superconducting half-wavelength coplanar waveguide resonator (CPWR) with Nb parallel nanowires ∼ 300 nm in width embedded in the center conductor was designed, fabricated, and measured. The frequency shift and the amplitude attenuation of the resonance peak under irradiation of 404-nm pulse laser were observed with different light powers at 4.2 K. The RF power supplied to such a CPWR can serve as current bias, which will affect the light response of the resonator.

Reconfigurable Dual-Stopband Filters With Reduced Number of Couplings Between a Transmission Line and Resonators

This letter proposes a new design method for a bandstop filter with two stopbands. Contrary to a conventional method, the presented method allows for achieving two stopbands without increasing the number of the couplings between resonators and the transmission line connecting the input and output ports. In addition, a filter designed using the presented method can not only have different center frequencies but also have different bandwidths by adjusting the resonant frequencies of the resonators. For verification of the proposed approach a dual-stopband filter using four tunable substrate-integrated waveguide resonators has been designed and measured.

Tunable pattern-free graphene nanoplasmonic waveguides on trenched silicon substrate.

Graphene has emerged as a promising material for active plasmonic devices in the mid-infrared (MIR) region owing to its fast tunability, strong mode confinement, and long-lived collective excitation. In order to realize on-chip graphene plasmonics, several types of graphene plasmonic waveguides (GPWGs) have been investigated and most of them are with graphene ribbons suffering from the pattern-caused edge effect. Here we propose a novel nanoplasmonic waveguide with a pattern-free graphene monolayer on the top of a nano-trench. It shows that our GPWG with nanoscale light confinement, relatively low loss and slowed group velocity enables a significant modulation on the phase shift as well as the propagation loss over a broad band by simply applying a single low bias voltage, which is very attractive for realizing ultra-small optical modulators and optical switches for the future ultra-dense photonic integrated circuits. The strong light-matter interaction as well as tunable slow light is also of great interest for many applications such as optical nonlinearities.

Cavity-photon-switched coherent transient transport in a double quantum waveguide

We study a cavity-photon-switched coherent electron transport in a symmetric double quantum waveguide. The waveguide system is weakly connected to two electron reservoirs, but strongly coupled to a single quantized photon cavity mode. A coupling window is placed between the waveguides to allow electron interference or inter-waveguide transport. The transient electron transport in the system is investigated using a quantum master equation. We present a cavity-photon tunable semiconductor quantum waveguide implementation of an inverter quantum gate, in which the output of the waveguide system may be selected via the selection of an appropriate photon number or “photon frequency” of the cavity. In addition, the importance of the photon polarization in the cavity, that is, either parallel or perpendicular to the direction of electron propagation in the waveguide system is demonstrated.

Novel Capacitor-Loaded Substrate-Integrated-Waveguide Structure and Its Electronically Controlled Leaky-Wave Antenna Application

A capacitor-loaded slotted substrate-integrated waveguide structure is presented to realize a tunable composite right-/left-handed substrate-integrated waveguide structure. The capacitor-loaded slotted substrate-integrated waveguide structure is realized on a half-mode substrate-integrated waveguide structure to reduce the size. The inter-digital slots and varactor diodes are inserted to offer series-tunable capacitance of the composite right-/left-handed circuit model. A long slot is inserted to isolate DC bias, and the chip capacitors are mounted on the long slot to create a path for RF signal flow. Based on the tunable capacitor-loaded slotted substrate-integrated waveguide structure, an electronically controlled composite right-/left-handed leaky-wave antenna is designed. It is experimentally demonstrated that the direction of the main beam is continuously varied from +4° to −6° at 5.6 GHz as the bias voltage increases from 1 to 20 V.

UV-soft Imprinted Tunable Polymer Waveguide Ring Resonator for Microwave Photonic Filtering

A tunable polymer waveguide ring resonator is proposed and demonstrated for microwave photonic filtering. The ring resonator consists of a Mach–Zehnder interferometer (MZI) as the tunable coupler and two micro-heaters as the thermo-optic phase shifters. It was fabricated with inorganic–organic hybrid optical material polysiloxane-liquid series by a novel and simple UV-soft selective imprint technique. The coupling conditions, over-, critical- and under-coupling, were obtained with the micro-heater on the arm of MZI and the maximum notch depth of about 18 dB was achieved. The resonant wavelength was also tuned with the micro-heater on the ring waveguide. The dispersion induced power fading of radio over fiber link was overcome by the tunable ring resonator with its notch filtering function.

Tunable erbium-doped fiber ring laser based on thermo-optic polymer waveguide Bragg grating

A tunable erbium-doped fiber ring laser incorporating a tunable thermo-optic polymer waveguide Bragg grating is proposed. Nano-imprinting technique was used to fabricate the polymer waveguide Bragg grating whose reflectivity and 3dB bandwidth are 25dB and 0.8nm, respectively. The polymer waveguide Bragg grating was used as wavelength selective element in the ring laser system and the center wavelength can be tuned by controlling the electrical power on the micro-heater. The fabricated tunable laser exhibits an output of 4.1dBm, side-mode suppression ratio of 55dB, 3dB bandwidth less than 16pm, and wavelength tuning range of 8.4nm.

Loop coupled resonator optical waveguides.

We propose a novel coupled resonator optical waveguide (CROW) structure that is made up of a waveguide loop. We theoretically investigate the forbidden band and conduction band conditions in an infinite periodic lattice. We also discuss the reflection- and transmission- spectra, group delay in finite periodic structures. Light has a larger group delay at the band edge in a periodic structure. The flat band pass filter and flat-top group delay can be realized in a non-periodic structure. Scattering matrix method is used to calculate the effects of waveguide loss on the optical characteristics of these structures. We also introduce a tunable coupling loop waveguide to compensate for the fabrication variations since the coupling coefficient of the directional coupler in the loop waveguide is a critical factor in determining the characteristics of a loop CROW. The loop CROW structure is suitable for a wide range of applications such as band pass filters, high Q microcavity, and optical buffers and so on.

Tunable nonlinear double-core PT-symmetric waveguides.

We propose a scheme for creating a tunable, highly nonlinear defect in a one-dimensional photonic crystal with an embedded atomic cell filled by a mixture of two isotopes of three-level atoms. The defect creates an effective double-core waveguide. The induced refractive index for a probe field can be made parity-time (PT) symmetric by means of a proper combination of a control field and a Stark field; hence the complex defect potential obtained contains double-well real and linear imaginary parts. We also show that it is possible to form various stable nonlinear defect modes supported by the focusing nonlinearity of the system.

Optimization of double-layer graphene plasmonic waveguides

Optimization of waveguides based on surface plasmons in double-layer graphene (DLG) is presented. In contrast to previous treatments, the effects of both extrinsic scattering and intrinsic Landau damping are simultaneously considered in this analysis. We show that an optimum frequency and an optimum spacing between two graphene sheets can be found to minimize the attenuation of the plasmon propagation. The optical mode is found to be less lossy than the acoustic mode below a certain frequency, but above this frequency the situation is reversed. All observable features of DLG are corroborated by analytical or numerical results, shedding light on the possibility of compact and tunable DLG-based plasmonic waveguides.

Electromagnetic analysis of graphene based tunable waveguide resonators

ABSTRACTThe electromagnetic analysis of the proposed graphene based tunable waveguide resonators for submillimeter‐wave applications is presented. Simple design based on the conventional E‐plane resonator is considered. The desired tunability up to 5% is provided by the change of the effective resonator length. Simulation results are presented to validate the argument. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2385–2388, 2014

Reliability study of a tunable Ka-band SIW-phase shifter based on liquid crystal in LTCC-technology

A tunable substrate-integrated waveguide phase shifter using low-temperature co-fired ceramic (LTCC)-technology is presented in this paper. By changing the effective permittivity in the liquid crystal (LC)-filled waveguide, the differential phase can be tuned continuously. This is achieved by means of an analog signal applied to the electrodes, surrounding the LC. The design allows for precise tuning of the differential phase, which is proven with a Monte Carlo measurement resulting in phase errors of less than 3° at 28 GHz. Besides that, the ambient temperature dependency of the module is shown. The phase shifter has a high integration level and can be included into a complete and lightweight single-phased array antenna module. The phase shifter is realized with a high level of integration which is available through the multilayer process of the LTCC. It has a length of 50 and provides a differential phase shift of more than 360° at 28 GHz. The figure of merit for tunable phase shifters is >40°/dB.

Attenuation characteristics of the guided THz wave in parallel-plate ferroelectric-graphene waveguides

Guided THz wave characteristics in a parallel-plate waveguide (PPWG) consisting of ferroelectric film (LiNbO3 and LiTaO3) and multilayer graphene (MLG) is studied in this paper, with their low and tunable attenuation valley predicted. The electrical conductivity of MLG is calculated by a set of closed-form equations with the coupling effect between the bottom graphene layer (BGL) and its substrate taken into account carefully, while the dispersive behavior of ferroelectric film itself is described by the Lorentz model over an ultra-wide THz band. It is shown that the guided TM-mode propagation can be adjusted effectively by changing temperature, frequency, optical pumping intensity, MLG layer number, film thickness and its transverse optical-phonon frequency. Moreover, one low attenuation valley of TM-mode in such ferroelectric-graphene waveguide is captured, which can be exploited for developing some THz planar tunable waveguides with ultra-low loss.

Highly confined and tunable plasmonic waveguide ring resonator based on graphene nanoribbons

A three-dimensional plasmonic open waveguide ring resonator (WRR) based on graphene nanoribbons, which has high confinement and multiple tunability, is proposed and numerically investigated. The intensity of edge graphene plasmons modes (EGSPs) in a nanoring resonator reaches the maximum at resonant frequencies, which indicates that EGSPs can efficiently propagate along the open graphene nanoring resonator even though in nanoscale. Furthermore, the resonant frequencies can be easily manipulated not only by adjusting the geometric parameters but also by changing the doping level of graphene via chemical doping or electrostatic gating without changing the physical size of the geometric structure. The proposed plasmonic WRR can find important potential applications in optoelectronic integrated circuits.

Rectangular waveguide enabling technology using holey surfaces and wire media metamaterials

A new enabling technology for implementing tunable rectangular waveguide components and circuits is reported for the first time with the use of 2D and 3D metamaterials; a holey metal surface and wire media, respectively. Traditional solid metal irises are replaced by a wire medium metamaterial. These media are well known and used to emulate plasma behavior and, therefore, can be used to replace solid metal. As proof of concepts, results for tunable rectangular waveguide filters are presented with the use of pin block inductive irises and capacitive posts. Furthermore, by adapting the traditional metal-pipe rectangular waveguide for tunability, regions of the solid metal walls are replaced by holey metasurfaces that enable adjustments in the position and spacing of the pin blocks. Prototype tunable structures were measured for verification and good agreement is achieved between full-wave simulations and measurements. The results clearly demonstrate the potential for this tunable/reconfigurable rectangular waveguide enabling technology. Potentially new applications for this permeable enabling technology include lightweight and forced-air/cryogenically cooled subsystems, gas/vapor/humidity/pressure/light sensors, optoelectronic and even real-time tunable/reconfigurable components, circuits and subsystems.

Fabrication of widely tunable ridge waveguide DBR lasers for WDM-PON

We report the fabrication of widely tunable ridge waveguide distributed Bragg reflector (DBR) lasers with InGaAsP butt-joint as grating material. The shape of the butt-joint interface is found to have significant effect on the properties of the lasers. It is shown that irregular mode jumps during wavelength tuning can be avoided by a V-shaped butt-joint interface. From the fabricated device, 23 channels with 0.8 nm spacing and greater than 35 dB side mode suppression ratios are obtained. The different tuning characteristics of the ridge waveguide and the previously reported buried ridge stripe DBR lasers are discussed. Combined with the wide tuning range and the simple structure, the ridge waveguide DBR lasers are promising for use in wavelength division multiplexing passive optical networks (WDM-PONs).

NEW DESIGN OF ALL-OPTICAL SLOW LIGHT TDM STRUCTURE BASED ON PHOTONIC CRYSTALS

This work demonstrates an all-optical slow light Time Division Multiplexing (TDM) structure based on photonic crystals (PCs). The structure shows good ability of dividing time domain signal into repetition time slots signal by four tunable group velocity waveguides from 0:006 ⁄ c to 0:248 ⁄ c where c is the velocity of light in the vacuum at the center wavelength of 1550nm and over a bandwidth 4.52THz with group velocity dispersion below 10 2 ps 2 /km. New high e-ciency Y-type directional coupling output can get larger than »1.4 times intensity and »93% loss improvement which are comparable to conventional output device. The proposed PCs waveguide structure is leading the way to achieve the TDM application and has good capability to extend the application of the optical communication and optical flber sensors systems.