Coupling Bandwidth Research Articles

八边形晶格双芯光子晶体光纤偏振分束器

Based on the birefringence effect,a novel duel-core photonic crystal fiber polarization beam splitter was proposed.Tellurite glass and SF6 glass were used as the material for the PCF,respectively.Using the full-vector finite element method(FEM),the effects of structural parameters on birefringence and relative coupling length were analyzed,and the characteristics of the splitters,such as coupling length,extinction ratio and bandwidth were simulated.The numerical simulation results demonstrate that the tellurite glass splitter has higher extinction ratio and bandwidth than the SF6 glass splitter.The extinction ratio of the tellurite glass splitter is-53.46 dB at the wavelength of 1.55 μm,and the bandwidth is over 120 nm when the extinction ratio is less than-20 dB.

Compact Wide-Band Branch-Line Coupler with Meander Line, Cross, and Two-Step Stubs

Despite being widely used, branch-line couplers (BLC) still suffer from large size. This makes it difficult to incorporate BLC into miniature microwave devices. The work presented here is the design and implementation of a 3-dB reduced-size wide-band 3-branch-line coupler (3-BLC). By combining meander line, cross, and two-step stubs techniques, size reduction and bandwidth improvement is successfully achieved on 3-BLC design. The 3-BLC length was reduced along the horizontal branches using two-step reduction technique while the center vertical branch was reduced using cross stubs. A simple two-turn meander line is utilized at the two ends vertical branches of the coupler to obtain balanced length with the middle vertical branch. Hence, its width was optimized to maximize the coupler bandwidth. The 3-BLC was designed to operate at 2.45 GHz wireless local area network frequency band (IEEE 802.11 b/g) and fabricated on a 1.6 mm thick FR-4 board. The simulated and measured results are in very good agreement and show a fractional bandwidth of 50% and a sized reduction of 61.64% at the center of the frequency band. The proposed coupler design provides BLC that occupies less space, simple to implement, and wide-band BLC architecture with generic 3-BLC wide-band characteristics retained. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1810–1815, 2013

Broadband directional coupling in aluminum nitride nanophotonic circuits

Aluminum nitride (AlN)-on-insulator has emerged as a promising platform for the realization of linear and non-linear integrated photonic circuits. In order to efficiently route optical signals on-chip, precise control over the interaction and polarization of evanescently coupled waveguide modes is required. Here we employ nanophotonic AlN waveguides to realize directional couplers with a broad coupling bandwidth and low insertion loss. We achieve uniform splitting of incoming modes, confirmed by high extinction-ratio exceeding 33dB in integrated Mach-Zehnder Interferometers. Optimized three-waveguide couplers furthermore allow for extending the coupling bandwidth over traditional side-coupled devices by almost an order of magnitude, with variable splitting ratio. Our work illustrates the potential of AlN circuits for coupled waveguide optics, DWDM applications and integrated polarization diversity schemes.

Dynamic electron localization initiated by particle-bath coupling

We consider the quantum evolution and relaxation of an electron or hole which is coupled to a set of bath modes. In most applications the bath modes would be the vibronic coordinates but the model considered applies to any type of dynamic boson environment. The method is developed specifically for the problem of dynamic polaron formation in small nonperiodic systems. It can describe a broad group of experimental situations, including in particular electron localization in organics and polymeric materials and devices. The immediate bath is allowed to dissipate energy to a secondary bath. The bath obeys classical dynamics which puts some restriction on the range of validity of this approach. Using the density matrix formalism on a tight binding model consisting of a linear chain coupled to vibronic coordinates, we demonstrate in real time how the interaction with a dissipative bath makes the initial quantum distribution reach a steady-state population. This calculation is based on the Ehrenfest dynamics approximation. As an example we consider coupling at a single impurity site and find that for given parameters (bath coupling, site energy, and relaxation rate), the particle becomes dynamically localized in space on a particular time scale. This localized particle can be called a polaron. We define a population formation time in the same way as done in the experimental measurement. This formation time is studied as a function of the coupling strength, bandwidth, and energy dissipation rate. Energy dissipation plays a crucial role in the spatial localization process. The formation time shortens as the electron-vibration coupling increases, and as the intersite tunneling increases, but lengthens with impurity trap depth. Polaron formation is suppressed for sufficiently wide electronic bands.

Cost-effective and high frequency surface acoustic wave filters on ZnO:Fe/Si for low-loss and wideband application

ZnO:Fe films with various piezoelectric coefficient d33 were employed to fabricate high frequency surface acoustic wave (SAW) filters on Si by conventional photolithography technology. Comparing with the SAW filters on undoped ZnO films, the electromechanical coupling factor and bandwidth, respectively, increases 75.7% and 14.8%, while the insertion loss decreases 20.3% when using Zn0.988Fe0.012O films with a d33 of ∼127 pC/N. Through annealing demonstration, d33 is considered as the intrinsic factor determining the SAW properties of filters, and the properties are improved by O2 annealing. ZnO:Fe films with enhanced d33 is promising for high frequency, low-loss, and wideband SAW applications.

A Wide-Band Antenna Design by Using Electromagnetic Simulation Software

A wide-band antenna coupling with an elliptical slot was discussed in this paper. To implement the wide band operation, an elliptical ring slot was etched on a polygonal patch. The properties of this design have been verified by using electromagnetic simulation software. Comparing to the conventional U-slot patch antenna fed by Π-shaped slot, the proposed structure is with the same impedance in bandwidth, but less than 10% in size.

Low moment NiCr radio frequency magnetic films for multiferroic heterostructures with strong magnetoelectric coupling

Magnetic/piezoelectric multiferroic heterostructures with a magnetic thin film on a piezoelectric slab provides a great opportunity to achieve a strong converse magnetoelectric coupling with great potential for voltage tunable magnetic devices. Efforts have been made in developing highly magnetostrictive RF magnetic materials with low magnetization using magnetic/piezoelectric heterostructures to generate large electric-field induced effective magnetic fields. In this work, we report on NiCr films having low magnetization and relatively large magnetostriction. Strong converse magnetoelectric coupling and large electric field tunable ferromagnetic resonance (FMR) bandwidths are achieved in layered NiCr/lead zirconate titanate (PZT) and NiCr/lead zinc niobate lead titanate (PZN-PT) multiferroic heterostructures. A large electric field induced effective magnetic field of 260 Oe for NiCr/PZT and 756 Oe for NiCr/PZN-PT was observed, corresponding to a giant magnetoelectric coupling coefficient of 13 Oe cm/kV in NiCr/PZT and 75.6 Oe cm/kV in NiCr/PZN-PT multiferroic heterostructures. A high voltage tunable FMR frequency range was observed, with fmax/fmin being 124 and 325% for NiCr/PZT and NiCr/PZN-PT. The strong converse magnetoelectric coupling of NiCr/PZT and NiCr/PZN-PT heterostructures provide great opportunities for electric field tunable RF magnetic devices.

Design for broadband high-efficiency grating couplers

In this Letter, we propose general optimization methods to design broadband high-efficiency grating couplers for planar waveguides. We attribute the coupling bandwidth to the mismatch of effective indices between the diffracted beam and the actual grating structure around the operation wavelength for fiber to waveguide excitation. The coupling bandwidth formula is deduced. A simple parameter-separate optimization procedure is proposed for general layered grating couplers for high coupling efficiency. Using our principle, we optimized a grating coupler for a horizontal slot waveguide operating at wavelength 1.55 μm for TM polarization. The grating coupler has 1 dB bandwidth of 60 nm and coupling efficiency of 65% with incident light from single-mode optical fiber (SMF) at 8°.

Ridge Substrate Integrated Waveguide (RSIW) Dual-Band Hybrid Ring Coupler

A novel dual-band ring coupler is proposed in Ridge Substrate Integrated Waveguide (RSIW) technology. The structure is based on two concentric rings with the outer ring loaded by a low insertion loss de-multiplexing scheme allowing independent dual band operation. The RSIW ensures a wide-band fundamental mode operation covering both frequency bands while providing a compact design. A C/K band coupler is experimentally verified showing coupling bandwidths of 6.9% and 14.6% centered at 7.25 and 20.5 GHz, respectively.

System Design Analysis of a 0.22-THz Sheet-Beam Traveling-Wave Tube Amplifier

The primary constituents of a 0.22-terahertz (THz) sheet-beam traveling-wave tube (TWT) amplifier, composed of a staggered double grating array waveguide, have been designed for broadband THz operation (~ 30%) using the fundamental passband (TE-mode). Currently, we are looking into the possibility of a pulsed low-duty test of this device as a proof of principle (POP) and have been making efforts to construct the system. The optimally designed input coupler has ≤ 1 dB insertion loss at 0.22 THz with ~ 75 GHz (34%) 1-dB matching bandwidths. A thin mica RF window provides a coupling bandwidth spanning multiple octaves. The collector is designed to have a jog for collecting the spent beam along the RF path coupled to the output RF window. Computer simulations show that the collector hybridized with a WR-4 window has ~ 60 GHz matching bandwidth with ~ - 0.5ndB insertion loss at 0.22 THz. The hybrid periodic permanent-magnet design combined with the quadrupole magnet (PPM-QM), intended for low-duty pulse operation in a proof-of-concept experiment, allows the elliptical sheet beam from an existing gun (25 : 1 aspect ratio) to unoptimized gun to have 73% beam transmission. The POP pulsed test is designed to be matched to our existing system, which will thereby tolerate beam transmission. However, a proper gun for the sheet-beam tunnel of the designed circuit will provide much better transmission. In our prior works, we successfully proved at W-band that the magnet design provided >; 99% beam transmission of a 10:1 aspect ratio sheet beam. Most of the TWT circuit components have been designed, and currently, a full simulation modeling effort is being conducted.

Performance enhancement of a piezoelectric linear array transducer by half-concave geometric design

A geometric design for array elements of a piezoelectric linear array transducer is proposed and evaluated. The design concept is based on the half-concave geometry, in which the radiating surface is concave while the other surface remains plane. A ∼1.8 MHz piezoelectric linear array transducer with half-concave elements has been designed, fabricated and evaluated. A dicing method was developed to shape the concave surfaces of the piezo elements and matching layers. By comparing the transducer performance, a traditional linear array transducer with similar dimension has been fabricated. It was found that the half-concave array transducer has significantly broader −6 dB bandwidth (96%), higher effective electromechanical coupling coefficient (0.62), and lower insertion loss (−21 dB) compared to those (76%, 0.55, and −25 dB, respectively) of the plane array transducer. The enhanced coupling coefficient and bandwidth are caused by the broaden resonance of the elements, which is induced by the continuously varying thickness in the designed geometry. The increased sensitivity is mainly attributed to the focused radiating surface.

A Novel Broad Bandwidth and Compact Backward Coupler with High Couplinglevel

A novel backward microstrip coupled-line coupler which has been designed based on the metamaterial and composite right/left handed (CRLH) transmission line (TL) concepts is proposed. Coupling coefficient, bandwidth and size of proposed microstrip coupler are improved by coupled interdigital TLs which have been realized only by one interdigital capacitor. The design procedure to reach the coupler with predefined coupling coefficient and characteristic impedance of its ports is clearly presented. The designed and fabricated prototype is a 3-dB microstrip coupler with 0.2 mm spacing between its coupled lines over a wide bandwidth of 60% from 2. 3∼ 4 GHz centered at 3.2 GHz. The coupled-line length and the width of the proposed structure are approximately λg/4 and λg/36, respectively, which makes it more compact than the conventional cascaded CRLH microstrip coupledline couplers.

Hybrid orthogonal junctions: wideband plasmonic slot-silicon waveguide couplers

In this paper, novel ultra compact and ultra wide band couplers between silicon and plasmonic slot waveguides are analyzed, characterized, and fabricated. This novel coupling scheme is fabricated using silicon on insulator platform. An orthogonal junction configuration is designed to provide non-resonate wideband coupling from a 400 nm silicon waveguide to 50-nm wide air-filled plasmonic slot. The 1 μm wide full-width half-max coupling spectrum can theoretically reach high peak of 70% coupling to the plasmonic slot centered around the 1550 nm wavelength. This center wavelength can be controlled by varying the silicon waveguide width. Theoretical analysis is in good agreement with FDTD simulated results, and experimental results. The fabrication procedure is also presented and discussed.

Wafer-Level Testable High-Speed Silicon Microring Modulator Integrated with Grating Couplers

A wafer-level testable silicon-on-insulator-based microring modulator is demonstrated with high modulation speed, to which the grating couplers are integrated as the fiber-to-chip interfaces. Cost-efficient fabrications are realized with the help of optical structure and etching depth designs. Grating couplers and waveguides are patterned and etched together with the same slab thickness. Finally we obtain a 3-dB coupling bandwidth of about 60 nm and 10 Gb/s nonreturn-to-zero modulation by wafer-level optical and electrical measurements.

Compact Printed Arrays with Embedded Coupling Mitigation for Energy-Efficient Wireless Sensor Networking

Wireless sensors emerged as narrowband, resource-constrained devices to provide monitoring services over a wide life span. Future applications of sensor networks are multimedia-driven and include sensor mobility. Thus, sensors must combine small size, large bandwidth, and diversity capabilities. Compact arrays, offering transmit/receive diversity, suffer from strong mutual coupling (MC), which causes lower antenna efficiency, loss of bandwidth, and signal correlation. An efficient technique to reduce coupling in compact arrays is described herein: a defect was inserted in the ground plane (GNDP) area between each pair of elements. The defect disturbed the GNDP currents and offered multidecibel coupling suppression, bandwidth recovery, and reduction of in-band correlation. Minimal pattern distortion was estimated. Computational results were supported by measurements. The bandwidth of unloaded arrays degraded gracefully from 38% to 28% with decreasing interelement distance (0.25 to 0.10). Defect-loaded arrays exhibited active impedance bandwidths 37–45%, respectively. Measured coupling was reduced by 15–20 dB.

Development of Packaged Ultra-Wideband Bandpass Filters

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, we present a very compact ultra-wideband (UWB) filter (patent pending), which is integrated in a commercial leaded package. This UWB filter is designed through quasi-equally allocating the first three resonant frequencies of the stub-loaded resonator. Input/output excitation is realized by a technique of wire-bonded interdigital capacitors for obtaining strong wideband coupling. After formulating the resonance conditions and analyzing the characteristics of the stub-loaded resonator, an equivalent-circuit topology is developed and a single-stage prototype is fabricated. Measured results agree well with the results generated from both circuit and full-wave simulations. In order to improve the selectivity, two stages of stub-loaded resonators are cascaded. A two-stage prototype is then assembled in a commercial leaded package and measured with a test fixture. Both simulation and measurement results validate our proposed design methods and packaging solutions. This filter is the first demonstration of integrated UWB filters with a commercial package, which can be conveniently applied in UWB communication and radar systems. </para>

Ultra-Broadband Mode Conversion With Acousto-Optic Coupling in Hole-Assisted Fiber

This paper describes the acousto-optic properties of hole-assisted fibers (HAFs) numerically and experimentally. We show that the HAF beat length between the guided and first higher-order modes has small wavelength dependence compared with that of the single mode fiber and so we can achieve broadband acousto-optic coupling. Ultra-broadband acousto-optic coupling is realized by using a HAF with flattened beat length characteristics. The coupling bandwidth reaches 120 nm, and can be controlled by designing the air hole structure.

Cladding-modulated Bragg gratings in silicon waveguides

A cladding-modulated Bragg grating implemented using periodic placements of cylinders along a waveguide is proposed in a silicon-on-insulator platform. The coupling strength is varied by changing the distance between the cylinders and the waveguide. This implementation enables precise control and a wide dynamic range of coupling strengths and bandwidths that can be practically achieved for applications with specific bandwidth requirements. Modeling results are verified experimentally, and we demonstrate coupling strengths differing by 1 order of magnitude (43 and 921 per cm) with bandwidths of 8 and 16 nm, respectively. This method scheme enables weakly coupled devices with high fabrication tolerance to be realized.

Generation of 20 GHz, sub-40 fs pulses at 960 nm via repetition-rate multiplication

Optical filtering of a stabilized 1 GHz optical frequency comb produces a 20 GHz comb with approximately 40 nm bandwidth (FWHM) at 960 nm. Use of a low-finesse Fabry-Pérot cavity in a double-pass configuration provides a broad cavity coupling bandwidth (Deltalambda/lambda approximately 10%) and large suppression (50 dB) of unwanted modes. Pulse durations shorter than 40 fs with less than 2% residual amplitude modulation are achieved.

Wideband two-layer SIW coupler: design and experiment

An original wideband two-layer substrate integrated waveguide directional coupler is presented. The structure provides attractive features including a flexible design with a wideband coupling and independent control of the transmission phase for arbitrary coupling levels. Characteristics of 18 dB isolation and 90° phase shift between direct and coupled ports are experimentally validated over 16% bandwidth.