High Input Power Levels Research Articles

Next-Generation Optical Fronthaul Systems Using Multicore Fiber Media

This paper proposes and investigates the use of multicore fiber (MCF) media performing space-division multiplexed transmission for next-generation optical fronthaul systems. We report the experimental demonstration of combined radio-over-fiber (RoF) transmission of full-standard LTE-Advanced (LTE-A) and WiMAX signals providing fronthaul connectivity in 150 m of 4-core fiber (4CF), transmitting simultaneously fully independent wireless services. Operating in linear and nonlinear optical power regimes, the experimental evaluation verifies that the error vector magnitude (EVM) is not degraded when intercore and intracore Kerr nonlinearities are excited in MCF with high input power levels. As a result, nonlinear regime is proposed as a key factor to reduce the temporal EVM fluctuation induced by the random nature of the intercore crosstalk in MCF. In addition, MCF fronthaul applied to converged fiber-wireless polarization multiplexed passive optical networks is demonstrated to transmit LTE-A and WiMAX signals over two orthogonal optical polarizations. The polarization-multiplexed signal is transmitted in RoF over 25.2 km of standard single-mode fiber and then demultiplexed and injected in different cores of the 4CF to provide fronthaul connectivity. Finally, the extension of multicore optical fronthaul capacity is proposed using MIMO LTE-A signals. The tolerance of the MIMO LTE-A RoF transmissions to in-band crosstalk is reported and compared to single-input single-output (SISO) configuration. The experimental results indicate that MIMO configuration is more tolerant than SISO to in-band crosstalk considering both internal and external interferences. MIMO and SISO configurations are compared when transmitted in RoF over a 4CF operating in linear and nonlinear regimes and core interleaving nonlinear stimulation is proposed to reduce the temporal and spectral EVM fluctuation when the same wireless standard is propagated in each core.

Plasma dissociation of zircon with concurrent in-flight removal of silica

Dissociation of zircon through thermal plasma has been conventionally carried out in argon or nitrogen medium at high input power levels. This paper discusses a promising one-step process for in-flight dissociation of zircon to produce zirconia in air plasma medium. A specially designed plasma torch consisting of a hollow cathode made of graphite and graphite anode nozzle was used to produce the air plasma jet. Further, the influence of carbon addition with zircon on the dissociation process in air plasma medium was examined. Thermodynamic analysis using free energy minimization plot showed that addition of carbon significantly promoted the reaction by lowering the dissociation temperature. Temperature profile of the plasma jet obtained from simulation studies showed that air plasma provided an extended hot zone with much lower temperature gradient and this facilitated efficient processing of zircon. Results of these investigations showed that addition of carbon enhances the dissociation of zircon along with simultaneous removal of silica at lower power level.

Non-reciprocal acoustic devices based on spatio-temporal angular-momentum modulation

Acoustic devices that break reciprocity, for instance acoustic isolators or circulators, may find exciting applications in a variety of fields, including imaging, acoustic communication systems, and noise control. Non-reciprocal acoustic propagation has typically been achieved using non-linear phenomena, which require high input power levels and introduce distorsions. In contrast, we have recently demonstrated compact linear isolation for audible airborne sound by means of angular momentum bias [Fleury et al., Science 343, 516 (2014)], exploiting modal splitting in a ring cavity polarized by an internal, constantly circulating fluid, whose motion is imparted using low-noise CPU fans. We present here an improved design with no moving parts, which is directly scalable to ultrasonic frequencies and fully integrable. Instead of imparting angular momentum in the form of a moving medium as in our previous approach, we make use of spatio-temporal acoustic modulation of three coupled acoustic cavities, a strategy that can be readily implemented in integrated ultrasonic devices, for instance, using piezoelectric effects. In this new paradigm, the required modulation frequency is orders of magnitude lower than the signal frequency, and the modulation efficiency is maximized. This constitutes a pivotal step towards practically realizing compact, linear, noise-free, tunable non-reciprocal acoustic components for full-duplex acoustic communications and isolation.

Triple transit region photodiodes (TTR-PDs) providing high millimeter wave output power

We report on a novel triple transit region (TTR) layer structure for 1.55 μm waveguide photodiodes (PDs) providing high output power in the millimeter wave (mmW) regime. Basically, the TTR-PD layer structure consists of three transit layers, in which electrons drift at saturation velocity or even at overshoot velocity. Sufficiently strong electric fields (>3000 V/cm) are achieved in all three transit layers even in the undepleted absorber layer and even at very high optical input power levels. This is achieved by incorporating three 10 nm thick p-doped electric field clamp layers. Numerical simulations using the drift-diffusion model (DDM) indicate that for optical intensities up to ~500 kW/cm(2), no saturation effects occur, i.e. the electric field exceeds the critical electric field in all three transit layers. This fact in conjunction with a high-frequency double-mushroom cross-section of the waveguide TTR-PD ensures high output power levels at mmW frequencies. Fabricated 1.55 µm InGaAs(P)/InP waveguide TTR-PDs exhibit output power levels exceeding 0 dBm (1 mW) and a return loss (RL) up to ~24 dB. Broadband operation with a 3 dB bandwidth beyond 110 GHz is achieved.

Compact waveguide broadband dual-polarized horn array with a novel orthomode transducer in Ku-band for high-power SAR systems

A novel compact waveguide-based broadband and dual-polarized Ku-band Synthetic Aperture Radar antenna with a high level of isolation between polarizations and high input power level has been designed for small platforms and unmanned aerial vehicles (UAV). The antenna design is composed of 8 dual-polarized horn antennas in an array configuration fed through a very efficient and novel structure to generate two orthogonal polarizations based on a orthomode transducer to achieve a large bandwidth and an excellent isolation between polarizations needed in a polarimetric system. Finally, as the antenna will be placed inside a pod under the UAV wings it must be lightweight, robust and of small size.

2–4 GHz wideband power amplifier with ultra‐flat gain and high PAE

Demonstrated is a 2–4 GHz wideband power amplifier (WPA) using Cree 10 W GaN HEMT CGH40010. Also a novel process to find the optimum impedances is presented, with which the gain flatness can be taken into account. A compact PCB has been fabricated and tested with continuous waves at low (20 dBm) and high (28 dBm) input power level. From the measured results, at low power level, the gain is 13.1–14.1 dB across 2.0–3.9 GHz and 12.3–14.1 dB across 2.0–4.0 GHz. For large signals, power gain is 11.1–12.6 dB with power-added efficiency (PAE) 36.5–53.4% while output power is around 40 dBm. Gain flatness keeps less than 1 dB beyond 95% of the band. For a 5 MHz WCDMA signal, the adjacent channel leakage ratio of the WPA with digital predistortion reaches − 45.3 dBc with an average drain efficiency of 46.7%.

A 3.5‐GHz three‐stage doherty power amplifier with bias controller using power tracking method

AbstractThis letter represents a three‐stage Doherty power amplifier with a bias controller.The driving amplifier controls the input power of the carrier cell to eliminate the gate current of the carrier cell at high input power levels. The gate bias voltage of the driving amplifier is controlled by a power tracking method according to input power levels. For verifications, the driving amplifier, carrier, and peaking cells are fabricated using 10‐W, 15‐W, 35‐W gallium nitride high electron mobility transistors, respectively, at 3.5 GHz. From a continuous wave, the power‐added efficiencies (PAEs) of 34.4 and 39.6% are achieved at ∼9.5‐ and 4.3‐dB back‐off powers, respectively. For a worldwide interoperability for microwave access signal, the proposed DPA has the PAE of 37.1 % at an output power of 41.5 dBm. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:23–26, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26474

Acoustic emission spectra and sonochemical activity in a 36 kHz sonoreactor

During ultrasound-induced cavitation in liquids, acoustic emissions at fundamental and harmonic frequencies can be detected. The effect of acoustic emissions at harmonic frequencies on the sonochemical and sonophysical activities has not been explored, especially in large-scale sonoreactors. In this study, the acoustic emissions in the range, 0–250 kHz in a 36 kHz sonoreactor with varying liquid heights were studied and compared with the sonochemical activities. The acoustic pressures at both fundamental and harmonics decreased drastically as the liquid height was increased due to the attenuation of sound energy. It was observed that the increase in input power resulted in only an increase in the acoustic emissions at derivative frequencies such as, harmonics and subharmonics. The sonochemical activity, evaluated in terms of sonochemiluminescence and H 2O 2 yield, was not significantly enhanced at higher input power levels. This suggests that at higher power levels, the “extra” acoustic energy is not effectively used to generate primary cavitation activity; rather it is converted to generate acoustic emissions at harmonic and subharmonic frequencies. This is an important observation for the design of energy efficiency large-scale sonochemical reactors.

Analog Pre-Distortion Linearizer Using Self Base Bias Controlled Amplifier

An analog pre-distortion linearizer employing a radio frequency (RF) transistor with a self base bias control circuit is proposed. The self base bias control circuit extracts the envelope from the modulated input RF signal of the RF transistor and automatically controls its base current according to the extracted envelope. As a result, the proposed linearizer realizes positive gain deviation at high input power level. By adding a resistor between the RF transistor and the self base bias control circuit, the negative gain deviation can be derived. The design of the proposed lineaizer is described with taking the envelope frequency response of the self base bias control circuit into consideration. The fabricated linearizer achieves the adjacent channel power leakage ratio (ACLR) improvement of 8.1dB for a 2GHz-band, 10W-class GaAs FET high-power amplifier (HPA) with negative gain deviation for W-CDMA base stations. It also achieves the ACLR improvement of 8.3dB for a LDMOS HPA with positive gain deviation for the same application.

A passive dual‐circulator based transmit/receive switch for use with reflection resonators in pulse electron paramagnetic resonance

In order to protect the low noise amplifier (LNA) in the receive arm of a pulsed 250 MHz EPR bridge, it is necessary to install as much isolation as possible between the power exciting the spin system and the LNA when high power is present in the receive arm of the bridge, while allowing the voltage induced by the magnetization in the spin sample to be passed undistorted and undiminished to the LNA once power is reduced below the level that can cause a LNA damage. We discuss a combination of techniques to accomplish this involving the power-routing circulator in the bridge, a second circulator acting as an isolator with passive shunt PIN diodes immediately following the second circulator. The low resistance of the forward biased PIN diode passively generates an impedance mismatch at the second circulator output port during the high power excitation pulse and resonator ring down. The mismatch reflects the high power to the remaining port of the second circulator, dumping it into a system impedance matched load. Only when the power diminishes below the diode conduction threshold will the resistance of the PIN diode rise to a value much higher than the system impedance. This brings the device into conduction mode. We find that the present design passively limits the output power to 14 dBm independent of the input power. For high input power levels the isolation may exceed 60 dB. This level of isolation is sufficient to fully protect the LNA of pulse EPR bridge.

Hot electron effects and nonlinear transport in hole doped manganites

We show that strong nonlinear electron transport in the ferromagnetic insulating (FMI) state of manganites, responsible for phenomena such as colossal electroresistance and current induced resistance switching, can occur due to a hot electron effect. In the FMI state, which we show is an insulator with a Coulomb gap, the temperature of the electron and lattice baths can decouple at high input power levels, leading to heating of the electron bath. Parameters of the hot electron effect model were independently determined via time dependence experiments and are in good agreement with the experimental values.

A Gaussian Approximation of High-Order Distortion Spectrum in Broadband Amplifiers

A novel analytical Gaussian approximation is developed for the evaluation of the distortion spectrum introduced by a nonlinear amplifier. This method allows to consider high-order distortion contributions when the device is driven by a broadband signal with Gaussian amplitude distribution. The results are applied to a ninth-order power series model based on well known single-tone and two-tone analysis parameters. The cascade of two or more amplifiers is investigated as well providing a complete set of tools for the early system specification of broadband transceivers. Simulations shows excellent agreement even for high input power levels, when former third-order and fifth-order approximations fail to yield accurate predictions.

Excitation of strongly confined scalar and vector self-trapped beams in one-dimensional arrays of Kerr-nonlinear channel waveguides

The excitation and propagation of both scalar and vector optical waves in one-dimensional nonlinear arrays of channel waveguides was investigated both theoretically and experimentally. In this arrangement vector discrete solitons are also possible through the coexistence of two orthogonally polarized fields. At high input power levels a rapid collapse of the power back to the incidence channel occurred over a small power range for both scalar and vector inputs.

A fully monolithic 260-/spl mu/W, 1-GHz subthreshold low noise amplifier

A micro-power complementary metal oxide semiconductor (CMOS) low-noise amplifier (LNA) is presented based on subthreshold MOS operation in the GHz range. The LNA is fabricated in an 0.18-μm CMOS process and has a gain of 13.6 dB at 1 GHz while drawing 260 μA from a 1-V supply. An unrestrained bias technique, that automatically increases bias currents at high input power levels, is used to raise the input P1dB to -0.2 dBm. The LNA has a measured noise figure of 4.6 dB and an IIP3 of 7.2 dBm.

All optical switching and continuum generation in silicon waveguides

First demonstration of cross phase modulation based interferometric switch is presented in silicon on insulator waveguides. By using Mach-Zehnder interferometric configuration we experimentally demonstrate switching of CW signal ~25 nm away from the pump laser. We present the effect of free carrier accumulation on switching. Additionally, we theoretically analyze the transient effects and degradations due to free carrier absorption, free carrier refraction and two photon absorption effects. Results suggest that at low peak power levels the system is governed by Kerr nonlinearities. As the input power levels increase the free carrier effects becomes dominant. Effect of free carrier generation on continuum generation and power transfer also theoretically analyzed and spectral broadening factor for high input power levels is estimated.

A time-delay equivalent-circuit model of ultrafast p-i-n photodiodes

A time-delay equivalent-circuit model of ultrafast p-i-n photodiodes (PDs) is proposed to describe the operation at high-input power levels. This model includes both the carrier transit-induced time-delay effect and stored charge effect of p-i-n PDs in high-power operation. These effects were represented as a linear RC circuit and capacitance, respectively, both combined in parallel to a voltage-controlled current source. The validity of this model was confirmed with good curve fitting to the measured optical-frequency responses of an ultrafast side-illuminated p-i-n PD.

Observation of highly nonlinear surface-acoustic waves on single crystal lithium–niobate plates by means of an optical sampling probe

A new type of laser probe for observation of surface-acoustic waves (SAWs) is presented. The probe operation is based on the knife-edge technique combined with an optical sampling method that employs a pulsed laser beam. The spatial resolution of the probe is 1.3 μm and its bandwidth is greater than 1 GHz. A highly nonlinear SAW involving 10 harmonics on single-crystal lithium-niobate (LiNbO3) plates has been studied at the input frequency 200 MHz. It is shown that the initially sinusoidal wave breaks into a train of pulses up to four per period with the evolution of time. The spectrum data were related to SAW harmonic generation studied previously under similar conditions. Head-to-head collision of two SAW wave packets of 500 ns duration has been studied. It was confirmed that the wave forms are preserved in the collision. In addition, the effect of nonlinear diffraction of a SAW driven by high input power levels was observed. The present probe is found to be a powerful tool for elucidation of SAW solitons.

Brillouin light-scattering observation of the nonlinear spin-wave decay in yttrium iron garnet thin films

The direct observation of nonlinear spin-wave decay in thin yttrium iron garnet (YIG) films is reported. The second-order parametric spin waves were excited by a series of nonlinear magnetostatic backward volume wave (MSBVW) pulses propagated in a microstrip structure at 5 GHz. Brillouin light-scattering techniques were used to detect spin waves in the YIG at a point along the propagation path. Data were obtained as a function of the input pulse duty cycle and peak power level. These data yielded the decay rate ${\ensuremath{\eta}}_{\mathrm{eff}}$ for the parametric spin waves vs input power ${P}_{\mathrm{in}}.$ This ${\ensuremath{\eta}}_{\mathrm{eff}}$ was equal to the usual spin-wave relaxation rate at low power, but decreased rapidly with increasing ${P}_{\mathrm{in}}.$ As ${P}_{\mathrm{in}}$ approached the threshold power for complete MSBVW soliton formation at the observation point, ${\ensuremath{\eta}}_{\mathrm{eff}}$ leveled off to a relatively constant value that was about a factor of 5--10 smaller than the low power value. The initial decrease in ${\ensuremath{\eta}}_{\mathrm{eff}}$ with power is due to the compensation of the usual spin-wave decay by the simultaneous parametric pumping of the spin waves by Suhl processes. The leveling off in ${\ensuremath{\eta}}_{\mathrm{eff}}$ at the soliton threshold is due to the spin-wave shedding that is needed to maintain order one eigenmode soliton propagation at high input power levels. These experiments demonstrate the reduction in the spin-wave decay rate with power below the threshold for spin-wave instability. This reduction is a key element in spin-wave instability theory that has never been observed directly. The data also demonstrate the enhanced production of parametric spin waves that accompanies microwave magnetic envelope soliton formation.

Nonlinear microwave-magnetic resonator operated as a bistable device

The excitation of large amplitude spin waves causes a shift in the resonance frequency of a ferrite resonator towards higher frequency values. Using this shift, a resonator can be designed to operate in a bistable mode where the history of the input power determines the output power. A theoretical calculation for a resonator with a linewidth of 1.5 MHz, measured at 10 GHz, predicts a discontinuous jump in output power by a factor of about 3.5 as the input power is increased to about 0.7 mW. The phenomenological model that describes the bistability also provides an explanation for the foldover of ferromagnetic resonance curves at high input power levels. An appropriate choice for the operating frequency ensures that the estimated input power required to observe the bistable behavior is below the predicted threshold power for spin-wave auto-oscillations at the main resonance.

Characteristics of resistance welding of lap shear coupons. Part I: Heat transfer

Abstract A transient three-dimensional finite element model for resistance welding of thermoplastic matrix composite lap shear specimens was established. The basic model assumes orthotropic heat conduction in the composite parts and accounts for heat losses by radiation as well as natural convection, involving latent heat effects. The rough contact surface between the heating ply and composite adherends was simulated by means of a thermal gap-conductance concept. Heat generation through the bundles of fibres in the heating ply was modelled. Different welding configurations of lap shear specimens were evaluated, namely APC-2 laminate/PEEK film, APC-2 laminate/PEI film and CF-PEI laminate/PEI film. `Time to melt' and `time to cause thermal degradation' were predicted and compared with experimental data available in the literature, and close agreement was obtained. Localised thermal degradation at the bonding interface was identified for high input power levels, and heat flow to the bulk laminate for long processing times was exhibited.