Improved switching uniformity and low-voltage operation in TaO x-based RRAM using Ge reactive layer

Significant improvements in the spatial and temporal uniformities of device switching parameters are successfully demonstrated in Ge/TaOx bilayer-based resistive switching devices, as compared with non-Ge devices. In addition, the reported Ge/TaOx devices also show significant reductions in the operation voltages. Influence of the Ge layer on the resistive switching of TaOx-based resistive random access memory is investigated by X-ray spectroscopy and the theory of Gibbs free energy. Higher uniformity is attributed to the confinement of the filamentary switching process. The presence of a larger number of interface traps, which will create a beneficial electric field to facilitate the drift of oxygen vacancies, is believed to be responsible for the lower operation voltages in the Ge/TaO x devices. © 1980-2012 IEEE.

Directly and parametrically excited bi-stable vibration energy harvester for broadband operation

Despite many recent advances, the wide-spread adoption of vibrational energy harvesting has been limited by the low levels of generated output power and confined operational frequency band. Recent work by the authors on parametrically excited harvesters has demonstrated over an order of magnitude power improvement. This paper presents an investigation into the simultaneous employment of both direct and parametric resonance, as well as the incorporation of bi-stability, in an attempt to further improve the mechanical-to-electrical energy conversion efficiency by broadening the output power spectrum. Multiple direct and parametric resonant peaks from a multi-degree-of-freedom system were observed and an accumulative ∼10 Hz half-power bandwidth was recorded for the first 40 Hz. Real vibration data was also employed to analysis the rms power response effectiveness of the proposed system. © 2013 IEEE.

Multi-frequency operation of a mems vibration energy harvester by accessing five orders of parametric resonance

The mechanical amplification effect of parametric resonance has the potential to outperform direct resonance by over an order of magnitude in terms of power output. However, the excitation must first overcome the damping-dependent initiation threshold amplitude prior to accessing this more profitable region. In addition to activating the principal (1st order) parametric resonance at twice the natural frequency ω0, higher orders of parametric resonance may be accessed when the excitation frequency is in the vicinity of 2ω0/n for integer n. Together with the passive design approaches previously developed to reduce the initiation threshold to access the principal parametric resonance, vacuum packaging (< 10 torr) is employed to further reduce the threshold and unveil the higher orders. A vacuum packaged MEMS electrostatic harvester (0.278 mm3) exhibited 4 and 5 parametric resonance peaks at room pressure and vacuum respectively when scanned up to 10 g. At 5.1 ms-2, a peak power output of 20.8 nW and 166 nW is recorded for direct and principal parametric resonance respectively at atmospheric pressure; while a peak power output of 60.9 nW and 324 nW is observed for the respective resonant peaks in vacuum. Additionally, unlike direct resonance, the operational frequency bandwidth of parametric resonance broadens with lower damping. © Published under licence by IOP Publishing Ltd.

Monolithic MZI-SOA hybrid switch for low-power and low-penalty operation.

We report the first experimental demonstration of a monolithically integrated hybrid dilated 2×2 modular optical switch using Mach-Zehnder modulators as low-loss 1×2 switching elements and short semiconductor optical amplifiers to provide additional extinction and gain. An excellent 40 dB cross-talk/extinction ratio is recorded with data-modulated signal-to-noise ratios of up to 44 dB in a 0.1 nm bandwidth. A switching time of 3 ns is demonstrated. Bit error rate studies show extremely low subsystem penalties of less than 0.1 dB, and studies indicate that, by using this hybrid switch building block, an 8×8 port switch could be achieved with 14 dB input power dynamic range for subsystem penalties of less than 0.5 dB.

Tailoring carbon nanostructure for high frequency supercapacitor operation

The possibility of enhancing the frequency performance of electrochemical capacitors by tailoring the nanostructure of the carbon electrode to increase electrolyte permeability is demonstrated. Highly porous, vertically oriented carbon electrodes which are in direct electrical contact with the metallic current collector are produced via MPECVD growth on metal foils. The resulting structure has a capacitance and frequency performance between that of an electrolytic capacitor and an electrochemical capacitor. Fully packaged devices are produced on Ni and Cu current collectors and performance compared to state-of-the-art electrochemical capacitors and electrolytic capacitors. The extension of capacitive behavior to the AC regime (100 Hz) opens up an avenue for a number of new applications where physical volume of the capacitor may be significantly reduced. © 2014 Pritesh Hiralal et al.

High efficiency operation of butt joint line-defect-waveguide microlaser in two-dimensional photonic crystal slab

Butt joint line-defect-waveguide microlasers are demonstrated on photonic crystal slabs with airholes in a triangular lattice. Such microlaser is designed to increase the output power from the waveguide edge directly. The output power is remarkably enhanced to 214 times higher by introducing chirped structure in the output waveguide. The lasing mode operates in the linear dispersion region of the output waveguide so that the absorption loss due to the band-edge effect is reduced. The laser resonance is illustrated theoretically using the finite difference time domain method. A practical high power efficiency of 20% is obtained in this microlaser. (C) 2008 American Institute of Physics.

Single mode operation of a Fabry-Perot laser locked by a tunable laser

In this article, the single mode operation of a Fabry-Perot laser (FP-LD) subject to the optical injection from a tunable laser is investigated. The maximum side mode suppression ratio (SMSR) is 53 dB, and the locked wavelength range is about 46 nm, which can cover 58 International Telecommunication Union (ITU) wavelengths with 100 GHz spacing or 115 ITU wavelengths with 50 GHz spacing for wavelength division multiplexing (WDM) system. In the wavelength range front 1535 to 1569 nm, the SMSR is over 46 dB, and the frequency response of the injection-locked FP-LD can be improved with the proper wavelength detuning. (c) 2008 Wiley Periodicals, Inc.

Continuous-wave operation of GaN based multi-quantum-well laser diode at room temperature

Room-temperature operation of cw GaN based multi-quantum-well laser diodes (LDs) is demonstrated. The LD structure is grown on a sapphire (0001) substrate by metalorganic chemical vapour deposition. A 2.5 mu m x 800 mu m ridge waveguide structure is fabricated. The electrical and optical characteristics of the laser diode under direct current injection at room temperature are investigated. The threshold current and voltage of the LD under cw operation are 110mA and 10.5V, respectively. Thermal induced series resistance decrease and emission wavelength red-shift are observed as the injection current is increased. The full width at half maximum for the parallel and perpendicular far field pattern (FFP) are 12 degrees and 32 degrees, respectively.

High-power operation of uncoated strain-compensated quantum cascade lasers at 4.8 mu m

High-power operation of uncoated 22-mu m-wide quantum cascade lasers (QCLs) emitting at lambda approximate to 4.8 mu m is reported. The emitting region of the QCL structure consists of a 30-period strain-compensated In0.68Ga0.32As/In0.37Al0.63As superlattice. For a 4-mm-long laser in pulsed mode, a peak output power is achieved in excess of 2240mW per facet at 81K with a threshold current density of 0.64kA/cm(2). The effects of varying the cavity lengths from 1 to 4mm on the performances of the QCLs are analysed in detail and the low waveguide loss of only about 1.4 cm(-1) is extracted.

High-Temperature Continuous-Wave Single-Mode Operation of 1.3 mu m p-Doped InAs-GaAs Quantum-Dot VCSELs

In this letter, we have demonstrated continuous-wave single-mode operation of 1.3-mu m InAs-GaAs quantum-dot (QD) vertical-cavity surface-emitting lasers (VCSELs) with p-type modulation-doped QD active region from 20 degrees C to 60 degrees C. The highest output power of 0.435mW and lowest threshold current of 1.2 mA under single-mode operation are achieved. The temperature-dependent output characteristics of QD-VCSELs are investigated. Single-mode operation with a sidemode suppression ratio of 34 dB is observed at room temperature. The critical size of oxide aperture for single-mode operation is discussed.

Quasi-continuous-wave operation of AlGaAs/GaAs quantum cascade lasers

Quasi-continuous-wave operation of AlGaAs/GaAs-based quantum cascade lasers (lambda similar to 9 mu m) up to 165 K is reported. The strong temperature dependence of the threshold current density and its higher value in high duty cycle is investigated in detail. The self-heating effect in the active region is explored by changing the operating duty cycles. The degradation of lasing performance with temperature is explained. (c) 2005 Elsevier B.V. All rights reserved.

High temperature operation of 5.5 mu m strain-compensated quantum cascaded lasers

We develop 5.5-mu m InxGa1-xAs/InyAl1-yAs strain-compensated quantum cascade lasers with InP and InGaAs cladding layers by using solid-source molecular-beam epitaxy. Pulse operation has been achieved up to 323 K (50 degrees C) for uncoated 20-mu m-wide and 2-mm-long devices. These devices display an output power of 36 mW with a duty cycle of 1% at room temperature. In continuous wave operation a record peak optical power of 10 mW per facet has been measured at 83 K.