High-speed wavelength conversion utilizing birefringence in semiconductor optical amplifiers

This paper describes a novel technique whereby a mixture of cross-phase and cross-gain modulation effects in an SOA causes polarization rotation of a cw probe beam in the presence of a signal pulse, enabling the transmission of the probe through a polarizer to be controlled. The benefits of this approach are: 1) Very high extinction ratios present in the wavelength converted signal (>30 achieved); 2) A non-inverted wavelength converted signal, which is advantageous for chirp-compensation;2 3) A simple and stable experimental set-up, 4) Converted pulses which can be shaped to be faster than the input pulses.

Chirp limitation on high-speed wavelength conversion using semiconductor optical amplifiers

The cross-gain-saturation effect in SOAs, has been shown to enable robust high-speed wavelength conversion. Under strong electrical and optical pumping, conversion speeds in excess of 20 Gbit/s have been illustrated. However, the effect of chirp on transmission distance at such ultrahigh bit rates has not been studied theoretically in detail. This paper considers the chirp introduced on conversion, employing cross-gain saturation, and studies its dependence on amplifier drive current and signal power. It further shows how an increase in injected cw optical power can reduce chirp while improving conversion speed.

High speed wavelength conversion utilising an integrated amplifier/DFB laser

Wavelength conversion in the 1.55-μm regime was achieved for the first time in an integrated SOA/DFB laser by modulating the output power of the laser with a light beam of a different wavelength externally injected into the SOA section. In terms of speed, response times as low as 13ps were observed, though at the expense of reduced extinction ratio. Generally, these results indicate that operation in the 10s of GB/s should be possible.

High speed performance of Mach-Zehnder all-optical regenerators using semiconductor optical amplifiers

Interferometric Optical Wavelength Converters (IOWCs) provide wavelength conversion functionality at high bit rates, and give low chip and enhanced extinction ratio compared with Cross-Gain wavelength converters. In paper, a numerical simulation is conducted to assess the noise performance of IOWC and its potential for cascading. The details of the experiment and the results obtained are presented.

Feasibility of AlGaInAs lasers for high speed uncooled communication systems

The feasibility of using AlGaInAs lasers for high-speed modulation at high temperatures was evaluated and compared with performance of GaInAsP devices. Both drift-diffusion and rate equation simulation were involved so that the temperature dependence of material parameters was found in terms of overall dynamic performance. Differential gain was estimated by means of drift-diffusion simulations.

Analysis of the mechanisms for impaired high-temperature, high-speed performance of 1.3 μm InGaAsP lasers

In this paper, the static and dynamic performance of multi quantum-well (MQW) 1.3 μm InGaAsP Fabry Perot lasers is assessed experimentally and theoretically to identify the mechanisms responsible for impaired high speed performance at elevated temperature. Initially, threshold currents and spontaneous emission spectra are characterized for a range of temperatures from room temperature to 85 °C to indicate a significant increase in non-radiative current contributions. Preliminary estimates are made for the contributions of leakage and Auger recombination rates, found from the dependence of integrated spontaneous emission with carrier density. Drift-diffusion modelling is found to accurately predict the trend of threshold currents over temperature. Using gain modelling good agreement is found between the measured and predicted integrated spontaneous emission intensity. Gain measurements at 85 °C indicate a reduction in RIN frequency to 63% of the 25 °C value which matches well with experimental small signal performance.

High speed reconfiguration of dual-purpose vertical cavity surface emitting laser/detector

High-speed configuration results of a conventional 850 nm VCSEL that is modified to operate as an efficient avalanche detector as well as a laser are discussed. The measured laser-to-detector reconfiguration delay of 3.2 ns is longer than the 1.2 ns detector-to-detector reconfiguration delay.

The effects of a trip wire and unsteadiness on a high speed highly loaded low-pressure turbine blade

This paper presents the effect of a single spanwise 2D wire upon the downstream position of boundary layer transition under steady and unsteady inflow conditions. The study is carried out on a high turning, high-speed, low pressure turbine (LPT) profile designed to take account of the unsteady flow conditions. The experiments were carried out in a transonic cascade wind tunnel to which a rotating bar system had been added. The range of Reynolds and Mach numbers studied includes realistic LPT engine conditions and extends up to the transonic regime. Losses are measured to quantify the influence of the roughness with and without wake passing. Time resolved measurements such as hot wire boundary layer surveys and surface unsteady pressure are used to explain the state of the boundary layer. The results suggest that the effect of roughness on boundary layer transition is a stability governed phenomena, even at high Mach numbers. The combination of the effect of the roughness elements with the inviscid Kelvin-Helmholtz instability responsible for the rolling up of the separated shear layer (Stieger [1]) is also examined. Wake traverses using pneumatic probes downstream of the cascade reveal that the use of roughness elements reduces the profile losses up to exit Mach numbers of 0.8. This occurs with both steady and unsteady inflow conditions.

High speed electro-thermal models for inverter simulations

This paper presents the application of advanced compact models of the IGBT and PIN diode to the full electrothermal system simulation of a hybrid electric vehicle converter using a look-up table of device losses. The Fourier-based solution model is used, which takes account of features such as local lifetime control and field-stop technology. Device and circuit parameters are extracted from experimental waveforms and device structural data. Matching of the switching waveforms and the resulting generation of the look-up table is presented. An example of the use of the look-up tables in simulation of inverter device temperatures is also given, for a hypothetical electric vehicle subjected to an urban driving cycle. © 2006 IEEE.

High speed titanium coatings by supersonic laser deposition

The importance of metal coating technologies drives the continuous improvement of metal deposition techniques for application in a wide range of industrial sectors. This work presents the foundations of a new process technology for the deposition of titanium coatings on steel tube substrates using supersonic powder streams and impact site laser heating, known as Supersonic Laser Deposition (SLD). Metallic deposits are obtained under appropriate impact conditions without the need for exceeding the melting point of the deposited material or substrate leading to improved coating quality. Details of the experimental approach are presented along with the general characteristics of the titanium coating produced using this novel coatings method. © 2011 Elsevier B.V. All rights reserved.