Ian Armstrong

An Adjustable Gain-Clamped Semiconductor Optical Amplifier (AGC-SOA)

The operation of a semiconductor optical amplifier (SOA)-ring laser-based subsystem, with the capability to provide adjustable gain-clamped operation, will be described, and preliminary characterization results will be presented. The device uses two SOAs in a ring-cavity topology: one to amplify the signal and the other to control the gain. This type of subsystem finds applications in packet-based dynamic systems where it may be used for power equalization and linear amplification.

Polarization-Insensitive SOAs Using Strained Bulk Active Regions

The polarization dependent gain (PDG) and its control is a key issue for semiconductor optical amplifier devices. For the case of a strained bulk active region with lateral tapers, an analysis of the parameters that affect PDG is performed, and the magnitude of its variation is calculated. The critical design parameters are thus identified, and the expected PDG variance is discussed in the context of typical fabrication tolerances

High-Performance Semiconductor Optical Amplifier Modules at 1300 nm

Semiconductor-based optical amplifiers (SOAs) offer solutions to a variety of amplification requirements covering operational wavelengths ranging from 600 to 1600 nm. This letter reports on the design and performance of buried heterostructure SOA modules exhibiting state-of-the-art performance within the 1300-nm operational window. The first, a high-gain variant, is optimized for preamplification applications while the second is designed for use as a booster amplifier. Record low noise figure performances for packaged devices are reported

Semiconductor optical amplifiers: performance and applications in optical packet switching (Invited)

Semiconductor optical amplifiers (SOAs) are a versatile core technology and the basis for the implementation of a number of key functionalities central to the evolution of highly wavelength-agile all-optical networks. We present an overview of the state of the art of SOAs and summarize a range of applications such as power boosters, preamplifiers, optical linear (gain-clamped) amplifiers, optical gates, and modules based on the hybrid integration of SOAs to yield high-level functionalities such as all-optical wavelength converters/regenerators and small space switching matrices. Their use in a number of proposed optical packet switching situations is also highlighted.

Detection of CH

This paper demonstrates detection of methane using tunable diode laser spectroscopy (TDLS) through difference frequency generation (DFG) in order to address fundamental rotational-vibrational absorption lines, located around 3404 nm. Direct detection confirms that wavelength referencing of recovered lineshapes, developed for Near infra-red (Near-IR) systems, has been successfully transferred to the presented Middle infra-red (Mid-IR) system. Traditional 1f and 2 f TDLS with WMS detection regimes are also functionally confirmed analogous to their Near-IR equivalents.

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We report on the development of three systems intended to provide fast, non-intrusive measurement of cross-sectional distributions of pollutant species within gas turbine exhaust flows, during ground-based testing. This research is motivated by the need for measurement systems to support the introduction of technologies for reducing the environmental impact of civil aviation. Tomographic techniques will allow estimation of the distributions of CO2, unburnt hydrocarbons (UHC), and soot, without obstruction of the exhaust, bypass or entrained flows, from measurements made in a plane immediately aft of the engine.

in the Mid-IR Using Difference Frequency Generation With Tunable Diode Laser Spectroscopy

The current work presents a correlation-based detection technique with application in modulated laser-ultrasonics. In standard use of coded sequences the impulse response of a system is recovered in the time domain with improved signal to noise ratio (SNR). The presented method is an extension of this technique, where the response to a chirped waveform is restored with improved SNR; hence, the response is in a well-defined frequency range. To achieve this goal the chirped waveforms are modulated by Golay codes. It will be shown that the response to this bandlimited carrier waveform can be recovered in the time domain with improved signal to noise ratio using a cross-correlation technique. Improvement in the SNR is discussed analytically and it is shown that this improvement is proportional to the square root of the length of the applied sequences. Experimental applications in laser-ultrasound are shown using modulated laser diodes as excitation sources with an output power of ∼1W. In the experiments a plate with a thickness of 50μm is investigated using Lamb waves in the MHz range to confirm the predicted improvement in the SNR. Golay codes with three different lengths were used with 7, 9 and 11 bits resulting in 2(7)=128, 2(9)=512, and 2(11)=2048 repetitions in an individual signal, respectively. The predicted improvements of 2 in the SNR between the 7 and 9 bits, and between the 9 and 11 bits waveforms, respectively, were well approximated by the experimentally obtained values of 1.83 and 2.17. As Lamb wave dispersion curves can be used for the characterization of plates or layered samples by inverse problems, it is also shown that by using multiple measurement points the recovered waveforms can be utilized in the evaluation of the dispersion relation.

Progress towards non-intrusive optical measurement of gas turbine exhaust species distributions

This paper reports a simple technique to measure the anisotropy of the Youngs modulus of MEMS materials using coupled cantilevers. The technique is demonstrated in single-crystal silicon with an array of cantilevers fabricated in (100) silicon following a “wagon wheel” configuration. The long axis of the cantilevers had different angular orientations to the [110] direction. The parasitic coupling due to undercut below the cantilevers, which is often observed during etching of MEMS, led to a collective behavior in the frequency response of the cantilevers. This collective behavior was used in association with an inverse eigenvalue analysis to obtain the Youngs moduli for the different orientations. Further analysis of the technique relating to accuracy and precision required in the resonance frequency measurement has also been presented.

Golay code modulation in low-power laser-ultrasound ☆

The development of a high-performance hybrid integration platform is demonstrated using an all-optical wavelength converter based on an integrated semiconductor optical amplifier (SOA) Mach-Zehnder interferometer (MZI). The device structure, transfer functions, power penalties and regenerative properties are presented for data rates up to 10 Gb/s.

Determination of the Anisotropy of Young's Modulus Using a Coupled Microcantilever Array

The use of low power modulated laser diode systems has previously been established as a suitable method for non-destructive laser generation of ultrasound. Using a quasi-continuous optical excitation amplified by an erbium-doped fibre amplifier (EDFA) allows flexible generation of ultrasonic waves, offering control of further parameters such as the frequency content or signal shape. In addition, pseudo-random binary sequences (PRBS) can be used to improve the detected impulse response. Here we compare two sequences, the m-sequence and the Golay code, and discuss the advantages and practical limits of their application with laser diode based optical excitation of ultrasound.