Peter M. Farrell

Switching Energy and Device Size Limits on Digital Photonic Signal Processing Technologies

The relationship between device size and power consumption of photonic signal processing devices is derived using device-specific models for photonic signal processing using semiconductor optical amplifiers, periodically poled lithium niobate, and highly nonlinear fibers. The results are then compared with the power-length characteristics of CMOS digital devices. The general conclusion is that photonic signal processing technologies demand significantly larger space and/or power than CMOS technologies.

Nondestructive imaging of a type I optical fiber Bragg grating

Nondestructive images of refractive-index variation within a type I fiber Bragg grating have been recorded by the differential interference contrast imaging technique. The images reveal detailed structure within the fiber core that is consistent with the formation of Talbot planes in the diffraction pattern behind the phase mask that had been used to fabricate the grating.

Extremum Seeking Control of Cascaded Raman Optical Amplifiers

This paper considers the control of a particular type of optical amplifier that finds application in long-haul wavelength division multiplexed optical communications systems. The objective of this consideration is to demonstrate an application of extremum seeking to the regulation of amplifier output signal power across a range of signal wavelengths, where limited control authority is available. Although such amplifiers are nonlinear and distributed parameter devices, an extremum seeking design is demonstrated to be a promising approach for achieving the stated amplifier control objectives.

Refractive index profiling of optical fibers using differential interference contrast microscopy

Here we demonstrate the use of differential interference contrast microscopy with the inverse Abel transform to accurately obtain the refractive-index profile of a single-mode optical fiber. The application of this nondestructive imaging analysis technique provides high precision refractive-index information about the fiber. This technique is robust, rapid, and has diffraction limited spatial resolution.

Determination of bending-induced strain in optical fibers by use of quantitative phase imaging

Quantitative phase microscopy with polarized light has been used to determine the change in refractive index introduced into an optical fiber when the fiber is bent through a constant radius of curvature. By obtaining phase images for two orthogonal directions of the polarization of the incident light, one can infer the induced axial strain profile within the fiber. Radii of curvature from 1 to 8 cm were considered, and in each case excellent agreement, within lambda/100, was obtained between experimental results and theory.

On linear control of backward pumped Raman amplifiers

Abstract This paper considers the modelling and control of a particular type of optical amplifier that finds application in long-haul wavelength division multiplexed optical communications systems. The objective of this consideration is to design and demonstrate a simple (and potentially cheap) linear control strategy for regulating amplifier output signal power across a range of signal wavelengths in the presence of upstream signal power uncertainty, where limited control authority is available. Although such amplifiers are highly nonlinear and distributed devices, the straight-forward application of linearization, model reduction and ℋ ∞ loopshaping design is demonstrated to be a promising approach for achieving the stated amplifier control objectives.

A portable device for the electrical extraction of scorpion venom.

An attractive technique to extract scorpion venom is the use of a physiologically stimulating electrical signal across the muscles of the venom gland, resulting in the expression of venom from the aculeus. A Grass™ stimulator is typically used for this purpose, but is difficult to use in the field. The present communication describes a circuit which is battery-powered and simply constructed. Also described is the technique for its construction and housing. The circuit was successfully tested on two species of scorpion. The method for calculating the required values of passive circuit components is given to allow the adaptation and refinement of this circuit for producing different signals, as may be required for use in other species.

Modelling and Estimation of Multicomponent

Estimation of multiple T2 components within single imaging voxels typically proceeds in one of two ways; a nonparametric grid approximation to a continuous distribution is made and a regularized nonnegative least squares algorithm is employed to perform the parameter estimation, or a parametric multicomponent model is assumed with a maximum likelihood estimator for the component estimation. In this work, we present a Bayesian algorithm based on the principle of progressive correction for the latter choice of a discrete multicomponent model. We demonstrate in application to simulated data and two experimental datasets that our Bayesian approach provides robust and accurate estimates of both the T2 model parameters and nonideal flip angles. The second contribution of the paper is to present a Cramér-Rao analysis of T2 component width estimators. To this end, we introduce a parsimonious parametric and continuous model based on a mixture of inverse-gamma distributions. This analysis supports the notion that T2 spread is difficult, if not infeasible, to estimate from relaxometry data acquired with a typical clinical paradigm. These results justify the use of the discrete distribution model.

T_{2}

Nonlinear spatial encoding fields for magnetic resonance imaging (MRI) hold great promise to improve on the linear gradient approaches by, for example, enabling reduced imaging times. Imaging schemes that employ general nonlinear encoding fields are difficult to analyze using traditional measures. In particular, the resolution is spatially varying, characterized by a position-dependent point spread function (PSF). Likewise, the use of nonlinear encoding fields creates an additional spatial dependence on the signal-to-noise ratio (SNR). Although the two properties of resolution and SNR are linked, in this work we focus on the latter. To this end, we examine the pixel variance, which requires a computation that is often not feasible for nonlinear encoding schemes. This paper presents a general formulation for the performance analysis of imaging schemes using arbitrary encoding fields. The analysis leads to the derivation of a practical and computationally efficient performance metric, which is demonstrated through simulation examples.

Distributions

We propose a new method to monitor chromatic dispersion, based on two-tap asynchronous sampling. We experimentally demonstrate sensitivity to dispersion between 160 and 800 ps/nm, which matches the tolerances of typical commercial 10 Gbit/s receivers.