Maurice Patrick Whelan

From the reflected spectrum to the properties of a fiber Bragg grating: a genetic algorithm approach with application to distributed strain sensing

We describe a genetic algorithm approach to solve an inverse problem in optics, which determines the characteristics of a fiber Bragg grating from its reflected spectrum. The validity of the proposed method is demonstrated by use of a Bragg sensor for the measurement of nonlinear strain acting on a uniaxial aluminum test specimen.

Optomechanical actuator for adaptive optics

This study describes the development of a novel opto- mechanical actuator suitable for integration in all-optical smart systems. Its action relies on the out-of-plane thermo- mechanical deflection of a thin optical-acrylic membrane due to the absorption of radiation from a laser source. The response of the actuator can be adapted to suit different applications by coating the surfaces of the element with either fully or partially absorbing or reflective coatings. The transient and steady state opto-thermo-mechanical behavior of different element configurations has been modelled analytically and using finite element analysis. In simple actuator configurations, the dynamic response of the element can be represented by that of a linear first order system. These modelling and simulation procedures have been verified with experimental data and have been used to optimize different actuator designs. One of these opto- mechanical actuators has been employed as an active optical element in the realization of a novel all-optical interferometric device employing active drift compensation.

Fiber optic sensors for characterization of composite structural materials and structural monitoring

We present recent work on fiber optic sensor systems for structural element characterization and monitoring. One particular application area currently under study is the characterization and testing of pultruded composite beams. The motivation behind this project and current status is described. Fiber optic sensor systems to suit the application have been developed. In particular, the development of both AO tunable filter and all-fiber passive demodulation schemes for in-fiber Bragg grating sensors is described.

Thin-cavity interferometric sensors for detection of weak radiation flux and microvibrations

Novel optical sensors for the detection of weak radiation flux transients and mechanical micro-vibrations have been developed. The sensors are based on the modulation of an interference pattern created during the optical interrogation of a thin air cavity similar to a low finesse Fabry-Perot or Fizeau interferometer, formed between two parallel glass holographic plates. In the detection of radiation flux the sensor demonstrates high sensitivity, good stability and a fast response. When adapted to the measurement of mechanical micro-vibrations, high sensitivity at low frequencies can be achieved. In order to understand and optimize sensor performance, the mechanical, thermal and optical characteristics of the devices have been modelled theoretically and with finite element analysis. A principal feature of the devices is their low cost and potential for miniaturization thus making them suitable for a wide range of industrial applications.