Very large scale and high performance time-multiplexing of fibre optic Bragg grating sensors

In this thesis we develop innovative and novel time multiplexed Bragg grating sensor systems that represent a significant advance in Bragg grating sensor multiplexing capabilities. In many applications there is a need to multiplex large serial arrays of sensors on a single fibre. A serial array allows distributed measurements, reduces the amount of fibre and minimizes the number of access points to a structure. Multiplexing also has tremendous cost advantages because expensive components can be shared among the sensors. To date, existing multiplexing methods have serious shortcomings such as small measurement range, poor resolution, long measurement time or being able to address only a small number of sensors. The techniques in this thesis overcome these limitations.; We develop a unique system incorporating optical amplifiers that reduces the needed power from the optical source and substantially increases the measurement accuracy of the sensors. Our analysis allows us to find sensor configurations that improve performance despite the broadband noise produced by optical amplifiers.; We use our techniques to achieve several novel results. Other sensor systems in the literature had to trade off important design criteria such as sensitivity, range, measurement speed or cost in order to multiplex large arrays of sensors. The achievements in this thesis allow large arrays to be measured without sacrificing performance. Our methods allow us to produce a sensor system with cross talk that is orders of magnitude lower than that predicted in the literature for comparable systems. We show that very low cost electronic demultiplexing can be done with large sensor arrays and the addition of an optical amplifier is demonstrated to provide performance beyond the shot noise of the equivalent unamplified measurement.; Experimental demonstrations within this work show for the first time that high performance measurements can be made with large arrays of Bragg grating sensors and implemented in a simple and low cost design. Specifically we showed that a 100 sensor multiplexed array could be measured to a accuracy of 0.038 microstrain resolution in a 1 Hz measurement bandwidth while using only 270 nW of average source power to interrogate the sensors.; Finally we find the fundamental limits for wavelength measurement of optical signals and show that our measurement methods are nearly ideal. The limits are only dependent on the optical power and source bandwidth, and are important in a wide range of wavelength measurement applications including fibre Bragg grating sensors. (Abstract shortened by UMI.)...