Low coherence interferometry: Applications to component metrology and high spatial resolution fiber Bragg grating sensors

This thesis is mainly addresses the application of low coherence interferometry (LCI) to provide a phase sensitive spectral characterization of optical components. LCI has been shown to be an effective means of obtaining a fast and accurate measurement of the complex spectral response of an optical component. It is shown that the LCI system used in this thesis has a wavelength resolution better than 6 pm with an absolute wavelength accuracy of 0.1 pm in the 1520-1610 nm range. It is also shown that the relative group delay of an optical component can be characterized with a resolution of 0.6 ps.; An inverse scattering algorithm known as layer peeling is applied to the LCI measured complex spectrum to deduce the refractive index in the grating as a function of position with a resolution better than 10-5. The spatial resolution of this measurement is 10.2 mum, limited by the wavelength bandwidth of the low coherence source. This technique is used for the calibration and error detection in a fiber Bragg grating writing system.; The LCI-LPA technique as also shown to be well suited for interrogating high spatial resolution fiber Bragg grating sensors. Environmental mechanical strain or temperature changes interact with the fiber's refractive index through the strain-optic or thermo-optic effect. These changes can be detected in the grating by an LCI measurement and the layer peeling algorithm. A novel method for detecting transverse stress in a fiber Bragg grating is demonstrated. Measuring transverse stress typically requires the use of polarization maintaining fiber and components. We show that transverse stress can be accurately measured in standard single mode fiber by combining a four-state polarization analysis with a layer-peeling algorithm to measure the stress-induced birefringence. We also demonstrate that our measurement is insensitive to temperature changes and spatial gradients, making it ideal for nonisothermal applications. It is also shown that thermal conductivity and material stiffness cause the spatial resolution to be much higher than the system limited resolution of 10.2 mum. The practical spatial resolutions are shown to be approximately 40 mum for transverse stress, 100 mum for longitudinal strain, and 900 mum for thermal gradients.