Curvature effects in single mode and multimode optical fibers and fiber Bragg gratings

This thesis presents an experimental study of the bending loss properties of different types of optical fiber. A novel fiber configuration based on the nonlinear buckling of a thin rod, known as the Elastics problem from the theory of elasticity, is used to measure the bending loss in single-mode and multimode optical fibers.; The bending loss for four different length, single-made fiber Elastica are measured sad compared with an existing bend loss model to better understand the accuracy and limitations of the theory, The experimental measurements agree with the theory when the model is corrected for the mechanical strain of the refractive index of the fiber and the displacement of the fiber coating. A reduction in amplitude of whispering gallery mode oscillations in the transmission response of a curved single-mode Elastica is demonstrated by index matching the fiber coating.; The bending loss response for the less bend sensitive multimode fiber is investigated. The bending loss in multimode fiber is much more difficult to model and predict due to the higher-order propagating modes in the fiber. Several single-mode/multimode fiber Elastica configurations are measured for different modal excitation conditions. A baseline measurement of a multimode fiber Elastica where primarily the fundamental mode is excited is compared to the same multimode fiber with selective modal excitation. A significant increase in bend sensitivity in the multimode fiber using both lateral and longitudinal offset modal excitation techniques is observed.; The third fiber investigated is the fiber Bragg grating (FBG). The transmission and reflection optical spectra for a highly curved fiber Bragg grating are measured so that the bending loss properties of the FBG Elastica can be determined.