PhD Thesis Defenses

Optically poled fibers for electro-optic applications


The work presented in this thesis shows the development of optically poleddevices for use in electro-optic experiments. In the form of papers published,it describes three optical poling methods: green light poling (Paper I), poling with a UV lamp (Paper II), and corona discharge poling (Paper V).Applications using the poled components are studied in distributed sensingby exploring Rayleigh scattering in poled fibers (Paper III), intermodal interference in poled fibers (Paper IV), and FBG inscribed in poled fibers forvoltage sensing (Paper VI).In thermal poling, heat increases the mobility of added ions to the fiber.An external electric field displaces the charges creating a depletion regionclose to the anode, where the fiber core is usually positioned. The proximityof the metal electrode to the core can cause optical losses, making electrooptic applications less efficient. The need for additional dopant in the preformcan make the production of these devices expensive.Optical poling explores the presence of Ge E’ centers in the fiber core torelease charges after light excitation. These centers are already present in anyfiber with Ge in the core. This enables the development of a fiber for opticalpoling very similar to a standard telecom fiber, making it cheaper and easyto integrate with standard components. Optical poling does not rely on theformation of a depleted region in the cladding, and the core can be positionedfar from the metal electrodes. This advantage allows low-loss electro-opticcomponents to be fabricated.Optical poling is usually thought to have lower induced effects when compared with thermal poling. In this work, experiments with optical polingwere made to study the possibility of increasing the induced second-ordernonlinearities to a level comparable with thermal poling.The fabricated poled fibers were used to investigate their potential usein fiber sensing. The emphasis was to explore new technologies such as CPϕOTDR, few-mode fiber sensing, which gained attention in the latest years,and FBGs, which is a mature technology.The results presented in the Papers I-VI show the advances and potentialapplications explored.