Study On Hindering Effect Of Core-cladding Interface In Thermally Poled Optical Fiber

Silica glasses are amorphous materials, lacking of second-order nonlinearity. The thermal poling technique could eliminate the macroscopic central symmetry of silica materials and introduce effective second-order nonlinearity. This technique is significant for manufacturing novel optical fibers and fiber based devices.The hindering effect of core-cladding interface would significantly affect the thermal poling process in optical fiber while the mechanism is not quite clear so far. In this paper, the hindering effect of core-cladding interface in thermally poled optical fiber was theoretically investigated, and a multilayered-core thermal poling fiber was proposed. Thermal poling processes in optical fibers were investigated based on the two-dimensional (2D) charge dynamics model. It was found that besides the low mobility of charge carriers at core-cladding interface, the initial concentration and the mobility of charge carriers in core region were key factors for hindering effect of core-cladding interface. The influences of these factors on hindering effect of core-cladding interface were theoretically analyzed and illustrated. Furthermore, a multilayered-core thermal poling fiber was proposed, in which the distributions of frozen-in electric field could be controlled, resulting in a large second-order nonlinearity. Thermal poling processes in multilayered-core fiber with various configurations were investigated. Since maximum magnitude of electric field are introduced at each interface, the second-order nonlinearity in fiber core increases with the number of core layer. Meanwhile, the influence of initial concentration and mobility of charge carriers in core region on thermal poling properties in multilayered-core fibers were investigated. It was found that the second-order nonlinearity in fiber core increased with the decrease of initial concentration and mobility of charge carriers in core region. The conclusions lead to a reasonable explanation for the hindering effect of core-cladding interface in thermally poled optical fibers, and are important for fiber thermal poling experiments. The proposed multi-layered core thermal poling fiber is of significant for controlling the distributions of frozen-in electric field, introducing large second-order nonlinearity and enhancing the performance of poled fiber devices.