Study On Electrically Tunable Thermally Poled Fiber Switching

Glass-based materials are of great interest in optical telecommunication field, because of their low cost and excellent optical properties. But in the dipole approximation, even-order nonlinear coefficients of amorphous media vanish because of the macroscopic inversion symmetry of material. Up to now, thermal poling technique is the most practical method to create such a second-order nonlinearity in glasses.In this paper, we propose an electrically tunable thermally poled fiber Bragg grating, and a Mach-Zehnder switch based on thermally poled fiber is experimentally demonstrated. The periodically poled Bragg fiber grating is designed utilizing the role of ultraviolet light in erasing second-order nonlinearity (SON) and manufacturing fiber grating. The tunability is achieved as the different refractive index response to modulating voltage in SON erased zone and SON zone. The influence of the initial refractive index and the length of the grating on the tunability are also investigated. The Mach-Zehnder interferometer is constructed based on the thermally poled twin-hole fiber. For the twin-hole fiber thermally poled for the first time, the depletion region has not reach the fiber core, and the core is overlapped by the reversed electric field. In this condition, the switching voltage is lower when the voltage is applied to the cathode (the cathode in thermal poling). After the fiber was thermally poled 1 hour again, the depletion region expands, and the fiber core was overlapped by the forward electric field and the reversed electric field simultaneously. In this condition, the switching voltage is lower when voltage is applied to the anode (the anode in thermal poling). The Mach-Zehnder switch based on thermally poled fiber is achieved for the first time by utilizing reversed electric field.The electrically tunable switch based on thermally poled fiber has the advantages of low insertion loss, high extinction and high switching speed. The conclusions on the electrically tunable optical switch are of significance for applications of thermally poled optical fiber in optical devices.