Multi-wavelength FBG based on thermal diffusion and phase mask techniques

A short multi-wavelength fiber Bragg grating (MW-FBG) fabrication method is proposed and demonstrated. The MW-FBG fabrication method includes making expanded core in the photosensitive single mode fiber (P-SMF) by the discharge-based thermal diffusion technique and writing FBGs on the pre-processed P-SMF through ultraviolet exposure technique. The effect of the arc discharge is to make the dopant in the core of the P-SMF diffuse to the cladding, which can reduce the refractive index of the core at the discharged region. As a result, a single exposure through one phase mask can produce a FBG with multiple resonant wavelengths. The strain and temperature responses of a two-wavelength FBG are experimentally investigated. Results show that the multiple wavelengths of the FBG have almost the same responses to the strain or temperature. The strain sensitivities of the two wavelengths of the FBG are 0.9025 pm/με and 0.9101 pm/με, respectively, and the temperature sensitivities are 10.55 pm/°C and 10.33 pm/°C, respectively. Such MW-FBGs have potential applications in the case of small size and high spatial resolution measurement.