Research On The Mechanism And Applications Of The Secondary-type-?a Fiber Bragg Grating

Fiber Bragg Gratings(FBG)is one of the paramount photonic devices due to its advantages of compact size,anti-electromagnetic interference,good wavelength selectivity,low insertion loss and easy networking,enabling a wide range of applications in the optical communication and optical sensing.FBG continues to develop for extend its applications,particularly in extreme environments.Therefore,new-type FBGs are continually pursued to address the challenges.In this essay,we proposed a novel FBG with dual resonances,called “Secondary-Type ?a Grating”,which was discovered in the fabrication of Type ?a grating on a special active fiber.According to the evolution of the grating,the secondary resonance presented later growth and shorter wavelength than the type I resonance which was designed primarily and then enhanced with the growth of the type ?a resonance.Furthermore,we investigated the mechanism of the formation of this new-type FBG.Through the theoretical analysis and experimental validation,the mechanism was mainly attributed to the intracore Talbot-type-fringes as a result of multi-order diffractions of the inscribing beams after crossing the phase mask.The secondary-type-?a grating had several characteristics such as high temperature resistance,different temperature responses between the two resonances,integration of the Bragg reflectivity,controllable resonant wavelength differential and strong third harmonic reflection.Based on these characteristics,we demonstrated the application of the gratings in distributed Bragg reflector fiber lasers,including high-temperature-resistant laser with ultra-short cavity,thermally-triggered laser,1 ?m-wavelength Yb laser as well as the double wavelength laser,manifesting that the proposed grating has a great potential for fiber lasers and sensing applications.