Study On Erbium-doped Dynamic Fiber Grating And F-P Cavity Formed By It With A Bragg Grating

The application of optical fiber Bragg grating(FBG)is more and more mature in optical communication field.However it is limited in the application because of its certain bandwidth and center wavelength.For example,although Fabry-perot cavity(F-P)structured by a pair of FBG has advantage of narrow bandwidth and been good usage in sensors,the technique is still need to be improved in terms of stability,flexibility.Recently,on the other hand,a new type fiber grating,that is the dynamic erbium-doped fiber grating(DFG),can overcome the disadvantages of FBG.DFGs become the hot topic and have been used in single frequency continuous fiber laser and tunable narrow-band filters,optical fiber sensor,the adaptive interferometer,optical storage.In this thesis,we propose a scheme of F-P interference cavity formed by both DFG and FBG to utilize their own advantages in optical devices such as an optical sensor of refractive index.The main results of this paper:In this dissertation,the coupled mode theory and transmission matrix method are used to analyze the characteristics of the reflection spectra of the erbium-doped dynamic fiber gratings and some of the F-P cavity by DFG and FBG.The influence of various parameters on the device,have been numerically simulated including Rabi frequency,depth of modulation,cavity length,and fiber change of the probe field.The two-level model is applied for the Erbium-doped dynamic fiber grating.We found that when the length of the optical fiber is not changed,the reflectivity of the dynamic grating increases with the increase of the power of the probe field but Rabi frequency reaches a saturation value.When the saturation value is exceeded,the reflectivity of the dynamic grating will decrease as the power of the probe field continues to increase.When the Rabi frequency of the probe field fixed,the length of the erbium doped fiber is increasing,the larger reflectance can be obtained until it reaches saturation.The longer the Erbium fiber,the larger the reflectance until the saturation Rabifrequency emerges.In order to prove the realization of DFG,we carryout out experiments by method of searching perfect standing wave signal.By using compassion of the amplitude ratios,we have drawn data graph of grating efficiency with different input powers.And experimental curves at four saturation points of different fiber lengths on oscilloscopes are shown at the same time.The experimental results are according to the analyses of numerical simulation.It will lay a foundation for further study of the erbium-doped dynamic fiber grating and the F-P cavity we proposed.We also studied the characteristics of F-P cavity formed by the erbium-doped dynamic fiber grating and a Bragg grating.We established the theoretical model for the erbium-doped dynamic fiber grating and obtain reflection spectra of F-P cavity by numerical simulation.The influence of parameters of the devices on the F-P reflection spectrum was analyzed including Rabi frequency of probe field,cavity length,fiber length,modulation depth,length of Bragg grating.It is a good precondition for further research later.