Study On The Characteristics As Well As The Sensing Application Of FBG With Cladding Made Of Electro-optic Crystal Material

In this paper,a new type of fiber Bragg grating(FBG)with cladding made of uniaxial crystal material(Li TaO3)is proposed.The effects of the core radius and the applied electric field on the grating performance are theoretically analyzed based on the coupled-mode theory and the principle of the electro-optic effect.Then,a novel FBG sensor is designed.The main results are listed as follows:1.The effects of the core radius and the applied electric field on fundamental mode energy distribution,Bragg wavelength ?B,reflectivity ?,group delay ?,second-order dispersion D and third-order dispersion ?3are investigated.The results show that:(1)When radius remains unchanged,the maximum energy increases as the field intensity increases,but the effective mode field area and the Bragg wavelength decrease gradually;hypsochromic shift is observed in the curves of r,?,D with the changing of the width,the maximum and the minimum.When ? = ?B,the value of ? and D reach to their maximum minimum value respectively.(2)When the wavelength ? is a constant,the curves of r,?,D will move to the high electric field area with the radius increasing,while the curves of r,?,D will move to the large radius area as the field intensity increases.(3)When the field intensity remains as a constant,the maximum value of ? will move towards the long wavelength as the radius increases;Additionally,the influence of the radius on the delay is related to the field intensity.(4)When ?=1550nm,the radius is 900 nm and the field intensity is 53×107 v/m,?3can reach the maximum.When ?3increases from minimum to maximum,the variation of field intensity is 1×106v/m while that of the radius change is about 0.1nm.Consequently,?3is not sensitive to the electric field owing to the big change of intensity,but it is sensitive to the radius owing to the tiny change of radius.2.A novel FBG sensor was designed.The cladding layer of the proposed FBG sensor is made of uniaxial crystal material(LiTaO3)and the FBG was divided into two halves.Then,the electric field is applied on one half of the sensor.The sensing performance was investigated by the coupled-mode theory,the principle of the electro-optic effect and dual-wavelength method.The results indicate that the temperature sensitivity of one half with no electric field is 14.31 pm/?.The center reflection wavelength shift is only affected by temperature.If the electric field increases from 0 to 400×107 v/m,the temperature sensitivity of the other half varies from 14.12-14.31 pm/?.The center reflection wavelength shift is not only affected by temperature,but also affected by electric field.So,the Bragg wavelength shift caused by electric field or temperature can be distinguished through this sensor.The measurement of temperature and electric field can be simultaneously achieved,especially in the field of high voltage.