Study On Propagation Characteristics Of Eccentric Core Optical Fiber

As a primary element of optical system, optical fiber has been widely used in sensing,laser technology and high speed communication. In addition, the enhancement of newtechniques has promoted the optical fiber technology which leads to appearance of specialoptical fiber. One of them is eccentric core optical fiber of which the propagationcharacteristics are different from conventional optical fiber. That is due to the core is offcentral axis even close to the cladding which leads to the asymmetry. At present, theeccentric core optical fibers are utilized for fiber attenuation, refractive index sensor andlaser etc.In this thesis, the current situation of different optical fibers is studied and thesuperiority of optical fibers in optical fiber integration and sensing is described. Thetransmission theory of optical fiber is stated, in addition, eigen parameters characterizedlight transmission of several single mode fibers are analyzed. The merit and demerit ofsimulation methods for transmission of optical fibers are introduced, furthermore, beampropagation method is finally selected to simulate the propagation characteristics. Thetheoretical model of eccentric core optical fiber is established based on the conventionallight transmission theory. The modal field distribution of eccentric core optical fiber isobtained by conformal transformation of electromagnetic field and the eigen equation ofcommon three-layer waveguide. The expression of evanescent wave of eccentric core isdeduced according to Fresnel equation so that the depth of penetration is solved. Theevanescent wave can pass across the cladding to external environment as the core is nearor closed to cladding, thus, the evanescent wave can be used for sensing. Structuremodeling of eccentric core optical fiber is completed by BeamPROP module of softwareRSoft. Modal field distribution and the trend of light power in eccentric core optical fiberare obtained. Hence, the variation trend of fundamental mode effective index andbirefringence are obtained with the distance between core and cladding.