The Applications In The Optical Fields Of The Optical Fiber By The Finite-Difference Time-Domain Method

Finite-difference time-domain method is a numerical calculation method of finding the solution to the electromagnetic field in the time-domain. It transfers the Maxwell Differential Equations with time variant to the difference equations so as to find the solution to each of electromagnetic fields. Since the foundation of the FD-TD method, it is mainly used in researching the effects of the common electromagnetic waves on various objects. However, there are still few reports of the applications in the research of optical fiber field. Analytic method was generally used to research the optical fiber. With the more extensive using of optical fiber and with its structure more and more complicated, it is impossible to find an accurate solution. Thus a numerical calculation method is required. Numerical calculation methods other than FD-TD method have limitation. The FD-TD method is directly perceived, rapid, simple in procedure, and commonly used. It saves the memory space and the time of calculation, give high accuracy and has clear data and pictures. This thesis introduces this method to the calculation of optical fields in the optical fiber. It has arrived at the same conclusions with the analytic method in many documents, thus proved the feasibility and efficiency of the FD-TD method in the researches of optical fiber fields. This thesis first converts the FD-TD method in orthogonal coordinates into the cylindrical coordinates, and then analyzes the distribution of mode field of step-index optical fiber in three-dimensional scalar FD-TD method. Furthermore, four kinds of optical source are used as stimuli, they are Guassian optical source, spherical optical source, SIN optical source and COS optical sources, respectively. The concluded distributions of optical fields after the stabilization of the II ) ~L~ii~ ~ MASTERS THESIS spreading of optical fields are identical with the results by the analytic method. In the meantime, the structural parameters of the optical fiber are changed under the same optical source. The stable distributions of the optical fields are different. It indicates that the distributions of the stable optical fields have nothing to do with the stimulated optical sources. They are just connected with the structural parameters of the optical fiber. This thesis also discusses the optical fields of the optical fiber taper by 3-D scalar FT-TD method. A stable field is input into two kinds of fiber tapers with different taper angle. The distribution inside the optical fiber taper is not stable while the output field is a stable distribution. According to the decreasing of the angle of taper, the radius of the stable field is decreasing and the magnitude is increasing.