The Diffraction Characteristics Analysis Of The Low Order TE And TM Of Step Index Fiber

Based on the mode field distributions and the relationship between the radial spatial spectrum and the mode field distributions of the TE01mode and the TM01mode in step index fiber, the expressions of the mode field radius defined by second moment algorithm and differential operator algorithm and the beam propagation factor of diffracted field are derived. Numerical calculation shows that the mode field radius defined by second moment algorithm and differential operator algorithm and the beam propagation factor of the TE01mode and the TM01mode of step index fiber are relatively close and the beam propagation factor of the TE01mode and the TM01mode of step index fiber are close to2when the normalized frequency is relatively large range.Take the TE01mode of step index fiber as an example, as the fitting expression of the relationship of the beam propagation factor and the normalized frequency is derived from curve fitting. Based on the method of the equivalent matching, the expressions of the equivalent mode field radius of the TE01mode and the TM01mode of step index fiber are proposed.According to the computational formula of the radial spatial frequency radius defined by second moment algorithm, the expressions of the radial spatial frequency radius of the TE02mode of step index fiber is derived when the variation is under the math concept, the relationship between the radial spatial frequency radius and the normalized frequency are analysed when the variation are under the math concept and physical meaning. Based on the definition of the power in the bucket, the power in the bucket within the limit of the spatial frequency radius is given when the variation are under the math concept and physically meaning. As the method of function fitting is engaged, the exponential function of the ralationship between the power in the bucket and the normalized frequency is given when the variation is under the math concept.According to the characteristics of the radial spatial spectrum of the TE02mode of step index fiber, the radial spatial frequency radius of the first zero position and second zero position of the radial spatial spectrum are increasing with the increase of the normalized frequency. The radial spatial frequency radius of the first peak and second peak of the radial spatial spectrum are increasing with the increase of the normalized frequency too, but the peak are decreasing with the increase of the normalized frequency, and the first peak is fall faster, the second peak is relatively slow.