Losses and Impulse Response of a Parabolic Index Fiber With Random Bends

Optical fibers with parabolic refractive index profile 1,2 have less pulse delay distortion t h a n conventional fibers with piecewise constant, discontinuous index distribution. 3 T h e width of the impulse response increases in direct proportion to the length of the fiber. It is well known t h a t an improvement of the impulse response results if the modes are coupled among each other. 4 - 5 In the presence of mode coupling the width of the impulse response increases only proportionally to the square root of the length of the fiber. Pulse propagation in multimode parabolic index fibers is studied in this paper by means of converting the coupled power equations to a partial differential equation. 5 - 7 R a n d o m changes of the direction of the waveguide axis are considered as the coupling mechanism. T h e problem is simplified by assuming t h a t the modes of the parabolic index fiber are essentially the same as the modes of an infinitely extended square-law medium. T h e fiber boundary is included in the 1423