Radiation losses of parabolic-index slabs and fibers with bent axes.

Using first-order perturbation theory, radiation losses of the lowest-order mode caused by deformations of the axes of slab waveguides and fibers with parabolic-index distributions were computed. It was found that sinusoidal bends, with a period that produces a very nearly forward directed radiation lobe, cause far more loss than bends with a shorter period that give rise to radiation escaping at larger angles relative to the axes of the waveguides. Parabolic-index fibers and slabs are far more tolerant of periodic sinusoidal axis distortions than step-index fibers and slabs, provided that the period of the distortion causes the beam to escape from the waveguide at relatively large angles (typically more than 10 degrees ). The result of this study suggests that single-mode fibers with parabolic-index profiles may have somewhat lower microbending losses than single-mode step-index fibers.