Abstract: Substantial reductions in the distortion loss in an optical fiber waveguide due to the influence of random external forces can be realized by encasing the fiber in a properly designed jacket. In accordance with the disclosed invention, the ability of a jacketed optical fiber structure to resist external forces is characterized by a parameter referred to as its retention length R, given by ##EQU1## WHERE H is the flexural rigidity of the jacketed fiber and D.sub.f is the lateral rigidity of the jacketed fiber. It is shown that minimum distortion loss can be achieved by designing the fiber jacket so that the retention length R of the combined fiber-jacket structure exceeds a critical coupling wavelength .LAMBDA..sub.c for the fiber. A variety of illustrative jacket designs are described.