Abstract: An optical fiber having three dopants in the core of the fiber and a pure silicon dioxide cladding is disclosed. Phosphorus pentoxide and germanium dioxide are radially graded in the core of an optical fiber to obtain minimum modal dispersion over a broad range of wavelengths. A uniform concentration of boron oxide is present throughout the core of the fiber in order to permit a pure silicon dioxide cladding without encountering any step discontinuity in the index of refraction at the core-cladding interface.

Abstract: A graded index optical fiber waveguide for use in an optical communication system is disclosed. The waveguide is a circular symmetric fiber having a cladding with an index of refraction n.sub.2 surrounding a core whose index of refraction is graded from an on axis value of n.sub.1 to a value of n.sub.2 at the core-cladding interface. The index of refraction within the core is defined in terms of a profile function F by the following equationn.sup.2 = n.sub.1.sup.2 (1-F)where F is O on the axis and a function of the radial coordinate r and wavelength .lambda. within the core and satisfies the following equation ##EQU1## where D is a function of .lambda. having a value approximately equal to 2 for minimum modal dispersion and ##EQU2## IS THE GROUP INDEX ON AXIS. The modal dispersion achieved with this design is only a function of n.sub.1 - n.sub.

Abstract: An optical cable which is relatively immune to the effects of bending and/or tension comprises a helical optical fiber loosely confined within a protective sheath. Apparatus is disclosed for fabricating the helical fiber. For example, as the fiber is drawn from a heated preform the fiber is subjected to periodic, pulsating jets of an inert gas, such as nitrogen, which physically deform the fiber into the desired helical configuration.

Abstract: The disclosed optical fiber communication system employs a fiber with a core having an index of refraction graded in an approximately parabolic fashion and a light-emitting diode joined directly to the fiber to serve as the light source for the system. It has been found that the overall electrical efficiency of the system, at least with respect to drive power for the diode, is maximized when the ratio of the diode radius to the radius of the fiber core is about 0.2. More broadly, the ratio of radii is found advantageously to lie in the range between about 0.1 and about 0.8, not only for efficiency reasons but also to maximize the amount of light injected into the fiber.

Abstract: The disclosure is directed to optical fiber waveguiding structures, and techniques for fabricating the same, which are designed to have reduced modal dispersion as a result of the deliberate enhancement of mode coupling in the fibers. The mode coupling is achieved in each of the structures by means of an enveloping outer jacket, typically of plastic, which is selectively deformed so as to modify the straightness of the fiber axes in a spatially periodic manner. Several alternative techniques are presented for properly deforming the outer jacket either before or after it is combined with the fibers. Since, with these structures and techniques, the outer jacket provides the desired fiber perturbations, the fibers themselves can be fabricated using standard techniques without the need for any special procedures for modifying their parameters.