Abstract: An optical fiber for signal amplification comprises a core, doped with at least 15% phosphorus by weight and a rare earth ion sufficient to provide amplification of an optical signal. The fiber also comprises a clad layer surrounding the core with an inner portion and an outer portion. The refractive index of the inner portion of the clad layer is lower than that at the outer radius of the core region. This depressed inner clad portion serves to confine electromagnetic radiation within a selected wavelength range to substantially only the core.

Abstract: An optical fiber for signal amplification comprises a core, doped with at least 15% phosphorus by weight and a rare earth ion sufficient to provide amplification of an optical signal. The fiber also comprises a clad layer surrounding the core with an inner portion and an outer portion. The refractive index of the inner portion of the clad layer is lower than that at the outer radius of the core region. This depressed inner clad portion serves to confine electromagnetic radiation within a selected wavelength range to substantially only the core.

Abstract: An optical waveguiding fiber has a photosensitive core and a cladding that includes a photosensitive inner cladding region adjacent the core and an outer cladding region. The inner cladding region and the outer cladding region have substantially equal indices of refraction. The photosensitivity of the inner cladding region is sufficient to cause a modulation of the index of refraction of the inner cladding when exposed to ultraviolet light. In another aspect of the invention, the optical fiber includes a grating in the core, which extends radially into the inner cladding region. The core and the inner cladding region of the optical fiber are doped with concentrations of Ge and B sufficient to impart photosensitivity to the inner cladding region, and to result in an index of refraction in the inner cladding region substantially equal to the index of refraction of the outer cladding region.