Dispersion compensating module and mode converter, coupler and dispersion compensating optical waveguide therein

Abstract

A dispersion compensating module, mode converter, coupler and dispersion compensated optical fiber therein. The dispersion compensating fiber has a plurality of core segments, the refractive index profile being selected to exhibit properties such that an LP mode at 1550 nm may be propagated a distance (generally 0.5-3.0 km), upon conversion to LP , to compensate for dispersion of a length of transmission waveguide preferably greater than 25 km propagating in an LP mode. In another embodiment, the dispersion compensating module has a mode converter having a reflective fiber grating for converting a first to a second mode interconnected to a dispersion compensated fiber propagating in the second mode. The mode converter has a coupler adapted to operatively couple light propagating in a first mode from a first fiber into a second, and a reflective fiber grating operatively coupled to the second fiber; the grating being capable of converting light from the first into the second mode. According to another embodiment, an optical fiber coupler is provided having a first fiber with a first propagation constant in a first mode, and a second fiber within the coupler having a second propagation constant, the second fiber including a necked-down portion which is formed prior to fusion of the fibers, the necked-down portion being formed such that the local propagation constant of the second fiber substantially matches the first propagation constant thereby enhancing first mode coupling.