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

A dispersion compensating module comprising:

• (a) a mode converter operatively coupleable with a transmission waveguide, the transmission waveguide adapted to propagate light in a first mode, the mode converter including a reflective fiber grating capable of converting the first mode into a second mode, and
• (b) a dispersion compensating fiber operatively coupled to the mode converter, the dispersion compensating fiber adapted to propagate light in the second mode such that dispersion of the transmission fiber may be compensated for wherein a refractive index profile of the dispersion compensating fiber is selected to result in a negative dispersion at 1550 nm in the second mode of less than −300 ps/nm/km and greater than −1000 ps/nm/km, and a kappa value between about 30 nm and about 70 nm, where kappa is defined as a ratio of dispersion in the second mode at 1550 nm divided by dispersion slope in the second mode at 1550 nm of the dispersion compensating fiber.

A mode converter, comprising:

• (a) an optical fiber coupler adapted to operatively couple light propagating in a first mode in a first fiber into a second fiber, and
• (b) a reflective fiber grating operatively coupled to the second fiber, the grating being capable of converting light propagating in a first mode into a second mode wherein the second fiber extends from the optical fiber coupler and is adapted to propagate light in the second mode and wherein the reflective fiber grating comprises a plurality of longitudinally spaced portions that have been exposed to UV radiation to change a refractive index of the portions and the longitudinally spaced portions are spaced at intervals that vary by up to 3% from a beginning to an end of the reflective fiber grating.

An optical fiber coupler, comprising:

• (a) a first optical fiber within the coupler having a first propagation constant in a first mode, and
• (b) a second optical fiber within the coupler, the second optical fiber having a second propagation constant in an undeformed portion thereof and in the first mode that is different than the first propagation constant, the second optical fiber including a necked-down portion formed on a glass portion thereof which is formed prior to fusion of the fibers, the necked-down portion having a dimension such that a propagation constant in the necked-down portion substantially matches the first propagation constant, and
• (c) a boron doped silica cane sleeve into which the first and second fibers are inserted, the cane sleeve and first and second fibers being fused together at a mid-region of the sleeve wherein coupling of light between the fibers in the first mode is enhanced.

A mode converter, comprising:

• (a) an optical fiber coupler adapted to operatively couple light propagating in a first mode in a first fiber into a second fiber, and
• (b) a reflective fiber grating operatively coupled to the second fiber, the grating being capable of converting light propagating in a first mode into a second mode wherein the second fiber extends from the optical fiber coupler and is adapted to propagate light in the second mode, wherein the second optical fiber includes a reflective fiber grating.

A optical fiber coupler, comprising:

• (a) a cane sleeve having a length, a mid-region, opposed ends and an aperture therethrough,
• (b) a first fiber adapted for carrying a light in a first mode received within the aperture of the cane sleeve and extending out of at least one of the opposed ends, and
• (c) a second fiber passing through the sleeve and extending out of both ends, the second fiber adapted for propagating light in a second mode and including a necked-down portion formed on a glass portion of the second fiber prior to fusion of the fibers, the necked-down portion having a length less than the length of the sleeve and being positioned approximately at the mid-region, the first fiber, second fiber and sleeve being fused and stretched under heat along the mid-region such that upon light transmission through one of the fibers, a portion of light is coupled into the other fiber.