Profile matching fiber patchcord for fundamental mode excitation in graded-index multimode fiber

A fiber optic communication system, comprising:

• a light source, emitting light into a first graded-index multimode fiber;
• a second graded-index multimode fiber for transmitting said light;
• a length of a singlemode fiber whose transmission mode profile closely matching the fundamental mode profile of said second graded-index multimode fiber;
• output end of said first graded-index multimode fiber attached coaxially to the input end of said singlemode fiber by butt-coupling means, launching said light into said singlemode fiber;
• said singlemode fiber cladding coated with coating for stripping light in cladding modes of said singlemode fiber;
• wherein a portion of the original power of the said light in said first graded-index multimode fiber is propagated in the bound singlemode to the output end of said singlemode fiber;
• said output end of said singlemode fiber attached coaxially with input end of said second graded-index multimode fiber by butt-coupling means;
• wherein profile-matching of said transmission mode profile of said singlemode fiber with said fundamental mode profile of said second graded-index multimode fiber permits said light in said output end of said singlemode fiber to be launched exclusively into said fundamental mode of said second graded-index multimode fiber.

A method for inserting a length of a special singlemode fiber between an arbitrary first optical fiber carrying light and a graded-index multimode fiber data transmission medium;

• providing said length of said special singlemode fiber whose single bound mode profile matches said fundamental propagation mode of said graded-index multimode fiber;
• providing transfer of said light in said arbitrary first optical fiber into said single bound mode of said special singlemode fiber so that only said single bound mode is supported at output end of said singlemode fiber after removal of cladding modes;
• eliminating said cladding modes in said special singlemode fiber by a coating on the cladding surface of said special singlemode fiber;
• resulting in said light launched exclusively into said fundamental mode of said graded-index multimode fiber.