Propagation in lowest order modes of multimode graded index fiber, resulting in: very low transmission loss, low modal noise, high data security, and high data rate capabilities

A fiber optic communication system comprising:

• M light sources, each launching modulated light into a singlemode fiber pigtail, where M is a positive integer;
• N multimode graded index fibers contained in transmission cables of said system, where N is a positive integer;
• M×N singlemode optical coupler, having M input singlemode fibers and N output singlemode fibers;
• each of said singlemode fiber pigtails of said M light sources connected to one of said M input singlemode fibers of said M×N coupler;
• light from each of said M light sources combined and distributed by said coupler to each of said N output singlemode fibers of said M×N coupler;
• each of said N multimode graded-index fiber aligned coaxially and in contact with one of said N output singlemode fiber of said M×N singlemode coupler;
• wherein said modulated light from said M light sources are distributed and launched into first small set of lowest order propagation modes of each of said N multimode graded-index fibers;
• a second limited small set of lowest order propagation modes, containing, at least, all modes of said first small set of lowest order propagation modes;
• wherein said modulated light launched into said first small set of lowest order modes in each of said multimode graded-index fiber may convert into modes of said second limited small set of lowest order propagation modes due to fiber bending perturbations occurring within said transmission cables;
• said modulated light at end of fiber detected by wavelength division demultiplexing means;
• whereby modulated light from said M sources, distributed to said N multimode graded-index fibers in cables, propagate to the ends of said N multimode graded-index fibers with low transmission loss, low modal noise, high data security, and high data rate capability, despite fiber bending perturbations within said transmission cables, where said high data rate is due to small modal time dispersion of the small number of modes in said second limited small set of lowest order propagation modes of said multimode graded-index fiber.

A method for transmitting digital data at high data rate in multimode graded-index fiber in a transmission cable, including:

• minimizing the number of lowest order propagation modes launched in said multimode graded-index fiber, by launching data light into a singlemode fiber, then coaxially contacting said singlemode fiber to said multimode graded-index fiber, thereby launching first small set of said lowest order propagation modes into said multimode graded-index fiber;
• providing for case of mode conversion due to fiber bending perturbations of said multimode graded-index fiber in cables, where modes of said first small set of lowest order modes convert into modes within a second limited small set of lowest order modes arising from said fiber bending perturbations, as shown experimentally and theoretically,
• by launching said first small set of lowest order propagation modes containing fewer lowest order modes than that contained in said second small set of lowest order modes arising from said fiber bending perturbations;
• whereby said modulated light, transmitted by said multimode graded-index fiber in said transmission cable, propagates with low transmission loss, low modal noise, high data security, and high data rate capability, despite fiber bending perturbations in said transmission cable, wherein said high data rate is due to small modal time dispersion of the small number of modes in said second limited small set of lowest order propagation modes of said multimode graded-index fiber.