Optical systems comprising multi-core optical fibers for realizing direct core to core coupling

A multicore optical fiber comprising:

• a plurality of cores disposed in a cladding, wherein:
• the plurality of cores comprise a first core, a second core, and a third core;
• the first core comprises a first propagation constant β1, the second core comprises a second propagation constant β2, the third core comprises a third propagation constant β3, the cladding comprises a cladding propagation constant β0, and
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• the first core and the second core comprise a modal mismatch M12;
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• where C12 is a coupling coefficient for coupling from the first core to the second core;
• and
• M12 is greater than 10.

A method of coupling light from a first core of a multicore optical fiber to a second core of the multicore optical fiber, the method comprising:

• directing a plurality of photons generated by a photon generator optically coupled to an input end of the multicore optical fiber comprising a plurality of cores disposed in a cladding into the first core of the plurality of cores, wherein:
• the plurality of cores comprise the first core and the second core;
• and
• the first core comprises a first propagation constant β1, the second core comprises a second propagation constant β2, the cladding comprises a cladding propagation constant β0, and
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• engaging the multicore optical fiber with a modulator, thereby generating a long period fiber grating comprising a grating period Ω in the multicore optical fiber, wherein (2π)/(|β1−β2|)=Ω such that the first core is coupled with the second core wherein:
• the first core and the second core comprise a modal mismatch M12;
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• 12
• =
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• β
• 1
• -
• β
• 2
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• 2
• ⁢
• C
• 12
• where C12 is a coupling coefficient for coupling from the first core to the second core;
• and
• M12 is greater than 10.

A method of coupling light from a first core of a multicore optical fiber to a second core of the multicore optical fiber, the method comprising:

• directing a plurality of photons generated by a photon generator optically coupled to an input end of the multicore optical fiber comprising a plurality of cores disposed in a cladding into the first core of the plurality of cores, wherein:
• the plurality of cores comprise the first core and the second core;
• and
• the first core comprises a first propagation constant β1, the second core comprises a second propagation constant β2, the cladding comprises a cladding propagation constant β0, and
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• ;
• and
• engaging the multicore optical fiber with a modulator, thereby generating a long period fiber grating comprising a grating period Ω in the multicore optical fiber, wherein (2π)/(|β1−β2|)=Ω such that the first core is coupled with the second core wherein:
• the plurality of cores comprise at least three cores;
• the at least three cores include one or more first cores each having the first propagation constant β1, one or more second cores each having the second propagation constant β2, and one or more third cores each having a third propagation constant β3;
• the third propagation constant β3 is different than both the first propagation constant β1 and the second propagation constant β2;
• and
• the at least three cores are arranged within the cladding of the multicore optical fiber such that a nearest neighboring core of each individual core comprises a different propagation constant than the individual core.