Coupler fabrication techniques for dissimilar fibers

Claim 2

A fused twin biconical taper fiber optic splitter comprised of a pair of non-identical monomode or nominally monomode optical fibers, said fibers each having a core and a cladding, having predetermined cladding diameters fused at respective narrowed waists, the cores being narrowed over biconical region adjacent said narrowed waists sufficiently to cause an optical signal carried by a core of one of said optical fibers to be passed into and to be carried by each said cladding, the cladding diameter of one fiber before coupler fabrication being greater than the other, whereby coupling between one and the other fiber is obtained.

Claim 3

A splitter as defined in claim 1 in which a monomode optical signal is coupled from the larger cladding diameter fiber to the smaller cladding diameter fiber.

Claim 4

A tuned splitter as defined in claim 2, in which coupling from the larger cladding diameter fiber to the smaller cladding diameter fiber is obtained at a predetermined wavelength or band, depending on the respective diameters of the fibers.

Claim 5

A splitter as defined in claim 1, in which the smaller cladding diameter fiber has the same core radius and the same cladding and core refractive indexes as the larger cladding diameter fiber but has been etched to a smaller cladding diameter to detune phase matching so that maximum coupling is 50%.

Claim 6

A splitter as defined in claim 1 in which the cross-section of the fibers at their junction in the coupler is dumb-bell shaped.

Claim 7

A splitter as defined in claim 1 in which a monomode optical signal is coupled from the smaller cladding diameter fiber of lower normalized frequency (V) to the larger cladding diameter fiber of higher normalized frequency (V) and an output signal from the larger cladding diameter fiber is in a higher order mode than said monomode signal.

Claim 8

A splitter as defined in claim 1, in which the smaller cladding diameter fiber is of similar type as the larger cladding diameter fiber but has been etched to a smaller cladding diameter.

Claim 9

A splitter as defined in claim 3 in which the predetermined wavelength or band is dependent on the cladding diameter ratios of the respective fibers.

Claim 10

A splitter as defined in claim 1, further including a third non-identical monomode or quasi monomode optical fiber having a biconical taper and being fused at its waist to the fused portion of said twin splitter to form a three input and three output splitter, the cladding diameter of the third fiber before splitter fabrication being different than other fibers of said pair, whereby selective coupling from one fiber to either of the other fibers can be obtained at different wavelengths.

Claim 11

A splitter as defined in claim 9 including means for bending the splitter to effect said selective coupling.

Claim 12

A splitter as defined in claim 1 in which the pair of fibers is hard fused.

Claim 13

A fused twin biconical taper fiber optic splitter as defined in claim 1 in which the fibers are tapered adiabatically to a waist region, the fibers being hard fused over the waist and which includes at least a portion of their tapered regions, an optical signal being carried by one fiber first passing through a decreasing taper region of one fiber and then passing through an increasing taper region of said one or the other fiber, the decreasing taper rate of said one fiber being such that the optical signal radiates out of the core and into the cladding, the increasing taper rates of said one and the other fiber being such that a predetermined coupling ratio is obtained at a predetermined wavelength or band and means for bending the coupler in the region of the waist whereby coupling can be selected at said wavelength or band between the decreasing taper or the waist region of said one fiber and the increasing taper or the waist of the other fiber.