Optical fiber coupler with tunable coupling ratio and method of making
First Claim
1. A unidirectional optical fiber coupler comprising a pair of virtually identical optical fibers each comprised of a core and cladding and being fused together at a narrow tapered waist, each fiber being tapered toward and away from the waist, means for translating an optical signal in single mode and carried by one fiber in the core at one side of the waist to multi-mode carried by the cladding at least adjacent the narrowest portion of the waist, and for translating the signal in multi-mode to single mode carried by the core of either said one or the other fiber or both fibers at the other side of the waist.
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Accused Products
Abstract
An optical coupler for single mode optical signals having a tunable (variable) coupling ratio, and a method of fabricating the coupler. A pair of virtually identical optical fibers are fused together at a narrowed waist region, each fiber being formed of a core and cladding, each being tapered toward the waist in such a manner as to ensure adiabatic propagation of light in the structure. An optical signal carried by one fiber first passes through a decreasing taper region and then passes through an increasing taper region of one or the other fiber (or both). The decreasing taper rate of the input portion of one fiber is such that the optical signal radiates out of the core (where V=1 locally) and into the cladding, as it approaches the waist. The increasing taper rates of the output portions of the two fibers are such that a predetermined coupling ratio is obtained. The coupler is bent in the region of the waist whereby a coupling ratio can be selected between the incoming fiber portions having the decreasing taper and the outgoing fibers having increasing tapers.
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Citations
11 Claims
- 1. A unidirectional optical fiber coupler comprising a pair of virtually identical optical fibers each comprised of a core and cladding and being fused together at a narrow tapered waist, each fiber being tapered toward and away from the waist, means for translating an optical signal in single mode and carried by one fiber in the core at one side of the waist to multi-mode carried by the cladding at least adjacent the narrowest portion of the waist, and for translating the signal in multi-mode to single mode carried by the core of either said one or the other fiber or both fibers at the other side of the waist.
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9. A unidirectional optical fiber coupler comprising a pair of virtually identical fibers each comprised of a core and cladding, the cladding of one being fused to the cladding of the other at a narrow waist portion in which the diameters of both the core and the cladding are narrowed, being tapered adiabatically to the waist region, the diameters of the refractive indices of the cores and cladding in the region of the waist portion being such that for the fiber core waveguide:
- V≦
1 where ##EQU6## in which;
V is the normalized frequency (local) of the coupler (dimensionless),a is the (local) radius of the core, λ
is the wavelength of an optical signal passing through the coupler and,ncore and ncladding are the indices of refraction of the core and cladding respectively, but that V associated with the waveguide formed by the air-cladding interface is greater than a value in which the antisymmetric transmission mode of the cladding waveguide radiates out of the cladding. - View Dependent Claims (10, 11)
- V≦
Specification