Directional coupler for coupling single-polarization optical fibers

Claim 1

A directional coupler for coupling together two single-polarization optical fibers each comprising a core, a cladding enclosing the core, an elliptic jacket enclosing the cladding to form a jacketed single-polarization optical fiber, the elliptic jacket having a major axis and a minor axis perpendicular to said major axis, and a support surrounding the elliptic jacket for applying a stress to the core due to a difference in thermal expansion between the jacket and the support; said coupler being prepared by the steps of: preparing first and second quartz substrates each of which has a channel on one major surface thereof, each channel having a size equal to or slightly wider than the outer diameter of the support surrounding the jacketed optical fiber; embedding and bonding the jacketed optical fibers with associated supports in the channels in the first and second substrates, respectively, such that the major axis of the elliptic jacket of each of the jacketed optical fibers extends approximately perpendicular to the major surface of the respective substrate; abrading away each of the first and second substrates together with the jacketed optical fiber embedded therein from the major surfaces of the substrates to a depth where light traveling in the core of the respective optical fiber may leak out; placing one of the first and second substrates on the other of the first and second substrates with the abraded surfaces of the first and second substrates facing each other; bonding the first and second substrates together in said facing relationship to keep the cores of said optical fibers in sufficiently close relation to establish evanescent wave coupling therebetween; and preventing stresses existing in each core prior to said abrading step from being released by; applying a stress to each jacketed optical fiber through its associated support by arranging stress applying means externally of said optical fibers, and applying said stress in a direction approximately perpendicular to the major axis of the elliptic jacket of the respective optical fiber.

Claim 13

A method of making a directional coupler for coupling two single-polarization optical fibers each comprising a core, a cladding enclosing the core, an elliptic jacket enclosing the cladding to form a jacketed single-polarization optical fiber, the elliptic jacket having a major axis and a minor axis perpendicular to said major axis, and a support surrounding the elliptic jacket for applying stress to the core due to a difference in thermal expansion between the jacket and the support; the method comprising the steps of: preparing first and second quartz substrates each of which has a channel on one major surface thereof, each channel having a size equal to or slightly wider than the outer diameter of the support surrounding the jacketed optical fiber; embedding and bonding the jacketed optical fibers with associated supports in the channels in the first and second substrates, respectively, such that the major axis of the elliptic jacket of each of the jacketed optical fibers extends approximately perpendicular to the major surface of the respective substrate; abrading away each of the first and second substrates together with the jacketed optical fiber embedded therein from the major surfaces of the substrates to a depth where light traveling in the core of the respective optical fiber may leak out; placing one of the first and second substrates on the other of the first and second substrates with the abraded surfaces of the first and second substrates facing each other; bonding the first and second substrates together in said facing relatinship to keep the cores of said optical fibers in sufficiently close relation to establish evanescent wave coupling therebetween; and preventing stresses existing in each core prior to said abrading step from being released by; externally applying a stress to each fiber in a direction approximately perpendicular to the major axis of the elliptic jacket of the respective optical fiber.

Claim 14

A method of making a directional coupler for coupling two single-polarization optical fibers each comprising a core, a cladding enclosing the core, an elliptic jacket enclosing the cladding to form a jacketed single-polarization optical fiber, the elliptic jacket having a major axis and a minor axis perpendicular to said major axis, and a support surrounding the elliptic jacket for applying stress to the core due to a difference in thermal expansion between the jacket and the support; the method comprising the steps of: preparing first and second quartz substrates each of which has a channel on one major surface thereof, each channel having a size equal to or slightly wider than the outer diameter of the support surrounding the jacketed optical fiber; embedding and bonding the jacketed optical fibers with associated supports in the channels in the first and second substrates, respectively, such that the major axis of the elliptic jacket of each of the jacketed optical fibers extends approximately perpendicular to the major surface of the respective substrate; abrading away each of the first and second substrates together with the jacketed optical fiber embedded therein from the major surfaces of the substrates to a depth where light traveling in the core of the respective optical fiber may leak out; placing one of the first and second substrates on the other of the first and second substrates with the abraded surfaces of the first and second substrates facing each other; bonding the first and second substrates together in said facing relatinship to keep the cores of said optical fibers in sufficiently close relation to establish evanescent wave coupling therebetween; and preventing stresses existing in each core prior to said abrading step from being released by; externally applying a stress to each fiber in a direction approximately perpendicular to the major axis of the elliptic jacket of the respective optical fiber.