Self-aligning optical fiber and fiber-ring optical resonator using same

Claim 2

An optical fiber as claimed in claim 1, wherein each of said flat surface-portions (29,30) is located closer to said guiding region than the fiber surface-portion on the opposite side of said guiding region from said flat surface-portion, so that etching the outer surface of the fiber exposes the guiding region only at the flat surface-portions.

Claim 3

An optical fiber as claimed in claim 1, wherein said core (26) has an elliptical cross-section.

Claim 4

An optical fiber as claimed in claim 1, which includes a support layer (28) surrounding said guiding region and forming said exterior flat surface-portions on said fiber (25).

Claim 5

An optical fiber as claimed in claim 4, wherein said support layer (28) has an index of refraction higher than that of said cladding (27).

Claim 6

An optical fiber as claimed in claim 1, wherein the fiber (25) is drawn from a preform having a non-circular cross-section similar in shape to the cross-section of the outer surface of the fiber.

Claim 7

An optical fiber as claimed in claim 1, wherein the core (26) of said fiber (25) has a non-circular cross-section defining two transverse orthogonal axes, said core (26) having a longer transverse dimension along one of said orthogonal axes than along the other of said axes for guiding two fundamental modes, one of said modes having an electric field parallel to the axis of the longer transverse dimension and the other of said modes having an electric field parallel to the axis of the shorter transverse dimension, the difference in the core dimensions along said orthogonal transverse axes and the difference between the refractive indices of said core and cladding is sufficiently large to de-couple the fundamental modes so that the polarization of said modes is preserved within the fiber, and said flat surface-portions (29,30) on the exterior of the fiber have a predetermined geometric relationship to said guiding region and said orthogonal transverse axes so that the location of said guiding region and the orientation of said axes can be ascertained from the geometry of said flat surface-portions on the exterior of the fiber.

Claim 8

A co-polarized directional coupler comprising a pair of optical fibers (51,52) each as claimed in claim 1 having the flat surface-portions (29,30) parallel to a common one of said orthogonal axes facing each other and having their fields coupled to each other along an interaction length.

Claim 9

A co-polarized directional coupler as claimed in claim 8, wherein said optical fibers (53,54) have cores with elliptical cross-sections, and the facing flat surface-portions are parallel to the major axes of said elliptical cores.

Claim 10

A co-polarized directional coupler as claimed in claim 8, wherein said optical fibers (51,52) have cores with elliptical cross-sections, and the facing flat surface-portions are parallel to the minor axes of said elliptical cores.

Claim 11

A cross-polarized directional coupler comprising a pair of optical fibers (55,56) as claimed in claim 1 having cores with elliptical cross-sections, the flat surface-portions of one fiber parallel to the minor axis of the elliptical core therein facing the flat surface-portion of the other fiber parallel to the major axis of the elliptical core therein.

Claim 12

A four-way directional coupler comprising four optical fibers (57-60) as claimed in claim 1, said fibers being positioned so that each flat surface-portion on each fiber is facing a flat surface-portion of another fiber.

Claim 14

The method of claim 13 wherein said preform and said fibers joined thereon have about the same coefficients of thermal expansion.

Claim 15

The method of claim 13 wherein said preform is shaped to form a longitudinal groove with orthogonal side walls so that in the drawn preform said orthogonal side walls are complementary to said orthogonal reference surface-portions.

Claim 16

A method of forming an optical fiber joint as set forth in claim 13, wherein the transverse cross-section of said guiding region is symmetrical about only a single transverse axis of said fiber, said orthogonal exterior flat surface-portions intersecting at a point on said single transverse axis.

Claim 17

An optical fiber rotation sensor comprising a sensing ring (46) formed by splicing the ends of an optical fiber comprising a core and cladding having different refractive indices and forming a single-mode guiding region, said guiding region being offset from the center of gravity of the transverse cross-section of the fiber, the outer surface of the fiber having a pair of orthogonal exterior flat surface-portions so that the location of said guiding region can be ascertained from the exterior geometry of the fiber, a source (40) of coherent light waves, a polarization-holding optical fiber loop (41a) having one end connected via a first directional coupler (42) to said source (40) for guiding light waves from said source (40) to said sensing ring (46), the first directional coupler (42) connected to both ends of said loop (41a) for coupling a portion of the light waves from said source (40) to the other end of said loop (41a) so that light waves from the source (40) are propagated in both directions around said loop, a second directional coupler (45) connecting said fiber loop (41a) and said sensing ring (46), and a third directional coupler (43,44) connecting said fiber loop (41a) and a photodetector (49,50).

Claim 18

An optical fiber rotation sensor as claimed in claim 17, wherein said second directional coupler (45) loosely couples lightwaves between said fiber loop (41a) and said sensing ring (46).

Claim 19

An optical fiber rotation sensor as claimed in claim 17, wherein said second directional coupler (45) is a 10-dB coupler.

Claim 20

An optical fiber rotation sensor as claimed in claim 17, wherein said first (42) and third (43,44) directional couplers are 3-dB couplers.

Claim 21

An optical fiber rotation sensor as claimed in claim 17, wherein said flat surface-portions on said spliced ends of the optical fiber forming said sensing ring (46) are aligned by engagement with common longitudinal surfaces of a substrate.

Claim 22

An optical fiber rotation sensor as claimed in claim 21, wherein said substrate has a transverse cross-section complimentary with that of the fibers, thereby forming said common longitudinal surfaces.

Claim 23

An optical fiber as claimed in claim 1, wherein the core of said fiber has a non-circular cross-section defining two transverse orthogonal axes, said core having a longer transverse dimension along one of said orthogonal axes than along the other of said axes for guiding two fundamental modes, one of said modes having an electric field parallel to the axis of the longer transverse dimension and the other of said modes having an electric field parallel to the axis of the shorter transverse dimension, the difference in the core dimensions along said orthogonal transverse axes and the difference between the refractive indices of said core and cladding is sufficiently large to de-couple the fundamental modes so that the polarization of said modes is preserved within the fiber, and said flat surface-portions on the exterior of the fiber have a predetermined geometric relationship to said guiding region and said orthogonal transverse axes so that the location of said guiding region and the orientation of said axes can be ascertained from the geometry of said flat surface-portions on the exterior of the fiber.

Claim 25

An optical fiber splice comprising a pair of optical fibers each of which has a core and cladding having different refractive indices and forming a single-mode guiding region, said fibers each having an outer surface having a pair of orthogonal exterior flat surface-portions so that the locations of the guiding regions can be ascertained from the exterior geometry of the fibers, said guiding regions being identically offset from the centers of gravity of the transverse cross-sections of the respective fibers and located sufficiently close to at least one of said flat surface-portions to allow coupling to a guided wave through that surface, and a substrate extending longitudinally along the spliced portions of said fibers and having a transverse cross section complementary to that of said fibers, the flat surface-portions of said fibers being aligned longitudinally by engagement with the corresponding flat surfaces of said substrate, the ends of said fibers being bonded to each other and to said substrate.