Fiber-optic rotation sensor

A fiber-optic rotation sensor comprising a coil of polarization-holding, single-mode optical fiber having a single core and cladding with different refractive indices and forming a single-mode guiding region,

• the core of said fiber having 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 being sufficiently large to de-couple the fundamental modes so that the polarization of said modes is preserved within the fiber,
• said guiding region being offset from the geometric center of the fiber and located sufficiently close to one side of the surface of the fiber to allow coupling to a guided wave through said one side by exposure or expansion of the field of the guiding region, and
• the outer surface of the fiber having a non-circular cross-section forming an indexing surface with 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 indexing surface on the exterior of the fiber,
• said coil being wound on a substrate with a constant geometric relationship between said indexing surface on said fiber and the surface of said substrate, thereby accurately locating said transverse axes of said fiber relative to said substrate, the shorter transverse dimension of said core being normal to the surface of said substrate so as to minimize the bending stresses in the fiber due to the winding of the fiber into a coil,
• a laser source for supplying optical signals to said coil, and
• a photodetector for receiving optical signals from said coil.

A fiber-optic rotation sensor comprising a coil of polarization-holding, single-mode optical fiber having a single core and cladding with different refractive indices and forming a single-mode guiding region,

• the core of said fiber having 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 being sufficiently large to de-couple the fundamental modes so that the polarization of said modes is preserved within the fiber,
• said guiding region being offset from the geometric center of the fiber and located sufficiently close to one side of the surface of the fiber to allow coupling to a guided wave through said one side by exposure or expansion of the field of the guiding region, and
• the outer surface of the fiber having a non-circular cross-section forming an indexing surface with 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 indexing surface on the exterior of the fiber,
• said coil being wound on a substrate with a constant geometric relationship between said indexing surface and the surface of said substrate, thereby accurately locating said transverse orthogonal axes of said guiding region relative to said substrate,
• a laser source for supplying optical signals to said coil, and
• a photodetector for receiving optical signals from said coil.

A fiber-optic rotation sensor comprising a coil of polarization-holding, single-mode optical fiber having a single core and cladding with different refractive indices, said fiber also having a directional coupler integral with each end portion of the coiled optical fiber,

• the core of said fiber having 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 being sufficiently large to de-couple the fundamental modes so that the polarization of said modes is preserved within the fiber,
• said guiding region being offset from the geometric center of the fiber and located sufficiently close to one side of the surface of the fiber to allow coupling to a guided wave through said one side by exposure or expansion of the field of the guiding region, and
• the outer surface of the fiber having a non-circular cross-section forming a flat indexing surface with 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 indexing surface on the exterior of the fiber,
• the directional coupler integral with one end portion of the fiber having an input fiber portion excited by and splitting light from a source of coherent light,
• the directional coupler integral with the other end portion of the fiber having an output fiber portion transmitting combined light from the two end portions of the coiled optical fiber,
• said optical fiber having a generally uniform cross-section along its entire length,
• said coil being wound on a substrate with said flat outer indexing surface of said fiber continuously facing the substrate to maintain a constant geometric relationship between said orthogonal transverse axes of the core of said fiber and the surface of said substrate, thereby accurately locating said tranverse axes relative to said substrate, and
• a photodetector receiving the combined light from said directional coupler integral with said other end portion of said fiber.