Abstract: A method of measuring fiber twist in a multi-core optical fiber bearing an FBG with polarization dependent reflectivity. The state of polarization of the launched light is adjusted until the reflected FBG wavelength is maximal, indicating that light reaching the FBG is linearly polarized, and the polarization axis of the light reaching the FBG is aligned with the slow birefringent axis of the FBG; the SOP of launched light is now measured. Bending experienced by the fiber is measured conventionally, and birefringence produced by bending of the multi-core optical fiber is calculated. A candidate amount of twist between the launch location and the FBG is proposed, and the corresponding twist-induced birefringence is calculated. When calculations show that light with the launched SOP becomes linearly polarized and aligned with the FBG after traversing a fiber section with the calculated birefringences and proposed rotation, the amount of twist has been properly identified.

Abstract: An apparatus and accompanying method to measure fiber twist. The method includes independent determination of fiber bending by measuring strain sensing in outer cores of the same fiber. The apparatus includes a multi-core optical fiber comprising a center core and a plurality of peripheral cores at a distance radially from the center core and running parallel to the center core. The center core includes at least one fiber Bragg grating with polarization-dependent reflectivity. The fiber Bragg grating reflects the launched light as reflected light. The apparatus includes a multi-core optical fiber bend sensing system operable to communicate with the multi-core optical fiber. The multi-core optical fiber bend sensing system is operable to sense a bend in the multi-core optical fiber. The apparatus includes a processor operable to communicate with the polarization controller.

Abstract: A method of measuring fiber twist in a multi-core optical fiber bearing an FBG with polarization dependent reflectivity. The state of polarization of the launched light is adjusted until the reflected FBG wavelength is maximal, indicating that light reaching the FBG is linearly polarized, and the polarization axis of the light reaching the FBG is aligned with the slow birefringent axis of the FBG; the SOP of launched light is now measured. Bending experienced by the fiber is measured conventionally, and birefringence produced by bending of the multi-core optical fiber is calculated. A candidate amount of twist between the launch location and the FBG is proposed, and the corresponding twist-induced birefringence is calculated. When calculations show that light with the launched SOP becomes linearly polarized and aligned with the FBG after traversing a fiber section with the calculated birefringences and proposed rotation, the amount of twist has been properly identified.

Abstract: An apparatus and accompanying method to measure fiber twist. The method includes independent determination of fiber bending by measuring strain sensing in outer cores of the same fiber. The apparatus includes a multi-core optical fiber comprising a center core and a plurality of peripheral cores at a distance radially from the center core and running parallel to the center core. The center core includes at least one fiber Bragg grating with polarization-dependent reflectivity. The fiber Bragg grating reflects the launched light as reflected light. The apparatus includes a multi-core optical fiber bend sensing system operable to communicate with the multi-core optical fiber. The multi-core optical fiber bend sensing system is operable to sense a bend in the multi-core optical fiber. The apparatus includes a processor operable to communicate with the polarization controller.

Abstract: An aspect of the present invention is an optical spectrometer for detecting a spectral signature of a input optical signal, including: (a) a collimating lens having an optical axis and focal plane, for collimating the input optical signal; (b) an input optical system, for directing the input optical signal to the collimating lens; (c) a diffraction grating, for scattering the collimated input optical signal, positioned in the path of collimated light from the collimating lens, oriented to reflect a majority of the scattered light through the collimating lens; and (d) a detector, in a focal plane of the collimating lens. Another aspect of the invention is a fiber-based sensing system using the optical spectrometer of the invention.

Abstract: A process for making an optical reflection grating in a glass fiber includes exposing an unjacketed optic fiber to a single writing pulse from a pair of interfering light beams that form an interference pattern in the fiber. A novel optical fiber has at least one optical grating with a preselected Bragg spacing in at least one region of the fiber, with a periodic modulation in its index of refraction, with high thermal stability and narrow linewidth. A process for making an array of optical reflection gratings in a glass fiber includes exposing a fiber to a plurality of writing pulse from a pair of interfering light beams that form an interference pattern in the fiber, where these pulses are applied sequentially as the fiber is drawn from a draw furnace. A novel optical fiber has a plurality of unspliced gratings with high thermal stability and narrow linewidth.

Abstract: A technique and apparatus for detecting the internal rotation of the principal axes in the fabrication of birefringent fibers is based upon a new method for producing and interpreting the interference fringe pattern backscattered power from a birefringent fiber side-illuminated with a laser light source to determine the internal orientation of the strain-inducing axes. An apparatus employing this technique for controlling internal rotation of the principal axes provides for adjustment of the orientation of at least one of the traction surfaces pulling the fiber during drawing fabrication to maintain parallel alignment of the planes of rotation of the surfaces to reduce the fiber rotation-inducing motion which leads to internal rotation of the fiber's principal axes.