Abstract: The specification describes tuning devices for controlling variable polarization dependent loss. These are based on the discovery that essential properties of TAP LPGs can be realized in birefringent fibers, i.e. in fibers where the propagation constants of the core and/or cladding modes are different for different SOPs of light. This yields a device that exhibits broadband loss of varying amounts for different SOPs of input light. Thus, the building block for a broadband in-fiber polarizer is realized. Tuning mechanisms are applied to vary the relative coupling magnitudes for two orthogonal SOPs of light in the device. This yields a polarizer in which the polarization is dynamically tuned.

Abstract: The specification describes optical mode converters wherein coupling is made between a fundamental, or near fundamental, propagation mode and the next, or closely adjacent, higher order mode (HOM). Both modes propagate in the core of the optical fiber, thus maintaining efficient transmission through the mode converter. Mode coupling is effected using a long period grating (LPG) and the strength of the mode coupling is dynamically varied by changing the period of the grating or by varying the propagation constants of the two modes being coupled. The period of the grating is varied by physically changing the spacing between grating elements, for example by changing the strain on the grating to physically stretch the LPG. The propagation constants of the modes can be varied using any method that changes the refractive index of the fiber containing the LPG, for example, by changing the temperature, or electrically changing the index using the electro-optic effect.

Abstract: An optical fiber-based device exhibiting tunable birefringence utilizes a section of fiber including an optically nonlinear core region (i.e., doped with a material such as vanadium or erbium), where the fiber is configured to exhibit circular asymmetry and thus introduce birefringence into the fiber. The circular asymmetry may be accomplished by depositing the nonlinear core material in an asymmetric pattern or by launching the pump signal into an asymmetric mode of the fiber waveguide (i.e., an LP[1,m] mode). Polarization control can be generated by such a device through controlling the intensity of an input optical pump signal, since the pump signal intensity has been found to control the birefringence of a circularly asymmetric fiber waveguide.

Abstract: The specification describes tuning devices for controlling variable polarization dependent loss. These are based on the discovery that essential properties of TAP LPGs can be realized in birefringent fibers, i.e. in fibers where the propagation constants of the core and/or cladding modes are different for different SOPs of light. This yields a device that exhibits broadband loss of varying amounts for different SOPs of input light. Thus, the building block for a broadband in-fiber polarizer is realized. Tuning mechanisms are applied to vary the relative coupling magnitudes for two orthogonal SOPs of light in the device. This yields a polarizer in which the polarization is dynamically tuned.

Abstract: The specification describes optical mode converters wherein coupling is made between a fundamental, or near fundamental, propagation mode and the next, or closely adjacent, higher order mode (HOM). Both modes propagate in the core of the optical fiber, thus maintaining efficient transmission through the mode converter. Mode coupling is effected using a long period grating (LPG) and the strength of the mode coupling is dynamically varied by changing the period of the grating or by varying the propagation constants of the two modes being coupled. The period of the grating is varied by physically changing the spacing between grating elements, for example by changing the strain on the grating to physically stretch the LPG. The propagation constants of the modes can be varied using any method that changes the refractive index of the fiber containing the LPG, for example, by changing the temperature, or electrically changing the index using the electro-optic effect.

Abstract: The specification describes an optical filter wherein long period gratings (LPGs) are used in a new configuration to provide in-line bandpass filtering of optical signals. In the basic embodiment, two dissimilar LPGs are installed in the optical fiber transmission line. The first LPG converts light, over a broad wavelength range, being transmitted in the fundamental, or LP01, mode of the optical fiber transmission line into light in a higher order mode (HOM) of the optical fiber. The mode-converted signal, with mode LPm,n, is then coupled to a second waveguide, the second waveguide having transmission characteristics different from those of the first. The second waveguide supports propagation of light in a LPm,n mode. The mode-converted signal is then transmitted through a second LPG where the signal over a selected narrow band of wavelengths that is accepted by the second LPG is converted back to a LP01 mode.