Abstract: Techniques for analyzing output modal content of optical fibers that support more than one spatial mode are disclosed. These techniques are based on spatially resolving interference between co-propagating modes and constructing a spatial beat pattern between the co-propagating modes. By doing so, these techniques provide information about the modes that propagate along the optical fiber.

Abstract: A fiber is wound into first and second coils lying substantially in respective first and second planar directions having a substantially orthogonal relationship. The first and second coils are configured to result in respective first and second birefringences that are dominated by bend-induced birefringence. The first and second birefringences have respective axes that are rotated with respect to each other in real space by an angle that is substantially equal to 90 degrees. Light traveling through the fiber has a state of polarization that evolves in substantially opposite directions as it travels respectively through the first and second coils. The first and second coils are configured such that light traveling through the fiber acquires respective, substantially opposite first and second phase shifts. Light traveling through the fiber acquires respective first and second differential group delays that substantially compensate for each other.