Asymptotic theory of strong spin-orbit coupling in optical fiber.

The spin-orbit coupling of light propagating in optical fiber can be dramatically enhanced by the presence of a high-contrast interface in the refractive index profile, even for modes that are highly paraxial. The resulting modes have spatial and polarization structures that depart greatly from the weak coupling form, and, in particular, are neither orbital nor spin angular momentum eigenstates. We explain the physical origins of this strong-coupling regime with a vector geometric theory of diffraction expansion.

Complex mode amplitude measurement for a six-mode optical fiber.

We propose a measurement protocol and parameter estimation algorithm to recover the powers and relative phases of each of the vector modes present at the output of an optical fiber that supports the HE11, TE01, HE21, and TM01 modes. The measurements consist of polarization filtered near-field intensity images that are easily implemented with standard off-shelf components. We demonstrate the accuracy of the method on both simulated and measured data from a recently demonstrated fiber that supports stable orbital angular momentum states.

Control of orbital angular momentum of light with optical fibers.

We present a fiber-based method for generating vortex beams with a tunable value of orbital angular momentum from -1ℏ to +1ℏ per photon. We propose a new (to our knowledge) method to determine the modal content of the fiber and demonstrate high purity of the desired vortex state (97% after 20 m, even after bends and twists). This method has immediate utility for the multitude of applications in science and technology that exploit vortex light states.

Impact of fiber design on polarization dependence in microbend gratings.

Polarization dependence in microbend gratings is an inherent problem. We formulate simple analytical expressions to describe it, and demonstrate their effectiveness via a comparison with experimental results on a standard transmission fiber. The ability to control polarization dependence with fiber design potentially enables replacing UV-LPGs within low-cost, tunable microbend gratings.