Manipulation of a Photon's Wave Function in Optical Fibers

Margaret E. Raabe


A method was developed to manipulate a photon's spatial wave function inside an optical fiber. This method involved placing physical stress on the fiber and utilized a phase-stable Sagnac interferometer that acts as a two-dimensional (2D) parity sorter. An out-of-plane Sagnac interferometer was successfully designed and built that sorts laser modes that exit the fiber based on their two-dimensional spatial symmetry into two separate ports. By comparing measured results to theoretical predictions, it was shown that this sorter can successfully separate modes with even 2D spatial parity into one output port and modes with odd 2D spatial parity into a separate output port. This condition is necessary in order to isolate the first-order Hermite-Gauss (HG) modes that are desired to study.

It was shown that by imparting physical stress on an optical fiber, one is able to transfer orbital angular momentum (OAM) to a laser mode's orthogonal components while it is propagating inside the fiber. This essentially induces a phase shift Φ on the propagating mode. The result from this is a different mode exiting the fiber than enters the fiber. A phase shift of π/2 and π were successfully induced on an incident HG+4510 mode. When this mode underwent a phase shift of π/2, it was output from the fiber as a Laguerre-Gauss (LG) mode. Using this device, one can manipulate any first-order mode input with a given Bloch sphere latitude θ to exist with any phase Φ with a given amount of stress. Most analysis was performed qualitatively by comparing measured data to theoretical data. The next step in furthering this research would be to develop a more quantitative method of analysis and improve the current crushing device to ensure more repeatability in results.