Understanding and Controlling Angular Momentum Coupled Optical Waves in Chirally-Coupled-Core (CCC) Fibers.

Abstract

In this dissertation a new type of fiber structure | so called Chirally-Coupled-Core (CCC) fiber | is extensively explored. Work presented here establishes theoretical, numerical and experimental foundations of describing optical phenomena in these novel structures, and provides with methods and tools required to design them. CCC fibers have been a very interesting topic of study due to their unusual symmetry (they are helically symmetric), novel nature of wave interactions within them, and the technological importance of their applications. We have discovered that operation of CCC fibers is based on optical wave interactions that involve both orbital and spin angular momentum of the propagating modes. This is the first and so far the only known example when optical angular momentum is involved in optical interactions.

In this thesis we first show experimental evidence of multitude of optical resonances that cannot be explained within the framework of conventional phase-matched interactions. Then we show that these observations can be explained through optical-angular momentum assisted optical interactions of optical waves in these structures. Based on this approach we demonstrate a primary application of CCC structures: large core fibers that perform as effectively single mode fibers. Furthermore, we develop a rigorous theoretical model starting from Maxwell equations in curvilinear helical coordinates to describe CCC fiber properties. We show that theoretically predicted optical-resonance positions agree very well with experimental results. We also address the ultimate core-size scaling potential of effectively -single-mode CCC fibers. Due to the unusual nature of wave interactions in CCC structures all previously known numerical beam-propagation methods appear to be unsuitable for CCC structures. In order to provide with the numerical tools necessary to design and explore these fibers we have developed a new beam-propagation approach, which appears to provide with accurate predictions of CCC fiber performance.