Design and measurements of novel electromagnetic properties in spiral transmission fibers

摘要

One dimensional photonic band gap fibers have proven to be fascinating and versatile devices, as demonstrated by many applications. The ability to control and design these fibers to achieve specific functionalities will enable us to advance the research done with these fibers and to gain new applications. In this work we explore our ability to control different fabrication parameters to design a fiber according to certain requirements. We use these capabilities to design and fabricate a near IR fiber for high peak power laser transmission. Since a multimode fiber supports many modes one can gain further control over fiber properties by controlling modal content in the fiber. We developed two techniques for controlled coupling and demonstrated them using one dimensional photonic band gap fibers. Using a spatial light modulator, one can dynamically control the modal content in the fiber, including superposition of more than one mode. We experimentally demonstrate this capability by coupling to one of two modes and superposition of the two. Using a static technique, we experimentally demonstrate a single-mode transmission of the azimuthally polarized mode (TEoi) in a highly multimode cylindrical photonic band gap fiber. Theoretical calculations verify the validity of this technique and accurately predict the coupling efficiency. Single-mode propagation in a large hollow core fiber can enable numerous applications, especially in control of particles along the entire length of the fiber. Finally, we examined the effects of the spiral cross-section of the fiber on its optical properties. The fiber's chiral symmetry combined with its infinite translational symmetry creates a truly planar chiral structure, similar to many artificial chiral structures recently studied. The low-symmetry geometry of the fiber, which lacks any rotational and mirror symmetries, exclusively supports modes with angular momentum greater than zero and shows in-principle directional optical activity and asymmetric propagation. We use general symmetry arguments to provide qualitative analysis of the waveguide's modes and numerically corroborate this using finite element simulation. We also demonstrated these properties experimentally using spiral fibers.