In Situ Characterization Of Single-Wall Carbon Nanotube Thin Film Growth Using The Polarization Properties Of Tilted Fibre Bragg Gratings.

摘要

In this thesis, we explore the polarization dependent properties of the tilted fibre Bragg gratings for the in situ characterization of single-wall carbon nanotubes deposited on the cladding of a fibre using a layer-by-layer deposition technique.;Next, we present the polarization dependent coupling properties of the tilted fibre Bragg gratings: id periodic index modulation in the core of an optical fibre with a tilt with respect to the fibre axis that enhances coupling of light from the linearly polarized core mode to the contra-directional cladding modes. We prove that by controlling the orientation of the core mode electric vector with respect to the plane of the tilt of the gratings, one can couple either only to the radially polarized or to the azimuthally polarized cladding modes. This is the first ever comprehensive theoretical description of the polarization dependent guided cladding mode coupling properties of the tilted fibre Bragg gratings.;Finally, we report the first ever effort to investigate the polarization dependent optical properties of randomly oriented single-wall carbon nanotubes on the nanometre scale. The carbon nanotube films are grown on the cladding of the fibre using a layer-by-layer technique. Weakly tilted Bragg gratings in the core of the fibre allows in situ characterization of the film. We report that such a film exhibits strong polarization dependent loss: radially polarized cladding modes experience up to five times more loss than azimuthally polarized modes for films of up to tens of nanometres thickness. This is the first ever observation of the polarization dependent loss on a nanometre scale thin randomly oriented carbon nanotube film. However, the film exhibits no birefringence and the optical constants are strongly thickness dependent.;First, we describe an exact analytical and fully-vectorial solution of the cladding modes of a standard telecom fibre. The cladding of an optical fibre is a multimode wave guide and can support many thousands of modes. We present an algorithm to efficiently solve the complex propagation constants of the cladding modes. Our analysis shows that based on the polarization properties, the cladding modes can be classified into two categories: dominant radial and dominant azimuthal. The formalism is then extended to an arbitrary four layer fibre structure.