Photonic Systems Based on Carbon Nanotubes: Photoluminescence Enhancement and Saturable Absorbers by Inkjet Printing and Integration on Fibre Tapers

Abstract

The multifunctional properties of single-wall carbon nanotubes (SWNTs) created a robust platform for unprecedented innovations in a variety of applications in photonics, sensors, electronics, smart manufacturing and drug delivery. This thesis presents an experimental study of the author’s research using innovative approaches for the development of photonic systems based on SWNTs’ dispersions and composites, featuring enhanced and effective optical properties. The first set of experiments demonstrates a novel approach for the enhancement of SWNTs’ photoluminescent (PL) properties via complexation with organic dyes. One of the more significant findings to emerge from this investigation is the interaction of the indopentamethinedioxaborine dye (DOB-719) with SWNTs, which resulted in new optical features in the spectral range of the intrinsic excitation of the dye, providing clear evidence of the resonance energy transfer from DOB-719 to the SWNTs. The findings from this study allowed for the proposal of the mechanism of interaction between the SWNT and DOB-719, where the dye is attracted to the SWNT surface via π-π stacking with the hydrophobic part facing the aqueous medium by polar groups. The second set of experiments examined a limitation imposed by the use of SWNT-polymer composites for saturable absorber (SA) applications. The integration of this device in the fibre cavity resulted in modification of the composite properties under continuous high power laser irradiation, which limits the use of composites to generate ultrashort pulses with stable parameters for a long operation time (>10,000 hours). This stimulated the design of advanced approaches in this work as an alternative to the composite method. The first approach describes a method for the controllable integration of SWNT directly on the core of a fibre edge, using the inkjet printing technique. It is important to note that a direct correlation between the number of printed layers and properties of SA was determined, showing that a SA with 20,000 layers gives the best parameters. The obtained output power and pulse energy are higher than all earlier reported results on SA for erbium-doped fibre lasers using sandwiched SWNT- composites. The second approach is to coat the tapered fibre with a low refractive index SWNT-polymer composite. This method depends on lateral interaction with the evanescence field of the propagating pulse in the laser cavity. The study reports SAs devices with controllable saturation intensity, low losses and large saturable to non-saturable loss ratios.