Polymer-based optical waveguides are a promising technology for integrating optical links onto standard printed circuit boards as they enable cost-effective manufacturing and assembly as well as offer high bandwidth. The motivation for this work is to address the lack of amplifying components the currently demonstrated polymer interconnects, which limits the complexity, functionality and reach of these systems. This dissertation studies combination of rare-earth-doped material with polymer platform to create compact erbium-doped waveguide amplifiers (EDWAs) for board-level interconnect applications.
Siloxane polymer materials developed by Dow Corning are used as they have shown the necessary optical, mechanical and thermal properties required for EDWA designs (such as the ability to withstand temperatures in excess of 350 °C). The feasibility of two approaches for integrating Er-doped materials into siloxane polymer layers is investigated, namely: (i) ultrafast laser plasma implantation (ULPI) and (ii) solution-based dispersion of Er-doped nanoparticles (NP). Er-doped thin films are prepared with these two methods and their properties investigated. The maximum dopant concentrations and lifetimes are determined to be 16.3, 4.4 and 1.5 × 1020 cm−3 and 12.1, 4.2 and 5.7 ms for ULPI into silica glass, ULPI into polymer and the dispersion of erbium NPs in a polymer matrix, respectively.
An EDWA numerical modelling framework is developed to optimise the erbium-ytterbium ratio to maximise the device gain while accounting for various potential integration methods and waveguide design parameters. Using a channel geometry based on the measured optical properties of Er-doped glass, an internal gain of 9.6 dB/cm is predicted at the optimal Er:Yb ratio of 9.0:7.3 × 1020 cm−3 when pumped at an optical power of 200 mW. A hybrid, polymer-glass strip-loaded design is proposed to combine the highly doped glass layer with the polymer material. While a slightly lower gain of 7.4 dB/cm is projected in the re-optimised design under the same operating conditions, it benefits from a simpler fabrication procedure.
An experimental study of devices prepared through the direct Er integration into polymer waveguides enables a comparison with developed theoretical models. A good agreement between measured and modelled results show that a practical amplifier operation with erbium concentration of 1.5 × 1020 cm−3 is prevented by the dopant NP clustering and the potential gain limited by the absence of ytterbium co-doping. The excess scattering loss of 9.3 dB/cm could not be further reduced only with the proposed additional ultrasonication and filtering fabrication steps indicating alternative approaches such as core-shell structures are required.Engineering and Physical Sciences Research Council (EPSRC
