Date of Award


Document Type

Doctoral Thesis

Degree Name

Doctor of Philosophy


Centre for Advanced Photonics and Process Analysis

First Advisor

Dr William Whelan-Curtain (Liam O'Faolain)

Second Advisor

Dr Donagh O'Mahony


The recent years' exponential growth of data transmission in datacom and telecom technology (such as in Wavelength Division Multiplexing - WDM) has highlighted the energy consumption challenges of electronics, shifting research and industry interest towards optical interconnects. Novel and more efficient integrated photonics is being given the objective to face the ever-increasing demand for speed and bandwidth. This has initiated, in both industrial and academic environments, a quest for low-power, compact and cost-effective optical interconnects that can be integrated on electronic boards of Datacentres and transceivers all over the world. In this thesis, different types of WDM compatible Hybrid External Cavity Lasers (HECLs) based on CMOS compatible photonic integrated circuits (PICs) are being investigated. The CMOS compatible PIC is composed by waveguides connected to photonic resonators on deposited Silicon (both amorphous and polycrystalline) and Silicon Nitride (SiN) platforms. Edge and side-coupled 1D Photonic Crystals (Bragg gratings and PhC cavities) on silicon nitride platform have been developed. These systems are also investigated in terms in the potential employment in high temperature excursion environments, such as Datacentres, demonstrating their ability to achieve lasing stability without the need of active cooling, achieving less than 87 GHz of lasing wavelength shift from 20ºC to 80ºC. The approach of vertically coupled 2D Photonic Crystal (PhC) resonators is also developed on amorphous (a:Si) and polycrystalline (poly:Si) silicon platform, on which the optimization of the optical performances of the deposited Silicon platforms is performed, reaching measured Q-factors up to 104. 2D PhC cavities acting as a resonant mirror of the laser cavity in HECLs are characterized, beside very accurate wavelength control and narrow resonance linewidths, by a large Free Spectral Range (FSR) while having a considerably small footprint on chip, enabling tighter channel spacing and higher integration densities, ideal for WDM links. A first principle numerical model on the thermo-optic dynamics of these 2D PhC cavities is also developed, able to match the experimental behaviour of the system at short (~ 10 ps) and long (over 20 μs) timescales. Moreover, as the PhC cavity resonance is also controlling the lasing wavelength of the laser, its modulation via free carrier plasma dispersion opens the possibility to tune the lasing wavelength, potentially solving laser-modulator wavelength mismatch issues and further reducing the modulation energy consumption. This paves the way towards a new family of energy efficient integrated modulated lasers to face the on-chip optical interconnect energy budget.

Creative Commons License

Creative Commons Attribution-Share Alike 4.0 International License
This work is licensed under a Creative Commons Attribution-Share Alike 4.0 International License.

Access Level


Project Identifier

info:eu-repo/grantAgreement/ERC/PE7 - Systems & Communication Engineering/ERC-2013-STG/IE/DAtacommunications based on NanophotoniC Resonators/DANCeR

Included in

Physics Commons