GaAs-based integration photonics: waveguides and splitting elements

With the development of long lived, epitaxially grown InAs quantum dot lasers in GaAs on silicon, GaAs-based photonics has become a promising system for integrating large numbers of small footprint active and passive components on the same substrate. To ensure high performance of a circuit, each component or building block, needs to be individually investigated so a library of optimised components can be developed. In this thesis, several GaAs-based passive integrated photonic components are proposed and analysed by employing commercially available multi-dimensional simulation tools with the aim of understanding the performance and tolerances of the important component functions prior to the manufacturing stage. These components will be useful as basic and composite building blocks in future GaAs-on-silicon photonic integrated circuits. Deeply etched waveguides are investigated, and single mode operation is shown to be maintained under -0.1 to +0.1 micrometre variation in width, etching depth, core height and variation in wavelength between 1.2 and 1.4 micrometre, making the waveguides tolerant against typical fabrication errors. Single mode operation is also mapped as a function of core width, height and etching depth for shallow etched waveguides. Efficient tapers are optimised for the propagation of light between multimode and single mode waveguides. The tapers are tolerant of width, etching depth and wavelength changes of -0.1 to +0.1 micrometre with transmission higher than 98%. Two compact splitters: multimode interferometer, MMI, and Y-branch are optimised at 1.3 micrometre. The multimode interferometer has efficiency up to 99% with reduction of about 4% over spectral and geometrical changes of width, length and etching depth of -0.1 to +0.1 micrometre. An efficient Y-branch is designed with efficiency up to 94% with less stability, compared to the multimode interferometer, against variations like etching depth and wavelength. It is found that waveguides of single mode operation at 1.3 micrometre are achievable and efficient tapers and splitters can be obtained within the fabrication capabilities available in a university facility. Hence, these components are appropriate for on-chip integration

Design and Characterisation of Multi-Mode Interference Reflector Lasers for Integrated Photonics

InAs quantum dot ridge waveguide lasers comprising single-port multi-mode-interference-reflectors (MMIR) and single-cleaved reflectors are designed, fabricated, and characterised, to demonstrate capability for optoelectronic-integrated-circuits. Simulations of an MMIR show high values of fundamental mode reflectivity ($> 80\% )$ and good selectivity against higher order modes. Deep-etched MMIR lasers fabricated with 0.5 mm long cavities have a threshold current of 24 mA, compared to 75 mA for standard Fabry–Perot cleaved–cleaved FP-RWG lasers of the same length, both at 25 °C, and 56 mA compared to 102 mA at 55 °C. MMIR lasers exhibit stable ground state operation up to 50 °C and show promise as small footprint sources for integrated photonics