The research presented in this thesis focuses on the development of a broadband and
low loss vertical coupling regime for photonic integrated circuits, using a combination
of laser lithography and grayscale lithography. Existing coupling regimes in photonic
integration often struggle to meet four key requirements: low optical loss, broad spectral
bandwidth, rapid fabrication turnaround, and wafer scale testability. To address this, a
low cost platform based on SU8 on glass was fabricated, employing a multistage process
with grayscale lithography to realise 2.5D turning mirrors at 45°, coated with a highly
reflective thin film comprising 50 nm titanium and 200 nm gold. Planar SU8 waveguides were fabricated to embed the turning mirrors, enabling a broadband edge coupled
waveguide to vertical mirror architecture. Optical characterisation of these devices was
carried out across a wavelength range of 516 to 1630 nm, with measurements of facet
coupling losses, propagation losses, and additional mirror related coupling losses. The
optical losses introduced by the mirror across the measured spectral band were below
1 dB when collected in free space. For wafer scale testability, direct coupling to single
mode fibre at 1550 nm was demonstrated with losses of 0.8 dB. Finally, hybrid integration of the waveguide vertical couplers was achieved through additional microfabrication
and transfer printing of µLEDs and VCSEL arrays. Successful probing of these active
photonic devices was achieved, and end facet imaging was recorded.
| Date of Award | 6 Feb 2026 |
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| Original language | English |
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| Awarding Institution | - University Of Strathclyde
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| Sponsors | University of Strathclyde |
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| Supervisor | Michael Strain (Supervisor) & Lucia Caspani (Supervisor) |
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