Thesis

Broadband planar waveguide to vertical mode couplers

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Awarding institution
  • University of Strathclyde
Date of award
  • 2026
Thesis identifier
  • T17603
Person Identifier (Local)
  • 202153458
Qualification Level
Qualification Name
Department, School or Faculty
Abstract
  • The research presented in this thesis focuses on the development of a broadband andlow loss vertical coupling regime for photonic integrated circuits, using a combinationof laser lithography and grayscale lithography. Existing coupling regimes in photonicintegration often struggle to meet four key requirements: low optical loss, broad spectralbandwidth, rapid fabrication turnaround, and wafer scale testability. To address this, alow cost platform based on SU8 on glass was fabricated, employing a multistage processwith grayscale lithography to realise 2.5D turning mirrors at 45°, coated with a highlyreflective thin film comprising 50 nm titanium and 200 nm gold. Planar SU8 waveguides were fabricated to embed the turning mirrors, enabling a broadband edge coupledwaveguide to vertical mirror architecture. Optical characterisation of these devices wascarried out across a wavelength range of 516 to 1630 nm, with measurements of facetcoupling losses, propagation losses, and additional mirror related coupling losses. Theoptical losses introduced by the mirror across the measured spectral band were below1 dB when collected in free space. For wafer scale testability, direct coupling to singlemode fibre at 1550 nm was demonstrated with losses of 0.8 dB. Finally, hybrid integration of the waveguide vertical couplers was achieved through additional microfabricationand transfer printing of µLEDs and VCSEL arrays. Successful probing of these activephotonic devices was achieved, and end facet imaging was recorded.
Advisor / supervisor
  • Strain, Michael
Resource Type
DOI

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