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Title: Micro-assembly of integrated photonic devices using a high accuracy transfer printing process
Author: McPhillimy, John
ISNI:       0000 0004 8509 8739
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2019
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The overall objective of this thesis is the development and implementation of a high accuracy transfer printing (TP) technique for the micro-assembly of integrated photonic devices. The method has particular relevance for the integration of hybrid photonic waveguides, and enables the production of passive/active photonic circuit technologies in a parallel and scalable manner. The initial work involves the design of an optical microscopy based absolute crosscorrelation alignment technique utilised within a custom-built TP system. Following this, the statistical characterisation of the method, with the measured absolute positional accuracy of fully fabricated devices integrated across multiple substrates is achieved. An absolute lateral alignment accuracy of ±385 nm (3σ) and rotational accuracy of ±4.8 mrad (3σ) are demonstrated. This is reported as the highest lateral alignment accuracy to date for transfer printing, lending itself a significant advantage for the micro-assembly of optical waveguiding components. Utilising the high alignment TP system, the micro-assembly of fully fabricated single-mode Si membrane micro-ring resonators on a target silicon-on-insulator (SOI) substrate is presented. The ultra-thin membrane resonators are vertically integrated with Si bus waveguides situated on a receiver SOI chip in a highly controllable manner, demonstrating variation in resonant coupling conditions with respect to the lateral coupling offset. Further to this, the TP method provides a means to produce 3D device architectures without any limiting multi-step full wafer bonding methods. By vertical assembling 3D stacked membrane devices, a 100 µm2 SOI distributed Bragg reflector (DBR) is produced taking advantage of high lateral and rotation placement accuracy. The structure exhibits a visible wavelength reflectance band in agreement with theoretical simulations. The micro-assembly of hybrid AlGaAs-on-SOI micro-disk resonators is also presented, demonstrating the highly controlled integration of pre-fabricated waveguide devices across multiple material platforms. Control over the integrated resonator's vertical and lateral coupling to the bus waveguides enables the precise and selective excitation of different mode families within the resonator cavity. By using the high accuracy TP method, the vertical micro-assembly of hybrid micro-disk resonators also allows selective mode coupling, with loaded Q-factors reaching ~40,000. The unique advantage of the assembled devices however come from the ability to perform (3) nonlinear processes on SOI without being limited by two-photon absorption and free-carrier losses. Four-wave mixing is shown with efficiency levels of -25 dB at a low input power of 2.5 mW, with a nonlinear coeffcient of 325 (Wm)-1 demonstrated. The measured nonlinearity is comparable to its monolithic silicon counterpart, whilst also detailing a clear reduction in the nonlinear losses inherent to this material platform.
Supervisor: Strain, Michael Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral