Advanced deep proton writing and its impact on optical fiber connector technology

Student thesis: Doctoral Thesis

Abstract

Micro-fabrication technologies play an important role in today's life, enabling a myriad of applications such as microelectronics, optical sensors, (ultra-)high-definition display and projection systems, and last but not least optical telecommunication. In this PhD, we explore and push the limits of "Deep Proton Writing" (DPW), our in-house developed rapid prototyping technology for fabricating various novel microstructures. In the DPW process, a high-energy (8.3-16 MeV) proton beam is used to irradiate a polymer resist. We focus on two polymer materials: polymethylmethacrylate (PMMA) and SU-8. The former is a positive resist material, in which the long polymer chains are broken into pieces by the proton beam, whereas the latter is a negative resist, in which a photo-initiator molecule is activated, catalyzing the crosslinking of monomers in the proton-irradiated zones. In both cases the resulting local change in the physical and chemical properties of the polymer allows for the etching of respectively the irradiated and non-irradiated zones of the material, resulting in micro-opto-mechanical structures. We fully optimize the DPW process for both materials such that high aspect ratio micro-components with high shape accuracy and very low sidewall surface roughness can be achieved.
Next to arrays of micropillars, with applications in short-distance optical interconnects and biophotonic labs-on-chips, we dedicate a large part of our work to the design, prototyping and characterization of novel single-mode optical fiber alignment structures for use in optical telecom fiber connectors. The fabrication tolerance (of typically 0.7 µm) on the cladding diameter of G.652 standard telecom fiber is fundamentally limiting the alignment accuracy (and hence the optical performance) in current ferrule-based physical contact connector solutions. To overcome this limitation, we propose a self-centering alignment structure, which makes use of micro-springs to allow for high-precision fiber alignment independently of their cladding diameter. We design this structure using theoretical calculations and finite element analysis, and use DPW to prototype it. The self-centering alignment prototypes are then extensively characterized and assembled into a fiber connector to measure the achievable coupling efficiency and to show their potential for fiber connector technology. Since DPW is not a mass fabrication technology as such, we also investigate the compatibility of the fabricated prototypes with polymer replication techniques (in casu hot embossing), and compare the performance of the replicas with the prototypes.
Date of Award30 Jan 2017
Original languageEnglish

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