Author: Abdolahi, Mahssa
Quick response (QR) codes enable optical machine-readable data storage in an image format, and are at the forefront of prevalent security systems with widespread applications in document and packaging authentication. Despite their popularity, they have been subject to ongoing investigations to boost their capacity and security without compromising their readability. This can be caused by various physical (e.g., cross-module interference in ink-based QR codes) and optical sources of interference in high-capacity multi-colour information storage. QR codes which function by employing different properties of light such as wavelength, polarization, amplitude, and phase, provide an unparalleled level of data protection. However, various constraints such as spectral overlap, multisource illumination, photobleaching, photoblinking, autofluorescence, fluorescence quenching, and prolonged read out processes limit their applicability. In this thesis, a new diffractive structural colour QR code with enhanced security, scalability, lifetime, readability, and capacity is developed to address these issues. The angle-dependent recovery, unique regional intensity signatures, and the technological difficulty of physical duplication provides strong security for protecting important products and documents. Colour is used as a means of pushing the limit of the information density to three times the maximum value obtained using conventional monochrome QR codes. However, leveraging colours for embedding higher volumes of data tends to elevate the noise level due to the presence of cross-module and cross-channel interference which may occur in both pigment-based and structural colours. As a result, various image processing techniques such as histogram equalization and decorrelation stretching are used to retrieve structural colour QR code images with different lighting conditions. The manufacturing technique is based on nanoimprinting, selective UV laser activation, and thermal treatment. For boosting its throughput, thermoplastic flow and crosslinking of exposed/unexposed nanostructured SU-8 as a long-lasting medium with high thermal, mechanical, and chemical stability is standardized. To enable mass-production of the developed QR code, a new method for origination of Ni stamps from the SU-8 master is developed. Also, contributions for the development of a new optical layer-by-layer alignment ruler for guiding 3D integration as a potential method for increasing the capacity of data storage devices are made. The optical ruler can function based on the two concepts of intensity transmission blocking and induced EOT resonance.
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Thesis advisor: Gray, Bonnie
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