Nanophotonics and two-dimensional material devices for optical security and computational imaging
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2025
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Melbourne Authors
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Electrical and Electronic Engineering
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PhD thesis
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Open Access
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© 2025 Seyed Saleh Mousavi Khaleghi
Abstract
Single-pixel imaging (SPI) and optical holography represent transformative technologies in nanophotonics, offering solutions to the limitations of conventional imaging systems and security applications. While traditional focal-plane arrays excel in visible spectral ranges, they face significant challenges in the infrared and Terahertz regions due to high costs and technical constraints. Similarly, conventional optical security features are increasingly vulnerable to sophisticated counterfeiting techniques. This thesis presents novel nanophotonic devices and an optical system that address these challenges through an integrated approach combining Van der Waals material-based photodetectors for advanced single-pixel imaging and dual mode metasurface holograms for optical security applications.
We fabricate MoS2 phototransistors photogated by substrate PN junctions, where photovoltage from the junction electrically gates the MoS2 channel. This architecture achieves responsivities up to 32 A/W at 780 nm (77 K) and 15 A/W at room temperature, with sub-millisecond response times, extending detection beyond MoS2's intrinsic absorption edge into the near-infrared (NIR). Additionally, we use a black phosphorus-MoS2 (bP-MoS2) heterostructure photodiode, which provides broadband response from visible to extended shortwave infrared (ex-SWIR). Employing these photodetectors, we achieve record-high-resolution SPI with the bP-MoS2 photodiode enabling 1023 x 768 pixels in the visible range and 512 x 512 pixels in extended SWIR, surpassing prior vdWs-material SPI demonstrations by >64x in pixel count. We introduce a cyclic S-matrix compressed sampling technique that reduces acquisition time fourfold while preserving image quality. Analog high-pass filtering enables edge detection, and infrared illumination allows imaging through silicon wafers, underscoring applications in biomedical imaging, non-destructive testing, and machine vision. The fabricated MoS2 phototransistor demonstrates high-resolution NIR SPI, establishing a new paradigm for vdW-material photodetectors.
Complementing these imaging advancements, we develop hybrid dielectric/plasmonic metasurfaces for optical security, functioning simultaneously as color filters and holographic elements. Aluminium nanohole arrays enable plasmonic color filtering, while amorphous titanium dioxide nanopillars provide phase control. Under white-light illumination, the device displays high-resolution tricolor images; under coherent laser illumination, it projects distinct holograms. With channel crosstalk below 17% and high transmission efficiency, it offers robust anti-counterfeiting for documents like banknotes and passports.
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Single-pixel imaging, Van der Waals material, 2D material, photodetector, dual mode metasurface hologram, photogating, MoS2 phototransistor, bP-MoS2 photodiode, metasurface, black phosphorus, compressed sampling, infrared imaging, optical security, optical security documents