Tyndall National Institute - Journal Articles
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Item Mixed-mode fiber array alignment and coupling to photonic integrated circuits(Institute of Electrical and Electronics Engineers Inc., 2025) Gradkowski, KamilThis study investigates alignment and coupling between a photonic integrated circuit (PIC) and a mixed-mode fiber array, where one of the channels in the normally single-mode (SM) array is replaced by a multi-mode fiber (MMF). As a result, the tolerances of alignment are significantly relaxed. The proposed method suggests using the SMF at the input and the MMF at the output of the PIC. In such a transmission configuration, the tolerances are relaxed by a factor of √2 (41%). As this scales with mode size, the beam-expansion mechanisms, e.g., utilizing micro-lenses, can further significantly reduce the requirements for fabrication and packaging of photonic devices, making them more robust and cheaper to manufacture.Item Compact modulators on silicon nitride waveguide platform via micro-transfer printing of thin-film lithium niobate(Nature Research, 2025) Badri, S. Hadi; Kotlyar, Maria V.; Das, Risov; Arafat, Yeasir; Moynihan, Owen; Corbett, Brian; O’Faolain, Liam; Ghosh, Samir; Horizon 2020; Research Ireland; Horizon EuropeWe explore the use of micro-transfer printing (µTP) technology to integrate thin lithium niobate (LN) films onto silicon nitride (SiN) waveguides, facilitating the development of compact electro-optical modulators. Three modulator architectures are investigated: Mach-Zehnder interferometer (MZI), Fabry-Perot (FP) resonator, and side-coupled FP resonators. By acting as a photonic molecule, the proposed coupled FP resonators enable improved spectral engineering with new functionalities while maximizing the transmission and quality-factor (Q-factor) of the resonances. Design, simulations, fabrication method, and experimental results are presented, demonstrating the potential of µTP in advancing electro-optical modulators. The half-wave voltage-length product (VπL) of the fabricated devices decreases as the Q-factor increases achieving VπL = 10.5, 4.3, and 2.74 V.cm for MZI, FP, and photonic molecule modulators, respectively.Item Strategies for passivating microneedle-based sensors: development, characterization and comparison(Elsevier B.V., 2025) Bocchino, Andrea; Rodrigues Teixeira, Sofia; Barry, Fiona; Thatte, Chinmay; Ryan, Adam; Rahman, Fahima; Hu, Yuan; Iadanza, Simone; Galvin, Paul; Kurzhals, Steffen; Melnik, Eva; Mutinati, Giorgio C.; O'Mahony, Conor; Higher Education Authority; European Regional Development Fund; Horizon 2020; Enterprise IrelandMicroneedles (MNs) are sharp, pillar-like structures shorter than 1 mm. They can painlessly pierce the stratum corneum (SC), the outermost layer of the skin, and interface with the underlying dermal interstitial fluid, rich in biomarkers. Due to these properties, MNs have been widely investigated for several diagnostic applications. In particular, MN-based biosensors could enable the development of the new generation of minimally invasive continuous monitoring systems. To become a biosensor, the body or the tip of the needles must be functionalized. In addition, the area surrounding the MNs is usually passivated to prevent substrate interferences. Although passivation layers are widely used, there is a lack of characterization of such layers. This work aims at filling this gap, by developing, characterizing, and comparing six different passivation techniques. These include the application of polymethyl methacrylate (PMMA), Epotek 353ND, silicon oxide (SiO2), parylene, varnish and an adhesive film to microneedle arrays. The performance of each method was then assessed using electrochemical measurements, optical and SEM imaging, and contact angle analysis. Significant variability was observed across the various methods and materials. When assessed in terms of the electrochemically active area available after passivation, the tape and parylene were the most promising layers, while varnish and epoxy were the worst performing materials. The PMMA performed better than the other liquid passivations, but still requires refinement due to the high degree of unwanted coverage of the needles. Finally, the SiO2 layer seemed to be a viable option, but also remains in need of additional optimization.Item Tiny deep learning model for insect segmentation and counting on resource-constrained devices(Elsevier B.V., 2025) Kargar, Amin; Zorbas, Dimitrios; Gaffney, Michael; O'Flynn, Brendan; Tedesco, Salvatore; Department of Agriculture, Food and the Marine; Irish Food and Agriculture Authority; European Regional Development FundAutomated insect monitoring is essential for early detection of insect pest infestations in orchards. It helps growers make an informed decision to control the insect pest population in their fields to avoid crop losses and improve crop quality. This study proposed a tiny deep-learning model for insect segmentation and counting suitable for battery-powered microcontroller (MCU)-based edge devices. For this aim, the critical layers in terms of peak memory usage in a U-Net-inspired model were recognized and then optimized to meet resources constraints on an MCU with 1 MB of RAM and 2 MB of flash storage. We then introduced an image dataset for the insect of interest, Halyomorpha halys, and the dataset-splitting strategy for the model training. The proposed model was investigated from different aspects to evaluate its performance and the feasibility of its implementation on battery-powered MCU-based edge devices. The proposed deep learning model only needs approximately 900 KB of RAM and 964 KB of storage to perform its computations and store its parameters, respectively, making it useful on edge, resource constrained systems. Moreover, each inference on an MCU-based board requires 2.6 s and consumes 4.9 J. In terms of segmentation, it achieved a Dice Similarity Coefficient (DSC) of 85% and an Intersection over Union (IoU) of 73% with a precision and recall of 83% and 86%, respectively. In terms of counting, it achieved a Mean Square Error (MSE) of 1.32, Mean Absolute Error (MAE) of 0.78 and R2 of 0.97.Item White light transmission spectroscopy for rapid quality control imperfection identification in nanoimprinted surface-enhanced raman spectroscopy substrates(American Chemical Society, 2025) Hardy, Mike; Chu, Hin On Martin; Pauly, Serene; Cavanagh, Katie F.; Hill, Breandán J.F.; Wiggins, Jason; Schilling, Alina; Goldberg Oppenheimer, Pola; Grover, Liam M.; Winfield, Richard J.; Scott, Jade N.; Doherty, Matthew D.; McCarron, Ryan; Hendren, William R.; Dawson, Paul; Bowman, Robert M.; Smart Nano NI; Engineering and Physical Sciences Research Council; UK Research and Innovation; Queen’s University Belfast; Wellcome TrustMiniaturized biomedical sensor development requires improvements in lithographic processes in terms of cost and scalability. Of particular promise is nanoimprint lithography (NIL), but this can suffer from a lack of high-fidelity pattern reproducibility between master and imprinted substrates. Herein, we present a multidisciplinary investigation into gold- and iron-coated NIL sensors including custom optics and spectroscopy, scanning probe microscopy, and data analysis insights. Polyurethane NIL-made nanodome arrays were interrogated with white light transmission spectroscopy, coupled with principal component analysis (PCA) to investigate potential offsets in the photon-substrate plane interaction angle, an imperfection in NIL substrates. Large-angle mismatches (2-10°) were found to be easily discernible by PCA with statistically significant differences (p = 0.05). Unexpected dips in some spectra are postulated to be due to interacting localized and propagating plasmon polaritons, which is supported with a coupled two-oscillator model. General insights are made regarding the interpretation of PCA loadings, which should be related to physical phenomena, and where maximum variance is not necessarily the most meaningful criterion. Smaller angles (<1°) show no significant differences with overlapping confidence intervals in PCA space. Surface-enhanced Raman spectroscopy (SERS) measurements on gold-coated nanodomes returned relative standard deviations of 6-10% via analysis of gelatin, which is of interest as a nasal lining approximation. Interestingly, nanodomes coated in iron produced small, but useful SERS enhancements, which was subsequently interrogated via scanning thermal probe microscopy showing temperature increases of up to 5 °C over the area of one nanostructure (∼1 μm2). Nanostructures remained intact despite the surprising large local temperature increase relative to a gold-coated comparison sample (∼2 °C). The current study provides a framework for the rapid and accurate quality control assessment of imperfections in NIL-produced nanostructures for sensing applications in SERS and surface plasmon resonance, which may need precisely fabricated nanostructures.