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Centre of Technology and Systems
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Grating coupler design for low-cost fabrication in amorphous silicon photonic integrated circuits
Publication . Almeida, Daniel; Lourenço, Paulo; Fantoni, Alessandro; Costa, João; Vieira, Manuela
Photonic circuits find applications in biomedicine, manufacturing, quantum computing and
communications. Photonic waveguides are crucial components, typically having cross-section orders
of magnitude inferior when compared with other photonic components (e.g., optical fibers, light
sources and photodetectors). Several light-coupling methods exist, consisting of either on-plane (e.g.,
adiabatic and end-fire coupling) or off-plane methods (e.g., grating and vertical couplers). The grating
coupler is a versatile light-transference technique which can be tested at wafer level, not requiring
specific fiber terminations or additional optical components, like lenses, polarizers or prisms. This
study focuses on fully-etched grating couplers without a bottom reflector, made from hydrogenated
amorphous silicon (a-Si:H), deposited over a silica substrate. Different coupler designs were tested,
and of these we highlight two: the superimposition of two lithographic masks with different periods
and an offset between them to create a random distribution and a technique based on the quadratic
refractive-index variation along the device’s length. Results were obtained by 2D-FDTD simulation.
The designed grating couplers achieve coupling efficiencies for the TE-like mode over −8 dB (mask
overlap) and −3 dB (quadratic variation), at a wavelength of 1550 nm. The coupling scheme considers
a 220 nm a-Si:H waveguide and an SMF-28 optical fiber.
Analog flat-level circuit synthesis with genetic algorithms
Publication . Gomes, Miguel; Tavares, Rui; Goes, João
This paper proposes new techniques for automatic simulation-based analog circuit synthesis using genetic algorithms. This is intended to contribute to the set of electronic design automation tools that use genetic algorithms in circuit synthesis, especially those that use the simulator-in-the-loop paradigm. In this study, a genetic algorithm was employed as the generation engine for analog circuits, and variable-length chromosomes were used to describe circuit topology. The entire process is carried out on a flat level (device level), i.e. using the transistor and other elementary devices (e.g. resistors) as the basic elementary blocks. Circuit synthesis is accomplished without any knowledge of previously defined topologies (or analog block cells). Three techniques are presented for analog circuit synthesis that are incorporated in the genetic algorithm, which contribute to its robustness, leading to better and faster results. These techniques can be summarized as follows: 1) adaptive probability of chromosome acceptance, 2) removal of redundant or useless components, and 3) segmented evolution. The automatic process starts with the circuit input and output specifications and proceeds with the evolution of both circuit topology and component sizing. The results shown in this paper include a 40 dB DC gain amplifier, which, when evaluated with SPECTRE/CADENCE 6.0, using a standard 130 nm technology, with a load capacitor of 10 pF, has a gain of 102 V/V, a GBW product of 70 MHz, and a figure of merit of 1436 MHz.pF/mW.
Transformerless ultra-high gain buck-boost DC-DC converter with single-switch of reduced voltage stress
Publication . Cordeiro, Armando; Gamboa, Paulo; Luís, Ricardo; Fonte, Pedro M; Monteiro, Joaquim; Martins, João F.; Silva, J. Fernando; Foito, Daniel; Fernao Pires, Vitor
This paper introduces a new DC-DC power converter topology capable of both step-up and step-down voltage
conversion, with an exceptionally high voltage gain ratio.. Besides the high extension of the voltage gain range, the converter is also characterized by the use of a single switch. Moreover, the stress imposed on the switch's voltage is minimized, enabling the utilization of low-voltage, low RDS-ON MOSFETs. Consequently, this modification leads to reduced costs and losses associated with switch conduction and turn ON. Another aspect concerning the proposed converter is that the input current exhibits a continuous behavior, which can be significant for various applications. The paper provides insights into the operational performance, steady state behavior, and mathematical underpinnings of the proposed dc-dc converter. Comparative evaluation of the static voltage gain of the proposed converter and other topologies with comparable characteristics will also be shown. Verification of the presented converter's key features are conducted through both simulation and experimental assessments using a 440-W laboratory prototype. Through these analyses, the efficacy and viability of the modified coupled-inductor SEPIC converter with enhanced voltage gain capability are confirmed.
Gold nanoflowers for colorimetric detection of NGAL antibodies
Publication . Serafinelli, Caterina; Fantoni, Alessandro; Alegria, Elisabete C. B. A.; Pacheco, Rita; Vieira, Manuela; Vieira, Manuela; Pacheco, Rita; Alegria, Elisabete; Fantoni, Alessandro
Colorimetric sensors are a type of sensing platform enabling visual measurements that offers an instant report. Due to their intrinsic advantages, such as low cost, simplicity, low acquisition time and no need for expensive instrumentation, colorimetric transducers are attracting a growing attention for the PoC devices. In light of their brilliant colors arising from their Localized Surface Plasmon Resonance (LSPR), gold nanoparticles have revealed a great potential to develop new analytical techniques and advanced assays. Stimulated by the need of PoC devices for an affordable and real-time detection of biomarkers outside clinical environment, in this work we explore the potential of gold nanoflowers (AuNFs) as sensing system to integrate in a PoC device. Firstly, gold AuNFs functionalized with NGAL antibodies along with antibodies conjugated onto AuNFs surface binding their complementary antigens will be synthesized and their transmittance spectra measured. In a successive step, the measured spectra have been converted into vectors in the L*a*b*, xyY and RGB Color spaces by means of simulation study. Transferring the study into real world application, the AuNFs will be integrated into the fiber network of paper to create the plasmonic paper that will be the transducer of a colorimetric device.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
6817 - DCRRNI ID
Número da atribuição
UIDP/00066/2020