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Determining Thin Film Characteristics by Prism Coupling Technique
Publication . Lourenço, Paulo; Vygranenko, Yuri; Costa, João; Fernandes, Miguel; Fantoni, Alessandro; Vieira, Manuela; Lavareda, G.; CTS - Centro de Tecnologia e Sistemas; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; DCM - Departamento de Ciência dos Materiais
Integrating optical components in a single package to perform a given functionality is now an established procedure when photonic integrated circuits are involved. These photonic integrated circuits may provide wider bandwidth, higher immunity to electromagnetic interference and lower power consumption operation, as opposed to their electronic counterparts, and these features preclude the development of more efficient Information and Communication Technologies devices when both technologies, optical and electronic, are combined for the development of already existing or new devices. Photonic integrated circuits consist of structures such as waveguides, ring resonators, multimode interference sections, and more, laid over a substrate and assembled in a way to perform a given functionality. These structures are usually accomplished through thin film deposition and subsequent lithography, to achieve the intended geometrical form. Characterization of such thin film structures is of utmost importance, being the refractive index and thickness of the structure two of the most relevant structural elements. Usually, these parameters are obtained by ellipsometry which requires a somewhat complex optical setup, generally consisting of a monochromatic light source, a polarizer, a compensator, an analyser, a photodetector and all the associated signals interpret, process and displaying in a human readable form environment, hence representing a significant investment to acquire such a commercially available device. In this work, we present the latest developments we have achieved in a simple experimental optical setup and the associated method developed to accurately determine the refractive index and thickness of thin film wave guiding structures. The refractive index and thickness of the analysed sample were found to be 1.8723 ± 0.0009 and 524.4 ± 1.4 nm, respectively.
Recent Progresses in Plasmonic Biosensors for Point-of-Care (POC) Devices
Publication . Serafinelli, Caterina; Fantoni, Alessandro; Alegria, Elisabete C. B. A.; Vieira, Manuela; CTS - Centro de Tecnologia e Sistemas; DEE - Departamento de Engenharia Electrotécnica e de Computadores; MDPI - Multidisciplinary Digital Publishing Institute
The recent progresses in the research of plasmonic phenomena and materials paved the route toward the development of optical sensing platforms based on metal nanostructures with a great potential to be integrated into point-of-care (POC) devices for the next generation of sensing platforms, thus enabling real-time, highly sensitive and accurate diagnostics. In this review, firstly, the optical properties of plasmonic metal nanoparticles will be illustrated, whereafter the engineering of POC platforms, such as microfluidics and readout systems, will be considered with another critical point which is surface functionalization. Attention will also be given to their potential in multiplexed analysis. Finally, the limitations for effective implementation in real diagnostics will be illustrated with a special emphasis on the latest trend in developing cutting-edge sensing systems.
Grating Coupler Design for Low-Cost Fabrication in Amorphous Silicon Photonic Integrated Circuits
Publication . Almeida, Daniel; Lourenço, Paulo; Fantoni, Alessandro; Costa, João; Vieira, Manuela; CTS - Centro de Tecnologia e Sistemas; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; Faculdade de Ciências e Tecnologia (FCT); MDPI - Multidisciplinary Digital Publishing Institute
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.
A Reconfigurable 1x2 Photonic Digital Switch Controlled by an Externally Induced Metasurface
Publication . Fantoni, Alessandro; Di Giamberardino, Paolo; CTS - Centro de Tecnologia e Sistemas; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; MDPI - Multidisciplinary Digital Publishing Institute
This work reports the design of a 1x2 photonic digital switch controlled by an electrically induced metasurface, configurated by a rectangular array of points where the refractive index is locally changed through the application of an external bias. The device is simulated using the Beam Propagation Method (BPM) and Finite Difference Time Domain (FDTD) algorithms and the structure under evaluation is an amorphous silicon 1x2 multimode interference (MMI), joined to an arrayed Metal Oxide Semiconductor (MOS) structure Al/SiNx/a-Si:H/ITO to be used in active-matrix pixel fashion to control the output of the switch. MMI couplers, based on self-imaging multimode waveguides, are very compact integrated optical components that can perform many different splitting and recombining functions. The input–output model has been defined using a machine learning approach; a high number of images have been generated through simulations, based on the beam propagation algorithm, obtaining a large dataset for an MMI structure under different activation maps of the MOS pixels. This dataset has been used for training and testing of a machine learning algorithm for the classification of the MMI configuration in terms of binary digital output for a 1x2 switch. Also, a statistical analysis has been produced, targeting the definition of the most incident-activated pixel for each switch operation. An optimal configuration is proposed and applied to demonstrate the operation of a digital cascaded switch. This proof of concept paves the way to a more complex device class, supporting the recent advances in programmable photonic integrated circuits.
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Fundação para a Ciência e a Tecnologia
Programa de financiamento
3599-PPCDT
Número da atribuição
2022.07694.PTDC