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Project Acronym: ASER-META

Project Name: ASER-META - Amorphous silicon optical Switch based on an Electrically Reconfigurable Metamaterial

Activity years: 2023 - 2024

Funding: Fundação para a Ciência e a Tecnologia, I.P

Budget: 49.927.20€

Reference:  2022.07694.PTDC

Host Institution: Instituto Superior de Engenharia de Lisboa

Researchers (ISEL):

Professor Alessandro Fantoni (Researcher in charge/ISEL) ORCID: 0000-0002-9938-0351
Professor António Filipe Ruas Trindade Maçarico ORCID: 0000-0001-6213-925X
Professor Daniel Gonçalves Pita Santos de Almeida ORCID: 0000-0003-2228-2507
Professor João Pedro Barrigana Ramos da Costa ORCID: 0000-0002-8058-3685
Professor Luís Miguel Tavares Fernandes ORCID: 0000-0002-0765-474X
Professor Manuela Vieira ORCID: 0000-0002-1150-9895
Professor Mário Pereira Véstias ORCID: 0000-0001-8556-4507
Professor Paula Maria Garcia Louro ORCID: 0000-0002-4167-2052


Integrated photonics represents an unmatched opportunity for implementing an unconstrained variety of programmable functions. It is considered as the key technology for future applications in optical transceivers, ASIC integration, 3D imaging and sensing device in biomedics or light detection and ranging (LIDAR) systems for automotive industry. Nevertheless, industry has failed, until now, in demonstrating large-scale deployment of Photonics Integrated Circuits (PICs) achieving an economy of scale like those attained by Application Specific Integrated Circuits (ASICs) in microelectronics. Anyway, there is still a great expectation for this roadmap and great interest has been posed, among others, in the application of photonic switching structures, aiming to the development of programmable devices for optical data processing. The switching operation in the devices proposed and described in literature are typically based on electro-optical and thermo-optical mechanisms. Induced phase changes have also been demonstrated to allow reconfigurable bistable functions. Whichever the supporting physical effect, the switching mechanism is based on fine tuning the refractive index of suitable materials incorporated in the device. An interesting approach, recently reported, uses a nanostructured material geometry to create an arbitrary distribution of the refractive index values, allowing power splitting with arbitrary input and output directions. The integration of subwavelength-structured metasurfaces and metamaterials on the standard optical waveguides is gradually reshaping the landscape of photonic integrated circuits, giving rise to numerous meta-waveguides with unprecedented control capabilities. Within this context, the application of machine learning techniques allows the project of metamaterialbased devices that can be fabricated in the traditional semiconductor process. At the same time, a novel approach, based on waveguide with multi-micron dimension, allowing a better polarization and process tolerance management, has been recently proposed, and the fabrication tolerance induced by a multi-micron dimension paves the way to a new efficient use of hydrogenated amorphous silicon (a-Si:H) deposited by the PECVD method. PECVD is the technique that enables the low-cost fabrication (and commercialization) of large area flat panel displays, where each pixel is controlled individually by a single a-Si:H Thin Film Transistor (TFT) in an active-matrix configuration. 
The idea hereby proposed is based on joining these three characteristics (metamaterial-based devices, PECVD materials and Active-Matrix control) to develop a programmable switching function on a MMI structure with multiple input/output ports. Due to its intrinsic low conductivity, a-Si:H lateral transport effects are naturally confined to the region of the charge source. So, a MOS structure (Au/ITO/SiNx/a-Si:H) can be used, in a process very much like the channel creation in a standard TFT, to electrically and dynamically create a localized accumulation of charge and a corresponding local alteration of the a-Si:H refractive index. A matrix distribution of these MOS structures, controlled by a programmable FPGA hardware, on the upper surface of a a-Si:H MMI allows the dynamical electrical configuration of the material refractive index. Each MOS is treated just like a pixel and controlled by an active-matrix scheme. A previous definition of the voltage images, optimized by joining FDTD simulations and a machine learning approach, permits the switching operation and a control over the output channels, allowing the generation of completely independent functions, with real-time reconfigurability controlled by FPGA hardware system.