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- Performance of an a-Si:H MMI multichannel beam splitter analyzed by computer simulationPublication . Costa, João; Almeida, Daniel; Fantoni, Alessandro; Lourenço, Paulo; Fernandes, Miguel; Vieira, ManuelaOptical power splitters are widely used in many applications and di_erent typologies have been developed for devices dedicated to this function. Among them, the multimode interference design is especially attractive for its simplicity and performance making it a strong candidate for low-cost applications, such as photonics lab-on-chips for biomedical point of care systems. Within this context, splitting the optical beam equally into multiple channels is of fundamental importance to provide reference arms, parallel sensing of di_erent biomarkers and allowing multiplexed reading schemes. From a theoretical point of view, the multimode structure allows implementation of the power splitting function for an arbitrary number of channels, but in practice its performance is limited by lithographic mask imperfections and waveguide width. In this work we analyze multimode waveguide structures, based on amorphous silicon (a-Si:H) over insulator (SiO2), which can be produced by the PECVD deposition technique. The study compares the performance of several 1 to N designs optimized to provide division of the fundamental quasi-TM mode as a function of input polarization and lithographic roughness. The performance is analyzed in terms of output power uniformity and attenuation and is based on numerical simulations using the Beam Propagation Method and Eigenmode Expansion Propagation Methods.
- Multi-micron dimensioning of amorphous silicon rib waveguidesPublication . Almeida, Daniel; Costa, João; Fantoni, Alessandro; Vieira, ManuelaWhile silicon photonics is considered as the key technology for future applications in optical transceivers, ASICs and sensing devices, there are still challenges to achieve generalized mass production of Photonic Integrated Circuits (PICs). One obstacle is the required extreme miniaturization of the photonic devices. Nevertheless, there is space for applications with equal interest and impact in the society that do not require the extreme performance associated with PICs built on a tenth of nanometer scale. Low-cost PICs can be obtained by increasing the size of the waveguides and devices to a multi-micron scale and in this case the machinery necessary for the device fabrication can be greatly simplified. The transfer of the amorphous silicon (a-Si:H) production technology developed in the past for the photovoltaic and flat panel displays can be adapted to the production of multi-micron size PICs targeting low-cost devices working with low frequency signals. To enable the use of such devices it is important to show that light and be coupled in and out of the waveguides efficiently without the need for diffraction gratings or other components that require sub-micron fabrication resolutions. In this article we perform simulation of the power transfer between a lensed 19.4 µm multimode optical fiber and a multi-micron a-Si:H rib waveguide, designed to support single-mode propagation. Light coupling efficiency is analyzed as a function of alignment and distance variations using the FDTD and the Beam Propagation methods. Results show a fundamental TM mode overlap over 80 % under optimal alignment conditions.