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- 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.
- Silicon nitride interferometers for optical sensing with multi-micron dimensionsPublication . Costa, João; Almeida, Daniel; Fantoni, Alessandro; Lourenço, Paulo; Vieira, ManuelaIncreasing the size of the smallest features of Photonic Integrated Circuits (PICs) to multi-micron dimensions can be advantageous to avoid expensive and complex lithographic steps in the fabrication process. In applications where extremely reduced chip size is not a requirement, the design of devices with multi-micron dimensions is potential interesting to avoid the need for e-beam lithography. Another benefit is that making the dimensions larger reduces the effect of lithographic imperfections such as waveguide surface roughness. However, the benefits do not come without limitations. Coupling the light in and out of the circuit is more challenging since diffraction gratings are not available when designing for such large dimensions. Circuit bends must have a larger radius of curvature and the existence of multimode propagation conditions can have detrimental impact in the performance of several devices, such as interferometers. In this study we perform simulations of the coupling between a lensed multimode optical fiber and a multi-micron a-SiN:H rib waveguide. Light coupling efficiency is analyzed as a function of distance variations using the FDTD method and compared with coupling to a strip waveguide. Moreover, we use numerical simulations to study the performance of a Mach-Zehnder interferometer sensitive to refractive index variations. Both the interferometer, splitters and combiners are designed with multi-micron dimensions