We numerically investigated the use of graphene nanoribbons placed on top of silicon-on-insulator (SOI) strip waveguides for light polarization control in silicon photonic-integrated waveguides. We found that two factors mainly affected the polarization control: the graphene chemical potential and the geometrical parameters of the waveguide, such as the waveguide and nanoribbon widths and distance. We show that the graphene chemical potential influences both TE and TM polarizations almost in the same way, while the waveguide width tapering enables both TE-pass and TM-pass polarizing functionalities. Overall, by increasing the oxide spacer thickness between the silicon waveguide and the top graphene layer, the device insertion losses can be reduced, while preserving a high polarization extinction ratio.
This paper presents the design and the experimental characterization of a 10 Gb/s electronic driver for silicon Mach-Zehnder modulators (MZMs). This driver is able to operate in harsh environments characterized by radiation levels up to 1 Grad(SiO 2 ) total ionizing dose (TID). To compensate for the detrimental effects that radiation produces on the target 65 nm bulk silicon technology both device-and circuit-level radiation hardened by design (RHBD) techniques are developed and implemented. Extreme TID levels are faced using longchannel transistors with enclosed layout, avoiding the use of p-MOSFETs, and implementing a differential self-biased cascode architecture with common-mode feedback. Band-widening techniques, e.g., inductive peaking, cross-coupled capacitors, and buffer chaining, have been used to improve the driver's frequency response and reach the targeted data rate. Electrical measurements show 10 Gb/s waveforms with an eye diagram amplitude suitable for MZM driving. Electro-optical measurements performed connecting the electronic driver to a silicon photonic MZM confirm the achievement of a 10 Gb/s systemlevel operability. The radiation hardness of the driver is verified by exposing the integrated circuit to X-rays. The measurements confirm the ability of the driver to work up to 1 Grad with an eye amplitude reduction of only 10% and a 7% increment in the rise and fall times, validating the effectiveness of the implemented RHBD techniques.
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