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A physical origin of cross-polarization and higher-order modes in two-dimensional (2D) grating couplers and the related device performance limitations
2021, Georgieva, Galina, Voigt, Karsten, Seiler, Pascal M., Mai, Christian, Petermann, Klaus, Zimmermann, Lars
We explore scattering effects as the physical origin of cross-polarization and higher-order modes in silicon photonic 2D grating couplers (GCs). A simplified analytical model is used to illustrate that in-plane scattering always takes place, independent of grating geometry and design coupling angle. Experimental investigations show furthermore that grating design parameters are especially related to the modal composition of both the target- and the cross-polarization. Scattering effects and the associated cross-polarization and higher-order modes are indicated as the main reason for the higher 2D GC insertion loss compared to standard 1D GCs. In addition, they can be responsible for a variable 2D GC spectrum shape, bandwidth and polarization dependent loss.
Cross-polarization effects in sheared 2D grating couplers in a photonic BiCMOS technology
2020, Georgieva, Galina, Voigt, Karsten, Mai, Christian, Seiler, Pascal M., Petermann, Klaus, Zimmermann, Lars
We investigate numerically and experimentally sheared 2D grating couplers in a photonic BiCMOS technology with a focus on their splitting behavior. Two realization forms of a waveguide-To-grating shear angle are considered. The cross-polarization used as a figure-of-merit is shown to be strongly dependent on the grating perturbation strength and is a crucial limitation not only for the grating splitting performance, but also for its coupling efficiency. © 2020 The Japan Society of Applied Physics.
Penalties From 2D Grating Coupler Induced Polarization Crosstalk in Silicon Photonic Coherent Transceivers
2022, Georgieva, Galina, Sena, Matheus, Seiler, Pascal M., Petermann, Klaus, Fischer, Johannes, Zimmermann, Lars
Silicon photonic two-dimensional grating couplers for C- and O-band dual-polarization coherent transceivers are analyzed with respect to their polarization splitting/combining performance. Due to scattered light in the grating's plane, a linear cross-polarization results. The latter is responsible for a limited polarization split ratio and a polarizations' non-orthogonality. The impact of these two quantities is evaluated by system-level simulations with regard to OSNR penalties in coherent systems. For both C- and O-band, a design modification for reduced penalties is proposed.