Penalties From 2D Grating Coupler Induced Polarization Crosstalk in Silicon Photonic Coherent Transceivers

Abstract

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.

Monolithically Integrated O-Band Coherent ROSA Featuring 2D Grating Couplers for Self-Homodyne Intra Data Center Links

“…The grating couplers used in our first generation cROSAs comprise circular perturbing elements. For this kind of 2D-GRC, it is known that low polarization crosstalk occurs in a limited wavelength range [16]. This is sufficient to achieve excellent results at a fixed wavelength, as demonstrated in the previous sections.…”

“…In commercial coherent transceivers, the two orthogonally transmitted signals are de-multiplexed in the DSP unit, but polarization crosstalk has to be kept small as to minimize associated penalties [16], [19]. To verify sufficiently low polarization crosstalk of the cROSA, we employ the following routine, indicated in Fig.…”

“…In essence, this effect is equivalent to the polarization dependent loss (PDL)-induced crosstalk in the fiber transmission link [18]. Although this kind of crosstalk may be compensated in coherent detection systems by dedicated DSP, some penalties will be introduced [16], [19]. For that reason, the optimization of This work is licensed under a Creative Commons Attribution 4.0 License.…”

“…The performance of the cROSA is evaluated in a system experiment at 64 GBd quadrature-phase shift-keying (QPSK). Compared to previous works [16], [17], we focus here on the evaluation of the 2D-GRC induced polarization crosstalk in real sub-systems. From the experimental results, the polarization crosstalk of the cROSA is estimated.…”

Advances in monolithic high-speed SiGe photonic electronic system integration

“…We showed that this effect scales with the grating's perturbation strength, leading thus to coupling efficiency limitations. The related polarization crosstalk was observed in experiments [4] and it was shown that it is associated with a loss of polarization orthogonality [5]. To address the issue of cross-polarization, its physical background was investigated [6].…”