This work analyzes the use of the K-means clustering algorithm to mitigate nonlinear phase noise in singlespan coherent systems, such as long-reach passive optical networks (LR-PONs). Simulations revealed that for a 100-km LR-PON employing 16-ary quadrature amplitude modulation (QAM) and considering a 1:64 splitting ratio, the adoption of K-means with K-means++ initialization achieves an optimum bit error ratio (BER) of 6.3 • 10 −4 , whereas employing maximum likelihood, 10 −3 is obtained. We also show that in order to achieve this performance improvement in 90% of the cases, K-means requires only 2,000 symbols.

Nonlinear phase-noise induced by the Kerr effect is the main nonlinear impairment in single-channel coherent long-reach passive optical networks (LR-PONs). In this work, we explore the capability of the K-nearest neighbors (KNN) algorithm to mitigate this impairment in links with non-negligible fiber dispersion. Simulation results show that when employing KNN in a 56-Gbps coherent LR-PON with a 100-km range and 1:64 splitting ratio, the effective Q-factor is improved by 0.15 dB with respect to maximum likelihood. This increment is achieved by setting the parameter K to 13, which leads to a minimum training data set size of 500 symbols.

Being a fundamental block for systems that utilize polarization-diversity schemes, such as coherent transceivers, polarization rotators allow the conversion of polarization states. In this work, we present an ultra-compact efficient silicon polarization rotator designed via an inverse design method. By optimizing a topology based on the adjoint method, we designed polarization rotators for several combinations of lengths and widths. Simulation results show that the best optimized device presents a polarization conversion loss of 0.67 dB and cross talk of − 18 d B for a central wavelength of 1550 nm. These results were achieved for a 7 µm long and 1.2 µm width device. Furthermore, the high coupling efficiency and low cross talk were achieved for a bandwidth exceeding 100 nm. The polarization conversion loss and cross talk were maintained below 0.82 dB and − 18 d B , respectively, for a band ranging from 1500 nm to 1600 nm.