Optical Phase Conjugation in a Silicon Waveguide with Lateral p-i-n Diode for Nonlinearity Compensation

In-line optical phase conjugation is a well-known technique to enhance the received signal quality through nonlinearity compensation. Being able to implement the conjugation in cm-scale highly nonlinear devices, which can be integrated on a silicon chip could potentially lead to several benefits in terms of small footprint and co-integration with linear signal processing functionalities, as well as lower power consumption. Here, we focus on silicon waveguides to implement the optical phase conjugation through four-wave mixing. The challenges in terms of conversion efficiency imposed by the presence of nonlinear loss are tackled by using a lateral p-i-n diode along the waveguide. When the diode is reverse biased, the conversion efficiency can be effectively enhanced by the decrease in free-carrier absorption. Low-penalty conversion can therefore be achieved for WDM signals and the high quality of the generated idlers is critical in demonstrating a 1-dB Q-factor improvement through optical phase conjugation in a 5 WDM channel 16-QAM transmission system after 644-km of dispersion compensated transmission. The performance improvement enables a performance better than the HD-FEC threshold for all the transmitted channels.