DC Restoration by Data-Aided Sequence in Kramers-Kronig Receiver

In recent years, Kramers-Kronig (KK) receiver has been widely studied because of its simple structure and the ability of digital signal processing (DSP) to recover complex value signals. One practical structure is detecting the optical signal with an AC-coupled photodetector. However, the direct current (DC) component of the photocurrent will be lost, in which case the KK algorithm ceases to be effective. To restore the lost DC component, we propose a simple data-aided method to estimate the DC component by the information of signal mean power stored in the designed data-aided sequences. We introduce a correction coefficient to evaluate the accuracy of our DC estimation by comparing it to the conventional DC sweeping method. Furthermore, the coefficient can be used to combat the DC estimation deviation. We carry out both simulations and experiments to study the performance of the proposed method. The results show that the DC component can be effectively recovered and the system performance is close to the results of the DC sweeping method. At the same time, in the case of low optical signal-to-noise ratio, optimization of correction coefficient can effectively improve the system performance.