DC Component Recovery in Kramers-Kronig Receiver Utilizing AC-Coupled Photo-Detector

The Kramers-Kronig (KK) receiver has recently drawn a great deal of attention due to its capability to extract the complex-valued electric field of optical signal from the directly detected signal. One practical issue is the recovery of the DC component lost upon the reception using an AC-coupled photo-detector. Due to the nonlinear operation of KK algorithm, it is necessary to recover the DC value of the signal before executing the algorithm. A common method to estimate the DC component was to sweep the DC value added to the detected signal, while measuring the system performance metrics such as bit-error ratio (BER). In this article, we propose and demonstrate a simple one-step DC recovery method for KK receiver. By inserting a zero-padded preamble in the modulation data and measuring a couple of statistical averages of the detected AC-coupled signal, we can estimate the DC component accurately even when the carrier-to-signal power ratio (CSPR) is low. Thus, this method estimates the DC component rapidly without time-consuming and power-hungry signal processing such as demodulation and BER calculation. We carry out a series of computer simulations and experiments to measure the accuracy of the proposed method. The results show that the proposed method incurs negligible sensitivity penalties compared with the conventional DC-sweep method. Also, provided in this paper is the design guideline on the proposed method.