Abstract

Coherent optical receivers based on digital signal processing (DSP) [1-4] have gained immense popularity because of their simple configuration; these devices offer flexibility in the adjustment of any parameter and connectivity of each compensation technique. Previously, we had proposed an adaptive threshold adjustment for distorted optical quadrature amplitude modulation (QAM) signals [5] and showed its effectiveness in increasing tolerance to signal distortion, particularly in the case of symbol misalignment in a constellation map. In our previous demonstration, high resolution histograms were adopted so that large size memory would be required on the signal processing. In this study, we evaluated the effect of the degree of histogram resolution on the bit-error rate (BER) of the optical QAM signal which can be precisely created by using a LiNbO₃ optical modulator [6, 7] and showed that it decreased to less than 20 divisions along each orthogonal axis in a constellation map.

© 2009 IEEE