Experimental demonstration of an efficient hybrid equalizer for short-reach optical SSB systems

We propose an efficient enhanced hybrid equalizer combining the feed forward equalization (FFE) with a modified Volterra filter to mitigate the linear and nonlinear interference for the short-reach optical single side-band (SSB) system. The optical SSB signal is generated by a relatively low-cost dual-drive Mach-Zehnder modulator (DDMZM). The two driving signals are a pair of Hilbert signals with Nyquist pulse-shaped four-level pulse amplitude modulation (NPAM-4). After the fiber transmission, the neighboring received symbols are strongly correlated due to the pulse spreading in time domain caused by the chromatic dispersion (CD). At the receiver equalization stage, the FFE followed by higher order terms of modified Volterra filter, which utilizes the forward and backward neighboring symbols to construct the kernels with strong correlation, are used as an enhanced hybrid equalizer to mitigate the inter symbol interference (ISI) and nonlinear distortion due to the interaction of the CD and the square-law detection. We experimentally demonstrate that the optical SSB NPAM-4 signal of 40 Gb/s transmitting over 80 km standard single mode fiber (SSMF) with a bit-error-rate (BER) of 7.59×10−4.