LAUSR

We propose and experimentally demonstrate a low- complexity constant modulus algorithm (CMA) based on FPGA for 4-channel wavelength-division-multiplexing passive optical network (WDM-PON) employing 4-level pulse amplitude modulation (PAM4). The FPGA processes the 4 wavelength channels sequentially. In order to reduce the logic resources required by parallel equalization algorithm, an optimization based on parallel structure of constant mode algorithm (PCMA) was proposed in this letter. Different from the classic all-parallel structure CMA, our proposed PCMA adopts a new tap update structure, which only needs to update few sets of taps. With the help of the proposed structure, the resource of DSP is reduced to 21% on average. The PAM4 signal with a net rate of 110.24Gb/s transmission over 25-km SSMF can be achieved with the bit error rate (BER) less than $3.8\times 10^{-3}$ .