The demand for 100 Gb/s or higher data rate transmission in next generation networks has induced a renewed interest for coherent detection and advanced modulation formats. Therefore, coherent detection of cross and square M-ary quadrature amplitude modulation (M-QAM) up to 128-QAM signals and digital signal processing (DSP) are promising solutions for the implementation of next generation optical transmission systems. However, as the number of modulation levels increases, the sensitivity to system impairments is exacerbated. It is therefore mandatory to compensate for (i) the random phase noise of the transmitter (Tx) and the local oscillator lasers or fiber nonlinearities, (ii) the amplitude and phase imbalances between the in-phase (I) and quadrature (Q) channels in the Tx and the front-end of the receiver (Rx), and (iii) the inter-symbol interference (ISI) that is unavoidable due to bandwidth limitations at the Tx/Rx and linear propagation effects during optical fiber transmission.
In this field, we are engaged in the derivation of new efficient algorithms such as carrier phase recovery (CPR), blind adaptive IQ imbalance compensator, and/or blind adaptive equalization schemes that are more suited for practical implementation with huge parallelization and minimization of the hardware resources (such as coefficient memories, number of look-up tables, required time for updating the filter coefficients) in real time field-programmable gate array (FPGA) platforms.