method and apparatus for reducing intra - channel distortions of received data resulting from non - linear signal propagation includes parallel detection subcircuits for determining output values of sequentially provided optical data bits such that each of the sequentially provided optical data bits is processed by only one of the parallel detection subcircuits . two parallel detection subcircuits process the input optical data bits according to even valued and odd valued clock signals . each subcircuit has first and second signal analyzers to detect the value of the input optical data bit and a first memory unit and a second memory unit connected to the first and second signal analyzers . the input value of clock information provided to the first and second memory units of the first parallel subcircuit are 180 ° out of phase with input values indicative of a clock speed provided to the second parallel subcircuit .