The use of electronic equalization and offset filtering in the performance improvement of low-cost DML transmitters

The use of electronic compensation techniques for the transmission improvement of low-cost directly modulated sources is studied and evaluated experimentally. More specifically the research efforts presented here targeting in enhancing the transmission reach of common DML sources with limited bandwidth fabricated for operation at 2.5 Gb/s, but operated at 10 Gb/s. Performance improvement is achieved by means of electronic feed-forward and decision-feedback equalization (FFE/DFE) as well as off-set optical filtering at the receiver end. Experimental studies consider both transient and adiabatic chirp dominated DMLs sources. Measurements presented both in terms of required OSNR for bit error rate (BER) values of 10^-9 versus transmission length and BER over OSNR for certain transmission distances. In all cases uncompensated links of standard single mode fibre (SSMF) are considered. Additionally, the optimum filter position is examined in combination with equalization and in terms of OSNR versus detuning from the centre wavelength.