Theoretical analysis and realization of optoelectrical predistortion optical transmitter for the simultaneous suppression of IM3 and IM5 signal

We present an opto-electrical predistortion optical transmitter showing significant reductions in both 3rd-order and 5th-order intermodulations (IM3 and IM5). The simultaneous reductions of IM3 and IM5 are achieved by choosing an appropriate bias current and RF input power for the LD, obtained by the analysis of the 3rd-order to 5th-order intermodulation distortion ratio (TFR). In our experiments, two DFB-LDs (master and slave LDs) with a similar performance are used; the matching circuits of the two LDs are designed to have equal properties. The experimental results show that reductions of 30 dB in the IM3 and 12 dB in the IM5 are achieved simultaneously under the optimum TFR conditions of a 12 mA bias current and a 0 dBm RF power at 2.2 GHz.