Advantageous effects of gain saturation in semiconductor optical amplifier-based integrated reflective modulators

Reflective modulators based on an electro-absorption modulator (EAM) and semiconductor optical amplifier (SOA) combination are attractive devices for applications in carrier distributed optical access networks due to the gain, provided by the SOA, and the high speed and low chirp modulation of the EAM. Monolithically integrated reflective EAM-SOAs (R-EAM-SOAs) have demonstrated unexpected and unintuitive behavior, which is related to the gain saturation properties of the SOA section and also to the internal loss present after the SOA section. Results from a simple analytical model and from an accurate numerical model show that a high value of internal loss and a high gain SOA allow utilization of these devices in a region where the output power is clamped around a maximum value for input carrier powers compatible with carrier distributed optical access networks. In this region of operation the R-EAM-SOA also exhibits low patterning distortion, despite being in a saturated regime, and noise reduction on the input carrier due to the noise squeezing in the SOA section. In this paper, we demonstrate that these three effects, which are highly desirable in carrier distributed optical access networks, can be readily achieved via a co-optimization of the SOA section parameters and the internal loss values in integrated R-EAM-SOAs.