Design Optimization of R-EAM-SOA for Long-Reach Carrier-Distributed Passive Optical Networks

Reflective electro-absorption modulators (R-EAMs) monolithically integrated with semiconductor optical amplifiers (SOAs) have strong potential as upstream transmitter in carrier-distributed long-reach passive optical networks (PONs). In these devices, the SOA provides the gain necessary to overcome the high loss of the PON power splitters, while the EAM allows the high speed and low chirp modulation required for long-reach PONs. It has previously been shown that purposely adding internal loss between the R-EAM and SOA compresses the burst-to-burst dynamic range on the upstream channels of the PON and that the SOA gain and the internal loss value between the SOA and the reflective surface are the key parameters which control this behavior. Dynamic range compression is an essential feature for carrier-distributed PONs, since both the carrier and the modulated signal experience the differential loss travelling through the optical distribution network of the PON. Other features of these modulators, which are also critical for the PON operation such as the output power and the patterning distortion, are also dependent on the SOA gain and internal loss value. In this paper, we demonstrate that careful design of the SOA gain and internal loss can provide an optimum balance between dynamic range compression, output power, and patterning distortion reduction. We model the R-EAM-SOA device in a network whose differential access loss is 15 dB. The dynamic range at the burst-mode receiver, using the optimized R-EAM-SOA, is found to be ~12 dB, well within the capabilities of current burst-mode receiver designs. The optimum SOA gain is 24 dB, and the device has an internal loss in the range of 21 to 24 dB.