Abstract

Semiconductor optical amplifiers (SOAs) are expected to increase the network application capabilities of future lightwave systems. Traveling-wave (TW) SOAs are particularly suitable for multi-channel coherent systems, where several tens of lightwave signals with different frequencies may be amplified by the TW-SOA after multiplexing [1]. Recently, a photonic integrated circuit with 4 DBR lasers, a combiner and a TW-SOA has been reported as an excellent example of the use of TW-SOAs in frequency division multiplexing (FDM) transmitters [2]. It has been pointed out, however, that for close channel spacing and at high amplifier input power level, there can be significant crosstalk among the channels arising from nondegenerate four-wave mixing (FWM) in the TW-SOA [3]. In this paper, we evaluated the FWM signal powers, including first and higher orders, under CW condition and with FSK modulation at 155 Mb/s. We find that a channel spacing larger than 10 GHz is necessary to avoid crosstalk due to FWM in a conventional TW-SOA with a high total input power level of about -7 dBm at the amplifier facet.

© 1990 Optical Society of America