Abstract

In optical frequency division multiplexed systems, the nonlinear interaction between signal channels may set the ultimate limit on the allowable channel spacing, total number of channels, and maximum power per channel.¹ The four-wave mixing (FWM) crosstalk in semiconductor amplifiers has been shown to cause a sensitivity degradation when the channel spacing is a few hundred megahertz.² In contrast, when fiber amplifiers are used, nonlinear interactions have been considered negligible because of the long fluorescence time constant.³ However, we recently found that for a fiber amplifier with a saturation power in the 5- 10-mW range, the transmission fiber following the amplifier can cause FWM crosstalk.⁴ Fiber FWM may also be observed without an amplifier if a wavelength selective coupler is used to combine the laser outputs with no splitting loss.

© 1990 Optical Society of America