Abstract

One can enhance the information-carrying capacity of a communication system by means of wavelength multiplexing. However, simultaneously propagating pulses at different wavelengths can interact through nonlinear optical processes to produce new frequencies. One such process is four-wave mixing (FWM). It is found that several pairs of sidebands are generated by FWM at sufficiently high peak powers. We investigate the relative threshold for the first pair of sidebands as a function of the detuning between the pump pulses. Two tuneable pulsed dye lasers, pumped by a frequency-doubled Nd:YAG laser, are coupled into single-mode or multimode optical fiber. The behavior of threshold versus detuning for the single-mode case is understood in terms of simple phase-matching arguments. The multimode case shows a richer behavior that includes enhancement of the Stokes FWM peak by stimulated Raman scattering for the larger detunings. Finally, for single-mode propagation we investigate the growth of various orders of FWM peaks as the pulse power at both laser wavelengths is simultaneously increased. For the lowest-order peaks one can see a rise in relative height and then a leveling off, which indicates saturation as higher-order peaks compete for pump power.

© 1990 Optical Society of America