Abstract

In the normal dispersion regime, two forms of modulation instability have been observed when birefringent single-mode fibers are subjected to intense pump pulses. These instabilities are the cross phase or XPMI process^1,2 and the coherent or PMI process.^3,4 The latter process is more interesting from the. point of view of its potential applications since the sidebands have the orthogonal polarisation to that of the pump, from which they can be readily separated, generating fully amplitude modulated pulses at terahertz frequencies. The frequency of the modulation has also been shown to be tunable, using stress-inducing geometries for the supporting spool on which the fiber is wound to modify the birefringence of the wound fiber.⁵ We report here a simple method for varying the frequency of the induced modulation, by using a winding geometry in which the birefringence of the fiber varies periodically along the fiber.

© 1996 Optical Society of America