Frequency shift in stimulated four-photon processes in few-mode glass fiber waveguides

An investigation was made of the frequency shift in stimulated four-photon processes involving various combinations of LP modes in fiber waveguides made of quartz glass. The dependence of the shift on the parameters of the waveguides, refractive index profile, and pump wavelength were determined. Propagation of the pump photons in various modes gave rise to a nonmonotonic dependence of the frequency shift on the core radius, but when the pump photons were carried by one mode, the frequency shift decreased on increase in the radius throughout the region where it varied and where phase locking was possible. A dip in the refractive index profile reduced considerably the frequency shift. The shift increased on increase in the pump wavelength and also on increase in the difference between the refractive indices of the core and cladding.