GENERATION OF A WIDE DISCRETE VISIBLE SPECTRUM IN A FREQUENCY-DOUBLING OPTICAL-FIBER

We describe some special features of frequency doubling in a Ge-doped SiO2 optical fiber. The generation of a multi-frequency visible spectr um in a single short fiber pumped with 1.06 mu m radiation is demonstr ated. This effect is the result of an interplay between the processes of frequency doubling and third-order nonlinear frequency mixing. Most of the new components coincide with the characteristic stimulated fou r-wave-mixing spectrum of the fiber, although the power of the interna lly generated 0.532 mu m pump was more than an order of magnitude belo w the respective thresholds.