3RD-HARMONIC GENERATION IN GEO2-DOPED SILICA SINGLE-MODE OPTICAL FIBERS

Third-harmonic generation of 1.319 mum Nd:YAG laser pulses in circular-core GeO2-doped silica single-mode fibers is reported. The experimental results have shown that the blue-violet light generated at 439 nm is less than 0.2 nm wide and its intensity depends strongly upon GeO2-doping concentration for fixed fiber length and pump power. It has been observed that for GeO2-doping concentrations greater than 9 mol %, the third-harmonic signal was the unique visible wavelength line exiting the fiber span throughout the spectral region of 400-800 nm. The frequency tripling process started immediately with fiber pump light illumination, i.e., no previous long-time preparation mechanism was required in order to have appreciable third-harmonic generation.