Experimental Investigations of Second Harmonic Generation in Germanium-doped Optical Glass Fibers

Experiments were carried out in order to investigate Second Harmonic Generation (SHG) in germanium-doped optical glass fibers, relying on a mode-locked Q-switched neodymium yttrium aluminum garnet (Nd:YAG) laser with high peak power intensity. The preparation or writing conditions for optical fibers were investigated. SHG was observed successfully under a synchronous pump of the fundamental infrared and seeding green lights, with a maximum of 82 mu W from second harmonic generation being observed in the optical fiber from a 60 mW input, corresponding to a conversion efficiency of 0.14%. The pump laser used in the experiments was a Nd: YAG laser, operated Q-switched and mode-locked at 1064 nm. The laser delivered approximately 100 ps mode-locked pulses at a 75.6 MHz repetition rate, modulated by a 2 kHz frequency Q-switched pulse envelope of 260 nanoseconds' duration (Full Width Half Maximum or FWHM).