Abstract

Praseodymium-doped gallium-lanthanum-sulphide (Ga:La:S) glasses are one of the most promising candidates for fabrication of optical fiber amplifiers in the wavelength region of 1.3 μm, due to their low phonon-energy and high quantum efficiency as compared to fluoride glasses [1,2]. The experimental investigation of Ga:La:S glasses under conditions of high optical powers around 1.3 μm and 1.0 μm is important because nonlinear processes that might occur, arc undesirable nonlinear loss mechanisms in optical fiber amplifiers. In the experiment, at 1.319 μm the laser delivered 150 ps pulses at 100 MHz repetition rate in a 700 ns Q-switch envelope at 1.0 kHz frequency. For operation at 1.06 μm the laser generated 100 ps pulse at 100 MHz repetition rate. Our investigations were conducted utilising Pr³⁺-doped Ga:La:S glass samples prepared by melt quenching in the molar ratio of 70Ga₂S₃:30La₂S₃, with typical dopant concentration of 500 ppm/wt. Figure 1 shows a typical power spectrum of the second-harmonic signal at 660nm generated in a 3 mm thick sample of Pr³⁺-doped Ga:La.S glass for an average fundamental power of 200 mW at 1.319 μm. The spectral bandwidth of 0.24 nm indicates a parametric frequency doubling process. The spectral characteristics at 1.06 μm has basically shown the same features. Time measurements revealed that the Q-switch envelope at 660 nm had a duration of ~500 ns and the individual pulses had duration of less than 200 ps. The second-harmonic signal intensity as a function of fundamental power was analysed and the results are depicted in figure 2. As can be inferred from log-log plot of data, the signal intensity at 660 nm presented, as expected, a quadratic dependence on fundamental radiation intensity For the highest fundamental power of 350 mW utilised to pump the sample, as much as 70 μW average power at 660 nm was generated and a frequency doubling conversion efficiency of 0.02% was obtained. A praseodymium-free Ga:La:S sample was tested and we have also obsened frequency doubled light generated from it. However, the samples doped with praseodymium presented a higher conversion efficiency.

© 1996 IEEE