Study of Integnated-Optic Amplifier Using Garnet Crystalline Thin-film Waveguide.

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Optical thin film amplifiers can be a basic element in integrated optic circuits for optical communication and signal processing.The thin film of 1.3 at. % Nd doped yttrium gallium garnet( Nd : YGG) were deposited on substrates of yttrium aluminium garnet (YAG) by RF sputtering. The amorphous films deposited at 600^ﾟC were crystallized by annealing at 1000^ﾟC. The minimum optical propagation loss (at 1064nm ) was 2.2dB/cm.The absorption spectrum and the fluorescence spectrum of Nd : YGG were minutely measured. The peak of the absorption spectrum was located at 808nm. The peaks of the fluorescence spectrum were located at 1057.5nm, 1060.0nm and 1061.87nm.To obtain a signal light of 1.06mum band, a tunable Nd : YAG laser pumped by LD was prepared. A thin etaron of thickness of 0.14mm was put in a cavity as the device to choose wavelength for 1064nm and 1061.5nm. A maximum output power of about 0.5mW and 2mW were obtained for 1061.5nm and 1064nm, respectively.The gain and the S/N characteristics measured by using signal at wavelength 1061.5nm. As the results, the gain saturation was confirmed by increasing the signal power. Approximately, linear gain characteristics were obtained for the signal power of 10muW. The maximum gain of 3.7dB was obtained for pumping of about 13mW and the S/N ratio was 5.4dB.The amplification characteristics of TW type amplifier for steady state were analyzed by rate equations for a fourーlevel system. From the numerical analysis, the gain of about 10dB is obtained for the signal power of 10muW with the pumping of lmW, the amplifier length of lcm and the film thickness of 2.5mum.