Noise Properties of Wavelength-Converted Light Generated in Periodically-Poled Lithium Niobate Waveguide

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● I investigated optical sum frequency generation (SFG) using quasi-phase-matched (QPM) nonlinear waveguide by means of periodically poled lithium niobathe (PPLN). Sum frequency light power of 2 mW at 0.6 μm wavelength was successfully demonstrated by mixing the 2.1 mW probe light at 1.55 μm and the 36 mW pump light at 0.976 μm. This frequency conversion efficiency of 2,600%/W is extremely high, which is well duplicated by the theoretical calculations.● Second harmonic generation (SHG) was also investigated using PPLN waveguide. The SHG light power of 24.6 mW at 0.532 μm wavelength was successfully demonstrated from 66.7 mW pump light at 1.064 μm wavelength, which corresponds to the total conversion efficiency of 37%. The SHG light power linearly increases with the square of the pump power. These characteristics are almost the same both for the single-mode pump light and the multi-mode pump light.● For the precise noise measurement, it is essential to use the single-mode laser light instead of the multi-mode one for the pump light source in the SHG. The noise characteristic of the SHG light was measured by the single detector technique using the Si-APD. The SHG light is revealed to be the shot-noise-limited without any excess noise.● In order to demonstrate the noise suppression mechanism in the SHG, it is important to achieve the more efficient SHG and to improve the detection efficiency of the SHG light.