Different frequency generation (DFG) and the cascaded second-order nonlinear interaction () based wavelength conversions in 5-mol MgO doped LiNbO3 QPM waveguides are studied and compared both experimentally and theoretically for the first time. It is shown that DFG based wavelength conversions have a higher conversion efficiency; while the cascaded based wavelength conversions have a wider 3-dB signal conversion bandwidth. It is also exhibited that the simulations are consistent well with the experimental results. Tolerance of pump wavelength for the cascaded based wavelength conversion is twice as large as that of DFG based devices. These results are very helpful in choosing suitable wavelength converters for practical optical communication systems according to the system requirements.
Cascaded (chi) <SUP>(2</SUP>) based wavelength conversions in quasi phase-matched periodically poled LiNbO<SUB>3</SUB> waveguide were theoretically analyzed by the step-by-step method. The analytic expressions were obtained and analyzed in detail to reveal the physical insight of the wavelength converters based on the cascaded (chi) <SUP>(2</SUP>) process. In addition, the phase shift of the converted light was studied using the obtained analytic expressions. Some of the simulated results were compared with our experimental results.