Difference-frequency generation (DFG) and cascaded second-order nonlinear interaction based wavelength conversions in quasi-phase-matched waveguides were studied systematically. The characteristics of the two conversion methods, such as conversion efficiency, conversion bandwidth, pump-wavelength tolerance, and temperature stability, were compared with both experimental and theoretical results of MgO-doped quasi-phase-matched waveguides. It was found that for shorter device length and lower pump power, DFG based wavelength converters had higher conversion efficiency, and the cascaded based wavelength conversions had slightly wider 3-dB signal-conversion bandwidth. The 3-dB signal wavelength-conversion bandwidth decreased exponentially with an increase in device length. For long devices and high pump power, however, the efficiency difference between the cascaded based conversions and DFG based ones was minor. Tolerance of pump wavelength for the cascaded based wavelength conversions was approximately two times that of DFG-based ones, which decreases with the increase of device length. In both cases, the tolerance of pump wavelength exponentially decreased with an increase of device length. It was found that the temperature stability of the cascaded based conversions was identical to that of DFG based conversions. These results are very helpful in choosing suitable wavelength converters for practical optical communication systems.
© 2003 Optical Society of America