Improved cascaded sum and difference frequency generation-based wavelength converters in low-loss quasi-phase-matched lithium niobate waveguides.

We numerically evaluate the wavelength converters based on cascaded sum and difference frequency generation in quasi-phase-matched lithium niobate waveguides with and without loss. A technique is also proposed to flatten the response by increased detuning of the pump wavelength. We present the criteria for the design of waveguide length and the assignment of pump power to achieve the desired efficiency, ripple and bandwidth, assuming a large pump wavelength difference of 75 nm.