Propagation modes in periodically poled lithium niobate waveguides exploiting cascaded second order nonlinearity

The improvement of cascaded second-order nonlinearity chi ((2)):chi ((2)) effects in a quasi-phase-matching (QPM) structure constituted by a periodically poled lithium niobate (PPLN) waveguide is obtained utilizing an integrated metal mirror placed after an additional waveguide segment. The resulting double-pass det,ice, which can be employed for wavelength conversion, is refined by choosing the most advantageous length of the segment waveguide and by taking into account both the thermal and electro-optic effects. In the ideal case of perfect QPM, for a grating length z(G4) = 25 mm, the calculated double-pass maximum efficiency is eta (d)p = 22.86 dB, which is almost the triple of eta (sp) = 8.20 dB, calculated for the single-pass version (without mirror) for the same value of the pump and signal powers.