Fig. 2: Theoretical analyses and spectral characterization of the cascaded processes.
From: Cascaded nonlinear down-conversion in poling-free lithium niobate nanophotonic waveguides
a Phase-matching conditions for the degenerate OPG process. The degenerate OPG process achieves perfect phase matching when the pump wavelength is 1.03 μm, and the signal wavelength is 2.06 μm, satisfying the condition \(\Delta {{{\bf{k}}}}_{1}=0\). b Phase-matching conditions for the DFG process: The DFG process achieves perfect phase-matching when the pump wavelength is 1.19 μm, the signal wavelength is 2.06 μm, and the difference-frequency wavelength is 2.82 μm, thereby satisfying the condition \(\Delta {{{\bf{k}}}}_{2}=0\). c Simulated GVM for the signal: The GVM of the signal light is simulated across the wavelength range of 1.8–3.2 μm within the reverse-polarization dual-layer nanophotonic TFLN waveguide. d Simulations of the GVD for the signal light within the wavelength range of 1.8–3.2 μm. e The calculated relative intensity of OPG (\({I}_{\omega /2}\)) and cascade (\({I}_{\omega {\prime} {\prime} }\)) versus the propagation distance. f The calculated relative intensities of OPG (\({I}_{\omega /2}\)), cascade (\({I}_{\omega {\prime} {\prime} }\)), and total (\({I}_{\omega /2}+{I}_{\omega {\prime} {\prime} }\)) versus the pump intensity. g The input pump spectrum after passing through LF. h The measured pump spectra versus the pump energy. i The measured OPG and cascaded spectra at various pump energy. The red arrow indicates the gradual increase of the input pump energy corresponding to different spectral curves, which are 37.1 pJ, 62.5 pJ, 102 pJ, 159.3 pJ, 203.3 pJ, 291.3 pJ, 355.7 pJ, 446.3 pJ, and 610.7 pJ, respectively.
