Fig. 4: The characterization of broadband spectral tuning and shaping from the χ⁽²⁾ micro-waveguide device with birefringence PM, when scanning the pump wavelength.

a–c and d–f are the measured and simulated optical parametric generation (OPG) spectra pumped at 2.4 μm, 2.5 μm and 2.6 μm, respectively. a A LWIR idler spectrum centered at 8 μm is measured pumped at 2.4 μm wavelength. b As the pump wavelength is increased to 2.5 μm, an octave-spanning idler covering 4.5 to 12 μm is generated, owing to a better PM condition at two wings of the spectrum. c Further increasing the pump wavelength to 2.6 μm, narrow-band idler spectrum centered at 9.3 μm is measured due to the reduced parametric bandwidth. d–f A semi-classical simulation of OPG is also conducted to study the spectral evolution in the χ⁽²⁾ waveguide with birefringence PM at different pump wavelengths, by solving the χ⁽²⁾-based coupled-wave equations. The measurement and simulation results qualitatively agree well with each other.