Octave-spanning supercontinuum generation from sub-millimeter-length integrated gallium phosphide waveguides

Integrated photonic platforms for supercontinuum generation are revolutionizing applications in metrology, imaging, sensing, and ultrafast photonics. Driven by the advantages of integrated nonlinear waveguides, research has focused on developing novel platforms with broad optical transparency, strong nonlinearity, high refractive index, and low fabrication costs. Here, we explore gallium phosphide (GaP) for supercontinuum generation, leveraging its strong second-order and Kerr nonlinearities, broad optical transparency, and low two-photon absorption at telecom C-band. We report the octave-spanning supercontinuum generation in a sub-millimeter GaP waveguide. The generated supercontinuum, when excited with transversely magnetically polarized light, features a gap-free spectrum and high coherence. Furthermore, our GaP waveguide demonstrates a figure of merit of 43.56 THz/mm/kW, which is the highest reported figure of merit among various integrated photonic platforms operating in the normal dispersion regime. We also observe and analyze the rich underlying physical mechanisms of multiple second harmonics. These results highlight the exceptional versatility of the GaP-on-isolator platform for broadband nonlinear photonics.