FIG. 1: Nanophotonic telecom-to-visible spectral translation and efficiency comparison.

a, Nanophotonic spectral translation uses a cavity-enhanced second-order or third-order nonlinear optical process (${\chi }^{(2)}$ or ${\chi }^{(3)}$) to efficiently transfer light into a new frequency with ultra-low laser pump power (see inset for a simplified scheme). ${\omega }_p$, ${\omega }_t$, and ${\omega }_v$ represent frequencies for pump, telecom, and visible light, respectively. b, Energy and momentum conservation requirements for sum-frequency generation (SFG, left) and degenerate four-wave mixing (dFWM, right) processes with single fundamental mode family (SFMF) operation. c, False-colored scanning-electron-microscope image of the nanophotonic device and the coupling scheme we use for spectral translation. The top pulley waveguide (red) and the bottom straight waveguide (blue) are used to couple pump/visible and telecom light, respectively, into and out of the microring (green). d, Order-of-magnitude comparison of the translation efficiency for the two processes in (b) with the device geometry of (c). For a microring with a finesse of $𝓕\approx 5000$ (red), the efficiency of the ${\chi }^{(3)}$ process can compete with, or even exceed, that of the ${\chi }^{(2)}$ process at mW-pumping levels, if the mode overlap can be sufficiently well-optimized. See Supplementary Information for details.