Cascaded Integration of Optical Waveguides With Third-Order Nonlinearity With Lithium Niobate Waveguides on Silicon Substrates

The cascaded integration of optical waveguides with third-order optical nonlinearity (
$\chi ^{(3)}$
susceptibilitiy) with lithium niobate (LiNbO
$_{3}$
) waveguides is demonstrated on the same chip. Thin-film (LiNbO
$_{3}$
) and chalcogenide (ChG) glass (Ge
$_{23}$
Sb
$_{7}$
S
$_{70}$
) waveguides are integrated on silicon (Si) substrates. An optical mode transition between the two waveguides is achieved through low-loss mode-converting tapers, with a measured loss of
$\sim$
1.5 dB for transverse-electric and
$\sim$
1.75 dB for transverse-magnetic input polarizations. For nonlinear characterization, wavelength conversion via four-wave mixing is demonstrated on the ChG-LN waveguides. This platform provides an efficient method for the utilization of second- and third-order optical nonlinearities on the same chip, rendering it ideal for nonlinear applications such as stabilized octave-spanning optical frequency comb generation.