Spontaneous four-wave mixing in silicon nitride waveguides for broadband coherent anti-Stokes Raman scattering spectroscopy

We present a light source for coherent anti-Stokes Raman
scattering (CARS) based on broadband spontaneous fourwave
mixing, with the potential to be further integrated.
By using 7 mm long silicon nitride waveguides, which offer
tight mode confinement and a high nonlinear refractive
index coefficient, broadband signal and idler pulses were
generated with 4 nJ of input pulse energy. In comparison
to fiber-based experiments, the input energy and the waveguide
length were reduced by two orders of magnitude,
respectively. The idler and residual pump pulses were used
for CARS measurements, enabling chemically selective and
label-free spectroscopy over the entire fingerprint region,
with an ultrafast fiber-based pump source at 1033 nm wavelength.
The presented simple light source paves the path
towards cost-effective, integrated lab-on-a-chip CARS
applications.