  We demonstrate a new approach to supercontinuum generation and
carrier-envelope-offset detection in dispersion-engineered nanophotonic
waveguides based on saturated second-harmonic generation of femtosecond pulses.
In contrast with traditional approaches based on self-phase modulation, this
technique simultaneously broadens both harmonics by generating rapid amplitude
modulations of the field envelopes. The generated supercontinuum produces
coherent carrier-envelope-offset beatnotes in the overlap region that remain in
phase across 100's of nanometers of bandwidth while requiring $<$10 picojoules
of pulse energy.
