  Vanadium dioxide (VO2) is one of the most promising materials for developing
hybrid photonic integrated devices (PICs). However, despite switching times as
low as a few femtoseconds have been reported, the all-optical temporal dynamics
of VO2 embedded in a waveguide using an in-plane optical signal remain still
hidden. Here, we experimentally investigate this behavior in hybrid VO2/Si
waveguides by using pump-probe measurements at telecom wavelengths. Our results
show switching times in the micro and nanosecond range, suggesting that the
phase transition is triggered thermally from the light absorbed by the VO2 and
the temporal response is governed by thermal conductive dynamics. By properly
engineering the optical pulse, we prospect switching times of nanoseconds with
an energy consumption of a few nanojoules. Our results unveil a new temporal
dynamic that would be useful for developing future all-optical VO2 photonic
integrated devices.
