  Slow light has been widely utilized to obtain enhanced nonlinearities,
enhanced spontaneous emissions, and increased phase shifts owing to its ability
to promote light-matter interactions. By incorporating a graphene microheater
on a slow-light silicon photonic crystal waveguide, we experimentally
demonstrated an energy-efficient graphene microheater with a tuning efficiency
of 1.07 nm/mW and power consumption per free spectral range of 3.99 mW. The
rise and decay times (10% to 90%) were only 750 ns and 525 ns, which, to the
best of our knowledge, are the fastest reported response times for microheaters
in silicon photonics. The corresponding record-low figure of merit of the
device was 2.543 nW.s, which is one order of magnitude lower than results
reported in previous studies. The influences of the graphene-photonic crystal
waveguide interaction length and the shape of the graphene heater were also
investigated, providing valuable guidelines for enhancing the graphene
microheater tuning efficiency.
