  Graphene is a rising star in nonlinear optics due to its saturable absorption
and giant Kerr nonlinearity, these properties are useful in digital optics
based on optical nonlinear devices. However, practical applications require
large optical nonlinearities and these are inherently limited by the
interaction length of atomically thin graphene. Here, we demonstrate optical
bistability in a Fabry Perot cavity containing monolayer and bilayer graphene
which have been restructured to form nanobubbles. We find that graphene
nanobubble can act as a new type of optical nonlinear media due to its vertical
side wall as well as added curvature, which enable strong non linear dispersive
effects leading to a large optically induced phase change. Unlike thermally
induced bistability, the all optical switching between two transmission states
happens within a time scale of tens of nanoseconds. Nanobubble based optical
devices with intrinsic optical nonlinearity help to overcome the optical path
length limitation of atomically thin two dimensional films and allow us to
explore the promise of using such elements as the building block of digital
all-optical circuitry.
