  On-chip integration of two-dimensional (2D) materials with unique structures
and distinctive properties endow integrated devices with new functionalities
and improved performance. With a high flexibility in modifying its properties
and a strong compatibility with various integrated platforms, graphene oxide
(GO) becomes an attractive 2D material for implementing functional hybrid
integrated devices. Here, we demonstrate novel functionalities that go beyond
the capabilities of conventional photonic integrated circuits, by harnessing
the photo-thermal effects in 2D GO films integrated onto them. These include
all-optical control and switching, optical power limiting, and non-reciprocal
light transmission. The 2D layered GO films are on-chip integrated with precise
control of their thicknesses and sizes. Benefitting from the broadband response
of 2D GO films, all the three functionalities feature a very wide operational
bandwidth. By fitting the experimental results with theory, we also extract the
changes in material properties induced by the photo-thermal effects, which
reveal interesting insights about 2D GO films. These results highlight the
versatility of 2D GO films in implementing functional integrated photonic
devices for a range of applications.
