2D Graphene Oxide Films Expand Functionality of Photonic Chips.

On-chip integration of 2D materials with unique structures and properties endow integrated devices with new functionalities and improved performance. With high flexibility in ways to modify its properties and compatibility with integrated platforms, graphene oxide (GO) is an exceptionally attractive 2D material for hybrid integrated photonic chips. Here, by harnessing unique property changes induced by photothermal effects in 2D GO films, novel functionalities beyond the capability of photonic integrated circuits are demonstrated. These include all-optical control and tuning, optical power limiting, and nonreciprocal light transmission. The 2D layered GO films are integrated onto photonic chips with precise control of their thickness and size. Benefitting from the broadband optical response of 2D GO films, all three functionalities feature a very wide operational optical bandwidth. By fitting the experimental results with theory, the changes in GO film properties induced by the photothermal effects are analyzed, revealing interesting insights about the physics of 2D GO films. These results highlight the versatility of 2D GO films in implementing new functions for integrated photonic devices for a wide range of applications.