Saturable Absorption and Bistable Switching of Single Mode Fiber Core‐Guided Light by a 6 nm‐thick, Few Layers Graphene Coating on the Cladding Surface

Abstract

AbstractThe coupling of less than 80 µW of in‐plane polarized near‐infrared light in a 6 nm‐thick graphene layer deposited on an optical fiber produces important permittivity changes leading to bistability and self‐starting 50% modulation of over 1 W of continuous wave light in the core. These features arise from resonant coupling of core‐guided light into the cladding by a 12‐degree tilted, 1 cm long fiber Bragg grating via narrowband, polarization‐dependent resonances that allow the selection of cladding modes with electric fields polarized in the plane of the graphene. The pulse repetition rate of the modulation increases from 10 to 269 Hz for input powers ranging from 0.3 to 1.33 W in the core, with no evidence of saturation. Investigations into the origin of these effects through physical modelling and different experimental conditions point to photo‐induced Joule heating in the graphene layer giving rise to temperature increases of the order of 60 °C and corresponding permittivity changes in the graphene and underlying silica fiber. Those changes lead to shifts in the resonance positions which result in the equivalent of saturable absorption for light guided in the core without direct contact with the absorbing graphene layer.