Ultrafast All-Optical Switching Incorporating in Situ Graphene Grown along an Optical Fiber by the Evanescent Field of a Laser

Abstract

Graphene, with its high optical nonlinearity and unique dispersionless nonlinear optical response over a broad wavelength range, has been studied extensively to implement optical devices such as fiber lasers, broadband modulators, polarizers, and optical switches. Conventionally synthesized graphene relying on high temperature and vacuum equipment suffers from deleterious transfer steps that degrade the graphene quality, thereby affecting the efficiency of nonlinear optical operation and lacking the customized patterning with minimized footprint as well as missing the facilitated fabrication process. Here, a laser-aided in situ synthesis of multilayered graphene directly onto the flat surface of a side-polished optical fiber in ambient condition is demonstrated for absolute investigation of an as-grown graphene crystal in the optical domain. The evanescent field of an amplified continuous wave laser, propagating through an optical fiber, provides activation energy for carbon atoms to diffuse through the nickel catalyst and grow graphene directly on the polished side of an optical fiber. Ultrafast all-optical switching near 1550 nm is elucidated by exploiting four-wave mixing with the grown graphene to confirm that the nonlinear response improvement of 58.5% originates from the graphene. The incident signal is modulated at the ultrafast speed of up to 20 GHz, and the modulation information is successfully copied in the newly generated signals at different wavelengths.