Conformal Integrated Graphene onto Lensed Optical Fiber-Based Nonlinear Interfaces

Abstract

Effective ultrafast signal control in integrated photonics requires high optical nonlinearities, making the integration of nonlinear nanomaterials such as graphene a promising strategy. However, conventional graphene transfer approaches face critical limitations in integration to devices with complex surface morphologies, leading to the damage to the nanomaterial quality and consequent degradation of device nonlinearity. We demonstrate the direct integration of graphene onto a lensed optical fiber (LOF) that can be employed as a nonlinear optical interface between fiber links and integrated photonic platforms. Our atomic carbon spraying (ACS) process enables the direct synthesis of a homogeneous graphene layer on the convex surface of an LOF with a tip radius of only a few micrometers while preserving its intact nonlinear optical properties. Systematic analysis confirms the high crystallinity of the synthesized graphene, and its nonlinear response is validated through the realization of a passive mode-locked fiber laser in which graphene functions as a saturable absorber. The resulting ultrashort pulses exhibit a duration of 460 fs at a center wavelength of 1562.5 nm. We expect that the ACS process provides an elegant and robust solution for graphene incorporation into future integrated photonics devices for nonlinearity-enhanced ultrafast signal processing.