The outstanding electronic and optical properties of black phosphorus (BP) in a two-dimensional (2D) but unique single-layer puckered structure have opened intense research interest ranging from fundamental physics to nanoscale applications covering the electronic and optical domains. The direct and controllable electronic bandgap facilitating wide range of tunable optical response coupled with high anisotropic in-plane properties made BP a promising nonlinear optical material for broadband optical applications. Here, we investigate ultrafast optical switching relying on the optical nonlinearity of BP. Wavelength conversion for modulated signals whose frequency reaches up to 20 GHz is realized by four-wave-mixing (FWM) with BP-deposited D-shaped fiber. In the successful demonstration of the FWM based wavelength conversion, performance parameter has been increased up to ~33% after employing BP in the device. It verifies that BP is able to perform efficient optical switching in the evanescent field interaction regime at very high speed. Our results might suggest that BP-based ultra-fast photonics devices could be potentially developed for broadband applications.

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.

Despite the long‐standing efforts to develop 3D graphene, which is critical for practical electronic, optoelectronic, and optical devices, the lack of synthetic methods and the use of conventional transfer approaches have limited its realization. Herein, a metal‐free, etching‐free, transfer‐free, direct synthesis of functional graphene is introduced that contours 3D‐structured surfaces of nonlinear optical devices, thereby maximizing the nonlinear interaction of graphene with guided light. Central to this method is the use of γ‐Al2O3, a ceramic catalyst, which generates carbon atoms from the precursor molecules and supplies them for the graphene synthesis on the 3D structures located near the catalyst through spatial diffusion, described as atomic carbon spraying (ACS). The optical nonlinearity facilitated by ACS‐processed 3D graphene is experimentally verified by realizing both passively mode‐locked laser with a pulse width of 770 fs and ultrafast optical switching with 67% enhancement in nonlinear effect over 6 mm interaction length.