Low-temperature direct synthesis of optically nonlinear graphene for integrated photonic platforms

Advanced photonic systems that exploit optical nonlinearities of graphene enable ultrafast signal processing and broadband on-chip functionalities. However, the high growth temperatures of conventional chemical vapor deposition processes limit their direct integration with Si-based photonic integrated circuits (PICs). In this work, we demonstrate low-temperature direct growth of graphene using the atomic carbon spraying (ACS) method without compromising its nonlinear optical response. We verify that the graphene growth at a low-temperature of 850 °C does not induce significant thermal damage on the Si wafer surface, while material analyses confirm the expected graphene crystallinity. To further evaluate its retained nonlinearity for device applications, graphene is directly synthesized onto the end facet of an optical fiber at 850 °C and employed in a fiber ring cavity for passive mode-locking. The resulting ultrashort pulses exhibit a central wavelength, 3 dB bandwidth, pulse duration, and repetition rate of 1567.45 nm, 1.32 nm, 3.26 ps, and 1.31 MHz, respectively. These results confirm that low-temperature ACS enables graphene synthesis compatible with Si substrates while preserving nonlinearity, thereby providing a practical route for the monolithic integration of graphene-based nonlinear elements into next-generation PICs. • Atomic carbon spraying conformally grows low-defect graphene directly on 3D surfaces. • Low-temperature growth avoids defects on the Si substrate observed above 950 °C. • Synthesized graphene retains optical nonlinearity, allowing passive mode-locking. • This approach provides a path to integrating graphene into advanced photonic systems.