Improved Transfer Quality of CVD-Grown Graphene by Ultrasonic Processing of Target Substrates: Applications for Ultra-fast Laser Photonics

In this paper, we experimentally found that the transfer quality of CVD-grown graphene could be improved by ultrasonic processing (UP) of target substrates thanks to the improved hydrophilicity. Atomic force micrograph and Raman spectroscopy revealed that the graphene films transferred onto the target substrate with UP possess less wrinkles and defects than that of the sample without UP. The improvement technique endows graphene more suitable for photonics applications because of its weaker optical loss, higher optical damage threshold and longer stability. By integrating a fiber pigtailed graphene (treated by UP) device into a fiber laser cavity, we could obtain narrower mode-locked pulse with higher optical-to-optical conversion efficiency and better optical spectral profile, in contrast with that without UP, which further verify the improved transfer quality of graphene by the UP technique. We anticipate that this transfer technique may be applicable to boost the performance of other graphene photonics devices, such as optical modulator, detector, polarizer, etc.