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Preparation Of Graphene By PECVD And Generation Of Mode-locked Laser Pulses

Posted on:2019-04-07Degree:MasterType:Thesis
Country:ChinaCandidate:C H YangFull Text:PDF
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Graphene,a representative two-dimensional layered material,has captured tremendous attention for its unique electronic and optical properties.Ultra-fast laser has been realized by using graphenebased saturable absorbers(GSAs)which are typically made through chemical methods,liquid phase exfoliation,oxidation-reduction methods,or chemical vapor deposition,etc.Up to present,conventional fabrication methods inevitably introduce mechanical damage and impurities;controllability of the graphene layer numbers has been hardly accomplished.In addition,in practical applications,GSA usually requires a polymer as a support or compounded with a polymer to facilitate the operation of transfer.In addition,many reported GSAs are based on graphene/polymer composites or stacks,whereas the low optical damage threshold of the polymer could severely limit the output power of the laser.Here,we presented a one-step fabrication of high quality graphene on optical fiberend as saturable absorber by plasma-enhanced chemical vapor deposition(PECVD).With the PECVD,graphene is grown on dielectric substrates without catalysts at low temperature,and desired number of graphene layers is prepared by controlling the deposition time.In this paper,the quality and morphology of graphene prepared by PECVD in different growth conditions were studied.As follows:1)Research on the growth parameters of graphene prepared by PECVDGraphene was prepared on a quartz substrate using PECVD with methane and hydrogen as precursors.The effects of those key parameters such as growth temperature,gas flow rate,and Plasma on the quality,morphology,and growth rate of graphene were systematically investigated.While the condition for the best growth of graphene were explored.The results showed that the graphene growth rate is relatively slow at low temperature and high hydrogen flow ratio,which is conducive to the growth of high quality graphene films.Under high temperatures,methane flow rates,and Plasma power,the growth rate is suitable for the preparation of vertical oriented graphene.(2)Preparation and characterization of GSA growth on the fiber end by PECVDDirect growth of graphene on single-mode optical fiber end by PECVD,and the morphology,linear optics,saturable absorption,insertion loss and mechanical damage of the graphene on the end face were investigated.The results showed that graphene can be uniformly and continuously covered on the fiber end.The device's modulation depth and insertion loss are positively related to the number of graphene layers that can be adjusted by controlling the growth time.While,the device has good physical stability,which proves the feasibility and controllability of this method in the preparation and practical application.(3)Generation of mode-locked laser pulsesExperimental analyzed and researched the one-step fabrication of GSA in the erbium-doped fiber laser for ultra-fast pulse output.The generated 991 fs soliton pulse was centered at 1559 nm.The experimental results showed that the as-prepared GSA has high damage threshold and can realize high power output for a long time,which can operation stably at mode locking state with the maximum pump power of 700 mW,the average output power reached 17.6 mW.The pulse output performance of GSA fabricated with different growth conditions were analyzed.It was found that the 3 dB bandwidth of the mode-locked spectrum of GSA grown with high hydrogen flow rate is significantly better than that similar number of layers of GSA grown with pure methane.
Keywords/Search Tags:Plasma-enhanced chemical vapor deposition(PECVD), Graphene, Saturable absorber, Modelocked fiber laser
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