The Characteristics And Applications Of The Graphene Integrted Fiber Devices

In recent decades,pulse fiber lasers have been extensively investigated because of their wide applications in the fields of medicine,sensing,communication,and material processing.Diff-erent pulses can be produced in various active or passive technologies.Because of its simple structure,much attention has been given to the passive fiber laser using a semiconductor saturable absorption mirror,nonlinear polarization rotation(NPR)technique,or saturable absorber.A lot of saturable absorbers have been used in ultrafast fiber lasers,such as dyes,semiconductors and colour filter glasses.But the saturable absorbers have their own limits,such as high cost,low response time and high loss.Graphene is a two dimensional material.It has been extensively investigated due to its unique characteristics,such as broad bandwidth,low loss,low cost,fast response time and easy to integrate into fiber systems.Researchers from all over the world have demonstrated various fiber lasers based on graphene.The most important thing of fiber lasers is how to integrate the graphene and fiber.In this thesis,we propose three graphene-integrated fiber devices.1.First,the theory and research progress of the fiber laser based on graphene are introduced.And the ways how to integrate the graphene and fiber are summarized.Based on these graphene fiber devices,various of fiber lasers are demonstrated.We analysis the graphene fiber devices which have been demonstrated.Evey graphene fiber device has its unique characteristics.In order to expand the functions of graphene fiber devices and combine the advantages of our lab,we design and fabricate three graphene integrated fiber devices,including graphene bonded fiber device,suspended graphene fiber device and graphene microfiber 3D device.2.We manipulate the modulation depth of all-in-fiber graphene device by electric current.By tuning the value of current from 0 mA to 9 mA,graphene is heated from 300 K to 900 K.It makes the optical conductivity of graphene change a lot.So the saturable absorption is changed by tuning the current.As a result,the modulation depth of graphene can be changed from 2.3%to 0.9%,the total variation exceeds 60%.Based on this characteristic,a fiber laser which can be varied in the state and pulse width by tuning the current is demonstrate.In addition,the high temperature also brings the deformation of fiber,the fiber end face with graphene can act as a gap adjustable cavity.The gap of the cavity is reduced by increasing the current,and the transmittance of the cavity is also reduced.So an all-fiber modulator which is controlled by electric current is realized.The modulation depth of this modulator exceeds 10%.And a tunable mode-locked fiber laser is demonstrated.3.We demonstrate a fiber laser based on graphene which is suspended in the air.Though the damage threshold of graphene is high,it's easy to be damaged when graphene is suspended in the air.And it will form a microvoid in the middle of the graphene which acts as a saturable absorber.A stable and polarization insensitivity mode-locked fiber laser can be realized based on this graphene.4.We demonstrate a state variable fiber pulse laser based on a graphene-integrated microfiber device.A 3D microfiber coil integrated with graphene acts as a polarization sensitive saturable absorber.By adjusting the polarization controllers,stable Q-switched pulses and mode-locked rectangular pulses are observed.To our knowledge,this is the first study conducted to achieve switching between rectangular pulses and Q-switched pulses while keeping the pump power constant.The rectangular pulses have a pulse width and repetition rate of~10 ns and-940 kHz,respectively,and the Q-switched pulses have a pulse width and repetition rate of-40 ?s and~4.8 kHz,respectively.