Tunable Mode-Locked Laser Based On Graphene Microfiber

Tunable mode-locked fiber lasers are widely used in fields such as optoelectronic sensing,wavelength division multiplexing,biomedicine,and other fields due to their extremely narrow time domain pulses,extremely wide frequency domain spectra,ultrastrong power,and high repetition rates.However,tunable mode-locked fiber lasers usually require additional filtering devices,which can cause random wavelength drift and make it difficult to control the tuning range accurately.Graphene has excellent optical properties and has been widely used as a saturable absorber in fiber lasers.This paper researches on graphene tunable mode-locked fiber lasers,utilizing the saturable absorption characteristics of graphene to achieve ultrashort pulse output using microfibers as optical waveguides,and studies the wavelength tuning mechanism using the polarization characteristics of graphene and birefringent filtering effects combined with nonlinear polarization rotation(NPR)structures.The main research contents are as follows:Firstly,the optical properties of microfibers are introduced.Using the finite element analysis software Comsol Multiphysics,the waist mode distribution of microfibers is simulated to predict the interaction of light with materials in the form of evanescent fields.Using the flame oxyhydrogen taper mechanism to prepare microfibers that meet the experimental requirements,the graphene microfiber composite structure was successfully prepared using the optical deposition method.A graphene microfiber mode-locked laser was designed experimentally.In the negative dispersion region,by adjusting the pump power to 400 m W,a conventional soliton mode-locked laser with a central wavelength of1558.56 nm,a 3 d B spectral width of 5.12 nm,a repetition frequency of 6.6 MHz,and a pulse width of 619 fs was achieved.The mode-locked state of the bright and dark soliton pairs was obtained by increasing the pump power to 650 m W and adjusting the polarization controller(PC)appropriately.By adjusting the polarization state,the birefringence of the ring cavity is changed to obtain a dual-wavelength with a tunable range of about 11 nm.Secondly,a series of studies were carried out on the dispersion management solitons and dissipative solitons generated in the near-zero dispersion and positive dispersion regions of the 1.5μm band,respectively,using a graphene-microfiber composite structure as a saturable absorber mode-locked device and a resonant cavity fiber dispersion management technique.The dispersion management soliton output is achieved by intracavity dispersion compensation to near-zero dispersion with a pulse width of 0.87 ps and a 3d B spectral bandwidth up to 20.96 nm.The dispersion compensating fiber(DCF)is added to compensate the dispersion in the near-zero dispersion region to the positive dispersion region.The dispersion management soliton output can be obtained by adjusting the intracavity polarization state.The dispersion solitons in the 1560 nm band with a pulse width of 5.56 ps and a 3d B spectral bandwidth of 21.85 nm were obtained by adjusting the intracavity polarization state,and the output characteristics of the graphene passive modelocked fiber laser in the three dispersion regions were compared and analyzed.Finally,the combination of graphene and NPR mechanism can effectively stabilize the pulse output and improve the wavelength tuning range of the fiber.The wavelength-tunable conventional soliton pulses were achieved in the negative dispersion region with a wavelength tuning range of 1530.8-1562.8nm,and the dispersion-managed soliton pulses were obtained by using the resonant cavity fiber dispersion management technique to compensate the resonant cavity to near zero dispersion with a wavelength tuning range of1549.3-1566.5 nm.