Research On Properties And Devices Realization Of Optical Fiber/Graphene Based Hybrid Waveguides

This thesis belongs to the major of optics engineering,area of micronano photonics.Graphene,a two-dimentional material composed by carbon atoms in honeycomb lattice,is hornored by Nobel prize of physics in 2010 for its discovery.Graphene and its derivative materials,has unique physical and chemical properties and widely applicable potentials,across conventional material science,mesoscopic electromagnetics,quantum informatics,thermodynamics and condensed matter physics,et al.They are bringing revolutionary breakthroughs in modern scientific society.Especially in recent years in terms of optoelectronics,researches on graphene based optics and photonics has proposed a series of new concepts,revealed a series of new theories,demonstrated sorts of new phenomena,reported a varity of new devices,forming a new branch – the graphene base optics.On the highway of graphene photonics progresses,its combination with optical fibers is an unavoidable trend.Fiber/graphene based hybride waveguides,inheriting merits from both fibers and graphene,has shown great value in scientific research and prospective in technical applications:(1)Conventional fiber needs graphene to provide functionalization and tunability to realize new devices,while graphene needs a stable,widely used,lossless and easy to operate substrate(fiber)to enable its practical properties,the combination of them is necessary;(2)As a large area flexible film,graphene can be well deposited on sorts of optical waveguides,while optical fiber could be fabricated to be evanescent wave supporter after etching or polishing,then interacts with graphene effectively,hence the combination of them is feasible.However,graphene based fiber optics / photonics is stilla new direction crossing multi fields and projects,need more investigations.For complicated targets,fiber / graphene hybrid waveguide is in front of many challenges,people have to make much more effort on its properties,structures,functions,and performances.As a result,this project is of a frontier insight,a rich content,and an extended practical view.It not only faces to the global research hotpoint,but also bridges the strategic layout of micronano photonics.Supported by the National Joint-traning Doctoral Project of China Scholarship Council(CSC 201506070043),projects of National Science Fundation of China(NSFC,Grant.61290312,61205048,61107072,61107073,61475032),progress plan of Innovative Research Team of Education Ministry(IRT1218),111 project of Education Ministry(B14039),and UESTC excellent doctoral projects of academy,it is our fortunate to investigate the fiber / graphene hybrid waveguides as pineers globally,achieve several important advances and breakthroughs,majorly including:The physical modelling and the guiding properties of a fiber / graphene hybrid waveguide is finished,a new all-optical method measuring the dispersion of graphene waveguide in 1500 nm – 1600 nm is proposed;it is demonstrated that the first fiber / graphene bybrid waveguide gas sensor,and the continuously enriched the structures,forming a family of bio-chemical sensors based on fiber / graphene hybrid waveguides,and refreshed the sensitivity record constantly;we designed and realized the first graphene pulsed random fiber laser and the first Q-switched graphene-DFB laser,approaching to the Fourier transform limit;by using electric techniques,the Fermi level of graphene in hybrid waveguides is effectively tuned,achieving worldclass gate tunable DFG-SPP on chip and Kerr frequency comb in semiconductor resonators.The main research work is briefly introduced as below,(1)Proposing a new models of fiber / graphene hybrid waveguide.We describe the transmission of fiber / graphene hybrid waveguides in details clearly,by regarding graphene as an ultrathin wavguide layer with thickness of 0.4 nm,whose optical index is determined by its conductivity.Hence,the complex index of the hybrid wavguide is tunable,showing diverse physical responses.In this thesis we begin with waveguide,interference and mode theory,analyze the temporal,spectral and special response of the fiber / graphene hybrid waveguides.(2)Proposing sorts of new fiber / graphene hybrid waveguide configurations,also introduced their fabrication processes,characterization methods and parameters in details.Through heating-drawing method,or chemical etching method,we fabricated microfibers with diameter in range of 1?m to 10+ ?m,with/without inner microstructures.Through mechanical polishing method,we fabricated D shaped fibers with material of silica and PMMA,with mode distribution of single mode and multimode,with polishing depth up to 60 ?m.Via CVD,wet transferring,liquid reduction and p/n doping method,we successfully cover graphene in range of single-layer to multilayer,in length of 5 mm to 2 cm,pristine and highy doped,even with functional groups onto fiber structures,forming graphene based micro-miniature structures such as MZI,FBG,MMI and SMS.(3)Paving a new way for fiber / graphene hybrid wavguide based sensors.Starting from its unique optical sensing principle,we designed and achieved a series of graphene based fiber sensors,for different target,in different cases,and showing different professionals.Based on microfiber / graphene hybrid waveguides and D shaped fiber / graphene MMI,we demonstrate high sensitive detection for chemical gases,e.g.acetone,xylene,NH3 and humidity.Best detect limit reached 40 ppb.Based on FBG in a graphene – PCF – PMMA hybrid,we demonstrated a sensing for the density of human red blood cells,the detect limit could be sub ppm level.Based on partically reduced graphene oxide / SMS hybrid,we pioneeringly integrated FRET and all-in-line interference together on fiber,which can detect heavy metal ion,organics and ssDNA selectively,with high resolutions.(4)Opening a new window for fiber / graphene bybrid waveguide based lasers.By using a D shaped fiber / graphene hybrid waveguide,we demonstrated its excellent polarization selectivity and ultrafast saturable absorption simultaneously,realized a cavity-less pulsed random fiber laser,for the first time,with orders level tunability in repetition rate and pulse width,as fast as ~ 900 ps,with PER higher than 41 dB.By wrapping a layer of graphene on a < 5 cm long DFB fiber laser,we reported the first integrated Q-switched fiber laser with both narrow bandwidth(< 1MHz)and fast pulses(< 1 ?s,energy ~ 10 nJ),approaching Fourier transform limit.(5)Revealling fiber / graphene hybrid based high order nonlinearities and their dispersion controlling.By specifically analyzing the physical processes and response properties of the nonlinearities,we theoretically investigated and experimentally demonstrated FWM and DFG on graphene based waveguides.By using CW laser and high energy pulsed laser as the pump respectively,we demonstrated non-degenerated FWM and cascade FWM with detuing > 10 nm,conversion efficiency >-20 dB,in microfiber / graphene hybrids,and also demonstrated DFG based SPP generation & control on graphene semiconductor chip,with SPP frequency 5 ~ 10 THz,conversion efficiency > 6×10-5.Moreover,we achieved wide tunability in Kerr frequency combs,via actively dispersion engineering and nonlinear parameter balance.