The Research Of Intergration Quantum Dots For Optical Fiber Devices

The optical fiber fabricated by silica is the most perfect waveguide for fiber communication and sensing application up to now.The development of controllable all-fiber-device and promoting the information processing ability of fiber is an important research area.However,traditional nonlinearity-based optical fiber devices suffer from the demerits of complex/expensive components,high peak power requirements,and poor efficiency.It was noticed the integration of functional materials into optical fiber structure is an important approach to design new type of optical devices.In this case,the key problem to develop optical fiber device is the seeking the proper functional materials to combine with silica fiber.Colloidal quantum dots?CQDs?are zero-dimensional semiconductor materials that can be utilized in the fabrication of fiber devices since they can offer several advantages.At first,solution-processed CQDs afford nanoscale dispersion,and thus,the functional material can easily and conformally be deposited on fiber to fabricate robust devices.The second,the electrons in a CQD are confined to a very small volume,typically several hundreds to thousands of atoms per particle.The concentration of photoexcited electrons can reach a high level,and therefore,obvious refractive index?RI?change induced by the enviroment will be observed.The last,CQDs are highly tunable materials.It means the fundamental properties of a CQD,including the composition,size and band gap can be tuned by different praperation conditions to meet the experimental requirements.In this thesis,the CQDs are used as functional material for the interation in microfiber strcture to fibracte optical fiber devices.The orginal achievements are includes:Firstly,we proposed a temperater independent fiber gas sensor.A special designed fiber interferometer?FI?with a sphere ending was fabricated.Besides,the lead sulfide?PbS?and stannic oxide?SnO₂?CQD was synthesized and they were deposited on the fiber ending by means of layer by layer methods under the assistance of light power.The CQD film was dispersed uniformly under the observation of scanning electron microscope?SEM?.The devices were used for the detection of gases after the ligand exchange progress.In the experiment,the PbS enabled fiber sensor could response to the increment NO₂ gas concentration with the increasing of extinction ratio of the FI spectrum.While the SnO₂sensitized devices could response to the increment of H₂S gas concentration with the decresing of extinction ratio.Meanwhile,experiment showed the extincation ration was not change as the temperature varied.In this regrad,the fiber gas sensor was irrelevant to temperature.After that,simulaitons were conducted and the RI change of CQD was the reason for the extincation ratio change.Moreover,the gas response was explained as the results of competitive adsorption between the detection gases and O₂ in the air.At last,experiments illustrated the gas sensitivity was influenced by the ligand exchange procedure.Sencondly,a scheme for low detection limit,high sensitivity and selective CQD enabled fiber gas sensor was proposed.The exposed core suspendent microstructure fiber was used to facility the deposition of CQD in fiber.At the beginning,FI structure was designed and the PbS and SnO₂ CQD was coated on the fiber structure successfully.After that,gas detection experiment was taken and the PbS CQD enabled devices was discovered to be NO₂ gas sensitive.In the experiment,blue shift was observed.The sensitivity and detection limit was calculated as 35 pm/ppm and 1 ppb respectively.While for SnO₂enabled devices,it was response to H₂S gas concentration and red shift was discovered.The sensitivity and detection limit was calculated as 131 pm/ppm and 3 ppb respectively.Moreover,the software of COMSOL was utilized to simulate the optical distribution in optical fiber.Besides,the RI of CQD was calculated by the RI dielectric function model for CQD.Based on the result,the relation of wavelength shift and the gas concentration was calculated,which was found to be accordant to the experiment.In addation,the influence factors for the gas sensing ability of PbS CQD enabled devices were researched.At last,a distribution sensing system for selective gas detection was demonstrated.Thirdly,we prepared a light power controlled optical fiber filter.In order to anlysis the working principle,different size of PbS CQD was synthesized.The influence factors of light power and wavelength were anlysised.The light control devices were discovered to have three features:?a?only the light with photo energy larger than the CQD band gap could applied as control light;?b?the wavelength shift of the fiber filter has a linear relationship with the light power;?c?the excition power for the CQD was at^mW level,which was 1000 times lower than the bulk semiconductor materials.After the experiment,the RI change of CQD under the light excited was calculated theoretically.At last,the light controlled fiber filter was used in a high speed communication system for chirp management and dispersion compensation.The experiments illustrate the CQD can be used to develop opto-electronic information processing devices in different waveguides,such as fiber,planar waveguide and so on.