PbSe Nanocrystal Quantum Dots To Achieve Large-mode Fiber Laser Experiments

Studies on semiconductor nanocrystals (quantum dots, QDs) develop rapidly for its unique optical properties in recent years. Compared to molecular beam epitaxy growth technology (MBE), the preparation of nanocrystal QDs by using the nanochemical method is simple and in low cost. Such nanocrystal QDs can be with very small sizes (～1nm), controllable sizes, and well-distributed density, to meet the requirements of real photoelectronic devices.In previous works, we observed experimentally the absorption-emission spectra of PbSe QD, and also the photoluminescence (PL) emission gain of the PbSe QD was simulated by numerical computation. It shows that the PbSe QD can produce stimulated emission upon pumping excitation with the short wavelength. In this dissertation, we achieve experimentally a PbSe nanocrystal QD doped fiber laser (QDFL) for the first time by doping the PbSe QD into the fiber and configuring an all-fiber ring resonator. This dissertation focuses on the four hands as follows.(1) Using a rotary evaporation method, the PbSe QD solution is fabricated choosing an ultraviolet (UV) curable adhesive as the fiber-core background material. We observe the size of PbSe QD and the density distribution by using transmission electron microscopy (TEM). The absorption-and PL spectra in the UV glue background are also measured by using a UV-visible near-infrared spectrophotometer and fluorescence spectrometer.(2) The prepared QD solution in different concentration was filled into a hollow fiber by pressure-difference method. Then, observing the filled fiber under a microscope (XTZ-D), and cutting out a part of the fiber with no visible air bubbles, and exposed under a UV lamp for solidifying the UV adhesive in the fiber. Finally, the available QDFs in different concentrations and lengths were prepared. The PL spectra of QDFs were measured, further, determing the PL-peak intensity as a function of fiber length and concentration.(3) A QD doped fiber laser (QDFL) was constructed in the laboratory. The fiber resonator is constituted by the QDF, fiber Bragg grating (FBG), optical isolator (ISO), fiber coupler and WDM (wavelength division multiplex).(4) The lasing output was observed varying with the pumping power, doping concentration, QDF length, and coupling ratio of the coupler by the PL Spectrometer and/or the Laser-power Meter. Upon980-nm LD pumping, we experimentally demonstrated steady and continuous1550nm laser generation for the first time, and determined the excitation threshold generating stimulated emission. A method of bending fiber was employed to select out single mode among multi-modes related with the gain fiber radius. Upon980-nm and68-mW pump input, a steady and continuous laser output of19.2mW (multimode) and6.31mW (single mode) were reached, with the pumping efficiency of28.2%(multimode), and9.3%(single mode), respectively.As the observed results presented in this dissertation are not optimized, therefore, it is possible to increase the output power by optimazing device parameters (such as, the doping concentration, fiber length, coupling ratio), which remains to the effort in the further.