Polarized random fibre lasers based on the tilted fibre Bragg grating

In the traditional random fibre lasers (RFLs), it is complicated to generate polarized random fibre lasing. In this thesis, I present a new method to obtain polarized random fibre lasers (RFLs). In my research, 45° tilted fibre Bragg grating (45° TFG) fabricated in single mode fibre (SMF) or in Erbium doped fibre (EDF) has been integrated with the fibre laser and the polarized random lasing was achieved using 45° TFG with high polarization extinction ratio (PER) characteristics. In this thesis, first of all, I present the review of random lasers (RLs), random fibre lasers (RFLs), and corresponding polarization characteristics. And then I present a detailed research work on the method, characteristics and applications of fibre gratings, including fibre Bragg gratings (FBGs), long period gratings (LPGs), and TFG with small and 45° titled structures. One of the major contributions of my work in this thesis is the investigation on phase-match conditions, transmission spectra, PER for different types of fibre gratings including the TFG, FBG, and LPG. The results show that 45o TFG has high PER with 14 dB and the 7o TFG has comb-like resonance transmission. And then I present the experimental research of the thermal sensing of different types of fibre grating. LPG with grating period of 480 m has the highest thermal sensitivity with 297.1 pm/°C, superior to the FBG, small angle TFG and LPG. Meanwhile, I also researched the strain sensing application of FBG. The strain sensitivity of the FBG is 0.71±0.01 pm/°C. The other important contribution from the work is that I researched the polarization random fibre lasing feature with 45° TFG in the two fibre laser systems, which are Raman distributed SMF system and EDF with Raman distributed SMF hybrid system. In the Raman distributed SMF with length of 20.1 km system, there are three kinds of emission spectra with the increase of pump power from 1.70 W to 3.00 W: Raman emission, non-stationary random lasing emission, and stationary random lasing emission. The random lasing threshold is measured as 2.10 W. When the 45°TFG is added in the system, the polarized random lasing with PER of 12.02 dB has been obtained. In the EDF (2 m length) and Raman distributed SMF (11 km length) hybrid system without 45° TFG, there are two kinds of emission with the increase of pump power from 2.60 W to 4.40 W: Raman emission, and non-stationary random lasing. The stationary random lasing has not been observed due to the pump power limit. When the 45° TFG has been integrated in the hybrid system, we observed two kinds of emission in a range of pump power of 1.00 W to 2.20 W: Raman and Er3+ emission, and stationary random lasing. Under the effect of weak cavity formed by 45° TFG reflection and SMF distributed feedback, there occurs stabilized random fibre lasing emission. The threshold has been determined as 1.44 W. In addition, under the effect of 45° TFG, the polarized random fibre lasing with PER of 15.3 dB has been obtained

Self-assembly of 3D fennel-like Co3O4 with thirty-six surfaces for high performance supercapacitor

Three-dimensional (3D) fennel-like cobalt oxide (II,III) (Co3O4) particles with thirty-six surfaces on nickel foams were prepared via a simple hydrothermal synthesis method and its growth process was also researched. The crystalline structure and morphology were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. The Brunauer-Emmett Teller (BET) analysis revealed that 3D fennel-like Co3O4 particles have high specific surface area. Therefore, the special structure with thirty-six surfaces indicates the good electrochemical performance of the micron-nanometer material as electrode material for supercapacitors. The cyclic voltammetry (CV), galvanostatic charge-discharge, and electrochemical impedance spectroscopy (EIS) were conducted to evaluate the electrochemical performances. Compared with other morphological materials of the similar sizes, the Co3O4 particles on nickel foam exhibit a high specific capacitance of 384.375 F.g(-1) at the current density of 3A.g(-1) and excellent cycling stability of a capacitance retention of 96.54% after 1500 galvanostatic charge-discharge cycles in 6M potassium hydroxide (KOH) electrolyte

Implementing the CSILE/KB Program of University of Toronto in English Teaching in China

This paper first proposes that Aims of English Teaching should go beyond communicative competence according to Bloom's taxonomy. Then it mainly analyzes that teaching English as a foreign language in China can learn from CSILE/KB Program of University of Toronto in terms of goal setting, active roles of thinking scaffolding and comprehensive English competence acquirement.To bring TEFL to a new stage,the integration of TEFL with KB and MOOCS is put forward and some suggestions are made in the end

Community Asynchrony Increased Its Stability by Mediating the Relationship of Diversity–Stability Relationships in Loess Plateau, China

Extreme weather such as heavy rainfall and drought are threatening the global grassland and its potential to mitigate climate change. Therefore, understanding the drivers that promote the stability of grassland ecosystems is considered to be critical to mitigate the adverse effects of climate change on grasslands. Here, we use precipitation addition (PA) + grazing experiment to explain how species richness, aboveground biomass, species asynchrony, functional group level stability, drought tolerance and grazing tolerance can maintain grassland productivity stability. The results showed that grazing counteracted the promoting effect of rainfall on vegetation to a certain extent, and weakened the sensitivity of species of grazing tolerant functional group to rainfall. Rainfall and grazing affect the asynchrony of the community through the influence of drought tolerance and grazing tolerance functional groups, and then affect the stability of the community through the mediation of the relationship between aboveground biomass and species richness. This effect was significantly correlated with the differences of vegetation characteristics and resource acquisition strategies, but not with the community species richness. This study provides more explanations for the maintenance mechanism of community stability