| The Er3+-doped SiO2-based fiber amplifier (EDFA) is widely used in tremendous capacity fiber communication system because of its some excellent characteristics such as high gain, lower noise and so on. However, the bandwidth of the conventional SiO2-based EDFA is limited (-35 nm), which only covers with a narrow bandwidth at 1.53μm communication window, and can not meet the demand of the modern dense wavelength division multiplexing (DWDM) optical network systems. For highly efficient amplification based on Tm+:1.46μm emission, the host glass must have low phonon energy because the amplification is difficult on a silicate glass due to the fast multi-phonon relaxation. So tellurite glass with low phonon energy has been studied in the thesis. The lasing (3H4→3F4) transition is limited by the fact that the lifetime of upper level (3H4), is lower than that of the lower level (3F4), which is called the "self-terminating" level for the 1.46μm transition. The results show that co-doping with other rare earth ions is essential for increasing the quantum efficiency. Tm3+ doped optical fibers have been used as optical amplifiers at the S-band (1 460-1 530 nm), this also have certain limitations. At last Er3+-Tm3+ co-doped optical fibers show the advantage of continuous spectra over the whole S, C and L bands while the cascaded amplifiers could present separated bands. In the last years, Tm3+ doped glasses have been generated a great deal of attention due to the interesting spectroscopic properties of their 1.46μm infrared emission, which is important to achieve a band extension in the spectral range corresponding to the S-band amplifier region. Therefore it is urgent to develop a new optical amplifier at S band.The exordium introduced the principles and researching development in the tellurite fiber amplifier, and studied the special merits of tellurite optical fiber as gain medium in fiber amplifier, comparing to conventional SiO2-based optical fiber and other based fiber. It also summarized the developing status of the glass structure, composition, thermal stabilities, chemical stabilities and optical properties in our country and abroad, it is believed that the tellurite glass can be used as an ideal glass host for broadband fiber amplifier. In the chapter 2, an introduction of the experimental materials, instrument and operating processes was given. And it explained the methods and principle of testing the physical properties, thermal properties and the spectroscopic properties in detail.In the chapter 3, the theoretical backgrounds which have been used in this thesis are introduced, including Judd-Ofelt theory, upconversion theory, McCumber theory and nonradiative transition theory.In the chapter 4, Tm3+ doped TeO2-K2O-Nb2O5-Ln2O3 (TKNL) glasses have been developed. Optical properties have been studied; Ho3+-Tm3+co-doped TKNL glasses have been developed. In the range of 1.3-2.2μm, the emission at 1.46μm and 1.8μm of Tm3+ and 2.02μm of Ho3+ were observed in Er3+-Tm3+co-doped TKNL glasses. Optical properties of Tm3+ doped TKNL glasses have been studied with doping different concentrations of HO2O3. A possible mechanism of energy transfer between Tm3+ and Ho3+ was discussed; A NIR broadband luminescence peak with a full width at half-maximum (FWHM) of 185 nm from 1.3-1.8μm was observed in Er3+-Tm3+ co-doped TKNL glasses. A possible mechanism of energy transfer between Tm3+ and Er3+ was discussed. This chapter divided into three parts.Firstly, tellurite glasses have attracted a considerable interest especially because of their high refractive index and low phonon energy. Moreover, these glasses combine good mechanical stability, with a wide transmission window (typically 0.4-6μm). The physical and optical charactics of tellurite glass with composition of TeO2-K2O-Nb2O5-Ln2O3 (TKNL) have been studied in this thesis. DTA curve was measured by synthesis thermal analyst, the result showed that△T= 139℃indicated very good stability against devitrification. According to absorption spectrum, Judd-Ofelt intensity parameters were calculated to beΩ2= 5.26×10-20 cm2,Ω4= 1.57×10-20 cm2,Ω6= 1.46×10-20 cm2. We also studied when the type of alkali oxides changing, the Judd-Ofelt intensity parameters and line strengths of electric-dipole transitions would be affected. This result indicated the lower ration value ofΩ4/Ω6,, the better of luminescence efficiency for 1.46μm (S band). TKNL glass is a more ideal glass host for broadband fiber amplifier compared with other glasses. This result is helpful to choose the host material which used in TDFA in future.Secondly, Ho3+-Tm3+ co-doped TKNL glasses have been developed. Optical properties have been studied doping with different concentrations of Tm2O3. The effective bandwidth and peak emission cross-section of the 3H4→3F4 transition (1.46μm) of Tm3+ have also been obtained. when the concentration of Ho3+ was increased, the Tm3+ emission peak at 1.46μm is hardly changed and the emission peak at 1.8μm decreased. On the other hand, the Ho3+ emission peak at 2.02μm increased firstly and then decreased with Ho3+ addition. A possible mechanism of energy transfer between Tm3+ and Ho3+ has been discussed. Co-doping of Ho3+ significantly decreased the population of 3F4 level of Tm3+, while the population of 3H4 level of Tm3+ reduced slightly. These results indicated that Ho3+-Tm3+ co-doped TKNL tellurite glass materials are attractive for broadband amplifiers.Finally, the optical properties at near-infrared region in Er3+-Tm3+ co-doped TKNL glasses have been studied. Based on the Judd-Ofelt (J-O) theory, the J-O intensity parameters were calculated to beΩ2= 7.21×10-20 cm2,Ω4= 1.45×10-20 cm2,Ω6= 1.21×10-20 cm2 from the absorption spectrum of Er3+ ions. A NIR broadband luminescence peak with a full width at half-maximum (FWHM) of 185 nm from 1.3-1.8μm was observed in Er3+-Tm3+ co-doped TKNL glasses under 808 nm excitation, and the ratio for the intensity of 1.46μm and 1.54μm was greatly changed by Tm3+ co-doping content. A possible mechanism of energy transfer between Tm3+ and Er3+ was discussed. The present glass materials may allow for the production of an optical amplifier in S, C and L telecommunication bands. |
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