The Spectroscopic Properties Of Multi-component Broadband Erbium-doped Glasses And Study Of Fiber Amplifying Performances

With the rapid developments of modern communication technologies, the requests of the fiber communication capacity and system integration are increasingly improved, which makes the joint use between erbium doped fiber amplifier (EDFA) and wavelength division multiplexing (WDM) technology become an indispensable condition to realize the multi-wavelength and ultra-distance transmission. Of which, EDFA has become a key component to improve WDM system channels and communication capacities. However, traditional commonly-used silicate-based EDFA which works mainly in the C-band (1530¹565 nm) region has not satisfied the developing requests so far. Therefore, developing the nonsilicate-based EDFAs with broad amplifying bandwidth and high signal gain per unit length, and directly realizing the seamless amplification of (C+L)-band (1530¹610nm) region has a very important practical significance to the capacity expansion and integration of WDM communication system.Based on the developing requests of modern fiber communication technologies, and the considerations to realize the entire research processes, which start from the broadband erbium-doped glass to the broadband erbium-doped glass fiber and finally to the broadband erbium-doped fiber amplifier, the paper chooses the multi-component tellurite- and bismuth-based oxide glasses, and gives them a number of experimental and theoretical studies around the improved spectral characteristics of multi-component broadband erbium-doped glass, the fabrication of multi-component broadband erbium-doped glass fiber, and the steady and transient state theoretical simulations of broadband erbium-doped fiber amplifiers. The main works of the paper are as follows:1. The effect study of single-doped rare-earth erbium ion concentration on the spectral characteristics of tellurite-based glassThe integration of WDM system requires improving the rare-earth erbium-doped concentration in the gain media of fiber amplifier as possible as can in order to obtain a high signal gain per unit length. However, higher erbium-doped concentration can also bring some negative effects and finally affect the performance specifications of fiber amplifier. Therefore, the effect studies of erbium ion doped concentration on the spectral characteristics of tellurite-based glasses with the compositions of TeO₂-ZnO- La₂O₃(Na2O) are presented in this paper, and the 1.53μm band fluorescence spectra, fluorescence intensities and lifetimes have been detailed investigated as a function of erbium-doped concentration. To this end, the measured 1.53μm band fluorescence spectra are decomposed and fitted with Lorentz line-style function, the relative intensity variation of each spectral component are analyzed with a proposed equivalent four-level model, and the 1.53μm band spectral expansion and the emission peak shift with erbium-doped concentration are investigated. Meanwhile, the non-radiative energy transfer mechanism in the erbium-doped tellurite-based glass is studied according to the Forster-Dexter theory, and the main effect factor resulting in the quenching of 1.53μm band fluorescence intensity and fluorescence lifetime under the higher erbium-doped concentration is pointed out. Also, the rare-earth solubility in tellurite-based glasses with different compositions is compared, and the critical concentration and critical interaction distance of Er³⁺ ion are calculated based on the non-radiative energy transfer mechanism. Finally, the optimal doped content is determined.2. The improved study of the spectral characteristics for multi-rare earth ions co-doped tellurite-based glassOptical pumping of 1480 or 980nm wavelength is generally applied in 1.53μm band EDFA. EDFA has a low noise figure (NF) pumped at 980nm, but it also has a low pumping efficiency due to the weak absorption of Er³⁺ ion and the strong upconversion emission. To improve the 980nm pumping efficiency and 1.53μm band spectral characteristics, the Yb³⁺ and Ce³⁺ ions are respectively introduced into the erbium-doped tellurite-based glasses with the compositions of TeO₂-ZnO-La₂O₃-Nb₂O₅ in this paper. The enhanced effects of Yb³⁺ ions on the 1.53μm band fluorescence and upconversion luminescence of Er³⁺, which are in good agreements with the theoretical simulations, are investigated by analyzing the energy transfer process of Yb³⁺/Er³⁺, while the enhanced effects of Ce³⁺ ions on the 1.53μm band fluorescence and the suppressed effects of Ce³⁺ ions on the upconversion luminescence are investigated by analyzing the energy transfer process of Er³⁺/Ce³⁺. It is concluded that Er³⁺/Yb³⁺/Ce³⁺ tri-doped is a more effective scheme to improve the 980nm pumping efficiency and 1.53μm band spectral characteristics than Er³⁺/Yb³⁺ co-doped. Based on these, the paper also proposed a scheme for the first time to further improve the energy transfer rate from Er³⁺ to Ce³⁺, which is a phonon assisted energy transfer process, by increasing the host phonon energy and decreasing the energy mismatch between Er³⁺ and Ce³⁺ relevant transitions, and it is well illustrated by the experimental results.3. The study of fluorescence decaying characteristics for single erbium-doped bismuth-based glassIt is known that OH- groups incorporated in the glass are responsible for the hydroxyl absorption at about 1385nm in silicate-based transmission fiber, and are also one of the dominant quenching centers of 1.53μm band fluorescence of Er³⁺. Based on the measured 1.53μm band fluorescence decaying behavior, the interaction mechanism between OH- groups and Er³⁺ ions, and the effects of OH^- groups on Er³⁺ fluorescence in bismuth-based glass with the compositions of Bi₂O₃-B₂O₃-GeO₂-Na₂O are investigated in this paper. It is shown that the energy transfer from Er³⁺ ions to OH^- groups results in an evident non-exponential decaying behavior for glasses with low Er³⁺-doped concentration, and the energy transfer microparameters from Er³⁺ ions to OH^- groups are obtained by fitting the decaying curves with Inokuti-Hirayama equation. Furthermore, a removing OH- group treatment by pouring dry oxygen gas into the high-temperature glass melting is investigated. Removing OH- group treatment can dramatically decrease the OH- group content in the glass, and hence improve the 1.53μm band fluorescence intensity, while the fluorescence decaying reveals a nearly exponential behavior.4. The suppressed study of excited-state absorption for erbium-doped bismuth-based glass with low phonon energyThe excited-state absorption is generally occurred in 980nm pumped erbium-doped oxide glasses with low phonon energy, it limits the pumping conversion efficiency and hence 1.53μm band fluorescence intensity. Therefore, the Ce³⁺ ion and B₂O₃ component are respectively introduced into erbium-doped bismuth-based glass with low phonon energy, which has the compositions of Bi₂O₃-GeO₂-Ga₂O₃-Na2O. The effects of two suppressed schemes on the excited-state absorption and 1.53μm band fluorescence are investigated and compared. It is found that both a proper Ce³⁺ ion or B₂O₃ component content introduction into the glass increases the non-radiative relaxation rate from Er³⁺:⁴I_11/2 to ⁴I_13/2 levels by the means of energy transfer or multi-phonon relaxation and decreases the Er³⁺:⁴I_11/2 level lifetime, and hence the excited-state absorption is suppressed effectively. Meanwhile, the introduction of Ce³⁺ ions further improves the total quantum efficiency of Er³⁺:⁴I_13/2 level and 1.53μm band fluorescence intensity, whereas the introduction of B₂O₃ component further broadens the 1.53μm band fluorescence spectrum, however, its intensity is somewhat weakened.5. The study of multi-component broadband erbium-doped glass fiber fabrication and its spectral propertyBased on the above improved studies of the spectral properties for multi-component erbium-doped glasses, the fabrication studies of multi-component tellurite- and bismuth-based erbium-doped glass fibers are presented in this paper. Relying on the independent experimental conditions, the fiber performs are fabricated with the combined rotation-casting and tube-rode techniques, and the multi-component tellurite- and bismuth-based erbium-doped fibers with the cladding diameter of 125μm and the core diameter of 5.1μm and 5.6μm, respectively, are drawn. The transmission loss and the amplified spontaneous emission (ASE) spectra of broadband erbium-doped fiber are measured. The measured transmission losses at 1310nm are 3.7dB/m and 3.4dB/m for tellurite- and bismuth-based erbium-doped fibers, respectively, and both ASE spectra coverage the C+L band. Finally, considering the high melting temperature difference between the bismuth-based glass fiber and silicate-based transmission fiber, the splice between them is tried by non-symmetric splicing technique, and it is of a practical significance to accumulate a number of technique experiences in fabricating high-quality broadband erbium-doped fiber and EDFA.6. The theoretical study of steady and transient characteristics for multi-component broadband erbium-doped glass fiber amplifierIn order to understand the amplifying process and provide theoretical basis for the design of broadband EDFA, both the steady and transient state characteristics are investigated theoretically in this paper. 1) For the bismuth-based EDFA, a theoretical model considering the energy transfer among Er³⁺ ions and excited-state absorption is proposed, the steady-state signal gain, noise figure (NF) and their variations as a function of input power and fiber length pumped at 1480nm and 980nm wavelength, respectively, are stimulated and compared. Meanwhile, due to the large amplified spontaneous emission (ASE) noise, the optimal design of Bi-EDFA is studied by suppressing or utilizing ASE noise, respectively. It is found that by suppressing the backward ASE of Bi-EDFA with an optical isolator inserted in the bismuth-based erbium-doped fiber, the signal gain is increased and the NF is decreased. While an optical circulator is utilized to direct the unwanted ASE of the former Bi-EDFA to pump an un-pumped bismuth-based erbium-doped fiber, the L-band signal gain is enhanced evidently. 2) For the tellurite-based EDFA, the transient response and its variations as a function of input power and pumping power are investigated theoretically when EDFA is inputted with a pulse signal. Furthermore, in order to suppress transient excursion of the output signal, a novel scheme to modify the step edge of pulse signal into a slowly changed edge waveform signal is proposed for the first time. Compared to the pulse signal with step edge, it is shown that the transient excursion of Te-EDFA output power is reduced effectively when a properly designed, slowly changed edge signal is inputted.Finally, the paper works and innovation points are summarized, and some problems that are needed to be investigated further are pointed out.