Shixun Dai

Spectroscopic properties and thermal stability of erbium-doped bismuth-based glass for optical amplifier

The spectroscopic properties and thermal stability of Er2O3 doped Bi2O3–B2O3–Na2O glasses are investigated experimentally. A close correlation is observed between the B2O3 content and the spectroscopic properties such as Judd–Ofelt intensity parameters Ωt (t=2,4,6), emission spectra, and lifetime of 4I13/2 level of Er3+. The value of Ω6 increases with an increase of B2O3 content, which is attributed to the decrease of the covalency of Er–O bond in terms of the glass microstructure and electronegativity theory. The emission spectra of 4I13/2→4I15/2 transition broadens as a consequence of the enhancement of the inhomogeneous distribution of Er3+ sites when increasing B2O3 content. The lifetime of 4I13/2 level of Er3+ in bismuth-based glass, compared with those in other glasses, is relative low due to the high-phonon energy of the B–O bond, the large refractive index of the host, and the existence of OH− in the glass. In addition, the glass stability is improved in which the substitution of B2O3 for Bi2O3 st...

Spectral properties and thermal stability of Er3+-doped oxyfluoride silicate glasses for broadband optical amplifier

Abstract Er 3+ -doped 50SiO 2 –(50− x )PbO– x PbF 2 glasses were prepared. The effect of PbF 2 content on refractive indices, densities, absorption spectra, the Judd–Ofelt parameters Ω t ( t =2,4,6), fluorescence spectra and the lifetimes of 4 I 13/2 level of Er 3+ in 50SiO 2 –(50− x )PbO– x PbF 2 glasses were investigated, and the stimulated emission cross-section was calculated from McCumber theory. With increasing PbF 2 content in the glass composition, the Ω 6 parameter, fluorescence full width at half maximum (FWHM) and lifetimes of 4 I 13/2 level of Er 3+ increase, while refractive indices and densities decrease. Compared with other glass hosts, the gain bandwidth properties of Er 3+ -doped 50SiO 2 –50PbF 2 glass is close to those of tellurite and bismuth glasses, and has an advantage over those of silicate, phosphate and germante glasses. The broad and flat 4 I 13/2 → 4 I 15/2 emission of Er 3+ around 1.55 μm can be used as host material for potential broadband optical amplifier in the wavelength–division–multiplexing (WDM) network system.

Optical transitions and upconversion luminescence of Er3+/Yb3+-codoped halide modified tellurite glasses

Er3+-doped halide modified tellurite glasses were synthesized by conventional melting and quenching method. The Judd–Ofelt analysis was performed on the absorption spectra and the transition probabilities, excited state lifetimes, and the branching ratios were calculated and discussed. The intense infrared and visible fluorescence spectra under 980 nm excitation were obtained. Strong upconversion signal was observed at pumping power as low as 30 mW in the glasses with halide ions. The upconversion mechanisms and power dependent intensities were discussed, which showed two-photon process are involved for the green and red emissions. The decay times of the emitting states and the corresponding quantum efficiency were determined and explained.

Effect of Bi 2 O 3 on the spectroscopic properties of erbium-doped bismuth silicate glasses

The spectroscopic properties of erbium-doped silicon dioxide, bismuth oxide, and sodium oxide glasses are investigated based on Judd–Ofelt analysis for absorption spectra, bandwidth analysis for emission spectra, and lifetime measurements of the 4I13/2 level of Er3+. The effects of bismuth oxide on these three optical parameters are discussed in terms of the local basic nature of the glass, of variations in ligand fields about Er3+ sites, and of the phonon energy and the refractive index of the glass host, respectively. The data obtained suggest that bismuth oxide does not have a promising composition for use with a broadband erbium-doped fiber amplifier.

Investigation on nonradiative decay of 4I13/2→-4I15/2 transition of Er3+-doped oxide glasses

Abstract Nonradiative decay of 4 I 13/2 → 4 I 15/2 transition of Er 3+ has been investigated in a series of oxide glasses. For Er 3+ -doped glass samples, the Judd–Ofelt analysis on absorption spectra was performed and the fluorescence lifetime was determined by extrapolating to zero Er 3+ concentration limit. Infrared spectra were measured in order to investigate the influence of OH − groups in different glasses. The effects of glass matrix on the decay rate were discussed from the viewpoint of phonon energy, variations of effective fields, and OH − groups. Compared to other glasses, phosphate glass presents low quantum efficiency and large nonradiative decay rate due to its high phonon energy and hygroscopic behavior.

The spectrum and laser properties of ytterbium doped phosphate glass at low temperature

Abstract Low-temperature absorption and fluorescence spectra of the Yb 3+ ions were measured in phosphate glass with compositions of (60–65)P 2 O 5 –(4–8)B 2 O 3 –(5–10)Al 2 O 3 –(10–15)K 2 O–(5–10)BaO–(0–2)La 2 O 3 –(0–2)Nb 2 O 5 –(4–8)Yb 2 O 3 (mol%). Temperature dependence of lifetime of Yb 3+ : 2 F 5/2 level was investigated. Laser performance of sample pumped by 940 nm laser diode at low temperature were presented. At 8 K, laser oscillation of diode pumped Yb 3+ : phosphate glass yielded a slope efficiency of 4% and a maximum power of 2 mW, the peak laser wavelength is 1001 nm.

Optical spectroscopy and gain properties of Nd 3+ -doped oxide glasses

Optical absorption and emission spectra and fluorescence lifetimes were measured for Nd3+ in a series of five oxide glasses. Spectroscopic parameters such as the stimulated-emission cross section, the effective bandwidth of the 4F3/2→4I11/2 transition, and the radiative lifetime of the 4F3/2 level were obtained, and their dependence on the composition of the glass is described. In addition, the relative gain properties for the 4F3/2→ 4I11/2 transition in various glasses are evaluated by the classic gain equation model.

Spectroscopic properties of Yb3+-doped silicate glasses

Abstract The absorption, emission and potential laser properties of silicate glasses doped with Yb 3+ ions are investigated in detail. The emission cross-sections ( σ emi ) are calculated on the basis of reciprocity method according to the measured absorption spectra. The potential laser properties for Yb 3+ -doped glasses are evaluated by the minimum fraction of Yb 3+ ( β min ), the pump saturation intensity ( I sat ), the minimum pump intensity ( I min ), and the product of emission cross-section ( σ emi ) and fluorescence lifetime ( τ f ). The σ emi near 1020 nm and τ f of Yb 3+ in 61SiO 2 –25PbO–6Na 2 O–8K 2 O glass are 0.49 pm 2 and 2.00 ms, respectively, which are comparable to those in phosphate glasses. Systematical factor of laser properties (SFL) is introduced to evaluate the potential laser properties of Yb 3+ -doped glasses, the results indicate that Yb 3+ -doped silicate glasses are potential materials for double cladding ytterbium fiber laser application.

Thermal stability and optical transition of Er3+ in sodium-lead-germanate glasses

The thermal stability and spectroscopic properties of Er3+-doped Na2O-GeO2-PbO glasses were investigated experimentally. The thermal analysis results show that the thermal stability of the investigated glasses is improved with replacing GeO2 by PbO. Subsequently, Judd-Ofelt (J-O) approach was applied to the room temperature absorption of Er3+ (4f11) transitions to determine J-O intensity parameters. The reduced values of Ω2 with the substitution of PbO for GeO2 indicate the decrease of covalency of Er—O bonding. The stimulated emission cross section of the 4I13/2 → 4I15/2 transition increases as a consequence of the increase of refractive index of glass hosts and the narrowing of fluorescence bandwidth with the increase of PbO. The abnormal large emission cross section and large bandwidth in the Na2O-0.8GeO2-0.1PbO glass arises from the change of germanium coordination with oxygen.

Fluorescence quenching in Er3+ doped tellurite glass due to the introduction of BO3/2

Er3+ doped tellurite glass is considered as a promising material for broadband applications because of its large stimulated emission cross section and broad emission bandwidth at the third communication window (1.55 μm) in order to increase the transmission capacity of the wavelength division multiplexing (WDM) system. The relatively low phonon energy of tellurite glass decreases the nonradiative transition probability of I13/2 → I15/2 emission and thus increases the quantum efficiency of Er3+. On the other hand, however, the nonradiative energy transfer rate from I11/2 level to I13/2 level of Er3+ in tellurite glass is lower than those in silicate and phosphate glasses with high phonon energies, which provides a long population duration on I11/2 level, which results in several undesirable effects [1] and hence leads to the decrease of the 980 nm pumping efficiency. 980 nm pumping is preferable to the success of an Er3+ doped amplifier since 1480 nm pumping cannot contribute to sufficient population inversion and a good signal-to-noise ratio. Several efforts have been made on methods of decreasing upconversion emission of Er3+ in tellurite glass. Choi et al. [2] studied the addition of energy acceptor ions such as Ce3+, Eu3+, and Tb3+ to deplete the I11/2 level by nonradiative energy transfer, because their electronic transition energies are approximately resonant with the energy gap corresponding to the I11/2 → I13/2 transition of Er3+. Hee Cho et al. [3] reported the introduction of BO3/2, which has the largest phonon energy (1400−1), into tellurite glass to increase the maximum phonon energy of the glass host to improve the I11/2 → I13/2 transition rate. However, a strong fluorescence quenching of I13/2 level was observed in our study when BO3/2 content is more than 10 mol% in the glass. In this letter, the effect of BO3/2 on lifetime of I13/2 level of Er3+ in tellurite glass was investigated. The quenching mechanisms of lifetime results from the BO3/2 addition are discussed based on nonradiative transition probability and interactions between rare earth ions. The glasses were prepared using conventional melting and quenching method from reagent-grade powders of H3BO3, ZnO, La2O3, Er2O3, and high purity powders of TeO2 (99.999%). About 20 g batches of starting materials were fully mixed and then melted in a platinum crucible at about 800–900 ◦C. The melt was poured into a brass mold and cooled in air and subsequently annealed to room temperature gradually. The obtained glasses were cut and polished carefully in order to meet the requirements for optical measurements. The fluorescence lifetime for the I13/2 level of Er3+ was measured with a 970 nm LD and a HP546800B 100 MHz oscilloscope. In order to minimize the influence of reabsorption on emission, the excitation beam was focused immediately below the surface of the samples so that the emitted light traveled only a short distance inside the sample. The radiative lifetime of I13/2 level of Er3+ is calculated according to the well-known Judd-Ofelt theory described anywhere. The quantum efficiency for the I13/2 → I15/2 transition was evaluated using the equation: η = τmea/τrad, where τmea is the measured lifetime and τrad is the calculated radiative lifetime. Fig. 1 illustrates the compositional dependence of the lifetimes and the quantum efficiency of Er3+ on BO3/2 concentration in tellurite glasses. The radiative lifetime τrad increases monotonically owing to the decrease of the refractive index of the glass host. The measured lifetime τmea and the quantum efficiency η initially decrease slightly up to BO3/2 = 8 mol% and then decrease rapidly as BO3/2 content increases. The lifetime of I13/2 level is also an important factor to the success of Er3+-doped amplifiers, since a long lifetime permits to obtain the required high-population inversion under steady-state condition using modest pump power [4]. The measured lifetime is mainly influenced by the maximum phonon energy of the glass host. If we neglect the energy transfer process between excited ions, the measured lifetime τmea is written as: