Table of Contents Author Guidelines Submit a Manuscript
Advances in OptoElectronics
Volume 2009 (2009), Article ID 278105, 8 pages
http://dx.doi.org/10.1155/2009/278105
Research Article

Numerical Simulation of 980 nm-LD-Pumped Yb𝟑+-Er𝟑+-Tm𝟑+-Codoped Fiber Amplifier for 1500 nm and 1600 nm Bands

State Key Laboratory of Advanced Optical Communication Systems and Networks, Shanghai Jiao Tong University, Shanghai 200240, China

Received 2 March 2009; Accepted 1 May 2009

Academic Editor: Samir K. Mondal

Copyright © 2009 Chun Jiang. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The theoretical model of Yb3+-Er3+-Tm3+-codoped fiber amplifier pumped by 980 nm laser is proposed, and the rate and power propagation equations are numerically solved to analyze the dependences of the gains at 1500 nm and 1600 nm bands on the activator concentrations, fiber length, pump power, and signal wavelength. The numerical results show that our model is in good agreement with experimental result, and with pump power of 200 mW and fiber length varying from 0.15 to 1.5 m, the gains at the two bands may reach 10.0–20.0 dB when the codoping concentrations of Yb3+, Er3+, and Tm3+ are in the ranges 1.0–3.0×1025, 1.0–3.0×1024, and 1.0–3.0×1024 ions/m3, respectively. The fiber parameters may be optimized to flatten the gain spectra.

1. Introduction

The All-wave fiber without residual OH group is being considered for Coarse Wavelength Division Multiplexing (CWDM) transmission systems and metro area optical networks because it has low-loss bandwidth of about 400 nm (1250–650 nm). WDM technology has been the most important technology of large-capacity optical transmission system, and optical amplifiers are key devices of WDM system. Although Fiber Raman Amplifier (FRA) using split-band and multipump schemes might simultaneously amplify multichannel signal within 130nm bandwidth, it would increase the power penalty of the system and degrade the performance of the system since the introduction of the multiplexing/de-multiplexing caused additional insertion loss [1]. Another kind of FRA could provide distributed amplification within 140 nm bandwidth using pump-signal interleaving method, but its gain spectra had relatively large ripple [1]. Later, a novel multiband FRA was reported theoretically providing flat bandwidth of 200 nm with ripple of 1 dB [2]. However, the FRA requires higher pump power due to its lower pump efficiency. Rare-earth doped fiber amplifiers have higher gain and pump efficiency, and in the past decades the researches on rare-earth-doped fiber amplifiers have been focusing on the singly-doped fiber amplifiers, and all of these amplifiers have their own bandwidths, Er3+-doped fiber amplifier (EDFA) with new parallel configuration [35] was reported providing gain bandwidth of more than 100 nm, and Tm3+-doped- and Pr3+-doped fiber amplifiers [69] could provide the gains in the ranges 1400–1500 nm, 1280–1340 nm, respectively. Recent reports on emission properties of Er3+-Tm3+-codoped silicate and telluride fibers showed that the combination of the emission at 1500 nm windows with that at 1400 nm windows in a single fiber may generate a large seamless emission spectra with emission width up to 200 nm in the codoped system [1014]. The upconversion and energy transfer in Yb3+-Er3+-Tm3+- and Er3+-Tm3+-codoped glasses were reported [15]. Energy transfer and upconversion luminescence of Bismuth, Tm3+/Ho3+, Tb3+/Yb3+, Er3+/Tm3+/Yb3+-codoped inorganic materials for display systems were reported [1630]. In our previous works [31, 32], we presented the numerical model of Er3+-Tm3+ codoped telluride fiber amplifier pumped at 800 nm and calculated the dependence of the gains at 1470 nm and 1530 nm bands on the fiber parameters, and analyzed the transmission performance of the WDM system based on the codoped amplifier. Although the rate equations of Er3+-Tm3+, Er3+-Yb3+-Tm3+-codoped fluoride glasses was reported in [15], the equations just considered the upconversion of infrared to visible light for display system, did not consider the spontaneous and stimulated emissions of 1470 nm, 1530 nm, and 1630 nm bands. Other references on this codoped system just concentrated on the spectral properties. Owing to importance of the double and multidoped systems for broadband amplification of telecommunication wavelength, a theoretical model will be desirable for designing and optimizing the codoped broadband amplifiers. In present paper, we propose a new numerical model of Yb3+ and Er3+ and Tm3+ codoped fiber system pumped by 980 nm laser for amplification of the signal at 1470, 1530, and 1630 nm bands. This model considers the excited state absorption and upconversion of Er3+ and Tm3+ ions and cross-relaxation of Tm3+-Er3+. The dependence of the gain spectra covering 1500 and 1600 nm bands on codoping concentrations, fiber length, and pump power is calculated and analyzed.

2. Theoretical Model

Figure 1 shows the schematic of the energy levels and electron transitions and energy transfer process of an Er3+-Tm3+-Yb3+ codoped telluride glass system pumped by 980 nm. With the excitation of 980 nm pump, the electrons of Yb3+ ions are excited from the ground state (2F7/2) to the excited state (2F5/2) and the energy at the 2F5/2 level transfers to the 4I11/2 level of Er3+ due to matching energy gap between the two levels, meanwhile, the energy at the level also can transfer to the 3F4 level of Tm3+ ion through multiphonon process. With the excitation, moreover, the electrons of Er3+ ions are excited from the ground state 4I15/2 to the excited state 4I11/2, then nonradiately relax to the 4I13/2 level through multiphonon process, and transit from the level to the ground state (4I15/2 level), emitting photons at 1500 nm band. In addition, the electrons at 4I11/2 level of Er3+ ions can be excited to the 4F7/2 level due to excited state absorption (ESA), and the electrons at the 4F7/2 level transit to the ground state with emission of red photon. On the other hand, energy transfer also can take place between Er3+-Tm3+ and Yb3+-Tm3+ via cross-relaxation process. The energy at the 4I13/2 level of Er3+ ions and the 2F5/2 level of Yb3+ ions can transfer to the 3F4, 3F2 levels of Tm3+ ions via the electron transition from the 3F4 level to 3F2 level of Tm3+ at which the electron nonradiately relax to 3H4 level from which is excited to the 1G4 level via another cross-relaxation process. Electron at the 1G4 level transit to the 3F2, 3F4, and 3H6 levels with emission of lights at 1630, 650, and 476 nm bands, respectively. The electron at 3F2 level nonradiately relaxes to 3H4 level and then transites to the 3F4 level with emission of light at 1470 nm band. The electrons at 3F4 level transit to ground state (3H6), emitting the light at 1680 nm band.

278105.fig.001
Figure 1: The schematic of energy level and transition configuration and energy transfer process of Yb3+, Er3+ and Tm3+ codoped telluride fiber system pumped with 980 nm LD.

According to Figure 1, a rate equation group can be written as follows: 𝜕𝑁1=𝑊𝜕𝑡12𝑊13𝑁1+𝑊21+𝐴21𝑁2+𝑊ET28𝑁2𝑁7+𝑊41𝑁4𝑊ET63𝑁6𝑁1,𝜕𝑁2𝜕𝑡=𝑊12𝑁1𝑊21+𝐴21𝑁2+𝐴32𝑁3𝑊ET28𝑁2𝑁7,𝜕𝑁3𝜕𝑡=𝐴32𝑁3+𝑊ET63𝑁6𝑁1𝑊34𝑁3+𝑊13𝑁1𝑊ET64𝑁6𝑁3,𝜕𝑁4𝜕𝑡=𝑊34𝑁3+𝑊ET64𝑁6𝑁3𝑊41𝑁4,𝜕𝑁6𝜕𝑡=𝑊56𝑁5𝑊ET63𝑁6𝑁1𝑊ET64𝑁6𝑁3𝑊ET68𝑁6𝑁7𝑊ET610𝑁6𝑁8𝑊ET611𝑁6𝑁9𝐴65𝑁6,𝜕𝑁7𝜕𝑡=𝐴87𝑁8+𝑊97𝑁9𝑊ET68𝑁6𝑁7𝑊ET28𝑁2𝑁7+𝐴117𝑁11,𝜕𝑁8𝜕𝑡=𝐴87𝑁8+𝑊ET68𝑁6𝑁7+𝑊ET28𝑁2𝑁7𝑊810+𝑊ET610𝑁6𝑁8+𝐴118𝑁11,𝜕𝑁9𝜕𝑡=𝐴109𝑁10𝑊ET611𝑁6𝑁9𝑊97𝑁9,𝜕𝑁10𝜕𝑡=𝐴109𝑁10+𝑊810+𝑊ET610𝑁6𝑁8𝑊1011𝑁10+𝑊1110𝑁11+𝐴1110𝑁11,𝜕𝑁11𝜕𝑡=𝑊1011𝑁10𝐴1110𝑁11𝑊1110𝑁11+𝑊ET611𝑁6𝑁9𝐴118+𝐴117𝑁11,(1) where 𝑁1, 𝑁2, 𝑁3,𝑁4 are the population densities of Er3+ at energy levels 1, 2, 3, and 4, and 𝑁5 and 𝑁6 are the population densities of Yb3+ at energy levels 1 and 2 and 𝑁7, 𝑁8,𝑁9, 𝑁10,𝑁11 are the population densities of Tm3+ at energy levels 1, 2, 3, 4, and 5, 𝑊13, 𝑊56, and 𝑊79 are the pump transition rates, 𝑊𝑖𝑗(𝑖,𝑗=111) is the transition rate between energy levels i and j of the activating ions (Er3+, Yb3+, Tm3+), and 𝑊ET𝑖𝑗(𝑖,𝑗=111) is the transfer rate between energy level 𝑖 and 𝑗. 𝐴𝑖𝑗(𝑖,𝑗=111) is the spontaneous transition rate between energy level 𝑖 and 𝑗. 𝑁er, 𝑁yb, 𝑁tm are total concentrations of Er3+, Yb3+, and Tm3+ ions, respectively. The transition rates are as follows: 𝑊13=𝜎13𝑃𝑃𝜈𝑃𝐴e,𝑊56=𝜎56𝑃𝑃𝜈𝑃𝐴e,𝑊810=𝜎810𝑃𝑃𝜈𝑃𝐴e,𝑊𝑖𝑗=𝜎𝑖𝑗𝑃𝑠𝜈𝑠𝐴e,(2) where 𝜎13,𝜎56,𝜎8-10 are the pump absorption cross-section, 𝜎𝑖𝑗 is the absorption and emission cross-sections of the transitions between levels 𝑖 and 𝑗. 𝐴e is the effective cross-section area of the fiber.

The power propagations of the pump and signal and amplified spontaneous emission (ASE) along the fiber are described by differential equation group (3), where 𝑃𝑃 is the pump power at 980 nm, 𝑃𝑆1, 𝑃𝑆2, and 𝑃𝑆3 are the power of the signals at 1470 nm, 1530 nm, and 1630 nm, respectively. 𝑃ASE1, 𝑃ASE2,𝑃ASE3 are the ASE powers in the 1470, 1530, and 1630 bands, and Γ_1470, Γ_1530, Γ_1630, and Γ_𝜆ASE are overlap factors at 1470 nm, 1530 nm, and 1630 nm, and ASE wavelength, respectively, and 𝜐𝑠,𝜐𝑝 are signal and pump frequencies, respectively. and 𝛼(𝑣) are Plank constant, the frequency-independent back-ground loss of the active fiber, respectively,

𝑑𝑃𝑆1𝑑𝑧=Γ1470𝑁9𝜎98𝑁8𝜎89𝑃𝑆1𝛼1470𝑃𝑆1,𝑑𝑃𝑆2𝑑𝑧=Γ1530𝑁2𝜎21𝑁1𝜎12𝑃𝑆2𝛼1530𝑃𝑆2,𝑑𝑃𝑆3𝑑𝑧=Γ1630𝑁11𝜎1110𝑁10𝜎1011+𝑁8𝜎87𝑃𝑆3𝑁7𝜎78𝑃𝑆3𝛼1630𝑃𝑆3,𝑑𝑃𝑃𝑑𝑧=Γ980𝑁1𝜎13𝑁3𝜎31+𝑁5𝜎56𝑁6𝜎65+𝑁10𝜎108𝑁8𝜎810𝑃𝑃𝛼980𝑃𝑃,𝜕𝑃ASE1𝜆𝜕𝑧=ΓASE1𝜎98𝑁9𝜎89𝑁8𝑃ASE1𝜆+ΓASE12ΔASE1𝜐𝜎98𝑁9𝛼𝑃ASE1,𝜕𝑃ASE2𝜆𝜕𝑧=ΓASE2𝜎21𝑁2𝜎12𝑁1𝑃ASE2𝜆+ΓASE22ΔASE2𝜐𝜎21𝑁2𝛼𝑃ASE2,𝜕𝑃ASE3𝜆𝜕𝑧=ΓASE3𝜎1110𝑁11𝜎1011𝑁10+𝜎87𝑁8𝑃ASE3𝜎78𝑁7𝑃ASE3𝜆+ΓASE32Δ𝜐ASE3𝑁8𝜎87+𝜎1110𝑁11𝛼𝑃ASE3.(3)

The above power propagation equation group forms a system of coupled differential equations, which will be solved by numerical integration using Newton and Lung-Kutta methods along the active fiber. It was assumed that the energy transfer rates 𝑊ET_YE,𝑊ET_YT,𝑊ET_ET were increasing functions of 𝑁Yb,𝑁Er, and 𝑁Tm [3335], and expressed in the following equation: 𝑊ET_YE=1.0×1022+4.0×1049𝑁Yb𝑁Er1/21.0×1025,𝑊ET_ET=1.0×1022+4.0×1049𝑁Er𝑁Tm1/21.0×1025,𝑊ET_YT=1.0×1022+4.0×1049𝑁Yb𝑁Tm1/21.0×1025.(4)

3. Results and Discussion

3.1. Comparison with Experimental Results

The spontaneous spectra of Yb3+-Er3+-Tm3+-telluride glasses excited near 980 nm were measured with two emission peaks [36]. The ratio of Yb3+, Er3+, Tm3+ ion concentrations in the glass samples with thickness of 1.5 mm was 1011 and 1012, two stronger emission peaks were observed in the samples. To verify our theoretical model, same parameters as the sample are used to calculated the luminescence intensity, and calculated emission spectra and measured emission spectra from the reference are normalized and plotted in Figure 2 where solid line represent calculated spectra, and the measured spectra from [36] are denoted using circle, it is shown that calculated spectra are in good agreement with the measured, verifying feasibility of our model.

278105.fig.002
Figure 2: Comparison of calculated normalized emission intensity of Yb3+-Er3+-Tm3+ codoped telluride glass excited at 980 nm with measured normalized emission intensity, the measured results from [36].
3.2. Activator Concentration Dependence

The gain spectra is calculated by solving numerically the equation groups (1)–(3). Table 1 is the spectroscopic parameters for the Er3+-doped and Tm3+-doped telluride glass fiber for this calculation, the parameters of Yb3+ is from [36], the core diameter of fiber is 5 𝜇m and numerical aperture is 0.21, and the input power of signal is 30 dBm.

tab1
Table 1: Spectroscopic parameters of Er3+-doped and Tm3+ doped telluride fiber for numerical calculation.

Dependence of the gain spectra in the range 1450–1700 nm on Er3+ concentration is shown Figure 3(a). With Yb3+ concentration of 20.0×1024 ions/m3 and Tm3+ concentration of 1.0×1024 ions/m and fixed fiber length at 1.5 m and when the Er3+ concentration increases from 1.0×1024 to 3.0×1024 ions/m3, the gains at the range 1510–1630-nm increase, where the gain at the 1530 nm increases from 10.0 to 21.0 dB, the gains beyond 1630 nm keep constant. Figure 3(b) demonstrates variation of the gain spectra with Tm3+ concentration. With Yb3+ concentration of 20.0×1024 ions/m3 and Er3+ concentration of 1.0×1024 ions/m and fixed fiber length at 1.5 m and when the Tm3+ concentration increases from 1.0×1024 to 3.0×1024 ions/m3, the gains at the range 1510–1650 nm increase, where the gain at the 1530 nm increases from 10.5 to 17.8 dB, and the gain at 1630 nm increases from 7.0 to 9.8-dB . Effect of Yb3+ concentration on the gain spectra is shown Figure 3(c). With both Er3+ and Tm3+ concentrations of 1.0×1024 ions/m3 and fixed fiber length at 1.5 m and when the Yb3+ concentration increases from 10.0×1024 to 30.0×1024 ions/m3, the gains at the range 1510–1610 nm decrease, and the gain at the 1610–1650 nm increase.

fig3
Figure 3: Variation of the gain spectra with Er3+ ion concentration (a), Tm3+ ion concentration (b), and Yb3+ ion concentration (c). Fiber length, pump power, and input signal power are 1.5 m, 980 nm, 200 mW, 30 dBm, respectively.
3.3. Fiber Length Effect

Effect of fiber length on the gain spectra is shown Figure 4. With Yb3+ concentration of 20.0×1024 ions/m3, Er3+ concentration of 1.0×1024 ions/m and Tm3+ concentration of 3.0×1024 ions/m, when fiber length increases from 0.15 to 0.25 m, the gains at the range 1500–1630 nm increase, where the gain at the 1530 nm increases from 12.5 to 24.5 dB, and the gains at 1630 nm decreases from 10.0 to 5.0 dB .

278105.fig.004
Figure 4: Dependence of the gain spectra with fiber length, the concentrations of Yb3+, Er3+, Yb3+, ion are 20.0 × 1024, 1.0 × 1024, 3.0 × 1024 ions/m3, respectively, and pump power, and input signal power are 200 mW, 30 dBm, respectively.
3.4. Variation with Pump Power

Variation of the gain spectra with pump power is shown in Figure 5. With Yb3+ concentration of 20.0 × 1024 ions/m3, Er3+ concentration of 1.0 × 1024 ions/m and Tm3+ concentration of 3.0 × 1024 ions/m and fiber length of 1.5 m, when pump power increases from 100 to 300 mW, the gains at the range 1500–1610 nm increase, where the gain at the 1530 nm increases from 14.0 to 27.0 dB, and the gain at 1630 nm decreases from 10.0 to 1.0 dB.

278105.fig.005
Figure 5: Effect of pump power on gain spectra. Concentrations of Yb3+, Er3+, Yb3+ ion are 20.0 × 1024, 1.0 × 1024, 3.0 × 1024 ions/m3, respectively. Fiber length, input signal power are 1.5 m, 30 dBm, respectively.

4. Discussion

In above results, one notes that with increasing Yb3+ concentration from 1.0 × 1025 to 3.0 × 1025 ions/m3, the gains at the range 1510–1610 nm decrease, and the gains at the 1610–1650 nm increase, showing different Yb3+ ion concentration dependences of gain spectra in different wave band. These different dependences, we think, may be explained using energy transfer from Yb3+ to Er3+ and from Yb3+ to Tm3+ ions. When Yb3+ ion concentration increases, the pump absorption induced by Yb3+ increases and the pump absorption by Er3+ decreases, this leads to (1) increased energy transfer from Yb3+ to Tm3+ ions and increased population inversion between 3H4 and 3F4 of Tm3+ ions and thus increased gain at 1630 nm band, and (2) increased energy transfer from Yb3+ to Er3+ ions, but reduced pump absorption of Er3+ probably dominates over the increased energy transfer, thus results in reduced population inversion between the 4I13/2 and 4I15/2 levels of Er3+ and decreased gain at 1530 nm band.

Meanwhile, one also notes that with increasing pump power, the increasing of the gain spectra in 1500–1610 nm and the decreasing of the gain spectra in 1610–1650 nm show different pump-power effect on the gain spectra in different wave band. These different effects may be explained using energy transfer from Yb3+ to Er3+ and from Yb3+ to Tm3+ ions. With the power increasing, the pump absorptions caused by Yb3+ and Er3+ and Tm3+ increase simultaneously, this leads to increased population inversion between the 4I13/2 and 4I15/2 levels of Er3+ and thus increased gain at 1500–1610 nm band. The efficiency of the increasing of pump absorption caused by Tm3+ is less than that caused by Er3+ because the former depends highly on the population number of the 3F4 level of Tm3+ ions coming from energy transfer from Yb3+ and Er3+ to Tm3+. Moreover, increasing pump absorption can increase the population of the 3F2 level of Tm3+ ions, hence the population inversion between 1G4 and 3F2 of Tm3+ ions and the gain at 1610–1650 nm band is reduced if the lifetime at 1G4 level is shorter than that at 3F2 level.

It is shown from Figures 3, 4, and 5 that two weak peaks in the gain spectra appear at 1470 nm and 1680 nm, resulting separately from the transitions from the 3H4 to 3F4 levels and from 3H4 to 3H6 levels of Tm3+ ions. If both pumps at 800 nm and 980 nm are used, the gain spectra covering 1470 nm, 1530 nm, 1630 nm, 1680 nm bands may appear, further study is needed to optimize the fiber parameter and pump configuration to reduce the ripple of the gain spectra.

5. Conclusions

In conclusion, we present the numerical model of Yb3+-Er3+-Tm3+-codoped fiber amplifier pumped by 980 nm laser and analyzed the dependences of the gains at 1530 nm and 1630 nm on the activator codoping concentrations, fiber length, signal wavelength. The numerical results showed that our model was in good agreement with experimental result, and with pump power of 200 mW and fiber length varying from 0.15 to 1.5-m, the gains at the two bands could reach 10.0–20.0 dB when the codoping concentrations of Yb3+, Er3+, and Tm3+ were in the ranges 1.0–3.0 × 1025, 1.0–3.0 × 1024, 1.0–3.0 × 1024 ions/m3, respectively. Two weak peaks in the gain spectra appeared at 1470 nm and 1680 nm, resulting separately from the transitions from the 3H4 to 3F4 levels and from 3H4 to 3H6 levels of Tm3+ ions. If both pumps at 800 nm and 980 nm will be used, the gain spectra covering 1470 nm, 1530 nm, 1630 nm, 1680 nm bands may appear. The optimization of the fiber parameter and two-pump configuration will be desirable for reducing the ripple of the gain spectra.

Acknowledgments

This work is supported in part by National Natural Science Foundation of China (Grant No.60377023 and No.60672017) and Program for New Century Excellent Talents in University and Shanghai Optical Science and Technology (No.05DZ22 0-09) and sponsored by Shanghai Pujiang Program. Thank is given to Mr. Jianda Liu for his numerical analysis code when he was with SJTU.

References

  1. T. Naito, T. Tanaka, K. Torii, N. Shimojoh, H. Nakamoto, and M. Suyama, “A broadband distributed Raman amplifier for bandwidths beyond 100 nm,” in Proceedings of the Optical Fiber Communication Conference and Exhibit (OFC '02), vol. 70, pp. 116–117, Anaheim, Calif, USA, March 2002.
  2. C. Jiang and W. Hu, “Multiband-fiber Raman amplifier,” in Proceedings of the 9th Opto-Electronics and Communications Conference & 3rd International Conference on Optical Internet, pp. 314–315, Pacifica Yokohama, Japan, July 2004.
  3. C. R. Giles and E. Desurvire, “Modeling erbium-doped fiber amplifiers,” Journal of Lightwave Technology, vol. 9, no. 2, pp. 271–283, 1991. View at Publisher · View at Google Scholar
  4. C.-H. Yeh, C.-C. Lee, and S. Chi, “120-nm bandwidth erbium-doped fiber amplifier in parallel configuration,” IEEE Photonics Technology Letters, vol. 16, no. 7, pp. 1637–1639, 2004. View at Publisher · View at Google Scholar
  5. Y. B. Lu, P. L. Chu, A. Alphones, and P. Shum, “A 105-nm ultrawide-band gain-flattened amplifier combining C- and L-band dual-core EDFAs in a parallel configuration,” IEEE Photonics Technology Letters, vol. 16, no. 7, pp. 1640–1642, 2004. View at Publisher · View at Google Scholar
  6. E. R. M. Taylor, L. N. Ng, J. Nilsson et al., “Thulium-doped tellurite fiber amplifier,” IEEE Photonics Technology Letters, vol. 16, no. 3, pp. 777–779, 2004. View at Publisher · View at Google Scholar
  7. R. M. Percival and J. R. Williams, “Highly efficient 1.064 μm upconversion pumped 1.47 μm thulium doped fluoride fibre amplifier,” Electronics Letters, vol. 30, no. 20, pp. 1684–1685, 1994. View at Publisher · View at Google Scholar
  8. T. Kasamatsu, Y. Yano, and T. Ono, “1.49-μm-band gain-shifted thulium-doped fiber amplifier for WDM transmission systems,” Journal of Lightwave Technology, vol. 20, no. 10, pp. 1826–1838, 2002. View at Publisher · View at Google Scholar
  9. Y. Ohishi, T. Kanamori, T. Nishi et al., “Concentration effect on gain of Pr3+ -doped fluoride fiber amplifier for 1.3?µm,” IEEE Photonics Technology Letters, vol. 4, no. 12, pp. 1338–1340, 1992. View at Google Scholar
  10. L. Huang, A. Jha, S. Shen, and X. Liu, “Broadband emission in Er3+-Tm3+ codoped tellurite fibre,” Optics Express, vol. 12, no. 11, pp. 2429–2434, 2004. View at Publisher · View at Google Scholar
  11. H. Jeong, K. Oh, S. R. Han, and T. F. Morse, “Characterization of broadband amplified spontaneous emission from an Er3+ -Tm3+ co-doped silica fiber,” Chemical Physics Letters, vol. 367, no. 3-4, pp. 507–511, 2003. View at Publisher · View at Google Scholar
  12. X.-S. Wang, Q.-H. Nie, L.-R. Liu et al., “Improved fluorescence from Tm3+/Er3+/Ce3+ triply doped bismuth-silicate glasses for S+C-bands amplifiers,” Chinese Physics Letters, vol. 23, no. 9, pp. 2553–2556, 2006. View at Publisher · View at Google Scholar
  13. Z. Xiao, R. Serna, and C. N. Afonso, “Broadband emission in Er-Tm codoped Al2O3 films: the role of energy transfer from Er to Tm,” Journal of Applied Physics, vol. 101, no. 3, Article ID 033112, 2007. View at Publisher · View at Google Scholar
  14. D. Chen, Y. Wang, F. Bao, and Y. Yu, “Broadband near-infrared emission from Tm3+/Er3+ co-doped nanostructured glass ceramics,” Journal of Applied Physics, vol. 101, no. 11, Article ID 113511, 2007. View at Publisher · View at Google Scholar
  15. D. C. Yeh, R. R. Petrin, W. A. Sibley, V. Madigou, J. L. Adam, and M. J. Suscavage, “Energy transfer between Er3+ and Tm3+ ions in a barium fluoridethorium fluoride glass,” Physical Review B, vol. 39, no. 1, pp. 80–90, 1989. View at Publisher · View at Google Scholar
  16. S. Tanabe, K. Suzuki, N. Soga, and T. Hanada, “Mechanisms and concentration dependence of Tm3+ blue and Er3+ green up-conversion in codoped glasses by red-laser pumping,” Journal of Luminescence, vol. 65, no. 5, pp. 247–255, 1995. View at Google Scholar
  17. X. Zou, A. Shikida, H. Yanagita, and H. Toratani, “Mechanisms of upconversion fluorescences in Er3+, Tm3+ codoped fluorozircoaluminate glasses,” Journal of Non-Crystalline Solids, vol. 181, no. 1-2, pp. 100–109, 1995. View at Google Scholar
  18. W. Lozano B., C. B. de Araújo, and Y. Messaddeq, “Enhanced frequency upconversion in Er3+ doped fluoroindate glass due to energy transfer from Tm3+,” Journal of Non-Crystalline Solids, vol. 311, no. 3, pp. 318–322, 2002. View at Publisher · View at Google Scholar
  19. M. Liao, L. Hu, Y. Fang et al., “Upconversion properties of Er3+, Yb3+ and Tm3+ codoped fluorophosphate glasses,” Spectrochimica Acta Part A, vol. 68, no. 3, pp. 531–535, 2007. View at Publisher · View at Google Scholar
  20. Z. Yang and Z. Jiang, “Frequency upconversion emissions in layered lead-germanate-tellurite glasses for three-color display,” Journal of Non-Crystalline Solids, vol. 351, no. 30-32, pp. 2576–2580, 2005. View at Publisher · View at Google Scholar
  21. S. Xu, H. Ma, D. Fang, Z. Zhang, and Z. Jiang, “Tm3+/Er3+/Yb3+-codoped oxyhalide tellurite glasses as materials for three-dimensional display,” Materials Letters, vol. 59, no. 24-25, pp. 3066–3068, 2005. View at Publisher · View at Google Scholar
  22. V. K. Tikhomirov, K. Driesen, C. Görller-Walrand, and M. Mortier, “Mid-infrared emission in Yb3+-Er3+-Tm3+ co-doped oxyfluoride glass-ceramics,” Materials Science and Engineering: B, vol. 146, no. 1–3, pp. 66–68, 2008. View at Publisher · View at Google Scholar
  23. Z. Duan, J. Zhang, W. Xiang, H. Sun, and L. Hu, “Multicolor upconversion of Er3+/Tm3+/Yb3+ doped oxyfluoride glass ceramics,” Materials Letters, vol. 61, no. 11-12, pp. 2200–2203, 2007. View at Publisher · View at Google Scholar
  24. V. K. Tikhomirov, K. Driesen, C. Görller-Walrand, and M. Mortier, “Broadband telecommunication wavelength emission in Yb3+-Er3+-Tm3+ co-doped nano-glass-ceramics,” Optics Express, vol. 15, no. 15, pp. 9535–9540, 2007. View at Publisher · View at Google Scholar
  25. C. Cao, W. Qin, J. Zhang et al., “Up-conversion white light of Tm3+/Er3+/Yb3+ tri-doped CaF2 phosphors,” Optics Communications, vol. 281, no. 6, pp. 1716–1719, 2008. View at Publisher · View at Google Scholar
  26. S. Ye, B. Zhu, J. Chen, J. Luo, and J. R. Qiu, “Infrared quantum cutting in Tb3+, Yb3+ codoped transparent glass ceramics containing CaF2 nanocrystals,” Applied Physics Letters, vol. 92, no. 14, Article ID 141112, 2008. View at Publisher · View at Google Scholar
  27. G. Lakshminarayana, R. Vidya Sagar, and S. Buddhudu, “NIR luminescence from Er3+/Yb3+, Tm3+/Yb3+, Er3+/Tm3+ and Nd3+ ions-doped zincborotellurite glasses for optical amplification,” Journal of Luminescence, vol. 128, no. 4, pp. 690–695, 2008. View at Publisher · View at Google Scholar
  28. S. Shen, B. Richards, and A. Jha, “Enhancement in pump inversion efficiency at 980 nm in Er3+, Er3+/Eu3+ and Er3+/Ce3+ doped tellurite glass fibers,” Optics Express, vol. 14, no. 12, pp. 5050–5054, 2006. View at Publisher · View at Google Scholar
  29. B. Richards, S. Shen, A. Jha, Y. Tsang, and D. Binks, “Infrared emission and energy transfer in Tm3+, Tm3+-Ho3+ and Tm3+-Yb3+-doped tellurite fibre,” Optics Express, vol. 15, no. 11, pp. 6546–6551, 2007. View at Publisher · View at Google Scholar
  30. S. Zhou, N. Jiang, B. Zhu et al., “Multifunctional bismuth-doped nanoporous silica glass: from blue-green, orange, red, and white light sources to ultra-broadband infrared amplifiers,” Advanced Functional Materials, vol. 18, no. 9, pp. 1407–1413, 2008. View at Publisher · View at Google Scholar
  31. L. Jin, D. Ma, Y. Ding, and C. Jiang, “Theoretical analysis of gain characteristics of Er3+-Tm3+-codoped tellurite fiber amplifier,” IEEE Photonics Technology Letters, vol. 18, no. 3, pp. 460–462, 2006. View at Publisher · View at Google Scholar
  32. W. Xu, Y. M. Lin, and C. Jiang, “Er3+- Tm3+-codoped tellurite fiber amplifiers for WDM systems: a theoretical analysis of BER and bandwidth,” IEEE Journal of Quantum Electronics, vol. 45, no. 1, pp. 3–9, 2009. View at Publisher · View at Google Scholar
  33. F. Di Pasquale and M. Federighi, “Improved gain characteristics in high-concentration Er3+/Yb3+ codoped glass waveguide amplifiers,” IEEE Journal of Quantum Electronics, vol. 30, no. 9, pp. 2127–2131, 1994. View at Publisher · View at Google Scholar
  34. M. Karásek, “Optimum design of Er3+-Yb3+ codoped fibers for large-signal high-pump-power applications,” IEEE Journal of Quantum Electronics, vol. 33, no. 10, pp. 1699–1705, 1997. View at Google Scholar
  35. E. Yahel and A. A. Hardy, “Modeling and optimization of short Er3+-Yb3+ codoped fiber lasers,” IEEE Journal of Quantum Electronics, vol. 39, no. 11, pp. 1444–1451, 2003. View at Publisher · View at Google Scholar
  36. S.-X. Dai, J.-H. Yang, S.-Q. Xu et al., “Multi-rare-earth ions codoped tellurite glasses for potential dual wavelength fibre-optic amplifiers,” Chinese Physics Letters, vol. 20, no. 1, pp. 130–132, 2003. View at Publisher · View at Google Scholar
  37. F. X. Gan, Optical and Spectroscopic Properties of Glasses, Shanghai Science and Technology Press, Shanghai, China, 1992.
  38. S. Shen, A. Jha, X. Liu et al., “Tellurite glasses for broadband amplifiers and integrated optics,” Journal of the American Ceramic Society, vol. 85, no. 6, pp. 1391–1395, 2002. View at Google Scholar