Sol-gel silica/titania-on-silicon Er/Yb-doped waveguides for optical amplification at 1.5 μm

Systematic studies of cooperative upconversion and Yb3+–Er3+ energy transfer in newly developed phosphate glasses were performed by a rate-equation formalism. The cooperative-upconversion coefficients of the  4I13/2 level for different Er3+ concentrations were determined from the luminescence-decay curves for high pump intensities. A small cooperative-upconversion coefficient of 1.1×10-18 cm3/s was obtained for a high Er3+ concentration of 4×1020 ions/cm3.Yb3+–Er3+ energy-transfer coefficients for an Er3+ concentration of 2×1020 ions/cm3 codoped with different Yb3+ concentrations were calculated from the lifetime measurements of the  2F5/2 level of Yb3+ ions. For Er3+ codoped with an Yb3+ concentration of 6×1020 ions/cm3, an energy-transfer coefficient of 1.1×10-16 cm3/s and an energy-transfer efficiency higher than 95% were determined from our measurements under weak excitation. The cooperative-upconversion coefficients of Yb3+–Er3+-doped samples were found to be consistent with that of an Er3+-doped sample with the same Er3+ concentration. The weak cooperative-upconversion effect of high Er3+ concentrations and efficient Yb3+–Er3+ energy transfer indicate that these newly developed Er3+- and Yb3+–Er3+-doped phosphate glasses are excellent for active device applications.

Cooperative upconversion and energy transfer of new high Er 3+ - and Yb 3+ –Er 3+ -doped phosphate glasses

Absorption and emission spectroscopy in Er3+–Yb3+ doped aluminum oxide waveguides

Fabrication process of efficient Yb/sup 3+/,Er/sup 3+/ codoped phosphosilicate fibers by modified chemical vapor deposition (MCVD) combined with the solution doping technique is studied in detail. We show that the process can be adapted to incorporate low viscosity phosphate glass and some important issues in the fabrication process are discussed. These include the sensitive presintering pass. We also report on the fabrication of a low loss all-glass double clad Yb/sup 3+/:Er/sup 3+/ codoped fiber. We explain how we evaluate the fibers and discuss the effect of the ytterbium to erbium concentration ratio on the laser characteristics. Finally, we present results of some investigations into the mechanisms which can affect the efficiency of the lasers, and show that the detrimental up-conversion from the metastable level of the erbium ions is dramatically reduced by the presence of the ytterbium ions.

Fabrication and characterization of Yb/sup 3+/:Er/sup 3+/ phosphosilicate fibers for lasers

Short high-concentration Yb/sup 3+/-sensitized Er/sup 3+/-doped fiber amplifiers are modeled and numerically investigated in the small-signal domain. Concentration quenching is included with a term quadratic in the concentration of excited Er/sup 3+/. We find that for fibers shorter than 1 m, the small-signal gain can be larger for sensitized fibers than for non-sensitized ones (31 dB gain vs. 22 dB at 5 cm). Without concentration quenching (e.g. for long fibers), Yb/sup 3+/-free amplifiers have a higher small-signal gain. The achievable gain of the sensitized amplifier is independent of the pump laser wavelength, if the Yb-concentration is correspondingly optimized. However, restrictions on allowable Yb-concentrations imply that for a specific pump wavelength, a finite range of amplifiers lengths is suitable. >

Modeling and optimization of short Yb/sup 3+/-sensitized Er/sup 3+/-doped fiber amplifiers

A comparative investigation is made of phosphate, germanate, and lithium silicate glasses activated with Yb3+ and Er3+ ions in order to determine their potential usefulness for the development of laser-pumped (λ = 1.06 μ) amplifiers for short (10−8 sec) pulses at the λ = 1.54 μ wavelength. Some features of the spectral and luminescence charactenstics and the kinetics of energy transfer in these glasses are studied. It is shown that the increase in the population inversion of the 4I13/2 level of Er3+ ions in lithium silicate and germanate glasses is considerably slower than the increase in the absorbed pump energy. Possible mechanisms for this anomalous behavior are discussed. It is shown theoretically and experimentally that the main reason for this is reverse transfer of excitation energy from Er3+ to Yb3+ ions, which is almost absent in phosphate glasses.

Some characteristics of population inversion of the 4I13/2 level of erbium ions in ytterbium–erbium glasses

An experimental investigation was made of the effect of sensitizing ytterbium- and erbium-activated lead barium phosphate glasses with Cr3+ ions on the energy parameters of lasing due to the 4I13/2 — 4I15/2 transition in Er3+ ions (λ1 = 1.54 μ). It was found that substantial sensitization was achieved in phosphate glasses for only low concentrations of Cr3+ ions ( 0.07 wt.%) so that the efficiency of flashlamp-pumped erbium lasers could be improved by a factor of 1.5-4. The optimal conditions for achieving the best energy parameters of these lasers under free-lasing conditions were determined allowing for the spectral and energy distributions of the flashlamp radiation in the absorption range of the coactivator ions. By implementing these conditions using active elements 6 mm in diameter and 85 mm long, containing 17 wt.% Yb2O3, 0.25 wt.% Er2O3, and 0.07 wt.% Cr2O3, it was possible to achieve an efficiency of 1.2% for an electrical pump energy of 1 kJ. This was the highest efficiency achieved so far for erbium lasers. Measurements were made of the efficiency of transfer of the excitation energy from Cr3+ ions to Yb3+ ions at high levels of excitation of the medium.

A. G. Murzin

Papers

Some characteristics of population inversion of the 4I13/2 level of erbium ions in ytterbium–erbium glasses

Energy parameters of lasers utilizing erbium glasses sensitized with ytterbium and chromium

Possibility of improving the efficiency of lamp pumping of erbium-glass lasers