ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF), considered as the most stable heavy metal fluoride glass and the excellent host for rare-earth ions, has been extensively used for efficient and compact ultraviolet, visible, and infrared fiber lasers due to its low intrinsic loss, wide transparency window, and small phonon energy. In this paper, the historical progress and the properties of fluoride glasses and the fabrication of ZBLAN fibers are briefly described. Advances of infrared, upconversion, and supercontinuum ZBLAN fiber lasers are addressed in detail. Finally, constraints on the power scaling of ZBLAN fiber lasers are analyzed and discussed. ZBLAN fiber lasers are showing promise of generating high-power emissions covering from ultraviolet to mid-infrared considering the recent advances in newly designed optical fibers, beam-shaped high-power pump diodes, beam combining techniques, and heat-dissipating technology.

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High-power ZBLAN glass fiber lasers: Review and prospect

We report on >9W transverse-fundamental-mode CW output near 3 μm from a 4m heavily erbium-doped ZBLAN double-clad fiber laser pumped by a collimated 100 W 975 nm laser diode array. The pump threshold of the fiber laser was about 1W, and the slope efficiency was 21.3%. The peak wavelength of free running was about 2708 nm at low pump power and moved to around 2785 nm at high pump power. Output of 9W was obtained when the launched pump power was 42.8W. The output, however, fluctuated intensively like a pulsed laser, and the operation broke down with optical damage of the pumping end facet when the pump was increased beyond 42.8 W. Therefore, alleviation of the operation fluctuation, heat management, and strengthening the pumping fiber are crucial considerations for the stable operation of 10-W-level mid-IR ZBLAN fiber lasers.

10-W-level diode-pumped compact 2.78 μm ZBLAN fiber laser

We present a detailed characterization of energy transfer processes in Er3+-doped and Er3+,Pr3+-codoped ZBLAN bulk glasses. For several Er3+ (0.25–8.75 mol%) and Pr3+ (0.25–1.55 mol%) concentrations, we investigate energy transfer upconversion (ETU) and cross relaxation in Er3+ as well as energy transfer (ET) from Er3+ to the Pr3+ codopant. The measured parameters of ETU from the Er3+ 4I13/2 and 4I11/2 levels are comparable to those of LiYF4:Er3+. ETU from 4I13/2, in particular, possesses a factor of 3 larger probability than ETU from 4I11/2. The parameters of ET from the Er3+ 4I13/2 and 4I11/2 levels to the Pr3+ codopant are larger than the corresponding ETU parameters. ET effectively quenches the 4I13/2 intrinsic lifetime of 9 ms down to 20 us for the highest Er3+ and Pr3+ concentrations investigated, and is more efficient than ET from 4I11/2, because the corresponding absorption transition in Pr3+ has a large oscillator strength and back transfer is inhibited by fast multiphonon relaxation from the corresponding Pr3+ level. In both cases, the ET parameters depend on Er3+ concentration in a similar way as the ETU parameters but depend only weakly on Pr3+ concentration. This shows that energy migration within the Er3+ 4I13/2 and 4I11/2 levels is fast. The presented results are important for the choice of the appropriate operational regime of the erbium 3-um fiber laser.

Energy transfer processes in Er3+-doped and Er3+,Pr3+-codoped ZBLAN glasses

We propose and theoretically analyze three-level cladding-pumped fiber lasers in which the laser-active dopant is placed in a ring around a single-mode core. A ring-doped laser can work efficiently at wavelengths with strong small-signal absorption. This is otherwise difficult in a cladding-pumped fiber. Moreover, ring doping makes the laser less sensitive to quenching of the laser-active dopant and to excited-state absorption of the lasing field. In simulations of a Yb3+-doped fiber laser, ring doping increased the slope efficiency to 62%, up from 13% for a conventional core-doped fiber.

Ring-doped cladding-pumped single-mode three-level fiber laser

The fiber optic laser system and associated lasing method amplifies and divides a primary laser signal into a plurality of secondary laser signals. The fiber optic laser system includes a distribution means, such as a distribution module, for dividing a primary laser signal, generated by a master oscillator into a number of secondary laser signals. The distribution module can include amplification means, such as an optical fiber amplifier, for amplifying the primary laser signal and a signal power splitter for dividing the amplified primary laser signal into a number of secondary laser signals. The secondary laser signals can then be further amplified, such as by a power amplification module including another optical fiber amplifier. The secondary laser signals can be recombined to produce a laser output having a power level greater than the predetermined power level of the primary laser signal. During the process of combining the secondary laser signals, the secondary laser signals can be collimated and the relative phases of the secondary laser signals can be controllably modulated such that the resulting laser output has a predetermined phase profile and relatively high beam qualities.

Fiber optic laser system and associated lasing method

The effective absorption coefficient in double-clad fibres

Saturation of the 2.71 μm laser output in erbium-doped ZBLAN fibers

The saturation of the 271 µm laser output has been measured in erbium-doped ZBLAN singlemode fibres with Er3+ concentrations of 1000, 5000 and 10000 ppm mol Limits of the single-mode-laser output are discussed

Limits of the output power in Er3+:ZBLAN singlemode fibre lasers

The 2.7 μm erbium laser in ZBLAN fibers is investigated in computer simulations and experiments. Strong excited-state absorption leads to the deposition of excitation in the 4S3/2 level. Simultaneous co-lasing at 850 nm from this level is responsible for the saturation of the output power in the region of 10 mW. The overcome of saturation by cascade lasing at 1.7 μm and 2.7 μm is predicted.

On the saturation of the 791 nm pumped erbium 3 µm fiber laser

This additional beatings can be explained by mode beating and self-phase modulation. This assumption is supported by the fact that the power density is well above the value for the onset of a relevant phase shift by the contribution of the nonlinear refractive index, which was published for other (single mode) solitary fiber lasers3 Whether this mechanism is present over the whole FBL or not will be the subject of further investigations. This work was supported by the Bundesministerium fur Forschung und Technologie of the Federal Republic of Germany under contract no. 13 N 5895.

S. Bedö

Papers

The effective absorption coefficient in double-clad fibres

Saturation of the 2.71 μm laser output in erbium-doped ZBLAN fibers

Limits of the output power in Er3+:ZBLAN singlemode fibre lasers

On the saturation of the 791 nm pumped erbium 3 µm fiber laser

Output saturation of the 2.71 /spl mu/m laser in erbium-doped ZBLAN fibers