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.
Since the first demonstration of laser emission from a ruby crystal (chromium-doped corundum) in 1960 [
Silicate glasses are outstanding hosts for rare-earth ions and most of recent fiber lasers are constructed with silica fibers due to their low loss, high tenability, and strong strength. Phosphate glass as the host for the fiber lasers has a high solubility that enables extremely high doping level of rare-earth ions (up to 20 wt%) and now is mostly used for high-gain fibers. Very high-gain per unit fiber length (~5 dB/cm) can be obtained and watt-level outputs have been delivered from short-length (<10 cm) fiber cavities that support oscillation with single longitude mode [
The paper is organized as follows. Progresses and properties of fluoride glasses and fabrication of fluoride fibers are briefly described in Section
Since detailed descriptions of heavy metal fluoride (HMF) glasses and complete investigations of their properties can be found in the literature [
In the history of science and technology, unexpected outcome of an experiment usually leads to a fantastic discovery. Poulain’s discovery of the fluorozirconate glasses was entirely a “surprise”. In 1974, he was working on the synthesis and characterization of ZrF4-containing crystalline compounds doped with rare earths in the laboratory of Jacques Lucas at the University of Rennes. When NaF was added to fill the voids in the crystal structure of a ZrF4-BaF2 phase, the mixture of ZrF4-BaF2-NaF-NdF3 system was unexpectedly a glass. One year later, the first description of “fluorozirconate” glasses was produced with additional vitreous compositions [
Compared to silica glasses, it is more complicated to make fluoride glasses. This is due to the fact that to achieve high quality fluoride glasses, not only extremely pure starting materials with infrared-absorbing impurities below 1 ppb are needed but also absolute absence of water and prevention of contamination are required at all synthesis stages. Ammonium hydrogen difluoride (NH4F
It should be noted that the basic ZBLAN composition is frequently modified to change the glass properties. For instance, viscosity and refractive index may be modified by the addition of small quantities of ZnF2, CaF2, and PbF2; infrared edge can be shifted from 6-7
Because of their broad transmission window, low optical dispersion, low refractive index, ease of machining and polishing, and small thermal dependence of the optical properties, HMF glasses have drawn significant attention since Poulain’s unexpected discovery. ZBLAN glass as the most stable HMF glass was extensively investigated for their ease of fiber drawing. In this subsection, properties of ZBLAN glass are summarized with a comparison to those of silica glass.
Because the fluoride ion is singly charged, bond strengths are lower in ZBLAN glass than in silica glass. The weaker bonding leads to greater infrared transparency and higher chemical reactivity. Simply speaking, infrared edge of ZBLAN glass is much longer than that of silica glass, but stability and hardness of ZBLAN glass is much lower than those of silica glass. This suggests that ZBLAN glass will be susceptible to handling damage and ZBLAN fibers need special coating to improve their strength for practical applications.
Optical glasses, especially those used for fiber fabrication, should have a background loss as small as possible due to the relative long length of optical fibers (from meters to kilometers). Attenuation of light propagating in an optical glass comes from intrinsic and extrinsic processes. Intrinsic processes include band-gap absorption, Rayleigh scattering, and multiphonon absorption. Because band-gap absorption and Rayleigh scattering are only significant at short wavelengths, lower intrinsic loss can be obtained by shifting infrared edge of multiponon absorption to longer wavelengths. It is straightforward that materials with the lower bond strength and the higher reduced mass would be expected to have fundamental absorptions at longer wavelengths. Both these criteria are met in ZBLAN glass since fluoride anion is only single charged and the average cation mass is typically 90. Consequently, the minimum loss coefficient for ZBLAN glass is predicted as low as 0.01 dB/km at 2.5
Physical properties of ZBLAN glass and silica glass are listed in Table
Comparison of basic properties between silica and ZBLAN glasses [
Glass property | Silica | ZBLAN |
---|---|---|
Approximate transmission range (1 mm thickness, | 0.16–4.0 | 0.22–8.0 |
Maximum phonon energy (cm-1) | 1100 | 600 |
Transition temperature (°C) | 1175 | 260 |
Specific heat (J/(g | 0.179 | 0.151 |
Thermal conductivity, W/(m | 1.38 | 0.628 |
Expansion coefficient (10-6/K) | 0.55 | 17.2 |
Density (g/cm3) | 2.20 | 4.33 |
Knoop hardness (kg/mm2) | 600 | 225 |
Fracture toughness (MPam1/2) | 0.72 | 0.32 |
Poisson’s ratio | 0.17 | 0.17 |
Young’s modulus (Gpa) | 70 | 58.3 |
Shear’s modulus (Gpa) | 31.2 | 20.5 |
Bulk’s modulus (Gpa) | 36.7 | 47.7 |
Refractive index (@ 0.589 um) | 1.458 | 1.499 |
Abbe number | 68 | 76 |
Zero material dispersion wavelength ( | 1.3 | 1.6 |
Nonlinear index (10-13 esu) | 1 | 0.85 |
Thermo-optic coefficient (10-6/K) | 11.9 | −14.75 |
Since ZBLAN glass can be cooled more slowly than 1 K/s without noticeable homogeneous nucleation, it has been considered to be as the most stable HMF glass and the most resistant to crystallization under optical fiber preform-making and drawing condition. Three years after Pollain’s discovery, fabrication of fluoride glass fibers was performed at the Center National d’Etudes des Telecommunications (CNET), France, and the Nippon Telephone and Telegraph Public Corporation (NTT), Japan [
Like the fabrication of silica fibers, the preform method in which the fiber is drawn from a preformed glass rod at a temperature below the glass melting temperature is mostly used for ZBLAN fiber fabrications. ZBLAN fiber performs can be prepared by different casting processes including cladding-over-core casting (Mitachi et al. [
For a fiber preform, refractive indices of the core and the cladding must be precisely controlled to obtain a required index difference. In typical fluoride glasses, PbF2 and BiF3 raise the index, and LiF and AlF3 lower the index. Replacing ZrF4 by HfF4 in a ZBLAN glass also leads to a small reduction in index; so the latter is often used in cladding glass.
During the drawing process, preform and drawing speed must be precisely controlled because of the narrow working range influenced by the ZBLAN glass viscosity and the crystallization rate. In order to reduce the crystallization rate ZBLAN fibers should be drawn with a high drawing speed at temperatures as low as possible. The drawing temperature is usually in the 340–400°C range. Because moisture induces devitrification through hydration reactions, all fibers guiding devices are flushed by dry nitrogen before the fiber is coated with a UV-curable acrylate polymer.
It should be noted that, for each particular glass composition, the largest piece that can be made is determined by its crystallization rate during cooling. Therefore, the dimension of a preform is limited and consequently so is the total length of a ZBLAN fiber. This consideration should be included in the design of double-clad ZBLAN fibers for high-power operations. Although ZBLAN fibers with unlimited length can be directly drawn utilizing the crucible technique [
Because of their wide transparency window, ZBLAN fibers have been suggested for a lot of applications including infrared imaging, remote infrared spectrometry, remote infrared spectrometric imaging, remote thermometry, laser power delivery, and fiber lasers. In the past decade, with advances in high-brightness semiconductor diode lasers, novel fiber designs, and new pumping schemes, fiber lasers have been developed with an tremendous speed due to the increasing demand of high-power fiber lasers in a variety of applications, such as material processing, telecommunications, spectroscopy, laser pumps, directed energy weapons, and medicine. ZBLAN fiber lasers have also experienced elevation of the output power level and expansion of the operation spectral region. In this section, ZBLAN fiber lasers are reviewed with three categories: infrared, upconversion UV and visible, and supercontinuum.
Shortly after the emergence of fluoride glasses it was suggested that they may make particularly good hosts for a lasing material due to the extended infrared edge and low phonon energy [
Activated by the increasing demand of high-power lasers for various applications, power scaling of fiber lasers has been mainly driven by the progresses of high-brightness semiconductor diode pumps, novel pump schemes, and new fiber designs. Rare-earth-doped ZBLAN fiber lasers have also benefited from these progresses. The highest output powers of infrared ZBLAN fiber lasers at different wavelengths are summarized in Figure
Summary of infrared rare-earth-doped ZBLAN fiber lasers with the highest output powers so far.
Rare-earth | Laser wavelength ( | Pump wavelength (nm) | Output power (W) | Rare-earth Concentration (mol%) | Slope efficiency (%) | Reference |
---|---|---|---|---|---|---|
Er | 1.55 | 980 | 0.012 | 0.5 | 30 | [ |
1.7 | 791 | 0.007 | 0.5 | 1.8 | [ | |
2.7 | 975 | 24 | 6 | 14.5 | [ | |
3.45 | 640 | 0.085 | 1 | 2.8 | [ | |
Tm | 1.48 | 1064 | 2.3 | 0.2 | 65 | [ |
1.94 | 792 | 20 | 2.5 | 49 | [ | |
2.3 | 790 | 0.001 | 0.1 | 10 | [ | |
Ho | 2 | 806 | 8.8 | 0.4 | 36 | [ |
2.86 | 1100 | 2.5 | 3 | 29 | [ | |
3.22 | 532 | 0.011 | 0.2 | 2.8 | [ | |
3.9 | 885 | 0.011 | 0.2 | 1.5 | [ | |
Dy | 2.9 | 1100 | 0.275 | 0.1 | 4.5 | [ |
Pr | 1.3 | 1064 | 0.0045 | 0.09 | 0.45 | [ |
Yb | 1 | 0.911 | 0.09 | 1.8 | 56 | [ |
Nd | 1.05 | 514.5 | 0.02 | 1.5 | 2.5 | [ |
1.34 | 800 | 0.0136 | 0.2 | 12 | [ |
Highest output powers of infrared rare-earth-doped ZBLAN fiber lasers at different emission wavelengths.
The partial energy level diagram of Er3+ ions to describe the transitions involving in infrared emissions is plotted in Figure
Partial energy level diagram of Er3+ ion in ZBLAN related to infrared laser emissions. Pump absorption transitions are indicated with green upward arrows. Radiative emission transitions are indicated with red downward arrows.
Although 1.55
Since 1.7
Because 2.7
Generally, the 2.7
In order to elevate the output power of 2.7
In 1999, Tobben reported the laser emission of 3.5
The partial energy level diagram of Tm3+ ions to describe the transitions producing infrared emissions is plotted in Figure
Partial energy level diagram of Tm3+ ion in ZBLAN related to infrared laser emissions. Pump absorption transitions are indicated with green upward arrows. Radiative emission transitions are indicated with red downward arrows.
The 1.47
In 1992, Komukai et al. [
In 1989, Allen and Esterowitz [
In 2008, Eichhorn and Jackson [
The partial energy-level diagram of Ho3+ ions to describe the transitions involving in infrared emissions is plotted in Figure
Partial energy level diagram of Ho3+ ion in ZBLAN related to infrared laser emissions. Pump absorption transitions are indicated with green upward arrows. Radiative emission transitions are indicated with red downward arrows.
In 1988, Brierley et al. [
Because of the larger water absorption coefficient at 3
In order to improve the efficiency of the 3
Because the strong absorption band of hydrocarbon and hydrochloride groups and a transparency window of atmosphere locate in the 3
In 1993, Tobben [
The partial energy-level diagram of Dy3+ ions is plotted in Figure
Partial energy level diagram of Dy3+ ion in ZBLAN related to the 2.9
There are few reports on Dy3+-dope ZBLAN fiber lasers. The first CW Dy3+-dope ZBLAN fiber laser was demonstrated in 2003 [
The partial energy-level diagram of Nd3+ ions to describe the transitions involving in infrared emissions is plotted in Figure
Partial energy level diagram of Nd3+ ion in ZBLAN related to infrared laser emissions. Pump absorption transition is indicated with green upward arrow. Radiative emission transitions are indicated with red downward arrows.
As mentioned above, the first fluoride fiber laser was demonstrated on a multimode Nd3+-doped ZBLAN fiber [
Compared to the rare-earth ions described above, there are few studies on Pr3+ and Yb3+ singly-doped ZBLAN fiber lasers. However, Pr3+ and Yb3+ ions have been extensively used as codpants in ZBLAN fibers to effectively enhance the desired transitions including laser emission and pump absorption and suppress competitive emissions [
Pr3+-doped ZBLAN fiber has been intensively investigated for 1.3
Yb3+-doped ZBLAN fiber laser was only demonstrated by Allain et al. [
Solid-state lasers operating in the UV and visible spectral region have a lot of applications including laser lighting displays, photolithography, optical data storage, holography, microscopy, and spectroscopy. So far, there are three general methods to generate UV and visible laser emissions. One is using nonlinear frequency doubling or tripling processes. Another is developing short wavelength semiconductor laser diodes such as GaN and ZnSe. The third is employing upconversion emissions in fluoride glasses and crystals in which the nonradiative decay probabilities are relatively low due to the small phonon energy. Because the relatively long effective lifetimes of excited states facilitate a sequential absorption of pump photons either by a single ion or via energy transfer between excited ions, two or more incoming photons can be absorbed by the materials and can be reemitted as a single higher energy photon. Thus, UV and visible emission can be generated by pumping upconversion materials with high intensity pumps at near infrared.
Upconversion emission was observed for the first time in flash-lamp-pumped Er3+-Yb3+ and Ho3+-Yb3+ codoped BaY2F8 crystals by Johnson and Guggenheim [
Upconversion ZBLAN fiber lasers are noted for their high efficiency, low threshold, compactness, and tenability. The confinement of both the pump and signal within the fiber core over the long distances reduces the pump threshold and increases output power significantly. High intensity coupled with the long interaction lengths results in optical-to-optical conversion efficiencies larger than 20% and threshold below 10 mW. Moreover, because rare-earth-doped ZBLAN glasses exhibit broad absorption and emission spectral band, it is possible to construct all-fiber wavelength-tunable UV and visible fiber lasers.
In the past twenty years, various upconversion ZBLAN fiber lasers have been demonstrated at UV and visible. Output power over 1 W has already been achieved. The spectrum of upconversion ZBLAN fiber lasers with the highest output powers is summarized in Figure
Summary of upconversion rare-earth-doped ZBLAN fiber lasers with the highest output powers so far.
Rare-earth | Laser Wavelength (nm) | Pump Wavelength (nm) | Output Power (mW) | Rare-earth Concentration (mol%) | Efficiency (%) | Reference |
---|---|---|---|---|---|---|
Er | 402 | 638 | 0.070 | 0.1 | 1.6 | [ |
470 | 638 | 0.040 | 0.1 | 3 | [ | |
544 | 970 | 50 | 0.1 | 11 | [ | |
Tm | 248 | 1064 | 0.042 | 1 | 9% | [ |
455 | 645+1064 | 3 | 0.1 | 1.5% | [ | |
481 | 1123 | 230 | 0.1 | 18.5% | [ | |
784 | 1120 | 5 | 0.1 | 0.7% | [ | |
808 | 1120 | 9 | 0.1 | 2.5% | [ | |
Pr/Yb | 491 | 840 | 165 | 0.3/2 | 12.1 | [ |
520 | 860 | 20 | 0.3/2 | 12.4 | [ | |
605 | 840 | 55 | 0.3/2 | 19 | [ | |
615 | 860 | 45 | 0.3/2 | 11.5 | [ | |
635 | 850+823 | 1020 | 0.3/2 | 19 | [ | |
Ho | 550 | 645 | 40 | 0.12 | 16.8 | [ |
Nd | 381 | 590 | 0.074 | 0.1 | — | [ |
412 | 590 | 0.5 | 0.1 | 1.5 | [ |
Highest output powers of upconversion rare-earth-doped ZBLAN fiber lasers at different emission wavelengths.
The partial energy-level diagram of Er3+ ions to describe the transitions involving in upconversion emissions is plotted in Figure
Partial energy level diagram of Er3+ ion in ZBLAN related to upconversion laser emissions. Pump absorption transitions are indicated with green upward arrows. Radiative transitions are indicated with blue downward arrows. Nonradiative decays are indicated with dotted arrows.
The first demonstration of upconversion lasing in an Er3+-doped ZBLAN fiber was realized using a pump at 801 nm of Ti:sapphire laser [
Aside from pumping at a wavelength of GSA, an upconversion laser can be excited with a wavelength far away from GSA due to the photon avalanche phenomenon which refers to the change in the order of magnitude of the fluorescence when the pump intensity is over a certain critical threshold. Chen et al. [
Generally, efficient shorter-wavelength emissions can be achieved if Er3+ ions are excited at a shorter pump wavelength. When the ZBLAN fiber is pumped with red lasers, Er3+ ions is excited to the 4F9/2 level and then relax to the 4I11/2 and 4I13/2 levels from which sequential ESA with pump photons results in populating on 2P3/2 and 4S3/2 levels. Green, blue, and violet emissions can be achieved through the radiative decays from the 4S3/2 and 2P3/2 levels [
The partial energy-level diagram of Tm3+ ions to describe the transitions involving in upconversion emissions is plotted in Figure
Partial energy level diagram of Tm3+ ion in ZBLAN related to upconversion laser emissions. Pump absorption transitions are indicated with green upward arrows. Radiative transitions are indicated with blue downward arrows. Nonradiative decays are indicated with dotted arrows.
In 1990, Allain et al. [
Another blue emission at 455 nm can be obtained from the transition 1D2→3F4. The 455 nm radiation is self-terminated; therefore the lower laser level 3F4 is required to be emptied for achieving high-efficiency CW operation. Three different approaches can be utilized to solve the problem: (
Aside from the blue band, upconversion emissions at other wavelengths have also been observed in Tm3+-doped ZBLAN fibers. Single wavelength (784 nm), two-wavelength (785 nm + 805 nm or 788 nm + 793 nm), three-wavelength (787 nm + 794 nm + 802 nm) upconversion laser has been demonstrated in a Tm3+-doped ZBLAN fiber pumped by a 1120 Raman fiber laser [
The partial energy-level diagram of Pr3+ ions to describe the transitions involving in the upconversion emissions is plotted in Figure
Partial energy level diagram of Pr3+ ion in ZBLAN related to upconversion laser emissions (Partial energy level diagram of Yb3+ ion is also plotted to indicate pump absorption and energy transfer from Yb3+ to Pr3+). Pump absorption transitions are indicated with green upward arrows. Radiative emission transitions are indicated with blue downward arrows.
The first visible oscillation in Pr3+-doped ZBLAN fiber was demonstrated by Allain et al. [
Using alternative pumping scheme can improve the performance of Pr3+-doped ZBLAN fiber and enhance the desired upconversion emission. When pumped at 835 nm and 1017 nm, an efficient blue Pr3+-doped fluoride fiber upconversion laser operating at 492 nm was demonstrated with a slope efficiency of more than 13% and output power more than 9 mW [
For these singly Pr3+-doped ZBLAN fiber lasers, however, two pump lasers are required to excite Pr3+ ions to the upper laser level. In an effort to relieve the constraint of two-wavelength pumping, Yb3+ ions was added as a sensitizer for Pr3+ upconversion emission because the broad absorption band of Yb3+ ions permits a wide pump wavelength, strong absorption of Yb3+ ions permits shorter length fiber that still yield adequate pump absorption, and the simple energy structure of Yb3+ ions reduces the possibility for backwards energy transfer from the activator ion.
The first upconversion laser operating at 635 nm was demonstrated in a Pr3+/Yb3+-codoped ZBLAN fiber pumped by a Ti:sapphire laser at 850 nm [
Goh et al. [
The partial energy-level diagram of Nd3+ ions to describe the transitions involving in upconversion emissions is plotted in Figure
Partial energy level diagram of Tm3+ ion in ZBLAN related to upconversion laser emissions. Pump absorption transitions are indicated with green upward arrows. Radiative transitions are indicated with blue downward arrows. Nonradiative decays are indicated with dotted arrows.
In 1994, Funk et al. [
The partial energy-level diagram of Ho3+ ions to describe the transitions involving in the emission around 550 nm is plotted in Figure
Partial energy level diagram of Ho3+ ion in ZBLAN related to upconversion laser emission in the blue band. Pump absorption transitions are indicated with green upward arrows. Radiative transition is indicated with blue downward arrow. Nonradiative decays are indicated with dotted arrows.
In 1990, Allain et al. [
Supercontinuum generation is a physical process leading to dramatic spectral broadening of laser as it propagates through a nonlinear medium. Though the resulted beam has a very broad spectral bandwidth (i.e., low temporal coherence), its spatial coherence usually remains high. This particular property leads to extensive applications including coherence tomography, fluorescence microscopy, flow cytometry, optical devices characterization, dense wavelength division multiplexing in optical fiber communications systems, light-imaging detection and ranging, and optical frequency metrology.
Since the first demonstration in bulk glass [
The first supercontinuum generation in ZBLAN fiber was demonstrated by Hagen et al. [
Using a similar fiber construction, Xia et al. [
With the advent of reliable and high-brightness diode pump lasers and double-clad fibers that facilitate coupling the highly elliptical pump light into the fiber, output power of single-mode fiber laser has been significantly increased over the past decade. Output power of 6 kW has been successfully demonstrated in the Yb3+-doped single-mode silica fiber [
Evolution of continuous-wave output of single-mode 1
Basically, nonlinear phenomena such as stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS), thermal effects, and optical damage are major constraints on power scaling of CW fiber lasers. SRS and SBS resulting from stimulated inelastic scattering processes transfer a part of the energy of the incident light to the glass host in the form of excited vibrational modes and red-shift the wavelength of the light. Both processes lead to significant power loss and deteriorate the performance of high-power fiber lasers. Though the chief advantage of fiber lasers over bulk solid-state lasers is their outstanding heat-dissipation capability due to the large ratio of surface area to volume of the fiber allowing effective heat dissipation with minimal heat-sinking requirements, heat generation during a very high-power operation can still destroy an optical fiber, via thermal damage of the coating, fracture, or even melting of the core. Due to the occurrence of self pulsing, optically induced damage is also a hindrance of power scaling of fiber lasers [
Self-pulsing has been frequently observed in high-power fiber lasers [
Optical damage threshold of a ZBLAN fiber with respective to its core diameter.
With recent ZBLAN fiber technology, sing-mode infrared fiber with a core diameter of tens of microns can be fabricated and thereby is capable of delivering tens of or even over 100 watts output. However, as the core size increases, thermal effects are enhanced and actively cooling is required for efficient heat dissipation. For a common rare-earth-doped fiber, the temperature distribution in the core and the cladding region can be calculated by the following equations [
Temperature in the pumping end of the Er3+-doped ZBLAN fiber as a function of radial coordinates for a 100 W 975 nm pump.
Core center temperature in the Er3+-doped ZBLAN fiber as a function of fiber position for a 100 W 975 nm pump.
Core center temperature in the Er3+-doped ZBLAN fiber as a function of heat transfer coefficient for a 100 W 975 nm pump (
Aside from optical damage and thermal effects, photodarkening, a phenomenon with significant increase of the core absorption at visible and near-infrared wavelengths when the fiber is pumped with high-power infrared light, also need to be taken into account for high-power upconversion ZBLAN fiber lasers. In 1995, Barber [
On the other hand, a fiber laser can produce more output power with less heat generation when the efficiency of optical conversion is increased. Using pump with a wavelength close to the desire laser wavelength can increase the conversion efficiency and reduce the heat generation accordingly. Upconversion energy transfer and cross-relaxation processes between ions in high-concentration fibers can be used for efficiency improvement due to the doubled quantum efficiency. Cascade lasing is also an effective method to enhance the desired laser emission and reduce the heat generation by replacing the nonradiative multiphonon process with radiative emission. For upconversion fiber lasers, proper pumping scheme can also increase the efficiency and effectively avoid nonradiative transitions.
It should be mentioned here that Bragg gratings can be directly inscribed on the ZBLAN fibers with femtosecond pulses now [
Following the development of high-power silica fiber lasers, performance of ZBLAN fiber lasers can be further improved and 100-watt-level output is possible with large-core ZBLAN fibers or beam combining techniques [
Fluoride glass properties and ZBLAN fiber fabrication are introduced briefly in this paper to give readers a general knowledge of this remarkable gain medium. Detailed progress of infrared, upconversion UV and visible, and supercontinuum ZBLAN fiber lasers were reviewed. Optical damage, thermal effects, and photodarkening are the three major constraints on power scaling of ZBLAN fiber lasers. Using novel fiber design and high-brightness diode pumps, output power of >20 W has recently been obtained by sufficiently cooling the ZBLAN fiber laser system. In the next decade, a variety of high-power ZBLAN fiber lasers covering from ultraviolet to mid-infrared will emerge.