ZrF4-BaF2-LaF3-AlF3-NaF Research Articles

Use of magnetic fields to impact glass-transition and crystallization during manufacturing of ZBLAN optical fibers

ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) is the most stable glass among the Heavy Metal Fluoride (HMF) family and has a wide range of applications in medical industry, telecommunication, IR transmission, among others. But, due to crystal formation while manufacturing of ZBLAN fiber its theoretical minimum loss has not been achieved yet. Some techniques such as high cooling rate and microgravity conditions have been utilized to reduce the crystal formation but are challenging to implement during manufacturing of these fibers. Alternatively, magnetic field (MF), also a body force like gravity, is expected to influence the crystal formation mechanism and glass kinetics. In this work, ZBLAN glass is processed under magnetic fields of various intensities while simulating fiber drawing manufacturing process conditions. Then, the processed ZBLAN is analyzed using Differential Scanning Calorimetry (DSC) at varying scanning rates. Various glass kinetics parameters such as activation energy, fragility, and preferred crystallization mechanism in terms of Avrami parameter (n) have been analyzed. The glass transition temperature (Tg) increases for a given sample as scanning rate (β) increases. Samples processed under varying magnetic fields, at the same scanning rate, displayed higher glass transition temperatures. Also, when the magnetic field increases, the activation energy required for glass transition decreases, and the fragility index (m) decreases. There is also a preference for surface crystallization over volume crystallization. These results encourage application of magnetic fields for reducing crystal formation while processing ZBLAN glass.

Optical Properties of Fluorozirconate Glasses Doped with Chromium Ions

Chromium trifluoride-doped fluoride glasses in the ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) system with partial substitution of fluorine for chlorine have been synthesized. The spectral data obtained confirm that chromium ions enter the glass structure and exhibit broadband luminescence caused by the 4T2 → 4A2 transition in the Cr3+ ion. The observed long-wavelength shift of the broadband luminescence band and Cr3+absorption bands in fluoride–chloride glass compared to fluoride glass corresponds to the expected behavior of the Cr3+ luminescence and absorption spectra when fluoride ions are replaced by chloride ions, which should lead to a weakening of the strength of the crystal field acting on Cr3+ ions. At room temperature, the luminescence of Cr3+ ions at 888 and 908 nm is strongly quenched due to the thermally stimulated nonradiative transition from the 4T2 excited state to the 4A2 ground state.

Influence of xenon difluoride on the optical properties of fluorozirconate and fluorohafnate glasses

To study the effect of xenon difluoride as a fluorinating agent on optical properties of glasses in ZBLAN (ZrF4–BaF2–LaF3–AlF3–NaF) and HBLAN (HfF4–BaF2–LaF3–AlF3–NaF) systems, their optical transmission in the range from UV to IR was investigated. The treatment of the initial fluorides with XeF2 was shown to lead to a broadening of the transmission region of the obtained glasses both in the UV and IR ranges. Moreover, the treatment of the batch with xenon difluoride leads to the removal of oxygen-containing impurities that absorb in the region of 2.8 μm.

Exploring interfacial reactions and optical properties of ZBLAN-based phosphor-in-glass color converters via spark plasma sintering for laser-driven lighting

Phosphor-in-glass (PiG) is extensively utilized as a color converter in laser-driven lighting. Despite its popularity, a noteworthy concern is the potential for interfacial reactions to occur between the phosphors and the glass matrix during high-temperature processing, leading to subsequent corrosion. Previous research suggests that spark plasma sintering (SPS) may effectively limit these reactions in silica glass-based PiGs. However, the reactivity of silica glass, lacking glass modifiers, towards phosphors is diminished, raising uncertainty about whether SPS can truly fabricate a PiG with improved interfacial morphology. Nonetheless, research pertaining to PiG fabrication using SPS with multi-component glass compositions remains scarce. In this study, an attempt is made to address this gap by employing a multi-component glass matrix - ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN), which is known for its high reactivity with phosphors, in the creation of PiGs through SPS. Lu3Al5O12:Ce3+ (LuAG) was embedded within ZBLAN glass, fabricated using SPS in merely 5 min at a temperature of 255 °C. The subsequent analysis focused on the interfacial microstructure and the optical properties of the thus prepared PiG samples. The results demonstrate that the lower-temperature and time-efficient sintering process of SPS successfully mitigate the interfacial reactions between the phosphor and the glass matrix. Consequently, a commendable luminous flux of 597 lm and luminous efficacy of 242 lm/W is achieved.

Nanosecond mid-infrared pulse generation modulated by platinum ditelluride nanosheets

We demonstrated the generation of nanosecond mid-infrared (MIR) pulse from an Er3+-doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber laser modulated by platinum ditelluride nanosheets experimentally. The platinum ditelluride nanosheets exhibit strong nonlinear absorption with the saturation intensity 46.5 GW cm−2 and modulation depth 27.8% at 2.8 μm wavelength, respectively. With the saturable absorber mirror fabricated by depositing the platinum ditelluride nanosheets on a gold mirror, we have obtained the stable Q-switched pulses with repetition rate of 173.4 kHz and pulse duration of 600 ns at 2.8 μm wavelength under the pump power of 5.6 W. In addition, the maximum average output power and pulse energy reach 591 mW and 3.41 μJ, respectively. The experimental results confirm that the platinum ditelluride nanosheets exhibit excellent nonlinear optical behavior towards the MIR spectral range, and may make inroads towards MIR photonics with group-10 transition-metal dichalcogenides.

Efficient UV-visible emission enabled by 532 nm CW excitation in an Ho3+-doped ZBLAN fiber.

Rare-earth-doped ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fibers have evolved to become promising candidates for efficient UV-visible emission because of their low phonon energy and low optical losses, as well as their well-defined absorption bands. We investigate the efficient emission of UV-visible light in a low-concentration (0.1 mol%) Ho3+-doped ZBLAN fiber excited by a 532 nm CW laser. In addition to the direct populating of the thermalized 5F4+5S2 levels by ground-state absorption, the upconversion processes responsible for UV-visible emission from the higher emitting levels, 3P1+3D3, 3K7+5G4, 5G5, and 5F3, of the Ho3+ ions are examined using excited-state absorption. The dependence of UV-visible fluorescence intensity on launched green pump power is experimentally determined, confirming the one-photon and two-photon characters of the observed processes. We theoretically investigate the excitation power dependence of the population density for nine Ho3+ levels based on a rate equation model. This qualitative model has shown a good agreement with the measured power dependence of UV-visible emission. Moreover, the emission cross-sections for blue, green, red, and deep-red light in the visible region are measured using the Füchtbauer-Ladenburg method and corroborated by McCumber theory, and the corresponding gain coefficients are derived. We propose an alternative approach to achieve efficient UV-visible emission in an Ho3+-doped ZBLAN fiber using a cost-effective, high-brightness 532 nm laser.

Widely wavelength tunable Dy3+/Er3+ co-doped ZBLAN fiber lasers.

Wavelength tunable dysprosium-erbium (Dy3+/Er3+) co-doped ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fiber lasers pumped at 980 nm were developed with a bulk grating blazed at 3.1µm in the Littrow configuration and their performances were investigated. A wavelength tunable range of 674.4 nm (2709.2 nm -3373.6 nm) was achieved with a 4.5-m 0.25 mol.% Dy3+/ 4mol.% Er3+ co-doped ZBLAN fiber. Our experiments demonstrated that either Er3+ or Dy3+ can be lasing individually in a Dy3+/Er3+ co-doped ZBLAN fiber and a fiber laser with wavelength tunable range from 2.7 µm to 3.4 µm or longer wavelengths can be achieved with proper fiber and cavity design.

Beyond 3 μm Dy3+/Er3+ co-doped ZBLAN fiber lasers pumped by 976 nm laser diode

Dysprosium-erbium (Dy3+/Er3+) co-doped ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fiber lasers operating at 3.2–3.35 μm were demonstrated by pumping at the 980 nm Er3+ absorption band. A maximum output power of 260 mW at 3.27 μm with a slope efficiency of 5.73% was achieved with 3.6 m 0.25 mol. % Dy3+/4 mol. % Er3+ co-doped ZBLAN fiber. Lasers operating at 3.23 μm and 3.35 μm were also demonstrated with 2 m and 9 m gain fibers, respectively, but with lower slope efficiencies. Our experiments confirm the possibility of pumping the Dy3+/Er3+-doped ZBLAN fiber laser with a low-cost high efficiency diode laser at 976 nm.

Crystallization Behavior and Spectroscopic Properties of Erbium-Doped Chlorine-Substituted Fluorozirconate Glasses

We have prepared ErF3-doped glasses in the ZrF4–BaF2–LaF3–AlF3–NaF system containing chlorine ions substituted for fluorine ions. The crystallization behavior of the chlorine-substituted glasses has been studied at various BaCl2 and ErF3 concentrations. We have identified phases precipitating during heat treatment of the glasses and assessed the effect of chlorine substitution for fluoride on the optical absorption and IR luminescence in the glasses. The results demonstrate that chlorine substitution for fluorine causes the UV absorption edge of the glass to shift to longer wavelengths and produces an additional absorption in the visible spectral region. The formation of crystalline phases during heat treatment of the glasses leads to significant changes in the shape of the Er3+ luminescence bands at 0.98 and 1.55 μm.

Highly coherent multi-octave polarization-maintained supercontinuum generation solely based on ZBLAN fibers.

We present a highly stable polarization-maintained supercontinuum (SC) using a setup solely based on ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) fibers. The pumping source consists of a femtosecond master oscillator fiber amplifier based on thulium-doped ZBLAN fibers. It provides multi-watts of output power with the center wavelength of 1920 nm at 1 MHz repetition rate. The SC generated by pumping an elliptical core passive single-mode ZBLAN fiber spans from 350 nm to 4.5 µm and exhibits high stability. We characterized the SC pulse using sum-frequency cross-correlation frequency resolved optical gating.

20.6 W Mid-Infrared Supercontinuum Generation in ZBLAN Fiber With Spectrum of 1.9–4.3 μm

A 20.6-W mid-infrared supercontinuum (MIR-SC) generation is demonstrated in a piece of step-index ZBLAN (ZrF4−BaF2−LaF3−AlF3−NaF) fiber. A silica-fiber-based SC laser operating at 1.9–2.6 μm is used as a pump source. Owing to the specially designed ZBLAN fiber which perfectly matches the pigtail of the pump source in mode-field-diameter, direct fusion splicing was achieved between the ZBLAN fiber and the pigtail of the pump source instead of being connected via a piece of transition fiber. The coupling loss of the fusion splicing joint between the silica fiber and the ZBLAN fiber was measured as 0.26 dB@2000 nm. Robust fiber endcap made of multimode AlF3 fiber also benefited high-power MIR-SC generation. Spectral and power characteristics of the generated SC under different pump pulse duration and pulse repetition rate were carefully studied. A 20.6-W SC was obtained with an overall spectral coverage and a 10-dB long wavelength edge of 1.92–4.29 μm and 4.08 μm, respectively. This is, to the best of the authors’ knowledge, the first demonstration of 20-W level SC laser based on ZBLAN fiber with long wavelength edge extending beyond 4 μm.

Watt-level ultra-flattened mid-infrared supercontinuum with high power stability generation in an all-fiber structured Tm-doped fiber amplifier pumped ZBLAN single-mode fiber

We demonstrate a 5-watt-level mid-infrared supercontinuum (MIR-SC) generation in a Tm-doped fiber laser (TDFL) pumped single-mode ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber. In the optimization of front end 2 µm laser system, the laser energy-transfer efficiency from 1.55 µm to 2 µm was improved to 25 % by using a 4 m-long single-mode Tm-doped fiber (SM-TDF), in combination with a tailored broad-band pass filter (bandwidth>1.8 µm), the pulse spectrum was well shaped, the spectral contrast was substantially improved and the follow-up laser amplification efficiency was significantly optimized. In the realization of all-fiber structured MIR-SC power boosting process, we successfully achieved the high robustness and ultra-low loss fusion splicing point between silica and ZBLAN fiber in the high power measurement condition. By comprehensively taking the above-mentioned measures, we eventually obtained a MIR-SC covering 1.9 µm to 4 µm, with average power as high as 5.4 W, power stability with a root mean square (RMS) value of 0.03 % in 2 h, spectral fluctuation less than 0.1 dB in the wavelength range from 2.1 µm to 3.5 µm and without any residual pump peaks appeared in the spectrum. To the best of our knowledge, this is the first investigation on the all-fiber structured MIR-SC generation with so high the long-term power stability and spectrum flatness simultaneously in average power of above 5-Watt level.

Efficient energy transfer from Er3+ to Ho3+ and Dy3+ in ZBLAN glass.

Spectroscopic properties of erbium (Er3+)-, holmium (Ho3+)-, dysprosium (Dy3+)-doped and Er3+/Ho3+, Er3+/Dy3+ co-doped ZBLAN (ZrF4-BaF2-LaF3-AlF3-NaF) glasses were studied. The experimental results show that efficient energy transfer from Er3+ to Ho3+ and Dy3+ occurs in the Er3+/Ho3+ and Er3+/Dy3+ co-doped ZBLAN glasses, respectively. This valuable discovery enables us to design and develop high power Ho3+-doped and Dy3+-doped ZBLAN fiber lasers in the 3 µm wavelength region that can be pumped with readily available high-efficiency, high-power diode laser pumps at 980 nm.

Spectral analysis of short-wavelength emission by up-conversion in a Tm3+:ZBLAN dual-diode-pumped optical fiber

The fluorescence evolution along Tm3+-doped ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) optical fibers, as well as amplified spontaneous emission in the UV-IR region with emphasis on 350 nm, 365 nm, and 450 nm, is studied, estimating optimal fiber lengths for amplification within the region. The fibers were diode-pumped with single and double lines (687 and/or 645 nm). Double-line pumping presents a quite superior efficiency for producing UV-blue signals with the benefit of requiring very short fibers, around 20 cm, compared to single-line pumping requiring more than 50 cm. A virtual cycle in which the pumps enhance each other’s absorption is the key to these systems.

Numerical analysis of a high-birefringent photonic quasi-crystal fiber with circular air holes

A high-birefringence(HB) photonic quasi-crystal fiber(PQF) with all-circular air holes is designed and ZrF4-BaF2-LaF3-AlF3-NaF(ZBLAN) is used to increase the birefringence and reduce confinement loss of the PQF in the infrared region. The structure of the PQF is analyzed and optimized numerically using the full-vector finite element method by adopting the perfectly matched layer boundary conditions. The PQF possesses higher birefringence in the wavelength range between 1.3 and 1.8μm and the maximum birefringence value of 4.1×10−2 is achieved at 1.55μm. This is the highest birefringence value reported from all-circular-hole PQFs so far suggesting that the novel structure has great potential in high-performance optical devices.

1.2-15.2 μm supercontinuum generation in a low-loss chalcohalide fiber pumped at a deep anomalous-dispersion region.

A novel low-loss selenium-based chalcohalide fiber, with a low zero-dispersion wavelength, was prepared by an innovative preparation process. The composition optimized fiber has a wide transmission range of up to 11.5μm, a lowest fundamental mode zero-dispersion wavelength of 4.03μm, and a minimum optical loss of 1.12dB/m at 6.4μm, which provides a possibility to replace As2S3 and As2Se3 in a cascade of ZrF4-BaF2-LaF3-AlF3-NaF(ZBLAN)-As2S3-As2Se3 fiber in the practical all-fiberized supercontinuum (SC) source. Meanwhile, the broadest SC spectrum, ∼1.2 to 15.2μm, was achieved by pumping a 12-cm-long fiber with a femtosecond laser at a deep anomalous-dispersion region. Furthermore, simulations are adopted to interpret the results as well as to demonstrate spectral evolution along the fiber. To the best of our knowledge, this is the broadest SC spectrum reported in any selenium-based chalcogenide fiber.

Optical Properties and Electron Paramagnetic Resonance Spectra of Zirconium Fluoride- and Hafnium Fluoride-Based Glasses Activated with MnO2 and EuF2

We have studied luminescence and electron paramagnetic resonance (EPR) spectra of manganese- and europium-activated fluorozirconate glasses in the ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) system and fluorohafnate glasses in the HfF4–BaF2–LaF3–AlF3–NaF (HBLAN) system in order to assess the oxidation state and spatial distribution of the activator ions. The manganese luminescence band has been shown to shift from the green (545 nm) to the red (610 nm) spectral region, and additional lines in the EPR spectrum of manganese have been observed to emerge in the EPR spectrum of manganese as a result of BaCl2 substitution for BaF2 in the ZBLAN glass. The ratio of the concentration of free activator ions to that of clustered ions has been estimated quantitatively. It has been shown that, at high doping levels, the manganese and europium ions in the glasses are predominantly clustered, and only a small part of them are present as isolated ions.

Grating Inscription Into Fluoride Fibers: A Review

First demonstrated over four decades ago, fiber gratings, and in particular fiber Bragg gratings (FBGs), have become indispensable and ubiquitous components within fiber laser cavities as well as optical communication networks and sensor systems. Because of their overwhelming use, the bulk of published work to date has concentrated on fibers that are composed of silica-based glasses, yet those become virtually opaque at wavelengths above 2 μm, i.e., in the technically increasingly important mid-infrared part of the electromagnetic spectrum. Soft glass fluoride fibers on the other hand, in particular those composed of ZBLAN (abbreviation for ZrF4-BaF2-LaF3-AlF3-NaF), offer low-loss transmission out to wavelengths of up to almost 4 μm. However, while fiber manufacturing itself has now reached a high level of maturity, with passive fiber attenuation levels as low as 1 dB/km becoming commercially available, grating fabrication in these fibers remains challenging, and research into suitable inscription techniques is still a very active and ongoing scientific field. This review aims to provide an overview of work that has been done in this area to date with an emphasis on femtosecond-laser based fabrication methods.

30-W supercontinuum generation based on ZBLAN fiber in an all-fiber configuration

We report an all-fiberized 30-W supercontinuum (SC) generation in a piece of ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber. The pump source is a thulium-doped fiber amplifier (TDFA) with broadband output spectrum spanning the 1.9 to ∼2.6 μm region. The used ZBLAN fiber has a core diameter of 10 μm, and was directly fusion-spliced to the pigtail of the TDFA without using a traditional mode field adapter (MFA) or a piece of transition fiber. Such a low-loss and robust fusion splice joint, together with a robust AlF3-fiber-based endcap, enables efficient and high-power SC generation in the ZBLAN fiber. An SC with an average power up to 30.0 W and a spectral coverage of 1.9–3.35 μm with 20-dB bandwidth of 1.92–3.20 μm was obtained. Moreover, an SC with a broader spectrum was achieved by raising the pump pulse peak power (via reducing the duty ratio of the pump laser pulse). An SC with an output power of 27.4 W and a spectral coverage of 1.9–3.63 μm (with 20-dB bandwidth of 1.92–3.47 μm) was obtained, as well as an SC with output power of 24.8 W and a spectral coverage of 1.9–3.70 μm (with 20-dB bandwidth of 1.93–3.56 μm). The power conversion efficiency was measured as >69%. To the best of the authors’ knowledge, this research demonstrates the record output power of SC lasers based on ZBLAN fibers, paving the way for broadband and efficient multi-tens-of-watts SC generation in soft-glass fibers.

The 2- to 6- mid-infrared supercontinuum generation in cascaded ZBLAN and As2Se3 step-index fibers**Project supported by the National Natural Science Foundation of China (Grant Nos. 61435009, 61235008, and 61405254), the Fund from China Scholarship Council (Grant No. 201803170210), and Hunan Provincial Innovation Foundation for Postgraduate (Grant No. CX2018B008).

Fiber-based mid-infrared (MIR) supercontinuum (SC) sources benefit from their spectral brightness and spatial coherence that are needed for many applications, such as spectroscopy and metrology. In this paper, an SC spanning from to is demonstrated in cascaded ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) and As2Se3 step-index fibers. The pump source is a ZBLAN fiber-based MIR SC laser with abundant high-peak-power soliton pulses between 3000 nm and 4200 nm. By concatenating the ZBLAN fiber and the As2Se3 fiber, efficient cascading red-shifts are obtained in the normal dispersion region of the As2Se3 fiber. The spectral behavior of cascaded SC generation shows that the long-wavelength proportion of MIR SC generated in the ZBLAN fiber plays a critical role for further spectral extension in the As2Se3 fiber.