page_title: ZBLAN
section_title: Comparison with alternative fiber technologies
hierarchical_section_title: ZBLAN / Fiber optics / Comparison with alternative fiber technologies
caption_attribution_description: English: ZBLAN glass grown with the same setup in zero-gravity (left; aboard a KC-135 plane) and in normal gravity (right)
context_page_description: ZBLAN is the most stable, and consequently the most used, fluoride glass, a subcategory of the heavy metal fluoride glass group. Typically its composition is 53% ZrF₄, 20% BaF₂, 4% LaF₃, 3% AlF₃ and 20% NaF. ZBLAN is not a single material but rather has a spectrum of compositions, many of which are still untried. The biggest library in the world of ZBLAN glass compositions is currently owned by Le Verre Fluore, the oldest company working on HMFG technology. Hafnium fluoride is chemically similar to zirconium fluoride, and is sometimes used in place of it.
  ZBLAN glass has a broad optical transmission window extending from 0.22 micrometers in the UV to 7 micrometers in the infrared. ZBLAN has low refractive index, a relatively low glass transition temperature of 260–300 °C, low dispersion and a low and negative temperature dependence of refractive index dn/dT.
context_section_description: Early silica optical fiber had attenuation coefficients on the order of 1000 dB/km, as reported in 1965. Kapron at al reported in 1970 fibers having an attenuation coefficient of ~20 dB/km at 0.632 µm, and Miya et al reported in 1979  ~0.2 dB/km attenuation at 1.550 µm. Nowadays, silica optical fibers are routinely manufactured with an attenuation of <0.2 dB/km with Nagayama et al reporting in 2002 an attenuation coefficient as low as 0.151 dB/km at 1.568 µm. The four order of magnitude reduction in the attenuation of silica optical fibers over four decades was the result of constant improvement of manufacturing processes, raw material purity, and improved preform and fiber designs, which allowed these fibers to approach the theoretical lower limit of attenuation. 
  The advantages of ZBLAN over silica are: superior transmittance (especially in the UV and IR), higher bandwidth for signal transmission, spectral broadening (or supercontinuum generation) and low chromatic dispersion. 
  The graph at right compares, as a function of wavelength, the theoretical predicted attenuation (dB/km) of silica (dashed blue line) with a typical ZBLAN formulation (solid gray line) as constructed from the dominant contributions: Rayleigh scattering (dashed gray line), infrared (IR) absorption (dashed black line) and UV absorption (dotted gray line). 
  The difficulties that the community encountered when trying to use heavy metal fluoride glasses in the early years of development for a variety of applications were mostly related to the fragility of the fibers, a major drawback that prevented their broader adoption. However, the developers and manufacturers have dedicated significant effort in the last two decades to better understand the underlying causes of fiber fragility. The original fiber failure was primarily caused by surface defects, largely related to crystallization due to nucleation and growth, phenomena induced by factors such as raw material impurities and environmental conditions (humidity of the atmosphere during drawing, atmospheric pollutants such as vapors and dust, etc.) during processing. The particular focus on processing improvements has resulted in a 10× increase in the fiber strength. Compared to silica fiber, the intrinsic fiber strength of HMFG is currently only a factor of 2–3 lower. For example, the breaking radius of a standard 125 µm single-mode fiber is < 1.5 mm for silica and < 4 mm for ZBLAN. The technology has evolved such that HMFG fibers can be jacketed to ensure that the bending radius of the cable will never reach the breaking point and thus comply with industrial requirements. The product catalogs usually call out a safe bending radius to ensure that end users handling the fiber stay within the safe margins.
  Contrary to current opinion fluoride glasses are very stable even in humid atmospheres and usually don’t require dry storage as long as water will remain in the vapor phase (i.e not being condensed on the fiber). Problems arise when the surface of the fiber comes in direct contact with liquid water (the polymeric coating usually applied to the fibers is permeable to water allowing water to diffuse through it). Current storage and transportation techniques require a very simple packaging strategy: the fiber spools are usually sealed with plastic together with a desiccant to avoid water condensation on the fiber. Studies of water attack on HMFG have shown that prolonged (> 1 hour) contact with water induces a drop in the pH of the solution which in turn increases the rate of the attack of water (the rate of attack of water increases with decreased pH). The leach rate of ZBLAN in water at pH = 8 is 10–5 g·cm²/day with five orders of magnitude decrease between pH = 2 and pH = 8. The particular sensitivity of HMFG fibers such as ZBLAN to water is due to the chemical reaction between water molecules and the F⁻ anions which leads to the slow dissolution of the fibers. Silica fibers have a similar vulnerability to hydrofluoric acid, HF, which induces direct attack on the fibers leading to their breakup. Atmosp
caption: ZBLAN produced with the same equipment in zero gravity (left) and in normal gravity (right)
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