ZBLAN is a type of fluoride-based optical fiber glass that has the potential to perform up to 100 times more efficiently than traditional silica-based fibers. However, when ZBLAN is produced on Earth, gravity-driven forces cause impurities to form in the fibers, significantly hindering their performance.
In the microgravity environment of the International Space Station's National Lab, ZBLAN fibers can be produced with significantly fewer imperfections, leading to higher-quality fibers than can be produced on the ground.
High-performance optical fibers produced in space would be extremely valuable back on Earth. Such fibers could not only improve the efficiency and cost of communications systems but also could lead to advancements in many industries, including sensors used in the aerospace and defense industries and improved medical devices (such as laser scalpels).
“Optics and photonics, an enabling technology with widespread impact, exhibits the characteristics of a general-purpose technology, that is, a technology in which advances foster innovations across a broad spectrum of applications in a diverse array of economic sectors. Improvements in those sectors in turn increase the demand for the technology itself, which makes it worthwhile to invest further in improving the technology, thus sustaining growth for the economy as a whole. . .
Although many of the innovations in optics and photonics (i.e., the science and engineering of optical waves and photons) have occurred in the United States, U.S. leadership is far from secure. The committee has heard compelling arguments that, if the United States does not act with strategic vision, future scientific advances and economic benefits might be led by others. It is the committee’s hope that this study will help policy makers and leaders decide on courses of action that can advance the future of optics and photonics; promote a greener, healthier, and more productive society; and ensure a leadership position for the United States in the face of increasing foreign competition.”
* National Research Council. Optics and Photonics: Essential Technologies for Our Nation. Washington, DC: The National Academies Press, 2013.
“From a materials perspective optical fibers are victims of their own success. The advent of the laser, 50 yr ago, coupled with an insatiable demand for information enabled by light-based communications, ushered in a golden age of glass science and engineering. It is somewhat ironic that the staggering ubiquity of information today, which is carried globally and almost instantaneously via optical fibers, is enabled largely by one material—silica—into which only a few components are added. The richness of the Periodic Table has largely been forgotten… In a way of thinking, photonic crystals take advantage of the age-old paradigm of materials scientists that properties can be defined by structure and processing; not just materials.”
* Rethinking Optical Fiber: New Demands, Old Glasses. John Ballato and Peter Dragic. J. Am. Ceram. Soc., 96  2675–2692 (2013)
* College of Optical Sciences, University of Arizona, 1630 East University Boulevard, Tucson, AR 85721, USA http://www.hindawi.com/journals/aoe/2010/501956/
"Fluoride and chalcogenide glasses have drawn much attention because they are found to have low phonon energy and mid-infrared transparency. These glasses are excellent candidates for fiber lasers in visible and mid-infrared regions where emissions are hard to be obtained from silicate and phosphate fibers. Comparing to chalcogenide fibers, fluoride fibers have been studied for lasing actions with more significant efforts due to their high allowable doping levels (up to 10 mol%), relatively high strength, high stability, and low background loss (<0.05 dB/m). "
"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, it is hard to eliminate crystallization during the fiber drawing. Moreover, this method cannot be used for specially-designed fibers such as double-clad fibers with D-shaped or rectangular pumping cladding and microstructured fibers."
Exotic glasses are made from a complex formulation of materials, including metal fluorides and rare earth elements, which can be melted together in a wide range of combinations and drawn into optical fibers for different applications.
Exotic optical fibers are used to transmit signals, create lasers and laser scalpels, act as sensors and lenses, enable telecommunications and high speed computer applications, and provide imaging capabilities in hard to reach areas, including inside the human body.
From a national perspective, exotic optical glasses and fibers enable technologies of the future: diverse and growing multibillion-dollar markets from applications serving industry, defense, aerospace, communications, computers, and medicine.
The Economics of New Glasses and Fibers. Currently more than 1.8 billion kilometers of optical fiber is deployed around the world, connecting people, businesses, communities, countries, and continents with voice, data, and video. In the last 10 years, the application and use of broadband technology enabled by optical fiber has exploded, driven by the push-pull effect of national communications priorities and ever-growing consumer demand.
At present, silica fibers provide virtually the entire backbone of today’s internet and telecommunication industry. However, there are significant limitations to silica. Compared to the exotic glass ZBLAN, for example, silica transmission losses are very high, transmission quality is poor, and the bandwidth available for signal transmission is very narrow. This is especially true in the mid-infrared (mid-IR) region where silica transmission cuts off at about 2µm. (Image 3). There are many industrial, military, computer, and medical applications that require fibers and glasses in this range. Further, as the demand for higher bandwidth communications increases exponentially worldwide, the demand for fibers that overcome the limitations of silica is increasing proportionally. Exotic fibers have been identified by the industry as one of the potential components that can help meet this demand.
Making exotic glasses requires melting the various components together to create a glass blank or preform. Fibers are produced by melting the end of the preform and drawing the fibers onto a take-up spool. One of the main problems with the production of exotic glasses on Earth is that they are made of different density materials with different crystallization temperatures. Some are immiscible in the molten state.
The crystallization temperatures for the components of ZBLAN and other exotic glasses are higher than the temperature at which the melted glass transforms into solid glass. Temperature differences within the melt may be caused or worsened by gravity-induced convection. This leads to unwanted crystallization in both the preform and the fiber.
It is further thought that gravity-induced sedimentation causes the separation of ZBLAN’s constituent materials by density, which further promotes crystallization and phase separation as well as structural instabilities. These flaws diminish the yield, transmission quality, strength, and value of a fiber and constrain the range of applications that can be developed from it. These same types of problems are seen in other exotic glasses as well.
However, after only 20 seconds in microgravity aboard a parabolic aircraft, the ZBLAN preform showed no evidence of the crystallization that plagued terrestrial manufacturing.
In comparison, it took an additional decade of research on Earth to achieve the same result for the commercial manufacture of ZBLAN. This has not been achieved to the same degree for almost any of the other exotic fibers.
Producing longer lengths of fibers requires thicker and longer preforms that are free of crystallization. This is a constraining factor in the production of kilometer length exotic fibers.
Recently, there has been renewed interest in exotic glasses by the military. In 2012, under a DoD SBIR grant, the Physical Optics Corporation demonstrated on a parabolic aircraft flight that 20 seconds of microgravity could also significantly improve the fibers produced from ZBLAN, not just the preform. Dr. Dmitry Starodubov, Director of Photonics for the Physical Optics Corporation, was the Principal Investigator.
A great resource referenced from CMAPP: Commercial Microgravity Applications Pilot Project found here, https://tinyurl.com/y2bb597o