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Case Study: Exotic Glasses and Fibers

See an excellent technical article on this:  New SpaceVol. 5, No. 3
Exotic Optical Fibers and Glasses: Innovative Material Processing Opportunities in Earth's Orbit
“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 [9] 2675–2692 (2013)

Great article on ZBLAN Manufacturing:

Advances in OptoElectronics
Volume 2010 (2010), Article ID 501956, 23 pages

Review Article
High-Power ZBLAN Glass Fiber Lasers: Review and Prospect
Xiushan Zhu and N. Peyghambarian

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 [36], 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.

Why Microgravity?

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 (Image 5). 

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 as shown in Image 6. 

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 (Table 1). 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. (Image 7).  

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. (Appendix G)

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 (Images 8, 9).  Dr. Dmitry Starodubov, Director of Photonics for the Physical Optics Corporation, was the Principal Investigator.

 1998 ZBLAN preform with fibers pulled in 1-g.  Tucker et al.
 1998 ZBLAN preform with fibers pulled in 0-g.  Tucker et al.

 ZBLAN Fibers pulled in 1-g in flight unit.
2012 Physical Optics Corporation.  Starodubov et al
 ZBLAN fibers pulled in µg in the same flight unit. 2012 Physical Optics Corporation.  Starodubov et al

 Side view of ZBLAN Fibers (above) pulled in 1-g in flight unit.
2012 Physical Optics Corporation.  Starodubov et al
  Side view of ZBLAN Fibers (above) pulled in 0-g in flight unit.
2012 Physical Optics Corporation.  Starodubov et al

In Space ManufacturingExotic glass fiber production in microgravity may be an area where the business case for in-space manufacturing could close in the relatively near future.

This is because very small quantities of the raw material (preform) can be launched and, if successfully drawn into uniform fibers, can potentially be sold for relatively high-prices per unit of mass. The size of the in-space manufacturing unit is also be relatively small and relatively inexpensive to produce.

One kilogram of exotic glass feedstock can be expected to produce from 3 to 7 kilometers of fibers in under an hour in microgravity, under optimized conditions.  At a nominal cost of $88K/kg, the launch costs for the preform and spool (estimated to be 2 kg) combined with the landed costs for the filled spools would be approximately $176,000.

The current low-end market price for ZBLAN fibers is $150/meter.   Therefore, even at today’s lowest market prices, a kilogram of ZBLAN launched to space could be sold on Earth for between $450,000 and $1,050,000.

However, the real value of microgravity will be in producing ZBLAN and other exotic fibers of exceptional quality.  Today, these custom fibers are sold between $300/meter and $3,000/meter.   At current market prices, a preform launched to a fiber manufacturing facility in orbit could yield from $900,000/kg to $21,000,000/kg.


Production of exotic fibers in microgravity is the strongest case the authors have found for in-space manufacturing over the next decade.

However, in-space proof-of-concept demonstrations are necessary to determine whether the quality and yield of the ZBLAN and other exotic fibers produced in microgravity are good enough to overcome the difficulty and expense of in-space manufacturing.  These are planned for the International Space Station in 2015.

Reference Links (and please see downloads below)

Optics and Photonics:  Essential Technologies for Our Nation

Committee on Harnessing Light: Capitalizing on Optical

Science Trends and Challenges for Future Research

National Materials and Manufacturing Board

Division on Engineering and Physical Sciences


Optics and photonics technologies are ubiquitous: they are responsible for the displays on smart phones and computing devices, optical fiber that carries the information in the internet, advanced precision manufacturing, enhanced defense capabilities, and a plethora of medical diagnostics tools. The opportunities arising from optics and photonics offer the potential for even greater societal impact in the next few decades, including solar power generation and new efficient lighting that could transform the nation's energy landscape and new optical capabilities that will be essential to support the continued exponential growth of the Internet.

NASA Technical Memorandum 4069 Volume 2

Microgravity Science and

Applications Flight Programs, January-March 1988


"Fluoride Glass

A variety of fluoride glasses based on zirconium, hafnium or thorium fluoride are being intensively investigated because they are transparent in the infrared to 8 pm and be~0nd.l'~ Optical components such as lenses, prisms, and fibers for use in the infrared can be made of these glasses.

An especially attractive application envisions fiber optic wave guides for long distance communication. Fibers of vitreous silica are already being used for this purpose. The length of each link in a comniunication chain is limited by optical scattering and absorption; silica has a minimum combinedabsorptionataboutoneum. Thefluorideglasseshaveintheory
a much deeper minimum than silica at longer wavelengths because their absorption edge is further into
the infrared. Much progress has b e e n made in forming fibers for these purposes and reducing their absorption and scattering losses.

Optical fibers are being investigated as sensors for a wide variety of environmental factors, including temperature, pressure, displacement, acousticfield,electromagneticwaves,andevencomposition.8 Availability of glasses with wider ranges of transparency in the infrared should provide new and improved sensors.

These fluoride glasses satisfy the requirements of high value and lowvolumematerialsforspaceprocessing. Ifdifferentcompositionswith a larger range of infrared transparency could be made because of the reduced contamination and wall nucleation during containerless processing, many more valuable glasses would be available."


Lynn Harper,
Mar 21, 2015, 4:56 PM
Lynn Harper,
Mar 21, 2015, 4:56 PM
Lynn Harper,
Mar 21, 2015, 4:56 PM
Lynn Harper,
Mar 21, 2015, 4:37 PM