Proceedings Article | 3 March 2020
KEYWORDS: Telecommunications, Supercontinuum generation, Fiber optics sensors, Silica, ZBLAN, Signal attenuation, Optical fibers, Manufacturing, Scattering, Fiber lasers
Materials power key technological advancements in areas such as communications, consumer electronics, aerospace, automotive and energy. Silica has become the status quo because of its abundance and affordability. Advances in areas such as quantum computing, AI and IoT will require new materials with performance envelope beyond the traditional (i.e. global internet data is rapidly growing beyond petabytes/s/km). A long-time competitor to silica, heavy metal fluoride glasses represent an attractive candidate due to their optical transmission window that extends deep into the infrared (IR) and recently also in the UV (200nm-800nm). Although ZBLAN was the early frontrunner for 2.5μm transatlantic links with no repeaters, silica won the race in the 1980’s, due to the development of repeaters at 1.5μm. Today this reliance on silica is hurting the industry by forcing retrofitting of new applications. It is becoming clear that the demands of the next generation of communications cannot be solved with additional investments in a silica-based infrastructure. Silica has now maxed out also its affordability not just its signal transmission capacity. An equivalent to Moore’s law applicable to information speed and capacity carried through optical fibers has been emerging, and silica is not up to the task. The time for ZBLAN is now. Building on advances of the past several decades, fluoride technology (i.e. ZBLAN, InF3) has the unique properties to transmit light over [0.3-5.3]μm with theoretical attenuation as low as ~6.4•10-3 dB/km at 2.32μm – two orders of magnitude better than silica. This paper provides a solid reference to calculate the theoretical spectrum of ZBLAN attenuation and includes a thorough discussion on areas of improvement that, once implemented, will lead to the manufacturing of ZBLAN that approaches its ultimate performance. An up-to-date ZBLAN-silica comparison is provided, including values of material properties that underlie both attenuation and stimulated Brillouin scattering (SBS) power threshold estimations. Contrary to existing beliefs, current ZBLAN intrinsic fiber strength is only a factor of 2-3 lower than that of silica. The breaking radius of a standard SMF-28 fiber is <1.5mm and <4mm for ZBLAN with the latter being available in jacketed form to comply with industrial requirements. Fluoride fibers inherently provide naturally a much wider bandwidth than silica with up to 100x usable number of data channels, <2 petabytes per second of data with no amplification for 1,000km or more and no need to carry power for said amplification lines. By comparison, current undersea cables use one repeater for amplification every 100-150km, at a cost of ~$1M each. In addition, the low phonon energy characteristic of fluoride glasses and the high solubility towards a wide spectrum of rare-earth elements are conducive to a broad range of robust and reliable fluoride fiber lasers emitting more power and/or at wavelengths inaccessible before. Last but not least, the dispersive properties of fluoride fibers and other nonlinear effects lead to supercontinuum spectral broadening that can be extended from 0.8-4.1μm up to 15 μm when cascading fluoride fibers with other types of fibers. Fluoride fiber technology is a solid and competitive solution for a wide spectrum of photonic applications (spectroscopy, medical diagnosis), data transmission (ultra-long haul, submarine) and beyond.
