Optical Fiber for Datacenter Connectivity

Abstract

Modern optical fiber communications originated from a paper published in 1966 by Dr. Charles Kao [1–3]. Kao proposed using a thin strand of glass to transmit an optical signal and outlined all basic properties of a single-mode optical fiber, in addition to the associated manufacturing processes. The conclusion of his paper stated the following: “Theoretical and experimental studies indicate that a fiber of glassy material constructed in a cladded structure with a core diameter of about lambda zero and overall diameter of about 100 lambda zero represents a possible practical waveguide with important potential as a new form of communication medium.” Kao’s prediction accurately described what would come to be known as optical fiber. When Kao published his paper, the attenuation of contemporary bulk glass was an enormous 1000 dB/km. That attenuation was reduced to the level of tens of dB/km applicable to telecommunication [4], but modern commercially available optical fiber has much less attenuation, as low as 0.15 dB/km for commercial submarine fiber [5]. The lowest reported attenuation is 0.1419 dB/km in [6]. The world as it is today, from homes to cities, through continents and oceans, is covered by an interwoven network of optical fiber telecommunication cables. The deployed optical fibers and cables from a single vendor, OFS Fitel, LLC (formerly Lucent Technologies), is enough to make 628 round-trips between the Earth and the Moon. This intricate web of connectivity forms the physical foundation of the World Wide Web, the three eras of which are defined by Steven Case [7]. The first era covers the construction of the internet between 1985 and 2000. The second era involves the creation of new internet-dependent services between 2000 and 2015 and also encompasses the foundation of global cloud infrastructure, including datacenters and interconnected networks. The third and current era involves creating an internet of everything (IoT), establishing a cloud-integrated network (CIN), and exploiting Augmented Intelligence, the ability to transform data into action based on big data analysis [7]. Some experts argue that the first and second eras of the internet form the beginning of a third industrial revolution, and that advancements in technology and economic processes, more radical than any previously experienced, lie ahead [7]. The current backbone fiber communication paradigm, based on single-mode fiber and the optical fiber amplification, is already within a factor of two from maximum usage of the current telecommunications spectrum [7]. Global networks are experiencing increased demand for high-quality optical fibers while next-generation data traffic is quickly surpassing that of traditional telecom across the internet backbone.