{"id":146,"date":"2017-12-04T00:48:47","date_gmt":"2017-12-04T05:48:47","guid":{"rendered":"https:\/\/itp.nyu.edu\/networks\/?page_id=146"},"modified":"2019-05-01T02:11:14","modified_gmt":"2019-05-01T06:11:14","slug":"fiber-optics-cables-for-information-exchange","status":"publish","type":"page","link":"https:\/\/itp.nyu.edu\/networks\/explanations\/fiber-optics-cables-for-information-exchange\/","title":{"rendered":"Fiber Optics for Information Exchange"},"content":{"rendered":"

<\/span>What is fiber?<\/b><\/span><\/h2>\n

If you\u2019ve seen a Verizon Fios commercial or heard Google Fiber is coming to your town, you may have heard of fiber and have some sense that it has to do with faster internet. Over the past several decades, the world\u2019s communications networks have been increasingly replaced with fiber optic connections. But what is fiber, how does it work, and why is it\u2019s use expanding so much?<\/span><\/p>\n

\"Novelty<\/a>
You may recognize fiber from this kind of novelty lighting fixture.<\/figcaption><\/figure>\n

Conventional<\/span> fiber optic filaments<\/b> or simply \u201cfiber,\u201d are thin strands of glass or plastic (the <\/span>core<\/b>) surrounded by another material with lower refractive index (the <\/span>cladding<\/b>), usually another type of glass or plastic. The <\/span>refractive index<\/b> is a number (the ratio of the speed of light in a vacuum to the speed of light in a material) <\/span>that represents how much light is bent, or refracted, when light enters the material. A vacuum has a refractive index of 1 while all materials have a refractive index greater than 1 (light always travels slower through a material than in a vacuum) and less than 4. <\/span><\/p>\n

A \u201cprimary buffer coating\u201d protects the interior layers from external elements that might damage them. For most applications, ultra-pure glass is used for both the core and cladding resulting in strands about the diameter of a human hair. This structure allows light to travel from one end to the other by reflecting against the core-cladding boundary down the length of the filament. <\/span><\/p>\n

Total internal reflection<\/b> is the principle that characterizes this propagation of light. The transmission is very fast: about two-thirds the speed of light. <\/span><\/p>\n

\"Diagram
Reflection and Refraction of light through water<\/figcaption><\/figure>\n

299,792,458 m\/s (speed of light) x 2\/3 = 199,861,639 m\/s<\/b>
\n<\/b>
\nThe illustration above shows the principle of total internal reflection. Air has a refractive index of about 1.0027 (n2) and water has a refractive index of 1.333 (n1). This means that light travels 1.333 times slower in water than in a vacuum. Because air has a lower refractive index than water, light travels faster in air than in water. Total internal reflection works whenever a ray of light travels through a medium and hits the boundary of another medium with a lower refractive index at one of several angles that allow the light to be reflected back.<\/span><\/p>\n

\"Inside<\/a>
A multi-fiber cable<\/figcaption><\/figure>\n
\"Cross<\/a>
A cross section of the shore-end of a modern submarine communications cable. 1\u2013Polyethylene 2\u2013Mylar tape 3\u2013Stranded steel wires 4\u2013Aluminium water barrier 5\u2013Polycarbonate 6\u2013Copper or aluminium tube 7\u2013Petroleum jelly 8\u2013Optical fibers<\/figcaption><\/figure>\n

Fiber optic cable<\/b><\/a> refers to one or more fiber filaments encased in a protective jacket. Depending on where the cable will ultimately be installed, different types of insulation, a strength member, or tubing may be used to encase the cable. Fiber optic cables have many applications across industries. <\/span>Timbercon<\/span><\/a>, a fiber optic manufacturer, includes information on several industries that rely on fiber on their website:<\/span><\/p>\n