How Fiber Optic Cables Work.docx

HOW FIBER OPTIC CABLES WORK The Digital data is packaged in zeros and ones, also called “binary.” Everything you see when you surf the Web is the product of streams of binary information — like the dots and dashes of morse code. Transmitting that stream of binary data via light pulses is straightforward: a pulse means 1, no pulse represents 0.

Binary Pulse

BROADBANDNOW Fiber-optic cables are designed to transmit those pulses quickly over long distances. The inside of a fiber-optic cable is packed with optical fibers made of glass, each about as thick as a human hair. Light particles that enter one end of an individual fiber exit at the other side. A transmitter at one end of the fiber transmits light pulses as ultra-fast LED or laser pulses. A single flash can travel as far as 60 miles before it begins to degrade. [4] This is possible because of a light phenomena called “total internal reflection.” Below a critical angle, light particles “bounce” within the fiber, like a marble dropped down a long pipe. Each fiber is

wrapped in a layer of glass or plastic “cladding” that has a lower optical density than the core fiber, causing total internal reflection to occur where they meet.

Fiber total internal reflection

BROADBANDNOW When light pulses reach the end of the fiber a receiver translates them back into binary data.

ANATOMY OF A FIBER-OPTIC CABLE Individual optical fibers are surrounded by several layers of material that strengthen, protect, and help keep light from escaping.

Single Optical Fiber

BROADBANDNOW A typical fiber-optic cable is packed with dozens to hundreds of individual optical fibers, allowing a high volume of data to travel over a single connection.

SINGLE-MODE VS MULTIMODE There are two types of optical fiber: single-mode and multimode. Single-mode has a smaller core and carries laser diode transmissions over large distances. Multimode transmits LED light through a bigger core, where light “bounces” in multiple paths over shorter distances.

Multimode is significantly cheaper than single-mode, making it common for shorter distances within city networks.

Single-Mode fiber vs Multimode fiber

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CABLE CONSTRUCTION: RIBBON VS LOOSE TUBE Complete fiber-optic cables come in two basic varieties: ribbon and loose tube.

Ribbon is cheaper and packs fibers more closely, while loose tube offers more padding and protection against the elements. There are many different sizes and varieties of cables available in either type, but the concept is always the same: bundles of fibers wrapped in protective material. Note that these examples are not representative of all cable products — there will be less or more protective layers based on application purpose, and the number of fibers contained in a cable can be anywhere from two to several hundred.

Cable Construction: Ribbon

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Cable Construction: Loose Tube

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FIBER-OPTIC CABLES ARE COLOR CODED When all the fibers within a cable are of the same type, the cable’s outer layer will be color-coded accordingly. Additionally, individual bundles of fiber within the cable are color-coded so installers can identify which interior bundles to connect when splicing cables together. [5]

Color coded fiber-optic cables

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SIMPLEX VS DUPLEX Fiber-optic connections usually go two ways, so cables are sold in two packaging styles: simplex and duplex.

Simplex vs Duplex

BROADBANDNOW Duplex cables include two separate fiber-optic cables connected by the outer coating, with two entry/exits on either end. Data only flows in one direction on either cable, making them a good fit for high-traffic connections like backbone ports, fiber switches and servers.

DARK FIBER Cables are often installed with additional unused fibers. These “dark fibers” can be lit up in the future if more capacity is needed. This makes fiber-optic networks highly scalable compared to DSL or coaxial cable, allowing a network to easily grow without burying additional cables.

COMPONENTS OF A FIBER-OPTIC NETWORK

Components of a fiber-optic network

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Fiber-optic cable: Cable that carries data as light pulses from one place to another. Transmitter: Device that translates digital signal into light pulses and sends them through a fiber-optic cable. Some transmitters can send multiple signals simultaneously using different wavelengths (colors) of light, multiplying the capacity of a single optical fiber. This technique is called Wavelength Division Multiplexing (WDM). Receiver: Device that translates light pulses into digital signal for delivery to a digital device. When WDM is used, the receiver is designed to translate multiple wavelengths from a single optical fiber. Amplifier: Device that amplifies light signals within a fiber-optic network. Amplifiers are used when the cable is too long for a single pulse to reach the other end undiminished — for example, connections between cities, or submarine cables connecting continents. [6]

Note that transmitters/receivers are often contained in the same product — called a transceiver — since data will usually go both ways on a simplex fiber-optic cable.

CONNECTION TYPES Companies that sell fiber broadband often describe themselves as "100% fiber networks". That term is misleading because there are several tiers of fiber broadband service recognized by the FCC, and most of them switch to coaxial or ethernet cable at some point between the ISP office and your modem jack. [7]

Fiber Connection Types

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IMPLEMENTATION CHALLENGES HIGH COST

The biggest challenge to the growth of fiber broadband in the US is the high cost of installing it. The FCC recognizes the high cost of laying cable as a “substantial barrier” to broadband infrastructure growth in the US. [8] Cities like Chattanooga with taxpayer-funded municipal broadband cite price tags in the hundreds of millions. [9] Analysts estimate the cost of Google Fiber’s nationwide expansion plan to be $3,000–$8,000 per home. [10]

HIGH COMPETITION

The increased viability of services like fixed wireless for “last mile” could cut into the market for highspeed cable alternatives. Companies like Starry Wireless are currently experimenting with urban wireless service that could rival wired broadband speeds.

LOBBYISTS AND POLITICS

Fiber is a common choice for cities that want to invest in municipal public broadband infrastructure. Unfortunately, complex state laws (many created under pressure from telecom lobbyists) often prohibit cities from installing their own fiber, on the grounds that it puts them in competition with private businesses. [11]

PROS AND CONS OF FIBER BROADBAND PROS

 Highly scalable Next-generation 1Gb speeds Resistant to electrical interference like storms that affect DSL, cable & wireless 

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CONS

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Expensive to install Speeds dramatically higher than average subscriber needs More fragile than coaxial cable