The Basics of Fiber Optic

Fiber Optic Basics The Basics of Fiber Optic

Getting Started in Fiber Optics

You need tools, test equipment and - most of all - training!

This guide will help you get started by providing very basic information (we will also point you to more advanced studies) and demonstrating that you don't need to break the bank to break into the field.

What is "Fiber Optics"? And a short history.

It's the communications technology that works by sending signals down hair thin strands of glass fiber (and sometimes plastic fiber.) It began about 30 years ago in the R&D labs (Corning, Bell Labs, ITT UK, etc.) and was first installed in Chicago, IL, USA in 1976. By the early 1980s, fiber networks connected the major cities on each coast.

By the mid-80s, fiber was replacing all the telco copper, microwave and satellite links. In the 90s, CATV discovered fiber and used it first to enhance the reliability of their networks, a big problem. Along the way, the discovered they could offer phone and Internet service on that same fiber and greatly enlarged their markets.

Computers and LANs started using fiber about the same time as the telcos. Industrial links were among the first as the noise immunity of fiber and its distance capability make it ideal for the factory floor. Mainframe storage networks came next, the predecessors of today's fiber SANs (storage area networks.)

Other applications developed too: aircraft, ship and automobile data busses, CCTV for security, even links for consumer digital stereo!

Today fiber optics is either the dominant medium or a logical choice for every communication system.

Which Fiber Optics?

Whenever you read an article or talk to someone about fiber optics, you need to know the point of view of the writer. Fiber optics, you see, is not all the same. Is the writer discussing "outside plant" fiber optics as used in telephone networks or CATV. Or is the article about "premises" fiber optics as found in buildings and campuses?

Just like "wire" which can mean lots of different things - power, security, HVAC, CCTV, LAN or telephone - fiber optics is not all the same. And this can be a big source of confusion to the novice. Lets define our terms.

Outside Plant (OSP)

Telephone companies, CATV and the Internet all use lots of fiber optics, most of which is outside buildings. It hangs from poles, is buried underground, pulled through conduit or is even submerged underwater. Most of it goes relatively long distances, from a few thousand feet to hundreds of miles

Outside plant installations are all singlemode fiber (we'll define the fiber types in the next chapter), and cables often have very high fiber counts, up to 288 fibers. Cable designs are optimized for resisting moisture and rodent damage. Installation requires special pullers or plows, and even trailers to carry giant spools of cable.

Long distances mean cables are spliced together, since cables are not longer than about 4 km (2.5 miles), and most splices are by fusion splicing. Connectors (SC, ST or FC styles) on factory made pigtails are spliced onto the end of the cable. After installation, every fiber and every splice is tested with an OTDR.

If this sounds like big bucks, you are right! The installer usually has a temperature controlled van or trailer for splicing and/or a bucket truck. Investments in fusion splicers and OTDRs can add up to over $100,000 alone.

Contractors doing outside plant work are few and far between. Most outside plant telephone installs are done by the telco themselves, while a small number of large, specialized installers do CATV work.

Premises Cabling

By contrast, premises cabling- cabling installed in a building or campus - involves short lengths, rarely longer than a few hundred feet, with 2 to 48 fibers per cable typically. The fiber is mostly multimode, except for the enlightened user who installs hybrid cable with both multimode and singlemode fibers.

Splicing is practically unknown in premises applications. Cables between buildings can be bought with double jackets, PE for outside plant protection over PVC for building applications requiring flame retardant cable jackets, so cables can be run continuously between buildings. Today's connectors often have lower loss than splices, and patch panels give more flexibility for moves, adds and changes.

Most connectors are ST style with a few SCs here and there. Termination is by installing connectors directly on the ends of the fibers, primarily using adhesive technology or occasionally some other variety of termination method. Testing is done by a source and meter, but every installer should have a flashlight type tracer to check fiber continuity and connection.

Unlike the outside plant technician, the premises cabler (who is often also installing the power cable and Cat 5 for LANs too!) probably has an investment of less