Topic: Fiber Optics: Basic Overview
Fiber optics refers to the technology of transmitting light down thin strands of highly transparent material, usually glass but sometimes plastic. Fiber optics is used in communications, lighting, medicine, optical inspections and to make sensors. The FOA is primarily interested in communications fiber optics, so this book will focus on that application.
Which Fiber Optics?
Whenever you read an article or talk to someone about fiber optics, you need to know the point of view. We're mainly concerned with communications fiber optics, but it's also used in medical or nondestructive testing inspection and lighting. Fiber optics, you see, is not all the same.
Even in communications, we have "outside plant" fiber optics as used in telephone networks, CATV, metropolitan networks, utilities, etc. or "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, virtually all of which is singlemode fiber and 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 hundred feet to hundreds of miles.
Outside plant cables often have very high fiber counts, up to 288 fibers or more. Cable designs are optimized for the application: cables in conduit for pulling tension and resisting moisture, buried cables for resisting moisture and rodent damage, aerial for continuous tension and extreme weather and undersea for resisting moisture penetration. Installation requires special equipment like pullers or plows, and even trailers to carry giant spools of cable.
Long distances mean cables are spliced together, since cables are not manufactured in lengths longer than about 4-5 km (2.5-3 miles), and most splices are by fusion splicing. Connectors (generally SC or LC 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 expensive, you are right! The installer usually has a temperature controlled van or trailer for splicing and/or a bucket truck. Investments in fusion splicers, OTDRs and other equipment can be quite expensive.
Most outside plant telephone installs are done by the telco themselves, while a small number of large, specialized installers do CATV, utility and municipal work.
By contrast, premises cabling- cabling installed in a building or campus - involves shorter lengths, rarely longer than a few hundred feet, typically with fewer fibers per cable. The fiber is mostly multimode, except for the enlightened user who installs hybrid cable with both multimode and singlemode fibers for future high bandwidth applications.
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 SC or ST style with LCs becoming more popular. Termination is by installing connectors directly on the ends of the fibers, primarily using adhesive or sometimes prepolished splice techniques. 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 cable installer (who is often also installing the power cable and Cat 5/6 for LANs too!) probably has an investment of less than $2,000 in tools and test equipment.
There are thousands of cabling installers who do fiber optic work. They've found out it isn't "rocket science," and their small initial investment in training, tools and test equipment is rapidly paid back.
Few installers do both outside plant and premises cabling. The companies that do are usually very large and often have separate divisions doing each with different personnel. Most contractors do nothing but premises cabling.
Fiber vs Copper
Where to Get Training?
Well, you can start right here at the FOA, of course! This reference guide is designed to get you started and you should have "hands-on" training leading to a recognized certification program like the FOA CFOT to be qualified to install fiber. Check the website of the Fiber Optic Association at http://www.TheFOA.org. for the leading fiber optic certification program in the industry. Finally, take advantage of the training offered by manufacturers and distributors whenever you can, often this training is free or cheap! (but limited to the manufacturer's equipment of course.)
More on standards.
Before we get started - Safety First!
You might think that eye damage from working with lasers would be the big concern in fiber optic installations. The reality is that high power lasers burning holes in metal or burning off warts mostly have little relevance to your typical fiber optic installation. Optical sources used in fiber optics are generally of much lower power levels (The exception is high power DWDM or CATV systems). Of course, you should always be careful with your eyes, especially when using a fiber optic microscope which can concentrate all the light from the fiber into your eye. NEVER look into a fiber unless you know no light is present - use a power meter to check it - and anyway, the light is in the infrared and you can't see anything anyway!
The real safety lecture will always be about small scraps of glass cleaved off the ends of the fibers being terminated or spliced. These scraps are very dangerous! The cleaved ends are extremely sharp and can easily penetrate your skin. If they get into your eyes, they are very hard to flush out. Don't even think about what happens if you eat one. Always wear safety glasses whenever working with fiber and always carefully dispose of all fiber scraps!
Always follow these safety rules when working with fiber.
1. Always wear safety glasses to protect your eyes from fiber scraps.
2. Dispose of all scraps properly. Always use a properly marked container to dispose of later and work on a black pad which makes the slivers of glass easier to spot.
3. Do not drop them on the floor where they will stick in carpets or shoes and be carried elsewhere.
4. Do not eat or drink anywhere near the work area.
Fiber optic splicing and termination use various chemical adhesives and cleaners as part of the processes. Follow the instructions for use (detailed on the chemical's MSDS - material safety data sheet) carefully. Remember, even simple isopropyl alcohol, used as a cleaner, is flammable.
Read more about fiber optic safety. View the FOA YouTube Video on Safety. Download a safety poster.
Zero Tolerance for Dirt
With fiber optics, our tolerance to dirt is near zero. Airborne particles are about the size of the core of SM fiber- they absorb lots of light and may scratch connectors if not removed! Dirt on connectors is the biggest cause of scratches on polished connectors and high loss measurements!
1. Try to work in a clean area. Avoid working around heating outlets, as they blow dust all over you
2. Always keep dust caps on connectors, bulkhead splices, patch panels or anything else that is going to have a connection made with it.
3. Use special fiber optic cleaners or lint free pads and isopropyl alcohol to clean the connectors.
4. Ferrules on the connectors/cables used for testing will get dirty by scraping off the material of the alignment sleeve in the splice bushing - creating an attenuator. You can see the front edge of the connector ferrule getting black! Use the metal or ceramic alignment sleeve bulkheads only for testing.
Read more about cleaning fiber optic components.
Test Your Comprehension
Table of Contents: The FOA Reference Guide To Fiber Optics