Fiber Optics 101- Understanding Fiber Cable
As projects involving HD video and other big data becomes the norm in the workplace, it’s quite possible you’ll hear your colleagues cursing the sluggish network and screaming, “DAMMIT JIM, I NEED MORE BANDWIDTH!” (Even if your name isn’t Jim…) With traditional Ethernet hobbled by bandwidth and distance limitations, the next step towards blazing network speeds of 10 Gbps and higher is to consider adding fiber optic cable to your network.
Made from high quality extruded glass or plastic and slightly thicker than a human hair, optical fiber is often referred to as “light pipe.” Quite literally, the glass or plastic fibers in the cable transmit light pulses representing digital signals between the two ends. Fiber optic cable allows for transmission over longer distances and at higher bandwidths than old school copper wiring. Plus, the light pulses travel along with less loss of signal and are immune to electromagnetic interference. These reasons alone make fiber optic cable a worthy successor to ethernet.
There are two categories of fiber optic cable. The fiber cable used by the pros — those guys who lay pipe outside for the telcos like Verizon and Telus — is very different from the consumer fiber now available for use in your office network. For our purposes, we’ll be mainly focussing on the consumer types.
So, without much further ado, let’s get started on our quick Understanding Fiber Optic Cable tutorial:
Fiber Cable Parts
Fiber optics, as we’ve described, is transmitting light signals down hair-thin strands of glass or plastic fiber.
The center part of the fiber cable where the light signal travels is called the Core and around the core is an optical material called the Cladding. The cladding’s job is to contain the light in the core using an optical technique called total internal reflection. Both the core and cladding are usually made of ultra pristine glass, although some fibers are all plastic or do a glass core with plastic cladding.
A layer of plastic covering called the Buffer strengthens the cable and protects the core and cladding from moisture and other damage. An outside final layer of PVC or LSFH Polymer called the Jacket provides more protection and makes the cable more durable.
Multimode vs. Singlemode
The two most common types of fiber being used today are Multimode and Singlemode.
Multimode Fiber is just as it sounds —multi rays of light or modes travelling in the core of the cable. Multimode fibers generally feature a wider core diameter to accommodate all these rays (usually 50 or 62.5 microns).
Multiple light rays limits the effective transmission distance for multimode fiber and is therefore used for short distance communication links like in your office LAN or server room.
Singlemode Fiber has a much smaller core (only about 9 microns) and the light pulses travel in only one ray. Because of this focus on delivering one light signal, singlemode fiber is ideal for communication links longer than 1,000 meters (about 3,500 ft) and delivers faster speeds. It is mostly used by the telcos, institutions and the big players with the mega-bucks to run long stretches of fiber cable.
Simplex vs. Duplex
Simplex Fiber cable consists of a single fiber and is used for applications that require only one-way data transfer. Think of a monitor at a remote site that transmits data one way back to the office. Simplex fiber is available in singlemode and multimode options.
Duplex Fiber cable consists of two fibers and allows for simultaneous, two directional data transfer. Also available in singlemode and multimode, it’s ideal for the office network, fiber switches and servers, etc.
When you see specs like 50/125 or 62.5/125 used to describe fiber cable, it’s referring to the size.
The first number in the sequence refers to the size of the core—the second to the size of the cladding. The most common size for multimode fiber is 62.5/125, meaning the core is 62.5 microns in size with a 125 micron cladding. This is pretty much industry standard, although another size, 50/125, is making a resurgence. 50/125 is better for 10 Gigabit networks, offering higher bandwidth and greater distances than the 62.5/125 standard.
For singlemode fiber, with only one ray of light to transmit, the standard size is 8 or 9 microns for the core and 125 microns for the cladding.
Alert: Do not attempt to mix and match fiber types or sizes. Connecting singlemode to multimode fiber can cause you to lose up to a 99% of the power. Even connections between 62.5/125 and 50/125 can cause you to lose half your signal power.
Fiber Cable Design
Inside or outside? Buried to cover a long distance or just a patch cord for the server room? Depending on your specific needs, there are different designs for fiber cables.
Loose Tube — Designed for outdoor use, Loose Tube has a gel fill in the cable to protect the fibers from water. Loose Tube offers a high fiber count, packing several fibers together inside a small plastic tube and then covered with a strengthening jacket. Armored fiber cable, a variation of Loose Tube, can be buried underground and features metal armouring that will protect the fiber from pesky gnawing rodents.
Distribution Cables — Also referred to as Tight Buffered Fibers, here the optic fibers are bundled together under the same jacket with the buffering material in direct contact with the fiber. The tight-buffered design provides a rugged cable structure to protect individual fibers during handling and connection. Suited for jumper cables, Tight Buffered cables are used for short conduit runs throughout an office or factory.
Terminating fiber cable must be done carefully and with precision in order to align the glass fibers perfectly, ensure a strong signal and minimize the loss of light pulses. For that reason, a ton of work has gone into developing connectors for fiber cable. Did we say a ton? How about upwards of 80 different connectors! Even with this many options, fiber cable connectors all share similar design characteristics and consist of three major components — the ferrule, the connector body and the coupling mechanism.
The Ferrule is a thin structure, most often cylindrical, that holds the glass fiber. It’s usually made from ceramic, metal or plastic and features a hollowed-out center that forms a tight grip on the fiber. The Connector Body is the plastic or metal structure attached to the jacket that holds the ferrule and strengthens members of the fiber cable itself. The Coupling Mechanism is the part that holds the connector in place when it’s attached to another device such as a switch, panel, etc. Options here include a latch clip or a bayonet-style nut.
Below are few of the most commonly used fiber cable connectors:
The most popular connector for multimode fiber networks, the ST or Straight Tip connector looks a bit like a heavy duty coax cable with a “twist-on/twist-off” bayonet mount, a 2.5mm ferrule and a long cylindrical ceramic, plastic or metal ring to hold the fiber. Popular for many years, the ST connector is now slowly being replaced with less clunky options.
SC is a squarish snap-in connector usually held together with plastic clips. It too uses a round 2.5mm ferrule to hold a single fiber and delivers excellent performance. Widely used in singlemode systems, it consists of a snap-in connector that latches with a simple push-pull motion.
FC or the Fixed Connector, once considered the standard for fiber optic connection, is slowly being replaced by SC and LC connectors. Incorporating a threaded barrel housing that you screw on firmly, FC is typical for singlemode applications and was designed for use in high-vibration environments.
Part of the Small Form Factor family (SFF) of connectors developed to make fiber connectors smaller and more conducive to a server rack/room, LC or the Lucent Connector (can you guess who invented it?) is similar to the SC connector, only it uses a smaller 1.25 mm ceramic ferrule. It is easily terminated using a retaining tab mechanism, similar to a phone or RJ45 connector.
Another popular SFF connector, MT-RJ stands for Mechanical Transfer-Registered Jack. It is a duplex connector that closely resembles an RJ-style modular plug. Consisting of two fibers in a single plastic ferrule and body, it locks into place with a tab just like an RJ-style plug.
The jacket on fiber optic patchcords is often color coded in order to make it easy to identify the type of fiber being used.
- Yellow – Singlemode optical fiber
- Orange – Multimode optical fiber
- Aqua – 10 Gbps laser-optimized 50/125 micrometer multimode optical fiber
- Blue – Polarization-maintaining optical fiber
4XEM specializes in 10GBps Aqua multimode fiber optic cable, delivering extremely high speed data transmissions. Laser optimized and made from quality materials, 4XEM fiber is ideal for the office network and makes a blazingly fast and dependable link in the server room. All of our fiber currently sports LC Connectors and comes in lengths ranging from 1 to 10 meters.