FIBER OPTICS

Benefits Of Fiber Over Copper

We provided this fiber optic basics page as a brief overview of how Fiber Optic Cable Advantages over Copper Cable as well as a resource for other fiber optic cable and technology developments and basics such as fiber optic cable design and WDM's or wave division multiplexing where you can get "more bandwidth for your buck" without adding additional fiber optic cable. Always feel free to come back to our site for additional information on fiber optic technology. We will also always be glad to help you with any questions you may have regarding fiber optics. Fiber optic cable functions as a "light guide," guiding the light introduced at one end of the cable through to the other end. The light source can either be a light-emitting diode (LED)) or a laser.The light source is pulsed on and off, and a light-sensitive receiver on the other end of the cable converts the pulses back into the digital ones and zeros of the original signal. Even laser light shining through a fiber optic cable is subject to loss of strength, primarily through dispersion and scattering of the light, within the cable itself. The faster the laser fluctuates, the greater the risk of dispersion. Light strengtheners, called repeaters, may be necessary to refresh the signal in certain applications. .

• SPEED: Fiber optic networks operate at high speeds - up into the gigabits
• BANDWIDTH: large carrying capacity
• DISTANCE: Signals can be transmitted further without needing to be "refreshed" or strengthened.
• RESISTANCE: Greater resistance to electromagnetic noise such as radios, motors or other nearby cables.
• MAINTENANCE: Fiber optic cables costs much less to maintain.

Installing Fiber Optic Cables in Buildings

The advantages of Optical Communications Systems for building applications are well recognized: expanded data handling capacity, electrical noise immunity, electrical isolation, plus enhanced safety and data security. Many large building projects have already used Fiber Optic components, a trend certain to continue.

Installing Fiber Optic Systems is, in many ways, similar to installing twisted-pair or coaxial cable. Despite common misconceptions, Fiber Optic Cables are quite easy to work with. They have excellent pull strength, even though they use glass fibers. Not only does their small size make them easier to pull than many copper cables, they have considerable resistance to crushing and cutting. Their flexibility makes them exceptionally easy to handle.

Fiber Optic Systems are relatively easy to install, and a quality Cable Assembly company such as Net Optics will ensure long-term system performance.

Interconnect Cable Description

Cables for interconnecting equipment are specially designed for Voice, Data and Video in Computer Process Control, Data Entry and Wired Office Systems. Available in one-fiber and two-fiber styles, these cables are optimized for ease of connectorization and use as "jumpers" for in-building distribution. Cables can be ordered for plenum or non-plenum environments.

Products include Single Fiber Cable, two-fiber Zipcord, two-fiber DIB, and Dual Subunit Cable. The less expensive two-fiber cable is better suited for longer distribution applications due to its smaller diameter, while the more impact-resistant DIB cable is recommended for equipment room use. Uncabled fiber, coated only with a thermoplastic buffer, is also available for pigtail applications inside equipment.

Features/Benefits:

* Small diameter and bend radius provide easy installation in space-constrained area.
* Allows for easy direct connectorization.
* Easily strippable jacket and fiber buffer.
* Available with 9/125um Singlemode or multimode 50/125um, 62.5/125um, and 100/140um fiber sizes.

Applications:

* Available with Type OFNR Listing (UL 1666) for riser applications or Type OFNP Listing (UL 910) for plenum applications.

Fibers and Cables

Fiber Optics is a technology in which signals are converted from electrical into optical signals, transmitted through a thin glass fiber, and reconverted into electrical signals. The basic optical fiber consists of two (2) concentric layers differing in optical properties, and a protective outer coating.

Core: the inner light-carrying member.
Cladding: the middle layer, which serves to confine the light to the core.
Buffer: the outer layer which serves as a "shock absorber" to protect the core and cladding from damage.

The concentric layers of an optical fiber include the light-carrying core, the cladding and the protective buffer.

Total Internal Reflection
Light injected into the core and striking the core-to-cladding interface at an angle greater than the critical angle will be reflected back into the core. Since angles of incidence and reflection are equal, the light ray continues to zigzag down the length of the fiber. The light is trapped within the core. Light striking the interface at less than the critical angle passes into the cladding and is lost.

Once light begins to reflect down a fiber it will continue to do so.

Rays of light do not travel randomly. They are channeled into modes, which are possible paths for a light ray traveling down the fiber. A fiber can support as few as one mode and as many as tens of thousands of modes. While we are normally not interested in modes per se, the number of modes in a fiber is significant because it helps determine the fibers bandwidth. More modes typically mean lower bandwidth. The reason is dispersion.

As a pulse of light travels through the fiber, it spreads out in time. While there are several reasons for such dispersion, two are of principal concern. The first is modal dispersion, which is caused by different path lengths followed by light rays as they bounce down the fiber. Some rays follow a more direct route than others. The second type of dispersion is material dispersion: different wavelengths of light travel at different speeds. By limiting the number of wavelengths of light, you limit the material dispersion.
Dispersion limits the bandwidth of the fiber. At high data rates, dispersion will allow pulses to overlap so that the receiver can no longer distinguish where one pulse begins and another ends.

Types of Fibers:
Singlemode or Multimode? In the simplest optical fiber, the relatively large core has uniform optical properties. Termed a step-index multimode fiber, this fiber supports thousands of modes and offers the highest dispersion - and hence the lowest bandwidth. By varying the optical properties of the core, the graded-index multimode fiber reduces dispersion and increases bandwidth. Grading makes light following longer paths travel slightly faster than light following a shorter path. Put another way, light traveling straight down the core without reflecting travels slowest. The net result is that the light does not spread out nearly as much. Nearly all multimode fibers used in networking and data communications have a graded index.

The structure of the fiber determines how the light propagates through it.

But the ultimate in high-bandwidth, low-loss performance is singlemode fiber. Here the core is so small that only a single mode of light is supported. The bandwidth of a singlemode fiber far surpasses the capabilities of today's network electronics. Indeed, the information-carrying capacity of the fiber is essentially infinite. Not only can the fiber support speeds of tens of gigabits per second, it can carry many gigabit channels simultaneously. This is done by having each channel carried by a different wavelength of light. The wavelengths do not interfere with one another. Singlemode fiber is the preferred medium for long distance telecommunications. It finds use in networks for interbuilding runs and will eventually become popular for high-speed backbones.
Applications for singlemode fiber to the desk are not anticipated.

The most popular fiber for networking is the 62.5/125 multimode fiber. The numbers mean that the core diameter is 62.5 micrometer and the cladding is 125 micrometer. Other common sizes recognized by building-cabling standards include 50/125, 100/140, and 200/230 micrometer, although these are declining in use.

Fiber Properties
Numerical aperture (NA) of the fiber defines which light will be propagated and which will not. NA defines the light-gathering ability of the fiber. Imagine a cone coming from the core. Light entering the core from within this cone will be propagated by total internal reflection. Light entering from outside the cone will not be propagated.

A high NA gathers more light, but lowers the bandwidth. A lower NA increases bandwidth.

NA has an important consequence. A large NA makes it easier to inject more light into a fiber, while a small NA tends to give the fiber a higher bandwidth. A large NA allows greater modal dispersion by allowing more modes in which light can travel. A smaller NA reduces dispersion by limiting the number of modes.

Bandwidth: Fiber bandwidth is given in MHz-km. A product of frequency and distance, bandwidth scales with distance: if you half the distance, you double the frequency. If you double the distance, you half the frequency. What does this mean in premises cabling? For a 100-meter run (as allowed for twisted pair cable), the bandwidth for 62.5/125-micrometer fiber is 1600 MHz at 850 nm and 5000 MHz at 1300 nm. For the 2-km spans allowed for most fiber networks, bandwidth is 80 MHz at 850 nm and 250 Mhz at 1300 nm. With singlemode fibers, the bandwidth for a 100-meter run is about 888 GHz.

Note: The bandwidth of a singlemode fiber is essentially infinite in that it surpasses the ability of today's electronics to exploit its capabilities.

Attenuation: Attenuation is loss of power. During transit, light pulses lose some of their energy. Attenuation for a fiber is specified in decibels per kilometer (dB/km). For commercially available fibers, attenuation ranges from approximately 0.5 dB/km for singlemode fibers to 1000 dB/km for large-core plastic fibers.
The wavelength of transmitted light should match fiber's low-loss regions at 850, 1300, and 1550nm.

Attenuation varies with the wavelength of light. There are three low-loss "windows" of interest: 850 nm, 1300 nm, and 1550 nm. The 850-nm window is perhaps the most widely used because 850-nm devices are inexpensive. The 1300nm window offers lower loss, but at a modest increase in cost for LEDs. The 1550nm window today is mainly of interest to long-distance telecommunications applications.

Cables The fiber, of course, must be cabled - enclosed within a protective structure. This usually includes strength members and an outer jacket. The most common strength member is Kevlar aramid yarn, which adds mechanical strength. During and after installation, strength members provide crush resistance and handle the tensile stresses applied to the cable so that the fiber is not damaged. Steel and fiberglass rods are also used as strength members in multifiber bundles.

The jacket protects against abrasion, oil, solvents, and other contaminates. The jacket usually defines the cable's duty and flammability rating. Heavy-duty cables have thicker, tougher jackets than light-duty cables. Equally important in a building is the cable's flammability rating. The NEC (National Electrical Code) establishes flame ratings for cables, while Underwriter's Laboratories has developed procedures for testing cables. The NEC requires that all cables run through plenums (the air-handling space between walls, under floors, and above drop ceilings), must either be run in fireproof conduits, or be constructed of low-smoke and fire-retardant materials. For building use, there are three categories of cables:

Plenum cables can be installed in plenums without the use of conduit. Meeting specific requirements for flammability and smoke generation, these cables are termed OFNP (optical fiber nonconductive plenum).

Riser cables can be used in vertical passages connecting one floor to another. These cables are termed OFNR (optical fiber nonconductive riser).

General-use cables cannot be used in riser or plenum applications without fireproof conduits. These cables are rated OFN (optical fiber nonconductive). OFN cables can be used in offices space - to connect from a wall jack to a computer, for example. A typical cable for premises applications includes the fiber, strength members, and jacket.

Bending Effects
So far we assume that the fiber is straight, but in any real application, it will bend around corners. In practice, fiber bends are gradual relative to the diameter of a typical step-index fiber core. Larger-core fibers are more rigid and have larger minimum bend radius.
To see how a bend can change transmission, recall the simple ray model of transmission and look at figure (doc.2007).

When light rays strike a bend in the fiber, those in higher-order modes can leak out if they hit the side of the fiber at an angle beyond the critical angle 0c. That increases the loss in the fiber. Lower-order modes are not likely to leak out, but they can be transformed into higher-order modes, which can leak out further along the fiber at the next bend. The bends need not be large to cause losses in the fiber. Indeed, the most serious bending losses in multimode fibers come from microbending, which causes tiny kinks. Typical bend radii should not be less than 2 inches in diameter.

Why Fiber?
The time for considering optical fiber as the main cabling medium for building cabling has finally arrived. No longer should fiber be considered an alternative to copper used only for applications with special requirements. Fiber is clearly superior in performance and is now competitive in price with the high-end twisted pair cable required for today's high-speed networks. Twisted pair cable is the most prevalent type of cable used in wiring new buildings.

These cables come in several grades based on performance: Category 3 for applications to 16 MHz, Category 4 for applications to 20 MHz, and Category 5 for applications to 100 MHz. Each supports cable runs of up to 100 meters. A standard fiber optic cable for building use can handle applications of several hundred megahertz at distances in excess of 2000 meters. As will be discussed, Category 5 cable, the cable required for emerging high-speed applications like asynchronous transfer mode (ATM) and 100Mbps Ethernet present some challenges in installation and operation.

The bottom line in the fiber versus copper debate is this: fiber has a performance edge. Copper, on the other hand, is a more widely understood and accepted technology. More important, the costs of fiber components are competitive with their copper counterparts. And if you add life cycle costs, including the costs of downtime and possible obsolescence, fiber is the better value. The Seven Advantages of Fiber optics would not even be considered if it did not offer distinct advantages over traditional copper media. Information-carrying capacity.

Fiber offers bandwidth well in excess of that required for today's network applications. The 62.5/125-micrometer fiber recommended for building use has a minimum bandwidth of 160 MHz-km (at a wavelength of 850 nm) or 500 MHz-km (at 1300 nm). Because bandwidth is a product of frequency and distance, the bandwidth at 100 meters is over 1 GHz. In comparison, Category 5 cable is specified only to 100 MHz over the same 100 meters.

With the high-performance singlemode cable used by the telephone industry for long distance telecommunications, the bandwidth is essentially infinite. That is, the information-carrying capacity of the fiber far exceeds the ability of today's electronics to exploit it. The bandwidth of optical fibers comfortably surpasses the needs of today's applications and gives room for growth tomorrow. Low loss. An optical fiber offers low power loss. Low loss permits longer transmission distances.
Again, the comparison with copper is important: in a network, the longest recommended copper distance is 100 meters; with fiber, it is 2000 meters. A principal drawback of copper cable is that loss increases with the signal frequency. This means high data rates tend to increase power loss and decrease practical transmission distances. With fiber, loss does not change with the signal frequency. Electromagnetic immunity.

By some estimates, 60% of all copper-based network outages are caused by cabling and cabling-related products. Crosstalk, impedance mismatches, EMI susceptibility are major factors in noise and errors in copper systems. What's more, such problems can increase with incorrectly installed Category 5 cable, which is more sensitive to poor installation than other twisted pair cable. Because a fiber is a dielectric, it is immune to electromagnetic interference. It does not cause crosstalk, which is a critical limiting factor for twisted pair cable. What's more, it can be run in electrically noisy environments, such as a factory floor, without concern since electrical noise will not affect fiber. There's no concern with proximity to noise sources like power lines or fluorescent lights. In short, fiber is inherently more reliable than copper. Light weight. Fiber optic cable weighs less than comparable copper cable.

A dual-fiber cable is 20% to 50% lighter than a comparable four-pair Category 5 cable. Lighter weight makes fiber easier to install. Smaller size. Fiber optic cable has a smaller cross section than the copper cables it replaces. Again, relative to Category 5 twisted pair cable, a duplex optical fiber takes up about 15% less space. Safety. Since the fiber is a dielectric, it does not present a spark hazard.

What's more, cables are available with the same flammability ratings as copper counterparts to meet code requirements in buildings. Security. Optical fibers are quite difficult to tap. Since they do not radiate electromagnetic energy, emissions cannot be intercepted. And physically tapping the fiber takes great skill to do undetected. Thus, the fiber is the most secure medium available for carrying sensitive data.

The summary: Fiber optics offers high bandwidth over greater distances with no danger of electrical interference. Its small size and lighter weight give it an installation edge for pulling and installing, especially in tight spaces. And it's safe and secure. Copper Fiber Multimode Singlemode Bandwidth (100 meters) 100 MHz 1 GHz > 100 GHz Transmission distance 100 meters 2000 meters 40,000 meters FCC EMI concerns Yes No EMI susceptibility Yes No Crosstalk Yes No Ground loop potential Yes No Weight Heavier Lighter Size Larger Smaller The Four Myths About Fiber Optics The clear advantages of fiber optics are too often obscured by concerns that may have been valid during the pioneering days of fiber, but that have since been answered by technical advances.
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