Introduction to Fiber Optic Cable

A Brief History of Fiber Optics

 Fiber Optics involves the transmission of communications signals over thin strands of glass or plastic.  This technology is not really new since the concept was originally formulated over a century ago and has been in commercial use for at least twenty-five years.  The first commercial fiber optic installation was for a telephone system in Chicago in 1976. By the early 1980s, the first long distance telephone fiber optics networks were operational. By the mid-1980’s, most of the modern, basic fiber technology was developed and began to be installed in the communications grid that now handles virtually all long distance telecommunications.

 The Technological Advantage of Fiber Optics

 A tiny strand of optical fiber can carry more communications signals over longer distances than a copper cable ten times its width.  For example, a copper-based communications cable with about 1000 pairs of conductors can only carry about 24 telephone conversations a distance of less than 3 miles.  A significantly thinner fiber cable can carry more than 32,000 conversations hundreds or even thousands of miles before it needs assistance in the form of signal regeneration. Beyond that, each fiber can simultaneously carry over 150 times more data by transmitting at different wavelengths of light, if desired.

Because of these technological issues, the cost of transmitting a single phone conversation over copper wire work is about 100 times more than the cost of transmitting it over fiber! That’s why fiber has become the transmission line of choice for long distance communications.

 Fiber Optics Applications

 Fiber optics are used in many non-communications applications, including lighting, signs, sensors and visual inspection (medicine and non-destructive testing).  Most people have probably seen at least a fiber optic Christmas tree or other lighting fixture that uses these versatile and flexible strand of glass.

 However, the focus of this introduction to fiber optics is on data communications applications, including telephony, cable TV, Internet connections, local area networks, industrial communications and control, closed circuit video monitoring, alarm and intrusion sensors and multiple other uses, including significant dependence by the military on this technology.

Fiber optics technology has made significant inroads into many of these applications and are known to be in over 50% of all local telephone systems, over 90% of all long distance telephone systems, the majority of cable TV networks, many video surveillance networks, and most computer network backbones.  While fiber optics technology has not yet become the dominant cable in desktop connections for LANs, as the cost of fiber continues to come down and the cost of copper as a raw material continues to rise based upon increased demand from developing countries, it is assumed by many that eventually fiber will come to play a dominant role networking desktops, as well.

The Benefits of Fiber Optics

•         Lower Overall Costs

•         Faster Data Speeds

•         Longer Transmission Distances

•         Lower Weight

•         Smaller Physical Size

•         No Electromagnetic Radiation Interference

•         Electrical Isolation

•         Improved Security

Quite simply, optical fiber can transmit more information over longer distances and in less time than any other data transport medium.  Further, electromagnetic radiation interference (the bane of copper wire cabling) does not affect fiber optic wire which makes it possible to transmit information and data with less noise and less errors thereby resulting in faster and more successful data transmissions. Fiber strands are also much lighter and take up less space than copper wires and that makes it more suitable for aircraft, automotive, and other applications in which weight and/or size is a concern.

Bottomline: Fiber Optical Networking is the least expensive and most reliable method for high speed and/or long distance communications and, just as important, we are only now scratching the surface in utilizing the potential bandwidth of fiber.  For example, while most networks today rely on gigahertz speeds, the singlemode fiber used in telecommunications and cable TV has a bandwidth of greater than a terahertz. Standard systems today can carry up to 64 channels of 10 gigabit signals - each at a unique wavelength and the future for increased transmission levels is quite bright.

Fiber Optics:  Premises Wiring versus Outside Plant Wiring

From an environmental perspective, there are two main types of fiber optics applications.. “Outside Plant Wiring” (OPW) refers to fiber optics used outdoors in telephony, networking or cable TV applications. “Premises Wiring” (PW) fiber optics are basically used indoors.  Telephone companies, cable TV companies, Internet Service Providers  (ISP’s), traffic signal vendors/installer, and the military all use significant amounts of OPW, whether hanging from poles, buried underground, running through conduits or even submerged underwater. Most OPW is used over relatively long distances, from a few thousand feet to hundreds of miles.  By contrast, PW involves cables installed in buildings usually for LANs, telecom, industrial control or security systems. Premise Wiring involves shorter lengths, rarely longer than a few hundred to a couple of thousand feet, of mostly “multimode” fiber.  OPW, by the way, typically uses “singlemode” fiber to achieve the greater distances that it requires.  Both OPW and PW applications are unique in the components, the installation methods and the testing procedures that are used to install and maintain them, but they do share the basic principles of fiber optic data transmission.

Basics of Fiber Technology

Optical fiber is made up of a light carrying core surrounded by a cladding which traps the light in the core via of total internal reflection which is all protected by a buffer or insulation. Most optical fibers are made of glass, though some are made of plastic. The core and cladding are usually fused silica glass which is covered by a plastic coating called the buffer or primary buffer coating which protects the glass fiber from physical damage and moisture. Glass optical fibers are the most common type used in communication applications, though some specialized applications prefer plastic fiber strands.

In the above Reflection diagram, the fiber core is made from a material with a higher refractive index than the cladding which will cause the light in the core to be totally reflected at the boundary of the cladding for all light that strikes at greater than a critical angle (which is determined by the difference in the composition of the  materials used in the core and cladding.)  This is what allows fiber cables to transmit data, in the form of lightwaves, along a bending and twisting cable over miles of distance, if necessary.

Standard fiber optic transmission systems consist of a transmitter which converts an electrical input into an optical output using an LED or laser diode as its light source for the cable.. This light from the transmitter is coupled into the fiber with a fiber optic connector and is transmitted through the fiber optic cable.  At the other end of the cable, the light is then coupled via another connector to a receiver where a Photo-diode detector converts the light back into an electrical signal which is then conditioned properly for use by the receiving equipment.  Much like other forms of transmission (e.g., copper wire or radio), the ultimate performance of the fiber optic data link is determined by how closely the reconverted electrical signal out of the receiver matches the input to the transmitter.

 Fiber optic systems use infrared light (invisible to the human eye) for transmitting data because these wavelengths are especially well-suited for maximizing distance the data can travel in the optical fiber.  This is because the ultra-pure glass that is used in making optical fiber has less attenuation (signal loss) at wavelengths (colors) in the infrared range, which also happens to be beyond the limits of the sensitivity of the human eye. The optical fiber, therefore, has been designed and manufactured to have the highest performance at these wavelengths, which are shown in the diagram below.

The particular wavelengths used, 850, 1300 and 1550 nm, also correspond to wavelengths where optical light sources (lasers or LEDs) are easily manufactured.  Some advanced fiber optic systems transmit light at several wavelengths at once through a single optical fiber to increase data throughput. This method is called “wavelength division multiplexing.”

Wavelength division multiplexing is not all that complicates.  With human eyesight, one can see many different colors of light: red, green, yellow, blue, etc., all at the same time. These colors (wavelengths of light) can be transmitted through the air together and may even mix, but they can be easily separated using the human eye or even a simple device like a prism.  Prisms, you may recall, separate the "white" light from the sun into the spectrum of colors that make it up.  The input end of a WDM system is much like the sun in this regard.. It is a simple coupler that combines or multiplexes all of the signal inputs into one output fiber. The demultiplexer then separates the light at the end of the fiber. It shines the light on a “grating” which is a mirror-like device that looks like the data side of a CD and it separates the light into the different wavelengths by sending them off at different angles much like a prism would do. Optical devices then capture each wavelength and focus it into another strand of fiber, thereby creating separate outputs for each wavelength of light. Current fiber optic systems range from 4 to 32 channels for separate wavelengths.  When utilizing  a system with higher numbers of wavelengths, this technology is often referred to as “Dense” Wavelength Division Multiplexing or DWDM.

Fiber Optic Cabling

Fiber Optic Cables enclose up to one thousand optical fibers to protect them against various environmental conditions in which they must operate.  For example, cables installed in trays in buildings require less protection than buried underground or placed under water.  These cables will include strengthening features such as a strong synthetic fiber called aramid fiber (or the DuPont trade name “Kevlar”) which prevents the stress of pulling the cable from affecting the delicate optical fibers.

The outside of the cable is called the “jacket”. It is the ultimate protection for the optical fibers and will be designed to withstand any extremes of temperature, moisture and the potential stress of installation.  Certain specialty cables even have a layer of thin metal under the jacket to prevent rodents from chewing through the cable.

Fiber Optic Connectors

When an optical fiber is to be connected to another fiber or to optical equipment, it can be spliced permanently by “welding”  it at high temperatures or by applying special adhesives.   Or it can be terminated with a connector that makes it possible to handle the individual fiber without damage.   These connectors tightly align optical fibers to minimize how much light is lost during transmission.  Most connectors use ceramic cylinders (known as “ferrules”)  about 2.5 mm in diameter with precisely aligned holes in the center that accept the fiber. Most connectors use adhesive to attach the fiber and the end is polished to a smooth finish.  The most common types of connectors used in fiber optic patch cables are FC, LC, MTRJ, SC, and ST.

Fiber Optics Jobs

The fiber optics industry is growing rapidly and requires many skilled people to perform a variety of functions.  Each function or job has unique requirements and requires different educational backgrounds.

Fiber Optic Component Design is one job in the industry.  Most of those who design components have at least a undergraduate degree and for components such as  connectors, a relevant degree might be in mechanical engineering. Optical components such as the fibers, themselves, will require knowledge of both optics and materials, so college degrees in physics, chemistry or materials might be the most appropriate.  A background in solid-state physics would be helpful for designing the lasers and other such optical equipment.

Fiber Optic Manufacturing jobs, like any other manufacturing position, will have differing requirements depending on the technical nature of the job. Some may require manual dexterity and skills while others may require advanced technical education to understand the complicated manufacturing processes involved in fiber optics.

Designers of complete fiber optic systems are typically electronic engineers. In this case, fiber optic components are used in the same way that integrated circuits are used to develop communications systems.

Fiber optic cable installers must be trained and experienced in the process of pulling, splicing and terminating these delicate cables. This position requires more manual dexterity than many other jobs, as well a real understanding of how the systems work.

Workers who install telephone and cable TV fiber optic networks do much of their work outdoors. They may have to operate heavy equipment that dig trenches and lay and/or pull cables. Then they bring the ends of the cables into special trucks or trailers where lengths of cable are spliced together and tested. Outside plant installations require more hardware (and, therefore, more investment.) including pullers, splicers, OTDRs and even splicing vans to perform this job..

 On the other hand, computer and security networks also use fiber cabling which is installed inside buildings. For these installations, cables are typically pulled through conduits or laid in cable trays and then terminated near the equipment. Unlike the significant equipment required for outside installers, premises installers usually only require a termination kit for attaching connectors and a simple kit for testing the cable and connection.

 Fiber optics, like any fast-growing technology, needs more trained workers. Some of those workers are trained in high schools  and colleges, where general courses will prepare the potential worker for most any aspect of fiber optics. All of these programs need qualified teachers, so fiber optics training is also an important job in the industry.

 Conclusions

 The fiber optics cable industry is dynamic and fast-growing because it offer so many advantages over other data transmission methods.  As users’ data transmission requirements continue to grow at a breath-taking pace, the fiber optics industry is assured of a long and economically healthy growth for the foreseeable future.  It is an exciting time to be in this industry and NetCablesPlus is proud to play its small part by providing high quality, low-cost fiber optic cabling to a wide array of users.

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