What is fibre for dummies?

While many of us have heard the term “fiber optics” or “optical fiber” technology to describe a type of cable or a technology using light, few of us really understand what it’s all about. Here we describe the basics about fiber optic technology, how to work with it, as well as its purpose, features, benefits, and what fiber optics are used for today.  We’ll explore answers to: How do fibre optics work? How do optical fibers work?  And, how does fiber optics work?

Discover more about NAI Group’s Cable Assemblies for Fiber Optics

Fiber optics, or optical fibers, are long, thin strands of carefully drawn glass about the diameter of a human hair. These strands are arranged in bundles called fiber optic cables. We rely on them to transmit light signals over long distances.

At the transmitting source, the light signals are encoded with data… the same data you see on the screen of a computer. So, the  fiber transmits “data” by light to a receiving end, where the light signal is decoded as data. Therefore, fiber optics is actually a transmission medium – a “pipe” to carry signals over long distances at very high speeds.

Fiber optic cables were originally developed in the 1950s for endoscopes. The purpose was to help doctors view the inside of a human patient without major surgery. In the 1960s, telephone engineers found a way to use the same technology to transmit and receive telephone calls at the “speed of light”. That is about 186,000 miles per second in a vacuum, but slows to about two-thirds of this speed in a cable.  So, what are fiber optics used for?  In a nutshell, for signal transmission, communication and vision (video).

Light travels down a fiber optic cable by bouncing off the walls of the cable repeatedly. Each light particle (photon) bounces down the pipe with continued internal mirror-like reflection.

The light beam travels down the core of the cable. The core is the middle of the cable and the glass structure. The cladding is another layer of glass wrapped around the core. Cladding is there to keep the light signals inside the core.

There are many types of fiber optic cables, often that end up in fiber optic cable assemblies to execute their function.

Fiber optic cables carry light signals in modes. A mode is a path that the light beam follows when traveling down the fiber. There are single mode and multimode fiber cables.

Single mode fiber is the simplest structure. It contains a very thin core, and all signals travel straight down the middle without bouncing off the edges. Single mode fiber optic cables are typically used for CATV, Internet, and telephone applications, where the signals are carried by single mode fibers wrapped into a bundle.

Multimode fiber is the other type of fiber optic cable. It is about 10 times larger than a single mode cable. The light beams can travel though the core by following a variety of different paths, or in multiple different modes. These cable types can only send data over short distances. Therefore, they are used, among other applications, for interconnecting computer networks.

There are four types of multimode fiber optic cables, identified by “OM” (optical multimode). An industry association  designated them as OM1, OM2, OM3 and OM4. They are described by ISO/IEC 11801. OM4’s standard was approved by TIA/EIA 492AAAD. Each OM has a minimum Modal Bandwidth requirement.

In addition, fiber optic cables can be made to comply with industry standard requirements for installation in air plenums. These are used inside buildings with special materials and compounds for jacketing. Called “plenum cables,” these meet flame and toxicity requirements in the event of fire.

Simplex fiber optic cable constructions contain a single strand of glass. Most often, simplex fiber is used where only a single transmit and/or receive line is required between devices or when a multiplex data signal is used (bi-directional communication over a single fiber).

A duplex fiber cable consists of two strands of glass or plastic

fiber. Typically found in a “zipcord” construction format, this cable is most often used for duplex communication between devices where a separate transmit and receive are required.

Besides plenum cable constructions, fiber optic cable assembly manufacturers create:

Shorter “patch cables” or “fiber jumpers” are used to interconnect various pieces of electronic equipment in a server room, telco closet or data center.

What are optical fibers used for?  You may have seen plastic fibers carrying colored lights in decorative applications. What you may not have seen are the real glass fiber optic cables that are now the foundation of our communication and computer networks. Many thousands of miles of installed fiber optic cable carry many types of information underground, in tunnels, building walls, ceilings, and other places you don’t see. For examples of uses of optical fiber in our daily life include applications such as:

An optical fiber is a flexible, transparent fiber made of very pure glass (silica) not much wider than a human hair that acts as a waveguide, or “light pipe“, to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics.

Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communication. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers.

An optical fiber junction box. The yellow cables are single mode fibers, the orange and blue cables are multi-mode fibers : 50/125 µm OM2 and 50/125 µm OM3 fibers respectively. Fibers that support many propagation paths or transverse modes are called multi-mode fibers (MMF), while those that only support a single mode are called single-mode fibers (SMF).

Single-mode fibers are used for most communication links longer than 1,050 meters (3,440 ft). Joining lengths of optical fiber is more complex than joining electrical wire or cable. Special optical fiber connectors for removable connections are also available. Fiber optics, though used extensively in the modern world, is a fairly simple and old technology. Tyndall also wrote about the property of total internal reflection in an introductory book about the nature of light in 1870: “When the light passes from air into water, the refracted ray is bent towards the perpendicular. When the ray passes from water to air it is bent from the perpendicular. The angle which marks the limit where total reflection begins is called the limiting angle of the medium. Unpigmented human hairs have also been shown to act as an optical fiber.

In 1952, physicist Narinder Singh Kapany conducted experiments that led to the invention of optical fiber. Modern optical fibers, where the glass fiber is coated with a transparent cladding to offer a more suitable refractive index, appeared later in the decade. Development then focused on fiber bundles for image transmission. The first fiber optic semi-flexible gastroscope was patented by Basil Hirschowitz, C. Wilbur Peters, and Lawrence E. Curtiss, researchers at the University of Michigan, in 1956.

In the process of developing the gastroscope, Curtiss produced the first glass-clad fibers; previous optical fibers had relied on air or impractical oils and waxes as the low-index cladding material. In the late 19th and early 20th centuries, light was guided through bent glass rods to illuminate body cavities. Alexander Graham Bell invented a ‘Photophone’ to transmit voice signals over an optical beam.

Jun-ichi Nishizawa, a Japanese scientist at Tohoku University, also proposed the use of optical fibers for communications in 1963, as stated in his book published in 2004 in India. Nishizawa invented other technologies that contributed to the development of optical fiber communications, such as the graded-index optical fiber as a channel for transmitting light from semiconductor lasers. Charles K. Kao and George A. Hockham of the British company Standard Telephones and Cables (STC) were the first to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer (dB/km), making fibers a practical communication medium.

NASA used fiber optics in the television cameras sent to the moon. The crucial attenuation limit of 20 dB/km was first achieved in 1970, by researchers Robert D. Maurer, Donald Keck, Peter C. Schultz, and Frank Zimar working for American glass maker Corning Glass Works, now Corning Incorporated. They demonstrated a fiber with 17 dB/km attenuation by doping silica glass with titanium. In 1981, General Electric produced fused quartz ingots that could be drawn into fiber optic strands 25 miles (40 km) long.

Attenuation in modern optical cables is far less than in electrical copper cables, leading to long-haul fiber connections with repeater distances of 70–150 kilometers (43–93 mi). The erbium-doped fiber amplifier, which reduced the cost of long-distance fiber systems by reducing or eliminating optical-electrical-optical repeaters, was co-developed by teams led by David N. Payne of the University of Southampton and Emmanuel Desurvire at Bell Labs in 1986.

Robust modern optical fiber uses glass for both core and sheath, and is therefore less prone to aging. The emerging field of photonic crystals led to the development in 1991 of photonic-crystal fiber, which guides light by diffraction from a periodic structure, rather than by total internal reflection. The first photonic crystal fibers became commercially available in 2000. Photonic crystal fibers can carry higher power than conventional fibers and their wavelength-dependent properties can be manipulated to improve performance.

It is especially advantageous for long-distance communications, because light propagates through the fiber with little attenuation compared to electrical cables. Each fiber can carry many independent channels, each using a different wavelength of light (wavelength-division multiplexing (WDM)). The net data rate (data rate without overhead bytes) per fiber is the per-channel data rate reduced by the FEC overhead, multiplied by the number of channels (usually up to eighty in commercial dense WDM systems as of 2008).

The current laboratory fiber optic data rate record, held by Bell Labs inVillarceaux,France, is multiplexing 155 channels, each carrying 100 Gbit/s over a 7000 km fiber. Nippon Telegraph and Telephone Corporation have also managed 69.1 Tbit/s over a single 240 km fiber (multiplexing 432 channels, equating to 171 Gbit/s per channel). For short distance applications, such as a network in an office building, fiber-optic cabling can save space in cable ducts.

LED Lights:

Simple battery powered on/of lights like these floralights which come in variety of colors are a good option for very basic fiber optic illumination. Their shape makes them easy to attach to a bundle of fibers (or a single large fiber) using just heat shrink tubing and glue. There are a lot of pre-packaged lighting options like this available that can provide simple and beautiful illumination to your fiber optic project.

Programable LEDs:

To take full advantage of the dynamic lighting possibilities of fiber optics, however, you really need programable lighting, or at least a light source that has been pre-programmed.

One relatively simple way to do this is to use individually addressable RGB LEDs with a microcontroller. I am just barely beginning to learn Arduino programming, but even with a minimum of knowledge, it is fairly easy to find interesting lighting programs online and load them into your microcontroller. I talk about how I've done this in more detail in my Fiber Optic Fairy Wings Instructable, and there are many other great Instructables that go into much more detail about programing LEDs.

Another, even easier way to access some great lighting programs, is to buy a pre-programmed chip like the Cool Neon Driver I used in my LED skirt project and wire that to addressable LEDs. This will give you many different lighting patterns to choose from and can be controlled by a remote.

Pre-Made Fiber Optic Products:

You can also buy pre-made products that are designed to light fiber optics. Natalina made her dress and coat using a fiber optic whip that comes pre-assembled with a large bundle of fibers attached to a bright RGB LED with many pre-loaded programs. In many ways these whips are great products, but the battery life is not as good as it should be and the shape and size of the whip is not particularly well suited to wearables.