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Fibre Optics Guide - Definition, Uses & FAQs | DesignSpark

Complete Guide to Fibre Optics

In this guide, we'll answer all the questions you might have regarding fibre optics, including:

  • What is fibre optics?
  • How does fibre optics work?
  • What are the advantages of fibre-optic cables?
  • What are fibre-optic cables used for?
  • Fibre optics FAQs

What is fibre optics?

Fibre optics is a technology that provides modern homes and businesses with a variety of communications services. It facilitates the transfer of data signals through pulses of light, allowing them to travel faster and over longer distances compared to other mediums.

Two key inventions make all of this happen: optical fibres and fibre-optic cables. We'll discuss them in more detail below and give an overview of the two main types of fibre-optic cable.

What is optical fibre?

Optical fibres are extremely thin threads of pure glass or plastic, roughly the same diameter as a strand of human hair. Optical fibres are made of either pure silica (glass) or polymethyl methacrylate (PMMA) – a transparent thermoplastic sometimes referred to as acrylic or acrylic glass.

What is a fibre-optic cable?

A fibre-optic cable is a type of network cable containing one or more optical fibres within multiple layers of casing. The typical fibre-optic cable is made up of three parts: core, cladding, and coating.

  1. The core: This is another name for the optical fibre itself i.e. the part of the cable that carries the light.
  2. The cladding: This is a layer that contains the core. It's made of a slightly different material, such that it keeps light inside the core and ensures it passes from one end of the optical fibre to the other.
  3. The coating: Standard fibre-optic cables have two final layers that protect the outer surface of the cladding from environmental hazards such as air, moisture, or chemical contaminants. Without the coating, exposure to the elements could cause flaws in the material and potentially lead to failure.

Fibre-optic cables allow engineers to create communications networks by running from hubs to various buildings such as homes, apartment blocks, and business premises. Additionally, many fibre-optic cables are installed to support communications between cities and even countries.

Types of fibre-optic cables

There are two main types of fibre-optic cables: single-mode and multimode.

  1. Single-mode cables: These are comprised of a single optical fibre with a thin diameter, usually made of glass. This type is typically used over longer distances.
  2. Multimode cables: Typically made of PMMA, multi-mode cables feature wider cores, capable of containing multiple beams of light at once. This makes them more suitable for applications requiring larger volumes of data.

So, we've learned about the main components of fibre optics, the essence of what they do and what they're made of. But how does this technology work?

How does fibre optics work?

Fibre optics works by transmitting data as beams of light through fibre-optic cables. Electrical signals are encoded into light signals, guided through a cable via a phenomenon known as total internal reflection, and then translated back into electrical signals at the other end.

In the most common types of fibre-optic transmission, electrical signals are encoded into optical signals using pulse code modulation. LEDs or lasers emit the light in a series of pulses at one end and photodetectors receive it at the other. The photodetectors measure the light intensity of each pulse in the series, translating the pulses into a stream of binary data as they do so.

Total internal reflection in fibre-optic cables

When a ray of light travelling through a medium reaches the boundary to another medium with a lower refractive index, it is either refracted, reflected or both. In a fibre-optic cable, the cladding has a lower refractive index than the core.

Now for every two mediums, there's a special angle called the critical angle. If the angle at which the light meets the boundary – called the angle of incidence – is greater than the critical angle, no refraction takes place. Instead, the light is totally reflected inside the first medium.

In fibre-optic cables, light is directed into the core in such a way that it hits the core-cladding boundary at a greater angle than the critical angle. This means that light bounces all the way from one end of the cable to the other.

How do different fibre-optic cables work?

Owing to the smaller core diameter of single-mode fibre-optic cables, light travelling through them typically undergoes fewer instances of reflection. Additionally, single-mode fibre optics interfaces tend to use lasers as a light source, which send a single wavelength of light through the core. These factors make single-mode fibre-optic cables better suited to sending data over long distances.

Multi-mode fibre-optic cables are wider and they typically use LEDs, which emit multiple wavelengths of light. The light beams follow a variety of different paths – usually referred to as 'modes'. These jagged travel paths result in a larger amount of signal dispersion – making multi-mode cables more suitable for short-distance applications.

What are the advantages of fibre-optic cables?

So, why use optical fibre instead of metal-based communication cables such as ethernet cables? Below are four of the most important advantages fibre-optic cables provide.

  • Faster transmission speeds: The speed of light is the fastest known to man. And while light travelling through optical fibre loses roughly 30% of its speed, it still transmits data at a far greater speed than any other type of cable.
  • Higher bandwidth: Compared to their predecessors, fibre-optic cables transfer more data per unit of time. Within the fibre optics, single-mode cables can deliver as much as twice the throughput as multimode cables.
  • Greater transmission distances: Fibre-optic cables can carry signals much farther than other communications cables. The rate at which they lose data signals – called attenuation – is significantly lower than with other cable-based forms of communication. In particular, single-mode fibre can transmit over longer distances than multi-mode.
  • Less interference: In metal cables, electromagnetic interference (EMI) causes errors and degrades the signal in cables individually. It also interferes with the performance of other cables nearby. Since fibre-optic cables are non-metallic and light doesn't carry an electromagnetic field, they aren't vulnerable to EMI.

What are fibre optic cables used for?

In general, fibre-optic cables are used for high-performance data communication over both short and long distances – primarily to provide internet, computer network, telephone, and cable television services.

Yet fibre-optic technology is also applied to many different purposes, such as in medicine, decorations and the automotive industry.

Some of the most popular uses of fibre-optic cables are listed below in detail.

Internet

Fibre-optic cables transmit large amounts of data at very high speeds. This technology is therefore widely used in internet cables, facilitating:

  • User downloads
  • Peer-to-peer transmissions
  • Audio and video streaming
  • Huge data transfers between data centres

The number of internet users worldwide is steadily increasing. And it's becoming increasingly common for individual households, and even individual users, to connect multiple devices at the same time.

Optical fibre helps meet this demand, with its higher bandwidth and faster transmission speeds offering users faster download speeds and more reliable connections.

Computer networks

Schools, universities, business premises, and industrial plants typically use a local area network (LAN) – groups of connected computers or systems. Communication between LAN consoles is significantly easier when using fibre optics.

  • Students need to access information to complete assignments
  • Office workers need to communicate and collaborate on projects
  • Industrial plants need to continuously collect data and monitor processes

The fast data transmission and high bandwidth that optical fibre provides make it a highly sought-after technology in each of these settings. Fibre optics also offers safety benefits; since no electricity runs through the cables, they don't pose a fire hazard.

Medicine

Optical fibres are widely used in many medical applications. Thanks to the function and properties of optical fibre, it's able to make medical procedures easier for physicians and less invasive for patients.

Medical fibre-optic cables are sterile, flexible and unharmful to the body. Lab technicians can easily sterilise them using the same procedures used on other medical instruments. Moreover, they allow medical practitioners to view inaccessible areas of the body, as well as provide the light needed to guide and control instruments during medical procedures.

The first and most well-known use of fibre optics is the surgical method popularly known as endoscopy. In this application, a minute, bright light is used to light up the surgery area within the body, making it possible to reduce the number and size of incisions made.

Automotive industry

Fibre optic cables play an important role in the lighting and safety features of present-day automobiles. They are widely used in lighting, both in the interior and exterior of vehicles, for several reasons.

Firstly, since optical fibre transmits 'cold' light – meaning it stays cool and doesn't pose a fire risk – it's a safer alternative to the traditional sealed beam or halogen lighting used in cars.

Secondly, fibre optics removes the need for light sources and outputs to be located close together within the car's body. This gives designers greater creative freedom and makes high-performance lighting possible, even when working with restricted space parameters.

Additionally, fibre-optic cables are invaluable in the operation of safety systems such as traction control and airbags. Since these systems are typically focused on emergency or even pre-emergency response, communicating signals between different parts of a vehicle at lightning speed is critical – and optical fibre is the most effective way to achieve this.

Telephone networks

Optical fibres are the backbone of the world's telephone system. Underground fibre-optic cables connect our urban areas and a vast system of submarine cables link every habitable continent, making it possible for us to have conversations with people on the other side of the world.

Telephone networks were one of the first applications of optical fibres, whose superior bandwidth and ability to travel longer distances made it a more effective and inexpensive alternative to the copper cables used in earlier times.

Today, calling telephones within or outside the country is easier than ever. With the use of fibre-optic telecommunication, you can connect faster and have clearer conversations without any lag on either side.

Lighting and decorations

The use of fibre optics in decorative illumination has also grown over the years. Optical fibre lets you transmit LED lighting to specific or remote locations, providing an easy, economical and attractive solution to aesthetic projects.  

Fibre-optic lighting offers many advantages, including:

  • Electrical safety: Lighting underwater spaces such as fountains or swimming pools is possible with optical fibres, as they don't carry any electrical current and you can place the light source in a remote and dry place.
  • Precision lighting: It's possible to combine optical fibres with lenses to focus light on extremely small areas such as displays or areas in hard-to-reach locations.
  • Colour variety: By using colour filters together with a white LED light source, it's easy and simple to control the colour of the lighting. This can even be automated through pre-programmed sequences.

As a result, fibre optics is widely used in creating lighting decorations in public spaces such as museums and art galleries.

Mechanical inspections

Optical fibres are widely used to conduct mechanical inspections in cramped or difficult-to-reach places.

Engineers use special cables called fibre-optic probes to inspect the welding finish quality of the interior surfaces of stainless-steel pipework, which impacts the performance in the intended application. The probes produce bright and distinct images of the inside of the pipes, allowing for easy and effective quality control.

Plumbers use fibre optics to conduct in-depth inspections of interior sections of domestic pipes, as well as drains and sewer lines. Even without direct access, plumbers can investigate the causes of plumbing issues, searching for drainage and structural problems such as clogs, backups, and cracks.

Cable television

The use of optical fibre in the transmission of television programming has grown exponentially over the years. Fibre-optic cables are ideal for transmitting signals for high-definition televisions because they have greater bandwidth and speed compared to coaxial-cable, antenna or satellite-dish transmission.

This results in greater performance for television users. Yet optical fibres also provide numerous benefits to cable companies, one of which is better customer relationships. Additionally, fibre optic cables are cheaper compared to the same quantity of copper wire. They also don't carry an electrical current, meaning that companies don't have to deal with the interference and potential fire hazards that result from this.

Military

In many military scenarios, time is of the essence and each piece of information is a valuable asset. It should therefore come as no surprise that fibre optic cables are used on military bases, ships and planes – even on the battlefield – since they offer the highest levels of data transmission performance available today.

Moreover, fibre-optic cables offer a higher level of data security than metal-based cables. This is because they don't carry any electrical signal, making them almost impossible to tap into or jam. They're also more reliable as they don't experience any electromagnetic interference. These factors make them well-suited to use in the military, where the lives of personnel hang in the balance.

Fibre optics FAQs

Hopefully, we've answered all the questions you might have regarding fibre optics. Yet, if you find this topic as fascinating as we do, you'll likely have more to ask.

With that in mind, here are the answers to more questions people frequently ask about fibre-optic cables.

Can you bend fibre optic cables?

Yes, you can bend fibre-optic cables. But you need to be careful not to bend them too sharply. At best this will create tiny cracks in the optical fibre, allowing light to escape and leading to data loss. At worst, your cables will be rendered completely useless.

Fibre-optic cables have a property called the maximum bend radius. This is a measurement of how much they can be bent before they're damaged. The maximum bend radius of a cable depends on other specifications such as pulling tension, tensile load, and the core and cladding material.

Make sure you find out the maximum bend radius specified by the manufacturer and don't bend your cables beyond this during installation.

Can you join fibre-optic cables?

Yes. You can join fibre-optic cables through a technique called 'splicing'. There are two main types of splicing: mechanical and fusion.

Mechanical splices are fixtures that use gel or glue to hold the two ends of fibre together. The gel or glue needs to match the refractive index of the core so that light can still pass through the cable. Different types of mechanical splice fixtures include Elastomeric, Ultrasplice and Camlock.

Fusion splices, on the other hand, are made by welding the ends of two fibres together using an electric arc. You do this using a specialist fusion splicing machine.

Can you repair fibre optic cables?

Yes. You can repair fibre optic cables in the same way you join them. But first, you need to locate the fault in the cable.

Types of tools used to do this include optical time domain reflectometers (OTDRs) and visual fault indicators.

Once you've located the damaged section of the cable, you need to remove it. You can then rejoin it using either mechanical or fusion splicing techniques.

I'm a Mechanical Engineer by qualification though I worked for a long time specialising in Motion Control systems and integration with various PLC systems. I've wide experience of many types of applications from packaging machines to military and some applications that I can't mention. At home, I like to tinker and make things with wood, metal, plastics, electronics and mechanical system. I'm never happier than with a hammer and a screwdriver in my hands....
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