Student Blog: Optical Fibres

This blog was inspired by Dr Eric Numkam Fokoua’s talk

What are optical fibres?

Fibre optics, or optical fibre, refers to the medium and the technology associated with the transmission of information as light pulses along a glass or plastic strand or fibre. Fibre optics is used for long-distance and high-performance data networking.

A fibre optic cable can contain a varying number of these glass fibres – from a few up to a couple hundred. Surrounding the glass fibre core is another glass layer called cladding. A layer known as a buffer tube protects the cladding, and a jacket layer acts as the final protective layer for the individual strand.

Fibre optics transmit data in the form of light particles -or photons- that pulse through fibre optic cable. The glass fibre core and the cladding each have a different refractive index that bends incoming light at a certain angle. When light signals are sent through the fibre optic cable, they reflect off the core and cladding in a series of zig-zag bounces, adhering to a process called total internal reflection.

Image source: https://cosmosmagazine.com/technology/how-do-fibre-optic-cables-work/

How are optical fibres made?

Making the preform:

In MCVD, (modified chemical vapour deposition) oxygen is bubbled through solutions of silicon chloride, germanium chloride and/or other chemicals. The precise mixture governs the various physical and optical properties. The gas vapours are then conducted to the inside of a synthetic silica or quartz tube (cladding) in a special lathe. As the lathe turns, a torch is moved up and down the outside of the tube. The extreme heat from the torch causes two things to happen:

  • The silicon and germanium react with oxygen, forming silicon dioxide and germanium dioxide.
  • The silicon dioxide and germanium dioxide deposit on the inside of the tube and fuse together to form glass. The glass moulds to the tube to make a preform.

Drawing Fibres from the Preform:

The preform is lowered into a graphite furnace at 1900-2200 degrees Celsius. The tip gets melted until a molten glob falls down by gravity. 

As it drops, it cools and forms a thread. The operator threads the strand through a series of coating cups (buffer coatings) and ultraviolet light curing ovens onto a tractor-controlled spool. The tractor mechanism slowly pulls the fibre from the heated preform and is precisely controlled by using a laser micrometre to measure the diameter of the fibre and feed the information back to the tractor mechanism. 

Fibres are pulled from the preform at a rate of 10 to 20 m/s and the finished product is wound onto the spool. It is not uncommon for spools to contain more than 1.4 miles of optical fibre.

Testing the finished optical fibre

  1. Tensile strength – Must withstand 100,000 lb/in2 or more
  2. Refractive index profile – Determine numerical aperture as well as screen for optical defects
  3. Fibre geometry – Core diameter, cladding dimensions and coating diameter are uniform
  4. Attenuation – Determine the extent that light signals of various wavelengths degrade over distance
  5. Information carrying capacity (bandwidth) – Number of signals that can be carried at one time (multi-mode fibres)
  6. Chromatic dispersion – Spread of various wavelengths of light through the core (important for bandwidth)
  7. Operating temperature/humidity range
  8. Temperature dependence of attenuation
  9. Ability to conduct light underwater – Important for undersea cables

What are optical fibres used for?

  • Computer networking is a common fibre optics use due to the optical fibre’s ability to transmit data and provide high bandwidth. Similarly, fibre optics is frequently used in broadcasting and electronics to provide better connections and performance.
  • Military and space industries also make use of optical fibre as a means of communication and signal transfer, in addition to its ability to provide temperature sensing.
  • Fibre optics is frequently used in a variety of medical instruments to provide precise illumination. It also suitable for MRI scans.
  • Can be used to make sensors
  • Used to make powerful lazers, which are used to cut and weld.
Image source: https://guce.techcrunch.com/copyConsent?sessionId=3_cc-session_cfd6f9f7-08ab-40b5-b00d-48b396df7780&lang=en-US

Research and development in optical fibres

Fibre optic technology plays a major part in many businesses today, as most demand a faster, more secure, and larger communication system for their network operations. In the next few years, an increasing number of industries will be looking for new innovative solutions offered by fibre optics, including opportunities in the healthcare and maritime industry. 

A study by Research and Market predicted that the fibre optic market will grow at a rate of 8.5% in the next few years, reaching approximately $7.25 billion by 2025. (USA)

 According to Forbes, many cities around the world are starting to consider using fibre optic cables for their communication networks.  The investment may be considerable, but the returns will be as well, with an astounding capacity of 144 TB.

Fibre optic technology continues to develop alongside the increased demand for greater speed and efficiency. New devices, such as optical couplers and optical switches, are supporting a recent trend known as All-Optical Networks or AON. This new technology allows data to be transmitted quickly without any electrical processing, which will result in further transmission distances.

Another recent improvement is ROF or Radio-over-Fibre, which allows for the transmission of radio signals using optical fibres. The radio frequencies are not impacted by electromagnetic interference, which has huge potential for development in the aviation industry as well as public work projects, stadium construction, and commercial building construction.

Challenges with Fibre Optics:

There are some harsh realities and challenges that fibre technology has to be able to manage going forward. For one, laying the fibre cable requires a complex trenching and building process which can be very costly. 

Another problem is logistic challenges. If we want to connect New York to San Francisco through fibre, we will first need to create a long-haul dark fibre network. However, we can’t simply stretch a fibre cable straight from one point to another. About every 40 to 60 miles, the connection needs to be re-amplified using an ILA (In-Line Amplification) Shelter, which can be costly to develop and maintain.

This issue is one of the main reasons why fibre optic is not widespread at the moment.

Closing words

Fibre optics is being used widely today by many industries, and the future is certainly bright going forward. As these networks continue to expand and user load continues to increase, the development of standardised fibre testing practices becomes increasingly important. 

It is an upcoming technology that is becoming widespread as we speak. As speed and efficiency is at the heart of everything we do in modern day life, the demand for this technology is becoming more sought after than ever.

Written by Malick, a Year 11 student at Haberdashers’ Aske’s Knights Academy

Thank you for reading and I hope this is informative!

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