Light in Fibre Optics, Things You Didn’t Know!

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We are comfortable with the idea of information travelling in different ways. We talk into a phone and a copper cable carries the sounds from our voice into a socket in the wall. From here another cable takes it to the local telephone exchange.



Mobiles work a different way; they send and receive information using invisible radio waves. Referred to as wireless technology. Due to the fact that there are no cables involved.

Fibre optics works a third way. It sends data coded in a beam of light through a glass or plastic cable. Developed for endoscopes in the 1950s. Designed to help doctors see inside the human body without having to cut it open first.

Engineers, in the 1960s, found a way of using the same technology to transmit telephone calls at the speed of light. Normally that’s 300,000km per second in a vacuum. This slows to about 200,000km per second in a fibre optic cable.

This technology is based around the transfer of information via pulses of light.


What is light?

Defined as an electromagnetic wave across the Electro-Magnetic Wave spectrum.

Categorized according to its frequency (f), or according to its wavelength (λ).

Wavelength and frequency are connected. Some energy is identified by its wavelength, others by their frequency.


Light includes

  • Visible light; (Light visible to a human) has a wavelength range from ~400 nm to ~700 nm.

  • Microwaves; Refers to the electromagnetic rays with frequencies between 300MHz and 300GHz in the electromagnetic spectrum. Most usual applications are within the range of 1 to 40 GHz. Microwaves are suitable for wireless transmission signals having higher bandwidth. Microwave heating is used in homes for the preparation of food (microwave ovens).

  • Radio waves; They have the longest wavelengths in the EM spectrum, according to NASA. From approximately 1cm to 1km, being 30 gigahertz (GHz) to 300 kilohertz (kHz) in frequencies.

  • Infrared radiation; Extends from 700 nanometers (nm) to 1 millimetre (mm) at the red edge of the visible spectrum. This range is compatible with a frequency range of somewhere between 430 THz down to 300 GHz.

  • Ultraviolet (UV) light; Is in the range of the EM spectrum in the middle of visible light and X-rays. The sun emits Ultraviolet radiation and is the reason skin colours or burns. Some objects in outer space emit UV radiation as well.

  • X-Rays; High-frequency electromagnetic radiation. The wavelength range is in the range of 0.01 to 10 nanometers, consistent with frequencies in the range 30 petahertz to 30 exahertz

  • Gamma Rays; They have the shortest wavelengths (< 0.01 nanometers) and the most energy of any region of the electromagnetic spectrum.


Wavelength or Frequency?

Each has a different wavelength and frequency (or colour). All are electromagnetic waves.

Wavelength is used to identify shorter wavelength radiation. Like Visible Light, UV light, and X-rays. Frequency is used for longer wavelengths like radio, TV, and microwaves.

The use of light to transfer information is what has made fibre optics very popular.




The visible band is a small piece of the electromagnetic spectrum.


How does digital communication use light for transmission?

We now understand what light is and the various wavelengths and frequencies used. How does fibre optic cable use this?

Fibre optic cable is constructed with thin strands of glass. Known as optical fibres. One cable can have as few as 2 fibres or as many as several hundred fibres. The size of which is smaller than that of a human hair. Can carry something like 25,000 telephone calls. An entire fibre optic cable can easily carry several million calls. How does it do this?

We send digital data through fibre cables using light pulses. It is a two-symbol Binary code system.  A strong pulse of light indicates a one, and no pulse indicates a zero. Referred to as “on” and “off” as well.  A telecommunications tower converts it to a light signal. This light signal transmits through the complex worldwide fibre optic network until it reaches its final destination. Through these rapid changes in the light, you can send or receive highly complex signals; data, voice, or video. 


Which light do we use in fibre optics?

We use light in the infrared region for glass fibres. These wavelengths are greater than visible light. The most common ones used are 850, 1300, 1310, 1490, 1550, and 1610 nm.



The reason we use these wavelengths is that attenuation (loss) that happens in fibre is much lower at these wavelengths.

Wavelengths drive everything we use, design, or operate. Examples of this are networking products and test and measurement equipment.

This SFP designed to operate at 1310nm wavelength.





This PON Power meter designed to operate at 1310-1490-550nm wavelengths.





An important thing to note is that these wavelengths are not in the visible spectrum. Which means you cannot see this light. Handle such equipment with caution and follow safety procedures!



Why use fibre optics? Well, that’s the easy part. You can send information faster and over longer distances using fibre optic technology. This is why worldwide we are making the switch from copper to fibre.