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5th November 2021

A practical guide to Plastic Optical fibres 

What is Optical Fibre? 

Fibre optic cables are an effective medium of data transmission. It is widely used in many industries. With this technology information is transmitted via light pulses, along transparent plastic, or glass tubes. 

Common applications of optical fibres 

Optical fibres are commonly used for data transfer in Communications, Broadcasting, Medicine and Military. In Power Electronics, optical fibres are widely used for interfacing controller circuitry and power devices in Power Stations, railways, and wind turbine generators. 

Why are optical fibres used in High Power Applications? 

Because optical fibres provide an excellent electrical isolation between control and power electronics. With optical fibres, control data can be transmitted safely, over long distances and with high immunity to external noise and interference. Optical cables are also thin in diameter and can be easily routed.  

How do optical fibres work? 

Optical fibres work by establishing a medium through which light can travel and be guided. To achieve this, optical fibre cables have a unique structure to allow light to reflect from its internal walls at a shallow angle in a phenomenon called  total internal reflection. This way light signals can be passed through with very little loss. 

How do optical fibres transmission lines work? 

An optical transmission line is composed by a light transmitter, an optical fibre and a light receiver. The Light Transmitter transforms electrical signals into light of a given wavelength. The optical fibre guides the light from the light source to the light receiver. The light receiver transforms the light signals back to electrical pulses. Transmitter, cable and receiver must be able to operate at the same wavelength for the communication channel to be established. 

What are the common types of optical fibres? 

The two primary types of optical cable are multimode and single mode:  

Multimode fibres can carry multiple light beams at the same time and operate in the 850nm window. Due to dispersion the range is limited so it tends to be used in less than 1Km applications. These fibres come in core sizes of 62.5 and 50 microns. 

Singlemode fibre have a smaller core size of around 9 microns and present a single light path. In these fibres, light can travel much longer distances of up to 100km. These fibres require more sophisticated electronics which operates in the 1310 and 1550nm window.  

A third type of optical fibreis the Plastic Optical Fibre (POF) 

Plastic optical fibres are made of polymer. Its greatest advantage over the glass products, is its robustness under bending and stretching. Also, its low cost and simplicity of assembly makes it the ideal choice for low volume applications. For this article, this is the optical fibre of choice. 

Why should you use Plastic Optical Fibre (POF) for your project? 

  • They are low cost and widely available at most recognised suppliers. 
  • They are very flexible and easy to work with. 
  • Mechanically resistant and easy to assemble with no specialized skill required.  
  • They can be used in pretty much any way the system requires even if there is specialised equipment on both ends.  
  • Their maintenance and repair can be done on the field.  

Drawbacks to be aware of when using POF) 

  • Certain types of connectors are not recommended for very high vibration environments; they can get damaged over time.  
  • Ageing optical fibre receivers and transmitters will change their response over time. In extreme cases they will need replacing. Generally, this occurs over decades rather than years.  
  • Some have better connections with different systems, so research is required.  
  • There can be limitations on the bandwidth but for most systems this is acceptable.  

What to consider when choosing optical fibres for your project 

Discuss Your Project 

  • Do I need Full Duplex, Half Duplex or Simplex transmission modes? 
  • What is the most appropriate POF cable to use? 
  • What is the most appropriate optical transmitter and receiver to use? 
  • Do we need to transmit data synchronously or asynchronously? 
  • Can data and clock signals be sent through the same optical fibre? 
  • Which kind of signals can I send over POF? 
  • Which bandwidth does my system require? 

When should you use POF? 

Electrical isolation and noise immunity are the main reasons why you should consider using Plastic Optical Fibres. If your controller system needs to operate safely away from your power electronics devices, POFs are the natural choice. With POFs a fault on the Power Electronics will not damage the controller electronics nor endanger the controlling person. 

What kind of data can we send using optical fibres? 

POFs can carry digital data within their specified bandwidth. This data can be encoded or not encoded. If more than one fibre is used, communication feedback can be implemented to provide data re-transmission. Standard error detection and correction systems can also be used on the receiver electronics. 

How POF are used at Ignys? 

When a specific project requires safe, isolated and noise immune transmission of data between two systems, POFs are often considered because of their advantages. Options are always presented and discussed with our clients in the earlier stages of the project to ensure the client needs are prioritised and mutual benefits are achieved. 

How the Ignys team can help 

Ignys Services

  • Are you considering using Optical Fibres on you project? 
  • Not sure if they are right for you? 
  • Would you like to replace a wired connection with an Optical Fibre connection? 
  • Would you like to know if your POF system needs a replacement? 
  • Do your Optical fibre transmitters and receivers need replacement? 

Authorship

Elias’s skill sets include Hardware Design with microcontrollers and FPGAs. Elias has a real interest in Power Electronics and Railways, particularly IGBT driving and control-load electrical isolation through optical fibre interfaces.

Meet The Ignys Team Here