Advantages of Semiconductor Optical Transmitters
Sean Braun
Assignment 9
There are two main types of fibre optic transmitter that are in use today. Both of them are based around semiconductor technology:
• Light emitting diodes (LEDs)
• Laser diodes
Semiconductor optical transmitters have many advantages. They are small, convenient, and reliable. However, the two different types of fibre optic transmitter have very different properties and they tend to be used in widely different applications.
LED transmitters These fibre optic transmitters are cheap and reliable. They emit only incoherent light with a relatively wide spectrum as a result of the fact that the light is generated by a method known as spontaneous emission. A typical LED used for optical communications may have its light output in the range 30 - 60 nm. In view of this the signal will be subject to chromatic dispersion, and this will limit the distances over which data can be transmitted
It is also found that the light emitted for a LED is not particularly directional and this means that it is only possible to couple them to multimode fibre, and even then the overall efficiency is low because not allt he light can be coupled into the fibre optic cable.
LEDs have significant advantages as fibre optic transmitters in terms of cost, lifetime, and availability. They are widely produced and the technology to manufacture them is straightforward and as a result costs are low.
Laser diode transmitters These fibre optic transmitters are more expensive and tend to be used for telecommunications links where the cost sensitivity is nowhere near as great.
The output from a laser diode is generally higher than that available from a LED, although the power of LEDs is increasing. Often the light output from a laser diode can be in the region of 100 mW. The light generation arises from what is termed stimulated emission and this generates coherent light. In addition to this the output is more directional than that of a LED and this enables much greater
Assignment 9
There are two main types of fibre optic transmitter that are in use today. Both of them are based around semiconductor technology:
• Light emitting diodes (LEDs)
• Laser diodes
Semiconductor optical transmitters have many advantages. They are small, convenient, and reliable. However, the two different types of fibre optic transmitter have very different properties and they tend to be used in widely different applications.
LED transmitters These fibre optic transmitters are cheap and reliable. They emit only incoherent light with a relatively wide spectrum as a result of the fact that the light is generated by a method known as spontaneous emission. A typical LED used for optical communications may have its light output in the range 30 - 60 nm. In view of this the signal will be subject to chromatic dispersion, and this will limit the distances over which data can be transmitted
It is also found that the light emitted for a LED is not particularly directional and this means that it is only possible to couple them to multimode fibre, and even then the overall efficiency is low because not allt he light can be coupled into the fibre optic cable.
LEDs have significant advantages as fibre optic transmitters in terms of cost, lifetime, and availability. They are widely produced and the technology to manufacture them is straightforward and as a result costs are low.
Laser diode transmitters These fibre optic transmitters are more expensive and tend to be used for telecommunications links where the cost sensitivity is nowhere near as great.
The output from a laser diode is generally higher than that available from a LED, although the power of LEDs is increasing. Often the light output from a laser diode can be in the region of 100 mW. The light generation arises from what is termed stimulated emission and this generates coherent light. In addition to this the output is more directional than that of a LED and this enables much greater