Optical communication networks and devices

Optical communication is used taken to mean devices that transmit data by sending pulses of light through an optical fibre. The light forms an electromagnetic carrier wave that is modulated to carry information. First developed in the 1970s, fibre-optic communication systems have revolutionized the telecommunication industry and have played a major role in the advent of the information age. Because of its advantages over electrical transmission, optical fibre is rapidly replacing copper wire in core networks in the developed world and is key for developing countries in bridging the digital divide.

Traditionally, optical devices include items such as polarizers, wave plates, reflectors, filters, and lenses. However, when we consider the concept of communication in optical devices, the scope widens to encompass beam-splitters, photo transistors, laser diodes and more, including:

  1. light emitters and receivers;
  2. linear image sensors;
  3. optoelectronic devices; and
  4. photodetectors.

The main advantages of using optical technologies in communication systems are that the high frequency of the optical carrier enables significantly more information to be transmitted over a single channel than is possible with a conventional radio or microwave system. Optical components are much smaller and lighter, with the additional benefit of consuming less power. Since energy conservation is gaining increasing interest nowadays, the energy-saving characteristics of optical technologies represent huge opportunities for reducing the carbon footprint of ICTs.

The communication process using optical fibre involves the following basic steps (shown in Figure 1):

  • creating and encoding the optical signal involves the use of a transmitter – lasers and light-emitting diodes (LEDs) are generally used for this purpose;
  • transmitting the signal along the fibre;
  • ensuring that the signal does not become too distorted or weak, hence the use of amplifiers; and
  • receiving the optical signal and converting it into an electrical signal using an optical receiver.

Figure 1: Basic steps in optical communication

Wavelength division multiplexing (WDM) can optimize the potential high bandwidth of optical fibres by enabling several distinct data signals to share a single fibre, provided that they have different wavelengths. Multiple wavelengths are therefore multiplexed into a single optical fibre and multiple light-path data are transmitted (See Figure 2).

Figure 2: Wavelength Division Multiplexing (WDM), functional model

Current communication networks using optical fibre still need to convert the electrical signal into an optical one for transmission, and then back into electrical form at the receiving end. Thus, the potential bandwidth of optical fibres is not being fully exploited. Therefore, future research and standardization work will be focused on developing purely optical devices for communication networks.

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