What is RF Over Fiber?

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- everything RF

Jan 3, 2019

RF over fiber (RFoF) or Radio over fibre (RoF) is a way of transmitting radio waves over a fiber optic cable by converting the RF signal into light by modulating the intensity of a light source (Laser or LED) with the RF signal. At the other end, the RF signal is recovered using an Optical-Electrical modulator (O/E).

RF over Fiber transmission is an analog process that provides high bandwidth, low-loss communication links to transport RF energy at optical frequencies/wavelengths. Unlike traditional copper coax cables whose losses limit their transmission distance to around 300 ft., RoF is not distance limited.

An RF Over Fiber (RoF) Link receives an RF Signal, converts it to an optical signal, transmits it over a distance and then converts its back to an RF signal which is then processed as required. A RoF Link consists of the following parts:

  • Light Source/Laser Diode - That acts as an optical carrier, usually provided by a laser diode. This laser diode is controlled by forward-biasing the semiconductor junction.
  • Electrical-optical Modulator (E/O) - To convert/modulate the light beam using the RF signal.
  • Transmission Medium - A single-mode fiber-optic cable. Single-mode has a lower number of light reflections, which lowers attenuation and allows the signal to go further than multimode.
  • Optical-electrical Modulator (O/E) - To recover the RF signal at the receiver side, usually by using a photodiode or avalanche photodiode (APD).

At this point, the original RF signal is recovered and can then be processed as required.

Advantages of RoF:

  • RF Signals can be sent over large distances with low losses
  • Large Bandwidths
  • Immune to Interference
  • Easy Installation and Maintenance

Due to the physical properties of fiber-optic cables, certain frequencies have less attenuation. The optical frequencies used most often for LEDs are 780nm, 850nm, 1300nm and for Laser Diodes are 1310, 1550nm, 1625nm.