What is RF over Fiber Technology?
RF over optical fiber is small in size, flexible, very low loss technology using intensity modulation to transmit RF signals. The continued fall in the cost of electro-optical conversion over recent years has led to RF over fiber being increasingly adopted for applications such as linking satellite teleports to control rooms, live outside broadcast TV, and enhancing coverage of wireless technologies such as GPS, GSM, WiMax, Tetra and P25 for example by linking remote antennas inside buildings, tunnels and mines.
There are numerous benefits of using optical fiber based solutions such as:- It offers a number of inherent advantages over the use of coaxial cables or free-space transmission, including:
- A loss of less than 0.5dB signal loss per km makes the link effectively transparent (see graph below comparing RF over fiber to coax over frequency).
- Immunity to EMI and RFI due to fiber being a non-conductive medium
- High reliability
- Security against signal interception
- Low maintenance – install and forget technology
- Flat frequency response
- Flexible and light weight for ease of deployment
- Simple installation.
A typical system will consist of three main elements:
- Optical transmitter
- Fiber optic cable
- Optical receiver (to convert back to RF).
The system is defined in terms of normal RF parameters, i.e. gain, noise figure, linearity etc., and can be treated as an RF black box by a systems designer.
ViaLite systems use intensity modulation, which is amplitude modulation in the optical domain. The RF signal applied by the user to the optical transmitter directly modulates the intensity of a light source (e.g. a laser diode).
No frequency conversion or analog-to-digital conversion is involved.
This technique results in the widest possible frequency response and highest possible dynamic range. At the optical receiver, the modulated light is converted back into an RF signal using a high frequency photodiode.
Intensity modulation places very demanding requirements on all components in the optical path – particularly the laser diode. In ViaLite products, these components have been designed for optimum efficiency, noise and linearity performance.