What is RF-over-fiber?

PPM has developed technology for converting an RF signal into an optical signal for transmission over optical fiber, and converting it back into an RF signal. A typical system will consist of three main elements: an optical transmitter, a fiber optic cable and an optical receiver.

The system is defined in terms of normal RF parameters i.e. gain, noise figure, linearity, and can be treated as an RF black box by a systems designer.

The RF-over-fiber systems generally use intensity modulation. This may be thought of as amplitude modulation in the optical domain. The RF signal applied by the user to the optical transmitter, is used to directly modulate the intensity of a light source (e.g. a laser diode). This technique results in the widest possible frequency response and highest possible dynamic range. At the optical receiver, the intensity 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 PPM's products, these components have been designed for optimum efficiency, noise and linearity performance.

There is no frequency conversion or analog-to-digital conversion involved. However PPM does offer analog to digital for DC products and DC modulation for its DC products where low drifts and high stability are critical.

Why Use Fiber?

Optical fiber is small in size, flexible, very low loss and is a very well established technology. It offers a number of inherent advantages over the use of coaxial cables or free-space transmission, including:

• Very low loss (less than 0.5dB signal loss per km!)
• Non-conductive medium, resulting in electrical isolation for safety.
• Immunity to electrical interference.
• Easy deployment due to small size and flexibility of rugged cable.

PPM's RF-over-fiber links offer unbeatable advantages for the transmission of analog, RF and digital data signals over optical fiber, and are used for the replacement of conventional coaxial cable in many different applications.

A diverse range of applications is catered for by products optimised for specific applications including: EMC Test and HV Monitoring.