High dynamic range microwave fibre optic links for the 2-18 GHz band

Abstract

The use of optical fibre links for the distribution and transmission of RF and microwave signals is of growing interest and has been under continuous development at GMMT for more than 10 years. Such links have the advantage of a low, frequency independent loss which, added to the lack of frequency dispersion, means that very long, wide bandwidth links are possible which are suitable for applications such as antenna remoting and microwave delay lines. Optical fibre cable is also more flexible, takes up less space and has a lower mass than its electrical equivalent, whilst being less sensitive to environmental fluctuations, electromagnetic interference and crosstalk effects. The principal difficulty, until recently, has been the availability of efficient lasers, optical modulators and receivers to achieve a link with the required electrical performance. With recent advances in high power, compact optical sources and low loss, low drive power modulators this performance barrier is no longer such a problem. This paper describes the design and build of compact, rugged optical transmitter and receiver modules which have been developed at GMMT for use in high performance 2 - 18 GHz microwave links. All of the critical components within the link, such as the laser source, waveguide modulator, wideband photodiode and MMIC pre-amplifier are deigned fabricated in-house, therefore providing a high degree of design and performance flexibility. (6 pages)