Measurements on an RF fiber-optic link suitable for antenna remoting

The authors report on an externally modulated fiber optic link and the necessary support equipment. This testbed permits measurement of link parameters under environmental and operational conditions representative of those that are likely to be present when these links are used in a system. All the control functions and the DC power required by the module are conveyed via fibers. The module comprises an RF filter, a Mach-Zehnder modulator, a control board, and a photodetector assembly. Module power of about 1 mA at 5 V is supplied by a photovoltaic cell that is illuminated by a 0.85- mu m, 50-mW fiber-coupled diode laser. The link gain, noise figure and intermodulation-free dynamic range vs. temperature for two such modules are reported. The gain plot shows that the link exhibits intrinsic gain since these measurements were made without any electronic or optical amplifiers in the link.