A NOVEL OPTICAL CONTROL TECHNIQUE USING TUNABLE INDUCTANCE CIRCUITS

Recently fiber optic links have been applied to radio signal distribut ion networks and also to signal feeder networks for phased array anten nas, because they are able to offer wide bandwidth for achieving the h igh bit-rates and large capacity needed in the multimedia age. In thes e networks, a great many modules are needed to convert optical signals to radio signals. In order to reduce the complexity and cost of these modules, direct optical control techniques, which inject optical sign als directly into microwave circuits, are very attractive. Thus, this paper proposes a novel optical control technique using tunable inducta nce circuits. This technique employs direct illumination as a means of optically tuning the inductance. Since the inductance value is invers ely proportional to the square of the transconductance, it varies wide ly when the FET is directly illuminated. With direct illumination, the measured inductance variation in an experimental inductance circuit b uilt with Pseudomorphic AlGaAs/InGaAs/GaAs HEMTs is more than 20 % fro m 0.5 to 2 GHz. As an application, a direct optically controlled oscil lator was fabricated. The measured optical tuning range of the oscilla tion frequency is more than 19 % with an output power of -5+/-1 dBm. T his is a promising technique for a variety of devices, including optic ally controlled oscillators, filters, phase shifters, and active anten nas.