Microstrip resonators for high speed opitical commutator switches

Using a planar microwave resonator as the electrode for modulating a high speed Y-branch optical commutator switch is a novel idea. For this purpose a "cul-de-sac" shape microstrip resonator is suggested and studied both theoretically and experimentally. It has two substantially parallel legs unconnected on one end and connected via an open ring on the other. It is the parallel legs that work as the electrode. Because of the stored energy the potential difference between the two legs can be much higher than the source voltage. Therefore, the resonator electrode has significant advantages over other kinds of electrodes. By using a resonator electrode the optical switch can operate at high frequencies while consuming little power. The field distribution, discontinuity effects, and the radiation loss of the "cul-de-sac" resonator are discussed. The structure parameters of the "cul-de-sac" resonator, were optimized for maximum output voltage and minimum consumed power using a computer program. The source power can be coupled into the resonator by tap point coupling through a quarter-wave-length transformer. The input impedance of the resonator and the coupling coefficient β were derived as functions of the coupling position θ using an equivalent lumped circuit. Then an important relationship between the output voltage V0,the source voltage Vs„ and the unloaded quality factor Qu. is derived which tells us that Vo is proportional to the product of Va, and the square root of Qu. From this relationship we proved that the most efficient and practical coupling condition is β