Development of optically controlled microwave devices and artificial materials

Optical-microwave interaction has been emphasized in optically reconfigurable antenna arrays (ORA) due to the unique advantage that transparency between the optical control signals and microwave signals makes the antenna less susceptible to jamming. One of the important parts in ORA is an optically controlled microwave switch (OMS) as synaptic elements. A gap-structure OMS has been developed as a low-cost and simple device, operated in wide frequency range. However, the OMS is essentially operated in CW-mode, hence adverse effects are observed in the CW-mode operation. Although a CW-mode OMS has been investigated previously, the detailed analysis including the best-case insertion loss has not been reported. We have demonstrated the limitations with the standard OMS and propose a new carrier-confined OMS. As a result, less than 2 dB of insertion loss and more than 20 dB of ON/OFF difference have been obtained with the new structure.; There has been an increasing interest in artificial composite materials due to the demands on low-loss high dielectric constant materials as well as highly lossy dielectric materials at microwave frequencies. Conductor-loaded composite materials have been developed as artificial materials. In this study we have analyzed the established models and discussed their limitations in high volume fraction and at microwave frequencies. In addition, a simple yet fast and reliable measurement technique for the complex dielectric constant of the composite materials has been developed using a transmission method and a genetic algorithm as an inversion process.; Periodic or layered structures are commonly used as microwave frequency selective surfaces to transmit certain frequencies or to reject unwanted frequencies. However, these structures usually have fixed transmission characteristics, and it is difficult to control the pass- and stop-band responses without changing the physical spacing or surface patterns. Hence, we have developed an optically tunable attenuator based on a layered structure using a silicon substrate. More than 20 dB of attenuation with 10% bandwidth of the center frequency have been obtained in the W-band.