Spectral dependence of microwave power transmission in laser-controlled solid-state microstrip switches

Abstract

Laser-controlled solid-state microstrip switches using a gap and a shunt structure in tandem offer the advantage of employing optical sources over a wide spectrum range. The spectral response of such an optoelectronic switch is mainly determined by the spectral dependence of power transmission through the illuminated semiconductor gap region. The physical and electronic processes within the excited semiconductor region are analysed quantitatively with special regard to the required high-speed laser pulse excitation. The corresponding effects on the microwave power transmission of the switch are studied successfully by using a simple π equivalent circuit. This equivalent circuit consists of several gap and shunt conductances that depend on the incident optical energy and on the optical wavelength of the controlling laser pulses. The optical bandwidth of the device is discussed with special regard to the long-wavelength cutoff, which, in this case, is determined by the specific functioning of the switch rather than by the decrease in photosensitivity. The analytical results are specified for a high-resistivity silicon substrate used in the corresponding experiments. Theoretical and experimental results were found to agree fairly well.