Variable Terahertz Attenuator Integrated on Nonradiative Guide Using Photoinduced Carriers

A terahertz variable attenuator integrated on a nonradiative guide controlled by externally induced photoconductivity is proposed. Our device is constructed using high-resistivity silicon as a dielectric channel of the waveguide sandwiched between parallel conducting plates. By irradiating an excitation light to the side surface of the channel, photoinduced carriers are generated involving attenuation for terahertz waves propagating through the channel. We experimentally demonstrate attenuation of 0.50 dB/cm/mW at 300 GHz. The use of the nonradiative guide simplifies the light irradiation scheme and contributes to integrate other functions such as bending, filtering, splitting, and combining without radiation losses. We also discuss its unique frequency dependence, in which the attenuation increases as the frequency decreases.