Design and analysis of a high-performance terahertz photoconductive modulator enhanced by photonic crystal cavity

We propose and design a high-speed and high-performance optically controlled terahertz (THz) intensity modulator based on the free carrier modulation of a GaAs semiconductor. The device comprises a photonic crystal cavity-waveguide coupling structure for operation in the THz region. This modulator benefits from the strong interaction between the THz wave and the photoconductive substance to obtain a deep modulation with GHz speed, even with a low external optical power. The finite element method was used to calculate the most important properties of the modulator, such as the modulation depth, insertion loss, and modulation rate. The proposed modulator also demonstrated external optical power-dependent characteristics. The results indicate that the THz intensity can be modulated at a switching frequency of 1 GHz with high modulation depths of 83% and 90.3% under the continuous wave laser pumping of 50 W/cm2 and 80 W/cm2 respectively. In addition, this modulator exhibits efficient performance under the same pumping power with a switching frequency of up to 3 GHz. The device exhibited higher modulation depths with higher laser power intensities. The outstanding properties of the proposed structure are promising for the development of modulators and switches in THz communication systems.