Terahertz Beam Steering With Doped GaAs Phase Modulator and a Design of Spatial-Resolved High-Speed Terahertz Analog-to-Digital Converter

In this paper, we have designed and characterized the beam steering structure for terahertz radiation based on doubly corrugated spoofed surface plasmon polariton (DC-SSPP) architecture and analyzed the design of a high-speed terahertz analog-to-digital converter (ADC). Two DC-SSPP waveguides comprising metal-covered GaAs are utilized to build an interferometric structure with localized doping in the groove region. Active modulation of free carrier density in the doped n-GaAs will cause relative phase differences between terahertz beams in separate arms of the interferometer, giving rise to deflected radiation in the far field. In this paper, both mathematical modeling and finite-element simulations are used to verify and optimize the design. Two different architectures operating on the enhancement mode and depletion mode are studied separately in detail. Applying the beam bender in the ADC design poses challenges such as structural symmetry and multibit resolution. With a full differential implementation of the input signal and combination of nonlinear detector arrays with carefully designed gain and saturation power, a 3-bit ADC is demonstrated with higher than 60 GS/s speed and direct digitized readout.