Design of Terahertz Low-Reflection Amplitude Modulator Using Quasi-π Reconfigurable Absorption Network

Current terahertz amplitude modulators predominantly employ reflective modulation principles, which often lead to impedance mismatch with terahertz sources during modulation process, resulting in degraded signal-to-noise ratio (SNR) and increased timing jitter in demodulated signals. This article proposes a terahertz absorption-type modulator designbased on quasi-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $</tex-math> </inline-formula> reconfigurable networks. When absorption conditions are met, the modulator maintains constant input port impedance during the “<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small>” to “<sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small>”-state transitions, achieving unidirectional reflectionless absorption modulation. Based on this design, we developed a 140-GHz band quasi-<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $</tex-math> </inline-formula> network unidirectional absorption-type amplitude modulator with an optimal voltage standing wave ratio (VSWR) of 1.1. Dynamic testing demonstrates that the absorption state exhibits superior eye diagram performance compared to the high-reflection state. The proposed absorption-type amplitude modulation technique thus provides robust support for high-speed and high-precision terahertz amplitude control while pioneering new pathways for integrated on-chip terahertz system design.