The developing terahertz wireless communication demands higher performance modulators. In this Letter, a mechanism of resonance mode transformation for a high-speed terahertz direct amplitude modulator with rather low insertion loss and high modulation depth is presented. By embedding an H-shaped resonance structure, which consists of a fin-line and two flip-flopped GaAs Schottky diodes, into the E-wall of a waveguide, the fed terahertz waves are modulated by the inductive-capacitive (LC) resonance transformation of the structure. Based on this mechanism, a modulator working in the frequency band around 140 GHz is fabricated and packaged. Thanks to the LC resonance transformation, the presented modulator exhibits a low insertion loss of 1.8 dB at 138 GHz, a large modulation depth higher than 99% at 148 GHz, and high modulation speeds up to 30 Gbps at 146 GHz. Accordingly, the presented mechanism paves a promising route to develop high performance terahertz direct modulators, which is of great significance for terahertz high-speed wireless communication.

As a key potential component of future sixth-generation (6G) communication systems, terahertz (THz) technology has received much attention in recent years. However, a lack of effective high-speed direct modulation of THz waves has limited the development of THz communication technology. Currently, most high-speed modulators are based on photonic systems that can modulate electromagnetic waves with high speed using sophisticated optoelectronic conversion techniques. Yet, they usually suffer from low conversion efficiency of light to the THz range, resulting in low output power of the modulated THz waves. Here, we describe a guided-wave modulator for THz signals whose performance nearly matches that of existing in-line fiber-optic modulators. Our results demonstrate a maximum modulation depth greater than 20 dB (99%) and a maximum sinusoidal modulation speed of more than 30 GHz, with an insertion loss around 7 dB. We demonstrate the capabilities of this modulator in a point-to-point communication link with a 25 Gbit/s modulation speed. Our modulator design, based on near-field coupling of a THz transmission line to a single resonant meta-element, represents a powerful improvement for on-chip integrated high-performance THz devices.

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