Broadband Terahertz Phase Modulation Using a GaAs Schottky Diode With Integrated Subwavelength Metal Microslits in Total Internal Reflection Geometry

Terahertz wireless communications provide ultra-high data rates, low latency, and high capacity, offering substantial benefits for future 6 G networks, virtual reality, and the Internet of everything. The modulator's uniform phase control across the entire bandwidth will support precise beamforming and enhanced security. However, current terahertz phase modulators typically operate in narrowband ranges. Here, we present a solid-state broadband terahertz modulator capable of continuous phase shifts up to 100<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> across the 0.5 to 0.6 THz band. Experimental results demonstrate 22.5<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula>, 45<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula>, 67.5<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula>, and 90<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> phase shifts with uniform intensity across this range, laying the foundation for 4-bit, quadrature, and higher-order PSK protocols. Our device utilizes a gallium arsenide (GaAs) Schottky diode integrated with subwavelength metal microslits (6 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu m$</tex-math></inline-formula> period, 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mu m$</tex-math></inline-formula> gap, with no plasmonic effect) in a total internal reflection (TIR) geometry. Applying reverse bias between the Schottky and ohmic contacts depletes free carriers within the microslits, enabling effective broadband phase control. This proof-of-concept device achieves a stable phase modulation speed over 20kHz. Future enhancements through optimized microslit design, refined diode geometry, and incident angle adjustments may further improve modulation efficiency and speed, advancing terahertz technology.