A 0.31-THz Orbital-Angular-Momentum (OAM) Wave Transceiver in CMOS With Bits-to-OAM Mode Mapping
Muhammad Ibrahim Wasiq Khan, Jongchan Woo, Xiang Yi, Mohamed I. Ibrahim, Rabia Tugce Yazicigil, Anantha P. Chandrakasan, Ruonan Han
Abstract
This article reports the first chip-based demonstration (at any frequency) of a transceiver front end that transmits and receives electromagnetic waves with a helical distribution of wavefront phase [namely, orbital angular momentum (OAM)]. The CMOS chip consists of eight 0.31-THz modulator/detector units, with an integrated patch antenna, which are placed in a uniform circular pattern with a diameter of one free-space wavelength. The chip transmits OAM modes that are digitally switched among the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$m\,\,=0$ </tex-math></inline-formula> (plane wave), +1 (left-handed), −1 (right-handed), and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(+1)+(-1)$ </tex-math></inline-formula> (superposition) states. The chip is also reconfigurable into a receiver mode that identifies different OAM modes with >10-dB rejection of mismatched modes. The array, driven by only one 310-GHz signal generation path, has a measured EIRP of −4.8 dBm and consumes 154 mW of dc power in the OAM source mode. In the receiver mode, it has a measured conversion loss of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 30$ </tex-math></inline-formula> dB and consumes 166 mW of dc power. Using a low-cost 65-nm bulk CMOS technology, the terahertz (THz)-OAM chip has an area of only 2.1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 2.6 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which is the smallest among all prior OAM prototypes. The output OAM beam profiles and modes’ orthogonality are experimentally verified. The dynamic mode switching capability of the chip is also verified in the time domain across 1-m distance, and a full-silicon OAM link is demonstrated.