This study is led by Prof. Baile Zhang (Nanyang Technological University), Dr. Yang Long (Nanyang Technological University) and Prof. Feng Wu (Guangdong Polytechnic Normal University). While quasi-bound states in the continuum (QBICs) are known for their ultra-high Q factors, most research has focused on their momentum-space characteristics. This work experimentally demonstrates how QBICs can also affect real-space beam shifts.
Using a compound grating waveguide with a folded Brillouin zone, the team established a QBIC band where all states become QBICs. When excited at specific incident angles, these QBICs introduce abrupt lateral beam shifts (LSs), which quickly disappear when the frequency deviates from the QBIC band. “This work offers alternative insights into QBIC behaviors,” says Baile Zhang.
Through terahertz imaging technology, the researchers observed these shifts at various incident angles and mapped the QBIC band. “This discovery offers a new approach to characterizing QBIC bands,” explains Yang Long. Notably, they recorded a maximum lateral shift of 41.16 times the wavelength at 1.0774 THz—about 3.35 times larger than any previously reported shift in the terahertz range.
“Our finding opens new possibilities for leveraging QBICs in advanced sensing and photonic devices. The ability to induce and control LSs in the terahertz domain could significantly impact the design of next-generation sensors and wavelength division multiplexers,” adds Minggui Wei, and Feng Wu.
The study, titled “Abrupt lateral beam shifts from terahertz quasi-bound states in the continuum”, was published in Science Bulletin .
Science Bulletin