A group of researchers from the Institute for Quantum Science and Technology, College of Science, National University of Defense Technology, have combined photonic crystals—arranged Distributed Bragg Reflector microstrips—with terahertz metal metasurface to create an optically controlled terahertz 2-bit encoding device. Their study was published in the journal Light Science & Applications.
a, Measured THz transmission spectral variation at various coded states. b-f, Pumping color driving THz spectral variation evolutions over the entire ultrafast on-off-on photoswitching cycle. Image Credit: Light: Science & Applications
Terahertz is a valuable frequency for nondestructive testing, high-speed wireless communication, and advancing science and technology. Effective modulators are necessary to fully utilize terahertz applications.
Due to their contactless, concise construction and rapid response-ability, light-driven reconfigurable terahertz metasurfaces have drawn a lot of attention and have significantly aided in the advancement of terahertz functional devices. Conversely, not much has been done on optical coding methods.
Existing terahertz light-coding systems suffer from low coding speed and single-channel modulation because they rely on optical masks or spatial light modulators. Therefore, more investigation into integrated and miniature light-coded metadevices is required for terahertz switching that is programmable ultrafast.
The multimode coupling effect is designed to yield exceptional sensitivity, multi-channel resonances, and improved modulation efficiency in terahertz metasurfaces. Split resonant resonators (SRRs) of metal metasurface are integrated with intrinsic epitaxial silicon islands to regulate non-radiative loss for ultrafast modulation behavior.
Positioned atop the metal metasurface units, the DBR microstrips that block light at 400 nm and 800 nm strongly integrate with the terahertz metasurface structure, leading to distinct coupling mode dissipations regulated by pump-color excitation. Scientists conducted an experimental evaluation of this integrated metadevice's 2-bit optical terahertz programming behavior. Both numerical models and experiments were used for mutual verification.
This approach further stimulates the investigation of optical programming terahertz devices based on metasurfaces and offers a new avenue for advancement in optical coding terahertz modulation.
The metadevice can be configured to generate the necessary terahertz modulation for various color pumps by combining optical and terahertz metasurfaces. It can handle ultrafast modulation within 1 ns for 2-bit terahertz code modulation. The scientists explain the operation of their metadevice as follows:
(i) “When the metadevice pumped by (400 nm), the non-radiative damping of CM1 increases and then the EIT resonance of the left channel is suppressed. (ii) When the metadevice pumped by (800 nm), the loss of CM2 increases and the right channel is quenched. (iii) When the metadevice is simultaneously pumped by and , both EIT resonances disappear.”
“The encoding process is 00-01/10-00 when each color ( or ) is excited independently …, showing an ultrafast on-off-on photo-switching cycle within 1000 ps. When two color lights are excited simultaneously, the ultrafast encoding modulation is 00-11-00. Also, alternatively activating one channel while modulating the other allows us to achieve an encoding process of 01/10-11-01/10,” they added.
“This coding approach can be extended to multi-bit information processes and may be applied in the field of optical-controlled terahertz imaging,” the scientists forecasted.
The research was funded by the National Natural Science Foundation of China, the National Key Research and Development Program of China, and the Youth Innovation Talent Incubation Foundation of the National University of Defense Technology.
Journal Reference:
He, W., et al. (2024) Color coded metadevices toward programmed terahertz switching. Light Science & Applications. doi.org/10.1038/s41377-024-01495-1.