Researchers at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), an autonomous institute of the Department of Science and Technology, have developed a novel silicon chip that enables terahertz waves to pass through engineered barriers with minimal signal loss while carrying data at speeds up to 100 gigabits per second. This breakthrough in topological photonics addresses a fundamental challenge in future sixth-generation (6G) wireless networks, which are expected to utilize terahertz frequencies between microwaves and infrared light that offer wide bandwidth but face signal degradation when guided through compact circuits with bends, junctions, and abrupt changes.
The technology uses a silicon photonic crystal with triangular holes arranged in a carefully designed pattern mimicking the honeycomb lattice of graphene. By creating barriers through changes in the sizes of these triangular holes over short sections of the waveguide, the researchers demonstrated that transmission remained close to barrier-free levels as long as the barrier strength stayed below a characteristic coupling strength of the crystal. A single barrier added only 1–2% signal loss, while two barriers in sequence added approximately 2–3% loss, significantly outperforming conventional non-topological waveguides where comparable barriers markedly reduce transmission.
Three devices were fabricated on high-resistivity silicon, a material compatible with established semiconductor manufacturing processes: one with two barriers in sequence, one with an omega-shaped route containing four sharp bends and a central barrier, and a power splitter with a barrier in one of its two branches. Measurements across the 310–360 GHz frequency range showed close agreement with simulations, and in the splitter device, the two output signals were nearly identical despite the presence of the barrier.
In high-speed data transmission tests, the double-barrier device carried 48 Gbit/s, the omega-shaped device carried 60 Gbit/s, and the splitter supported 100 Gbit/s using QAM-32 modulation which encodes information in the signal's amplitude and phase. At this maximum rate, a 5-gigabyte high-definition film could theoretically be transferred in under half a second. The research team was led by Dr. Abhishek Kumar, Assistant Professor at JNCASR and head of the Meta Optics Laboratory, with Samina Mulla and Sangram Kumar Sadhu as joint first authors, collaborating with researchers from IISER Kolkata, IIT Bombay, Institute of Microelectronics (A*STAR, Singapore), and University of Lille and CNRS (France).
The work, published in Advanced Materials (DOI: https://doi.org/10.1002/adma.75322), represents a practical design tool for terahertz chips that could enable development of circuits that route and split signals on a single chip with low loss. The team's next research direction involves developing methods to tune the barriers electrically, thermally, or mechanically, which could allow devices to redirect signals between paths on demand for dynamic signal routing applications in future 6G communication technologies.