A research team at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), an autonomous institute under the Department of Science and Technology (DST), has developed a silicon chip that enables terahertz waves to pass through engineered barriers with minimal signal loss while supporting data transmission speeds of up to 100 Gbit/s, announced PIB.

The achievement could help accelerate the development of compact terahertz circuits for future 6G communication systems. Terahertz frequencies, which sit between microwaves and infrared light on the electromagnetic spectrum, offer exceptionally wide bandwidths and are widely regarded as a key technology for next-generation wireless networks.

One of the major challenges in using terahertz waves is guiding them through compact circuits. Bends, junctions and abrupt structural changes can scatter or reflect signals, weakening their strength and reducing transmission efficiency.

To overcome this limitation, the researchers employed topological photonics. They engineered a silicon photonic crystal containing carefully arranged triangular holes that mimic the honeycomb lattice structure of graphene. This design creates protected boundary channels that guide terahertz waves while resisting certain forms of backscattering.

The team introduced an engineered barrier by altering the size of the triangular holes along a short section of the waveguide.

Despite the deliberate obstacle, terahertz signals continued to propagate with very little degradation, demonstrating a phenomenon known as photonic Klein tunnelling.

Experiments showed that a single barrier introduced only around 1–2% transmission loss, while two consecutive barriers resulted in approximately 2–3% loss.

Equivalent barriers in conventional non-topological waveguides would typically cause a far greater reduction in signal transmission.

The researchers found that transmission remained close to barrier-free levels provided the barrier strength remained below a characteristic coupling strength of the photonic crystal. Because the barrier can be controlled through hole geometry, the finding offers a practical design principle for future terahertz photonic devices.

Three devices fabricated on high-resistivity silicon were used to validate the concept. High-resistivity silicon is particularly significant because it is compatible with established semiconductor manufacturing processes.

The first device incorporated two barriers in sequence. The second featured an omega-shaped pathway containing four sharp bends and a central barrier. The third was a power splitter with a barrier integrated into one of its two branches.

Testing across frequencies ranging from 310 GHz to 360 GHz produced results that closely matched computer simulations. In the power splitter, the outputs from both branches were nearly identical, confirming that the barrier had little impact on transmission performance.

During high-speed data transmission trials, the double-barrier device achieved 48 Gbit/s, while the omega-shaped structure reached 60 Gbit/s. The power splitter delivered data rates of up to 100 Gbit/s using QAM-32 modulation, a technique that encodes information through variations in a signal's amplitude and phase.

At such speeds, a 5-gigabyte high-definition film could theoretically be transferred in less than half a second.

The study was led by Dr Abhishek Kumar, Assistant Professor at JNCASR and head of the Meta Optics Laboratory (MetoLab). Samina Mulla and Sangram Kumar Sadhu of JNCASR served as joint first authors. The project also involved collaborators from JNCASR, IISER Kolkata, IIT Bombay, the Institute of Microelectronics at A*STAR in Singapore, and the University of Lille and CNRS in France.

The findings were published in Advanced Materials, highlighting the growing international interest in terahertz photonics and topological light-guiding technologies.

“Showing that terahertz waves can cross a barrier created simply by changing the hole geometry, while carrying 100 gigabits per second, suggests that this effect can become a useful design tool for terahertz chips,” said Dr Abhishek Kumar.

The research could pave the way for low-loss terahertz circuits capable of routing, splitting and managing signals on a single chip. Looking ahead, the team plans to make the barriers tuneable through electrical, thermal or mechanical control, potentially enabling devices that can dynamically redirect signals between different pathways on demand.

The work also addresses a broader challenge in the terahertz domain, often referred to as the "terahertz gap", where practical components such as waveguides, filters and integrated devices remain relatively immature compared with microwave and optical technologies. As global efforts towards commercial 6G systems continue, innovations such as photonic Klein tunnelling may provide important building blocks for future ultra-high-speed communication infrastructure.

PIB