A silicon chip capable of carrying terahertz waves across a deliberately engineered barrier while sustaining data transmission at up to 100 gigabits per second (Gbit/s) has been developed by researchers at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), an autonomous institute of India's Department of Science and Technology (DST), pointing toward compact terahertz circuits for sixth-generation (6G) communications.
Future 6G wireless networks are expected to operate at terahertz frequencies — the band between microwaves and infrared light — which offer wide bandwidth but present significant engineering challenges. Bends, junctions and abrupt changes in a waveguide can scatter or reflect a signal, weakening it in transit. The JNCASR team addressed this through topological photonics, patterning triangular holes in a carefully designed arrangement across a silicon slab to form a photonic crystal whose structure mimics the honeycomb lattice of graphene. Terahertz waves are guided along the boundary between two regions of that crystal.
The key result is that a single engineered barrier — created simply by altering the size of the triangular holes over a short section — added only about 1–2% loss, while two barriers in sequence produced about 2–3% loss. In a conventional, non-topological waveguide, a comparable barrier markedly reduces transmission. Transmission remained close to its barrier-free level as long as the barrier strength stayed below a characteristic coupling strength of the crystal, which the team describes as a practical design rule for such devices.
Three devices were fabricated on high-resistivity silicon, a material compatible with established semiconductor manufacturing: 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 310–360 GHz agreed closely with simulations. In high-speed data tests, the double-barrier and omega-shaped devices carried 48 and 60 Gbit/s respectively, while the splitter reached 100 Gbit/s using QAM-32 modulation. At that rate, the researchers note, a 5-gigabyte high-definition film could in principle be transferred in under half a second.
The study was led by Dr Abhishek Kumar, Assistant Professor at JNCASR and head of its Meta Optics Laboratory (MetoLab), with Samina Mulla and Sangram Kumar Sadhu as joint first authors. Collaborating institutions included IISER Kolkata, IIT Bombay, the Institute of Microelectronics at A*STAR in Singapore, and the University of Lille and CNRS in France.
"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 team next plans to tune barriers electrically, thermally or mechanically, which could allow a device to redirect signals between paths on demand. The findings have been published in the journal Advanced Materials.
This article is based on a primary source and has undergone editorial review prior to publication.
