JNCASR Silicon Chip Carries Terahertz Data at 100 Gbit/s

Researchers at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), an autonomous institute of the Department of Science and Technology, have demonstrated a silicon chip on which terahertz waves cross a deliberately built barrier with almost no loss while carrying data at 100 Gbit/s. The result points towards compact terahertz circuits for sixth-generation, or 6G, communication.

The problem being solved

Future 6G networks are expected to work at terahertz frequencies, which sit between microwaves and infrared light and offer very wide bandwidth. Routing such waves through small circuits is hard: bends, junctions and sudden changes in a waveguide scatter or reflect part of the signal and weaken it along the way.

What the team built

The group used topological photonics. Triangular holes were arranged in a silicon slab in a pattern that mimics the honeycomb lattice of graphene, creating a photonic crystal that guides terahertz waves along the boundary between two regions. A barrier was then formed simply by altering the sizes of the triangular holes over a short stretch of the waveguide, an effect known as photonic Klein tunnelling. One such barrier added only about one to two per cent loss, and two barriers in sequence about two to three per cent, where an ordinary non-topological waveguide would have cut transmission sharply. Transmission stayed near its barrier-free level so long as the barrier strength remained below a characteristic coupling strength of the crystal, which gives designers a usable rule of thumb.

The devices and the speeds

Three devices were fabricated on high-resistivity silicon, a material that suits established semiconductor manufacturing: one with two barriers in sequence, one with an omega-shaped route holding four sharp bends and a central barrier, and a power splitter with a barrier in one branch. Measurements over 310 to 360 GHz matched simulations closely. The double-barrier device carried 48 Gbit/s and the omega-shaped one 60 Gbit/s, while the splitter reached 100 Gbit/s using QAM-32 modulation, a rate at which a five-gigabyte film could in principle move in under half a second.

Who did the work

The study was led by Dr Abhishek Kumar of JNCASR, who heads the Meta Optics Laboratory, with Samina Mulla and Sangram Kumar Sadhu as joint first authors. Collaborators came from IISER Kolkata, IIT Bombay, the Institute of Microelectronics at A*STAR in Singapore and the University of Lille with CNRS in France. The work appeared in the journal Advanced Materials.