New Delhi: Researchers have developed a novel silicon chip that allows terahertz waves to pass through engineered barriers with minimal signal loss while supporting data transmission speeds of up to 100 gigabits per second (Gbit/s).
The development could pave the way for compact terahertz circuits and advanced communication technologies for future sixth-generation (6G) wireless networks.
Future 6G wireless networks are expected to use terahertz frequencies, which lie between microwaves and infrared light and offer wide bandwidth.
However, guiding terahertz waves through compact circuits remains challenging. Bends, junctions and sudden changes in a waveguide can scatter or reflect parts of the signal, weakening it as it travels.
To address this challenge, researchers have developed a technique that allows terahertz waves to navigate engineered barriers without significant transmission losses.
By arranging triangular holes in a carefully designed pattern within a silicon slab, researchers can create a photonic crystal that guides terahertz waves along the boundary between two regions.
These boundary channels can resist certain types of backscattering. However, practical terahertz circuits must also be capable of handling deliberately introduced obstacles and changes in geometry without compromising signal transmission.
Researchers at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), an autonomous institute of the Department of Science and Technology (DST), addressed this challenge using an approach based on topological photonics.
The team demonstrated data transmission of up to 100 gigabits per second across an engineered barrier.
The experiments showed that a single barrier introduced only around 1–2% signal loss, while two barriers placed sequentially resulted in approximately 2–3% loss.
In comparison, a conventional, non-topological waveguide experiences a significant reduction in transmission when a comparable barrier is introduced.
How the New Silicon Chip Guides Terahertz Waves
The research team designed a silicon photonic crystal whose structure mimics the honeycomb lattice of graphene. They created barriers by changing the sizes of triangular holes over a short section of the waveguide.
The researchers found that transmission remained close to its barrier-free level as long as the barrier strength remained below a characteristic coupling strength of the crystal.
Since the barrier can be controlled through the geometry of the holes, the approach provides a practical design rule for developing silicon-based terahertz devices.
The team tested the concept using three devices fabricated on high-resistivity silicon, a material compatible with established semiconductor manufacturing processes.
The three devices included:
- A device featuring two barriers arranged sequentially.
- An omega-shaped route incorporating four sharp bends and a central barrier.
- A power splitter with a barrier introduced in one of its two branches.
Measurements conducted across the 310–360 GHz frequency range closely matched the simulation results.
In the power splitter, the two output signals were nearly identical, indicating that the engineered barrier had little effect on signal transmission.
Silicon Chip Demonstrates 100 Gbit/s Data Transmission
The researchers also evaluated the performance of the devices through high-speed data transmission tests.
The double-barrier and omega-shaped devices supported data transmission speeds of 48 Gbit/s and 60 Gbit/s, respectively.
Meanwhile, the power splitter achieved a transmission speed of 100 Gbit/s using QAM-32 modulation, a technique that encodes information through the amplitude and phase of a signal.
At this speed, a 5-gigabyte high-definition film could theoretically be transferred in less than half a second.
The results demonstrate the potential of topological photonics to enable terahertz waves to travel through complex chip structures while maintaining high-speed data transmission and low signal loss.
JNCASR Research Team and Collaborators
The study was led by Dr Abhishek Kumar, Assistant Professor at JNCASR, where he heads the Meta Optics Laboratory (MetoLab).
Samina Mulla and Sangram Kumar Sadhu of JNCASR were the joint first authors of the research.
Other collaborators included Asif Iqbal M and N. S. Vidhyadhiraja from JNCASR; Siddhartha Lal from IISER Kolkata; Anshuman Kumar from IIT Bombay; Zhonghua Gu and Prakash Pitchappa from the Institute of Microelectronics, A*STAR, Singapore; and Pascal Szriftgiser and Guillaume Ducournau from the University of Lille and CNRS, 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.
Future Applications of Terahertz Chip Technology
The findings could help researchers develop advanced terahertz circuits capable of routing and splitting signals on a single chip with minimal transmission loss.
The research team plans to explore ways to control the barriers electrically, thermally or mechanically.
Such control mechanisms could eventually allow devices to redirect signals between different paths on demand, opening up possibilities for more flexible and adaptable terahertz circuits.
The research has been published in the journal Advanced Materials.
Publication Link: https://doi.org/10.1002/adma.75322
