Novel silicon chip allowing terahertz waves to pass through barriers could enable future 6G networks

Researchers at JNCASR demonstrated that a silicon photonic crystal chip can guide terahertz waves across deliberately engineered barriers while carrying high-speed data. The result matters because future 6G networks may use terahertz frequencies, but compact circuits usually lose signal at bends, junctions, and obstacles.

The team changed the sizes of triangular holes in a silicon slab to create barriers. One barrier added only about 1–2% loss, while two barriers added about 2–3%. The chip was also tested in an omega-shaped route with four sharp bends and in a power splitter. The splitter carried data at 100 Gbit/s using QAM-32 modulation.

The work shows that topological photonics can help build practical terahertz circuits, not just ideal straight waveguides. Tests across 310–360 GHz closely matched simulations. The researchers now plan to tune barriers electrically, thermally, or mechanically, potentially redirecting signals between paths on demand.

Terahertz waves are electromagnetic waves with frequencies between microwaves and infrared light. The article highlights their wide bandwidth, meaning they can provide broad channels for communication. That capacity makes terahertz frequencies attractive for possible sixth-generation, or 6G, wireless networks.

The chip study focused on frequencies from 310 to 360 GHz. At these frequencies, waves can carry very fast data, but guiding them through small circuits is difficult. Bends, junctions, and sudden changes in a waveguide can scatter or reflect part of the signal, weakening transmission.

Terahertz technology is therefore important not only because of its frequency, but also because circuits must handle it efficiently. The reported silicon chip carried up to 100 Gbit/s while crossing engineered barriers. This suggests that compact terahertz components could eventually help route, split, and manage signals in future 6G systems, although the article presents 6G as a future possibility.

The highest reported data rate was 100 Gbit/s. It was achieved by the power splitter using QAM-32 modulation, which encodes information through both a signal’s amplitude and phase. At that rate, a 5-gigabyte high-definition film could theoretically be transferred in under half a second.

Barrier performance was also strong. A single engineered barrier added approximately 1–2% loss. Two barriers placed in sequence added about 2–3% loss. The team also tested an omega-shaped device with four sharp bends and a central barrier, plus a splitter with a barrier in one branch.

The devices did not all reach the same data rate. The double-barrier device carried 48 Gbit/s, while the omega-shaped device carried 60 Gbit/s. The splitter reached 100 Gbit/s, and its two output signals were nearly identical. These results show that barriers can be introduced without greatly disrupting transmission.

The researchers built a silicon photonic crystal whose triangular holes mimic graphene’s honeycomb lattice. Photonic crystals control how electromagnetic waves move by arranging material and holes in a carefully designed pattern. This structure guided terahertz waves along the boundary between two regions.

To make a barrier, the team changed the sizes of the triangular holes over a short section of the waveguide. The altered geometry changed the local coupling conditions, creating an obstacle without physically blocking the channel. The waves could still cross it through the device’s topological boundary channel.

The experiments found a practical design rule. Transmission stayed close to its barrier-free level while the barrier strength remained below a characteristic coupling strength of the crystal. One barrier caused only about 1–2% loss. This approach makes the barrier easy to define during fabrication because its strength is controlled by hole geometry.

The chip preserved transmission because its photonic crystal created a topological boundary channel. Such channels can resist certain kinds of backscattering, which occurs when waves are redirected backward by imperfections or changes in a route. That protection is useful when a circuit includes obstacles or abrupt geometry changes.

The researchers tested more than a straight path. One device placed two barriers in sequence. Another followed an omega-shaped route with four sharp bends and a central barrier. A third was a power splitter with a barrier in one branch. The splitter’s two output signals were nearly identical, showing that the barrier had little effect.

A conventional, non-topological waveguide suffered a marked transmission reduction from a comparable barrier. The silicon devices performed better because their boundary-channel design tolerated the engineered changes. However, the article describes resistance to certain kinds of backscattering, not unlimited protection from every possible loss.

The demonstrated approach could help researchers build compact terahertz circuits that route and split signals on a single silicon chip. That matters for possible 6G networks, which are expected to use terahertz frequencies and need practical ways to guide their wide-bandwidth signals through small devices.

The experiments already showed several useful functions. Signals crossed one or two barriers, travelled through an omega-shaped route with four sharp bends, and passed through a power splitter. The splitter carried 100 Gbit/s with QAM-32 modulation, while its two outputs were nearly identical. These results suggest that barriers need not prevent useful signal processing.

The next step is active control. The team plans to tune barriers electrically, thermally, or mechanically. If successful, that could allow a device to redirect signals between paths when needed. The article presents this as a future possibility, not as a completed feature or deployed 6G system.

Electromagnetic frequency describes how rapidly a wave oscillates, while wavelength is the distance between repeating wave peaks. They are linked: higher frequency means shorter wavelength in the same medium. Bandwidth is the range of frequencies available around a signal. In general, a wider usable bandwidth allows more information to be transmitted, provided the signal remains distinguishable from noise and distortion.

Waveguide geometry determines whether the electromagnetic field can travel efficiently. Its dimensions and shape must suit the wave’s wavelength and mode. Bends, junctions, abrupt changes, or poorly matched sections can scatter or reflect energy. That reduces the signal available for carrying data and may distort its amplitude or phase.

The article illustrates this at terahertz frequencies. Its silicon photonic crystal used triangular-hole geometry to guide waves along a boundary. Engineered barriers added little loss when kept below a characteristic coupling strength. The broader relationships here are established electromagnetic principles; the article specifically reports the chip’s terahertz results.