A New Method for Detecting Stability Characteristics of Optical Devices

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In optical fibers, chips, and other devices that guide light, small defects can scatter photons and disrupt their paths. A new study presents a method that reveals properties which help light wave behavior resist such defects in certain systems. This method could accelerate research into new types of electronic and optical technology and contribute to more reliable quantum devices.

In a study published in Physical Review Letters, researchers at the KTH Royal Institute of Technology have unveiled a programmable chip capable of detecting and measuring “topological properties”—the wave behavior characteristics that remain unchanged even when a system is altered.

KTH Associate Professor Ali Elshaari says that understanding these features can help devices continue operating despite their flaws.

Elshaari says that topological properties can make materials remarkably stable. “When explaining topology to students, I start with a knot on a string,” he says. “You can stretch it, bend it, or shake it; the knot stays in place until you cut the string.”

Physicists have discovered that certain materials and devices share similar nodal patterns in the way waves propagate through them.

Andrea Cataldo, the paper’s lead author and a KTH doctoral student, says that such resilience would be attractive for technologies that need to work despite noise and flaws, such as future electronics and quantum devices.

In the real world, every system loses some energy,” says Cataldo. “That’s why we need ways to examine these features under realistic conditions.

The light-based chip can mimic energy-dissipating systems and directly reveal their hidden stable properties, they say.

According to Cataldo, the chip reliably distinguished “topological” states from ordinary ones. It also identified a special point called the exceptional point, where energy-dissipating systems behave unusually.

“We use a mathematical trick to run the lossy system on-chip without actually losing the signal,” he says. The researchers then compare the light against reference beams—an approach they liken to tuning an instrument against a reference tone.

“This allows us to read information that energy loss would normally hide,” he says.

Since the chip is programmable, many different scenarios can be tested on a single device.

Andrea Cataldo et al. Interferometric readout of momentum-space topology in a programmable dissipative photonic circuit, (2026). DOI: 10.1103/xkht-64kc On DOI: 10.48550/arxiv.2609.38352

Provided by: KTH Royal Institute of Technology

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