An international team of researchers has conducted experiments with an optical fiber featuring a liquid core, which was frozen to create sharp phase transitions. The results demonstrated that this approach opens up new possibilities for neuromorphic computing.

Changes in Properties During Phase Transitions

When a substance transitions from one phase to another, its characteristics change significantly. For example, lava solidifies into hard rock as it cools, and a frozen rubber shoe sole becomes brittle. Physical, electrical, and mechanical properties, as well as refractive index and density, all shift, affecting how light passes through the material.

Features of Liquid-Core Optical Fiber

Traditional optical fiber is made by drawing a thin thread from molten glass, allowing light to travel over long distances. There are also other types of optical fibers, such as those with hollow cores that can be filled with various gases or liquids. These systems are used in detectors, fiber lasers, and endoscopes, and can also function as miniature chemical laboratories or precise thermometers.

A New Type of Optical Fiber

The researchers developed a quartz glass optical fiber with a cavity filled with liquid carbon disulfide (CS₂). For the experiments, the core was frozen to 77 Kelvin in a nitrogen atmosphere. As a result, the system demonstrated significantly higher efficiency compared to conventional optical fibers.

During the experiments, Mandelstam–Brillouin scattering was observed, indicating a strong interaction between light and sound in the chosen medium. The phase transition creates a region with a sharply changing refractive index, which leads to a substantial enhancement of the Brillouin effect.

Experimental Results

In the frozen liquid-core optical fiber, the Brillouin gain coefficient was found to be 1,000 times higher than in standard fibers, exceeding 3,000 W⁻¹·m⁻¹. To achieve this result, the researchers used a fiber segment only 27.5 centimeters long and a pump laser with very low power (0.03 milliwatts).

Optoacoustic Memory

Based on the new fiber, the team created an optoacoustic memory. Information was transferred from a fast light wave to slower acoustic waves and then converted back into light. Acoustic waves retain information about the light signal for a longer period, allowing data to be read during the reverse conversion. This technology could reduce energy consumption in fiber-based photonic neuromorphic computing.

Application Prospects

This development paves the way for new physical platforms with extreme nonlinear properties and simple operation. The high efficiency of optoacoustic memory and the strong coupling between light and sound can be used not only in neuromorphic computing, but also in quantum information processing, microwave photonics, and high-precision measurements.