This advancement allows you to handle large amounts of data etc. It may enable the development of compact 3D photonic integrated devices that can process Researchers have developed a new way to control and manipulate optical signals by directly placing a liquid crystal layer on waveguides created by laser writing. The new devices provide electro-optical polarization control, which could open new opportunities for chip-based devices and complex photonic waveguide-based circuits with femtosecond recording.

“Laser waveguide recording and electro-optical modulation using liquid crystals have not been combined in this way before,” said Alessandro Alberucci of the Friedrich Schiller University of Jena in Germany. “We hope that this technology can be used to create a new class of integrated photonic devices that can process large amounts of information for data centers and other data-intensive applications.”

In the magazine Optical Material Express The researchers describe how they created a tunable waveplate inside a fused silica waveguide. When voltage is applied to the liquid crystal, its molecules rotate, which changes the polarization of the light passing through the waveguide. In experiments, the researchers demonstrated complete modulation of optical polarization at two different visible wavelengths.

“Our work paves the way for the integration of new types of optical functions into the entire volume of a single glass chip, creating compact 3D photonic integrated devices that were previously impossible,” Alberucci said. “The unique three-dimensional nature of femtosecond waveguides can be used to create new spatial light modulators in which each pixel is processed individually by a single waveguide. The technology may also find application in the experimental application of dense optical neural networks.”

Combination of two core technologies

Femtosecond lasers can be used to write waveguides deep into the material rather than just writing on the surface like other methods; this makes it a promising approach to maximizing the number of waveguides on a single chip. This approach involves focusing an intense laser beam into a transparent material. When the optical density is high enough, the beam displaces the material under illumination, thus acting as a kind of pencil with micrometer precision.

“The major drawback of using femtosecond laser recording technology to create waveguides is the difficulty of modulating the optical signal in these waveguides,” Alberucci said. “Since a complete communications network requires devices that can monitor the transmitted signal, our work explores new solutions to overcome this limitation.”

In a new paper, researchers combined two fundamental photonic technologies by placing a liquid crystal layer in a waveguide. When the beam propagating inside the waveguide hits the liquid crystal layer, it changes the phase and polarization of the light when an electric field is applied. The modified beam then passes through the second section of the waveguide, thus emitting a beam with modulated properties.

“Hybridization allows access to the advantages of both technologies in a single device: the high light concentration due to the guiding effect and the high degree of tunability associated with liquid crystals,” Alberucci said. “This research paves the way for using the properties of liquid crystals as modulators in photonic devices with waveguides embedded throughout their volumes.”

Advantages of hybrid approach

While optical modulation in laser-written femtosecond waveguides has previously been achieved by locally heating the waveguide, the use of liquid crystals in the new study allows direct control of polarization. “Our approach has many potential advantages: lower power consumption, the ability to independently treat individual waveguides collectively, and lower crosstalk between adjacent waveguides,” Alberucci said.

To test the devices, the researchers injected laser light into a waveguide and then varied the voltage applied to the liquid crystal layer, which modulated the light. The polarization measured at the output varied according to theory. They also found that by integrating the liquid crystal with waveguides, the modulation properties of the liquid crystals remained intact.

The researchers note that this study is only a proof of concept, so more work needs to be done before the technology is ready for practical use. For example, the current device modulates each waveguide equally, so they work to provide independent control of each waveguide.