Polarization of Laser Writing Waveguides Controlled by Liquid Crystal

German researchers have developed a method for controlling and manipulating optical signals by embedding liquid crystal layers into waveguides created by direct laser writing. This work has produced devices capable of electro-optic control of polarization, which may open up possibilities for chip based devices and complex photonic circuits based on femtosecond write waveguides.

Researcher Alexandro Albertucci from Jena Friedrich Schiller University suggests that this progress may benefit other data intensive applications both inside and outside the data center.

Researchers combine two basic photon technologies by embedding a layer of liquid crystal inside the waveguide. When the light beam propagating inside the waveguide enters the liquid crystal layer, it will change the phase and polarization of the light when an electric field is applied. Then, the modified beam passes through the second part of the waveguide, propagating a beam with modulation characteristics. The fused silica waveguide comprises a tunable wave plate. Researchers demonstrated the complete modulation of light polarization at two visible light wavelengths using this system.

Alberucci said, "Our work paves the way for integrating new optical functions into the entire volume of a single glass chip, enabling compact 3D photonic integrated devices that were previously impossible to achieve. The unique 3D characteristics of femtosecond written waveguides can be used to create new spatial light modulators, where each pixel is individually addressed by a waveguide.".

Albertucci added that this technology can also be applied in the experimental implementation of dense optical neural networks.
Femtosecond lasers can be used to write waveguides deep into the material, rather than just writing waveguides on the surface like other methods, making it a promising method to maximize the number of waveguides on a single chip. This method involves focusing a strong laser beam inside a transparent material. When the optical intensity is high enough, the beam will change the material under illumination, resembling a pen with micrometer level accuracy.

"The most important drawback of using femtosecond laser writing technology to create waveguides is the difficulty in modulating the optical signals in these waveguides," said Alberucci. Due to the need for devices capable of controlling the transmission of signals in a complete communication network, our work explores new solutions to overcome this limitation.

Although the optical modulation of femtosecond laser writing into waveguides was previously achieved through local heating of waveguides, the use of liquid crystals, such as in recent works, can directly control polarization. Albertucci said that the benefits of this method include lower power consumption; Can independently handle individual waveguides in bulk; And reduce crosstalk between adjacent waveguides.

In addition, although the use of liquid crystals as modulators has become mature, this work helps to map the route for using liquid crystal properties as modulators in photonic devices embedded with waveguides throughout the entire volume, said Alberucci.

Researchers say that as this study is still a proof of concept, more work needs to be done before the technology is ready for practical application. For example, current devices modulate each waveguide in the same way. Therefore, the goal of the researchers is to achieve independent control of each waveguide.
This study was published in Optical Materials Express.

Source: Laser Net