Researchers leverage liquid crystal structures to design simple yet versatile bifocal lenses

Researchers have developed a new type of bifocal lens that provides a simple way to obtain two foci (or spots) whose intensities can be adjusted by applying an external voltage. The lenses, which use two layers of liquid crystal structures, could be useful for various applications such as optical interconnects, biological imaging, augmented/virtual reality devices and optical computing.

“Most liquid crystal-based devices are made from single-layer structures, but this limits the modulation of the light field to a confined area,” said Fan Fan, head of the research team from Hunan University. in China.

“We used bilayer structures composed of a liquid crystal cell and a liquid crystal polymer to achieve more complex and functional modulation of incident light.”

In the magazine Optical lettersresearchers show that the new bifocal lenses can be used for polarization imaging, which is often used to improve image contrast, and for edge imaging, which highlights the contours of objects, making it easier viewing fine details or detecting certain shapes. The article is entitled “Bifocal lenses with adjustable intensities using bilayer liquid crystal structures”.

“In virtual or augmented reality devices, bifocal lenses are commonly used to adjust the image viewing distance to overcome vergence-accommodation conflict, which can cause visual discomfort and eye fatigue,” a Fan said.

“We believe that the light control mechanism we created using the multilayer structure could also be used to design other optical devices, including holographic devices and beam generators, or for optical processing images.”

Inspiration for a new design

The design of the bi-layer bifocal lens was inspired by the rapid development of multifunctional holographic devices. “Researchers have developed many methods to improve the information capacity of holographic devices, including holographic devices based on multilayer structures,” Fan said.

“We thought this type of structure could be useful beyond the field of holographic displays, so we tried to expand its application scenarios.”

Although some bifocal lenses can create different focal points depending on the polarization of the incident light, newer bifocal lenses actively manipulate the polarization states of the output beams. This allows bilayer lenses to split left-handed circularly polarized light into two focused light beams, one with left-handed circular polarization and the other with right-handed circular polarization.

The liquid crystal cell layer also allows bifocal lenses to quickly change focus intensity in response to external voltage. Previously developed bifocal lenses required mechanical rotation of the wavy blade to achieve this.

After confirming that the bifocal lens’ point spread function (a measure of the ability to focus light) conformed to theoretical calculations, researchers incorporated the lens into imaging systems for polarization and imaging. edges. For polarization imaging, the separation distance between the two foci is large (2 millimeters), while edge imaging uses a small separation distance (0.03 millimeters) with equal intensity for both focal points . They showed that the bifocal lens worked well for both types of imaging.

Expanding to more applications

Researchers are currently working to design and manufacture more multifunctional devices based on bilayer structures for use in other research applications. They note that making these optical components practical will require reducing the cost of their mass production, integrating the ability to adapt to different environments, and designing fast and precise layer-to-layer alignment technology.

“With this research, we aimed to illustrate the enormous potential of bilayer structures for optical devices and the advantages of liquid crystal devices in terms of electrical tunability,” Fan said. “We hope these unique features will inspire scientists to develop even more advanced applications.”