Optical fibers provide an excellent platform for transmitting light over long distances, manipulating it and enhancing light-matter interaction. Now, the “Ultrafast & Twisted Photonics” research group at the Max Planck Institute for the Science of Light (MPL) has developed a new hollow-core fiber that selectively guides optical vortices depending on their helicity and has potential applications in chiral sensing, vortex mode generation, and optical communications.

The results were recently published in the journal ACS Photonics.

In addition to transmitting light over long distances, optical waveguides provide convenient ways of enhancing the interaction of light with matter and manipulating the properties of the guided light. Among several light attributes, pure polarization states are crucial for many applications and research areas.

Over the years, several waveguides and structured materials have been developed to preserve linear and circular polarization over long distances and analyze these states with a sufficient degree of discrimination. In the past two decades, light with more complex polarization states, such as optical vortices, has also found multiple applications.

The recent development of optical fibers guiding optical vortices has provided a route for using the orbital angular momentum carried by light for data multiplexing, thus increasing the capacity of fiber networks. Optical vortices have also been employed for chiral discrimination, which has applications in the pharmaceutical industry, and for controlling the motions of electrons.

As a result, there is growing interest in developing new optical elements that can distinguish the helicity of optical vortices. However, the few structured materials developed for this purpose have not demonstrated high levels of discrimination.

In their work, the MPL scientists moved beyond the control and manipulation of light with linear and circular polarization and reported a new hollow-core waveguide which exhibits a strong helical dichroism. This means that the optical attenuation depends on the orbital angular momentum of the guided light. Thus, the waveguide transmits optical vortices with a specific helicity and largely attenuates vortices with the opposite helicity.

The hollow waveguide can also be designed for spectral regions inaccessible using other optical systems, and filling it with liquid or gaseous media allows the study of light-matter interaction over extended lengths.

Therefore, these helically dichroic waveguides promise the realization of new devices with exceptional discrimination capabilities—comparable to and even exceeding those obtained for linear polarization using crystal-based polarizers.