Integrated photonics has transformed optical technology, yet conventional on-chip waveguides remain constrained to planar geometries with limited design flexibility. At the same time, applications spanning chiral sensing, quantum optics, nonlinear optics, and lab-on-chip spectroscopy require more versatile waveguide platforms for strong light-matter interaction. In this issue, researchers introduce the concept of the twisted hollow-core light cage, a chiral on-chip waveguide platform with an air core fabricated via 3D nanoprinting. These sidewise-open structures leave the air core accessible to external species while their built-in twist imparts a strong chiral response, achieving twist rates and circular dichroism over two orders of magnitude higher than in twisted hollow-core fibers.

The cover of Advanced Photonics Volume 7, Issue 4, features a schematic of the chiral waveguide transmitting one circular polarization. By uniting hollow-core guidance, lateral accessibility, and structural chirality, twisted light cages offer functionalities that surpass those of conventional on-chip waveguides and twisted fibers, establishing a new building block for integrated chiral photonics.

The image is based on the research presented in the article by Johannes Bürger, Jisoo Kim, Thomas Weiss, Stefan A. Maier, and Markus A. Schmidt, “On-chip twisted hollow-core light cages: enhancing planar photonics with 3D nanoprinting,” Adv. Photon. 7(4), 046002 (2025), doi: 10.1117/1.AP.7.4.046002.