Femtosecond Laser Line‐Exposure Fabrication of Planar Chiral Microstructures for OAM‐Sign Discrimination and Spatial Encoding

ABSTRACT Orbital angular momentum (OAM) provides an additional degree of freedom for structured‐light information encoding, yet vortex beams with opposite topological charges have nearly identical transverse intensity profiles, making the sign of l difficult to determine by direct intensity detection. Here, a spatial‐light‐modulator (SLM)‐assisted femtosecond laser line‐exposure method is developed for programmable fabrication of planar chiral microstructures and arrays. Based on actual processing comparisons, the throughput of the linear exposure per structure is approximately 47.8 times higher than that of point‐by‐point path writing. Mirror‐enantiomeric structures exhibit vortex‐dependent differential‐reflection responses of opposite sign, converting the OAM phase handedness into a measurable intensity difference, with a reflection‐mode vortex dichroism (VD) magnitude reaching approximately 0.25. Using this response, all 100 randomly ordered positive‐ and negative‐OAM inputs are correctly classified under the tested conditions. The concept is further extended to OAM‐keyed spatial encoding and optical readout using chiral microstructure arrays. This approach combines programmable microfabrication, planar chiral optics, and OAM‐sign readout in an array‐compatible platform for structured‐light state analysis.