Side Illumination Behavior and Mechanical Properties of Twisted End-Emitting Polymer Optical Fiber Bundles

Polymer optical fibers (POFs), including side-emitting POF (SEPOF) and end-emitting POF (EEPOF) are developed for luminous textiles. The SEPOF is more common for usage but suffers from significant intensity decay, which limits its effective usage length. In contrast, the EEPOF can provide a much more stable side illumination behavior than SEPOF since the light is largely confined within the EEPOF, while its side illumination requires special treatment. In this work, 0.5 mm diameter EEPOFs were firstly assembled into bundles with 10 EEPOFs (B10) and 15 EEPOFs (B15), and then twisted. The morphology, tensile properties, and side illumination behavior of the twisted EEPOF bundles are evaluated. With an increased twisting degree, the initial modulus of twisted sample B10 increases (due to shortening of bundle diameter) from 1.06 to 1.17 GPa while the initial modulus of twisted sample B15 decreases from 1.01 to 0.91 GPa. The increased twisting degree also results in the higher flexibility (indirectly connected with modulus) of the twisted EEPOF bundles. Besides, the increased twisting degree results in a higher side illumination intensity meantime causes a decreased side illumination intensity along the light penetration path. When the twisting degree is low (e.g., 10 T m⁻¹), the highest decrease rate of side illumination intensity along the light penetration path is found.