CO $_{2}$ Laser-Written Long-Period Fiber Gratings in a Germanium–Boron Codoped Fiber: Effects of Applying Tension During the Writing Process

In this letter, we investigate CO₂ laser writing of long-period fiber gratings in a germanium-boron codoped fiber subjected to applied axial tension. We discover that, with sufficient tension, the rejection bands for axially symmetric cladding modes can be suppressed, while new rejection bands for nonaxially symmetric cladding modes are generated. We can keep on erasing and generating these rejection bands by removing and applying the tension along the fiber alternately during the writing process.