All-Fiber Waveplate Made of Helically Wound Spun Highly Birefringent Optical Fiber

Waveplates are elements that are widely used in the optical system for polarization transformation. In the fiber optical system, it is highly desired to utilize waveplates in the all-fiber form with minimum insertion loss and stable performance. In this paper, we propose an all-fiber waveplate that is made of the helically wound spun highly birefringent (SHB) optical fiber. To function as waveplates, the torsion of the helix should be equal to the inherent polarization rotation of the SHB fiber so that the geometric rotation can match the inherent polarization rotation. Therefore, the phase difference between two orthogonal components of the incident polarized light can increase almost linearly with the fiber length. Because the SHB fiber is insensitive to external perturbations, the proposed waveplate can provide a definite and stable polarization transformation. We develop a model based on the perturbation theory to characterize the polarization evolution of the helically wound SHB fiber. Simulations and experiments have demonstrated the excellent performance of our all-fiber waveplates.