Broadband circular polarizer based on chiral fiber grating

Based on the adiabatic coupling principle, a new scheme of a broadband circular polarizer formed by twisting a high-birefringence (Hi-Bi) fiber with a slowly varying twist rate is proposed. The conditions of adiabatic coupling for the adiabatic polarizer are identified through analytical derivations for the first time. The key design procedure is then suggested for achieving the required performance specifications such as the bandwidth and extinction ratio of the polarizer. The dependencies of the performance on structure parameters such as length and birefringence of the twisted fiber is discussed by simulations, and the broadband characteristics of the proposed polarizer are successfully demonstrated.