Fast analyses and designs of long-period fiber grating devices with cosine-class apodizations by using Fourier mode coupling theory

Abstract

This paper presents an analytical approach to fast analyzing and designing long-period fiber grating (LPFG) devices with cosine-class apodizations by using the Fourier mode coupling (FMC) theory. The LPFG devices include LPFGs, LPFG-based in-fiber Mach-Zehnder and Michelson interferometers, which are apodized with the cosine-class windows of cosine, raised-cosine, Hamming, and Blackman. The analytic models (AMs) of the apodized LPFG devices are derived from the FMC theory, which are compared with the preferred transfer matrix (TM) method to confirm their efficiencies and accuracies. The AM-based analyses are achieved and verified to be accurate and efficient enough. The AM-based analysis efficiency is improved over 1318 times versus the TM-based one. Based on the analytic models, an analytic design algorithm is proposed and then applied to designing these LPFG devices, which has the complexity of O(N) and is far faster than the existing design methods.