Single-channel broadband and multichannel narrowband filtering characteristics of linear chirped long-period fiber gratings

Abstract

Band-stop optical fiber filters based on linear chirped long-period fiber gratings (LPFGs) were investigated. The transmission characteristics of the linear chirped LPFGs were analyzed in detail with transfer matrix method. Linear chirp coefficient had a remarkable influence on the bandwidth of the transmission spectra. When the linear chirp coefficient was 10 −9 and the transmission spectra corresponding to multiple cladding modes were superposed, the bandwidth of the transmission spectra could be expanded to >1000 nm . So the linear chirped LPFGs can be used for single-channel broadband band-stop filters, and the relationships between the grating parameters and the bandwidth of the transmission spectra were given. When the linear chirp coefficient is 10 −8 , several narrow and separated loss peaks appeared in the transmission spectra, which indicated that the linear chirped LPFGs can be used for multichannel narrowband filters. The variations of the grating parameters caused the shifts of the transmission spectra and the changes of the intervals between separated loss peaks. The conclusions that are significant in optimizing the fiber grating filters’ design were obtained.