Theoretical Design of Band Pass Filter Utilizing Long Period Fiber Grating Having Cladding Refractive Index Perturbation

Abstract

In this work, theoretical design of a novel band pass filter based on the turning-around-point long period fiber grating (TAP-LPFG) having cladding index modulation is proposed and demonstrated. Cladding modes are excited by introducing the incident light into the fiber cladding of the input end of the TAP-LPFG. At the grating region, only those cladding modes that satisfy the phase matching condition couple back to the fiber core to obtain the band pass transmission. It is shown that a band pass filter with –3 dB width of from ~115 to ~198 nm with the center wavelength of ~1554.4 nm can be obtained, and the suppression of more than 10 dB for the side-lobes is achieved in a wide wavelength range. This novel TAP-LPFG based device can find applications in optical communications for wide band pass filter.