Bandwidth analysis of long-period fiber grating for high-order cladding mode and its application to an optical add-drop multiplexer

Abstract

The spectrum bandwidth of long-period fiber grating (LPG) for various high-order cladding modes are analyzed in detail by two-mode coupled-mode equations and applied to design narrow bandwidth optical add-drop multiplexer (OADM) based on two parallel LPGs. In addition, in order to obtain the maximal power transmission, we further derive the structure parameters of OADM such as the distance between two parallel fibers and the length of two long-period fiber gratings according to four-mode coupled-mode equations. As far as this OADM structure is concerned, it is obvious that LPG will dominate the entire bandwidth if LPG has enough narrow bandwidth in comparison with the 2×2 coupler. In other words, we can easily use LPG to estimate the bandwidth of OADM before starting to design it. In order to survey the feasibility of the above statement, the spectrum bandwidths of LPG and OADM for the various bandwidth of high-order cladding modes are compared and analyzed. Utilizing the four steps proposed in this paper, the numerical results have demonstrated that we can use the high order cladding mode =125 to design the OADM that possesses narrow FWHM (<0.4 nm) and meets the DWDM system