Evaluation of transmission dispersion characteristics of nonuniform gratings for DWDM systems

Summary form only given. In their role as optical add-drop multiplexers for channel-specific routing in optical networks, as well as in their use as clean-up filters to reduce network crosstalk, fiber Bragg gratings will provide an important enabling technology for dense wavelength-division multiplexed (DWDM) communication systems. While grating-based filters have strong reflectivities over narrow frequency ranges, especially when apodization is used to reduce out-of-band reflections, dispersion is still present in the wings of the grating spectrum where the transmission is essentially unity. Because in a DWDM network a given channel may pass numerous adjacent gratings during propagation, the degradation of the signal due to the dispersion of the fiber gratings could limit the bit rate or transmission distance achievable. With the advent of grating structures with engineered profiles, it becomes important to be able to estimate fiber grating dispersion in the wings of arbitrarily designed grating so that various system parameters can be varied to achieve optimum performance. In this paper, we analyze theoretically and experimentally the dispersion in the wings of such gratings and derive asymptotic expression, which should find use in system designs involving many gratings.