We propose a new method to narrow the linewidth of photon pairs generated from spontaneous parametric down conversion (SPDC). The single structure device incorporates an internal Bragg grating onto a nonlinear optical waveguide. We study theoretically the spectral characteristics of SPDC under two Bragg grating structures. We show that using the Bragg grating with a midway π- phase shifter is a promising way to implement narrow-line (~GHz to sub-GHz) entangled photon sources.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.