We have demonstrated the bandwidth control of a Ti-diffused periodically poled LiNbO3 (Ti:PPLN). Solc filter by a temperature-gradient-control technique. Up to 2.8 nm of filtering bandwidth was achieved with a simple temperature-gradient-control technique in a 78-mm-long of Ti:PPLN waveguide, which has a 0.2 nm filtering bandwidth at an uniform temperature. We have also analyzed the experimental results with the theoretical calculation which is derived from the codirectional coupled mode equations. (c) 2008 Optical Society of America.