In order to improve the signal-to-noise ratios for free-space communication, remote sensing and lidar systems, a rubidium laser induced dispersion optical filter (LIDOF) at 775.9 nm was experimentally studied. Owing to unbalance of occupancy among in sublevels of the excited state, which is caused by selective excitation of a linearly polarized pump beam at 780 nm, dichroism and birefringence of the excited state are induced. So the polarization direction of 775.9 nm probe beam is rotated and transmitted. The filter has a peak transmission of 4% with a single bandwidth of 605 MHz. The peak transmission versus the cell temperature and pump intensity is also given.