Laterally gain-coupled distributed feedback GaInAsP/InP lasers were fabricated by focused ion-beam implantation and rapid thermal annealing of ridge waveguide structures. An absorption grating, which interacts with the evanescent light field, is formed by a periodic reduction of the band-gap absorption in the passive sections along the ridge. Room-temperature single-mode emission was observed at 1.5 &mgr;m with a 30 dB side-mode suppression ratio. Simultaneously, the increase of the band gap in the implanted section results in improved carrier confinement, which reduces the leakage current and improves the laser performance in comparison to unimplanted ridge waveguide lasers. ©1998 American Institute of Physics.