Laser having a substantially planar waveguide

In a laser comprising an optical cavity which contains an active medium and a substantially planar waveguide to substantially confine the laser light within a plane, wherein said waveguide is comprised of both high-gain and low-gain regions of the active medium, the improvement which comprises a waveguide which is comprised of varying combination of said high-gain and low-gain regions along the direction of laser light propagation so that the cumulative gain from one end of the optical cavity to the other varies from point to adjacent point along a line within the plane of said waveguide which is perpendicular to said direction of light propagation, wherein said points are uniformly spaced along said line at a distance not greater than 10 .mu.m, wherein said cumulative gain varies in a nonrepetitive manner from one pair of adjacent points to the next pair of adjacent points along said line, and wherein said variation is effective to cause some of the lateral modes of the optical cavity to experience a relatively higher gain than the rest of the lateral modes of said optical cavity.