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High-frequency (0.02-1.8 GHz) noise power measurements of both index- and gain-guided DH (AlGa)As injection lasers were carried out by means of single detector equipment. The index-guided structures include a new diffused index-guided type and some channeled substrate planar (CSP) structures, whereas the gain-guided lasers all have a stripe defined by proton bombardment, but they differ in the width of their stripe ( m) and the depth of the bombardment. From the measurements it was concluded ihat although, generally speaking, index-guided lasers show the lowest intensity noise level, the gain-guided lasers can approach this level, provided that their structure is optimized. The results of some of the various types of lasers studied are compared qualitatively with predictions of McCumber's theory.