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Ridge waveguide double heterostructure (DH) lasers are theoretically investigated over the gain-guiding and the index-guiding regions. To determine the lasing mode profiles, the spatial variations of the complex refractive index (the gain-guiding and the anti-index-guiding effects) caused by the distribution of injected carriers, as well as the index-guiding effect due to the ridge waveguide, are self-consistently taken into account. From the self-consistent results for the carrier distribution and the lasing mode profiles, various static properties such as the threshold current, lasing of higher lateral modes, and the astigmatism are obtained as functions of the distance between the active layer and the base of the ridge. The results show a gradual transition from the index-guiding to the gain-guiding regions, and the anti-index-guiding effect is found to play an important role in the latter region.