A semiconductor laser is provided with one or more rear ports and one front port and with a multi-mode interference optical waveguide that has an active layer (light emitting layer) in all regions in plan view. The front port corresponds to an imaging point at which fundamental mode light forms an image in the active layer (light emitting layer) perpendicular to the waveguide direction of the multi-mode interference optical waveguide, and in plan view the front port is disposed along a central line, off center with respect to a central line, along the waveguide direction of the multi-mode interference optical waveguide.