Laser diodes (120) emit laser beams along a vertical YZ plane at different distances from the YZ plane. The beams are collimated in their fast and slow axes, and are redirected by turning mirrors (162) to form a beam stack (130C) traveling along the XZ plane. The beam stack is turned by about 90.degree., then converged by a focusing lens (174) into an optical fiber (180). A compact assembly is thus provided. Each laser diode (120.i), its collimating optics (154.i, 158.i, i=1, 2, . . . ) and its turning mirror (162.i) are rigidly attached to a flat, heat-spreading surface (144.i) and thus remain aligned with each other in thermal cycling.