An apparatus for coupling radiation of individual laser diode emitters into a common optical fiber is disclosed. The radiation is collimated along fast axis and combined by using crossed pairs of flat mirrors. The combined beams are collimated by a common slow axis collimating lens. The laser diode emitters are disposed on both sides of an optical axis of the slow axis collimating lens such that the optical path lengths from the emitters to the slow axis collimating lens are equal.