Beam compressors include separated surfaces having positive and negative optical powers. A surface spacing is selected so that a collimated beam input to the beam compressor is output as a collimated beam. In some examples, beam compressors are situated to compress a laser beam stack that includes beams associated with a plurality of laser diodes. Beam compression ratios are typically selected so that a compressed beam stack focused into an optical waveguide has a numerical aperture corresponding to the numerical aperture of the optical waveguide.