the output optical beam from an angled - facet semiconductor laser diode is made to propagate parallel to the optical axis of the laser package with low optical back - reflection . in this way , the angled - facet devices are made compatible with conventional semiconductor laser packages enabling them to be economically incorporated in a wide - range of external semiconductor lasers and amplified spontaneous emission sources . the parallel beam is achieved by tilting the laser diode with respect to the front and back surfaces of the package .