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An analysis concerning the coupling efficiency and the threshold current density is presented for a ridge-waveguide distributed feedback laser. Particular attention is paid to the grating efficiency that is different under and beyond the ridge region because of different lateral environments and generally different corrugation depths. The threshold current density and its optimization are discussed for 1.55 μm InGaAsP lasers after considering the design parameters, such as the ridge width and the layer thicknesses. Both the TE and TM modes are considered. A narrow ridge helps to reduce the device threshold if the grating under the ridge is absent or is partially washed out during the ridge-overgrowth procedure.