The waveguiding properties of double heterostructure lasers with nonsymmetrical structure have been investigated. Either large optical cavity (LOC) lasers with separate carrier and optical confinement or distributed feedback (DFB) and distributed Bragg reflector lasers (DBR), respectively, can be investigated easily with the aid of our analytical expressions for the near-field distribution, the confinement factors and the DFB coupling coefficients. Formulas are given here for the first time in analytical form; in connection with analytical expressions for the bulk refractive indexes of the quaternary InGaAsP/InP system they have been used for the design of 2nd-order λ = 1.55 μm DFB lasers. Thus, threshold currents of 12 mA have been achieved experimentally.