Far-field solution of the Helmholtz equation for double heterostructure diode lasers

On the basis of the Helmholtz equation the far-field distribution is derived for double heterostructure lasers. The results show that the far-field distribution in the direction normal to the junction plane approaches a Lorentzian function, but parallel to the junction it may be approximated by a Gaussian function. The far-field intensity patterns have analogous elliptic form. It is also shown, for the first time, that the separability condition is not strictly valid for the far-field of a laser diode. Only in the vicinity of the optical axis the field can be expressed as a product of two separate functions, each of which depends only on one of the two transverse coordinates parallel and perpendicular to the diode junction.