Coupled mode theory: a powerful tool for analyzing complex VCSELs and designing advanced device features

Vertical-cavity surface-emitting lasers (VCSELs) have become leading light sources in plenty of applications due to their good characteristics and low costs. There are, however, some features that need improvements; therefore, optimized or new designs ideas are necessary. To this aim, an electromagnetic simulation tool, which is fast and precise at the same time, is desirable; to cover all the possible requirements, it should be fully three-dimensional (3-D) and vectorial. A model with such features was first proposed by Bava et al. ("Three-Dimensional Model for Vectorial Fields in Vertical-Cavity Surface-Emitting Lasers", Phys. Rev. A, vol. 63, p. 23816, 2001), based on coupled-mode theory. Here, a review of its applications will be given, related to particular devices: nonperfectly circular VCSELs and phase-coupled arrays. The comparison with the corresponding experimental results turns out to be very satisfactory. Therefore, we were encouraged to use the model for obtaining design criteria of polarization maintaining VCSELs by using a small relief grating. The capability of gratings to pin the VCSEL polarization was already demonstrated; however, the different configurations do not allow one to have a clear overview of this technique. Moreover, to the best of our knowledge, a full simulation of a VCSEL with a grating was never presented, due to the complexity of treating the corresponding fully 3-D and vectorial problem. For the first time, we have the possibility of comparing different configurations on the same footing; in particular, we will evaluate the performances of dielectric and metal gratings. With the design we propose here, single-transverse and single-polarization-mode operation are predicted with a suppression of the other polarization easily in the order of 45 dB.