Spin-VCSELs with Local Optical Anisotropies: Toward Terahertz Polarization Modulation

We present a semiclassical model for spin-injected vertical-cavity surface-emitting lasers (spin-VCSELs) with local optical anisotropies. Particular focus is put on highly anisotropic spin lasers with broad application potential. A generalized matrix formalism for extraction of the laser modes is introduced, which enables us to calculate the spatial distribution of vectorial modes in arbitrary spin-VCSELs. The time dependence of such laser modes is further studied by means of the generalized coupled-mode theory, which is the natural anisotropic generalization of the conventional mode-decomposition approach. We use the circularly polarized optical modes as the basis for coupled-mode theory, which leads to extension of the well-known spin-flip model. In contrast to the conventional spin-flip model, the only input parameters are the geometric and local optical properties of the multilayer structure and properties of the gain media. The advantages of the theory are demonstrated in the design and optimization of spin-VCSEL structures with a high-contrast grating. We show that the proposed structures can be used for (i) polarization modulation in the terahertz range with tremendous applications for future ultrafast optical communication and (ii) as prospective compact terahertz sources.