Polarization and transverse-mode selection in quantum-well vertical-cavity surface-emitting lasers: index- and gain-guided devices

Abstract

We study polarization switching and transverse mode competition in Vertical Cavity Surface Emitting Lasers in the absence of temperature e ects. We use a model that incorporates the vector nature of the laser eld, saturable dispersion, di erent carrier populations associated with di erent magnetic sublevels of the conduction and heavy hole valence bands in quantum well media, spin-ip relaxation processes and cavity birefringence and dichroism. We consider both index-guided and gain-guided VCSELs, and we nd that spin-ip dynamics and linewidth enhancement factor are crucial for the selection of the polarization state corresponding to a given injection current. For index-guided VCSELs the e ect of spatial hole burning on the polarization behavior within the fundamental mode regime is discussed. For gain-guided VCSELs, transverse mode and polarization selection is studied within a Maxwell-Bloch approximation which includes eld di raction and carrier di usion. Polarization switching is found in the fundamental mode regime. The rst order transverse mode starts lasing orthogonally

Transient response of vertical-cavity surface-emitting lasers of different active-region diameters

“…In addition, we studied the polarization properties of the transient response. It had been shown that these devices usually present a dominant polarization state during dc operation [14], [15] and that the characteristic time for achieving this state is of the order of a few nanoseconds [16], [17]. Our measurements complement this knowledge, showing that the two polarization states of all the transverse modes are present during subnanosecond excitation and that they evolve with the same dynamics.…”

Polarization Dynamics of Current-Modulated Vertical-Cavity Surface-Emitting Lasers

“…We simulated the model equations with typical parameters indicated in Table I [4], [5], [37]. To study the polarization competition induced by the interplay of current modulation, spatial hole burning and waveguiding effects, we vary the modulation parameters, , , , the carrier diffusion rate, , and the refractive index of the polarization in the active region, .…”

“…Full details of the model are given in [5], [37] and thus here we simply highlight its main features. The equations for the two linearly polarized slowly-varying complex amplitudes of the optical field, and , the total carrier density , and the population difference , between the carrier densities with positive and negative spin values, are…”

“…Birefringence is taken into account assuming that the refractive index in the core region in the direction is different from that in the direction , while in the cladding region is isotropic [5] for for (7) Here is the radius of the core region of the waveguide. As a consequence of birefringence, the transverse profiles and are different, and thus, the two polarizations have different modal gains, given by (5).…”

“…In this work we study the dynamics of current-modulated VCSELs, including both transverse and polarization effects. We use the framework of the spin-flip model [4] to take into account the polarization, and the index-guided approximation to include transverse effects [3], [5]. The transverse optical profiles and modal frequencies are determined by the built-in refractive index distribution, thus allowing a description in terms of modal amplitudes.…”