High-frequency operation of spin vertical-cavity surface-emitting lasers: towards 100 GHz

Spin-controlled vertical-cavity surface-emitting lasers (spin-VCSELs) have a high potential to overcome limitations of conventional purely charge-based lasers. Probably the most important feature of such spin-lasers lies in their ultrafast spin and polarization dynamics which are decoupled from the intensity dynamics and their limitations. This yields the potential to modulate the polarization state of spin-VCSELs with frequencies far above the barriers known for the intensity modulation dynamics of conventional VCSELs. Such a quality makes them ideal devices for fast optical interconnects. While in conventional devices relaxation oscillations provide insights in the intensity dynamics and modulation bandwidth, in spin-VCSELs oscillations in the circular polarization degree are an ideal measure for investigating the dynamics of the coupled spin-photon system. These polarization oscillations (P0s) can be generated using pulsed spin injection and have been proven to be much faster than intensity dynamics in the devices. Their frequency is mainly dependent on the birefringence in the cavities and can be increased by adding mechanical strain. Using an approach for manipulating the birefringence via mechanical strain we demonstrated tunable POs with frequencies up to 44 GHz, recently. Taking our results for strain-induced birefringence splitting of more than 250 GHz into account, the concept has the potential to overcome conventional limitations and to provide polarization modulation in VCSELs with bit rates beyond 100 Gbit/s. In this paper we investigate numerically the influence of the spin decay rate on the PO amplitude and frequency in order to investigate potential limitations for future ultrafast polarization modulation schemes.