  Injecting spin-polarized carriers into semiconductor lasers provides
important opportunities to extend what is known about spintronic devices, as
well as to overcome many limitations of conventional (spin-unpolarized) lasers.
By developing a microscopic model of spin-dependent optical gain derived from
an accurate electronic structure in a quantum well-based laser, we study how
its operation properties can be modified by spin-polarized carriers, carrier
density, and resonant cavity design. We reveal that by applying a uniaxial
strain, it is possible to attain a large birefringence. While such
birefringence is viewed as detrimental in conventional lasers, it could enable
fast polarization oscillations of the emitted light in spin lasers which can be
exploited for optical communication and high-performance interconnects. The
resulting oscillation frequency ($>200$ GHz) would significantly exceed the
frequency range possible in conventional lasers.
