Birefringent Spin-Laser as a System of Coupled Harmonic Oscillators

Adding spin-polarized carriers to semiconductor lasers strongly changes their properties and, through the
transfer of angular momentum, leads to the emission of the circularly polarized light. In such spin-lasers the
polarization of the emitted light can be modulated an order of magnitude faster than its intensity in the best
conventional lasers1. This ultrafast operation in spin-lasers relies on the large linear birefringence, usually viewed
as detrimental in spin and conventional lasers, which couples the two linearly polarized emission modes. We
show that the dynamical properties of birefringent spin-lasers under intensity and polarization modulation are
accurately described as coupled harmonic oscillators2. Our model agrees with the intensity-equation description3
which, unlike the common complex field components describing the role of birefringence in laser dynamics, uses
simpler real quantities and allows analytical solutions. We further predict unexplored operation regimes and
elucidate the difference between the weak and strong coupling in spin-lasers2 and how they can build on the
recent breakthroughs in spin-light emitting diodes4.