Abstract

We provide an experimental and theoretical investigation of polarization switching and transverse mode locking of a vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection. The VCSEL (slave laser, SL) is biased such that it emits a horizontally polarized fundamental mode (LP_01x) without external optical injection. A vertically polarized (y-LP) beam from a master laser (ML) is then injected in the VCSEL cavity and the output characteristics are mapped as a function of the injection strength (P_inj) and the frequency detuning between the master and the free-running slave lasers (Δν = ν_ML − ν_SL). Our experimental mapping, presented in Fig. 1 (a), has been carried out for a very large positive detuning range (up to 180 GHz) and extends what has been reported in [1]. We observe two minima of the injection power needed to achieve polarization switching (PS) between the fundamental modes, i.e. between LP_01x and LP_01y (triangles). The first minimum, also previously reported in [1], appears for a detuning of 2 GHz which is close to the birefringence of the VCSEL. On the other hand, the second minimum is resolved for a relatively large detuning (Δν =150 GHz) which is close to the frequency splitting between LP_01y and the first order transverse mode (LP_11y). Interestingly, our theoretical results unveil the effect of LP₁₁ on the position of the second minimum. To this end, we use a model which accounts for polarized multi-transverse modes and is based on a modal expansion [2] built within the framework of the Spin Flip model. We show that the depth as well as the detuning at which the second minimum is located depends on the relative losses (κ_r) between LP₀₁ and LP₁₁ modes. The mapping in Fig. 1(b), which has been obtained for κ_r =1.2, shows the two minima in the PS curve and agrees qualitatively with our experiments.

© 2007 IEEE