Mode hopping in single-mode microchip Nd：YAG lasers induced by optical feedback

The mode hopping phenomenon induced by optical feedback in single-mode microchip Nd：YAG lasers is presented. With optical feedback, mode hopping strongly depends on two factors： the ratio of external cavity length to intra-cavity length, and initial gains of the two hopping modes, When external cavity length equals an integral multiple of intracavity length, there is almost no mode hopping. However, if the external cavity length does not equal an integral multiple of intra-cavity length, mode hopping occurs. The ratio of external cavity length to intra-cavity length determines the position of two-mode hopping, The initial gains of the two hopping modes determine the corresponding peak values and oscillating periods of them in the intensity modulation curves.

Mode hopping and polarization switching of mutually coupled vertical-cavity surface-emitting lasers

We perform a theoretical study on the polarization-resolved compound lasing mode （CLM） of two mutually coupled vertical-cavity surface-emitting lasers （VCSELs）. Different solutions of CLMs are derived though stability analysis of the spin-flip model. The dynamical evolvements of CLMs with the existence of polarization degrees of freedom are also charactered. The most stable CLM with the smallest carrier density tend to be excited, since the gain needed for this mode to emit is the lowest. In the given system, varying values of injection rate or birefringence, etc., will change the generation of the preferred CLMs in the two polarization directions, and thus influence the polarization switching （PS） characteristics. Thus, hoppings between CLMs are also companied by PSs. Through mapping of average power in the parameter space, the influences of coupling rate and anisotropy parameters （linear dichroism and linear birefringence） on PS and hopping between CLMs are discussed.