Abstract: In this work we report on an experimental investigation of the bistability found in 1550 nm multitransverse-mode VCSELs subject to orthogonal optical injection. The VCSEL emits in two transverse modes that are linearly polarized in a direction referred as parallel. We study the dependence of the bistable behaviour on the detuning between the frequency of the externally injected signal and the frequency of the subsidiary orthogonal linear polarization of the fundamental mode of the VCSEL. Different qualitative behaviors of the power of each polarized transverse mode versus the optically injected power appear depending on the value of the frequency detuning. Bistable regions are very narrow for positive and small negative values of the frequency detuning. However very wide hysteresis cycles are obtained for large and negative values of the frequency detuning. Bistability is found for both the fundamental and the high-order transverse mode. The shape of the hysteresis cycle depends on the transverse mode under consideration. The power of the parallel polarized fundamental transverse mode decreases gradually as the injected power is increased. However the behaviour of the parallel polarized high-order transverse mode is different because its power remains constant as the optical injected power is increased until it suddenly drops to low levels. This kind of behaviour is of interest for obtaining good quality all-optical inversion and all-optical regeneration.

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