Abstract: We have performed an experimental investigation of the RIN spectra of multimode 1550 nm VCSELs. Several types of multi-transverse mode VCSELs have been considered. The first one emits in two transverse modes for large values of the bias current. Both modes are linearly polarized and have parallel polarizations. Two resonance peaks appear in the noise spectra of the individual modes and total power of the VCSEL in agreement with previous theoretical studies (A. Valle et al, IEEE J. Quantum Electron, vol. 40, 597, 2004). We have measured the frequencies corresponding to both peaks as a function of the bias current. We have obtained a similar dependence to the one found in the previous work. The second VCSEL type corresponds to a laser emitting at three different transverse modes for large values of the bias current. Similar behaviors are found while the bias current is small. Emission in three transverse modes with different polarizations is accompanied by the appearance of additional peaks in the noise spectra. It is suggested that the VCSEL polarization plays an important role in determining the multi-peaked structure of noise spectra. That is confirmed by measuring with another two-transverse mode VCSEL showing polarization instabilities in both transverse modes. It is shown that large values of the bias current applied to this VCSEL result in a complex dynamics characterized by the appearance of many additional peaks in the noise spectra.

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