Mode polarization partition noise in multimode short-wavelength VCSELs

Vertical cavity surface emitting lasers (VCSELs) designed for 10G Ethernet over 300 m graded index multimode fiber in general have optical aperture diameters of 7 to 10 mu m; cavities of these sizes stipport, multiple transverse modes. The circularly symmetric structures are assumed to have no polarization selection, however, we show that orthogonally polarized lasing modes are often present and cause polarization partition noise which degrades the link bit error rate (BER). When a polarization selector was used in the link to allow only one polarization, the BER improved by two-order of magnitude even with the loss of more than 32 permit of the VCSEL average emitted power.