Polarization-stable 940nm VCSELs for sparing (Conference Presentation)

We demonstrate multimode 940 nm flip chip VCSELs with >20dB polarization suppression and small signal modulation bandwidth > 25 GHz (3dB) in 2x4 arrays for 50 Gbit/s/channel NRZ transmission. The VCSELs have surface gratings for polarization suppression. The high bandwidth operation is achieved in part by using a relatively small oxide aperture. The arrays are comprised of pairs of VCSELs with orthogonal polarizations, which enable cold sparing; if a primary (P-polarized) VCSEL fails, a system turns on a secondary (S-polarized) VCSEL. The light beam is routed through optics to the same 50 μm core fiber for both polarizations thus keeping the link integrity intact.