Reducing the spectral width of high speed oxide confined VCSELs using an integrated mode filter

We have reduced the spectral width of high speed oxide confined 850 nm VCSELs using a shallow surface relief for suppression of higher order transverse modes. The surface relief acts as a mode filter by introducing a spatially varying and therefore mode selective loss. The VCSEL employs multiple oxide layers for reduced capacitance which leads to a strong index guiding and a large spectral width in the absence of a mode filter. With an appropriate choice of surface relief parameters, the RMS spectral width for a 5 μm oxide aperture VCSEL is reduced from 0.6 to 0.3 nm. The small signal modulation bandwidth is 19 GHz. Due to reduced effects of chromatic and modal fiber dispersion, the maximum error-free (bit-error-rate < 10-12) transmission distance at 25 Gb/s over OM3+ fiber is increased from 100 to 500 m.