3.6-MHz linewidth 1.55-mu m monomode vertical-cavity surface-emitting laser

We report on high-resolution linewidth measurement of proton-implanted bottom-emitting InGaAsP long-wavelength vertical-cavity surface-emitting lasers (VCSELs) employing the heterodyne method. Devices with 35-mum active diameter exhibit record linewidths of 3.6 MHz and negligible extrapolated linewidth for infinite power, at room temperature. This result relies on the long-cavity-designed VCSEL.