Noise Performance of Single-Mode VCSELs: Dependence on Current Confinement and Optical Loss

We investigate the intensity and phase noise properties of GaAs-based 1060 nm oxide-confined single-mode vertical-cavity surface-emitting lasers (VCSELs) and their dependence on slope efficiency and current spreading, parameters that control the achievable output power. We find strong dependence of the linewidth on slope efficiency because it affects the optical resonator loss and therefore the spontaneous emission rate and the photon density. Likewise, we find strong dependence of the relative intensity noise on the slope efficiency since the optical resonator loss controls the photon lifetime, and therefore the damping of the relaxation oscillations. There is no noticeable dependence on transverse current confinement and current spreading. We measure linewidths as small as 6 MHz which we attribute to a small linewidth enhancement factor. This assumption is supported by calculations of the linewidth enhancement factor from optical resonator and optical gain simulations. The dependencies of noise on design parameters are general and therefore valid for single-mode VCSELs at other wavelengths and in other material systems.