Gain mechanism of the vertical-cavity surface-emitting semiconductor laser

The vertical-cavity surface-emitting single quantum well laser is examined in terms of the short Fabry–Perot cavity’s effect on optical gain. It is suggested that for this vertical- cavity structure the optical gain mechanism is fundamentally altered as compared to the case of the more standard edge-emitting device with longer cavity lengths. The short cavity and highly reflecting mirrors of the vertical cavity structure lead to an enhanced gain coefficient at fixed carrier densities, due to enhanced spontaneous emission into the Fabry–Perot modes of the optical cavity, and the resultantly reduced spontaneous linewidth.