An optical amplifier has a low polarization dependent gain. The amplifier includes a gain medium including a plurality of adjoining semiconductor layers to provide optical gain wherein the adjoining semiconductor layers define one or more quantum wells for electrons and are operative to provide both direct and indirect electron-hole transitions in the gain medium. A first quantized electron energy level in the conduction band and a first quantized hole energy level in the valence band is located in a first layer. A further first quantized hole energy level in the valence band is located in an adjacent second layer.