Patent ID: 8687269

Claim:
An optical amplifier for accepting input light and outputting amplified light, the optical amplifier comprising: an optical waveguide for accepting input light and outputting amplified light; a gain medium comprising a plurality of adjoining semiconductor layers to provide optical gain, wherein the adjoining semiconductor layers include a first layer and a second layer, the second layer having a different material composition than the first semiconductor layer; and electrodes to pump electric current through the gain medium; wherein the plurality of 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; wherein a first quantized electron energy level in the conduction band is located in the first layer; wherein a first quantized hole energy level in the valence band is located in said first layer; wherein a further first quantized hole energy level in the valence band is located in the second layer; wherein the first quantized hole energy level in the first layer is either a light hole state or a heavy hole state and the further first quantized hole energy level in the second layer is a different hole state to the first quantized hole energy level in the first layer; and wherein the first layer comprises one of the wells and the second layer comprises a barrier for the electrons, and the heavy hole energy level and the light hole energy level diverge in the first layer.