An optical memory device comprising: a substrate; a first barrier layer formed on the substrate; a quantum well layer formed on the first barrier layer, wherein the quantum well layer has an energy band gap which is narrower than an energy band gap of the first barrier layer; a second barrier layer formed on the quantum well layer, wherein the second barrier layer has an energy band gap which is wider than the energy band gap of the quantum well layer, and wherein the energy band gap of the second barrier layer is narrower than the energy band gap of the first barrier layer; a quantum dot layer including a plurality of quantum dots formed on the second barrier layer, wherein the quantum dot layer has an energy band gap which is narrower than the energy band gap of the quantum well layer; and a third barrier layer formed on the quantum dot layer, wherein the third barrier layer has an energy band gap which is wider than the energy band gap of the second barrier layer characterized by: further comprising a light source which is arranged to irradiate light of a first wavelength in an operation of recording information, to irradiate light of a second wavelength in an operation of erasing recorded information, and to irradiate light of a third wavelength in an operation of reproducing recorded information, wherein the first wavelength, the second wavelength and the third wavelength are all different from each other. a substrate; a first barrier layer formed on the substrate; a quantum well layer formed on the first barrier layer, wherein the quantum well layer has an energy band gap which is narrower than an energy band gap of the first barrier layer; wherein the quantum well layer has an energy band gap which is narrower than an energy band gap of the first barrier layer; a second barrier layer formed on the quantum well layer, wherein the second barrier layer has an energy band gap which is wider than the energy band gap of the quantum well layer, and wherein the energy band gap of the second barrier layer is narrower than the energy band gap of the first barrier layer; wherein the second barrier layer has an energy band gap which is wider than the energy band gap of the quantum well layer, and wherein the energy band gap of the second barrier layer is narrower than the energy band gap of the first barrier layer; a quantum dot layer including a plurality of quantum dots formed on the second barrier layer, wherein the quantum dot layer has an energy band gap which is narrower than the energy band gap of the quantum well layer; and wherein the quantum dot layer has an energy band gap which is narrower than the energy band gap of the quantum well layer; and a third barrier layer formed on the quantum dot layer, wherein the third barrier layer has an energy band gap which is wider than the energy band gap of the second barrier layer characterized by: wherein the third barrier layer has an energy band gap which is wider than the energy band gap of the second barrier layer characterized by: further comprising a light source which is arranged to irradiate light of a first wavelength in an operation of recording information, to irradiate light of a second wavelength in an operation of erasing recorded information, and to irradiate light of a third wavelength in an operation of reproducing recorded information, wherein the first wavelength, the second wavelength and the third wavelength are all different from each other. wherein the first wavelength, the second wavelength and the third wavelength are all different from each other.