An optical device includes a light-emitting device integrated with a memory device. The memory device include a first electrode and a second electrode, and the light-emitting device includes a third electrode and the second electrode. In such configuration, a first voltage between the second electrode and the third electrode causes the light-emitting device to emit light of a first wavelength, and a second voltage between the first electrode and the second electrode while the memory device is at OFF state causes the light-emitting device to emit light of a second wavelength shorter than the first wavelength or while the memory device is at ON state causes the light-emitting device to emit light of a third wavelength longer than the first wavelength.