To provide a multiplex diffraction grating capable of emitting polarized light having a high SP ratio, when the multiplex diffraction grating is used for a display device having a transparent substrate and light sources of two or more colors.

The multiplex diffraction grating is constituted so that a grating line is arranged to obtain such a state that each of n diffraction gratings corresponding to each wavelength of n colors (n≥2) is arranged and superimposed. Each of the n diffraction gratings is arranged so that in each one grating line located at one common end of each of the n diffraction gratings, when n is two, the center line of the grating line of the diffraction grating corresponding to the wavelength of light whose wavelength is long is not superimposed on the center line of the diffraction grating corresponding to the wavelength of light whose wavelength is short (a), and when n is three or more, the center line of the grating line of the diffraction grating corresponding to the wavelength of light whose wavelength is longest is not superimposed on the center line of the grating line of the diffraction grating corresponding to the wavelength of light whose wavelength is shortest (b), and all of the grating lines constituting the diffraction grating are nearly parallel with each other.

COPYRIGHT: (C)2011,JPO&INPIT