Optical element, light source device, and projection-type display device

An optical element comprising:

• a light guide body into which light is irradiated from a light source, said light guide body having a first surface and a second surface that is opposite the first surface;
• a first polarization-separation layer that is laminated on said first surface of said light guide body, said first polarization-separation layer transmitting, of light irradiated from said light guide body, first linearly polarized light in which a polarization component is of a specific direction, and that reflects second linearly polarized light in which a polarization component is of a direction orthogonal to the first linearly polarized light;
• a polarization-hologram layer that is laminated on said first polarization-separation layer and that both diffracts said first linearly polarized light that is irradiated within a predetermined range of angles of incidence to a predetermined angle of diffraction and converts said first linearly polarized light to second linearly polarized light;
• a second polarization-separation layer that is laminated on said polarization-hologram layer and that transmits, of light irradiated from said polarization-hologram layer, said second linearly polarized light, and moreover, that reflects said first linearly polarized light;
• a reflection layer that is provided on said second surface side of said light guide body;
• and
• a phase-difference layer that is provided between said first surface of said light guide body and said reflection layer and that imparts a phase difference to mutually orthogonal polarization components belonging to incident light before and after transmission of said incident light.