Patent ID: 8228576

Claim:
A transmission type optical element comprising: a first hologram having a first surface and a second surfaces; and a second hologram having a third surface and a fourth surface; the first surface of the first hologram and the third surface of the second hologram being oppositely arranged; wherein a first light beam having a first wavelength is made to enter the first hologram from the side of the second surface, be transmitted through the first hologram, exit the first hologram from the side of the first surface, enter the second hologram from the side of the third surface, be diffracted by the second hologram, exit the second hologram from the side of the third surface, enter the first hologram from the side of the first surface, be diffracted by the first hologram, exit the first hologram from the side of the first surface, and enter the second hologram from the side of the third surface, be transmitted through the second hologram and exit the second hologram from the side of the fourth surface wherein a second light beam having a second wavelength different from the first wavelength is made to enter the first hologram from the side of the second surface, to be transmitted through the first hologram, exit the first hologram from the side of the first surface, and enters the second hologram from the side of the third surface, to be transmitted through the second hologram and exit the second hologram from the side of the fourth surface.