Patent ID: 6480332
Filing Date: 2002-11-12
Classification: G02B

Abstract:
A diffractive optical element having a first diffraction grating surface formed at a boundary between first and second layers made of materials of different dispersions and a second diffraction grating surface formed at a boundary between the second layer and air to enhance diffraction efficiency of a design order over a wavelength region,wherein at least one of the layers is made of a plastic resin material, wherein, rates of change in refractive index due to temperature variation of the materials of the first and second layers are dn1/dt, respectively, a thickness of a first diffraction grating formed by the first layer is d1, a thickness of a second diffraction grating formed by the second layer having the first and second diffraction grating surfaces is d2, and wherein said diffractive optical element satisfies the following conditions: &phgr;t=(dn1/dt)d1âˆ’(dn2/dt)d2&Dgr;t=30 degrees wherein m is the design order, &lgr;0 is a predetermined wavelength in the wavelength region, and &phgr;t is a sum of values obtained by multiplying the rates of change in refractive index due to temperature variation &Dgr;t by the grating thicknesses of the first and second diffraction gratings, wherein the value of |&phgr;tÂ·&Dgr;t| is equal to or less than m&it;â€ƒ&CenterDot;â€ƒ&it;108â€ƒof the predetermined wavelength.