Diffractive optical element and optical system having the same
AssigneeCanon Kabushiki Kaisha
InventorTakehiko Nakai
Life of this patent
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Abstract
In a diffractive optical element having a diffraction grating formed at an interface between different substances, a total sum of values obtained by multiplying rates of change in refractive index due to temperature variations of the substances by a grating thickness of the diffraction grating is smaller than a useful wavelength.
Claims11
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:
- φt=(dn1/dt)d1−(dn2/dt)d2
- Δt=30 degrees
- wherein m is the design order, λ0 is a predetermined wavelength in the wavelength region, and φt is a sum of values obtained by multiplying the rates of change in refractive index due to temperature variation Δt by the grating thicknesses of the first and second diffraction gratings, wherein the value of |φt·Δt| is equal to or less than m · 10 8
- of the predetermined wavelength.
A diffractive optical element having diffraction gratings formed by a plurality of layers made of at least two kinds of materials of different dispersions to enhance diffraction efficiency of a design order over a wavelength region,
- wherein at least one of the plurality of layers is made of a plastic resin material,
- wherein, a rate of change in refractive index due to temperature variation of the material of the L-th layer is dnoL/dt, a thickness of the diffraction grating formed by the L-th layer is dL, and
- wherein said diffractive optical element satisfies the following conditions:
- φt=(dno1/dt)d1±(dno2/dt)d2± . . . ±(dnoL/dt)dL
- Δt=30 degrees
- wherein m is the design order, λ0 is a predetermined wavelength in the wavelength region, and φt is a sum of values obtained by multiplying the rates of change in refractive index due to temperature variation Δt by the grating thickness of each diffraction gratings, wherein the value of |φt·Δt| is equal to or less than m · λ0 8
- of the predetermined wavelength.
Dependencies are inferred from the claim text.