Diffraction grating lens and imaging device in which the same is used

1. A diffraction grating lens comprising:

a lens body; and

a diffraction grating provided on a surface of the lens body, the diffraction grating having a plurality of diffraction steps relative to a base shape and a plurality of concentric annular zones each sandwiched by an adjoining pair among the plurality of diffraction steps, wherein,

the lens body is made of a first material having a refractive index n 1 (λ) at a used wavelength λ;

the diffraction grating is in contact with air;

the relationship of

0.9

⁢

d

≤

m

·

λ

n

1

⁡

(

λ

)

-

1

≤

1.1

⁢

d

is satisfied, where d is a design step length of the diffraction steps, and m is an order of diffraction;

each of the plurality of annular zones includes an intermediate portion and a pair of end portions sandwiching the intermediate portions along a radial direction, and in at least one of the plurality of annular zones, either one of a recess and a protrusion is provided in at least a portion of one of the pair of end portions, and the other one of the recess and the protrusion is provided in at least a portion of the other of the pair of end portions;

at positions excluding an outer peripheral edge of the diffraction grating, the plurality of diffraction steps include a plurality of first diffraction steps and at least one second diffraction step adjoining at least one of the plurality of first diffraction steps;

edges of the plurality of first diffraction steps according to the design step length are located on a first face resulting from translating the base shape along an optical axis direction of the diffraction grating, and an edge of the at least one second diffraction step according to the design step length is located on a second face resulting from translating the base shape along the optical axis direction; and

the first face and the second face are at respectively different positions along the optical axis.

2. The diffraction grating lens of claim 1 , wherein,

the plurality of diffraction steps include a plurality of second diffraction steps; and

the first diffraction steps and the second diffraction steps alternate with each other.

3. The diffraction grating lens of claims 1 , wherein an interval L between the first face and the second face along the optical axis satisfies the following inequality

0.4d≦L≦0.9d.

4. The diffraction grating lens of claim 3 , wherein the interval L between the first face and the second face along the optical axis satisfies the following inequality

0.4d≦L≦0.6d.

5. The diffraction grating lens of claim 4 , wherein the interval L between the first face and the second face along the optical axis satisfies L=0.5d.

6. The diffraction grating lens of claim 1 , wherein,

the plurality of diffraction steps include a plurality of second diffraction steps; and

the plurality of first diffraction steps and the plurality of second diffraction steps are disposed in successive units of i (where i is an integer of 2 or more) and successive units of j (where j is an integer of 2 or more), respectively, the i first diffraction steps alternating with the j second diffraction steps.

7. The diffraction grating lens of claims 1 , wherein at least one of the protrusion and the recess is provided in a substantially entire circumference of the at least one annular zone.

8. The diffraction grating lens of claims 1 , wherein a width of the protrusion and the recess along a direction which is on a plane containing the optical axis of the diffraction grating and which is perpendicular to the optical axis is in a range of no less than 5% and no more than 25% of a width of the at least one annular zone along a direction which is on a plane containing the optical axis of the diffraction grating and which is perpendicular to the optical axis.

9. The diffraction grating lens of claims 1 , wherein a height of the protrusion and the recess along the optical axis direction of the diffraction grating is in a range of no less than 3% and no more than 20% of a design step length d of the diffraction step.

10. The diffraction grating lens of claims 1 , wherein, the protrusions and the recesses are provided in the plurality of annular zones.

11. The diffraction grating lens of claims 1 , wherein the protrusions and the recesses are provided in at least two or more of the plurality of annular zones that are near an outer periphery of the diffraction grating.

12. The diffraction grating lens of claims 1 , wherein the used wavelength λ is a wavelength in a visible light region, such that λ satisfies the inequality for any wavelength in the entire visible light region.

13. An imaging device comprising:

the diffraction grating lens of claims 1 ; and

an imaging sensor.

14. A diffraction grating lens comprising:

a lens body;

a diffraction grating provided on a surface of the lens body, the diffraction grating having a plurality of diffraction steps relative to a base shape and a plurality of concentric annular zones each sandwiched by an adjoining pair among the plurality of diffraction steps; and

an optical adjustment layer provided on the lens body, the optical adjustment layer covering the diffraction grating, wherein,

the lens body is made of a first material having a refractive index n 1 (λ) at a used wavelength λ;

the optical adjustment layer is made of a second material having a refractive index n 2 (λ) at the used wavelength λ;

the relationship of

0.9

⁢

d

≤

m

·

λ

n

1

⁡

(

λ

)

-

n

2

⁡

(

λ

)

≤

1.1

⁢

d

is satisfied, where d is a design step length of the diffraction steps, and m is an order of diffraction;

each of the plurality of annular zones includes an intermediate portion and a pair of end portions sandwiching the intermediate portions along a radial direction, and in at least one of the plurality of annular zones, either one of a recess and a protrusion is provided in at least a portion of one of the pair of end portions, and the other one of the recess and the protrusion is provided in at least a portion of the other the one of the pair of end portions;

at positions excluding an outer peripheral edge of the diffraction grating, the plurality of diffraction steps include a plurality of first diffraction steps and at least one second diffraction step adjoining at least one of the plurality of first diffraction steps;

edges of the plurality of first diffraction steps according to the design step length are located on a first face resulting from translating the base shape along an optical axis direction of the diffraction grating, and an edge of the at least one second diffraction step according to the design step length is located on a second face resulting from translating the base shape along the optical axis direction; and

the first face and the second face are at respectively different positions along the optical axis.

15. A diffraction grating lens comprising:

a lens body; and

a diffraction grating provided on a surface of the lens body, the diffraction grating having a plurality of diffraction steps relative to a base shape and a plurality of concentric annular zones each sandwiched by an adjoining pair among the plurality of diffraction steps, wherein,

the lens body is made of a first material having a refractive index n 1 (λ) at a used wavelength λ;

the diffraction grating is in contact with air;

the relationship of

0.9

⁢

d

≤

m

·

λ

n

1

⁡

(

λ

)

-

1

≤

1.1

⁢

d

is satisfied, where d is a design step length of the diffraction steps, and m is an order of diffraction;

each of the plurality of annular zones includes an intermediate portion and a pair of end portions sandwiching the intermediate portions along a radial direction, and in at least one of the plurality of annular zones, either one of a recess and a protrusion is provided in at least a portion of one of the pair of end portions, and the other one of the recess and the protrusion is provided in at least a portion of the other of the pair of end portions; and

the plurality of annular zones include first, second, and third annular zones adjoining one another, the second annular zone being interposed between the first and third annular zones, widths of the first annular zone and the third annular zone being substantially identical, and a width of the second annular zone being narrower than the width of the first annular zone.