Diffraction type filter having an aberration correction function and wave length selectivity
First Claim
1. A diffraction type filter, having a wavelength selectivity, disposed in a luminous flux;
- said filter comprising a first region constituting a center portion of said filter, and a second region positioned outside the center portion of said filter, said first region being formed with a zone plate having an aberration correcting function for only one of two light beams respectively having wavelengths of λ
1 and λ
2 which are different from each other, said second region being formed with a diffraction grating substantially having a light shielding function for only one of said two light beams respectively having wave lengths of λ
1 and λ
2,wherein said diffraction grating is constituted by a plurality of protrusions, each having a height corresponding to a height 3 h of three stages of a step portion forming said zone plate, the height h of one stage of said step portion forming said zone plate, the height h of one stage of said step portion satisfying the following conditional expressions;
space="preserve" listing-type="equation">h=Lλ
.sub.1 /(n.sub.1 -1)
space="preserve" listing-type="equation">h=Mλ
.sub.2 /(n.sub.2 -1)+Kλ
.sub.2 /2(n.sub.2 -1)whereλ
1 and X2 are the respective wavelengths of the two incident light beams;
n1 is the refractive index of the zone plate or diffraction grating with respect to light having the wavelength of λ
1 ;
n2 is the refractive index of the zone plate or diffraction grating with respect to light having the wavelength of λ
2 ;
L is a positive integer;
M is the maximum value among 0 and positive integers satisfying a conditional expression of h>
Mλ
2 /(n2 -1); and
K is a value at least 0.27 but not greater than 0.45 or a value at least 1.55 but not greater than 1.73.
1 Assignment
0 Petitions
Accused Products
Abstract
A zone plate having an aberration correcting function in a wavelength selecting manner and a diffraction grating substantially having a light shielding function in a wavelength selecting manner are formed, respectively, in a center region and a marginal region of a filter, whereby only a predetermined wavelength of light is converged or diverged by the zone plate and is diffracted sideways by the diffraction grating, whereby the luminous flux diameter of the irradiation light is changed while the aberration caused by a convergent lens is favorably corrected. The diffraction type filter 8A is constituted by a first region 11 comprising a central circular portion and a second region 12 comprising a marginal portion thereof. The first region 11 is provided with a zone plate 11A (diffraction grating formed like concentric circles) having such a wavelength selectivity that light at a wavelength of 635 nm is transmitted therethrough as it is and that light at a wavelength of 780 nm is converged thereby. The second region 12 is provided with a diffraction grating 12A having such a wavelength selectivity that light at a wavelength of 635 nm is transmitted therethrough as it is and that a major part of light at a wavelength of 780 nm is diffracted sideways so as to be substantially blocked out.
52 Citations
20 Claims
-
1. A diffraction type filter, having a wavelength selectivity, disposed in a luminous flux;
- said filter comprising a first region constituting a center portion of said filter, and a second region positioned outside the center portion of said filter, said first region being formed with a zone plate having an aberration correcting function for only one of two light beams respectively having wavelengths of λ
1 and λ
2 which are different from each other, said second region being formed with a diffraction grating substantially having a light shielding function for only one of said two light beams respectively having wave lengths of λ
1 and λ
2,wherein said diffraction grating is constituted by a plurality of protrusions, each having a height corresponding to a height 3 h of three stages of a step portion forming said zone plate, the height h of one stage of said step portion forming said zone plate, the height h of one stage of said step portion satisfying the following conditional expressions;
space="preserve" listing-type="equation">h=Lλ
.sub.1 /(n.sub.1 -1)
space="preserve" listing-type="equation">h=Mλ
.sub.2 /(n.sub.2 -1)+Kλ
.sub.2 /2(n.sub.2 -1)where λ
1 and X2 are the respective wavelengths of the two incident light beams;n1 is the refractive index of the zone plate or diffraction grating with respect to light having the wavelength of λ
1 ;n2 is the refractive index of the zone plate or diffraction grating with respect to light having the wavelength of λ
2 ;L is a positive integer; M is the maximum value among 0 and positive integers satisfying a conditional expression of h>
Mλ
2 /(n2 -1); andK is a value at least 0.27 but not greater than 0.45 or a value at least 1.55 but not greater than 1.73. - View Dependent Claims (2)
- said filter comprising a first region constituting a center portion of said filter, and a second region positioned outside the center portion of said filter, said first region being formed with a zone plate having an aberration correcting function for only one of two light beams respectively having wavelengths of λ
-
3. A diffraction type filter, having a wavelength selectivity, disposed in a luminous flux;
- said filter comprising a first region constituting a center portion of said filter, and a second region positioned outside the center portion of said filter, said first region being formed with a zone plate having an aberration correcting function for only one of two light beams respectively having wavelengths of λ
1 and λ
2 which are different from each other, said second region being formed with a diffraction grating substantially having a light shielding function for only one of said two light beams respectively having wave lengths of λ
1 and λ
2,wherein said zone plate is constituted by a plurality of continuous protrusions arranged like concentric circles, each protrusion being continuous and having one sectional side formed like a step, wherein said zone plate is a Fresnel zone plate, m-th radius Rm of said zone plate being represented by the following conditional expression;
space="preserve" listing-type="equation">R.sub.m ={λ
.sub.i m(2f+λ
.sub.i m)}.sup.1/2where m=0, 1, 2, . . . , n; λ
i is λ
1 or λ
2 ;f is the focal length of the zone plate; and n is a number satisfying a conditional expression of Rn =(1/2)φ
;wherein φ
being a beam diameter of a light beam effectively contributing to recording/reproducing in light whose aberration is corrected by the zone plate. - View Dependent Claims (4, 5, 6)
- said filter comprising a first region constituting a center portion of said filter, and a second region positioned outside the center portion of said filter, said first region being formed with a zone plate having an aberration correcting function for only one of two light beams respectively having wavelengths of λ
-
7. A diffraction type filter, having a wavelength selectivity, disposed in a luminous flux;
- said filter comprising a first region constituting a center portion of said filter, and a second region positioned outside the center portion of said filter, said first region being formed with a zone plate having an aberration correcting function for only one of two light beams respectively having wavelengths of λ
1 and λ
2 which are different from each other, said second region being formed with a diffraction grating substantially having a light shielding function for only one of said two light beams respectively having wavelengths of λ
1 and λ
2 ;said diffraction grating being constituted by a plurality of protrusions, each having a height corresponding to a height 2 h of two stages of a step portion forming said zone plate, the height h of one stage of said step portion satisfying the following conditional expressions;
space="preserve" listing-type="equation">h=Lλ
.sub.1 /(n.sub.1 -1)
space="preserve" listing-type="equation">h=Mλ
.sub.2 /(n.sub.2 -1)+Kλ
.sub.2 /2(n.sub.2 -1)where λ
1 and λ
2 are the respective wavelengths of the two incident light beams;n1 is the refractive index of the zone plate or diffraction grating with respect to light having the wavelength of λ
1 ;n2 is the refractive index of the zone plate or diffraction grating with respect to light having the wavelength of λ
2 ;L is a positive integer; M is a maximum value among 0 and positive integers satisfying a conditional expression of h>
Mλ
2 /(n2 -1); andK is a value at least 0.32 but not greater than 0.68 or a value at least 1.32 but not greater than 1.68. - View Dependent Claims (8, 9, 10, 11, 12, 13)
- said filter comprising a first region constituting a center portion of said filter, and a second region positioned outside the center portion of said filter, said first region being formed with a zone plate having an aberration correcting function for only one of two light beams respectively having wavelengths of λ
-
14. A diffraction type filter, having a wavelength selectivity, disposed in a luminous flux;
- said filter comprising a first region constituting a center portion of said filter, and a second region positioned outside the center portion of said filter, said first region being formed with a zone plate having an aberration correcting function for only one of two light beams respectively having wavelengths of λ
1 and λ
2 which are different from each other, said second region being formed with a diffraction grating substantially having a light shielding function for only one of said two light beams respectively having wavelengths of λ
1 and λ
2 ;said diffraction grating being constituted by a plurality of protrusions, each having a height corresponding to a height h of one stage of a step portion forming said zone plate, the height h of one stage of said step portion satisfying the following conditional expressions;
space="preserve" listing-type="equation">h=Lλ
.sub.1 /(n.sub.1 -1)
space="preserve" listing-type="equation">h=Mλ
.sub.2 /(n.sub.2 -1)+Kλ
.sub.2 /2(n.sub.2 -1)where λ
1 and λ
2 are the respective wavelengths of the two incident light beams;n1 is the refractive index of the zone plate or diffraction grating with respect to light having the wavelength of λ
1 ;n2 is the refractive index of the zone plate or diffraction grating with respect to light having the wavelength of λ
2 ;L is a positive integer; M is a maximum value among 0 and positive integers satisfying a conditional expression of h>
Mλ
2 /(n2 -1); andK is a value at least 0.64 but not greater than 0.77 or a value at least 1.23 but not greater than 1.36. - View Dependent Claims (15, 16, 17, 18, 19, 20)
- said filter comprising a first region constituting a center portion of said filter, and a second region positioned outside the center portion of said filter, said first region being formed with a zone plate having an aberration correcting function for only one of two light beams respectively having wavelengths of λ
Specification