JPH0713009A - Reflection diffraction type chromatic aberration correction element and chromatic aberration correction device - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain a reflection type correction element that can satisfactorily correct chromatic aberration occurring in a lens. [Arrangement] The orthographic shape on the plane orthogonal to the optical axis is
A central reflecting surface having rotational symmetry about the optical axis and a reflecting surface composed of a number of annular reflecting surfaces concentric with the central reflecting surface are provided. The matching ring zone reflecting surface is in the direction orthogonal to these reflecting surfaces,
The positions are displaced by the same step distance t, and macroscopically the surface is concave or convex as a whole.
For light of the reference wavelength, light incident as a plane wave is emitted as a plane wave, and for light of different wavelengths different from the reference wavelength, light incident as a plane wave is emitted as a divergent or condensed wave front. A reflection-diffraction-type chromatic aberration correction element that is specified to

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an optical element for correcting chromatic aberration by utilizing reflection diffraction of light.

[0002]

2. Description of the Related Art The chromatic aberration of conventional glass has been corrected by forming a positive lens and a negative lens from glass materials having different Abbe numbers. However, in an optical system with a narrow wavelength range to be used, for example, an information recording / reproducing system using a laser, an objective lens is composed of only one aspherical single lens in order to meet the demands for cost reduction, size reduction, and speedup. Is being done. The single lens has a chromatic aberration determined by the characteristics of the material, and cannot correct this by itself. Therefore, even in the case of a semiconductor laser, when the oscillation wavelength changes with the change in output, or when the light emission width of the LED is large.
In some cases, such as when using, there is a problem that the focus position shifts for each wavelength.

[0003]

SUMMARY OF THE INVENTION In view of the above background, it is an object of the present invention to provide a reflection type correction element which can satisfactorily correct chromatic aberration occurring in a lens.

[0004]

SUMMARY OF THE INVENTION The present invention is a reflection-diffraction chromatic aberration correction element that utilizes the diffraction phenomenon when light is reflected. First, the orthogonal projection shape with respect to a plane orthogonal to the optical axis is centered on the optical axis. And a reflection surface consisting of a rotationally symmetrical center reflection surface and a large number of annular reflection surfaces concentric with the center reflection surface. Secondly, this center reflection surface and the annular reflection surface outside thereof. , And adjacent ring zone reflecting surfaces are displaced in the direction orthogonal to these reflecting surfaces by the same step distance t, and macroscopically form a convex surface or a concave surface as a whole,
And thirdly, with respect to the light of the reference wavelength, the step distance t is such that the light incident as the plane wave is emitted as the plane wave, and the light having the different wavelength different from the reference wavelength is incident as the plane wave. It is characterized in that the light is set to exit as a divergent wavefront or a condensed wavefront.

According to this element, it is possible to correct the chromatic aberration generated in the single lens when the used wavelength deviates from the reference wavelength. That is, in the reflection-diffraction chromatic aberration correction element of the present invention, the wavefront aberration (chromatic aberration) caused by the single lens when the used wavelength deviates from the reference wavelength occurs on the reflection surface.
It is offset by a diverging wavefront or a converging wavefront having the opposite tendency.

The reflection-diffraction type chromatic aberration correction element according to the present invention can be used not only for correcting chromatic aberration of a single lens but also of a combination lens. Even with a combination lens, color correction may not be possible due to other reasons such as refractive index, transmittance, etc. In particular, at a short wavelength of about λ = 300 nm, only one type of glass material can be used, and color correction is difficult. . According to the reflective diffraction type chromatic aberration correction element of the present invention,
It is possible to correct chromatic aberration in such a short wavelength range.

The chromatic aberration correcting element of the present invention is specifically
For example, the contours of the central reflecting surface and the annular reflecting surface are circular when viewed from the direction orthogonal to these reflecting surfaces, the reference wavelength in the used wavelength band is λ, the refractive index on the reflecting surface entrance side is n, and the reflecting surface is The step distance t between them may be set to t = λm / 2n (m is an integer).

Alternatively, in the case of oblique installation in the optical path, the contours of the central reflecting surface and the annular reflecting surface are made elliptical when viewed from the direction orthogonal to these reflecting surfaces, and the reference wavelength in the used wavelength band is set. The step distance t may be set to t = Aλm / 2n (m is an integer), where λ is n, the refractive index on the reflecting surface entrance side is n, and the ratio of the major axis to the minor axis of the ellipse is A.

It is preferable that the range of m satisfies 1 ≦ | m | ≦≦ 10. When the value of m is 0, it means a reflecting mirror having a flat surface as a whole. Therefore, unless it is 1 or more, a reflective diffraction type chromatic aberration correction element cannot be constructed. Further, when the value of m exceeds 10, when the wavelength fluctuation is large,
There is an inconvenience that the proportion of high-order diffracted light increases and the light utilization efficiency decreases. The sign of the value of m indicates whether the reflecting surface is macroscopically convex or concave as a whole.

On the other hand, by setting the width of each annular zone reflecting surface in inverse proportion to the square of the distance from the optical axis, the wavefront generated when the wavelength changes can be made into a substantially spherical wave. If the spherical aberration change due to wavelength variation of the combined lens is large, it is possible to correct it by adjusting the ring width of the reflecting surface by design, but considering general versatility, It is sufficient to set the width in inverse proportion to the square of the distance from the optical axis.

The central reflecting surface and the ring-shaped reflecting surface group may be composed of plane surfaces parallel to each other or may be composed of curved surface groups. The reflection-diffraction chromatic aberration correction element of the present invention is used in combination with a lens to correct the chromatic aberration of the lens. That is, the wavefront state of the different wavelength light is changed by reflection so as to correct the chromatic aberration generated by the lens when the different wavelength light having a wavelength different from the reference wavelength is incident.

In this chromatic aberration correction device, the reflection diffraction type chromatic aberration correction element can be installed in the optical path between the collimator lens for collimating the light incident on the lens into a parallel light beam. This chromatic aberration correction device can be used to correct the chromatic aberration when, for example, a single lens is used as a lens for converging laser light on an optical disc of an optical information recording / reproducing device.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to illustrated embodiments. 1 and 2 show the principle of the chromatic aberration correction element according to the present invention.

Reflection Diffraction Type Chromatic Aberration Correction Element 1 According to the Present Invention
1 includes a circular central reflecting surface 11 _ac around the optical axis of O, positioned outside the circular central reflecting surface 11 _ac, outline also circular concentric circular annular reflecting surface 11 _bc, 11 _cc, 11 _dc
It consists of In the illustrated embodiment, the number of annular reflecting surfaces is three.
However, actually, about 10 to 100 are provided. The number of ring zones of the conventional diffraction lens reaches several hundreds, and the reflective diffraction type chromatic aberration correction element 11 of the present invention is also distinguished from the conventional diffraction lens by the number of ring zones.

The circular center reflecting surface 11 _ac and the circular ring-shaped reflecting surfaces 11 _bc , 11 _cc , and 11 _dc are made up of mutually parallel planes, and their positions are different by a step distance t in the optical axis O direction. , Macroscopically, it has a convex shape. To simplify the description, it is assumed that the reflection-diffraction chromatic aberration correction element 11 is placed in the air (refractive index n = 1), and the reference wavelength incident on the reflection surface is λ.
This step distance t is given by t = λ / 2.
This is because m = 1, n = 1 in the equation of t = λm / 2n.
Corresponds to the case of.

Consider a case where a plane wave (parallel light beam) having a reference wavelength λ is incident on the reflection / diffraction chromatic aberration correction element 11. Adjacent lines 12 indicate positions in the light traveling direction of the specific phase light (for example, 0 °) of the plane wave having the reference wavelength λ.
Since the relation of t = λ / 2 holds for this reference wavelength light, the circular center reflection surface 11 _ac or the circular ring-shaped reflection surface 11 _dc.
The plane wave state is maintained even after being reflected by each of the reflecting surfaces of.

More generally, the optical path length difference generated when reflecting in a medium having a refractive index n and a thickness t along the optical path is given by 2 nt. Therefore, when the reflection-diffraction-type chromatic aberration correction element 11 has a stepwise reflection surface with a step distance t or an integer m times t (h) = λ / 2n (h is the distance from the optical axis O), the reference wavelength In the wavefront of the light of λ, the light reflected by the adjacent reflection regions shifts by exactly mλ and travels again without changing the shape of the wavefront.

On the other hand, FIG. 2 shows a case where a plane wave having a wavelength λ ′ slightly longer than the reference wavelength λ enters the same catadioptric chromatic aberration correction element 11. The distance between the adjacent lines 12 ′ is longer than the distance between the adjacent lines 12 in FIG. 1 by the wavelength shift. When the light is reflected by the chromatic aberration correcting element 11 of the present invention, the light reflected by the circular center reflecting surface 11 _ac has the shortest traveling distance in the medium, and the light reflected by the circular ring-shaped reflecting surface 11 _dc has the same traveling distance. Longest. Light having a wavelength longer than the reference wavelength λ has a property that the wavefront advances as the traveling length increases. As a result, the phase of the wavefront of the light reflected by the circular center reflecting surface 11 _ac or the circular ring-shaped reflecting surface 11 _dc is
The part farther from the optical axis O advances, and the entire wavefront after reflection is curved to form a condensed wavefront. That is, the catadioptric diffractive chromatic aberration correcting element 11 having a stepwise reflecting surface macroscopically convex on the light incident side, uses light incident as a plane wave as a converging wave surface for light having a wavelength longer than the reference wavelength light. It will be reflected. This means that the reflective diffraction type chromatic aberration correction element 11
This is synonymous with the occurrence of chromatic aberration that cancels out the chromatic aberration of the positive lens that utilizes refraction, and thus chromatic aberration can be corrected.

On the contrary, the light having a wavelength shorter than the reference wavelength is delayed by the wavefront as it travels through the medium, so that it is diverged by the same reflection-diffraction chromatic aberration correction element 11. That is,
The reflection-diffraction-type chromatic aberration correction element 11 that has a stepwise reflecting surface that is convex on the light incident side macroscopically reflects light that is incident as a plane wave as a divergent wavefront for light having a wavelength shorter than the reference wavelength light. Becomes This is synonymous with the occurrence of chromatic aberration that cancels out the chromatic aberration of the negative lens utilizing refraction due to the reflection by the catadioptric diffractive chromatic aberration correction element 11, and thus the chromatic aberration can be corrected.

Macroscopically, the stepwise reflecting surface of the reflection-diffraction-type chromatic aberration correction element 11 is convex or concave depending on whether the chromatic aberration to be corrected is caused by a positive lens or a negative lens. Will be decided.

The widths s ₁ , s ₂ and width s ₃ of the circular ring-shaped zone reflecting surfaces 11 _bc , 11 _cc and 11 _dc are set in inverse proportion to the square of the distance from the optical axis O.

Next, FIG. 3 and FIG. 4 show an embodiment in which the reflection-diffraction chromatic aberration correction element 11A of the present invention is installed at an angle of 45 ° with respect to the optical axis O. The reflection surface of the catadioptric diffractive chromatic aberration correction element 11A has an elliptical reflection surface 11 _ae located at the center of the optical axis O when viewed from a direction orthogonal to the reflection surface.
And the elliptical ring-shaped reflective surfaces 11 _be , 11 _ce , 1 which are located outside the elliptical reflective surface 11 _ae and have the same elliptical contour.
It _{consists of} 1 _de . Ratio of the major axis of this ellipse to the uniaxial A
_Are defined so that the orthographic projections of these elliptical reflecting surfaces 11 _ae and elliptical ring reflecting surfaces 11 _be , 11 _ce , and 11 _{de on} the planes orthogonal to the optical axis O are circular. . That is, A is 2 ^1/2 .

The ellipse of the elliptic reflecting surface 11 _ae is in the XY coordinate ^{system, (X 2 / A 2)} + (Y 2/1) = r 2 When (r is a constant) represented by the elliptical reflecting surface 11 _ae, Step distance t between elliptical ring-shaped reflective surfaces 11 _be , 11 _ce , and 11 _de
Is given by t = λ · 2 ^−1/2 . This is t = A
In the formula of λm / 2n (m is an integer), the case is n = 1 and m = 1 as in the embodiment shown in FIGS. 1 and 2.
Therefore, also in this embodiment, it is possible to obtain the same effect as that of the first embodiment.

The above example is the case where m = 1. However, when the used wavelength width is not wide, when the step distance t is determined, even if m-order diffracted light is used with m being 2 or more, the There is no problem because the efficiency does not decrease. Especially in the case where the zone width becomes narrow in the peripheral part,
It is also possible to gradually increase the value of m from 1. In this case, the distance in the optical axis direction from the center reflecting surface of the ring-shaped reflecting surface Δ
Let X (h) be a function of the distance h from the optical axis O,

[0025]

[Expression 1] ΔX (h) = (mλ / 2n) Int {[r- (1- (1-h ² / r ² ) ^1/2 ) /
(mλ / 2n)] + 0.5} However, Int (x) may be determined according to a function that gives an integer that does not exceed x.

FIG. 5 shows an embodiment in which the reflection / diffraction type chromatic aberration correction element 11 of the present invention is applied to an optical information recording / reproducing apparatus. The laser light from the laser light source 21 is made into a parallel light flux by the collimator lens 22, and the beam shaping prism 23
After being shaped into a circular cross section by the beam splitter 24
Incident on. The laser light split by the beam splitter 24 is reflected by the catadioptric diffractive chromatic aberration correction element 11 A fixed on the carriage 34 and enters the objective lens 26. The carriage 34 is moved in the radial direction of the optical disc 27 by the guide rail 35. The laser light incident on the objective lens 26 is condensed on the optical disk 27, and the reflected light is returned to the beam splitter 24 by the reflective diffraction type chromatic aberration correction element 11A. The reflected light from the optical disc 27 returning to the beam splitter 24 is reflected by the signal reproducing optical system 2.
It is incident on the sensor 32 through the lens 30 of No. 8. Also,
The light enters the sensor 33 via the lens 31 of the servo optical system 29.

Various types of such optical information recording / reproducing apparatus are known, but they are constructed of a single lens by using a combination of the objective lens 26 which is a single lens and the reflection diffraction type chromatic aberration correction element 11A. It is possible to correct chromatic aberration that occurs in the objective lens 26.

The present invention will be described below based on specific examples. Each of these examples is intended to correct the chromatic aberration of the objective lens composed of a positive lens.

[Embodiment 1] As shown in FIG. 6, the reflecting surface has an optical axis O.
Reflection diffraction type chromatic aberration correction element 11 of a type orthogonal to
Is. This reflection diffraction type chromatic aberration correction element 11 is shown in FIG.
And the chromatic aberration of the objective lens 41 having the characteristics shown in FIG. 12 is corrected. Reference numeral 42 in FIG. 11 indicates an optical disc. The objective lens 41 forms an image of the parallel light beam laser light incident through the collimator lens on the inner recording surface of the optical disc 42. The objective lens 26 in the apparatus configuration of FIG.
Equivalent to.

The specifications of the objective lens 41 are: focal length; 3.3 mm, working wavelength (reference wavelength) λ; 780 nm, back focus deviation amount df _B / dλ; 11 μm / nm when wavelength changes by a unit amount. Table 1 shows numerical data of the objective lens 41.

In the aberration charts of Table 1 and FIG. 12, SA is spherical aberration, SC is sine condition, d line, g line and C line are chromatic aberration and magnification chromatic aberration indicated by spherical aberration at respective wavelengths, and S is Sagittal and M indicate meridional. Further, r _i is the radius of curvature of each surface of the lens, d _i is the lens thickness or the lens interval, and N is the refractive index.

[0032]

[Table 1] NA = 0.55 f = 3.30 ω = 1.7 ＊ Aspherical surface No.1; K = -0.3265, A4 = -0.2263 × 10 ^-2 , A6 = -0.5014 × 10
^-3 , A8 = -0.7162 × 10 ^-5 , A10 = -0.3194 × 10 ^-4 No.2; K = -0.9120, A4 = 0.1648 × 10 ^-1 , A6 = -0.5064 × 10
^-2 , A8 = 0.7995 × 10 ^-3 , A10 = -0.4848 × 10 ^-4

Reflection-diffraction chromatic aberration correction element 1 of this embodiment
Reference numeral 1 denotes surface reflection of normal incidence. If this reflection diffraction type chromatic aberration correction element 11 is made to correspond to a positive lens having a focal length of 126 mm, the power of the diffractive lens is proportional to the wavelength, and the chromatic aberration correction by the objective lens 41 is performed. Is possible. However, as it is, the incident height of the light flux on the objective lens changes due to the change in the distance between the objective lens and the chromatic aberration correction element, and therefore it can be used only in a system in which the objective lens and the chromatic aberration correction element are integrated. Therefore, the chromatic aberration correcting element according to the present invention macroscopically has a shape of a negative lens having a focal length f = -126 mm, and has a reflecting surface which is a flat surface in order to prevent the first-order light from being refracted by diffraction. .

When the reflection is the surface reflection in air, n =
1.0, and in order to form a negative lens of f = -126 mm with a reflecting surface, the radius of curvature r = 252.0 mm, and this curved surface has a step distance t = λ / 2 = 390 nm = 0.3 in the optical axis direction.
When flattened by 90 μm, the action as a diffractive lens with f = 126 mm and the action as a refraction lens with f = −126 mm are obtained, and the primary light goes straight.

More specifically, the annular reflecting surfaces 11 _bc , 1
Optical axis direction distance from the center reflection surface 11 _ac of 1 _cc and 11 _dc
Let X (h) be a function of the distance h from the optical axis O,

[Expression 2] ΔX (h) = (λ / 2n) Int {[r- (1- (1-h ² / r ² ) ^1/2 ) /
(λ / 2n)] + 0.5} However, if Int (x) has a shape given by a function that gives an integer not exceeding x, chromatic aberration due to the objective lens 41 can be corrected. Table 2 shows the shape of the reflective diffraction type chromatic aberration correction element 11 of FIG.

[0036]

[Table 2]

This reflection-diffraction chromatic aberration correction element 11 is arranged in a parallel light beam between the collimator lens and the objective lens 41, and the reflected light from the reflection-diffraction chromatic aberration correction element 11 is separated by a beam splitter. The focus shift (chromatic aberration) due to the wavelength fluctuation can be canceled. That is, the objective lens 41 including a single lens
It is possible to correct the chromatic aberration shown in FIG.

FIG. 10 schematically shows the chromatic aberration generated by the objective lens 41 and the manner of chromatic aberration correction by the reflective diffraction type chromatic aberration correction element 11. When the wavelength of the laser light used is the reference wavelength λ = 780 nm, a correct image forming system for forming an image on, for example, the sensor 22 of FIG. 5 is configured via the objective lens 41 and the catadioptric chromatic aberration correcting element 11. That is, no focus shift occurs.

On the other hand, the wavelength of the laser light used is λ '=
If it is changed to 770 nm, the objective lens 41 has B
Chromatic aberration (wavefront aberration) indicated by a line occurs. This wavefront aberration tends to be under in the peripheral portion. In contrast,
Since the wavelength of the reflection / diffraction chromatic aberration correction element 11 is shifted to the single wavelength side, the light that is incident as a plane wave and reflected is a divergent wavefront. This diverging wavefront exhibits an over-tendency indicated by the line C in FIG. 10, so that the combined wavefronts of both are canceled by each other, and an image can be obtained without defocus. That is, the chromatic aberration generated in the objective lens 41 due to the wavelength shift can be corrected by the reflection diffraction type chromatic aberration correction element 11.

[Embodiment 2] In Embodiment 1, since the reflected light from the reflection diffraction type chromatic aberration correction element 11 is separated by the beam splitter, a loss is likely to occur in the beam splitter. Therefore, as in the example of FIG. 5, it is preferable to dispose the reflection-diffraction chromatic aberration correction element 11A at an angle of 45 ° with respect to the optical axis. In this case, as described with reference to FIGS. 3 and 4, the reflecting surfaces are elliptical reflecting surfaces 11 _ae and elliptical annular reflecting surfaces 11 _ae.
It consists of _be to 11 _de . The step distance t is
The effective phase difference that one step gives to the wavefront is sin 45 ° ≈ 0.70
7 becomes 1 / sin 45 ° ≈1.41 as compared with the first embodiment.
Double. Therefore, the same operation as that of the first embodiment is performed.
The shape of the reflection diffraction type chromatic aberration correction element 11A with 5 ° incidence is
As shown in FIG. 7 and Table 3.

[0041]

[Table 3] Minor axis direction h (mm) Major axis direction h (mm) △ X (μm) 0.000〜0.313 0.000〜0.443 0.0〜0.542〜0.767 0.55〜0.700〜0.991 1.10〜0.829〜1.172 1.65〜0.940〜1.330 2.20 ~ 1.039 ~ 1.470 2.75 ~ 1.130 ~ 1.598 3.30 ~ 1.214 ~ 1.717 3.86 ~ 1.292 ~ 1.827 4.41 ~ 1.366 ~ 1.932 4.96 ~ 1.436 ~ 2.031 5.51 ~ 1.503 ~ 2.126 6.06 ~ 1.567 ~ 2.216 6.61 ~ 1.628 ~ 2.303 7.17 ~ 1.688 〜 1.745 〜 2.468 8.27 〜 1.800 〜 2.546 8.82 〜 1.854 〜 2.622 9.37 〜 1.906 〜 2.696 9.92 〜 1.957 〜 2.768 10.47 〜 2.007 〜 2.838 11.03

This reflection / diffraction type chromatic aberration correction element 11A is
If the collimator lens and the objective lens 41 (in the example of FIG. 5, between the collimator lens 22 and the objective lens 26) are arranged in a parallel light flux, the focus shift (chromatic aberration) due to the wavelength variation of the semiconductor laser can be canceled. .

[Third Embodiment] In the first and second embodiments, the reflecting surface is provided on the surface of the chromatic aberration correcting element. However, the reflection-diffraction chromatic aberration correcting element of the present invention may be constructed as a back surface reflection type. it can. FIG. 8 shows an embodiment of this back surface reflection type reflection diffraction type chromatic aberration correction element 11B. The back surface reflection type has an advantage that even if dust adheres to a step on the back surface of the reflection surface, it is not affected. In the case of back surface reflection, in the medium (n> 1), the wavelength ratio used shortens, so
The step distance t becomes shorter than in the first and second embodiments (since n> 1 in the equation of t = λm / 2n). Table 4 shows
An example of the shape in the case where the reflection-diffraction chromatic aberration correction element 11B with an incident angle of 45 ° is composed of an optical material of n = 1.51072 is shown.

[0044]

[Table 4] Minor axis direction h (mm) Major axis direction h (mm) △ X (μm) 0.000 to 0.313 0.000 to 0.443 0.0 to 0.542 to 0.767 0.36 to 0.700 to 0.991 0.73 to 0.829 to 1.172 1.09 to 0.940 to 1.330 1.46 ~ 1.039 ~ 1.470 1.82 ~ 1.130 ~ 1.598 2.19 ~ 1.214 ~ 1.717 2.55 ~ 1.292 ~ 1.827 2.92 ~ 1.366 ~ 1.932 3.28 ~ 1.436 ~ 2.031 3.65 ~ 1.503 ~ 2.126 4.01 ~ 1.567 ~ 2.216 4.38 ~ 1.628 ~ 2.303 4.74 ~ 1.61 1.688 〜 1.745 〜 2.468 5.47 〜 1.800 〜 2.546 5.84 〜 1.854 〜 2.622 6.20 〜 1.906 〜 2.696 6.57 〜 1.957 〜 2.768 6.93 〜 2.007 〜 2.838 7.30

[Embodiment 4] The angle of incidence on the reflection-diffraction chromatic aberration correction element of the present invention is not limited to 0 ° and 45 °.
In short, it suffices that the orthogonal projections of the central reflecting surface and the ring-shaped reflecting surface on the planes orthogonal to the optical axis have a rotationally symmetrical shape about the optical axis. FIG. 9 and Table 5 show examples of the shape of the catadioptric diffractive chromatic aberration correction element 11C that operates in the same manner as in Examples 1 to 3 when the incident angle is 30 °. In this example,
Since 1 / sin30 ° = 2, the one-step distance t becomes larger than in the first to third embodiments. Therefore, there is an advantage that manufacturing becomes easy.

[0046]

[Table 5] Minor axis direction h (mm) Major axis direction h (mm) △ X (μm) 0.000 to 0.313 0.000 to 0.626 0.0 to 0.542 to 1.085 0.78 to 0.700 to 1.401 1.56 to 0.829 to 1.658 2.34 to 0.940 to 1.880 3.12 〜 1.039 〜 2.079 3.90 〜 1.130 〜 2.260 4.68 〜 1.214 〜 2.428 5.46 〜 1.292 〜 2.585 6.24 〜 1.366 〜 2.733 7.02 〜 1.436 〜 2.873 7.80 〜 1.503 〜 3.006 8.58 〜 1.567 〜 3.134 9.36 〜 1.628 〜 3.257 10.14 〜 1.688 〜 1.745 〜 3.490 11.70 〜 1.800 〜 3.601 12.48 〜 1.854 〜 3.709 13.26 〜 1.906 〜 3.813 14.04 〜 1.957 〜 3.915 14.82 〜 2.007 〜 4.014 15.60

[Embodiment 5] The reflection-diffraction chromatic aberration correction element of the present invention can be arranged in a portion other than the parallel light flux portion. In this embodiment, the present invention is applied to the reflecting surface 44 of the catadioptric lens 43 shown in FIG. Table 6 shows the numerical data of the catadioptric lens 43, and FIG. 14 shows various aberrations. ν is the Abbe number.

[0048]

[Table 6] F _NO = 1: 5.6 f = 44.68 Surface No. rd N ν 1 25.000 3.00 1.77250 49.6 2 252.451 1.00 3 -26.100 2.00 1.49176 57.4 4 -800.000 The four surfaces of this lens system are reflection surfaces 44.

This catadioptric lens 43 is
Although it is a lens that forms an image at a magnification of 1/6, for example, a lens that can form an image of an upper half object with respect to the optical axis downward, axial chromatic aberration correction is insufficient and 588
In the vicinity of nm, df _B /dλ=7.0 um / nm.
According to the principle of the present invention, the reflecting surface 44 of this lens is formed in an annular shape, so that the axial chromatic aberration can be corrected as a reflection diffraction type chromatic aberration correction surface. That is, the reflection surface 44 is configured as a vertically incident back surface reflection type (a type in which the reflection surface of the embodiment of FIG. 6 is formed by the back surface reflection of the embodiment of FIG. 8). Table 7 shows an example of the shape of the reflecting surface 44 when the lens is made of the optical material of n = 1.49176.

[0050]

[Table 7] According to this reflection surface shape, the chromatic aberration shown in FIG. 14 can be corrected.

[0051]

As described above, according to the catadioptric diffraction type chromatic aberration correcting element of the present invention, it is possible to satisfactorily correct the chromatic aberration generated in the lens used in combination with the single reflecting element. Since the reflective element is widely used in optical systems, by converting the reflective element into the chromatic aberration correction element of the present invention, chromatic aberration can be corrected without adding a special optical element. When used in an optical information recording / reproducing apparatus, it is possible to correct a focus shift due to a wavelength variation of laser light with an inexpensive apparatus configuration.

[Brief description of drawings]

FIG. 1 is a cross-sectional view illustrating the principle of a reflective diffraction type chromatic aberration correction element according to the present invention.

FIG. 2 is a cross-sectional view illustrating the principle of a reflective diffraction type chromatic aberration correction element according to the present invention.

FIG. 3 is a sectional view illustrating the principle of another mode of the catadioptric chromatic aberration correction element of the present invention.

FIG. 4 is a view on arrow A in FIG.

FIG. 5 is a perspective view showing an embodiment in which the reflective diffraction type chromatic aberration correction element of the present invention is applied to an optical recording / reproducing apparatus.

FIG. 6 is a cross-sectional view showing a first embodiment of a reflective diffraction type chromatic aberration correction element of the present invention.

FIG. 7 is a cross-sectional view showing a second embodiment of the reflective diffraction type chromatic aberration correction element of the present invention.

FIG. 8 is a cross-sectional view showing a third embodiment of the reflective diffraction type chromatic aberration correction element of the present invention.

FIG. 9 is a sectional view showing a fourth embodiment of the catadioptric chromatic aberration correction element of the present invention.

FIG. 10 is a diagram schematically showing chromatic aberration caused by a single lens and a state of this chromatic aberration correction by the reflection diffraction type chromatic aberration correction element of the present invention in the embodiment of FIG.

FIG. 11 is a diagram showing an example of a single lens used in combination with the reflective diffraction type chromatic aberration correction element of the present invention.

FIG. 12 is a diagram of various types of aberration of the single lens of FIG.

FIG. 13 is a diagram showing an example of another lens system to which the reflective diffraction type chromatic aberration correction element of the present invention is applied.

14 is a diagram of various types of aberration of the lens system in FIG.

[Explanation of symbols]

11 11A 11B 11C Reflective diffraction type chromatic aberration correction element 11 _ac Circular center reflective surface 11 _bc 11 _dc 11 _ec Circular ring reflective surface 11 _ae Elliptical reflective surface 11 _be 11 _ce 11 _de Elliptical annular reflective surface

Claims (11)

[Claims] 1. A reflection surface having a center reflection surface having a rotational symmetry centering on the optical axis and a large number of annular reflection surfaces concentric with the center reflection surface, which has an orthogonal projection shape with respect to a plane orthogonal to the optical axis. The central reflecting surface, the ring-shaped reflecting surface on the outside thereof, and the adjacent ring-shaped reflecting surfaces are displaced by the same step distance t in the direction orthogonal to these reflecting surfaces, and macroscopically as a whole. It has a concave surface or a convex surface, and at this step distance t, light that is incident as a plane wave is emitted as a plane wave for light of a reference wavelength, and is incident as a plane wave for light of a different wavelength different from the reference wavelength. A reflection-diffraction-type chromatic aberration correction element, characterized in that light is set to exit as a divergent wavefront or a condensed wavefront. 2. The center reflecting surface and the annular reflecting surface according to claim 1, wherein the contours of the central reflecting surface and the annular reflecting surface are circular when viewed from a direction orthogonal to these reflecting surfaces, and the reference wavelength in the used wavelength band is λ and the reflecting surface incident side. The refractive index is n, and the step distance t is given by: t = λm / 2n (m is an integer). 3. The center reflecting surface and the annular reflecting surface according to claim 1, wherein the contours of the center reflecting surface and the annular reflecting surface are elliptical when viewed from a direction orthogonal to these reflecting surfaces, and the reference wavelength in the used wavelength band is λ and the reflecting surface is incident. The refractive index on the side is n, and the ratio of the major axis to the minor axis of the ellipse is A
The step distance t is given by: t = Aλm / 2nt (m is an integer). 4. A reflection diffraction type chromatic aberration correction element according to claim 1, wherein 1 ≦ t · 2n / λ ≦ 10 is satisfied. 5. The reflection diffraction type chromatic aberration correction element according to claim 1, wherein the width of each ring-shaped reflective surface is set in inverse proportion to the square of the distance from the optical axis. 6. The catadioptric chromatic aberration correction element according to claim 1, wherein the central reflecting surface and the annular reflecting surface group are plane groups parallel to each other. 7. The reflection-diffraction-type chromatic aberration correction element according to claim 1, wherein the central reflecting surface and the ring-shaped reflecting surface group includes a curved surface group. 8. The reflection-diffraction chromatic aberration correction element according to claim 1, wherein the reflection-diffraction chromatic aberration correction element is installed in combination with a lens, and when a different wavelength light having a wavelength different from a reference wavelength is incident, A chromatic aberration correction device provided so as to change the wavefront state of the different wavelength light by reflection so as to correct the chromatic aberration caused by the lens. 9. The chromatic aberration correction device according to claim 8, wherein the reflection-diffraction-type chromatic aberration correction element is installed in an optical path between a collimator lens that makes a light beam incident on a lens into a parallel light beam and the single lens. 10. The chromatic aberration correction device according to claim 9, wherein the lens is a single lens that focuses laser light on the optical disc. 11. The chromatic aberration correction device according to claim 10, wherein the single lens is an aspherical lens.