JP2001059905A - Diffraction type optical element and optical pickup using this diffraction type optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element capable of taking out diffracted light beams in accordance with the pattern of a diffraction optical element outside a substrate even when the pattern pitch of the patter of the diffraction optical element is less than the wavelength of incident light. SOLUTION: The first pattern 4 of the diffraction optical element which has the pattern pitch less than the wave length of the incident light is formed on one part of the main surface 2 of the substrate 1 made of glass, etc., and polarization is imparted thereto. On the other hand, second patterns 5, 6 of the diffraction optical element are disposed on the parts which are respectively irradiated with +1st diffracted light beams and -1st diffracted light beams which are diffracted by the first pattern 4 of the diffraction optical elements on the main surface 3 of the substrate 1. The -1st diffracted light beams L22, L32 which are respectively refracted on the second patterns 5, 6 of the diffraction optical element are made incident to the boundary surface of the main surface 2 with an angle smaller than the critical angle of total reflection and are taken outside the substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffractive optical element used in the fields of optical information processing equipment and optical communication equipment, and more particularly to a diffractive optical element having a polarization property. Further, the present invention relates to an optical pickup using the diffractive optical element.

[0002]

2. Description of the Related Art FIG. 20 shows a conventional diffractive optical element 200.
It is sectional drawing which shows a structure of. The arrows in the figure indicate the traveling directions of the light rays (the same applies to the following drawings). As shown in FIG. 20, the diffractive optical element 200 is configured by forming a diffractive optical element pattern 203 on a main surface 202 of a substrate 201 made of transparent flat glass. When the monochromatic incident light L0 enters the diffractive optical element pattern 203 perpendicularly from the main surface 202 side, transmission diffraction occurs in the diffractive optical element pattern 203, and forms a zero-order diffracted light L1 and a diffraction angle θ1 with the 0th-order diffracted light inside the substrate 201. + 1st-order diffracted light L2 and -1st-order diffracted light L3 are generated.

Here, the wavelength of the incident light L0 is λ, the substrate 20
1 is n (n> 1), and the diffractive optical element pattern 203
If the pattern pitch of is Λ, the value of the diffraction angle θ1 is
It can be easily obtained by the following well-known equation 1. θ1 = sin ^-1 ｛(λ / n) / Λ｝ (Equation 1) The diffraction angle θ1 obtained as described above is usually calculated on the substrate surface (more precisely, on the main surface of the substrate). Since the angle is smaller than the critical angle of total reflection at the boundary surface, the zero-order diffracted light L1, +
The first-order diffracted light L2 and the -1st-order diffracted light L3 are respectively transmitted through the substrate 201 and emitted to the outside from the opposite main surface 204.

Further, like a diffractive optical element 210 shown in FIG. 21, a main surface 21 of a substrate 211 on which incident light L0 is incident.
In the case where the diffractive optical element pattern 213 is formed on the main surface 214 on the opposite side to the second order, the + 1st-order diffracted light L in the direction outside the substrate at the 0th-order diffracted light L1 and the diffraction angle θ2 determined by the following equation
2, -1st-order diffracted light L3 is generated, and the 0th-order diffracted light L1,
The + 1st-order diffracted light L2 and the -1st-order diffracted light L3 pass through the substrate 211 and are emitted to the outside.

Θ 2 = sin ⁻¹ (λ / Λ) (Equation 2) In the diffractive optical element having the above configuration,
In general, it is known that when the pattern pitch の of a diffractive optical element pattern is reduced, polarization occurs, and it is greatly expected as a new optical element.

[0006]

However, when the pattern pitch の of the pattern of the diffractive optical element becomes equal to or smaller than the wavelength λ of the incident light, the diffraction angle also becomes large as is clear from the above equations (1) and (2). Inconvenience occurs that the diffracted light cannot be taken out of the substrate. FIG. 22 is a diagram showing the course of diffracted light when the pattern pitch of the diffractive optical element pattern in FIG. 20 is reduced. As shown in the figure, a diffractive optical element pattern 303 having a pattern pitch equal to or less than the wavelength の of the incident light L0 is provided on the main surface 302 of the diffractive optical element 300. The folded light L2 and the -1st-order diffracted light L3 travel at a diffraction angle θ3 larger than the diffraction angle θ1 in FIG. 20, but are totally reflected at the boundary surface of the main surface 304 because the diffraction angle θ3 satisfies the condition of total reflection. Thereafter, total reflection is repeated at all the boundary surfaces on which the reflected light is incident, and the substrate 30
1 Diffracted light cannot be extracted outside.

Similarly, in FIG. 21, if the pitch Λ of the diffractive optical element pattern is smaller than the wavelength λ of the incident light, there arises a problem that the diffracted light cannot be extracted to the outside. That is, as shown in the diffractive optical element 310 in FIG.
11 is a diffractive optical element pattern 3 formed on the main surface 314 side.
The incident light L0 incident on 13 generates a 0th-order diffracted light L1, a + 1st-order diffracted light L2, and a -1st-order diffracted light L3.
Is the + 1st-order diffracted light L2 although emitted from the main surface 314
And the -1st-order diffracted light L3 does not satisfy the transmission diffraction condition, and θ4 = sin ^-1 ((λ / n) / Λ) (Equation 3)
The light again travels inside the substrate as reflected diffracted light at the diffraction angle θ4 determined by the above, and the total reflection is repeated at the boundary surface between the main surfaces 312 and 314, and the diffracted light cannot be taken out of the substrate.

As described above, even if the diffractive optical element pattern has a polarization property, the diffracted light cannot be taken out of the substrate, so that its usefulness as an optical element is poor. On the other hand, an optical pickup used in a magneto-optical disk reproducing device irradiates a laser beam onto an information recording surface of the magneto-optical disk, and separates the returned light by a prism-shaped polarizing beam splitter to read recorded information. Or, it is configured to obtain a servo signal such as a focus error signal or a tracking error signal. However, since the prism-shaped polarizing beam splitter has a relatively large volume,
There is a problem that it is difficult to reduce the size of the optical pickup.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. Even if the pattern pitch of the pattern of the diffractive optical element is smaller than the wavelength of the incident light, the diffracted light of the pattern of the diffractive optical element is transmitted to the outside of the substrate. A first object is to provide a diffractive optical element that can be extracted. A second object of the present invention is to provide a smaller optical pickup by utilizing such a diffractive optical element.

[0010]

A diffractive optical element according to the present invention for achieving the first object is a diffractive optical element for diffracting an incident light beam. A substrate having a main surface and a refractive index of n (n>1); and a pattern pitch provided on a part of the first main surface of the substrate, the pattern pitch of which is equal to or less than the wavelength λ of the incident light beam. And a first diffractive optical element pattern larger than λ / n and one of the first and second main surfaces of the substrate, wherein the diffracted light by the first diffractive optical element pattern is A second diffractive optical element pattern provided at a position where the light enters through a predetermined path in the substrate.

According to this structure, a light beam is incident on the first diffractive optical element pattern having a pattern pitch smaller than the wavelength of the incident light, and the diffraction angle of the reflected or transmitted diffracted light increases to increase the principal surface of the substrate. Even if the condition of total reflection at the interface with the substrate is satisfied, the angle of incidence on the interface with the main surface of the substrate is made smaller by making the diffracted light incident on the second diffractive optical element pattern and diffracting it. And the diffracted light can be taken out of the substrate.

Here, the first main surface may be a main surface of the substrate on a side on which the light beam enters, or a main surface of the substrate on a side opposite to a side on which the light beam enters. Further, the second diffractive optical element pattern is formed on the second main surface of the substrate, and the light diffracted by the first diffractive optical element pattern is even-numbered times including zero times in the substrate, and all times. It may be provided at a position where the light is reflected and then incident.

Further, the second diffractive optical element pattern is formed on the first main surface of the substrate, and the light diffracted by the first diffractive optical element pattern is emitted an odd number of times in the substrate. It may be provided at a position where the light is incident after being totally reflected. Here, the position where the second diffractive optical element pattern is provided is such that the diffracted light generated when a light beam having a wavelength λ is perpendicularly incident on the first diffractive optical element pattern,
It is desirable to set the position to be incident through a predetermined path.

Further, the invention is characterized in that the diffracted light is at least one of a + 1st-order diffracted light and a -1st-order diffracted light. Further, the first and second principal surfaces of the substrate are:
They are parallel to each other. Further, the present invention relates to a main surface on a side opposite to the main surface on which the second diffractive optical element pattern is provided, and a position where diffracted light by the second diffractive optical element pattern is to be emitted out of the substrate. A reflection film for reflecting the diffracted light toward the inside of the substrate.

According to this configuration, the diffracted light can be extracted to the outside of the substrate from the main surface opposite to the main surface of the substrate provided with the reflection film. In the present invention, the pattern pitch of the second diffractive optical element pattern may be equal to or smaller than the wavelength λ of the incident light beam and larger than λ / n. The pattern pitch of the second diffractive optical element pattern may be the same as the pattern pitch of the first diffractive optical element pattern.

With this configuration, the diffracted light from the first diffractive optical element pattern can be extracted in a direction parallel to the direction of the principal ray of the incident light. Further, the present invention provides the second aspect,
The cross-sectional shape of each groove of the diffractive optical element pattern in a plane including the principal ray of the incident light and the principal ray of the diffracted light,
A hypotenuse portion may be included, and the diffracted light may be incident on the hypotenuse portion.

According to this configuration, when the diffracted light from the first diffractive optical element pattern is incident on the oblique side of each groove of the second diffractive optical element pattern, the incident angle on the boundary surface is substantially reduced. Therefore, the critical angle of the total reflection can be made smaller, and the transmitted light can be directly transmitted and diffracted by the second diffractive optical element pattern to take out the diffracted light to the outside of the substrate.

Here, the cross-sectional shape of each groove of the second diffractive optical element pattern in a plane including the principal ray of the incident light and the principal ray of the diffracted light may be substantially a right triangle. . Further, when the incident light is perpendicularly incident on the first diffractive optical element pattern, the diffraction angle of the diffracted light is θ, the inclination angle of the hypotenuse portion with respect to the direction orthogonal to the incident light is θb, Is defined as θt, and the magnitude of the inclination angle θb is set so as to satisfy the expression (θ−θb) <θt, so that the diffracted light can be surely transmitted to the second diffractive optical element pattern. The light can be transmitted and diffracted and taken out of the substrate.

Further, the present invention is characterized in that the second diffractive optical element pattern is constituted by a plurality of groove groups having a curved shape in a plane parallel to a main surface on which the second diffractive optical element pattern is provided. According to this configuration, the second diffractive optical element pattern has a lens function, so that the wavefront of the diffracted light diffracted by the second diffractive optical element pattern is controlled so that the light beam is parallel, divergent or converged. Then, it can be taken out of the substrate.

In order to achieve the second object, an optical pickup according to the present invention is an optical pickup for optically reading information recorded on an optical recording medium, including a light source for emitting laser light. A laser beam irradiating means for converging and irradiating the laser beam onto the information recording surface of the optical recording medium; a first polarized light beam as reflected light of the laser beam from the information recording surface; A polarizing beam splitter that separates the light into a second polarized light having a different polarization direction from light, and a photoelectric conversion unit that receives the first polarized light and the second polarized light, respectively, and converts them into an electric signal. One polarizing beam splitter has first and second principal surfaces and has a refractive index of n.
A first substrate (n> 1) and a portion of the first main surface of the first substrate, the pattern pitch of which is equal to or smaller than the wavelength λ of the incident light beam; / N, a first diffractive optical element pattern larger than / n
A second diffractive optical element provided at one of the principal planes of the first and second principal planes, where the diffracted light from the first diffractive optical element pattern enters through a predetermined path in the first substrate. And an element pattern.

With this configuration, a relatively small diffractive optical element according to the present invention can be used in place of the prism-shaped polarizing beam splitter which occupies a large space in the conventional optical pickup, and the entire optical pickup can be used. The size can be reduced. Further, the optical pickup according to the present invention, in an optical path from the light source to the information recording surface of the optical recording medium, while transmitting the laser light emitted from the light source of the laser light irradiation means, from the information recording surface Further comprises a second polarizing beam splitter for changing the direction of the reflected light in the direction of the first polarizing beam splitter, wherein the second polarizing beam splitter has first and second principal surfaces, A second substrate having a refractive index of n ′ (n ′> 1) and a portion of the first main surface of the second substrate, the pattern pitch of which is equal to or smaller than the wavelength λ of the incident light beam; And a third diffractive optical element pattern larger than λ / n ′, and one of the first and second main surfaces of the second substrate, wherein the first diffractive optical element is Light diffracted by the element pattern enters through a predetermined path in the second substrate. And a fourth diffractive optical element pattern provided at a position where light is emitted.

As a result, the compact diffractive optical element of the present invention can be used as a polarizing beam splitter for separating return light from the information recording surface, and the size can be further reduced. Further, in the optical pickup according to the present invention, the second substrate may be common to the first substrate, and the first diffractive optical element pattern may include first and second substrates of the first substrate. Is provided at a position where the light diffracted by the fourth diffractive optical element is incident. By doing so, two polarizing beam splitters can be formed on one substrate, and the size of the optical pickup can be further reduced.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. The diffractive optical element according to the present invention is roughly divided into a type in which incident light is polarized by transmitting and diffracting a diffractive optical element pattern (hereinafter, referred to as a “transmission polarization type”) and a type in which incident light is diffracted. It can be classified into two types: a type that is polarized by being reflected and diffracted by an optical element pattern (hereinafter, referred to as a “reflection polarization type”).

In this specification, first, a transmission polarization type diffraction optical element will be described with reference to Embodiments 1 to 4, and thereafter, a reflection polarization type diffraction optical element will be described with reference to Embodiment 5.
This will be described with reference to FIGS. The configuration of an optical pickup using a diffractive optical element according to the present invention will be described in Embodiments 9 to 10. (Embodiment 1) FIG. 1 is an external perspective view showing a shape of a transmission polarization type diffractive optical element 100 according to Embodiment 1 of the present invention.

As shown in FIG.
00 is the main surface 2 of the substrate 1 made of a transparent material such as glass.
A first diffractive optical element pattern 4 is formed thereon, and second diffractive optical element patterns 5 and 6 are formed on the main surface 3 on the back surface thereof. First diffractive optical element pattern 4 and second diffractive optical element pattern 4
Each of the diffractive optical element patterns 5 and 6 has a slit shape, and the pattern pitch of the first diffractive optical element pattern 4 is
The groove has a rectangular shape which is equal to or shorter than the wavelength λ of the incident light and has a groove. Such a fine pitch pattern is
It can be formed by dry etching, for example, reactive ion beam etching using chlorine gas. Since the diffractive optical element pattern having such a fine pattern pitch has a polarization property as described above, it is also referred to as a “for polarization” diffractive optical element pattern below.

Since the diffraction angle θ cannot be more than 90 °, from the above equation 1, ｛(λ / n) / Λ｝ <
Must be 1. From this, (λ / n) <Λ, and eventually the pattern pitch of the diffractive optical element pattern for polarization becomes λ when the refractive index of the substrate 1 is n (n> 1).
/ N <Λ ≦ λ.

On the other hand, the second diffractive optical element patterns 5 and 6 formed on the main surface 3 have a pattern pitch larger than the wavelength λ, and the cross-sectional shapes of these grooves are also formed in a rectangular shape. The second diffractive optical element patterns 5 and 6 can be formed by plasma etching or the like in addition to the ion beam etching. These second diffractive optical element patterns 5, 6 change the traveling direction of specific diffracted light in the first diffractive optical element pattern 4 as described below, and extract the diffracted light from the substrate 1 to the outside. In the following, the pattern may be referred to as a “diffraction light extraction” diffractive optical element pattern.

FIG. 2 is a diagram showing the path of light incident on the diffractive optical element 100 and the positional relationship between the diffractive optical element patterns 4, 5, and 6. FIG.
00 is shown in a vertical vertical sectional view at the center in the width direction.
Further, although a large number of diffracted lights are actually generated by the diffraction of the respective diffractive optical element patterns, only the paths of the 0th-order diffracted light, the + 1st-order diffracted light, and the -1st-order diffracted light having a large light intensity are shown below for convenience. I will.

As shown in FIG. 2, the incident light L having a wavelength λ
When 0 enters the first diffractive optical element pattern 4 for polarization from a direction perpendicular to the main surface 2 of the substrate 1, the 0th-order diffracted light L1 passes through the substrate 1 as it is, and the + 1st-order diffracted light L2,- The first-order diffracted light L3 travels in a direction forming a diffraction angle θ determined by Equation 1 with respect to the zero-order diffracted light L1.

The second diffractive optical element pattern 5 is formed on the main surface 3 of the substrate 1 at a position where the + 1st-order diffracted light L2 is first incident.
2 is reflected and diffracted to further generate a 0th-order diffracted light L21, a -1st-order diffracted light L22, and a + 1st-order diffracted light L23. Among them, -1
The angle of incidence of the next-order diffracted light L22 on the boundary surface of the main surface 2 becomes smaller than θ and does not satisfy the condition of total reflection, so that it can be emitted from the main surface 2 side of the substrate 1 as it is.

On the other hand, the second diffractive optical element pattern 6 is on the main surface 3 of the substrate 1 and is provided with the first diffractive optical element pattern 4.
Is provided at a position where the -1st-order diffracted light L3 is totally reflected on the boundary surface of the main surface 2 and then enters, where it is reflected and diffracted, and further, the 0th-order diffracted light L31, the -1st-order diffracted light L32, and the + 1st-order diffracted light This produces L33. Among them, the -1st order diffracted light L32
Since the angle of incidence on the boundary surface of the main surface 2 becomes smaller than θ and does not satisfy the condition of total reflection, the light can be emitted from the main surface 2 side of the substrate 1 as it is.

Here, specifically, the refractive index of the substrate 1 is set to 2.
0, the wavelength λ of the incident light L0 is 800 nm, the pattern pitch of the first diffractive optical element pattern 4 is 700 nm, and the pattern pitch of the second diffractive optical element patterns 5 and 6 is 2 μm. When the light is incident on the main surface 2 from a substantially perpendicular direction, the first-order diffraction angle θ inside the substrate 1 is 34.85 degrees as calculated from the above equation 1.

In the structure of the conventional diffractive optical element (see FIG. 22), the incident light L0 is
Is diffracted into a 0th order diffracted light L1, a + 1st order diffracted light L2 and a -1st order diffracted light L3, and a + 1st order diffracted light L2 and a -1st order diffracted light L3
Satisfies the condition of total reflection (30 degrees or more in the case of a substrate having a refractive index of 2), so that the diffracted light can be taken out of the substrate 1 without the second diffractive optical element patterns 5 and 6. Can not.

However, by providing the second diffractive optical element patterns 5 and 6 for extracting diffracted light on the main surface 3 of the substrate 1 on which the first-order diffracted light diffracted by the first diffractive optical element pattern 4 is incident, Diffracted light can be extracted out of the substrate 1.
That is, in the second diffractive optical element patterns 5 and 6, the + 1st-order diffracted light L2 and the -1st-order diffracted light L3 are respectively the 0th-order diffracted light L
21, L31 and -1st-order diffracted lights L22, L32 and + 1st-order diffracted lights L23, L33, and the exit angles of the 0th-order diffracted lights L21, L31 are the same as the incident angle of 34.85 degrees, but the -1st-order diffracted light L22. , L32 are smaller than the incident angles (34.85 degrees) of the + 1st-order diffracted light L2 and the -1st-order diffracted light L3 to the second diffractive optical element patterns 5, 6 due to the diffraction effect.
The output angle of the + 1st-order diffracted light L23 is larger than the incident angle (34.85 degrees) of the + 1st-order diffracted light L2 to the second diffractive optical element pattern 6 due to the diffraction effect.
0.48 degrees.

Thus, the -1st-order diffracted light L22 and the -1st-order diffracted light L32 in the second diffractive optical element patterns 5 and 6 are obtained.
Can be suppressed within the critical angle, so that the light can pass through the main surface 2 and be extracted to the outside. As described above, since the first diffractive optical element pattern 4 has a polarization property,
Zero-order diffracted light L1, + first-order diffracted light L2, -1st-order diffracted light L3
Has a different polarization direction, and as a result, the zero-order diffracted light L
1 and -1st-order diffracted light beams L22 and L32 having different polarization directions.
Can be taken out of the substrate 1 and can function as a polarizing beam splitter.

The same effect can be obtained if the second diffractive optical element patterns 5 and 6 are formed at positions where light rays after total reflection in the substrate 1 are more incident. Each time the reflection is repeated, the light intensity is attenuated by what percentage, and the wavefront tends to be disturbed. Therefore, it is desirable that the number of total reflections be as small as possible. This is the same in other embodiments.

FIGS. 3A and 3B are views showing a modification of the diffractive optical element 100 shown in FIG. In the diffractive optical element shown in FIG.
A reflection film 7 made of a metal or a multilayer dielectric is formed at a position on the main surface 2 of the substrate 1 where the -1st-order diffracted light L22 diffracted by the above is incident, for example, by sputtering or the like. As a result, the -1st-order diffracted light L22 in the second diffractive optical element pattern 5
Is reflected by the reflection film 7 and can be extracted from the main surface 3 side to the outside, so that the degree of freedom of design in an apparatus incorporating the diffractive optical element can be increased. Of course, a reflection film may be provided on the main surface 2 at the position where the -1st-order diffracted light L32 by the second diffractive optical element pattern 6 is incident.

On the other hand, if the pattern pitch of the second diffractive optical element patterns 5 and 6 is the same as the pattern pitch of the first diffractive optical element pattern 4, as shown in FIG.
Since the -1st-order diffracted lights L22 and L32 in the second diffractive optical element patterns 5 and 6 have the same diffraction effect as the diffraction angle θ of the first diffractive optical element pattern 4, the primary surface 2
In the direction perpendicular to the direction of the incident light L0, and can be extracted in a direction parallel to the direction of the principal ray of the incident light L0, and an element which is optically easy to handle can be obtained.

(Embodiment 2) FIG. 4 shows a configuration of a diffractive optical element 110 according to Embodiment 2 of the present invention. Unlike the first embodiment, the first diffractive optical element pattern 4
And the first principal surface 2 in which the second diffractive optical element patterns 5 and 6 are the same.
It is provided above. In the following embodiments, components having the same reference numerals as those in FIG. 2 indicate the same configuration.
Detailed description will be omitted.

As shown in FIG. 4, the diffractive optical element 110
Is provided with a first diffractive optical element pattern 4 for polarization on the principal surface 2 side of the substrate 1, and diffracted light diffracted by the first diffractive optical element pattern 4 on the principal surface 2 side of the substrate 1. Second diffractive optical element patterns 5 and 6 for extracting diffracted light are provided at portions where the light is totally reflected once or three times on the surface and is incident.

Specifically, the refractive index of the substrate 1 is 2, the wavelength of the incident light L0 is 800 nm, the pattern pitch of the first diffractive optical element pattern 4 is 700 nm, and the pattern of the second diffractive optical element patterns 5 and 6 is With the pitch being 2 μm, the incident light L0
Is incident on the main surface 2 of the substrate 1 from a substantially perpendicular direction, the first-order diffraction angle θ inside the substrate 1 is 34.85 degrees. The first diffractive optical element pattern 4 uses the incident light L0
Is diffracted into the 0th-order diffracted light L1, the + 1st-order diffracted light L2 and the -1st-order diffracted light L3, and the diffraction angles of the + 1st-order diffracted light L2 and the -1st-order diffracted light L3 are determined by the total reflection condition (3 in the case of a substrate having a refractive index of 2).
0 ° or more), and if the second diffractive optical element patterns 5 and 6 are not provided, diffracted light cannot be taken out of the substrate 1.

However, after the diffracted light diffracted by the first diffractive optical element pattern 4 is reflected on the boundary surface of the main surface 3, the second diffractive optical element pattern 5 is provided at the position of the main surface 2 where the light enters. As a result, the + 1st-order diffracted light L2 further becomes the 0th-order diffracted light L2
The light is branched into 1st, + 1st-order diffracted light L23 and -1st-order diffracted light L22, and the exit angle of the 0th-order diffracted light L21 is the same as the incident angle of 34.85 degrees, but the exit angle of the -1st-order diffracted light L22 is +1 due to the effect of diffraction. Second diffractive optical element pattern 6 of next-order diffracted light L2
21.80 degrees, which is smaller than the incident angle (34.85 degrees) to the second diffractive optical element pattern 5 of the + 1st-order diffracted light L2 due to the diffraction effect. 34.85 degrees), which is 50.48 degrees. Thereby, since the -1st-order diffracted light L22 in the second diffractive optical element pattern 5 can be suppressed within the critical angle in the total reflection, it can be extracted outside on the principal surface 3 side in the traveling direction.

Similarly, the -1st-order diffracted light L3 is totally reflected three times in the substrate 1 and then enters the second diffractive optical element pattern 6 to enter the 0th-order diffracted light L31, the -1st-order diffracted light L32, and the + 1st-order diffracted light. L33, the -1st-order diffracted light L32 no longer satisfies the condition of total reflection, and is extracted from the main surface 3 to the outside. The number of times that the diffracted light is totally reflected within the substrate 1 may be five or more as long as it is an odd number, and accordingly, the position where the diffractive optical element pattern is provided is more than the first diffractive optical element pattern 4. Also get far away.

By providing the second diffractive optical element pattern 5 and the second diffractive optical element pattern 6 at appropriate positions on the main surface 2 as described above, the first-order diffracted light reflected an odd number of times inside the substrate 1 can be obtained. It is possible to extract from the same side as the zero-order diffracted light L1. As shown in FIG. 5A, a reflection film made of a metal or a multilayer dielectric is provided at a position on the main surface 3 of the substrate 1 where the -1st-order diffracted light L22 diffracted by the second diffractive optical element pattern 5 is incident. By providing the light 8, the -1st-order diffracted light L22 of the second diffractive optical element pattern 5 is reflected by the reflection film 8 and can be extracted from the main surface 2 side to the outside.

Further, as shown in FIG. 5 (b), the incident light L0 is incident on the main surface 2 of the substrate 1 from the vertical direction, and the pattern pitch of the second diffractive optical element patterns 5, 6 is changed to the first diffraction light. If the pitch is the same as the pattern pitch of the optical element pattern 4,
The -1st-order diffracted lights L22 and L32 in the second diffractive optical element patterns 5 and 6 are given the same diffraction effect as the diffraction angle θ of the first diffractive optical element pattern 4, so that the principal surface 3 of the substrate 1
In the direction perpendicular to the direction of the incident light L0, and can be extracted in a direction parallel to the direction of the principal ray of the incident light L0, and an element which is optically easy to handle can be obtained.

(Embodiment 3) FIG. 6 is a sectional view showing a configuration of a diffractive optical element 120 according to Embodiment 3 of the present invention. As shown in FIG.
The first diffractive optical element pattern 4 for polarization is provided on the principal surface 2 side, and the diffracted light diffracted by the first diffractive optical element pattern 4 on the principal surface 3 side of the substrate 1 is directly or on the substrate surface. A second diffractive optical element pattern for taking out diffracted light, which is formed of a triangular concave shape group (hereinafter, referred to as a “sawtooth shape”) as a whole with a triangular cross-section of each groove at a portion where the light is totally reflected twice and is incident. 9 and 10 are provided.

FIG. 7 is an enlarged view of one groove of the second diffractive optical element pattern 10. As shown in FIG. 7, a slope 11 having a tilt angle θb with respect to the main surface 3 is formed. The groove is formed so as to turn away from the diffracted light that has just entered. Here, for example, let the refractive index of the substrate 1 be 2,
When the wavelength of the incident light L0 is 800 nm, the pattern pitch of the first diffractive optical element pattern 4 is 700 nm, and the incident light L0 is incident on the main surface 2 of the substrate 1 from a substantially perpendicular direction,
The first-order diffraction angle θ inside the substrate 1 becomes 34.85 degrees, and the incident light L0 is converted into the zero-order diffracted light L1 by the first diffractive optical element pattern 4.
And + 1st order diffracted light L2 and -1st order diffracted light L3,
Since the diffraction angles of the + 1st-order diffracted light L2 and the -1st-order diffracted light L3 satisfy the total reflection condition (30 degrees or more in the case of a substrate having a refractive index of 2), if the second diffractive optical element patterns 9 and 10 are not provided, Total reflection is repeated inside the substrate 1 and diffracted light cannot be taken out of the substrate 1.

However, the second diffractive optical element patterns 9, 1
0 has a sawtooth shape as described above, and each triangular recess has a slope 11 having an inclination angle θb, so that the angle of incidence for diffracted light incident on the boundary surface of the slope 11 is (θ−θb). ). As described above, the diffraction angle θ is 34.
Since the critical angle of total reflection is 30 °, it is possible to suppress the inclination angle θb to a value larger than 4.85 degrees so as to be within the critical angle of total reflection.

By doing so, as shown in FIG. 6, the + 1st-order and -1st-order diffracted lights L2 and L3 of the first diffractive optical element pattern 4 are converted into the second diffractive optical element patterns 9,
All of the diffracted light beams L21 to L23 and the diffracted light beams L31 to L33 diffracted by the respective elements 10 can be taken out of the substrate 1, and the loss of light quantity can be reduced as compared with the other embodiments.

The second pattern having the sawtooth-shaped pattern
The diffracted light diffracted by the first diffractive optical element pattern 4 on the principal surface 2 or the principal surface 3 of the substrate 1 on the principal surface 2 or the principal surface 3 of the substrate 1 is reflected twice or more on the boundary surface of the substrate principal surface and is incident. Needless to say, even if it is provided at the portion where the light is applied, it can be similarly taken out. The cross-sectional shape of each groove of the second diffractive optical element patterns 9 and 10 does not necessarily have to be a right triangle as shown in FIG. 7, and at least the diffracted light from the first diffractive optical element pattern 4 is As long as the inclined portion 11 is present at the incident portion, the effect that the diffracted light can be directly taken out of the substrate can be obtained.

Also, the principal surface on which the second diffractive optical element patterns 9 and 10 are provided is not necessarily parallel to the principal surface on which the diffractive optical element pattern for polarization is provided. When the incident light L0 is perpendicularly incident on the substrate 1 as shown in FIG. 6, the inclined surface 11 of each groove of the second diffractive optical element patterns 9, 10 is oriented in the direction orthogonal to the incident direction of the incident light L0. It is sufficient to incline by the above θb.

(Embodiment 4) FIG. 8A is a longitudinal sectional view showing a configuration of a diffractive optical element 130 according to Embodiment 4 of the present invention, and FIG. Optical element 1
30 is a plan view of FIG. Embodiment 4 is characterized in that the second diffractive optical element pattern for extracting diffracted light has a lens function.

As shown in FIG. 8A, the main surface 2 of the substrate 1 is
A first diffractive optical element pattern 4 for polarization is provided on the side,
A second diffractive optical element pattern 12 having a lens function is provided at a portion where the + 1st-order diffracted light L2 is reflected once on the boundary surface of the main surface 3 and enters. As shown in the plan view of FIG. 8B, the second diffractive optical element pattern 12 is composed of a curved group showing a clam shell-like pattern.
It is designed to have the function of a collimator lens for convergent light.

That is, as shown in FIG. 8A, when the incident light L0 is convergent light, the + 1st-order diffracted light L2 diffracted by the first diffractive optical element pattern 4 also becomes convergent light, and the main surface 3 After the light is totally reflected once at the boundary surface, the light enters the second diffractive optical element pattern 12. Here, the second diffractive optical element pattern 12 has the function of a collimator lens as described above, and converts the + 1st-order diffracted light L2 of the first diffractive optical element pattern 4 into the second diffractive optical element. -In pattern 12
The pattern shape and pattern pitch of the second diffractive optical element pattern 12 are set so that the first-order diffracted light L22 becomes parallel light.

It is generally known that a predetermined lens effect can be obtained by forming a diffractive optical element pattern into a curved group, and by setting the shape of the concave portion and the pattern pitch to predetermined values, the second diffraction pattern can be obtained. In the optical element pattern 12,
Various effects such as a concave lens and a convex lens can be provided, and in addition to the parallel light beam, a light beam having a desired wavefront such as a divergent light beam and a convergent light beam can be extracted.

The second diffractive optical element pattern 16 having the pattern formed by the group of curved shapes is reflected and diffracted by the first diffractive optical element pattern 4 on the principal surface 2 or principal surface 3 of the substrate 1. It is needless to say that the same effect can be obtained even if it is provided at a position where the light is reflected directly or in the substrate two or more times. (Embodiment 5) The diffractive optical elements according to Embodiment 5 and Embodiments 6 to 8 to be described hereinafter relate to the above-mentioned reflective polarization type diffractive optical element. That is, in the transmission polarization type diffractive optical element described in the first to fourth embodiments, the diffractive optical element pattern for polarization is provided on the main surface of the substrate where incident light first enters. In the following embodiments, the only difference is that the diffractive optical element pattern for polarization is provided on the main surface of the substrate opposite to the side on which the incident light is incident. Therefore, there are many parts in common with the above-described embodiment,
Hereinafter, the description will be made as simple as possible.

The following embodiments 5, 6, 7, and 8
Correspond to the first, second, third and fourth embodiments, respectively. FIG. 9 is a longitudinal sectional view showing the configuration of the reflective polarization type diffractive optical element 140 according to the fifth embodiment. As shown in the drawing, the diffractive optical element 140 is provided with a first diffractive optical element pattern 4 for polarization on the main surface 3 side of the substrate 1, and the first diffractive optical element pattern 4 on the main surface 2. Second diffractive optical element patterns 5 and 6 for extracting diffracted light are provided at positions where the diffracted light is reflected directly or twice in the substrate 1, and corresponds to the embodiment shown in FIG. ing.

When the incident light L0 is perpendicularly incident from the main surface 2 side of the substrate 1, it is reflected and diffracted by the first diffractive optical element pattern 4 on the main surface 3 side of the substrate 1 and is diffracted by + 1st-order and -1st-order diffracted light L2. L3 is generated, and the former directly enters the second diffractive optical element pattern 5, and the latter enters the second diffractive optical element pattern 6 after being totally reflected twice within the substrate 1. The angles of incidence of the −1st-order diffracted light L22 and −1st-order diffracted light L32 on the boundary surface of the main surface 3 in the second diffractive optical element patterns 5 and 6 are determined according to the embodiment of the transmission polarization type diffractive optical element. As described above, since the angle is smaller than the critical angle under the total reflection condition,
From the outside.

By adopting the reflection polarization type configuration as in the present embodiment, the 0th-order diffracted light L1 and the + 1st-order diffracted light L2,
The -1st-order diffracted light L3 can be extracted from the same side of the substrate 1. Note that, even in such a reflective polarization type diffraction optical element, since the diffraction angle θ in the polarization diffraction optical element pattern cannot be 90 ° or more, ｛(λ / n ) / Λ｝ <1 (n is the refractive index of the substrate 1). From this, (λ / n) <Λ, and in this case as well, the pattern pitch の of the polarization diffractive optical element pattern is limited to a range satisfying the inequality λ / n <Λ ≦ λ.

Here, as shown in FIG.
-Order diffracted light L reflected and diffracted by the diffractive optical element pattern 6 of FIG.
By forming the reflective film 13 made of a metal or a multilayer dielectric by sputtering or the like at the position of the main surface 3 where the light 22 enters, the -1st-order diffracted light L22 can be extracted from the main surface 2 to the outside. Further, as shown in FIG. 10B, the incident light L0 is incident on the first diffractive optical element pattern 4 in the vertical direction, and the pattern pitch of the second diffractive optical element patterns 5 and 6 is changed to the first diffractive optical element pattern. By setting the pitch to be the same as the pattern pitch of the element pattern 4, the minus first-order diffracted light L22 reflected and diffracted by the second diffractive optical element patterns 5, 6 is equal to the diffraction angle of the first diffractive optical element pattern 4. Since the light is emitted in a direction perpendicular to the main surface 3 of the substrate 1 in order to provide a diffraction effect, it can be extracted in a direction parallel to the direction of the main light of the incident light L0.
As in the case of (b), an element that is easy to handle optically is obtained.

(Embodiment 6) FIG. 11 is a sectional view showing a configuration of a diffractive optical element 150 according to Embodiment 6 of the present invention. As shown in the drawing, in the diffractive optical element 150, the second diffractive optical element patterns 5 and 6 for taking out diffracted light have the same principal surface 3 of the substrate 1 as the first diffractive optical element pattern 4 for polarized light. It is characterized in that it is provided on the side, and corresponds to the embodiment shown in FIG. 4 described above.

Also according to this configuration, the second diffractive optical element patterns 5 and 6 are
By providing the diffracted light at an appropriate position where the first-order diffracted light L2 and the -1st-order diffracted light L3 are incident, the diffracted light can be taken out of the substrate 1 as in the case of FIG. In the present embodiment, the second diffractive optical element pattern 5 is provided at a position where the + 1st-order diffracted light L2 from the first diffractive optical element pattern 4 is reflected once in the substrate 1 and then enters. The third diffractive optical element pattern 6 is provided at a position where the -1st-order diffracted light L3 from the first diffractive optical element pattern 4 is reflected three times in the substrate 1 and then incident thereon. It may be provided at a position where total reflection has occurred.

Here, as shown in FIG.
-Order diffracted light L reflected and diffracted by the diffractive optical element pattern 5
By providing a reflective film 14 made of metal or a multilayer dielectric at a position on the main surface 2 of the substrate 1 where the light 22 enters,
The next-order diffracted light L22 is reflected by the reflection film 14 and can be taken out from the main surface 3 side. As shown in FIG. 12B, the incident light L0 is incident on the first diffractive optical element pattern 4 in the vertical direction, and the pattern pitch of the second diffractive optical element patterns 5 and 6 is changed to the first diffractive optical element pattern. By setting the same pitch as the pattern pitch of the element pattern 4, the -1st-order diffracted light L reflected and diffracted by the second diffractive optical element patterns 5, 6
22 and L32 have the same diffraction effect as the diffraction angle of the first diffractive optical element pattern 4, and can be extracted in a direction parallel to the direction of the principal ray of the incident light L0.

(Embodiment 7) FIG. 13 is a longitudinal sectional view showing a configuration of a diffractive optical element 160 according to Embodiment 7 of the present invention. As shown in FIG.
Is provided with a first diffractive optical element pattern 4 on the main surface 3 side of the substrate 1, and diffracted light reflected and diffracted by the first diffractive optical element pattern 4 on both sides thereof is totally reflected once on the substrate surface. The second diffractive optical element patterns 15 and 16 having a saw-tooth cross section are provided at the positions where the light is incident. This corresponds to the embodiment shown in FIG. 6 described above.

FIG. 14 shows the second diffractive optical element pattern 16.
It is an enlarged view which shows the shape of one triangular recess. The incident angle of the diffracted light incident on the inclined surface 17 of the triangular concave portion is θ−θb, and by setting θb to an appropriate size, the incident angle becomes equal to or less than the critical angle of total reflection and can be emitted to the outside of the substrate. . The sawtooth-shaped second diffractive optical element pattern 15,
The same effect can be obtained by providing the light diffracting element 16 at a position where the light diffracted by the first diffractive optical element pattern 4 enters the substrate 1 after being reflected three or more times an odd number of times.

(Eighth Embodiment) FIG. 15A is a sectional view showing a configuration of a diffractive optical element 170 according to an eighth embodiment, and FIG. 15B is a plan view of the diffractive optical element 170. It is. In this diffractive optical element 170, a first diffractive optical element pattern 4 for polarization is provided on the principal surface 3 side of the substrate 1, and the first diffractive optical element pattern 4 on the principal surface 2 side of the substrate 1 reflects the light. A second diffractive optical element pattern 18 composed of a group of curved shapes is provided at a portion where the diffracted diffracted light is incident, and corresponds to the embodiment shown in FIGS. 8A and 8B described above.

As shown in the plan view of FIG. 15B, the second diffractive optical element pattern 18 composed of a group of curved shapes forms a clam shell-like pattern, and a collimator lens as in FIG. 8A. Act as When the incident light L0 is convergent light, the + 1st-order diffracted light L2 reflected and diffracted in the first diffractive optical element pattern 4 area also becomes convergent light and is incident on the second diffractive optical element pattern 18. At this time, since the second diffractive optical element pattern 18 has a pattern composed of a curve group having a predetermined lens effect, for example, as shown in FIG. The first-order diffracted light L22 to be diffracted can be converted into a parallel light flux. In addition, by giving various effects such as a concave lens and a convex lens as a diffractive optical element pattern, it becomes possible to extract a light beam having a desired wavefront such as a divergent light beam and a convergent light beam, in addition to the parallel light beam.

The diffracted light reflected and diffracted by the first diffractive optical element pattern 4 on the principal surface 3 side of the substrate 1 and the second diffractive optical element pattern 18 having the pattern composed of the group of curved shapes is reflected on the substrate surface. It goes without saying that the same effect can be obtained even if it is provided at a portion where the light is totally reflected once or a plurality of times. (Embodiment 9) Next, the configuration of an optical pickup for a magneto-optical disk utilizing the above-described diffractive optical element 100 having polarization will be described. And the principle of detecting a recording signal will be briefly described.

FIG. 16 is a diagram showing an example of the configuration of a conventional optical pickup. The optical pickup includes a laser diode 401, a collimator lens 402, a beam shaping prism 403, a polarizing beam splitter 404, an objective lens 405, a return light detection unit 410, and the like. In addition, the return light detection unit 410 is provided with the first half prism 41.
1, second half prism 413, knife edge 414,
Polarizing beam splitter 417, photo sensors PD1 to P
D4 and the like.

The laser light emitted from the laser diode 401 is converted into parallel light by a collimator lens 402, and then is adjusted via a beam shaping prism 403 so that the light beam has a substantially circular cross-sectional shape. The light enters the beam splitter 404. The polarization beam splitter 404 sets the reflectance of S-polarized light to 100%,
The transmittance of polarized light is set so as to be 40% to 60%, and the laser beam emitted from the laser diode 401 is P-polarized light, so that a laser beam of approximately half the amount of light passes through the polarizing beam splitter 404. The information recording surface 45 of the magneto-optical disk 450 via the objective lens 405
The light is focused on 1. The return light reflected by the information recording surface 451 travels backward, is reflected by the polarization beam splitter 404, and proceeds toward the return light detection unit 410.

The return light that has proceeded to the return light detection unit 410 is split into two light beams by the first half prism 411, and the straight light becomes a servo signal acquisition light beam for controlling tracking and focusing. 1 half prism 41
The reflected light at 1 becomes a recording signal detection light beam. The former servo signal acquisition light beam is converged by a condenser lens 412 and then split into two by a second half prism 413. Of the straight light, the upper half is cut off by a knife edge 414 and split into two. Is incident on the sensor surface of the photosensor PD1, and a focus error amount is detected by a known knife edge method. Further, the light beam reflected downward by the second half prism 413 enters the two-part photosensor PD2, and the tracking error amount is detected by a known push-pull method. A drive mechanism (not shown) composed of a magnetic coil and a magnet is driven by the two types of servo signals obtained as described above, focus adjustment and tracking adjustment are performed, and information recorded on the information recording surface 451 can be accurately acquired. It is configured as follows.

On the other hand, a recording signal is detected by detecting return light reflected downward by the first half prism 411 with the photosensors PD3 and PD4. As is well known, since the polarization direction of the return light from the information recording surface 451 of the magneto-optical disk 450 is rotated by a predetermined angle (Kerr rotation angle) due to the Kerr effect, it is reflected downward by the first half prism 411. The obtained signal detection light beam is a λ / 2 wavelength plate 4
The light beam whose polarization direction is shifted by the Kerr rotation angle is adjusted by the polarization beam splitter 415 so as to have the polarization direction most easily separated by the polarization beam splitter 417 at the subsequent stage.
Is converted into convergent light by the polarization beam splitter 417.
It is further separated into P-polarized light and S-polarized light. The separated light beams are supplied to the photosensor PD3 and the photosensor PD4, respectively.
By detecting the difference between the two detection values, it is possible to obtain a high-precision recording signal in which noise is canceled.

However, in the configuration of the conventional optical pickup as shown in FIG. 16, the number of components in the return light detecting section 410 is large, both the component cost and the assembly cost are high, and the prism-shaped beam splitter is relatively expensive. There is a problem that it is difficult to miniaturize the polarization because it is large. Therefore, the present inventors have invented a more miniaturized optical pickup using the diffractive optical element according to the present invention.

FIG. 17A is a diagram showing the structure of the optical pickup. The laser diode 401, the collimator lens 402, the beam shaping prism 403, the polarization beam splitter 404, and the objective lens 405 are as shown in FIG.
However, the configuration of the return light detection unit 420 is greatly different. Laser diode 401
Return light emitted from the optical disk and reflected by the information recording surface 451 is
The light is reflected by the boundary surface inside the polarization beam splitter 404 and changes the optical path in the direction of the return light detection unit 420. The return light detector 420 includes a condenser lens 421 and a diffraction optical element 4.
22, flat glass 427, photosensor unit 426
The return light reflected from the polarization beam splitter 404 is first converted into convergent light by the condenser lens 421, and then is incident on the diffractive optical element 422.

The diffractive optical element 422 has the structure of the above-mentioned reflective polarization type diffractive optical element, and the pattern pitch on the surface opposite to the incident surface of the return light is smaller than the wavelength λ of the incident light. A first diffractive optical element pattern 423 is provided, and a pattern pitch greater than the wavelength λ is provided at the incident position of the + 1st-order diffracted light L2 and the -1st-order diffracted light L3 by the first diffractive optical element pattern 423 on the incident surface side. Are provided at symmetrical positions with respect to the principal ray of the return light.

The return light incident on the diffractive optical element 422 is converted into the 0th-order diffracted light L1, the + 1st-order diffracted light L2, and the -1st-order diffracted light L by the diffraction effect of the first diffractive optical element pattern 423.
The 0th-order diffracted light L1 becomes P-polarized light due to the polarization of the first diffractive optical element pattern 423, and +1.
The first-order diffracted light L2 and the -1st-order diffracted light L3 are both set to be S-polarized light.

The first diffractive optical element pattern 423 having such characteristics has, for example, a refractive index of a glass substrate of 2.
In the case of No. 4, it can be obtained by setting the depth of the lattice of the pattern to 0.3 to 0.35 times the wavelength of the incident light and the pattern pitch to 0.72 to 0.74 times the wavelength of the incident light. It has been confirmed by experiments that the lattice depth and the pattern pitch can be determined appropriately by experiments or computer simulations according to the refractive index of the glass substrate.

On the other hand, the + 1st-order diffracted light L2 and the -1st-order diffracted light L3 from the first diffractive optical element pattern 423
Are diffracted by the diffractive optical element patterns 424 and 425, and their -1st-order diffracted lights L22 and L32 escape the total reflection condition.
It is emitted on the same side as the zero-order diffracted light L1. The photo sensor unit 426 includes a photo sensor PD11,
PD12 and PD13 are formed at a predetermined interval, the photosensor PD11 detects the 0th-order diffracted light L1, and the photosensors PD12 and PD13 respectively have the -1st-order diffracted light L2.
2. Detect L32. In particular, the central photo sensor PD1
Reference numeral 1 denotes a four-division photo sensor having four independent detection areas d1 to d4 as shown in FIG.

Since the 0th-order diffracted light L1 is a convergent light, when passing through the flat glass plate 427 inclined in one direction, the amount of change in the optical path length varies depending on the incident angle, and astigmatism is reduced. appear. Such astigmatism light is detected by the four-divided photosensor PD11, and the sum of the outputs of the detection areas d1 and d3 is compared with the sum of the outputs of the detection areas d2 and d4. The focus error amount can be detected.

If the direction in which the tracking error occurs is a direction perpendicular to the plane of the drawing, the detection area d
By comparing the outputs of 2, d4, the tracking error amount by the above-described push-pull method can be detected. Using these two types of error detection values as servo signals,
By driving a servo mechanism (not shown) composed of a magnetic coil and a magnet, the focus error and the tracking error are corrected.

The sum V1 of the output values of the detection areas d1 to d4 of the four-part photosensor PD11 and the photosensor P
Difference V1-V2 of sum V2 of output values of D12 and PD13
, An output of a read signal with less noise can be obtained. As described above, by using the reflective polarization type diffractive optical element according to the present invention, the number of parts is reduced as compared with the conventional optical pickup shown in FIG. Since the required man-hour is also reduced, the assembly cost can be reduced. In addition, the overall configuration of the optical pickup can be reduced in size, and the size of the magneto-optical disk player in which the optical pickup is incorporated can be reduced.

(Embodiment 10) FIG. 18 is a diagram showing another configuration of an optical pickup using a reflection polarization type diffractive optical element as Embodiment 10 of the present invention. In this example, the return light detection unit 430 includes two diffractive optical elements 4
31 and a diffractive optical element 434.

The diffractive optical element pattern 432 provided on the lower main surface of the diffractive optical element 431 is designed to transmit a certain percentage of the P-polarized light.
The P-polarized laser light emitted from the laser beam passes through the diffractive optical element 431, is collimated by the collimator lens 406, and is condensed on the information recording surface 451 of the magneto-optical disk 450 via the objective lens 407. I do.

The return light reflected by the information recording surface 451 and whose polarization direction has been rotated by the Kerr rotation angle is reflected by the objective lens 40.
7. The collimator lens 406 travels backward, is reflected and diffracted by the diffractive optical element pattern 432 of the diffractive optical element 431, and the + 1st-order diffracted light L2 is further transmitted to the diffractive optical element pattern 43.
3, and the -1st-order diffracted light L22 is emitted out of the diffractive optical element 431.

Incidentally, the diffractive optical element pattern 433 corresponds to FIG.
It has a pattern of the same curve group as the diffractive optical element pattern 18 of FIG. 5B, and the -1st-order diffracted light L22 is a parallel light. The -1st-order diffracted light L22 further enters the diffractive optical element pattern 435 of the second diffractive optical element 434, where it transmits the 0th-order diffracted light (first polarized light: P-polarized light) and is reflected and diffracted by the + 1st-order diffracted light. (Second polarized light: S-polarized light) L222
And the + 1st-order diffracted light L222 is further reflected and diffracted by the diffractive optical element pattern 436, and the -1st-order diffracted light L222
2222 is emitted out of the diffractive optical element 434.

The photo sensor unit 439 includes a four-division photo sensor PD21 and a photo sensor PD22.
The zero-order diffracted light L221 is incident on the four-division photosensor PD21 via the condenser lens 437 and the plate glass 438 for generating astigmatism, and detects the focus error amount and the tracking error amount in the same manner as in FIG. Is performed.

The -1st-order diffracted light L2222 in the diffractive optical element pattern 436 is incident on the photosensor PD22, and the output value of this sensor and the quadrant photosensor PD2
A read signal of the information recording surface 451 of the magneto-optical disk 450 is obtained from the difference from the output value of 1. If the shape of the pattern 433 is designed so that the −1st-order diffracted light L22 becomes convergent light, the condenser lens 437 can be omitted,
If it is designed to have astigmatism, the flat glass 4
38 can also be omitted.

According to the configuration of the optical pickup shown in FIG. 18, the relatively large polarizing beam splitter 404 in the optical pickup shown in FIG. 17 can be omitted, so that the size can be further reduced. The diffractive optical element 431 and the diffractive optical element 434 in FIG. 18 can be integrated as shown in FIG. That is, the return light detector 4
In FIG. 30, one diffractive optical element 441 is used instead of the two diffractive optical elements 431 and 434 in the configuration of FIG.
Is installed. The diffractive optical element 441 has two diffractive optical element patterns formed on the upper surface and the lower surface, respectively, and the diffractive optical element patterns 442, 443, 444, and 44 are formed.
5 are the diffractive optical element patterns 432, 4 in FIG.
It is formed in a pattern shape corresponding to 33, 435, 436. The other configuration is exactly the same as that of FIG. 18, and the description is omitted here.

According to the configuration shown in FIG. 19, the number of components of the optical pickup can be further reduced, and the configuration shown in FIGS.
8, it is possible to further reduce the size and cost of the device. It should be noted that the above embodiments 9 and 10
Has described an optical pickup for reading recorded information when the optical recording medium is a magneto-optical disk. However, the present invention relates to another optical recording medium of a reflectance control type (CD (compact disk) or DVD (digital multipurpose disk). )
The present invention can also be applied to an optical pickup for reading recorded information of a pit-shaped disk or a phase-change disk such as a disk.
In this case, for example, in the configuration of the optical pickup shown in FIGS. 18 and 19, only the detection value of the photosensor PD21 may be used as the read signal. Thus, by changing the signal processing system, the optical pickup of the present invention can be used as an optical pickup dedicated to an optical disk, or as an optical pickup for both a magneto-optical disk and an optical disk. In addition, effects such as miniaturization and cost reduction can be enjoyed as described above.

[0090]

As described above, according to the diffractive optical element according to the present invention, the pattern pitch of the first diffractive optical element pattern is set to be equal to or less than the wavelength of the incident light. Polarization can be provided.
The first diffractive optical element pattern allows the first
Since the diffracted light by the diffractive optical element pattern is reflected and diffracted, it is possible to generate diffracted light that does not satisfy the total reflection condition, and it is possible to extract the diffracted light out of the substrate.

Further, the diffractive optical element having the above-described structure can be formed relatively small because only a predetermined pattern is formed on a thin substrate. By using this as a polarization beam splitter of an optical pickup, the light can be obtained. The size of the pickup itself can be reduced.

[Brief description of the drawings]

FIG. 1 is an external perspective view of a diffractive optical element according to Embodiment 1 of the present invention.

FIG. 2 is a longitudinal sectional view of the diffractive optical element according to the first embodiment.

FIG. 3A is a longitudinal sectional view of a diffractive optical element having a reflective film according to the first embodiment, and FIG. 3B is a pattern pitch of each diffractive optical element pattern according to the first embodiment; It is a figure showing the course of diffracted light at the time of being equal.

FIG. 4 is a longitudinal sectional view of a diffractive optical element according to Embodiment 2 of the present invention.

FIG. 5A is a longitudinal sectional view of a diffractive optical element having a reflective film according to the second embodiment, and FIG. 5B is a pattern of each diffractive optical element pattern according to the second embodiment. It is a figure which shows the course of a diffracted light when a pitch is equal.

FIG. 6 is a longitudinal sectional view of a diffractive optical element according to Embodiment 3 of the present invention.

FIG. 7 is an enlarged sectional view of a principal part of the diffractive optical element according to the third embodiment.

8A is a longitudinal sectional view of a diffractive optical element according to Embodiment 4 of the present invention, and FIG. 8B is a plan view of the diffractive optical element.

FIG. 9 is a longitudinal sectional view of a diffractive optical element according to a fifth embodiment.

10A is a longitudinal sectional view of a diffractive optical element provided with a reflection film according to the fifth embodiment, and FIG. 10B is a pattern pitch of each diffractive optical element pattern according to the fifth embodiment. It is a figure showing the course of diffracted light at the time of being equal.

FIG. 11 is a sectional view of a diffractive optical element according to Embodiment 6 of the present invention.

FIG. 12A is a cross-sectional view of a diffractive optical element having a reflective film according to the sixth embodiment, and FIG. 12B is a pattern pitch of each diffractive optical element pattern according to the sixth embodiment. It is a figure showing the course of diffracted light at the time of being equal.

FIG. 13 is a longitudinal sectional view of a diffractive optical element according to Embodiment 7 of the present invention.

FIG. 14 is an enlarged fragmentary cross-sectional view of the diffractive optical element according to Embodiment 7;

FIG. 15A is a sectional view of a diffractive optical element according to Embodiment 8 of the present invention, and FIG. 15B is a plan view of the diffractive optical element.

FIG. 16 is a diagram showing a configuration of a conventional magneto-optical pickup.

FIG. 17 is a diagram showing an embodiment of a magneto-optical pickup according to the present invention.

FIG. 18 is a diagram showing another embodiment of the magneto-optical pickup according to the present invention.

FIG. 19 is a view showing still another embodiment of the magneto-optical pickup according to the present invention.

FIG. 20 is a longitudinal sectional view of a conventional diffractive optical element.

FIG. 21 is a longitudinal sectional view of another conventional diffractive optical element.

FIG. 22 is a diagram showing the course of diffracted light when the pitch of the optical diffraction element pattern is set to be equal to or smaller than the wavelength of incident light in the diffractive optical element of FIG.

FIG. 23 is a diagram showing the course of diffracted light when the pitch of the optical diffraction element pattern is set to be equal to or smaller than the wavelength of incident light in the diffractive optical element of FIG. 21;

[Explanation of symbols]

1 Substrate 2, 3 Main surface 4, 423, 432, 435 First diffractive optical element pattern 5, 6, 9, 10, 12, 15, 16, 18, 424,
425, 433, 436, 443, 445 Second diffractive optical element pattern 7, 8, 13, 14 Reflective film 11, 17 Slope portion 100, 110, 120, 130, 140, 150, 1
70, 200, 210, 300, 310, 422, 43
1,434,441 Diffractive optical element 401 Laser diode 402,406 Collimator lens 403 Beam shaping prism 404,417 Polarizing beam splitter 405,407 Objective lens 410,420,430 Light detector 412,416,421,437 Condenser lens 426,439 Photosensor unit 427,438 Flat glass 450 Magneto-optical disk 451 Information recording surface

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G11B 11/105 551 G11B 11/105 551N (72) Inventor Shinichi Ijima 1-1-1, Komachi, Takatsuki-shi, Osaka Matsushita Electronics Industry Co., Ltd. (72) Inventor Akio Yoshikawa 1-1, Yukicho, Takatsuki-shi, Osaka, Japan Inside Matsushita Electronics Co., Ltd. (72) Inventor Teruhiro Shiono 1-1-1, Yukicho, Takatsuki-shi, Osaka, Matsushita Electronics Co., Ltd.

Claims (18)

[Claims] 1. A diffractive optical element for diffracting an incident light beam, comprising: a substrate having first and second principal surfaces and having a refractive index of n (n>1); A first diffractive optical element pattern whose pattern pitch is equal to or smaller than the wavelength λ of the incident light beam and is larger than λ / n; A second diffractive optical element pattern provided at a position on one principal surface of the second principal surface, where the diffracted light by the first diffractive optical element pattern enters through a predetermined path in the substrate; A diffractive optical element, comprising: 2. The diffractive optical element according to claim 1, wherein the first main surface is a main surface of the substrate on a side where the light beam enters. 3. The diffractive optical element according to claim 1, wherein the first main surface is a main surface of the substrate opposite to a side on which the light beam enters. 4. The second diffractive optical element pattern is formed on a second main surface of the substrate, and the diffracted light by the first diffractive optical element pattern is an even number including zero times in the substrate. The diffractive optical element according to any one of claims 1 to 3, wherein the diffractive optical element is provided at a position where the light is incident after being totally reflected. 5. The second diffractive optical element pattern is on the first main surface of the substrate, and the light diffracted by the first diffractive optical element pattern is totally reflected an odd number of times within the substrate. The diffractive optical element according to any one of claims 1 to 3, wherein the diffractive optical element is provided at a position where the light is incident thereafter. 6. The position where the second diffractive optical element pattern is provided is such that diffracted light generated when a light beam having a wavelength λ is perpendicularly incident on the first diffractive optical element pattern passes through a predetermined path. The diffractive optical element according to any one of claims 1 to 5, wherein the diffractive optical element is at a position where light enters. 7. The diffracted light includes a + 1st-order diffracted light and -1
The diffractive optical element according to claim 1, wherein the diffractive optical element is at least one of next-order diffracted lights. 8. The diffractive optical element according to claim 1, wherein the first and second main surfaces of the substrate are parallel to each other. 9. A main surface opposite to the main surface on which the second diffractive optical element pattern is provided, and at a position where light diffracted by the second diffractive optical element pattern is to be emitted out of the substrate. The diffractive optical element according to any one of claims 1 to 8, further comprising a reflection film that reflects the diffracted light toward the inside of the substrate. 10. A pattern pitch of the second diffractive optical element pattern is equal to or less than a wavelength λ of the incident light beam,
9. The diffractive optical element according to claim 1, wherein the diffractive optical element is larger than λ / n. 11. The diffractive optical element according to claim 10, wherein a pattern pitch of the second diffractive optical element pattern is the same as a pattern pitch of the first diffractive optical element pattern. 12. The cross-sectional shape of each groove of the second diffractive optical element pattern in a plane including the principal ray of the incident light and the principal ray of the diffracted light includes a hypotenuse portion. 2. The device according to claim 1, wherein the diffracted light is incident.
9. The diffractive optical element according to any one of items 1 to 8. 13. A sectional shape of each groove of the second diffractive optical element pattern in a plane including a principal ray of the incident light and a principal ray of the diffracted light is substantially a right triangle. Item 13. The diffractive optical element according to item 12. 14. When the incident light is perpendicularly incident on the first diffractive optical element pattern, the diffraction angle of the diffracted light is θ, and the inclination angle of the oblique side with respect to the direction orthogonal to the incident light is θb. The magnitude of the inclination angle θb is set so as to satisfy the equation of (θ−θb) <θt, where a critical angle of total reflection in the substrate is θt. The diffractive optical element according to the above. 15. The second diffractive optical element pattern is constituted by a plurality of groove groups having a curved shape in a plane parallel to a main surface on which the second diffractive optical element pattern is provided.
9. The diffractive optical element according to any one of items 1 to 8. 16. An optical pickup for optically reading information recorded on an optical recording medium, comprising a light source for emitting a laser beam, and irradiating the information recording surface of the optical recording medium with the laser beam converged. A laser beam irradiating means, and a polarization beam splitter for separating reflected light of the laser light from the information recording surface into a first polarized light and a second polarized light having a different polarization direction from the first polarized light. Photoelectric conversion means for receiving the first polarized light and the second polarized light, respectively, and converting the polarized light into an electric signal, wherein the first polarized beam splitter has a first and a second principal surface. , The first of which the refractive index is n (n> 1)
A first substrate provided on a part of a first main surface of the first substrate, and having a pattern pitch equal to or smaller than a wavelength λ of the incident light beam and larger than λ / n. A diffractive optical element pattern; and one of the first and second principal surfaces of the first substrate, wherein the diffracted light by the first diffractive optical element pattern is a predetermined light in the first substrate. An optical pickup comprising: a second diffractive optical element pattern provided at a position where light enters through a path. 17. An optical path from the light source to the information recording surface of the optical recording medium, while transmitting laser light emitted from the light source of the laser light irradiating unit and reflecting light from the information recording surface. The device further includes a second polarizing beam splitter that changes a path in the direction of the first polarizing beam splitter. The second polarizing beam splitter has first and second main surfaces, and has a refractive index of n ′ (n '> 1) a second substrate, provided on a part of the first main surface of the second substrate, the pattern pitch of which is equal to or less than the wavelength λ of the incident light beam; a third diffractive optical element pattern larger than n ′, and one of the first and second principal surfaces of the second substrate, wherein the diffracted light by the first diffractive optical element pattern is A fourth substrate provided at a position of incidence through a predetermined path in the second substrate; The optical pickup according to claim 16, characterized in that it comprises a diffractive optical element pattern. 18. The second substrate is common to the first substrate, and the first diffractive optical element pattern is provided on one of the first and second principal surfaces of the first substrate. The main surface,
The optical pickup according to claim 17, wherein the optical pickup is provided at a position where the light diffracted by the fourth diffractive optical element pattern is incident.