JP2007323762A - Diffraction grating, method of manufacturing the same, and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffraction grating having less wavelength dependency for a plurality of wavelengths. <P>SOLUTION: The diffraction grating comprises a glass transparent substrate 2 consisting of a transparent substrate such as glass; and a diffraction grating part 5 formed on one surface of the glass transparent substrate 2. The diffraction grating part 5 comprises a low refractive index material 3 having low refractive index; and a high refractive index material 4 having refractive index different from that of the low refractive index 3 and higher than that of the low refractive index 3. The diffraction grating is formed with a phase modulation pattern designed so that the diffraction lights in a plurality of wavelengths is separated at angles that each of the diffraction lights needs. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a diffraction grating capable of diffracting a plurality of lights having different wavelengths, a manufacturing method thereof, and an optical pickup device including the diffraction grating.

2. Description of the Related Art In recent years, optical pickup apparatuses that reproduce information from or record information on different types of optical recording media (hereinafter referred to as optical disks) such as CD (Compact Disc) and DVD (Digital Versatile Disc) have been developed. .
In the optical pickup device as described above, tracking control is performed so that a laser spot on which the laser beam is focused follows a track formed on the information recording surface of the optical disc. As a tracking control method, a three-beam method or a differential push-pull method is widely used. In the three-beam method or the differential push-pull method, a diffraction grating is used to convert one laser beam from a laser light source into three beams. It is used.
In recent years, in order to reduce the size and cost of an optical pickup device, for example, D
A so-called monolithic integrated two-wavelength in which a semiconductor laser that emits laser light in the VD wavelength band (650 nm) and a semiconductor laser that emits laser light in the CD wavelength band (785 nm) are formed in one chip. Laser light sources have been put into practical use.

However, for example, CD and DVD have different recording formats, so that the diffracted light of the diffraction grating needs to be separated at an appropriate angle. However, since the conventional diffraction grating is formed with a single concavo-convex, each separation is separate. There was a problem that the angle could not be controlled.
Therefore, a diffraction grating capable of diffracting two different wavelengths of laser light has been proposed. For example, in Patent Document 1, the cross-sectional shape is uneven, the ratio of the width of the convex portion of the grating to the grating period is set to a value other than 0.5, and the phase difference of the transmitted light between the convex portion and the concave portion is 2π for light of one wavelength,
A two-wavelength diffraction grating is disclosed in which a diffraction grating whose zero-order diffraction efficiency is adjusted to a predetermined value with respect to light of the other wavelength is formed on each surface of a translucent substrate.

FIG. 11 is a diagram schematically showing the structure of a conventional two-wavelength compatible diffraction grating disclosed in Patent Document 1. In FIG. In FIG. 11, the wavelength λ ₁ and the wavelength λ ₂ are shown for easy understanding.
Although the optical paths of the laser beam are separated from each other, the light beams of the respective wavelengths actually propagate through the same optical path.
The diffraction grating 100 corresponding to two wavelengths shown in FIGS. 11A and 11B is a diffraction grating 1 having a uniform refractive index in which the cross-sectional shape is periodic unevenness on the incident surface side of the transparent substrate 101 made of glass or the like.
02 is formed, and a diffraction grating 103 having a uniform refractive index is formed on the emission surface side of the transparent substrate 101. As a result, when the laser light having the wavelength λ ₁ is emitted from the two-wavelength laser light source 10, the zero-order diffracted light I ₁ (0) that becomes the main beam of the laser light having the wavelength λ ₁ by the diffraction grating 102 and its side beam Two ±
The first-order diffracted light I ₁ (± 1) is diffracted. When laser light having a wavelength λ ₂ is emitted from the two-wavelength laser light source 10, the diffraction grating 103 converts the laser light having a wavelength λ _{2 into} a 0th-order diffracted light I ₂ (0) as a main beam and its side beam. Diffracted into two ± first-order diffracted lights I ₂ (± 1).

Further, the conventional two-wavelength diffraction grating 100 shown in FIG. 11 has a width dimension W _{11 of the} diffraction grating 102.
And the ratio of the grating period P ₁₁ W ₁₁ / P ₁₁ (hereinafter, referred to as duty ratio) are set to a value other than 0.5, 0 next wavelength lambda ₁ for DVD diffracted light I ₁ and (0) 1 The diffraction efficiency of the next diffracted light I ₁ (± 1) is adjusted to be a predetermined value. By setting a value other than 0.5, the duty ratio W ₁₂ / P ₁₂ similarly diffraction grating 103 also 0-order diffracted light I ₂ (0) of the wavelength lambda ₂ for CD and 1-order diffracted light I ₂ (± The diffraction efficiency of 1) is adjusted to a predetermined value.
JP 2001-281432 A

FIG. 12 shows the diffraction gratings 102 and 10 constituting the two-wavelength diffraction grating 100 described above.
3 is a diagram showing the relationship between the wavelength of 3 and the diffraction efficiency. FIG. 12A shows a diffraction grating 10 for DVD.
FIG. 12B is a diagram showing the relationship between the wavelength and diffraction efficiency in the diffraction grating 103 for CD, respectively.
In the diffraction grating 102 for DVD shown in FIG. 12A, the diffraction efficiency of the 0th-order diffracted light I ₁ (0) and the ± 1st-order diffracted light I ₁ (± 1) at a 650 nm wavelength for DVD is a predetermined value. It has been adjusted to be. In the diffraction grating 103 for CD shown in FIG. 12B, the diffraction efficiencies of the 0th-order diffracted light I ₂ (0) and the ± 1st-order diffracted light I ₂ (± 1) at a 785 nm wavelength for CD are predetermined values. It has been adjusted to be.

However, the diffraction grating 102 has a wavelength λ ₁ (6 for DVD) as shown in FIG.
The diffraction efficiency in the vicinity of (50 nm) is greatly changed by a slight wavelength change. In the diffraction grating 103, as shown in FIG. 12B, the wavelength λ ₂ (785 nm) for CD is used.
There is a drawback that the diffraction efficiency changes greatly due to a slight wavelength change in the vicinity of the diffraction efficiency.
That is, the above-described conventional two-wavelength diffraction grating 100 has a large wavelength dependency and has a problem that the diffraction efficiency changes greatly due to a wavelength change caused by a temperature drift of the two-wavelength laser light source 10.

Further, the light quantity loss in the diffraction grating is the smallest when the duty ratio of the diffraction grating is 0.5, and increases as the distance from the diffraction grating increases. For this reason, 2 shown in FIG.
When the value of the duty ratio of the diffraction grating is adjusted to a value other than 0.5 so that the diffraction efficiency of the 0th-order diffracted light and the 1st-order diffracted light becomes a predetermined value as in the wavelength-corresponding diffraction grating 100, Light loss increases. As a result, there is a problem that it cannot be applied to, for example, an optical pickup device of an optical recording apparatus that writes information on a DVD that requires a high light quantity.
Further, in the conventional two-wavelength compatible diffraction grating 100, the grating patterns of the diffraction gratings 102 and 103 corresponding to the respective wavelengths are formed on the front and back of the transparent substrate 101, respectively. There was a problem.

The present invention has been made in view of the above points, and has an object of generating diffracted light in an appropriate direction with respect to each wavelength and having a small wavelength dependency with respect to a plurality of wavelengths. To do. It is another object of the present invention to provide a diffraction grating that can suppress light loss due to higher-order light. It is another object of the present invention to provide a diffraction grating in which no positional deviation occurs in the grating pattern of the diffraction grating. It is another object of the present invention to provide an optical pickup device provided with these diffraction gratings.

In order to achieve the above object, the present invention is a diffraction grating on which light of at least one wavelength is incident among a plurality of lights having different wavelengths, and includes a transparent base material and a diffraction grating part. Comprises a first refractive index material having a first refractive index and a second refractive index material having a second refractive index different from the first refractive index material, and diffracting in a predetermined wavelength band. The first refractive index material and the second refractive index material are used on one surface of the transparent substrate so that the efficiency is substantially constant so that the diffracted light at each wavelength is separated at an appropriate angle. The designed phase modulation pattern was used.
According to such a diffraction grating of the present invention, the diffraction efficiency can be maintained at a predetermined value at a plurality of different wavelengths, so that the wavelength dependency can be reduced. Thereby, it is possible to prevent the diffraction efficiency from fluctuating even when the wavelength changes due to the temperature drift of the semiconductor laser.
Also, since the diffracted light at each wavelength used is separated at an appropriate angle, for example, CD, D
It can cope with optical discs with different recording formats such as VD.
Further, since the grating pattern of the diffraction grating portion is formed only on one side of the transparent substrate, there is no occurrence of positional deviation of the grating pattern.

Further, the diffraction grating of the present invention is provided with a polarizing means for absorbing the return light to the incident surface side on the other surface of the transparent substrate. With this configuration, the return light can be prevented from being incident on the incident surface side by the polarizing means, so that the return light can be prevented from interfering with the incident light.

In the diffraction grating of the present invention, the first refractive index material is SiO ₂ and the second refractive index material is TiO ₂ or Ta ₂ O ₅ . Thus, the first refractive index material is SiO _{2 and} the second refractive index material is Ti.
When a dielectric is used as each material such as O ₂ or Ta ₂ O ₅ , for example, a diffraction grating suitable for an optical pickup device of an in-vehicle optical disk device that requires high reliability can be realized.

In the diffraction grating of the present invention, the first refractive index material is an ultraviolet curable resin or a thermosetting resin, and the second refractive index material is TiO ₂ or Ta ₂ O ₅ . Thus, if a resin material is used as the first refractive index material, the cost of the diffraction grating can be reduced. In particular, the diffraction grating having such a configuration is suitable for an optical pickup of a home-use optical disc apparatus in which the use conditions are mild and cost reduction is required.

The optical pickup device of the present invention includes a light source that emits light of at least two different wavelengths, and an objective lens that condenses the emitted light from the light source onto an optical recording medium, and records or / or records information on the optical recording medium. And an optical pickup device for performing reproduction, wherein the diffraction grating of the present invention is arranged in an optical path between a light source and the objective lens. As a result, the monolithic integrated type 2
Even when a combination of wavelength lasers is used, information can be reliably recorded or reproduced on different types of optical recording media such as CDs and DVDs.

The method for producing a diffraction grating according to the present invention includes a step of forming a first refractive index material having a first refractive index on the surface of a transparent substrate, and a photosensitive resin on the surface of the first refractive index material. Applying step;
A step of selectively exposing the photosensitive resin; a step of developing the photosensitive resin; a step of etching the first refractive index material in a region not covered with the photosensitive resin; and on the surface of the transparent substrate. It comprises a step of forming a second refractive index material having a second refractive index different from that of the first refractive index material, and a step of peeling the photosensitive resin. In this way, the diffraction grating of the present invention can be produced.

As described above, a two-wavelength diffraction grating for diffracting two types of laser beams emitted from a two-wavelength laser light source used in an optical pickup device capable of recording and reproducing CDs and DVDs having different recording formats is shown in FIG. As described above, it is required to diffract the incident laser light at different separation angles (diffraction angles) and separation directions (diffraction directions) so as to correspond to the CD and DVD tracks. In a conventional binary binarized grating composed of simple irregularities, the beam is diffracted in a direction perpendicular to the groove direction of the grating. Therefore, two diffraction patterns as shown in FIG. It is necessary to arrange the grid on the front and back.
Therefore, the present inventor has come up with the idea of solving this limitation by devising the diffraction grating pattern. Since the structure shown in FIG. 11, that is, the binary grating, has a problem that the wavelength dependency and the pattern direction accuracy on the front and back sides are extremely limited, a method for diffracting the beam in a necessary diffraction direction for each pattern has been studied.

In order to design a pattern (phase modulation pattern) that diffracts in the required diffraction direction for each of the two wavelengths in one pattern in this way, it is extremely impossible to implement with a simple binary grating design method.
Therefore, the inventor of the present application has been forced to construct a new calculation method.
2. Description of the Related Art In recent years, computer-generated holograms (hereinafter referred to as CGH) that synthesize hologram interference fringes using a computer have attracted attention due to remarkable developments in computer technology. CGH is a calculation method for calculating an object light wave from an object model held in a computer.
The calculation method is a method of calculating each necessary diffraction pattern by inverse Fourier transform. When laser beams having different wavelengths are made incident on the phase modulation pattern obtained by this calculation method, diffracted light diffracted at different diffraction directions and diffraction angles can be obtained.
FIG. 3 shows a phase modulation pattern calculated by performing this inverse Fourier transform. If a low refractive index material is disposed in the white portion of this pattern and a high refractive index material is disposed in the black portion, a desired two-wavelength diffraction grating can be obtained.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram schematically showing the structure of a diffraction grating for two wavelengths according to an embodiment of the present invention.
(A) is a schematic perspective view, (b) is sectional drawing seen from the arrow AA direction shown to (a).
A two-wavelength compatible diffraction grating 1 shown in FIGS. 1A and 1B includes a glass transparent substrate 2 made of a transparent base material such as glass, and a diffraction grating portion 5 formed on one surface of the glass transparent substrate 2. Yes.
The diffraction grating portion 5 is a low refractive index material (first refractive index material) 3 having a low refractive index (first refractive index) and a refractive index different from that of the low refractive index material 3 and has a low refractive index. And a high refractive index material (second refractive index material) 4 having a higher refractive index (second refractive index) higher than the refractive index of the material 3 so that the diffraction efficiency in a predetermined wavelength band is substantially constant. A phase modulation pattern designed to separate the low refractive index material 3 and the high refractive index material 4 on one surface of the glass transparent substrate 2 so that the diffracted light at each wavelength is separated at an appropriate diffraction angle and direction is formed. Has been. Further, the grating depth (thickness) between the low refractive index material 3 and the high refractive index material 4 is appropriately set.

FIG. 4 is a view showing the relationship between the wavelength and the diffraction efficiency in the two-wavelength diffraction grating 1 of the present embodiment. As shown in FIG. 4, the two-wavelength diffraction grating 1 of the present embodiment has at least D
The diffraction efficiency values of the 0th-order diffracted light I (0) and the ± 1st-order diffracted light I (± 1) in the wavelength band from the wavelength λ ₁ (650 nm) for VD to the wavelength λ ₂ (785 nm) for CD are almost the same. Can be.
Therefore, according to the two-wavelength compatible diffraction grating 1 of the present embodiment, the wavelength dependence in the wavelength band including the wavelength λ ₁ for DVD and the wavelength λ ₂ for CD can be reduced, so the two-wavelength laser light source 1
Even when the wavelength of the laser beam changes due to a temperature drift of 0, fluctuations in diffraction efficiency can be prevented.
In addition, since the grating pattern of the diffraction grating portion 5 is formed only on one side of the glass transparent substrate 2, there is no problem that the grating pattern is displaced.

Here, the relationship between the grating depth and the diffraction efficiency of the low refractive index material 3 and the high refractive index material 4 will be described with reference to FIG.
FIG. 5 is an enlarged cross-sectional view showing the diffraction grating portion of the two-wavelength diffraction grating 1 of the present embodiment. As shown in FIG. 5, the refractive index of the low refractive index material 3 is n _L , and the high refractive index. The refractive index of material 4 is n _H
The pitch of the diffraction grating is P, the width of the low refractive index material 3 portion is W, and the grating depth of the low refractive index material 3 is d.
_L , and the grating depth of the high refractive index material 4 is d _H.
Assuming that the diffraction efficiency of the m-order light of the diffraction grating is η _m , the diffraction efficiency η _m is expressed by the formula (
It can be shown by a function like 1).

位相変調量Γは波長により変化するため、異なる波長で回折効率η_mを同じ値にするた
めには、波長が変化しても位相変調量Γが変化しないように補償すれば良い。
ここで、位相変調量Γは式（２）のように示すことができる。

Since the phase modulation amount Γ changes depending on the wavelength, in order to make the diffraction efficiency η _{m the} same value at different wavelengths, it is only necessary to compensate so that the phase modulation amount Γ does not change even if the wavelength changes.
Here, the phase modulation amount Γ can be expressed as in Expression (2).

Further, since the refractive index of the grating material has wavelength dispersion, the refractive index of the low refractive index material 3 at the wavelength λ ₁ is n _L1 , the refractive index of the high refractive index material 4 is n _H1 , and the low refractive index at the wavelength λ _2. The refractive index of the index material 3 is n _L2 ,
When the refractive index of the high refractive index material 4 is n _H2 , the phase modulation amount at the wavelength λ ₁ is Γ ₁ , and the wavelength λ
_The amount of phase modulation in ₂ can be expressed by the following equations (3) and (4).

を満足するように各条件を設定すれば良い。 And in order to make the diffraction efficiencies at the wavelengths λ ₁ and λ ₂ the same, Γ ₁ = Γ ₂ suffices,

Each condition may be set to satisfy

Here, as an example, the low refractive index material 3 is SiO ₂ , the high refractive index material 4 is Ta ₂ O ₅ , wavelength λ _1.
Is 660 nm and wavelength λ ₂ is 785 nm, SiO ₂ and Ta at wavelengths λ ₁ and λ ₂
The refractive index of ₂ O ₅ is
Wavelength λ ₁ (660 nm) SiO ₂ = 1.470, Ta ₂ O ₅ = 2.164
Wavelength λ ₂ (785 nm) SiO ₂ = 1.467, Ta ₂ O ₅ = 2.147
It becomes.
By substituting these values into the above equation (5), the result of the following equation (6) is obtained.

Thus, the grating depth d _L of the low refractive index material 3 so as to satisfy the equation (6), by setting the grating depth d _H of the high refractive index material 4, 0-order diffracted light at the wavelength lambda ₁ for DVD The diffraction efficiency of I (0) and the diffraction efficiency of the 0th-order diffracted light I (0) at the wavelength λ ₂ for CD can be set substantially the same. Note that description is omitted, similarly first order diffracted light at the wavelength lambda ₁ for DVD I (
The diffraction efficiency of ± 1) and the diffraction efficiency of the first-order diffracted light I (± 1) at the wavelength λ ₂ for CD can be set substantially the same.
Here, considering the case of setting the diffracted light quantity ratio (0th order diffracted light / 1st order diffracted light) = 15.0, the phase modulation amount Γ ₁ = 0.123 at the wavelength λ ₁ may be set. D _H = 1
430 nm, and d _L = 3718 nm is obtained from Equation (6).

FIG. 6 shows the grating depth d _H = 1430 nm of the low refractive index material 3 and the grating depth d _L of the high refractive index material 4.
It is the figure which showed the simulation result of the relationship between the wavelength and diffraction efficiency when setting to 3718nm.
Also from the simulation results shown in FIG. 6, the wavelength λ ₁ for DVD to the wavelength λ ₂ for CD
It was confirmed that the diffraction efficiencies of the 0th-order diffracted light I (0) and the 1st-order diffracted light I (± 1) in FIG.

In the two-wavelength diffraction grating 1 of this embodiment, for example, SiO ₂ that is a dielectric is used as the low refractive index material 3, and TiO ₂ or Ta ₂ O ₅ that is also a dielectric is used as the high refractive index material 4, respectively. I made it.
Thus, when the low refractive index material 3 is made of SiO ₂ and the high refractive index material is made of TiO ₂ or Ta ₂ O ₅ , for example, diffraction suitable for an optical pickup device of an in-vehicle optical disk device requiring high reliability. A lattice can be realized.

Here, the manufacturing method of the diffraction grating 1 for two wavelengths according to the present embodiment will be described in detail with reference to FIG.
First, a transparent glass substrate 2 is prepared as shown in FIG. 7A, and a film deposition apparatus such as a vacuum vapor deposition machine or sputter film formation is used on the surface of the transparent glass substrate 2 as shown in FIG. 7B. Thus, a low refractive index material (SiO ₂ ) 3 is formed. Next, as shown in FIG. 7C, a photoresist 31 is applied on the surface of the low refractive index material 3, and is patterned with a predetermined dimension based on the specifications of the diffraction grating as shown in FIG. 7D. FIG. 7E shows that the photoresist 31 is exposed using the mask 32 and the photoresist 31 is developed. Then, as shown in FIG. 7F, the low refractive index material 3 in the region not covered with the photosensitive portion 31a of the photoresist is removed by etching. Next, as shown in FIG. 7G, the transparent glass substrate 2 and the photoresist 3
A high refractive index material (for example, T
a ₂ O ₅ ) 4 is formed. Then, as shown in FIG. 7 (h), the photoresist 31a is stripped using a stripping solution to complete the two-wavelength diffraction grating 1.

In the two-wavelength diffraction grating 1 of this embodiment, the low refractive index material 3 may be an ultraviolet curable resin or a thermosetting resin, and the high refractive index material 4 may be TiO ₂ or Ta ₂ O ₅ . Thus, when a resin material is used as the low refractive index material 3, the cost of the two-wavelength diffraction grating 1 can be reduced. In particular, the two-wavelength compatible diffraction grating 1 having such a configuration is suitable for an optical pickup of a home optical disc apparatus that is used under mild conditions and is required to be reduced in price.

Below, the manufacturing method of the diffraction grating 1 for two wavelengths when the ultraviolet curable resin is used for the low refractive index material 3 will be described in detail with reference to FIG.
First, a transparent glass substrate 2 is prepared as shown in FIG. 8A, and a film deposition apparatus such as a vacuum vapor deposition machine or sputter film formation is used on the surface of the transparent glass substrate 2 as shown in FIG. 8B. Thus, a high refractive index material (Ta ₂ O ₅ ) 34 is formed. Next, as shown in FIG. 8C, a photoresist 31 is applied on the surface of the high refractive index material 34, and is patterned with a predetermined dimension based on the specifications of the diffraction grating as shown in FIG. 8D. FIG. 8E shows that the photoresist 31 is exposed using the mask 32 and the photoresist 31 is developed. Then, as shown in FIG. 8 (f), the high refractive index material 34 in the region not covered by the photoresist photosensitive portion 31a is removed by etching, and the photoresist photosensitive portion 31a is removed as shown in FIG. 8 (g). Peel off.
Next, an ultraviolet curable resin 33 is applied on the surface of the transparent glass substrate 2 and the high refractive index material 4 as shown in FIG. And as shown in FIG.8 (j), the surface 2a of the transparent glass substrate 2 is shown.
The ultraviolet curable resin 33 is exposed by irradiating ultraviolet rays from the main surface 2b on the opposite side. here,
A region that is not shielded by the high refractive index material (Ta ₂ O ₅ ) 34 of the ultraviolet curable resin is exposed to light and cured. Next, as shown in FIG. 8 (k), the film is not exposed to light using a stripping solution (
The two-wavelength diffraction grating 1 is completed by removing the UV curable resin 33b in the uncured region.

Note that the two-wavelength compatible diffraction grating 1 of the present embodiment is manufactured using a mold having a nano-order pattern called a nanoimprint technique, although the diffraction grating is manufactured using a photolithography technique and an etching technique. Anyway. In the case of producing a lattice pattern using the nanoimprint technology, it is possible to produce a lattice at a lower cost than the above-described photolithography technique. However, when using the nanoimprint technique, it is necessary to use a resin for the lattice material, and therefore it is preferable to use an ultraviolet curable resin or a thermal effect resin for the low refractive index material 3.

In the two-wavelength diffraction grating 1 of this embodiment, the low refractive index material 3 is an ultraviolet curable resin or a thermosetting resin, and the high refractive index material 4 is TiO ₂ or Ta ₂ O ₅ . Thus, when a resin material is used as the low refractive index material 3, the cost of the two-wavelength diffraction grating 1 can be reduced. In particular, the two-wavelength compatible diffraction grating 1 having such a configuration is suitable for an optical pickup of a home optical disc apparatus that is used under mild conditions and is required to be reduced in price.

Note that the two-wavelength compatible diffraction grating 1 of the present embodiment may be manufactured by dry etching or lift-off using a photolithography technique, or a mold having a nano-order pattern called a nanoimprint technique is used. Thus, a lattice may be produced. In the case of producing a lattice pattern using the nanoimprint technology, it is possible to produce a lattice at a lower cost than the above-described photolithography technique. However, when the nanoimprint technology is used, it is necessary to use a resin for the lattice material, and therefore it is necessary to use an ultraviolet curable resin or a thermosetting resin for the low refractive index material 3.

FIG. 9 is a view showing a configuration of an optical pickup device provided with the two-wavelength diffraction grating of the present embodiment.
In the optical pickup device shown in FIG. 9, the light emitted from the two-wavelength laser light source 10 is 2
The light enters the wavelength-corresponding diffraction grating 1 and is diffracted into 0th-order diffracted light and ± 1st-order diffracted light by the two-wavelength corresponding diffraction grating 1. The 0th-order diffracted light and the ± 1st-order diffracted light diffracted by the two-wavelength diffraction grating 1 pass through the beam splitter 21 and are collimated by the collimator lens 22 and then collected on the information recording surface of the optical disc 30 by the objective lens 23. To be lighted. Then, the light reflected by the optical disk 30 passes through the objective lens 23 and the collimating lens 22 again, is reflected by the beam splitter 21, and is received by the light receiving surface of the photodetector 24.
If the optical pickup device is configured using the two-wavelength diffraction grating 1 of the present embodiment as described above, even when the two-wavelength laser light source 10 is used as the laser light source, different types of optical disks such as CD and DVD are used. Information can be recorded or reproduced.

By the way, when the above-described two-wavelength diffraction grating 1 is applied to an optical pickup device for an optical disk, part of the return light from the optical disk is incident on the light source side via the two-wavelength diffraction grating 1 and emitted from the light source. There is a possibility that the light intensity of the emitted light emitted from the light source may vary with the laser light.
Therefore, in order to prevent variation in the light intensity of the light emitted from the light source, the two-wavelength diffraction grating may be configured as follows in this embodiment.

FIG. 10 is a diagram schematically showing the structure of a two-wavelength compatible diffraction grating according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the same site | part as FIG. 1, and detailed description is abbreviate | omitted.
In the two-wavelength-corresponding diffraction grating 20 shown in FIG. 10, the polarizing film 6 is provided on the other surface of the glass transparent substrate 2, that is, the surface on which the diffraction grating portion 5 is not formed. The polarizing film 7 is made of, for example, polyvinyl alcohol (PVA (polyvinyl alcohol)), and polarizes return light from the exit surface side to prevent returning to the entrance surface side.
With this configuration, the return light can be prevented from being incident on the incident surface side by the polarizing means, so that the return light can be prevented from interfering with the incident light.
In the present embodiment, the example of the diffraction grating having the polarizing means according to the present invention has been described using the resin-made polarizing means (polarizing film). It goes without saying that is also applicable.

In the present embodiment, as an example of the diffraction grating of the present invention, a two-wavelength compatible diffraction grating corresponding to two different wavelengths has been described as an example. However, this is merely an example, and the surface of the glass transparent substrate 2 is described. By changing the grating depth of the low refractive index material 3 and the high refractive index material 4 formed on the top, the wavelength in a wavelength band including a blue-violet laser (405 nm) used for Blu-ray Disc, HD DVD, etc. It is possible to realize a diffraction grating with low dependency.

The figure which showed typically the structure of the diffraction grating corresponding to 2 wavelength which concerns on the 1st Embodiment of this invention. The figure which showed the characteristic requested | required in the 2 wavelength diffraction grating which diffracts two types of laser beams from a 2 wavelength laser light source. The figure which showed the phase modulation pattern calculated by performing an inverse Fourier transform. The figure which showed the relationship between the wavelength and diffraction efficiency in the diffraction grating corresponding to 2 wavelengths of this embodiment. The figure which expanded and showed the diffraction grating of this embodiment. The figure which showed the simulation result. The figure which showed the manufacturing method of the diffraction grating corresponding to 2 wavelength which concerns on embodiment of this invention. The figure which showed the manufacturing method of the diffraction grating corresponding to 2 wavelength which concerns on embodiment of this invention. The figure which showed the structure of the optical pick-up apparatus provided with the diffraction grating for 2 wavelengths of this embodiment. The figure which showed typically the structure of the diffraction grating corresponding to 2 wavelength which concerns on the 2nd Embodiment of this invention. The figure which showed typically the structure of the conventional 2 wavelength corresponding | compatible diffraction grating. The figure which showed the relationship between the wavelength and diffraction efficiency in each diffraction grating which comprises the conventional 2 wavelength corresponding | compatible diffraction grating.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,20 ... 2 wavelength corresponding | compatible diffraction grating, 2 ... Glass transparent substrate, 3 ... Low refractive index material, 4 ... High refractive index material, 6 ... Polarizing film, 10 ... Semiconductor laser, 21 ... Beam splitter, 22 ... Collimating lens, 23 ... Objective lens, 24 ... Photodetector, 30 ... Optical disc, 31 ... Photoresist, 31a ... Photosensitive part

Claims (6)

A diffraction grating on which light of at least one wavelength is incident among a plurality of lights having different wavelengths,
It consists of a transparent substrate and a diffraction grating part,
The diffraction grating portion includes a first refractive index material having a first refractive index, and a second refractive index material having a second refractive index different from the first refractive index material, and a predetermined refractive index material. The first refractive index material and the second refractive index material are alternately placed on one surface of the transparent substrate and the diffracted light at a plurality of wavelengths is emitted so that the diffraction efficiency in the wavelength band is substantially constant. A diffraction grating characterized in that it is formed with a phase modulation pattern designed to be separated into each required angle. 2. The diffraction grating according to claim 1, further comprising polarizing means for absorbing the return light on the other surface of the transparent substrate. 3. The diffraction grating according to claim 1, wherein the first refractive index material is SiO ₂ , and the second refractive index material is TiO ₂ or Ta ₂ O ₅ . The first refractive index material is an ultraviolet curable resin or a thermosetting resin, and the second refractive index material is Ti.
A diffraction grating according to claim 1 or 2, characterized in that the O ₂ or Ta ₂ O _5. An optical pickup apparatus that includes a light source that emits light of at least two different wavelengths and an objective lens that condenses the light emitted from the light source onto an optical recording medium, and records or / and reproduces information on the optical recording medium. And
5. The optical pickup device according to claim 1, wherein the diffraction grating according to claim 1 is arranged in an optical path between the light source and the objective lens. Forming a first refractive index material having a first refractive index on the surface of the transparent substrate;
Applying a photosensitive resin on the surface of the first refractive index material;
Selectively exposing the photosensitive resin;
Developing the photosensitive resin;
Etching the first refractive index material in a region not covered by the photosensitive resin;
Forming a second refractive index material having a second refractive index different from the first refractive index material on the surface of the transparent substrate;
Peeling the photosensitive resin;
A method for manufacturing a diffraction grating, comprising:

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