JP4570992B2 - Optical pickup and optical information recording apparatus - Google Patents

Description

  The present invention relates to an optical pickup and an optical information recording medium in which a plurality of types of optical information recording media having different light source wavelengths can be recorded, erased, and reproduced using a common optical system.

An optical pickup device that irradiates a recording surface on an optical recording information medium with a light beam from a light source and records, erases or reproduces information while receiving a return light beam reflected by the recording surface by a light receiving means is known. For example, it is applied to a CD-type optical information recording apparatus, a DVD-type optical information recording apparatus, and the like.
Furthermore, in recent years, there has been a high demand for higher recording density in optical information recording media, and a blue-violet semiconductor laser having a light source oscillation wavelength of about 400 nm and an objective having a numerical aperture (NA) of about 0.85 or 0.65. Development of systems using lenses is in progress. For example, when the current DVD (NA = 0.6, λ = 650 nm) has a recording capacity of 4.7 GB, for example, NA = 0.85, λ = 400 nm, information of about 25 GB can be recorded.
Further, as described above, development of a plurality of optical information recording media having different recording / reproducing laser wavelengths and transparent substrate thicknesses has progressed, and recording and reproduction can be performed on these optical information recording media using the same optical pickup. There is a need to make it possible.
In order to realize miniaturization and cost reduction in a compatible optical pickup using a plurality of light sources having different wavelengths, it is desirable that the objective optical system including the objective lens be used. For this reason, various types of optical pickups have been proposed in which a plurality of light sources corresponding to the used wavelengths are provided and light is converged to a recording surface with a necessary numerical aperture with the same objective lens.

For example, Patent Document 1 discloses a technique for converging light from three light sources onto a recording surface of an optical information recording medium using a single objective lens.
However, in Patent Document 1, since the light sources of the respective wavelengths are provided separately, the number of parts of the pickup is large, and the number of parts to be adjusted for assembling the optical system is increased. The configuration is unsuitable for achieving miniaturization and miniaturization.
As a means for solving such a problem, it is conceivable to use a light source module in which a plurality of light sources are incorporated in one package.
In order to improve detection stability in a plurality of optical information recording media, it is desirable to perform tracking error signal detection by a differential push-pull method or a three-beam method using three beams formed by passing light through a diffraction grating. . This is because the above-described detection method can correct the offset of the tracking error signal and can improve stability.
Further, in order to separate light beams having different wavelengths into three beams, it is necessary to add a plurality of diffraction gratings. However, in an optical pickup in which a plurality of light sources are built in one package, the light emitting points of the plurality of light sources are very close to each other and pass through a common optical path. In such a case, light inevitably passes through a plurality of diffraction gratings, and the following problem occurs.
First, light of each wavelength is diffracted by a plurality of diffraction gratings, and unnecessary diffracted light is generated. For this reason, the light utilization efficiency is lowered, and it is necessary to increase the output power of the light, or the flare light causes deterioration of the reproduction signal, detection accuracy, and reduction.
Therefore, as means for solving such a problem, a diffraction grating in which a decrease in light use efficiency is suppressed at two types of wavelengths is disclosed (Patent Documents 2 to 5, etc.).
JP 2004-006004 A JP 2004-039109 A JP 2003-288735 A JP 2003-006891 A JP 2003-196860 A

By the way, in an optical pickup, in order to reduce the size, reduce the number of parts, and simplify the adjustment of the diffraction grating, it is desirable that the diffraction grating be integrated.
For this reason, the above-described conventional technology has proposed a configuration in which diffractive surfaces are formed on both the front and back surfaces of the substrate or formed integrally. That is, since only one wavelength corresponds to one grating constant, two diffraction surfaces having different grating constants are provided for two wavelengths. However, such a configuration has a problem that the number of parts and the number of production processes increase because the number of diffraction surfaces must be provided as many as the number of wavelengths of the light source.
In addition, since the conventional technology uses a diffraction grating that supports only two wavelengths, it does not have a configuration that suppresses generation of unnecessary diffracted light with respect to light of three wavelengths. Further, when the integral formation for reducing the number of parts is performed, three diffractive surfaces are required to cope with the three wavelengths, and there is a problem that it is not suitable for simple integral formation by bonding or the like.
Further, Patent Document 5 discloses a configuration corresponding to two wavelengths with a single diffractive surface. However, in order to realize downsizing and cost reduction, a single objective for a plurality of wavelengths is disclosed. It is desirable to form a condensing optical system with a lens. In this case, the focal length of the objective lens is approximately the same for a plurality of wavelengths, and the spot is condensed on the plurality of optical information recording media by means of switching the numerical aperture.
On the other hand, the pitch of the diffraction grating to be separated into three beams is determined by the focal length of the objective lens and the interval between the 0th order light and the 1st order diffracted light on the optical recording information medium. For example, a case where three beams are condensed on a CD and DVD optical information recording medium by a single objective lens will be described below. In order to configure this with a single diffractive surface, it is necessary to leave several tracks between the data track on which the 0th order light is collected and the guide track on which the 1st order diffracted light is collected. . For example, in the case of the differential push-pull, as shown in FIG. 13, the first-order diffracted light 111 of the CD is guided to the guide track 102 at a position exceeding two data tracks 101, and the position at a position exceeding three data tracks is guided. If the first-order diffracted light of the DVD is condensed on the track, a two-wavelength differential push-pull signal can be detected on the same diffraction surface.

However, when several tracks exist between the data track 101 and the guide track 102 as described above, the following problems occur.
As shown in FIG. 13, the interval between the zeroth-order light spot 110 and the first-order diffracted light 111 is Δ, and the angle between the radial direction and the direction connecting the zeroth-order diffracted light 110 and the first-order diffracted light 111 is β. When several tracks are included between the data track 101 and the guide track 102, Δ and β need to be increased. When Δ and β increase, there arises a problem that adjustment error of the angle β and track error signal amplitude fluctuations at the inner and outer circumferences of the optical information recording medium are large. Further, in order to increase Δ, it is necessary to reduce the pitch of the diffraction grating, which causes a problem that processing accuracy becomes severe.
The present invention has been made in view of the above circumstances, and can divide three types of light having different wavelengths into three beams without generating unnecessary diffracted light, and can reduce the number of components and the adjustment process. An object of the present invention is to provide an optical pickup having a diffraction grating with a large adjustment margin.

を満足するように決定されることを特徴とする。
請求項２に記載の発明は、請求項１記載の光ピックアップにおいて、前記回折格子は、前記第一の光源からの光束と前記第二の光源からの光束に対しては０次光と１次回折光との３つ以上のビームに分離し、前記第三の光源からの光束に対しては１次以上の回折効率が略ゼロとなる溝形状を有する回折面を有することを特徴とする。 In order to achieve the above object, the invention described in claim 1 emits three light beams having different wavelengths in an optical pickup that performs one or more of recording, reproducing, and erasing information on three or more types of optical information recording media. First, second and third light sources, a condensing optical system for condensing a light beam emitted from the light source onto the optical information recording medium, and a light receiving element for receiving return light reflected by the optical information recording medium And a plurality of grooves formed between the light source and the optical information recording medium, and a plurality of grooves for separating two or more light beams from the light source into at least three beams. A diffraction grating, and the light beams from the first, second, and third light sources have wavelengths of λ ₁ , λ ₂ , λ ₃ , wavelengths λ _{1, and} λ ₂ , respectively. The grating direction of the diffraction surface that separates into three or more beams with the first-order diffracted light The angle between the radial direction of the optical information recording medium and beta, the focal length f ₁ of the objective lens for the wavelength lambda ₁ of the light beam, the track pitch of the optical recording information medium for TP _1, the wavelength lambda ₂ of the light beam objective focal length f ₂ of the lens, a track pitch of the optical recording information medium and TP _2, and m _1, m ₂ are positive integers, l _1, l ₂ is 1 or 2 a positive integer, a is the track error signal When the amplitude reduction rate is allowed, the pitch P of the diffraction grating is

It is determined to satisfy
According to a second aspect of the present invention, in the optical pickup according to the first aspect, the diffraction grating has zero-order light and first-order light for the light flux from the first light source and the light flux from the second light source. It is separated into three or more beams of folding light, and has a diffractive surface having a groove shape in which the first-order or higher diffraction efficiency is substantially zero with respect to the light beam from the third light source.

を満足するように決定されることを特徴とする。 According to a third aspect of the present invention, in the optical pickup according to the first aspect, the wavelengths of the light beams from the first, second, and third light sources are respectively λ ₁ , λ ₂ , λ ₃ , and the diffraction grating is formed. When the refractive index for the light beam with wavelength λ ₁ is n ₁ , the refractive index for the light beam with wavelength λ ₂ is n ₂ , and the refractive index for the light beam with wavelength λ ₃ is n ₃ , the groove depth of the diffraction surface d, the groove width ratio q is

It is determined to satisfy

を満足するように決定されることを特徴とする光ピックアップ。
請求項６に記載の発明は、請求項４又は請求項５に記載の光ピックアップにおいて、
前記回折格子の２つの回折面が、光軸を中心として一体回転可能な状態で保持されていることを特徴とする。 According to a fourth aspect of the present invention, in the optical pickup according to the first or third aspect, the diffraction grating includes a zero-order light and a first-order diffracted light with respect to the light beam from the third light source. The light beam is separated into three or more beams, and a second diffractive surface having a first-order or higher diffraction efficiency of substantially zero is provided for the light beams from the first and second light sources.
According to a fifth aspect of the present invention, in the optical pickup according to the fourth aspect, the wavelengths of the light beams from the first, second, and third light sources are respectively λ ₁ , λ ₂ , λ ₃ , and the diffraction grating. When the refractive index for the light beam with wavelength λ ₁ of the material to be formed is n ₁ , the refractive index for the light beam with wavelength λ ₂ is n ₂ , and the refractive index for the light beam with wavelength λ ₃ is n ₃ , the second diffraction surface The groove depth d and the groove width ratio q are

An optical pickup characterized by being determined to satisfy
The invention according to claim 6 is the optical pickup according to claim 4 or claim 5, wherein
The two diffractive surfaces of the diffraction grating are held so as to be integrally rotatable around the optical axis.

According to a seventh aspect of the present invention, in the optical pickup according to any one of the first to sixth aspects, the condensing optical system is formed by a single objective lens. The

According to an eighth aspect of the present invention, in the optical pickup according to any one of the first to seventh aspects, the rotation adjustment with the optical axis of the diffraction grating as the rotation axis uses light having a shorter wavelength. It is characterized by performing.
The invention described in claim 9, the reproduction of information by irradiating a light beam to the recording surface of the optical information recording medium, the optical information processing apparatus for recording or erasing, any one of claims 1 to 8 The optical pickup according to the above is provided.

  According to the present invention, it is possible to form a single diffractive surface having two types of wavelengths and the pitch of the diffraction grating corresponding to the optical recording information medium within a desired rate of decrease in the track error signal amplitude. An optical pickup can be provided in the production process.
According to the present invention, an optical information recording apparatus capable of stably recording, reproducing, and erasing two or more types of optical information recording media having different wavelengths, having a small number of components and adjustment steps, and having a large adjustment margin is provided. Can be provided.

Hereinafter, embodiments of the present invention will be described in detail.
[First Embodiment]
(Constitution)
First, a first embodiment of the present invention will be described in detail.
FIG. 1 is a schematic diagram showing the overall configuration of an optical pickup according to the first embodiment of the present invention.
The optical pickup shown in FIG. 1 records or reproduces three types of optical information recording media 11, 12, and 13. Hereinafter, in this embodiment, as these three types of optical information recording media, an optical information recording medium (blue laser next-generation high-density optical disc) 11 having a transparent substrate thickness t1 and an optical information recording having a thickness t2 of the transparent substrate are used. The description will be made as a medium (DVD) 12 and an optical information recording medium (CD) 13 having a transparent substrate thickness t3.
Here, the thickness of the transparent substrate is t1 = 0.1 mm, t2 = 0.6 mm, and t3 = 1.2 mm. The track pitches TP1, TP2, and TP3 of the optical information recording media 11, 12, and 13 are set to TP1 = 0.32 um, TP2 = 0.74 um, and TP = 1.2 um, for example.
The optical pickup shown in FIG. 1 has a blue laser (wavelength λ ₁ = 405 nm) 1a as a first light source as a light source, a red laser (wavelength λ ₂ = 660 nm) 1b as a second light source, and an infrared laser (a third light source). Wavelength λ ₃ = 780 nm) 1c. The first light source 1a, the second light source 1b, and the third light source 1c are used according to the optical information recording medium to be recorded and reproduced. In the present embodiment, these three light sources 1 a to 1 c are configured as one module 1. In the present embodiment, the light source is composed of one module, but may be mounted individually. Further, although the light receiving elements are also shared, they may be provided individually.
A collimator lens 2, a diffraction grating 9, a beam splitter 3, a prism 4, and a quarter-wave plate for converting the divergence angles of light beams emitted from the first, second, and third light sources 1a, 1b, and 1c shown in FIG. 5. Condensed on one of the information recording surfaces of the optical information recording media 11 to 13 via the objective lens 6, and the light reflected from any of the optical information recording media 11 to 13 is returned by the beam splitter 3. A detection lens 8 and a light receiving element 10 for receiving and detecting light separated from the forward path and separated from the forward path by the beam splitter 3 are provided. Details of the objective lens 6 and the diffraction grating 9 will be described later.
The numerical aperture of the objective lens 6 is NA 0.85 for the light of the first light source 1a, NA 0.65 for the light of the second light source 1b, and NA0 for the light of the third light source 1c. .45.

(Objective lens)
The objective lens 6 used in the present embodiment is composed of, for example, concentric annular diffractive surfaces and aspherical refracting surfaces in order to collect light of three different wavelengths with a single objective lens. In general, when only an aspheric refracting surface is used, when spherical aberration is corrected for _a certain wavelength λ _a , the spherical aberration becomes under for a wavelength λ _b shorter than λ _a .
On the other hand, when the diffractive surface is used, when the spherical aberration is corrected for _a certain wavelength λ _a , the spherical aberration is over for a wavelength λ _b shorter than λ _a . Therefore, it is possible to correct spherical aberration between different wavelengths by combining the refractive power and the diffraction power by appropriately selecting the aspherical optical design by the refractive surface and the phase function coefficient of the diffraction surface. . Therefore, light can be condensed on the information recording surface of each transparent substrate even for different wavelengths.

(Diffraction grating)
On the optical path between the light source module 1 on which the first, second, and third light sources 1a, 1b, and 1c are mounted and the beam splitter 3, the light from the first light source 1a and the third light source 1c are transmitted. A diffraction grating 9 is disposed that separates the light into three beams and transmits the light from the second light source 1b. This is for detecting a tracking error capable of reducing the offset.
As shown in FIG. 2, the diffraction grating 9 has a diffraction surface 9b formed on only one surface of the substrate 9a. At this time, the 0th-order light transmittance of the light from the second light source 1b is desirably 90% or more.
In general, when the diffraction grating 9 as shown in FIG. 2 forms a pattern, the transmission intensity I ₀ of the 0th-order light and the intensity I _{± 1} of the _1st-order diffracted light can be expressed by the following equations.
I ₀ = (2q−1) ² sin ² θ + cos ² θ (Expression 1)
I _{± 1} = 4 ((sin πq) / π) ² sin ² θ (Expression 2)
However, θ = π / λ · (n−n ′) d (Expression 3)
And
n is the refractive index of the medium on the output side of the diffraction grating, n ′ is the refractive index of the medium on the incident side, d is the groove depth of the diffraction grating, λ is the wavelength of the light source, and q is the ratio of the grooves of the diffraction grating.
In particular, when q = 0.5, Equations 1 and 2 are I ₀ = cos ² θ (Equation 4)
I _{± 1} = (2 / π) ² sin ² θ (Formula 5)
It can be expressed as.
The above equation can be obtained by calculation based on a scalar theoretical approximation that is established when the groove depth d is sufficiently smaller than the pitch P of the diffraction grating 9 and the pitch P is sufficiently larger than the wavelength λ.
The diffraction efficiency can be easily changed by changing the groove depth of the diffraction grating 9. For example, SF6 is used as the material of the diffraction grating. Table 1 shows the constants used when calculating the diffraction efficiency. FIG. 3 is a graph showing the change in diffraction efficiency with respect to the change in the groove depth d of the diffraction grating.
From this graph, the optimum depth d of the diffraction grating 9 according to this embodiment can be determined.
Table 1

さらに、それぞれ波長の異なる光はトラックピッチの異なる光情報記録媒体へ集光されるため、３分割された光は、必要とされるスポット間隔でそれぞれの光情報記録面上に集光される必要がある。例えば、トラックエラー信号に差動プッシュプル法を用いる場合は、０次光の光スポットＳ０と１次回折光の光スポットＳ１は図４のような位置関係にいる必要がある。また３ビーム法を用いる場合には、０次光の光スポットＳ０と１次回折光の光スポットＳ１は図５のような位置関係にいる必要がある。 Since the diffraction grating 9 of the present embodiment is disposed in the optical path between the light source module 1 and the beam splitter 3, all the light from the first, second, and third light sources 1a, 1b, and 1c is diffracted. Passes through the grid 9. When the light from the first and third light sources 1a and 1c is selectively divided into three, the light from the first and third light sources 1a and 1c is separated into zero-order light and first-order diffracted light. For the light from the second light source 1b, the first-order or higher diffraction efficiency is preferably 10% or less.
For example, when d = 4.15 μm, the efficiency of the 0th order light and the 1st order diffracted light of each wavelength is as shown in Table 2, and the light of the first light source 1a is −1st order, 0th order, +1 The next light is divided into three at a ratio of 1: 10: 1, the second light is substantially 100% transmitted, and the third light is divided into three at a ratio of 1: 6: 1.
Table 2

Furthermore, since light having different wavelengths is condensed on optical information recording media having different track pitches, the light divided into three needs to be condensed on each optical information recording surface at a required spot interval. There is. For example, when the differential push-pull method is used for the track error signal, the zero-order light spot S0 and the first-order diffracted light spot S1 need to have a positional relationship as shown in FIG. When the three-beam method is used, the light spot S0 of the 0th-order light and the light spot S1 of the 1st-order diffracted light need to be in a positional relationship as shown in FIG.

When the pitch of the diffraction grating 9 is P, the first-order diffracted light is intensified under the condition of λ = Psinα, and therefore the first-order diffracted light is diffracted in the angle α direction (see FIG. 2). When the pitch of the diffraction grating 9 of the present embodiment and 150 [mu] m, is 1 order diffraction angle α of each wavelength is 0.24 ° for 0.15 °, lambda ₃ for lambda ₁ as shown in Table 3 .
For example, when the focal length fOL of the objective lens 6 is 2.4 mm at any wavelength, the interval Δ between the 0th-order light and the 1st-order diffracted light can be expressed as Δ = fsinα, and as shown in the table, λ _{For 1} and λ ₃ , Δ becomes Δ ₁ = 6.4 um and Δ ₃ = 12.2 um, respectively.
This is for the third light lambda ₃ on the optical information recording surface, by adjusting the angle of the diffraction grating 9 shifted 1/4 track relative to the track pitch TP3 as shown in FIG. 7, with respect to lambda ₁ As shown in FIG. 6, the 0th-order light spot S0 and the 1st-order diffracted light spot S1 are condensed with a shift of 1/2 track with respect to the track pitch TP1.
Therefore, for the light from the first light source 1a, a tracking error signal is detected using a differential push-pull method that calculates the difference between the push-pull signal of the 0th order light and the push-pull signal of ± 1st order diffracted light. For the light from the third light source 1c, a tracking error signal can be detected using the three-beam method.
Table 3

・・・（式６）
そして、同じ回折面を用いる波長をλ₁、λ₂とする。
波長λ₁の光束に対する前記対物レンズの焦点距離をｆ₁、光記録情報媒体のトラックピッチをＴＰ₁、光情報記録媒体上の０次光と１次光の間隔をΔ１、１次回折光の角度をα₁
波長λ₂の光束に対する前記対物レンズの焦点距離をｆ₂、光記録情報媒体のトラックピッチをＴＰ₂、光情報記録媒体上の０次光と１次光の間隔をΔ２、１次回折光の角度をα₂
とする時、
Δ１＝ｆ₁ｓｉｎα₁ ・・・（式７）
Ｐｓｉｎα₁＝λ₁ ・・・（式８）
（式７、８）より
Δ１＝ｆ₁λ₁／Ｐ ・・・（式９）
となる。 A generalized method for calculating the pitch of the diffraction grating 9 as described above will be described.
Of the parameters of the diffraction grating 9, β and P are constant regardless of the wavelength. Therefore, the ratio is γ.

... (Formula 6)
The wavelengths using the same diffractive surface are λ ₁ and λ ₂ .
The focal length of the objective lens with respect to the light beam of wavelength λ ₁ is f ₁ , the track pitch of the optical recording information medium is TP ₁ , the distance between the 0th order light and the primary light on the optical information recording medium is Δ1, and the angle of the 1st order diffracted light Α ₁
The focal length of the objective lens with respect to the light beam of wavelength λ ₂ is f ₂ , the track pitch of the optical recording information medium is TP ₂ , the distance between the 0th order light and the primary light on the optical information recording medium is Δ2, and the angle of the 1st order diffracted light Α ₂
When
Δ1 = f ₁ sin α ₁ (Expression 7)
Psin α ₁ = λ ₁ (Formula 8)
From (Equations 7 and 8)
Δ1 = f ₁ λ ₁ / P (Equation 9)
It becomes.

・・・（式１０）
と書ける。ｍ₁は正の整数であり、データトラックと最隣接の関係にある案内トラックとの間隔を算出する場合はｍ₁が１となり、例えば、図１３の場合はｍ₁＝３となる。またｌ₁は差動プッシュプルか３ビーム法を用いるかで値が異なる。差動プッシュプル法の場合は、図４のようになるため、ｌ₁は１、３ビーム法の場合は図５のようになるため、ｌ₁は２となる。
（式９）と（式１０）より求まるλ₁に対するｃｏｓβ／Ｐをγ₁とすると、

・・・（式１１）
と表すことができる。
同様に、λ₂に対するｃｏｓβ／Ｐをγ₂とすると、

・・・（式１２）
と表すことができる。
最適な回折格子９のピッチＰに設定するためには、
γ＝γ₁＝γ₂ ・・・（式１３）
となるようにすることが理想的である。 Δ1 is

... (Formula 10)
Can be written. m ₁ is a positive integer, and m ₁ is 1 when calculating the distance between the data track and the nearest guide track, for example, m ₁ = 3 in FIG. The value of l ₁ differs depending on whether the differential push-pull or the three beam method is used. In the case of the differential push-pull method, as shown in FIG. 4, l ₁ is 1, and in the case of the 3-beam method, as shown in FIG. 5, l ₁ is 2.
When cos β / P for λ ₁ obtained from (Equation 9) and (Equation 10) is γ ₁ ,

... (Formula 11)
It can be expressed as.
Similarly, if cos β / P for λ ₂ is γ ₂ ,

... (Formula 12)
It can be expressed as.
In order to set the optimum pitch P of the diffraction grating 9,
γ = γ ₁ = γ ₂ (Equation 13)
Ideally it should be.

・・・（式１４）

・・・（式１５）
を導くことができ（式１４）（式１５）を満足するようピッチＰを設定すればよい。
例えば上記に示したようにピッチＰが１５０ｕｍ、ｃｏｓβが０．０２４７の場合、トラックエラー信号の理想的な振幅から９０％までの低下を許容値とすると、波長λ₁を４０５ｎｍ、波長λ₁の光束に対する光記録情報媒体１１のトラックピッチを０．２７〜０．４ｕｍ、波長λ₂を７８０ｎｍ、波長λ₂の光束に対する光記録情報媒体１２のトラックピッチを１．０５〜１．４ｕｍとする時、第一の光源１ａの１次回折光は差動プッシュプル法、第二の光源１ｂの１次回折光は３ビーム法に用いて、トラックエラー信号を検出すれば、０次光と１次回折光の位相差による振幅低減が９０％以内に抑えられた信号を検出することができる。 However, in practice, it is not necessary to satisfy the condition as in Expression 13.
Even when the condition of Expression 13 is not satisfied, it is sufficient that the differential push-pull signal or the track error signal amplitude by the three-beam method does not fall below a desired value.
If the permissible decrease rate is set to A, an error in the phase difference between the 0th-order light and the 1st-order diffracted light may be suppressed so as not to be smaller than A.
From the above,

... (Formula 14)

... (Formula 15)
The pitch P may be set so as to satisfy (Equation 14) and (Equation 15).
For example, as described above, when the pitch P is 150 μm and cos β is 0.0247, assuming that the drop from the ideal amplitude of the track error signal to 90% is an allowable value, the wavelength λ ₁ is 405 nm and the wavelength λ ₁ When the track pitch of the optical recording information medium 11 with respect to the light beam is 0.27 to 0.4 μm, the wavelength λ ₂ is 780 nm, and the track pitch of the optical recording information medium 12 with respect to the light beam with the wavelength λ ₂ is 1.05 to 1.4 μm. The first-order diffracted light of the first light source 1a is used for the differential push-pull method, the first-order diffracted light of the second light source 1b is used for the three-beam method, and if the track error signal is detected, the zero-order light and the first-order diffracted light A signal in which the amplitude reduction due to the phase difference is suppressed within 90% can be detected.

(effect)
The diffraction grating 9 shown in this embodiment detects two types of light having different wavelengths on a single diffraction surface 9b when detecting a tracking error signal using three beams for reducing the occurrence of an offset of the tracking error signal. Since it is divided into three, an optical pickup can be provided with a small number of parts and a production process.
Even when three types of light are used, since the diffraction grating avoids generation of unnecessary diffracted light for the remaining light, it is possible to provide an optical pickup in which a decrease in light use efficiency is suppressed.
Furthermore, even when light beams of different wavelengths are collected by a single objective lens, a tracking error signal can be obtained using the nearest guide groove, and three beams with a large rotation adjustment margin of the diffraction grating can be generated. it can.
In this embodiment, the SF6 material is used. However, the diffraction grating material, groove depth, and pitch may be selected in accordance with the wavelength used, the track pitch and tracking signal detection method, and the focal length of the objective lens. .

[Second Embodiment]
This embodiment shows an optical pickup provided with a diffraction grating that divides three lights having different wavelengths into three. The configuration and the objective lens 6 used are the same as those in the first embodiment.
(Diffraction grating)
FIG. 8 shows the configuration of a diffraction grating that divides three lights into three. The diffraction grating 9 has first and second diffraction surfaces 9b and 9c formed on both surfaces of a substrate 9a. One surface is the first diffractive surface 9b corresponding to two wavelengths having different wavelengths, for example, λ ₁ and λ ₃ as shown in the first embodiment. On the remaining one surface, a second diffractive surface 9c corresponding to λ ₂ is formed. The material of the diffraction grating 9 of this embodiment is SF6. The groove depth of the first diffractive surface 9b is 4.15 μm as in the first embodiment. The efficiency of each wavelength at this time is shown in Table 1. The groove depth of the second diffractive surface 9c is, for example, 0.94 um. Table 4 shows the efficiency of each wavelength at this time. The light from the first light source 1a is substantially 100% transmitted, and the light from the second light source 1b is divided into three parts at a ratio of −1: 1, 0th order, and + 1st order 1: 9.8: 1, and the third light source 1c. 97% of light is transmitted. Therefore, the light from the first and third light sources 1a and 1c is divided into three on the first diffractive surface 9b, the light from the second light source 1b is transmitted, and the second light source 1b is transmitted from the second diffractive surface 9c. Are divided into three, and the light of the first and third light sources 1a and 1c is transmitted, so that three types of light having different wavelengths are generated using the same substrate without generating unnecessary diffracted light. Can be divided.
Table 4

The light divided into three needs to be condensed on each optical information recording surface at a spot interval required on each information recording medium having a different track pitch.
For example, the differential push-pull method is used for the track error signal for the light from the first and second light sources 1a and 1b, and the three-beam method is used for the light from the third light source 1c.
As shown in the first embodiment, the pitch P of the first diffractive surface 9b is 150 μm, and the wavelength λ ₃ of the third light source 1c is diffracted by ¼ track with respect to the track pitch TP3. When the grating angle β is adjusted, the zero-order light spot S0 and the first-order diffracted light spot S1 are collected with a shift of 1/2 track with respect to the track pitch TP1 with respect to the wavelength λ ₁ as shown in FIG. It will be in a shining state. The light from the first light source 1a and the light from the third light source 1c are transmitted through the second diffraction surface 9c. The second diffractive surface 9c divides only the light of the second light source 1b into three.
If the pitch of the diffraction grating 9 is, for example, 106 μm, the first-order diffraction angle α is 0.36 °. When the focal length f of the objective lens 6 is 2.4 mm, Δ ₂ is 15 μm, and the light from the second light source 1 b is shifted by 1/2 track, and the light spot of the 0th order light and the light spot of the 1st order diffracted light n are collected. It will be in a shining state.
Then, using the differential push-pull method for calculating the difference between the push-pull signal of the 0th order light and the push-pull signal of ± 1st order diffracted light at the wavelengths λ ₁ and λ ₂ of the first and second light sources 1a and 1b, In the light of the third light source 1c, the tracking error signal can be detected using the three-beam method.

(effect)
The diffraction grating 9 shown in the present embodiment can detect only the first and second diffraction surfaces 9b and 9c when detecting a tracking error signal using three beams for reducing the occurrence of an offset of the tracking error signal. Three beams of wavelengths can be generated.
Therefore, since diffraction gratings corresponding to three types of light can be easily formed integrally on the same substrate or bonded together, an optical pickup can be provided with a small number of parts and a production process.
In addition, since the diffraction grating avoids generation of unnecessary diffracted light, an optical pickup that suppresses a decrease in light utilization efficiency can be provided.
In this case, SF6 is used as the material of the diffraction grating. However, the material of the diffraction grating, the groove depth, and the pitch can be selected according to the wavelength used, the track pitch and tracking signal detection method, and the focal length of the objective lens. It ’s fine.

[Third Embodiment]
(Constitution)
FIG. 9 is a schematic view showing the overall configuration of the optical pickup according to the third embodiment. The same blocks as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.
The optical pickup shown in FIG. 9 differs from the first embodiment shown in FIG. 1 in the configuration of the diffraction grating and the objective lens. Also, the type of optical information recording medium on which recording or reproduction is performed is different.
In this case, as the three types of optical information recording media, an optical information recording medium (next-generation high-density optical disk using blue laser) 14 having a transparent substrate thickness t1 and an optical information recording medium (DVD) 12 having a transparent substrate thickness t2 are used. And an optical information recording medium (CD) 13 having a transparent substrate thickness t3. Here, the thickness t1 = 0.6 mm, t2 = 0.6 mm, and t3 = 1.2 mm of the transparent substrate. The track pitches TP1, TP2, and TP3 of the optical information recording media 11, 12, and 13 are set to TP1 = 0.32 um, TP2 = 0.74 um, and TP = 1.2 um, for example.
Further, the track pitches TP1, TP2, and TP3 of each optical information recording medium are, for example, TP1 = 0.44 μm, TP2 = 0.74 μm, and TP3 = 1.2 μm.
In this case, the numerical aperture of the objective lens 21 is NA 0.65 for the light from the first light source 1a, NA 0.65 for the light from the second light source 1b, and the light from the third light source 1c. In this case, NA is 0.45.

(Diffraction grating)
Next, the configuration of the diffraction grating of the present embodiment will be described. Since the configuration of the diffraction grating of the present embodiment is the same as that of the diffraction grating of the present embodiment, the description will be given with reference to FIG.
The diffraction grating 22 that divides three light into three has first and second diffraction surfaces 22b and 22c formed on both surfaces of a substrate 22a shown in FIG. One surface is a first diffractive surface 22b corresponding to two types of wavelengths having different wavelengths, for example, wavelengths λ ₁ and λ ₂ as shown in the first embodiment. A second diffractive surface 22c corresponding to the wavelength λ ₃ is formed on the remaining one surface. The material of the diffraction grating 22 of this embodiment is also SF6 as before.
The groove depth of the first diffractive surface 22b is 0.87 m. The efficiency of each wavelength at this time is shown in Table 5. The groove depth of the second diffractive surface 22c is, for example, 10.78 μm. The efficiency of each wavelength at this time is shown in Table 5. From Table 5, on the first diffractive surface 22b, the light of the first and second light sources 1a and 1b is divided into three, the light of the third light source 1c is transmitted, and on the second diffractive surface 22c, the third light is transmitted. Since the light from the light source 1c is divided into three parts and the light from the first and second light sources 1a and 1b is transmitted, three types of light having different wavelengths are generated using the same substrate without generating unnecessary diffracted light. Can be divided into three.
Table 5

The light divided into three needs to be condensed on each information recording surface at a required spot interval. In this embodiment, a tracking error signal using a differential push-pull is detected.
The pitch P of the first diffractive surface 22b is 106 μm, the first-order diffraction angle α of the wavelength λ ₁ is 0.22 °, and the first-order diffraction angle α of λ ₂ is 0.36 °. Δ is 9.9 μm and 15 μm, respectively. This is a state where the 0th-order light and the 1st-order diffracted light are condensed with a shift of 1/2 track with respect to the first and second light sources 1a and 1b.
The second diffractive surface 22c divides only the light of the third light source 1c into three.
If the pitch of the diffraction grating 22 is, for example, 77 μm, the first-order diffraction angle α is 0.58 °. When the focal length f of the objective lens 21 is 2.4 mm, Δ is 24.3 μm, the light of the third light source 1 c is shifted by 1/2 track, and the 0th order light and the 1st order diffracted light are condensed. Become.
As described above, the first diffractive surface 22b divides the light of the first and second light sources 1a and 1b into three parts, and the second diffractive surface 22c divides the light of the third light source into three parts. Tracking error signals can be detected using differential push-pull at the wavelength.
Further, from the formulas 14 and 15, the track pitch and diffraction grating to be used can be freely selected with a certain width.
For example, as described above, when the pitch P is 106 μm and cos β is 0.0247, assuming that the drop from the ideal amplitude of the track error signal to 90% is an allowable value, the wavelength λ ₁ is 405 nm and the wavelength λ ₁ The track pitch of the optical recording information medium 14 for the light flux of 0.38 to 0.57 um, the wavelength λ ₂ of 660 nm, and the track pitch of the optical recording information medium 12 for the light flux of wavelength λ ₂ of 0.62 to 0.9 um. For example, if a track error signal is detected using the differential push-pull method, a signal in which the amplitude reduction due to the phase difference between the 0th-order light and the 1st-order diffracted light is suppressed within 90% can be detected.

(effect)
The diffraction grating 22 shown in the present embodiment detects three types of light with two different grating constants and different wavelengths when detecting a tracking error signal using a differential push-pull signal in order to reduce the occurrence of an offset of the tracking error signal. Is divided into three, three beams of three wavelengths can be generated with only two diffractive surfaces.
Therefore, since diffraction gratings corresponding to three types of light can be easily formed integrally on the same substrate or bonded together, an optical pickup can be provided with a small number of parts and a production process.
In addition, since the diffraction grating avoids generation of unnecessary diffracted light, an optical pickup that suppresses a decrease in light utilization efficiency can be provided.
In this case, SF6 is used as the material of the diffraction grating. However, the material of the diffraction grating, the groove depth, and the pitch can be selected according to the wavelength used, the track pitch and tracking signal detection method, and the focal length of the objective lens. It ’s fine.

[Fourth Embodiment]
The diffraction grating 9 (22) adjusts the spot position on the information recording surface of the 0th-order diffracted light and the 1st-order diffracted light in order to optimize the phase difference between the track signals of the 0th-order diffracted light and the 1st-order diffracted light according to the detection method. Adjust to an appropriate position as shown in FIGS. Adjustment is performed by rotating the diffraction grating about the optical axis. At this time, if they are integrally formed, the rotation adjustment is performed so that the spot positions of the light of the first light source 1a having the shortest wavelength on the information recording surface of the first-order diffracted light and the first-order diffracted light are optimized. It is desirable. This is because the light of the first light source 1a has a small ratio of the track pitch to the spot interval Δ between the 0th order diffracted light and the 1st order diffracted light. When this ratio is small, the spot position deviation of the first-order diffracted light when a rotation angle error occurs is large, and the influence of a decrease in the amplitude of the track signal using three beams becomes large.
Thus, a stable tracking error signal can be easily obtained by rotating and adjusting the integral diffraction grating using light having the smallest rotation angle error margin.
If the first and second diffractive surfaces 9b (22b) and 9c (22c) are formed on different substrates, the rotation of the diffraction gratings can be adjusted so that the zero-order diffracted light and the first-order diffracted light Each spot position on the information recording surface can be optimally adjusted, and a stable tracking error signal can be obtained.

[Fifth Embodiment]
Next, an optical pickup according to a fifth embodiment will be described.
(Diffraction grating)
As shown in FIG. 10A, in the diffraction grating 31, first, second, and third diffraction surfaces 32b, 33b, and 34b having different lattice constants are formed on three substrates 32a, 33a, and 34a, respectively. In this case, the first diffractive surface 32b divides the light of the first light source 1a into three beams and transmits the second and third light sources 1b and 1c. The second diffractive surface 33b divides the light from the second light source 1b into three beams and transmits the first and third light sources 1a and 1c. The third diffractive surface 34b divides the light from the third light source 1c into three beams and transmits the light from the first and second light sources 1a and 1b. Also in this case, the material of the diffraction grating is SF6. Table 6 shows the groove depth of the diffraction surface and the diffraction efficiency at each wavelength.
Further, as shown in FIG. 10B, the diffraction grating 31 can also be configured such that the second and third diffraction surfaces 33b and 34b are bonded to both surfaces of the substrate 34a.

(effect)
The diffraction grating of this embodiment can divide three types of light having different wavelengths into three without generating unnecessary diffracted light.
Moreover, since the lattice constant can be set uniquely, the detection method can be freely selected according to the type of the optical information recording medium at each wavelength. In addition, the degree of freedom in design can be widened, such as a diffraction grating that allows a wide margin such as seek shift of the optical recording information device and crosstalk between divided light receiving elements, and a diffraction grating that can be easily manufactured. .
Furthermore, since the rotation angle can be individually adjusted, the spot positions of the 0th-order diffracted light and the 1st-order diffracted light on the information recording surface can be optimally adjusted, and a stable tracking error signal can be obtained.
Further, for example, the second and third diffractive surfaces having a wide margin for the rotation angle adjustment error may be formed on the same substrate so that the rotation angle can be adjusted integrally. Rather than forming on each individual substrate, adjusting the direction of one grating also sets the direction of the other grating to a suitable direction, so that the time required for adjusting the diffraction grating can be shortened.
Table 6

３分割された光はそれぞれトラックピッチの異なる情報記録媒体上で、検出方式に合わせて必要とされるスポット間隔と角度で情報記録面上に集光される必要がある。
例えばピッチを１５０ｕｍとすると、第三の光源１ｃの光に対しては、１／４トラック第一の光源１ａの光に対しては１／２トラックずれて０次光と１次回折光が集光している状態となるため、それぞれ３ビーム法と差動プッシュプル法でトラッキングエラー信号を得ることができる。しかしながら、第二の光源１ｂの光に対しては３／８トラック程度ずれて、０次光と１次回折光が集光している状態となる。そのため、３ビーム法の場合は１／４トラック、差動プッシュプル法の場合は１／２トラックずれて０次光と１次回折光が集光している状態になるように回折格子の回転角度を調整すればよい。
本実施形態では、第二の光源１ｂの光のみ異なる角度に調整しているが、各波長に応じて回転角度を切り換えても良い。回転角度の切り換えは、組付け時に使用波長に応じた角度を設定してもよい。また、光記録情報装置が動作するごとに、トラッキングエラー信号の振幅が最大になるよう調整すれば、常により安定したトラッキングエラー信号を得ることができる。 [Sixth Embodiment]
Next, an optical pickup according to the sixth embodiment will be described.
The optical pickup according to the sixth embodiment includes a diffraction grating that divides three lights having different wavelengths into three. Since the configuration and the objective lens used are the same as those in the first embodiment, illustration is omitted.
(Diffraction grating)
In the diffraction grating of this embodiment, as shown in FIG. 2, a diffraction surface 9b is formed on only one surface of the substrate 9a. FIG. 11 shows the efficiency of each wavelength with respect to the groove depth when the material is SF6.
From FIG. 11, Table 7 shows the efficiency of each wavelength when the groove depth is 5.09 μm. The first, second, and third lights are in the ratio of −1st order, 0th order, and + 1st order light in the ratio of 1: 8.4: 1, 1: 9.8: 1, and 1: 7.5: 1, respectively. Divided into three. Three types of light having different wavelengths on a single diffractive surface can be divided into three parts with appropriate diffraction efficiency.
Table 7

The light divided into three parts needs to be condensed on the information recording surface on the information recording medium having different track pitches at the spot interval and angle required for the detection method.
For example, when the pitch is 150 μm, the 0th-order light and the 1st-order diffracted light are condensed with a shift of 1/2 track with respect to the light of the third light source 1c and the light of the 1/4 light source 1a. Therefore, tracking error signals can be obtained by the 3-beam method and the differential push-pull method, respectively. However, the light of the second light source 1b is shifted by about 3/8 track, and the zero-order light and the first-order diffracted light are condensed. Therefore, the rotation angle of the diffraction grating is such that the zero-order light and the first-order diffracted light are focused with a shift of 1/4 track in the case of the 3-beam method and 1/2 track in the case of the differential push-pull method. Can be adjusted.
In the present embodiment, only the light of the second light source 1b is adjusted to a different angle, but the rotation angle may be switched according to each wavelength. The rotation angle may be switched by setting an angle corresponding to the wavelength used during assembly. Further, if the tracking error signal is adjusted to have the maximum amplitude every time the optical recording information apparatus operates, a more stable tracking error signal can always be obtained.

(effect)
The diffraction grating shown in the present embodiment divides three types of light having different wavelengths with one type of grating constant into three when detecting a tracking error signal using three beams for reducing the occurrence of tracking error signal offset. Therefore, it is only necessary to provide a single diffractive surface, and an optical pickup can be provided with a small number of parts.
Since the rotation angle of the diffraction grating is adjusted each time the optical information recording apparatus operates for recording and reproducing signals, a stable tracking error signal can be obtained at all times.

[Seventh Embodiment]
FIG. 12 is a diagram showing the configuration of the optical information recording apparatus of this embodiment.
The optical information recording apparatus shown in FIG. 12 uses at least one of reproduction, recording, and erasing of information with respect to the optical recording information medium using the optical pickup of any of the first to sixth embodiments. It is a device that performs.
The optical recording / reproducing apparatus is roughly constituted by a spindle motor 42, a feed motor 44, an optical pickup 41, and the like, and these are controlled by a system controller 46 that controls the entire optical recording / reproducing apparatus. Then, the movement of the optical pickup in the tracking direction is performed by a control driving means composed of a feed motor 44. For example, when reproducing the optical recording information medium 40, a control signal from the system controller 46 is supplied to the servo control circuit 45 and the modem circuit 43.
In the servo control circuit 45, the spindle motor 42 is rotated at a set number of revolutions and the feed motor 44 is driven.
The modulation / demodulation circuit 43 is supplied with the focusing error signal detected by the photodetector of the optical pickup 41, the tracking error signal, the position information of where the optical recording information medium 40 is read, and the like. The focusing error signal and tracking error signal are supplied to the servo control circuit 45 via the system controller 46.
The servo control circuit 45 drives the focusing coil of the actuator by a focusing control signal, and drives the tracking coil of the actuator by a tracking control signal. The low frequency component of the tracking control signal is supplied to the servo control circuit 45 via the system controller 46 to drive the feed motor 44. As a result, feedback servo of focusing servo, tracking servo, and feed servo is performed.
Also, the position information of where the optical recording information medium 40 is read is processed by the modulation / demodulation circuit 43 and supplied to the spindle motor 42 as a spindle control signal, and a predetermined rotational speed corresponding to the reproduction position of the optical recording information medium 40. The actual reproduction is started from here. The reproduction data processed and demodulated by the modem circuit 43 is transmitted to the outside via the external circuit 47.

When data is recorded, a process similar to that of reproduction is performed until the feedback servo of the focusing servo, tracking servo, and feed servo is applied.
A control signal indicating where the input data input via the external circuit 47 is to be recorded on the optical recording information medium 40 is supplied from the system controller 46 to the servo control circuit 45 and the modem circuit 43.
In the servo control circuit 45, the spindle motor 42 is controlled to a predetermined rotational speed, and the feed motor 44 is driven to move the optical pickup 41 to the information recording position.
The input signal input to the modulation / demodulation circuit 43 via the external circuit 47 is modulated based on the recording format and supplied to the optical pickup 41. In the optical pickup 41, the modulation of the emitted light and the emitted light power are controlled, and recording on the optical recording information medium 40 is started.
If the optical pickup 41 of the present invention is configured in an optical pickup 41 provided in a reproduction-only optical reproduction apparatus and an optical recording / reproduction apparatus capable of both recording and reproduction, two or more types of optical information recording media having different wavelengths can be stably used. In addition, it is possible to provide an optical information recording apparatus which can be recorded, reproduced and erased, and which is small in size and has few parts and adjustment processes.

1 is a schematic diagram showing the overall configuration of an optical pickup according to a first embodiment of the present invention. The figure which showed the structure of the diffraction grating. The figure which showed the change of the diffraction efficiency with respect to the change of the groove depth d of a diffraction grating. The figure which showed the relationship between the 0th order light at the time of using a differential push pull method, and 1st order diffracted light. The figure which showed the relationship between the 0th-order light and the 1st-order diffracted light in the case of using 3 beam method. The figure which showed the relationship of the light spot on an optical information recording medium. The figure which showed the relationship of the light spot on an optical information recording medium. The figure which showed the structure of the diffraction grating. Schematic which showed the whole structure of the optical pick-up concerning 3rd Embodiment. The figure which showed the structure of the diffraction grating. The figure which showed the change of the diffraction efficiency with respect to the change of the groove depth d of a diffraction grating. The figure which showed the structure of the optical information recording device. The figure which showed the positional relationship of the light spot when 3 beams are condensed on the optical information recording medium of CD and DVD with a single objective lens.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Semiconductor laser, 2 Collimating lens, 3 Beam splitter, 4 Prism, 5 1/4 wavelength plate, 6 21 Objective lens, 8 Detection lens, 9 22 Diffraction grating, 9a Substrate, 9b 9c 22b 22c 32b 33b 34b Diffraction surface, 10 Light receiving element, 11 12 13 14 40 Optical information recording medium, 41 Optical pickup, 42 Spindle motor, 43 Modulation / demodulation circuit, 44 Feed motor, 45 Servo control circuit, 46 System controller, 57 External circuit

Claims (9)

In an optical pickup that performs one or more of recording, reproducing, and erasing information on three or more types of optical information recording media,
First, second, and third light sources that emit three light beams having different wavelengths;
A condensing optical system for condensing the light beam emitted from the light source onto the optical information recording medium;
A light receiving element for receiving the return light reflected by the optical information recording medium;
A diffraction grating provided between the light source and the optical information recording medium, having a plurality of grooves and a plurality of grooves for separating two or more light beams from the light source into at least three beams And comprising
The light beams from the first, second, and third light sources have three wavelengths, λ ₁ , λ ₂ , λ ₃ , and wavelengths λ _1, λ ₂ , zero-order light and first-order diffracted light, respectively. The angle formed by the grating direction of the diffraction surface separated into the above beams and the radial direction of the optical information recording medium is β,
The focal length of the objective lens with respect to the light beam with wavelength λ ₁ is f ₁ , the track pitch of the optical recording information medium is TP ₁ , the focal length of the objective lens with respect to the light beam with wavelength λ ₂ is f ₂ , and the track pitch of the optical recording information medium is Is TP ₂ and m ₁ and m ₂ are positive integers, l ₁ and l ₂ are positive integers of 1 or 2, and A is a permissible value of the rate of decrease in track error signal amplitude,
The pitch P of the diffraction grating is

An optical pickup characterized by being determined to satisfy The optical pickup according to claim 1,
The diffraction grating separates the light beam from the first light source and the light beam from the second light source into three or more beams of zero-order light and first-order diffracted light, and from the third light source. An optical pickup having a diffractive surface having a groove shape in which the diffraction efficiency of the first-order or higher is substantially zero with respect to the luminous flux. In the optical pickup according to claim 1 or 2,
The wavelengths of the light beams from the first, second, and third light sources are λ ₁ , λ ₂ , and λ ₃ , respectively, and the refractive index for the light beam of wavelength λ ₁ of the material forming the diffraction grating is n ₁ and the wavelength λ _2. Where n _{2 is} the refractive index of the light beam and n _{3 is} the refractive index of the light beam having the wavelength λ ₃ .
The groove depth d and groove width ratio q of the diffractive surface are:

An optical pickup characterized by being determined to satisfy In the optical pickup according to claim 1 or 3,
The diffraction grating separates the light flux from the third light source into three or more beams of zero-order light and first-order diffracted light, and the light flux from the first and second light sources. An optical pickup comprising a second diffractive surface in which the first-order or higher diffraction efficiency is substantially zero. The optical pickup according to claim 4,
The wavelengths of the light beams from the first, second, and third light sources are λ ₁ , λ ₂ , and λ ₃ , respectively, and the refractive index for the light beam of wavelength λ ₁ of the material forming the diffraction grating is n ₁ and the wavelength λ _2. Where n _{2 is} the refractive index of the light beam and n _{3 is} the refractive index of the light beam having the wavelength λ ₃ .
The groove depth d and groove width ratio q of the second diffractive surface are:

An optical pickup characterized by being determined to satisfy In the optical pickup according to claim 4 or 5,
2. An optical pickup characterized in that two diffraction surfaces of the diffraction grating are held so as to be integrally rotatable about an optical axis. The optical pickup according to any one of claims 1 to 6, wherein the condensing optical system is formed by a single objective lens. The optical pickup according to any one of claims 1 to 7,
  An optical pickup characterized in that the rotation adjustment using the optical axis of the diffraction grating as a rotation axis is performed using light having a shorter wavelength. 9. An optical information processing apparatus that reproduces, records, or erases information by irradiating a recording surface of an optical information recording medium with a light beam, comprising the optical pickup according to any one of claims 1 to 8. An optical information processing apparatus.

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