JP2001351263A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a side beam, having proper balance, in which aberrations are controlled by providing a diffraction element, in which proper corrections are added to a pattern shape, in an optical pickup device which has the diffraction element and a beam shaping means and uses a differential push-pull method as a track signal generating means. SOLUTION: In the optical pickup device which is provided with a semiconductor laser 1, a diffraction element 3 diffracting a beam emitted by the semiconductor laser, a beam-shaping means 4 for enlarging the diameter of the beam, and an objective lens 7 for condensing the beam on an optical recording medium 8, the diffraction element, which forms a pattern, in accordance with formula (1) ϕ(x,y)=α.y+σ(x,y)...(1) where higher order correction term σ(x, y) which is not less than the first order is added to a first order phase transfer function α.y in an orthogonal coordinate (x, y) system, which forms y axis in the diffraction separating direction, is used as the diffraction element 3. Thus, aberration is restrained to be minimum, and a side beam having proper balance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source for recording and / or reproducing information on and from an optical storage medium such as a CD (Compact Disk) optical disk and a DVD (Digital Versatile Disk) optical disk. It relates to a pickup device.

[0002]

2. Description of the Related Art In recent years, DVD-type optical discs capable of higher-density recording have been put into practical use in addition to CD-type optical discs that have been widely used in the past. Also, with respect to an optical pickup device for performing reproduction and / or reproduction, high-performance signal detection and servo control capable of coping with high-density recording are required.

FIG. 4 shows an example of the configuration of a conventional optical pickup device. In FIG. 4, a light beam emitted from a semiconductor laser 1 is converted into a parallel light beam by a collimator lens 2, passes through a beam splitter 5, and passes through an objective lens 7.
After being condensed on the recording surface of the optical storage medium 8, the light is reflected by the recording surface of the optical storage medium 8. The reflected light from the optical storage medium 8 has an information signal based on the shape of the guide groove formed on the recording surface of the optical storage medium 8, and the reflected light is
The light passes through the objective lens 7 again, is reflected by the beam splitter 5, travels through the detection lens 9 and the cylindrical lens 10 to the light receiving element 11, reaches the light receiving element 11, and is received. Then, a track error signal and a focus error signal are generated from the light receiving signal, and servo control can be performed. Further, an information signal is generated from the light receiving signal of the light receiving element 11, and the recorded information is reproduced.

Next, a method of generating a track error signal in the optical pickup device will be described with reference to FIG. As shown in FIG. 5A, the light receiving surface of the light receiving element 11 is divided into two light receiving areas 11-a and 11-b.
The reflected light from the optical storage medium 8 received on the light receiving surface is
The regions are divided into regions A and B where positive and negative first-order diffracted light and zero-order diffracted light generated by the guide groove overlap, and a region C composed of only zero-order diffracted light. When a position shift occurs between the spot on the recording surface of the optical storage medium 8 and the guide groove, the intensity of the regions A and B where the positive and negative first-order diffracted light and the zero-order diffracted light of the light flux incident on the light receiving surface of the light receiving element 11 overlap. A change occurs and the two light receiving areas 11
The intensity change occurs in the received light signals of -a and 11-b. Therefore, a push-pull signal as a track error signal is detected by taking a difference signal between the light receiving signals of the two light receiving areas 11-a and 11-b.

However, when the objective lens 7 is largely moved by the tracking control (the optical axis shifts) or when the relative tilt (tilt) occurs between the optical storage medium 8 and the objective lens 7. The situation changes as shown in FIG. That is, FIG. 5B shows a case where the position of the light beam incident on the light receiving surface of the light receiving element 11 is shifted to the left, and the areas A and B where the positive and negative first-order diffracted light and the zero-order diffracted light overlap each other are: A pair of light receiving areas 11-a,
Although the light is incident on the light receiving area 11-b, since the entire light beam is moving to the left in the drawing, the amount of light incident on the left light receiving area 11-a is larger than that on the right light receiving area 11-b. Therefore, the track error signal composed of the difference signal between the pair of light receiving areas 11-a and 11-b has an offset corresponding to the movement of the incident light beam, which is an obstacle in performing the tracking control. was there.

FIG. 6 shows an example of the configuration of an optical pickup device that addresses the above-mentioned problems. The optical pickup device shown in FIG. 6 differs from the configuration shown in FIG. 4 in that a diffraction element 3 is arranged between a semiconductor laser 1 and a collimator lens 2. The luminous flux emitted from the semiconductor laser 1 is divided into three beams by the diffraction element 3, condensed on the recording surface of the optical storage medium 8, reflected, and reflected from three light receiving areas corresponding to the respective beams. Light receiving element 1
1 (for example, as shown in FIG.
(Divided light receiving element) composed of 11-1, 11-2, 11-3) and the track error signal TE1,
TE2 and TE3 are detected. Hereinafter, a differential push-pull (DP) method for detecting a track error signal at this time is described.
P) method (for example, see JP-A-4-34212)
Will be described with reference to FIG.

As shown in FIG. 7, the three beams generated by diffraction by the diffractive element 3 cause both side beams Bs on the recording surface of the optical storage medium 8 with respect to the main beam Bm in the radial direction (track (guide)). (The direction perpendicular to the groove)) and are shifted by half the track pitch (Tp). Then, the push-pull signals TE1, TE2, TE3 are respectively applied to the spots (spot 1, spot 2, spot 3) of the main beam Bm and the side beam Bs by the two-divided light receiving elements 11-1, 11-2, 11-3. Is detected and the differential signal TE DPP is obtained. This method is represented by the following equation. TE1 = E1-F1 (push-pull signal of main spot (spot 1)) TE2 = E2-F2 (push-pull signal of side spot (spot 2)) TE3 = E3-F3 (push-pull signal of side spot (spot 3)) According to the differential push-pull method, the push-pull signal of the main beam Bm and the push-pull signal of the side beam Bs are both light beams of the objective lens 7. Misalignment with respect to the axis,
Since the offset amounts due to the relative tilt between the objective lens 7 and the optical storage medium 8 are equal, the occurrence of the offset due to these can be canceled.

Next, the necessity of beam shaping means in the optical pickup device will be described. A semiconductor laser emits a laser beam having a different divergence angle depending on an axis perpendicular to an axis parallel to the active layer. Therefore, the intensity distribution of the light beam collimated by the collimator lens in the cross section perpendicular to the optical axis becomes elliptical, and the ratio of the laser beams emitted from many semiconductor lasers is 1: 2.
That is all. A beam shaping prism is known as a means for shaping the elliptical intensity distribution into a substantially circular shape. FIG. 8 shows an example of an optical pickup device using a beam shaping prism. The difference between the optical pickup device shown in FIG. 8 and the configuration shown in FIG.
The point is that the beam shaping prism 4 is arranged between the beam splitter 5 and the beam splitter 5.

In FIG. 8, an elliptical beam whose horizontal direction is short is made incident on a surface 4a of the beam shaping prism 4 inclined with respect to the horizontal direction, and is refracted by this surface 4a to reduce the beam diameter in the horizontal direction. Spreading. In the refraction on the surface 4a, the width of the beam in the direction perpendicular to the paper surface does not change, so that the intensity distribution of the elliptical beam is shaped, and a substantially circular intensity distribution can be obtained. The beam having a substantially circular intensity distribution is condensed by the objective lens 7. In this configuration, a laser beam shaped into a substantially circular shape can be applied to the optical storage medium 8, so that the spot diameter can be reduced and a more circular spot can be obtained. An optical pickup device suitable for recording and reproduction of an optical storage medium can be realized.

As an optical pickup device that compensates for the two problems of the above-described countermeasures for the offset of the track error signal and the beam shaping, for example, Japanese Patent Laid-Open No. 11-5375.
Japanese Unexamined Patent Publication No. 4 (KOKAI) No. 4 is known. FIG. 9 shows a schematic configuration of the above-described conventional optical pickup device. FIG.
, 1 is a semiconductor laser, 2 is a collimator lens, 3 is a diffraction element, 4 is a beam shaping prism, 5 is a beam splitter, 7 is an objective lens, 8 is an optical storage medium, 9 is a detection lens, 10 is a cylindrical lens, 11 Numeral denotes a light receiving element, and 12 denotes a grating. In the optical pickup device having the configuration shown in FIG. 9, three beams are generated by the diffraction element 3 and the beam diameter is expanded by the beam shaping prism 4. However, the diffraction element 3 used in the optical pickup device having the configuration shown in FIG. 9 has a rectangular coordinate (x, y) system with the y axis taken in the diffraction separation direction.
Since the pattern is formed in a pattern according to the phase transfer function α · y with an appropriate constant α, the following problems will occur.

[0011]

Generally, the emitted light of a semiconductor laser has astigmatism such that the light emitting point position is shifted between the horizontal direction and the vertical direction. The position of the light emitting point in the vertical direction is substantially at the emission end face of the laser beam, but the position of the light emitting point in the horizontal direction is often moved inward from the emission end face in units of several μm to several tens of μm. For this reason, when condensing outgoing light, astigmatism also occurs at the converging point, and it becomes difficult to form a minute spot. On the other hand, the beam shaping prism causes astigmatism in the transmitted light when the incident light deviates from the parallel light and becomes convergent light or divergent light. Therefore, in the optical pickup device configured as described above,
The beam shaping prism 4 is changed by changing the distance between the collimator lens 2 and the semiconductor laser 1 while observing the amount of aberration at the focal point.
The astigmatism of the semiconductor laser 1 is corrected by shifting the incident light to the parallel light and canceling the astigmatism at the converging point. However, since this correction is performed on the main beam, the coma aberration and astigmatism of the sub beam generated when the beam enters the beam shaping prism 4 cannot be completely removed, and the side beam spot for generating the track signal is deteriorated. At the same time, the wavefront between the side beams becomes unbalanced. As a result, the performance of the servo control is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art. An optical pickup apparatus having a diffractive element and a beam shaping means, and using a differential push-pull method as a track signal generating means, has a pattern. An object of the present invention is to provide an optical pickup device capable of generating a well-balanced side beam in which aberration is suppressed by providing a diffraction element whose shape is appropriately corrected.

[0013]

According to a first aspect of the present invention, there is provided a semiconductor laser, a diffraction element for diffracting a beam emitted by the semiconductor laser, and a beam diameter of the beam. Beam shaping means for enlarging
In an optical pickup device provided with an objective lens for condensing the beam on an optical storage medium, the diffraction element has a primary coordinate system in a rectangular coordinate system (x, y) having a y-axis in a diffraction separation direction. Equation (1) in which a first-order or higher-order correction term σ (x, y) is added to the phase transfer function α · y of φ, (φ (x, y) = α · y + σ (x, y) ( 1) A diffraction element formed by forming a pattern according to the following. That is, according to the first aspect of the present invention, in the optical pickup device including the diffraction element and the beam shaping unit, the diffraction element has a first-order orthogonal coordinate system (x, y) with the y-axis taken in the diffraction separation direction. By using a diffraction element having a pattern formed in accordance with the above equation (1) in which a first-order or higher-order correction term σ (x, y) is added to the phase transfer function α · y, aberrations can be reduced. It is possible to generate a well-balanced side beam spot that is minimized.

According to a second aspect of the present invention, in the optical pickup device according to the first aspect, the beam from the semiconductor laser is diffracted and separated into three beams of zero-order diffracted light and positive and negative first-order diffracted light by the diffractive element. After the beam diameter is expanded by the beam shaping means, the beam is condensed on an optical storage medium by the objective lens to generate a main beam spot and a pair of side beam spots. That is, in the invention according to claim 2, the beam from the semiconductor laser is diffracted and separated into three beams of zero-order diffracted light and positive and negative first-order diffracted light by the diffractive element according to claim 1, and the beam diameter is determined by the beam shaping means. After enlarging the beam, it is focused on the optical storage medium by the objective lens, and the main beam spot and a pair of side beam spots are generated, so that a well-balanced side beam spot with minimal aberration can be generated. Thus, a good servo signal can be obtained using a pair of side beams (positive and negative first-order diffracted lights).

The invention according to claim 3 is the invention according to claim 1 or 2
In the optical pickup device described above, a y-axis, which is a diffraction separation direction of the diffraction element, substantially coincides with a direction in which a beam diameter is expanded by the beam shaping unit. That is, in the invention according to claim 3, in the optical pickup device including the diffractive element and the beam shaping means, as the diffractive element, a first-order linear coordinate system (x, y) having a y-axis in the diffraction separation direction is used. Equation (1) in which a first-order or higher-order correction term σ (x, y) is added to the phase transfer function α · y, φ (x, y) = α · y + σ (x, y) (1 ), The aberration is minimized even when the direction in which the diffracted light is generated by the diffraction element and the direction in which the beam is expanded coincide with each other. A well-balanced side beam spot can be generated, and a good servo signal can be obtained using a pair of side beams (positive and negative first-order diffracted lights).

According to a fourth aspect of the present invention, in the optical pickup device according to the first, second or third aspect, the correction term σ
(X, y) is expressed by the following equation (2) using the constants β and γ: ψ (x, y) = β · x ² · y + γ · y ³ (2) (X, y). That is, in the invention according to claim 4, in the optical pickup device including the diffraction element and the beam shaping means, the coma aberration correction term ψ (x) represented by the above equation (2) is included in the phase transfer function of the diffraction element. , Y), it is possible to generate a well-balanced side beam spot with minimized aberration, and to obtain a good servo signal using a pair of side beams (positive and negative first-order diffracted light). Becomes possible.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction, operation and operation of the present invention will be described below in detail with reference to the illustrated embodiments. FIG. 1 is a schematic configuration diagram of an optical pickup device showing one embodiment of the present invention, wherein reference numeral 1 denotes a semiconductor laser, 2 denotes a collimator lens, 3 denotes a diffraction element, 4 denotes a beam shaping prism,
5 'is a polarization beam splitter, 6 is a 1/4 wavelength plate, 7 is an objective lens, 8 is an optical storage medium, 9 is a detection lens, 10 is a cylindrical lens, and 11 is a light receiving element.

In FIG. 1, a light beam emitted from a semiconductor laser 1 is diffracted by a diffraction element 3 and divided into three beams of 0-order diffracted light and positive and negative first-order diffracted lights. Is converted. The three divided beams enter the following beam shaping prism 4,
After only the horizontal beam diameter is enlarged by the beam shaping prism 4, a polarizing beam splitter (PBS) 5 '
Then, the light passes through the 波長 wavelength plate 6, is condensed on the recording surface of the optical storage medium 8 by the objective lens 7, and is reflected from the recording surface. The reflected light has an information signal based on the shape of the guide groove formed on the recording surface of the optical storage medium 8, and this reflected light passes through the objective lens 7 again, and
Incident on. The quarter-wave plate 6 has a function of rotating the plane of polarization of light that has traveled from the light source 1 as linearly polarized light on the outward path, and is orthogonal to the outward path on the return path after being reflected by the optical storage medium 8. It generates linearly polarized light having a plane of polarization. Thus, when the reflected light enters the polarization beam splitter 5 again, the reflected light is reflected on the polarization separation surface in a substantially right angle direction, and travels to the light receiving element 11 via the detection lens 9 and the synchronous lens 10. When the reflected light reaches the light receiving surface of the light receiving element 11 (in this embodiment, three light receiving elements are provided as in FIG. 7 since three beams are used), the light receiving element 11 A light reception signal is output, and a track error (TE) signal, a focus error (FE) signal, and an information signal are generated from the light reception signal in an error signal generation circuit (not shown).

Next, a method of detecting a track error signal and a method of generating three beams will be described. Irradiation to the optical storage medium 8 is performed by irradiating a spot by the main beam (0th-order diffracted light) Bm onto the recording surface, and by irradiating the main beam Bm
Of the track pitch Tp in the radial direction (the direction perpendicular to the track (guide groove)) of the optical storage medium 8 in front of and behind the track pitch Tp.
A spot by a pair of side beams (positive / negative first-order diffracted light) Bs is applied to a position shifted by one-half. The signal detection using these three beams is performed by the differential push-pull method in the same manner as that shown in FIG. 7, and as shown in FIG. 7, each reflected light of the main beam Bm and the pair of side beams Bs is separated. Separate two-part light receiving elements 11-1 and 11
−2 and 11-3, respectively, and detects a push-pull signal which is a difference output between left and right detection levels of each of the two divided light receiving elements 11-1, 11-2 and 11-3. Here, the push-pull signal of the main beam Bm is TE1, the push-pull signals of the pair of side beams Bs are TE2,
Assuming TE3, the value TE DPP of the calculation of TE1− (1/2) · (TE2 + TE3) = TE DPP is obtained as a track error signal.

According to the differential push-pull method, the push-pull signal of the main beam Bm and the push-pull signal of the pair of side beams Bs are both displaced with respect to the optical axis of the light of the objective lens 7, Since the offset amounts due to the relative tilt of the optical storage medium 8 are equal, there is an advantage that the occurrence of the offset can be canceled as described in the conventional example.

Next, beam shaping will be described. As described above, the beam shaping prism 4 is for shaping the intensity distribution of the elliptical beam into a circular shape. In the optical pickup device having the configuration shown in FIG. 1, an elliptical beam whose horizontal direction is short is made incident on a surface 4a of the beam shaping prism 4 inclined with respect to the horizontal direction.
The beam diameter in the horizontal direction is widened by refraction at. In the refraction on the surface 4a, the width of the beam in the direction perpendicular to the paper surface does not change, so that the intensity distribution of the elliptical beam is shaped and a substantially circular intensity distribution can be obtained. Then, the beam having the circular intensity distribution is focused on the recording surface of the optical storage medium 8 by the objective lens 7. In this configuration, a circularly shaped laser beam can be applied to the optical storage medium 8, so that the spot diameter can be reduced and a more circular spot can be obtained.
An optical pickup device suitable for recording and reproduction on a high recording density optical storage medium such as a DVD optical disk can be realized.

Next, the diffraction element 3 used in the optical pickup device of the present invention will be described. In order to easily understand the effects of the present invention, the description will be made with a simple diffraction grating used in the conventional example as a starting point. The diffraction element used in the conventional example has rectangular coordinates (x, y) with the y-axis taken in the diffraction separation direction.
A pattern is formed for the system according to a phase transfer function α · y with an appropriate constant α. However, if a side beam for detecting a track signal is generated with such a simple pattern, an aberration will occur after transmission through the beam shaping prism 4. Therefore, in the present invention, as the diffraction element 3, orthogonal coordinates (x, y) taking the y-axis in the diffraction separation direction are used.
In the system, equation (1) in which a first-order or higher-order correction term σ (x, y) is added to the first-order phase transfer function α · y, φ (x, y) = α · y + σ ( x, y) A diffraction element having a pattern formed according to (1) is used.

In particular, when the direction in which the beam is expanded by the beam shaping prism 4 and the direction in which the beam is diffracted by the diffraction element 3 match, the above correction term σ (x,
By using appropriate constants β and γ for y), a coma aberration correction term ψ (x) expressed by the following equation (2), ψ (x, y) = β · x ² · y + γ · y ³ (2) , Y), it is possible to correct the aberration generated when the light passes through the beam shaping prism 4 and obtain a good side beam spot. Therefore, a well-balanced side beam spot with minimized aberration can be generated, and a good servo signal can be obtained using a pair of side beams (positive and negative first-order diffracted light).

(Specific Example) A specific example in which the direction in which the beam is expanded by the beam shaping prism 4 and the direction in which the beam is diffracted by the diffraction element 3 coincides with each other will be described below.
In the optical pickup device having the configuration as shown in FIG. 1, φ (x, y) = (2π / λ) · (1.6799E−2.y) (where λ is the production wavelength, and E−2 is × 10 ^−2). The wavefront aberration at the pupil of the positive and negative first-order diffracted light in the case of using a simple diffraction grating having the phase transfer function shown in FIG.
(B) shows each. As is clear from FIG. 2, it can be seen that coma is generated by transmission through the beam shaping prism 4. In addition, the amount of generation of aberration differs between positive and negative first-order diffracted lights.

On the other hand, a correction term σ (x, y) is added to the above phase transfer function as in equation (1), and the equation (2) is added to the correction term.
Including the coma aberration correction term ψ (x, y) represented by the following equation, φ (x, y) = (2π / λ) × (1.6803E−2 · y−3.118)
^{0E-4 · x 2 · y} -3.6266E-4 · y 3) ( where, lambda is manufactured wavelength, E-2 is × 10 ^-2, E-4 is × 10 ^-4
(A) and (b) of FIGS. 3A and 3B respectively show the state of the wavefront aberration at the pupil of the positive and negative first-order diffracted light when the diffractive element 3 having the phase transfer function shown in FIG. As is clear from FIG. 3, the coma aberration is greatly reduced,
The imbalance that occurs between FIGS. 2A and 2B is also reduced. Therefore, a well-balanced side beam spot with minimal aberration can be generated.

[0026]

As described above, according to the first aspect of the present invention, in the optical pickup device including the diffraction element and the beam shaping means, the diffraction element is orthogonal to the diffraction separation direction on the y-axis. Under the coordinate (x, y) system, the first-order or higher-order correction term σ is given to the first-order phase transfer function α · y.
Since a diffraction element having a pattern formed in accordance with the equation (1) to which (x, y) is added and φ (x, y) = α · y + σ (x, y) (1) is used, aberration is minimized. And a well-balanced side beam spot is obtained. As a result, good servo control becomes possible.

According to a second aspect of the present invention, in the optical pickup device according to the first aspect, the beam from the semiconductor laser is converted into three beams of zero-order diffracted light and positive and negative first-order diffracted light by the diffraction element. After the beam was diffracted and separated, and the beam diameter was expanded by the beam shaping unit, the beam was condensed on the optical storage medium by the objective lens to generate a main beam spot and a pair of side beam spots, so that aberration was minimized. A well-balanced side beam spot is obtained, a good servo signal can be obtained using a pair of side beams (positive and negative first-order diffracted light), and good servo control can be performed.

According to the third aspect of the present invention, in the optical pickup device including the diffraction element and the beam shaping means, the direction in which the diffracted light is generated by the diffraction element and the direction in which the beam is expanded are matched. In spite of this, as a diffraction element, orthogonal coordinates (x,
y) Under the system, equation (1) in which a first-order or higher-order correction term σ (x, y) is added to the first-order phase transfer function α · y, φ (x, y) = α · Since a diffraction element having a pattern formed according to y + σ (x, y) (1) is used, aberration is minimized, and a well-balanced side beam spot is obtained. As a result, a good servo signal can be obtained using the pair of side beams (positive and negative first-order diffracted light), and good servo control can be performed.

According to the fourth aspect of the present invention, in the optical pickup device including the diffraction element and the beam shaping means, the following equation (2), ψ (x, y) is included in the phase transfer function of the diffraction element. = Β · x ² · y + γ · y ³ (2) (where β and γ are arbitrary constants)
Since (x, y) is included, aberration is minimized, and a well-balanced side beam spot is obtained.
As a result, a good servo signal can be obtained using the pair of side beams (positive and negative first-order diffracted light), and good servo control can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical pickup device showing one embodiment of the present invention.

FIG. 2 is a diagram illustrating a state of a wavefront aberration at a pupil of positive and negative first-order diffracted light when a simple diffraction grating is used as a diffraction element in the optical pickup device having the configuration illustrated in FIG.

FIG. 3 shows the optical pickup device having the configuration shown in FIG. 1, in which a positive-negative first-order diffracted light at the pupil is used when a diffraction element having a phase transfer function satisfying Expressions (1) and (2) is used as the diffraction element. It is a figure showing a situation of wavefront aberration.

FIG. 4 is a schematic configuration diagram of an optical pickup device showing an example of a conventional technique.

5 is an explanatory diagram of a method of generating a track error signal in the optical pickup device shown in FIG.

FIG. 6 is a schematic configuration diagram of an optical pickup device showing another example of the related art.

FIG. 7 is an explanatory diagram of a configuration of an error signal generation unit that generates a track error signal by a differential push-pull method using three beams and a signal generation method.

FIG. 8 is a schematic configuration diagram of an optical pickup device showing still another example of the related art.

FIG. 9 is a schematic configuration diagram of an optical pickup device showing still another example of the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Collimator lens 3 Diffraction element 4 Beam shaping prism 5 'Polarization beam splitter 6 1/4 wavelength plate 7 Objective lens 8 Optical storage medium 9 Detection lens 10 Cylindrical lens 11 Light receiving element

Claims (4)

[Claims] 1. A semiconductor laser, a diffraction element for diffracting a beam emitted by the semiconductor laser, a beam shaping means for expanding a diameter of the beam, and an objective lens for condensing the beam on an optical storage medium. In the optical pickup device, the diffraction element has a first-order or higher-order phase transfer function α · y with respect to a first-order phase transfer function α · y in a rectangular coordinate system (x, y) taking a y-axis in a diffraction separation direction. Equation (1) to which a higher-order correction term σ (x, y) is added, φ (x, y) = α · y + σ (x, y) (1) An optical pickup device characterized by the following. 2. The optical pickup device according to claim 1, wherein the beam from the semiconductor laser is diffracted and separated by the diffraction element into three beams of zero-order diffracted light and positive and negative first-order diffracted light, and the beam shaping means. An optical pickup device comprising: a main beam spot and a pair of side beam spots, which are condensed on an optical storage medium by the objective lens after the beam diameter is enlarged by the objective lens. 3. The optical pickup device according to claim 1, wherein a y-axis, which is a diffraction separation direction of the diffraction element, substantially coincides with a direction in which a beam diameter is expanded by the beam shaping unit. Optical pickup device. 4. The optical pickup device according to claim 1, wherein the correction term σ (x, y) is calculated by using the following equations (2) and ψ (x, y) using constants β and γ. ) = Β · x ² · y + γ · y ³ (2) An optical pickup device including a coma aberration correction term ψ (x, y).