JP2001249272A - Objective lens, optical pickup device, and adjusting method for optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an objective lens used for an optical pickup device using two laser light sources and having an interchangeability with reference to plural optical information recording media, capable of satisfactorily keeping coma aberration at reproducing/recording from/on both plural optical information recording media, to provide an optical pickup device including the objective lens, and to provide a method for adjusting the position of the objective lens in the optical pickup device. SOLUTION: The objective lens 16 satisfies a sine condition at the maximum numerical aperture, and also, the lens is provided with the 5th order coma aberration within a prescribed extent at the maximum numerical aperture in a specific direction with reference to a position reference part. By adjusting the 5th order coma aberration appearing at the maximum numerical aperture within a prescribed extent, the total 3rd order coma aberration as much as a prescribed amount can be obtained at the prescribed numerical aperture which is equal to or below the maximum numerical aperture. Besides, as for the optical pickup device, by controlling the 5th order coma aberration so that it may appear in the specified direction with reference to the position reference part, the objective lens is easily adjusted at assembling the objective lens in the device, and also, the objective lens is positioned with reference to the 2nd light source so that off-axial 3rd order coma aberration and the 3rd order coma aberration which is caused by providing the 5th order coma aberration of the prescribed amount at the maximum numerical aperture may counterbalance each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an objective lens used in an optical pickup device for reproducing or recording a plurality of types of optical information recording media by using two or more light sources, an optical pickup device including the objective lens, And an adjustment method of the optical pickup device.

[0002]

2. Description of the Related Art In recent years, a CD / DVD compatible type optical pickup device capable of recording and reproducing information on both DVD and CD optical information recording media with the same optical pickup device has become mainstream. There are many compatible optical pickup devices that perform recording and reproduction using a different light source for each optical information recording medium. Usually, the two light sources are respectively adjusted so as to be located at the center line of the focusing optical system. The center line of the condensing optical system means the optical axis of the objective lens when the tracking system is a single-stage system, and the light of the objective lens passes through the operation center of the fine movement tracking actuator when the tracking system is the two-stage system. It means a line parallel to the axis, and the angle changes on a reflecting surface such as a mirror. However, recently,
An optical pickup device using a light source unit in which two light sources are integrated in order to reduce the number of parts and the number of mounting steps has appeared. In this optical pickup device, since at least one light source exists at a position deviated from the center line of the light-converging optical system, off-axis coma generated due to axis deviation of the light source poses a problem.

FIG. 10 schematically shows a conventional CD / DVD compatible optical pickup device. The CD / DVD compatible optical pickup device includes a CD light source 92 and a DVD light source 91.
The light from the light source unit in which the optical information recording medium 95 is packaged by the objective lens 94 via the collimator 93.
The information is collected and / or reproduced by focusing on the top. Normal,
From the viewpoint of emphasizing DVD performance, the principal ray p of the objective lens 94
The DVD light source 91 is arranged as shown by a solid line, and the CD light source 92 deviates from the principal ray p as shown by a broken line.

Similarly, from the viewpoint of emphasizing DVD performance, DV
Since the objective lens is designed so as to satisfy the sine condition in accordance with the thickness of the transparent substrate of D, the objective lens does not satisfy the sine condition with the thickness of the transparent substrate of CD. As a result, a considerable amount of off-axis third-order coma aberration occurs for a CD.

Conventionally, an objective lens used in an optical pickup device has been mainly used when the numerical aperture is small as compared with a DVD, such as a CD. However, coma aberration when the numerical aperture is small is small. Most of the third-order coma is
The fifth-order coma is small, and attention has not been paid to the fifth-order coma.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present invention relates to an optical pickup device which uses two or more laser light sources and is compatible with a plurality of optical information recording media. To provide an objective lens capable of maintaining good coma aberration performance during reproduction or recording with respect to any of the optical information recording media, an optical pickup device including the objective lens, and a method of adjusting the optical pickup device. With the goal.

[0007]

In order to achieve the above object, the present inventors have made intensive studies and found that the fifth-order coma aberration generated when the numerical aperture of an objective lens is large and the fifth-order coma aberration generated when the numerical aperture is small Has a correlation with the third-order coma aberration, that is, if the fifth-order coma aberration generated when the numerical aperture is large, the third-order coma aberration generated when the numerical aperture is small increases. It was made based on.

When the numerical aperture is small (CD), the coma is almost a third-order coma component, and when the numerical aperture is large (DV),
In the coma aberration of D), the fifth-order coma component is added to the third-order coma component. When the fifth-order coma component of the DVD is large, the third-order coma component of the CD is also large.

The objective lens according to the present invention has a fifth-order coma in the range shown by the following equation. 0.064 (NA) ⁵ ≤ CM5 ≤ 0.39 (NA) ⁵ where NA: numerical aperture CM5: fifth-order coma aberration in NA (RMS (λ))

[0010] The aberration in the present specification is a standard deviation value (RMS) of wavefront aberration, and the unit is a wavelength (λ).

According to this objective lens, the objective is 0.064 (NA) ⁵ ≦ CM5 ≦ 0.39 (NA) ⁵ (N
A: numerical aperture, CM5: fifth-order coma at NA (RM
By manufacturing the objective lens so as to have the fifth-order coma aberration represented by S (λ)), the objective lens can have a predetermined amount of the third-order coma aberration with a predetermined numerical aperture equal to or less than the maximum numerical aperture of the objective lens. This is because, as described above, the third-order coma at a predetermined numerical aperture equal to or smaller than the maximum numerical aperture of the objective lens has a correlation with the fifth-order coma. By providing the objective lens with a predetermined amount of tertiary coma caused by fifth-order coma aberration, it is possible to obtain other parameters such as off-axis tertiary coma generated at a predetermined numerical aperture when the objective lens is used in an optical pickup device or the like. Can be eliminated, and the total tertiary coma at a predetermined numerical aperture can be reduced. In addition, the total third-order coma aberration in this specification refers to three-dimensional coma aberration of the entire condensing optical system.
This is the sum of the next coma.

At this time, the fifth-order coma aberration is 0.064 (N
A) If it is ⁵ or less, the third-order coma aberration component at a predetermined numerical aperture equal to or less than the maximum numerical aperture is small, and it is not possible to sufficiently eliminate off-axis third-order coma. In addition, the fifth-order coma aberration is 0.
If it is more than 39 (NA) ⁵ , on the contrary, the third-order coma aberration component at a predetermined numerical aperture less than the maximum numerical aperture becomes too large, and the off-axis third-order coma aberration at the predetermined numerical aperture less than the maximum numerical aperture. Even if these are eliminated, they remain as third-order coma aberration.

It is preferable that the objective lens has a display section for displaying a direction having fifth-order coma aberration. This facilitates adjustment when incorporating the objective lens into the device. This display section may be formed in the direction having the fifth-order coma of the objective lens, or by arranging that it has the fifth-order coma in a specific direction from the gate position, for example, by setting the gate position of the objective lens. May be used as the display unit. This display section cuts the objective lens, marks it with a pen, etc.
Any method can be used as long as the direction in which the objective lens has the fifth-order coma aberration when the lens is attached to the apparatus is known. Note that the sign of coma aberration in this specification is defined by FIG.

The above-mentioned objective lens is suitable for an optical pickup device for recording and / or reproducing information on at least two types of optical information recording media having different thicknesses of transparent substrates.

In the optical pickup device according to the present invention, a light beam from a light source is condensed on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system including an objective lens to record information. An optical pickup device configured to perform reproduction and / or to perform recording and / or reproduction of information on at least two types of optical information recording media having different thicknesses of transparent substrates, wherein a first light source having a wavelength λ ₁ is provided. A second light source having a wavelength λ ₂ , and a photodetector that receives a transmitted light or a reflected light of the light flux emitted from the first light source and the second light source from the optical information recording medium, The necessary numerical aperture on the optical information recording medium side of the condensing optical system required for recording and / or reproducing information on the optical information recording medium ₁ with light of wavelength λ ₁ is NA _1.
The required numerical aperture on the optical information recording medium side of the condensing optical system required for recording and / or reproducing the second optical information recording medium with light of wavelength λ ₂ is NA ₂ (where NA ₂ < N
A ₁ ), and the total third-order coma at the numerical aperture NA ₂ is 0.1.
02 (RMS (λ ₂ )) or less.

According to the optical pickup device, the numerical aperture NA
_{By making} the total tertiary coma aberration at 0.02 or less to 0.02 (RMS (λ ₂ )) or less, troubles during recording or reproduction on the second optical information recording medium can be reduced.

In another optical pickup device according to the present invention, a light beam from a light source is condensed on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system including an objective lens. It is configured to perform recording and / or reproducing, a recording and / or an optical pickup apparatus for reproducing information of the thickness of the transparent substrate at least two different optical information recording medium, the first wavelength lambda ₁ , A _second light source having a wavelength of λ ₂ , and a photodetector that receives transmitted light or reflected light of an emitted light beam from the first light source and the second light source from an optical information recording medium. The required aperture on the optical information recording medium side of the condensing optical system necessary for recording and / or reproducing the first optical information recording medium with light of wavelength λ ₁ is NA _1.
The required numerical aperture on the optical information recording medium side of the condensing optical system required for recording and / or reproducing the second optical information recording medium with light of wavelength λ ₂ is NA ₂ (where NA ₂ < N
A ₁ ), and the objective lens is in a range of 5 represented by the following equation.
It is characterized by having secondary coma. ^{_{0.064 (NA 1) 5 ≦ CM5}} 1 ≦ 0.39 (NA 1) 5 However, CM5 _1: 5 order coma aberration at NA ₁ (RMS
(Λ ₁ ))

According to this optical pickup device, the fifth-order coma aberration at the numerical aperture NA ₁ of the objective lens used in the optical pickup device is adjusted to a predetermined range.
A predetermined amount of third-order coma can be provided by the numerical aperture NA ₂ . This is because the fifth-order coma aberration at the numerical aperture NA _1, that there is a correlation between the third-order coma aberration at the numerical aperture NA _2. Thus, by using the optical pickup device an objective lens having a third-order coma aberration of a predetermined amount in the numerical aperture NA _2, other 3 of off-axis third-order coma aberration and the like generated by the numerical aperture NA ₂ of the optical pickup device The second-order coma aberration can be eliminated, and the total tertiary coma aberration at the numerical aperture NA ₂ can be reduced as the entire optical pickup device.

In still another optical pickup device according to the present invention, a light beam from a light source is condensed on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system including an objective lens. It is configured to perform a recording and / or reproducing, a recording and / or an optical pickup apparatus for reproducing information of an optical information recording medium thickness of at least 2 kinds different transparent substrate, the wavelength lambda ₁ second A first light source, a _second light source having a wavelength λ ₂ , and a photodetector that receives transmitted light or reflected light of the light flux emitted from the first light source and the second light source from the optical information recording medium. The required numerical aperture on the optical information recording medium side of the condensing optical system required for recording and / or reproducing the first optical information recording medium with light of wavelength λ ₁ is NA ₁ , an information recording medium for recording and / or reproducing with light having a wavelength lambda ₂ The necessary numerical aperture on the optical information recording medium side of the converging optical system necessary to NA ₂ (However, NA ₂ <N
A ₁ ), the objective lens satisfies the sine condition with respect to the light flux from the first light source of λ ₁ and the first optical information recording medium, and has a fifth-order coma aberration;
When the thickness of the transparent substrate of the optical information recording medium is t ₁ , and the thickness of the transparent substrate of the second optical information recording medium is t ₂ ,
If t ₂ > t ₁ , the second position from the center line of the focusing optical system
The objective lens and the second light source are positioned such that an angle between a shift direction of the light source and a direction having the fifth-order coma aberration of the objective lens is within a range of 0 ° ± 30 °, When t ₁ > t _2, the angle between the direction in which the second light source deviates from the center line of the condensing optical system and the direction in which the objective lens has fifth-order coma is in a range of 180 ° ± 30 °. The objective lens and the second light source are positioned so as to be inside.

According to this optical pickup device, it is usually difficult to maintain good aberration performance as the numerical aperture is large. Therefore, the light from the first light source of λ ₁ and the thickness t ₁ of the transparent substrate of the transparent substrate are difficult to maintain. It is preferable that the sine condition is satisfied for one optical information recording medium. When the objective lens satisfies the sine condition with respect to the light from the first light source of λ ₁ and the first optical information recording medium with the thickness t ₁ of the transparent substrate, the second light source of λ ₂ is focused. Unless it coincides with the center line of the optical system, an off-axis third-order coma aberration occurs in the second optical information recording medium having the thickness t ₂ (2t ₁ ) of the transparent substrate. When t ₁ > t ₂ , when the second light source is viewed from the objective lens, a third-order coma aberration due to the fifth-order coma occurs in a direction opposite to a direction in which the second light source is located. For this reason, the same direction (0 ° ± 30 °) as the direction in which the second light source is shifted from the center line of the focusing optical system is used.
By setting the objective lens in the optical pickup device with the direction of the fifth-order coma adjusted so as to satisfy (°), off-axis third-order coma can be eliminated. When t ₂ > t ₁ , when the second light source is viewed from the objective lens, a third-order coma aberration due to the fifth-order coma occurs in the same direction as the direction in which the optical axis of the second light source exists. Therefore, by installing the objective lens in the optical pickup device by aligning the fifth direction with the fifth direction so that the second light source is in the opposite direction (180 ° ± 30 °) to the direction in which the second light source is located, off-axis The third-order coma can be eliminated, and the total third-order coma at the numerical aperture NA ₂ can be reduced.

In this case, it is preferable that the fifth-order coma has a fifth-order coma in a range represented by the following equation. ^{_{0.064 (NA 1) 5 ≦ CM5}} 1 ≦ 0.39 (NA 1) 5 However, CM5 _1: 5 order coma aberration at NA ₁ (RMS
(Λ ₁ ))

It is preferable from the viewpoint of the performance of the optical pickup device that the first light source of the optical pickup device is disposed so as to coincide with the center line of the light collecting optical system.

Further, since the objective lens used in the optical pickup device has a display portion indicating a direction having fifth-order coma aberration, adjustment when the objective lens is incorporated in the device becomes easy.

In still another optical pickup device according to the present invention, a light beam from a light source is condensed on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system including an objective lens. It is configured to perform a recording and / or reproducing, a recording and / or an optical pickup apparatus for reproducing information of an optical information recording medium thickness of at least 2 kinds different transparent substrate, the wavelength lambda ₁ second A first light source, a _second light source having a wavelength of λ ₂ , and a light detector that receives transmitted light or reflected light from an optical information recording medium located east of the light emitted from the first light source and the second light source. Wherein the required numerical aperture on the optical information recording medium side of the condensing optical system necessary for recording and / or reproducing the first optical information recording medium with light of wavelength λ ₁ is NA ₁ , and recording and / or reproducing an optical information recording medium with light having a wavelength lambda ₂ The optical information recording medium side necessary opening致of the light converging optical system necessary to NA ₂ (However, NA ₂ <N
A ₁ ), the objective lens satisfies the sine condition for the light from the first light source having the wavelength λ ₁ and the first optical information recording medium, and the second light source The objective lens and the second light source are positioned so as to coincide with the center of the optical system of the system.

According to this optical pickup device, the objective lens used in the optical pickup device has an off-axis coma aberration in the second optical information recording medium because the second light source is located at the center line of the focusing optical system. Does not occur. Further, since the sine condition is satisfied for the light from the first light source of λ ₁ and the first optical information recording medium, even if the first light source does not coincide with the center line of the condensing optical system, Off-axis coma in the first optical information recording medium is suppressed. Thereby, the first
In addition, off-axis coma aberration in the second optical information recording medium can be suppressed.

Further, the first light source and the second light source can be unitized, and the optical pickup device can be made compact.

Further, in the method of adjusting an optical pickup device according to the present invention, a light beam from a light source is condensed on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system including an objective lens. consists of a recording and / or to perform reproduction, recording and / or performs the reproduction of the information of the thickness of the transparent substrate at least two different optical information recording medium, a first light source of the wavelength lambda _1, optical pickup device comprising a second light source of the wavelength lambda _2, and a photodetector for receiving the transmitted or reflected light from the optical information recording medium of the emitted light flux from the first light source and the second light source Wherein the required numerical aperture of the converging optical system on the optical information recording medium side required for recording and / or reproducing the first optical information recording medium with light of wavelength λ ₁ is NA _1. , the second optical information recording medium with light having a wavelength lambda ₂ Recording and / or the necessary numerical aperture on the optical information recording medium side of the converging optical system necessary for reproducing NA ₂ (However, NA ₂ <NA ₁₎ and said objective lens is in the range represented by the following formula The objective lens is positioned so as to have fifth-order coma and to reduce the total third-order coma at the numerical aperture NA ₂ . _{0.064 (NA 1) ≦ CM5 1} ≦ 0.39 (NA 1) 5 However, CM5 _1: 5 order coma aberration at NA ₁ (RMS
(Λ ₁ ))

According to this method of adjusting the optical pickup device, the objective lens used in the optical pickup device has a predetermined amount of fifth-order coma at a numerical aperture NA ₁ ,
By utilizing the fact that having a third-order coma aberration of a predetermined amount by the numerical aperture NA _2, rotating the lens so cancel out the off-axis third-order coma aberration at the numerical aperture NA _2, by positioning the like angle adjustment The total third-order coma at the numerical aperture NA ₂ of the optical pickup device can be reduced.

In another adjustment method for an optical pickup device according to the present invention, a light beam from a light source is condensed on an information recording surface via a transparent substrate of an optical information recording medium by a condensing optical system including an objective lens. Te is configured to perform recording and / or reproducing information, the thickness of the transparent substrate at least two different optical惰報recording medium recording and / or performs the reproduction of the information, the wavelength lambda ₁ of the first A light source, a _second light source having a wavelength of λ ₂ , and a photodetector that receives transmitted light or reflected light of an emitted light beam from the first light source and the second light source from an optical information recording medium. a method of adjusting an optical pickup device, the necessary numerical aperture on the optical information recording medium side of the converging optical system necessary for recording and / or reproducing the first optical information recording medium wavelength lambda ₁ of the light and NA _1, the second optical information recording medium of the wavelength lambda ₂ In recording and / or necessary numerical aperture on the optical information recording medium side of the converging optical system necessary for reproducing NA ₂ (However, NA ₂ <NA ₁₎ and said objective lens, the wavelength lambda ₁ The luminous flux from the first light source and the first optical information recording medium satisfy a sine condition and have fifth-order coma, and the thickness of the transparent substrate of the first optical information recording medium is t. ₁ , when the thickness of the transparent substrate of the second optical information recording medium is t _2, and when t ₂ > t ₁ , the direction of displacement of the second light source from the center line of the condensing optical system Positioning the objective lens and the second light source such that the angle between the objective lens and the direction having the fifth-order coma aberration is within the range of 0 ° ± 30 °, and when t ₁ > t ₂ Has a shift direction of the second light source from the center line of the condensing optical system and a fifth-order coma aberration of the objective lens. Wherein the angle between the direction to position said objective lens and the second light source so as to be in the range of 180 ° ± 30 °.

According to the method for adjusting the optical pickup device, the objective lens used in the optical pickup device is λ ₁
Sine conditions are satisfied for the light from the first light source and the first optical information recording medium, and the transparent substrate thickness t ₁ of the first optical information recording medium and the transparent substrate of the second optical information recording medium Thickness t ₂
However, when t ₂ > t ₁ , when the second light source is viewed from the objective lens, off-axis third-order coma aberration is shifted in a direction in which the second light source is displaced from the center line of the focusing optical system. From what happens,
The objective lens is installed in the optical pickup device by adjusting the direction of the fifth-order coma aberration so that the second light source is in the same direction (0 ° ± 30 °) as the direction deviated from the center line of the condensing optical system. Accordingly, off-axis third-order coma can be canceled by third-order coma caused by fifth-order coma. t
_1> if the t ₂ is the off-axis third-order coma aberration on the side opposite to the direction in which the second light source is deviated from the center line of the focusing optical system when viewed a second light source from the objective lens From what happens,
The direction opposite to the direction in which the second light source is located (180 ° ± 30 °)
By setting the objective lens in the optical pickup device so that the direction of the fifth-order coma aberration is adjusted so as to satisfy (°), the off-axis third-order coma aberration can be eliminated, and the total third order at the aperture NA ₂ Coma can be reduced.

In this case, the fifth-order coma can have the fifth-order coma within the range shown by the following equation. ^{_{0.064 (NA 1) 5 ≦ CM5}} 1 ≦ 0.39 (NA 1) 5 However, CM5 _1: 5 order coma aberration at NA ₁ (RMS
(Λ ₁ ))

Preferably, the first light source is positioned such that the first light source substantially coincides with the center line of the light-collecting optical system.

It is preferable that the objective lens is provided with a display section indicating a direction having the fifth-order coma aberration, and the display section is used as a reference for the positioning.

It is preferable that the first light source and the second light source are unitized.

The condensing optical system in the present invention is one or more sets of optical systems capable of recording or reproducing, for example, CDs and DVDs, and records information on an optical information recording medium. And / or may mean not only the entire optical system for enabling information on the optical information recording medium to be reproduced, but also a part of the optical system, including an objective lens.

The optical information recording medium of the present invention includes, for example, various CDs such as CD, CD-R, CD-RW, CD-Video, and CD-ROM, DVD, DVD-ROM, DVD-RAM, and DVD. -R, DVD-RW, DV
Various types of DVDs such as D-RW and DVD + RW, and disc-shaped optical information recording media such as MDs can be used. Generally, a transparent substrate exists on an information recording surface of an optical information recording medium.

Recording and reproducing information on and from the optical information recording medium means recording information on the information recording surface of the optical information recording medium and reproducing the information recorded on the information recording surface. That means. The condensing optical system according to the present invention may be used for performing only recording or reproduction, or may be used for performing both recording and reproduction. Further, it may be used for performing recording on a certain optical information recording medium and performing reproduction on another optical information recording medium, or may be used for performing reproduction on a certain optical information recording medium. May be used to perform recording and / or reproduction and to perform recording and reproduction on another optical information recording medium. Note that reproduction here includes simply reading information.

In the present invention, the first light source (wavelength λ ₁ ) and the second light source (wavelength λ ₂ ) emit light having wavelengths having a sufficient wavelength difference from each other. The light having different wavelengths from the first and second light sources may be, for example, different in the thickness of the transparent substrate of the optical information recording medium in addition to the difference in the type and the recording density of the optical information recording medium. It is used for the difference between recording and reproduction.

In a narrow sense, an objective lens is a state in which an optical information recording medium is loaded in an optical pickup device.
At the position closest to the optical information recording medium, it refers to a single lens having a light-condensing action arranged to face the lens. In a broad sense, together with the lens, a lens group that can be actuated at least in the optical axis direction by an actuator Shall be referred to.
Here, such a lens group refers to at least one or more lenses, and includes a lens composed of only a single lens. Therefore, in this specification, the numerical aperture NA of the objective lens on the optical information recording medium side refers to the numerical aperture NA of the lens surface of the objective lens closest to the optical information recording medium. Further, the numerical aperture NA is substantially equal to the luminous flux from the light source to be used by devising a part or member having a diaphragm function such as a diaphragm or a filter provided in the optical pickup device or a shape of a step formed in the objective lens. Is the numerical aperture NA defined as a result of the limitation.

[0040]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an optical path diagram showing a schematic configuration of an optical pickup device showing an embodiment of the present invention, and FIG. 2 is a plan view of the objective lens of FIG. 1 when viewed from the optical information recording medium side. It is.

The optical pickup device shown in FIG. 1 reads information from the information recording surface of each of the optical information recording media, for example, CDs and DVDs by using light having wavelengths of 650 nm and 780 nm from the first and second light sources, respectively. It is configured as follows.

As shown in FIG. 1, the optical pickup device has a D
A first semiconductor laser 111 that emits light of wavelength 650 nm for VD and a second semiconductor laser 112 that emits light of wavelength 780 nm for CD are unitized as light sources. A beam splitter 120 is disposed between the collimator 13 and the objective lens 16, and the collimator 1
The light almost collimated in 3 passes through the beam splitter 120 and goes to the objective lens 16. Further, the optical path is changed so that the light flux reflected from the information recording surface 22 of the optical disk 20 having the transparent substrate 21 is directed to the photodetector 30 by the beam splitter 120 as an optical path changing means. Objective lens 16
Has a flange portion 16a on the outer periphery thereof, and the objective lens 16 can be easily attached to the optical pickup device by the flange portion 16a. Also, the flange portion 16a
Has a surface extending in a direction substantially perpendicular to the optical axis of the objective lens 16, so that mounting with higher precision can be easily performed.

When reproducing the first optical disk (DVD), the light beam emitted from the first semiconductor laser 111 passes through the collimator 13 and becomes a parallel light beam, as shown by the solid line in the figure. Further, the aperture is stopped down by a stop 17 via a beam splitter 120, and the first optical disc 2 is stopped by an objective lens 16.
The light is condensed on the information recording surface 22 through the transparent substrate 21 of No. 0. The light flux modulated and reflected by the information pits on the information recording surface 22 is reflected again by the beam splitter 120 via the objective lens 16 and the aperture 17, is given astigmatism by the cylindrical lens 180, and is given a concave lens 50. After that, the light is incident on the photodetector 30 and the photodetector 30
A signal for reading information recorded on the first optical disk 20 is obtained using the signal output from the first optical disk 20.

Further, by detecting a change in the light amount due to a change in the shape and position of the spot on the photodetector 30, focus detection and track detection are performed. Based on this detection, the two-dimensional actuator 150 moves the objective lens 16 so that the light beam from the first semiconductor laser 111 forms an image on the information recording surface 22 of the first optical disk 20, and the first semiconductor laser Moving the objective lens 16 so that the light beam from the laser 111 is focused on a predetermined track;

Next, when reproducing the second optical disk (CD), the second semiconductor laser 112 is reproduced as shown by the broken line in FIG.
Are transmitted through the collimator 13 and become parallel light beams. Further, the stop 1 is passed through the beam splitter 120.
Then, the light is focused by the objective lens 16 and focused on the information recording surface 22 via the transparent substrate 21 of the second optical disc 20 by the objective lens 16. The light flux modulated and reflected by the information pits on the information recording surface 22 is again reflected by the objective lens 16 and the aperture 1.
7, reflected by the beam splitter 120, given astigmatism by the cylindrical lens 180, passed through the concave lens 50, incident on the photodetector 30, and using a signal output from the photodetector 30, Second optical disk 2
A read signal of the information recorded in 0 is obtained. Also,
A change in the amount of light due to a change in the shape and position of the spot on the photodetector 30 is detected to perform focus detection and track detection. Based on this detection, the two-dimensional actuator 150 forms an image of the light beam from the second semiconductor laser 112 on the information recording surface 22 of the second optical disc 20 by using the objective lens 1.
6 is moved, and the objective lens 16 is moved so that the light beam from the second semiconductor laser 112 is focused on a predetermined track.

As shown in FIGS. 1 and 2, the principal ray p of the light beam from the first semiconductor laser 111 coincides with the center of the optical system as shown by the solid line in FIG.
Is shifted from the center of the optical system as indicated by the broken line in FIG. Note that the principal ray means a ray at the center of a light beam passing through an aperture such as a diaphragm.

The objective lens 16 has a predetermined amount of fifth-order coma at the maximum numerical aperture. In the objective lens 16, by adjusting the fifth-order coma appearing at the maximum numerical aperture to a predetermined range, a predetermined amount of the third-order coma can be provided at a predetermined numerical aperture equal to or less than the maximum numerical aperture.

Next, the objective lens 16 is in the circumferential direction of FIG. Position adjustment will be described with reference to FIG. The objective lens 16 has a position reference portion 16b in which a part of a circular body is cut linearly in a chord direction, and the fifth-order coma aberration is directed from the center of the objective lens 16 (coincident with the principal ray p) to the direction m in FIG. have.

In this specification, the sign of the coma is defined as shown in FIG. If the optical information recording medium with a small numerical aperture is thicker than the optical information recording medium at the maximum numerical aperture, the objective is set so that the principal ray p ′ from the semiconductor laser 112 is located in the same direction n as the direction m. The position of the lens 16 in the circumferential direction is determined and fixed.

As described above, the objective lens 16 is located at a position where the third-order coma at a predetermined numerical aperture equal to or less than the maximum numerical aperture caused by off-axis third-order coma and fifth-order coma having the maximum numerical aperture cancels out. Positioning can be performed, and the total third-order coma of the objective lens when the numerical aperture is small can be improved.

In this case, the direction n is 0 ° ± 30 from the direction m.
Within the range of °, the total third-order coma can be improved, and there is no practical problem. In addition, by manufacturing the objective lens 16 such that the direction m having the fifth-order coma aberration and the position reference portion 16b have a fixed relationship, if the objective lens 16 is attached with the position reference portion 16b as a reference, the direction n The chief ray p ′ from the second semiconductor laser 112 can be positioned at the position. Note that the above-described position adjustment can also be performed by adjusting the position on the semiconductor laser 112 side. However,
When the position of the semiconductor laser 112 is changed, it is necessary to adjust the position of the photodetector accordingly.

Next, the objective lens 16 will be described.
The objective lens 16 has two aspheric surfaces on both sides. The coma of the objective lens will be described. FIG.
When the Zernike expansion is performed in the coordinate system shown in, the Zernike polynomial relating to coma aberration is limited to the following three terms shown in Expression 1 when including the fifth order of coma aberration.

[0053]

(Equation 1) The wavefront aberration _WCM (ρo) due to these three terms is
It is represented as

[0054]

(Equation 2) Here, assuming that the variable in the coordinate system when the aperture diameter is a times smaller is ρ (−1 ≦ ρ ≦ 1) as shown in FIG. 4, the wavefront aberration _WCM (ρo = aρ) is expressed by the following equation (3). Is done.

[0055]

(Equation 3) When this expression is rearranged for ρ, the following Expression 4 is obtained.

[0056]

(Equation 4) As a result, the Zernike coefficient in the coordinate system when the aperture diameter is a times smaller is as shown in the following Expression 5.

[0057]

(Equation 5) DVD layout (NA0.6) and CD layout (NA0.45)
The aperture diameter ratio of a = 0.45 / 0.6 = 0.75
Therefore, the fifth-order coma in the CD arrangement is a5 = 0.24 times the fifth-order coma in the DVD arrangement. 4a contributions fifth-order coma aberration fifth-order coma aberration in DVD disposed leads to third order coma aberration in the CD located ⁵ -4a ³ = -0.7
4 times. Therefore, the fifth-order coma aberration in the DVD arrangement is reduced to about 1/4 in the CD arrangement, and a third-order coma aberration having a magnitude of about 3/4 of the fifth-order coma is generated.

The wavefront aberration can be expressed in polar coordinates using a Zernike polynomial. (FIG. 11) The radius is normalized on the aperture, and any point in the aperture is represented by polar coordinates (ρ, θ) (0 ≦ ρ ≦ 1, 0 ≦ θ <2π). The wavefront aberration W (ρ, θ) is developed as shown in the following Expression 6 using the Zernike polynomial.

[0059]

(Equation 6) A mode number j is defined to determine a consistent order separately from n and m. Table 1 shows the relationship between j and n, m.

[0060]

[Table 1] A _nm and A _nm are calculated using the Gram-Schmidt orthogonalization method. Among them, the term of m = 1 is a term related to the coma aberration as in the following Expression 7.

[0061]

(Equation 7) A _nm, contribution W _nm on the standard deviation of each term and the wavefront aberration of A _nm, the relationship between the W _nm are shown in the following equation 8.

[0062]

(Equation 8) The standard deviation value W _CM3 of the third-order coma aberration and the standard deviation value W _CM5 of the fifth-order coma aberration are calculated as in the following _Expression 9.

[0063]

(Equation 9) The direction θ _CM3 of the third-order coma aberration and the direction θ _CM5 of the fifth-order coma aberration are calculated as in the following Expression 10.

[0064]

(Equation 10) Next, the off-axis coma will be described. When the object point is located away from the optical axis, coma aberration generally occurs,
This coma is called off-axis coma. However, in the case of an optical system that satisfies the sine condition, coma does not occur at an object point near the axis.

The sine condition will be described. A coordinate system is defined as shown in FIG. 5, and it is assumed that the object point P ₀ and the image point P1 are on a plane where Z ₀ = 0 and Z ₁ = 0, respectively. P0, P1
Where x ₀ = 0 and x ₁ = 0, respectively, the sine condition is represented by the following equation (1).

N ₁ y ₁ sin γ ₁ = n ₀ y ₀ sin γ ₀ (1) where n ₀ , n ₁ are the refractive indexes of the object and the image, y ₀ ,
y ₁ is the y coordinate of the object and the image, and γ ₀ , γ ₁ are the angles formed by the rays passing through O ₀ , O ₁ with the z axis.

As shown in FIG. 6, when the object point is at infinity, the height at which the incident ray parallel to the optical axis intersects the first surface is h _0.
Then, the sine condition is transformed into the following equation (2).

H ₀ / sin γ ₁ = f ₁ (2) where f1 is the focal length on the image side.

[0069]

Next, an example of an objective lens which can be used in the optical pickup device according to the embodiment of the present invention will be described.

Both surfaces of the objective lens are formed in an aspherical shape represented by the following equation (3).

Z = (H ² / r ² ) / (1 + √ (1- (1 + κ) H ² / r ² )) + A 2 · H ² + A 4 · H ⁴ + A 6 · H ⁶ + (3) , A2, A4, A6,...: Aspherical surface coefficient H: height from optical axis κ: conical coefficient r: paraxial radius of curvature

Tables 2, 3 and 4 show lens data in this embodiment.

[0073]

[Table 2]

[Table 3]

[Table 4] The data of the collimating lens (Table 2) is described from the objective lens side. CD for the above objective lens
The total remaining third-order coma in the case of the arrangement was calculated as follows.

That is, in the optical system as shown in FIG. 7, data of an objective lens in which coma (third and fifth order) is present in a DVD arrangement is created, and lens tilt is performed to correct third order coma. , The value of the remaining third-order coma aberration in the case of the CD arrangement was calculated.

First, the DVD arrangement (disc thickness = 0.6 m)
m, λ ₁ = 650 nm, NA ₁ = 0.6) Lens data in which the fifth-order coma is in the range of −0.015 to +0.015 λrms and the third-order coma is in the range of −0.02 to +0.02 λrms It was created. The sign of the coma is shown in FIG.
It is defined as follows.

Next, lens tilt was performed in the DVD arrangement, and the third-order coma was corrected to be zero.

Next, as an example where the CD light source is off-axis,
Arrangement (disk thickness = 1.2 mm, λ _Two= 780 nm, N
A_Two= 0.452, object height (distance between light source and optical axis) =
0.1 mm) to calculate the third-order coma aberration. Table 5 shows
The results are shown. The fifth-order coma aberration in the DVD arrangement is +0.
Total third-order coma in CD arrangement when 01λ is present
Has been corrected to almost zero. Total third-order coma of CD arrangement
If you try to keep the size of 0.005λrms or less
In this case, the fifth-order coma aberration in the DVD arrangement is + 0.005λ.
rm = to + 0.015λrms
is good. Attach the objective lens to the optical pickup device
At the time, the direction of fifth-order coma aberration in DVD arrangement is CD light
Mount so that it is oriented in the same direction as the source axis misalignment
As a result, C caused by fifth-order coma aberration in the DVD arrangement
CD due to third-order coma aberration and light source misalignment in D arrangement
Off-axis third-order coma in the arrangement cancels each other
In addition, the total third-order coma aberration in the CD arrangement is reduced. Further
The value of the fifth-order coma aberration in the DVD arrangement is within a predetermined range.
If you use the objective lens at
Optical pickup so that coma is within a certain value
Can be provided.

[Table 5]

Contrary to the embodiment, the thickness of the first optical information recording medium for recording and / or reproducing at the numerical aperture NA ₁ is equal to the numerical aperture N.
A ₂ (where NA ₂ <NA ₁ ), which is thicker than the second optical information recording medium for recording and / or reproducing, and when the sine condition is satisfied when recording and / or reproducing the first optical information recording medium, The direction of the axis shift of the light source used when recording and / or reproducing the second optical information recording medium and the direction of the tertiary coma generated by the axis shift are opposite by 180 °.
Therefore, when the direction of the fifth-order coma aberration at NA ₁ and the axis shift direction of the second light source are opposite by about 180 °, the total third-order coma aberration when recording and / or reproducing the second optical information recording medium is reduced. It is reduced.

Next, another embodiment of the present invention will be described with reference to FIG. FIG. 9 is an optical path diagram schematically showing an optical pickup device. In this optical pickup device, light from a light source unit in which a CD light source 52 and a DVD light source 51 are packaged in one package is passed through an objective lens via a collimator 53. At 54, information is reproduced or recorded by focusing on the optical information recording medium 55.

The principal ray r 'of the light beam from the DVD light source 51 is deviated from the center line of the condensing optical system as shown by the broken line in FIG.
The principal ray r of the light beam from the CD light source 52 coincides with the center line of the condensing optical system as shown by the solid line in the figure.

According to the optical pickup device described above, the CD
Since the position of the light source 52 coincides with the center line of the condensing optical system,
Since off-axis coma does not occur during recording and / or reproduction of a CD, and the objective lens satisfies the sine condition during recording and / or reproduction of a DVD, the occurrence of off-axis coma is suppressed. Therefore, CD and DVD recording and / or
Alternatively, the total coma can be improved during reproduction.

As described above, the present invention has been described with reference to the embodiment and the examples. However, the present invention is not limited to these, and various modifications can be made within the technical idea of the present invention. . For example, an optical information recording medium is a CD / DVD
It is needless to say that the optical information recording medium of the next generation may have a higher recording density.

[0083]

According to the present invention, at least two laser light sources are used in an optical pickup device compatible with a plurality of optical information recording media, and reproduction or recording is performed on any of the plurality of optical information recording media. An objective lens capable of maintaining good coma aberration performance at the time, an optical pickup device including the objective lens, and a method of adjusting the position of the objective lens in the optical pickup device can be provided.

[Brief description of the drawings]

FIG. 1 is an optical path diagram illustrating a schematic configuration of an optical pickup device according to an embodiment of the present invention.

FIG. 2 is a plan view of the objective lens of FIG. 1 when viewed from the optical information recording medium side.

FIG. 3 is a diagram illustrating a coordinate system for explaining coma of the objective lens of FIG. 1;

FIG. 4 is a diagram showing a coordinate system when an aperture diameter is smaller by a times in FIG. 3;

FIG. 5 is a diagram for explaining a sine condition in the present embodiment.

FIG. 6 is a diagram for explaining a sine condition when an object point is at infinity in FIG. 5;

FIG. 7 is a diagram showing an optical system for explaining coma aberration in the present embodiment.

FIG. 8 is a diagram for explaining signs of coma aberration in the present embodiment.

FIG. 9 is a schematic optical path diagram of an optical pickup device showing another embodiment of the present invention.

FIG. 10 is a schematic optical path diagram of a conventional optical pickup device.

FIG. 11 is a diagram for describing polar coordinates in the present embodiment.

[Explanation of symbols]

16 Objective lens 16b Position reference part m Direction from the origin of the fifth-order coma aberration of the objective lens n Direction from the origin of the second light source p Principal ray of light beam from the first semiconductor laser p 'From the second semiconductor laser 20 optical information recording medium 22 information recording surface 30 photodetector 111 (first light source) 112 second semiconductor laser (second light source) 51 DVD light source (first light source) 52 CD light source ( (Second light source) 54 Objective lens 55 Optical information recording medium r Principal ray of light flux from CD light source r 'Principal ray of light flux from DVD light source

Claims (17)

[Claims] 1. An objective lens having fifth-order coma aberration in a range represented by the following expression. 0.064 (NA) ⁵ ≤ CM5 ≤ 0.39 (NA) ⁵ where NA: numerical aperture CM5: fifth-order coma aberration in NA (RMS (λ)) 2. The objective lens according to claim 1, wherein a display unit that indicates a direction having the fifth-order coma aberration is formed. 3. The optical pickup device according to claim 1, wherein the transparent substrate is used as an objective lens of an optical pickup device for recording and / or reproducing information on at least two types of optical information recording media having different thicknesses. The objective lens as described. 4. Condensing a light beam from a light source including an objective lens
The optical system records information through the transparent substrate of the optical information recording medium.
Recording and / or reproducing information by focusing on the recording surface
And at least two types of transparent substrates having different thicknesses
For recording and / or reproducing information on an optical information recording medium
A pickup device, the wavelength λ₁A first light source of wavelength λ_TwoA second light source; and light beams emitted from the first light source and the second light source.
Optical detector that receives transmitted light or reflected light from an information recording medium
A first optical information recording medium having a wavelength λ₁Recording and / or
Optical information recording medium of the condensing optical system required for reproduction
The required numerical aperture on the side is NA₁And the second optical information recording medium has a wavelength λ_TwoRecording and / or
Optical information recording medium of the condensing optical system required for reproduction
The required numerical aperture on the side is NA_Two(However, NA_Two<NA ₁)When
And the numerical aperture NA_TwoIs 0.02 (RM
S (λ_Two)) An optical pickup characterized by the following:
Device. 5. Condensing a light beam from a light source including an objective lens
The optical system records information through the transparent substrate of the optical information recording medium.
Recording and / or reproducing information by focusing on the recording surface
And at least two types of transparent substrates having different thicknesses
For recording and / or reproducing information on an optical information recording medium
A pickup device, the wavelength λ₁A first light source of wavelength λ_TwoA second light source; and light beams emitted from the first light source and the second light source.
Optical detector that receives transmitted light or reflected light from an information recording medium
A first optical information recording medium having a wavelength λ₁Recording and / or
Optical information recording medium of the condensing optical system required for reproduction
Necessary opening teaching on the side of NA₁And the second optical information recording medium has a wavelength λ_TwoRecording and / or
Optical information recording medium of the condensing optical system required for reproduction
The required numerical aperture on the side is NA_Two(However, NA_Two<NA ₁)When
And the objective lens has a fifth-order coma aberration in a range represented by the following equation.
An optical pickup device comprising: 0.064 (NA₁)^Five≤CM5₁≤0.39 (NA₁)^Five However, CM5₁: NA₁Fifth-order coma (RMS
(Λ₁)) 6. Condensing a light beam from a light source including an objective lens
The optical system records information through the transparent substrate of the optical information recording medium.
Recording and / or reproducing information by focusing on the recording surface
And at least two types of transparent substrates having different thicknesses
For recording and / or reproducing information on an optical information recording medium
A pickup device, the wavelength λ₁A first light source of wavelength λ_TwoA second light source; and light beams emitted from the first light source and the second light source.
Optical detector that receives transmitted light or reflected light from an information recording medium
A first optical information recording medium having a wavelength λ₁Recording and / or
Optical information recording medium of the condensing optical system required for reproduction
The required numerical aperture on the side is NA₁And the second optical information recording medium has a wavelength λ_TwoRecording and / or
Optical information recording medium of the condensing optical system required for reproduction
The required numerical aperture on the side is NA_Two(However, NA_Two<NA ₁)When
And the objective lens is the λ₁Flux from the first light source of
And sine conditions are satisfied for the first optical information recording medium.
And the thickness of the transparent substrate of the first optical information recording medium is t₁,Previous
The thickness of the transparent substrate of the second optical information recording medium is t_TwoMade
Sometimes t_Two> T₁In the case of
The direction of displacement of the second light source and the fifth order frame of the objective lens
The angle between the direction having the aberration and the angle within the range of 0 ° ± 30 °
The objective lens and the second light source are positioned so that
And t₁> T_TwoIn the case of, the center line of the focusing optical system
The direction of displacement of the second light source from
180 ° ± 30 ° with the direction having the next coma
The objective lens and the second light source so as to fall within the range of
Optical pickup characterized in that
Device. 7. The optical pickup device according to claim 6, wherein the fifth-order coma has a fifth-order coma in a range represented by the following equation. ^{_{0.064 (NA 1) 5 ≦ CM5}} 1 ≦ 0.39 (NA 1) 5 However, CM5 _1: 5 order coma aberration at NA ₁ (RMS
(Λ ₁ )) 8. The objective lens and the first light source are positioned so that the first light source substantially coincides with the center line of the light-converging optical system.
8. The optical pickup device according to claim 7. 9. The objective lens according to claim 6, wherein a display portion indicating a direction having the fifth-order coma aberration is formed, and the display portion is used as a reference when performing the positioning.
The optical pickup device according to any one of claims 1 to 8. 10. A luminous flux from a light source is collected by a collector including an objective lens.
Information is transmitted through the transparent substrate of the optical information recording medium by the optical optical system.
Recording and / or reproducing information by focusing it on the recording surface
At least two types with different thicknesses of the transparent substrate
Recording and / or reproducing information on optical information recording media
An optical pickup device, comprising: a wavelength λ.₁A first light source of wavelength λ_TwoA second light source, and light east of the light emitted from the first light source and the second light source.
Optical detector that receives transmitted light or reflected light from an information recording medium
A first optical information recording medium having a wavelength λ₁Recording and / or
Optical information recording medium of the condensing optical system required for reproduction
The required numerical aperture on the side is NA₁And the second optical information recording medium has a wavelength λ_TwoRecording and / or
Optical information recording medium of the condensing optical system required for reproduction
NA required opening on the side_Two(However, NA_Two<NA ₁)When
And the objective lens has the wavelength λ.₁Light from the first light source
And the sine condition is satisfied for the first optical information recording medium.
And the second light source is an optical device of the focusing optical system.
The objective lens and the second light so as to coincide with the system center;
An optical pick-up characterized in that the source is positioned.
Backup device. 11. The light source according to claim 4, wherein the first light source and the second light source are unitized.
The optical pickup device according to any one of the above. 12. A luminous flux from a light source is collected by a collector including an objective lens.
Information is transmitted through the transparent substrate of the optical information recording medium by the optical optical system.
Recording and / or reproducing information by focusing it on the recording surface
At least two types with different thicknesses of the transparent substrate
Recording and / or reproducing information on optical information recording media
Together with the wavelength λ₁And a wavelength λ_TwoThe second light of
A light source and light emitted from the first light source and the second light source
To receive transmitted light or reflected light from a bundle of optical information recording media.
For adjusting an optical pickup device including a light detector
Wherein the first optical information recording medium has a wavelength λ₁Recording and / or
Optical information recording medium of the condensing optical system required for reproduction
The required numerical aperture on the side is NA₁And the second optical information recording medium has a wavelength λ_TwoRecording and / or
Optical information recording medium of the condensing optical system required for reproduction
The required numerical aperture on the side is NA_Two(However, NA_Two<NA ₁)When
The objective lens has a fifth-order coma aberration in a range represented by the following equation.
The numerical aperture NA _TwoTotal third-order coma aberration at
Characterized in that the objective lens is positioned such that
Of adjusting the optical pickup device. 0.064 (NA₁)^Five≤CM5₁≤0.39 (NA₁)^Five However, CM5₁: NA₁Fifth-order coma (RMS
(Λ₁)) 13. A luminous flux from a light source is collected by a collector including an objective lens.
Information is transmitted through the transparent substrate of the optical information recording medium by the optical optical system.
Recording and / or reproducing information by focusing it on the recording surface
At least two types with different thicknesses of the transparent substrate
Record and / or reproduce information on a kind of optical inertia recording medium
Together with the wavelength λ₁And a wavelength λ_TwoThe second light of
A light source and light emitted from the first light source and the second light source
To receive transmitted light or reflected light from a bundle of optical information recording media.
For adjusting an optical pickup device including a light detector
Wherein the first optical information recording medium has a wavelength λ₁Recording and / or
Optical information recording medium of the condensing optical system required for reproduction
The required numerical aperture on the side is NA₁And the second optical information recording medium has a wavelength λ_TwoRecording and / or
Optical information recording medium of the condensing optical system required for reproduction
The required numerical aperture on the side is NA_Two(However, NA_Two<NA ₁)When
The objective lens has the wavelength λ.₁Light from the first light source
A sine condition for the bundle and the first optical information recording medium.
The first optical information recording medium has a thickness of t₁,Previous
The thickness of the transparent substrate of the second optical information recording medium is t_TwoMade
Sometimes t_Two> T₁In the case of
The direction of displacement of the second light source and the fifth order frame of the objective lens
The angle between the direction having the aberration and the angle within the range of 0 ° ± 30 °
Position of the objective lens and the second light source so that
Rice, t₁> T_TwoIn the case of the above, the second
Of the objective lens and the fifth order coma of the objective lens.
Angle with the direction to be made is within the range of 180 ° ± 30 °
Position the objective lens and the second light source as described above.
A method for adjusting an optical pickup device, comprising: 14. The apparatus according to claim 13, wherein the fifth-order coma has a fifth-order coma in a range represented by the following equation.
3. The method for adjusting an optical pickup device according to claim 1. ^{_{0.064 (NA 1) 5 ≦ CM5}} 1 ≦ 0.39 (NA 1) 5 However, CM5 _1: 5 order coma aberration at NA ₁ (RMS
(Λ ₁ )) 15. The apparatus according to claim 12, wherein said objective lens and said first light source are positioned such that said first light source substantially coincides with a center line of said condensing optical system.
15. The method for adjusting the optical pickup device according to 3 or 14. 16. The objective lens according to claim 12, wherein a display portion indicating a direction having the fifth-order coma aberration is formed, and the display portion is used as a reference for the positioning.
16. The method for adjusting an optical pickup device according to any one of items 15 to 15. 17. The light source according to claim 12, wherein the first light source and the second light source are unitized.
7. The method for adjusting the optical pickup device according to any one of 6.