JPH09128792A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize an optical pickup device and to reduce a cost. SOLUTION: A main beam and a sub-beam are converged on an optical disk 8 by objective lenses 5a, 5b, and a tracking error signal is obtained from detection outputs of reflected light of the main beam on a main spot and that of the sub-beams on a pair of sub-spots arranged across the main spot. Plural pieces of the objective lenses 5a, 5b are provided switchably individually corresponding to plural kinds of optical disks 8 with at least different track pitches, and a ratio between focal distances of plural objective lenses 5a, 5b each other and the ratio between the track pitches of plural kinds of optical disks 8 each other are set to be nearly equal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for recording and / or reproducing information on an optical recording medium such as an optical disc,
In particular, the present invention relates to an optical pickup device capable of handling a plurality of types of optical recording media having different recording densities, that is, track pitches.

[0002]

2. Description of the Related Art For example, a compact disc (hereinafter referred to as a CD), which is an optical recording medium, has been widely used as a medium for mainly recording music information. On the other hand, in recent years, CD-size optical discs have been developed that can record and reproduce not only music information but also data such as color still images and color moving images for a long time.

A color still image or a color moving image has a very large data amount as compared with music information. Therefore, an optical disc for recording such information requires a large recording capacity, and therefore the recording density is increased by narrowing the track pitch. As a result, at present, there are a plurality of types of optical discs having different specifications, that is, different track pitches, depending on the application such as music, color still images, and color moving images. It is required to be compatible with such different types of optical disks.

To meet such demands, Japanese Patent Laid-Open Nos. 6-236567 and 5-234107.
Japanese Patent Laid-Open No. 2003-242242 proposes a configuration in which a tracking error signal is accurately obtained from each of the above types of optical discs by a 5-beam method that is an application of the 3-beam method.

In the three-beam method, the light of the light source is split by the diffractive element to obtain the 0th-order diffracted light as the main beam and the ± 1st-order diffracted light as the pair of sub-beams.
Then, the recording information is read from the reflected light from the optical disc by the main beam, and the tracking error signal is obtained from the reflected light from the optical disc by the pair of sub-beams.

On the other hand, in the above 5-beam method, the light of the light source is split by one diffractive element, and the 0th-order diffracted light which becomes the main beam and the ± 1st-order diffracted light which becomes two pairs of sub-beams are ±. The second-order diffracted light is obtained. Or,
Use two diffractive elements to obtain two pairs of sub-beams,
There will be two pairs of sub-beams, one from each diffractive element ±
The first-order diffracted light is obtained. Of these two pairs of sub-beams, a first sub-beam which is a predetermined pair of sub-beams is set to correspond to a predetermined narrow track pitch, and a second sub-beam which is another pair of sub-beams is
It is set so as to correspond to a predetermined wide track pitch. Also, for the first and second sub-beams, S
In order to obtain a good tracking error signal of / N, the relationship between the center position S of the sub-spot on the optical disc by the sub-beam and the track-to-track distance T is S = T / 4
Is set to

For example, FIG. 7A and FIG. 7B show the track scanning state of the optical disc by the 5-beam method using high-order diffracted light, that is, ± 2nd-order diffracted light. FIG. 9A shows a track scanning state of an optical disc having a narrow track pitch, and the sub-spots BS ₂ and BS ₃ formed by ± 1st-order diffracted light correspond to the narrow track pitch. Therefore, for example, a reproduction signal is obtained at the main spot BS ₁ formed by the 0th-order diffracted light, and a tracking error signal is obtained at the sub-spots BS ₂ and BS ₃ . FIG. 11B shows a track scanning state of an optical disc having a wide track pitch, and the sub-spots BS ₄ and BS ₅ formed by the ± 2nd order diffracted light correspond to the wide track pitch. Therefore, tracking error signals can be obtained at the sub-spots BS ₄ and BS ₅ .

[0008]

However, in the above-mentioned conventional optical pickup device based on the 5-beam method, as shown in FIG. 8, in the light receiving device 51, one light receiving element for receiving the reflected light BS ₁ ′ of the main beam is received. In addition to 51a, four light receiving elements 51b to 51e that receive the reflected lights BS ₂ ′ to BS ₅ ′ of the sub beams are required. Furthermore, in order to obtain the tracking error signal, two operational amplifiers 51f / 5
You also need 1g. Therefore, there is a problem that the device becomes large and the cost is increased.

Japanese Patent Laid-Open No. 6-333255 discloses an optical pickup device in which a plurality of objective lenses corresponding to different kinds of optical disks are simply arranged in parallel. However, in the configuration of this optical pickup device, for example, half mirrors for guiding light to the plurality of objective lenses are individually required, which leads to an increase in size and cost of the device. Further, the optical discs having different track pitches are not provided with a configuration that appropriately corresponds to them, and the above-mentioned problems cannot be solved.

[0010]

In order to solve the above-mentioned problems, the optical pickup device according to the invention of claim 1 condenses a main beam and a sub-beam on an optical recording medium by an objective lens, and uses the main beam. Main spot,
In an optical pickup device that obtains a tracking error signal from a detection output of reflected light from a pair of sub-spots formed by the sub-beams sandwiching the main spot, the objective lens is a plurality of types of optical recording media having different track pitches. A plurality of switches are provided so as to be switchable corresponding to each, and the ratio of the focal lengths of the plurality of objective lenses and the ratio of the track pitches of the plurality of types of optical recording media are set to be substantially the same. It has a feature.

With the above arrangement, the ratio of the focal length between the object side and the image side of the optical pickup optical system, that is, the lateral magnification is determined by the objective lens used, and the main spot and the sub-spots on the optical disk are determined. , The beam pitch on the optical disc changes depending on the focal length of the objective lens used. Therefore, for example, if the objective lens with the focal length F ₁ is used for the first optical disc with the track pitch T ₁ ,
If the phase difference is adjusted in advance by rotating the beam, if an objective lens having a focal length F ₂ is used, for example, when reproducing a second optical disc having a track pitch T ₂ , it becomes almost
From the relationship of T ₁ / T ₂ = F ₁ / F ₂ , the beam pitch is automatically adapted to the track pitch T ₂ of the second optical disk.

As described above, in the present optical pickup device,
3 for multiple optical discs with different track pitches
A good tracking error signal can be obtained by the beam method, and when the different objective lenses are used, the converging position of the reflected light of each of the three beams on the light receiving side does not change. Therefore, the number of light receiving elements and operational amplifiers for obtaining the tracking error signal may be small. This makes it possible to reduce the size and cost of the optical pickup device.

Further, since the three-beam method can be constructed by using one diffractive element, the light beam can be compared with a configuration using a plurality of diffractive elements or a configuration using high-order diffracted light. Use efficiency increases. Therefore, it is not necessary to switch the amplification factor according to the amount of light received in the light receiving system, and the configuration of the light receiving system can be simplified.

Further, in the optical pickup device of the invention of claim 2, the light source, the first diffractive element and the objective lens are provided in this order in the traveling direction of the light beam emitted from the light source, and the main beam and the sub beam are described above. An optical pickup device that obtains a tracking error signal from the detection output of the reflected light of a main spot formed by the main beam and a pair of sub spots formed by the sub beam with the main spot sandwiched by the objective lens. In the above, a second diffractive element is provided at a position on the opposite side of the objective lens from the recording medium side, and a distance between the objective lens and the convergence position of the 0th-order diffracted light obtained by the second diffractive element is defined by the objective lens. The first distance, the convergence position of the ± 1st order diffracted light obtained from the second diffraction element by the objective lens, and the second diffraction When the distance between the child and the second distance,
It is characterized in that the ratio of the first distance and the second distance and the ratio of the track pitches of the plurality of types of optical recording media are set to be substantially the same.

According to the above construction, assuming that the first distance is D ₁ and the second distance is D ₂ , the first distance D ₁ and the second distance D ₂ are the focal lengths of the construction of claim 1, respectively. Corresponding to F ₁ and focal length F ₂ , almost T ₁ / T ₂ = D ₁
From the relationship of / D ₂ , the main beam and the sub beam with which the first and second optical discs are irradiated have beam pitches adapted to the track pitches T ₁ and T ₂ , respectively. Therefore, the optical disc 8a having different track pitches
It is possible to irradiate 8b with a main beam and a sub-beam adapted by the three-beam method, respectively, in a matched state.

As described above, in the present optical pickup device,
3 for multiple optical discs with different track pitches
A good tracking error signal can be obtained by the beam method, and when the different objective lenses are used, the converging position of the reflected light of each of the three beams on the light receiving side does not change. Therefore, the number of light receiving elements and operational amplifiers for obtaining the tracking error signal may be small. This makes it possible to reduce the size and cost of the optical pickup device.

The optical pickup device of the invention of claim 3 is the optical pickup device of the invention of claim 2,
The second diffractive element is provided concentrically with the objective lens on a surface of the objective lens opposite to the recording medium side, and has a region smaller than the surface of the objective lens,
It is characterized in that the light is diffracted so that the second distance becomes longer than the first distance.

According to the above arrangement, the second diffractive element is used for forming a main spot and a sub spot on an optical disc having a wide track pitch and a relatively low recording density. In this case, Can be a small numerical aperture,
The area of the second diffraction element can be made smaller than the surface of the objective lens. Therefore, the second diffractive element may be a low-cost small-area device, and the cost can be reduced.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. The present optical pickup device is included in an optical disc device that performs recording and / or reproduction on / from the optical disc 8 or one of these operations. The basic configuration of the optical pickup device is as shown in FIG. That is, the optical pickup device includes a semiconductor laser 1, which is a light source, a diffraction grating 2, a half mirror 3,
A collimator lens 4, objective lenses 5a and 5b, a condenser lens 6 and a light receiving device 7 are provided.

The semiconductor laser 1 emits a laser beam,
The diffraction grating 2 splits the laser beam into 0th-order diffracted light as a main beam and ± 1st-order diffracted light as two sub-beams. The half mirror 3, the collimator lens 4, the objective lens 5a, the condenser lens 6, and the light receiving device 7 are aligned in a straight line. The half mirror 3 bends the laser beam incident through the diffraction grating 2 in the direction of the collimator lens 4, and the collimator lens 4 collimates the laser beam. The condenser lens 6 condenses the reflected light from the optical disc 8 that has passed through the half mirror 3 onto the light receiving device 7.

The light receiving device 7 converts light into an electric signal and outputs an electric signal of a level corresponding to the amount of received light. As shown in FIG. 2, this light receiving device 7 has three light receiving elements 7a, 7b, 7c. Light receiving element 7b ・ 7
Each of c is an area for receiving the reflected light from the optical disc 8 by the two sub beams. Light receiving element 7b
The output signals Sb and Sc from 7c are input to the operational amplifier 7d, and the tracking error signal is obtained by the calculation of (Sb-Sc) here.

The light receiving element 7a is an area for receiving the reflected light of the main beam from the optical disk 8 and is divided into four. The four divided regions as 7a ₁ ~7a ₄ as shown in the drawing, when the output signal from these regions and Sa ₁ -SA _4, the reproduction signal _{is, (Sa 1 + Sa 3)} + (Sa 2 + Sa ₄ ), and the focus error signal is obtained by (Sa ₁ + Sa ₃ ) − (Sa ₂ + Sa ₄ ).

The objective lenses 5a and 5b have different focal lengths and are used individually for two types of optical disks 8 having different track pitches. That is, two types of optical disks 8 to which the present optical pickup device is applied are used.
3a, the optical discs 8a and 8b are the same as those in FIG.
As shown in (a) and (b), the track pitches are different from each other. The optical disc 8a has a narrow track pitch and is for high density recording of data, for example.
The track pitch b is wide and is for recording music information, for example. Here, the objective lens 5a is the optical disk 8a.
, And the objective lens 5b is used for the optical disk 8b.

When the focal lengths of the objective lenses 5a and 5b are F ₁ and F ₂ and the track pitches of the optical discs 8a and 8b are T ₁ and T ₂ , respectively, these focal lengths F
The relationship between ₁ · F ₂ and the track pitches T ₁ · T ₂ is set to almost F ₁ / F ₂ = T ₁ / T ₂ .

The objective lenses 5a and 5b corresponding to one of the optical discs 8a and 8b to be used are the optical disc 8a or 8b and the collimating lens 4.
And a predetermined operating position between them. This replacement operation is performed by a lens driving device (not shown). This lens driving device replaces the objective lenses 5a and 5b by moving the objective lenses 5a and 5b in parallel to the surface of the optical disk 8 as shown by an arrow in FIG. 1, and may be configured by appropriately adopting a known mechanism. it can. Further, the operation of the lens driving device may be configured to be interlocked with, for example, an operation of a disc selection key provided on the optical disc device by an operator. Alternatively, the optical discs 8a and 8b are placed on the disc mounting trays individually provided for the optical discs 8a and 8b.
In the configuration in which the mounting state is detected by the sensor, the configuration may be linked to the detection operation of the sensor.

Further, at the time of recording or reproducing operation,
An optimum distance between the recording surface, which is a portion of one optical disk 8a where information is recorded, and one objective lens 5a,
The recording surface of the other optical disk 8b and the other objective lens 5b
And the optimal distances between and are different from each other. This is because the focal lengths F ₁ and F ₂ of the objective lenses 5a and 5b are different, the thickness of the base material of the optical discs 8a and 8b is different, and the position of the recording surface in the optical discs 8a and 8b is different. by. Therefore, the operating position where the objective lenses 5a and 5b are arranged or the mounting position of the optical disks 8a and 8b during use are appropriately set according to the position of the recording layer and the focal lengths F ₁ and F ₂ . For example, both objective lenses 5a and 5b
Have the same operating position and different mounting positions of the optical disks 8a and 8b, or conversely, the optical disks 8a and 8b.
The mounting positions of b may be the same, and the operating positions of the objective lenses 5a and 5b may be different. Moreover,
Since the positions of the recording layers of the optical discs 8a and 8b are different, the distance between the optical disc 8a and the objective lens 5a that match the focal length F ₁ and the distance between the optical disc 8b and the objective lens 5b that match the focal length F ₂ match. In this case, the operating positions of both objective lenses 5a and 5b and the mounting positions of both optical disks 8a and 8b can be made to coincide with each other.

The optical pickup device, when assembled, has an objective lens 5a having a focal length F ₁ with respect to an optical disk 8a having a track pitch T ₁ shown in FIG. 3A, for example.
Is placed in the operating position, the phase difference is adjusted by rotating the three beams, that is, the angle θ ₁ shown in the figure is adjusted. This adjustment is, for example, as shown in the figure, when the distance from the center of the track main spot BSa ₁ scans the center of the sub-spots BSa ₂ · BSa ₃ was _{d 1, d 1 = T 1} /4 It is what

In the above structure, for example, the optical disk 8
When reproducing the information recorded in a, the objective lens 5a is arranged at the operating position in the optical pickup device. In this state, the laser beam emitted from the semiconductor laser 1 is split by the diffraction grating 2 into the 0th order diffracted light which is the main beam and the ± 1st order diffracted lights which are the two sub beams,
It is bent in the direction of the collimator lens 4 by the half mirror 3. After that, the laser beam is collimated by the collimator lens 4, collimated by the objective lens 5a, and irradiated onto the recording surface of the optical disc 8a as a beam spot.

This state is shown in FIG. 3 (a),
The main beam forms the main spot BSa ₁ and the sub beams form the sub spots BSa ₂ and BSa ₃ .
When the optical disk 8b and the objective lens 5b are used, the state shown in FIG. 9B is obtained, and the main beam forms the main spot BSb ₁ and the sub beams form the sub spots BSb ₂ and BSb ₃ .

The reflected light from the recording surface enters the half mirror 3 through the objective lens 5a and the collimator lens 4 and is transmitted therethrough. After that, the reflected light is condensed on the light receiving device 7 by the condenser lens 6. At this time,
As shown in FIG. 2, the reflected light BSa ₁ ′ from the main spot BSa ₁ is incident on the light receiving element 7a and the sub-spot B
Light reflected by Sa ₂ · BSa ₃ BSa ₂ ′ · BSa ₃ ′
Enters the light receiving elements 7b and 7c. Then, the tracking error signal, the reproduction signal and the focus error signal are obtained by the above calculation.

On the other hand, when reproducing the information recorded on the optical disk 8b, for example, the objective lens 5b is arranged at the operating position in the optical pickup device, and the same operation as the above case is performed. In this case, the relationship between the focal lengths F ₁ · F _{2 of} the objective lenses 5a and 5b and the track pitches T ₁ · T ₂ of the optical discs 8a and 8b is set to F ₁ / F ₂ = T ₁ / T ₂ . It is possible to appropriately irradiate the optical discs 8a and 8b with the main beam and the sub-beam without performing adjustments every time the objective lenses 5a and 5b are exchanged, and it is possible to obtain good signals described above. This function will be described below.

The principle diagram of the optical pickup device in each state in which the objective lenses 5a and 5b are arranged at the operating positions is shown in FIG.
The result is as shown in FIG. In the figure, LF indicates an object plane, which corresponds to a light source surface and a light receiving surface in the present embodiment. CH indicates the main surface of the collimator lens 4, and cf indicates the focal length of the collimator lens 4. O ₁ H and O ₂ H represent the objective lenses 5 a and 5 b, and F ₁ and F ₂ represent the focal lengths of the objective lenses 5 a and 5 b, respectively. O ₁ F / O ₂ F
Indicates the image plane, and in the present embodiment, the optical disks 8a and 8b.
It corresponds to the recording surface of. Further, G corresponds to the diffraction grating 2, that is, the grating, and the light beam diffracted by G passes through the path shown by the broken line in the figure, and y ₁ · y _{2 on the} recording surface.
Reach with a distance of. The difference between the configuration of FIG. 3A and that of FIG. 2B is the focal length F of the objective lenses 5a and 5b.
Is only ₁ · F _2, Therefore, as the lateral magnification of the optical system, F ₁ / F ₂ = relation y ₁ / y ₂ holds. That is, in the optical system of the optical pickup device, the position of the sub-spot on the optical disk 8, that is, the distance between the main spot and the sub-spot can be arbitrarily set by changing only the focal length of the objective lens. Therefore,
The relationship between the focal lengths F ₁ · F ₂ and the track pitches T ₁ · T ₂ of the optical disks 8 a · 8 b is F ₁ / F ₂ = T ₁ / T ₂
For example, for the optical disc 8a having the track pitch T ₁ shown in FIG. 3A, the objective lens 5a having the focal length F ₁ is used.
If the phase difference is adjusted by rotating the three beams, that is, the angle θ ₁ shown in the same figure is adjusted in the state where is placed in the operating position, in order to reproduce the optical disk 8b having the track pitch T ₂ , the objective lens When the objective lens 5b is placed in the operating position in place of 5a, the main spot B shown in FIG.
The pitch between Sb ₁ and the sub-spots BSb ₂ and BSb ₃ automatically changes to a state that fits the track pitch T ₂ .

Thus, in the present optical pickup device,
Since three beams are formed by the 0th-order diffracted light and the ± 1st-order diffracted light by one diffraction grating 2, tracking error signals are obtained from a plurality of optical discs 8a and 8b having different track pitches. You can get a signal.

That is, the optical discs 8a and 8b having different track pitches are formed by using up to higher-order diffracted light such as the 5-beam method.
In the case of the method of obtaining the tracking error signal from the above, even if the intensity of the diffracted light is optimized, a difference in intensity between the ± 1st-order diffracted light and the ± 2nd-order diffracted light occurs, and it is necessary to switch the tracking gain. Become. Even when the diffracted light intensity is optimized, since the high-order diffracted light is used, a decrease in the intensity of the 0th-order diffracted light cannot be avoided, and a decrease in the S / N of the reproduction signal is caused. Will come.

The problem of the decrease in the intensity of the 0th-order diffracted light is that five beams are formed by providing two diffraction gratings, the 0th-order diffracted light is used for signal reading, and the ± 1st-order diffracted light by the first diffraction grating is used. The same applies to a configuration in which, for example, it is used to obtain a tracking error signal from an optical disc having a narrow track pitch, and ± 1st order diffracted light from the second diffraction grating is used to obtain a tracking error signal from an optical disc having a wide track pitch, for example. Is. Further, providing two diffraction gratings leads to an increase in cost, and in the configuration in which two kinds of diffraction grating patterns are formed in the same plane, the spot shape of the diffracted light deteriorates and a good tracking error signal can be obtained. I can't.

Therefore, in the present optical pickup device, the light utilization efficiency is high and the present optical pickup device is higher than the configuration using a plurality of diffractive elements and the configuration using high-order diffracted light of ± 2 or more. When using, it is possible to obtain a good tracking error signal, reproduced signal, or the like.

In the optical pickup device of the present invention, the distance y _{3 on} the light receiving surface LF is the same regardless of which of the objective lenses 5a and 5b is used. That is, the pitch between the main spot and the sub-spot on the light receiving device 7 due to the reflected light is constant L ₁ shown in FIG. 2 and does not change. Therefore, in the light receiving device 7, light receiving elements for sub-spots are added in accordance with the pitch of the beam spot on the optical disk 8, the light receiving area of the light receiving elements is expanded, and a large number of light receiving elements are switched and used. Is unnecessary. As a result, in the present optical pickup device, the light receiving device 7
May have one main beam light-receiving element 7a and a pair of sub-beam light-receiving elements 7b and 7c, and one operational amplifier 7d can obtain a tracking error signal. It is possible to achieve simplification and cost reduction.

The optical pickup device includes not only the structure shown in FIG. 1 but also a Cube type half mirror 11 instead of the half mirror 3 as shown in FIGS. 5 (a) and 5 (b). It may be configured. It should be noted that FIG. 1A is a plan view and FIG. 1B is a front view. In the configuration shown in the figure, the laser light emitted from the semiconductor laser 1 is split by the diffraction grating 2 into 0th-order diffracted light and ± 1st-order diffracted light, passes through the half mirror 11, passes through the collimator lens 4, and then rises. The light is diffracted perpendicularly to the direction of the optical disk 8 by the mirror 12 and is condensed on the optical disk 8 by the objective lens 5a or 5b. On the other hand, the reflected light is the objective lens 5
After passing through a or 5b, the rising mirror 12 and the collimating lens 4, it is diffracted by the half mirror and is condensed on the light receiving device 7 by the condenser lens 6.

Further, in the above description, the configuration using the two objective lenses 5a and 5b is shown, but the number of objective lenses is not limited to this, and the number of objective lenses can be appropriately changed according to the type of the optical disc 8. It is also possible to adopt an increased configuration.

[Embodiment 2] Another embodiment of the present invention will be described below with reference to FIG. Incidentally, for convenience of explanation, the same reference numerals are given to the means having the same functions as those shown in the above-mentioned drawings, and the explanation thereof will be omitted.

As shown in FIG. 6, the present optical pickup device includes the semiconductor laser 1, the diffraction grating 2, and the half mirror 3.
And the light receiving device 7, and the objective lens 5
The objective lens 21 with the diffractive element is provided in place of a and 5b. The objective lens 21 with a diffractive element has an objective lens 22 and a diffractive element 23, which is a second diffractive element. The diffractive element 23 is provided in an area within a predetermined range concentrically with the objective lens 22 near the central portion of the surface of the objective lens 22 opposite to the optical discs 8a and 8b side. Since the diffractive element 23 is for obtaining a beam spot for reading the music information recorded on the optical disc 8b at a low recording density, for example, it may have a small numerical aperture, and the diffraction element 23 may have a smaller numerical aperture than that of the objective lens 22. Is provided only in a small area as described above.

The diffraction element 23 is the objective lens 2
The laser beam is diffracted in a direction away from the converged position of the laser beam passing through 2. Therefore, FIG.
As shown in, the focal length of the objective lens 22 itself is F ₁ , and the convergent position of the 0th-order diffracted light by the diffraction element 23 is P ₁
On the other hand, the convergent position of the ± first-order diffracted light by the diffractive element 23 is P _{2 which} is farther from the objective lens 21 with the diffractive element than the convergent position P ₁ .

The optical disc 8a is, for example, a 0.6 mm disc, which is a laminated type of two discs and has a thickness of 1.2 mm.
The recording surface 8a ₁ is provided at the center in the thickness direction. This optical disc 8a is used as an objective lens 22 in the optical disc device.
Focal length F _1, i.e. the recording surface 8a to the position of the convergence position P ₁ of
Placed so that ₁ is located. Also, the optical disc 8b
Is of a single plate type having a thickness of 1.2 mm, and has a recording layer 8b ₁ substantially at the upper surface position. The optical disc 8b is in the optical disc apparatus, the recording surface 8b ₁ to the position of the convergence position P ₂ by the objective lens 21 with a diffraction element is mounted so as to be located. In the configuration of FIG. 6, the optical disk 8a
The placement positions of 8b are the same, and the convergence positions P ₁ and P ₂ are set to match the positions of the recording surfaces 8a ₁ and 8b ₁ , respectively.

Further, in the present optical pickup device, the distance between the convergence position P _{1 of} the 0th-order diffracted light obtained from the diffraction element 23 by the objective lens 22 and the main surface of the objective lens 22 is set to the first distance D ₁ , and the diffraction element Assuming that the distance between the convergence position P _{2 of} the ± 1st-order diffracted light obtained from the objective lens 22 and the main surface of the diffraction element 23 is the second distance D ₂ , the first and second distances D ₁ and D ₂ And the relationship between the track pitches T ₁ and T _{2 of} the optical discs 8a and 8b shown in FIGS. 3 (a) and 3 (b) is set to be approximately D ₁ / D ₂ = T ₁ / T _2. There is.

In the above structure, the laser beam emitted from the semiconductor laser 1 is split by the diffraction grating 2 which is the first diffraction element into 0th-order diffracted light as the main beam and ± 1st-order diffracted light as the two sub-beams. And is diffracted by the half mirror 3 in the direction of the objective lens 21 with the diffraction element,
The light enters the objective lens 21 with the diffraction element.

After that, the 0th-order diffracted light of the main beam and the two sub-beams at the diffraction element 23 is converged at the convergence position P ₁ . Therefore, when the optical disc 8a is used, Its recording surface 8a _1, as shown in FIG. 3 (a), the main spot BSa ₁ and the sub-spots BSa ₂ · BSa ₃ is formed.

On the other hand, the diffraction element 23 of the main beam and the two sub beams formed by the diffraction grating 2 is used.
The ± first-order diffracted lights at are converged at the convergence position P ₂ . Therefore, when the optical disc 8b are used, to its recording surface 8b _1, as shown in FIG. 3 (b), the main spot BSb ₁ and the sub-spots BSb ₂ · BSb ₃ is formed.

The reflected light from the main spots BSa ₁ and BSb ₁ is incident on the light receiving element 7a of the light receiving device 7 shown in FIG. 2, and the sub-spots BSa ₂ and BSa ₃ are received by the light receiving element 7b.
The reflected light of the sub-spots BSb ₂ and BSb ₃ is incident on the light receiving element 7c. Thereby, the optical disk 8a
A tracking error signal, a reproduction signal and a focus error signal can be obtained from 8b.

The reflected light from the main spot BSa ₁ and the sub-spots BSa ₂ and BSa ₃ and the main spot B
Which of Sb ₁ and the reflected light of the sub-spots BSb ₂ and BSb ₃ is used can be selected by identifying the optical disks 8a and 8b by the method described in the first embodiment.

In this optical pickup device, as described above, the first and second distances D ₁ and D ₂ are the focal lengths F ₁ and F in the optical pickup device shown in the first embodiment.
_Since it corresponds to ₂ , a good tracking error signal can be similarly obtained from both the optical discs 8a and 8b having different track pitches according to the principle shown in FIG.

As described above, the present optical pickup device has a simple structure in which each of the three beams corresponding to the optical disks 8a and 8b is formed by one diffraction grating 2 and the objective lens 21 with the diffraction element. .

Further, in the present optical pickup device, as in the optical pickup device shown in the first embodiment, when the optical pickup device operates on both optical disks 8a and 8b, the main spot on the light receiving device 7 by the reflected light becomes. The pitch with the sub-spot does not change. Therefore, similarly, the configuration of the light receiving device 7 can be simplified.

[0053]

As described above, in the optical pickup device according to the invention of claim 1, a plurality of objective lenses are provided so as to be switchable corresponding to at least a plurality of types of optical recording media having different track pitches. The ratio of the focal lengths of the plurality of objective lenses and the ratio of the track pitches of the plurality of types of optical recording media are set to be substantially the same.

As a result, the present optical pickup device can obtain a good tracking error signal by the three-beam method for a plurality of optical discs having different track pitches, and when different objective lenses are used, The converging position of the reflected light of each of the three beams does not change. Therefore, the number of light receiving elements and operational amplifiers for obtaining the tracking error signal may be small, and the size and cost of the optical pickup device can be reduced.

Further, since the three-beam method can be constructed by using one diffractive element, the light beam can be compared with a configuration using a plurality of diffractive elements or a configuration using high-order diffracted light. Use efficiency increases. Therefore, it is not necessary to switch the amplification factor according to the amount of light received in the light receiving system, and it is possible to further simplify the configuration of the light receiving system.

Further, in the optical pickup device of the second aspect of the invention, the second diffractive element is provided at a position on the opposite side of the objective lens from the recording medium side, and the 0th-order diffracted light obtained from the second diffractive element is provided. A first distance is the distance between the objective lens and the convergent position, and a second distance is the distance between the convergent position of the ± 1st order diffracted light obtained by the second diffraction element and the objective lens and the second diffraction element. In terms of distance, the ratio of the first distance to the second distance and the ratio of the track pitches of the plurality of types of optical recording media are set to be substantially the same.

As a result, this optical pickup device can obtain a good tracking error signal by the three-beam method for a plurality of optical discs having different track pitches, like the optical pickup device of the first aspect of the present invention.
Further, when different objective lenses are used, the converging position of the reflected light of each of the three beams on the light receiving side does not change. Therefore, the number of light receiving elements and operational amplifiers for obtaining the tracking error signal may be small, and the optical pickup device can be downsized and the cost can be reduced.

The optical pickup device of the invention of claim 3 is the optical pickup device of the invention of claim 2, wherein
The second diffractive element is provided concentrically with the objective lens on a surface of the objective lens opposite to the recording medium side, and has a region smaller than the surface of the objective lens,
The light is diffracted so that the second distance is longer than the first distance.

As a result, the second diffractive element may be of a low cost and in a small area, and the cost of the device can be further reduced.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an optical pickup device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a light receiving device shown in FIG.

3A is an explanatory view showing the relationship between the tracks of the optical disc shown in FIG. 1 having a narrow track pitch and the main and sub spots, and FIG. 3B is a track of the optical disc having a wide track pitch. It is explanatory drawing which shows the relationship between a main and a sub-spot.

4 (a) is a principle diagram of a state in which an objective lens having a short focal length of the optical pickup device shown in FIG. 1 is used,
FIG. 2B is a principle diagram of a state in which an objective lens having a long focal length of the optical pickup device is used.

5A is a plan view showing another example of the optical pickup device shown in FIG. 1, and FIG. 5B is a front view thereof.

FIG. 6 is a schematic front view showing an optical pickup device according to another embodiment of the present invention.

FIG. 7A is an explanatory diagram showing a scanning state by an optical pickup device for an optical disc having a narrow track bitch by the conventional 5-beam method, and FIG. 7B is a conventional 5-beam method. It is explanatory drawing which shows the scanning state by the optical pickup device with respect to the optical disk with a wide track bitch.

FIG. 8 is an explanatory diagram showing a configuration of a light receiving portion of an optical pickup device according to a conventional 5-beam method.

[Explanation of symbols]

2 Diffraction Grating (First Diffraction Element) 4 Collimating Lens (Optical Means) 5a Objective Lens 5b Objective Lens 7 Light-Receiving Device 7a Light-Receiving Element 7b Light-Receiving Element 7c Light-Receiving Element 8a Optical Disc 8b Optical Disc 21 Objective Lens with Diffraction Element 22 Objective Lens 23 Diffraction Element (Second diffraction element) BSa ₁ main spot BSa ₂ sub-spot BSa ₃ sub-spot BSb ₁ main spot BSb ₂ sub-spot BSb ₃ sub-spot T ₁ track pitch T ₂ track pitch

Claims (3)

[Claims] 1. A main beam and a sub-beam are condensed on an optical recording medium by an objective lens, and a main spot of the main beam and a reflected light of a pair of sub-spots of the sub-beam sandwiching the main spot are provided. In an optical pickup device that obtains a tracking error signal from a detection output, a plurality of the objective lenses are provided so as to be switchable corresponding to at least a plurality of types of optical recording media having different track pitches. An optical pickup device, wherein a ratio of focal lengths and a ratio of track pitches of the plurality of types of optical recording media are set to be substantially the same. 2. A light source, a first diffractive element, and an objective lens are provided in this order in a traveling direction of a light beam emitted from the light source, and a main beam and a sub beam are focused on an optical recording medium by the objective lens. In an optical pickup device that obtains a tracking error signal from a detection output of reflected light of a main spot of the main beam and a pair of sub spots of the sub beam sandwiching the main spot, the recording medium side of the objective lens is A second diffractive element is provided at a position on the opposite side, and a distance between the objective lens and the convergence position of the 0th-order diffracted light obtained by the second diffractive element with the objective lens is defined as a first distance. When the distance between the converged position of the obtained ± first-order diffracted light by the objective lens and the second diffraction element is the second distance, the first distance is The ratio to the second distance,
An optical pickup device, wherein a ratio of track pitches of the plurality of types of optical recording media is set to be substantially the same. 3. The second diffractive element is provided concentrically with the objective lens on a surface of the objective lens opposite to the recording medium side, and has a region smaller than the surface of the objective lens. The optical pickup device according to claim 2, wherein the light is diffracted so that the second distance is longer than the first distance.