JP3294092B2 - Optical pickup device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical pickup device for recording and / or reproducing and / or erasing information on a recording medium.

[0002]

2. Description of the Related Art FIG. 14 shows an example of a conventional optical pickup device for recording and / or reproducing and / or erasing information on a recording medium. In this example, a luminous flux composed of divergent light emitted from a light source 11 composed of a semiconductor laser is converted into substantially parallel light by a collimating lens 12, transmitted through a beam splitter 13, and deflected by a deflecting prism 14.
The light is deflected in the direction of 5, and is condensed by an objective lens 16 at a predetermined position of an information track on a recording surface of a recording medium 15 such as an optical disk. The recording medium 15 is driven to rotate by a spindle motor, and laser light from the objective lens 16 scans an information track on a recording surface.

The light beam reflected by the recording surface of the recording medium 15 is converted into substantially parallel light by an objective lens 16, reflected by a deflecting prism 14, given a tendency to converge by a detection lens 17, and detected by a light receiving element. Thus, servo signals such as a reproduction signal, a focus signal, and a track signal are detected. When focus detection is performed by the general knife edge method, a part of the detection light (reflected light to be detected) from the detection lens 17 is reflected by the knife edge prism 18 and the other part goes straight.

In the vicinity of the focal point of the detection light that has traveled straight from the detection lens 17, a light receiving element 19 composed of a two-part photodiode is provided.
Is installed so that the division line is parallel to the edge of the knife edge prism 18, and the detection light that has traveled straight from the detection lens 17 is detected by the two-division photodiode 19. The difference between the output signals of the respective divided portions of the two-division photodiode 19 is obtained by a circuit (not shown) to generate a focus signal, thereby performing focus detection. Also,
The detection light reflected by the knife edge prism 18 is detected by a light receiving element 20 composed of a multi-division photodiode, and a reproduction signal and a track signal are detected.

Also, Sharp Technical Report No. 48-21-26
Page "Hologram pickup for laser disk" 199
In March 2001, there is described an optical pickup device which uses a hologram to reduce the size and weight and simplify the optical system. In this optical pickup device, the laser beam from the semiconductor laser is divided into three light beams of two tracking sub-beams and an information signal reading main beam by a tracking beam generating diffraction grating formed on the back surface of the hologram element. These three light beams pass through the hologram element and the collimator lens, and are condensed on a disk as a recording medium by an objective lens.

[0006] The light reflected by the disk is condensed again by the objective lens and the collimating lens, is incident on the hologram element, and is diffracted. The light diffracted by the hologram element is guided onto a light receiving element composed of a five-division photodiode. However, since the hologram element is divided into two regions having different grating periods, one of the hologram elements in the reflected light of the main beam Is incident on the dividing line of the two divided portions of the five-divided photodiode, and the reflected light of the main beam that is incident on the other region of the hologram element is the other one of the five divided photodiodes.
The light is focused on two divided parts. The reflected light of the sub-beam is condensed on each of the other two divided portions of the five-divided photodiode, and a reproduction signal, a focus signal, and a radial error signal are detected from the output signals of the respective divided portions of the five-divided photodiode. .

[0007]

In the optical pickup device described in the above Sharp Technical Report, which uses a hologram to reduce the size and weight and simplify the optical system,
The collimating lens functions as a condenser lens that collects the reflected light on the light receiving element. In the case of a finite system without a collimating lens, the objective lens functions as the condenser lens. However, when the focal length of the condenser lens is short, sensitivity is generally increased as shown in FIG. 15 when focus detection is performed by the knife edge method.

When the numerical aperture of the objective lens is increased due to the demand for higher density of the recording medium, the focus detection sensitivity is further increased as shown in FIG. From the standpoint of focus control using a focus signal, a problem occurs if the sensitivity of focus detection is extremely high and the linear range is narrow with respect to the focus error of the focus signal. In order to obtain a certain focus control range, the sensitivity of focus detection must not be too high.

In the conventional optical pickup device, if an objective lens having a high numerical aperture is used, that point becomes a problem. That is, when an objective lens having a high numerical aperture is used in accordance with the increase in density of the recording medium, the sensitivity of the focus signal must be reduced by some method to increase the linear range of the focus signal.

According to the present invention, by reducing the sensitivity of the focus signal, the linear range of the focus signal can be widened and the focus control range can be widened, and the detection light can be effectively used, cost can be reduced, and reliability can be reduced. It is an object of the present invention to provide an optical pickup device capable of improving the performance.

[0011]

In order to achieve the above object, according to the present invention, a light source for irradiating a recording medium with a light beam and a light beam from the light source are transmitted to an information track on a recording surface of the recording medium. An objective lens for condensing, and a light receiving element for receiving and detecting reflected light from a recording surface of the recording medium through the objective lens, to record and / or reproduce and / or erase information on the recording medium. An optical pickup device that performs focus control for generating a focus signal for performing focus control of a condensed spot on the recording surface by using a part of the reflected light. F, the numerical aperture of the objective lens is NA, the spatial frequency of the shortest mark recorded on the recording surface is ν, the wavelength of the light source is λ, and the light from the light source is Determined by the bundle frequency and the NA
The objective lens is reflected on the recording surface of the recording medium.
Let k be a constant proportional to the diameter of the reflected light that has passed through , the y-axis in the information track direction, orthogonal to the information track direction, with the origin of the center of the reflected light in a plane perpendicular to the optical axis of the reflected light. When the x axis is taken in the direction, it is represented by x ² + y ² ≦ (kfNA) ² and represented by −kf (νλ-NA) ≦ y ≦ 0 or 0 ≦ y ≦ kf (νλ-NA) A focus signal is generated by detecting a light beam inside the first region by dividing the light beam by a light beam region dividing unit. The sensitivity of the focus signal can be reduced to widen a linear range of the focus signal. The range can be expanded.

According to a second aspect of the present invention, in the optical pickup device of the first aspect, the reflected light is represented by x ² + y ² ≦ (kfNA) ² , and −kf (νλ−NA) ≦ a track detecting means for generating a track signal by splitting and detecting a light flux of a second area other than the first area by a light flux area splitting means, represented by y ≦ kf (νλ-NA) Thus, the reflected light can be effectively used.

[0013] The invention according to claim 3 is the invention according to claim 1 or 2.
In the optical pickup device described above, a light beam region dividing unit that divides a light beam in a region other than the first region and the second region in the reflected light, and one light beam that receives the light beam divided by the light beam region dividing unit. Since the light-receiving element is provided, the cost can be reduced and the circuit configuration can be simplified.

According to a fourth aspect of the present invention, in the optical pickup device according to the first, second or third aspect, the light beam area dividing means is a hologram, so that the degree of freedom of design is improved, the size is reduced, and the cost is reduced. Can be achieved.

According to a fifth aspect of the present invention, there is provided the optical pickup device of the fourth aspect, further comprising a λ / 4 plate provided between the hologram and the recording medium, wherein the hologram is a polarization separation hologram. Thus, miniaturization, improvement in light utilization rate, and improvement in reliability can be achieved.

The invention according to claim 6 is the invention according to claim 4 or 5.
The optical pickup device according to the above, wherein the light source and the light receiving element are arranged in the same package,
The size, the number of parts, the cost, and the reliability can be improved.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a description will be given of a first optical pickup device which is a premise of an embodiment of the present invention. The first optical pickup device is different from the conventional optical pickup device shown in FIG. 15 in the following points. That is, the first embodiment is different from the conventional optical pickup device in the manner in which the detection light is blocked by the knife edge, that is, the luminous flux region used for focus detection.

In the conventional optical pickup device, FIG.
(A) As shown in (b), the detection light 21 from the detection lens 17 is divided into two right and left parts by a straight line, one of them 21a is reflected by the knife edge prism 18, and the other 12b goes straight. On the other hand, in the first optical pickup device, as shown in FIG. 2C, the detection light 21 from the detection lens 17 is divided into three by the luminous flux region dividing means, and the band portion 21d near the center goes straight. And the other parts 21e, 2
1f is reflected by the light beam area dividing means.

As shown in FIG. 1, the light beam area dividing means uses a flat mirror 22 having a band-shaped transmission portion 22a at the center, and the flat mirror 22 has a reflection film 22b provided in an area other than the transmission section 22a. ing. As for the detection light 21 from the detection lens 17, the belt-like portion 21 d near the center passes through the transmission portion 22 a of the flat mirror 22 and proceeds straight, and the other portion 21
e and 21f are reflected by the flat mirror 22. The detection light 21d that has passed through the transmission part 22a of the flat mirror 22 from the detection lens 17 and travels straight is detected by the two-part photodiode 19, and the difference between the output signals of the two parts of the two-part photodiode 19 is determined by a circuit (not shown). Then, a focus signal is generated to perform focus detection. The detection light reflected by the flat mirror 22 is detected by a light receiving element 20 composed of a multi-division photodiode, and a reproduction signal and a track signal are detected by a circuit (not shown) from an output signal of each divided portion of the light receiving element 20. .

Next, the second embodiment which is a premise of the embodiment of the present invention will be described.
Will be described. This second optical pickup device is different from the first optical pickup device in that the knife edge prism 18 and the light shielding plate 23 are used instead of the flat mirror 22 as the light beam area dividing means as shown in FIG. Detection light 21 from detection lens 17
Is that the band-like portion 21d near the center passes through the space between the knife edge prism 18 and the light shielding plate 23 and goes straight, and the other portion 2
1e and 21f are the knife edge prism 18 and the light shielding plate 2
3 is reflected.

Detection light 21d that has traveled straight from the detection lens 17
Is detected by the two-segment photodiode 19, the difference between the output signals of the respective divided portions of the two-segment photodiode 19 is taken by a circuit (not shown), and a focus signal is generated to perform focus detection. The detection light reflected by the knife edge prism 18 and the light shielding plate 23 is detected by a light receiving element 20 composed of a multi-segmented photodiode. A signal is detected.

Next, the third embodiment which is the premise of the embodiment of the present invention will be described.
Will be described. In the third optical pickup device, as shown in FIG. 4, two knife edge prisms 18 and 24 are used as the light beam area dividing means in the first optical pickup device. The detection light 21 from the detection lens 17 is applied to the band 2 near the center.
1d passes through the knife edge prisms 18 and 24 and travels straight, and the other portions 21e and 21f are reflected by the knife edge prisms 18 and 24.

Detection light 21d that has traveled straight from the detection lens 17
Is detected by the two-segment photodiode 19, the difference between the output signals of the respective divided portions of the two-segment photodiode 19 is taken by a circuit (not shown), and a focus signal is generated to perform focus detection. The detection light reflected by the knife edge prism 18 is detected by a light receiving element 20 composed of a multi-segmented photodiode, and the detection light reflected by the knife edge prism 24 is detected by a light receiving element 25 to detect the light receiving elements 19 and 25. A reproduction signal and a track signal are detected from the output signal by a circuit (not shown).

As described above, the first to third optical pickup devices include the semiconductor laser 11 as a light source for irradiating the recording medium 15 with a light beam, and the light source 1
An objective lens 16 for condensing the light flux from 1 on an information track on a recording surface of the recording medium 15 and light receiving elements 19 and 20 for receiving reflected light from the recording surface of the recording medium 15 through the objective lens 16 for detection. In an optical pickup device for recording and / or reproducing and / or erasing information on the recording medium 15, a focus for performing focus control of a condensed spot on the recording surface using a part of the reflected light. Detection lens 17, plate mirror 22, light receiving elements 19, 20 and a circuit not shown, or detection lens 17, knife edge prism 18, light shielding plate 23, light receiving elements 19, 20 and a circuit not shown as focus detection means for generating a signal Or a detection lens 17, knife edge prisms 18, 24, light receiving elements 19, 20 and a circuit (not shown). Flat mirror 2 of the central strip portion in the vicinity of the slag detecting means the reflected light as a beam region dividing means
2 or the knife edge prism 18 and the light shielding plate 23 or the knife edge prisms 18 and 24 are divided and detected to generate a focus signal, so that the sensitivity of the focus signal can be reduced and the linear range of the focus signal can be widened. The focus control range can be expanded.

Next, a first embodiment of the present invention will be described. This first embodiment is an embodiment of the first and second aspects of the invention. In the first optical pickup device, as shown in FIG. 5, the focal length of the objective lens 16 is f, and the focal length of the objective lens 16 is f. The numerical aperture is NA, the spatial frequency of the shortest mark recorded on the recording surface of the recording medium 15 is ν, the wavelength of the laser light from the semiconductor laser 11 is λ, and a constant proportional to the diameter of the laser light is k. The y-axis in the information track direction on the recording surface of the recording medium 15 with the center of the detection light 21 as the origin in a plane perpendicular to the optical axis of the detection light 21 from
When the x axis is taken in a direction perpendicular to the information track direction,
A first region represented by x ² + y ² ≦ (kfNA) ² and a first region represented by −kf (νλ−NA) ≦ y ≦ 0 or 0 ≦ y ≦ kf (νλ-NA) The light flux inside the area is divided and detected by the light flux area dividing means to generate a focus signal. This is to detect.

The information track pattern is symmetric with respect to the y-axis as shown by the dotted line in FIG.
5 is a region surrounded by a straight line y = kf (νλ-NA) parallel to the x-axis and the x-axis in a plane perpendicular to the optical axis of the detection light 21 from FIG. Further, the area is the detection lens 1
In a plane perpendicular to the optical axis of the detection light 21 from 7, a region surrounded by a straight line y = −kf (νλ−NA) parallel to the x-axis and the x-axis (shaded portion in FIG. 5).

As shown in FIG. 6, the detection light 21 from the detection lens 17 is split by a splitting prism 26 as a light beam area splitting means.
As shown in FIG. 5, the light receiving element 27 is divided into a plurality of regions within a plane perpendicular to the optical axis, and one of the light beams inside the region is divided into two photodiodes.
Is received and detected. The two-divided photodiode 27 is divided into two parts by a dividing line in the x-axis direction orthogonal to the information track direction, and the difference between the output signals b and c of each divided part of the two-part photodiode 27 is calculated by an arithmetic circuit (not shown). A focus signal FE = bc is generated. Therefore, the detection lens 17, the split prism 26, the split photodiode 27, and the arithmetic circuit (not shown) constitute a focus detection unit.

The other light beam among the light beams inside the region is a light receiving element 28 composed of a two-part photodiode.
The two-divided photodiode 28 is divided into two by a dividing line in the y-axis direction parallel to the information track direction. The difference between the output signals d and e of the respective divided portions of the two-divided photodiode 28 is obtained by an arithmetic circuit (not shown) to generate the track signal TE = de, and the detection lens 17, the divided prism 26, and the two-divided photodiode 28 An arithmetic circuit (not shown) constitutes a track detecting means.

Light beams inside the other areas are received and detected by light receiving elements 29 and 30 each formed of a non-divided photodiode, and an arithmetic circuit (not shown) calculates the sum of output signals a and f of the photodiodes 29 and 30. To generate the reproduction signal Rf = a + f, or take the sum of the output signals of the photodiodes 27 to 30 to obtain the reproduction signal Rf = a + f.
+ B + c + d + e + f.

FIG. 7 shows a signal detector according to a second embodiment of the present invention. The second embodiment is another embodiment of the invention described in claims 1 and 2, and in the first embodiment, a plurality of knife edge prisms 18, 31, instead of the splitting prism 26 are used as the light beam area splitting means. 32, and the other parts are configured in the same manner as in the first embodiment.

As for the detection light 21 from the detection lens 17, one of the light beams inside the region goes straight and is received by the two-division photodiode 27, and the other light beam among the light beams inside the region is Edge prism 18
And is received by the two-divided photodiode 28. In addition, the detection light 21 from the detection lens 17 is such that the luminous flux inside the other area is the knife edge prism 18, 32.
Are reflected by the photodiode 30 and received by the photodiode 30, and the light flux inside the area is reflected by the knife edge prism 31 and received by the photodiode 29.

As described above, the first embodiment and the second embodiment are the embodiments of the present invention described in claim 1, and the semiconductor laser 11 as a light source for irradiating the recording medium 15 with a light beam.
An objective lens 16 for condensing a light beam from the light source 11 on an information track on a recording surface of a recording medium 15;
5, a light receiving element 27 to 30 for receiving and detecting the reflected light from the recording surface through the objective lens 16;
In an optical pickup device for recording and / or reproducing and / or erasing information with respect to 5, a focus for generating a focus signal for performing a focus control of a condensed spot on the recording surface using a part of the reflected light. The focus detecting means includes a detecting lens 17 as a detecting means, a splitting prism 26 or knife edge prisms 18, 31, a two-part photodiode 27, and an arithmetic circuit (not shown). Is the numerical aperture of NA, the spatial frequency of the shortest mark recorded on the recording surface is ν, the wavelength of the light source 11 is λ, a constant proportional to the diameter of the light flux is k, and the numerical value is perpendicular to the optical axis of the reflected light. With the center of the reflected light as the origin within the plane, the y-axis is taken in the information track direction, and the x-axis is taken in a direction perpendicular to the information track direction. Where x ² + y ² ≦ (kfNA) ² and a first region or an interior of −kf (νλ−NA) ≦ y ≦ 0 or 0 ≦ y ≦ kf (νλ-NA) Is divided and detected by the splitting prism 26 or the knife edge prisms 18 and 31 as a light beam area dividing means to generate a focus signal, so that the sensitivity of the focus signal is lowered and the linear range of the focus signal is widened. Can,
The focus control range can be expanded, and the S / N of the reproduction signal can be improved.

For example, when the recording medium 15 is an optical disk made of a compact disk, the shortest signal in the jitter direction with respect to the clock period T is 3T, and the longest signal is 11T.
T. If the diameter of the light spot on the recording medium 15 determined by the NA of the objective lens 16 and the wavelength of the semiconductor laser 11 is constant, if the recording density of the recording medium 15 increases, 3T
Since the overlap of the 0th-order light and the 1st-order light of the diffraction pattern due to the pits on the recording medium 15 in the signal amplitude is reduced, the signal change generated by their interference is reduced. But,
By partially shielding the detection light from the detection lens 17, the noise component included in the 3T signal can be reduced without reducing the amplitude of the 3T signal, and the S / N of the 3T signal can be improved. Further, since the central portion of the detection light from the detection lens 17 is shielded, the amplitude of the 11T signal is reduced, and an effect equivalent to a waveform is obtained.

The first embodiment and the second embodiment are
A embodiment of the invention of claim 2, wherein the optical pickup apparatus of claim 1, wherein, represented by ^{x 2 + y 2 ≦ (kfNA} ) 2 of the reflected light, and, -kf (νλ-NA ) ≦ y ≦ kf (νλ−NA), and a light beam in a second region other than the first region is used as a light beam region dividing means.
Alternatively, it comprises a detection lens 17 as a track detecting means for generating a track signal by dividing and detecting by the knife edge prisms 18 and 32, a split prism 26 or a knife edge prism 18, 32, a two-part photodiode 28, and an arithmetic circuit (not shown). Therefore, it is possible to effectively use the detection light.

FIG. 8 shows a signal detector according to a third embodiment of the present invention. The third embodiment is an embodiment of the third aspect of the present invention. In the first embodiment, the light inside the outer region of the detection light 21 from the detection lens 17 is used as one light receiving element 33. , And is configured to receive light. As the light beam area dividing means, a dividing prism 34 is used instead of the dividing prism 26.

The detection light 21 from the detection lens 17 is divided into a light beam inside the region, a light beam inside the region, and a light beam inside another region, and one of the light beams inside the region. The light beam is received by the light receiving element 27 formed of a two-division photodiode, and the other light beam of the light beam inside the region is received by the light receiving element 28 formed of the two-division photodiode, and the light beam inside the other region becomes 1 The light is received by the two non-divided light receiving elements 33. An arithmetic circuit (not shown) outputs the output signal a of the photodiode 33 as a reproduction signal Rf, or generates a reproduction signal Rf = a + b + c + d + e by taking the sum of the output signals of the photodiodes 27, 28, and 33.

As described above, the third embodiment is an embodiment of the present invention described in claim 3 and claims 1 or 2
3. The optical pickup device according to claim 1, wherein the first region (one of the first region) and the second region (the second region) of the reflected light are provided.
Since the light-emitting device is provided with a splitting prism 34 as a light beam area splitting means for splitting a light beam in an area other than the other one) and one light receiving element 33 for receiving the light beam split by the light beam area splitting means 34, the circuit is simplified. Can be planned,
The number of expensive high-bandwidth amplifiers for amplifying the output signal of the light receiving element can be reduced to one at a minimum, and the cost can be reduced. Further, the band can be improved by downsizing the light receiving element.

FIG. 9 shows a signal detector according to a fourth embodiment of the present invention. This fourth embodiment is an embodiment of the invention according to claim 4, and in the first optical pickup device, a hologram 35 is used as a light beam area dividing means, and a light receiving element including a two-division photodiode is used as a light receiving element. 36 and a light receiving element (P
D) 37-39.

The hologram 35 converts the detection light 21 from the detection lens 17 into a region,
The light flux inside the area is diffracted to the PD 37, the light flux inside the area is diffracted to the PD 36, the light flux inside the area is diffracted to the PD 38, and the light flux inside the area is divided. Diffracts to PD39. The PD 36 is divided into two by a dividing line in the x-axis direction orthogonal to the information track direction.

An arithmetic circuit (not shown) calculates the difference between the output signals b and c of the respective divided portions of the PD 36 and calculates the focus signal FE.
= Bc, and the difference between the output signals d and e of the PDs 38 and 39 is calculated to generate a track signal TE = d-e.
7 is output as the reproduction signal Rf = a, or the sum of the output signals of the PDs 36 and 37 to 39 is taken to generate the reproduction signal Rf = a + b + c + d + e.

As described above, this fourth embodiment is an embodiment of the fourth aspect of the present invention. In the first optical pickup device, since the luminous flux region dividing means is the hologram 35, the hologram is Since it is excellent in mass productivity, cost reduction can be achieved. In addition, a hologram that has the same function as a prism having a complicated shape can be formed in a single plate at a low cost, so that an effect equivalent to that of a prism having a complicated shape can be obtained with a simple configuration, and the degree of freedom in design is improved. Can be done. In addition, it can contribute to miniaturization in the sense of function integration. The invention described in claim 4 may be applied to each embodiment of the inventions described in claims 1 to 3, and the light beam area dividing means may be constituted by a hologram.

FIG. 10 shows a fifth embodiment of the present invention. This fifth embodiment is an embodiment of the invention described in claim 6. In the fifth embodiment, in the fourth embodiment, the plurality of light receiving elements 36 to 39 are arranged on the same substrate, for example, a silicon substrate, and the semiconductor laser 11 and the light receiving elements 36 to 3 are arranged.
9 are arranged in the same package and one unit 4
0 is configured.

The luminous flux composed of the divergent light emitted from the semiconductor laser 11 passes through the hologram 35, is converted into substantially parallel light by the collimating lens 12, is deflected by the deflecting prism 14 toward the recording medium 15, and is deflected by the objective lens 16. The light is focused on a predetermined position of the information track on the recording surface of the recording medium 15. The light beam reflected by the recording surface of the recording medium 15 is converted into substantially parallel light by the objective lens 16, reflected by the deflecting prism 14, given a condensing tendency by the collimating lens 12, and enters the hologram 35.

The hologram 35 is a collimating lens 12
As described above, the detection light 21 is divided into the region and the region, and the light beam inside the region is diffracted to the PD 37, the light beam inside the region is diffracted to the PD 36, and the light beam inside the region is diffracted to the PD 38. The light flux inside the area is
Diffracts to An arithmetic circuit (not shown) calculates the difference between the output signals b and c of the respective divided portions of the PD 36 to calculate the focus signal FE.
= Bc, and the difference between the output signals d and e of the PDs 38 and 39 is calculated to generate a track signal TE = d-e.
7 is output as the reproduced signal Rf = a. In a system for detecting a reproduction signal, a configuration in which a first-stage amplifier is formed on the substrate in order to reduce noise may be considered.

In the fifth embodiment, the collimating lens 12
Although the sixth embodiment of the present invention is another embodiment of the invention described in claim 6, the sixth embodiment of the present invention differs from the fifth embodiment in that a collimating lens as shown in FIG. This is a finite system configuration in which only 12 are missing.

As described above, the fifth and sixth embodiments are embodiments of the invention described in claim 6, and are described in claim 4.
In the optical pickup device described above, since the semiconductor laser 11 as a light source and the light receiving elements 36 to 39 are arranged in the same package, it is possible to reduce the size, the number of parts, and the cost. In addition, the relationship between the light source, the light receiving element, and the hologram can always be kept constant, the signal quality can be kept constant with time and temperature, and reliability can be improved.

FIG. 13 shows a seventh embodiment of the present invention. This seventh embodiment is an embodiment of the invention described in claim 5. In the seventh embodiment, the polarization separation hologram 41 and the λ /
Four plates 42 are used. The linearly polarized light beam emitted from the semiconductor laser 11 is transmitted through the polarization separation hologram 41 and then transmitted through the λ / 4 plate 42 to be converted into circularly polarized light, and is converted into substantially parallel light by the collimating lens 12.
The light is deflected by the deflecting prism 14 in the direction of the recording medium 15 and is condensed by the objective lens 16 at a predetermined position of the information track on the recording surface of the recording medium 15.

The light beam reflected by the recording surface of the recording medium 15 is converted into substantially parallel light by the objective lens 16 and reflected by the deflecting prism 14. 42, the polarization direction of the light emitted from the semiconductor laser 11 is 90 °.
The light becomes the rotated linearly polarized light, is diffracted by the polarization separation hologram 41, and is divided into a predetermined shape.

The polarization separation hologram 41 is a hologram having a polarization separation function, for example, a hologram having a function of transmitting S-polarized light and diffracting P-polarized light. The polarization separation hologram 41 divides the detection light 21 from the λ / 4 plate 42 into a region and a region as described above, diffracts the light beam inside the region to the PD 37, and diffracts the light beam inside the region to the PD 36. Then, the light flux inside the area is diffracted to the PD 38, and the light flux inside the area is diffracted to the PD 39. An arithmetic circuit (not shown) calculates the difference between the output signals b and c of the respective divided portions of the PD 36 and calculates the focus signal FE =
bc is generated, and a difference between the output signals d and e of the PDs 38 and 39 is calculated to generate a track signal TE = d-e.
Is output as the reproduced signal Rf = a.

Since the λ / 4 plate 42 is disposed between the polarization separation hologram 41 and the recording medium 15, even if the illumination light from the semiconductor laser 11 passes through the polarization separation hologram 41, the illumination light is recorded without being diffracted. Only the reflected light from the medium 15 can be diffracted, that is, the illumination light and the reflected light can be set on substantially the same optical path. Further, both the illumination system for illuminating the recording medium and the detection system for detecting various signals from the reflected light from the recording medium can improve the light use efficiency.

As described above, the seventh embodiment is an embodiment of the invention described in claim 5, and is provided between the hologram 41 and the recording medium 15 in the optical pickup device described in claim 4. Since the hologram 41 has a λ / 4 plate 42 and the hologram 41 is a polarization separation hologram, it is possible to improve the light use efficiency of both the illumination system and the detection system, and thereby the light spot on the recording surface of the recording medium for rewriting or the like. If it is necessary to use a light spot having a high power, a light source with a lower output can be used, and the cost can be reduced. Further, the influence of the return light from the recording medium (output fluctuation of the semiconductor laser, etc.) can be suppressed by the isolation by the λ / 4 plate and the polarization separation hologram.

[0052]

As described above, according to the first aspect of the present invention, a light source for irradiating a recording medium with a light beam and an objective lens for condensing the light beam from the light source on an information track on a recording surface of the recording medium. And an optical pickup device for receiving and detecting reflected light from a recording surface of the recording medium through the objective lens, and for recording and / or reproducing and / or erasing information on the recording medium. A focus detection unit that generates a focus signal for performing focus control of a condensed spot on the recording surface using a part of the reflected light, and the focus detection unit includes:
The focal length of the objective lens is f, the numerical aperture of the objective lens is NA, the spatial frequency of the shortest mark recorded on the recording surface is ν, the wavelength of the light source is λ, and the constant is proportional to the diameter of the light beam. k and y in the information track direction with the center of the reflected light as the origin within a plane perpendicular to the optical axis of the reflected light.
When the x axis is taken in a direction perpendicular to the axis and the information track direction, it is represented by x ² + y ² ≦ (kfNA) ² , and −kf (νλ−NA) ≦ y ≦ 0 or 0 ≦ y ≦ Since the luminous flux inside the first area represented by kf (νλ-NA) is divided and detected by the luminous flux area dividing means to generate a focus signal, the sensitivity of the focus signal is lowered to widen the linear range of the focus signal. And the focus control range can be expanded.

[0053] According to the second aspect of the present invention, in the optical pickup apparatus of claim 1, wherein, represented by ^{x 2 + y 2 ≦ (kfNA} ) 2 of the reflected light, and, -kf (νλ-NA Track detection means for generating a track signal by detecting a light flux in a second area other than the first area by splitting the light flux by a light flux area splitting means. , The detection light can be effectively used.

According to a third aspect of the present invention, in the optical pickup device according to the first or second aspect, a light beam area for dividing a light beam in an area other than the first area and the second area in the reflected light. Since there is provided a splitting unit and one light receiving element for receiving the light beam split by the light beam region splitting unit, the circuit can be simplified and the cost can be reduced.
Further, the band can be improved by downsizing the light receiving element.

According to the fourth aspect of the present invention,
4. In the optical pickup device described in 2 or 3, since the light beam area dividing means is a hologram, cost reduction can be achieved and design flexibility can be improved.
This can contribute to downsizing.

According to a fifth aspect of the present invention, in the optical pickup device of the fourth aspect, there is provided a λ / 4 plate provided between the hologram and the recording medium, wherein the hologram is a polarization separation hologram. Therefore, the light use efficiency can be improved in both the illumination system and the detection system, and when the light spot on the recording surface of the recording medium needs to be a light spot having a high power for rewriting or the like, a lower light efficiency can be obtained. An output light source can be used, and the cost can be reduced. Further, the influence of the return light from the recording medium can be suppressed by the isolation by the λ / 4 plate and the polarization separation hologram.

According to the sixth aspect of the present invention, in the optical pickup device according to the fourth or fifth aspect, the light source and the light receiving element are arranged in the same package.
The size, the number of parts, and the cost can be reduced, the relationship between the light source, the light receiving element, and the hologram can be kept constant, and the signal quality can be kept constant over time and temperature. Reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a part of a first optical pickup device as a premise of an embodiment of the present invention, and a plan view showing a flat mirror thereof.

FIG. 2 is a cross-sectional view showing a light beam used for focus detection of the first optical pickup device and a conventional device.

FIG. 3 is a schematic view showing a part of a second optical pickup device which is a premise of the embodiment of the present invention.

FIG. 4 is a schematic view showing a part of a third optical pickup device which is a premise of the embodiment of the present invention.

FIG. 5 is a sectional view showing a light beam used for focus detection according to the first embodiment of the present invention.

FIG. 6 is a schematic diagram showing a part of the first embodiment and a plan view showing a light receiving element thereof.

FIG. 7 is a schematic view showing a part of a second embodiment of the present invention.

FIG. 8 is a schematic view showing a part of a third embodiment of the present invention and a plan view showing a light receiving element thereof.

FIG. 9 is a schematic diagram illustrating a part of a fourth embodiment of the present invention, a plan view illustrating a hologram thereof, and a plan view illustrating a light receiving element thereof.

FIG. 10 is a schematic view showing a fifth embodiment of the present invention.

FIG. 11 is a plan view showing a semiconductor laser and a light receiving element of the fifth embodiment.

FIG. 12 is a schematic view showing a sixth embodiment of the present invention.

FIG. 13 is a schematic view showing a seventh embodiment of the present invention.

FIG. 14 is a schematic view showing a conventional optical pickup device.

FIG. 15 is a characteristic diagram showing a relationship between a focal length of a detection lens and focus detection sensitivity.

FIG. 16 is a characteristic diagram showing a relationship between NA of an objective lens and focus detection sensitivity.

[Explanation of symbols]

Reference Signs List 11 semiconductor laser 12 collimating lens 13 beam splitter 14 deflection prism 15 recording medium 16 objective lens 17 detection lens 18, 31, 32 knife edge prism 19, 20, 25, 27 to 30, 33, 36 to 39
Light receiving elements 22, 24 Flat mirror 23 Light shielding plate 26, 34 Split prism 35 Hologram 40 Unit in which light source and light receiving element are arranged in the same package 41 Polarization separation hologram 42 λ / 4 plate

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 7 / 135,7 / 09

Claims (6)

(57) [Claims] A light source for irradiating the recording medium with a light beam; an objective lens for condensing the light beam from the light source on an information track on a recording surface of the recording medium; An optical pickup device for recording and / or reproducing and / or erasing information on the recording medium having a light receiving element for detecting and receiving light through an objective lens, wherein a part of the reflected light is used on the recording surface. Focus detecting means for generating a focus signal for performing focus control of the condensed spot, wherein the focus detecting means comprises: a focal length f of the objective lens; a numerical aperture of the objective lens NA; the spatial frequency of the recorded shortest mark [nu, the wavelength of the light source lambda, or the light source
The recording medium determined by the frequency of the light flux and the NA
Reflected by the recording surface and passing through the objective lens
Let k be a constant proportional to the diameter of the reflected light, and set the y-axis in the information track direction and the x-axis in a direction perpendicular to the information track direction with the origin of the center of the reflected light in a plane perpendicular to the optical axis of the reflected light. When taken, the first region represented by x ² + y ² ≦ (kfNA) ² and represented by −kf (νλ−NA) ≦ y ≦ 0 or 0 ≦ y ≦ kf (νλ-NA) An optical pickup device wherein an internal light beam is divided and detected by a light beam region dividing means to generate a focus signal. 2. The optical pickup device according to claim 1, wherein said reflected light is represented by x ² + y ² ≦ (kfNA) ² , and −kf (νλ−NA) ≦ y ≦ kf (νλ− NA), and further includes a track detecting means for generating a track signal by detecting a light flux in a second area other than the first area by the light flux area dividing means. Optical pickup device. 3. The optical pickup device according to claim 1, wherein the first area and the second area of the reflected light are provided.
An optical pickup device comprising: a light beam area dividing means for dividing a light beam in an area other than the area; and one light receiving element for receiving the light beam divided by the light beam area dividing means. 4. An optical pickup device according to claim 1, wherein said light beam area dividing means is a hologram. 5. The optical pickup device according to claim 4, further comprising a λ / 4 plate provided between said hologram and said recording medium, wherein said hologram is a polarization separation hologram. apparatus. 6. The optical pickup device according to claim 4, wherein the light source and the light receiving element are arranged in the same package.