JP2006127566A - Diffraction grating element and optical pickup using the same - Google Patents

Abstract

An object of the present invention is to provide an optical pickup that can share different tracking error detection methods such as the DPP method and the DPD method with a single light receiving element and can simplify the circuit configuration.
Light emitted from a semiconductor laser 6 is condensed on the surface of the optical disk 1 and then reflected, and the reflected light 7 enters the first diffraction grating element 3 through the original optical path. Divided into ± first-order diffracted beams 8a and 8b. After reaching the second diffraction grating element 4, the + 1st order diffracted light 8 a is further divided into ± first order diffracted lights 9 a and 9 b by the diffraction grating 4 a and received by the light receiving regions 5 b and 5 a of the light receiving element substrate 5. The −1st order diffracted light 8b is further divided into ± 1st order diffracted lights 10a and 10b by the diffraction grating 4b and received by the light receiving regions 5d and 5c of the light receiving element substrate 5. The light receiving areas 5a to 5d are divided into three in parallel with the radial direction of the optical disk, and a photoelectric conversion signal from each area is calculated to obtain a tracking error detection signal.
[Selection] Figure 1

Description

  The present invention relates to an optical pickup that can be used in a semiconductor laser device, an optical disk device, and the like, and a diffraction grating element that is a component of the optical pickup.

  At present, there are various standards for optical disks such as CD-ROM, CD-R, MD, DVD-ROM, and DVD-R, and different servo signal detection methods are employed for each. The focus error signal detection method is a spot size detection method (hereinafter referred to as an SSD method), and the tracking servo signal detection method is a three beam method, a differential push-pull method (hereinafter referred to as a DPP method), a phase difference detection method (hereinafter referred to as a “difference” method). The DPD method is used.

  Furthermore, in recent years, composite systems that can handle discs of different standards with the same system have become mainstream, and the DPP method has been adopted in composite systems that can handle CD-ROM, CD-R, and CD-RW with the same system. There is something.

  However, even within the same standard disc, there are those having different constituent resins, pit depths, etc., and in a CD-ROM, an optical disc with a pit depth of λ (= laser light wavelength) / 4 cannot detect a push-pull signal. In order to cope with such a disc, it has been found that a tracking error signal detection by the DPD method is also assisted in the above-described CD-based composite system.

  As conventional examples of optical pickups that can be used in an optical disk system compatible with the DPD method, those shown in Patent Document 1 and Patent Document 2 have been proposed.

  11 is a schematic perspective view of an optical pickup according to the prior art, FIG. 12 is a plan view of a diffraction grating element used in the optical pickup, and FIG. 13 is a plan view of a light receiving element substrate used in the optical pickup.

  In FIGS. 11 to 12, light emitted from a semiconductor laser (not shown) reaches the optical disk 101 as an information recording medium along the optical axis 103 and is reflected there. A diffraction grating element 106 and a light receiving element substrate 109 are arranged in a predetermined positional relationship along the optical axis 103 from the optical disc 101 side.

  As shown in FIGS. 11 and 12, a hologram 107 having light diffraction and lens action is formed at the center of the diffraction grating element 106. The hologram 107 passes through the optical axis 103 and is a pit row of the optical disc 101. The region is divided into a first region 107a and a second region 107b with a straight line parallel to the tangential direction 104 (hereinafter referred to as a tangential direction) as a boundary.

  The first region 107a and the second region 107b are configured by the same group of curves that generate diffracted light having the same continuous wavefront, and the first region 107a and the second region 107b are made different from each other by changing the center directions of the wavefronts. The disc reflection light 102 incident on the region 107b has the same diffraction angle, but the diffraction directions are different from each other.

  Further, among the diffracted lights in the first region 107a and the second region 107b, a lens effect is added so that the diffracted light diffracted in the direction of the wavefront center converges and the diffracted light diffracted in the direction opposite to the wavefront center direction diverges. ing.

The reflected light 102 incident on the first region 107a is divided into + 1st order diffracted light 108a ⁺ and −1st order diffracted light 108a ⁻ , and the reflected light 102 incident on the second region 107b is divided into + 1st order diffracted light 108b ⁺ and −1st order diffracted light. 108b ^- is divided into.

The light receiving element substrate 109 has four light receiving regions 109a ⁺ , 109a ⁻ , 109b ⁺ , 109b ⁻ on the same light receiving surface, and the respective light receiving regions are formed in the positional relationship shown in FIG. However, the intersection of the first straight line 110a passing through the centers of the light receiving regions 109a ⁺ and 109a ⁻ and the second straight line 110b passing through the centers of the light receiving regions 109b ⁺ and 109b ⁻ passes substantially in the vicinity of the optical axis 103. Four diffracted beams 108a ⁺ , 108a ⁻ , 108b ⁺ , and 108b ⁻ are respectively incident on these four light receiving regions 109a ⁺ , 109a ⁻ , 109b ⁺ , and 109b ⁻ .

Here, as shown in FIG. 12, the diffraction direction of the ⁺ 1st order diffracted light diffracted in the first region 107a is 119a ⁺ , the diffraction direction of the −1st order diffracted light is 119a ⁻ , and the ⁺ 1st order diffracted light diffracted in the second region 107b. Is 119b ⁺ , and the diffraction direction of −1st order diffracted light is 119b ⁻ .

Further, the first straight line 110a passing through the centers of the light receiving regions 109a ⁺ and 109a ^{− on} the light receiving element substrate 109 is on the diffraction direction 119a ⁺ and the diffraction direction 119a ⁻ , and the centers of the light receiving regions 109b ⁺ and 109b ⁻ are arranged. A second straight line 110b passing therethrough is on the diffraction direction 119b ⁺ and the diffraction direction 119b ^{− described} above.

As shown in FIG. 13, the light receiving regions 109a ⁺ and 109a ⁻ are each divided into four in a direction parallel to the first straight line 110a passing through the center of these regions, and two central region portions Ea1 and Ea2 and two The outer region portions Eb and Ec are respectively configured. Similarly, the light receiving regions 109b ⁺ and 109b ⁻ are each divided into four in a direction parallel to the second straight line 110b passing through the center of these regions, and two central region portions Ea1 and Ea2 and two outer region portions Eb. , Ec.

FIG. 14 is a schematic diagram illustrating a method for obtaining a focus error signal by the SSD method from diffracted light incident on four light receiving regions 109a ⁺ , 109a ⁻ , 109b ⁺ , and 109b ⁻ .

Receiving regions 109a ⁺ center region portion Ea1, and a photoelectric conversion signal obtained from Ea2 R ⁺ i, 2 two outer area part Eb, the photoelectric conversion signal obtained from Ec and R ⁺ o, the light receiving region 109a ^- the central region portion The photoelectric conversion signals obtained from Ea1 and Ea2 are R ^- i, the photoelectric conversion signals obtained from the two outer region portions Eb and Ec are R ^- o, and the photoelectric conversion obtained from the central region portions Ea1 and Ea2 of the light receiving region 109b ⁺ signal L ⁺ i, 2 two outer area part Eb, the photoelectric conversion signal obtained from Ec and L ⁺ o, the light receiving region 109b ^- a photoelectric conversion signal obtained from the central region portion Ea1, Ea2 of ^L - i, 2 two A photoelectric conversion signal obtained from the outer region portions Eb and Ec is L ^- o.

  At this time, the focus error signal FE is calculated as follows.

FE = (L ⁺ i + L ^- o) + (R ⁺ i + R ^- o)-(L ^- i + L ⁺ o)-(R ^- i + R ⁺ o) (Formula 1)
FIG. 15 is a schematic diagram showing a method for obtaining a tracking error signal by the DPD method from diffracted light incident on the four light receiving regions 109a ⁺ , 109a ⁻ , 109b ⁺ , and 109b ⁻ .

The sum of the photoelectric conversion signals of the central region Ea1 and the outer region Eb of the light receiving region 109a ⁺ is Ru ⁺ , the sum of the photoelectric conversion signals of the central region Ea2 and the outer region Ec is Rd ⁺ , and the light receiving region 109.
a ^- the sum of the photoelectric conversion signal of the central region portion Ea2 an outer area portion Ec Ru ^-, the sum of the photoelectric conversion signal of the central region portion Ea1 an outer area portion Eb Rd ^-, light receiving areas 109b ⁺ the central region of the The sum of photoelectric conversion signals of the portion Ea1 and the outer region portion Eb is Lu ⁺ , the sum of photoelectric conversion signals of the central region portion Ea2 and the outer region portion Ec is Ld ⁺ , and the central region portion Ea2 and the outer region of the light receiving region 109b ⁻ The sum of photoelectric conversion signals with the portion Ec is Lu ⁻ , and the sum of photoelectric conversion signals with the central region portion Ea1 and the outer region portion Eb is Ld ⁻ .

At this time, the tracking error signal is obtained by comparing the phase difference between (Ru ⁺ + Ru ⁻ ) + (Ld ⁺ + Ld ⁻ ) and (Lu ⁺ + Lu ⁻ ) + (Rd ⁺ + Rd ⁻ ).

In this way, the focus error signal by the SSD method and the tracking error signal by the DPD method can be obtained by using the ± first-order diffracted light diffracted by the hologram 107 in the disc reflected light information.
JP 11-296873 A JP 2000-235716 A

  However, the above optical pickup has the following problems.

  The first problem is that the signal information necessary for error detection differs between the SSD method and the DPD method, so that the circuit provided on the light receiving element substrate becomes complicated and the number of external output terminals increases.

  In the conventional example, when only the SSD method is considered, since signals from Ea1 and Ea2 in the central area are always added in the four light receiving areas, division is not necessary, and each light receiving area is divided into three. It's okay. Further, when considering only the DPD method, the signals from Ea1 and Eb and the signals from Ea2 and Ec are always added in the four light receiving regions, and each light receiving region may be divided into two.

  However, as described above, in the portion where the diffracted light is incident on each light receiving area, the parts having the signal information required for the SSD method and the DPD method are different. Therefore, each light receiving area is divided more finely into at least four parts. Thus, it is necessary to extract and calculate the necessary part.

  As described above, since the light receiving area is subdivided, the existing light receiving circuit is greatly changed or complicated, or the number of external output terminals is increased.

  Significant changes in the circuit will cause incompatibility with existing products, and circuit complexity and an increase in external output terminals will lead to an increase in the area of the light receiving element and an increase in the package area. Contrary to the flow of conversion.

FIG. 16 to FIG. 18 show connection examples of each region and an external output terminal when the light receiving regions 109a ⁺ , 109a ⁻ , 109b ⁺ , and 109b ⁻ are each divided into four.

  When no arithmetic circuit is provided in the light receiving element substrate 109 and no calculation is performed, 16 external output terminals are required (FIG. 16). Further, when only the signal in parentheses in the detection signal calculation formula (formula 1) described in the above-described conventional example is calculated by a circuit in the light receiving element substrate, four terminals are used for the focus error detection signal and the tracking servo detection signal. Therefore, there are a total of 8 terminals, 4 terminals (FIG. 17).

FIG. 18 shows an example of connection when the external output terminal is minimized in this configuration, and there are a total of 4 terminals, 2 terminals for the focus error detection signal and 2 terminals for tracking servo detection.

In FIG. 17, four terminals for focus error detection signal, signal (L ⁺ i + L ^- o) detection terminal, (R ⁺ i + R ^- o) detection terminal, (L ^- i + L ⁺ o) detection terminal, (R ^- i + R). ⁺ o) When the signals output to the detection terminals are further calculated by a circuit in the light receiving element substrate, the [(L ⁺ i + L ⁻ o) + (R ⁺ i + R ⁻ o)] terminal and the (( L ^- i + L ⁺ o) + (R ^- i + R ⁺
o)] The number of terminals is reduced to a total of two terminals.

Similarly, the four terminals for tracking error detection signal are (Ru ⁺ + Ru ⁻ ), (Ld ⁺ + Ld ⁻ ), (Lu ⁺ + Lu ⁻ ), and (Rd ⁺ + Rd ⁻ ). Erasing the (Ld ⁺ + Ld ⁻ ) and (Rd ⁺ + Rd ⁻ ) terminals and (Ru ⁺
The DPD method is applied by phase comparison between the (+ Ru ⁻ ) terminal and the (Lu ⁺ + Lu ⁻ ) terminal.

  In the example shown in FIG. 18, the arithmetic circuit in the light receiving element substrate is simpler than that of FIG. 17, and the number of external output terminals is also halved. However, as a drawback, since the output signal for the focus error detection signal is originally output from one terminal, the terminal output is saturated unless the signal amount permissible range per terminal is twice or more. In addition, the amount of signal for the tracking error detection signal is halved.

  In addition, when the optical pickup of the conventional example is applied to a CD-based composite system, a tracking error detection method by a push-pull method (hereinafter referred to as a PP method) is further added, resulting in a complicated circuit and an external output terminal. The method for avoiding the increase is further limited.

  In the PP method, the radial direction 105 (perpendicular to the tangential direction) between the optical axis 103 and the center of the pit row on the optical disc 101 due to the difference in the amount of reflected light 102 incident on the first area 107 a and the second area 107 b of the hologram 107. This is a method of detecting a (direction) deviation.

  When the codes used in FIG. 14 are used, the tracking error detection signal TE by the PP method is described as follows.

TE = (R ⁺ i + R ^- o) + (R ^- i + R ⁺ o)-(L ⁺ i + L ^- o)-(L ^- i + L ⁺ o) (Formula 2)
In other words, the tracking error detection signal based on the PP method can be obtained by dividing each light receiving region into three, similarly to the focus error detection signal based on the SSD method. In FIG. 17, the 4-terminal output used for the focus error detection signal is exactly the same as the 4 signals used for the tracking error detection signal calculation. Error detection by the SSD method and the PP method can be executed only by a difference in external calculation by a common output signal.

  However, in the example shown in FIG. 18, since the calculation in the circuit is excessive to obtain the tracking error detection signal by the PP method, it is necessary to add a circuit and an external output terminal separately, that is, the merit, that is, The effect of suppressing the increase in the number of external output terminals will not be achieved.

  In this way, except for the case shown in FIG. 16, the external terminal output is independent by each error detection method and cannot be shared. Therefore, the circuit in the light receiving element substrate cannot be complicated and the number of external output terminals cannot be avoided. . As described above, depending on the method of selecting the circuit operation and the external output terminal, the signals necessary for the SSD method and the PP method can be shared, but the signals necessary for the DPD method are difficult to share. .

  Accordingly, in view of the above problems, the present invention provides an optical pickup that can share different tracking error detection methods such as the DPP method and the DPD method with a single light receiving element and can simplify the circuit configuration, and a diffraction grating element used therefor. Objective.

  In order to solve the above-described problems, the diffraction grating element of the present invention has two diffraction grating regions that are spaced apart from each other on the same plane, and each of the diffraction grating regions is a straight line that becomes a first dividing line. The diffraction grating element is divided into upper and lower parts, and an upper region of the first dividing line is further divided by a straight line that becomes a second dividing line orthogonal to the first dividing line, and The region has the first diffraction grating pattern, the other region has the second diffraction grating pattern different from the first diffraction grating pattern, and the lower region of the first dividing line is the second diffraction grating pattern. The plurality of divided regions are alternately arranged with the regions having the first diffraction grating pattern and the regions having the second diffraction grating pattern. Features.

  It is preferable that a boundary line between at least one set of adjacent regions among the plurality of divided regions is on an extension line of the second dividing line.

  In addition, another diffraction grating element of the present invention has two diffraction grating regions that are spaced apart from each other on the same plane, and the diffraction grating region is divided vertically by a straight line that becomes a first dividing line. The upper part of the first dividing line is further divided by a straight line that becomes a second dividing line orthogonal to the first dividing line, and one divided area is The first diffraction grating pattern has a second diffraction grating pattern different from the first diffraction grating pattern, and the lower region of the first dividing line has the first diffraction grating pattern. A third diffraction grating pattern different from the pattern and the second diffraction grating pattern is provided.

  It is preferable that a three-beam diffraction grating is formed between the two diffraction grating regions.

  The optical pickup of the present invention is an optical pickup that irradiates an information recording medium with light and reads information on the information recording medium using reflected light from the information recording medium. The optical pickup receives a light source and the reflected light. A light receiving element that converts an optical signal into an electrical signal, a first diffraction grating element that diffracts reflected light from the information recording medium to generate diffracted light, and a diffraction from the first diffraction grating element A second diffraction grating element that receives light, further generates diffracted light, and guides it to the light receiving element, and the second diffraction grating element is the diffraction grating element of the present invention. The second dividing line is parallel to the tangential direction of the pit row formed on the information recording medium, and the optical axis of light emitted from the light source toward the information recording medium is the second axis. Intersect with the dividing line or its extension line And wherein the Rukoto.

  It is preferable that the optical axis and the first dividing line do not intersect.

  The light receiving element has at least first to fourth light receiving regions formed in the same plane, and the first light receiving region is one of two diffraction grating regions formed in the second diffraction grating element. , Receiving the −1st order diffracted light from the one diffraction grating region, the second light receiving region receiving the + 1st order diffracted light from the one diffraction grating region, and the third light receiving region receiving the second diffraction light. Of the two diffraction grating regions formed in the grating element, -1st order diffracted light from the other diffraction grating region is received, and the fourth light receiving region receives + 1st order diffracted light from the other diffraction grating region. It is preferable.

  The first to fourth light receiving regions are each divided into three in a direction parallel to the first dividing line, and a photoelectric conversion signal from each divided region in the first to fourth light receiving regions is processed. It is preferable to further include a circuit.

  The focus error signal is preferably detected by a spot size detection method (SSD method), and the tracking error signal is preferably detected by a differential push-pull method (DPP method) or a phase difference detection method (DPD method).

  The first diffraction grating element is formed on one surface of an optical member made of a material transparent to light emitted from the light source, and the second diffraction grating element is formed on a surface opposite to the one surface. It is preferable that

  According to the present invention, in an optical pickup that irradiates an information recording medium with light and reads information using reflected light from the information recording medium, the circuit in the light receiving element substrate is relatively simple and the number of external output terminals is small. A small, simple, and low-cost optical pickup capable of detecting a focus error detection signal by the SSD method and a tracking error detection signal by the DPP method and the DPD method can be realized.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a schematic perspective view of an optical pickup according to an embodiment of the present invention, FIG. 2 is a plan view of a diffraction grating element used in the optical pickup, and FIG. 2 (a) is a first diffraction grating element. FIG. 2B is a plan view of the second diffraction grating element 4. FIG. 3 is also a plan view of a light receiving element substrate used in the optical pickup.

  Light emitted from the semiconductor laser 6 is emitted in a direction perpendicular to the surface of the light receiving element substrate 5, and one main beam and two side beams are emitted from the three-beam diffraction grating 4 c formed on the diffraction grating element 4. Then, the light passes through the second diffraction grating element 4, the first diffraction grating element 3, and the objective lens 2 in order, and is focused on a pit row on the surface of the optical disk 1 that is an information recording medium. The reflected light 7 reflected by the optical disk 1 enters the first diffraction grating element 3 through the original optical path, and is divided into ± first-order diffracted lights 8a and 8b. After the + 1st order diffracted light 8a reaches the second diffraction grating element 4, it is further divided into ± 1st order diffracted lights 9a and 9b by the diffraction grating 4a formed on the diffraction grating element 4 to receive the light receiving region 5b of the light receiving element substrate 5. Light is received at 5a. After the −1st order diffracted light 8b reaches the diffraction grating element 4, it is further divided into ± 1st order diffracted lights 10a and 10b by the diffraction grating 4b formed in the diffraction grating element 4 and received in the light receiving regions 5d and 5c of the light receiving element substrate 5. Received light.

  In FIG. 1, only the optical path of the reflected return light of the main beam is shown, and the light receiving areas 5e to 5h on the light receiving element substrate 5 are also omitted.

As shown in FIG. 3, in the first diffraction grating element 3, a diffraction grating aligned in a direction parallel to the tangential direction of the optical disk 1 is formed. When the pitch of the diffraction grating is Λ and the wavelength of the incident light is λ, the diffraction angle θ of the ± first-order diffracted lights 8a and 8b of the reflected light 7 incident on the diffraction grating element 3 is
Λ × n2 × sin θ = n1 × λ (Formula 3)
Determined by Here, n1 is a positive integer, and n2 is the refractive index of the medium between the diffraction grating element 3 and the diffraction grating element 4. When the distance between the diffraction grating element 3 and the diffraction grating element 4 is z1, the incident positions of the ± first-order diffracted lights 8a and 8b of the reflected light 7 on the second diffraction grating element 4 are represented by (x, y). When
x = z1 × tan θ (Formula 4)
Determined by Here, if the coordinates of the intersection of the surface of the diffraction grating element 4 and the optical axis of the main beam of the laser are (0, 0), the incident position (x _8a , y _8a ) of the + 1st order diffracted light 8a, the −1st order diffracted light The incident positions (x _8b , y _8b ) of _8b are respectively
(X _8a , y _8a ) = (+ z1 × tan (sin ⁻¹ ((n1 / n2) × (λ / Λ)), 0) (Expression 5)
(X _8b , y _8b ) = (− z1 × tan (sin ⁻¹ ((n1 / n2) × (λ / Λ)), 0) (Expression 6)
It is represented by

The diffraction gratings 4a and 4b on the second diffraction grating element 4 are designed so that the centers when viewed from above coincide with (x _8a , y _8a ) and (x _8b , y _8b ), respectively.

  The diffraction grating 4a has dividing lines in a direction parallel to the radial direction of the optical disc 1 and a direction parallel to the tangential direction, and is divided into four.

  Here, assuming that the divided areas are the areas (I) to (IV) in the clockwise direction, the areas (III) and (IV) are divided at equal intervals in the direction parallel to the tangential direction, and the hologram The strip-shaped region 4d where the pattern 11 is formed and the strip-shaped region 4e where the pattern 11 is not formed are alternately arranged.

  Further, a hologram pattern 11 having a light diffraction action and a lens action is formed on the entire surface in the region (I), and no hologram pattern is formed in the region (II).

  The diffraction grating 4b also has dividing lines in a direction parallel to the radial direction of the optical disc 1 and a direction parallel to the tangential direction, and is divided into four.

  Here, assuming that the divided areas are the areas (V) to (VIII) in the clockwise direction, the areas (VII) and (VIII) are divided at equal intervals in the direction parallel to the tangential direction. The strip-shaped region 4f in which the pattern 12 is formed and the strip-shaped region 4g in which the pattern 12 is not formed are alternately arranged.

  Further, a hologram pattern 12 having a light diffraction action and a lens action is formed on the entire surface in the region (VI), and no hologram pattern is formed in the region (V).

  The diffraction gratings 4a and 4b have the same outer shape when viewed from above, but the hologram patterns 11 and 12 are designed to have different condensing distances.

  Further, the diffraction efficiency of the diffraction grating element 106 shown in FIG. 14 is made equal to the total diffraction efficiency of the diffraction grating element 4 in the present embodiment.

  FIG. 4 is a diagram for explaining ± first-order diffracted optical paths of reflected return light generated by the second diffraction grating element in the present embodiment.

  When the distance between the surface of the first diffraction grating element 3 and the emission point of the semiconductor laser 6 is L1, and the arc S1 is drawn around the intersection of the surface of the first diffraction grating element 3 and the outgoing optical axis, the second The first-order diffracted light 9b or 10b diffracted by the diffraction grating element 4 is focused on an arc S2 with a radius L2 or an arc S2 ′ with L2 ′ such that L1> L2 and L2 ′.

  On the other hand, the + 1st order diffracted light 9a or 10a is focused on an arc S3 of radius L3 or an arc S3 'of L3' where L3, L3 '> L1. The focus position differs between the + 1st order diffracted light and the −1st order diffracted light because the converging distances are different between the hologram patterns 11 and 12 as described above.

  As shown in FIG. 3, light receiving areas 5a to 5h are arranged on the surface of the light receiving element substrate 5, and in the light receiving areas 5a to 5d, a virtual straight line extending in the radial direction passes through the center of each area. It is arranged. Further, when the diffraction grating element 4 is viewed from above, the radial dividing lines of the diffraction gratings 4a and 4b and the virtual straight line passing through the centers of the light receiving regions 5a to 5d described above are arranged to overlap.

  The + 1st order diffracted light 9a generated by the diffraction grating 4a diffracting the −1st order diffracted light 8b diffracted by the diffraction grating element 3 is incident on the light receiving region 5b, and the −1st order diffracted light 9b is incident on the light receiving region 5a. The + 1st order diffracted light 10a generated by diffracting the + 1st order diffracted light 8a diffracted by the diffraction grating element 3 is further incident on the light receiving region 5d, and the −1st order diffracted light 10b is incident on the light receiving region 5c.

  The light receiving regions 5a to 5d are each divided into three in a direction parallel to the radial direction, and outer region portions Eb and Ec are arranged with the central portion Ea of each light receiving region interposed therebetween.

  Further, in the light receiving areas 5e to 5h, two side beams are reflected by the optical disc 1, and are further arranged at positions where + 1st order diffracted light (not shown) diffracted by the diffraction grating elements 3 and 4 is incident. .

  ± 1st order diffracted lights 9a and 9b incident on the light receiving areas 5a and 5b are arranged in the hologram pattern 11 of the diffraction grating 4a, and ± 1st order diffracted lights 10a and 10b incident on the light receiving areas 5c and 5d are the hologram pattern 12 on the diffraction grating 4b. The projection pattern reflects each of the arrangements. That is, a ¼ circular diffracted light pattern and a half circular diffracted light pattern projected in a strip shape are incident on the light receiving region. At this time, assuming that the diffraction efficiency of the hologram patterns 11 and 12 is the same, a ¼ circular diffracted light pattern incident on each light receiving region and a ½ circular diffracted light pattern projected in a strip shape And the same amount of light.

  FIG. 5 is a connection diagram between the light receiving regions in the embodiment of the present invention.

  As shown in FIG. 5, among the diffracted light incident on the light receiving regions 5a to 5d, a photoelectric conversion signal generated in the central region portion Ea of 5a and a photoelectric conversion signal generated in the outer region portions Eb and Ec of 5b Are added to obtain the signal FE1.

  Hereinafter, the photoelectric conversion signal generated in the outer region portions Eb and Ec of 5a and the central region portion Ea of 5b are added in order, and the signal FE2 is generated, and the photoelectric conversion signal generated in the central region portion Ea of 5c, and 5d. The signal FE3 is added by adding the photoelectric conversion signals generated in the outer region portions Eb and Ec of the current signal, and the signal FE3 is added to the photoelectric conversion signal generated in the outer region portions Eb and Ec of 5c and the central region portion Ea of 5d. Each of the signals FE4 is obtained.

  Although not shown, the return light from the sub beam is received by the light receiving regions 5e to 5h, the diffracted light generated by the diffraction grating 4a is received by 5e and 5g, and the photoelectric conversion signals generated by them are added. The signal E is obtained, the diffracted light generated by the diffraction grating 4b is received by 5f and 5h, and the photoelectric conversion signals generated by them are added to obtain the signal F.

  On the other hand, as shown in FIG. 4, the ± first-order diffracted lights 9a, 9b, 10a, and 10b diffracted by the diffraction grating 4a or 4b have different distances to the focal point due to the lens action of the hologram pattern. Therefore, when the objective lens 2 is shifted in the direction of the outgoing optical axis and the focal position is changed, the focal point is also changed.

  When the objective lens 2 moves a predetermined distance from the reference position toward the light receiving element substrate 5 side, the focal point moves to the surface of the light receiving element substrate 6 and is condensed on the light receiving region.

  Conversely, when the objective lens 2 moves a predetermined distance from the reference position to the optical disc 1 side, the focal point moves to the surface of the light receiving element substrate 6 and is condensed on the light receiving region.

  This indicates that the focus error signal can be detected by the SSD method. At this time, unlike the conventional technique, the diffracted light pattern has a shape as shown in FIG. 3, but as described above, the diffraction gratings 4a and 4b have the same diffraction efficiency, and the hologram patterns 11 and 12 have the same diffraction efficiency. Are the same in shape, the amount of light of each diffracted light reaching the light receiving region and the focal point are the same, so that the focus error signal by the SSD method can be detected by the following equation.

(Focus error detection signal) = (FE1 + FE3) − (FE2 + FE4) (Expression 7)
Next, what kind of pit information the diffracted light diffracted by the diffraction grating element 4 has will be described with reference to FIG.

  FIG. 6 is a schematic diagram showing information included in the emitted light and diffracted light in the embodiment of the present invention.

  A case is considered where the convergent light emitted from the semiconductor laser 6 and collected by the objective lens 2 is incident on the pit row on the surface of the optical disc 1 and is reflected at a position slightly shifted to the left in the radial direction (see FIG. 6 (a)). Since the pit row surface has a lower reflectance than the optical disc surface other than the pit row, the reflected light 13a reflected from the pit row surface out of the reflected return light reaching the diffraction grating element 4 is other than the pit row. The amount of light is lower than that of the reflected light 13b reflected from the surface (FIG. 6B). The reflected light is divided into two beams of ± first-order diffracted light 8a and 8b by the diffraction grating element 3, and these are further diffracted by the two diffraction gratings 4a and 4b in the diffraction grating element 4, so that the + 1st-order diffracted light 9a As described above, the pattern shape of the + 1st order diffracted light 9a and 10a when there is a light amount difference in the reflected light as described above is shown in FIG. 6C. It becomes like this.

  The diffraction light from the region (I) in the diffraction grating 4a is 14a, the diffraction light from the regions (III) and (IV) is 14b, the diffraction light from the region (VI) in the diffraction grating 4b is 15a, the region (VII), The diffracted light from (VIII) is 15b. If the hologram patterns 11 and 12 are the same pattern, the diffracted lights 14a and 15a have the same shape. On the other hand, the difference in the amount of light caused by the pit rows is reflected inside each diffracted light pattern, so that the deviation between the center of the pit row and the outgoing optical axis can be read by comparing the light amount difference between the diffracted beams 14a and 15a. Is possible.

  On the other hand, the diffracted beams 14b and 15b are projected in the same pattern onto the light receiving regions 5b and 5d, respectively, and the light amounts thereof are the same in each light receiving region. That is, the information regarding the radial direction of the pit row is obtained from the diffracted lights 14a and 15a, and cannot be obtained from the diffracted lights 14b and 15b.

  However, since the information regarding the presence or absence of the pit row in the tangential direction is not lost, the reading ability of data on the optical disk is not lowered.

  Further, in the diffraction gratings 4a and 4b having the same shape, if the strip-shaped regions 4d and 4f in which the same hologram patterns 11 and 12 are formed are arranged at the same positions of the diffraction gratings 4a and 4b, respectively, the servo operation is performed. Even if the objective lens 2 moves in the radial direction due to the above, even if the incident position and the amount of light incident on the regions (III), (IV), (VII), and (VIII) in the diffraction gratings 4a and 4b change, For the same reason, it is possible to obtain a highly reliable servo signal without affecting the servo signal at all.

  However, in the regions (III), (IV), (VII), and (VIII), if the number of divisions is small, the total received light amount may change more than the total light amount change due to passage of the pit row. When the number of diffraction gratings forming a hologram pattern arranged in each region is extremely small, the diffraction of the hologram and the lens function may be lowered, so care must be taken.

  Next, a tracking error signal detection method using the DPP method and the DPD method in the present embodiment will be described. As shown in FIG. 5, six photoelectric conversion signals FE1 to FE4, E, and F are used for these detections.

The tracking error detection signal TE _DPP by the DPP method is expressed as follows.

TE _DPP = (FE1 + FE2) − (FE3 + FE4) + k × (E−F) (Formula 8)
On the other hand, the tracking error detection signal TE _DPD by the DPD method is obtained from the phase difference between (FE1 + FE2) and (FE3 + FE4).

  Next, the tracking error detection method by the DPP method in this embodiment will be described in detail.

  As shown in FIG. 3, the sum of the photoelectric conversion signals FE1 and FE2 is the ± 1st order diffracted light 9a, 9b incident on the light receiving regions 5a, 5b, that is, the photoelectric conversion signal generated from the diffracted light at the diffraction grating 4a. Is the sum of As shown in FIG. 3, the sum of the photoelectric conversion signals FE3 and FE4 is the ± 1st order diffracted light 10a and 10b incident on the light receiving regions 5c and 5d, that is, the photoelectric conversion signal generated from the diffracted light at the diffraction grating 4b. Is the sum of As described above, the signal E is a photoelectric conversion signal generated from the diffracted light at the diffraction grating 4a, and the signal F is a photoelectric conversion signal generated from the diffracted light at the diffraction grating 4b.

  Therefore, as can be seen from (Equation 8), the tracking error detection signal in the DPP method is obtained by comparing the diffracted light amount at the diffraction grating 4a with the diffracted light amount at the diffraction grating 4b. .

  Further, as described above, the tracking servo detection signal is determined by the pit row position radial direction information included in the diffracted light in the regions (I) and (VI), and the regions (III), (IV), and (VII). , (VIII) pit row position radial direction information included in the diffracted light does not contribute at all. Therefore, the tracking servo detection signal is obtained by comparing the amounts of diffracted light generated in the regions (I) and (IV) among the diffraction gratings 4a and 4b.

  As described above, according to the present embodiment, a tracking error detection signal by the DPP method can be obtained. However, as described above, for example, compared to the conventional case shown in FIGS. 11 to 18, only half of the diffracted light is used, so the detection signal level is also halved.

  Next, a tracking error detection method using the DPD method will be described.

  The tracking error signal detection method by the DPD method in the prior art is as already described with reference to FIGS.

  In the prior art, if the four light receiving areas are divided into two and the external output terminals are four terminals, it is possible to detect at least a tracking error by the DPD method. Let's analyze this in more detail.

The signal (Ru ⁺ + Ru ⁻ ) in FIG. 18 is the sum of photoelectric conversion signals generated in the light receiving regions 109 a ⁺ and 109 a ⁻ , that is, generated from the first region of the hologram 107 formed in the diffraction grating element 106. Due to the diffracted light 108a ⁺ and 108a ⁻ . Further, (Lu ⁺ + Lu ⁻ ) is a sum of photoelectric conversion signals generated in the light receiving regions 109b ⁺ and 109b ⁻ , that is, diffraction generated from the first region of the hologram 107 formed in the diffraction grating element 106. Due to light. Further, in consideration of the direction of the diffracted light from each region of the hologram 107 shown in FIG. 12, the phase difference between the signal (Ru ⁺ + Ru ⁻ ) and the signal (Lu ⁺ + Lu ⁻ ) , The phase difference between the signal from region (I) and region (III) and the signal from region (II) and region (IV).

  As can be seen from FIG. 12, region (I) and region (IV), region (II) and region (III) each contain the same phase information. In the conventional configuration, according to the DPD method, a ranking error signal is generated. In order to detect, it was necessary to further divide the central part of each light receiving area.

  However, according to the present embodiment, the diffracted light from the regions (III), (IV), (VII), (VIII) of the diffraction gratings 4a, 4b corresponding to the regions (III), (IV) in FIG. Information on the radial direction of the pit row position is not reflected in. That is, only the diffracted light from the regions (I) and (IV) has information regarding the radial direction of the pit row positions.

  As can be seen from FIGS. 3 and 6, the diffracted light from the regions (I) and (IV) is incident on the light receiving regions 5b and 5d, respectively, and whether or not the central portion of each light receiving region is divided. Regardless, the information of the diffracted light from the region (I) is finally reflected in the signal (FE1 + FE2), and the information of the diffracted light from the region (IV) is all reflected in the signal (FE3 + FE4). It is possible to detect a tracking error signal by the DPD method without further division at the center. As a result, the connection between the light receiving regions is simplified, and the area of the light receiving element can be reduced. However, the detection signal amount is halved compared to the conventional example.

  In this embodiment, the regions (III), (IV), (VII), and (VIII) are each divided into five. However, the number of divisions is not limited to this, and the division interval and the division direction are also limited. It is not limited by the present embodiment.

  Further, the position of the dividing line in the tangential direction region in the diffraction grating element 4 is not limited depending on the present embodiment.

  FIG. 7 is another example of the second diffraction grating element in the present embodiment. Except for the position of the dividing line in the tangential direction region, the configuration is the same as that shown in FIG.

  In this example, the dividing line in the tangential direction region is separated by a distance X in the tangential direction from the straight line passing through the center of the diffraction grating, as compared with the example shown in FIG.

  Assuming that the semiconductor laser output after passing through the objective lens 2 has the same value and the optical characteristics such as transmission and diffraction efficiency of each system constituent material are all the same, in this embodiment, a focus error detection signal by the SSD method is used. The output of the tracking error detection signal by the DPP method and the tracking error detection signal by the DPD method are the same, 1/2, and 1/2 times that of the conventional example, respectively.

  Decreasing the error detection signal amount increases the instability in the control surface, so it is desirable to suppress it as much as possible. In this respect, the configuration of the present embodiment is disadvantageous to the conventional configuration. Have

  In the first place, in the CD-ROM, CD-R, and CD-RW composite system, the DPP method is mainly used as a tracking error detection method, and the DPD method is an auxiliary system for an optical disc that cannot use the DPP method. is there. The modification shown in FIG. 7 has a configuration that can suppress the decrease in the detection signal by the DPP method at the expense of the decrease in the detection signal by the DPD method in consideration of this point.

  FIG. 8 is a schematic diagram showing the relationship between the displacement amount of the dividing line in the tangential direction of the second diffraction grating element and the tracking error detection signal amount by the DPP method and DPD method in the present embodiment.

  The detected signal amount by the DPP method is X <0, that is, when the dividing line is shifted in the (−) direction shown in FIG. 7, the signal level increases, and X> 0, that is, (+) shown in FIG. When the dividing line shifts in the direction, the signal level decreases.

  On the other hand, the detection signal level by the DPD method becomes maximum when X = 0, and decreases as the dividing line is displaced from here. Therefore, by appropriately selecting the position X of the dividing line, it is possible to suppress the decrease in the detection signal level by the DPP method while securing the detection signal level by the DPD method, and realize stable control of the optical pickup. it can.

  In this embodiment, since the hologram patterns of the three-beam diffraction grating and the reflected light diffraction grating are formed on the same plane, the number of members and the cost can be reduced. Normally, these hologram patterns are completed by engraving a pattern in a molding die and pouring an optically transparent resin into the die, but in this embodiment, the positions of the two hologram patterns are processed with precision. However, the number of adjustments of the optical axis of the diffraction grating during assembly of the optical pickup can be reduced.

  Further, if the diffraction grating element 3 is formed on one surface of the optical member and the diffraction grating element 4 is formed on the opposite surface, the number of members can be further reduced and the apparatus can be downsized. . Further, the number of optical axis adjustments can be reduced in the same manner as described above.

  The pattern of the three-beam diffraction grating may be as shown in FIG.

  If the main beam is generated from a non-grating area having no diffraction grating pattern in this way, there is no diffraction loss, the amount of light of the main beam can be increased, and substantially the same effect as improving the laser output. Bring. According to such a configuration, it is possible to easily cope with an increase in the speed of the optical disk drive.

  Note that when the three-beam diffraction grating shown in FIG. 9 is used, there is a possibility that the optical characteristics may be affected by the displacement in the radial or tangential direction due to the arrangement relationship with the laser. According to the embodiment, the diffraction grating element 3 that once receives the reflected light from the optical disk and generates the diffracted light does not have a pattern feature in the radial or tangential direction, and therefore has a three-beam diffraction grating. Even if the arrangement of is shifted, the influence on the optical characteristics is mitigated.

  In this embodiment, the diffraction gratings 4a and 4b are provided with non-grating areas. However, these areas may be, for example, stray light processing diffraction grating patterns.

  Further, as shown in FIG. 10, the present invention can also be applied to the regions (III) and (IV) of the diffraction gratings 4a and 4b having the same hologram pattern and the regions (VII) and (VIII) being different hologram patterns. The above-described effects obtained by

  Since the optical pickup according to the present invention can cope with various types of tracking error detection, it is useful when applied to an optical disc apparatus having a recording / reproducing function.

1 is a schematic perspective view of an optical pickup according to an embodiment of the present invention. It is a top view of the diffraction grating element used for the optical pick-up in embodiment of this invention, (a) is a top view of the 1st diffraction grating element, (b) is a top view of the 2nd diffraction grating element. The top view of the light receiving element board | substrate used for the optical pick-up in embodiment of this invention The figure for demonstrating the +/- 1st order diffractive optical path of the reflected return light generate | occur | produced in the 2nd diffraction grating element in embodiment of this invention Connection diagram between light receiving regions in the embodiment of the present invention The schematic diagram shown about the information contained in the emitted light and diffracted light in embodiment of this invention The figure which shows another example of the 2nd diffraction grating element in embodiment of this invention The schematic diagram which showed the relationship between the displacement amount of the dividing line of the tangential direction of the 2nd diffraction grating element in embodiment of this invention, and the tracking error detection signal amount by DPP method and DPD method The figure which shows an example of the diffraction grating for 3 beams in embodiment of this invention The figure which shows another example of the 2nd diffraction grating element in embodiment of this invention Schematic perspective view of an optical pickup in the prior art Plan view of diffraction grating element used in optical pickup in conventional technology Plan view of a light receiving element substrate used in an optical pickup in the prior art Schematic diagram showing a method for obtaining a focus error signal by the SSD method from diffracted light incident on four light receiving regions in the prior art Schematic diagram showing a method for obtaining a tracking error detection signal by the DPD method from diffracted light incident on four light receiving regions in the prior art The figure which shows an example which showed the connection of each area | region part and external output terminal at the time of dividing each of the four light-receiving area | regions into 4 in a prior art The figure which shows another example which showed the connection of each area | region part and external output terminal at the time of dividing each of the four light-receiving area | regions in a prior art into four The figure which shows another example which showed the connection of each area | region part at the time of dividing each of the four light reception area | regions in a prior art into 4 each, and an external output terminal

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk 2 Objective lens 3 1st diffraction grating element 4 2nd diffraction grating element 4a, 4b Diffraction grating 4c 3 beam diffraction grating 5 Light receiving element board | substrate 5a-5h Light receiving area 6 Semiconductor laser 7 Reflected light from optical disk 8a, 8b ± 1st order diffracted light at first diffraction grating element 9a, 9b ± 1st order diffracted light from diffraction grating 4a 10a, 10b ± 1st order diffracted light from diffraction grating 4b 11 Hologram pattern 12 Hologram pattern 13a Reflected at pit row surface Reflected reflected light 13b Reflected light reflected by the surface other than the pit row 14a Diffracted light from region (I) in diffraction grating 4a 14b Diffracted light from regions (III) and (IV) in diffraction grating 4a 15a Diffraction grating 4b Diffracted light from region (VI) at 15b Diffracted light from regions (VII) and (VIII) at diffraction grating 4b 1 1 optical disc 102 reflected light 103 optical axis 104 tangential direction 105 radial 106 diffraction grating 107 a hologram 107a first region 107b second region 108a ⁺ ~108b ^- diffracted light pattern 109 receiving element substrate 109a ⁺ ~109b ^- receiving region

Claims (10)

Having two diffraction grating regions spaced apart on the same plane;
The diffraction grating region is a diffraction grating element that is divided vertically by a straight line that is a first dividing line,
The upper region of the first dividing line is further divided by a straight line that becomes a second dividing line orthogonal to the first dividing line, and one divided region is the first diffraction grating pattern, The region has a second diffraction grating pattern different from the first diffraction grating pattern,
The lower region of the first dividing line is divided into a plurality of regions in a direction parallel to the second dividing line, and the plurality of divided regions are the region having the first diffraction grating pattern and the second diffraction line. A diffraction grating element, wherein regions having a grating pattern are alternately arranged. 2. The diffraction grating element according to claim 1, wherein a boundary line between at least one pair of adjacent regions among the plurality of divided regions is on an extension line of the second divided line. Having two diffraction grating regions spaced apart on the same plane;
The diffraction grating region is a diffraction grating element that is divided vertically by a straight line that is a first dividing line,
The upper region of the first dividing line is further divided by a straight line that becomes a second dividing line orthogonal to the first dividing line, and one divided region includes the first diffraction grating pattern and the other. The region has a second diffraction grating pattern different from the first diffraction grating pattern,
The diffraction grating element, wherein a lower region of the first dividing line has a third diffraction grating pattern different from the first diffraction grating pattern and the second diffraction grating pattern. The diffraction grating element according to any one of claims 1 to 3, wherein a three-beam diffraction grating is formed between the two diffraction grating regions. An optical pickup that irradiates an information recording medium with light and reads information on the information recording medium using reflected light from the information recording medium,
A light source; a light receiving element that receives the reflected light and converts an optical signal into an electrical signal; a first diffraction grating element that diffracts reflected light from the information recording medium to generate diffracted light; A second diffraction grating element that receives diffracted light from one diffraction grating element, generates further diffracted light, and guides it to the light receiving element;
The second diffraction grating element is the diffraction grating element according to any one of claims 1 to 4,
The second dividing line is parallel to a tangential direction of a pit row formed on the information recording medium, and an optical axis of light emitted from the light source toward the information recording medium is the second dividing line. An optical pickup characterized by crossing a line or its extension. 6. The optical pickup according to claim 5, wherein the optical axis and the first dividing line do not intersect. The light receiving element has at least first to fourth light receiving regions formed on the same plane,
The first light receiving region receives -1st order diffracted light from one of the two diffraction grating regions formed in the second diffraction grating element,
The second light receiving region receives + 1st order diffracted light from the one diffraction grating region,
The third light receiving region receives -1st order diffracted light from other diffraction grating regions of the two diffraction grating regions formed in the second diffraction grating element,
7. The optical pickup according to claim 5, wherein the fourth light receiving region receives + 1st order diffracted light from the other diffraction grating region. The first to fourth light receiving regions are each divided into three in a direction parallel to the first dividing line,
8. The optical pickup according to claim 7, further comprising a circuit for performing arithmetic processing on a photoelectric conversion signal from each divided region in the first to fourth light receiving regions. The focus error signal is detected by a spot size detection method (SSD method), and the tracking error signal is detected by a differential push-pull method (DPP method) or a phase difference detection method (DPD method). 8. The optical pickup according to 8. The first diffraction grating element is formed on one surface of an optical member made of a material transparent to light emitted from the light source, and the second diffraction grating element is formed on a surface opposite to the one surface. The optical pickup according to claim 5, wherein the optical pickup is provided.

Images