JP3983632B2 - Optical pickup device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup device for optically recording or reproducing information on an information recording medium such as an optical disk.
[0002]
[Prior art]
Conventionally, a three-beam method and a push-pull method are mainly known as tracking servo systems for optical disk devices. When these methods are used in an optical disc apparatus, an offset is caused by recording, reproduction, access, or disc tilt. A DPP (differential push pull) method has been proposed as a method for removing this offset.
[0003]
In recent years, the DPP method is used in an optical disc apparatus such as a DVD player that records information at a high density. The present applicant has proposed an optical pickup device using an optical integrated unit capable of using the DPP method in Japanese Patent Application Laid-Open No. 2001-273666.
[0004]
FIG. 13 shows a schematic configuration of a conventional optical pickup device. FIG. 13A shows a top view and FIG. 13B shows a side view. Referring to FIGS. 13A and 13B, the light 120 emitted from the semiconductor laser 105 is divided into a main beam (0th order light) and two sub beams (± 1st order diffracted light) by a three-beam diffraction grating 106. Then, the light passes through the polarization beam splitter (PBS) surface 107a of the composite prism 107, passes through the quarter-wave plate 108, and travels toward a collimator lens (not shown). In order to avoid complication of the figure, the sub beam is not shown. Return light 121 from an optical disk (not shown) is transmitted through the quarter-wave plate 108, reflected by the PBS surface 107 a and the reflection mirror surface 107 b, and enters the hologram element 109. The return light 121 incident on the hologram element 109 is diffracted and incident on the light receiving element 110. Here, the polarized light of the light emitted from the semiconductor laser 105 is linearly polarized light (P-polarized light) in the X direction shown in the figure, is transmitted through the PBS surface 107a, is circularly polarized by the quarter wavelength plate 108, and is incident on the optical disk. To do. The return light again enters the quarter-wave plate 108 and becomes Y-direction polarized light (S-polarized light) and is reflected by the PBS surface 107a.
[0005]
Accordingly, almost all of the light emitted from the semiconductor laser 105 can be guided to the optical disk, and almost all of the return light can be guided to the detector side, so that the light utilization efficiency is improved. .
[0006]
The hologram element 109, the light receiving element 110, and the servo signal detection method will be described. FIG. 14 is a diagram illustrating a relationship between a hologram element of a conventional optical pickup device, light diffracted by the hologram element, and a light receiving element. FIG. 14 shows in which region of the light receiving element 110 the light diffracted by each region of the hologram element 109 is received.
[0007]
The hologram element 109 is divided into three regions 109a to 109c by a dividing line 109l in the X direction corresponding to the radial direction of the optical disc and a dividing line 109m in the Y direction corresponding to the track direction. The light receiving element 110 includes six light receiving areas 110a to 110f that receive the + 1st order diffracted light from the hologram element 109 and three light receiving areas 110g to 110i that receive the −1st order diffracted light. The outputs of the light receiving areas 110a to 110i are Sa to Si, respectively.
[0008]
The + 1st order diffracted light diffracted in the region 109a of the hologram element 109 in the return light of the main beam is detected on the dividing line 110l of the region 110a and the region 110b of the light receiving element 110, and the −1st order diffracted light is detected at 110g. It is configured. Further, the −1st order diffracted light in the region 109b of the hologram element 109 is detected in the region 110h of the light receiving element 110, and the −1st order diffracted light in 109c is detected at 110i.
[0009]
Further, when the two sub beams are represented by sub beam A and sub beam B, for sub beam A, the + 1st order diffracted light diffracted at 109b is detected at 110e, and the + 1st order diffracted light diffracted at 109c is detected at 110c. For sub-beam B, the + 1st order diffracted light diffracted at 109b is detected at 110f, and the + 1st order diffracted light diffracted at 109c is detected at 110d.
[0010]
The calculation processing of various signals detected by the hologram element 109 and the light receiving element 110 configured as described above is performed as follows.
[0011]
The focus error signal (FES) is detected by equation (1). The tracking error signal (TES1) can be detected by Equation (2) based on the push-pull method using Si and Sh. However, for the reasons already described, the push-pull signals TES (A ) And TES (B) are also mainly used in the DPP (differential push-pull) method. That is, the tracking error signal (TES2) by the DPP method is detected by the equation (3).
[0012]
In equation (3), the constant k is for correcting the difference in intensity between the main beam and the sub beam. If the intensity ratio is main beam: sub beam A: sub beam B = a: b: b, k = a / (2b) Is given in.
[0013]
Further, when reproducing an optical disc on which pit information is recorded, a change in the phase difference between Sh and Si can be detected to detect TES3 by the DPD (phase difference) method. The recorded information signal (RF) is detected by equation (4).
[0014]
FES = Sa−Sb (1)
TES1 = Sh-Si (2)
TES2 = TES1-k {TES (A) -TES (B)]
= (Sh-Si) -k [(Sc-Se) + (Sd-Sf)] (3)
RF = Sh + Sg + Si (4)
[0015]
[Problems to be solved by the invention]
In the optical pickup device described in Japanese Patent Laid-Open No. 2001-273666, the light emitted from the semiconductor laser 105 has a larger beam diameter as it travels toward the optical disk (see FIG. 13B). For this reason, in FIG. 13B, the main beam and the sub-beams A and B exist in a state of being substantially overlapped above the three-beam diffraction grating 106, and the outer shape of the beam is considered to be the light 120. But there is no big difference. However, in the region where the beam diameter is small, the deviation between the main beam and the sub beams A and B becomes significant.
[0016]
FIG. 15 shows the beam shape on the hologram element 109. It can be seen that on the hologram element 109, the main beam M121a, the sub beam A121b, and the sub beam B121c are shifted. When the state of the light beam in the optical path is examined between the hologram element 109 and the light receiving element 110, for example, in the X′-X ′ cross section in FIG. 13B, the main beam M passing through the hologram element 109 in the state of FIG. Each of the sub beams A and B is diffracted by the three regions 109a to 109c of the hologram element 109, and each diffracted light is as shown in FIG. In the figure, a beam with a symbol indicates light used for servo signal generation, reproduction signal generation, and the like, and a beam without a symbol indicates light not used in the optical pickup device of the conventional example. .
[0017]
The + 1st order diffracted lights 130e and 130c in which the sub beam A is diffracted in the areas 109b and 109c, and the + 1st order diffracted lights 130f and 130d in which the sub beam B is diffracted in the areas 109b and 109c are shown. The difference in shape between the diffracted lights of the sub beam A and the sub beam B is remarkable. This indicates that the amount of diffracted light is different. This is because the diffraction efficiencies of the sub-beams A and B in the three-beam diffraction grating 106 are the same, and therefore the amount of light differs if the beam shape after passing through the hologram is different. The difference in the amount of light between the sub beams A and B is due to the fact that the sub beam A 121 b and the sub beam B 121 c are not divided at the center by the dividing line 109 l of the hologram element 109 as shown in FIG.
[0018]
When the difference in the amount of light between the sub beams A and B occurs, the following problem occurs. If there is a difference in the light amounts of the sub-beams A and B, that is, even if there is an imbalance in the light amounts of the sub-beams A and B due to being cut at the dividing line 109l, the constant k is appropriate if the unbalance is always constant. By setting to a small value, stable tracking servo can be performed regardless of the pickup device. That is, since the intensity ratio between the main beam and the sub beams A and B is M: A: B = a: b1: b2, the constant k in equation (3) may be set to k = a / (b1 + b2).
[0019]
However, in an actual optical pickup device, an installation error of the semiconductor laser 105, a manufacturing error related to a housing portion such as a package, a stem, or a housing, a manufacturing error of an optical component used for an optical pickup such as a beam splitter or a reflection mirror, and the optical The position and interval of the main beam and the sub beams A and B on the hologram element 109 are different for each optical pickup device due to the influence of component mounting errors and the like.
[0020]
Therefore, even if an attempt is made to correct the difference in light intensity between the main beam and the sub-beams A and B by determining the constant k, the intensity ratio of the sub-beams A and B is determined for each optical pickup apparatus in consideration of the error of the optical pickup apparatus. Because of the difference, there was a problem that it could not be corrected sufficiently. For this reason, the conventional optical pickup device has a problem that it is difficult to perform stable tracking servo.
[0021]
The present invention has been made to solve the above-described problems, and one of the objects of the present invention is to provide an optical pickup device capable of performing stable tracking servo.
[0022]
[Means for Solving the Problems]
In order to achieve the above object, according to one aspect of the present invention, an optical pickup device includes a light source that irradiates light to an optical recording medium, and a light source disposed between the light source and the optical recording medium. Condensing means for condensing light, a photodetector formed with a plurality of light receiving portions for receiving return light from the optical recording medium, and a light source disposed in between the light source and the condensing means. A first optical branching unit that branches into one sub-beam and a second sub-beam; a second optical branching unit that is disposed between the focusing unit and the photodetector and further splits the main beam, the first sub-beam, and the second sub-beam; The second optical branching unit is disposed at an optical position at a predetermined interval between the first sub-beam and the second sub-beam.
[0023]
According to the present invention, the second optical branching unit that is disposed between the focusing unit and the photodetector and further splits the main beam, the first sub-beam, and the second sub-beam includes the first sub-beam and the second sub-beam. The sub-beams are arranged at optical positions separated by a predetermined distance. For this reason, the 1st sub beam and the 2nd sub beam can be branched independently, and the freedom degree of utilization of a sub beam can be raised. When the first sub-beam and the second sub-beam are used for tracking error signal detection, a stable tracking error signal can be obtained. As a result, an optical pickup device capable of performing stable tracking servo can be provided.
[0024]
Preferably, the second optical branching unit has a plurality of regions divided by a dividing line parallel to the radial direction of the optical recording medium and a dividing line perpendicular to the radial direction.
[0025]
According to the present invention, the second optical branching means has a plurality of regions divided by a dividing line parallel to the radial direction and a dividing line perpendicular to the radial direction of the optical recording medium. Only the main beam and the first and second sub beams can be divided. Therefore, the beam for generating the tracking error signal by the DPP method and the beam for generating the focus error signal can be easily divided, and the optical pickup device can be simplified.
[0026]
Preferably, in the second optical branching unit, each of the first sub-beam and the second sub-beam is disposed at an optical position with a predetermined distance from the main beam.
[0027]
According to the present invention, the second optical branching unit is disposed at an optical position at a predetermined distance from the main beam, so that the first sub-beam and the second sub-beam are related to the branch of the main beam. The first sub-beam and the second sub-beam can be branched instead. Further, when the first sub-beam and the second sub-beam are used for detection of the tracking error signal, the entire first sub-beam and the second sub-beam are used to generate a push-pull signal for offset removal in the tracking error signal by the DPP method. Can be used. As a result, the degree of freedom in using the sub-beam is further improved, and the signal quality is improved.
[0028]
Preferably, the second optical branching unit includes a region divided by a dividing line that divides each of the first sub-beam and the second sub-beam in the radial direction of the optical recording medium, and the main beam in the track direction of the optical recording medium. One of the regions delimited by the dividing line for dividing the main beam in the track direction of the optical recording medium further includes the main beam in the radial direction of the optical recording medium. It has the area | region divided by the dividing line to divide | segment.
[0029]
According to the present invention, each of the first sub-beam and the second sub-beam is not divided by a dividing line that divides the main beam in the track direction of the optical recording medium. An error signal can be generated. As a result, the quality of the tracking error signal is improved and the tracking servo operation can be stabilized.
[0030]
Preferably, the second optical branching unit is divided by a dividing line for dividing the first and second sub beams in the track direction of the optical recording medium so that the shapes of the first sub beam and the second sub beam are substantially the same. And a region delimited by a dividing line that divides the main beam in the track direction of the optical recording medium, and at least delimited by a dividing line that divides the first sub-beam in the track direction of the optical recording medium. One area has an area delimited by a dividing line that divides the first sub-beam in the radial direction of the optical recording medium, and delimited by a dividing line that divides the second sub-beam in the track direction of the optical recording medium. At least one area has an area delimited by a dividing line dividing the second sub-beam in the radial direction of the optical recording medium, and delimited by a dividing line dividing the main beam in the track direction of the optical recording medium. One band has a region separated by the division line further divide the main beam in the radial direction of the optical recording medium.
[0031]
According to this invention, the second optical branching unit divides the first and second sub beams in the track direction of the optical recording medium so that the shapes of the first sub beam and the second sub beam are substantially the same. Since the region is divided by lines, the first sub-beam and the second sub-beam used for the tracking error signal by the DPP method can be divided and partially used. Therefore, even if a part of the first or second sub beam overlaps the main beam on the second optical branching means, the tracking error signal by the DPP method is generated using the light of the part not overlapping the main beam. Can be generated. As a result, it is not necessary to separate the first or second sub beam from the main beam, and the design of the components of the optical system is facilitated.
[0032]
Preferably, of the main beam, the first sub-beam, and the second sub-beam that pass through the second optical branching unit, each light related to tracking error signal generation has substantially the same shape.
[0033]
According to the present invention, the light quantity ratio of each light related to the tracking error signal generation among the main beam, the first sub beam, and the second sub beam that passes through the second optical branching unit becomes constant, so that stable tracking is achieved. An error signal can be obtained.
[0034]
Preferably, there is further provided a third light branching unit that is disposed between the first light branching unit and the light collecting unit, transmits the light from the light source and guides it to the light collecting unit, and reflects the return light. The third light branching means is constituted by a boundary surface between the first optical medium through which light from the light source passes and the second optical medium through which return light passes.
[0035]
According to this invention, the light from the light source is guided to the light collecting means and the return light is reflected by the third light branching means disposed between the first light branching means and the light collecting means. For this reason, since the second light branching unit can be arranged separately from the optical path from the light source, the second light branching unit can be arranged at a position where the sub beam is separated or an optical position where the main beam and the sub beam are separated. It becomes easy.
[0036]
Preferably, the second optical medium has a reflecting surface disposed between the boundary surface and the second light branching means and parallel to the boundary surface.
[0037]
According to the present invention, the second optical medium has a reflecting surface that is arranged between the boundary surface and the second light branching means and is parallel to the boundary surface. Therefore, the boundary surface can be controlled by controlling the position of the reflecting surface. And the reflecting surface can be changed, and the position of each beam on the second optical branching means can be easily changed.
[0038]
Preferably, there is further provided a diffraction grating which is disposed between the first light branching unit and the light collecting unit, transmits light from the light source and guides it to the light collecting unit, and guides the return light to the second light branching unit. .
[0039]
According to the present invention, since the diffraction grating is used for branching the return light, it can be easily configured and the position of the beam on the second light branching means can be easily separated by the hologram effect of the diffraction grating. Can do.
[0040]
Preferably, the first light branching means is a diffraction grating.
According to this invention, since the first light branching means is a diffraction grating, the first light branching means can be easily manufactured, and the optical pickup device can be easily manufactured.
[0041]
Preferably, the second light branching means is a diffraction grating.
According to this invention, since the second light branching means is a diffraction grating, the second light branching means can be easily manufactured, and the optical pickup device can be easily manufactured.
[0042]
Preferably, the first and second light branching units are formed on one optical substrate. According to the present invention, since the first and second light branching means are formed on one optical substrate, the configuration of the optical pickup device is simplified and the size can be reduced.
[0043]
Preferably, the first and second light branching means are formed on opposing surfaces of the optical substrate.
[0044]
According to the present invention, since the first and second light branching means are formed on the opposing surfaces of the optical substrate, when the first and second light branching means are diffraction gratings, the grooves Even if the conditions such as depth are different, they can be manufactured without being affected by each other's conditions.
[0045]
Preferably, the third light branching unit is formed on the same optical substrate as the first light branching unit or the second light branching unit.
[0046]
According to this invention, since the diffraction grating is formed on the same optical substrate as the first light branching means and the second light branching means, the diffraction grating, the first light branching means, and the second light branching means. Can be easily manufactured, and the relative positions of the diffraction grating, the first light branching means, and the second light branching means can be prevented from shifting. In addition, the configuration of the optical pickup device can be further simplified and the size can be reduced.
[0047]
Preferably, the light source and the photodetector are housed in one package, and the optical substrate is fixed to the outside of the package.
[0048]
According to the present invention, the light source and the photodetector are housed in one package, and the optical substrate is fixed to the outside of the package, so that the productivity and reliability of the optical pickup device are improved.
[0049]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol in the figure shows the same or equivalent member, and the overlapping description is not repeated.
[0050]
(First embodiment)
FIG. 1 is a diagram illustrating a schematic configuration of an optical system of the optical pickup device according to the first embodiment. 1A shows a plan view, and FIG. 1B shows a side view of the plan view of FIG. 1A viewed from the right side of the drawing. Referring to FIGS. 1A and 1B, linearly polarized light (P-polarized light) emitted from a semiconductor laser 11 (light source) is diffracted by a three-beam diffraction grating 1 (first light branching means). As a result, the light is branched into three light beams: a main beam that is 0th-order diffracted light, a first subbeam that is ± 1st-order diffracted light, and a second subbeam. Since ± first-order diffracted light is generated in the Y direction shown in the drawing, it is not shown in the plan view of FIG. Although slightly higher order diffracted light than ± 1st order diffracted light is generated, it is not mentioned here because it is not related to the function of the optical pickup device.
[0051]
The three-beam diffraction grating 1 has a linear grating shape as shown in FIG. The three lights that have passed through the three-beam diffraction grating 1 pass through the beam splitter 3 (third light branching means). The beam splitter 3 is configured by a boundary surface in which an optical glass material 8 (first optical medium) having a triangular cross section and an optical glass material 6 (second optical medium) having a parallelogram cross section are bonded together. As a whole, the optical block 3a is used. The beam splitter 3 is a polarization beam splitter (hereinafter referred to as “PBS”). For convenience of explanation, the PBS 3 may be expressed as the inclined surface 3.
[0052]
The three lights transmitted through the PBS 3 are circularly polarized by the quarter wavelength plate 9 disposed on the PBS 3 and enter the collimating lens 12. The three lights converted into parallel light by the collimator lens 12 are collected by the objective lens 13 and applied to the optical disk 10 as an optical recording medium.
[0053]
The three return lights from the optical disk 10 return in order to the objective lens 13, the collimating lens 12, and the ¼ wavelength plate 9 and pass through the ¼ wavelength plate 9 to become linearly polarized light (S-polarized light). Reflected in the right direction in FIG. 1A and further reflected downward in the drawing by a reflecting surface 14 configured in parallel with the inclined surface 3, the light enters the hologram 2 (second light branching means). In the hologram 2, each of the three return lights is diffracted into ± first-order diffracted lights 4 and 5 and enters the photodetector 7.
[0054]
The three-beam diffraction grating 1 and the hologram 2 are diffraction gratings formed on the opposing surfaces 15 a and 15 b of the optical substrate 15. The three-beam diffraction grating 1 is formed on the surface 15a, and the hologram 2 is formed on the surface 15b. In the present embodiment, the refractive index of the optical glass material 6 is 1.87, and the refractive index of the optical substrate is 1.457.
[0055]
FIG. 1B shows the state of the optical path of the return light from the optical disc 10. A dotted line indicates the main beam M, and a thin solid line indicates the first sub-beam A and the second sub-beam B, respectively. The hologram 2 is disposed at a position (Z1 in FIGS. 1A and 1B) where the sub beams A and B are separated from each other. Note that the reason why each light beam is shown in the optical block 3a as being interrupted and shifted is that in the return path, as shown in FIG. 1A, the optical path between the PBS 3 and the reflecting surface 14 (the optical path in the optical glass material 6). This is because the beam diameter is different between the PBS 3 surface and the reflecting surface 14. In FIG. 1B, the ± first-order diffracted light from the hologram 2 is not shown in order to prevent the drawing from being complicated.
[0056]
FIG. 3 is a diagram illustrating the shape of the hologram 2 and the position of light on the hologram 2. The substantially circular portions in the figure indicate the main beam M, sub beam A, and sub beam B. Referring to FIG. 3, sub-beams A and B are separated without overlapping. This is because the hologram 2 is installed at the position Z1 in FIGS. 1 (A) and 1 (B). The position Z1 where the hologram 2 is installed is called an optical position where the sub-beams A and B are separated.
[0057]
The hologram 2 has a diffraction grating formed in a rectangular region H, and a dividing line T1 parallel to the track direction (Y direction) of the optical disk and a dividing line R1, R2, parallel to the radial direction (X direction) of the optical disk. It has areas b, c, d, e, f, g, i, j divided by R3. The dividing line T1 divides the sub beams A and B and the main beam M into two in the radial direction. Further, the dividing line R1 divides the main beam M into two parts (divided into two equal parts) in the track direction at a position that does not reach both sub-beams between the separated sub-beams A and B. The dividing line R2 divides the sub-beam A and the dividing line R3 divides the sub-beam B into two in the track direction (Y direction).
[0058]
Thus, the hologram 2 has a plurality of regions b, c, d, e, f, g, i, and j divided by the dividing line inside the region H, and the diffraction direction of the diffraction grating in these regions. The diffraction angle is different. Here, the diffraction efficiencies of the regions b, c, d, e, f, g, i, and j are constant, but the diffraction efficiencies can be varied.
[0059]
In addition, each region described below using a dividing line is limited to the inside of the region H. That is, regions i and j obtained by dividing the region sandwiched by the dividing lines R1 and R2 in the radial direction by the dividing line T1, and regions b and c obtained by dividing the region sandwiched by the dividing lines R1 and R3 in the radial direction by the dividing line T1. Regions d and e obtained by dividing the upper region of the dividing line R2 in the radial direction by the dividing line T1, and regions f and g obtained by dividing the lower region of the dividing line R3 in the drawing by the dividing line T1 in the radial direction. is there.
[0060]
The hologram 2 shifts in the Y direction of the beam due to the Y 2 mounting tolerance of the hologram 2 and a tolerance that changes the relative mounting position of the hologram 2 and the beam splitter 3 in the Y direction. This is particularly effective when the direction position varies.
[0061]
FIG. 4 shows a beam arrangement on the photodetector 7 of the return light diffracted by the hologram 2. Normally, each beam is designed to be focused on the photodetector 7, so that the beam shape is substantially a point. In FIG. 4, in order to make it easier to understand the light divided in each region of the hologram 2. It is expressed with a slightly defocused beam shape. The beam group on the right side of the drawing shows a group of + 1st order diffracted light 4 by the hologram 2, and the beam group on the left side shows a group of −1st order diffracted light 5. The code | symbol attached | subjected to each beam has the following meaning.
[0062]
(1) First character of code: “4” is added to the + 1st order diffracted light, and “5” is added to the −1st order diffracted light.
[0063]
(2) Second character of the code: “M” is attached to the main beam and “A” or “B” is attached to the sub beam.
[0064]
(3) Third character of the code: indicates the divided area of the hologram 2 in which the light is diffracted, and “b”, “c”, “d”, “e”, “f” corresponding to the diffracted divided area , “G”, “i”, “j”.
[0065]
For example, the symbol 4Mc means light that has passed through the region c of the hologram 2 in the main beam M of the + 1st order diffracted light.
[0066]
Moreover, the code | symbol attached | subjected to the light-receiving part has the following meaning.
(1) First character of code: “7” indicating a photodetector is attached.
[0067]
(2) Second character of the code: “M” is attached when the received beam is the main beam, “A” is attached when the beam is sub-beam A, and “B” is attached when the beam is sub-beam B.
[0068]
(3) The third character of the code indicates the divided area of the hologram 2 diffracted by the received beam, and “b”, “c”, “d”, “e”, “f” corresponding to the diffracted divided area. , “G”, “i”, “j”.
[0069]
Further, the output signal of the light receiving unit is represented by a code in which the code 7 attached to each light receiving unit is replaced with S. Further, when both the + 1st order diffracted light and the −1st order diffracted light of the same beam are used, numbers such as 1 and 2 are added to the end, such as 7Mi1 and 7Mi2. Further, 7Mc1 and 7Mc2 for detecting the focus error signal are not limited to the above, but each differential needs to be taken and two light receiving parts are required, so that 1 and 2 are added to the end. . The light indicated by the reference numerals with () indicates light that is not used for signal detection in the present embodiment, but is not limited thereto, and each light may be used as appropriate.
[0070]
Next, a detection form of the tracking error signal will be described. Since the main beam diffracted lights 5Mb and 5Mc in the regions b and c contain optical diffraction components generated in the tracks, the main beam push-pull signal (MPP) is generated by the differential of the output signals of the 5Mb and 5Mc. , Generated by equation (5). Similarly, for the diffracted lights 4Ad and 4Ae of the sub beam A in the regions d and e, the push-pull signal (SPPA) of the sub beam A is generated by the equation (6) by the differential of the output signal. Similarly, for the diffracted beams 4Bb and 4Bc of the sub-beam B in the regions b and c, the push-pull signal (SPPB) of the sub-beam B is generated by the equation (7) by the differential output signal. The tracking error signal (TES2) by the DPP method is detected using Expression (8).
[0071]
MPP = SMb−SMc (5)
SPPA = SAd−SAe (6)
SPPB = SBb−SBc (7)
TES2 = MPP-k [SPPA + SPPB] (8)
Next, the constant k in Expression (8) will be described. The constant k is a constant for correcting the intensity ratio between the main beam M and the sub beams A and B. In the present embodiment, the intensity ratio of the main beam M: sub beam A: sub beam B in the three-beam diffraction grating 1 is 10: 1: 1, and the two sub beams A and B and the main beam M are divided by the dividing line R2, R2. Each of R3 and R1 is divided in half. Therefore, the beam intensity ratio detected by the light receiving element is M: A: B = 10 × 1/2: 1 × 1/2: 1 × 1/2 = 10: 1: 1. Therefore, if k = 10 / (1 + 1) = 5 and k = 5, the DC offset generated by the lens shift or the like can be canceled in the equation (8).
[0072]
In the present embodiment, the dividing lines R2 and R3 bisect the sub-beams A and B, respectively, and further, since the dividing line T1 is located at the center of the sub-beams A and B, the regions b, c, d, The light quantity of e becomes equal. Therefore, since the outputs of SPPA and SPPB are equal, it is possible to eliminate the unbalance of the output signal due to the amount of light rays related to offset removal.
[0073]
The optical pickup device in the present embodiment was compared with a conventional optical pickup device under the following conditions.
[0074]
(1) As the condenser lens system, an objective lens 13 having a focal length of 2.15 mm and NA = 0.65 and a collimating lens 12 having a focal length of 13.6 mm and NA = 0.13 were used.
[0075]
(2) A DVD-RW disc having a track pitch of 0.74 μm, a groove width of 0.24 μm, and a groove depth of 0.028 μm was used as the optical recording medium 10 as an optical recording medium.
[0076]
(3) The semiconductor laser 11 having a wavelength of 650 nm, a radiation angle of 22 ° corresponding to the track direction, and a radiation angle of 8 ° corresponding to the radial direction was used.
[0077]
(4) The light on the disk is positioned at a radius r = 24 mm of the substantially innermost circumference of the disk, the distance between the main beam and the sub beam on the disk is 12 μm, and the sub beams A and B cross the guide groove of the disk. A phase difference of 30 ° was given.
[0078]
FIG. 5 shows the detrack amount of the main beam with respect to the intensity ratio of the sub beams. In the optical pickup device according to the present embodiment, the intensity ratio of the sub-beams related to the tracking signal is always a constant value (here, 1) even if the beam is shifted on the hologram due to the tolerance, so that the detrack is a constant value regardless of the tolerance. (About 3 nm). Here, the reason why the detrack is slightly generated (about 3 nm) is that the position where the detrack is performed is a substantially innermost part of the disk and the track has a large degree of curvature. It is.
[0079]
In contrast, in the conventional optical pickup device, the detrack is minimized when the intensity ratio of the sub-beam is about 4.8. However, when the intensity ratio of the sub-beam is shifted from 4.8, the detrack becomes large. The tracking servo is unstable.
[0080]
FIG. 6 is a diagram illustrating a state in which the beam position is shifted on the hologram due to a manufacturing error of the optical pickup device. FIG. 6 shows a state in which three beams are shifted upward in the drawing with respect to the dividing lines R1 to R3 in the radial direction. FIG. 7 is a diagram schematically showing the shapes of the sub beams A and B and the main beam M in a predetermined region of the hologram. FIG. 7 shows the shapes of the sub-beams A and B and the main beam M shown in FIG. 6 in the regions b, c, d, e, i, and j. Other portions of each beam are omitted for convenience of explanation. As is apparent from FIG. 7, the ratio at which the sub beam A is divided by the dividing line R2, the ratio at which the sub beam B is divided by the dividing line R3, and the ratio at which the main beam M is divided by the dividing line R1 are equal. That is, the shapes of the diffracted beams Bb and Bc in the regions b and c, the shapes of the diffracted beams Ad and Ae in the regions d and e, and the shapes of the main beams Mi and Mj in the regions i and j are equal. For this reason, the light amounts of the diffracted lights Bb and Bc by the regions b and c are equal to the light amounts of the diffracted lights Ad and Ae by the regions d and e.
[0081]
Therefore, even when the beam position is shifted with respect to the dividing line due to a manufacturing error or the like, the outputs of SPPA and SPPB are equal, so that the output signal unbalance due to the amount of light rays related to offset removal can be eliminated. In this way, when the sub-beams are divided by the dividing lines R2 and R3 parallel to the radial direction, a part of the sub-beams on the same direction side with respect to the dividing lines R2 and R3 (in FIG. 7, the dividing lines R2 and R3 By using the diffracted lights Ad and Ae and the diffracted lights Bb and Bc) shown by diagonal lines in the upper sub-beam, the respective sub-beam push-pull signals can be generated, so that the SPPA and SPPB outputs can always be made equal and the sub-beam imbalance is eliminated. Is done.
[0082]
Other forms of signal detection are as follows. At the time of reproduction of an optical disk on which pit information is recorded, TES3 can be detected by the DPD method by detecting a change in the phase difference between SMc and SMb.
[0083]
The focus error signal (FES) can be detected by using the equation (9) by receiving the light beam 4Mc of the + 1st order diffracted light of the hologram 2 on the dividing line of the light receiving portions 7Mc1 and 7Mc2, and by differentially outputting the light receiving portions. . Also, the recorded information signal (RF) can be detected using equation (10).
[0084]
FES = SMc1-SMc2 (9)
RF = SMb + SMc + SMi + SMj (10)
The three-beam diffraction grating 1 and the hologram 2 used in the present embodiment are formed on the optical substrate 15. In particular, when the depths of the two diffraction gratings are different, the manufacturing conditions are different, so that they are formed on the opposing surfaces 15a and 15b, respectively. Therefore, by appropriately controlling the thickness of the optical substrate 15, the hologram 2 can be arranged at an optical position where the sub beams A and B are separated from each other.
[0085]
The arrangement of the hologram 2 can be controlled in addition to the thickness of the optical substrate 15. As described above, the optical glass material 6 has a parallelogram shape in cross section and has a reflective surface 14 parallel to the inclined surface 3. Therefore, by controlling the distance between the inclined surface 3 and the reflecting surface 14 (for example, controlling the thickness of the substrate material of the optical glass material 6 by polishing or the like), a state where the sub beams A and B are separated on the hologram 2 is obtained. Can do. This is possible because the inclined surface 3 makes the optical path of the return light different from the optical path until the light irradiated from the semiconductor laser 11 reaches the optical recording medium.
[0086]
Further, the hologram 2 and the three-beam diffraction grating 1 are formed integrally on one optical substrate, and the PBS 3 and the reflecting surface 14 are shaped like the optical block 3a, so that the optical element can be manufactured and the optical pickup device can be used. Can be mounted and fixed on the package 16 such as CAN, and semiconductor elements such as the semiconductor laser 11 and the photodetector 7 can be accommodated in the package 16, so that the productivity of the optical pickup device and Reliability is improved.
[0087]
(Second Embodiment)
Next, an optical pickup device in the second embodiment will be described. Constituent elements of the same type as those of the first embodiment are denoted by the same reference numerals, and redundant description will not be repeated.
[0088]
The optical pick-up device according to the second embodiment differs from the optical pickup device according to the first embodiment in the following points. In the optical pickup device according to the first embodiment, the optical position where the hologram 2 is arranged is the position where the sub beams A and B are separated (position Z1 shown in FIG. 1). On the other hand, in the optical pickup device in the second embodiment, the optical position of the hologram 2 is different in that the main beam M and the sub beams A and B are separated from each other as shown in FIG.
[0089]
FIG. 8 is a diagram illustrating the shape of the hologram 2 and the position of light on the hologram 2 of the optical pickup device according to the second embodiment. Referring to FIG. 8, a dividing line T1 parallel to the track direction divides sub-beams A and B and main beam M in the X direction, and a dividing line parallel to the radial direction is only R1, and the main beam in the Y direction. To divide. The hologram 2 has four regions b, c, d, and e in the region H by the dividing lines T1 and R1. As described above, the hologram 2 has a simple configuration in which the number of dividing lines and the divided areas are reduced. Constructing the hologram 2 in this way is particularly effective when the height tolerance in the Z direction changes and variations occur such that the intervals between the sub beams are increased.
[0090]
FIG. 9 shows the arrangement of the light diffracted by the hologram 2 on the photodetector 7 and the arrangement of the light receiving parts for receiving them. The reference numerals assigned to the beam and the light receiving unit have the same meaning as described in the first embodiment. The reference numeral 7 of each light receiving unit is changed to S to represent the output.
[0091]
The diffracted light beams 4Mb and 4Mc of the main beam in the regions b and c of the hologram 2 include a diffraction component of light due to reflection on the track. Therefore, a push-pull signal (MPP) of the main beam is obtained by differential of the output signals. It is generated using equation (11). Alternatively, the diffracted light 4Md and 4Me of the main beam in the hologram areas d and e may also be used and the equation (11 ′) may be used. Alternatively, the push-pull signal MPP3 may be generated using Expression (11 ′) using 5Mb, 5Mc, 5Md, and 5Me of the −1st order diffracted light in the regions b, c, d, and e.
[0092]
Similarly, for the diffracted lights 4Ad and 4Ae of the sub-beam A in the areas d and e of the hologram 2, a push-pull signal (SPPA) of the sub-beam A is generated by using the equation (12) by the differential of the output signals. . Similarly, for the diffracted lights 4Bb and 4Bc of the sub-beam B in the regions b and c of the hologram 2, the push-pull signal (SPPB) of the sub-beam B is generated using the equation (13) by the differential of the output signals. . Therefore, the tracking error signal (TES2) by the DPP method can be detected using the equation (14).
[0093]
MPP = SMb−SMc (11)
MPP2 = (SMb + SMd) − (SMc + SMe) (11 ′)
SPPA = SAd−SAe (12)
SPPB = SBb−SBc (13)
TES2 = MPP2-k [SPPA + SPPB] (14)
In the case of Expression (14), for the constant k, the intensity of each beam by the three-beam diffraction grating 1 related to the generation of the tracking error signal detected by the photodetector is M: A: B = 10: 1: Since the diffracted light in the regions b, c, d, and e (that is, the light in the entire main beam) is used for the main beam M, the beam intensity ratio detected by the light receiving element is M: A: B. = 10 × 1: 1 × 1: 1 × 1 = 10: 1: 1. Therefore, k = 10 / (1 + 1) = 5 may be set. Thereby, in the formula (14), the DC offset generated by the lens shift or the like can be canceled.
[0094]
In the present embodiment, a push-pull signal (SPPA, SPPB) is generated using the entire sub-beams A and B. Furthermore, since the only division in parallel with the radial direction is R1, even if the division line R1 shifts due to manufacturing variations of the optical pickup device, the sub-beams are not lost, and the entire sub-beams A and B are always generated as a push-pull signal. Can be used. Accordingly, since the outputs of SPPA and SPPB are always equal, it is possible to eliminate the unbalance of the output signal due to the amount of light rays related to offset removal. Further, since the entire sub-beam is used for the push-pull signal generation, the S / N of the tracking error signal is improved.
[0095]
Other forms of signal detection are as follows. At the time of reproduction of an optical disk on which pit information is recorded, TES3 can be detected by the DPD method by detecting a change in the phase difference between SMc and SMb.
[0096]
Regarding the focus error signal (FES), since the entire main beam is divided by the dividing line T1, the diffracted lights 4Md and 4Me are separated and incident on different positions on the photodetector 7. Accordingly, a separate light receiving unit is formed at each position, the light beam 4Md is received on the dividing line of the light receiving units 7Md1 and 7Md2, the light beam 4Me is received on the dividing line of the light receiving units 7Me1 and 7Me2, and the output of the light receiving unit is differentially differentiated. Is detected using equation (15). The recorded information signal (RF) is detected using equation (16).
[0097]
FES = (SMd1-SMd2) + (SMe1-SMe2) (15)
RF = SMb + SMc + SMd + SMe (16)
The three-beam diffraction grating 1 and the hologram 2 used in the optical pickup device in the present embodiment are formed on the optical substrate 15. In particular, when the depths of the two diffraction gratings are different, the manufacturing conditions are different. Therefore, the diffraction gratings are formed on the opposing surfaces 15a and 15b as in the present embodiment. By appropriately controlling the thickness of the optical substrate 15, the hologram 2 can be disposed at an optical position where the sub beams A and B and the main beam M are separated from each other.
[0098]
The arrangement of the hologram 2 can be controlled in addition to the thickness of the optical substrate 15. As described above, the optical glass material 6 has a parallelogram shape in cross section and has a reflective surface 14 parallel to the inclined surface 3. Therefore, the main beam M and the sub beams A and B are separated on the hologram 2 by controlling the distance between the inclined surface 3 and the reflecting surface 14 (for example, controlling the thickness of the base material of the optical glass material 6 by polishing or the like). The state can be obtained.
[0099]
Further, the hologram 2 and the three-beam diffraction grating 1 are formed integrally on one optical substrate, and the PBS 3 and the reflecting surface 14 are shaped like the optical block 3a, so that the optical element can be manufactured and the optical pickup device can be used. Can be mounted and fixed on the package 16 such as CAN, and semiconductor elements such as the semiconductor laser 11 and the photodetector 7 can be housed in the package 16, so that the productivity and reliability of the optical pickup device can be accommodated. Improves.
[0100]
Note that the hologram 2 used in the second embodiment may be used at an optical position where the sub-beams A and B are separated from each other.
[0101]
<Modification of Hologram 2>
Next, a modification of the hologram 2 of the optical pickup device in the second embodiment will be described. FIG. 10 is a diagram illustrating the shape of another hologram 2 and the position of light on the hologram 2 of the optical pickup device according to the second embodiment. Referring to FIG. 10, another hologram 2 is divided into five regions a, b, c, d, e by dividing lines R1, R2 parallel to the radial direction and dividing lines T1, T2 parallel to the track direction. Divided. The dividing line T1 divides the sub beam A in the X direction, and the dividing line T2 divides all of the sub beam B and a part of the main beam M in the X direction. The dividing line R1 divides the main beam in the Y direction. If another hologram 2 is configured in this way, it is particularly effective when the height tolerance in the Z direction changes and a variation occurs such that the interval between the sub beams is increased. Further, since the beam for generating the focus error signal can be the light diffracted in the region a in the main beam M, the number of light receiving portions can be reduced.
[0102]
FIG. 11 shows the arrangement of the light diffracted by another hologram 2 on the photodetector 7 and the arrangement of the light receiving parts for receiving them. The reference numerals assigned to the beam and the light receiving unit have the same meaning as described in the first embodiment. The reference numeral 7 of each light receiving unit is changed to S to represent the output.
[0103]
The main beam diffracted lights 5Mb and 5Mc in the regions b and c of the other hologram 2 contain light diffracted components due to reflection at the track, so that the main beam push-pull signal (MPP) is obtained by the differential of these output signals. Is generated using equation (5). Similarly, for the diffracted lights 4Ad and 4Ae of the sub-beam A in the regions d and e of another hologram 2, the push-pull signal (SPPA) of the sub-beam A is generated using the equation (6) by the differential of the output signals. Is done. Similarly, for the diffracted lights 4Bb and 4Bc of the sub-beam B in the regions b and c of the other hologram 2, the push-pull signal (SPPB) of the sub-beam B is generated using the equation (7) by the differential of the output signals. Is done. Therefore, the tracking error signal (TES2) by the DPP method can be detected using Expression (8).
[0104]
In the case of Expression (8), for the constant k, the intensity of each beam by the three-beam diffraction grating 1 related to the generation of the tracking error signal detected by the photodetector is M: A: B = 10: 1: Since the diffracted light in the regions b and c, that is, semicircular light is used for the main beam M, the beam intensity ratio detected by the light receiving element is M: A: B = 10 × 1/2: 1 × 1: 1 × 1 = 5: 1: 1. Therefore, k = 5 / (1 + 1) = 2.5 may be set. Thereby, in Formula (8), the DC offset generated by the lens shift or the like can be canceled.
[0105]
In the present embodiment, a push-pull signal (SPPA, SPPB) is generated using the entire sub-beams A and B. Accordingly, since the outputs of SPPA and SPPB are always equal, it is possible to eliminate the unbalance of the output signal due to the amount of light rays related to offset removal. Further, since the entire sub-beam is used for the push-pull signal generation, the S / N of the tracking error signal is improved.
[0106]
Other forms of signal detection are as follows. At the time of reproduction of an optical disk on which pit information is recorded, TES3 can be detected by the DPD method by detecting a change in the phase difference between SMc and SMb.
[0107]
For the focus error signal (FES), diffracted light 4Ma that passes through the region a of the main beam M is used. Therefore, the diffracted light 4Ma is received on the dividing lines of the light receiving parts 7Ma1 and 7Ma2, and is detected by using the expression (17) by adding the outputs of the light receiving parts. The recorded information signal (RF) is detected using equation (18).
[0108]
FES = SMa1-SMa2 (17)
RF = SMb + SMc + SMa3 (18)
(Third embodiment)
FIG. 12 is a side view of the optical system of the optical pickup device according to the third embodiment. The same or corresponding members as those in the optical pickup devices in the first and second embodiments are denoted by the same reference numerals, and redundant description will not be repeated.
[0109]
The optical pickup device in the third embodiment is different from the optical pickup device in the first embodiment in that a diffraction grating is used instead of the beam splitter 3. As this diffraction grating, it is preferable to use a diffraction grating having a hologram effect in order to separate the sub beams A and B and the main beam.
[0110]
Referring to FIG. 12, the linearly polarized light (P-polarized light) emitted from the semiconductor laser 11 (light source) is diffracted by the three-beam diffraction grating 1 (first light branching means), thereby becoming a main beam that becomes zero-order diffracted light. The first sub-beam and the second sub-beam, which are ± first-order diffracted light, are branched into three lights. Since diffraction occurs in the Y direction in the drawing, the sub-beams A and B are not shown. Although slightly higher order diffracted light than ± 1st order diffracted light is generated, it is not mentioned because it is irrelevant to the function of the optical pickup device.
[0111]
The three lights that have passed through the three-beam diffraction grating 1 pass through the diffraction grating 30 (third light branching means). The diffraction grating 30 is formed on one surface (upper surface in the drawing) of the optical substrate 30a. The three-beam diffraction grating 1 and the hologram 2 are formed on the surface (the lower surface in the drawing) facing the surface on which the diffraction grating 30 is formed of the optical substrate 30a.
[0112]
The three lights transmitted through the diffraction grating 30 become circularly polarized light by the quarter wavelength plate 9 disposed on the optical substrate 30 a and enter the collimating lens 12. The three lights converted into parallel light by the collimator lens 12 are collected by the objective lens 13 and applied to the optical disk 10 serving as an optical recording medium. The three return lights from the optical disk 10 return in order to the objective lens 13, the collimating lens 12, and the ¼ wavelength plate 9 and pass through the ¼ wavelength plate 9 to become linearly polarized light (S-polarized light). 30 is diffracted rightward in the drawing and enters the hologram 2 (second optical branching means).
[0113]
In the hologram 2, each of the three return lights is diffracted into ± first-order diffracted lights 4 and 5 and enters the photodetector 7. The hologram 2 is composed of a hologram similar to that described in the first or second embodiment, and the optical position at which the sub-beams A and B are separated (see FIG. 3), or the sub-beams A and B and the main beam. M is disposed at an optical position (see FIGS. 8 and 10) at a distance. The same photodetector as that described in the first or second embodiment is also applied to the photodetector 7.
[0114]
Also, the tracking error signal detection mode by the DPP method and other signal detection methods are applied in the same manner as in the first or second embodiment.
[0115]
By appropriately determining the thickness and refractive index of the optical substrate 30a, the separation of the beams on the hologram 2 is facilitated. Accordingly, the diffraction grating 30 can be used for simple configuration, and the diffraction grating 30 has a hologram effect. By appropriately configuring the hologram effect, the degree of convergence of the beam from the diffraction grating 30 toward the hologram 2 is controlled. it can. For this reason, the separation structure of each beam on the hologram 2 becomes easy. Further, the diffraction grating 30 has an effect of promoting the beam separation action on the hologram 2.
[0116]
Further, by forming the diffraction grating 30, the hologram 2 and the three-beam diffraction grating 1 in an integrated manner on one optical substrate 30a, it becomes easy to manufacture an optical element and to arrange and attach it in the optical pickup device, such as CAN. Since the semiconductor elements such as the semiconductor laser 11 and the photodetector 7 can be housed in the package 16, the productivity and reliability of the optical pickup device are improved.
[0117]
According to the optical pickup device in the present embodiment, the hologram 2 is installed at an optical position where the sub-beams A and B related to the tracking error signal are separated on the hologram 2. Since the division line R1 that divides the main beam M in the track direction in the hologram 2 can be configured not to divide the sub beams A and B, the degree of freedom in using the sub beams A and B is improved, and a stable tracking error signal is obtained. Can do.
[0118]
Further, since the hologram 2 has a plurality of regions divided by a dividing line parallel to the radial direction of the optical recording medium and a dividing line parallel to the track direction, the main beam M and the sub beams A and B can be divided. The tracking error signal can be generated by the DPP method and the focus error signal can be generated by one hologram.
[0119]
Further, since the hologram 2 is installed at an optical position where the sub beams A and B and the main beam M are separated from each other on the hologram 2, the entire sub beam is used to generate a push-pull signal for offset offset in the tracking error signal by the DPP method. As a result, the degree of freedom in using the sub-beam is further improved, and the signal quality is improved.
[0120]
Further, since the sub-beams A and B are not divided on the hologram 2 by the dividing line R1 parallel to the radial direction, a tracking error signal by the DPP method can be generated using the whole sub-beam, and the signal quality is improved. Servo is stable.
[0121]
Further, on the hologram 2, the sub beams A and B are divided by the dividing lines R2 and R3 so that the shapes of the beams are substantially the same, so that the sub beams A and B used for the tracking error signal by the DPP method are divided by the dividing lines. It can be divided and used partially. Therefore, even if a part of the sub beam overlaps with the main beam on the hologram 2, a tracking error signal by the DPP method can be generated using the light that does not overlap with the main beam. In other words, the main beam and the sub beam do not need to be separated from each other on the hologram 2, and the design of the optical block including the PBS 3, the optical substrate 15, and the like becomes easy.
[0122]
Furthermore, since the light related to the tracking error signal generation in the main beam and the sub beam that have passed through the hologram 2 has substantially the same shape, the constant k in the equation (8) or the equation (14) is constant regardless of the tolerance, A stable tracking error signal can be obtained.
[0123]
Furthermore, since the hologram 2 can be arranged separately from the optical path from the light source by providing the beam splitter 3, it becomes easy to arrange the hologram 2 at a position where the sub beam is separated or a position where the main beam and the sub beam are separated. .
[0124]
Further, since the reflection surface 14 that reflects the light reflected by the beam splitter 3 and guides it to the hologram 2 is provided, the distance between the beam splitter 3 and the reflection surface 14 can be changed by controlling the position of the reflection surface 14. The position of each beam on the hologram 2 can be easily changed.
[0125]
Further, since the diffraction grating 30 is used for branching the return light, it can be easily configured, and the hologram effect of the diffraction grating 30 can be appropriately configured to promote the effect of separating the beam on the hologram 2. Can play. As a result, the beams on the hologram 2 can be easily separated.
[0126]
Further, since the three-beam diffraction grating 1 is used, it can be easily manufactured by a processing means such as photolithography, and the manufacture of the optical pickup device is facilitated.
[0127]
Further, since the hologram 2 is used, it can be easily manufactured by a processing means such as photolithography, and the manufacture of the optical pickup device is facilitated.
[0128]
Furthermore, since the three-beam diffraction grating 1 and the hologram 2 are formed on the same optical substrate 15, the configuration of the optical pickup device is simplified and the size can be reduced.
[0129]
Further, since the three-beam diffraction grating 1 and the hologram 2 are formed on opposite surfaces of the same optical substrate 15, when the three-beam diffraction grating 1 and the hologram 2 are diffraction gratings, the depth of the groove, etc. Even if the conditions are different, they can be manufactured without being affected by each other's conditions.
[0130]
Further, since the three-beam diffraction grating 1, the hologram 2 and the diffraction grating 30 can be formed on one optical substrate 30a, the three-beam diffraction grating 1, the hologram 2 and the diffraction grating 30 can be easily manufactured, and the three-beam diffraction grating 1, It is possible to prevent the relative positions of the hologram 2 and the diffraction grating 30 from shifting. In addition, the configuration of the optical pickup device can be further simplified and the size can be reduced.
[0131]
Furthermore, since semiconductor elements such as the semiconductor laser 11 and the photodetector 7 can be accommodated in the package 16, the productivity and reliability of the optical pickup device are improved.
[0132]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a schematic configuration of an optical system of an optical pickup device according to a first embodiment.
FIG. 2 is a plan view of a three-beam diffraction grating 1 of the optical pickup device according to the first embodiment.
FIG. 3 is a diagram showing the shape of a hologram and the position of light on the hologram of the optical pickup device in the first embodiment.
FIG. 4 is a diagram showing a beam arrangement on a photodetector 7 of return light diffracted by a hologram.
FIG. 5 is a diagram illustrating a detrack amount of a main beam with respect to an intensity ratio of sub beams.
FIG. 6 is a diagram showing a state in which the beam position is shifted on the hologram due to a manufacturing error or the like of the optical pickup device according to the first embodiment.
FIG. 7 is a diagram schematically showing the shapes of a sub beam and a main beam in a predetermined region of a hologram.
FIG. 8 is a diagram showing the shape of the hologram 2 and the position of light on the hologram 2 of the optical pickup device in the second embodiment.
FIG. 9 is a diagram showing each arrangement of light diffracted by the hologram 2 on the photodetector 7 and an arrangement of a light receiving unit for receiving them.
FIG. 10 is a diagram showing the shape of another hologram 2 and the position of light on the hologram 2 of the optical pickup device in the second embodiment.
FIG. 11 is a diagram showing each arrangement of light diffracted by another hologram 2 on the photodetector 7 and an arrangement of a light receiving unit for receiving them.
FIG. 12 is a side view of an optical system of an optical pickup device in a third embodiment.
FIG. 13 is a diagram showing a schematic configuration of a conventional optical pickup device.
FIG. 14 is a diagram illustrating a relationship between a hologram element of a conventional optical pickup device, light diffracted by the hologram element, and a light receiving element.
FIG. 15 shows a beam shape on a hologram element 109 in a conventional optical pickup device.
FIG. 16 is a diagram showing return light diffracted by a hologram in a conventional optical pickup device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 3 beam diffraction grating, 2 hologram, 3 beam splitter (inclined surface), 3a optical block, 6 optical glass material, 7 photodetector, 8 optical glass material, 9 1/4 wavelength plate, 10 optical disk, 11 semiconductor laser, 12 collimating lens, 13 objective lens, 14 reflecting surface, 15 optical substrate, 16 package, 30 diffraction grating, 30a optical substrate.

Claims (14)

A light source for irradiating the optical recording medium with light;
A light condensing means disposed between the light source and the optical recording medium for condensing the light of the light source onto the optical recording medium;
A photodetector formed with a plurality of light receiving portions for receiving return light from the optical recording medium;
A first light branching unit disposed between the light source and the light collecting unit and branching the light of the light source into a main beam, a first sub beam, and a second sub beam;
A second optical branching unit arranged between the condensing unit and the photodetector and further splitting the main beam, the first sub-beam and the second sub-beam;
The second optical branching means is
A first dividing line that divides the main beam in a first direction at a position that does not cover both the first sub-beam and the second sub-beam;
And a second dividing line that divides the first sub-beam or the second sub-beam in the first direction. The second optical branching unit further includes a third dividing line that divides the main beam, the first sub-beam, and the second sub-beam in a second direction perpendicular to the first direction. Item 4. The optical pickup device according to Item 1 . A light source for irradiating the optical recording medium with light;
A light condensing means disposed between the light source and the optical recording medium for condensing the light of the light source onto the optical recording medium;
A photodetector formed with a plurality of light receiving portions for receiving return light from the optical recording medium;
A first light branching unit disposed between the light source and the light collecting unit and branching the light of the light source into a main beam, a first sub beam, and a second sub beam;
A second optical branching unit arranged between the condensing unit and the photodetector and further splitting the main beam, the first sub-beam and the second sub-beam;
The second optical branching means is
A first dividing line that divides the main beam in a first direction at a position that does not cover both the first sub-beam and the second sub-beam;
A fourth dividing line that divides the first sub-beam in a second direction perpendicular to the first direction;
An optical pickup device comprising: a fifth parting line that divides a part of the main beam and the second sub-beam in the second direction starting from a contact point with the first parting line . 4. The optical pickup device according to claim 3, wherein the second optical branching unit is arranged such that each of the first sub-beam and the second sub-beam is optically spaced from the main beam by a predetermined distance. Of the main beam, the first sub-beam, and the second sub-beam passing through the second optical branching unit, each light related to tracking error signal generation has substantially the same shape on the second optical branching unit. characterized in that there, the optical pickup device according to any one of claims 1-4. A third light branching unit that is disposed between the first light branching unit and the light collecting unit, transmits light from a light source and guides the light to the light collecting unit, and reflects the return light;
The said 3rd light branch means is comprised by the interface of the 1st optical medium through which the light from a light source passes, and the 2nd optical medium through which the said return light passes, The any one of Claims 1-4 The optical pickup device described in 1. The optical pickup device according to claim 6 , wherein the second optical medium has a reflecting surface that is disposed between the boundary surface and the second light branching unit and is parallel to the boundary surface. A diffraction grating disposed between the first light branching unit and the light collecting unit, which transmits light from a light source and guides it to the light collecting unit, and guides the return light to the second light branching unit; further comprising an optical pickup device according to any one of claims 1-4. It said first optical branching means is a diffraction grating, an optical pickup device according to any one of claims 1-4. It said second optical branching means is a diffraction grating, an optical pickup device according to any one of claims 1-4. It said first and second optical branching means is formed on one optical substrate, the optical pickup device according to any one of claims 1-4. The optical pickup device according to claim 11, wherein the first and second light branching units are formed on opposing surfaces of the optical substrate. The optical pickup device according to claim 8 , wherein the diffraction grating is formed on the same optical substrate as the first light branching unit and the second light branching unit. The light source and the photodetector are housed in one package;
Wherein the optical substrate is fixed to the outside of the package, the optical pickup device according to any one of claims 11 to 13.

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