JPH08273172A - Optical pickup device and method therefor - Google Patents

Abstract

PURPOSE: To realize on optical pickup device and method capable of reducing the track detecting error due to the deviation of an optical axis. CONSTITUTION: An optical disk 5 is irradiated by the luminous flux from a semiconductor laser 1 through in order of a collimate lens 2, a polarized light separating element 3, an objective lens 4, and a substrate 9 being a refractive index ellipsoid with uniaxial anisotropy such as the optical anisotropy having the main axis in the thickness direction. After the reflected light is passed through the substrate 9 and the objective lens 4, the component perpendicular to the polarization direction X of the semiconductor laser is separated by the polarized light separating element 3, then the light is received by a photodetector 6. Since the reflected light S is received on the position separated from a dividing line 8 on the light receiving surface 7, the track detecting error is reduced even when the deviation ▵S of the optical axis occurs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device and method, and more particularly to an optical pickup device and an optical disc for an optical disc device for reducing a track detection error due to an optical axis shift.

[0002]

2. Description of the Related Art FIGS. 10A and 10B are views for explaining an example of a conventional optical pickup device. FIG. 10A is a main part configuration diagram, and FIG. 10B is a BB line in FIG. 10A. Arrow view, Figure 1
0 (c) is a detailed view of the light receiving surface when the optical axis shift occurs. In this example, the light flux emitted from the semiconductor laser 21 is made into substantially parallel light by a collimator lens 22, passes through a beam splitter 23, and an optical disk 25 by an objective lens 24.
The information is recorded on the optical disc 25 or the optical disc 25 is irradiated with it as a minute spot.
The above information is reproduced, and the light reflected from the optical disc 25 is reflected by the objective lens 24 and the beam splitter 2.
The light is received by the two-divided light receiving element 26 via the light receiving element 3 and the two-divided light receiving element 26 is composed of two light receiving surfaces 27a and 27b.
The tracking error is detected by the signal output from the light receiving surface 27 of the.

Further, in this example, the light receiving surface 27a, and
The signal output from 27b is the same as 27a, and
When represented by 27b, the tracking error signal TE is T
E = 27a-27b (this signal TE
The detection method is called a push-pull method and is widely used.) This signal TE is mainly used to move the objective lens 24, whereby a laser beam (a minute spot of light flux) is generated. Is designed to accurately track a predetermined track on the optical disk 25.

[0004]

FIG. 11 is a diagram for explaining the tracking error signal TE when the optical axis shift occurs in the example shown in FIG. In the example shown in FIG. 10, the semiconductor laser 21 and the collimator lens 2
2, due to a feed error of the optical pickup main body to which the beam splitter 23, the two-divided light receiving element 26, etc. are fixed,
The objective lens 24 is 200 to 200
There is a case where the deviation is about 400 μm (this deviation is generally called an optical axis deviation). When this optical axis deviation does not occur, as shown in FIG. The center of the reflected light S from the optical disk 25 is on the dividing line 28 of the light receiving surface 27, and the tracking error signal TE is 0 on each track as shown in FIG.
become.

However, if there is an optical axis shift, FIG.
As shown in FIG. 11, the center of the reflected light S from the optical disc 25 on the light receiving surface 27 deviates from the dividing line 28 of the light receiving surface 27 by ΔS, and as shown in FIG. Due to the movement, even if an attempt is made to perform tracking on n tracks, the tracking error signal TE is shifted to the n + 1 track side by ΔS, and the tracking error signal TE does not become 0 on the tracks. As described above, when the optical axis is displaced, an offset occurs in the tracking error signal TE, and as a result, a track detection error (ΔS in the example shown in FIG. 11B) occurs. .

To solve the above problems, for example, Japanese Patent Publication No. 4-3013 discloses an information recording medium (optical disk).
By using the fact that the above plurality of tracks act as a diffraction grating, the light receiving surface (light receiving element) for detecting track deviation is arranged in the interference region of the 0th order diffracted light and the ± 1st order diffracted light of the photodetector,
The light-receiving surface has an axially symmetrical shape with respect to the track direction, and is arranged in an area narrower than the interference area by the maximum movement amount of the optical axis shift of the reflected light caused by the track following or the tilt of the disk. In order to reduce the track detection error due to the shift of the optical axis in the push-pull method, the one in which the light receiving range of the photodetector is limited is proposed. However, in this example, the light receiving surface for detecting the track deviation has to be arranged within the limited range of the photodetector, and there is a concern that it takes time to manufacture the photodetector.

The present invention has been made in view of the above circumstances, and an object thereof is to realize an optical pickup device and an optical disk capable of reducing a track detection error due to an optical axis shift. .

[0008]

In order to solve the above-mentioned problems, the present invention irradiates a light beam emitted from a semiconductor laser onto an optical disc through a polarization separation element and an objective lens, and reflects light reflected from the optical disc. In an optical pickup device for receiving a light through a light receiving element through an objective lens and the polarization separation element and tracking a spot on the optical disc according to the output of the light receiving element, (1) the optical anisotropy has a main axis in the thickness direction. The optical disc, which has a substrate that is a uniaxially anisotropic refractive index ellipsoid, and irradiates the optical flux through the polarization separation element, the objective lens, and the substrate onto the optical disc. After passing the reflected light from the substrate and the objective lens in this order, a component orthogonal to the polarization direction of the semiconductor laser is separated by the polarization separation element. Then, the separated light is received by the light receiving element, or (2) a polarizing element and a substrate which is a uniaxial anisotropic refractive index ellipsoid having a principal axis in the thickness direction. A light beam emitted from the semiconductor laser, the polarization separation element, the polarization element, the objective lens,
After irradiating the optical disc through the substrate in this order, and passing the reflected light from the optical disc through the substrate, the objective lens, and the polarizing element in this order, the polarization separating element is orthogonal to the polarization direction of the semiconductor laser. The components are separated and the separated light is received by the light receiving element, or (3) the light beam emitted from the semiconductor laser is the polarization separating element,
Through the order of the objective lenses, an optical disc made of a substrate which is a uniaxially anisotropic refractive index ellipsoid whose optical anisotropy has a principal axis in the thickness direction is irradiated, and the reflected light from the optical disc is irradiated onto the optical disc. After passing through the polarizing element in this order, a component orthogonal to the polarization direction of the semiconductor laser is separated by the polarization separating element, and the separated light is received by the light receiving element, or (4) from the semiconductor laser The radiated light flux is passed through the polarization separation element, the polarization element, and the objective lens in this order, and the optical anisotropy is formed on a substrate which is a uniaxially anisotropic refractive index ellipsoid having a principal axis in the thickness direction. After irradiating, the reflected light from the optical disc is passed through the objective lens and the polarization element in this order, and then the polarization separation element separates a component orthogonal to the polarization direction of the semiconductor laser,
The separated light is received by the light receiving element.

[0009]

[Action]

(1) The optical disc is irradiated with the light flux from the semiconductor laser through a substrate arranged between the objective lens and the optical disc,
The reflected light from the optical disc is received by the two-divided light receiving element via the substrate, so that the reflected light is radiated with emphasis on the position apart from the dividing line on the light receiving surface.
Reduces the occurrence of tracking error signal offset. (2) In addition to the configuration of (1), by disposing a polarizing element that gives a phase difference to the light beam in front of the objective lens, the reflected light emitted to the light receiving element is positioned at a position more limited than that of (1). And the occurrence of the tracking error signal offset is made smaller than that in (1). (3) By using a material which is a uniaxially anisotropic refractive index ellipsoid having a principal axis in the thickness direction for the optical disc, the same as when using the substrate without using the substrate To act.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining an embodiment of the invention of claim 1, FIG. 1 (a) is a main part configuration diagram, and FIG. 1 (b) is BB of FIG. 1 (a). FIG. 1 (c) is a detailed view of the light-receiving surface when the optical axis shift occurs, where 1 is a semiconductor laser (L
D), 2 is a collimating lens, 3 is a polarization beam splitter (an element that transmits approximately 100% of P-polarized light and reflects approximately 100% of S-polarized light), 4 is an objective lens, 5 is an optical disk, and 6 is a two-divided light receiving element (PD ) And 9 are substrates (hereinafter referred to as substrates) which are uniaxially anisotropic refractive index ellipsoids having a principal axis in the thickness direction.

The light beam emitted from the semiconductor laser 1 is applied to the optical disk 5 through the collimator lens 2, the polarization beam splitter 3, the objective lens 4 and the substrate 9, and the light reflected from the optical disk 5 is the substrate 9 and the objective lens. 4, and enters the two-divided light receiving element 6 through the polarization beam splitter 3. In this case, the convergent light from the semiconductor laser 1 is incident on the substrate 9 which is a uniaxially anisotropic refractive index ellipsoid whose optical anisotropy has the main axis in the thickness direction, and the incident angle θ on the substrate 9 is A large light beam in a direction parallel or not orthogonal to the polarization direction of the semiconductor laser 1 (LD) becomes elliptically polarized light and is irradiated onto the optical disc 5. The reflected light from the optical disk 5 is further propagated through the substrate 9 into the above-mentioned elliptically polarized light, and is incident on the two-divided light receiving element 6 via the objective lens 4 and the polarization separation element 3.

FIGS. 2 to 4 are graphs for explaining the amount of light received by the light receiving element (PD) 6 in the example shown in FIG. 1. r is the light emitted from the semiconductor laser 1 in the above path. After that, the ratio of reaching the light receiving element 6, that is, the light amount ratio, α is the azimuth angle with respect to the LD initial polarization direction X on the light receiving element 6, and θ is the incident angle of light incident on the substrate 9. The refractive index n _e for extraordinary ray of the substrate 9, the refractive index with respect to ordinary rays n _o, the difference between the refractive index n _o for the refractive index n _e and the ordinary ray for the extraordinary ray _{Δ (= n e -n o)} , When the thickness of the substrate 9 is t (mm), Δ = 0.00 in FIG.
FIG. 3 shows that when 06, t = 1.2, Δ = 0.0012, t
= 1.2, FIG. 4 shows Δ = 0.0018, t = 1.2.
The relationship between the azimuth angle α and the light amount ratio r at each incident angle θ at the time of is shown. In any of the examples shown in FIGS. 2 to 4, the light amount ratio r at each incident angle θ is equal to the azimuth angle α. = 45
Maximum at °, 135 °, 225 °, 315 °, azimuth α = 0 ° (360 °), 90 °, 180 °, 270 °
Is minimum (r = 0).

Suitable materials for the substrate 9 are KDP (potassium dihydrogen phosphate), ADP (ammonium dihydrogen phosphate), calcite, sapphire, ZnS, LN, quartz, polycarbonate, and the like. For example, when a crystal is used as the substrate 9, the difference Δ _{1 in the} refractive index of the crystal is 0.008.
Therefore, if the thickness t ₁ of the quartz substrate for obtaining the same result as in the example shown in FIGS. 2 to 4 is obtained, t ₁ is obtained in order to obtain the same result as in the example shown in FIG. = 0.0006 / 0.
0089 × 1.2 = 0.08 (mm), and in order to obtain the same result as the example shown in FIG. 3, t ₁ = 0.0012 /
Since 0.0089 × 1.2 = 0.16 (mm), in order to obtain the same result as the example shown in FIG. 4, t ₁ = 0.001
It is 8 / 0.0089 × 1.2 = 0.24 (mm).

When polycarbonate is used as the substrate 9, since the difference Δ _{2 in} refractive index of polycarbonate is about 0.0006, the thickness t ₂ of the substrate of polycarbonate is t _2.
When is 1.2 mm, the same result as the example shown in FIG. 2 is obtained.

As shown in FIG. 1 (a), the light beam emitted from the semiconductor laser 1 becomes substantially parallel light by the collimator lens 2, and the polarization beam splitter 3 which is a polarization separation element.
Is incident on the objective lens 4 as P-polarized light. The convergent light from the objective lens 4 enters the substrate 9, and as described above, the incident angle θ on the substrate 9 is large, that is, θ = 25 to 30 °, and parallel to the LD initial polarization direction X, or Non-orthogonal azimuth angle α, that is, α = 0 ° (360 °), 90 °, 180 °, 270
Light beams other than ° become elliptically polarized light, and are irradiated onto the optical disc 5. The light reflected from the optical disk 5 is further partially elliptically polarized through the substrate 9 and is reflected by the polarization beam splitter 3 through the objective lens 4 to reflect only the S-polarized component, that is, the elliptically polarized light. It is incident on the two-divided light receiving element 6.

As can be seen from the graphs shown in FIGS. 2 to 4, the light receiving surface 7 of the two-divided light receiving element has an azimuth angle α with respect to the LD initial polarization direction X as shown in FIG. Are irradiated with a part S of the reflected light from the optical disk 5 at four positions in the directions of approximately 45 °, 135 °, 225 °, and 315 °, and the signals output from the light receiving surface 7a and the light receiving surface 7b are respectively 7a. , And 7b, the tracking error signal T
E = 7a-7b can be obtained.

According to the present invention, as shown in FIG. 1 (c), almost no reflected light S from the optical disk 5 is received on the dividing line 8 of the light receiving surface 7, so that even if there is an optical axis deviation ΔS, it is received. The difference between the outputs of the surface 7a and the light receiving surface 7b is small, and the occurrence of offset of the tracking error signal TE can be reduced.

FIG. 5 is a diagram for explaining an embodiment of the invention of claim 2, FIG. 5 (a) is a main part configuration diagram, and FIG. 5 (b) is a BB arrow of FIG. 5 (a). FIG. 5C is a detailed view of the light-receiving surface when the optical axis shift occurs. In addition to the configuration of the example shown in FIG. 1, a λ / 8 plate () which gives a phase difference of 45 ° to the light flux ( (Polarizing element) 10 is arranged between the polarizing beam splitter 3 and the objective lens 4, and the optical disc 5 is arranged so that the track direction T of the optical disc 5 forms an angle of 45 ° with the LD initial polarization direction X. And the split line 8 of the two-divided light receiving element 6 is 4 with respect to the LD initial polarization direction X.
It is arranged so as to form an angle of 5 °.

FIGS. 6 and 7 are graphs for explaining the amount of light received by the light receiving element (PD) 6 in the example shown in FIG. 5, and FIG. 6 shows the difference in refractive index Δ = 0.000.
6, when the thickness t of the substrate 9 = 1.2 mm, Δ =
It shows the relationship between the azimuth angle α and the light amount ratio r at each incident angle θ when 0.0012 and t = 1.2. In the example shown in FIG. 6, the light amount ratio r at each incident angle θ is equal to the azimuth angle α =
Maximum at 135 ° and 315 °, azimuth α = 45 °,
It becomes a minimum at 225 °. Further, in the example shown in FIG. 7, the light amount ratio r at each incident angle θ except the incident angle θ = 30 ° is
Azimuth α = 135 °, maximum at 315 °, azimuth α
It becomes the minimum at = 45 ° and 225 °.

As the material of the substrate 9, the same material as in the example shown in FIG. 1 is suitable. For example, when quartz is used as the substrate 7, the same calculation as in the example shown in FIG. And, the thickness t ₁ of the quartz substrate for obtaining the same result as the example shown in FIG. 7 is t ₁ = 0.008 (mm) and 0.24 (mm), respectively. Further, when polycarbonate is used as the substrate 9, the thickness t ₂ of the polycarbonate substrate for obtaining the same result as in the example shown in FIG. 6 is 1.2 mm by the same calculation as in the example shown in FIG. .

As shown in FIG. 5A, the light beam emitted from the semiconductor laser 1 goes through the same process as in the example shown in FIG.
At a phase difference of 45 °. 45 °
The light flux to which the phase difference of 2 is given enters the substrate 9 through the objective lens 4, and as described above, the azimuth angles α are 45 ° and 225 °.
The phase difference of the light beam of 90 ° becomes small, that is, the elliptically polarized light approaches the linearly polarized light, and the light beams of azimuth angles α of 135 ° and 315 ° have the larger phase difference, that is, the elliptically polarized light further advances, It is irradiated to 5.

The reflected light from the optical disk 5 passes through the substrate 9, the objective lens 4 and the λ / 8 plate 10, and the S-polarized light component is reflected by the polarization beam splitter 3 toward the two-divided light receiving element 6 to receive the two-divided light. As reflected from the graphs shown in FIGS. 6 and 7, the reflected light S on the light-receiving surface 7 is incident on the element 6.
Is emphasized when the azimuth angle α is approximately 135 ° and 315 °.

According to the present invention, as shown in FIG. 5B, the track on the optical disk 5 is inclined by 45 ° with respect to the LD initial polarization direction X, and the two-divided light receiving element 6 is also in the track direction on the optical disk 5. So that T and dividing line 8 match
That is, since the LD is inclined by 45 ° with respect to the initial polarization direction X, the reflected light S is emitted while being emphasized at a position farther from the dividing line 8 than in the example shown in FIG.
As shown in (c), even if there is an optical axis shift ΔS, the occurrence of offset of the tracking error signal TE can be made smaller than that in the example shown in FIG.

FIG. 8 is a main part configuration diagram for explaining an embodiment of the invention of claim 3, in which 15 is the same material as the substrate 9 of the example shown in FIG. 1, that is, an optically anisotropic material. An optical disc using a uniaxially anisotropic refractive index ellipsoid having a principal axis in the thickness direction. In this example, the optical disc 15 is mounted on the substrate 9
The optical disc 15 has, for example,
It can be made of polycarbonate, in which case the light quantity ratio as shown in FIG. 2 can be obtained on the two-divided light receiving element 6.

According to the present invention, as can be seen by comparison with the example shown in FIG. 1, the same effect as that of the example shown in FIG. 1 can be obtained without using the substrate 9 in the example shown in FIG.

FIG. 9 is a schematic view of the essential portions for explaining the embodiment of the invention of claim 4, and 15 is the substrate 9 of the example shown in FIG.
It is an optical disc using the same material as. In this example, an optical disk 15 is provided with the function of the substrate 9, and the optical disk 15 can be made of, for example, polycarbonate. The light quantity ratio as shown can be obtained.

According to the present invention, as can be seen by comparison with the example shown in FIG. 5, the same effect as that of the example shown in FIG. 5 can be obtained without using the substrate 9 in the example shown in FIG.

In the above invention, it goes without saying that the substrate 9 and the optical disk 15 made of the material of the substrate may be used at the same time. In addition, the polarization beam splitter 3
A semiconductor laser 1 and a collimating lens 2 for
The position relationship of the two-divided light receiving element 6 may be reversed (it is only necessary to change the direction of the LD polarization direction X by 90 °).
Then, the substrate 9 may be adhered to the objective lens 4, or the substrate 9
It can be easily understood that the can be fixed to the optical pickup body.

[0029]

As is apparent from the above description, the present invention has the following effects. (1) Effects corresponding to Claims 1 and 2: A uniaxially anisotropic refractive index ellipsoid in which a light beam from a semiconductor laser is arranged between an objective lens and an optical disk and the optical anisotropy has a principal axis in the thickness direction. By irradiating the optical disc through the substrate, which is the optical disc, and receiving the reflected light from the optical disc by the two-division light receiving element through the substrate, the light flux is further transmitted through the polarizing element arranged in front of the objective lens. The optical disc and the reflected light from the optical disc is received by the two-division light receiving element via the polarizing element, so that only the light flux corresponding to a part of the objective lens is guided to the two-division light receiving element for track detection. As a result, the intensity of the light beam on the dividing line of the two-division light receiving element can be reduced, so that it is possible to reduce the track detection error due to the optical axis shift. (2) Effects corresponding to claims 3 and 4: By making the optical disk itself using the same material as the substrate, the same effect as when using the substrate can be obtained without using the substrate. it can.

[Brief description of drawings]

FIG. 1 is a main part configuration diagram for explaining an embodiment of the invention of claim 1;

FIG. 2 is a diagram for explaining the amount of light received by a light receiving element in the example shown in FIG.

FIG. 3 is a diagram for explaining the amount of light received by a light receiving element in the example shown in FIG.

FIG. 4 is a diagram for explaining the amount of light received by a light receiving element in the example shown in FIG.

FIG. 5 is a main part configuration diagram for explaining an embodiment of the invention of claim 2;

6 is a diagram for explaining the amount of light received by a light receiving element in the example shown in FIG.

7 is a diagram for explaining the amount of light received by a light receiving element in the example shown in FIG.

FIG. 8 is a main part configuration diagram for explaining an embodiment of the invention of claim 3;

FIG. 9 is a main part configuration diagram for explaining an embodiment of the invention of claim 4;

FIG. 10 is a main part configuration diagram for explaining an example of a conventional optical pickup device.

11 is a diagram for explaining a tracking error signal in the example shown in FIG.

[Explanation of symbols]

1 ... Semiconductor laser, 2 ... Collimating lens, 3 ... Polarizing beam splitter (polarization separating element), 4 ... Objective lens, 5
... Optical disc, 6 ... Two-division light receiving element, 7 ... Light receiving surface, 8 ...
Dividing line, 9 ... Substrate which is a uniaxially anisotropic refractive index ellipsoid having a principal axis in the thickness direction, 10 ... λ / 8 plate (polarizing element), 15 ... Optical anisotropy is thickness An optical disc using a substrate which is a uniaxially anisotropic refractive index ellipsoid having a principal axis in the direction.

Claims (4)

[Claims] 1. A light beam emitted from a semiconductor laser is irradiated onto an optical disk through a polarization separating element and an objective lens, and reflected light from the optical disk is received by a light receiving element through the objective lens and the polarization separating element, and the received light is received. In an optical pickup device for tracking a spot on the optical disk according to the output of an element, the optical anisotropy includes a substrate which is a uniaxially anisotropic refractive index ellipsoid having a principal axis in the thickness direction, After the light beam emitted from the laser passes through the polarization separation element, the objective lens, and the substrate in this order to irradiate the optical disc, and the reflected light from the optical disc passes through the substrate and the objective lens in this order,
An optical pickup device, wherein a component orthogonal to a polarization direction of the semiconductor laser is separated by the polarization separating element, and the separated light is received by the light receiving element. 2. A light beam emitted from a semiconductor laser is irradiated onto an optical disk through a polarization separating element and an objective lens, and reflected light from the optical disk is received by a light receiving element through the objective lens and the polarization separating element, and the received light is received. In an optical pickup device for tracking a spot on the optical disk according to the output of the element, a polarizing element and a substrate whose optical anisotropy is a uniaxially anisotropic refractive index ellipsoid having a principal axis in the thickness direction are included. Then, the light beam emitted from the semiconductor laser is the polarization separation element, the polarization element,
After irradiating the optical disc through the objective lens and the substrate in this order, and passing the reflected light from the optical disc through the substrate, the objective lens, and the polarizing element in this order, polarization of the semiconductor laser is performed by the polarization separating element. An optical pickup device, wherein a component orthogonal to the direction is separated, and the separated light is received by the light receiving element. 3. A light beam emitted from a semiconductor laser is irradiated onto an optical disk through a polarization separating element and an objective lens, and reflected light from the optical disk is received by a light receiving element through the objective lens and the polarization separating element, and the received light is received. In an optical pickup device for tracking a spot on the optical disc according to the output of an element, a light beam emitted from the semiconductor laser is passed through the polarization separation element and the objective lens in this order, and optical anisotropy is measured in the thickness direction. After irradiating on an optical disk made of a substrate which is a uniaxially anisotropic refractive index ellipsoid having a principal axis, the reflected light from the optical disk is passed through the objective lens and the polarization element in this order, and then the polarization separation element An optical disk device characterized in that a component orthogonal to the polarization direction of a semiconductor laser is separated and the separated light is received by the light receiving element. Pickup method in storage. 4. A light beam emitted from a semiconductor laser is irradiated onto an optical disk through a polarization separating element and an objective lens, and reflected light from the optical disk is received by a light receiving element through the objective lens and the polarization separating element, and the received light is received. In an optical pickup device that tracks a spot on the optical disk according to the output of an element, the light beam emitted from the semiconductor laser is passed through the polarization separation element, the polarization element, and the objective lens in this order to obtain an optical anisotropy. Is irradiated onto an optical disk made of a substrate which is a uniaxially anisotropic refractive index ellipsoid having a principal axis in the thickness direction, and reflected light from the optical disk is passed through the objective lens and the polarizing element in this order, and then the polarized light is separated. An element separates a component orthogonal to the polarization direction of the semiconductor laser, and the separated light is received by the light receiving element. Optical pickup method in disk device.