JP3136758B2 - Optical information recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus for recording / reproducing / erasing information by using a plurality of light spots, and particularly for stably arranging light spots at predetermined positions. It relates to the optical correction hand stage.

[0002]

2. Description of the Related Art In an optical information recording / reproducing apparatus, recording / reproducing or erasing of information is generally performed by switching the intensity of light emitted from a laser as a light source. Therefore, the recording of new information ends after the previous information is erased and then the information is recorded, and thereafter, it is confirmed whether or not the information has been correctly recorded, that is, through a so-called verify operation. For this reason, recording of information requires at least three optical disc rotations.

In order to shorten the recording time, a DRAW (Dire) in which information is recorded on a recording light spot and the recording state is immediately confirmed by another reproducing light spot following the information is recorded.
An optical information recording / reproducing device having a (ct Read After Write) function has been proposed.

FIG. 24 shows the structure of an optical head of an optical information recording / reproducing apparatus disclosed in Japanese Patent Application Laid-Open No. 60-157730.

[0005] Two semiconductor lasers 20 and 4 as light sources
The light beam emitted from 0 is narrowed down to slightly different positions on the surface of the optical disk 1 by one objective lens 26 as two light spots 162 and 172, and recording and reproduction are performed. The light beam emitted from the semiconductor laser 20 is converted into a parallel light beam by a collimating lens 21, passes through a polarizing prism 22, a λ / 4 plate 23, and a wavelength selection prism 24, is reflected by a galvanomirror 25, and is attached to an actuator 27. The light spot 162 is narrowed down by the objective lens 26. The reflected light of the light spot 162 is reflected by the objective lens 26, the galvano mirror 25, the wavelength selection prism 2
4. The light is transmitted through the λ / 4 plate 23 and is reflected by the polarizing prism 22 in a substantially right angle direction. Further, this light beam is transmitted to the convex lens 28.
Is guided to the photodetector 30 by the cylindrical lens 29. The photodetector 30 is divided into four parts. A focus error and a tracking error are detected by a known method, and the actuator 27 and the galvanomirror 25 are driven via the main focus control circuit 6a and the main tracking control circuit 10, respectively. Then, focus control and tracking control of the light spot 162 are performed. On the other hand, the light beam emitted from the semiconductor laser 40 is converted into a parallel light beam by a collimating lens 41, passes through a polarizing prism 42, a λ / 4 plate 43, and passes through a movable lens 44 and a fixed lens 46 attached to an actuator 45. As a result, the light is reflected by the galvanomirror 47 and enters the wavelength selection prism 24. The light beam from the semiconductor laser 20 and the semiconductor laser 40 in the wavelength selection prism 24
Are combined into almost the same light beam, and follow the same optical path as the light beam of the semiconductor laser 20 to be focused on the recording surface of the optical disc 1 as a light spot 172. The reflected light flux of the light spot 172 passes through the λ / 4 plate 43, the polarizing prism 42, the convex lens 48, and the cylindrical lens 49,
It is guided to the split detector 50 to detect a focus error and a tracking error by a known method, and to drive the actuator 45 and the galvanomirror 47 via the sub-focus control circuit 6b and the sub-tracking control circuit 8, respectively. ing. In this case, the light spot 1 is controlled by the main focus control system and the main tracking control system by the objective lens 26 mounted on the actuator 27 and the galvano mirror 25.
Numeral 72 is almost at a predetermined position, and the correction by the movable lens 44 and the galvanomirror 47 attached to the actuator 45 may be slight.

Another optical information recording / reproducing apparatus using a plurality of light spots is disclosed in, for example,
No. 92144 is disclosed. This is because, with a simple structure, two light spots can always follow the same recording track, so that a wedge-shaped prism provided immediately after the collimating lens is rotated, and a light beam that passes through the prism and reaches the objective lens. And the position correction is performed so that the relative position of the two light spots is always kept constant. According to this method, the irradiation positions of the plurality of light spots can be maintained with high accuracy, and the sensitivity of the tilt angle of the light beam to the rotation angle of the wedge prism can be sufficiently reduced.

[0007]

However, the above-mentioned conventional method has the following problems.

The first problem is that when the light beam incident on the objective lens is deflected by the rotation of the galvanomirror or the wedge prism, the incident position of the light beam incident on the objective lens is correspondingly changed to the radius of the optical disk. Shift in the direction
As a result, the position of the reflected light beam irradiated on the photodetector shifts in a direction corresponding to the radius of the optical disk. When this shift occurs, an offset occurs in the tracking error signal in the push-pull method, which is a general tracking error detection method. In particular, in a so-called separation type optical head configured to move only the objective lens and the rising mirror portion in the radial direction of the optical disk, the amount of deviation of the reflected light beam on the photodetector is further increased.

[0009]

[0010]

[0011]

An object of the present invention, the positional displacement amount of the reflected light beam to be irradiated onto the photodetector low Hesi suppressing offset of the tracking error signal, thereby improving the tracking control performance of a plurality of light spots optically To provide an information recording and reproducing apparatus.

[0013]

For the above purpose, the present invention uses the following means.

With respect to the displacement of the reflected light beam on the photodetector due to the position shift of the incident light beam on the objective lens,
In the optical path between the beam splitter for guiding the reflected light beam to the photodetector and the objective lens, a light beam deflecting means constituted by a rotatable wedge prism having a predetermined shape and an initial installation angle is arranged. This is achieved by changing the deflection angle of the light beam by rotating the mold prism and simultaneously shifting the position at which the light beam exits the prism.

[0015]

[0016]

[0017]

[0018]

The light beam deflecting means, which is a wedge-shaped prism, transmits an incident light beam toward the objective lens and a reflected light beam from the optical disc from opposite directions. Since the light returns to the original deflecting direction, no misalignment due to the deflection occurs. Furthermore, by optimizing the shape of the wedge-shaped prism and the initial setting angle of the wedge-shaped prism, the shift amount of the light beam on the objective lens can be significantly reduced.

[0019]

[0020]

[0021]

[0022]

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

FIG. 1 is a block diagram showing the configuration of an optical information recording / reproducing apparatus according to an embodiment of the present invention. In order to explain the schematic configuration, the details of the optical head are omitted here. A substrate discriminating circuit or a track pitch discriminating circuit is provided so that compatibility can be maintained even with a difference in optical disc substrate or a difference in track pitch, and a focus control circuit 6, tracking error detecting circuits 7 and 9, a speed detecting circuit 11 And the speed command circuit 12 is switched. This will be described in detail below with reference to the drawings taking two light spots as an example.

First, with respect to the optical head 3, the principle of reducing the displacement of the reflected light beam on the photodetector due to the rotation of the wedge prism will be described with reference to FIGS.

FIG. 2 shows a wedge prism for deflecting a light beam. Such a wedge prism 140
When the light beam passes through the first wedge prism 140,
An angle δ between the traveling direction of the incident light beam entering the surface and the traveling direction of the outgoing light beam emitted from the second surface (hereinafter, referred to as the deflection angle of the outgoing light beam) is a wedge-shaped as shown by the following equation. It changes according to the incident angle φ ₁ of the incident light beam incident on the first surface of the prism 140.

[0026]

(Equation 1)

In the above equation, β is the angle between the first surface (light beam entrance surface) and the second surface (light beam exit surface) of the wedge prism 140, and n is the refractive index of the prism.

That is, by rotating the prism with the direction perpendicular to the paper plane as the rotation axis and changing the incident angle,
The direction of the emitted light beam can be deflected in a plane parallel to the paper surface. At this time, the shift amount Δη of the light beam incident position on the objective lens due to the deflection of the light beam emitted from the prism (that is, the light beam incident on the objective lens) depends on the deflection angle δ of the light beam emitted from the prism and the distance from the prism to the objective lens. The following equation can be expressed using L.

[0029]

(Equation 2)

On the other hand, the light beam is also the distance ζ between the optical axes of the emitting point P and an incident light beam of the optical axis when exiting the prism as shown in the following equation, the light flux incident angle phi ₁ to the wedge-shaped prism 140
It changes according to.

[0031]

(Equation 3)

In the above equation, t is the first of the wedge-shaped prisms 140.
The distance between the surface and the second surface is shown. As is clear from this equation,
When the prism is rotated by an angle θ from the state where the light beam exit position in the initial setting state (light beam incident angle = φ ₀ ) is used as the reference and the light beam incident angle becomes φ ₁ (= φ ₀ + θ) The shift amount Δζ of the luminous flux emission position is expressed by the following equation.

[0033]

(Equation 4)

FIG. 3 shows, as an example from Expressions 1 and 3, a light beam incident angle φ ₁ and a light beam emitted from the prism when a wedge prism of β = 1 °, n = 1.51, t = 3.3 mm is used. And the relationship between the deflection angle δ and the emission position shift amount Δζ.

The horizontal axis φ ₁ in FIG. 3 indicates that the direction in which the wedge prism 140 rotates counterclockwise around the axis perpendicular to the paper surface is positive, and one vertical axis δ indicates the light of the incident light beam in FIG. The direction in which the optical axis of the emitted light beam tilts counterclockwise with respect to the axis is defined as positive. The other vertical axis, ie, the emission position shift amount Δζ, is positive when the emission position is shifted upward from the optical axis of the incident light beam.

As is clear from FIG. 3, when the light beam is transmitted through such a wedge-shaped prism, the deflection direction (deflection angle δ) of the light beam emitted from the prism is independent of the incident direction (positive or negative of the incident angle φ ₁ ). ) Are in the same direction. (In the example shown in FIG. 3, δ is always on the negative side.) On the other hand, the sign of the shift amount Δζ of the emission position coincides with the sign of the incident angle φ ₁ . Therefore, for example, in the example of FIG. 3, the incident angle phi ₁
Is changed to the plus side, the exit position of the prism exit light beam and the light incident position on the objective lens surface due to the deflection of the prism exit light beam are shifted in opposite directions. Accordingly, when such a wedge-shaped prism is used, the substantial shift amount Δε of the incident position of the light beam on the objective lens due to the deflection of the light beam depends on the deflection of the light beam emitted from the prism, as shown in the following equation. It is expressed by the difference between the shift amount Δη and the emission position shift amount Δ 出 射 from the prism.

[0037]

(Equation 5)

Therefore, the angle β between the first surface and the second surface of the wedge prism 140, the surface interval t, the refractive index n, and the initial incident angle of the light beam incident on the prism, that is, the initial installation angle φ _{0 of the} prism. And the prism rotation angle θ (φ ₁
= Φ ₀ + θ), the substantial shift Δε of the light beam and the displacement of the reflected light beam on the photodetector can be greatly reduced.

FIG. 4 shows an embodiment in which the light beam deflecting means using the wedge-shaped prism is applied to the optical head 3. 4, 101 is a first semiconductor laser comprising a first light source, the first light flux 160 of the wavelength lambda _1, 121
Is a second semiconductor laser serving as a second light source, and outputs a second light beam 170 having a wavelength λ ₂ .

The first light beam 160 emitted from the semiconductor laser 101 is converted into parallel light by the collimating lens 102, and then the beam shaping prism 103 and the beam splitter 10
4. The chromatic aberration of the wavelengths λ ₁ and λ ₂ is corrected through the wavelength selection mirror 105 (reflected for the light beam of the wavelength λ ₁ and transmitted for the light beam of the wavelength λ ₂ ) and the triangular mirror 106 for changing the optical path. The light enters the objective lens 110. Then, the first optical spot 162 is formed on the track of the disk-shaped optical disc 1 by the objective lens 110. Further, the reflected light 163 of the first light spot 162 reflected from the optical disc 1 is again transmitted to the objective lens 110 and the triangular mirror 10.
6. Beam splitter 10 via wavelength selection mirror 105
4 is reflected and enters the first photodetector 107. The focus error detection circuit 5 and the main tracking error detection circuit 9 are connected to the first photodetector 107, and the focus error signal and the tracking error signal of the light spot 162 are detected by known detection means (not shown). obtain. The error signals obtained here drive the actuator 111 connected to the objective lens 110 via the focus control circuit 6 and the main tracking control circuit 10, respectively.
Position control in the optical axis direction of 0 and in the radial direction of the optical disc 1 is performed.

On the other hand, the second
Is converted into parallel light by the collimator lens 122, passes through the beam splitter 124, passes through the wedge prism 140 for deflecting light of the present invention, further passes through the wavelength selection mirror 105, and the first light 161 Following substantially the same optical path, the light enters the objective lens 110. And
The second light spot 1 is positioned at a position close to the first light spot 162 on the optical disc 1 by the objective lens 110.
72 is formed. Further, the second
The reflected light 173 of the light spot 172 passes through the objective lens 110, the triangular mirror 106, and the wavelength selection mirror 105 again, passes through the wedge prism 140 in the opposite direction to the incident light beam 170, and reaches the beam splitter 124. Then, after being reflected by the beam splitter 124, the second
Incident on the photodetector 127. The sub-tracking error detection circuit 7 is connected to the second photodetector 127, and a tracking error signal of the light spot 172 is obtained by a known detection means (not shown) similarly to the first photodetector 107.
Note that the optical head 3 shown in the present embodiment has an objective lens 110
151 consisting of the actuator 111 and the triangular mirror 106 and the part 1 consisting of other optical components
Reference numeral 50 denotes a so-called separated type optical head, and only 151 moves in the radial direction of the optical disc 1.

In the drawing, a wedge prism 140 has an actuator 1 for rotating the wedge prism 140 about the Z axis (the axis perpendicular to the paper surface) in the figure.
41 are provided. By controlling the position of the objective lens 110 described above, the first
The position of both the light spot 162 and the second light spot 172 is controlled. On the other hand, the deviation of the two light spots due to adjustment or temperature is caused by feeding back the tracking error signal obtained from the second photodetector 127 and the sub tracking error detection circuit 7 to the actuator 141 via the sub tracking control circuit 8. Then, the wedge prism 140 is rotated to a predetermined angle, and the deflection angle of the second light beam 170 incident on the objective lens 110 is changed as described above, so that the second light spot 172 is moved in the tracking direction (optical disk). (1 radial direction) to correct the relative positional deviation in this direction.

FIG. 5 shows the amount of position correction of the light spot 172 (the amount of movement of the spot on the optical disk 1) in the optical head having the structure shown in FIG. 4, and the amount of incident light beam position shift generated on the objective lens 110 accordingly. It is an example of the result of having calculated the relationship with (DELTA) (epsilon). The solid line shows the case where the wedge-shaped prism (β = 1 °, n = 1.51, t = 3.3 mm) of the present invention is arranged at the initial setting angle (spot moving distance = 0 μm) φ ₀ = 45 °. The broken line shows the case where a galvanomirror generally used conventionally as a light beam deflecting means is used instead of the wedge-shaped prism of the present invention. In addition,
A conventional light beam deflecting means using a wedge-shaped prism also exhibits the same characteristics as those using a galvanomirror. In the calculation, the focal length f of the objective lens was set to 3.3 mm, and the distance L from the objective lens to the wedge prism or the galvano mirror was set to 85 mm (assuming the separated optical head described above).

As is apparent from the drawing, the movement amount of the light spot can be reduced by using a wedge-shaped prism designed to have a predetermined shape, size and installation angle based on the above-mentioned formula.
Within the range of 5 μm to +5 μm, the position shift amount of the incident light beam on the objective lens can be made 10 μm or less. This is 1/10 or less of the position shift amount when a conventional galvanomirror is used. As a result, the tracking offset caused by the shift of the incident light position on the objective lens can be sufficiently reduced.

In the embodiment shown in FIGS. 4 and 5, the prism rotation angle for moving the light spot on the optical disk by 1 μm is about 0.8 °, which is higher in sensitivity than the conventional galvanomirror system. Is very low. However, the relative position correction of the light spot corrects a slight temporal relative position shift of the second light spot 172 with respect to the first light spot 162, and the correction means having low sensitivity like the wedge prism of the present invention. On the contrary, more stable correction can be made even for an external shock or the like. A configuration using a magnetic circuit, a piezoelectric element, or the like may be used as the rotating means 141 of the wedge-shaped prism, but any configuration may be used as long as the effects of the present invention can be expected. The above
As (Equation 1) to (Equation 5) are solved analytically,
The angle between the first surface and the second surface of the wedge prism
Degree β is 3 ° or less, and the first
Angle between the surface normal of the surface and the optical axis of the light beam incident on the first surface
The wedge type prism so that φ ₀ is 30 ° to 60 °
The objective lens that accompanies the deflection of the light beam
The light beam incident position shift amount Δε above is sufficiently small.
As a result, this light flux incident position shift
Tracking offset caused by
I found out.

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096]

[0097]

[0098]

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105]

[0106]

[0107]

[0108]

[0109]

[0110]

[0111]

In the embodiments of the present invention, the case where two light spots are mainly used has been described. However, the present invention is not limited to this, and the same method can be applied to the case where two or more light spots are used. For example, in the case of the light beam deflecting unit, the position of the objective lens is controlled for one of the irradiated light spots (hereinafter, this light spot is referred to as a main spot), and the other light spots are controlled. The rotation wedge prism of the present invention may be provided in each optical path, and the relative position of the main spot may be corrected from each tracking error signal.

The embodiment shown in FIG. 4 is an example in which the relative positions of the two light spots are corrected. Of course, the light spot (FIG. In the example of 4, the present invention can be used for the light spot 162). That is, the light beam 16 in the fixed portion 150
The wedge-shaped prism 140 and the actuator 141 of the present invention are arranged in the optical path 0, thereby performing tracking control of the light spot 162. With such a configuration, the actuator for tracking control provided in the movable section 151 can be omitted, so that the weight of the movable section can be reduced, which is very effective in shortening the access time.

[0114]

As described above, according to the present invention, the offset of the tracking error signal generated due to the position correction of the light spot can be sufficiently suppressed, and the optical information recording / reproducing for irradiating the optical disk with a plurality of light spots. Each tracking control performance of the device can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of an optical information recording / reproducing apparatus showing a configuration of the present invention.

FIG. 2 is a diagram for explaining the operation of a wedge prism.

FIG. 3 is a diagram showing characteristics of a wedge prism.

FIG. 4 is a diagram showing an embodiment when a wedge prism is applied.

FIG. 5 is a diagram for explaining a light beam position shift amount when a wedge prism and a galvanomirror are used.

FIG. 6 is a block diagram showing the configuration and control method of a conventional optical head .
FIG.

FIG. 7 shows an embodiment of a two-spot tracking control.
FIG.

FIG. 8 shows a focus position correction method for a disc substrate material .
It is a block diagram showing an example.

FIG. 9 shows two light spots focused on the same information recording surface.
It is the top view and side view which show the state .

FIG. 10 shows an example of a refractive index wavelength characteristic of an optical disk substrate .
FIG.

FIG. 11 shows one of two light spots condensed on an information recording surface.
And a plan view showing a state where the other is defocused .
It is a side view.

FIG. 12 shows the other of the two light spots condensed on the information recording surface
It is, one Deformation in the opposite direction - flat showing a state of being mosquito scan
It is a side view and a side view.

FIG. 13 is a focus position correction method for a disc substrate material .
FIG. 14 is a block diagram showing another embodiment of the present invention .

FIG. 14 shows two light spots in the embodiment of FIG .
Is a plan view showing a state where light is focused on the same information recording surface, and
It is a side view.

FIG. 15 is a block diagram illustrating an embodiment of an error detection circuit.
You.

FIG. 16 shows a first example when the speed detection circuit is of a period measurement type.
It is a block diagram showing an example.

FIG. 17 shows a second example when the speed detection circuit is a period measurement type.
It is a block diagram showing an example.

FIG. 18 is a third example in the case where the speed detection circuit is a period measurement type.
It is a block diagram showing an example.

FIG. 19 is a fourth example when the speed detection circuit is of a period measurement type.
It is a block diagram showing an example.

FIG. 20 shows an embodiment in which the speed detection circuit is of a differential type.
It is a block diagram.

FIG. 21 is a timing chart when the speed detection circuit is a differential type.
It is a figure which shows a chart.

FIG. 22 is a block diagram showing a first embodiment of a speed command circuit;
FIG.

FIG. 23 is a block diagram showing a second embodiment of the speed command circuit;
FIG.

FIG. 24 is a block diagram showing the configuration and control method of a conventional optical head .
It is a lock figure.

──────────────────────────────────────────────────続 き Continued on the front page (31) Priority claim number Japanese Patent Application No. 4-116315 (32) Priority date May 8, 1992 (1992.5.5.8) (33) Priority claim country Japan (JP) (72) Inventor Motoyuki Suzuki 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Hitachi, Ltd.Video Media Research Laboratories (72) Inventor Yoshio Suzuki 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Hitachi, Ltd. Inside Media Research Laboratory (72) Inventor Michio Miura 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Hitachi Video Media Research Laboratory (72) Inventor Akira Saito 2880 Kozu, Kofu, Odawara-shi, Kanagawa Prefecture Odawara Plant, Hitachi, Ltd. (72) Kazuo Shigematsu 2880 Kozu, Odawara City, Kanagawa Prefecture Inside Odawara Plant, Hitachi, Ltd. (72) Yasuo Kitada, Inventor 2880 Kozu, Odawara-shi, Kanagawa Prefecture Odawara Plant, Hitachi, Ltd. (56) References JP-A-4-263127 (JP, A) JP-A-62-92144 (JP, A) JP-A-62-285240 (JP) JP-A-2-29491 (JP, A) JP-A-6-28693 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B ^7/ 09-7/22

Claims (2)

(57) [Claims] 1. A semiconductor laser, the semiconductor and the objective lens for the laser light beam emitted by the forming the condensed light spot in a predetermined position close to each other on the optical information recording medium, the optical information recording of the light spot A photodetector for detecting a light beam reflected from a medium, and in a light path between the semiconductor laser and the objective lens, first and second non-parallel to each other.
A wedge-shaped prism having a surface is arranged such that a light beam emitted from the semiconductor laser is incident on the wedge-shaped prism from the first surface and is emitted from the second surface, and the wedge-shaped prism is An optical information recording / reproducing apparatus comprising means for deflecting a traveling direction of the light beam by rotating about a predetermined rotation axis substantially parallel to the first and second surfaces, wherein the wedge-shaped prism The following equations (Equation 1) to (Equation 3) are used. Ltan δ−Δζ ≒ 0 (Equation 1) δ = Sin ⁻¹ [n · sin ｛β + Sin ⁻¹ (sin (φ ₀ + θ) / n) ｝] − (Φ ₀ + θ) (Equation 2) Δζ = t · [｛1−cos (φ ₀ + θ) / √ (n ² −sin ² (φ ₀ + θ)) · sin (φ ₀ + θ) ) − {1−cos (φ ₀ ) / {(n ² −sin ² (φ ₀ )) · sin (φ ₀ )} (Equation 3) [where, L is the objective from the second surface of the wedge prism. The optical distance to the lens, where n is the wedge-shaped pre- Refractive index of the beam, theta any small angle. The angle β between the first surface and the second surface of the wedge prism, the distance t between the first surface and the second surface, and the surface normal of the first surface in the initial state. An optical information recording / reproducing apparatus, wherein an angle φ ₀ formed between the optical axis of the light beam incident on the first surface and the optical axis is determined. 2. The wedge-shaped prism included in the light beam deflecting means, wherein the angle between the first surface and the second surface is 3 ° or less, and the normal to the first surface is equal to or less than 3 °. The angle formed by the light axis of the light beam incident on the first surface is 30 ° to 60 °
2. The optical information recording / reproducing apparatus according to claim 1, wherein: