JPH04172627A - Optical pickup - Google Patents

Abstract

PURPOSE:To realize stabilized tracking operation by disposing a third diffraction element which is paired with a first diffraction element to block the path, at the opposite ends, of a beam directing from a second difraction element toward a light receiving element. CONSTITUTION:A semiconductor laser 1, a first diffraction element, i.e. a grating 2, a second diffraction element, i.e. a hologram 3, a collimate lens 4 and an objective lens 56 are arranged on a line normal to the recording surface 6a of a record carrier 6. A third diffraction element, i.e. a grating 8, is further disposed closely in the radial direction of the grating 2 in a plane containing the grating 2 and parallel with the recording surface 6a. The gratings 2, 8 are paired each other and block the paths Lma, Lmb of beams impinging from the hologram 3. According to the constitution, offset can be eliminated from a radial error signal even if a flaw is present in the record carrier 6 resulting in a stabilized tracking operation.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to an optical pickup device used for recording and reproducing compact discs, video discs, etc.

[Conventional technology]

Conventionally, as this type of optical pickup device, there is one shown in FIG. 5, for example. This optical pickup device includes a semiconductor laser 11. Grating l 2. Hologram 13. Collimator lens 14 and objective lens I5
are arranged on one straight line perpendicular to the recording surface 16a of the record carrier 16. Further, a light receiving element 17 is arranged near the radial direction R of the semiconductor laser 11 within a plane that includes the semiconductor laser 11 and is parallel to the recording surface 16a. When viewed from the record carrier 16 side, as shown in FIG. 6(b), the grooves 12d of the grating 12 are in the radial direction R.
is formed parallel to. Further, as shown in FIG. 6(a), the pattern of the hologram 13 is formed perpendicularly to the radial direction R in a plane parallel to the recording surface 16a, and the pitch is small due to the dividing line 13r in the radial direction R. It is divided into two regions, a region 13a and a region 13b with a large pitch. As shown in FIG. 6(c), the surface of the light-receiving element I7 is divided into regions 17a and I7b divided by a dividing line 17r in the approximately radial direction R, and a region 17c adjacent to the regions 17a and 17b on the inside in the radial direction. , these areas 17
a,] 7b, I7c in parallel to the radial direction R, and consists of regions +7d and I7e. As shown in FIG. 5, the laser light emitted from the semiconductor laser 11 first enters the crating I2. The grating 12 allows the 0th order diffracted light (referred to as the "main beam") Lm that goes straight and the inner 3 of the main beam Lm to
A pair of first-order diffracted lights (hereinafter referred to as sub-beams) ±Ls (not shown) passing through the front are split into one pair. These three beams Lm, ±Ls are shown in the photogram 13. Collimating lens 14. The record carrier 16 passes through the objective lens 15 in turn.
The light is focused on the recording surface 16a. Each beam Lm,=Ls is reflected by the recording surface 16a, and is reflected by the objective lens 15. After passing through the collimating lens 14, the light is diffracted by the hologram 13. The first-order diffracted light of each of the beams Lm and Ls passes through the side of the crating 12 and passes through the light receiving element 17.
guided by. As shown in FIGS. 6(a) to 6(c), among the first-order diffracted lights of the main beam Lm, the beam Lma that is diffracted by the area 13a of the hologram 13 is transmitted to the light receiving element 1.
The beam Lmb diffracted by the area 13b is focused onto the area 17c of the light receiving element 17. Also, sub beam ±
Ls/J)! The second-order diffracted light is focused on regions 17d and I7e of the light receiving element 17, respectively. Here, the light receiving element 17
Each area 17a, 17b, 17c, 17d, 1
The signals obtained from 7e are respectively S la+ S +b
, S + C, S + d, S Ie, the bit signal representing recorded information is (S , a + S 1b-I-S
lc), a focus error signal representing the focus shift on the recording surface 16a is obtained by the calculations (S, a-S, b), and a radial error signal representing the tracking shift is obtained by the calculations (S ta-5le), respectively.

[Problem to be solved by the invention]

By the way, as shown in FIG. 9(b), when the recording surface 16a of the record carrier 16 is flat and has no scratches, the beam Li that is perpendicularly incident on the recording surface 16a is reflected with the same beam shape. For example, when a circular beam Li is incident as shown in FIG. 5C, the shape of the reflected beam Lr is also circular, as shown in FIG. However, as shown in Figures (a) and (e), the recording surface 1
If there is a scratch 20 on 6a, even if a circular beam 1 is incident as shown in FIG. 6(f), the shape of the reflected beam Lr will be as shown in FIG. It has an elliptical shape that is short in the direction it extends and long in the direction perpendicular to it. As a result, the objective lens 15. The main beam Lm that has passed through the collimating lens 14 is incident on the hologram 13 in an elliptical shape, for example, as shown in FIG. 8(a). Then, as shown in FIG. 7, area 1 of the hologram 13
3a and 13b, and enters the light receiving element 17 in a spread state in the radial direction R. In detail, as shown in FIG. 8(c), the hologram I3
The beam Lma having a larger diffraction angle is diffracted by the region +3a of the light receiving element 17 from the region 17a to the region 17d.
On the other hand, the beam Lmb, which is diffracted by the region 13b of the hologram 13 and has a smaller diffraction angle, is incident from the region 17c to the region 17e of the light receiving element I7. Here, the beam Lma with a larger diffraction angle is entirely incident, but a portion of the beam Lmb with a smaller diffraction angle is blocked by the grating 12, as shown in FIG. 8(b). Therefore, as shown in FIG. 8(c), a portion Lmb+ (in the figure,
As a result, the amount of light becomes unbalanced on the surface of the light receiving element 17, resulting in a radial error signal, that is, the difference (S, d-S) between the output signals of the regions 17d and 17e.
, e). For this reason, the conventional optical pickup device has a problem in that tracking performance is impaired if there is a scratch 20 on the record carrier 16. SUMMARY OF THE INVENTION An object of the present invention is to provide an optical pickup device that can prevent offset from occurring in the radial error signal even if there is a scratch on the record carrier, and can therefore perform stable tracking.

[Means to solve the problem]

In order to achieve the above object, the present invention includes a light source and a first light source.
It has a second diffraction element and a lens system, the light emitted from the light source is split into a plurality of beams by the first diffraction element, and each of the beams is passed through the second diffraction element and the lens system. The beam reflected by the recording surface is diffracted by the second diffraction element and incident on the light receiving element through the side of the first diffraction element. In the optical pick amplifier device, in which a radial error signal representing the tracking deviation on the recording surface is obtained by balancing the light amount of The third diffraction element is characterized in that a third diffraction element is arranged to form a pair with the first diffraction element and block the above-mentioned first diffraction element.

[Effect]

When the recording surface of the record carrier is flat and without scratches, the shape of the beam diffracted by the second diffraction element is circular, and the shape of the beam diffracted by the second diffraction element is circular. It does not spread in the direction connecting the third diffraction element. Therefore, the beams are connected to the first . The first diffraction element is not obstructed by the third diffraction element. All of the light passes through the gap in the third diffraction element and enters the light receiving element as it is. Thereby, a radial error signal can be properly obtained. On the other hand, if there is a scratch on the recording surface of the record carrier, the shape of each beam diffracted by the second diffraction element is elliptical, and the shape of each beam diffracted by the second diffraction element is elliptical. It may spread in the direction connecting the third diffraction element. When expanded in this way, the expanded portion of the beam will be the first . It is evenly blocked by the third diffraction element. Therefore, on the surface of the light receiving element, the first diffraction element side and the third
The amount of light on the diffraction element side is balanced, and the occurrence of an offset in the radial error signal is suppressed. Therefore, dragging performance is improved compared to the conventional method.

【Example】

DESCRIPTION OF THE PREFERRED EMBODIMENTS The optical pickup device of the present invention will be explained in detail below with reference to illustrated embodiments. As shown in FIG. 1, this optical pickup device includes a semiconductor laser 1. Grating 2 as the first diffraction element
．． Hologram as second diffraction element3. The collimating lens 4 and the objective lens 5 are arranged side by side on one straight line perpendicular to the recording surface 6a of the recording carrier 6. Further, a light receiving element 7 is arranged near the radial direction R of the semiconductor laser 1 in a plane parallel to the recording surface 6a including the semiconductor laser 1,
Further, in the vicinity of the radial direction R of the grating 2 within a plane including the grating 2 and parallel to the recording surface 6a, a third
A grating 8 as a diffraction element is arranged. The gratings 2.8 form a pair and block the paths of beams Lma and Lmb (described later) from the hologram 3 on both sides. When viewed from the record carrier 6 side, as shown in FIG. 2(b), each i2d of the grating 2.8
, 8d are formed parallel to the radial direction R. Further, as shown in FIG. 2(a), the pattern of the hologram 3 is formed perpendicularly to the radial direction R in a plane parallel to the recording surface 6a, and is divided into two by a dividing line 3r in the radial direction R. It is divided into two regions: a region 3a with a small pitch and a region 3b with a large pitch. As shown in FIG. 2(c), the surface of the light receiving element 7 has a dividing line 7 in the approximately radial direction R.
Regions 7a and 7b divided by r and regions 7a and 7
It consists of a region 7c adjacent to the inner side in the radial direction of b, and regions 7d and 7e sandwiching these regions 7a, 7b, and 7c in parallel to the radial direction R. As shown in FIG. 1, laser light emitted from a semiconductor laser 1 first enters a grating 2. As shown in FIG. The grating 2 divides the beam into a main beam LI11 that travels straight and a pair of sub-beams ±Ls (not shown) that pass one step in front of the main beam Lm. These three beams Lm, ±Ls form the hologram 3. Collimating lens 4. The light passes through the objective lens 5 in order and is focused on the recording surface 6a of the record carrier 6. Each beam Lm, ±Ls
is reflected by the recording surface 6a, and is reflected by the objective lens 5. After passing through the collimating lens 4, it is diffracted by the hologram 3. Then, the first-order diffracted light of each of the beams La+ and ±Ls is guided to the light receiving element 7 through the side of the grating 2. As shown in FIGS. 2(a) to 2(c), the beam Lma that is largely diffracted by the region 3a of the hologram 3 is focused on the dividing line 7r between 78 and 7b of the light receiving element 7, while the The beam Lmb that has been slightly diffracted by the light receiving element 3b is focused onto the region 7C of the light receiving element 7. Also, sub beam ±
The first-order diffracted light of Ls is transmitted to regions 7d and 7d of the light-receiving element 7, respectively.
The light is focused on 7e. Here, each region 7 of the light receiving element 7
The signals obtained from a, 7 b, 7 c, 7 d, and 7 e are respectively S + a, S + b, S, c
, S Id, S Ie, the bit signal representing recorded information is (S, aJL S,
l) + S, c), the focus error signal representing the focus deviation on the recording surface 6a is (S, a-S1b), and the radial error signal representing the tracking deviation is (S, d,
−5+e) respectively. Here, the recording surface 6a of the record carrier 6 is shown in FIG. 9(a). If there is a scratch 20 similar to that shown in FIG. 9(e), the shape of the main beam Lm becomes elliptical as shown in FIG. 9(f) after being reflected by the recording surface 6a, and the objective lens 5 ．． The light passes through the collimating lens 4 and enters the hologram 3 in an elliptical shape as shown in FIG. 4(a). Then, as shown in FIG. 3, areas 3a and 3 of the hologram 3
b, spreads in the lanoal direction R, and enters the f-shaped paddy light receiving element 7. Specifically, as shown in FIG. 4(c), the beam Lma that is diffracted by the region 3a of the hologram 3 and has a larger diffraction angle is incident on the light receiving element 7 from the region 7a to the region 7d, while the beam Lma is diffracted by the region 3a of the hologram 3.
The beam Lmb having a smaller diffraction angle diffracted by the region 3b enters the light receiving element 7 from the region 7C to the region 7e. Here, the beam L11b with a smaller diffraction angle
As shown in FIG. 4(b), a part of it is blocked by the grating 2, and as shown in FIG. 4(c), a region 7 is formed.
A portion Lmb+ where the amount of light is small occurs on e. If this were the case, the amount of light would become unbalanced on the surface of the light receiving element 7, as in the conventional case. However, at the same time, as shown in FIG. 4(b), the beam Lma with a larger diffraction angle is also blocked by the grating 8, and the beam Lma has a larger diffraction angle.
As shown in Figure (c), a portion L where the amount of light is small on the area 7e
n+a+ occurs. Therefore, the amount of light incident on the region 7d and the region 7e on the surface of the light receiving element 7 is balanced, and the occurrence of an offset in the radial error signal (S ld - S le) is suppressed. Therefore, tracking can be performed more stably than in the past.

【Effect of the invention】

As is clear from the above, in the optical pickup device of the present invention, in a plane including the first diffraction element, both sides of the beam path from the second diffraction element to the light receiving element are paired with the first diffraction element. Since the third diffraction element is disposed to form a shield and block the beam, even if there is a scratch on the record carrier, it is possible to suppress the occurrence of an offset in the radial error signal. Therefore, stable tracking can be performed.

[Brief explanation of drawings]

FIG. 1 is a side view showing the configuration of an optical pickup device according to an embodiment of the present invention, and FIGS. 2(a), (b), (c)
) are nA-IIA line and IIB- line in Fig. 1, respectively.
IIB line, NC-NC line arrow view, Figures 3 and 4 (
a), (b), and (c) are diagrams showing the state of the main beam in the optical pickup device when the record carrier has scratches, and FIG. 5 is a side view showing the configuration of the conventional optical pickup device. FIGS. 6(a), (b), and (c) are the VIA-VIA line, VIB-VIB line, and VIB-VIB line in FIG. 5, respectively.
v+c-VIC line arrow view, Figures 7 and 8 (a)
, (b) and (c) are diagrams showing the state of the main beam in a conventional optical pickup device when the record carrier has scratches, and Figure 9 (a) is a diagram showing a record carrier with scratches. (b), (c). (d) is a diagram showing the state of incident light and reflected light when there is no scratch on the record carrier, and (e), (r), and (g) are diagrams showing the incident light and reflected light when there is a scratch on the record carrier. FIG. 1 Semiconductor laser, 2.8 grating, 3...
Hologram, 4... Collimating lens, 5... Objective lens, 6... Record carrier, 6a... Recording surface,
7...-light receiving element.

Claims (1)

[Claims] (1) It has a light source, first and second diffraction elements, and a lens system, and the light emitted from the light source is divided into a plurality of beams by the first diffraction element, and each of the beams is divided into a plurality of beams by the second diffraction element. The beam is passed through a diffraction element and a lens system to be focused on the recording surface of the record carrier, and the beam reflected by the recording surface is diffracted by the second diffraction element and passed through the side of the first diffraction element to the light receiving element. In the optical pickup device, the light receiving element is made incident on the light receiving element to obtain a radial error signal representing a tracking deviation on the recording surface by balancing the amount of light on the light receiving element. An optical pickup device characterized in that a third diffraction element is disposed to form a pair with the first diffraction element and to block both sides of the path of the beam heading toward.