JPS5942648A - Disk device - Google Patents

Abstract

PURPOSE:To eliminate an ineffective part of a photodetecting part for detecting an RF signal, and to maintain a high level of the RF signal, for forming separately the photodetecting part for detecting the RF signal and a photodetector for detecting a focus. CONSTITUTION:Laser light which is made incident to a disk passes through a lambda/4 plate two times when going and returning, the plane of polarization of return light is rotated by 90 degrees, and it is made incident to a detector 21. Five photodetecting faces 22-25 and 26 are formed on the detector 21. The photodetecting part 22 is used for detecting an RF signal, and photodetects a spot (a) of main light. The photodetecting parts 23, 24 are used for tracking-servo, and photodetect spots (b), (c) of auxiliary light, respectively. Also, the photodetecting parts 25, 26 are used for detecting a focus, and photodetect spots (d), (e) of auxiliary light. Not only the photodetecting parts 23, 24 but also the photodetecting part 22 are constituted of a single photodetector, therefore, an ineffective part is eliminated, and a loss of about a half can be eliminated. Accordingly, sensitivity of the photodetecting part 22 becomes large, and a large level of the RF signal can be maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application Disc devices are known that read out a series of optical transitions formed on a disc using an optical head to reproduce a video signal or an audio signal. As is well known, in this disk device, a tracking server and a focus serve are performed. □It has also been proposed to perform radial skew correction as necessary. In this case, it is necessary to provide a diffraction grating to split the laser beam into multiple beams. Of course, the amount of light incident on the light receiving section for reading out the series of optical transitions also decreases in accordance with the division.

In particular, even if the amount of light incident on the light receiving section for reading out the optical transition series becomes small, the readout output of the optical transition series can be made sufficient by increasing the photoelectric conversion efficiency. The present invention relates to a disk device that can be maintained.

BACKGROUND TECHNOLOGY AND PROBLEMS Here, we will first consider an example of a conventional disk device that employs the so-called three-spot method in which laser light is divided into three parts.

FIG. 1 mainly shows the optical system (1) of such an apparatus.

This optical system (1) detects the presence or absence of bits formed on the disk (2) based on, for example, the phase (interference) of laser light. This well-known optical system (1)
In this case, it is necessary for the laser beam to connect a beam spot on a series (track) of bits. Therefore, in this example, there are three spots for tracking sensors. And focus servo is performed.

In Fig. 1, the semiconductor laser (3) is connected to the disk (2).
) A diffraction grating (4), a polarization beam splitter (5), a collimator lens (6), a 7λ plate (7), and an objective lens (8) are arranged in this order on the optical path toward the optical system. Radical light from the semiconductor laser (3) enters the signal surface of the disk (2) along this optical path.

The diffraction grating (4) is for separating the above-mentioned Sirede light into one main light and two auxiliary lights. The main light is the second
The spots are connected to the pit rows as shown by a in the figure. This main light is used to read the presence or absence of bits and to reproduce the RF signal. In this case, for example, the optical path at the depth of the bit is set to 7 so that the light reflected on the bit and the light reflected around it interfere and become dark. Therefore, the presence or absence of a bit is detected as the brightness or darkness of the light. Is this main light used for focus detection in addition to this? Also used for These two auxiliary lights are shown in Figure 2 as b+c.
Connect the spots so that they are aligned roughly along the track as shown in . These spora) b and c are slightly shifted in the direction in which the tracks are lined up, and by keeping these shifts constant, the main light's spora? The bit a can be made to accurately track the bit string. Such tracking is performed, for example, by driving a lens holder (not shown) of the objective lens (8) in the left-right direction in the figure.

The Radhe light incident on the disk (2) is reflected and returns along the same optical path to the beam sgeritter (5). During this time, the laser beam passes through the 1λ plate (7) twice in the round trip, and as a result, an optical path difference occurs between the linearly polarized light λ in the direction of the amphitheater, and as a result, the polarization plane of the returned light is rotated by 90°. I am made to do so. Therefore, the returned light is reflected by the beam sgelitter (5), and is then made incident on the detector αa via the plano-concave lens (9) and the cylindrical convex lens α1.

The detector α force has three light receiving parts 0 as shown in Figure 3.
2. α1. (1→ is formed. Light receiving part α ne, α group.

α→ are the main light and auxiliary light spots @ -s-
Corresponds to C. Light receiving section 01. α→ is composed of a single light receiving element. It is unnecessary to explain that a tracking error is detected from these light reception outputs and a tracking serve is performed.

On the other hand, the light-receiving part α force has four light-receiving elements A and B.

C, D Juji axis - Composed of morning mackerel. These light receiving elements
, B, O, l), 0)→→D, the mass RF ('ffi) is formed.At the same time, this light receiving part ←'s receiving ffi &) A, B, C, Output is extracted from D as shown in FIG. 5, and focus detection is performed as will be understood below. Is this focus detection focus detection? Therefore, the main light crossover point is connected to the signal surface of the disk (2), thereby improving the resolution (cutoff frequency).

A so-called astigmatism method is adopted for focus detection. That is, the laser beam that passes through the cylindrical convex lens θQ has astigmatism, and therefore, the horizontal plane ray bundle crosses the cylindrical convex lens 01 more than the vertical plane ray bundle. As a result, the spot shape at each position becomes as shown in FIG. As for the spot shape, the spot position is cylindrical convex lens θ1
As you move away from the object, it changes from a vertically long ellipse to a perfect circle, and then to a horizontally long ellipse.

In the astigmatism method, when the crossover point of the laser beam is on the signal surface of the disk (2), the spot shape of the light receiving section α is made to be exactly circular. In this way, when the disk (2) moves away from the semiconductor laser (3), that is, when the distance of the object point (crossover point) becomes long, the image point distance becomes small, and therefore the plane ray flux Both will cross over to the left of the position shown in FIG. Therefore, the spot shape above the light receiving section is a horizontally long ellipse. Conversely, when the disk (2) approaches the semiconductor laser (3),
The spot shape on the light receiving part (a) is an ellipse long in the vertical direction.

The above change in spot shape is detected as shown in FIGS. 5A, B, and C. In this case, when the disk (2) is too close, an output of +V is obtained, and when it is in focus, an output of 0 is obtained. When the disk (2) is still too far away, an output of 1 is obtained.

There is no need to explain these matters.

This concludes the explanation of the previous example in which the three-spot method was adopted.

By the way, in such a disc device, there is a demand to further increase the number of spots and correct the skew in the radial direction of the disc (2). This is because there is a risk of causing instability of the system.

In this case, as shown in FIG. 6, a spora) dte is added, and correspondingly, as shown in FIG. 7, a light receiving section (1→, αQ) is provided at the detector α.A light receiving section α0. α0
has light-receiving elements (A, B, C, D) similar to the light-receiving element α, and can perform focus detection in the same way.

Then, the radial skew is corrected by tilting the disk (2) so that this focus detection error is reduced.

The diffraction grating (4) is, for example, cross-shaped, and the 0th-order diffracted light is used as the main light, and the 1st-order diffracted light is used as the auxiliary light.

However, if this is done, it becomes difficult to sufficiently increase the RF multiplied signal level.

This is because compared to the 3-spot method, Figures 6 and 7
This is because in the five-spot method shown in the figure, the amount of zero-order diffracted light for RF signal detection is largely reduced. In the light intensity distribution of the 3-spot method, for example, the 0th order light for RF signal detection is 60%, the 1st order light for racking is 15%,
The other first-order light is in the 15th order, but in the 5-spot method, the 0th-order light is much below this 60th order.

From this point of view, the inventor of the present invention has developed a system that, even if the amount of light for RF signal detection decreases, by improving the sensitivity of the light receiving section to compensate for this decrease, a signal of a sufficient level can be obtained as a W signal. I thought it would be better to do so.

It has also been discovered that the conventional light receiving section (6) for detecting RF signals has a large number of ineffective parts because it also performs focus detection.

That is, as shown in Fig. 8, the light receiving section (6) consists of four light receiving elements A to D as described above, and an ineffective part (12a) (shown by diagonal hatching) is required for isolation between these elements. becomes. In the invalid part (12a),
Although it depends on how the device is constructed, it is generally not possible to perform photoelectric conversion completely due to its structure, or the sensitivity is extremely poor because no bias is applied.

This ineffective portion (12a) has a considerable influence on the photoelectric conversion efficiency. For example, consider that the width of the ineffective portion (12a) is 15 μm and that a 70 μm wide laser beam (indicated by a soft spot) hits the center of the light receiving portion αa. In this case, the spot area is 3848 (-π×352) μm2, and the area of the invalid part (12a) is 1875 (= 15
x70x2-152) μm2. Approximately 48 (=■)% of the spots, that is, almost half, becomes a loss.

To maintain a high RF multiplied signal level, the ineffective portion (12
Hayashi should try to eliminate a).

Purpose of the Invention The present invention has been made in consideration of the above-mentioned circumstances.
It is an object of the present invention to provide a disk device that can maintain a high double signal level.

Summary of the Invention In order to achieve the above object, the present invention separately forms a light receiving section for RF signal detection and a light receiving section for focus detection.

In the disk device of the present invention, the sensitivity of the light receiving section for RF signal detection is improved. Even when the 5-spot method is adopted, a sufficiently large RF multiplied signal can be obtained.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIG. Here, the configuration of the detector 01) will be mainly described. The configuration of the other optical systems is almost the same as that in FIG. 1, so the description will not be repeated.

In FIG. 9, five light receiving sections (A), El, H, (C), and (C) are formed in the detector e2. ) is for RF signal detection, and the main light spot IL (
(see Figure 6). The light receiving parts (to) and (c) are for tracking laser beams, respectively, and are the auxiliary light spots b.
, c. The light receiving sections (c) and (c) are for focus detection and receive the auxiliary light (spora) d and e. A focus sensor and radial skew correction are performed based on the detection outputs of these light receiving sections (c) and (c).

This example is characterized in that not only the light receiving section (c) but also the light receiving section (a) is constructed from a single light receiving element. Therefore, the ineffective portion (12a) shown in FIG. 8 is eliminated, and the loss of about half of p1 can be eliminated. Therefore, the light receiving part (
The sensitivity of b) has increased (twice as much as before), and as a result,
Can maintain double signal level. This is particularly effective when employing the 5-sode method as in this example.

Note that the light receiving sections (c) and (c) are comprised of four light receiving elements A, B, C, and D in order to perform focus detection.

Also, in this example, focus sir? Light receiving part (a)
Or, since (c) and the light receiving section (b) for RF signal detection are coincident with each other, the focus servo can be said to be indirect. Even if there is no focus error in the light receiving sections (C) and (C), the crossover point of the main light (2) (
This is because it may not be on the signal plane shown in Figure 1). However, in this example, the radial skew is corrected in the light receiving sections (C) and (C) so that the signal surface of the disk (2) and the optical system are parallel, so this inconvenience is hardly a problem in practice. No. (to the light receiving part) and the light receiving part (c), (c)
Considering that the distance between
It is thought that there is almost no difference between performing focus servo in the light receiving sections (C) and (C) and performing focus servo in the light receiving section (A).

As described in detail, according to the present invention, focus detection is not performed in the light receiving section of the RF multiplied signal, so that there is no invalid portion in the light receiving section.

Therefore, the sensitivity of the light receiving section can be improved. This invention employs the so-called 3-spot method, 5-spot method, etc., and is effective when applied to the case where a light beam is divided into a main light and an auxiliary light.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a conventional example, FIGS. 2 to 5 are diagrams for explaining the conventional example shown in FIG. 1, and FIGS. 6 and 7 are diagrams for explaining radial skew correction. Figure 8 is the third
FIG. 9 is a diagram showing an enlarged view of the light receiving section o in FIG. 7 and FIG. 7, and FIG. 9 is a diagram showing an embodiment of the present invention. (1) is an optical system, (2) is a disk, (3) is a semiconductor laser, α1 is a silica/trical convex lens, αρ is a detector, (A) is a light receiving part for RF signal detection, (C), QQ
is a light receiving section for focus detection. Same as Hidemori Matsukuma 71, Figure 5, Figure 6, Figure 7, Figure 8, 911 ■卜24゛ゝC

Claims (1)

[Claims] The system detects the optical transition sequence of the disc by receiving the reflected light of the light beam projected onto the disc, and also imparts astigmatism to the reflected light so that the spot shape changes depending on the focal state with respect to the disc. a light receiving section that receives the optical transition series; and a light receiving section including the plurality of light receiving elements described above are configured as separate light receiving sections.