JPS62270034A - Optical reproducing device - Google Patents

Abstract

PURPOSE:To decrease a secondary maximum to form an airy ring and to obtain a reproducing signal with a small quantity of the crosstalk by inserting a filter, in which the transmitting part of the aperture narrower than a beam width is formed, into the laser light path of an optical device. CONSTITUTION:A reflecting light by an optical system 17 to catch the reflecting light from an optical disk 16 is converted to a signal by a light detecting device 18. The oblique part of a filter 20, in which a belt-shaped transmitting part 21 with a size (m) is formed at the central part, is made into a mask part 22 in which a light is attenuated. The transmission factor of the transmitting part 21 is set to 100% and the transmission factor of the mask part 22 is set to 10-40%. Into the surface of a grating 11 which is the outward trip part of the laser projecting light path of an optical device, the filter 20 is inserted which is provided with the mask part 22 to limit the width of a laser beam B in the radius direction of the optical disk 16. Thus, the light strength of the secondary maximum is reduced and the crosstalk is decreased.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical playback device that reads information recorded on an optical disk, and particularly relates to an optical playback device that reads out information recorded on an optical disc. The present invention relates to an optical reproducing device that can reduce talk signals.

[Summary of the invention]

In the optical playback device of the present invention, a filter is provided in the outgoing optical system of the optical head to reduce the intensity of the primary light (secondary maximum) of the laser spot irradiated onto the optical disc, and the filter that reduces the intensity of the primary light (secondary maximum) of the laser spot irradiated onto the optical disc is provided in the outgoing optical system of the optical head. This is designed to reduce crosstalk components.

[Conventional technology]

Optical playback devices that read information from optical discs on which various types of information are recorded at high density use a narrow recording track that is irradiated with a focused laser spot and the reflected light (return light) detected. An optical device is required to reproduce the information.

FIG. 6 shows an optical system showing an example of such an optical head, in which 10 is a laser emission source, 11 is a grating for forming a tracking spot, 12 is a beam splitter, 13 is a collimator lens, and 14 is a grating for forming a tracking spot. Enter/4
A wavelength plate, 15 an objective lens, and 16 an optical disk on which information is recorded.

Reference numeral 17 denotes an optical system that captures reflected light from the optical disk 16, and this reflected light is converted into an electrical signal by a photodetector 18.

In such an optical system, the laser beam (S) irradiated onto the optical disk surface is focused to approximately the width of the recording track T as shown in FIG. 7, and while tracking the recording track by a tracking servo system (not shown), Information on the recording track can be read from the reflected light.

[Problem that the invention seeks to solve]

In this case, since the track formed on the optical disk surface is formed with an extremely narrow width of 1 to 2 pm, the irradiated laser spora) S also needs to be focused into a small spot by the objective lens 15 with a high NA. At the same time, it is also required to increase the light intensity of the spot.

However, in general, in order to reduce the spot diameter, it is necessary to reduce the beam diameter of the incident laser beam and use an objective lens with a high numerical aperture (NA). A near ring (secondary maximum) occurs in a focused spot, and when this second maximum S1 spreads to adjacent tracks as shown in Figure 7, crosstalk occurs. There's a problem.

Therefore, an optical member (for example, N
If a coupling lens with a large A is provided, an effect of reducing the second maximum can be obtained, but such an optical member is expensive, and there is a problem in that it increases the cost of the optical device.

The present invention was made in view of these problems, and provides an optical playback device that can play back recorded information with less crosstalk by reducing the binary maximum component of a spot irradiated onto an optical disc. This is what I am trying to do.

[Means for solving problems]

In the optical playback device of the present invention, an optical attenuation filter (ND filter) is inserted into a part of the optical path of an optical device arranged to irradiate a laser beam onto an optical disc, and the laser beam passes through the ND filter. A light-transmitting portion with a transmittance close to 100% is provided, which is opened in the track direction of the optical disk with a width narrower than the beam width of the laser beam.

[Effect]

By providing the filter as described above, the intensity distribution of the laser beam incident on the objective lens can be arbitrarily adjusted, and the intensity of the second maximum in the laser spot formed on the optical disk surface is reduced. As a result, crosstalk components can be suppressed even when the track width is narrow.

〔Example〕

FIG. 1 shows an optical device of an optical reproducing apparatus showing an embodiment of the present invention, and the same parts as in FIG. 6 are given the same reference numerals.

The shaded area 20 is a filter in which a band-shaped transparent part 21 with a dimension of m is formed in the center as shown in FIG. This is a mask portion 22 in which light is attenuated.

FIG. 2(b) shows the light transmittance of the light transmitting part 21 and the mask part 22, where the transmittance of the light transmitting part 21 is 100%, and the transmittance X of the mask part 22 is 10%, as will be described later. ~40%
It is preferable to set it to .

In the optical reproducing apparatus of the present invention, as shown in FIG. 1, a laser beam B as shown in FIG. Since a filter 20 is inserted which is provided with a mask portion 22 that limits the width in the radial direction of the optical disc, the intensity of the secondary extremely thick light decreases, reducing crosstalk, as shown in the data below. can do.

Figure 3 (L) shows the light-transmitting part 21 with respect to the width dimension of beam B.
The ratio of the width m, that is, l-m/1Xlo.

The figure shows the light intensity at each point.

Moreover, FIG. 3(b) shows the average value of the data from the center to the distance 11i 1.2 to 1.71 Lm in FIG. 3(a).

As can be understood from this Figure 3(b), the sentence -m/1Xl
The light intensity around the spot, that is, the second-order maximum light intensity, becomes the lowest near 0%, and crosstalk can be reduced accordingly.

FIG. 4 shows the light transmittance of the mask portion 22 (0 to 100
%) changes, the intensity at the center of the spot is similarly 1.2 to 1.7 pml from the center! The figure shows the light intensity at the point where the image falls. In addition, the data indicates that the peripheral light intensity of the objective lens entrance pupil is 67% in the radial direction relative to the central light intensity.
, 91% in the tangential direction.

As can be understood from the data in FIG.
When the light transmittance is in the range of 10 to 40%, the secondary maximum light intensity generated around the spot decreases the most.

Moreover, FIGS. 5(a) and 5(b) show the light intensity of the spot irradiated from the same optical head with and without the filter 20 of the present invention. / 1 , the dotted line is data in the radial direction.

As can be understood from this figure, in the case of FIG. 5(a) in which the filter of the present invention is inserted, the distribution of light intensity in the radial direction is particularly different from the distribution of light intensity in the tangential direction. On the other hand, in the case without the filter shown in Fig. 5(b), the distribution of light intensity in the tangential direction and the distribution of light intensity in the radial direction are , are almost identical, and clearly in the case of the present invention it is sports.

The effect of reducing the spread of light, that is, the second-order maximum, is observed.

In the above embodiment, the filter 20 is provided on the surface of the grating 11. However, in the case of an outgoing laser beam system, for example, the emission surface 2 of the laser light source 10
0a, the back surface 20b of the grating 11, the entrance surface 20c of the beam splitter 12, etc., the filter 20 may be provided.

[Effects of the Invention] As explained above, in the optical regeneration installation of the present invention, a filter in which a light-transmitting part with an aperture narrower than the beam width is formed is inserted into the laser light path (outgoing path) of the optical device. By reducing the secondary maximum that forms a near ring, it is possible to obtain a reproduced signal with less crosstalk.

In addition, such a filter can be easily manufactured by forming a predetermined light-transmitting part by etching a part of an ND filter formed by metal vapor deposition technology, etc. This has the advantage of not causing an increase in costs.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the optical head of the optical reproducing device of the present invention, FIGS. 2(a) and (b) are plan views showing the shape of the filter and a graph showing its light transmittance, and FIG. 3 (a),
(b) is a data diagram showing the relative light intensity with respect to the center light intensity when changing the ratio of the beam width m and the filter width,
Figure 4 is a data diagram of relative light intensity with respect to the center light when changing the light transmittance of the mask part, and Figures 5 (a) and (b).
) is a waveform diagram showing the light intensity characteristics of the laser beam with and without a filter, Figure 6 is a schematic diagram of a conventional optical head, and Figure 7 is a waveform diagram showing the optical intensity characteristics of the laser beam with and without a filter.
The figure is an explanatory diagram of a laser spot irradiated onto a disc. In the figure, 10 is a laser emission source, 11 is a grating, 1
2 is a beam subrifter, 13 is a collimator lens, 14
15 is an objective lens, 20 is a filter,
Reference numeral 21 indicates a light-transmitting section, and 22 indicates a mask section. Rough surface of the filter hfq cfi various ν1 Fig. 2 40F j+ in the beam: ↑Trouble Fig. 3 (a) Fig. 3 (b)

Claims (1)

[Claims] In an optical disc playback device that is configured to read out recorded information by irradiating a laser spot onto an optical disc and detecting light modulated on the recording surface, the outgoing optical path of the laser light irradiated onto the optical disc is A light attenuation filter with a transmittance of 10 to 40% is inserted into the system, and a light beam whose width is narrower than the width of the beam passing through the light attenuation filter and whose transmittance is 100% in the track direction is inserted into the system. An optical reproducing device characterized in that the secondary maximum intensity of the laser spot is reduced by forming a light section.