JPH02123526A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain a stable information reproducing signal and simultaneously to realize recording and reproducing with high density by obtaining such constitution that a recording track is obliquely irradiated from a vertical direction to the recording track by converged light flux outgoing from a condensing lens. CONSTITUTION:Incident light flux 11 is made incident on one lens pupil of the condensing lens 4 parted by a pupil parting line X which runs parallel with the direction of the recording track 13. The incident light flux 11 is deviated in the vertical direction to the recording track 13. As the result, the light flux reflected on the oblique surface of the swollen part 16 of a pit 15 is not returned to a semiconductor laser and the output of the semiconductor laser is stabilized. Besides, when the incident light flux 11 is made incident on the condensing lens 4 by forming it in a slender state in the direction of the recording track 13, the width of a generated light spot is made narrow and the recording and the reproducing with high density are realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical information recording/reproducing device for recording and reproducing information on an optical recording medium such as a card or disk.

[Conventional technology]

In order to reproduce information recorded on an optical recording medium, a semiconductor laser is used as a light source, and the laser light from the semiconductor laser is focused by a lens and projected onto the optical recording medium. The reflected light is detected by a photodetector. However, when using a semiconductor laser in this way, there is a problem that noise is likely to be generated when the reflected light from the recording medium returns to the semiconductor laser, and this noise deteriorates the S/N of the reproduced signal. . In order to solve such problems, conventionally, as shown in FIG. The 174-wave plate 3 and the polarizing prism 2 are used to create an optical isolator. It has been proposed to form a semiconductor laser 1, thereby eliminating the return light to the semiconductor laser 1 and preventing the generation of noise. However, even in this optical system, since the optical recording medium 5 is generally covered with a protective layer such as plastic, if this holding layer has birefringence, the polarization state is disturbed and the polarizing prism 2
There is a problem in that the optical isolator based on the 174-wavelength exclusion 3 becomes ineffective, and the return light from the recording medium 5 enters the semiconductor laser 1, causing noise.

As a countermeasure to such problems, for example,
-150391, a method in which a light beam for recording and reproduction is incident obliquely on an optical recording medium (hereinafter referred to as r
``Off-axis method'') was proposed. As shown in FIG. 6, in this off-axis method, the laser beam 7 emitted from the semiconductor laser 1 is made parallel and decentered to the optical axis 8 of the condenser lens 4, and then passes through the condenser lens 4 to the recording medium 5. The reflected light 9 is made to enter the photodetector 6 via the condenser lens 4 and the mirror 10. With this configuration, the laser beam 7 will be obliquely incident on the surface of the recording medium 5, so that the reflected light 9 from the recording medium 5 will not go backwards toward the semiconductor laser 1 and will pass through the condenser lens. The light is effectively guided to the photodetector 6 via the 4° mirror 10. Therefore, even if there is birefringence in the protective layer 5a of the recording medium 5, the entire amount of light can be made incident on the photodetector 6 regardless of the birefringence, so that noise due to the light returning to the semiconductor laser 1 will not occur. .

The relationship between the direction of incident light, the direction of reflected light, and the recording track direction in the off-axis method shown in FIG. 6 is as shown in FIG. 7. An incident light beam 11 that is spaced apart from the lens optical axis and parallel to the lens optical axis is irradiated toward the condenser lens 4 . The light beam emitted from the condenser lens 4 forms a light spot on the recording medium intersecting the optical axis of the lens. Thereafter, the light beam reflected by the recording medium becomes a reflected light beam 12 and exits the condenser lens 4. FIG. 8 is a view of FIG. 7 viewed from the lens optical axis direction of the condenser lens 4. Incident light flux 1 inside the condenser lens 4
In the conventional off-axis method, the pupil division line
It is almost a right angle.

[Problem to be solved by the invention]

However, the conventional off-axis system described above has the following drawbacks. The maximum NA of the incident light beam 11 in the direction of the recording track 13 in FIGS. 7 and 8 is approximately half the NA of the condenser lens 4, and compared to a non-off-axis method (a method in which the light beam is incident over almost the entire area of the lens pupil),
The spot diameter of the focused luminous flux becomes approximately twice as large.

If the diameter of the beam spot is large as described above, there is a drawback that it becomes impossible to read high-density information recorded on the recording medium. In order to reduce the diameter of the beam spot, a condensing lens with a large NA may be used, but it is expensive, large in size, and heavy, which is disadvantageous for miniaturization.

Next, pit reading using the conventional off-axis method will be described. When forming recording pits, the pits are recorded while moving the recording medium 5 in FIG. 6 in either the recording track direction A, ie, arrows (a) or (b). Let us consider the case where the recording medium 5 is moved in the direction (A) of FIG. 6 and the recording medium surface is melted by the recording beam from the semiconductor laser 1 to form pits.

In this case, the pits recorded on the recording medium are as shown in FIG. 15 is a recorded pit, which is blackened and has a slight depression formed therein.

Reference numeral 16 denotes a raised portion of the pit. When the recording medium is moved in the direction shown in FIG. 6(A), this raised portion 16 occurs near the left end of the pit 15 in FIG. 9.

- If recording is performed while moving the recording medium 5 in the direction (b) of the cylinder 6, the pit shape will be as shown in FIG. 10.

In this case, unlike the case shown in FIG. 9, the raised portion 16 of the pit 15 occurs near the right end of the pit 15 as shown in FIG. 1O. The case of reading a pit in which a raised portion 16 as shown in FIG. 9.10 is formed will be described below.

FIG. 11 explains the case of reading the pit 15 of FIG. 9. An incident light beam 11 entering the condenser lens 4 from the left side of the optical axis of the condenser lens 4 passes through the condenser lens 4 and is then converged toward the lens optical axis. At this time, when the beam spot illuminates the right downward surface 16' of the raised portion 16, the reflected light beam 17 becomes like a broken line. That is, most of the reflected light beam 17 is emitted to the right with respect to the optical axis of the condenser lens 4.

Therefore, in the case of FIG. 11, the reflected light beam 17 does not return to the semiconductor laser. Next, FIG. 12 will be described in which a light spot is irradiated onto the pit 15 in FIG. 10 using the same optical system as in FIG. 11. The light emitted from the condenser lens 4 is focused on the upper right surface 16' of the raised portion 16 to form a light spot. The reflected light beam 18 at this time becomes a broken line, and a part of it enters the pupil on the left side with respect to the optical axis of the condenser lens 4. As a result, a portion of the reflected light 18 reaches the semiconductor laser 1. When the reflected light returns to the semiconductor laser 1, the output of the semiconductor laser 1 fluctuates, causing noise.

In this way, in the above-mentioned conventional off-axis method, the bulge caused by the running direction of the recording medium when recording pits causes playback when reading pits. It has a drawback that the output of the semiconductor laser varies as the FW number fluctuates.

〔Example〕

Next, one embodiment of the present invention will be described below based on the drawings.

FIG. 1 explains the basic configuration of the shaft off-axis system according to the present invention. The difference from the conventional off-axis method shown in FIGS. 7 and 8 mentioned above is that the pupil division line
This point is almost parallel to 3. That is, the pupil division line X in Figure 1
The direction almost coincides with the recording track 13 direction.

FIG. 2(a) shows the optical system of FIG. 1 viewed from the lens optical axis direction. As is clear from FIG. 2(a), the incident light beam 11 is made to enter one lens pupil of the condensing lens 4 divided by the pupil dividing line X, and the reflected light from the recording medium is made to exit from the other lens pupil. Make it. As described above, this embodiment differs greatly from the conventional off-axis method in that the incident light beam 11 is deviated in a direction perpendicular to the recording track 13.

As a result, as explained in FIG. 12, the light beam reflected on the slope of the raised portion 16 of the pit 15 does not return to the semiconductor laser, and the output of the semiconductor laser becomes stable.

On the other hand, when the incident light beam 11 is formed into an elongated shape in the recording track direction as shown in FIG. 2(b) and is made incident on the condenser lens 4, a light spot 21 as shown in FIG. 2(c) is formed on the recording medium. It is formed. @ of the recording track 13 direction of this light spot 21
d can be made as small as about 172 compared to @D of the optical spot 22 (indicated by the broken line in FIG. 2(c)) on the recording medium due to the circular beam in the case of FIG. 2(a).

As a result, reading with a light spot having a small width in the recording track direction, such as the light spot 21, has the advantage of enabling high-density recording and reproduction.

Next, improvements to the above embodiment will be described below.

For tracking purposes, the condenser lens 4 moves in the tracking direction T, T' of FIG. 2(b), which is perpendicular to the recording track direction. need to be moved. On the other hand, since the incident light beam 11 is not displaced, the amount of displacement of the condenser lens 4 in the T direction becomes large, and when the optical axis of the condenser lens 4 enters the incident light beam 11, part of the reflected light from the recording medium is reflected by the semiconductor laser. Noise occurs again.

In order to prevent such a phenomenon, even if the condensing lens 4 moves in the tracking direction, all of the incident light flux should always be made to enter the pupil on one side of the lens with respect to the lens optical axis. For this purpose, if the gap between the optical axis of the condensing lens and the incident light beam in FIG. Bye.

Next, another solution will be explained based on FIG. 1
Reference numeral 9 denotes an elongated aperture stop fixed to the condenser lens 4. FIG. 3(b) is a view seen from the lens optical axis direction of FIG. 3(a). The recording track direction in FIG. 3(a) is perpendicular to the paper surface. The incident light beam 11 has an elliptical shape in consideration of efficiency, but it may also have a circular shape.

The incident light beam 11 passes through an aperture stop 19. After passing through the condensing lens 4, the recording medium 20 is irradiated with the condensed light, and then the reflected light beam 1
2, exits the condenser lens, and reaches the photodetector 6 after being reflected by the mirror 10.

In FIG. 3, even if the condenser lens 4 is moved to the left within the distance M between the right end of the light shielding part 23 and the incident light beam 11, the light does not return to the semiconductor laser. The structure shown in FIG. 3 has a simple structure, and has the advantage that it can prevent light from returning to the semiconductor laser even when the condenser lens 4 performs a tracking movement.

FIG. 4 shows yet another solution. This case is characterized in that the condenser lens 4 and the reflection mirror 10 are integrally fixed, and one end of the one reflection mirror 10 is arranged in contact with the lens optical axis.

In such a configuration, even if the condensing lens 4 moves considerably to the left, the reflecting mirror 1 is on the right side with respect to the optical axis of the condensing lens 4.
Since the incident light beam 11 is blocked by 0, no light returns to the semiconductor laser. Moreover, with this configuration, half of the pupil of the condenser lens 4 can be used 100%, so the light spot on the recording medium can be minimized.

[Effects of the present invention]

In the off-axis method of the present invention, as explained in FIG. It is not affected by the raised portion 16 as shown in the figure.

Therefore, even when reading a pit having such a raised portion 16, there is no return light from the semiconductor laser, and there is an advantage that a stable information reproduction signal can be obtained.

Furthermore, according to the off-axis method of the present invention, the width d of the light spot
It has the advantage that it can be made small and high-density recording and reproduction is possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing the basic configuration of the present invention, and FIG. 2 is a perspective view of FIG. 1 from a condensing lens toward a recording medium. Recording medium 10...Reflection mirror 12...Reflected light beam 19...Aperture diaphragm Patent originator "S"<8 Kogaku Kogyo Co., Ltd. <1. . 4... Converging lens 6... Photodetector 11... Incident light beam 13... Recording tracks 21, 22... Light spot No. Figure @4 Figure □ (A) Figure □ (B) Figure 0 Figure 12

Claims (1)

[Scope of Claims] A light beam is passed through a region of a condensing lens separated from a lens optical axis, and a medium is irradiated with the focused light of the condensing lens, and the reflected light is received by a photodetector. An optical information recording and reproducing apparatus using an off-axis method, characterized in that an incident light beam is deviated in a direction perpendicular to the recording track direction with respect to the optical axis of the condenser lens.