JPS63306546A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To sharply increase the recording capacity of an information recording medium by arranging a condenser lens for forming a condensing point on a position conjugate with a recording layer in front of a detector and positioning a pin hole on the condensing point. CONSTITUTION:The condenser lens 6 for forming its condensing point on a position conjugate with the recording layer 5b is arranged in front of the detector 8 and the pin hole 7 is positioned on the condensing point to constitute a detecting system as a confocal system. Since the pin hole 7 is arranged on the condensing position of the condenser lens 6 which is a conjugate position with the recording layer 5b, reflected light from recording layers 5a, 5c other than the recording layer 5b is not reached to the detector 8. Thereby, only the information on the recording layer 5b is detected. Even if an interval between the recording layers in the information recording medium is short, no detecting error is generated, so that the recording capacity of the information recording medium can be sharply increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording and reproducing apparatus for optical discs, magneto-optical discs, and the like.

[Prior art and problems to be solved by the invention] In recent years, perpendicular magnetic recording has been invented in magnetic recording and the recording density has improved, but a further increase in recording capacity is desired in optical recording as well. Therefore, it has recently been considered to increase the recording capacity by creating a three-dimensional recording system by making the recording layer of an information recording medium multi-layered.

However, since conventional optical recording/reproducing is based on the concept of recording and reproducing information two-dimensionally on a flat surface, optical recording/reproducing devices do not take any measures to distinguish information in the depth of focus direction. There wasn't. In other words, in the case of a conventional optical recording/reproducing device, even if light is focused on a certain recording layer of an information recording medium having multiple recording layers, not only light reflected from that recording layer but also light reflected from other recording layers is generated. Since reflected light is also detected, reading errors are unavoidable. In order to avoid such problems, it is necessary to make the distance between the recording layers sufficiently large, and as a result, the objective of increasing the recording capacity cannot be fully achieved.

In view of the above-mentioned problems, the present invention provides an optical recording and reproducing apparatus that does not cause reading errors even if the distance between recording layers of an information recording medium is small, and can therefore dramatically increase the recording capacity of an information recording medium. The purpose is to provide.

[Means and effects for solving the problems] The optical recording and reproducing apparatus according to the present invention includes a light source, an objective lens that focuses light emitted from the light source onto a recording layer of a recording medium, and a return light from the recording layer. In an optical recording/reproducing device comprising: a detector that detects light; a condensing lens that forms a condensing point at a position conjugate with the recording layer in front of the detector; and a condensing lens located at the condensing point. By providing a pinhole, the detection system is configured as a confocal system.

More details will be explained with reference to the conceptual diagram of the present invention shown in FIG.

In FIG. 1, 1 is a semiconductor laser light source, 2 is a collimator lens, 3 is a beam splitter, 4 is an objective lens, and 5
6 is a recording medium having multilayer recording layers 5a, 5b, and 5c;
is a condensing lens, and the condensing point of the laser light source 1 and the objective lens 4 and the condensing point of the condensing lens 6 are optically conjugate positions. In other words, it is a confocal system.

7 is a pinhole placed at the focal point of the condenser lens 6, and 8 is a photodetector.

A laser beam emitted from a laser light source 1 is collimated by a collimator lens 2, reflected by a beam splitter 3, and focused by an objective lens 4 onto, for example, a recording layer 5b in a recording medium 5. The light reflected by the recording layer 5b is turned into parallel light by the objective lens 4, passes through the beam splitter 3, is condensed by the condensing lens 6, and enters the pinhole 7.
The information is read by being detected by the photodetector 8.

will be held. In this case, since the pinhole 7 is provided at the condensing position of the condensing lens 6, which is a position conjugate with the recording layer 5b, the principle of the confocal method allows light to be detected from the recording layers 5a and 5c other than the recording layer 5b. The reflected light does not reach the detector 8, so only the information on record 1''5b is detected.

Furthermore, when detecting information on the recording layer 5a or 5C, the position of the recording medium 5 may be moved in the vertical direction to adjust the focal point of the objective lens 4 to be on the recording layer 5a or 5C. .

〔Example〕

Hereinafter, the present invention will be described in detail based on an illustrated embodiment.

Figure 2 shows an optical recording and reproducing device that utilizes the magneto-optical effect (the effect in which the rotation direction of the polarization plane of reflected light and transmitted light differs depending on the magnetization direction of the recording medium), where 11 is a semiconductor laser light source, and 12 is a collimator. A lens 13 is a shaping prism for shaping the laser beam into a perfect circle, 14 and 15 are non-polarized beam splitters, and 16 is an objective lens for condensing the laser beam onto a recording medium 17 such as a magneto-optical disk. The recording medium 17 has a multilayer structure, for example, as shown in FIG. 3, a groove material 17b is laminated on a glass substrate 17a, and a protective layer 17c of TbFeCo or GdFeC is layered on top of the groove material 17b.

The recording layer 17d, the protective layer 17C, and the intermediate layer i7s are repeatedly laminated and bonded on top of the uppermost protective layer 17c.
It is made by laminating f and a glass retaining layer 1'7g. 18 is 1/ for rotating the direction of linearly polarized light.
2 wavelength plate, 19 a polarizing beam splitter that also serves as an analyzer, 20.21 a condensing lens, 22.23 a pinhole placed at each condensing point of the condensing lens 20.21, 2
4.25 is a photodetector connected to a differential amplifier (not shown), and the focal point of the laser light source 11 and the objective lens 16 and the focal point of the condensing lens 22.23 are at optically conjugate positions. It becomes. 26 is a cylindrical lens,
Reference numeral 27 denotes a four-part detector for detecting focusing and tracking, which uses the astigmatism method for focusing, and the heterogain method, push-pull method, etc. for tracking.

Since the present embodiment is configured as described above, the laser light emitted from the laser light source 11 enters the objective lens 16 through the collimator lens 12, the shaping prism 13, the beam splitter 14, and the recording medium 17. recording layer 17 with
The light is focused on d. That record 1! The reflected light from the l117d, that is, the laser light with information, is returned to the objective lens 16.
After entering the beam splitter 15.1/2 wavelength plate 18
and is separated into two polarized components by a polarizing beam splitter 19. The two polarized light components pass through pinholes 22 and 23, respectively, and are detected by photodetectors 24 and 25, and the difference in their outputs is amplified by a differential amplifier (not shown) to read information. The principle of reading magneto-optical disks using the differential method is well known, so
A detailed explanation thereof will be omitted. In this case, the reflected light from the other recording layer 17d does not reach the photodetectors 24 and 25 due to the principle of the confocal method. Further, when reading information on another recording layer 17d, the position of the recording medium 17 may be moved in the vertical direction so that the focal point of the objective lens 16 is placed on the other recording layer 1117d.

In this way, information on any recording layer in the recording medium 17 can be read out. However, since the optical recording/reproducing apparatus according to the present invention has a confocal detection system,
Record 1' of 7! Even if the distance between the recording medium 117d is small, no reading error occurs, and therefore the recording capacity of the recording medium 17 can be dramatically increased.

Note that the recording medium 17 may be a bulk one, in which case there is no fixed layer, so it is necessary to perform formatting in advance according to the distance from the surface of the medium. Further, if an address trunk indicating an address is provided, the recording layer to be read can be easily found. Also, recording medium 17
may be a normal read-only optical disc.

〔Effect of the invention〕

The optical recording/reproducing device according to the present invention has extremely important practical advantages in that reading errors do not occur even if the distance between the recording layers of the information recording medium is small, and therefore the recording capacity of the information recording medium can be dramatically increased. have.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of the present invention, FIG. 2 is a diagram showing an optical system of an optical recording/reproducing apparatus according to the present invention, and FIG. 3 is a sectional view of a recording medium. 1.11... Semiconductor laser light source, 2.12...
Collimator lens, 3, 14.15... Beam splitter, 4.16... Objective lens, 5, 17...
・Recording medium, 6,20.21...Condensing lens, 7°22.23...Pinhole, 8,24.25...
・Photodetector, 13... Shaping prism, 18...
172 wavelength plate, 19...polarizing beam splitter, 2
6... Cylindrical lens, 27... Quadrant detector.

Claims (1)

[Claims] An optical recording and reproducing apparatus comprising a light source, an objective lens that focuses light emitted from the light source onto a recording layer of a recording medium, and a detector that detects return light from the recording layer, wherein the detector An optical recording/reproducing device comprising: a condenser lens that forms a condensing point at a position conjugate with the recording layer in front of the recording layer; and a pinhole located at the condensing point.