JP2879601B2 - Optical information recording / reproducing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical information recording / reproducing apparatus for recording, reproducing, and erasing information using an optical recording medium such as a magneto-optical disk.

(Prior Art) In a conventional optical pickup of an optical information recording / reproducing apparatus, an information track formed at an interval of about 1.6 μm on a recording medium is irradiated with a laser beam by an objective lens having a diameter of about 1 μm.
Irradiation is performed by focusing on a fine beam spot of μm to record, reproduce, and erase information. For this reason, it is necessary to irradiate a beam spot with a precision of about 0.1 μm to approximately the center of the information track while maintaining a gap between the recording medium and the objective lens at a precision of about 1 μm and a spacing of about 4 mm.

Further, the recording medium rotates at a high speed of several thousand rotations per minute in order to improve the information processing speed, and the position change of the information track occurs at a high speed due to the surface deflection, the core deflection and the like of the recording medium. Therefore, focus control for driving the objective lens in the focal direction and tracking control for controlling the beam spot position in the direction perpendicular to the information track are performed. A known push-pull method, a critical angle method, an astigmatism method, a knife edge method, or the like is used for detecting an error signal for this control. Light reflected from a recording medium is received by a divided light receiving element, and the divided light is received. The control is performed based on a difference output obtained by calculating a difference between outputs from the respective divided light receiving elements.

In the magneto-optical recording method, recording is performed by magnetizing a magnetic film of a recording medium, and reproduction is performed by detecting a force-rotation of a rotation of a polarization plane of a laser beam irradiated by the magnetization, and a recording signal (RF signal). Is being read. In general, a Wollaston prism composed of a birefringent material separates laser reflected light from a recording medium having an RF signal into P-waves and S-waves having polarization properties orthogonal to each other, and each of them is divided by a light-receiving element. The RF signal is extracted by receiving the light and converting it to an electric signal.

The above-described signal detection method needs to have a very high detection sensitivity to a change in the position of the information track, and can control the beam spot at high speed and with high accuracy.

(Problems to be Solved by the Invention) In the above-mentioned conventional technology, in order to increase the detection sensitivity, a signal is converted into an electric signal with as much light as possible, and C /
It is necessary to improve the N ratio.

However, in the conventional technology, an optical path system for detecting a tracking error signal, a focus error signal, and an RF signal is:
The light reflected from the recording medium is split by optical means such as a beam splitter, a knife edge prism, and a half mirror. For this reason, the amount of light decreases every time the light passes through the optical means.

For example, in the apparatus disclosed in Japanese Patent Application Laid-Open No. 61-280034, the reflected light is used commonly for various signals in order to effectively utilize the limited reflected light from the recording medium. RF that can distribute a considerable amount of light from a magnetic pickup
Only about 50% of the light amount is shared in the signal, and the light amount is not used effectively.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical information recording / reproducing apparatus capable of extracting an RF signal and a tracking error signal with a large amount of light and improving the reliability of a detection signal.

(Means for Solving the Problems) In order to achieve the above object, the present invention irradiates a light beam as a beam spot on a recording medium via an objective lens, and reflects reflected light from the recording medium via a birefringent crystal. Optical splitting of the polarization plane by the recorded information of the reflected light is selectively separated by the birefringent crystal according to the polarization direction, and a recording signal is extracted by a difference output obtained by the split light receiving element. In the information recording / reproducing apparatus, astigmatism generating means provided in an optical path of reflected light for extracting the recording signal, the reflected light is condensed on a light receiving surface of the divided light receiving element in a direction in which the polarization component is divided, and It is installed near the birefringent crystal so as not to converge light in the tracking error detection direction that is substantially orthogonal to the division direction, and a recording signal is collected by the division light receiving element. And a tracking error signal can be extracted.

(Operation) By adopting the above means, the RF signal and the tracking error signal can be detected by one optical system (optical path) including the birefringent crystal, the astigmatism generating means, and the divided light receiving element. As a result, the light amount loss is reduced, and the amount of reflected light from the recording medium for detecting the RF signal and the tracking error signal can be effectively used.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a structural view of one embodiment of the present invention, and FIG. 2 is a perspective view showing a main part of the embodiment of FIG. 1, wherein 1 is a laser diode, 2 is a coupling lens, 3 is a beam splitter, Reference numeral 4 denotes an objective lens, 5 denotes a recording medium such as a magneto-optical disk, 6 denotes a condenser lens provided in an optical branch of the beam splitter 3, 7 denotes a knife edge prism, and 8 denotes a divided light receiving device for a focus signal. The element 9 is divided into four parts (a
-D) divided photodetectors for RF / tracking signals, 10
Is a Wollaston prism that is a birefringent crystal that receives the light reflected by the knife edge prism 7; It is.

In FIG. 1, a laser beam emitted from a laser diode 1 passes through a coupling lens 2, a beam splitter 3, and an objective lens 4 and is condensed on a recording medium 5, and the reflected light from the recording medium 5 is again reflected by the objective lens. The beam proceeds to the lens 4 and the beam splitter 3, and the entire or a part of the light amount is directed to the detection system by the beam splitter 3, is collected by the condenser lens 6 in the detection system, and is further focused by the knife edge prism 7. The signal is divided into a divided light receiving element for signal 8 and a divided light receiving element 9 for RF / tracking signal. Also. In the RF / tracking signal detection system, a P-wave component and an S-wave component are separated by a Wollaston prism 10 and condensed on an RF / tracking signal split light receiving element 9, as shown in FIG. The light passing through 10 and entering the split light receiving element 9 for RF / tracking signal is transmitted through a cylindrical lens 11.
In the surface of the light-receiving element, astigmatism such that it becomes a converging point in the direction of division of the P-wave component and S-wave component of light (direction of arrow A) and does not become a converging point in the tracking error signal direction (direction of arrow B) Will be presented. As a result, from the following equations (1) and (2), it is possible to extract the tracking error signal from the reflected light, which has been used only for the RF signal, without deteriorating the characteristics of the RF signal.

RF signal = (a + c)-(b + d) (1) Tracking error signal = (a + b)-(c + d)
(2) The detection of the tracking error signal will be described more specifically. As shown in FIGS. 3A and 3B, a large number of track grooves 5a are formed in the recording medium 5, and the minute spot S of the laser beam needs to be located at the center of the groove 5a. is there. FIG. 3A shows the intensity distribution of the reflected light when the spot S is located at the center of the groove 5a, and FIG.
Shows the intensity distribution of the reflected light when the spot S deviates from the center of the groove 5a. In the state of FIG. 3 (b), the spot S deviates from the center and diffracts at the wall of the groove 5a. The intensity distribution changes asymmetrically in the tracking direction to generate an intensity distribution difference. This asymmetry is detected by the divided light receiving element 9 for RF / tracking signals, and tracking control is performed by changing the position of the spot S in a direction in which the asymmetry is corrected.

In this case, the size of the optical pickup is reduced by making the divided light receiving element 9 for RF / tracking signal for detection smaller.
Since the price can be reduced, the reflected light can be collected to some extent
It is necessary to reduce the diameter of the spot S on the light receiving surface of the signal splitting light receiving element 9 for RF / tracking. However, if the diameter of the spot S is minimized by setting the focal point on the light receiving surface, the intensity distribution of the reflected light changes and the tracking error signal is disturbed. Generally, the position is sufficiently far from the light spot.

Next, detection of an RF signal will be described more specifically. RF
The signal is extracted by detecting the direction of the magnetization recorded on the recording medium 5. The reflection surface of the recording medium 5 slightly rotates the polarization plane of the irradiated laser beam according to the direction of the recorded magnetization. When this rotation of the polarization plane occurs, the light amount ratio between the P-wave component and the S-wave component of the light incident on the Wollaston prism 10 changes.
As shown in the diagram, the P-wave component and the S-wave component are separated from each other, and by detecting each component, the direction of rotation can be measured to detect the magnetization direction. The Wollaston prism 10 combines a birefringent material such as quartz having a characteristic in which the refractive index varies depending on the direction of the polarization plane, and changes the traveling direction of light by the difference in the polarization plane to separate the P wave component and the S wave component. Although the separation angle of the Wollaston prism 10 can be changed arbitrarily, the separation angle is preferably 0.5 ° to 2 ° due to size restrictions. Even if the separation angle is small as shown in FIG. It is preferable that the reflected light is condensed and made incident on the divided light receiving element 9 for RF / tracking signal so that the light is completely reflected.

In the above embodiment, the RF signal and the tracking control signal are conventionally detected by separate optical systems. However, since these signals can be detected by one optical system (optical path), the amounts of the RF signal and the tracking control signal are increased. It becomes possible. According to the inventor's experience so far, it is particularly effective to improve the recording / reproducing speed and the recording density of the optical information recording / reproducing apparatus by increasing the signal amount of the tracking signal and the RF signal. Thus, the performance of the optical recording / reproducing apparatus can be improved. Further, by using one optical system, the size of the optical pickup can be reduced, and the number of components can be reduced.

(Effects of the Invention) As described above, according to the present invention, since the RF signal and the tracking error signal can be detected using one optical system (optical path), the light amount can be obtained from the limited reflected light from the information medium. A signal can be detected without reduction, and a highly reliable optical information recording / reproducing apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of the optical information recording / reproducing apparatus of the present invention, FIG. 2 is a perspective view showing a main part of the embodiment of FIG.
3 (a) and 3 (b) are explanatory diagrams of tracking error signal detection, and FIG. 4 is an explanatory diagram of a Wollaston prism. 1 ... laser diode, 3 ... beam splitter, 4
... Objective lens, 5... Recording medium, 7... Knife edge prism, 8...
... Divided light receiving element for RF / tracking signal, 10 ... Birefringent crystal, 11 ... Astigmatism generation means.

Claims (1)

(57) [Claims] A recording medium is irradiated with a light beam through an objective lens as a beam spot, and reflected light from the recording medium is made incident on a divided light receiving element via a birefringent crystal, and polarization of the reflected light according to recorded information is obtained. In an optical information recording / reproducing apparatus which selectively separates a deflection angle of a surface by a polarization direction by the birefringent crystal and extracts a recording signal by a difference output obtained by the divided light receiving element, the optical path of reflected light from which the recording signal is extracted The reflected light is condensed on the light-receiving surface of the divided light-receiving element in a direction in which the polarization component is divided, and is not reflected in a tracking error detection direction substantially orthogonal to the division direction. It is installed in the vicinity of the birefringent crystal so as to collect light, and the recording light signal is extracted by the divided light receiving element and the tracking error signal is extracted. The optical information recording and reproducing apparatus being characterized in that the capacity.