JPS6190337A - Optical information recording/reproducing device - Google Patents

Abstract

PURPOSE:To detect an accurate error signal without being influenced by an astigmatism by attaching a lens so that the focus direction of astigmatism of the objective lens and the direction of split line of a photodetector may coincide. CONSTITUTION:When an objective lens 6 is attached to the actuator, the lens is attached so that the focus direction of the lens may coincide with X axis or Y axis of the split line of a photodetector. If the lens is attached in this way, the variation of light distribution which may occur to bit refraction pattern projected on the optical detector 9 due to an astigmatism will be symmetrical against the split line, so the difference factor is not infused into the error signal. Therefore, the influence of the astigmatism of lens will be eliminated and error signals can be accurately detected enabling correct follow-up.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an optical information recording/reproducing device, and particularly to an optical information recording/reproducing device that eliminates the influence of astigmatism of lenses constituting an optical system.

(Prior Art) Optical information recording and reproducing devices that optically record and/or reproduce information by projecting a light beam onto a recording medium such as an optical disk have been put into practical use.

In this optical information recording/reproducing 1A device, a light beam converged into a minute spot from a pickup is projected onto a bit surface where optical information is recorded via an optical system, and reflected light or transmitted light from the bit surface is converted into an optical beam. Create a tracking error signal and a focusing error signal by making it incident on a detector,
The optical system is configured to supply these signals to a tracking servo loop and a focusing servo loop to perform accurate tracking operations, and the optical system includes a collimator lens that converts the light beam emitted from the light source into a parallel beam. It is configured to create a light beam for recording and reproducing optical information using a lens system such as an objective lens that projects a light beam converged into a minute spot onto an optical disk.

Therefore, the optical performance of the lenses that make up the optical system plays an important role in driving and controlling the light beam. It is not possible to project an accurate beam spot pattern, resulting in the inconvenience that not only is it impossible to accurately record and reproduce optical information, but also that accurate tracking operation cannot be performed. In particular, if there is a slight astigmatism in the lens, a linear dark line is projected on the photodetector in the direction of the aberration, and this dark line becomes noise in the tracking error signal and focusing error signal. This results in the inconvenience of crosstalk that affects each other. In this state, tracking control and focusing control can no longer be performed independently, and
The actuator that drives the objective lens, which is one of the optical systems, will no longer be able to operate accurately.

(Objective of the Invention) The object of the present invention is to eliminate the above-mentioned drawbacks, eliminate the influence of astigmatism of the lenses constituting the optical system, detect accurate tracking error signals and focusing error signals, and ensure accurate tracking operation. 3. (Summary of the Invention) The optical information recording and reproducing apparatus according to the present invention projects a light beam emitted from a light source onto a recording medium as a minute spot, It has an optical system that makes the light beam reflected or transmitted from the recording medium enter a photodetector divided into four parts, and generates an error signal representing the positional deviation between the recording medium and the spot from the output of this photodetector. The optical information recording/reproducing device is characterized in that the lens constituting the optical system is attached to the optical system so that its astigmatism line coincides with the dividing line of the photodetector.

(Embodiment) FIG. 1 is a diagram showing the configuration of an example of an optical information recording/reproducing apparatus according to the present invention, and FIG. 2 is a diagram showing the configuration of an example of an error signal generating section thereof.

A light beam (linearly polarized in the plane of the paper) emitted from a laser light source 1 is expanded by an expander lens 2, and then converted into a parallel beam by a collimator lens 3, which is then passed through a polarizing prism having a polarizing film. The light passes through a beam splitter 4, is converted into clockwise or counterclockwise circularly polarized light by a quarter-wave plate 5, is focused into a minute spot by an objective lens 6, and is incident on a disk 7. An information track 7a having pits made of an aluminum reflective film is formed on the disk 7, and the incident light beam is reflected by this information track 7a and passes through the objective lens 6 again.
/4 wavelength plate 5. And this 1/4 wavelength plate 5
The light is converted into light linearly polarized in a direction perpendicular to the polarization direction of the light emitted from the laser light source 1, reflected by the beam splitter 4, and incident on the critical angle prism 8. This critical angle prism 8 has a reflecting surface 8a set at a substantially critical angle with respect to the optical axis of the incident light beam. The light beam emitted from this critical angle prism 8 is made incident on a photodetector 9 arranged in the far field of the information track. This photodetector 9 is arranged in a direction (X-axis) perpendicular to the direction of the information track projected onto the light-receiving surface with the optical axis of the output beam from the critical angle prism 8 as the center, and in an information track direction (Y-axis).
four light-receiving areas 9A, 9 arranged separately in the direction).
It is composed of 8.9G and 9D.

With this configuration, if a racking error occurs to 1, a difference will occur in the beam spot distribution in the X-axis direction of the beam spot pattern projected onto the photodetector 9. , a tracking error signal of 14 is detected by detecting the difference between the sum of the outputs of the light receiving areas 9B and 9D.
It will be done. Furthermore, since a focusing error causes brightness and darkness in the Y-axis direction, a focusing error signal can be obtained at the same time by detecting the difference between the sum of the outputs of the light receiving areas M9A and 9B and the sum of the outputs of the light receiving areas M9C and 9D. be able to.

FIG. 3 is a circuit diagram showing the configuration of an example of a signal processing circuit according to the present invention. The outputs of the light receiving areas 9A and 9B arranged in the X-axis direction are connected to the adder 10, and the outputs of the light receiving areas 9C and 9D are connected to the adder 10.
The outputs of are connected to the adder 11 to find the sum of each, and
The outputs of the devices 10 and 11 are connected to the caulking device 12, and an information signal is reproduced from the sum of each. In addition, Q adders 10 and 1
Connect the output of 1 to the reducer 13 and convert the focusing error signal from the difference signal to 4j? Ru. Furthermore, the amount of received light [9A and 9
Connect the output of C to the adder 14 to create light receiving areas 9B and 9D.
The output of is connected to caulking 15, and these adders 14 and 15
The output of the subtracter 16 is connected to extract a tracking error signal from the difference signal.

FIG. 4 is a diagram showing the beam spot pattern shape projected onto the photodetector 8, and FIG. FIG. B shows a pattern shape when the objective lens 6 has astigmatism. If there is no astigmatism, the photodetector 9
A nearly circular pattern is formed in the image, and when a focusing error occurs, brightness and darkness occur in the Y-axis direction with the X-axis as the border.
When a tracking error occurs, the long axis and short axis are
This results in an oval pattern located in the middle of the axis.

On the other hand, if the objective lens has astigmatism, a linear dark line passing through the center of the circular pattern will occur within the circular pattern. In this specification, this dark line will be referred to as an astigmatism line. This astigmatism line maintains almost the same darkness regardless of the focusing error and tracking error, and when rotated about the objective lens 5, it rotates on the photodetector 8 in accordance with the rotation. Therefore, this astigmatism line is unique to each lens and occurs at a unique position for each lens.

Next, changes in the focusing error signal and tracking error signal when this astigmatism occurs will be explained. FIG. 5 is a diagram showing the relationship between the pattern projected on the photodetector 9 and the astigmatism line when an error signal occurs, and FIG. 5A shows a state where a focusing error occurs, B in the figure shows a state where a tracking error has occurred. If a focusing error occurs,
A difference in brightness occurs in the Y-axis direction with the axis as a boundary. Therefore, for example, if the amount of light received by the light receiving areas 9A and 9B above the X-axis should change due to the occurrence of a focusing error, the amount of light that should be received will be greatly reduced due to the presence of the astigmatism line. Resulting in. On the other hand, since the amount of light received by the light receiving regions 9C and 9D below the X-axis changes to decrease, there is little deviation in the amount of light received due to the presence of the astigmatism line. As a result, a misaligned focusing error is detected. When a tracking error occurs, the projected pattern becomes an ellipse as shown in FIG. 5B. Even in this case, the amount of light received by the light receiving regions 9A and 9C, which should increase, decreases, making it impossible to form a tracking error signal that corresponds to the amount of deviation of the actuator.

FIG. 6 is a diagram showing the relationship between the beam spot pattern projected onto the photodetector 9 and the astigmatism line by the optical information recording/reproducing apparatus according to the present invention.

In the present invention, before installing the objective lens 5, the image from the objective lens 5 to be used is projected onto a screen to confirm and mark the position where astigmatism occurs, and the objective lens 5 is installed in the optical system. When doing so, the photodetector 9 is mounted so that it coincides with the division line 11 or a2 of the photodetector 9, which is obtained by dividing the astigmatism line L' into four parts. If the photodetector 9 is mounted so as to match the dividing line, the amount of light received due to astigmatism ML will decrease by 4
It acts equally on each of the light receiving areas 9A to 9D,
There is no influence on the formation of focusing error signals and tracking error signals, and correct drive signals can be generated.

The present invention is not limited to the embodiments described above, but can be modified and modified in many ways. For example, in the embodiments described above, the astigmatism of the objective lens was explained, but the present invention can also be applied to all lenses constituting the optical system, such as collimator lenses and expander lenses.

Furthermore, the configuration in which the error signal is detected from the reflected light from the optical disc in the above-described embodiment can also be applied to the case where the error signal is detected from the transmitted light.

(Effects of the Invention) As explained above, according to the present invention, the astigmatism line due to the astigmatism of the lens is configured to coincide with the dividing line of the photodetector, so that the astigmatism line of the lens constituting the optical system is The influence of astigmatism can be removed, and a correct focusing error signal and tracking error signal corresponding to the actuator shift amount can be detected. This prevents the occurrence of crosstalk and allows accurate tracking control of the light beam.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an example of an optical information recording/reproducing device according to the present invention, FIG. 2 is a perspective view showing the configuration of an error signal detection section, and FIG. 3 is a diagram showing the configuration of an example of a signal processing circuit. Circuit diagram: - Figures 4A and B are diagrams showing the shape of the beam spot pattern projected onto the photodetector; Figure 5A is the relationship between the beam spot pattern and the astigmatism line when a focusing error occurs; FIG. 5B is a diagram showing the relationship between the beam spot pattern and the astigmatism line when a tracking error occurs. FIG. FIG. 3 is a diagram showing the relationship between a beam spot pattern and an astigmatism line when an error and a tracking error occur. 1... Laser light source 2... Expander lens 3... Collimator lens 4... Beam brick 5... 1/4 wavelength plate 6... Objective lens 7...
Disk 8...Critical angle prism 9...Photodetector 10, 11.12.14.15...Adder 13, 16
...subtractor

Claims (1)

[Claims] 1. It has an optical system that projects a light beam emitted from a light source onto a recording medium as a minute spot, and makes the light beam reflected or transmitted from the recording medium enter a photodetector divided into four parts, and this photodetector In an optical information recording and reproducing apparatus that generates an error signal representing a positional deviation between a recording medium and a spot from the output of An optical information recording and reproducing device characterized in that it is attached to an optical system so as to match.