JPS6142745A - Optical information reader - Google Patents

Abstract

PURPOSE:To perform defocusing detection with high precision over a wide range and to obtain a tracking deviation signal precisely by processing output signals of two-division photodetecting elements provided across a specific optical system in directions orthogonal to an optical axis and a four-division photodetecting element provided on an optical axis. CONSTITUTION:Light emitted by a semiconductor laser 1 is converged on a disk 6 through a polarization beam splitter (PBS)2, lambda/4 plate 3, collimator lens 4, and objective lens 5. Its reflected light is passed through the PBS2 and split in three directions by a beam splitter 7 to enter the four-division photodetecting element 10 through the two-division photodetecting elements 8 and 8' at image non-formation points B and B' at equal short or long distance from the conjugate points A and A' of the laser 1 and a cylindrical lens 9 on the optical axis. A defocusing signal is obtained from the sum signal of difference components obtained by subtracting outputs of the photodetecting elements 8 and 8' from the output of the photodetecting element 10 and the sum signal of difference signal of the diagonal sums of two couples of photodetecting elements 10 and the tracking deviation signal is obtained from the difference signal of the outputs of photodetecting elements 8 and 8'.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical information reading device that reads information recorded on a VD, CD, etc. using a light beam, or an optical information reading device that reads information recorded on a VD, CD, etc. using a light beam. [Prior Art] Conventionally, optical information reading devices have been known that use an astigmatism method as a defocus detection method and a pushinable method as a tracking shift detection method.

A diagram of an optical ↑U information reading device using the method described above is shown in FIG.

The light emitted from the conductor laser 1 is 100% reflected in the direction of the disk 6 by the polarizing beam splitter 2.
'ζ,, x IJ meter lens 4 via '/4 wavelength plate 3
The light is converted into parallel light, and the light is focused onto a disk 6 via an objective lens 5. This light beam is reflected by the information track having a concave and convex bit shape, and is reflected by the objective lens 5. Collimator lens 4° 1/4 wavelength plate 3. It passes through the polarizing beam splitter 2 in a direction perpendicular to the incident light beam,
The light enters the cylindrical lens 9 which is rotated by 45° in a plane perpendicular to the optical axis. The four-part light-receiving elements are arranged so that the same amount of light enters each light-receiving element during focusing. As the disk approaches, the beam becomes an ellipse, as shown in Figure 5 (α), and as the disk moves away, the beam (α) becomes an ellipse in the direction of the nest, as shown in Figure 3 (b). Therefore, (10A+I
A defocus signal was obtained from 0C)-(10B+10D), and a tracking deviation signal was obtained from the change in direction of the first-order diffracted light due to the uneven pits carved on the disk. The above-mentioned tracking deviation signal was obtained from (10A+10B)-(10C+10D) because the detector is rotated by about 90 degrees due to the action of the cylindrical lens 9.

[Problem that the invention seeks to solve]

However, in the conventional astigmatism method and push-pull method, the beam shape on the four-split light receiving element during focusing is not a perfect circle due to the aberrations of the collimator lens 4 and the cylindrical lens 9, and is spindle-shaped. Moreover, since the light-receiving element is placed between both focal lines, the disk image is not rotated by exactly 90 degrees.

Therefore, when focusing, the direction change of the -order diffracted light is exactly 4
The dark line in the tracking direction of the split light receiving element did not appear at the boundary, but had a slight inclination. Therefore, a false signal is mixed into the tracking error signal, making it impossible to trace the track accurately. Furthermore, since the defocus signal and the tracking deviation signal are obtained from the same four-split light receiving element, they influence each other's signals, making it difficult to extract a stable and accurate error signal. Furthermore, since the astigmatism method has a relatively narrow error detection range, a focus pull-in circuit or the like is required.

Therefore, in order to solve these disadvantages of the conventional technology, this invention completely separates the focus shift signal and the tracking shift signal,
The purpose of the present invention is to obtain an optical reading device that obtains highly accurate and stable error signals without mutual interference, and that does not require special circuits such as a focus pull-in circuit.

- [Means for solving the problem] In order to solve the above problem, the present invention provides a lens that converges the reflected light from the disk, an optical axis direction between the objective lens and the lens, and an optical axis direction. In a plane perpendicular to
A beam splitter that divides into two beams of equal light intensity in opposite directions or orthogonal directions with the plane formed by the optical axis and the track as a boundary, and a cylindrical lens and a 4-split light receiving element are arranged in the direction of the original axis. Then, on each optical axis in a plane perpendicular to the optical axis direction, at least two or more divided light receiving elements having a division uJ49 in a direction parallel to the track direction are placed equidistantly apart from the imaging point. , one is placed on the side close to the disk and the other is placed on the side far from the disk, and the defocus signal is transmitted to one of the two split light receiving elements.
The second value is calculated by subtracting the output of the light receiving element that includes the optical axis from the output of the light receiving element that does not include the optical axis from the output of the light receiving element that includes the optical axis.
A tracking deviation signal is obtained from the sum signal of the difference component of the two pairs of diagonal sums of the four-split light-receiving elements, and a tracking deviation signal is obtained from the difference signal between the two two-split light-receiving elements. As a result, the mutual interference between the defocus signal and the tracking deviation signal is eliminated, and both error signals are obtained with high accuracy and stability.

[Operation] When arranged as above and obtaining an error signal, the defocus signal component obtained from the two-split pot element is used to pull in a wide range of focus, and the defocus signal component obtained from the λ-split photodetector element is used to draw the focus over a wide range. , since high-precision focus servo is performed and an optical element that rotates the disk image is not placed in the reflected optical path from the disk, using the tracking deviation signals obtained from both of the above two-split light receiving elements, Highly accurate tracking servo can be realized.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

At C) in FIG. 1, the light emitted from the semiconductor laser 1 passes through the polarizing beam splitter 21'/4 wavelength plate 5, is made into parallel light by the collimator lens 4, and is sent to the disk via the objective lens 5. 6. disk 6
The light reflected by the objective lens 5. Collimator lens 4
(via the action of the /4 wavelength plate 5 and the polarizing beam splitter 2), the incident light beam is divided into directions perpendicular to the incident light beam, and enters the beam splitter 7. At this time, due to the action of the beam splitter 7, the reflected light flux that has passed through one half of the plane bordered by the plane formed by the optical axis and the track direction, and the reflected light flux that has passed through the other half, are directed in opposite directions to the optical axis. It is divided into three directions: the direction perpendicular to the direction of the optical axis, and the direction of the optical axis. Now, in the direction perpendicular to the optical axis direction, one is equidistant from the conjugate points A and A' at the emission end of the semiconductor laser, one is at the non-imaging point B which is farther from the beam splitter 7, and the other is at the non-imaging point B from the beam splitter 7. A two-split light receiving element 8.8' having a dividing line parallel to the track direction is placed at a non-imaging point B' close to Adjust the two-split light receiving element 8.8' so that they are the same.

FIG. 5 shows, on the same optical axis, the light beams split into left and right by the beam splitter 7 among the reflected light beams, and the 174-wavelength plate 5
．． Polarizing beam splitter 2. 2 is a diagram showing an optical path diagram with the beam splitter 7 omitted and a beam state on each light receiving element 8° 8'. FIG. The figure (α) shows the state in focus, the figure (b) shows the state in which the disc 6 is close, and the figure (C) shows the state in which the disc 6 is far away. In reality, the half-luminous flux passing through the upper and lower sides of the lens is reflected by the beam splitter 7 into left and right sides, as shown in FIG. 1, so that they do not affect each other. Now, at the time of focusing, the outputs of the light receiving elements α, b, c, and d are all the same, as shown in figure (α). When the disk approaches, the state of the light receiving element 8 becomes the same as the state of the light receiving element 8' when the disk moves away. Furthermore, when the disk moves away, the state of the light receiving element 8 becomes the same as the state of the light receiving element 8' when the disk approaches.

In this way, (8α-8b)±(B'c-B'd
), it is possible to obtain a defocus signal. That is, it becomes 0 when in focus, becomes negative when the disc approaches, and becomes positive when the disc moves away.

Furthermore, the output characteristics of each of the light receiving elements 8 and 8' are as follows:
As shown in Figure 6, the error output becomes non-linear with respect to disc deviation, but by taking the complementary signals as described above, the error output becomes as shown in Figure 7. , an error output with extremely good linearity can be obtained for disk misalignment. Furthermore, it becomes possible to draw the focus over a wide range,
I am worried about the automatic lead-in circuit.

On the other hand, in the optical axis direction, a suitable cylindrical lens 9 is arranged, and the four-divided light receiving element 10 is arranged so that the output of each light receiving element becomes the same when focusing. As shown in Figure 5, the direction in which the beam becomes an ellipse differs depending on the disc displacement, so (10A+10(ri-(10B+10D))
As a result, an error output as shown in FIG. 8 is obtained.

Further, as shown in FIG. 1, the tracking deviation signal can be accurately obtained from (8α+s b )−(aC+ad). This is because the first-order diffracted light generated on the track does not pass through an optical element that rotates the image while reaching the light-receiving element 8.8', so it is deflected in the direction perpendicular to the track direction due to track deviation. This is because the light enters the light receiving element 8.8' with different intensities. Conventionally, the tracking deviation signal was obtained from (10A+10B)-(100+10D), but as mentioned above, mutual interference with the focus deviation signal occurs and pseudo signals are mixed in, so this is not suitable for high-precision tracking servo. Not suitable.

In addition, the RIF signal is the sum of the outputs of each light receiving element, that is, (8α
It can be obtained from +ah)+CB'c+s'd)+(10A+10En+(100+10D).

Therefore, the defocus detection by the two-split light receiving element 8,8' is set to a wide range, and the defocus detection by the four-divided light receiving element 10 is set to extremely high sensitivity, and the sum signal of both defocus signals is used as the defocus signal. If so, an error output as shown in FIG. 9 will be obtained. Therefore, it is possible to focus in a wide range and detect defocus with high precision. Therefore, a special circuit such as an automatic focus pull-in circuit is not required. Furthermore, since the track deviation signal is obtained from the output of the two-part light receiving lattice element 8, 8' which accurately captures the first-order diffracted light generated on the track, extremely high-precision tracking servo is possible.

Note that the beam splitter 7 used in the above embodiment is the 10th beam splitter 7.
As shown in the figure, the reflected light beam may be divided into five directions, one in each orthogonal direction and the other in the optical axis direction.

〔Effect of the invention〕

As described above, according to the present invention, defocus detection can be performed over an extremely wide range with extremely high accuracy, and since the tracking deviation signal can be accurately grasped, it is possible to detect defocus with extremely high precision. Tracking detection can be performed.

[Brief explanation of drawings]

Fig. 1 Diagram of the optical system according to the present invention Fig. 2 Diagram of the optical system in the conventional astigmatism method Fig. 5 Beam state diagram (α) disk on the 4-split light receiving element in the conventional astigmatism method (b) When the disk is far away. Figure 4. Beam state diagram when focused on the 4-split light receiving element in the conventional astigmatism method. Figure 5. Optical path diagram in the defocus detection method according to the present invention. Beam state diagram on the two-split photodetector (α) When in focus (b) When the disk approaches (C) When the disk is far away Figure 6: Defocus of the one-sided two-split photodetector according to the present invention
Figure 7 shows the relationship between the amount of defocus and the amount of error Figure 8 shows the relationship between the amount of defocus and the amount of error in the defocus detection method according to the present invention Defocus amount and error in the conventional astigmatism method Fig. 9 shows the relationship between the amount of defocus and the amount of error in the defocus detection method according to the present invention Fig. 10 shows the relationship between the directions perpendicular to each other and the optical axis direction according to the present invention Figure 1 shows a beam splitter that divides the beam into five axial directions...Semiconductor laser 2...Polarizing beam splitter 5...1/4 wavelength plate 4...Collimator Lens 5-1...Objective lens 6...Disc 7...Beam splitter 8.8'...Two-split light receiving element 9... Cylindrical lens 10...4 division light receiving element or more

Claims (1)

[Claims] In a device that optically detects information recorded on a disk, etc. without contact, or in a device that aims to optically record information on a disk, etc., at least a beam reflected from the disk is condensed. an objective lens, a lens that converges light passing through the objective lens, an optical axis direction between the objective lens and the lens, and a plane formed by the optical axis and the track in a plane perpendicular to the optical axis direction. A beam splitter that divides the beam into two light beams having equal amounts of light in directions opposite to each other or perpendicular to each other, and a cylindrical lens and a four-split light receiving element arranged in the optical axis direction, On each optical axis in the vertical plane,
At least two or more light-receiving elements having dividing lines parallel to the track direction are placed equidistantly apart from the imaging point, one on the side closer to the disk and the other on the side farther from the disk, and The signal is a first difference component obtained by subtracting the output of a light receiving element that does not include the optical axis from the output of one of the two-split light receiving elements that includes the optical axis, and the other of the two split light receiving elements. From the output of the photodetector that does not include the optical axis,
The tracking deviation signal is obtained from the sum signal of the second difference component obtained by subtracting the output of the light receiving element including the optical axis, and the difference signal of the two pairs of diagonal sums of the four-divided light receiving element, and An optical information reading device characterized in that information is obtained from a difference signal between both two-split light-receiving elements.