JPS6142743A - Optical information reader - Google Patents

Abstract

PURPOSE:To perform defocusing detection with high precision over a wide range by performing focusing operation based upon a defocusing signal from a two- division photodetecting element over a wide range through a specific optical system and obtaining an RF signal, and then switching said signal to a defocusing signal from a four-division photodetecting element and performing high-precision focus servocontrol. 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 travels backward and passes through the PBS2 and is split through a beam splitter 7 in directions crossing an optical axis at right angles to enter two-division photodetecting elements 8 and 8' which are provided at image non-formation points B and B' at equal distance from conjugate points A and A' of the laser 1 and have division lines parallel to a track direction and the four-division photodetecting elements 10 through a cylindrical lens 9 on the optical axis. Wide-range defocusing is detected from defocusing signals of the photodetecting elements 8 and 8' and high-precision focus servocontrol is performed with the defocusng signal of the photodetecting element 10.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention provides an optical information reading device for reading out information recorded on a VD, CD, etc. using a light beam, or for reading information onto a disk, etc. using a light beam. This invention relates to an optical information writing/passing device.

(Prior Art) Conventionally, optical information reading devices have been known that use an astigmatism method to detect defocus and a pull-pull method to detect tracking deviation.

A diagram of an optical information reading device using the above method is f4
Shown in Figure 2.

The beam emitted from the semiconductor laser 1 is reflected by the polarizing beam splitter 2 toward the disk direction button 100,
The parallel light passes through the 174 wavelength plate 3, is collimated by the collimator lens 4, and is converged onto the disk 6 via the objective lens 5. This light beam is reflected by the information tray 9, which has an uneven pit shape, and is transmitted through the objective lens 5, collimator lens 4, 1/4 wavelength plate 3, and polarizing beam splitter 2 in a direction perpendicular to the incident light beam. , enters the cylindrical lens 9 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, Figure 3 (α
), the beam becomes an ellipse, and as the disk moves away, it becomes an ellipse in a different direction as shown in Figure 3 (6). For this reason, ioA+100)-(10B+1
07)), and a tracking deviation signal was obtained from the change in the direction of the first-order diffracted light due to the grooves and grooves carved on the disk. The above-mentioned tracking deviation signal is rotated by about 90° on the diraktor due to the action of the cylindrical lens 9, so that (10A+10B)
)-(10G++ 10D).

[Problem that the invention seeks to solve]

However, in the conventional astigmatism method and pushinable method, the beam shape on the 4-split light receiving element at the time of one focus, the aberration of the collimator lens 4 and the cylindrical lens 9, etc. prevent it from being a perfect circle, and the beam becomes spindle-shaped. Since a trap light receiving element is placed between both focal lines, the disk image is not rotated exactly 90 degrees. For this reason, the direction change of the first-order diffracted light when the first focus is
The dark line in the tracking servo direction of the 4-split light-receiving element did not appear exactly at the boundary, but had a slight inclination. Therefore, a false signal was mixed into the tracking error i signal, and the track could not be accurately traced. Furthermore, since the defocus signal and the tracking deviation signal are obtained from the same 4-split photodetector, they affect each other's signals, making it difficult to obtain a stable and accurate error signal. . In addition, since the astigmatism method has a relatively narrow error detection range, it requires a focus pull-in circuit. Completely separate the
The purpose is to obtain a highly accurate and stable error signal without causing mutual interference, and to obtain a sensual reading device that does not require a complicated circuit such as a focus drawing circuit.

[Means for solving problems]

In order to solve the above problems, the present invention provides a lens that converges the reflected light from the disk, an optical axis direction between the objective lens and the above lens, and an optical axis 1 in a plane perpendicular to the optical axis direction. A cylindrical lens and a 4-split light receiving element are arranged in the optical axis direction, and a beam splitter 9 divides the beam into two light beams with a large amount of light in directions opposite to each other or perpendicular to each other using the plane formed by the and the track as a boundary. On each optical axis in a plane perpendicular to the optical axis direction, at least two or more divided light receiving elements each having a dividing line in a direction parallel to the track direction are placed equidistantly apart from the imaging point, and one One is for sensing close to the disk, and the other is for sensing far from the disk, and the defocus signal is transferred from the output of one of the two-split photodetectors that includes the optical axis to the output of the photodetector that does not include the optical axis. From the sum signal of the first difference component subtracted, the output of the light receiving element including the optical axis from the output of the other of the two-split light receiving elements, which does not include the optical axis, and the second difference component. After obtaining the RF flaw signal, a tracking error signal is obtained from the difference signal of the diagonal sum of the two pairs of light-receiving elements divided into four parts, and a tracking deviation signal is obtained by calculating the difference component Q between the two light-receiving elements divided into two parts. In this way, the mutual interference between the defocus signal and the tracking deviation signal is eliminated, and highly accurate and stable error signals of both are obtained.

[Operation] When arranged as described above and obtaining an error signal, the defocus signal obtained from the two-split light receiving element is used to pull in a wide range of focus, and after obtaining the RF multiplied signal, the 4-split light receiving element rejects the focus. High-precision focus servo is performed by switching to the focus deviation signal, and tracking servo is performed using the tokutomo tracking and knocking deviation signals from both of the above-mentioned two-split light receiving elements, so both error signals can be obtained from separate light receiving elements. Gadebero.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, the light emitted from the semiconductor laser 1,
The light is collimated by a collimator lens 4 through a polarizing beam splitter 2 and a 1A wavelength plate 3, and is irradiated onto a disk 6 via an objective lens 5. ``The light reflected by the disk 6 passes through the objective lens 5 and the collimator lens 4, and is divided into the incident light beam and the plane orthogonal to f'i by the action of the 1A wavelength plate 3 and the polarizing beam splitter 20, and is then sent to the beam splitter. At this time, due to the action of the beam splitter 7, the reflected light beam that has passed through one half of the plane bounded by the plane formed by the optical axis and the track direction, and the reflected light beam that has passed through the other half of the plane, are separated and are directed in opposite directions. The direction is perpendicular to the optical axis direction, and the direction perpendicular to the optical axis direction is divided into three directions. ', equidistant apart from each other, and one side is
A two-split light-receiving element 8' having a dividing line parallel to the rear direction, one at a non-imaging point B' near the beam splitter 7, and the other at a non-imaging point B' farther from the beam sub+1,
A two-split light-receiving element 8' is arranged so that each half-luminous flux is incident on the light-receiving element 8, and the output of each light-receiving element is the same at the time of focusing.

Adjust 8.

The tas diagram shows the beam split into left and right beams by the beam splitter 7 out of one reflected beam on the same optical axis, and shows an optical path diagram with the quarter-wave plate 5, polarizing beam splitter 21, and beam splitter 7 omitted, and each light receiving beam. FIG. 9 shows the state of the beam on the element 8°8'. (B)) Figure shows the state in focus, ω) Figure shows the state in which the disc 6 is approaching, and 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 divided by the beam splitter 7 as shown in FIG.
Since the light is reflected on the left and right sides, they do not affect each other.

At the time of focusing, as shown in the figure (2)), each light receiving element α
.

The outputs of b, c, and d are all the same. 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, a defocus signal can be obtained from (8cL-ah)+(8'c-8'd). In other words, when in focus, the value becomes 0,
It becomes negative when the disc approaches, and becomes positive when the disc moves away. In addition, the output characteristics of each of the light-receiving elements 8 and 8' are as shown in FIG. 6, and the error output is non-linear with respect to the amount of disc deviation. By taking the following method, the error output becomes the 7th
As shown in the figure, an error output with extremely good linearity can be obtained with respect to the amount of disk deviation. ζ et al., it becomes possible to pull in a focus over a wide range, and an automatic pull-in circuit becomes unnecessary.

Next, in the optical axis direction, a suitable cylindrical lens 9 is arranged, and the four-divided light receiving element 1o is adjusted so that the output of each light receiving element is the same during focusing, as shown in Fig. 3. , the direction in which the beam becomes elliptical differs depending on the disc displacement, so (10A+1oe)-NoBs1oD)
As a result, an error output as shown in FIG. 8 is obtained.

Bate, tiger, -? As shown in Figure 1, the tracking deviation signal can be obtained accurately from (8a+8b)-(8c+8dl).This is because the first-order diffracted light generated by the track 9 is caused by the deviation perpendicular to the track direction due to the track deviation. This is because the tracking deviation signal is incident on the light receiving elements 8 and 8' with different intensities because it is deflected in the direction
A+10B'1-(10C+1Or)), but as mentioned above, mutual interference with the defocus signal occurs, and
It is not suitable for high-precision tracking servo because the return signal is mixed in.
That is, (8a+8b)+(8'c+8'd)+(10A+
It can be obtained from 10B) + (10c! + 10D).

Therefore, the defocus detection by the two-divided light receiving element 868' is set to a wide range, and the defocus detection by the four-divided light receiving element 10 is set to extremely high accuracy. Switching to the latter, high-precision focus shift detection is performed, and tracking shift detection is performed using the two-split light-receiving element 8.8'. In this way, defocus detection can be performed over a very wide range and with high precision.Furthermore, tracking deviation detection can be obtained from a completely different light receiving element.

Mutual interference with the defocus signal is eliminated, and false signals are no longer mixed. In general, an automatic focus retraction circuit is no longer required, and only a simple switching circuit for switching bullet point detection is required. Alternatively, the reflected light beam may be divided into five directions, one in each direction perpendicular to the other and in the optical axis direction.

〔Effect of the invention〕

As stated above, according to the present invention, defocus detection can be performed over an extremely wide range and with extremely high accuracy.In addition, since there is no mutual interference between tracking deviation signals and defocus signals, extremely high accuracy can be achieved. It is possible to perform 9-king deviation detection,

[Brief explanation of the drawing]

Figure 1: Diagram of the optical system according to the present invention Figure 2: Diagram of the optical system in the conventional astigmatism method Figure 5: Beam on the 4-split light receiving element in the conventional astigmatism method State diagram (b)) When the disc approaches (b) When the disc moves away Figure 4: Beam state diagram when focused on the 4-split light receiving element in the conventional astigmatism method Figure 5: Book Optical path diagram and beam state diagram on the two-split light-receiving element in the out-of-focus detection method according to the invention 6) When the disk approaches (at the time of focusing) (c) When the disk moves away Figure 6: According to the invention Figure 7 is a diagram showing the relationship between the amount of defocus and the amount of error for a two-split light receiving element on one side; Figure 8 is a diagram showing the relationship between the amount of defocus and the amount of error in the defocus detection method according to the present invention.・Figure f49 showing the relationship between the amount of defocus and the amount of error using the conventional astigmatism method Tlc:I. 1...Semiconductor laser 2...Polarizing beam splitter 3...1A wave plate 4...Collimator lens 5... ...Objective lens 6...Disc 7...Beam splitter 8.8'...Two-split light receiving element? ......Cylindrical lens 10...Four-division light receiving element Above 1st
Figure/Travel direction 4- + racking servo direction Figure 7 Figure 9

Claims (1)

[Claims] In a device that optically detects information recorded on a disk or the like in a non-contact manner, or in a device that aims to optically record information on a disk or the like, an objective lens that focuses at least a reflected light beam from the disk. and a lens that converges the light passing through the objective lens, the optical axis direction of the objective lens and the objective lens, and a plane formed by the optical axis and the track in a plane perpendicular to the optical axis direction as the boundary. A beam splitter that splits the beam into two light beams having equal amounts of light in directions opposite to each other or orthogonal to each other, and a cylindrical lens and a four-split light receiving element arranged in the optical axis direction, each in a plane perpendicular to the optical axis direction. On the optical axis, a light receiving element divided into at least two parts, each having a dividing line in a direction parallel to the track direction, is spaced equidistantly from the image forming point, one on the side closer to the disk and the other on the side farther from the disk. and a first difference component obtained by subtracting the output of the light receiving element not including the optical axis from the output of the optical element including the optical axis of one of the two split light receiving elements, and the two split light receiving elements. A sum signal is obtained by subtracting the output of the light receiving element including the optical axis from the output of the other light receiving element not including the optical axis, and an RF signal is obtained. An optical information reading device characterized in that a tracking deviation signal is obtained from a difference signal between two pairs of diagonal sums, and a tracking deviation signal is obtained from a difference signal between the two split light receiving elements.