JPH02265038A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To detect a stable signal by making reflected light beam incident on an optical path separation means where a diffraction grating having equal pitch is formed on one side and a reflecting surface is formed on the other side, detecting zeroth order light and 1st order light and making the light incident on a three division photodetector. CONSTITUTION:When the reflected light beam 23 is made incident on the diffraction grating 27a having equal pitch of a one-side grating 26 through a detection lens 25, the incident light is separated in a crossing polarization direction to be the zeroth order light T and the 1st order light K. The light T advances in a substrate 27, is totally reflected by the reflecting surface 27b and returns to the grating 27a again to be projected to the outside. Meanwhile, the light K returns to the grating 27a and diffracted to be projected to the outside in the same way. Thereafter, the zeroth order light T which is transmitted light and the 1st order light K which is diffracted light are respectively received by the three division photodetectors 28 and 29. Since the grating 27a where the light passes for the first time and the grating 27a where the light passes for the second time are the same one, the directions of the gratings are completely coincident and the accuracy of the spot interval of the light T and the light K and the reproducibility of information are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical information recording and reproducing apparatus that detects a focus error signal and a track error signal using reflected light from an optical information recording medium.

BACKGROUND OF THE INVENTION The first conventional example of an optical information recording/reproducing apparatus is disclosed in Japanese Patent Application Laid-Open No. 1983-1999. There is one disclosed in Japanese Patent No.-230634. This will now be explained based on FIG.

The light emitted from the semiconductor laser 1 passes through the collimating lens 2
The parallel light is made into parallel light, and this parallel light is incident on the polarizing beam splitter grating 3, whereby the polarization direction of the incident beam 4 is such that its electric vector is parallel to the grooves of the polarizing beam splitter grating 3, so that the diffracted light is 5 becomes 1
The light enters the /4 wavelength plate grating 6, becomes a circularly polarized light beam, is focused by a lens 7, and is irradiated onto the surface of an optical disk 8 serving as an optical information recording medium. Further, the reflected light from the optical disk 8 is converted into a linearly polarized light wave by the quarter-wave plate grating 6, passes through the polarization beam splitter grating 3, becomes O-order diffraction light 9, and enters the critical angle diffraction grating 10. The incident light undergoes critical angle diffraction twice and total internal reflection, and the diffracted light 11
and is detected by the 4-split photodetector]2. As a result, the focus error signal is detected by the difference signal between the left and right light-receiving surfaces, and the l-rack error signal is detected by the difference signal between the light-receiving surfaces in the direction perpendicular to the page.

Further, as a second prior art example, there is a patent application filed by the present applicant in Japanese Patent Application No. 1518/1983. As shown in FIG. 9, the light emitted from the semiconductor laser 13 is collimated by the collimator lens 14, passed through the beam shaping prism 15, reflected by the beam splitter 16, and condensed by the mirror lens 17. The light is then irradiated onto the surface of the magneto-optical disk 18, thereby recording information. Further, the reflected light from the magneto-optical disk 18 passes through the beam splitter 16, is focused by the detection lens 19, and is guided to the dual grating 20. In this dual grating 20, gratings 20a and 20b having different diffraction efficiencies depending on the polarization direction are formed on both the front and back surfaces, and light is transmitted through these two gratings 20.
a and 20b, the light is separated into O-order light T and first-order light, and the O-order light T is guided to a four-divided light-receiving element 21, and the first-order light is guided to a two-divided light-receiving element 22, respectively.

Then, when detecting the magneto-optical signal, it is detected by the difference in light intensity between the O-order light T and the first-order light, the focus error signal is detected by the O-order light T using the astigmatism method, and the track error signal is detected by the O-order light T using the astigmatism method. It can be detected by secondary light K.

Problems to be Solved by the Invention First of all, in the case of the first conventional example, it can be applied when a CD or a write-once optical disk 8 is used as the optical information recording medium. There is no function to detect signals. Furthermore, in the case of this device, the problem that the diffraction angle fluctuates in response to wavelength fluctuations, which is a fundamental drawback of gratings themselves such as the polarizing beam splitter grating 3 and the quarter-wave plate grating 6, has not been solved. .

Therefore, as in the second conventional example, a dual grating 20 is used, which is compatible with not only the optical disk 8 but also the magneto-optical disk 18, and which has gratings 20a and 20b formed on the front and back surfaces of the substrate. In the case of the device thus constructed, it is possible to greatly suppress spot positional deviation by adjusting for wavelength fluctuations. However, when two gratings 20a and 20b are used as in this device, the two gratings 20a and 2ob are
If it is very difficult to align the lattice directions, and if the lattice directions do not match and shift, the accuracy of the spot spacing between the 0th-order light T and the 1st-order light will deteriorate, and this will cause problems in the fabrication process. There is a drawback that the variation in signal detection sensitivity for each dual grating 20 increases.

Means for Solving the Problem Therefore, in order to solve such problems, claim 1
The described invention records information by irradiating light emitted from a laser light source onto an optical information recording medium, and guides reflected light from the optical information recording medium to a signal detection optical system to detect track error signals and focus. In an optical information recording and reproducing device that detects an error signal and furthermore a reproduced signal, a diffraction grating with an equal pitch is formed on one side of the substrate on the optical path of the signal detection optical system via a detection lens, and on the other side. An optical path separation means formed with a reflective surface was provided, and at least two three-split light receiving elements were provided for respectively detecting the zero-order light and the first-order light separated by the optical path separation means.

Further, the invention according to claim 2 records information by irradiating light emitted from a laser light source onto an optical information recording medium, and guides reflected light from the optical information recording medium to a signal detection optical system. Track error signal, focus error signal,
Furthermore, in an optical information recording and reproducing apparatus that detects a reproduced signal, a diffraction grating having a modulation pitch or curvature is formed on one surface of the substrate via a detection lens on the optical path of the signal detection optical system; An optical path separating means having a reflective surface formed thereon was provided, and at least two three-split light receiving elements were provided for respectively detecting the o-blown light and the primary light separated by the optical path separating means.

According to the invention as claimed in claim 1, the reflected light from the optical information recording medium passes through the equal-pitch diffraction grating of the optical path separation means through the detection lens, thereby splitting the reflected light into two types: 0th-order light and 1st-order light. The light is separated into light, reflected by a reflective surface, passed through a diffraction grating, and emitted to the outside. The light is guided to a light receiving element divided into three parts, thereby detecting a magneto-optical signal, a focus error signal, and a track error signal. be able to.

According to the invention set forth in claim 2, the reflected light from the optical information recording medium passes through the diffraction grating having the modulation pitch or curvature of the optical path separation means through the detection lens, so that the reflected light is reduced to zero.
The 0th order light and the 1st order light are separated into two lights, the 0th order light and the 1st order light, are reflected by the reflective surface, pass through the diffraction grating, and are emitted to the outside, causing astigmatism between the 0th order light and the 1st order light. By guiding each of the astigmatized lights to three divided light receiving elements, it is possible to detect a magneto-optical signal, a focus error signal, and a track error signal with higher detection sensitivity.

Example First, an example of the invention described in the claims is shown in FIGS. 1 and 2.
This will be explained based on FIGS. (a), (b), and (c). Note that the description of the overall configuration of the optical information recording/reproducing apparatus will be omitted here, and only the signal detection optical system according to the present invention will be described.

A single-sided grating 26 as an optical path separation means is disposed on an optical path on which reflected light 23 from a magneto-optical disk (not shown) as an optical information recording medium is guided into a signal detection optical system 24 via a detection lens 25. has been done. In this single-sided grating 26, linear diffraction gratings 27a with equal pitches are formed on the front side of a substrate 27, and a reflective surface 27b is formed on the back side. The diffraction grating 27a is
The diffraction efficiency changes depending on the polarization direction of the light incident on it. Further, the single-sided grating 26
Two 3-part light receiving elements 28 and 29 are arranged in the same plane on an optical path perpendicular to the optical path of the light incident thereon.

In this case, the three-divided light receiving element 28 has light receiving surfaces a, b, and c, and one of the three divided light receiving elements 29 has light receiving surfaces d, e, and f, and the direction of the dividing line of these light receiving surfaces is It is divided in a direction perpendicular to the grating direction of the diffraction grating 27a.

In such a configuration, reflected light 23 having a certain polarization direction from the magneto-optical disk passes through the detection lens 25, and
Diffraction grating 27 with equal pitch of single-sided grating 26
When the incident light enters a, the incident light is separated into orthogonal polarization direction components, and is separated into two lights, a zero-order light T and a first-order light. Then, the separated O-order light T travels through the substrate 27 according to Snell's law, is totally reflected by the reflecting surface 27b, returns to the diffraction grating 27a again, transmits therethrough, and is emitted to the outside. On the other hand, the separated first-order light is diffracted by the diffraction angle by the diffraction grating 27a and is reflected by the substrate 27.
After proceeding inside and being reflected by the reflective surface 27b, again,
The light returns to the diffraction grating 27a and is diffracted and emitted to the outside.

Thereafter, the O-order light T, which is the transmitted light, and the first-order light, which is the diffracted light, are received by the three-split light receiving elements 28 and 29, respectively. In this case, the convergence point of the primary light is located in front of the convergence point of the O-order light T, and the two three-part light receiving elements 28.
29 is located between these focal points.

Figures 2 (a), (b), and (C) show the principle of detecting the focus error signal, which is detected based on the difference in light intensity between the two light-receiving surfaces on both sides and the central light-receiving surface. This shows the areal density method. Figure 2(b) shows when the magneto-optical disk is at the focused point, and the second
Figures (a) and (C) show cases where the focus is shifted forward or backward.

At this time, the focus error signal Fo is Fo-(a+c
-b) -(d+fe)-(1) can be detected.

Furthermore, the magneto-optical signal MO can be detected using the difference in light intensity between the two three-part light receiving elements as follows: Mo=(a+c)-(d+e+f)-(2), and the track error signal Tr is , using the light-receiving surfaces at both ends, it can be detected as follows: Tr=(a+d)(c+f)-(3).

As described above, by passing through the diffraction grating 27a twice, the light incident on the single-sided grating 26 can obtain the primary light K, similar to the conventional dual grating 20 (see FIG. 9). As a result, it is possible to significantly reduce the spot position shift on the light-receiving surface 2 due to wavelength fluctuations as in the prior art. In addition, as in this embodiment, since the diffraction grating 27a that passes through the first time and the diffraction grating 27a that passes through the second time are the same, their grating directions also match completely. The accuracy and reproducibility of the spot spacing between the secondary light T and the primary light can be extremely improved, and the troublesome adjustment of the grating direction of the dual grating 2o, which is conventional, is also eliminated. Furthermore, by forming the dividing lines of the three-part light receiving elements 28 and 29 in a direction perpendicular to the grating direction of the diffraction grating 27a, the spot shift due to the varying wavelength of the laser light source or the optical axis shift due to the galvanometer mirror can be avoided in the same direction. Since this is the same as the direction of the dividing line, offset and sensitivity reduction due to spot deviation can be further suppressed compared to the conventional method.

Next, an embodiment of the invention according to claim 2 will be described based on FIGS. 3 to 5(a), (b), and (c).

This describes a case where the configuration of the optical path separation means is changed.

In the embodiment of the invention described in claim 1, a circular spot is used to detect the focus error signal by the areal density method, and the diameter of the circular spot increases or decreases depending on the displacement of the magneto-optical disk. However, with this detection method, it is impossible to perform highly sensitive detection compared to other astigmatism methods or Naifetsu methods of detecting focus error signals. .

Therefore, in this embodiment, in order to detect a focus error signal with higher sensitivity, the configuration of the optical path separation means is as follows. That is, in the single-sided grating 30 as an optical path separation means, a diffraction grating 31a having a curvature having a modulation pitch as shown in FIG. 4 is formed on the front side of a substrate 31, and a reflective surface 31b is formed on the back side. It is formed. [Diffraction path] 4 The diffraction efficiency of the element 31a changes depending on the polarization direction of the incident light. In this case, the thickness of the substrate 31 is made thicker than in the above-described embodiment (see FIG. 1). Note that there is no change in other configurations.

In such a configuration, by forming the substrate 31 thicker, it is possible to generate a large astigmatism difference, so that astigmatism can be generated in the O-order light T, and, Since the diffraction grating 31a has a shape having a curvature of the modulation pitch, astigmatism is produced in the primary light due to the detection lens 25 and the diffraction grating 31a having a lens function. As a result, the O-order light T and the first-order light are guided to the three-split light receiving elements 28 and 29, respectively, with astigmatism occurring.

FIGS. 5(a), 5(b), and 5(c) show the principle of detection of the focus error signal in this embodiment.

In this case, as shown in FIG. 5(b), when the magneto-optical disk is at the focused point, both the O-order light T and the first-order light are circular spots, but they are out of focus and the front focus is In this state, as shown in FIG. 5(a), the spot shape of the O-order light T becomes a horizontally long ellipse, and the spot shape of the first-order light becomes a vertically long ellipse. Furthermore, when the focus shifts to the rear focus state, as shown in FIG. 5(C), the spot shape of the ○th order light T becomes vertically elongated, and the spot shape of the first order light becomes horizontally elongated.

By causing astigmatism in the O-order light T and the first-order light in this way, the spot shape becomes a vertically long or horizontally long ellipse when it deviates from its focal position, and the embodiment according to claim 1 described above Compared to deforming the circular spot as shown in the figure, it is possible to obtain a larger difference in the amount of light received, so the signal detection sensitivity can be further increased.

In this embodiment, the diffraction grating 31a of the single-sided grating 30 serving as the optical path separation means has a modulation pitch and a curvature. effect can be obtained.

In addition, as shown in FIGS. 6 and 7 (a), (b), and (c), one of the three-split light receiving elements 29 is arranged in a rotated state by 90', thereby generating spot shapes in the same direction. Although it is possible to obtain the same effect as the above-mentioned embodiment in this case, since astigmatism is also used in this case, care must be taken to ensure that the influence of spot deviation is small. There is a need.

Effects of the Invention The invention described in claim 1 produces zero-order light by making reflected light from an optical information recording medium incident on an optical path separation means in which a diffraction grating with an equal pitch is formed on one side and a reflecting surface is formed on the other side. It is possible to detect signals such as focus error signals by generating and primary light and making these lights incident on the 3-split light receiving element.This makes it possible to detect signals such as focus error signals by simply forming a diffraction grating on one side. This eliminates the trouble of creating diffraction gratings on both the front and back surfaces and matching the grating directions during manufacturing, and since a three-part light receiving element is used as the light receiving element, there is no misalignment of the light spot. Since it has a large tolerance, it is possible to perform stable signal detection even with respect to assembly, changes over time, and wavelength fluctuations.

In addition, the invention as claimed in claim 2 is characterized in that the diffraction grating formed in the optical path separating means has a shape having a modulation pitch or a curvature, so that the spot shape received by the three-split light receiving element has astigmatism. The light can be irradiated in an elliptical shape, and as a result, the difference in the amount of light received between the in-focus state and the out-of-focus state can be increased, so that the detection sensitivity is further improved compared to the invention described in the claim. It is something that can be done.

[Brief explanation of drawings]

FIG. 1 is an optical path diagram of a signal detection optical system showing an embodiment of the invention as claimed in claim 1, and FIGS. 2(a), (b), and (c) are three-part light reception showing the principle of detecting the focus error signal. 3 is a front view of the element, FIG. 3 is an optical path diagram of a signal detection optical system showing an embodiment of the invention as claimed in claim 2, FIG. 4 is a front view showing the shape of its diffraction grating, and FIG. b) (c) is a front view of the 3-split light receiving element showing the principle of detecting the focus error signal in Fig. 3, and Fig. 6 is a front view of the 3-split light receiving element shown in Fig. 3 when the arrangement of one of the 3-split light receiving elements is changed by 90'. 7(a), 7(b), and 7(c) are front views of the three-part light receiving element showing the principle of detecting the focus error signal, and FIG. 8 is the first conventional method. FIG. 9 is a block diagram showing a second conventional example. 1.13...Laser light source, 8. ] 8... Optical information recording medium, 23... Reflected light, 24... Signal detection optical system, 2 detection lens, 26... Optical path separation means, 27 - Group 27a
...Diffraction grating, 27b...Reflection surface, 28°9...
3-split light receiving element, 30... Optical path separation means, 3... Substrate, 31a... Diffraction grating, 31b... Reflective surface, 0th order light, K... 1st order light Applicant Rico Co., Ltd. Pity: Go■＋

Claims (1)

[Claims] 1. Information is recorded by irradiating light emitted from a laser light source onto an optical information recording medium, and the reflected light from the optical information recording medium is guided to a signal detection optical system to detect track errors. In an optical information recording and reproducing device that detects a signal, a focus error signal, and furthermore a reproduction signal, a diffraction grating with an equal pitch is formed on one surface of a substrate on the optical path of the signal detection optical system via a detection lens. An optical path separation means having a reflective surface formed on the other surface is provided, and at least two three-split light receiving elements are provided for respectively detecting the zero-order light and the first-order light separated by the optical path separation means. Optical information recording and reproducing device. 2. The light emitted from the laser light source is irradiated onto the optical information recording medium to record information, and the reflected light from the optical information recording medium is guided to the signal detection optical system to detect track error signals, focus error signals, Furthermore, in an optical information recording and reproducing apparatus that detects a reproduced signal, a diffraction grating having a modulation pitch or curvature is formed on one surface of the substrate via a detection lens on the optical path of the signal detection optical system; Optical information characterized in that an optical path separating means having a reflective surface is provided on the optical path separating means, and at least two three-split light receiving elements are provided for respectively detecting the zero-order light and the first-order light separated by the optical path separating means. Recording and playback device.