JPH02265037A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To make the difference of optical path small and to prevent diffraction efficiency from lowering by allowing reflected light beam from an optical information recording medium to pass through a substrate which is provided with diffraction gratings having equal pitch on both surface and back face and has higher refractive index than that of the diffraction grating. CONSTITUTION:Reflected light beam 23 is made incident on the diffraction grating 27a on the surface side of a dual grating 26 through a detection lens 25 and separated to two light beams, zeroth order light T and 1st order light K, which pass the substrate 27 to be emitted to the outside by the diffraction grating 27b on the back face side. Since the refractive index of the substrate 27 is set to be larger than that of the gratings 27a and 27b, the zeroth order light T and the 1st order light K trace an optical path shown by a continuous line and the difference of optical path between the light T and the light K is made small. In the case of arranging a photodetector 28 which respectively detects the light T and the light K on the same surface, the photodetector of large area need not be arranged on a 1st order light side.

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.

2. Description of the Related Art A first conventional example of an optical information recording/reproducing apparatus is disclosed in Japanese Patent Application Laid-Open No. 61-230634. This will now be explained based on FIG. The light emitted from the semiconductor laser 1 is collimated by the collimating lens 2, and this collimated light is incident on the polarizing beam splitter grating 3, whereby the polarization direction of the incident beam 4 is changed so that its electric vector is the same as that of the polarizing beam splitter grating 3. Because it is parallel to the groove, the diffracted light becomes 5]/
The light enters a four-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 1/4 wavelength plate grating 6, transmitted through the polarization beam splitter grating 3, and the O-order diffracted light 9
critical angle diffraction grating ]O. The incident light undergoes critical angle diffraction twice and total reflection, becomes diffracted light 11, and is detected by a four-split photodetector 12. This results in
The focus error signal is detected by the difference signal between the left and right light receiving surfaces, and the track error signal is detected by the difference signal from the light receiving surface 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. 5(a), the light emitted from the semiconductor laser 13 is collimated by the collimating lens 14, passed through the beam shaping prism 15, and reflected by the beam splitter 16. The light is focused and irradiated onto the surface of the magneto-optical disk 18, thereby recording information. Further, the reflected light from the magneto-optical disk 18 is
It passes through the beam splitter 16 and passes through the detection lens 19.
The light is focused and 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 20a.

By passing through 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-split light receiving element 21, and the first-order light is guided to a two-split 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 θ-order light T using the astigmatism method, and the track error signal is detected by the θ-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.

Further, in the case of the second conventional example, it is possible to correspond to the magneto-optical disk 18, but in this case, however, a dual grating 20 is used in which gratings 20a and 20b are formed on the front and back surfaces of the substrate. Therefore, when light passes through this, an optical path difference occurs between the 0th order light T and the 1st order light, and in particular, this optical path difference increases as the thickness of the substrate increases. Therefore, when two spots are detected on the same surface, the light spot of the primary light becomes larger, and a light-receiving element with a correspondingly larger area is required. Therefore, if the thickness of the substrate itself is made thinner, the optical path difference can be reduced and the spot for the primary light will not become large, but the occurrence of aberration will be reduced for the 0th order light T, and as a result, The astigmatism method makes it very difficult to obtain detection of the focus error signal.

Means for Solving the Problems The invention according to claim 1 records information by irradiating light emitted from a laser light source onto an optical information recording medium, and detects a signal from reflected light from the optical information recording medium. In an optical information recording and reproducing apparatus that detects a track error signal, a focus error signal, and a reproduction signal by guiding the light to an optical system, the reflected light from the optical information recording medium is guided to the signal detection optical system on the optical path. A dual grating is provided through a detection lens, in which diffraction gratings are formed at equal pitches on both the front and back surfaces of the substrate, and the refractive index of the substrate is higher than that of the diffraction grating, and the light passing through this dual grating is detected. A photodetector was installed.

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 to detect tracking errors. In an optical information recording and reproducing device that detects a signal, a focus error signal, and furthermore a reproduced signal, reflected light from the optical information recording medium is passed through a detection lens onto an optical path guided to the signal detection optical system. A dual grating in which a diffraction grating with an equal pitch was formed on one side of the substrate and a diffraction grating with a modulation pitch on the other side was provided, and a photodetector was provided to detect the light that passed through this dual grating.

The invention according to claim 3 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 errors. In an optical information recording and reproducing device that detects a signal, a focus error signal, and furthermore a reproduced signal, reflected light from the optical information recording medium is passed through a detection lens onto an optical path guided to the signal detection optical system. , a dual grating is provided in which a diffraction grating with an equal pitch is formed on one side of the substrate and a diffraction grating with a modulated pitch is formed on the other side, the refractive index of the substrate is higher than the refractive index of the diffraction grating, and the light beam passes through the dual grating. A photodetector was installed to detect the emitted light.

The invention described in [Operation Claim] allows the reflected light from an optical information recording medium to pass through a substrate having a diffraction grating with an equal pitch on both the front and back surfaces and having a refractive index higher than that of the diffraction grating. It is possible to reduce the optical path difference between the 0th-order light and the 1st-order light of the light that has passed through the substrate, thereby preventing a decrease in diffraction efficiency.

The invention according to claim 2 allows the reflected light from the optical information recording medium to pass through the diffraction gratings of equal pitch and modulation pitch formed on both the front and back surfaces of the substrate, so that 0 The optical path difference between the secondary light and the primary light can be reduced.

The invention according to claim 3 allows the reflected light from the optical information recording medium to pass through a diffraction grating having a modulation pitch, and also to pass through a substrate having a refractive index higher than the refractive index of the diffracted light. It is possible to more easily correct the optical path difference between the primary light and the primary light.

Embodiment An embodiment of the invention set forth in claim 1 will be described based on FIG. Here, a description of the overall configuration of the optical information recording/reproducing apparatus will be omitted, and only the =9 =10 signal detection optical system according to the present invention will be described.

A detection lens 25 is disposed on the optical path on which reflected light 23 from a magneto-optical disk (not shown) as an optical information recording medium is guided to an optical information detection optical system 24. A dual grating 26 is arranged on the optical path. In this dual grating 26, linear diffraction gratings 27a and 27b with equal pitches are formed on both the front and back surfaces of a substrate 27, and the refractive index of the substrate 27 is higher than that of the diffraction gratings 27a and 27b. It becomes. Furthermore, a photodetector 28 is disposed on the optical path of the light that has passed through the dual grating 26. This photodetector 28 can be constructed by combining a two-segment light receiving element 22 and a four-segment light receiving element 21, for example, as in the second conventional example described above (see FIG. 5(b)). .

Note that glass or polycarbonate can be used as the material for the substrate 27, and 2P resin can be used as the material for the diffraction grating.

In the second configuration, the role of the dual grating 26 according to the present invention will be explained.

The reflected light 23 from the magneto-optical disk enters the diffraction grating 27a on the front surface side of the dual grating 26 via the detection lens 25, and is separated into two lights, the O-order light T and the first-order light. 27 and the diffraction grating 27 on the back side.
b is emitted to the outside.

At this time, the refractive index of the substrate 27 and the diffraction grating 27a.

If the refractive index of 27b is the same, the O-order light T and the first-order light will follow the optical path shown by the broken line, and as a result, the optical path difference between the O-order light T and the first-order light will be large. Become. but,
As in the present invention, the refractive index of the substrate 27 is adjusted by using the diffraction grating 27 a
By setting the refractive index to be larger than the refractive index of , 27b, the O-order light T and the first-order light will follow the optical path shown by the solid line, and this will cause the O-order light T and the first-order light to The optical path difference between them can be made small. In this way, O order light T
By reducing the optical path difference between and the primary light, O
When arranging the light-receiving elements (here, the photodetector 28) that detect the secondary light T and the primary light respectively on the same surface, a large-area light-receiving element is placed on the primary light side as in the conventional method. There is no need to place it.

Note that the method of detecting the signal by the photodetector 28 is as in the second conventional example (see FIG. 5(b)), in which the zero-order light T is guided to the four-split light-receiving element 21 and the focus error is detected by the astigmatism method. The signal is detected, the first-order light K is guided to the two-split light receiving element 22, and a track error signal is detected, and a magneto-optical signal can be detected based on the difference in the amount of light between the O-order light T and the one-dimensional light.

Next, an embodiment of the invention according to claim 2 is shown in FIGS. 2 and 3.
This will be explained based on FIGS. (a) and (b). This example describes a case where the configuration of the dual grating is changed.

In the dual grating 29, a linear diffraction grating 30a with an equal pitch is formed on the front side of a substrate 30, and a diffraction grating 30b having a curvature of a modulation pitch is formed on the back side. Here, an attempt is made to correct the optical path difference generated between the zero-order light T and the one-dimensional light by the concave lens action of the diffraction gratings 30a and 30b.

In other words, since the first-order light has a longer optical path and is focused on the front side than the O-order light T, the photodetector 28 is placed on the optimal surface for detecting the focus error signal with the O-order light T. Even if the primary light is placed, there is a focal point P on the front side as shown by the broken line.
As a result, the light is in a diverging state on the surface of the photodetector 28. Therefore, as in this embodiment, by forming the diffraction grating 30b on the back surface with a modulation pitch, the concave lens effect due to the modulation pitch can be
It becomes possible to extend the focal length of the primary light K converging on the front side as shown by the solid line and form an image on the surface of the photodetector 28. In this way, the optical path difference generated between the O-order light T and the first-order light can be corrected by the concave lens effect due to the modulation pitch of the diffraction grating 30b.

Note that the focal length of the concave lens action can be changed by changing the degree of modulation of the pitch of the diffraction grating 30b, so the optimum modulation pitch is formed by taking into consideration the optical path difference that occurs and the focal length of the detection lens. Just do it like this.

Next, an embodiment of the invention according to claim 3 will be described. This describes an example in which the embodiment of the invention as claimed in claim 1 and the embodiment of the invention as claimed in claim 2 are combined.

That is, in a dual grating (not shown), a linear diffraction grating with an equal pitch is formed on the front surface of a substrate, and a diffraction grating with a curvature of a modulation pitch is formed on the back surface, and the refractive index of the substrate is as described above. The refractive index is set higher than the refractive index of the diffraction grating. In this way, by simultaneously having two functions for correcting the optical path difference between the O-order light T and the first-order light, the extent to which the optical path difference is corrected by the modulation pitch is reduced, and the diffraction efficiency is increased accordingly. In addition, the degree of freedom in design is increased, making it possible to realize an optimal configuration.

Effects of the Invention In the invention described in claim 1, reflected light from an optical information recording medium is passed through a substrate having a diffraction grating with an equal pitch on both the front and back surfaces and having a refractive index higher than that of the diffraction grating. Therefore, it is possible to reduce the optical path difference between the 0th-order light and the 1st-order light of the light that has passed through the substrate, which prevents a decrease in diffraction efficiency, and also reduces the difference in optical path compared to the conventional method. This also eliminates the need for a light-receiving element with a large area.

The invention as claimed in claim 2 allows the reflected light from the optical information recording medium to pass through the diffraction gratings with equal pitch and modulation pitch formed on both the front and back surfaces of the substrate, so that the concave lens effect due to the diffraction grating with the modulation pitch is achieved. This makes it possible to reduce the optical path difference between the 0th-order light and the 1st-order light, thereby achieving the same effect as the invention described in claim 1, and by modulating the pitch, it is possible to reduce the optical path difference between the 0th-order light and the 1st-order light. Since it is possible to deal with this, the degree of freedom in design can be increased.

The invention as claimed in claim 3 allows the reflected light from the optical information recording medium to pass through a diffraction grating having a modulation pitch and also to pass through a substrate having a refractive index higher than the refractive index of the diffracted light. Effect of the invention described in claim 1 and claim 2
The effects of the described invention can be obtained at the same time, and a device with a more optimal configuration can be obtained.

[Brief explanation of drawings]

FIG. 1 is an optical path diagram of an optical information detection optical system showing an embodiment of the invention as claimed in claim 1, and FIG. 2 is an optical path diagram of a signal detection optical system showing an embodiment of the invention as claimed in claim 2. Figure 3 is a perspective view showing the shape of the diffraction grating formed on both the front and back sides of the dual grating, Figure 4 is a configuration diagram showing the first conventional example, and Figure 5 (a) shows the second conventional example. Configuration diagram, Figure 5 (
b) is a circuit diagram showing the state of the photodetector. 1... Laser light source, 8, 18... Optical information recording medium, 2
3... Reflected light, 24... Signal detection optical system, 25...
・Detection lens, 26...Dual grating, 2
7... Substrate, 27a, 27b... Diffraction grating, 28.
...Photodetector, 29...Dual grating, 3
0...Substrate, 30a, 30b...For diffraction grating Applicant Rico Co., Ltd.

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 reproduced signal, reflected light from the optical information recording medium is passed through a detection lens onto an optical path guided to the signal detection optical system. A dual grating is provided, in which diffraction gratings are formed at equal pitches on both the front and back surfaces of the substrate, and the refractive index of the substrate is higher than that of the diffraction grating, and a photodetector is provided to detect light passing through the dual grating. An optical information recording/reproducing device characterized by: 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/reproducing apparatus that detects a reproduced signal, the reflected light from the optical information recording medium is directed onto an optical path led to the signal detection optical system, via a detection lens, and onto one surface of the substrate. An optical information recording and reproducing device comprising a dual grating in which a pitch diffraction grating is formed and a modulation pitch diffraction grating is formed on the other side, and a photodetector that detects light passing through the dual grating. Device. 3. 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/reproducing apparatus that detects a reproduced signal, the reflected light from the optical information recording medium is directed onto an optical path led to the signal detection optical system, via a detection lens, and onto one surface of the substrate. A dual grating is provided, in which a diffraction grating with a pitch is formed and a diffraction grating with a modulation pitch is formed on the other side, the refractive index of the substrate is higher than the refractive index of the diffraction grating, and light that passes through the dual grating is detected. An optical information recording/reproducing device characterized by being provided with a detector.