JPH02260132A - Optical pickup device - Google Patents

Abstract

PURPOSE:To facilitate the installation and the adjustment of the under-mentioned light receiving elements by letting reflected light from an information recording medium pass through a double-sided grating element, and leading transmitted or diffracted light to the approximately same direction, and receiving it by separate trisected light receiving elements. CONSTITUTION:The reflected light from an optical disk is converged 26, and is made incident to an approximately straight line-shaped diffraction grating 31 on the surface of the double-sided grating element 27, and is separated into the transmitted light T and the diffracted light K. The separated trisected light receiving elements 29, 30 are irradiated with these lights T, K after being transmitted and diffracted through/by the approximately straight line-shaped diffraction grating 32 on a rear surface. At that item, since the optical path of the light K becomes longer than that of the light T, the focusing point P of the light P and the focusing point Q of the light T are positioned at this side and in the rear of a light receiving surface respectively. A focus can be controlled by using these elements 29, 30. Namely, since astigmatism is caused by arranging the element 27 at a Bragg's angle thetab, and the focusing point at the time of a focus error signal FE=0 becomes larger than that at the time of no astigmatism, the installation and the adjustment of the elements 29, 30 can be facilitated to be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical pickup device that performs focus control and tracking control using reflected light from an optical information recording medium.

2. Description of the Related Art Conventionally, as a method for performing focus control and tracking control using reflected light from an optical information recording medium, there is a device as shown in FIG. 5 as a first conventional example. This involves collimating light emitted from a semiconductor laser 1 through a collimating lens 2, transmitting it through a beam splitter 3, condensing it through an objective lens 4, and irradiating it onto a magneto-optical disk 5 as an optical information recording medium. This reflected light is reflected by the polarizing beam splitter 3 and guided to the magneto-optical disk signal detection optical system 6. In this magneto-optical disk signal detection optical system 6, the reflected light passes through a 1/2 wavelength plate 7, and then is condensed by a condenser lens 8 to form a microprism 10 of a microprism detector 9 (see FIG. 6). The transmitted light is transmitted or reflected by the polarizing beam splitter 11, and the transmitted light is directly guided to a light receiving element (not shown) divided into three parts of the detector 12, and the reflected light is transmitted to the mirror 13.
The light is guided through the detector 12 to three divided light receiving elements (not shown). In this case, the focus error signal and magneto-optical signal are detected by checking the amount of light detected by each of the two light-receiving elements using the well-known beam size method, and the focus control and information of the magneto-optical disk are detected. Playing is in progress.

As a second example, there is a device as shown in FIGS. 7(a), (b), and (c). This is because the light emitted from the semiconductor laser 14 is collimated by a collimating lens 15, reflected by a polarizing beam splitter 16, and then reflected by a quarter-wave plate 17.
is focused by the objective lens 18 to the optical disk 1.
After the reflected light from the optical disk 19 is transmitted through the polarization beam splitter 16, it is guided into the optical disk signal detection optical system 20. In this optical disk signal detection optical system 20, the reflected light from the optical disk 19 is focused by a condensing lens 21, and then transmitted or reflected by a beam splitter 22, and a light receiving element 23 arranged on each optical path, 24, a focus error signal or the like is detected by the beam size method, and thereby the focus control of the optical disc 19 or the like is performed.

Problems to be Solved by the Invention First, in the case of the first conventional example, the signal is detected by the microprism detector 9 of the magneto-optical disk signal detection optical system 6, but in this case, the microprism 1o and the detector 12 are Since it is integrated with the substrate, it is transmitted or reflected by the polarizing beam splitter 3,
There is a problem in that the positions of the two light spots guided to separate light receiving elements cannot be adjusted independently.

On the other hand, in the case of the second conventional example, since the two light receiving elements 23 and 24 are arranged orthogonally in the optical disk signal detection optical system 20, there is a problem in that the space cannot be saved.

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 determine the position of the optical information recording medium. In an optical pickup device that performs control, a condenser lens is provided on the optical path of the signal detection optical system to converge the reflected light from the optical information recording medium, and a condenser lens is provided on both surfaces that transmit or diffract the condensed light from the condenser lens. A double-sided grating element on which a substantially linear diffraction grating was formed was disposed, and two three-part light receiving elements for receiving light transmitted or diffracted through the double-sided grating element were disposed in the same plane.

Further, the invention according to claim 2 records information by irradiating the light emitted from the laser light source onto the optical information recording medium, and guides the reflected light from the optical information recording medium to the signal detection optical system. In an optical pickup device that controls the position of an optical information recording medium, a condenser lens for converging reflected light from the optical information recording medium is provided on the optical path of the signal detection optical system, and the condensed light from the condensing lens is A double-sided grating element is provided, in which a diffraction grating with a unidirectional lens effect is formed on one surface that is transmitted or diffracted, and a substantially linear diffraction grating is formed on the other surface, and the light transmitted or diffracted through this double-sided grating element is Two three-part light-receiving elements for receiving light were arranged in the same plane.

Therefore, according to the invention described in claim 1, the reflected light from the optical information recording medium is focused by the condensing lens in the signal detection optical system, and is transmitted by the substantially linear diffraction grating formed on both sides of the double-sided grating element. or diffracted in almost the same direction 2
The light receiving element is divided into two beams, and these two beams are separately irradiated onto the three-split light receiving element, thereby making it possible to detect a focus error signal or the like.

Further, according to the invention as set forth in claim 2, the reflected light from the optical information recording medium is condensed by the condensing lens in the signal detection optical system, and the diffraction grating with the unidirectional lens action of the double-sided grating element and the substantially linear It is transmitted or diffracted by the shaped diffraction grating and is divided into two beams in almost the same direction, and these two beams are separately irradiated onto the three-split photodetector, thereby detecting focus error signals, etc. can do.

Embodiment An embodiment of the invention set forth in claim 1 will be described based on FIGS. 1 and 2. FIG. Note that the description of the overall configuration of the optical pickup device will be omitted here, and only the signal detection optical system according to the present invention will be described.

A condensing lens 26 is disposed on the optical path of the reflected light reflected by an optical disk (not shown) as an optical information recording medium and guided to the signal detection optical system 25, and the optical path of the light transmitted through the condensing lens 26 is A double-sided grating element 27 is disposed on the substrate 28 in the same plane on the optical path of the light transmitted or diffracted through the double-sided grating element 27. are arranged.

The double-sided grating element 27 is made of a transparent substrate, and substantially linear diffraction gratings 31 and 32 are formed on both the front and back surfaces, and the grating direction is perpendicular to the plane of the paper on both surfaces, and the Bragg angle θb is set to increase the diffraction efficiency. It is placed at an angle. In this case, the substantially linear diffraction grating 31 on the surface
The grating pitch of is determined by Bragg angle polarization characteristics and the like. Further, the grating pitch of the substantially linear diffraction grating 32 on the back surface may be the same as the grating pitch of the substantially linear diffraction grating 31 on the front surface, or the pitch of the substantially linear diffraction grating 32 on the surface may be determined by the interval of separated light (transmission, diffraction). It is formed slightly shifted from the grating pitch of the substantially linear diffraction grating 31. The substantially linear diffraction gratings 31 and 32 on the front and back surfaces are formed at the same pitch over the entire surface, or at different pitches due to astigmatism in the diffracted light.

In such a configuration, the reflected light from the optical disk is
The light is condensed by the condenser lens 26, enters the substantially linear diffraction grating 31 on the surface of the double-sided grating element 27, and is separated into two lights: a transmitted light T and a diffracted light. These two separated transmitted light T and diffracted light are transmitted and diffracted through the substantially linear diffraction grating 32 on the back surface, and then separately irradiated onto the three-split light receiving element 29,30. At this time, the optical path of the diffracted light is longer than that of the transmitted light T, so the focal point P of the diffracted light is located in front of the light receiving surface, and the focal point Q of the transmitted light T is located on the light receiving surface. located at the rear of the

Incidentally, the amount of the step difference between these focal points P and Q can be determined by the inclination ob and the thickness t of the substrate of the double-sided grating element 27. Further, at this time, each light beam has astigmatism, and the focal points of the diffracted light and the transmitted light '1' in the direction perpendicular to the plane of the paper are Po and Qo, respectively, as shown in the figure.

Therefore, the function of these three-split light receiving elements 29 and 30 is
This will be described based on figures (a), (b), and (c). The light-receiving surfaces of the three-part light-receiving element 29 on the side where the diffracted light K is received are a, b, and c.
The light-receiving surfaces of the three-part light-receiving element 30 on the side where the transmitted light T is received are d, e, and f.

Now, when the optical disc is in focus with no defocus, the lateral spot diameters of the light spots on the 3-split light receiving element 29 and 30 surfaces are equal, as shown in Fig. 2(b). The value of the focus error signal FE at
When calculated from the equation -eel, FE=○, and the signal FE is not detected.

However, the optical disc became out of focus, as shown in Figure 2 (
As shown in a) and (c), when the spot diameter becomes larger or smaller, FE>Ol or FE<
O, a focus error signal is detected, and as a result, focus control of the optical disc is performed.

In this way, focus control can be performed by using the two three-part light receiving elements 29 and 30, and since the double-sided grating element 27 is placed at the Bragg angle Ob, both Equal amounts of light have astigmatism, and the focal point when FE=O is larger than when there is no astigmatism, making it easier to install and adjust the three-split light receiving element 29.30. Become. In this case, the 3-split light receiving elements 29 and 30 may each be independent, or both may be provided on the same substrate.
Installation and adjustment can be performed by moving and rotating.

In addition to the focus error signal FE described above, the track error signal TE can be detected by TE=a-c (or d-f). In the case where a magneto-optical disk (not shown) is used instead of using a magneto-optical disk, the magneto-optical signal MO is as follows: MO=(a ten su ten c) −(d+e+f)−= (3)
It can be detected by

Next, an embodiment of the invention according to claim 2 is shown in FIGS. 3 and 4.
This will be explained based on the diagram. This describes a case where one of the front and back surfaces of the double-sided grating element 27 is provided with a unidirectional lens effect.

That is, in the double-sided grating element 27, a diffraction grating 3] having a unidirectional lens effect is formed on one surface, and a substantially linear diffraction grating 32 is formed on the opposite surface.

Therefore, the reason why the diffraction grating 31 formed on one surface is given a unidirectional lens effect will now be explained. Third
As shown in the figure, the unidirectional lens action of the diffraction grating 31 moves the focal point Po of the diffracted light in the direction perpendicular to the plane of the paper to a symmetrical position with P in between. At this time, Fig. 4(a) (
b) As shown in (c), two three-part light receiving elements 2
The spot diameter of the light spot received at 9.30 is FE
When =O, they are both circular and equal, and when FE>01FE<O, they deform into elongated shapes in directions perpendicular to each other. The second mentioned above
It is possible to discern the difference in the amount of received light more clearly than when the device is deformed in the state shown in FIGS. (a), (b), and (c), thereby increasing the signal detection sensitivity.

In addition, in the invention described in claim 1 and claim 2,
The position of the diffracted light generated by passing through the double-sided grating element 27 moves depending on the wavelength;
As shown in c), by making the direction of the dividing line of the three-split light receiving elements 29 and 30 coincide with the moving direction of the diffracted light, the influence of the movement can be eliminated.

Effects of the Invention In the invention described in claim 1, reflected light from an optical information recording medium is passed through a double-sided grating element having substantially linear diffraction gratings formed on both sides, and the transmitted or diffracted light is guided in substantially the same direction. , it is possible to detect a focus error signal, a track error signal, and a magneto-optical signal by receiving the light with separate three-split light receiving elements, which allows signal detection to be performed while significantly reducing the space required for the entire optical system. It is something that can be done.

Furthermore, in the invention set forth in claim 2, by providing a unidirectional lens effect to the diffraction grating on one side of the double-sided grating element, the sensitivity of signal detection can be further increased compared to the invention set forth in claim 1. It is something.

[Brief explanation of drawings]

FIG. 1 is a side view showing an embodiment of the invention as claimed in claim 1;
FIGS. 2(a), (b), and (C) are explanatory diagrams showing the principle of detecting a focus error signal by the three-split light receiving element, and FIG. 3 is a side view showing an embodiment of the invention as claimed in claim 2. Figures 4 (a), (b) and (c) are explanatory diagrams showing the principle of detecting the focus error signal, Figure 5 is an optical path diagram showing the first conventional example, and Figure 6 is a side view of the micro prism detector. 7A is an optical path diagram showing a second conventional example, and FIGS. 7B and 7C are front views of the light receiving element. 1... Laser light source, 5... Optical information recording medium, 14.
Laser light source, 19... Optical information recording medium, 25... Signal detection optical system, 26... Condensing lens, 27 ・Double-sided grating, 29. 30... 3-split light receiving element, 31...
・Substantially linear diffraction grating (diffraction grating), 32...Substantially linear diffraction grating

Claims (1)

[Claims] 1. Recording information by irradiating light emitted from a laser light source onto an optical information recording medium, and guiding the reflected light from the optical information recording medium to a signal detection optical system for said optical information recording. In an optical pickup device that controls the position of a medium, a condenser lens that converges reflected light from the optical information recording medium is provided on the optical path of the signal detection optical system, and the condensed light from the condenser lens is transmitted or diffracted. A double-sided grating element having substantially linear diffraction gratings formed on both sides of the grating is disposed, and two three-part light-receiving elements for receiving light transmitted or diffracted through the double-sided grating element are disposed in the same plane. Optical pickup device. 2. Recording information by irradiating light emitted from a laser light source onto an optical information recording medium, and guiding the reflected light from the optical information recording medium to a signal detection optical system to control the position of the optical information recording medium. In the optical pickup device, a condenser lens is provided on the optical path of the signal detection optical system to converge the reflected light from the optical information recording medium, and the condenser lens transmits or diffracts the converged light from the condenser lens. A double-sided grating element in which a diffraction grating with a linear lens action is formed and a substantially linear diffraction grating is formed on the other side is disposed, and light transmitted or diffracted through this double-sided grating element is received.
An optical pickup device characterized in that two three-part light receiving elements are arranged in the same plane.