JPS61113137A - Optical head - Google Patents

Abstract

PURPOSE:To hold a stable focus condition by separating a light beam reflected from information recording media into plural pieces and calculating the output of the light detecting device installed in the forward direction from an image- forming point of the separated light beam. CONSTITUTION:As a method for detecting a focusing error, detection is executed by obtaining the difference between the light quantity of the first light detecting device 30 and the light quantity of the second detecting device 31. Namely, by obtaining (30a+30b)-(31a+31b), the signal goes to zero at the time of focusing, and when an objective lens 25 and recording media 26 are too close as compared with the time of focusing, the signal of the negative value is obtained, and when they are too far, the signal of the positive value is obtained. The signal is processed, the feedback is given to the position of the objective lens 25, and the objective lens 25 is shifted to the correct position and as the result, the focusing can be executed.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention uses a light beam to record and reproduce information on an information recording medium, or to erase the contents of recorded information. Relating to improvements in optical heads.

[Technical background of the invention and its problems]

In information recording and reproducing heads using light beams,
When the beam waist (the narrowest part) of the light beam does not reach the recording layer or light reflection layer of the information recording medium, that is, when the focus is buried, information is recorded normally.

Cannot be exogenous. Therefore, in such an optical head, it is safe to detect focusing errors in order to record and reproduce information normally. The wedge method and the astigmatism method are known. First, Figure 6 shows the knife-wedge method.

The light beam generated from the semiconductor laser l.

The collimator lens 2 converts the light into parallel light. After passing through the polarizing beam sinter 3, the light becomes circularly polarized by the λ/4 wavelength plate 4. The objective lens 5 converts the light into an information recording medium 6 (hereinafter abbreviated as "recording medium"). 0) Connect the K spot. The light beam reflected from the recording medium 6 becomes circularly polarized light with reverse rotation.

After passing through the λ/4 wavelength plate 4, the light becomes a linearly polarized light whose vibration direction is perpendicular to the direction of vibration of the incident light, and is reflected by the polarizing beam screener 3.
The light beam reflected by the prism 7 has half its wavefront cut by the knife quencher 8, and is then split into two parts by the condenser lens 9 and then split into two by the photodetector 10.
is incident on the This two-split photodetector 100 detects the %7 orcus error by taking the difference in the amount of light between the two. -7%-7 The light beam transmitted through the prism 7 enters the two-split photodetector 12 at a position where it is somewhat focused by the condenser lens 11, and the difference in the light intensity between the two split photodetectors 120 to detect the tracking error, and 2
The information reproduction signal is detected by calculating the sum of the two light amounts.

However, with this knife wedge method, a photodetector to detect focusing errors must be installed at or near the focal point of the light, so if the optical axis shifts due to changes in the external environment such as temperature or shock, However, this method had the disadvantage of falsely detecting focusing errors.

Next, an example of the astigmatism method is shown in FIG.

The light beam generated from the semiconductor laser 1 is guided to the recording medium 6 in the same manner as in the knife wedge method shown in FIG. IK, and the light beam reflected from the recording medium 6 is also reflected by the polarized beam currant 3. In the astigmatism method, this reflected original beam is passed through a spherical lens 13 and a cylindrical lens 14.
After passing through, the light is made to enter a four-split photodetector 15.

In this way, focusing errors, tracking errors, and information reproduction signals are detected using the signals obtained from the 4-split photodetector 15. However, when detecting focusing errors using this astigmatism method, , the focus is blurred due to the luminance distribution of the light due to the diffraction pattern when it crosses the group on the recording medium 6, resulting in false focus detection.0 [Object of the Invention] The present invention has the disadvantage that This was done based on the circumstances, and when detecting the 7-o-cutting error, the influence of the original axis misalignment,
It is an object of the present invention to provide an optical head that can perform accurate detection at any time and maintain a stable focus state without causing erroneous detection of focusing errors due to the influence of diffraction.

[Summary of the invention]

In order to achieve the above object, the present invention separates a light beam reflected from an information recording medium into a plurality of light beams, and provides a first photodetector in front of the imaging point of the separated first light beam,
An optical head is provided, characterized in that a second photodetector is provided behind the imaging point of the second light beam, and the outputs of the first and second photodetectors are calculated.

[Embodiments of the invention]

The present invention will be described below with reference to an embodiment shown in FIG.

In FIG. 1, a light beam emitted from a semiconductor laser 21 is turned into parallel light by a collimator lens 22, and then passes through a polarizing beam subrifter 23.

The light becomes circularly polarized by the λ/4 wavelength plate 24, and a spot is formed on the recording medium 26 by the objective lens 25.

After passing through the objective lens 25, the reflected light is λ/4
The wavelength plate 24 converts the beam into a linearly polarized original beam whose vibration direction is perpendicular to the vibration direction of the incident light, and the polarized beam splinter 23
Reflective type.

Further, the reflected light beam is amplitude-divided by a half prism 27, and the transmitted light beam passes through a condenser lens 28 and is projected onto a first photodetector 30 provided in front of this light beam focusing point. be done. Also, the light beam on the 1 reflection side is
The light beam passes through the condensing lens 29 and is projected onto a second photodetector 31 provided behind the imaging point of this light beam. Here, the first photodetector 30 and the second photodetector 31 needs to be installed at a position sufficiently distant from the focal point of the light beam from the information medium 6.

In the present invention, the first photodetector 30 and the second photodetector 31 are respectively installed at positions that are separated from the imaging point by a focal depth of 2 or more determined as follows.

z = L (f > 2λ π a However, a: Radius of incident light on the projection lens f: Focal length of the projection lens λ: Wavelength of the incident light Also, the first photodetector 30 and the second photodetector 31 meet the above conditions. is satisfied and the beam diameter of the light beam is larger than 5 times the diameter ω of the spot at the imaging point.In other words, the beam of reflected light is % at a position where the diameter is large, at a position at a focal depth of 2 or more from the imaging point, and at a position where the size of the light-receiving surfaces of the first and second photodetectors 30 and 31 is equal to the size of the beam diameter of this light beam. A photodetector 30.31 is provided.

Normally, in an optical head, defocus occurs when the distance between the objective lens 25 and the recording medium 26 in FIG. The focusing error is detected by the detectors 30 and 31, and the focus is adjusted by moving the objective lens 25. Therefore, an embodiment of the method for detecting focusing error in the optical head of the present invention will be described below. This will be explained with reference to FIGS. 2 to 5.

Figure 2 shows the light receiving surface of the first photodetector 30 (Figure A) and the second photodetector 30.
It is a diagram showing the light-receiving surface (Figure B) of the photodetector 31, and each photodetector has a first light-receiving surface 3oa, 3ia,
Second light receiving surface 30b.

31b, respectively.

Figure 3 shows the light-receiving surface of the first photodetector 30 when in focus (Figure A).
This shows the state of the light-receiving surface (Figure B) of the second original extractor 31.

Figure 4 shows the objective lens 25 and recording medium 26 in Figure 1.
The first photodetector 3 when the distance is too short compared to the first photodetector 3
0 (Figure A) and the light receiving surface of the second photodetector 31" (
Figure B) shows the state. In this case, the light beam reflected by the recording medium 26 becomes a diverging light after passing through the objective lens 25, and the imaging point of the light beam converged by the projection lenses 28 and 29 is different from that at the time of focusing. optical lens 28.2
Move to a position far from 9. Therefore, the first photodetector 30
At the position, as shown in Figure 4 (5), the hemoptysis of the light beam is .compared to when in focus.

and at the position of the second photodetector 31.

As shown in FIG. 4 111, the cross section of the light beam becomes smaller than when it is focused.

Conversely, Fig. 5 shows the light receiving surface of the first photodetector 30 (Fig. A) and the light receiving surface of the second photodetector 31 (Fig. The states shown in Figure B) are shown respectively. In this case, after the light beam reflected by the recording medium 26 passes through the objective lens 25, it becomes a convergent light trap, and the focal point of the light converged by the light projecting lenses 28 and 29 is different from that at the time of focusing. Move the lens to the 28°/29 side. Therefore, at the position of the first photodetector 30, as shown in FIG.
5), the light beam [i] is smaller than when it is in focus, and at the position of the second optical analyzer 31, the light beam is The illumination surface becomes larger.As a method for detecting focusing errors based on the state shown in FIGS. This can be done by calculating the difference in the light intensity of the detector 31. That is, (3
0a + 30b) - (31a + 31b) From K, this signal should not be 0 when in focus, and if the objective lens 25 and recording medium 26 are too close compared to when in focus, a negative value signal will be obtained, or it will reach too far. and a positive value signal is obtained. This signal is processed, feedback is applied to the position of the objective lens 25, the objective lens 25 is moved to the correct position, etc.
Orcasing becomes possible 0 Also using these two photodetectors 30.31.

Tracking errors can be detected and information reproduction signals can be detected o Trunking errors can be detected using the diffracted light method* (30a+axa)-(3ob
+atb), or (30a+30b)
+31a+31b), the information reproduction signal can be detected.In the above embodiment, the condenser lens 28.29 is provided after the half prism 27, but the condenser lens 28.29 is The two photodetectors 30 and 31 may be provided in front of the half prism 27, and although the two photodetectors 30 and 31 have been explained using a two-split photodetector, a similar 7-o-cutting error may occur even if a four-split photodetector or the like is used. Detection and tracking error detection and information reproduction signal detection can be performed.

In addition, it goes without saying that the present invention can be modified in various ways without departing from the gist of the present invention.As described above, according to this embodiment, the light receiving surfaces of the two photodetectors 30 and 31 are [By providing two photodetectors 30 and 31, the structure is relatively simple, and the influence of diffraction of the groups provided on the recording medium is reduced. I won't receive it. For example, if the size of the spot of the light beam is larger than the size of the photodetector, Kti, a part of the spot will be detected, and if the intensity distribution of the spot is non-uniform due to the influence of diffraction, that influence will be ignored. However, in this embodiment, by performing 7-o-katung error detection using zero or two photodetectors 30 and 31, which can perform stable detection without being affected by this effect. , since the same diffraction pattern is generated on both edges of the two photodetectors 30 and 31, there is a sufficient tolerance for the influence of defocus when crossing the group caused by the astigmatism method.
Stable focusing error detection can be performed.

The photodetectors 30 and 31 are installed at a distance M from the imaging point with a depth of focus of 2 or more, and at a location where the beam diameter of the light is larger than 5 times the beam diameter ω of the spot at the imaging point. Therefore, it is possible to have sufficient tolerance for optical axis deviation due to changes in the external environment such as temperature and impact.

In addition to the above effects, in this embodiment, the focusing error signal, tracking interference signal, and information reproduction signal are detected using all the light beams reflected by the recording medium 26, so astigmatism is detected. Compared to the aberration method, the amount of signal is larger, and S/
This has the effect of improving the N ratio and enabling stable 7-cutting error detection, tracking error detection, and information reproduction signal detection.0 In addition, apertures are provided at the positions of the two photodetectors in this embodiment, and the optical Although it is conceivable to provide a detector, the structure of this embodiment has a single structure rather than the structure provided with an aperture. [Effects of the Invention] As explained above, according to the present invention, the structure is relatively simple. The optical head is equipped with a photodetector that has sufficient tolerance against the effects of diffraction due to groups formed on the recording medium and the effects of optical axis misalignment due to changes in the external environment such as temperature and shock. By having this, it is possible to perform focused difference detection at any time without being affected by these external conditions.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an optical head according to one of the inventions, and FIG. 2 is a diagram showing an example of the configuration of a light-receiving surface of a photodetector provided in an optical head according to the present invention. Figures 3 to 5 are diagrams showing changes in the size of the spot shape of the light beam on two photodetectors depending on the distance l between the objective lens and the information recording medium, and Figure 6 is a diagram showing the change in the size of the spot shape of the light beam on two photodetectors. 7. A configuration diagram of an optical head showing an example of the knife quedge method, which is a method for detecting orthogonal errors. It is a block diagram of the 10-character head shown in FIG. 1.21...Semiconductor laser, 2.22...Collimator lens, 3.23...(h light beam splitter, 4
．． 24...λ/4tBL long plate, 5.25...Objective lens, 6.26...Information recording medium, 7.27...Half prism, 8...Knife wedge, 9,11゜2
8.29... Condensing lens, 13... Spherical lens, 1
4. Cylindrical lens! 0.12.15.30°31...
- Photodetectors, 30a, 30b... The first light-receiving surface (a) and the second light-receiving surface (b) of the photodetector of the shrine 1. 31a, 31b...the first light-receiving surface of the second photodetector (
a) and a second light-receiving surface (b). Agent: Patent attorney Noriyuki Chika (and 1 other person) Figure 6 Figure 7

Claims (4)

[Claims] (1) a light source section that generates a light beam, an optical means that guides the light beam from the light source section to an information recording medium, and a separation means that separates the reflected light from the information recording medium into a plurality of light beams; , a first photodetector provided in front of the focal point of the first light beam separated by the separating means, and a first photodetector provided behind the focal point of the second light beam separated by the separating means. an optical head provided with a second photodetector, and calculating outputs of the first and second photodetectors. (2) at a position where the size of the spot created by the light beam reflected from the information recording medium upon focusing is approximately equal to the area of the light-receiving surfaces of the first photodetector and the second photodetector; , the first photodetector and the second photodetector, respectively. (3) A focusing error signal is obtained by detecting a difference in the amount of light between the first photodetector and the second photodetector.
Optical head described in section. (4) A tracking error signal and an information reproduction signal are obtained by using respective light quantities of the first photodetector and the second photodetector. Optical head described in section.