JPH0468690B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an optical information recording/reproducing device, and more specifically, to a means for automatically adjusting the focus of a light spot focused on a recording medium. The present invention relates to an optical information recording/reproducing device equipped with the following.

[Conventional technology]

A conventional device of this type will be explained with reference to FIGS. 1 to 7. In FIG. 1, a half prism 3 whose cemented surface 4 of a triangular prism forms a half mirror and forms a beam splitter is placed on an emitted light beam 2 from a light source 1 such as a semiconductor laser, and the emitted light beam 2 is converted into an irradiation light beam. 5 and a reflected beam 6. The emitted light beam 5 is made into a parallel light beam 8 by a collimating lens 7,
The parallel light beam 8 is transmitted to the optical disk 1 by an objective lens 9.
The light is focused on the information plane 11 of 0 as a light spot 12. The optical disk 10 is rotationally driven by a motor (not shown). As shown in FIG. 2, the information surface 11 is formed with a guide groove 13 whose depth is 1/8 to 1/4 of the wavelength of the light source 1 in terms of optical path length.
As shown in the figure, information bits 14 are written, and when a light spot 12 is focused on this bit 14, its reflectance decreases.

A nearly parallel reflected beam 15 that reads the information on the information surface 11 and passes through the objective lens 9 again becomes a focused beam by the collimator lens 7, is reflected by the half prism 3, and becomes a reflected beam 6, and the reflected beam 6 becomes a beam The light beam is split into two light beams 17 and 18 by a half mirror 16 serving as a separation element. Luminous flux 17
The first photodetector 19 that receives the light is placed at a position closer to the half mirror 16 than the convergence point P of the light beam 17, and the photodetector is divided into sections 19a to 19c as shown in FIG. , photodetectors 19a and 19 at both ends
c is electrically connected. The second photodetector 20 that receives the light beam 18 also includes photodetectors 20a to 20.
It is placed at a position farther from the half mirror 16 than the convergence point P' of the light beam 18, and the photodetectors 20a and 20c at both ends are connected.

In FIG. 4, the received light beams on the photodetectors 19 and 20 are indicated by reference numerals 21 and 22, respectively. Also, a first differential amplifier 23 that obtains a differential output between the divided portions 19a and 19b of the photodetector 19, and a photodetector 2
A second differential amplifier 24 obtains a differential output between the divided portions 20a, 20c and 20b of 0, and a third differential amplifier 25 obtains a differential output between the first and second differential amplifiers 23, 24. It is connected to photodetectors 19 and 20. The focusing actuator 26 shown in FIG. 1 controls the position of the objective lens 9 in the X direction in response to the output of the third differential amplifier 25. Further, the adder 27 in FIG.
Add the outputs of 9a, 19b, and 19c,
This is to obtain a reproduced signal output.

The conventional automatic focus adjustment of the light spot 12 in the above configuration will be explained. When the focal point of the objective lens 9 is on the optical disk 10 (hereinafter referred to as the focus position), the emitted light beam 2 is focused on the information surface 11, and the reflected light beam 15 reflected from the information surface 11 is transmitted to the photodetector 19. , 20. Photodetector 19, 2
0 are placed at a position equidistantly closer to and faster than the refocusing points P and P' to the half mirror 16, respectively, so the sizes of the light beams 21 and 22 in FIG. 4 are approximately equal. Therefore, the third differential amplifier 2
The output of 5 becomes zero.

When the optical disk 10 is displaced from the focal position of the objective lens 9 in the X direction, the refocusing points P and P' are displaced in the optical axis direction, and the sizes of the light beams 21 and 22 change. 5 and 6 show the optical disk 10 and objective lens 9.
This is a characteristic diagram with the horizontal axis arrow D representing the direction in which the distance between 23 and 24 change as shown.
Therefore, the third differential amplifier 25 shown in FIG.
By controlling the focusing actuator 26 so that the focusing system becomes a negative feedback system with the output G25 of It was intended to be carried out.

However, the conventional device having the above configuration has the following drawbacks. That is, since the guide groove 13 has an optical path depth of 1/8 to 1/4 of the light source wavelength, the intensity distribution of the light beams 21 and 22 on the photodetectors 19 and 20 is such that the light spot 12 is located at the guide groove 13. The light beams 21, 22 on the photodetectors 19, 20 when crossing the
Up and down (Z direction), left and right (X and Y directions respectively)
The symmetry of is destroyed. Therefore, even if the information surface 11 is at the in-focus position, the output of the third differential amplifier 25 does not become zero, causing a sensor error in the focus system, and as a result, information is lost from the in-focus position of the objective lens 9. X of the objective lens 9 so that the surface 11 is shifted.
This means that the directional position is controlled. Note that this disadvantage appears most significantly when the depth of the guide groove 13 is λ/8, and the influence becomes smaller as the depth approaches λ/4.

[Summary of the invention]

The purpose of this invention is to eliminate the above-mentioned drawbacks of the conventional method and to enable highly accurate automatic focus adjustment.The purpose of this invention is to focus light diffracted in a direction perpendicular to the guide groove onto a photodetector. This provides an optical information recording and reproducing device that can minimize sensor errors caused by deviation of a light spot from a guide groove.

[Embodiments of the invention]

8 and 9 show a first embodiment of the present invention. In FIG. 8, the convergence of the light beam 17 in two directions perpendicular to the guide groove 13 is increased, and the convergence point P in that direction is
A cylindrical convex lens 30 serving as a converging element for moving the light to a point Q on the first photodetector 19 is arranged. Further, a cylindrical concave lens 31 is arranged as a diverging element to reduce the convergence of the light beam 18 in two directions perpendicular to the guide groove 18 and move the convergence point P' in that direction to the point Q' of the second photodetector 20. do. FIG. 9 shows the light beams 32 and 33 on the photodetectors 19 and 20 with the above configuration. Note that the dividing lines of the photodetectors 19 and 20 are in the X direction and in the Y direction, respectively, as in the conventional one.
selected in the direction.

Next, the operation will be explained. Photodetector 19, 2
The output of the third differential amplifier 25 corresponding to the magnitude of the light beams 32 and 33 in the Z direction above 0 corresponds in the same way as the conventional one. On the other hand, as was the case with conventional devices, changes in the magnitude of the luminous flux in the Z direction do not significantly affect sensor characteristics. Therefore, even in this embodiment, the output of the third differential amplifier 25 changes in the same way as shown in FIG. It is similar to However, in this embodiment, when the information surface 11 is at the focused position of the objective lens 9, the light beams 32 and 33 on the photodetectors 19 and 20 are focused in the Z direction, so the light spot 12 is guided. Groove 13
Even when the guide groove 13 is crossed, the intensity distribution of the light beams 32 and 33 on the photodetectors 19 and 20 in the direction intersecting the guide groove 13 does not change. Therefore, sensor errors occurring in the focus system are kept to a minimum. Also, guide groove 1
Needless to say, the influence of the change in depth in step 3 is eliminated.

10 and 11 show a second embodiment of the present invention. As shown in FIG. 10, instead of the half mirror 16 in the first embodiment, a mirror surface 40 and a half mirror surface 41 are parallel to each other. Opposed prism 4
The first photodetector 19 and the second photodetector 20 are arranged side by side on the same plane 43, and the reflected light beam 6 is divided into two and guided in the same direction. Then, as shown in FIG. 11, the photodetector 19,
Luminous fluxes 32, 33 are obtained on 20, and the effect is similar to that of the first embodiment. In this case, photodetector 1
9 and 20 may be formed monolithically.

FIG. 12 shows a third embodiment of the present invention, in which a stepped reflecting mirror 44 is arranged in place of the prism 42 of the second embodiment, and the reflected light beam 6 is divided into half light beams 45 and 4.
A similar effect can be obtained by configuring it to be divided into 6 parts.

FIG. 13 shows a fourth embodiment of the present invention, in which a reflecting mirror 49 having a reflecting cylindrical concave surface 47 and a reflecting cylindrical convex surface 48 is used as the reflecting mirror, and a stepped reflecting mirror and a cylindrical converging element are used. It exhibits the functions of a convex lens and a cylindrical concave lens which is a diverging element, and similar effects can be obtained.

14 and 15 show a fifth embodiment of the present invention, in which the reflecting mirror 49 in FIG. 13 is replaced with a reflecting mirror 50 with reflective surfaces 51 and 52 in the form of a blind grating. be. In this case, the reflective surface 51 functions as a converging element as a reflective cylindrical concave surface, and the reflective surface 52 functions as a diverging element as a reflective cylindrical convex surface, producing the same effect.

16 to 18 show a sixth embodiment of the present invention, in which a trapezoidal prism 53 is attached to a part of the end face of the half prism 3 as shown in FIGS. 16 and 17. It has a similar effect. The trapezoidal prism 53 may be arranged close to a part of the end face of the half prism 3, as shown in FIG.

19 and 20 show a seventh embodiment of the present invention. In FIG. 19, a prism 5 having a cylindrical convex surface 55 and a cylindrical concave surface 55 is shown.
4 is attached to the end face of the half prism 3, similar effects can be obtained. The prism 54 is the second
It may be arranged close to the end face of the half prism 3 as shown in FIG.

FIG. 21 shows an eighth embodiment of the invention, in which a cylindrical convex surface 58 and a cylindrical convex surface 58 are shown.
and a prism 57 having a cylindrical concave surface 59
are arranged close to the photodetectors 19 and 20, respectively, and produce similar effects.

FIGS. 22 and 23 each show a ninth embodiment of the present invention, in which dividing lines 19d and 20d of photodetectors 19 and 20 arranged on the same plane are shifted from parallel. With this configuration, in addition to the same effect, the offset of the focusing sensor system caused by the positional deviation in the optical axis direction of the photodetectors 19 and 20 arranged on the same plane can be reduced.
The effect is that correction can be easily performed by in-plane adjustment.

Further, the connection between the differential amplifier and the photodetector is as shown in FIG. 24 shown as the tenth embodiment, as shown in FIG.
c, 20a and 20c may be directly connected to the third differential amplifier 25, or the focus sensor characteristics can be obtained by differential amplification between the central portions 19 and 20b as shown in FIG. I can do it.

Furthermore, as an eleventh embodiment, instead of using a photodetector divided into three as shown in FIG. 26 or FIG. A focus sensor output can also be obtained by the first and second photodetectors 70 and 71.

Further, in the present invention, as in the twelfth embodiment shown in FIG. The present invention may also be applied to a recording device that writes information on the surface 83, and similar effects can be obtained.

〔Effect of the invention〕

As is clear from the above explanation, this invention
The structure is such that the light beam equivalent to the direction perpendicular to the guide groove on the optical disk is focused on the photodetector.
The sensor error when the light spot crosses the guide groove can be minimized, resulting in a special effect of significantly improving the accuracy of the device.

[Brief explanation of the drawing]

Figures 1 to 7 show a conventional device. Figure 1 is an optical arrangement diagram, Figure 2 is a partial sectional view of an optical disk, Figure 3 is a partial plan view of the information surface, and Figure 4 is an electrical The wiring diagrams and FIGS. 5 to 7 are operating characteristic diagrams, respectively. 8 and 9 show a first embodiment of this invention, FIG. 8 is an optical layout diagram, FIG. 9 is an electrical wiring diagram, and FIGS. 10 and 11 are a second embodiment of this invention. An example is shown, FIG. 10 is an optical layout diagram, FIG. 11 is a partial plan view, FIG. 12 is an optical layout diagram of a third embodiment of this invention, and FIG. 13 is a fourth embodiment of this invention. 14 and 15 show a fifth embodiment of the present invention, FIG. 14 is an optical layout diagram, FIG. 15 is a partial plan view, and FIGS. 16 to 18 are Respective optical layout diagrams of essential parts of the sixth embodiment of the invention,
19 and 20 are optical layout diagrams of the main parts of the seventh embodiment of the present invention, FIG. 21 is a diagram of the optical layout of the main parts of the eighth embodiment of the invention, and FIGS.
3 is a plan view of essential parts of the ninth embodiment of the present invention, FIGS. 24 and 25 are electrical connection diagrams of the tenth embodiment of the invention, and FIGS. 26 and 27 are diagrams of the present invention. Main part plan view of the eleventh embodiment, second
FIG. 8 is an electrical connection diagram of a twelfth embodiment of the present invention. 1... Light source, 3... Half prism (beam splitter), 7... Collimating lens, 9... Objective lens, 10... Optical disk, 11... Information surface, 12... Light spot, 13... Guide groove, 14
... pit, 16 ... half mirror (light beam separation element), 19, 20 ... first and second photodetectors, 2
3, 24, 25...first, second, third differential amplifier, 26...focusing actuator, 3
0...Cylindrical convex lens (convergent element), 31
... Cylindrical concave lens (divergent element), 40
...Mirror surface, 41...Half mirror surface, 42...
... Prism (light beam splitting element), 44... Stepped reflecting mirror (light beam separating element), 47... Reflective cylindrical concave surface, 48... Reflective cylindrical convex surface, 49... Reflecting mirror (light beam separating element), 51,
52...Reflecting surface, 50...Reflecting mirror (light beam splitting element), 53...Trapezoidal prism, 54...Prism, 55...Cylindrical concave surface, 56...Cylindrical concave surface, 57...Prism, 58...Cylindrical convex surface , 59... Cylindrical concave surface, 70, 71... First and second photodetectors, 81
... Signal source, 82 ... Modulator, 83 ... Recording surface.
In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A light source, an objective lens that focuses the light beam emitted from the light source onto an information surface having a guide groove on an optical disk, and a reflection of a light condensing spot from the information surface through the objective lens. a beam splitter that separates the light beam from the output light beam; a beam splitter that separates the separated reflected light beam into two light beams; and a plurality of divided first and second photodetectors arranged at respective positions. In an optical information recording and reproducing device that automatically adjusts the focus of a spot, the photodetector is arranged such that the dividing direction thereof is orthogonal to the direction in which the guide groove is projected onto the photodetector, and the two light beams are comprising a converging element and a diverging element that converge and diverge the two light beams, respectively, so that the shape on the photodetector becomes a linear light beam in a direction in which the guide groove is projected onto the photodetector. An optical information recording and reproducing device characterized by: 2. The optical information recording and reproducing device according to claim 1, comprising a converging element made of a cylindrical convex lens and a diverging element made of a cylindrical concave lens. 3. Claim 1, comprising: a beam splitting element made of a prism with a mirror surface and a half mirror surface facing each other in parallel; and first and second photodetectors arranged on one plane. The optical information recording and reproducing device described above. 4. The optical information recording and reproducing device according to claim 1, comprising a beam separating element made of a stepped reflection mirror, and first and second photodetectors arranged on one plane. 5. The optical information recording and reproducing device according to claim 1, comprising a beam splitting element comprising a reflecting mirror having a cylindrical concave surface forming a converging element and a cylindrical convex surface forming a diverging element. 6. The optical information recording and reproducing device according to claim 1, comprising a light beam splitting element in which a reflecting surface is formed of a blind grating and forms a converging element and a diverging element. 7. The optical information recording and reproducing device according to claim 1, comprising a beam splitting element formed by coupling a trapezoidal prism to a part of the end face of a half prism forming a beam splitter. 8. The optical system according to claim 1, comprising a beam splitting element in which a prism having a cylindrical concave surface forming a converging element and a cylindrical convex surface forming a diverging element is coupled to an end face of a half prism forming a beam splitter. Expression information recording and reproducing device. 9 A beam splitting element made of a prism having a cylindrical convex surface forming a converging element and a cylindrical concave surface forming a diverging element is arranged in close proximity to the first and second optical detectors arranged on one plane. An optical information recording and reproducing device according to claim 1. 10. The optical information recording and reproducing device according to claim 1, comprising a photodetector divided into three parts with non-parallel dividing lines.