JPS59113532A - Optical information reproducer - Google Patents

Abstract

PURPOSE:To enable focus error detection which is stable against a temp. change by maintaining the optical position relation of a photodetector with respect to a light emitting point constant against the temp. change so that a part of the detecting luminous flux does not transmit excess optical elements between a light separating means and a photoelectric detector. CONSTITUTION:A detecting luminous flux 17 is obtd. from the light reflected from a reading light spot. The 1st part (lower half) separated of the flux 17 is divided from the remaining 2nd part by an eccentric lens 16, and forms a far field pattern of a spot light source 11 on a photoelectric detector 18. The 2nd part forms likewise a near field pattern. Both field patterns are spatially separated by means of the lens 16. The photoelectric detector 18 consists of four photodetecting cells 18a-d (T is a track projection direction). If there is no focus error, a near field pattern 20a is formed on a boundary line 19a, but when a focus error arises, asymmetrical out of focus is resulted like 20a' or 20a'', and the focus error can be detected by comparing the output signals of cells 18a and 18b. If the light source 11 and the detector 18 have a mutually equivalent positional relation with a light separating means 13, the error detection is not affected by the temp. change.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical information reproducing head, and more particularly to an optical information reproducing apparatus such as an optical disc player having improved focus error detection means.

Conventional configuration and its problems Optical playback devices, such as videotask players and digital audio disc (DAD) players, require focus control, tracking, and knocking control.
The optical information reproducing head used for this generally has optical focus error detection means and tracking error detection means.

As a focus error detection means, astigmatism is imparted to the reflected light beam obtained by condensing the reflected light from the information recording carrier (hereinafter simply referred to as a disk) with a focusing lens, and the resulting reflected light beam is focused on the photoelectric detector. A method is already known that utilizes changes in the amount of astigmatism of an image formed in
(See Publication No. 561). Specifically, the magnitude of astigmatism in two directions perpendicular to each other can be determined by using a photoelectric detector having four light receiving cells and comparing the summed outputs of the light receiving cells in the diagonal directions. This is to obtain a focus error signal.

On the other hand, as a tracking error detection means, a method is already known in which the imbalance due to a tracking error in the light intensity distribution of the far-field image of the reflected light beam is detected as a differential output of two light-receiving cells of a photoelectric detector ( For example, JP-A-49-
80919) FIG. 1 is a schematic diagram of a conventional example using the above-described focus error detection method and tracking error detection method. In the figure, an irradiation light beam 2 emitted from a light emitting point 1 of a substantial point light source is focused onto the information recording surface of a disk 5 by a focusing lens system 4, and a reading light spot 9 is a conjugate image of the light emitting point. form. The reflected light from this reading light spot 9 is again focused by the focusing lens system 4, and the detection light beam 7
is obtained. When the reading light spot 9 is accurately focused on the information recording surface, the detection light beam 7 takes the optical path of the irradiation light beam 2 toward the light emitting point 1 in the opposite direction. Therefore, if the detection light beam 7 is not separated from the optical path of the irradiation light beam 2 by the beam splitter 3, then the light emitting point 1
It is focused to form a conjugate image at a position isometric to . When a cylindrical lens 6 having a unidirectional positive or negative lens action is inserted into the optical path of the separated detection light flux 7 f', the detection light flux within the plane in which the cylindrical lens 6 has a lens action as shown in - The focal point 1'' of the detection beam 7 is shifted forward or backward from the position of the conjugate image.In the plane in which the cylindrical lens 6 has no lens action, the focal point 1'' of the detection light beam 7 is shifted forward or backward from the position of the conjugate image.
' of course coincides with the position of the conjugate image, if the thickness of the cylindrical lens 6 is ignored. A photoelectric detector 8 is installed at a suitable position between the focusing points 1' and 1''. It is also possible to make the polarities of the astigmatism in the directions opposite to each other and equal in magnitude.In order to make the above image easier to understand, an enlarged view of the photoelectric detector 8 is shown in Fig. 2. As shown in the figure, the image of the photoelectric detector 8'' does not become a point due to astigmatism, but becomes a blurred far-field image 10. When the focal point 751 of the reading light spot 9 on the disk 5 shifts, the far-field image becomes 10' or 10' depending on the direction of the shift.
''.The four light receiving cells 8a, sb of the photoelectric detector 8.

A focus error can be detected by comparing the sum of the diagonals of 8C and 8d, that is, the sum of the outputs of light receiving cells 8a and 80 and the sum of the outputs of light receiving cells 8b and 8d.

On the other hand, if the information track movement direction of the disk 5 is projected in the direction of T in FIG. 2, the sum of the outputs of the light receiving cells 8a and 8b and the sum of the outputs of the light receiving cells 8C and 8d are compared with each other. This makes it possible to detect tire knocking errors. Furthermore, light receiving cells 8a, sb, 8c
The information signal can be read by adding all the outputs of 8d and 8d.

As described above, this conventional example has the advantage of being able to detect all of the focus error, tracking error, and information signal from one reflected light beam. However, if the focal length of the cylindrical lens 6 changes due to changes in temperature, etc., there is a problem in that an error occurs in the detection of the focus error signal. It is an object of the present invention to provide an optical information reproducing device that can stably detect focus errors.

Structure of the Invention The optical information reproducing device of the present invention includes a point light source and a light spot that is a conjugate image of the light emitting point by focusing the irradiation light beam emitted from the light emitting point of the point light source onto an information storage carrier. a detection light beam that is reflected from the light spot by the information recording carrier and passes back through the light focusing means toward the light emitting point, between the point light source and the light focusing means; a light separating means for separating and extracting the irradiated light beam; a photoelectric detector installed at or near a conjugate image position of the light emitting point where the detection light beam is formed at a position optically equivalent to the light emitting point; It is located between the separating means and the photoelectric detector, and the detected light beam is spatially divided by a dividing line substantially perpendicular to the information track of the information recording carrier. Second
The part is a lens that does not transmit light, and has an eccentric lens whose principal point is outside the detection light beam, and the point light source, the light separation means, and the photoelectric detector are fixed with a fixing member having a substantially uniform coefficient of thermal expansion. Furthermore, the above photoelectric detector is
consisting of a first pair of light-receiving cells that are adjacent to each other and whose boundary lines are substantially substantially parallel to the information track; and two light-receiving cells that are adjacent to each other and whose boundary lines are substantially perpendicular to the information track. a second light-receiving cell pair, the first portion of the detection light beam is sized approximately equally to the two light-receiving cells of the first light-receiving cell pair, and a far-field image of the light emitting point is formed. , and a second portion of the detection light beam forms the second
A near-field image, which is a conjugate image of the light-emitting point, is formed on the boundary line of the pair of light-receiving cells. In the above configuration,
The tracking error signal is obtained as the differential output of the first pair of light receiving cells, and the focus error signal is obtained as the differential output of the second pair of light receiving cells. Therefore, the focus error signal may also be detected as the near-field image. More specifically, the focus error is detected by detecting the shift of the near-field image from a position optically equivalent to the light emitting point. In the present invention, the point light source, the light separation means, and the photoelectric detector are fixed in position with respect to each other by a fixing member having a substantially uniform coefficient of thermal expansion, and a second portion of the detection light beam is transmitted to the light separation means and the photoelectric detector. Since no extra optical elements are transmitted between the photoelectric detectors, the optical positional relationship of the photoelectric detectors with respect to the light emitting point is kept constant against temperature changes, and stable focus error detection is possible against temperature changes. It is possible.

For example, a semiconductor laser can be used as the point light source, and a half mirror or a beam splitter can be used as the light separation means. As the decentered lens, a plastic lens whose focal length is highly dependent on temperature may be used.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a schematic diagram of an embodiment of the present invention. 1st
As in the case shown in the figure, the irradiation light beam 12 emitted from the light emitting point of the point light source 11 is passed through the focusing lens system 14 to the focal point 15.
The light is focused upward to form a reading light spot which is a conjugate image of the light emitting point.

The focusing lens system 14 constitutes a light focusing means.

The reflected light from the reading light spot is focused by the focusing lens system 14 to obtain a detection light beam 17.
7 is separated from the illumination beam 12 by a beam splitter 13. The beam splitter 13 constitutes a light separating means. The first part (lower half in the figure) of the separated detection light beam 17 is converted into a second part, which is the remaining part of the detection light beam 17, by an eccentric lens 16 whose principal point is shifted to the outside of the detection light beam 17. , and forms a blurred image of the point light source 11, that is, a far-field image, on the photoelectric detector 18f:.

On the other hand, the remaining second portion of the detection light beam 17 that does not pass through the eccentric lens 16 is focused toward the conjugate image 11' of the light spot and is formed on the photoelectric detector 18. That is,
Both a near-field image and a far-field image of the point light source 11- are formed on the same surface of the photoelectric detector 18. Since the principal point of the decentered lens 16 is still outside the detection light beam 17, the far-field image and the near-field image are spatially separated.

As mentioned above, the decentered lens 16 has a lens function that converts the image on the photoelectric detector 18 by the first part from a near-field image into a far-field image, and also converts the far-field image by the first part. This also has the effect of spatially separating the near-field image from the second portion. For this purpose,
As long as the principal point of the eccentric lens 16 is outside the detection light beam 17, it may be a positive or negative lens. The principal point mentioned above is the object point position where the magnification of the conjugate image of the object point on the optical axis of the lens is 1, that is, the intersection of the optical axis and the principal plane, and in the case of a single lens. , generally called the center of the lens.

Next, focus error detection and tracking error detection will be explained in more detail. FIG. 4 shows the photoelectric detector 18
It is an enlarged view of. As shown in the figure, the photoelectric detector 1
8 is four light receiving cells 18a.

Consisting of 18b, 18C and 18d, the light receiving cell 18c
and 18d are adjacent to each other across a first boundary line 19b that is approximately parallel to the direction T in which the information track is projected, and the light receiving cells 18a and iab are adjacent to each other across a first boundary line 19b that is approximately parallel to the direction T in which the information track is projected. They are adjacent to each other with 19a in between.

When there is no focal error of the reading light spot, Fig. 4(a)
As shown in , the near-field image 20a from the second portion
is formed on the second boundary line 19a. However,
When a focus error occurs in the reading light spot, the focus error is 20a' in FIG. 4(b) or 20a' in FIG. 4(c) depending on the direction.
0d''. Therefore, by comparing the output signals of the light receiving cells 18a and 18b, it is possible to detect a focus error. Also, it is possible to detect whether the reading light spot is correctly focused. , the reading light spot is a conjugate image of the light emitting point of the point light source 11 by the focusing lens system 14, and further,
Since the near-field image 20a is a conjugate image of the reading light spot when the focusing lens system 14 is used in reverse,
The light emitting point and the near-field image 20a are at optically equivalent positions to each other. That is, for example, when a beam splitter in which the hypotenuses of two right-angled prisms are glued together with a reflective layer in between is used as the light separation means, the light emitting point and the near-field image 20a are based on the reflection of the beam splitter. They are mirror images of each other in terms of surfaces. Therefore, the point light source 11 and the photoelectric detector 18.

If the relative positional relationship with respect to the light separation means is equivalent to each other, focus error detection is extremely stable, and even if the focal length of the focusing lens system changes due to temperature changes, for example, focus error detection will not be affected. . Since the fixed member 21 has a uniform coefficient of thermal expansion, even if there is a temperature change, the beam splitter 1 of the point light source 11 and the photoelectric detector 18
The relative positional relationship with respect to 3 is kept equivalent.

On the other hand, a first portion of the detection light beam 17 is transmitted between the two light receiving cells 18C and 18 across the first boundary line 19b.
The far-field image 20b is formed so as to span approximately the same amount as d. If the center of the reading light spot deviates from the center of the information trunk due to a tracking error, the light amount distribution of the far-field image 20b becomes asymmetrical with respect to the first boundary line 19b. Therefore, by comparing the output signals of the two light-receiving cells 18C and 18d with each other, tracking errors can be detected.

0 can be detected by adding all the output signals of 18C and 18d. Effects of the Invention As described above, the present invention can detect focus errors, tracking errors, and information signals with a relatively simple configuration.
Furthermore, the conventional drawback that errors tend to occur in the detection of focus error signals due to temperature changes is significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the main parts of a conventional optical information reproducing device.
FIG. 2 is a partially enlarged view of the conventional example, FIG. 3 is a schematic diagram of the main part of an embodiment of the present invention, and FIGS. 4(a) and (b)
, (C) is a partially enlarged view of the embodiment of the present invention.0 11...point light source, 13...beam splitter, 14...focusing lens system, 15...information Record J
'Q body, 16... Eccentric lens, 18...
Photoelectric detector. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 3

Claims (1)

[Claims] a point light source, a light focusing means for focusing an irradiation light beam emitted from a generation point of the point light source onto an information recording carrier to form a light spot that is a conjugate image of the light emitting point; a light separating means for separating and extracting a detection light beam reflected from the spot and passing back through the light focusing means toward the light emitting point from the irradiation light beam between the point light source and the light focusing means; a photoelectric detector installed at or near a conjugate image position of the light emitting point where the light beam is formed at a position optically equivalent to the light emitting point; and a photoelectric detector located between the light separating means and the photoelectric detector to detect the detected light beam. A lens that is spatially divided by a dividing line substantially perpendicular to the information track of the information recording carrier and transmits only one first part and does not transmit the other second part, the principal point of which is has an eccentric lens located outside the detection light beam, and the main point light source, the light separation means, and the photoelectric detector are fixed with a fixing member having a substantially uniform coefficient of thermal expansion, and the photoelectric detector is a first pair of light-receiving cells that are adjacent to each other and whose boundaries are substantially parallel to the information track;
a second light-receiving cell pair consisting of two light-receiving cells that are adjacent to each other and whose boundaries are substantially perpendicular to the information track; A far-field image of the light-emitting point is formed across two light-receiving cells of the cell pair in approximately equal amounts, and a second portion of the detection light beam is spread over the boundary line of the second light-receiving cell pair of the light-emitting point. An optical information reproducing device characterized in that it is configured to form a near-field image that is a conjugate image.