JPH0249227A - Structure of optical head - Google Patents

Abstract

PURPOSE:To detect a focusing error state satisfactorily even when focus setting is performed by making a reflecting plane to reflect split light pass the intersection of the reflecting plane and the optical axis of the split light, and extending the split that at both sides of a straight line in parallel with a knife edge. CONSTITUTION:A photometric sensor 11 to detect each error state and recording state of focusing and tracking is arranged in the optical path of detecting light 10. The bottom plane of a prism 16 is stuck closely with the light receiving plane 13a of a photodiode 13 on a substrate 12, and polarized reflecting planes 17 and 18 which pass the P-polarized component of the detecting light 10 and reflect the S-polarized component are arranged at the inside of the prism 16 so that the end parts of them can be abutted with each other at a position to pass the optical axis of the detecting light 10. And only the S-polarized component of the detecting light 10 is bi-sected in semicircular shape in a direction intersecting orthogonally to the incident direction of the detecting light 10 setting the abutted end part 19 as the knife edge, and bi-sected light are reflected as split light 10a and 10b in a direction in parallel with the substrate 12. The split 10a and 10b pass the intersection of the reflecting planes 21 and 23 and the optical axis of each split light, and are extended at the both sides of the straight line in parallel with the abutting part 19.

Description

Detailed Description of the Invention [Objective of the Invention] <Industrial Application Field> The present invention relates to an optical head structure of an optical recording device that records and reproduces information on a recording medium, and particularly relates to an optical head structure for tracking and focusing directions of an optical head. The present invention relates to an optical head structure for optically detecting each error condition.

<Prior art> Conventionally, for example, information is recorded by irradiating the recording surface of an optical disk as a magneto-optical recording medium with relatively strong convergent light, and also by irradiating relatively weak convergent light and detecting the reflected light. There is a high-density recording/reproducing device that reproduces the above information by using the above information. The optical discs used in this device generally have some warpage or distortion, and there is eccentricity due to errors in mounting the optical disc on the rotating shaft, but the optical head can be moved to the recording track of the optical disc without being affected by these. In order to track the optical head, each error state of focus and tracking of the optical head is detected and its position is controlled.

Japanese Unexamined Patent Publication No. 63-146237 discloses an example of a structure for detecting each of the above error states.

In this structure, a pair of polarization separation films that reflect only one polarization component at right angles are provided adjacent to each other at an angle in the optical path of the detection light obtained by deflecting the reflected light from the optical disk using a beam splitter. The prism body is attached to the beam splitter so that the adjacent part, that is, the edge part of the double-width optical separation film passes through the optical axis of the detection light. Therefore, the detection light incident on this prism body is separated by only one polarization component by each polarization separation film, and is divided into two halves in the shape of a half moon at the edge, each of which is divided into two halves by a reflection light integrally provided in this prism body. The light is reflected by the surface and focused on the central boundary of a pair of two-split light-receiving elements for focus error detection.

However, in this structure, since the prism body is attached to the beam splitter, the edge between the polarization anti-polarization surfaces and the upper end of the reflection surfaces are at the same point perpendicular to the traveling direction of the detection light. However, when the optical head focuses, for example, the focus position of the head is significantly deviated. For example, if the focus of the detection light is significantly in front of the light receiving element, the polarization separation film In some cases, the half-moon-shaped split light reflected by the lens does not fall within the reflecting surface, and it is not possible to appropriately detect a focus error state.

In addition, in the above structure, when the focus position is optimal, each divided light is irradiated so that the central boundary of the two-divided light receiving element for focus error detection becomes the focal position, but this boundary is actually Since there is a gap, if the detection light is concentrated in this gap, a large error will occur when the light receiving element for focus error detection detects the light intensity of one polarization component, especially in magneto-optical recording devices. There is a problem when reading information based on the light intensity of the double-width light component of the detection light, as in the above example.

<Problems to be Solved by the Invention> In view of the problems of the prior art, the purpose of the present invention is to:
It is an object of the present invention to provide an optical head structure that is small and lightweight, and that can suitably detect a focus error state even during focus pull-in.

A second object of the present invention is to provide an optical head structure that can suitably detect a focus error state without hindering information reading.

<Means for Solving the Problems> According to the present invention, an optical head structure is provided for optically detecting each error state in the tracking and focusing directions of an optical head. a first light-receiving element disposed in the optical path of convergent detection light to detect either one of the error states; a second light-receiving element provided therein; a means for dividing the detected light into a semicircular portion using a knife means and changing the direction of the divided light; and a means for reflecting the divided light toward the second light-receiving element. The present invention is achieved by providing an optical head structure having means, wherein the reflecting surface of the reflecting means extends in all directions centering on the optical axis of the split light.

A second object of the present invention is to provide an optical head structure for optically detecting an error state in the focusing direction of an optical head, which includes means for converting detection light into convergent non-parallel light, and The optical axis of the non-parallel light is at a non-focal position in the optical path of the non-parallel light and the optical axis of the non-parallel light is oriented to one side so that the difference in the amount of received light changes as the size of the light image changes. It is characterized by comprising a pair of light receiving means provided adjacent to each other at offset positions, and means for detecting the focus error state by comparing the difference in the amount of light received by the two light receiving means with a predetermined value. This is achieved by providing an optical head structure that achieves this.

<Function> By doing this, the reflecting surface of the means for reflecting the detection light toward the focus error detection light receiving element becomes larger.
Since the light does not deviate from the reflective surface, it is possible to suitably detect a focus error state even when the optical head is being focused. In addition, a pair of light receiving means for detecting focus errors of the optical head are arranged so that the difference in the amount of light received differs depending on the size of the image of the detection light at the non-focal position of the detection light, and this difference is compared with a predetermined value. By doing so, it is possible to suitably detect a focus error state without affecting reading of information.

<Embodiments> Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing the main parts of an optical head to which the present invention is applied. A polarizing beam splitter 2, a collimator lens 4, and an objective lens 7 are provided, and the output light 5 that has passed through these is irradiated onto a magneto-optical disk 6. Here, the polarizing beam splitter 2 has a polarizing reflecting film 2a provided at a diagonal position, and the film totally reflects the S-polarized component of the light incident on the polarizing beam splitter 2, and also partially reflects the P-polarized component. part is reflected and the rest is passed through. Furthermore, the collimator lens 4 has a circular outline and is configured to shape the emitted light 5 from the semiconductor laser 1 from an elliptical cross section to a circular cross section.

The emitted light 5, which has been converged by the objective lens 7, is reflected by the recording surface 8 of the magneto-optical disk 6, and enters the polarizing beam splitter 2 as reflected light 9 in a direction opposite to that described above.

Here, since the polarization plane of the reflected light 9 from the recording surface 8 is rotated, the polarized light reflection film 2a in the polarized beam splitter 2 causes part of the P-polarized light component of the reflected light 9 and The S-polarized light component is emitted from the right side of FIG. 1 as detection light 10.

A photometric sensor 11 is disposed in the optical path of the detection light 10 to detect each error state of focus and tracking and the state of magneto-optical recording. Further, a λ/2 plate 3 is interposed between the polarizing beam splitter 2 and the photometric sensor 11, and this plate adjusts the ratio of the two-width light components of the detection light 10 incident on the photometric sensor 11 to a predetermined value. It is for adjusting to.

In this embodiment, each of the above-mentioned elements is arranged in the optical path of the emitted light 5 that is a straight line from the semiconductor laser 1 to the optical disk 6, but in reality, this optical path can be freely changed by arranging a mirror or the like. Needless to say, you can get it.

FIG. 2 is a sectional view of the photometric sensor 11 taken along the axial direction, and FIG. 3 is a sectional view taken along the line I-II in FIG. The substrate 12 of the photometric sensor 11 includes a photodiode 13 as a light receiving element for tracking error detection located on the optical axis of the detection light 10, and a predetermined distance from the photodiode up and down in FIG. 74- Photodiodes 14 and 15 as light-receiving elements for detecting a cass error are arranged on the light-receiving surfaces 13a and 14 of each photodiode.
a and 15a are integrally fixed to each other so as to be located on the same plane.

As shown in FIG. 3, each of these photodiodes 13 to 15 is constituted by a photodiode element divided into four by mutually orthogonal dividing lines. The photodiode 13 is arranged such that one dividing line runs along a direction perpendicular to the direction in which the optical axis shifts when a tracking error occurs in the detection light 7, and the photodiode 14 has one dividing line along the direction perpendicular to the direction in which the optical axis shifts when a tracking error occurs in the detection light 7. No. 13 is arranged so as to be located on an extension line of the above-mentioned dividing line. Note that in this embodiment, each of the diodes 13 to 15 is divided into four parts, but in reality, it is sufficient if it is divided into two or more.

As shown in FIG. 2, the photodiode 13 on the substrate 12
The bottom surface of the cubic prism body 16 is in close contact with the light receiving surface 13a. Inside the prism body 16, there are polarized light reflecting surfaces 17 and 18 that pass the P88 light component of the detection light 10 and reflect the S-polarized light component, and their ends touch each other at a position passing through the optical axis of the detection light 10. They are installed at an angle so that they touch each other.

This abutting end 19 is used as a knife to detect S of the detection light 10.
Only the polarized light component is divided into two halves in a half-moon shape in a direction perpendicular to the direction of incidence of the detection light 10, and is reflected as divided lights 10a and 10b in a direction parallel to the substrate 12, that is, in the vertical direction in FIG. There is.

The reflected light 10a, 10b is transmitted to the light receiving surfaces 14a, 15a of the photodiode 14.15.
The bottom surface of a prism body 20.22 in the form of a triangular prism having a reflective surface 21.23 is in close contact with the prism body 20.22 in order to change the direction toward 5. The prism bodies 20, 22 are also in close contact with the prism body 16 on their side surfaces. For example, the substrate 12
The lower portions of the prism bodies 16, 20, 22 are fixed to the substrate 12 by filling the inside of the concave portion 12a with a resin mold.

In this way, the P-polarized component of the detection light 10 is directly focused on the photodiode 13, and a pair of half-moon-shaped split lights 10a and 10b consisting of the S8 light component are transmitted to the prism body 20.2.
The light is reflected by the reflective surfaces 21 and 23 of the photodiodes 14 and 23, and is focused on approximately the middle of each of the photodiodes 14 and 15, which are each divided into four parts. Note that each of the photodiodes 13 to 15 is electrically connected to a control circuit via a lead wire (not shown) extending from the substrate 12.

Here, for example, when the focus position of the divided beams 10a and 10b shifts to the front side in the traveling direction of the divided beams and comes to a focus in front of the reflecting surface 21.23 when the optical head is focused, the divided beams' The images of 10a and 1ob are inverted and reach the reflective surface 21.23, but within the movement range of the optical head in the focus direction, the reflective surface 21.23 is
In order to ensure that the divided beams 10a and 10b fall within the plane,
It extends on both sides of a straight line that passes through the intersection of each reflective surface and the optical axis of each split light and is parallel to the abutting end 19 as a knife. Therefore, each photodiode 13
．． The divided beams 10a and 10b can be suitably reflected toward the beam 14.

Next, the method of detecting each error in tracking and focusing by each of the photodiodes 13 to 15 will be explained.

As shown in FIG. 4, detection signals E-H corresponding to each irradiation pattern are transmitted from each photodiode element (e, f, g, h) of the four-division photodiode 13 to (E0F) and (G
+H) and are input to each amplifier 24.25, respectively, and the output value from each amplifier 24.25 is input to an amplifier 26. And amp 2
6, subtract (G+H> from (E0F>) and calculate the operation n
The value is output to the control circuit. Here, each photodiode element of the photodiode 13 has a P of the detection light 10.
The polarized light components are focused in a circle as shown by the imaginary line, and if a tracking error occurs, there will be a difference in brightness between the left and right diode elements. Quantity can be easily detected.

On the other hand, as shown in FIG.
4, the corresponding output signals A-D from each diode element (a, b, c, d) are (A0S> and (C0D)
The output values from each amplifier 27 and 28 are inputted to an amplifier 29, respectively. Then, the amplifier 29 subtracts (C+D> from (A+B)) and outputs the calculated value to the control circuit.

As shown in FIG. 5, the polarization reflecting film 17 of the prism body 16
The divided light 10a consisting of the S-polarized component of the detection light 10 whose direction has been changed at It is irradiated like a eggplant. At this time, the divided light 10a is transmitted to each diode element of the 4-split photodiode 14 in such a way that the sum of their output values (A+8> and (C+D>) are equal to each other, and the optical axis is on the side of diode elements c and d. The light is irradiated in a biased position.

If a focus error occurs, either (A+B) or (C+D> becomes larger, as shown by the imaginary line V or W in FIG. Direction and error amount can be easily detected.

Similarly, the output signals of each diode element (i, j, k, 1) of the four-division photodiode 15 (I+
J) and (K0L), and from the output signal (I0J), (K
10L) may be subtracted to detect the focus error.
The focus error may be detected by calculating both (A0B) - (C0D) and (I+Ji (K+L)).Furthermore, the tracking error may be determined by (A10B) - (C0D) and (I+Ji (K+L)).
10+G+H+J10K>), and in this case, the tracking error state can always be suitably detected regardless of the ratio of the two-width light components of the detection light 10.

Incidentally, the read signal is from the detection signal A-L of the diode elements a to 1 of each photodiode 13 to 15 (E1F1G
It can be detected by calculating +1> to 10F+>-(A+B10±D+IfJ10).

According to this embodiment, since the photodiodes for detecting errors in focus and tracking are provided on one substrate, wiring to the photodiodes is simplified, and noise resistance can be improved. Since the tip shaft adjustment only needs to be done in one place, it has the effect of shortening the adjustment time.

[Effects of the Invention] As described above, according to the present invention, the reflective surface of the means for reflecting the detection light toward the focus error detection light receiving element becomes large, and the light does not deviate from the reflective surface, so that the optical head It is possible to suitably detect a focus error state even during focus pull-in. Furthermore, by bringing the deflecting means and the reflecting means into close contact with the light receiving surface of the light receiving element, the components can be made smaller and their position adjustment can be simplified. Furthermore, a pair of light receiving means for detecting a focus error of the optical head is arranged at a non-focus position of the detection light so that the difference in light reception varies depending on the size of the image of the detection light, and this difference is compared with a predetermined value. By doing so, it is possible to suitably detect a focus error state without affecting reading of information. From the above, the effects of the present invention are extremely large.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of main parts showing an optical head to which the present invention is applied. FIG. 2 is a cross-sectional view of the photometric sensor in the optical head shown in FIG. 1 along the axial direction. FIG. 3 is a sectional view taken along the line ■--■ in FIG. 2. FIG. 4 is a schematic circuit diagram showing how to detect a tracking error. FIG. 5 is a schematic circuit diagram showing a focus error detection procedure. 1... Semiconductor laser 2... Polarizing beam splitter 3... λ/2 plate 4... Collimator lens 5... Outgoing light 6... Magneto-optical disk 7.
...Objective lens 8...Recording surface 9...Reflected light
10...Detection light 10a, 10b-...Divided light 11...Photometry sensor 12...Substrate 12a...
Concave portions 13 to 15...Photodiodes 13a, 14a, 15a...Light receiving surface 16...Prism body 17.18...Polarized light reflecting surface 19
...Abutting end portion 20.22...Prism body 21
．． 23... Reflective surface 24-29... Amplifier

Claims (5)

[Claims] (1) An optical head structure for optically detecting each error state in the tracking and focusing directions of the optical head, and an optical path of detection light that is converged to detect either of the error states. a second light-receiving element arranged in parallel with the first light-receiving element to detect the other of the error states; and a knife-edge means to detect the detected light. means for dividing the semi-moon-shaped portion from the surface and changing the direction of the divided light; and means for reflecting the divided light toward the second light-receiving element; The optical head structure is characterized in that the optical head structure extends on both sides of a straight line that passes through the intersection of the split beam and the optical axis of the split light and is parallel to the edge of the knife edge means. (2) A third light-receiving element is provided in parallel on a side opposite to the second light-receiving element, sandwiching the first light-receiving element; comprising a polarizing beam splitter having a pair of polarized light reflecting surfaces that deflect the light into a pair of half-moon-shaped split lights in mutually opposite directions; The optical head structure according to claim 1, comprising a pair of reflecting means for reflecting the split light. (3) The light-receiving elements are arranged such that their light-receiving surfaces are located on the same plane, and the deflection means and the reflecting means are in close contact with the light-receiving surfaces of the corresponding light-receiving elements. An optical head structure according to claim 1 or 2. (4) An optical head structure for optically detecting an error state in the focus direction of the optical head, comprising means for converting detection light into converging non-parallel light, and a size of an image of the non-parallel light changing. They are provided adjacent to each other at a non-focal position in the optical path of the non-parallel light and at a position where the optical axis of the non-parallel light is biased to either side, so that the difference in the amount of light received by the non-parallel light changes. 1. An optical head structure comprising: a pair of light-receiving means, which are arranged in the same direction; and means for detecting an error state of the focus by comparing a difference in the amount of light received by the two light-receiving means with a predetermined value. (5) A means for dividing the convergent light into a half-moon shape using a knife-edge means, and a means for reflecting the divided light toward both the light receiving means, and a reflecting surface of the reflecting means is connected to the reflecting surface. The optical system according to claim 4, wherein the optical system extends on both sides of a straight line that passes through the intersection of the split light with the optical axis and is parallel to the edge of the knife edge means. head structure.