JPH0264917A - Optical head structure for magneto-optical recorder - Google Patents

Abstract

PURPOSE:To reduce the number of parts, to make a magneto-optical recording device small in size and light in weight and to easily position the respective constituting parts by unifying a polarizing separating means and a dividing means. CONSTITUTION:A polarizing beam splitter 2 has a polarizing reflecting film 2a, which is provided in a diagonal position. Then, by this film, the whole S-polarizing component of a light to be incident to the polarizing beam splitter is reflected and one part of an S-polarizing component is reflected. The remaining part of the S-polarizing component is passed through. Namely, the polarizing separating means to separate the detecting light to the respective polarizing components and the means to divide one part of the separated detecting light in order to use it for focus error detection, for example, can be unified. Thus, the number of the parts in an optical head is reduced and optical axis control, etc., is made easy.

Description

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

<Prior art> Conventionally, information has been recorded by irradiating relatively strong convergent light onto the recording surface of a magneto-optical disk as a magneto-optical recording medium, and also by irradiating relatively weak convergent light and carving out the reflected light. There is a magneto-optical recording/reproducing device that reproduces the above information by detecting a rotation angle.

The magneto-optical disk used in this device generally has some warpage or distortion, and there is eccentricity due to errors in mounting the magneto-optical disk on the rotating shaft. In order to make the optical head follow the recording track of the magnetic disk, each error state in focus and tracking of the optical head is detected and its position is controlled. An example of the configuration is shown in FIG.

In FIG. 6, output light 31 is emitted from a semiconductor laser (not shown) as a light source and is parallelized and shaped into a circular cross section. The output light 31 passes through a polarizing beam splitter 32 and passes through an objective lens 33. The magnetic disk 34 is irradiated with light. Then, the light is reflected on the recording surface of the disk, passes through the objective lens 33 in the opposite direction, and then enters the polarizing beam splitter 32 again. At this time, the magneto-optical disk 34
Since the plane of polarization of the light reflected from the is rotated, a part of the P-polarized light component and the S-polarized light component are reflected by the polarized light reflection film in the polarizing beam splitter 32, and the reflected light is transmitted from the right side of the figure as the detection light 35. Emits light.

The detection light 35 enters a polarization beam splitter 36, and the splitter converts the error detection light 3 consisting only of the P polarization component.
7, and information detection light 38 consisting of a part of the P-polarized light component and the S-polarized light component.

The error detection light 37 is converted into convergent light by a condensing lens 39, and then split into two by a half prism 40, one of which travels straight and focuses on a photometric sensor 42 for focus error detection via a knife lens 41. The other light is reflected and sent to the photometric sensor 4 for tracking error detection.
Focus the light on 3. And each of these photometric sensors 42.4
3, tracking and focusing errors are detected, and the objective lens 33 is driven and corrected according to the amount of error.

Further, the information detection light 38 passes through a λ/2 plate 44 for adjusting the ratio of both width light components, is converted into convergent light by a condensing lens 45, and is then converted into convergent light by a polarizing beam splitter 46.
The light is divided into a P-polarized component and an S-polarized component, each focused on a photometric sensor 47.48, and the information recorded on the magneto-optical disk 34 is read based on the difference in the amount of light received by both sensors 47.48. .

In this way, since the above structure is composed of a large number of optical parts, and the fixed frame that holds the optical head is also large, there is a problem that the optical head as a whole becomes larger and heavier. was there. Furthermore, there is a problem in that the work involved in assembling each part is complicated, and highly accurate optical axis adjustment is difficult.

<Problems to be Solved by the Invention> In view of the problems of the prior art, the main purpose of the present invention is to reduce the number of parts, reduce the size and weight, and facilitate the positioning of each component. An object of the present invention is to provide an optical head structure for a magneto-optical recording device.

[Structure of the Invention] <Means for Solving the Problems> According to the present invention, the object is to detect each error state in the tracking and focusing directions of the optical head using the detection light reflected from the magneto-optical recording medium. An optical head structure for a magneto-optical recording device for reproducing information, the optical head structure comprising: a first light receiving means disposed in an optical path of the detection light; polarized light separating means for passing through the light receiving means and reflecting the other polarized light component in different directions; means for splitting the reflected light into two different directions at the edge; and a third light receiving means arranged in the other optical path of the divided reflected light, wherein the polarized light separating means and the dividing means are integral with each other. This is achieved by providing an optical head structure for a magneto-optical recording device characterized by the following.

<Function> In this way, by integrating the polarization separation means for separating the detection light into each polarization component and the means for dividing a part of the separated detection light for use, for example, in focus error detection, The number of parts in the optical head is reduced, and optical axis adjustment becomes easier.

<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 thereof, and the polarizing beam splitter 2
The S-polarized light component of the incident light is totally reflected, a part of the P-polarized light component is reflected, and the rest is passed through.

In addition, the collimator lens 4 has a circular outline,
The emitted light 5 from the semiconductor laser 1 is shaped 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 plane of polarization of the reflected light 9 from the recording surface 8 is rotated, the P(Iff light component) of the reflected light 9 is affected by the polarization reflection film 2a in the polarization beam splitter 2, as described above. The S-polarized light component and the S-polarized light component are emitted from the right side of FIG. 1 as detection light 10.

A photometric sensor 11 is arranged 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 cross-sectional view of the photometric sensor 11 taken along the axial direction, and FIG. 3 is a cross-sectional view taken along the line ■--■ 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. The photodiodes 14 and 15 as light-receiving elements for focus error detection are arranged on the light-receiving surfaces 13a and 14a of each photodiode.
, 15a are integrally fixed to each other so as to be located on the same plane.

The photodiodes 13 and 14 are as shown in FIG.
It is composed of photodiode elements divided into four parts by dividing lines perpendicular to each other.

One of the dividing lines of the photodiode 13 is the detection light 7
The photodiode 14 is arranged so as to be perpendicular to the direction in which the optical axis shifts when a tracking error occurs, and the photodiode 14 is arranged so that one of its dividing lines is located on an extension of the dividing line of the photodiode 13. There is. Further, the photodiode 15 is divided into two by a dividing line located on an extension of the dividing line of the photodiode 13 .

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 this prism body 16, in the diagonal direction, there is a polarization separation film 17 that allows the P polarized light component of the detection light 10 to pass to the right side of the figure and reflects the S polarized light component as separated light 18 toward the bottom of the figure. It is provided. Further, on the lower surface of the prism body 16, there is a reflective film 20 that reflects half of the luminous flux of the λ/4 plate 1 sheet metal 9 separated light 18 as divided light 18b in the opposite direction, that is, toward the polarization separation film 17 again. are placed in close contact with each other. Here, divided light 18 having a half-moon shape is divided by using the end of the reflective film 20 as a knife.
Since b passes through one λ/4 plate and one sheet metal nine times, only the P-polarized light component is present and is not reflected by the polarization separation film 17 and is transmitted to the substrate 12.
It passes parallel to the top of the figure.

The light-receiving surfaces 14a and 115a of the photodiodes 14 and 15 are provided with divided beams 18a and 18b of the separated light 18 that are not reflected by the reflective film 20, respectively, to be directed toward the photodiodes 14 and 15. reflective surface 22
．． The bottom surfaces of the prism bodies 21 and 23 which form a triangular prism having 24 and 24 are in close contact with each other. The prism bodies 21, 23 are also in close contact with the prism body 16 on their side surfaces. The lower portions of the prism bodies 16, 21, and 23 are fixed to the substrate 12 by, for example, filling the concave portion 12a of the substrate 12 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 18a and 18b consisting of the S-polarized component are transmitted to the prism body 21.2.
The light is reflected by the reflective surfaces 22 and 24 of the 4-split photodiode 14 and the 2-split photodiode 15, respectively, and is focused on approximately the middle of the 4-split photodiode 14 and the 2-split photodiode 15, respectively. In addition, each photodiode 13 to 1
5 is electrically connected to a control circuit via a lead wire (not shown) extending from the substrate 12.

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, from each photodiode element (e, f, q, h) of the four-division photodiode 13, the detection signal E-H corresponding to each irradiation pattern is expressed as (E0F> and (
The output values from the amplifiers 25 and 26 are input to the amplifier 27, respectively. Then, the amplifier 27 subtracts (G+H) from (E1F) and outputs the calculated value to the control circuit. Here, on each photodiode element of the photodiode 13, the P-polarized component of the detection light 10 is focused in a circular shape as shown by the imaginary line.
When a tracking error occurs, a difference in light amount occurs between the left and right sides of the figure, so the direction of the tracking error and the error position can be easily detected using the above-mentioned calculated values.

On the other hand, as shown in FIG.
4, the corresponding output signals A-D from each diode element (a, b, c, d) are (A + B> and (C + D)
The signal is input to each amplifier 28 and 29 so as to be divided into two parts, and the output value from each amplifier 28 and 29 is further input to an amplifier 30. Then, the amplifier 30 subtracts (C+D) from (A+8>) and outputs the calculated value to the control circuit.

As shown in FIG. 5, the polarization reflecting film 17 of the prism body 16
S(
! The half-moon-shaped divided light 18a composed of the i-light component is irradiated onto the light-receiving surface 14a of the four-part photodiode 14 by the reflecting surface 22 of the prism body 21 in a half-moon shape as shown by the imaginary line U. At this time, the divided light 18a is applied to each diode element of the 4-split photodiode 14 so that the sum of the output values (A+B> and (C10) are equal to each other).
The light is irradiated so that its optical axis is biased toward the diode elements c and d. Here, if a focus error occurs, either (A + B) or (C + D) will become larger, as shown by the imaginary line V or W in Fig. 5, so the focus will be adjusted according to the above calculated value. The direction of the error and the extent of the error can be easily detected.

Here, in this embodiment, since the focus error is detected at a position before the focal position, the optical path length of the divided light 18a can be shortened.

Incidentally, the tracking error state is determined by (A+D+E+F+
It may be detected by calculating I)-(B10+G+H+J). 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. In addition, the read signal is calculated from the detection signal A-J of the diode elements a-j of each photodiode 13 to 15 to (E1F+G1H)-(A10B0C+[)+
It can be detected by calculating IJ).

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 also has the effect of shortening the adjustment time.

[Effects of the Invention] As described above, according to the present invention, there is provided a polarization separation means for separating detection light into each polarization component, and a means for dividing a part of the separated detection light for use, for example, in focus error detection. By integrating the optical head, the number of parts of the optical head is reduced and optical axis adjustment becomes easier. Furthermore, by bringing the polarized light separating means and dividing 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 further simplified. 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 the focus error detection procedure. FIG. 6 is a schematic diagram of main parts showing the structure of a conventional optical head for a magneto-optical disk. 1... Semiconductor laser 2... Polarizing beam splitter 2a... Polarizing reflective film 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 11...Photometric sensor 12...Substrate 12a...Concave portion 13
~15... Photodiodes 13a, 14a, 15a... Light receiving surface 16... Prism body 17... Polarization separation film 18.
...Separated light 18a, 'l, 8 b...Divided light 19...λ/4 20...Reflection film 21.23
... Prism body 22.24... Reflective surface 25-30... Amplifier 31
... Output light 32 ... Polarization beam splitter 33 ... Objective lens 34 ... Magneto-optical disk 3
5...Detection light 36...Polarization beam splitter 37...Error detection light 38...Information detection light 39.
...Condensing lens 40...Half prism 41...
・Naifetsuji 42.43...Photometric sensor 44...
・λ/2 plate 45...Condensing lens 46...Polarizing beam splitter 47.48...Photometry sensor

Claims (4)

[Claims] (1) An optical head structure for a magneto-optical recording device for detecting error states in the tracking and focusing directions of an optical head using detection light reflected from a magneto-optical recording medium and reproducing information, the detection light comprising: a first light receiving means arranged in the optical path of the detection light; a polarization separating means for passing one polarized light component of the detection light to the first light receiving means and reflecting the other polarized light component in a different direction; means for splitting the light into two different directions at an edge; and a second splitter disposed within one optical path of the split reflected light.
a third light receiving means disposed within the other optical path of the divided reflected light;
An optical head structure for a magneto-optical recording device, characterized in that the polarization separation means and the division means are integral with each other. (2) The magneto-optical recording according to claim 1, wherein the splitting means reflects the one split light in a direction that crosses the polarization separation means via a compensating plate. Optical head structure for equipment. (3) Each of the light receiving means is arranged such that their light receiving surfaces are located on the same plane, and the polarization separating means and the dividing means are in close contact with the light receiving surface of each of the light receiving means. Claim 1 or 2
The optical head structure for a magneto-optical recording device as described in 2. (4) A means for converting at least one of the split beams into a converging non-parallel beam, which receives the non-parallel beam among the second and third light receiving means and detects the focus error state. The light receiving means on the detecting side is located at a non-focal position within the optical path of the non-parallel light so that the difference in the amounts of received light changes as the size of the image of the non-parallel light changes. It consists of a pair of light-receiving elements that are provided adjacent to each other at positions where the optical axis of non-parallel light is biased to one side, and the focus is determined by comparing the difference in the amount of light received by both of the light-receiving elements with a predetermined value. An optical head structure for a magneto-optical recording device according to any one of claims 1 to 3, characterized in that an error state is detected.