JPH02193347A - Optical head structure for magneto-optical recorder - Google Patents

Abstract

PURPOSE:To miniaturize constitution components by separating respective polarized components of detected light into two directions, detecting a tracking error with one polarized light component, splitting the other polarized component into a couple of crescent shapes to detect a focus error. CONSTITUTION:A couple of polarized light separation films 18a, 18b reaching the optical axis of a detected light 10 are arranged in the inside of a prism 15 in parallel with a step. The P polarized light component of the detected light 10 passes through the films 18a, 18b and irradiates the light receiving face 16a of a photo diode 16. The S polarized component of the detected light 10 is reflected in the films 18a, 18b, split as separated lights 19a, 19b of different optical lengths in a crescent form and irradiates the light receiving face 17a of the photo diode. The diode 16 is bisected by a split line intersecting orthogonally with the optical axis of the detected light 10 and a tracking error is detected. Moreover, the diode 17 is quadripartitioned in a direction along the optical axis of the detected light 10 and a focus error is detected. Then the information of the recording face is read by comparing both polarized components.

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 tracking and focusing directions of an optical head. 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 is recorded by irradiating the recording surface of a magneto-optical disk as a magneto-optical recording medium with relatively strong convergent light, and also by irradiating relatively weak convergent light and performing Kerr rotation of the reflected light. There is a magneto-optical recording and reproducing device that reproduces the above information by detecting corners. 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 of focus and tracking of the optical head is detected and its position is controlled. An example of the configuration is shown in Section 8.
As shown in the figure.

In FIG. 8, emitted light 32 emitted from a semiconductor laser 31 as a light source is collimated by a collimator lens 33, shaped into a circular cross section by a shaping prism 34, and then sent to a first polarizing beam splitter. 35 and is irradiated onto a magneto-optical disk 37 via an objective lens 36. Then, it is reflected by the recording surface of the disk, and is reflected by the objective lens 3.
6 in the opposite direction, it enters the first polarizing beam splitter 35 again. At this time, since the polarization plane of the reflected light from the magneto-optical disk 37 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 polarized beam splitter 35, and the detected light is The light is emitted from the right side of the figure as 38.

The detection light 38 enters a second polarization beam splitter 39, where it is divided into an error detection light 40 consisting only of the P polarization component and an information detection light 41 consisting of a part of the P polarization component and an S polarization component. be divided.

The error detection light 40 is converted into convergent light by a condensing lens 42, and then split into two by a half prism 43, one of which travels straight and focuses on a photometric sensor 45 for focus error detection via a knife lens 44. The other light is reflected and sent to the photometric sensor 4 for tracking error detection.
The light is focused on 6. And each of these photometric sensors 45.4
6, tracking and focus errors are detected, and the objective lens 36 is driven and corrected according to the amount of error.

Further, the information detection light 41 passes through a λ/2 plate 47 for adjusting the ratio of both polarization components, is changed into convergent light by a condensing lens 48, and is then converted into a convergent light by a third polarization beam splitter 49. The light is divided into a polarized light component and an S-polarized light component, each focused on a photometric sensor 50.51, and the information recorded on the magneto-optical disk 37 is read based on the difference in the amount of light received by both sensors 50.51.

As described above, the above-mentioned structure is composed of a large number of optical parts, and the fixed frame for holding the optical head is also enlarged, so there is a problem that the optical head as a whole becomes larger and heavier. Furthermore, the assembly of each component and the wiring work become complicated, and there is a problem that highly accurate optical axis adjustment becomes 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, make it smaller and lighter, and facilitate the positioning and wiring 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; a pair of polarization separation means arranged in the optical path of the detection light to transmit the detection light toward the light reception means, reflect the other polarization component in different directions, and divide it into a pair of half-moon-shaped parts;
a second light receiving means disposed within the optical path of one portion of the divided reflected light; and a third light receiving means disposed within the optical path of the other divided portion of the reflected light. , achieved by providing an optical head structure for a magneto-optical recording device, characterized in that the optical path length of one part of the reflected light and the optical path length of the other part of the reflected light are set to different lengths. be done. In particular, the pair of polarization separation means includes a polarization beam splitter having a pair of polarization planes spaced apart from each other along the optical path of the detection light,
Preferably, the light receiving means are arranged such that their light receiving surfaces are located on the same plane, and the polarizing beam splitter is in close contact with the same plane.

<Operation> In this way, a tracking error can be detected by one polarization component of the detection light that passes through the polarization separation means, and the other polarization component reflected by the pair of polarization separation means By dividing the light into two parts and reaching the light receiving means with different optical path lengths, it is possible to detect focus errors in the same way as the Naifetsu method, and by combining the semicircular parts of one polarized light component and the other polarized light component. By comparing the two, the Kerr rotation angle can be detected and information on the magneto-optical recording medium can be read. Further, the light receiving surfaces of each light receiving means are located on the same plane, and a polarizing beam splitter having a pair of polarizing planes spaced apart from each other along the optical path of the detection light is brought into close contact with the same plane. This allows the light receiving section to be made more compact.

<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 collimator lens 3 for shaping the parallel light 2 and a shaping prism 4 for shaping the parallel output light 2 into a circular cross section are provided. Detection light 2 passing through shaping prism 4
In the optical path, there is a polarizing beam splitter 5 and an objective lens 6.
are arranged in this order, and the emitted light 2 that passes through these and becomes convergent light with a circular cross section is directed to the recording surface 8 of the magneto-optical disk 7.
is irradiated. Here, the polarization beam splitter 5 has a polarization separation film 5a provided at a diagonal position, and the polarization separation film 5a separates all of the S polarization component and the P polarization component of the light incident on the polarization beam splitter 5. A portion of the P-polarized light component is reflected, and the rest of the P-polarized light component is passed through.

The emitted light 2 that has become converged by the objective lens 6 is reflected by the recording surface 8 of the magneto-optical disk 7 and enters the polarizing beam splitter 5 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, a 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.

In the optical path of the detection light 10, a λ/2 plate 11 attached to the output surface of the detection light 10 of the polarizing beam splitter 5, a condenser lens 12, and a photometric sensor 13 are placed at predetermined positions in this order. It is arranged.

The above-mentioned λ/2 plate 11 is for adjusting the ratio of both polarization components of the detection light 10 incident on the photometric sensor 13 to a predetermined value.

Note that the arrangement of each optical element is not limited to this example.
In reality, it goes without saying that the optical path can be freely changed by arranging a mirror or the like.

FIG. 2 is a cross-sectional view of the photometric sensor 13 along the axial direction.
5, a substrate 14a disposed at a distance from the bottom surface of the prism body 15 on the optical axis of the detection light 10, and a substrate 14a disposed at a distance from the side surface of the prism body 15 on the axis perpendicular to the optical axis of the detection light 10. It has a substrate 14b disposed at a distance.

A photodiode 16 as a light receiving element for detecting a tracking error is fixed to one substrate 14a, and a photodiode 17 as a light receiving element for detecting a focus error is fixed to the other substrate 14b.

As shown in FIG. 2, inside the prism body 15, a pair of polarization separation films 18a and 18b extending from a pair of diagonally located corners to the optical axis of the detection light 10 are arranged parallel to each other. And they are arranged at different levels. polarization separation film 18a,
Reference numeral 18b indicates that the P-polarized component of the detection light 10 passes to the right side of the figure, and the S-polarized component is reflected toward the bottom of the figure as separated beams 19a and 19b. The P-polarized component of the detection light 10 passes through the light separation films 18a and 18b on both sides and is irradiated onto the light receiving surface 16a of the photodiode 16 in a circular shape. Using the edges of the optical axis side of the detection light 10 of the double-sided light separation films 18a and 18b as a splitting means and in the same manner as the Knifezi method, each separated light 19a and 19b is split into a half-moon shape and received by the photodiode 17. It is designed to irradiate the surface 17a.

As shown in FIGS. 2 and 3, the photodiode 16 is composed of a photodiode element eSf that is divided into two by a dividing line perpendicular to the optical axis of the detection light 10, and the dividing line is the detection light. The optical axis is perpendicular to the direction in which the optical axis shifts when a tracking error occurs. The photodiode 17 receives the detection light 10 as shown in FIG.
It is composed of photodiode elements aSb and cSd that are divided into, for example, four at equal intervals along the optical axis of the
The knife edge of the separated light 19a is located on the dividing line between the pair of photodiode elements a and b on the right side of the figure, and the edge of the pair of photodiode elements c and d on the left side of the figure Separated light 1 on the dividing line
The knife edge of 9b is located.

In this way, the P-polarized component of the detection light 10 is directly focused on the photodiode 16, and a pair of half-moon-shaped separated lights 19a and 19b consisting of the S-polarized component are transmitted to the left and right pairs of the four-split photodiode 17. diode element aSb
, c, and d. Note that each photodiode 16 and 17 is electrically connected to a control circuit via a lead wire (not shown) extending from the substrate 14.

Next, the procedure for detecting each error in tracking and focusing by each photodiode 16 and 17 will be explained.

As shown in FIG. 3, detection signals ESF corresponding to each irradiation pattern are manually inputted to the amplifier 21 from each of the photodiode elements e and f of the two-part photodiode 16. And at 1 amp 21 (E - F)
The calculated value is output to the control circuit. Here, the detection light 1 is placed on the photodiode 16.
The circular P-polarized light component of 0 is equally focused on each photodiode element e and f as shown in the figure, and if a tracking error occurs, a difference in sight will occur between the left and right sides of the figure. Therefore, the direction and amount of tracking error can be easily detected using the above-mentioned calculated values.

On the other hand, as shown in FIG.
7, each diode element aSb,c.

d, its corresponding output signals A-D are A, B and C
and D, respectively, are input to each amplifier 22 and 23, and become (B-A) at the amplifier 22, and the amplifier 2
3, the output values from each amplifier 22 and 23 are manually inputted to the amplifier 24. Then, at the amplifier 24 (B-
A) and (CD) are added and the calculated value is output to the control circuit. By the way, separated lights 19a and 19 composed of S-polarized light components whose directions are changed and divided by the polarization separation films 18a and 18b of the prism body 15 and each form a half-moon shape.
b is on the light receiving surface 17a of the 4-split photodiode 17,
As shown in FIG. 4, one of each pair of left and right diode elements is irradiated in a half-moon shape. Here, if a focus error occurs, it will become as shown in the broken line or imaginary line in Fig. 4, and in the case of the broken line (B
+C) gives a positive value, and in the case of an imaginary line (-A-
Since D) results in a negative value, it is possible to easily detect a focus error using the above-mentioned calculated value.

Further, the read signal is converted from the detection signal A-F of each diode element a-f of each photodiode 16.17 to (A+
It can be detected by calculating B + C + D) - (E + F).

As described above, according to this embodiment, by simply separating the detection light 10 into two directions for each polarization component, it is possible to detect each error in focus and tracking, and (1) to detect the Kerr rotation angle for information reading. This simplifies the configuration of the optical head. In this embodiment, by arranging the pair of polarization separation films 18a and 18b at intervals along the optical path of the detection light, the respective optical path lengths of the separated lights 19a and 19b are made to be different. However, both sides of the light separation film 1
8a and 18b may be arranged on the same plane, and the diode elements a and b and C and d of each pair of the photodiode 17 may be provided at different levels from each other.

FIG. 5 is a diagram similar to FIG. 1 showing the second embodiment, and the same parts as in the above-described embodiment are given the same reference numerals and detailed explanation thereof will be omitted.

In this second embodiment, as shown in FIG. 6, a light-receiving surface 16a of a photodiode 16 for tracking error detection and a photodiode 17 for focus error detection are mounted on a flat substrate 25. The light receiving surface 17a is
They are integrally fixed so that they are located on the same plane. The bottom surface of the prism body 15 that emits the P-polarized light component is fixed to the substrate 25 so as to be in close contact with the light-receiving surface 16a of the photodiode 16, and the side surface of the prism body 15 that emits the S-polarized light component is Separated light 19a, 19
reflective surface 2 that deflects b toward the photodiode 17;
The side surfaces of the prism body 26, which forms a triangular prism having 6a, are in close contact with each other. Note that the bottom surface of this prism body 26 is attached to the substrate 2 so that it also comes into close contact with the light-receiving surface 17H of the photodiode 17.
It is fixed to 5.

As shown in FIG. 7, the P-polarized light component of the detection light 10 is directly focused on the photodiode 16 in a circular shape, and a pair of separated lights 19a, 19 each having a half-moon shape consisting of the S-polarized light component is formed.
b is reflected by the reflective surface 26a of the prism body 26, and the light is focused on each dividing line between the upper and lower pairs of diode elements a and b and C and d in the diagram of the four-split photodiode 17. . Note that the detection procedures for each error in focus and tracking are the same as those in the embodiments described above, and therefore the description thereof will be omitted.

The entire optical head using the photometric sensor 13 in this second embodiment is shown in FIG. 5, and its configuration is further simplified. According to this second embodiment, since the photodiodes for detecting errors in focus and tracking are provided on one substrate, wiring to the photodiodes can be simplified and noise resistance can be improved. In addition, since the optical axis adjustment only needs to be performed at one location, the adjustment time can be shortened.

Note that by changing the inclination angle of each polarization separation film 18a, 18b, both separated lights 19a, 19b can be directly irradiated onto the photodiode 17 without being reflected by the reflective surface 26a.

[Effects of the Invention] As described above, according to the present invention, the detection light is divided into two parts for each polarized light component.
By simply separating in the direction, tracking errors are detected using one polarization component, and the other polarization component is divided into a pair of half-moon shapes to detect focus errors in the same manner as the Naifetsu method, and the two-sided light components are compared. This makes it possible to read information from the magneto-optical recording medium, reducing the number of parts in the optical head and facilitating optical axis adjustment.

Furthermore, by bringing the polarizing beam splitter as a polarization separation means into close contact with the light receiving surface of the light receiving means, the effects of the present invention are extremely large, such as miniaturization of the component parts and further simplification of position adjustment and wiring. be.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of main parts showing the configuration of 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 shows a view of line 2 in FIG. 2 and a schematic circuit showing how to detect a tracking error. FIG. 4 shows a view of line 2 in FIG. 2, and a schematic circuit showing how to detect a focus error. FIG. 5 is a schematic diagram of main parts showing the configuration of an optical head showing a second embodiment. FIG. 6 is a cross-sectional view along the axial direction of a photometric sensor showing a second embodiment. FIG. 7 is a view of the line ■-■ in FIG. 6. FIG. 8 is a schematic diagram of main parts showing the configuration of a conventional optical head for a magneto-optical disk. 1... Semiconductor laser 2... Outgoing light 3... Collimator lens 4... Shaping prism 5... Polarization beam splitter 5a... Polarization separation film 6... Objective lens 7...
Magneto-optical disk 8...Recording surface 9...Reflected light
10...Detection light 11...λ/2 plate 12.
... Condensing lens 13 ... Photometric sensor 14a, 14
b... Substrate 15... Prism body 16.17... Photodiode 16a, 17a... Light receiving surface 18a, 18b... Polarization separation film 19a, 19b... Separated light 21-24... Amplifier 25... Substrate 26... Prism body 26a... Reflective surface 31... Semiconductor laser 32... Output light 33... Collimator lens 34... Shaping prism 35... First polarized light Beam splitter 36...Objective lens 37...Magneto-optical disk 38...Detection light 39...Second polarizing beam splitter 40...Error detection light 41...Information detection light 42...Collection Optical lens 43...Half prism 44...Nifetsuji 45.46...Photometric sensor 47...λ/2 plate
48... Condensing lens 49... Third polarizing beam splitter 50.51... Photometric sensor

Claims (2)

[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 and reproducing information using detection light reflected from a magneto-optical recording medium, the detection light comprising: a first light receiving means disposed in the optical path of the detection light; a pair of polarization separation means disposed within the optical path of the detected light in order to divide the detected light into two parts; a second light receiving means disposed within the optical path of one of the divided reflected light; and a third light receiving means disposed within the optical path of the other portion of the reflected light, the optical path length of one portion of the reflected light and the optical path length of the other portion of the reflected light being different from each other. An optical head structure for a magneto-optical recording device, characterized in that the length can be set. (2) The pair of polarization separation means includes a polarization beam splitter having a pair of polarization planes spaced apart from each other along the optical path of the detection light, and each of the light reception means has a polarization beam splitter whose light reception surfaces are mutually arranged. 2. The optical head structure for a magneto-optical recording device according to claim 1, wherein the polarizing beam splitter is arranged so as to be located on the same plane, and the polarizing beam splitter is in close contact with the same plane.