JPS61233441A - Optical head device - Google Patents

Abstract

PURPOSE:To eliminate the effects of the wavelength variance of a light source by increasing the size of a photodetecting surface in the direction where it is diffracted by a diffraction grating in comparison with the size of said photodetecting surface in the direction orthogonal the first mentioned direction. CONSTITUTION:The traveling direction of the diffracted light 11 is changed slightly by the wavelength variance of a light source 1. The change of direction due to said wave motion variance is coincident with the direction due to said wave motion variance is coincident with the direction diffracted by a diffraction grating. Therefore 11a'-11c' have vertical fluctuations to the distribution of light quantity of 11a-11c. Here the photodetecting surfaces 13a-13d of a photo detector 13 have relatively large sizes in the direction where the luminous flux is shifted by said wavelength fluctuation. At the same time, the dividing line of each photodetecting surface is set in parallel to said direction. As a result, the output of each photodetecting part is not substantially affected despite the wavelength variance of the light source 1. This attains the correct auto- focusing and auto-tracking actions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical head device that detects or records information by irradiating an information recording surface of an information carrier with light.

[Prior art]

Conventionally, in optical head devices such as those described above, in order to detect focus errors and tracking errors,
It was common to place a specially shaped prism, a special aspherical lens such as a cylindrical lens, a dori, or a lens in the optical path in which the light beam reflected by the information recording carrier was guided to the photodetector.

Such special optical components do not cause high costs when manufacturing optical devices, and also have the disadvantage that arrangement adjustment becomes complicated because each optical component exists individually. Was. In order to compensate for these drawbacks, various nine-optical head devices have been proposed in which a diffraction grating is provided in the optical path that guides the light beam to the photodetector. For example, as an example of replacing a cylindrical lens with a diffraction grating element, JP-A-53-100
No. 808, JP-A-54-43005, JP-A-54-6
No. 1503, JP-A-54-134605, etc. In these optical head devices, the cylindrical lens or toric lens is replaced with a flat-plate diffraction grating, so the device can be configured to produce inexpensive light.
Since it is bonded to other parts, it has advantages such as easy position adjustment.

However, serious problems arise when such a grating element is combined with a semiconductor radar light source. This is because the wavelength stability of the semiconductor radar light source is lower than that of gas lasers such as helium/neon lasers, so the wavelength of the light source changes due to changes in the environmental temperature and drive current during use, and the above-mentioned optical In the case of a head device, this means that correct autofocus operation etc. cannot be performed.

For example - by way of example, a semiconductor radar with a wavelength of λ=830 nm undergoes a wavelength shift of approximately 0.3 nm for a temperature increase of 1 DEG C., resulting in a wavelength variation of as much as dnm for a temperature increase of 20 DEG C. In normal astigmatic focus error detection, when a hologram lens is used as a cylindrical lens, if the wavelength changes from 830 pixels to 836 pixels, the focus position will drift due to a change in the direction of diffraction of light. Without special correction, correct autofocus operation will not be performed.

In addition, when the diffraction grating used in the device is a grating that is blazed with higher-order diffraction light,
When the wavelength fluctuation as mentioned above occurs, the diffracted light becomes 1
It is not possible to concentrate on a specific order, and the energy is distributed to several adjacent orders. When such a diffraction grating is used for light, if the photodetector is made to detect only a specific order of light,
This results in a decrease in the amount of detection. Furthermore, when the diffraction efficiency of a specific diffraction order light is sensitive to the wavelength of the light source, there is also the problem that the amount of detected light is strongly influenced by the wavelength fluctuation of the light source.

[Purpose of the invention]

An object of the present invention is to provide an optical head device that is not affected by the wavelength fluctuations of a light source as described above.

[Summary of the invention]

According to the present invention, the above object is to make light from a light source incident on an information recording surface and convert the reflected light from the information recording surface into a light beam having a diffraction grating arranged in the optical path of the incident light. The splitter guides the light as diffracted light to a photodetector, where it is used to detect or record information.

In the photodetector, the photodetector has a single or plurally divided photodetection surface, and a dimension of the photodetection surface in a direction in which it is diffracted by the diffraction grating is a dimension in a direction perpendicular to the direction. In comparison, a light beam characterized in that the light is set to be large enough to include fluctuations in the diffracted light caused by wavelength fluctuations of the light source is achieved by a de-device.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a schematic diagram of an embodiment of an optical head device according to the present invention.

In the figure, the P-polarized light emitted from the semiconductor radar 1 is converted into a parallel beam by the collimator lens 2, and the parallel plate 4, 6
and a volume type diffraction grating 5. Linearly polarized light (P polarized light) transmitted through this light splitter 3
is focused by the objective lens 7 onto the information recording surface 9 on the substrate 8 into a stub with a diameter of about 1 μm. On the recording surface 9 on which information is magnetically recorded, the reflected light 10 whose polarization plane has been rotated (Kerr rotation) according to the information enters the light splitter 3 again, and is subjected to wavelength and diffraction by the volume type diffraction grating 5. The light is diffracted at a predetermined diffraction angle determined by the pitch of the grating 5. This diffracted light 11 is guided while undergoing repeated total reflection on the surface of the parallel plate 4 or 6, and enters a four-split photodetector 13 provided at the end face of the light splitter 3. An analyzer 12 is provided immediately in front of the photodetector 13, and converts the magneto-optical signal into a change in the amount of light.

FIG. 2 shows a view of the light splitter 3 shown in FIG. 1 viewed from the semiconductor radar 1 side. The volume type diffraction grating 5 of this embodiment has a conical grating and has a lens function to focus the diffracted light 11. In addition, the 4-split photodetector 13 has 4
Two light-receiving surfaces are arranged in series in the direction of the paper. The light intensity distribution on the photodetector 13 changes depending on the focusing state of the spots on the recording surface 9 in FIG. For example, when the focal position of the objective lens 7 coincides with the recording surface 9, the reflected light 10 becomes parallel light, and the diffracted light 11 becomes K as shown by the solid line in FIG. It is incident in the shape shown. tfc, when the objective lens 7 is too close to or too far away from the recording surface, the reflected light 10 becomes a diverging light or a convergent light, and the diffracted light 11 becomes as shown in FIG. 11C or 11D, respectively, on the photodetector 13. The principle of detecting a focus error signal using such a change in the shape of the light beam will be explained in detail below.

Figures 3 (a), (b), and (e) are nine views of the 4-split photodetector 13 from the light incident side, and (b) shows the focused state;
, ), (C) shows an out-of-focus condition. Here, 13
a 513b +13c*13d indicate the divided light detection surfaces, and the shape of the incident light flux is 11M$ as described above.
11b, lie. In addition, lla' I ll
b'#tie' will be described later. Light detection surface 1
The outputs from 3as13b+13c+13d are respectively Ia
, Ib, IC, and Id, by performing the calculation (Ib+Ic)-(Ia+Id) in the electrical system shown in FIG. 4(&), the output terminal 15 of the differential amplifier 14 becomes A focus error signal as shown in b) is obtained. In FIG. 4(b), the horizontal axis indicates the distance (focus error) between the objective lens and the recording surface when the in-focus position is zero, and the vertical axis indicates the signal output. According to the obtained focus error signal, autofocus is possible by moving the objective lens 7 or the entire optical head relative to the disk along the optical axis of the incident light via an actuator (not shown) or an actuator (not shown). becomes.

Next, the principle of auto-tracking in the embodiment shown in the first diagram will be explained. Figure 5 (51) # (b) t (
Assuming that grooves 8 are formed in the substrate 8 of the information recording carrier as shown in e), the incident light beam is focused by the objective lens 7 in the vicinity of this $ g m. Here (b), a spot is generated above the target groove 8 (Todoroki).

(e) shows a state in which the spot is shifted to the right or left with respect to the groove, respectively. The light beam reflected by the recording surface 9 on the substrate 8 contains tracking information due to diffraction or scattering at the grooves 81. In the quadrant photodetector 13 shown in the second diagram, when the reflected light is received, the photodetecting surface 13a.

The amount of light received by 13b, 13c, and 13d is as shown in FIG. 6(a) depending on the conditions shown in FIGS. 5(fi), (b), and (c), respectively.

(b) t Changes as shown in (e). Therefore, by performing the calculation (I Todo + Ib) - (Ic + Id) in the electrical system as shown in Figure 7 (-), the output terminal 17 of the differential amplifier 16 is outputted as shown in Figure 7 (b) A tracking error signal as shown is obtained. In FIG. 7(b), the horizontal axis shows the tracking error and the vertical axis shows the signal output.

Auto-tracking is possible by driving a tracking actuator (not shown) in accordance with the obtained tracking and king error signals to move the objective lens 7 perpendicular to the optical axis. Here, a case has been described in which a groove as a guide track is formed in advance on the substrate 8, but even if there is no such groove, the portion of the recording surface 9 where information is recorded (recording track), In other parts, the amount of light passing through the analyzer 12 is different due to the above-mentioned magneto-optic effect, and an imbalance occurs in the light amount distribution on the photodetector 13 depending on the positional relationship between the recording track and the spot. Therefore, even in such a case, a tracking error signal can be obtained in the same way as by calculating the output of each photodetecting surface of the four-split photodetector 13, as shown in FIG. 7(-).

Furthermore, in the embodiment shown in FIG. 2, the diffracted light from the diffraction grating 5 is diffracted as a focused light, but a diffraction grating that produces a lens effect in this way can be made, for example, in a conical shape. This can be achieved by

Next, a method of eliminating the influence of wavelength fluctuations of a light source, which is the content of the present invention, will be described.

Assume that in the optical head device shown in FIG. 1, the wavelength of the semiconductor radar light source 1 changes. Due to this wavelength change, the traveling direction of the diffracted light 11 changes slightly, but in FIG. 1, the direction of this change is in the plane of the paper. Of the light intensity distributions shown in Figures 2 and 3, 11a'+ 11"
e lie' is the light amount distribution that occurs when the light source wavelength changes. The change in direction caused by this wave fluctuation is the direction that is diffracted by the diffraction grating, so in Fig. 3, 11 m', 1 l b', and 11 c' are the vertical fluctuations in the light intensity distribution of the eyes, a, 11b, and 11c, respectively. It becomes K to do. Here, as shown in FIG. 3, each light detection surface 13 m of the photodetector 13 is 5K = 13 b - 13 c @ 1
By making 3d relatively large in the direction in which the light flux moves due to this wavelength variation, and by making the dividing line of each light detection surface parallel to this direction, even if the wavelength variation of the light source occurs, each The output of the photodetector is hardly affected and correct autofocus and autotracking can be performed.

If there is no ingenuity like the present invention, as shown in Figure 8 (Hata),
If the dimensions are not relatively large in the direction in which the light flux moves, or as shown in FIG. 8(b), each light detection surface 13 a e 13 b a 13 c * 13
If the dividing lines d are not parallel, the photodetector 1
3, the overall amount of received light decreases and each light detection surface 13a.

A problem arises in that the outputs of 13b, 13c, and 13d change due to wavelength fluctuations of the light source.

FIG. 9 is a diagram showing a second embodiment of the present invention. 1st
As in the illustrated embodiment, the light beam 11 diffracted by the diffraction grating 5 passes through an analyzer 12 and enters a photodetector 13 . Now, when the oscillation wavelength of the semiconductor laser 1 becomes longer, the angle at which the diffracted light 11 occurs becomes larger in proportion to this change in wavelength. , this will result in a loss.

FIG. 10 is a diagram showing the relationship between the photodetector 130 division method and the light spots. Even if the light spot 11 changes to the light spot 11', the dividing line of the photodetector 13 is set in the direction in which the diffracted light moves due to fluctuations in the light source wavelength, so no AF operating point drift occurs. .

Next, an example of making a mold for manufacturing the diffractive structure used in the present invention will be shown. In making the mold, as shown in FIG. Create a mold while moving the

The apex angle of the cutting edge of the cutter 19 is determined by the angles α and β, and in the above example, the angle is approximately 65°. The mold material 18 may be made of metal such as phosphor bronze or brass Ni, or may be made of a polymeric material such as brazing disc, plasti, or resin. However, metal shapes have the advantage that they can be used directly as stumps and armholes, and there is no need for the process of creating stuns and arms by electroforming or the like. When cut by the method shown in FIG. 11, a concentric relief structure as shown in FIG. 12(B) is obtained. Figure 12 (6) is an enlarged view of a part of Figure (B), with 35° to α, 80° to β, pitch ~2
It is 0 μm.

Next, as shown in FIG. 13, combination/transfer is performed on a plastic material 20 such as acrylic. At this time, by applying appropriate temperature and pressure to the mold 18 and the acrylic material 20, it is possible to faithfully transfer the relief structure of the υ mold 18 to the acrylic material 20.

As shown in FIG. 14, a reflective layer 21 is provided on the transferred relief structure of the acrylic material by, for example, vapor deposition. reflective layer 2
1 may have a multilayer structure or a single layer structure. Also, Mg
It may be a dielectric film such as F2*TlO2*ZrO2* 81029 or a metal film such as Au, Ag, kL, Cu or the like.

Next, as shown in FIG. 15, the relief portion is filled with a substance 22 having a refractive index close to that of the acrylic material 20. At this time, cover material 2
By providing 3t, the surface can be made optically smooth. For this reason, it is preferable that the substance 22 has a bonding effect, and for example, an acrylic ultraviolet curing adhesive is advantageous. Further, the cover material 23 may be the same as the acrylic material 20 or may be made of another material (for example, glass).

Through the above process, the light splitter of the present invention is produced.

[Effects of the Invention] As described above, the optical device of the present invention makes it possible to detect signals without causing drift even when the wavelength of the light source fluctuates due to temperature changes or other factors. became.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing the optical head device of the present invention, and FIGS. 2 and 3 are diagrams showing the optical head device of the present invention. FIG. 3 is a diagram showing the light amount distribution generated in the hard drive device. FIG. 4 shows the focus error detection circuit and its factors, FIGS. 5 and 6 show the principles of tiger and king error detection and the factors, and FIG. 7 shows the tracking error detection circuit. FIG. 8 is a diagram showing an example of a light detection surface of a photodetector that is affected by wave fluctuations. FIG. 9 is a schematic configuration diagram showing a second embodiment of the present invention,
FIG. 10 is a diagram showing the shape of each photodetecting surface of the photodetector in the second embodiment. Also, FIGS. 11, 12, 13, and 14. FIG. 15 is a diagram showing a method of manufacturing a diffraction grating used in the optical head device of the present invention. 1: Rede light source, 2: Collimator lens, 3: Beam gooseberry, tar, 4, 6: Parallel plate, 5: Diffraction grating, 7:
Objective lens, 8: Substrate, 9: Information recording carrier, 10: Reflected light, 11: Diffracted light, 12: Analyzer, 13: Photodetector. Agent Patent Attorney Seki Yamashita Children Figure 2 (0) (b) (c) Fourth cause (b) Figure 5 (0) (b) (C) Figure 6 +50 +5c 15e) 1,5
C13t) 13c Fig. 7(b) Fig. 8

Claims (1)

[Claims] (1) Light from a light source is made incident on an information recording surface, and the reflected light from the information recording surface is transmitted to a photodetector as diffracted light by a light splitter having a diffraction grating placed in the optical path of the incident light. In the optical head device for guiding, detecting or recording information, the photodetector has a single or plurally divided photodetecting surface, and the photodetecting surface has a dimension with respect to a direction in which it is diffracted by the diffraction grating. , an optical head device characterized in that the size is set to be larger than the dimension in a direction perpendicular to the direction so as to include fluctuations in the diffracted light caused by wavelength fluctuations of the light source.