JP3641896B2 - Optical head - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical head of an optical disc apparatus.
In recent years, although a magneto-optical disk (MO) has been widely used, an optical disk having a higher recording density than the MO, such as a digital video disk (DVD), has been developed as a large-capacity ROM disk. There is a strong demand that such a high recording density optical disk and a low recording density optical disk can be handled by a single magneto-optical disk device, that is, data can be reproduced and recorded / reproduced by a single optical head.
[0002]
[Prior art]
FIG. 3 illustrates an optical system of an optical head of a conventional magneto-optical disk apparatus.
The light beam emitted from the light source 1, that is, the laser diode (LD), becomes parallel light by the collimator lens 2 and becomes a parallel light beam having a circular cross section by the perfect circle correction prism 3. The parallel light beam passes through the first beam splitter 4 and is condensed by the objective lens 5 to form a light spot for recording / reproducing data on the MO 6. Reflected light from the MO 6 is converted into parallel light by the objective lens 5 and then reflected by the first beam splitter 4 at a right angle. The reflected light is divided by the second beam splitter 7 and is reflected by a right angle. In order to perform focusing and tracking, a focus track including a condenser lens 8, a cylindrical lens 9, and a four-divided photodetector 10 is used. A data reproduction signal detection system comprising a half-wave plate 11, a polarization beam splitter 12, and a photodetector 13 for reproducing data when the control signal detection system passes through the second beam splitter 7 straightly. To be guided to.
[0003]
The focusing and tracking of the objective lens 5 are performed by the actuator 15 shown in the exploded perspective view of FIG.
The actuator 15 is composed of a rotor 15a and a stator 15b. The rotor 15a has a rhombus plate 15a- that is wound around a bearing 15a-1 with a tracking coil 15a-2 and a focusing coil 15a-3, and is fixed to the upper end of the bearing 15a-1. 4, the objective lens 5 and the balancer 15 a-5 are attached to both ends, respectively, and the stator 15 b is a slide provided at the center of a pair of N and S permanent magnets 15 b-1 and 15 b-2. The movable shaft 15b-3 is inserted in a freely floating manner.
[0004]
The actuator generates an electromagnetic force in the focusing coil / tracking coil in accordance with the focus / track control signal obtained from the focus / track control signal detection system, and moves the objective lens in the focus direction Y (on the disk surface) along the sliding axis. The optical spot is moved up and down in the vertical direction to control the focus on the MO, and the objective lens is rotated in the track direction X (disk radial direction) to move the optical spot following the MO recording track.
[0005]
The preformat data and magneto-optical recording data recorded in the MO are reproduced from the reproduction signal obtained from the data reproduction signal detection system.
When data is recorded on the MO with this optical head, the ratio of the effective diameter D of the objective lens to the parallel light beam diameter 1 / e ² (e is the base of natural logarithm), D / W (FIG. 5). In order to obtain optical power I ₀ for recording data in MO, the vignetting by the objective lens is suppressed, the D / W is set to about 0.93, and the objective lens at that time is transmitted. The objective lens transmitted light amount ratio is 0.83 from the relationship diagram between the vignetting coefficient D / W (horizontal axis) and the objective lens transmitted light amount ratio (vertical axis) in FIG. 6, and sufficient data is recorded in the MO. can do.
[0006]
Also in the case of reproducing data, the length of the conventional MO recording mark is 0.64 μm at the shortest, and the vignetting coefficient D / W (horizontal axis) and the light expressed by 1 / e ² in FIG. From the relationship diagram with the spot diameter (vertical axis), since the D / W was 0.93 and the light spot diameter was 1.03 μm, it was sufficiently reproducible.
[0007]
[Problems to be solved by the invention]
Thus, the optical head of the conventional magneto-optical disk apparatus can record / reproduce data with respect to the MO. On the other hand, the shortest pit length of an optical disc having a high recording density, such as a DVD, is 0.40 μm. In general, since the reproduction waveform resolution needs to be about 20% or more for stable reproduction of data, the light spot diameter is the light spot diameter 1 / e ² (horizontal axis) in FIG. 8 and the DVD reproduction waveform resolution (vertical axis). It is necessary to make it 0.97 μm or less from the relationship diagram.
[0008]
However, the conventional optical system of the above optical head cannot achieve a reproduction waveform resolution of about 20% or more and a light spot diameter of 0.97 μm or less necessary for data reproduction of a high recording density optical disc such as a DVD. However, the same light spot cannot be used for a high recording density optical disc (DVD) and a low recording density optical disc (MO), and there is a problem in that they are not compatible.
[0009]
In view of the above problems, an object of the present invention is to provide an optical head capable of reproducing data and recording / reproducing data by one according to the type of optical disk depending on the recording density.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, in the optical head of the present invention, the ratio D / W between the parallel light beam diameter W incident on the objective lens and the effective diameter D of the objective lens corresponds to the recording density of the optical disc. Configure to change.
[0011]
With this configuration, due to changes in D / W, for example, in the case of DVD, if D / W is set to 0.4 or less, it is possible to obtain a DVD that cannot be obtained with a conventional MO optical head as shown in FIG. An optical spot diameter of 0.97 μm or less necessary for data reproduction can be obtained, and for example, reproduction compatibility between MO and DVD becomes possible.
[0012]
With this D / W, the objective lens transmitted light amount ratio decreases to 0.27, so that it is impossible to irradiate the MO with optical power for recording, but there is no problem because the DVD is only for reproduction. Recording / reproducing to / from the MO can be performed in the same manner as in the prior art by setting the D / W to about 0.93, which is the same as in the past, by changing the D / W.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the gist of the present invention will be described in detail based on the embodiments shown in the drawings.
FIG. 1 illustrates an optical system of an optical head of the present invention. In addition, the part demonstrated in the conventional FIG. 3 uses the same code | symbol, and abbreviate | omits the description.
[0014]
In the first embodiment, as shown in the figure, a fourth beam splitter 16 that splits a parallel light beam that has passed through the first beam splitter 4 and a parallel light beam that is reflected by the fourth beam splitter 16 at a right angle are obtained. Further, it differs from the conventional configuration in that it includes a mirror 17 that reflects at right angles and a beam diameter conversion optical system 18 that includes a convex lens 18a and a concave lens 18b for enlarging the diameter of the parallel light beam reflected by the mirror 17.
[0015]
This beam diameter converting optical system 18 expands the branched parallel light beam to a diameter larger than the effective diameter of the objective lens 5 and vignetting coefficient D / W so as to reproduce the data of the optical disk 19 having high recording density, that is, DVD. Is set to 0.4.
[0016]
On the other hand, the diameter of the parallel light beam that has passed straight through the fourth beam splitter 16 remains the same, and the D / W is set to 0.93 so as to record or reproduce data with respect to the optical disk 6 having a low recording density, that is, MO. The D / W is switched to 0.4 or 0.93 by setting and moving the objective lens 5.
[0017]
When the transmitted light amount ratio of the fourth beam splitter 16 is 75% and the reflected light amount ratio is 25%, the light spot power for MO6 data reproduction is normally 1.5 mW, and the objective lens transmits at D / W = 0.93. Since the light intensity ratio is 0.83,
1.5 mW / 0.83 / 0.75 = 2.4 mW
Is input to the fourth beam splitter 16 to reproduce the data of MO6.
[0018]
On the other hand, the light spot power for DVD data reproduction is 0.2 mW, and the objective lens transmitted light amount ratio at D / W = 0.4 is 0.27.
0.2 mW / 0/27 / 0.25 = 3.0 mW
Is input to the fourth beam splitter 16 to reproduce the DVD 19 data.
[0019]
The light spot power for recording data in MO6 is reduced to 75% due to the presence of the fourth beam splitter 16, but if this is the case, for example, the data can be sufficiently recorded by reducing the disk rotational speed from 3600 rpm to 2700 rpm. be able to.
[0020]
The focusing and tracking of the objective lens 5 of this optical head can be performed using the conventional actuator 15 shown in FIG.
Further, since the actuator 15 has a large movable range in the tracking direction by rotation around the sliding axis of the objective lens 5, the objective lens 5 is moved by rotating the objective lens 5 with respect to the MO 6 or the DVD 19. The ratio D / W between the beam diameter D of the parallel light beam incident on the objective lens 5 and the effective diameter W of the objective lens can be switched to either 0.93 or 0.4, and after switching the optical path Focus and track control can be performed as usual.
[0021]
Next, FIG. 2 shows a second embodiment.
In the second embodiment, the objective lens 5 is not moved as in the first embodiment, but the beam diameter converting optical system in which the beam diameter converting optical system 18 is taken in and out of the parallel light beam optical path incident on the objective lens 5. The system moving means, that is, the actuator shown in FIG. 4 (not shown in FIG. 2) is provided, and the D / W is set to 0 depending on whether or not the beam diameter converting optical system 18 is inserted into the parallel light beam optical path. .Switch to 93 or 0.4.
[0022]
The beam diameter converting optical system moving means is rotated by placing a convex lens and a concave lens constituting the beam diameter converting optical system on the actuator shown in FIG. 4 and inserting or not in the parallel beam optical path. .Switch to 93 or 0.4.
[0023]
In the second embodiment, as in the above-described embodiment, one optical head performs data reproduction and recording / reproduction corresponding to each of a high recording density optical disc (DVD) and a low recording density optical disc (MO). Can be done.
[0024]
Furthermore, since the parallel light beam transmitted through the first beam splitter is not divided into two as in the first embodiment, there is an advantage that the optical power loss is smaller than that in the first embodiment.
[0025]
【The invention's effect】
As described above, according to the present invention, the vignetting coefficient D / W can be changed, and a parallel light beam having a diameter larger than the effective diameter of the objective lens in the optical path of the parallel light beam is incident on the objective lens. Thus, a predetermined light spot diameter can be easily obtained. For example, by changing D / W to 0.4 or less, a light spot diameter of 0.97 μm or less that could not be obtained by an optical head of a conventional optical disc apparatus. With the same optical head, the magneto-optical disk device can be compatible with data recording / reproduction of a high recording density optical disk such as a DVD and data recording / reproduction of a low recording density optical disk such as MO. Exhibits extremely useful effects in industry.
[Brief description of the drawings]
FIG. 1 is an optical system diagram of an optical head according to another embodiment of the present invention. FIG. 2 is an optical system diagram of an optical head according to another embodiment of the present invention. FIG. 5 is an exploded perspective view of the actuator used in FIGS. 1 and 3. FIG. 5 is an explanatory diagram of vignetting by the objective lens. FIG. 6 is a diagram of the relationship between the vignetting coefficient D / W and the transmitted light ratio of the objective lens. Relationship between coefficient and optical spot diameter [Fig. 8] Relationship between optical spot diameter and DVD playback waveform resolution [Explanation of symbols]
5: Objective lens 6: Low recording density optical disk (MO)
15: Objective lens moving means (actuator)
18: Beam diameter conversion optical system 19: High recording density optical disc (DVD)
W: Diameter of parallel light beam D: Effective diameter of objective lens

Claims (1)

The light beam emitted from the light source is converted into a parallel light beam by a collimating lens, and focused on an optical disk by an objective lens to form a light spot for recording or reproduction, and the error for focus / track control from the reflected light of the optical disk In an optical head that obtains a signal and performs focus / track control of the light beam, and obtains a data reproduction signal recorded on the optical disk from the reflected light,
A beam splitter that splits the parallel light beam incident on the objective lens, a beam diameter conversion optical system that converts one of the split parallel light beam diameters, and an objective lens movement that moves the objective lens to the beam diameter conversion optical system Means and
The objective lens moving means also serves as a light spot track control means on the optical disc,
Depending on the type of optical disk depending on the recording density, the objective lens is moved by the objective lens moving means, and the ratio D / W of the beam diameter W of the parallel light beam incident on the objective lens and the effective diameter D of the objective lens. an optical head, characterized in that Modulate.

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