JP2001331955A - Optical head controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve problems that astigmatism becomes large and excellent servo signals and RF signals are not obtained because a light emitting point other than the light emitting point used in an adjustment for an optical head has an angle of field to an objective lens when plural light emitting points exist. SOLUTION: The objective lens is offset in the position where the optical axis of the objective lens coincides with the light emitting point which is actually emitted among plural light emitting points by using positional signals obtained by the objective lens movement detecting means, and tracking control is performed around the coincident position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical head control device having a plurality of light emitting points, among optical heads for recording or reproducing signals using optical means.

[0002]

2. Description of the Related Art In recent years, optical disk media have been diversified, and C
D, CD-R, CD-RW, DVD-ROM, DVD-
R, DVD-RW and the like have been developed. However, CD-R and DVD-R among the optical disk media have high wavelength dependency at the time of recording / reproducing, and cannot perform recording / reproducing with light of different wavelengths. Therefore, in order to record / reproduce these with the same optical head, it is necessary to have a plurality of light sources of different wavelengths in the optical head. The present invention relates to a control device of the optical head for an optical disk.

FIG. 16 is a diagram for explaining an operation when a first light source emits light by an optical head having two light sources.
FIG. 17 is a diagram for explaining the operation when the second light source emits light, and FIG. 18 is a graph showing the angle-of-view characteristics of the objective lens. The configuration and operation will be described below.

1 is a semiconductor laser as a first light source, 2 is a light beam emitted from the semiconductor laser 1, 2a is a light spot where the light beam 2 is condensed on a recording medium 9, and 3 is a semiconductor light source as a second light source. The semiconductor laser 4 has a wavelength different from that of the laser 1, 4 is a light beam emitted from the semiconductor laser 3, 4a is a light spot where the light beam 4 is condensed on the recording medium 9, 5 is the semiconductor laser 1 and the semiconductor laser 3, which are fixed and radiated. Stem for the
6 is a package, 7 is a prism for separating a light beam emitted from the light source and a light beam reflected by the recording medium 9 and returned, 7a is a reflection surface of the prism, and 8 is a light beam emitted from the light source. Objective lens for focusing on top, 9
Is a recording medium, 9a is a guide groove formed on the recording medium 9, 10 is a cylindrical lens that gives astigmatism to reflected light from the recording medium 9, and 17 detects reflected light from the recording medium 9. Photodetector.

In the optical head constructed as described above, the light beam 2 emitted from the semiconductor laser 1 passes through the prism 7 and is condensed by the objective lens 8 to be condensed on the recording medium 9 to form a light spot 2a. . The recording medium 9 has a concave / convex shape called a recording film or a pit and a reflection film (not shown). Light modulated by the recording film or the pit is reflected by the reflection film, and then the reflection surface of the prism 7. The light is reflected by 7a, is incident on the cylindrical lens 10, is provided with astigmatism for generating a focus error signal, is incident on the photodetector 17, is converted into an electric signal of a focus error signal, a tracking error signal, and an RF signal. You.

The light beam 4 emitted from the second semiconductor laser 3 having a wavelength different from that of the semiconductor laser 1 and located at a distance of ΔX from the second semiconductor laser 3 enters the photodetector 17 via a similar path and is converted into an electric signal.

[0007]

However, such a configuration has the following problems.
Even when there are a plurality of light emitting points, the adjustment of the optical head is performed for one of the plurality of light emitting points. The objective lens 8 has a field angle characteristic as shown in FIG. That is, as the deviation of the optical axis of the objective lens from the light emitting point increases as the objective lens moves, astigmatism increases. Therefore, an optical axis shift occurs between the light source other than the light emitting point used for adjustment and the objective lens, and the off-axis aberration increases. When the adjustment is performed on the semiconductor laser 1 of the conventional example, the semiconductor laser 3 which is ΔX away from the semiconductor laser 1 already has an angle of view at the neutral position, and furthermore, eccentricity of the disk, droop of its own weight due to a difference in posture, and the like are added. Moving the objective lens in the negative direction in FIG. 16 further increases the angle of view, increases off-axis aberrations, and has a problem that good servo signals and RF signals cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a method for controlling an optical head so that sufficient characteristics can be obtained with respect to off-axis performance.

[0009]

According to a first aspect of the present invention, there is provided a light source having a plurality of light emitting points arranged in parallel with a radial direction of a recording medium, and a light source having a plurality of light emitting points. One objective lens for converging the focused light beam on the recording medium, an objective lens driving unit for following the eccentricity and surface deflection of the recording medium, and detecting reflected light from the recording medium. An optical head comprising: a light detecting means for detecting the movement of the objective lens; and an object lens movement detecting means for detecting a distance moved by the objective lens. The objective lens is offset to a position where an optical axis of the lens and a light emitting point to be actually emitted among a plurality of light emitting points coincide with each other, and tracking control is performed around the coincided position. An optical head control device for detecting the position of the objective lens by an objective lens movement detecting means at a neutral position of the objective lens with respect to a light emitting point having an angle of view among a plurality of light emitting points. However, by offsetting to a position where the angle of view is cancelled, there is an effect that deterioration due to off-axis aberration can be suppressed.

According to a second aspect of the present invention, there is provided the optical head control device according to the first aspect, wherein the light detecting means also serves as the objective lens movement detecting means, thereby reducing the number of parts. It has the effect of reducing costs.

According to a third aspect of the present invention, there is provided an optical head control device according to the second aspect, wherein a groove traversing signal detected by the light detecting means is used as an objective lens movement detecting signal. By counting the groove crossing signal, the amount of movement of the objective lens is detected, and the light emitting point of the light source is moved so as to be on the optical axis of the objective lens, thereby suppressing the deterioration due to off-axis aberration.

[0012]

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

(Embodiment 1) Hereinafter, the configuration and operation of Embodiment 1 of the present invention will be described with reference to FIGS.

FIG. 1 is an operation diagram when the first light source according to the first embodiment of the present invention is operating, and FIG. 2 is an operation diagram when the second light source is operating and the objective lens is at the neutral position. FIG. 3 is an operation diagram when the light emitting point light of the second light source is moved to the optical axis of the objective lens. FIG. 4 is a light beam when the first light source operates and the objective lens is at the neutral position. FIG. 2 is a diagram showing a circuit for generating a light spot on a detector and an objective lens position signal,
FIG. 5 is a diagram showing a light spot on the photodetector when the first light source operates and the objective lens moves to the minus side (a circuit for generating an objective lens position signal is omitted), and FIG. 6 is a first light source. Is a diagram showing a light spot on the photodetector when the objective lens moves to the + side due to the operation (the circuit for generating the objective lens position signal is omitted). FIG. 7 shows that the second light source operates and the objective lens is neutral. FIG. 8 is a diagram showing a circuit for generating a light spot on the photodetector and the objective lens position signal when the objective lens is in the position. FIG. 8 shows the circuit on the photodetector when the second light source operates and the objective lens moves to the negative side. FIG. 9 is a diagram showing a light spot (a circuit for generating an objective lens position signal is omitted), and FIG. 9 is a diagram showing a light spot on a photodetector when the second light source operates and the objective lens moves to the + side (object). A circuit for generating a lens position signal is omitted), FIG.
0 is a graph showing the relationship between the objective lens movement and the objective lens position signal when the first light source is operating, and FIG.
6 is a graph showing a relationship between an objective lens movement and an objective lens position signal when the light source is operating.

In FIG. 1, reference numeral 1 denotes a semiconductor laser as a first light source, 2 denotes a light beam emitted from the semiconductor laser 1, 2a
Is a light spot where the light beam 2 is condensed on the recording medium 9, 3 is a semiconductor laser which is a second light source located at a distance of ΔX from the semiconductor laser 1, 5 is a semiconductor laser and a semiconductor laser 3. A stem for dissipating heat; 6 a package; 7 a prism for separating a light beam emitted from the light source and a light beam reflected back from the recording medium 9;
a is a reflecting surface of the prism; 8 is an objective lens for condensing a light beam emitted from a light source on a recording medium 9; 10 is a cylindrical lens that gives astigmatism to reflected light from the recording medium 9; This is a photodetector for detecting the reflected light from the medium 9.

In FIG. 2, reference numeral 4 denotes a light beam emitted from the semiconductor laser 3, which is the second light source, and the other components are the same as those in FIG.

In FIG. 4, 11a, 11b, 11c,
11d, 11e, 11f, 11g, and 11h are the detection areas of the divided photodetector, 12 is a light spot on the photodetector 11, 12a and 12b are interference areas which are modulated by the grooves 9a of the recording medium 9, Reference numeral 13 is a differential circuit for generating an objective lens position signal.

The operation of the optical head configured as described above will be described. The path of the light beam 2 emitted from the semiconductor laser 1, which is the first light source, is the same as in the conventional example, and will not be described. What differs from the conventional example is a detecting means for detecting the position of the objective lens by the photodetector 11.

Next, the objective lens position detecting means will be described. In the optical head, as shown in FIG. 1, an objective lens 8, a cylindrical lens 10, and a photodetector 11 are adjusted by using a semiconductor laser 1 as a first light source. The light spot 12 on the photodetector 11 at that time is adjusted so as to come to the center of the division as shown in FIG. At this time, light that has not been modulated by the groove 9a enters the detection regions 11a, 11b, 11c, and 11d. When the objective lens 8 moves in the minus direction or the plus direction, the light spot moves as shown in FIGS. At this time, the objective lens position signal is converted by the differential circuit 13 into (11a + 11b)-(11
c + 11d), and this objective lens position signal is a straight line having an inclination a with the objective lens position signal being almost 0 at the neutral position as shown in FIG. Here, detection area 1
The dividing lines 1a, 11b, 11c, and 11d may be formed by oblique lines as shown by broken lines in FIG. It does not matter even if there is, and it is not necessary to be a straight line parallel to each division line as shown in FIG. Any division may be used as long as light that is not modulated by the groove 9a is incident and the left and right areas are equal to the center division line.

Next, when the semiconductor laser 3 as the second light source emits light and the objective lens 8 is at the neutral position, it moves from the position shown in FIG. 4 to the minus side as shown in FIG. When the objective lens 8 moves in the-direction or the + direction from this state, the light spot moves as shown in FIGS. 8 and 9, respectively. As shown in FIG. 11, the objective lens position signal resulting from this movement has a form in which the graph of FIG. 10 is shifted by + ΔX. Therefore,
When the objective lens 8 is moved so that the objective lens position signal becomes a · ΔX, the emission point of the semiconductor laser 3 can be brought on the optical axis of the objective lens 8 as shown in FIG.
Tracking control is applied around that position.

As described above, according to the present embodiment, in the optical head having a plurality of light sources, the distance between the semiconductor laser used for adjustment and the semiconductor laser actually used is determined using the objective lens position signal. By moving the light source 8, the light emitting point of the light source can be moved on the optical axis of the objective lens 8, so that an optical head capable of recording and reproducing with little off-axis aberration is obtained.

In this embodiment, two semiconductor lasers are used as light sources, but it goes without saying that there may be three or more semiconductor lasers.

(Embodiment 2) Hereinafter, the configuration and operation of Embodiment 2 of the present invention will be described with reference to FIGS. 12, 13, 14, and 15.

In FIG. 12, the components 1 to 10 are the same as the components shown in FIG. 1, and 14 is a photodetector having a different divided shape. In FIG. 13, 14a, 14
b, 14c, 14d are detection areas of the divided photodetector,
15 is a light spot on the photodetector 14, 15a and 15b are interference areas modulated by the grooves 9a of the recording medium 9, 16
Is a differential circuit for generating a groove crossing signal (tracking error signal). FIG. 14 shows a groove crossing signal generated by the differential circuit. FIG. 15 is a diagram showing the relationship between the objective lens actuator application voltage and the number of groove crossing signals.

The operation of the optical head configured as described above will be described. The operation until the light beam 2 enters the photodetector 14 of the optical head shown in FIG. 12 is the same as that in FIG. As shown in FIG. 13, a light crossing signal of the light spot 15 incident on the photodetector 14 is obtained by the differential circuit 16 by calculating (14a + 14b) − (14c + 14d). The pitch P of the groove traversing signal matches the pitch from the groove of the recording medium 9 to the adjacent groove, and this pitch P is determined by the standard of the recording medium. A voltage is applied to the objective lens actuator while counting the groove traversing signals, and an application voltage of the objective lens actuator is obtained in which the number of traversing grooves (= ΔX / P) corresponding to the interval between the semiconductor laser 1 and the semiconductor laser 3 becomes T.

By superimposing this voltage on the drive voltage of the objective lens actuator, the light emitting point of the semiconductor laser 3 can be brought on the optical axis of the objective lens 8, and tracking control is performed with that position as the center.

As described above, according to the present embodiment, in an optical head having a plurality of light emitting points, the distance between the semiconductor laser used for adjustment and the semiconductor laser actually used is counted by the groove crossing signal to obtain the objective. By moving the lens, the emission point of the semiconductor laser can be brought on the optical axis of the objective lens, and an optical head capable of recording and reproducing with little off-axis aberration can be obtained. Further, since a groove crossing signal, which is a tracking error signal, is used, a component for detecting the amount of movement of the objective lens is not required, so that an inexpensive optical head can be realized.

In the present embodiment, two semiconductor lasers are used as light sources, but it goes without saying that three or more semiconductor lasers may be provided.

[0029]

As described above, according to the present invention, in an optical head having a plurality of light emitting points, the objective lens is offset so that the light emitting point to be used is located on the optical axis of the objective lens. And a tracking operation is performed around that point.

Thus, it is not necessary to use an objective lens having good off-axis aberration characteristics for a plurality of light emitting points, so that the cost can be reduced and the objective lens can be used in a region where off-axis aberration is small. Thus, an effect that good recording and reproduction can be performed can be obtained.

[Brief description of the drawings]

FIG. 1 is an operation diagram of an optical head when a first light source according to a first embodiment of the present invention is operating.

FIG. 2 is an operation diagram of the optical head when the second light source according to the first embodiment of the present invention operates and the objective lens is at a neutral position.

FIG. 3 is an operation diagram when the objective lens according to the first embodiment of the present invention is moved so that a light emitting point of a second light source comes to an optical axis of the objective lens.

FIG. 4 is a diagram showing a circuit for generating a light spot on the photodetector and an objective lens position signal when the first light source is operated and the objective lens is in the neutral position according to the first embodiment of the present invention;

FIG. 5 is a diagram showing a light spot on the photodetector when the first light source according to the first embodiment of the present invention operates and the objective lens moves to the − side.

FIG. 6 is a diagram showing a light spot on a photodetector when the first light source according to the first embodiment of the present invention operates and the objective lens moves to the + side.

FIG. 7 is a diagram showing a circuit for generating a light spot on the photodetector and an objective lens position signal when the second light source operates and the objective lens is in the neutral position according to the first embodiment of the present invention;

FIG. 8 is a diagram showing a light spot on the photodetector when the second light source according to the first embodiment of the present invention operates and the objective lens moves to the − side.

FIG. 9 is a diagram showing a light spot on the photodetector when the second light source according to the first embodiment of the present invention operates and the objective lens moves to the + side.

FIG. 10 is a graph showing a relationship between an objective lens movement and an objective lens position signal when the first light source according to the first embodiment of the present invention is operating.

FIG. 11 is a graph showing a relationship between an objective lens movement and an objective lens position signal when the second light source according to the first embodiment of the present invention is operating.

FIG. 12 is an operation diagram of the optical head when the first light source according to the second embodiment of the present invention is operating.

FIG. 13 is a diagram showing a circuit for generating a light spot and a groove crossing signal on the photodetector when the first light source operates and the objective lens is in the neutral position according to the second embodiment of the present invention;

FIG. 14 is a diagram illustrating a groove crossing signal according to the second embodiment of the present invention.

FIG. 15 is a graph showing the relationship between the number of traversing grooves and the voltage applied to the objective lens actuator according to the second embodiment of the present invention.

FIG. 16 is an operation diagram of an optical head when a first light source of the conventional optical head is operating.

FIG. 17 is an operation diagram of the optical head when a second light source of the conventional optical head is operating.

FIG. 18 is a graph showing a relationship between an angle of view and an aberration of an objective lens.

[Explanation of symbols]

 Reference Signs List 1,3 semiconductor laser 2,4 light flux 5 stem 6 package 7 prism 8 objective lens 9 recording medium 10 cylindrical lens 11,14,17 photodetector 12,15 light spot 13,16 differential circuit

Claims (3)

[Claims] A light source having a plurality of light-emitting points arranged in parallel with a radial direction of a recording medium; one objective lens for converging a light beam emitted from the light source on the recording medium; Objective lens driving means for following the eccentricity and surface deflection of the recording medium, light detecting means for detecting reflected light from the recording medium, and objective lens movement for detecting the distance moved by the objective lens In the optical head configured by the detecting unit, the optical axis of the objective lens and a light emitting point to be actually emitted among a plurality of light emitting points coincide with each other using the position signal obtained by the objective lens movement detecting unit. An optical head control device, characterized in that the objective lens is offset and tracking control is performed around the matched position. 2. An optical head control device according to claim 1, wherein said light detecting means also serves as an objective lens movement detecting means. 3. The optical head control device according to claim 2, wherein the groove crossing signal detected by the light detecting means is used as an objective lens movement detection signal.