JPH09115176A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize signal jitters, to reduce the error rate in a signal reproducing system and to improve the reliability to an optical head by providing a light shielding mask for return light from an optical disk. SOLUTION: This optical head is applied to an optical disk device having an optical disk 70 having a wobbled track groove (wobbled groove) 71 such as recording type CD, MD, etc. The optical head 1 is provided with a light shielding mask 48 between a beam splitter 40 and a Wallaston prism 41. The light shielding mask 48 is provided with a rectangular aperture 48a whose longitudinal direction nearly coincides with the track groove direction for signal modulation luminous flux 37 of signal modulated return luminous flux from the optical disk 70, and applied aperture control in the direction corresponding to the direction orthogonally crossing the wobbled groove 71 and from the outside of the return luminous flux 37. Thus, the light in a wobble modulation area in the return luminous flux 37 is shielded, and a wobble component superimposed on a regenerative signal is eliminated effectively, and the signal jitters are stabilized, and the error rate in the signal reproducing system is reduced, and the reliability to the device is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head of a type for recording / reproducing information on / from an optical disk using an optical recording system, a dye-based write-once system or a phase change recording system. In the field of recordable CDs, these optical discs are CD-MO (O
RANGE-BOOK PART1 standard), CD-R
(Same PART2 standard), CD-E (same PART3 standard), MD (mini disk, RAINBO)
W-BOOK standard) also falls into these categories.

These optical disks have a commonality in that information is recorded on wobbled grooves (meandering track grooves) modulated with address information.

[0003]

2. Description of the Related Art Conventionally, an optical head for recording / reproducing information on / from a wobbled groove of this type is a conventional optical head for recording / reproducing information on a groove without wobbles. .
However, when the signal recorded on the wobbled groove is reproduced by the conventional optical head, the following inconvenience occurs.

The wobble is a meandering in a radial direction of a continuous spiral groove (groove) with a frequency of several tens Khz and a minute amplitude (about 2% of the track pitch). This meander is formed in the stamping process in the process of manufacturing an optical disc. The purpose of wobbling is performed in advance to engrave address information in the unrecorded continuous track groove, and does not hinder the track servo because the amplitude is minute. Since the wobble frequency is also outside the control band of the track servo, the spot (focus) formed by the objective lens traces on the average center line of the meandering groove. The address information can be detected from the track error signal through a bandpass filter.

As shown in FIG. 6A, the information pits 272 recorded on the wobbled groove 271 exist meandering in the radial direction. When this information is reproduced by a conventional optical head as a signal, a wobble frequency of several tens of kHz is added (superposed) to a reproduction signal 280 of several hundred kHz as shown in FIG. Occurs. Generally, in a recordable CD, a slice level 282 is set for a reproduction signal 280 and a pulse is detected as a digital signal at a zero cross point. However, if the reproduction signal 280 has a “waviness” of several tens of kHz as described above, this zero cross point becomes a time. Fluctuate.
This time variation causes jitter, which significantly deteriorates the error rate of the signal reproducing system and causes the reliability of the optical disk device to be impaired.

[0006]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems, and eliminates the "waviness" of the reproduced signal generated when the recorded information on the wobbled groove is reproduced to stabilize the jitter. The main purpose is to make it happen.

[0007]

The structure of the optical head of the present invention for solving the above-mentioned problems is as follows: 1) In an optical disk apparatus of the type for recording and reproducing information on an optical disk having a wobbled groove, a signal modulated from the optical disk is modulated. A light-shielding mask having a substantially rectangular opening whose longitudinal direction substantially coincides with the track groove direction is provided for the return light beam, and the aperture is restricted from the outside of the return light beam in the direction corresponding to the direction orthogonal to the track groove. Is characterized by.

2) Regarding the above 1), the optical disk is a magneto-optical recording medium, a dye-based write-once medium or a phase change recording medium.

[0009]

According to the above-mentioned structure of the present invention, 1) Since the aperture limit is applied from the outside of the return light beam in the direction corresponding to the direction orthogonal to the track groove, the light in the modulation area due to the wobble superimposed on the return light beam is shielded. You can It should be noted that since the aperture restriction hardly acts in the tangential direction, that is, the signal train direction, there is no adverse effect of reducing the reproduction signal amplitude.

2) With an optical disc having a wobbled groove, the wobble component superimposed on the reproduction signal can be removed regardless of the recording principle.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 1 is a perspective view showing an optical head 1 according to Embodiment 1 of the present invention. An actuator 10 drives the objective lens 60. 70 is an optical disk,
The recording surface has a wobbled groove 71, that is, a track groove, which meanders with a minute amplitude. Here, the first embodiment
The optical disk 70 is assumed to be a magneto-optical storage medium, and the optical head 1 is of a type that reproduces a magneto-optical signal.

The actuator 10 is controlled by a servo control circuit (not shown) so that the hologram laser unit 20 will be described later.
The energization is controlled based on the error signal (focus error signal and track error signal) detected by the objective lens 60.
Is precisely positioned in the vertical direction (focusing direction) and the radial direction (tracking direction) of the optical disk 70. In this way, servo control is performed so that the recording surface of the optical disk 70 is focused and at the same time the track groove is followed.

The optical system of the optical head 1 of the present embodiment includes an objective lens 60, a hologram laser unit 20, a collimator lens 30, a beam splitter 40, a mirror 50, a Wollaston prism 41, a condenser lens 45, and a second light receiving element 46. The optical components other than the objective lens are mounted on the chassis (not shown) on the fixed side. The hologram laser unit 20 houses a laser light source 22 which is a semiconductor laser and a first light receiving element 25 (FIG. 2, FIG.
(See FIG. 3).

The beam splitter 40 is a polarization beam splitter, which is formed by joining two triangular prisms made of general-purpose optical glass, and is the inclined surface 40 which is the joining surface.
A dielectric multilayer thin film is formed on a and functions as a polarization splitting surface. In this embodiment, the optical specifications of the beam splitter 40 having polarization are set to S wave reflectance ≈80% and P wave transmittance ≈100%.

The Wollaston prism 41, which is an analyzer, is formed by joining two thin triangular prisms made of lithium niobate (lithium niobate; abbreviation LN) to form an incident light flux (signal modulation light flux 37). A pair of detected light beams 38 detected into two components of +/- 45 degrees with respect to the polarization plane are separated and emitted.

In the first embodiment, the beam splitter 40
A light blocking mask 48 serving as an aperture limiting unit is provided between the Wollaston prism 41 and the Wollaston prism 41. The light-shielding mask 48 restricts the opening of the signal-modulated light beam 37 from both outer sides in the radial direction of FIG. 1, that is, in the direction orthogonal to the track groove (groove 71), and the longitudinal direction of the opening 48a is the track groove. Arranged to be parallel.

Next, the internal structure of the hologram laser unit 20 will be described with reference to FIGS. Reference numeral 22 is a laser light source which is a semiconductor laser, 23 is a cover plate, 24 is a hologram element in which a diffraction grating for branching a light beam is formed, and 25 is a first light receiving element which is a multi-division photodiode. Reference numeral 26 is a package for holding and housing the laser light source 22 and the first light receiving element 25, which is formed of epoxy resin or the like. The package 26 is a frame body having only one opening, and the opening surface is adhered and sealed by the cover plate 23. The hologram laser unit 20 of this embodiment is formed by combining these elements.

The optical function of the optical head 1 of the present embodiment configured as described above will be described separately for two types, that is, an error signal detection system for servo and a magneto-optical signal detection system.

<Error Signal Detection System> In FIGS. 2 and 3, the divergent light beam 29 emitted from the laser light source 22 is the cover plate 23.
And exits the hologram element 24, and its 0th-order light (light flux not diffracted by the hologram element 24) 31
Is converted into a substantially parallel light beam 32 by the collimator lens 30 of FIG. The light flux 32 is reflected by the inclined surface 40a of the beam splitter 40 by about 80%, and then is bent by the mirror 50 to become an incident light flux 33 to the objective lens 60. The incident light flux 33 is condensed by the objective lens 60 and forms a spot 75 on the recording surface of the optical disc 70. Optical disc 7
The reflected light flux 34 from 0 follows the reverse optical path, is reflected again by about 80% on the slope of the beam splitter 40, and enters the hologram element 24 as a light flux 35. The first backward luminous flux 36, which is the +/− 1st order light diffracted by the hologram element 24.
Passes through the cover plate 23 and enters the light receiving surface of the light receiving element 25, that is, the surface. In this embodiment, the astigmatism method is used as the focus error signal detection method, while the push-pull method is used as the track error signal detection method.
A detailed description of the diffraction pattern of the hologram 24 is omitted,
In order to embody such a detection method, the diffraction pattern is divided into two, and each diffraction pattern generates a pair of +/- 1st order diffracted light. The first light receiving element 25 has a light receiving portion of at least 4 channels.

<Optical Magnetic Signal Detection System> In FIG.
The reflected light flux 34 that is reflected at 0 and has undergone the polarization plane rotation modulation according to the optical modulation component, that is, the Kerr rotation angle is incident on the beam splitter 40 and is transmitted through the inclined surface 40a that is the polarization separation surface by about 20% of the reflected light flux 34. Signal modulated light beam 37
Becomes The signal-modulated light beam 37 is separated by the Wollaston prism 41 into a pair of detection light beams 38 which are detected as two components of +/− 45 degrees with respect to the light beam polarization plane. The light amount of each of the two detected light beams 38 changes differentially according to the change of the Kerr rotation angle. The detected light flux 38 is collected by the condenser lens 4
At 5, the second returning light beam 39 having a converging property is formed and is taken into the second light receiving element 46 which is a two-divided photodiode. Each of the second backward-direction light flux 39 also differentially changes its light amount according to the change of the Kerr rotation angle, and the output signals of the two channels of the second light receiving element 46 also change differentially. Therefore, this 2
A magneto-optical signal is generated by differentially calculating the output signal of the channel.

Next, the function of the light-shielding mask 48 which is the aperture limiting means, which is the greatest feature of the present invention, will be described with reference to FIG. Of the return light from the optical disc 70, the signal-modulated light beam 37 that has passed through the beam splitter 40 has a beam diameter D shown in FIG. 4A, in which the signal-modulated region 37a mainly subjected to the magneto-optical signal modulation. And a wobble modulation area 37b on which the light diffracted by the track groove (wobbled groove) is superimposed. The wobble modulation areas 37b are present on both left and right sides in parallel with the track groove (groove 71). When the entire region of the signal modulated light beam 37 is detected by the Wollaston prism 41 to generate a magneto-optical signal, the components of the wobble modulation region 37b are mixed and the wobble modulation component is unbalanced with respect to the pair of detected light beams 38. It is superimposed. Ideally, almost no imbalance should occur, but since the imbalance occurs due to the characteristics of the optical components, especially the Wollaston prism, it generally remains as a component that cannot be eliminated even by differential calculation. Therefore, as shown in FIG. 6 (b) of the conventional example, this has been a cause of causing "swell" in the reproduced signal 280 in synchronization with the wobble.

However, as in this embodiment, the light shielding mask 48
When the light in the wobble modulation area 37b is shielded with, the wobble component does not mix into the light flux incident on the Wollaston prism 41, so that the detected light flux 38 is purely the component modulated by the magneto-optical signal. Therefore, as shown in FIG. 4B, the reproduced signal 80, which is a magneto-optical signal, has no "waviness" and the envelope 81 becomes linear. Slice level 8 for the reproduced signal 81 in this state
When digital conversion is performed at the zero-cross point with 2, the stable signal detection with less jitter is performed, and the error rate of the optical disk device is significantly improved.

The transparent portion width H of the light shielding mask 48 shown in FIG. 4A is about 60 of the beam diameter D of the signal-modulated light beam 37.
It has been confirmed experimentally that the best setting is%.

In this case, since the light in the wobble modulation area 37b can be shielded and the light in the signal modulation area 37a is transmitted without being shielded, it is not necessary to reduce the amplitude of the reproduction signal.
Further, the light shielding mask 48 can be formed integrally with a chassis (not shown), which does not cause a cost increase. Further, although the light shielding mask 48 is installed immediately after the beam splitter 40 in this embodiment, the same effect can be obtained even if it is installed immediately after the Wollaston prism 41.

(Embodiment 2) Embodiment 2 relates to an optical head 2 assuming a dye-based write-once medium or a phase change recording medium, which will be described with reference to FIG. These two types of optical discs have different signal reproducing principles from the magneto-optical recording medium of the above-described first embodiment, and therefore have different optical head 2 structures.
An analyzer such as a Wollaston prism is unnecessary. That is, the brightness (that is, the contrast) of the recording signal is directly detected as the reproduction signal. However, on the recording surface of the optical disc 170, a wobbled groove 1 meandering with a minute amplitude is formed.
71 is the same as that of the first embodiment.

As shown in FIG. 5, the optical head 2 of the second embodiment has a laser light source 122, a collimator lens 130, a mirror 150, an objective lens 160 and a beam splitter 14.
0, the detection lens 145, and the light receiving element 146, and these optical components other than the objective lens are mounted on the fixed side chassis (not shown). The beam splitter 140 is a simple beam splitter without polarization and may be a plate-shaped half mirror. Also in the second embodiment, a light blocking mask 148 which is an aperture limiting unit is provided between the beam splitter 140 and the detection lens 145. The light blocking mask 148 has the same shape as the light blocking mask 48 of the first embodiment.

The principle of the servo error signal detection system and reproduction signal detection system of the optical head 2 configured as shown in FIG.
Since this is a well-known technique similar to that of the D playback device and the like, it will be omitted here. The laser light source 122 must have a high output (several tens of mW) in order to secure the writing power required as a recordable optical head.

Light-shielding mask 1 which is an aperture limiting means
The function related to 48 is similar to that of the first embodiment described above. That is, although the component of the wobble modulation area is mixed in the signal-modulated light flux 137 of the return light from the optical disc 170 that has passed through the beam splitter 140 as described in FIG. 4 of the first embodiment, it is shielded as in the present embodiment. When the light in the wobble modulation area is shielded by the mask 148, the signal-modulated component is purely extracted. Therefore, since the reproduced signal has no "waviness" and the envelope is linear, stable signal detection with little jitter is performed, and the error rate of the optical disk device is significantly improved.

[0029]

As described above, according to the present invention, 1) Since the aperture limit is applied from the outside of the returning light beam in the direction corresponding to the direction orthogonal to the track groove, the light in the modulation region due to the wobble is shielded in the returning light beam. be able to. It should be noted that since the aperture restriction hardly acts in the tangential direction, that is, the signal train direction, there is no adverse effect of reducing the reproduction signal amplitude. Therefore, it is possible to effectively remove the wobble component superposed on the reproduction signal in the related art, stabilize the signal jitter and reduce the error rate of the signal reproduction system, and as a result, it greatly contributes to the improvement of the reliability of the optical disk device. In addition, no special means is required, and the cost does not increase.

2) An optical disc having a wobbled groove can be widely applied to recordable CD devices, MD devices, etc. because it can remove the wobble component superimposed on the reproduction signal regardless of the recording principle.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an optical head according to a first embodiment of the present invention.

FIG. 2 is an exploded perspective view showing the periphery of the hologram laser unit in the optical head of the first embodiment.

FIG. 3 is a cross-sectional view showing the periphery of a hologram laser unit in the optical head of the first embodiment.

FIG. 4 is a diagram showing a function of a light-shielding mask which serves as an aperture limiting unit in the optical head of the first embodiment.

FIG. 5 is a perspective view showing an optical head of Example 2 of the present invention.

FIG. 6 is a diagram for explaining a reproduction signal waveform of a conventional optical head.

[Explanation of symbols]

 1, 2 Optical head 20 Hologram laser unit 22, 122 Laser light source 25 First light receiving element 30, 130 Collimator lens 36, 136 Signal modulated light beam 40, 140 Beam splitter 46 Second light receiving element 48, 148 Shading mask 50, 150 Mirror 60 , 160 Objective lens 70, 170 Optical disk 71, 171 Wobbled groove 80, 280 Playback signal 81, 281 Envelope 82, 282 Slice level 145 Detection lens 146 Photodetector

Claims (2)

[Claims] 1. An optical disk device of the type for recording and reproducing information on an optical disk having a meandering track groove (wobbled groove), wherein a longitudinal direction is the track groove direction with respect to a signal-modulated return light beam from the optical disk. An optical head comprising a light-shielding mask having a substantially rectangular opening that substantially coincides with, and limiting the opening from the outside of the return light beam in a direction corresponding to the direction orthogonal to the track groove. 2. The optical head according to claim 1, wherein the optical disk is a magneto-optical recording medium, a dye-based write-once medium, or a phase change recording medium.