JP2626279B2 - Optical recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus which detects a tracking error signal and monitors the state of an information track before and after information recording to detect a defect or the like at the time of recording.

[0002]

2. Description of the Related Art Conventionally, an optical recording / reproducing apparatus for recording / reproducing information concentrically or spirally on a rotating disk-shaped information recording medium by using optical means, for example, a laser beam, is well known. I have. This type of device has the advantages of being able to perform high-density recording and having a large recording capacity as compared with a magnetic disk device.

[0003] On the other hand, however, the information recording medium has more defects than the magnetic disk, and thus requires a function for ensuring the reliability of the recorded information. For this reason,
A method of determining the presence or absence of a recording defect by detecting the reproduction signal by rotating the information recording medium on which the information is recorded by one rotation is conceivable, but has a disadvantage that it takes time for one rotation to detect the defect. In order to prevent this, an optical recording / reproducing apparatus capable of detecting a reproduction signal in real time has been considered.

FIG. 4 is a block circuit diagram showing a configuration of a conventional optical recording / reproducing apparatus described in, for example, Japanese Patent Application No. 1-162662 capable of detecting such a reproduced signal. In the figure, 1 is a semiconductor laser that emits a laser light beam B, 2 is a drive circuit that drives the semiconductor laser 1,
Reference numeral 3 denotes a collimator lens arranged on the beam emission side of the semiconductor laser 1.

[0005] Reference numeral 4 denotes a diffraction grating for dividing the parallel light beam from the collimator lens 3 into zero-order light (first beam) and ± first-order light (second and third beams).
, A polarizing beam splitter arranged to receive the first, second, and third beams that have passed through
Reference numeral 9 denotes a reflection mirror, 7 denotes an objective lens, 8 denotes an information recording medium (optical disk) disposed close to the objective lens 7, and the quarter-wave plate 6, the reflection mirror 19, and the objective lens 7 are polarized beam splitters. 5 and the information recording medium 8.

Although the diffraction grating 4 is arranged between the collimator lens 3 and the polarizing beam splitter 5, it may be arranged between the semiconductor laser 1 and the collimator lens 3.

[0007] As shown in FIG. 5 or FIG. 6, the information recording medium 8 has information tracks T along the rotation direction of the disk (see arrows). A first beam B1 to a third beam B3 are irradiated on the information track T.
A plurality of pits P are recorded and reproduced by the light spot S1 of the beam B1. Therefore, the light spot S1 of the first beam B1 is always located at the center of the information track T.

On the other hand, the second beam B2 preceding the first beam B1 and the third beam B3 following the first beam B1 contribute as sub-beams for generating a tracking error signal during reproduction, as shown in FIG. Then, light spots S2 and S3 are radiated to positions deviated from the center of the information track T, and during recording, the state of the information track T is monitored as shown in FIG. , S3.

At the time of recording, the first beam B1 has a high light intensity, and the second beam B2 and the third beam B3
Is only set to a sufficiently small light intensity because it only contributes to monitoring of the state of the information track T.

Reference numeral 20 denotes a tilting mechanism provided in the diffraction grating 4, which responds to a switching signal C from the signal switching circuit 13 to
The diffraction grating 4 is slightly tilted in the direction of the arrow θ via a drive mechanism (not shown) so as to switch the directions of the beams B1 to B3. The light spot switching means 30 for switching the positions of the spots S2 and S3 of the second beam B2 and the third beam B3 is configured.

The semiconductor laser 1 to the objective lens 7, the reflection mirror 19 and the tilt mechanism 20 are provided on an information track T of the information recording medium 8 by a first beam B 1 to a third beam B 3.
A beam irradiation device for irradiating light.

9 and 10 are polarization beam splitters 5
Is a sensor system lens group that collects the parallel light fluxes of the beams B1 to B3 reflected by the optical system, and includes, for example, a convex lens 9 and a cylindrical lens 10. 11 is a sensor lens group 9
And 10 denotes an optical detection known device for receiving the transmitted beam, as shown in FIG. 7, 6 divided light receiving surfaces 11a~11f
have.

The center light receiving surfaces 11a to 11d are irradiated with a light spot S1 'by the reflected light of the first beam B1, and the light receiving surfaces 11e and 11f on both sides are irradiated with the second light spots S1'.
The spots S2 ′ and S3 ′ are irradiated by the reflected light of the beam B2 and the third beam B3, and the respective light receiving surfaces 11a to 11a
11f, the first beam B1 to the third beam B3 are individually detected.

In FIG. 4, Dad is a light amount signal corresponding to the sum of the light amount signals Da and Dd from the light receiving surfaces 11a and 11d, and Dbc is a sum of the light amount signals Db and Dc from the light receiving surfaces 11b and 11c. Light signal, D
e is a light receiving surface 11e corresponding to reflected light of the second beam B2.
Is a light amount signal from the light receiving surface 11f corresponding to the reflected light of the third beam B3.

Reference numeral 12 denotes light amount signals Dad and Dbc,
An interlocking switch 13 for simultaneously switching and selecting De and Df; a signal switching circuit 13 for operating the interlocking switch 12 to switch the detection system of the tracking error signal E; A differential amplifier 15 that outputs a tracking error signal E based on the difference between the light amount signals, 15 is a tracking error signal detector that detects the tracking error E from the differential amplifier 14, and 16 is an information track based on the light amount signal De. A pre-recording monitor for detecting the pre-recording state of T, 17 is a post-detection monitor for detecting the recording state of the information track T based on the light amount signal Df, and 18 is an output from the pre-recording monitor 16 and the post-recording monitor 17. A recording / reproduction control unit that detects information such as a recording state and a sector number based on the information.

Next, the operation of the conventional optical recording / reproducing apparatus will be described with reference to FIGS. First, when reproducing information already recorded on the information recording medium 8, the beam B composed of a divergent light beam emitted from the semiconductor laser 1 becomes a parallel light beam via the collimator lens 3, and transmits through the diffraction grating 4. Are divided into a zero-order first beam B1 emitted in the same direction as the incident parallel light beam, and ± first-order second and third beams B2 and B3 emitted slightly deflected with respect to the incident parallel light beam. You. Thereafter, the light is irradiated onto the information recording medium 8 via the polarizing beam splitter 5, the quarter wavelength wave 6 and the objective lens 7, and on the information track T, as shown in FIG. Form S3.

At this time, the light intensity of each of the beams B1 to B3 is not modulated and has a constant output.
And the light intensity ratio between the second beam B2 and the third beam B3 are arbitrarily set by the design of the diffraction grating 4. Further, the light spot S1 of the first beam B1 illuminates the center of the information track T, and the second beam B2 and the third beam B3 serving as sub-beams for tracking error signal detection
The light spots S2 and S3 are respectively radiated to positions shifted from the center of the information track.

Subsequently, each of the beams B1 to B3 reflected by the information recording medium 8 again passes through the objective lens 7 and the quarter-wave plate 6, and reaches the polarization beam splitter 5.
By reciprocating the quarter-wave plate 6, the polarization direction becomes 90.
゜ Because it is rotated, it is reflected by the polarization beam splitter 5. Each beam B1~B3 This reflected further via a sensor system lens group 9 and 10 is focused on the optical detection knowledge 11, to form a light spot S1'～S3 'as in FIG.

At this time, since the light spot S1 'by the first beam B1 includes the recording information of each pit P on the information track T, the light amount signal of the light receiving surfaces 11a to 11d irradiated with the light spot S1' By taking the sum of Da to Dd, a reproduced signal can be obtained. Note that the configuration of the detection system for obtaining the reproduction signal is well known, and is not illustrated here.

Further, six light receiving surface 11a of the optical detection knowledge 11
Each of the light amount signals Da to Df detected at 11f to 11f is used for a calculation based on a known signal detection method, whereby a focusing error signal by the astigmatism method and a tracking error signal by the three-beam method are generated. Although not described in detail here, as a tracking error signal detection method, the above-mentioned three-beam method is generally used in a read-only type optical disk such as a CD (compact disk) player. This is known to be a simple and effective method.

At the time of reproduction, the interlocking switch 12 is switched from the state shown in FIG. 4 by the signal switching circuit 13, and selects the light amount signals De and Df from the light receiving surfaces 11e and 11f, respectively. At this time, the tracking error signal output from the differential amplifier 14 is E =
De-Df, which is the difference between the light amount signals De and Df. This tracking error signal E is input to the tracking error signal detector 15, and it is determined whether or not the reproduction information is normal. Also, the light amount signals De and Df
Are the monitor 16 before recording and the monitor 17 after recording, respectively.
However, the monitor operation is not performed during reproduction.

On the other hand, when information is recorded on the information recording medium 8, the driving circuit 2 operates based on the recorded information.
Is pulsed to emit a beam B containing recording information (for example, information corresponding to a pulse width). This beam B
Is divided into a first beam B1 to a third beam B3 in the same manner as described above, and is irradiated on the information track T as light spots S1 to S3. Here, the signal switching circuit 13 controls the tilting mechanism 20 by the switching signal C to rotate the diffraction grating 4 in the direction of the arrow θ, and moves the light spots S2 and S3 to the center position of the information track T as shown in FIG. Irradiate.

At this time, the light intensity of the first beam B1 for recording is large, but the light intensity of the second beam B2 and the third beam B3 is set to a light intensity sufficiently smaller than that of the first beam B1. So it has no effect on the record.

The light spot S1 is reflected at the same time that pits P having a shape corresponding to recording information are sequentially formed on the information track T. Light spot S preceding light spot S1
2 is reflected on the information track T before recording, and the light spot S3 following the light spot S1 is reflected on the pit P after recording.

Hereinafter, similarly to the above, each of the beams B1 to B3
The reflected light, but become a light spot S1'～S3 'is applied to the optical detection knowledge 11, the generation process of the recording time of the tracking error signal E is different from that during reproduction, the push-pull method is used .

The push-pull method is a method of superimposing the reflected light of the first beam B1 diffracted under the influence of the groove formed along the information track T and the directly reflected light of the first beam B1 from the information track T. This is a method of detecting a deviation of the information track T from a far field pattern (a light spot pattern having a spread) due to the alignment. Therefore, the interlock switch 12 selects the light amount signals Dad and Dbc in the state shown in FIG.
Is: E = (Da + Dd) − (Db + Dc) = Dad−Dbc

At this time, the second beam B2 and the third beam B3 are not used for detecting the tracking error signal E, but are inputted to the pre-recording monitor 16 and the post-recording monitor 17, and the information before and after the recording is recorded. Used for detecting the state of the track T. That is, whether or not the information track T before recording has a defect is checked by the reflected light of the second beam B2, and whether the pit P is normally recorded on the information track T by the reflected light of the third beam B3. Check whether or not.

The pre-recording monitor 1 thus obtained
6 and a monitor signal from the post-recording monitor 17 are input to the recording / reproduction control unit 18. If the recording / reproduction control unit 18 determines that there is a defect, it performs processing such as recording again to improve the recording error rate on the information recording medium 8.

[0029]

Since the conventional optical recording / reproducing apparatus is configured as described above, it is necessary to rotate the diffraction grating between recording and reproducing. But 3
In the beam method, the position of the sub-beam requires sub-micron accuracy with respect to the center of the information track,
There is a problem that the driving mechanism of the diffraction grating becomes complicated, responsiveness deteriorates, and the cost increases.

Further, when the set angle of the diffraction grating deviates from the design value, there is another problem that the amplitudes of the monitor signal and the tracking error signal decrease.

The present invention has been made in order to solve the above-described problems, and deflects the direction of the diffracted light while fixing the demultiplexing means such as a diffraction grating, thereby providing the diffracted light with
An object of the present invention is to provide an optical recording / reproducing apparatus which can have a monitoring function at the time of recording and a function of detecting a tracking error signal by a three-beam method at the time of reproduction.

[0032]

An optical recording / reproducing apparatus according to the present invention uses a liquid crystal panel for light spot switching means.
The two narrow striped electrodes of this liquid crystal panel are
It is characterized in that by combining them with a slight shift in angle, a function of a diffraction grating diffracting in two directions is provided.

[0033]

The liquid crystal panel constituting the light spot switching means in the present invention can obtain the same effect as rotating the diffraction grating without rotating the liquid crystal panel by selectively switching the electrodes to be applied. it can.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. First, the liquid crystal panel 28 constituting the light spot switching means 30 will be briefly described with reference to FIG. Liquid crystal 25
Is sandwiched between two glass plates 27, and polarizing plates 22 and 26 are provided on both sides. No voltage applied V = 0 (FIG. 3
In (a)), when the linearly polarized light 21 transmitted through the incident polarizer 26 is transmitted through the liquid crystal 25, the polarization direction is rotated by 90 ° due to the light-emitting properties of the liquid crystal, and the polarization axis of the incident-side polarizer 26 is orthogonal to the polarization axis. Through the exit-side polarizing plate 22 arranged so that

On the other hand, when a voltage V equal to or higher than the threshold voltage Vth is applied (FIG. 3B), the light-emitting property of the liquid crystal 25 decreases, and the amount of light transmitted through the exit-side polarizing plate 22 increases. It decreases with. A one-dimensional comb-shaped transmission control element can be formed by forming electrodes in a one-dimensional array using such a transmittance control action. The liquid crystal 25 shown in FIG. 3 has a TN (Twisted) angle of 90 °.
Nematic liquid crystal was used in the normally white mode. As is well known, other types of modifications are known for the type of the liquid crystal phase, the size of the light application angle, and the like. However, since they are not related to the subject of the present invention, the description is omitted.

Next, the apparatus of this embodiment will be described with reference to FIGS. FIG. 1 is a configuration diagram of an optical recording / reproducing apparatus according to an embodiment of the present invention. The components other than the liquid crystal panel 28 and the polarizing plate 22, which are the components of the light spot switching means 30, are the same as those of the conventional example, and therefore the description is omitted. In the figure, 28 is a liquid crystal panel, and 22 is a polarizing plate.

Next, the structure of the liquid crystal panel 28 will be described with reference to FIG.
Will be described. In the figure, a liquid crystal 25 is sandwiched between two glass substrates 27, and a pair of striped transparent electrodes 23a and 23b is arranged between the glass substrates 27. Each of the electrodes is formed in a stripe shape having a width of several tens of μm, and is configured so that a voltage can be applied to every other electrode. Also, the striped transparent electrodes 23a, 23
An angle θ is provided between b. The angle θ is determined by the light spots S2 and S3 irradiated on the information recording medium 8.
Is an angle formed by a straight line connecting the light spots S2 and S3 between the case where the light spot S is arranged on the information track T and the case where the light is emitted to a place shifted by about 1/4 track pitch from the information track T.

Next, the operation will be described. First, the operation of the light spot switching means 30 will be described. When a voltage V equal to or higher than the threshold is applied, a voltage is applied to every other transparent electrode 23 in the form of a stripe. Can alternate. That is, the state becomes the same as the state where the diffraction grating exists, and the light beam incident on the liquid crystal panel 28 is split.

Next, recording and reproduction will be described. At the time of recording, the signal switching circuit 13 applies the electrode V to the transparent electrode 23a on the stripe by the switching signal C. The transparent electrode 23a in the form of a stripe forms the second beam B2
And the light spot S of the third beam B3 on the information recording medium
Since the directions of the electrodes are set so that 2 and S3 irradiate the information track T, the light spots S2 and S3 irradiate the center position of the information track T. Therefore, the amount of reflected light is sufficient, and a monitor signal with a high SN ratio is obtained from the pre-recording monitor 16 and the post-recording monitor 17, thereby improving the reliability of defect detection in the recording control unit 18. At the same time, the signal switching circuit 13
The interlock switch 12 is switched to the state shown in FIG.
And Dbc, and detecting (Dad-Dbc) as the tracking error signal E is the same as in the conventional example.

Next, at the time of reproduction, the signal switching circuit 13
A voltage V is applied to the stripe-shaped transparent electrode 23b by the switching signal C. The striped transparent electrode 23b is
The spots S2 and S3 of the beam B2 and the third beam B3 on the information recording medium are positioned one (1) from the center of the information track T.
Since the direction (angle θ) of the electrode is set so as to irradiate a position shifted by / 4 track pitch, the light spots S2 and S3 are about 1 distance from the center position of the information track T.
Irradiate a place shifted by / 4 track pitch. Therefore, the signal switching circuit 13 switches the interlock switch 12 from the state shown in FIG.
The tracking error signal by the beam method has the maximum amplitude.

Therefore, in the optical recording / reproducing apparatus of this embodiment, the liquid crystal panel 2 is selected by selecting a stripe-shaped transparent electrode to which a voltage is applied during recording and during reproduction.
It is possible to select to use the sub-beam obtained in step 8 as a monitor for information tracks before and after recording during recording and to use it as a beam for detecting a tracking error signal by the three-beam method during reproduction. In FIG. 3, the polarizing plate 26 is also provided on the incident side. However, since the beam B emitted from the semiconductor laser 1 is generally linearly polarized, the light beam shown in FIG. The incident side polarizing plate 26 is unnecessary.

In the above embodiment, the width of one stripe-shaped transparent electrode 23 is on the order of several tens of μm, and the diffraction grating is formed so that every other electrode can be turned on / off. If the width of one electrode 23 is made narrower and the structure can be controlled one by one, the pitch and duty of the diffraction grating can be controlled, so that the monitor position can be changed or the track pitch can be changed. Can respond.

In the above-described embodiment, the diffraction grating is formed so that transmission / non-transmission is formed every other stripe-shaped transparent electrode 23. However, a stripe-shaped transparent electrode and a retardation plate are used. Thereby, a phase difference diffraction grating may be formed.

[0044]

As described above, according to the present invention, the transparent electrodes of the liquid crystal panel are formed in stripes, and the two transparent electrodes in stripes are arranged at a predetermined angle θ.
By selecting the transparent electrode to which the voltage is applied, the same action as the diffraction grating is performed, the light spot is switched, and the position of the sub beam on the information track is controlled, so that recording is performed without mechanical movement. An optical recording / reproducing apparatus capable of detecting a high-quality monitor signal during recording and a stable tracking error signal during reproduction can be obtained.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing a configuration of an optical recording / reproducing apparatus according to one embodiment of the present invention.

FIG. 2 is a perspective view of the liquid crystal panel of the present embodiment.

FIG. 3 is a perspective view for explaining the operation of the liquid crystal panel of the present embodiment.

FIG. 4 is a block circuit diagram showing a configuration of a conventional optical recording / reproducing apparatus.

FIG. 5 shows a light spot irradiation position at the time of reproduction.
FIG. 2 is an enlarged perspective view showing a recording surface of an information recording medium in the inside.

FIG. 6 shows a light spot irradiation position at the time of recording;
FIG. 2 is an enlarged perspective view showing a recording surface of an information recording medium in the inside.

7 is a plan view showing a light receiving surface of the test known device in FIG.

[Explanation of symbols]

1 semiconductor laser 8 information recording medium 11 light detection intelligence unit 11a~11f receiving surface 13 signal switching circuit 16 before recording the monitor 17 after recording the monitor 22 polarizing plate 28 liquid crystal panel 30 an optical Suppoto switching means

Claims (1)

(57) [Claims] A first beam, a second beam preceding the first beam, and a third beam following the first beam along an information track on the information recording medium; and an optical detector having a plurality of light receiving surfaces for detecting separately the light reflected from the information recording medium of the second and third beams, the light receiving corresponding to the reflected light of the second and third beam during reproduction An optical recording / reproducing apparatus configured to detect a tracking error signal based on each light amount signal from a surface and to monitor a state before and after recording on the information track based on each light amount signal during recording, The beam irradiation device is provided with a liquid crystal panel having at least two stripe-shaped transparent electrodes formed so as to intersect at a predetermined angle, and disposed in contact with the liquid crystal panel. An optical recording / reproducing apparatus, comprising: a light spot switching means comprising a polarizing plate and a means for selectively applying a voltage to the stripe-shaped transparent electrode.