JP3006827B2 - Optical head 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 head device used for recording, reproducing or erasing information on an optical disk, for example, and more particularly to recording information using a phase change medium. The present invention relates to an optical head device for performing the operation.

[0002]

2. Description of the Related Art Research on an external storage device that satisfies both the high-speed accessibility of a magnetic disk for a computer and the storage capacity of an optical disk is rapidly progressing. The next-generation external storage device is capable of high-speed random access at a high transfer rate, has a large capacity, and has excellent storage characteristics of a medium. An optical disk device that satisfies these conditions and has the characteristic of non-contact medium durability is most promising as a next-generation external storage device.

[0003] Among such optical disk devices, rewritable devices can write data to the same area many times. Such devices include a magneto-optical recording type and a phase change recording type. In the latter device,
Recording and reproduction are performed using the fact that the reflectance changes depending on whether the recording film is in a crystalline state or an amorphous state.

FIG. 5 shows an example of a configuration of an optical head device corresponding to a phase change medium.
No. 08643. This optical head device includes two types of lasers, a first laser 11 and a second laser 12. The first laser 11 outputs, for example, 680 nm laser light, and is used for recording or reproducing information. The light emitted from the first laser 11 is converted into parallel light 14 by a first collimator lens 13, and the first beam splitter 1 disposed in front thereof
5 and the second beam splitter 16. After passing through the 波長 wavelength plate 17, the light enters the objective lens 18 and is condensed, and a recording or reproducing beam is formed on the optical disk 19. This beam and its reflected light are shown by solid lines in FIG.

[0005] A recording beam is a beam that is switched based on a recording signal. For the reproduction beam, an output smaller than the average power during recording is used.

On the other hand, the second laser 12 is for erasing information. This beam, for example at a wavelength of 780 nm, is indicated by the dashed line in FIG. The emitted light of the second laser 12 is converted into a parallel light 22 by a second collimator lens 21 and a first beam splitter 15 disposed in front of the parallel light 22.
And is deflected by 90 degrees. Then, the aforementioned 680
After multiplexing with the laser light of nm, the same optical path is followed to the objective lens 18. The erasing beam having a wavelength of 780 nm is focused by the objective lens 18 to form an erasing beam on the optical disc 19.

By the way, the reflected light of the light beam applied to the optical disk 19 travels through the objective lens 18, the quarter-wave plate 17, and the second beam splitter 16 in the reverse direction. The reproducing or erasing beam 34 is the second beam.
The light is deflected by 90 degrees by the beam splitter 16 and condensed by the converging lens 35. Between the converging lens 35 and its focal point, a two-divided optical sensor 36 also serving as a knife edge is arranged to detect a tracking error signal. The light beam that travels straight without being blocked by the two-part light sensor 36 is a semicircular beam. This semicircular beam is received by another two-divided optical sensor 37 arranged on the focal plane. The two-part light sensor 37 is for detecting a focus error signal. These two split optical sensors 3
An RF signal is obtained from the combined outputs of 6, 37.

FIG. 6 shows the wavelength characteristics of a dichroic mirror for multiplexing two types of light beams for recording and reproduction and for erasing. The wavelength point of the recording laser is 680 nm as indicated by the arrow, and the wavelength point of the erasing laser is 780 nm as indicated by the other arrows. In this case, the ratio (polarization ratio) between the transmittance (T) and the reflectance (R) of the laser at 680 nm is 96/96 from the figure.
4, which is “24”. Similarly, the ratio between the reflectance and the transmittance at 780 nm (polarization ratio) is 97/3 from the figure.
And “32”, and these 680 nm and 780 n
Both wavelengths of m can be multiplexed as straight light and 90-degree polarized light.

FIG. 7 shows the sizes of the reproducing beam and the erasing beam on the optical disk shown in FIG. 5, respectively. On the optical disk 19, a reproduction beam 31 having a width t and a shape close to a perfect circle having a length a ₁ and a length having the same width t and a longer diameter in the tangential direction 32 of the optical disk 19 than the length a _1. a ₂
Is formed. In the case of a phase-change medium, by making the shape of the erasing beam 33 longer in the tangential direction of the optical disc 19, the heat distribution in this direction can be made gentle. This facilitates the formation from a non-crystalline (amorphous) state to a crystalline state.

In order to increase the size of the erasing beam 33 with respect to the tangential direction 32 of the optical disk 19, the aspect ratio of the beam composed of the parallel light to the objective lens 18 may be increased. That is, in order to narrow the light beam in the radial direction of the optical disk 19, the diameter of the parallel beam is increased to make the diameter of the entrance pupil of the objective lens 18 full, and the numerical aperture (NA) is increased. Further, in order to increase the beam convergence in the tangential direction of the optical disk 19, the diameter of the parallel beam is formed small, and the apparent numerical aperture NA is reduced.
And the convergent beam can be an elliptical beam.
In this equation (1), λ is a wavelength, and K is a constant.

[0011]

(Equation 1)

However, there has been a problem that the method of erasing information by the two-beam configuration including the erasing beam and the recording / reproducing beam cannot perform erasing sufficiently.

FIG. 8 shows the relationship between the bit error rate and the number of erasures. The vertical axis indicates the bit error rate (BER), and the horizontal axis indicates the number of times of erasing information. This figure shows a bit error rate when overwriting (OW) is performed without erasing and a state where the bit error rate is reduced by repeating erasing. In order to reproduce a digital video signal in a favorable state, it is necessary to secure a bit error rate of 3 × 10 ⁻⁵ or less as a BER limit indicated by oblique lines 41.

For this purpose, an optical head having a two-beam configuration as shown in FIG. 7 is used, or a plurality of optical heads are arranged and a synchronous operation is performed on the same track. Will be. Such a method is pseudo overwrite (QOW) recording in which a signal is written by a recording head after information is erased by an erasing head in advance. The recording signal was (1,7) RLL digital modulation, and the bit error rate was measured when the shortest bit length was 0.335 μm / bit. At 12 m / s, the recording rate is 12 / 0.335 × 10 ⁶ , which is 35.8
Mbps. With this recording rate, NTSC
In the case of a (National Television System Committee) digital video signal, recording and reproduction can be performed with 1/4 compression, and a recording and reproduction system with less deterioration in image quality can be realized.

[0015]

The bit error rate is better when pseudo overwrite is performed than when overwrite is performed. However, even if the size of the erasing beam 33 is increased as shown in FIG. 7, the bit error rate is 1 × 10 ⁻⁴ and the BER limit is 3 × 10 ^−4.
A bit error rate of 10 ^-5 or less cannot be secured. As described above, when information is to be erased by the conventional optical head, there is a problem that even if the size of the beam for erasing is increased, the information cannot be sufficiently erased by the pseudo overwrite.

In the method of performing synchronous operation using a plurality of erasing lasers, it is necessary to record the track address of an optical disk in advance and perform synchronous operation of a plurality of heads. Therefore, there is a problem that it can be realized but lacks reliability.

An object of the present invention is to provide an optical head device which can obtain good erasing characteristics in a phase change medium without using a plurality of heads for erasing information.

Another object of the present invention is to provide an optical head device capable of realizing high-density recording using such a phase change medium.

[0019]

According to the first aspect of the present invention, (a) a first laser for emitting a plurality of erasing beams having a first wavelength, and (b) different from the first wavelength. A second laser that emits a recording / reproducing beam having a second wavelength, and (c) a phase change medium that rotates in a predetermined direction.
A plurality of the rotation direction of the erasing beam optical emitted from the first laser on the same track of that disc
Preceded by the relationship are arranged at different positions that do not overlap each other, irradiating in parallel these beams each temporally on the track as the recording beam of the second laser is arranged after these And an optical system to be provided.

That is, according to the first aspect of the present invention, a plurality of erasing beams having a first wavelength are emitted from the first laser, and a laser having a second wavelength different from the first wavelength is emitted from the second laser. Inject. Then, a plurality of erasing beams emitted from the first laser are radiated onto the same track of the optical disk made of the phase change medium so as to be arranged at different positions in advance, and after that, a second beam is erased. By irradiating so that the recording beam of the laser is arranged, erasing can be performed a plurality of times with the first laser before recording with the second laser, and good erasing characteristics can be obtained. . Further, the recording density can be improved by reducing the bit error rate.

According to the second aspect of the present invention, (a) a first laser for emitting an erasing beam having a first wavelength;
(B) beam splitting means for entering the beam emitted from the first laser and splitting the beam into a plurality of beams; and (c) emitting a recording / reproducing beam having a second wavelength different from the first wavelength. a second laser consists (d) phase change medium
A plurality of erasing beams split by the beam splitting means on the same track of the optical disc rotating in a predetermined direction are arranged at different positions which do not overlap with each other in advance in relation to the rotation direction of the optical disc. The optical head device is provided with an optical system for irradiating the recording beams of the second laser on the track in parallel with each other so that the recording beams are arranged after the recording. .

That is, according to the second aspect of the invention, while the erasing beam of the first wavelength is emitted from the first laser, the beam is split into a plurality of erasing beams by the beam splitting means. In addition, a laser having a second wavelength different from the first wavelength is emitted from the second laser. A plurality of erasing beams emitted from the first laser are radiated onto the same track of the optical disk made of the phase change medium so as to be arranged at different positions in advance, and
After that, by irradiating the recording beam of the second laser so as to be arranged, it is possible to perform erasing a plurality of times with the first laser before performing recording with the second laser, and to obtain good erasing characteristics. I'm trying to get. Further, the recording density can be improved by reducing the bit error rate.

According to the third aspect of the present invention, (a) a first laser for emitting a plurality of erasing beams having a first wavelength, and (b) a plurality of beams emitted from the first laser. (D) a beam splitting means for entering each of them and splitting them into a plurality of beams; (c) a second laser for emitting a recording / reproducing beam having a second wavelength different from the first wavelength; times in a predetermined direction becomes a phase change medium
A plurality of erasing beam optical disks times divided by the beam splitting means on the same track of the optical disc to rolling
These beams are arranged on the track so that the recording beams of the second laser are arranged at different positions which do not overlap with each other in advance in relation to the turning direction, and thereafter the recording beams of the second laser are arranged. The optical head device is provided with an optical system for irradiating each in parallel in time .

That is, according to the third aspect of the present invention, while a plurality of erasing beams are emitted from the first laser, each erasing beam is divided into a plurality of erasing beams by the beam dividing means. Thus, for example, if the first laser emits two erasing beams and the beam splitting unit divides one erasing beam into two, a total of four erasing beams are created. A laser having a second wavelength different from the first wavelength is emitted from the second laser. As a result, information can be recorded on the same track of the optical disk made of the phase change medium after erasure is repeatedly performed with all the erasing beams after division, so that good erasing characteristics can be obtained. In addition, the recording density can be improved by reducing the bit error rate.

According to a fourth aspect of the present invention, the optical system is characterized in that a beam guided onto an optical disk is multiplexed by a dichroic mirror.

According to the fifth aspect of the present invention, there is provided the second aspect.
The beam splitting means according to the third aspect of the present invention comprises a Wollaston prism for splitting the incident beam into two, and a quarter for converting the split beam into circularly polarized light.
And a wave plate.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows the configuration of an optical head device according to an embodiment of the present invention. This optical head device has a 680 nm laser 51 and a 780 nm two beam laser 52. The divergent light 53 emitted from the laser 51 is converted into an elliptical parallel light by the collimator lens 54. The parallel light is obliquely incident on a wedge-shaped composite prism 55 and travels straight through a polarization beam splitter 56. Then, the light is reflected by a 45-degree mirror 57 formed on the prism surface, is deflected by 90 degrees, changes its course upward in the figure, and passes through a quarter-wave plate 58 disposed on the upper outside of the composite prism 55 to form a straight line. It is converted from polarized light to circularly polarized light. The converted light beam travels straight through a flat dichroic mirror 59 and is converged as a recording / reproducing beam 65 on an optical disk 64 that rotates about a central axis 63 by an objective lens 62 incorporated in a biaxial actuator 61. .

On the other hand, the light emitted from the two-beam laser 52 having a wavelength of 780 nm for erasing is converted into parallel light by the collimator lens 71 disposed in the cylinder of the laser pen 70, and is incident on the surface of the dichroic mirror 59 at an angle of 45 degrees. And are reflected at the same angle. After all, this outgoing light is 9
The light is deflected by 0 degrees, is multiplexed with the 680 nm beam emitted from the mirror, and is incident on the objective lens 62. Then, the beams converge on the optical disk 64 as erasing beams 72 and 73.

Of the three beams 65, 72 and 73 converged on the optical disk 64 in this manner, signal reproduction, focus error detection and tracking error detection are performed by the 680 nm recording / reproducing beam 65. That is, the reflected light of the recording / reproducing beam 65 of 680 nm on the optical disk 64 again enters the objective lens 62 as shown by the solid line, passes through the dichroic mirror 59 this time, and is attached to the upper portion of the composite prism 55.
The light passes through the 波長 wavelength plate 58. At this time, circularly polarized light is converted to linearly polarized light. Then, 45 formed on the prism surface
The light is reflected by the degree mirror 57 and deflected by 90 degrees, and is incident on the polarization beam splitter 56 as an S wave.

The 680 nm beam 65 is partially reflected by the polarization beam splitter 56, deflected by 90 degrees, emitted from the composite prism 55, and reflected by a first beam splitter 75 provided therebelow. The beam deflected by 90 degrees in this manner is converted into a convergent lens 76.
Converges on the first optical sensor 78, and the detection of the RF signal is performed.

On the other hand, the first beam splitter 7
The light beam that travels straight through 5 and is transmitted is divided by the second beam splitter 77 into a beam that travels straight and a beam that reflects and deflects 90 degrees. The beam that goes straight among them reaches the second optical sensor 79, and the tracking error is detected. The beam reflected by the second beam splitter 77 and deflected by 90 degrees is supplied to the third optical sensor 80.
, And the focus error is detected. These detection signals 81 and 82 are input to a servo drive circuit 83,
Drive control of the two-axis actuator 61 is performed.

Modification

FIG. 2 shows a main part of an optical head device as a modification of the present invention. The same parts as those in the previous embodiment are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

In this modification, a one-beam laser 102 is attached to a laser pen 101. The light emitted from the one-beam laser 102 enters the Wollaston prism 103. The polarization axis of the incident beam is set to 45 degrees with respect to the joint surface of the Wollaston prism 103. The Wollaston prism 103 divides this beam into a P wave and an S wave into two at a full angle of about 1 degree and an output ratio of 1: 1 to obtain linearly polarized light having orthogonal polarization planes. These beams divided into two beams in this manner are incident on the 波長 wavelength plate 104. When the crystal axis of the quarter-wave plate 104 is set to 45 degrees with respect to the polarization axis of the beam, the light becomes clockwise and counterclockwise circularly polarized light with respect to the linearly polarized light. These two beams enter the collimator lens 105 and are emitted from the laser pen 101 as parallel light.

The two beams emitted from the laser pen 101 obliquely enter the dichroic mirror 59 and
Deflected by 0 degrees, the composite prism 55 described in the previous embodiment,
Quarter wavelength plate 58 and dichroic mirror 59
And a beam having a wavelength of 680 nm. Then, the light is incident on the objective lens 62, and on the optical disk 64, in the same track as in the previous embodiment, a recording / reproducing beam 65 having a wavelength of 680 nm and erasing beams 72 and 73 having a wavelength of 780 nm.
Will converge.

In the optical head device of this modified example, similarly to the previous embodiment, the reflected light of the 680 nm beam is used to generate an RF signal.
Signal detection, focus error detection, and tracking error detection are performed.

In the embodiment and the modified example described above, 2
The number of erasures for the phase change medium was set to two using two erasing beams 72 and 73. For a phase change medium requiring more erasure times, this condition can be satisfied by, for example, combining the optical system of the above embodiment and the modified example. That is, the two beams emitted from the two-beam laser 52 in FIG. 1 are incident on the Wollaston prism 103 shown in FIG.
It is also possible to form four beams, converge four erasing beams on the same track on the light beam 64, and record information after performing four erasing operations.

FIG. 3 shows the bit error rate characteristics with respect to the recording bit wavelength for both the overwrite and the pseudo overwrite. In the figure, the broken line shows the overwrite curve 111, and the solid line shows the pseudo overwrite curve 112. The criterion 113, which is the limit of the bit error rate at which the digital video signal can be rendered by good signal processing, is 3 × 10 ⁻⁵ . In the case of the overwrite curve 111, the bit length in the reference 113 is a position 114 where the bit length is 0.36 μm.
It becomes 15. That is, in the case of the pseudo overwrite curve 112, the recording density in the tangential direction of the optical disc 64 is improved by 1.2 times as compared with the overwrite curve 111.

FIG. 4 shows the linear velocity dependence of the bit error rate due to recording and reproduction for both overwrite and pseudo overwrite. In the figure, the broken line shows the overwrite curve 121, and the solid line shows the pseudo overwrite curve 122.
Is shown. Assuming that the evaluation criterion of the bit error rate is 3 × 10 ^−5, which is the same as that in FIG.
In the case of 21, a linear velocity of 16 m / S corresponds to this. On the other hand, in the case of the pseudo overwrite curve 122, 2
A linear velocity of 5 m / S corresponds to this. In optical recording, high-density recording and high-speed recording are important, and it can be seen that pseudo overwriting is more advantageous than overwriting.

In this embodiment, it is possible to improve the bit error rate by intentionally recording a phase-change medium that can be overwritten by pseudo overwriting.
In addition, high-density recording becomes possible as a result of the bit error rate characteristics corresponding to the bit wavelength. In this embodiment, the recording density can be improved about 1.2 times by this position overwriting.

In the embodiment, two laser pens are used.
Although three beams are emitted, three or more beams may be emitted. Also,
In the modified example, the beam is split into two using the Wollaston prism 103, but it is obvious that the beam may be split into two or more using other optical elements. In the embodiment and the modification, 680 is used.
Although lasers of nm and 780 nm are used, it goes without saying that lasers of other wavelengths may be used.

[0043]

As described above, according to the first aspect of the present invention, a plurality of erasing beams having a first wavelength are emitted from a first laser and the first laser is emitted from a second laser.
And a plurality of erasing beams emitted from the first laser are previously arranged at different positions on the same track of an optical disk made of a phase change medium. In addition to the above, irradiation is performed so that the recording beam of the second laser is disposed after these. This allows the first laser to time the same spot on the track before recording with the second laser.
A plurality of erase operations can be performed at different intervals, and good erase characteristics can be obtained. Further, the recording density can be improved by reducing the bit error rate.

According to the second aspect of the present invention, the first
While the laser beam of the first wavelength is emitted from the laser beam, the beam is split into a plurality of erase beams by the beam splitting means. Accordingly, a plurality of erasing beams can be obtained as a result from the same laser, and the beam emitted from the first laser before recording with the second laser can be obtained.
A plurality of erasing operations can be performed on the same portion of the track at different times, and good erasing characteristics can be obtained. Further, the recording density can be improved by reducing the bit error rate.

According to the third aspect of the present invention, while a plurality of erasing beams are emitted from the first laser, each erasing beam is divided into a plurality of erasing beams by beam splitting means. Therefore, tiger beam emitted from the first laser before performing the recording by the second laser
It is possible to perform the erasing operation at the same place on the disk at a greater number of times at different times, and the more the number of erasing times, the better the information erasure becomes. It is possible to obtain better erasing characteristics than the invention described in claim 1 or 2. In addition, it is possible to further improve the recording density by reducing the bit error rate.

[Brief description of the drawings]

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

FIG. 2 is a schematic configuration diagram illustrating a main part of an optical head device according to a modified example of the invention.

FIG. 3 is a characteristic diagram showing bit error rate characteristics with respect to a recording bit wavelength for both overwrite and pseudo overwrite.

FIG. 4 is a characteristic diagram showing a linear velocity dependency of a bit error rate by recording / reproduction for both overwrite and pseudo overwrite.

FIG. 5 is a schematic configuration diagram showing a main part of a conventional example of an optical head device corresponding to a phase change medium.

FIG. 6 is a characteristic diagram showing wavelength characteristics of a dichroic mirror for multiplexing two types of light beams for recording and reproduction and for erasing.

FIG. 7 is an explanatory diagram showing the sizes of a reproducing beam and an erasing beam on the optical disk shown in FIG. 5, respectively.

FIG. 8 is a characteristic diagram showing a relationship between a bit error rate and the number of erasures.

[Explanation of symbols]

 Reference Signs List 51 (680 nm) laser 52 (780 nm) two-beam laser 54, 105 Collimator lens 55 Composite prism 59 Dichroic mirror 62 Objective lens 64 Optical disk 65 Recording / reproducing beam 70, 101 Laser pen 72, 73 Erasing beam 102 1-beam laser 103 Wollaston prism 104 1/4 wavelength plate

Claims (5)

(57) [Claims] 1. A first laser for emitting a plurality of erasing beams having a first wavelength, and a second laser different from the first wavelength.
And a plurality of erasing beams emitted from the first laser on the same track of an optical disk made of a phase change medium and rotating in a predetermined direction. In relation to the rotation direction of the optical disk, these beams are arranged at different positions which do not overlap with each other beforehand, and these beams are respectively timed on this track so that the recording beam of the second laser is arranged thereafter. An optical system for irradiating the laser beam in parallel with the first laser, and recording the first laser beam before recording with the second laser beam.
An optical head device wherein a user can perform erasing a plurality of times . A first laser for emitting an erasing beam having a first wavelength; a beam splitting means for entering a beam emitted from the first laser and splitting the beam into a plurality of beams; A second laser for emitting a recording / reproducing beam having a second wavelength different from the first wavelength, and a plurality of laser beams split by the beam splitting means on the same track of an optical disk made of a phase change medium and rotating in a predetermined direction. Erasing beams are arranged at different positions which do not overlap with each other in advance in relation to the rotation direction of the optical disk, and these beams are arranged so that the recording beam of the second laser is arranged after them. comprising an optical system for irradiating each temporally parallel on the track, the second Les
Erase multiple times with the first laser before recording by the user
An optical head device characterized by being able to perform . 3. A first laser for emitting a plurality of erasing beams having a first wavelength, and a plurality of beams emitted from the first laser are incident and split into a plurality of beams, respectively. A beam splitting means, a second laser for emitting a recording / reproducing beam having a second wavelength different from the first wavelength, and the beam splitting means on the same track of an optical disk made of a phase change medium and rotating in a predetermined direction. A plurality of erasing beams divided by the means are arranged at different positions which do not overlap with each other in advance in relation to the rotation direction of the optical disk, and the recording beam of the second laser is arranged after them. wherein before these beams comprises an optical system for irradiating respectively in parallel temporally on the track to record in the second laser
An optical head device wherein erasing can be performed a plurality of times by a first laser . 4. The optical head device according to claim 1, wherein said optical system multiplexes a beam guided onto an optical disk by a dichroic mirror. 5. The beam splitting means according to claim 1, wherein
4. The optical head device according to claim 2, comprising a Wollaston prism for splitting, and a quarter-wave plate for converting the split beams into circularly polarized light.