JPH05334680A - Reproducing system for optical record - Google Patents

Abstract

PURPOSE:To increase recording density without changing laser wavelength and the number of apertures of an objective lens by providing thin film by which permeability can be heightened by temperature rise between a substrate and reflecting film. CONSTITUTION:The irradiation of a beam spot 8 converged on the objective lens is performed from the upper side, and an optical disk is comprised of the substrate 15, the thin film 16 whose permeability is changed by temperature. and the reflecting film 17 in sequence from the upper side. and a recording pit 18 is formed between the substrate 15 and the film 17. When the disk is irradiated with a 0t-order beam, the permeability of the film 16 irradiated with the spot 8 is increased. When reproduction is performed, the spot diameter of light intensity distribution of the beam spot on the film 17 is decreased by irradiating a spot part where the permeability is heightened. Therefore, since reflected return light is only of one pit string even when a neighboring pit 18 is irradiated with the beam spot by increasing the recording density, the recording density can be heightened by reducing track pitch.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing system of an optical pickup device for reading information recorded by using a laser beam from an optical disk.

[0002]

2. Description of the Related Art In the reproduction of optical recording, a laser beam focused to the diffraction limit is usually formed on the recording surface of an optical disc having concave and convex pits formed on a spiral on the basis of recorded information. Irradiation is performed, and the change in the amount of reflected light is detected. The beam spot size at this diffraction limit is
It is determined by the wavelength of the laser and the effective numerical aperture of the objective lens. Further, the beam spot diameter at this time needs to be small enough not to be influenced by diffraction of an adjacent pit row when the beam spot traces a certain pit row.

Conversely, the track pitch of the optical disk can be reduced only to the extent that the crosstalk amount due to the adjacent pits during reproduction does not hinder the reproduction. Further, in order to reduce the beam spot, it has been considered to shorten the wavelength of the laser used and to use an objective lens having a large numerical aperture, but at present, problems remain in each.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a reproducing system capable of reading information from an optical disc having a higher recording density without changing the wavelength of a laser used and the numerical aperture of an objective lens. Has a purpose.

[0005]

Therefore, in claim 1,
In an optical pickup device for reading a recording pit signal by irradiating a converged laser beam on an optical disc on which recording pits are spirally or concentrically formed, a thin film whose transmittance increases due to temperature rise on the optical disc. When the optical disc is reproduced, a converged laser beam is irradiated from the substrate side of the optical disc to raise the temperature of the thin film to increase the transmittance, and the recording pits in the portion where the transmittance is increased are read.

According to another aspect of the present invention, the converged laser beam is a first converged laser beam for increasing the temperature of the thin film of the optical disk to increase the transmittance, and a first read pit of the recording pit where the transmittance is increased. And a second convergent laser beam that follows the convergent laser beam of.

According to a third aspect of the present invention, a converged laser beam for raising the temperature of the thin film of the optical disc to increase the transmittance and a converged laser beam for reading the recording pits in the portion where the transmittance is increased are one converged laser beam. It is characterized by doing in.

According to a fourth aspect, the first convergent laser beam and the second convergent laser beam according to the second aspect are
The first converged laser beam is a 0th order diffracted light, and the second converged laser beam is a 1st order diffracted light.

According to a fifth aspect, the ferroelectric ceramic PLZT [(Pb (1-x), La
(x)) (Zr (y), Ti (1−y)) O3] is used.

[0010]

According to the present invention, when reproducing an optical disk,
First, the thin film is heated by the high-power beam spot due to the temperature rise, the transmittance is gradually reduced with the center of the beam spot as a peak, and a small spot diameter that can be reflected and read is formed. This is equivalent to a smaller reproduction beam spot diameter when viewed relatively,
Since the amount of relative crosstalk is also reduced, it is possible to make the track pitch smaller than before. That is, the recording density can be increased. In addition, the heated portion cools during one rotation of the disc and the transmittance returns to the original value, so that the next pit can be read without any problem.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A reproducing apparatus according to an embodiment of the present invention will be described with reference to the schematic block diagram of FIG. The light beam emitted from the semiconductor laser 1 is converted into parallel light by the collimator lens 2 and then high-order diffracted light is generated by the diffraction grating 3. This light beam further passes through the polarization beam splitter 4, passes through the λ / 4 plate 5, and forms a beam spot 8 on the recording surface of the optical disc 7 by the objective lens 6. This is shown in FIG. In this case, the 0th order beam 9
Is used to raise the temperature of the thin film of the optical disk 7 described later, and the primary beam 10 is used as a reproducing beam.

The intensity ratio between the 0th order beam 9 and the 1st order beam 10 is determined by the diffraction grating 3. Then, the light beam reflected by the recording surface passes through the objective lens 6 and the λ / 4 plate 5 again, is reflected by the polarization beam splitter 4, and is a condensing lens 11 that is an optical system that generates astigmatism and a cylindrical lens. A beam spot 14 is formed on the four-divided photodiode 13 by being guided to the lens 12. This is shown in FIG. Here, only the beam spot 14 corresponding to the beam spot 9 in FIG. In this embodiment,
Focus error detection is performed using the astigmatism method, and tracking error detection is performed using the push-pull method.

Next, the structure of the optical disk will be described with reference to FIG. In the figure, the beam spot 8 converged by the objective lens 6 is assumed to be irradiated from the upper part, and the optical disk 7 is formed by superposing the substrate 15, the thin film 16 whose transmittance changes with temperature, and the reflective film 17 in order from the upper part. The recording pit 18 is formed between the substrate 15 and the reflective film 17.

As shown in the characteristic diagram of FIG. 5, the thin film 16 is made of PLZT [(Pb (1-
x), La (x)) (Zr (y), Ti (1-y)) O3],
A material whose light transmittance increases with temperature is used. P
In the case of LZT, when the La concentration is in the range of 2.5 at% to 6 at%, the transmittance changes as shown in FIG. 5, and when the La concentration is 2.5 at%, it is about 5 at room temperature.
%, The light transmittance becomes about 55% at 200 degrees Celsius.

Next, a state in which the optical disk 7 having such a thin film 16 is reproduced by the reproducing apparatus will be described. When the optical disc 7 is irradiated with the 0th-order beam 9,
As shown in the temperature distribution characteristic diagram of FIG. 6, the temperature of the central portion of the thin film 16 where the beam spot hits is about 200 ° C.
It is close to the Gaussian distribution of. If the thin film 16 at this time is PLZT having a La concentration of 2.5 at% shown in the characteristic diagram of FIG. 5, the light transmittance distribution of the thin film 16 is as shown in FIG.

Next, the primary beam 10 is used as a reproducing beam. The light intensity distribution of this beam spot is shown in FIG. This beam spot has a generally used spot diameter. However, when the beam spot having the above-mentioned light transmittance is irradiated, the light intensity distribution of the beam spot on the reflection film 17 is as shown in FIG. As shown in FIG. Therefore, as shown in FIG. 2, even if the recording densities are increased and the adjacent recording pits 18 are also irradiated with the beam spots 9 and 10, since the reflected return light is only for one pit row, the track pitch is reduced. The recording density can be increased.

Another embodiment will be described with reference to the schematic block diagram of FIG. In this embodiment, the wavelengths of the temperature raising beam spot and the reproducing beam spot are different. The beams emitted from the high-power semiconductor laser 19 for temperature rise and the semiconductor laser 20 for reproduction are collimated by the collimator lenses 21 and 22, respectively. A higher-order diffracted beam is further generated from the reproduction beam by the diffraction grating 23 and used for tracking error detection.

After the two beams are combined by the wavelength selection mirror 24, the beam splitter 25 and the objective lens 2 are combined.
A beam spot is formed on the recording surface of the optical disk 7 through the beam spot 6. At this time, the two beam spots are
However, since there is a ± 1st order beam spot of the reproducing beam, it is necessary to separate the two beams by a distance equal to or more than the interval between the 0th order beam spot for reproducing and the ± 1st order beam spot.

The reflected light passes through the objective lens 26, is reflected by the beam splitter 25, and then the wavelength selection mirror 27.
After transmitting only the reproduction beam, the light passes through the condenser lens 28 and the cylindrical lens 29, and is condensed by the six-divided photodiode 30.

As means for obtaining two beam spots,
In addition to the above, it is also conceivable to use a semiconductor laser that emits a plurality of laser beams. Further, in the present invention, the beam spot for temperature increase and the beam spot for reproduction are separately provided, but if the transmittance of the thin film material changes rapidly, it is possible to perform temperature increase and reproduction with one beam spot.

[0021]

According to the present invention, the recording density of the optical disk can be increased without shortening the wavelength of the laser used and increasing the numerical aperture of the objective lens.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory view showing a beam spot on a recording surface during reproduction of FIG.

FIG. 3 is an explanatory view showing a beam spot on a photodiode at the time of reproduction of FIG.

FIG. 4 is a sectional view of an optical disc showing an embodiment of the present invention.

5 is a characteristic diagram of the thin film of FIG.

FIG. 6 is a temperature distribution characteristic diagram of a thin film of a beam spot irradiation part showing an embodiment of the present invention.

FIG. 7 is a distribution characteristic diagram of light transmittance of a thin film of a beam spot irradiation part showing an embodiment of the present invention.

FIG. 8 is a light intensity distribution chart of a reproducing beam spot showing an embodiment of the present invention.

FIG. 9 is an explanatory diagram of a light intensity distribution of a beam spot on a reflective film showing an embodiment of the present invention.

FIG. 10 is a schematic configuration diagram showing another embodiment.

[Explanation of symbols]

1 ... semiconductor laser 2,21,22 ... collimator lens 3,23 ... diffraction grating 4 ... polarization beam splitter 5 ... λ / 4 plate 6,26 ... objective lens 7 ... optical disk 8,14 .... Beam spot 9 …… 0th order beam 10 …… Primary beam 11,28 …… Condensing lens 12,29 ……
Cylindrical lens 13 ...... 4-division photodiode 15 ...... Substrate 16 ...... Thin film 17 ...... Reflective film 18 ...... Recording pit 19 ...... High power semiconductor laser 20 ...... Reproducing semiconductor laser 24, 27 ...... Wavelength selection mirror 25 ... Beam splitter 30 ... 6-division photodiode

Claims (5)

[Claims] 1. An optical disc having spiral or concentric recording pits, and an optical pickup device for irradiating a converged laser beam onto the optical disc to read a recording pit signal, wherein the optical disc is provided between a substrate and a reflective film. A thin film whose transmittance increases with temperature rise is provided, and when reproducing the optical disk, the converged laser beam is irradiated from the substrate side of the optical disk to increase the temperature of the thin film to increase the transmittance and increase the transmittance. An optical recording / reproducing system characterized by reading the recording pits in the open area. 2. The convergent laser beam is a first convergent laser beam for increasing the temperature of a thin film of the optical disk to increase the transmittance, and a first convergent laser beam for reading a recording pit in a portion where the transmittance is increased. 2. The reproducing system for optical recording according to claim 1, wherein the reproducing system is configured with a second convergent laser beam that follows. 3. A convergent laser beam for raising the temperature of the thin film of the optical disk to increase the transmittance and a convergent laser beam for reading the recording pits of the portion where the transmittance is increased are performed by one converged laser beam. The optical recording / reproducing system according to claim 1, which is characterized in that: 4. A reproducing system for optical recording according to claim 2, wherein the first convergent laser beam is a 0th-order diffracted light and the second convergent laser beam is a 1st-order diffracted light. 5. A ferroelectric ceramic PLZT [(Pb (1−x), La (x)) (Zr (y), Ti (1−
The optical disk according to claim 1, characterized in that y)) O3] is used.