JP3048902B2 - Optical recording medium playback 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 medium reproducing apparatus capable of reproducing a plurality of optical disks having different recording densities and different positions in the depth direction where information is recorded.

[0002]

2. Description of the Related Art As read-only optical disks, LD, C
D, CD-ROM, digital video disk (DV
D), and information is recorded at a constant angular velocity or a constant linear velocity in LDs and CDs. In a disk recorded at a constant angular velocity, the pits increase from the inner circumference to the outer circumference, and the pits are smaller in CDs and DVDs than in CDs because DVDs have a higher density. CD and D
In VD, the position in the depth direction where information is recorded is different. Therefore, if it is attempted to play back a plurality of discs using an apparatus compatible with optical discs having different track pitches and pit sizes and information recording positions, the track pitches and pit sizes are different. The reproduction is performed by changing the wavelength of the laser beam and the optical system such as the objective lens depending on the position where the information and the information are recorded. For example, optical disks with different track pitches
In the case where two semiconductor lasers having different wavelengths are incorporated in a reproducing apparatus in order to reproduce data in accordance with the track pitch of the disk, the optical component A is used as compared with the case where only one semiconductor laser is used as shown in FIG. It had to be added, and the optical system was larger than the conventional pickup. Also,
The position where information is recorded differs between the CD and the SD which is a kind of DVD in the depth direction of the disk.
Since the distance is 2 mm and that of SD is 0.6 mm, if the same optical system is used, the position of the focal point is different as shown in FIG. 7. Therefore, these disks are reproduced by separate reproducing devices having optical systems suitable for each disk. I had to.

[0003] Conventionally, the reproduction of an optical disk is performed as shown in FIG.
Was used. This semiconductor laser
Two materials having different band gaps (E_g1And E_g2E_g1
> E _g2), The band gap is E_g2The material of the van
De gap is E_g1It is configured to be sandwiched between materials
In general, light of a single wavelength is extracted from one chip
I can do it. The semiconductor laser shown in FIG.
In addition, as shown in FIG.
There is a conductor laser. This laser is a welllayer
And two semiconductor materials called barrier layers
And the band gap of the barrier layer (E_bg) Is a well layer
Band gap (E_wg) Is much larger than. Follow
When the width W of the well layer is reduced to several tens of mm or less,
Existing carriers are confined in this layer, resulting in quantum
The effect transfers only the energy represented by
E indicating the bottom of the conduction band_wcNew level E at higher level_wc1To
Form.

[0004]

(Equation 1)

Similarly, a new level E _wv1 is formed on the valence band side at a level higher than the bottom E _wv of the valence band on the valence band side for holes. Then, in order to emit light having an energy corresponding to the energy difference between these new levels, the above E _g1 is used.

[0006]

(Equation 2)

[0007] Light having a large energy, that is, light having a short wavelength can be emitted. As is clear from the above, the new level for electrons and holes in the well layer is the well layer width W
When the well layer width is reduced, a new level formed by the quantum effect becomes higher, and light of a shorter wavelength can be emitted. Therefore, in order to manufacture semiconductor lasers having different wavelengths, the material having the smaller band gap is changed in FIG. 10 or, if the same material is used, two well layer widths of the quantum well semiconductor laser shown in FIG. There is a way. Conventionally, when a laser beam of a different wavelength is required in one reproducing apparatus for reproducing an optical disk, two semiconductor lasers shown in FIG. 10 are installed and used. Also, FIG.
The quantum well semiconductor laser shown in No. 1 was not used.

[0008]

In order to reproduce a plurality of optical discs having different recording densities, that is, recording pits and track pitches, using a compatible reproducing apparatus, semiconductor lasers having different wavelengths are installed in the equipment, and the recording pits and track pitches are changed. It is necessary to drive a semiconductor laser with a wavelength suitable for the track pitch,
Conventionally, since two separate semiconductor lasers having different wavelengths are provided, the number of components of the optical system increases, so that the ratio of the optical system to the entire reproducing apparatus increases, the optical axis alignment becomes difficult, and the cost increases. There was a problem. Further, there is a problem that it is difficult to reproduce a plurality of optical discs on which information is recorded at different positions from the light incident surface by using one reproducing apparatus.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides an optical disk reproducing apparatus capable of reproducing a plurality of optical disks in accordance with each optical disk by using one reproducing apparatus.

[0010]

SUMMARY OF THE INVENTION The present invention provides a quantum well semiconductor laser chip capable of independently oscillating a laser beam of a first wavelength and a laser beam of a second wavelength different from the first wavelength. A condensing unit for condensing the laser beams of the first and second wavelengths emitted from the quantum well semiconductor laser chip on a recording surface of an optical recording medium; and reflecting light reflected from the optical recording medium with incident light. A reproduction pickup comprising a half mirror that reflects light in different directions and a light receiving unit that receives light reflected by the half mirror is used.

In addition, the present invention employs a configuration in which an optical filter having selective permeability to laser beams of first and second wavelengths emitted from a quantum well semiconductor laser chip is added to the above configuration. It is characterized by. further,
The present invention is characterized in that the optical filter includes a portion that transmits the laser beams of the first and second wavelengths and a portion that transmits only the laser beam of the first wavelength.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the first of two quantum well semiconductor lasers.
An embodiment will be described. As shown in FIG. 1A, the quantum well semiconductor laser chip 10 includes two quantum well semiconductor lasers 1.
1 and 12. The quantum well semiconductor laser 11 has a band gap of 2.0 as the barrier layers 2a and 2b.
The barrier layer 2 is made of Al _0.8 Ga _0.2 As of 7 eV and GaAs having a band gap of 1.42 eV as the well layer 3.
Electrodes 1a and 1b for current injection are attached to a and 2b, respectively. Similarly, the quantum well semiconductor laser 12 has Al _0.8 Ga _0.2 A as the barrier layers 5a and 5b.
s, the well layer 6 is made of GaAs, and the barrier layers 5a and 5b are provided with current injection electrodes 4a and 4b, respectively.
b is attached. The quantum well semiconductor laser 1
1 and 12 are electrically separated by an insulating layer 7 and can be driven independently. FIG.
FIG. 2A is an energy band diagram of the quantum well semiconductor laser chip 10 shown in FIG. The well layer width W1 of the quantum well semiconductor laser 11 is 12 °, and the energy difference between the levels newly formed by the quantum effect is 1.95.
eV, 635 nm (allowable range: 630 to 640 n
m). On the other hand, the quantum well semiconductor laser 1
2, the well layer width W2 is 21 °, and the energy difference between levels newly formed by the quantum effect is 1.59 eV.
Becomes 780 nm (allowable range: 775 to 785 nm)
Emits light.

In the first embodiment, the quantum well semiconductor laser chip 10 emits laser beams having wavelengths of 635 nm and 780 nm, but is not limited to this. FIG. 2 shows a second embodiment of the quantum well semiconductor laser chip. The materials of the barrier layer, the well layer, the insulating layer, and the electrode are the same as those in the first embodiment, and a description thereof will be omitted. The quantum well semiconductor laser chip 20 is composed of a quantum well semiconductor laser 21 and a quantum well semiconductor laser 22, and is electrically insulated similarly to the first embodiment. The well layer width of the quantum well semiconductor laser 21 is the same as the well layer width W1 of the quantum well semiconductor laser 11, and is 635 nm (allowable range: 630 to 640 n).
m). On the other hand, the well layer width W3 of the quantum well semiconductor laser 22 is 14 °, and the energy difference between levels newly formed by the quantum effect is 1.80 eV,
It emits light of 690 nm (allowable range: 685 to 695 nm).

In the first and second embodiments, Al _0.8 Ga _0.2 As is used as the barrier layer. However, the present invention is not limited to this, and any material having a band gap larger than 2.07 eV can be used. And Al _x Ga _1-x A
s (x: 0.8 to 1) may be used. Also, the well layer is made of GaAs.
The band gap is not limited to s.
Al _x Ga _1-x As (x: 0.0
1 to 0.13). For example, x is 0.07
, The band gap of Al _0.07 Ga _0.93 As is 1.5
Since it is 0 eV, the well layer width W1 is set to 13 ° in the quantum well semiconductor laser 11 or 21, the well layer width W2 is set to 29 ° in the quantum well semiconductor laser 12, and the well layer width W3 is set to 16 ° in the quantum well semiconductor laser 22. I just need.
Even when the band gap of the well layer is other than 1.50 eV, the oscillation wavelength is 635 nm (allowable range: 630 to 640 nm).
And 780 nm (allowable range: 775 to 785 nm) or 635 nm (allowable range: 630 to 640 nm) and 6
The quantum well semiconductor lasers 11, 12, 21 and 2 are set to 90 nm (allowable range: 685 to 695 nm).
The well layer widths W1, W2 and W3 can be set using the above. Further, applicable as a barrier layer _{Al x Ga 1-x As (} x: 0.8~1) Al x Ga 1-x As for each material of the (x: 0.01~0.13) each of The material can be applied as a well layer. in this way,
If the ultra-thin semiconductor layer is formed by molecular beam epitaxy,
It can be easily formed at a level of Å with good controllability and good reproducibility.

FIG. 3 shows a pickup for reproducing an optical disk to which a quantum well semiconductor laser chip having two quantum well semiconductor lasers arranged as described above is applied. The pickup 50 according to the present invention comprises two quantum well semiconductor lasers 5.
It comprises a semiconductor laser chip 51 composed of 1a and 51b, a diffraction grating 52, a half mirror 53, a condenser lens 54, and a detector 55. The quantum well semiconductor laser 51a is 635 nm (allowable range: 630 to 640 n).
m), and the quantum well semiconductor laser 51b emits 780
nm (allowable range: 775 to 785 nm).
In the quantum well semiconductor laser chip 51, the oscillating portions of the quantum well semiconductor lasers 51a and 51b are only a few microns apart, so that the optical path of the light incident on the disk does not change regardless of which semiconductor laser is selected.

In an optical disk reproducing apparatus to which the pickup 50 is applied, reproduction of a plurality of disks having different track pitches is performed as follows. FIG. 4 is a diagram schematically showing a reproducing apparatus. The disc to be reproduced has a recording linear velocity of 1.
A standard disk recorded at 2 to 1.4 m / sec and a track pitch of 1.6 μm, and a recording linear velocity of 3.3 to 4 m / sec
c, a high-density disc recorded with a track pitch of 0.74 to 0.85 μm. In this embodiment, the standard disk is set to a wavelength of 780 nm (allowable range: 775 to 785 nm).
Laser beam of 635nm at high density disc
(Permissible range: 630 to 640 nm) It is assumed that reproduction is performed using a laser beam. When the disk 72 is mounted, light is emitted from the laser 71 and the reflected light is detected. The pitch detector 73 identifies the track pitch of the disk based on the position of the detected reflected light. This identification signal enters the semiconductor laser selection section, and selects a quantum well semiconductor laser that oscillates at a wavelength suitable for the track pitch. If the identified track pitch is 0.74 to 0.85 μm, the quantum well semiconductor laser 51 a is selected, and the laser beam of 635 nm (allowable range: 630 to 640 nm) is applied to the disk 7.
2 and the disk is reproduced. The signal reproduced by the pickup 50 undergoes predetermined signal processing in a circuit 60, one of which is input to a demodulation circuit 61 as an information signal, and the other is input to a motor servo circuit 63 as a control signal for a disk motor 62. . Quantum well semiconductor laser 5
The same functions when 1b is selected. The quantum well semiconductor laser chip 51 is 635 nm (allowable range: 63
0 to 640 nm) and 690 nm (acceptable range: 686 to 6)
The same function as described above is also realized when the device comprises a quantum well semiconductor laser emitting a laser beam having a wavelength of 95 nm).

Next, a case will be described in which a CD and an SD in which information is recorded at different positions in the depth direction of the disc are reproduced by a compatible reproducing apparatus. The light source used is the quantum well semiconductor laser chip 51 provided with the quantum well semiconductor lasers 51a and 51b as described above. In this case, only the laser beam having a wavelength of 780 nm is cut as shown in FIG.
A portion 80 that transmits a laser beam having a wavelength of 630 to 640 nm, and 635 nm (allowable range: 630 to 640 n)
m) and 780 nm (acceptable range: 775 to 785 nm)
The optical filter (F) comprising a portion 90 transmitting a laser beam having a wavelength of
Insert before 4. In this case, the diameter of the center of the filter is smaller than the diameter of the condenser lens 54, and is 780 nm.
The aperture ratio (NA) is set so that the side lobe does not increase when the laser beam of (allowable range: 775 to 785 nm) is focused at a position 1.2 mm from the incident surface of the optical disk (FIG. 5). (A), (b)). The optical filter of FIG. 5C is not limited to a flat plate type, and may have a filter film having an angle dependence on the incident side of the objective lens. That is, 635 nm (allowable range: 630 to 640)
780 nm (allowable range: 775 to 785 n).
m) (or 690 nm (allowable range: 686 to 695)
The laser light having the wavelength of (nm)) has an angle dependence of transmittance as shown in FIG. Depending on the angle between the objective lens and the curved surface on the incident side, the light passes near the center of the lens and is reflected at the peripheral portion, and an effect similar to that obtained when an aperture is inserted can be obtained. As shown in FIG. 8, the angle at which the transmittance becomes 50% is
Depending on the curvature of the lens, the effective NA is 0.3-
An angle of about 0.4 is selected. The reproduction of the disc in this case is performed by the pickup 50 of FIG.
(C) This is performed with the optical filter described in (or FIGS. 8 and 9) inserted in front of the condenser lens 54. When the disk 72 is mounted, light is emitted from the laser 71,
The reflected light is detected. The pitch detector 73 identifies the track pitch of the disk based on the position of the detected reflected light. This identification signal enters the semiconductor laser selection section, and selects a quantum well semiconductor laser that oscillates at a wavelength suitable for the track pitch. If the identified track pitch corresponds to SD, 635 nm (allowable range: 630 to 6
40 nm), and the laser beam focuses on a position 0.6 mm from the incident surface of the optical disc, as in the case where no optical filter is present as shown in FIG. To play. If the identified track pitch corresponds to a CD, 7
A laser beam of 80 nm (allowable range: 775 to 785 nm) is selected, and as shown in FIG. 5B, the same effect as when a lens having a small NA is used by an optical filter appears. 1.2mm
And the recorded information can be reproduced. The signal reproduced by the pickup 50 undergoes predetermined signal processing in a circuit 60, one of which is input to a demodulation circuit 61 as an information signal, and the other is a disc motor 6
2 is input to the motor servo circuit 63 as a control signal.

In this embodiment, 635 nm (allowable range:
630-640 nm) and 780 nm (allowable range: 775)
Although a case where a laser beam having a wavelength of about 785 nm is required has been described, when a laser beam having another wavelength is required, the width of the well layers 3 and 6 of the quantum well semiconductor laser shown in FIG. Thereby, a laser beam having a desired wavelength can be extracted. For example, 780n
Similar functions and effects can be obtained by using a wavelength of 670 to 690 nm instead of the m laser beam.

[0019]

According to the present invention, it is possible to realize an optical disk reproducing apparatus incorporating a pickup capable of independently oscillating two different wavelengths, and reproduce a plurality of optical disks having different recording densities with a compact reproducing apparatus. be able to. Also, a plurality of discs on which information is recorded at different positions in the depth direction of the disc can be reproduced by one reproducing apparatus.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of two quantum well semiconductor lasers.

FIG. 2 is a diagram showing a second embodiment of two quantum well semiconductor lasers.

FIG. 3 is a diagram showing a pickup of the present invention.

FIG. 4 is a diagram showing an embodiment of a reproducing apparatus according to the present invention.

FIG. 5 is a diagram showing an optical filter and an image in the embodiment of the present invention.

FIG. 6 is a view showing a conventional pickup.

FIG. 7 is a diagram showing image formation in a conventional optical system.

FIG. 8 is a diagram showing transmission characteristics of a filter according to the present invention.

FIG. 9 is a diagram showing a structure of a filter according to the present invention.

FIG. 10 is an energy band diagram of the semiconductor laser.

FIG. 11 is an energy band diagram of the quantum well semiconductor laser.

[Explanation of symbols]

1, 1 ', 4, 4' ... current injection electrode 2, 2 ', 5, 5' ... barrier layer 3, 6 ... well layer 7 ... insulating layer 10 ... quantum well Semiconductor laser chips 11, 12, 51a, 52b Quantum well semiconductor laser 51 Semiconductor laser chip 52 Diffraction grating 53 Half mirror 54 Condensing lens 55 Detector 80 ... A portion through which only the first wavelength laser beam passes 90. A portion through which the first and second laser beams pass

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI H01S 3/18 (72) Inventor Seiji Kajiyama 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-6-259804 (JP, A) JP-A-5-189799 (JP, A) JP-A-60-223040 (JP, A) JP-A-64-60829 (JP, A) JP-A-5 -242520 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B 7/125, 7/135

Claims (2)

(57) [Claims] An apparatus for reproducing an optical recording medium, comprising: a quantum well semiconductor capable of independently oscillating a laser beam having a first wavelength and a laser beam having a second wavelength different from the first wavelength. A laser chip; and the first laser oscillated from the quantum well semiconductor laser chip.
An outer peripheral portion that transmits only a laser beam having a wavelength of
An optical filter comprising: an inner peripheral portion that transmits a laser beam having a wavelength of; a condensing section that condenses the laser beams having the first and second wavelengths on a recording surface of the optical recording medium; Optical recording characterized by using a reproducing pickup comprising: a reflecting means for reflecting light reflected from a recording medium in a direction different from the incident light; and a light receiving unit for receiving the reflected light reflected by the reflecting means. Media playback device. 2. The laser according to claim 1, wherein the outer peripheral portion is a laser of the second wavelength .
2. The reproducing apparatus for an optical recording medium according to claim 1, wherein the beam is cut by the incident angle dependency on the optical filter.