JP2768572B2 - Optical information 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 information reproducing apparatus such as a CD (compact disk) and an LD (laser disk), and more particularly to controlling the intensity of a light beam emitted for reproducing information.

[0002]

2. Description of the Related Art FIG. 5 shows a schematic configuration around an optical pickup of an optical disk apparatus.

A light beam emitted in front of a semiconductor laser 31 is divided into one main beam and two sub-beams by a first diffraction element 32, and then divided by a second diffraction element 3.
3. After passing through the collimator lens 34, the objective lens 35
Converges on the optical disk 36. Information is recorded on the optical disk 36 by pits having irregularities. The reflected light from the optical disk 36 is condensed by an objective lens 35, passes through a collimator lens 34, and passes through a second diffraction element 33.
And is guided to the light receiving element 37. The output of the light receiving element 37 is input to the signal processing circuit 38, and the output of RF (Radio Freq
uency) signal, a focus error signal and the like are extracted.

In order to obtain a binary signal from an RF signal, an RF signal
The signal amplitude is limited by a predetermined slice level V _S. As a result, for example, as shown in FIG. 6, if the RF signal is a sine wave, even for “1”,
The same pulse width and Δt are obtained for “0”. In the figure, the horizontal axis indicates time (t), and the vertical axis indicates level.

On the other hand, the intensity of the light beam emitted behind the semiconductor laser 31 is detected by a light receiving element 39 for monitoring. ALPC (Automatic Laser Power Control)
The circuit 40 controls the driving current of the semiconductor laser 31 based on the output of the light receiving element 39 so that the intensity of the light beam becomes constant. Since the intensity of the light beam emitted forward is proportional to the intensity of the light beam emitted backward,
By the above control, the intensity of the light beam emitted forward can be made constant. Thereby, an RF signal with a stable output level can be obtained. The intensity of the light beam can be set by a semi-fixed resistor R _V provided on the power supply Vcc side of the light receiving element 39. Incidentally, the output side of the ALPC circuit 40 in order to prevent deterioration and damage of the semiconductor laser 31 due to excessive drive current, resistance R ₇ are connected in series.

[0006]

However, in the above-mentioned conventional configuration, the difference in the surface reflectance of the optical disk 36 causes
The output level of the RF signal differs for each optical disc 36 or for each reproduction area even if the same optical disc 36 is used. The difference in the surface reflectivity is caused by variations in the pit shape at the time of manufacturing the optical disc 36, contamination during handling, and the like. R
If the output level of the F signal is different, for example, as shown in FIG. 7, even if the RF signal is a sine wave, the binary signal obtained by limiting the amplitude at the slice level V _S is “1”. Is different from the pulse width Δt ₁ corresponding to “0” and the pulse width Δt ₂ corresponding to “0”, so that it is difficult to accurately reproduce information.

[0007]

According to a first aspect of the present invention, an optical information reproducing apparatus irradiates an optical recording medium with a light beam emitted from a light source and receives reflected light. While reproducing information by detecting with the element ,
When the output level of the light receiving element has exceeded the reference level
An optical information reproducing apparatus for starting the focus control can, so that the output level of the light receiving element reaches a predetermined level, and the light beam intensity control means for controlling the intensity of the light beam in accordance with the output level, the output level is characterized by until than the reference level and the light beam intensity fixing means for fixing the intensity of the light beam at a predetermined intensity is provided.

[0008]

SUMMARY OF] According to the first aspect, the optical information reproducing apparatus for reproducing information by a light beam emitted from the light source focus control and by irradiating the optical recording medium, detects the reflected light by a light receiving element The light beam intensity control means for controlling the intensity of the light beam according to the output level so that the output level of the light receiving element becomes a predetermined level is provided, regardless of the surface reflectance of the optical recording medium. Therefore, a predetermined output level can be obtained. As a result, accurate information can be reproduced.

[0009] In addition, the output level of the light-receiving element is focus
Light beam intensity fixing means for fixing the intensity of the light beam to a predetermined intensity until the light level becomes equal to or higher than a reference level serving as a reference for starting the light control, for example, when the light beam is focused on the optical recording medium. Otherwise, the intensity of the light beam does not abnormally increase. Thereby, deterioration of the optical recording medium can be prevented.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a schematic configuration around an optical pickup of an optical disk apparatus (optical information reproducing apparatus) according to this embodiment.

A light beam emitted from a semiconductor laser 1 (light source) is divided into one main beam and two sub beams by a first diffraction element 2, and then passes through a second diffraction element 3, The light is converted into a parallel beam by a collimator lens 4 and converged on an optical disk 6 (optical recording medium) by an objective lens 5. Information is recorded on the optical disk 6 by pits having irregularities. The reflected light from the optical disk 6 is collected by the objective lens 5, passes through the collimator lens 4, is diffracted by the second diffraction element 3, and is guided to the light receiving element 7.

As shown in FIG. 2, the light receiving element 7 has five divided light receiving sections D _{1 to} D ₅ . On the other hand, in the second diffraction element 3, two semicircular regions having different grating pitches are formed. Therefore, the reflected lights of the one main beam and the two sub beams are diffracted in two different directions.

When the focus of the objective lens 5 is just on the optical disk 6, the reflected light of the main beam is
₄ and a light spot is formed on the boundary between the light receiving sections D ₂ and D ₃ . On the other hand, the reflected lights of the two sub beams are respectively
To form a light spot on the light receiving portion D ₁ and D _5.

When the focal point of the objective lens 5 is farther than the optical disk 6, each light spot is, as shown in FIG.
The second diffraction element 3 spreads in a semicircular shape reflecting the shape of the semicircular region. When the focal point of the objective lens 5 is closer to the optical disk 6, as shown in FIG. 4, the arc of each semicircular light spot is on the opposite side from FIG.

The tracking error signal is detected by a so-called three-beam method, and is given by the difference between the light receiving sections D ₁ and D ₅ . Focus error signal, by a so-called Foucault method, given by the difference of the light receiving portion D ₂ and D _3. The RF signal is given by the sum of the light receiving units D ₂ , D ₃ and D ₄ .

The optical system including the light receiving element 7 is
The optical system is the same as that described in Sharp Technical Report No. 48, page 21, issued by Sharp Corporation in March 1991.

The above-mentioned RF signal, focus error signal and the like are taken out by a signal processing circuit 8.

The signal processing circuit 8 includes amplifiers 11 to 15 for amplifying the outputs of the light receiving sections D _{1 to} D ₅ respectively. The outputs of the amplifiers 11 and 15 are respectively
Are input to the non-inverting input terminal and the inverting input terminal. In the operational amplifier 19, the subtraction is performed, and the obtained tracking error signal is taken out from the output terminal 22. Amplifier 12
14 are input to the amplifier 16. Thereby, the addition is performed, and the obtained RF signal is taken out from the output terminal 23. The outputs of amplifiers 12 and 14 are both resistors R
₂ is input to the inverting input terminal of the operational amplifier 20 via
The output of amplifier 13 and 14 is input to the non-inverting input terminal of the operational amplifier 20 together via the resistor R _3. Operational amplifier 2
At 0, the subtraction is performed, and the obtained focus error signal is taken out from the output terminal 25.

The RF signal output from the amplifier 16 is also input to the comparator 17 via a resistor R _5. Comparator 17
Then, the level of the RF signal is compared with the reference voltage V _O. If the level of the RF signal is equal to or higher than the reference voltage V _O (reference level), a focus-on signal for operating the focus servo is output. The focus-on signal is extracted from the output terminal 24.

Next, the ALP of the optical disk device of this embodiment
C (Automatic Laser Power Control) will be described below.

The ALPC of this embodiment is performed based on the level of an RF signal. The basic configuration of the ALPC system is ALP
C circuit 18 (light beam intensity control means) and switch circuit 21 for switching a signal input to ALPC circuit 18
(Light beam intensity fixing means).

A reference voltage V ₁ is applied to _one terminal 21 a of the switch circuit 21 via a resistor R ₁ .
An amplifier 16 is connected to the other terminal 21b of the switch circuit 21.
RF signal output from is supplied via the resistor R _4. The common terminal 21c of the switch circuit 21 is
It is connected to the input terminal of the circuit 18. Switch circuit 2
1, the output of the comparator 17 is supplied to the control terminal 21d, and when the control terminal 21d goes low, the terminal 2
1a and the common terminal 21c are connected,
When the control terminal 21d goes high, the terminal 21b and the common terminal 21c are connected. ALPC
The output of circuit 18 is input to the semiconductor laser 1 through the resistor R ₆ for preventing the deterioration and damage the semiconductor laser 1 due to excessive drive current.

In the above configuration, when the focus-on signal is not output from the comparator 17, in other words, when the level of the RF signal is lower than the reference voltage V _O , the common terminal 21c of the switch circuit 21 is connected to the terminal 21a. As a result, the constant reference voltage V ₁
Since the input to the ALPC circuit 18 via the _1, ALP
The drive current supplied from the C circuit 18 to the semiconductor laser 1 becomes constant. That is, the intensity of the light beam emitted from the semiconductor laser 1 is fixed at a predetermined intensity.

When the focus-on signal is output from the comparator 17, that is, when the level of the RF signal is higher than the reference voltage V _O , the common terminal 21c of the switch circuit 21 is connected to the terminal 21b. . With this, RF
Since the signal is input to the ALPC circuit 18 via a resistor R _4, a driving current supplied from the ALPC circuit 18 to the semiconductor laser 1 in accordance with the level of the RF signal is controlled.
That is, the intensity of the light beam emitted from the semiconductor laser 1 is controlled so that the level of the RF signal becomes a predetermined level.

As described above, since the intensity of the light beam is controlled based on the level of the RF signal, an RF signal of a predetermined level can be obtained regardless of the surface reflectivity of the optical disk 6. Thereby, even if the optical disk 6 has a pit shape variation at the time of manufacturing, a stain during handling, etc., accurate information can be reproduced.

Further, when the focus servo is not working or the optical disk 6 is not loaded, the level of the RF signal is set higher than the reference voltage V _O in order to prevent the intensity of the light beam from being carelessly increased. Is smaller, the driving current of the semiconductor laser 1 is kept constant. This prevents the optical disk 6 from deteriorating due to irradiation with an excessively strong light beam, and also prevents the semiconductor laser 1 from deteriorating due to an increase in drive current.

In the above embodiment, the intensity of the light beam is controlled by the driving current of the semiconductor laser 1. However, the intensity of the light beam may be controlled by a stop, a filter, or the like.
Further, the present invention is applicable not only to compact disk devices and laser disk devices, but also to optical information recording / reproducing devices such as magneto-optical disk devices. Further, the present invention can be applied to a card device and a tape device in addition to the above disk device.

[0029]

The optical information reproducing apparatus according to the invention of claim 1 according to the present invention, as described above, by irradiating a light beam emitted from the light source into light SL <br/> recording medium, detecting the reflected light by a light receiving element To reproduce information, and the output level of the
Focus control starts when the level exceeds the reference level.
An optical information reproducing apparatus for, so that the output level of the light receiving element reaches a predetermined level, and the light beam intensity control means for controlling the intensity of the light beam in accordance with the output level, the upper
Serial output level is configured to Until than the reference level is provided with the light beam intensity fixing means for fixing the intensity of the light beam at a predetermined intensity.

[0030] Thus, regardless of the surface reflectance of the optical recording medium, it is possible to obtain a predetermined output level, thereby, it becomes possible to reproduce accurate information, for example, a light beam an optical recording medium When not focused on
To prevent an abnormal increase in light beam intensity at
Can, thereby, Ru prevents degradation of the optical recording medium.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing the periphery of an optical pickup of an optical disk device according to the present invention.

FIG. 2 is a configuration diagram illustrating a light receiving unit of the light receiving element.

FIG. 3 is an explanatory diagram showing a light spot on a light receiving element when a focus of an objective lens is farther than an optical disk.

FIG. 4 is an explanatory diagram showing a light spot on a light receiving element when a focal point of an objective lens is closer to an optical disk;

FIG. 5 is a schematic configuration diagram showing the periphery of an optical pickup of a conventional optical disk device.

FIG. 6 is a waveform diagram showing a relationship between an RF signal of a predetermined level and a slice level V _S.

FIG. 7 is a waveform chart showing a relationship between a low-level RF signal and a slice level V _S.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser (light source) 6 optical disc (optical recording medium) 7 light receiving element 8 signal processing circuit 18 ALPC circuit (light beam intensity control means) 21 switch circuit (light beam intensity fixing means)

Claims (1)

(57) [Claims] An information recording medium is reproduced by irradiating an optical recording medium with a light beam emitted from a light source and detecting reflected light with a light receiving element, and the output level of the light receiving element is set to a reference level.
An optical information reproducing apparatus that starts focus control when the output level is equal to or higher than a level, such that an output level of the light receiving element becomes a predetermined level,
A light beam intensity control means for controlling the intensity of the light beam in accordance with the output level until the output level is above the reference level feature and the light beam intensity fixing means for fixing the intensity of the light beam at a predetermined intensity An optical information reproducing apparatus, comprising: