JP2003223733A - Laser generator for optical pickup and its driving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To fully suppress unnecessary radiation even though implementing overlaying of a high frequency having adequate amplitude. <P>SOLUTION: In an LD light generation quantity control circuit 1, voltage corresponding to desired quantity of light is output. Supplied voltage is converted to an electric current in a V/I conversion circuit 3. In an LD light generation logic control circuit 2, a control signal for controlling generation of light in an LD 9 is controlled. In an LD driver 4, a desired drive current is supplied to the LD 9 based on the supplied current and the control signal. In an overlap frequency control circuit 6, a frequency overlapping to the drive current and reaching to a several hundreds MHz is controlled. In an overlap amplitude control circuit 7, the amplitude of the frequency controlled in the overlap frequency control circuit 6 is controlled. In the overlap frequency control circuit 6 and the overlap amplitude control circuit 7, the controlled frequency and its amplitude are overlayed by the drive current output from the LD driver 4. In the LD 9, the light generation is made at the light quantity corresponding to the supplied drive current. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser generator for an optical pickup capable of sufficiently suppressing unnecessary radiation even if high frequency superimposition is performed in order to stabilize light emitted from a laser, and a driving method thereof. Regarding

[0002]

2. Description of the Related Art As shown in FIG. 8, an optical pickup generally used for reading data from an optical disk is at least a laser diode (hereinafter referred to as "LD") 21, a collimator lens 22, and an optical isolator. 23, an objective lens 26, and a photodiode (hereinafter referred to as “PD”) 27. In addition,
The optical isolator 23 includes a polarization beam splitter 24 and
It is composed of a λ / 4 wave plate 25.

The incident linearly polarized light P emitted from the LD 21 is
After passing through the polarization beam splitter 24 and the λ / 4 wavelength plate 25, it becomes circularly polarized light and is incident on the optical disk surface 28.
The reflected light from the optical disk surface 28 becomes circularly polarized light having the opposite rotation direction, and when passing through the λ / 4 wavelength plate 25 again, becomes linearly polarized light S orthogonal to the incident linearly polarized light P. Linearly polarized light S
When it passes through the polarization beam splitter 24 again, it is reflected by the polarization film surface of the polarization beam splitter 24, and the linearly polarized light S is received by the PD 27.

At this time, the linearly polarized light S from the optical disk surface 28 is not 100% reflected by the polarization beam splitter 24, and a part of it is so-called return light, which is LD.
Return to 21. This is because it is possible to produce the polarization beam splitter 24 that reflects 100% of the linearly polarized light S, but the productivity is remarkably reduced, and therefore the polarization beam splitter 24 that reflects 100% is not actually used. is there. Further, the returning light is also generated due to variations in the characteristics of individual components such as the LD 27 and the λ / 4 wavelength plate 25 and imperfections when incorporated in the optical system. Therefore, in the optical pickup, the return light always exists.

Since the return light and the light in the resonator of the LD 21 cause a coupling resonance effect in the resonator,
The oscillation of the LD 21 becomes unstable. That is, the return light causes return light noise or scoop noise (hereinafter, referred to as “return light noise”) that makes the oscillation of the LD 21 unstable. In order to suppress this return light noise,
A high-frequency signal having a sufficient amplitude is superimposed on the drive current of the LD 21.

Specifically, the spectrum of the incident linearly polarized light P emitted from the LD 21 becomes a line spectrum as shown in FIG. 9A. In the spectrum emitted from this LD, the fundamental wave is Fo, the second harmonic is 2Fo, the third harmonic is 3Fo, ..., And the nth harmonic is nFo. When a high frequency signal having a sufficient amplitude is superimposed on the drive current, the spectrum of the incident linearly polarized light P has individual frequencies Fo, 2Fo, 3Fo, ..., N as shown in FIG. 9B.
It has a width around Fo. In this way, since the spectrum width is widened by superimposing the high-frequency signal, it is possible to reduce coherence and make external resonance less likely to occur, that is, to stabilize.

As described above, in order to suppress the return light noise generated by the inevitable return light and improve the productivity, it is necessary to superimpose a high frequency signal of sufficient amplitude on the drive current of the LD 21.

[0008]

However, since the high frequency signal to be superposed has a frequency of several hundreds of MHz, it is easily accompanied by the emission of electromagnetic waves. Therefore, there is a problem that unnecessary radiation increases as the amplitude of the superimposed high-frequency signal increases. That is, in order to suppress the return light noise, the LD9
There is a problem that unnecessary radiation increases due to the high-frequency signal superimposed on the drive current of.

In addition, in applications where the unwanted radiation is severely limited, measures such as covering the part related to high frequency superposition with a shield case have been taken. At this time, there is a problem that the shield case increases the size of the device.

Further, there are cases where the unnecessary radiation cannot be sufficiently suppressed only by the shield case. In such a case, the amplitude of the superimposed high frequency signal must be reduced,
As a result, the return light noise cannot be suppressed sufficiently, which may result in dissatisfaction with the performance.

Therefore, an object of the present invention is to provide a laser generator for an optical pickup capable of suppressing unnecessary radiation even if a high frequency signal having a sufficient amplitude is superimposed on a drive current of an LD in order to suppress return light noise. It is to provide the driving method.

[0012]

According to the present invention, there is provided a high-frequency signal generating means for generating a high-frequency signal and controlling the frequency in a laser generator for an optical pickup for generating a laser for irradiating an optical disk. A control signal generating means for generating a control signal for controlling the frequency of the high frequency signal at a frequency lower than that of the high frequency signal, and a superimposing means for superimposing the frequency controlled high frequency signal on the laser drive signal. This is a laser generator for an optical pickup.

According to the present invention, in a method of controlling a laser generator for an optical pickup, which generates a laser for irradiating an optical disk, a high frequency signal having a controllable frequency is generated, and the frequency is lower than that of the high frequency signal. A method of controlling a laser generator for an optical pickup, wherein a control signal for controlling the frequency of a high-frequency signal is generated by the method, and the frequency-controlled high-frequency signal is superimposed on a laser drive signal. .

By superimposing a high frequency signal whose frequency is controlled on the drive signal of the laser, it is possible to suppress return light noise and unnecessary radiation due to the high frequency signal.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. It should be noted that components having the same function throughout the drawings are designated by the same reference numerals to avoid duplication of description. FIG. 1 shows an embodiment of a control unit of an LD used in an optical pickup to which the present invention is applied. L
The D light emission amount control circuit 1 outputs a voltage corresponding to the light emission required for recording on the optical disc or a voltage corresponding to the light amount required for reproducing the optical disc. V /
In the I conversion circuit 3, the supplied voltage is converted into a current. The converted current is supplied to the LD driver 4.
In the LD light emission logic control circuit 2, a control signal for controlling ON / OFF of the LD 9 and light emission of the LD 9 for recording / reproducing is supplied to the LD driver 4.

In the LD driver 4, the supplied current and
The drive current (drive signal) based on the control signal is LD
9 is supplied. The high frequency signal supplied from the high frequency superposition generating circuit 5 is superposed on the drive current output from the LD driver 4.

The high frequency superposition generation circuit 5 is composed of a superposition frequency control circuit 6 and a superposition amplitude control circuit 7.
The superposed frequency control circuit 6 is composed of a voltage controlled oscillator (VCO) as an example. The superposed frequency control circuit 6 controls the frequency of the high frequency signal to be superposed on the drive current. As an example, in the superposed frequency control circuit 6, the high frequency signal is controlled to several hundred MHz.

A fluctuation signal is supplied from the frequency fluctuation control signal generating circuit 8 to the superposed frequency control circuit 6. The supplied fluctuation signal is used for the superimposed frequency control circuit 6
It is a control signal for controlling the high frequency signal output from the. This fluctuation signal has a frequency of several hundreds Hz as will be described later, and is a sufficiently low frequency as compared with a high frequency signal of several hundreds MHz output from the superposition frequency control circuit 6, that is, a frequency of fluctuation. Therefore, in this embodiment,
The signal of several hundred Hz output from the frequency fluctuation control signal generation circuit 8 is referred to as a "fluctuation signal". Therefore, the high frequency signal output from the superposed frequency control circuit 6 changes according to the fluctuation signal.

The superposition amplitude control circuit 7 controls the amplitude of the high frequency signal output from the superposition frequency control circuit 6.

As described above, in the superposition frequency control circuit 6 and the superposition amplitude control circuit 7, the high frequency signal whose frequency and amplitude are controlled is superposed on the drive current output from the LD driver 4. The LD 9 emits light with an amount of light corresponding to the supplied drive current.

Here, the frequency fluctuation control signal generation circuit 8
An example will be described with reference to FIG. Spindle motor 1
1 is composed of, for example, a brushless DC motor.
The spindle motor 11 is driven by a spindle servo (not shown) to have a constant linear velocity (CLV).
Since it is controlled by the Velocity method, the optical disk is driven to rotate at a predetermined linear velocity. Since this example can be applied regardless of the rotation speed of the optical disc, the rotation speed is constant (CAV: Constant Angular Velocit).
y) method may be used.

An FG (Frequency Generator) circuit 12 detects the number of rotations of the spindle motor 11 and generates a frequency based on the detected number of rotations. In this example, a frequency of 400 Hz to 600 Hz can be obtained in the FG circuit 12. The frequency obtained by the FG circuit 12 is converted into a pulse signal as shown in FIG.
Is supplied to. The integrating circuit 13 integrates the supplied pulse signal to generate a signal as shown in FIG. 3B.
The generated signal is supplied to the amplitude adjusting circuit 14.

The amplitude adjusting circuit 14 adjusts the supplied signal to a desired amplitude, and supplies it to the superposition frequency control circuit 6 as a fluctuation signal. At this time, waveform shaping is performed at the same time to shorten the time for which the high-frequency signal superimposed on the drive current has a similar frequency as much as possible. Therefore, the waveform adjusted by the amplitude adjusting circuit 14 becomes a triangular wave-like signal as shown in FIG. 3C.

In this example, the frequency generated from the spindle motor of 18 waves / circle is used. Therefore, when the optical disc is rotated at 4 × speed, the linear velocity is 1.4 m when the optical disc is rotated by the constant linear velocity method. / S, the frequency from the inner circumference to the outer circumference is 810 Hz to 400 Hz. When the optical disk is rotated at 8 times speed, if it is rotated by the constant rotation speed method,
In terms of the outermost circumference of an 8 cm optical disc, the frequency is
It becomes 800Hz. Since the fluctuation signal is generated from such a frequency, the high-frequency signal controlled by the fluctuation signal also changes the cycle from the maximum to the minimum and the maximum in accordance with the fluctuation signal.

Here, an example of a margin up to a predetermined limit value when the LD 9 is driven by the drive current superposed with the high frequency signal controlled by the fluctuation signal will be described. In this example, a 250 MHz margin as a fundamental wave and a 500 MHz margin as a second harmonic are measured.

The margin values up to the limit value in the conventional example and the first, second and third examples obtained from the measurement results are shown in FIG. 4A, and the respective values are shown in the graph of FIG. 4B. First, the margin up to the limit value at 250 MHz, which is the fundamental wave, was 6 dB in the conventional example, was 8 dB in the first example, and was 7 dB in the second example, and the third example. In case of, it becomes 4.7 dB.

Next, at 500 MHz of the second harmonic, a high-frequency signal controlled by the fluctuation signal is superimposed, so 4
Two peaks appear around 80 MHz and 500 MHz. Therefore, FIGS. 4A and 4B show margins up to the limit values at 480 MHz and 500 MHz, respectively. The margin up to the limit value at 480 MHz is 1.1 dB in the first example, 2.8 dB in the second example, and 6.3 dB in the third example. The margin up to the limit value at 500 MHz was 2 dB in the conventional example, but was 3.9 dB in the first example and 3.3 dB in the second example. When
It becomes 13 dB.

The values of these margins are shown in the graph of FIG. 4B. In the graph of FIG. 4B, the conventional example is indicated by “◇”, the first example is indicated by “□”, the second example is indicated by “Δ”, and the third example is indicated by “◯”.

Here, an example of high frequency signals to be superimposed in the conventional example and the first, second and third examples will be described with reference to FIG. In the conventional example, only the high frequency signal shown in FIG. 5A is superimposed on the drive current. In the first example, the high frequency signal (see FIG. 5B) controlled by the fluctuation signal shown in FIG. 3B is superimposed on the drive current. In the second example, a high-frequency signal controlled by the fluctuation signal such that it is between the fluctuation signal shown in FIG. 3B and the fluctuation signal shown in FIG. 3C is superimposed on the drive current. In the third example, the high frequency signal (see FIG. 5C) controlled by the fluctuation signal shown in FIG. 3C is superimposed on the drive current.

Next, in an apparatus different from the above example, another example of the margin up to a predetermined limit value when the LD 9 is driven by the drive current superposed with the high frequency signal controlled by the fluctuation signal Will be explained. In this other example, a 250 MHz margin as a fundamental wave and a 500 MHz margin as a second harmonic are measured.

In the conventional example and the first example, the LD9 is driven with the same drive current as in the conventional example and the first example of the above-mentioned example, and the spectrum thereof is measured. Then, the margin values up to the limit value in the conventional example and the first example obtained from the measurement results are shown in FIG. 6A, and the respective values are shown in FIG.
It is shown in the graph of B. First, the margin up to the limit value at 250 MHz, which is the fundamental wave, is 5.
Although it was 6 dB, it becomes 3.9 dB in the case of the first example.

Next, at 500 MHz of the second harmonic, a high frequency signal controlled by the fluctuation signal is superimposed, so
Two peaks appear around 80 MHz and 500 MHz. Therefore, FIGS. 6A and 6B show margins up to the limit values at 480 MHz and 500 MHz, respectively. The margin up to the limit value at 480 MHz is 4.8 dB in the first example. The margin up to the limit value at 500 MHz was 3.5 dB in the conventional example, but was 7.2 dB in the first example. These values are shown in the graph of Figure 6B. In the graph of FIG. 6B, the conventional example is indicated by "◇",
The first example is indicated by "□".

Here, an example of high frequency signals to be superimposed in the conventional example and the first example will be described with reference to FIG. In the conventional example, only the high frequency signal shown in FIG. 7A is superimposed on the drive current. In the first example, the high frequency signal (see FIG. 7B) controlled by the fluctuation signal shown in FIG. 3B is superimposed on the drive current.

As described above, since the high frequency signal superimposed on the drive current is controlled by the fluctuation signal, the frequency superimposed on the drive current is fixed, so that the power of the generated radiation is concentrated at a specific frequency, as compared with the conventional case. Then, the high-frequency signal to be superimposed fluctuates according to the controlled fluctuation signal, and the frequency of the drive current is evenly distributed in the variable range of the frequency of the fluctuation signal, so that the radiation power can be dispersed. The power of can be suppressed.

In this embodiment, the fluctuation signal is generated by using the frequency generated from the spindle motor by the FG circuit 12, but the invention is not limited to this, and a fluctuation signal of several hundred Hz is generated. As long as it is possible, any one may be used to generate the fluctuation signal. For example, an oscillator may be used to generate the frequency of the fluctuation signal.

In this embodiment, an optical disc is used as an example for explanation, but the same action and effect can be obtained not only by using the optical disc but also by using a magneto-optical disc. That is, when the light emitted from the laser diode returns to the laser diode, the same action and effect can be obtained by applying the configuration.

In this embodiment, a laser diode (semiconductor laser) is used as an example of the laser, but the laser is not limited to the laser diode, and the same action and effect can be obtained by using a gas laser. .

[0038]

According to the present invention, by driving the LD 9 with the drive current on which the high frequency signal controlled by the fluctuation signal is superposed, the spectrum of light is bleeding and the level can be greatly lowered. If the level of the spectrum can be greatly reduced, the level of unwanted radiation can also be greatly reduced. At this time, the bleeding spectrum does not deteriorate the quality of light because it is deviated from the width of the frequency of light by a slight amount. Further, return light noise can be sufficiently suppressed.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining an embodiment of the present invention.

FIG. 2 is a block diagram of an example of a frequency fluctuation control signal generation circuit of the present invention.

FIG. 3 is a waveform diagram for explaining the frequency fluctuation control signal generation circuit of the present invention.

FIG. 4 is a table and a graph showing measurement results to which the present invention is applied.

FIG. 5 is an example waveform diagram for explaining a high frequency signal controlled by a fluctuation signal according to the present invention.

FIG. 6 is a table and a graph showing measurement results to which the present invention is applied.

FIG. 7 is an exemplary waveform diagram for explaining a high frequency signal controlled by a fluctuation signal according to the present invention.

FIG. 8 is a schematic view of an example of an optical pickup.

FIG. 9 is a characteristic diagram for explaining conventional high frequency superposition.

[Explanation of symbols]

1 ... LD light emission amount control circuit, 2 ... LD light emission logic control circuit, 3 ... V / I conversion circuit, 4 ... LD driver, 5 ... High frequency superposition generation circuit, 6 ... The number of superposition is a number control circuit, 7 ... Superposition amplitude control circuit, 8 ... Frequency fluctuation control signal generation circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shinichi Haseno             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation F-term (reference) 5D119 AA01 AA12 BA01 BB01 BB05                       DA05 FA03 FA05 HA41 HA59                 5D789 AA01 AA12 BA01 BB01 BB05                       DA05 FA03 FA05 HA41 HA59

Claims (10)

[Claims] 1. A laser generator for an optical pickup for generating a laser beam applied to an optical disk, comprising: a high-frequency signal generator capable of generating a high-frequency signal and controlling the frequency of the high-frequency signal; A control signal generating means for generating a control signal for controlling the frequency of the high frequency signal at a low frequency; and a superimposing means for superimposing the high frequency signal having the controlled frequency on the drive signal of the laser. Laser generator for optical pickup. 2. The laser generator for an optical pickup according to claim 1, wherein the frequency of the high frequency signal is several hundred MHz. 3. The laser generator for an optical pickup according to claim 1, wherein the frequency of the control signal is several hundred Hz. 4. The laser generator for an optical pickup according to claim 1, wherein the control signal is a triangular wave signal. 5. The laser generator for an optical pickup according to claim 1, wherein the control signal is generated based on a detection signal of a drive unit that rotates a recording medium. 6. A method of controlling a laser generator for an optical pickup, which generates a laser for irradiating an optical disc, wherein a high frequency signal having a controllable frequency is generated, and a high frequency signal is generated at a frequency lower than that of the high frequency signal. A control method of a laser generator for an optical pickup, wherein a control signal for controlling the frequency of the high frequency signal is generated, and the high frequency signal having the controlled frequency is superimposed on a drive signal of the laser. 7. The method of controlling a laser generator for an optical pickup according to claim 6, wherein the frequency of the high frequency signal is several hundred MHz. 8. The method for controlling a laser generator for an optical pickup according to claim 6, wherein the frequency of the control signal is several hundred Hz. 9. The method of controlling a laser generator for an optical pickup according to claim 6, wherein the control signal is a triangular wave signal. 10. The control method of a laser generating device for an optical pickup according to claim 6, wherein the control signal is generated based on a detection signal of a driving unit that rotates a recording medium.