JP2731237B2 - Optical information recording / reproducing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus that controls a light output of a semiconductor laser by superimposing a high-frequency signal.

[Prior Art] In recent years, instead of using a magnetic head, an optical information recording / reproducing apparatus capable of recording information and reproducing the recorded information by irradiating a focused light beam has been put into practical use. Was done.

This optical device has a great advantage in that information can be recorded at a high density by using a laser beam, and is becoming increasingly popular in the future.

As a source of the laser light, a laser diode (semiconductor laser) that can be downsized is widely used.

By the way, in an apparatus using the above laser diode, it is effective to modulate the driving current at a high frequency of 500 MHz to 1000 MHz as disclosed in JP-B-59-9086 for reducing the noise of the laser diode. It is known.

It is also known that this modulation is effective for noise reduction if it is modulated with an amplitude that covers the threshold value of laser emission.

[Problems to be Solved by the Invention] Conventionally, when modulation is performed so as to cover the threshold value of the laser diode, the noise reduction effect is increased as described above. Current change ΔIo flowing to laser diode at ON / OFF
p was increased. The maximum value of the current change amount ΔIop was used without any particular limitation.

By the way, in the state in which the high-frequency signal is superimposed, information cannot be normally recorded. Therefore, in the recording mode, the superimposition of the high-frequency signal is switched off and turned on in the reproduction mode.

On the other hand, a recording medium (hereinafter, referred to as a disk) has each track divided into a plurality of sectors, and each sector is provided with a pre-pit portion in which an address number of the sector is written at a leading portion thereof. Even if
In the pre-pit part, it is necessary to read the address,
The mode is switched to the reproduction mode, and recognition as to whether or not the sector is to be recorded is performed.

For this reason, the operation of the high-frequency superimposition module that generates the high-frequency superimposition signal is often turned on / off to switch the high-frequency superimposition signal on and off.

However, the magnitude of the current change ΔIop when the high-frequency superimposed signal is turned on / off by the high-frequency superimposed module ON / OFF,
The ON time until the high-frequency superimposed signal rises has a substantially proportional relationship, and when the current change ΔIop becomes too large,
When switching from the recording mode to the reproduction mode, there is a problem that it takes time to start up and information such as the address of the pre-pit portion cannot be read.

The present invention has been made in view of the above points, and has as its object to provide an optical information recording / reproducing apparatus capable of reading recorded information when switching from a recording mode to a reproduction mode.

Means and Action for Solving the Problems In the present invention, the amount of change in the high-frequency superimposed current between when the high-frequency superimposed current is turned on and when the high-frequency superimposed current is turned off is controlled within a predetermined range, and the high-frequency superimposed current rises. The time required for reading is less than a time that does not hinder the reading of the recorded information, so that the reading can be surely performed.

EXAMPLES Hereinafter, the present invention will be described specifically with reference to the drawings.

1 to 7 relate to a first embodiment of the present invention, and FIG. 1 is a configuration diagram of a current variation control system in the first embodiment;
FIG. 2 is an overall configuration diagram of the first embodiment, FIG. 3 is a characteristic diagram showing a relationship between a driving current and an emission power when a high frequency superimposed current is superimposed and not superimposed, and FIG. 4 is a laser diode. 5 is a characteristic diagram showing the relationship between the noise and the current change amount of FIG.
FIG. 6 is a waveform diagram showing the rise of the high frequency superimposed current when switching from write light emission to read light emission. FIG. 6 is a characteristic diagram showing the relationship between the current change and the time required for the high frequency superimposed current to rise. FIG. 7 is an explanatory diagram showing that the time required for the high frequency superimposed current to rise increases as the current change amount increases.

As shown in FIG. 2, in the optical information recording / reproducing apparatus 1 of the first embodiment, an optical (scientific) pickup 4 is arranged so as to face an optical disc 3 which is driven to rotate by a spindle motor 2. The optical pickup 4 is mounted on a movable base 5 and is moved in a radial direction of the optical disc 3 (that is, in a direction crossing a concentric or spiral track of the optical disc 3) by an optical pickup moving means such as a voice coil motor 6.
It is movable freely.

The optical pickup 4 has a radar diode 7 and transmits the light beam of the laser diode 7 to the optical disk 3.
To condense and irradiate the information so that information can be recorded or reproduced. The laser diode 7 has a monitoring photodetector such as a pin photodiode 8 enclosed in a housing 9 (see FIG. 1). Thus, the front light of the laser diode 7 is used for recording and reproduction, while the back light is received by the pin photodiode 8, and the light emission amount of the laser diode 7 is controlled by this photoelectric conversion output.

 The pickup 4 has the following configuration.

The front light of the laser diode 7 is converted into a parallel beam by a collimator lens 11 and then transmitted to a polarization beam splitter 12 by a P beam.
It is incident with polarized light and is almost 100% transmitted. The light beam transmitted through the polarizing beam splitter 12 is converted into a circularly polarized light by a quarter-wave plate 13, and then condensed by an objective lens 14 to irradiate the disk 3.

The return light from the disk 3 is converted into S-polarized light through the objective lens 14 and the quarter-wave plate 13, is incident on the polarization beam splitter 12, and is almost 100% reflected. The reflected light is incident on the critical angle prism 15, and the light passing through the critical angle prism 15 is incident on a four-division photodetector 16 arranged at the far field position.

The output signal of the photodetector 16 is input to an addition / subtraction circuit 17, and a reproduction signal is generated by addition. Also, radial direction R
The focus error signal FER is generated by a pair of differential outputs divided by a line parallel to the track, and the track error signal TR is generated by one differential output divided by a line parallel to the tangential direction of the track. Is generated. These two signals FER, TE
R is applied to a focusing coil 21 and a tracking coil 22 which form lens actuators via drive circuits 18 and 19, respectively, to form a servo system for holding the objective lens 14 in a focus state and a tracking state.

By the way, the output of the pin photodiode 8 (see FIG. 1) for monitoring the back light of the laser diode 7 is input to the recording light emission amount control unit 24 and the APC circuit 25 constituting the reproduction light amount control means.

The recording light emission amount control unit 24 controls the light emission amount in the recording mode so as to maintain the light emission amount at an appropriate value. The output of the recording light emission amount control unit 24 controls the recording light emission amount of the laser diode 7 via the laser drive circuit 26. For example, the light emission amount is held at a preset light emission amount.

On the other hand, the APC circuit 25 is for controlling the amount of reproduced light (the amount of read light) in the reproduction mode to be a constant value, so that the amount of read light of the laser diode 7 becomes constant via the laser drive circuit 26. Automatic light quantity control is performed.

In this reproduction mode, the laser drive circuit 26 includes:
A high-frequency superimposed signal from a high-frequency superimposition module (hereinafter abbreviated as HFM) 27 as high-frequency signal generation means for reducing noise of the laser diode 7 is superimposed on the DC component of the APC circuit 25 and input.

In this embodiment, the difference between the drive currents I1 and I2 supplied to the laser diode 7 when the HFM 27 is turned ON / OFF, that is, the current for controlling the current change ΔIop (I2−I1) to be within a certain value. A change amount control unit 28 is provided.

The current change amount control unit 28 detects a current flowing from the laser drive circuit 26 to the laser diode 7, and controls the high frequency superimposed output Iosc of the HFM 27 based on the detected output.

The specific configuration of the peripheral part of the current change amount control unit 28
Shown in the figure.

The anode of the laser diode 7 is connected to GND, and its cathode is a transistor constituting the laser drive circuit 26.
It is connected to the collector of Q1, its emitter is connected to the negative power supply terminal -Vcc via the resistor R1, and its base is connected to the APC circuit 25.
And controls the drive current I flowing through the laser diode 7 at the output level of the APC circuit 25.

The input terminal of the APC circuit 25 is a pin photodiode 8
Connected to the anode. The cathode of this pin photodiode 8 is connected to GND, and its anode is connected to a resistor R.
2 is connected to the negative power supply terminal -Vcc. The anode potential of the pin photodiode 8 changes according to the amount of light from the laser diode 7, and the change is determined by the APC circuit 25.
The drive current of the laser diode 7 is controlled to be constant via the transistor Q1 with an error output from a reference value (not shown) in the APC circuit 25.

The output terminal of the HFM 27 is connected to the collector of the transistor Q1, and the high-frequency superimposed signal Iosc is supplied when the HFM 27 is operating. The HFM 27 is switched between an operating state and a non-operating state by an HFM ON / OFF signal.

The drive current of the laser diode 7 is detected by a differential amplifier 31 that detects a voltage across the resistor R1.
The differential amplifier 31 includes an OP amplifier A1, and each input terminal of the OP amplifier A1 is connected to both ends of the resistor R1 via the resistors R3 and R4. The non-inverting input terminal of the OP amplifier A1 is connected to GND via a resistor R5, and the inverting input terminal is connected to an output terminal via a resistor R6. The voltage corresponding to the drive current I detected by the differential amplifier 31 is converted into a digital signal by the A / D converter 32 and
Is input to The CPU 33 switches the HFM 27 between an operating state and a non-operating state at the time of initial diagnosis, and drives the driving currents I1 and I2 via the A / D converter 32 in each state.
Are detected, and a current change amount ΔIop is detected from the difference between the two. The current change amount ΔIop is converted into an analog amount via the D / A converter 34 and applied to one input terminal of the differential amplifier 35. A reference voltage Vr serving as a target value of the current change amount ΔIop is applied to the other input terminal of the differential amplifier 35,
The differential amplifier 35 calculates an error voltage with respect to the reference voltage Vr.
Applied to the oscillation output control terminal of HFM27.

That is, when the current change ΔIop is smaller than the target value, the amplitude of the high frequency superimposed current of the HFM27 is increased, while when the current change ΔIop is larger than the target value, the amplitude of the high frequency superimposed current of the HFM27 is reduced, The current change amount ΔIop is set so as to coincide with the target value. The above reference voltage
Vr is set so that the current change amount ΔIop is, for example, between 2 mA and 6 mA.

The HFM 27 is turned on / off in this way, and the CPU 33 calculates the change amount ΔIop of the currents I1 and I2 flowing through the laser diode 7 at that time, and determines the magnitude of the change amount ΔIop to supply the high frequency superposition supplied to the laser diode 7 from the HFM 27. The amplitude of the current is controlled so that the amount of change ΔIop becomes a target value.

By setting this variation ΔIop to a target value, the HFM27
The rise time ton of the HFM 27 when is changed from OFF to ON is set to a predetermined value or less.

FIG. 3 shows the relationship between the laser drive current I and the emission power P of the laser diode 7 when the operation of the HFM 27 is turned on / off, that is, when the superposition of the high frequency signal is turned on / off.

When the read power is RPa and the HFM 27 is turned on, the curve is indicated by B, and when the HFM 27 is turned off, the curve is indicated by A. The high-frequency superimposed signal Iosc shown in the lower part of FIG.
Is added to the DC component I1 and supplied to the laser diode 7, the output power becomes as shown on the right side of FIG.

When the above HFM27 is turned off, the current becomes I2 and HFP2
The change amount ΔIop when ON / OFF of 7 is I2−I1.

When the variation ΔIop is increased, the R / N noise can be reduced as can be seen from the characteristics of the R / N noise (laser diode noise) shown in FIG.
If the minimum value of is set to ΔIopm (for example, 2 mA) or more, R / N
Noise can be kept small.

On the other hand, as shown in FIG. 5 (a), the light emission (WP) state is changed to the read light emission (RP) state, and at the same time, the HFM 27 is turned on by the HFM ON / OFF control signal as shown in FIG. 5 (b). The high frequency superimposed current of this HFM27
Iosc shows a rising characteristic as shown in FIG. In other words, after turning on the HFM27, the high frequency superimposed current Io
Since sc does not rise instantaneously, a time ton is required until the read power RP reaches 90% of the stable state value RPa on the pin monitor output.

From Fig. 4, it is better to increase the high frequency superimposed current Iosc.
Since noise can be reduced, it is desirable to make the noise as large as possible.

On the other hand, when the high frequency superimposed current Iosc is increased, the time ton required for the rise is also increased, and the relationship shows a linear relationship as shown in FIG.

FIG. 7 shows how the time ton required for rising increases when the high-frequency superimposed current Iosc is increased.

When the write power WP is turned off and the read power is set, a locus like an arrow C follows the curve of the HFM OFF, and the locus falls below the read power RP, and the DC level Ia set according to the magnitude of the high frequency superimposed current. Alternatively, the flow moves from Ib or Ic toward the characteristics at the time of HFM ON as indicated by arrows a, b, and c.

From the locus of this transition, it can be seen that as the current change amount ΔIop is increased, it takes a longer time to shift to the predetermined read power state in the order of ΔIopa, ΔIopb, ΔIopc.

For this reason, if the current change amount ΔIop is increased, the light emission state is switched to the read emission state, and for example, even if an attempt is made to read the address or the like of the pre-pit portion, the read power is increased.
Since it takes too much time for the RP to reach the predetermined value, the error rate at which reading fails will increase.

Therefore, in this embodiment, the HFM27 is turned on as shown in FIG.
The current change amount ΔIop between the time of turning off and the turning off is controlled to be constant, and the time ton until the read power RP reaches a predetermined level is set within a time that does not affect data reading.

Therefore, according to this embodiment, the noise can be reduced and the reading error rate can be prevented from increasing.

FIG. 8 shows a main part of an optical system according to a second embodiment of the present invention.

The second embodiment differs from the optical system of the first embodiment shown in FIG. 2 in that a collimator lens 11 and a polarizing beam splitter are provided.
A light-reducing filter 41 is provided between the light-receiving device 12 and the light-reducing filter 41 to reduce the amount of laser light irradiated on the disk 3 via the polarization beam splitter 12. That is, by actually using only a part of the beam emitted from the laser diode 7 instead of the entire beam, the actual emission level can be increased as compared with the case where the neutral density filter 41 is not used, and the current change ΔIop is small. Use under such conditions.

As described above, by setting the emission power of the laser diode 7 to be high and reducing the amount of light irradiated on the recording medium side by the filter 41, the current change amount ΔIop is used under a small condition (for example, 2 mA to 6 mA).

In this case, the control of the oscillation current Iosc as shown in FIG. 1 is not performed.

Further, the filter 41 reduces the level at which the higher output power is applied to the disk 3 to a level suitable for the read power.

In FIG. 8, a mirror 42 is interposed between the quarter-wave plate 13 and the objective lens 14.

According to the second embodiment, there is an advantage that it is not necessary to control the current change amount ΔIop to a constant value.

In the first embodiment, the current change ΔIop is controlled to be constant, but may be controlled to be within a predetermined range.

[Effect of the Invention] As described above, according to the present invention, the magnitude of the current change when the high-frequency superimposed current is switched between the operation state and the non-operation state is controlled to be within a predetermined range. When switching from the light emitting state to the reading state,
The time required for the high-frequency superimposed current to rise can be set within a time that does not hinder reading.

[Brief description of the drawings]

FIGS. 1 to 7 relate to a first embodiment of the present invention.
FIG. 2 is a block diagram of a current change control system in the first embodiment, FIG. 2 is an overall block diagram of the first embodiment, and FIG. 3 is a diagram showing drive currents when a high-frequency superimposed current is superimposed and when it is not superposed. FIG. 4 is a characteristic diagram showing the relationship between the output power and the laser diode noise, and FIG. 5 is a characteristic diagram showing the relationship between the laser diode noise and the current change amount. FIG. FIG. 6 is a characteristic diagram showing the relationship between the amount of current change and the time required for the high-frequency superimposed current to rise. FIG. 7 is a graph showing the relationship required for the high-frequency superimposed current to rise as the current change increases. FIG. 8 is a side view showing a part of an optical system according to a second embodiment of the present invention. DESCRIPTION OF SYMBOLS 1 ... Optical information recording / reproducing apparatus 3 ... Disc 4 ... Optical head 7 ... Laser diode 8 ... Pin photodiode 24 ... Recording light emission amount control part 25 ... APC circuit 27 ... High frequency superimposing module ( HFM) 28: Current variation controller 31: Differential amplifier, 33: CPU

Claims (2)

(57) [Claims] 1. A semiconductor laser used as a light source of an optical head having a function of irradiating a recording medium with a light beam and receiving its return light, a high-frequency oscillator for supplying a high-frequency superimposed current for reducing noise thereof, In an optical information recording / reproducing apparatus including on / off control means for controlling on / off of the high-frequency oscillator and an output control unit for controlling the output of the semiconductor laser to be constant, the high-frequency superimposed current rises. Control means for controlling the difference in drive current to the semiconductor laser when the high-frequency oscillator is turned off and when the high-frequency oscillator is turned on to be within a predetermined range so that the time required for reproduction does not hinder reproduction. Characteristic optical information recording / reproducing device. 2. The apparatus according to claim 1, wherein a means for increasing the emission power of said semiconductor laser to reduce the amount of laser light irradiated on the recording medium side is provided, and a difference between said driving currents is made relatively small. Item 2. The optical information recording / reproducing device according to Item 1.