JPH05120716A - Method and device for controlling laser diode - Google Patents

Abstract

PURPOSE:To freely vary the depth of modulation in high frequency modulation while applying automatic power control to a laser diode. CONSTITUTION:Threshold value current Ith where the laser diode 10 is started to emitting light and read emitting current Ir obtaining specified read power after emitting light are detected, and the differential current (x) of both currents is found, and high frequency modulation current Ihfm is added to the current subtracting the current (nx) multiplying the difference current (x) by (n) to be a coefficient (n) deciding the depth of the modulation from the read emitting current Ir and simultaneously the increase of the current is stopped to be fixed at the point of time when the mean value of light emitting power arrives at read power Pr. After the process flowing the current subtracting the current (nx) multiplying the difference current (x) by (n) from the read emitting current Ir to the laser diode 10 is stopped, the automatic power control making the read power Pr a setting target value is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode control method and apparatus for controlling the intensity of a read beam emitted from a laser diode when reading an optical disk medium. In an optical disc device using an optical disc medium such as a rewritable magneto-optical disc and a non-rewritable optical disc, the emission power level is in the noise region of the laser diode during reading, and the S / N ratio of the reproduction signal is Therefore, the read modulation method is adopted in which modulation is performed so that the peak power level exceeds the noise level at a frequency higher than the recording frequency by one digit or more, and the execution power is suppressed to the noise area even if the peak power is high. ing.

In addition, automatic power control (hereinafter referred to as "APC"; Automa
tic Power Control) is required. However, APC
There is no good way to control the depth of high frequency modulation while multiplying by, and improvement of this point is desired.

[0003]

2. Description of the Related Art In a conventional laser diode control system for radiating a read beam, the drive current is determined so that the read power can be obtained in a region beyond the noise region of the laser diode. Is low enough to be in the noise region.

Therefore, the read power is set in the noise region, and in order to ignore the influence of the noise, the high frequency modulated read modulation power is emitted at a frequency higher by one digit or more than the recording frequency. On the other hand, it is necessary to provide an APC circuit in order to suppress power fluctuations due to aging and temperature changes of the laser diode.

The APC circuit controls the drive current so that the light receiving power of the monitor light receiving element matches the read power, and suppresses the fluctuation of the light emitting power due to temperature and aging.

[0006]

However, in such a conventional laser diode control system for a read beam, the depth of high frequency modulation is performed while light is emitted while automatic power control is applied and as a countermeasure against noise and backtalk. There was a problem that there was no good method to freely change the size.

The present invention has been made in view of the above conventional problems, and a laser diode control method and apparatus capable of freely varying the modulation depth in high frequency modulation while performing automatic power control. The purpose is to provide.

[0008]

FIG. 1 is a diagram for explaining the principle of the present invention. First, the present invention is directed to a laser diode control method for controlling the intensity of a read beam emitted from the laser diode 10 when reading an optical disk medium. The present invention as a method of controlling such a laser diode includes the following steps.

First step: A threshold current I _th for starting light emission by adjusting a first control current source 12 connected in series with a laser diode 10 and a lead light emission current I _r for obtaining a specified read power P _r after light emission are detected. Then, the difference current x between them is obtained.

Second step: Subsequently, the current flowing through the high frequency modulating means 14 connected in series to the laser diode 10 is adjusted by the second control current source 16 to determine the modulation depth of the difference current x = I _r −I _th. The high frequency modulation current I _hfm is added to the current obtained by subtracting the current nx multiplied by n by the coefficient n from the read light emission current I _r, and the high frequency modulation current I _hfm is increased so that the average value of the light emission power is the read power P. _When it reaches _r , the increase is stopped and fixed.

Third step: Next, by the first controlled current source 12
Lead emission current I_r Current nx which is the difference current x multiplied by n
The process of subtracting and flowing to the laser diode 10 is separated
Read power P_r Automatic power with set target value
-Controls the first controlled current source 12 by the output of the control means 18.
To do. The present invention also provides a laser for reading an optical disk medium.
Controls the intensity of the read beam emitted from the diode 10.
This is intended for laser diode control devices that
1 setting signal V₁ Based on the flow to the laser diode 10
The first control current source 12 for adjusting the current
The recording current is supplied to the laser diode 10 by the source 12.
A high-frequency modulation voltage with a frequency at least one digit higher than the wave number.
Flow I_hfm High frequency modulation means 14 for adding
High frequency modulation current I flowing by the means 14_hfm The size of the second
Setting signal V₂The second control current source 16 which is adjusted based on
And a monitor for detecting the light emission power of the laser diode 10.
Light receiving element 20 and target setting signal V ₃ And monitor light receiving element
Emission power detection signal V corresponding to the received light current of 20_M With
An automatic power control for controlling the first controlled current source 12 based on the deviation.
The work control means 18 and the adjusting means 22 are further provided.

The adjusting means 22 adjusts the first control current source 12 connected in series with the laser diode 10 to obtain a threshold current I _th for starting light emission and a read light emission current I _r for obtaining a specified read power P _r after light emission. Is detected to obtain a difference current x between them, and subsequently, the second control current source 16 adjusts the current flowing through the high frequency modulation means 14 connected in series to the laser diode 10.
A current n obtained by multiplying the difference current x by a factor n that determines the depth of modulation.
x is added to the current obtained by subtracting the lead emission current I _r ,
When the average value of the light emission power reaches the read power P _r , the addition of the high frequency modulation current I _hfm is increased and stopped to be fixed, and then the read light emission current by the first control current source 12 is increased. After subtracting the current nx obtained by multiplying the difference current x by an integer n from I _r to separate the process of flowing to the laser diode 10,
The first control current source 12 is controlled by the output of the automatic power control means 18 having the read power P _r as the set target value.

The high frequency modulating means 14 converts the pulse signal oscillated at a predetermined frequency into a waveform of a substantially sine wave by a low pass filter and supplies a modulation current to the laser diode 10. Further, as the first and second control current sources 12 and 16, a voltage-current conversion circuit that inputs a voltage setting signal output from the adjusting means 22 and causes a corresponding current to flow through the laser diode 10 is used.

Further, the first setting signal V ₁ is input to the input of the first control current source 12 via the first switch SW1, and the automatic power control means 1 is input via the second switch SW2.
8 is connected, and the adjusting means 22 uses the first switch SW1.
Is turned on and the second switch SW2 is turned off, the first control current source 12 is adjusted, and the first switch SW1 is turned off.
The automatic power control means 18 is controlled with the second switch SW2 turned on.

[0015]

According to the laser diode control method and apparatus of the present invention having such a configuration, the following operation can be obtained.
As shown in the characteristic diagram of FIG. 1B, first, the read current I _r for emitting the read power P _r and the threshold current I _th for stopping the emission of the laser are converted into the received current of the power monitor light receiving element 20 by voltage conversion. Then, the detection voltage V _{M is used} for confirmation.

Next, a current nx obtained by multiplying a difference current x (= I _r −I _th ) between the read current I _r and the threshold current I _th by a coefficient n is subtracted from the read current I _r , and this high frequency modulation current is obtained. I
Add _hfm . At this time, the high frequency modulation current I _hfm is increased while monitoring the light emission power, and is fixed to the current I _{hfm at} which the average power becomes the read power P _r . Then, the remaining current I obtained by subtracting the previous current nx from the read current I _r
By controlling _apc with the output of the automatic power control means 18, the depth of high frequency modulation can be freely controlled with a constant average value of the light emission amount (= read power P _r ).

[0017]

FIG. 2 is a block diagram of an embodiment showing one embodiment of the present invention. In FIG. 2, reference numeral 10 denotes a laser diode, which emits a read beam when reading information from a rewritable magneto-optical disk or a non-rewritable optical disk. A voltage / current conversion circuit (V / I circuit) 12 as a first control current source is connected in series with the laser diode 10. Further, a series circuit of a high frequency modulation circuit (HFM) 14 and a voltage / current conversion circuit 16 as a second control current source is connected in parallel with the voltage / current conversion circuit 12.

On the other hand, a monitor light receiving element 20 is provided for the laser diode 10, and receives light from the laser diode 10 and outputs a light receiving current according to the light emission power. To the voltage-current conversion circuit 12, the output of the DA converter 24 is connected via the first switch SW1, and the output of the APC circuit 18 is connected via the second switch SW2. Further, the output of the DA converter 26 is connected to the voltage-current conversion circuit 16.

The APC circuit 18 receives at one input a standardized power detection voltage V _M generated at both ends of a resistor R to which a reference voltage V _ref is applied based on a light receiving current of a monitor light receiving element 20. , DA converter 28 on the other input
Receiving the target set voltage V ₃ from the power detection voltage V 3
_The voltage-current conversion circuit 12 feedback-controls the current flowing through the laser diode 10 so that _M matches the set target voltage V ₃ . Therefore, the APC circuit 18 is composed of an error amplifier and an integrating circuit.

Reference numeral 22 denotes an MP having a function as adjusting means.
U, which takes in the power detection voltage V _M obtained from the light receiving current of the monitor light receiving element 20 from the AD converter 30, and outputs the setting signals V ₁ , V ₂ , and V ₃ from the DA converters 24, 26, and 28. Digital data D ₁ for output,
It outputs D ₂ and D _3, and also outputs control signals E ₁ and E ₂ for controlling the switches SW1 and SW2.

FIG. 3 is a circuit diagram of an embodiment showing one embodiment of the high frequency modulation circuit 14 of FIG. 2 and the voltage-current conversion circuit 16 connected in series thereto. In FIG. 3, the high frequency modulation circuit 1
An oscillation circuit 4 is composed of a positive feedback circuit using ECL circuits 32 and 34 and resistors R1 and R2, and outputs a pulse signal having a frequency higher than the recording frequency by one digit or more.

The inverted output and the non-inverted output from the ECL circuit 34 provided in the output stage are respectively the capacitor C1 and the resistor R.
It is supplied to the bases of the transistors 40 and 42 through a low-pass filter 36 using 3 and a low-pass filter 38 using a resistor R4 and a capacitor C2. In this way, the pulse signal from the oscillator circuit is passed through the low-pass filters 36, 3
The high-frequency component is attenuated by passing the signal through the signal 8, and the pulse waveform is converted into a sinusoidal waveform.

The laser diode 10 is connected to the emitter of the transistor 42 as a load, and the transistor 36
And the emitters of 42 are commonly connected, and the voltage-current conversion circuit 1
6 is connected to the collector of the transistor 46.
The voltage-current conversion circuit 16 includes an amplifier 44 and has resistors R5 and R5.
The voltage setting signal V ₂ from the DA converter 26 is input through the input circuit formed of R6, and the transistor 46 is driven through the amplifier 44 to be converted into a current. A resistor R9 for current detection is connected to the emitter of the transistor 46,
The voltage corresponding to the current generated across the resistor R9 is the resistance R8.
The constant current control is performed so that the voltage is divided by the voltage dividing circuit including the resistor R7 and fed back to the amplifier 44, and an output current corresponding to the input voltage setting signal V ₂ is obtained.

FIG. 4 is a flow chart showing a processing procedure for freely determining the modulation depth of the high frequency modulation current I _hfm flowing through the laser diode 10 executed by the MPU 22 of FIG. 2, and FIG. The control characteristic of the drive current and light emission power with respect to the laser diode 10 according to the processing procedure is shown. In FIG. 4, first, in step S1, all of the DA converters 24, 26 and 28 are reset to set the voltage setting signals V ₁ , V ₂ and V ₃ to 0, and subsequently in step S2, the switch SW1 is turned on to perform DA conversion. The voltage setting signal V ₁ converted by the converter 24 can be input to the voltage-current conversion circuit 12. At this time, the switch SW2 is off and the APC circuit 1
8 is separated.

Subsequently, in step S3, the setting data D ₁ for the DA converter 24 is increased by one, and the drive current supplied to the laser diode 10 is sequentially increased by the voltage / current conversion circuit 12, and in the next step S4, the laser diode 1
0 starts emitting light and data D ₄ from the AD converter 30
Check from the power detection signal V _M obtained as

When it is determined in step S4 that the laser diode 10 starts to emit light, the drive current at this time is stored as the threshold current I _th as shown in FIG. 5, and the process proceeds to the next step S5. In step S5, the same D
The setting data D ₁ for the A converter 24 is increased by one, and it is determined in the next step S6 whether or not a predetermined read power P _r can be obtained. When it is determined in step S6 that the read power P _r is obtained due to the increase in the drive current of the laser diode 10, the read current I _r at that time is stored as shown in FIG.

Then, in step S7, a difference current x obtained by subtracting the threshold current I _th obtained in step S4 from the read current I _r obtained in step S6 is used as a coefficient n for determining the depth of modulation.
The value obtained by multiplying by
The setting data D ₂ indicating xn is supplied to the DA converter 26 to set the voltage setting signal V ₂ to the voltage / current conversion circuit 16. This is shown in FIG.

Next, in step S8, the output of the DA converter 26 is increased by one, and the voltage / current conversion circuit 16 sequentially increases the modulation current I _hfm by the high frequency modulation circuit 14. As described above, while the high frequency modulation current I _hfm is increased, _whether the average light emission power received by the monitor light receiving element 20 by the modulated light emission of the laser diode 10 in step S9 reaches the same specified read power P _r as in step S6. Determine whether or not. When it is determined in step S9 that the read power P _r has been reached, the increase of the high frequency modulation current I _hfm by the DA converter 26 is stopped and fixed. That is, the state shown in FIG.

The above processing determines the modulation depth of the high frequency modulation signal to be passed through the laser diode 10.
For example, when the coefficient x is x = 1, the modulation depth is 100%.
And the coefficient n is n = 2, the modulation depth is 20
It becomes 0%. Subsequently, in step S10, the DA converter 28 is subjected to high frequency modulation of the standardized power detection voltage V _M taken in from the AD converter 30 when the read power P _r is obtained by the light emission by the high frequency modulation current in step S9. It is given as the read power instruction value obtained in the performed state, and DA
The converter 28 sets the target set voltage V ₃ in the APC circuit 18.

Then, in step S11, the switch SW1 is turned off to disconnect the DA converter 24 from the voltage-current conversion circuit 12, and the switch SW2 is turned on to turn on the APC circuit 1.
The output of 8 is connected to the voltage-current conversion circuit 12, and feedback control is performed so that the average value of the light emission power by the high frequency modulation becomes the read power P _r . That is, the APC circuit 18
_Performs feedback control so that the average value of the light emission power by the high frequency modulation current I _hfm by controlling the current amount that becomes I _apc shown in FIG. 5 is always the read power P _r .

[0031]

As described above, according to the present invention, in the high frequency modulation of the laser diode, it becomes possible to freely control the modulation depth while performing automatic power control. It is possible to control the read beam according to the characteristics of the head.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the principle of the present invention.

FIG. 2 is a block diagram of an embodiment of the present invention.

FIG. 3 is a circuit diagram of an embodiment of the high frequency modulation circuit and the voltage-current conversion circuit of FIG.

FIG. 4 is a control characteristic diagram showing an adjustment procedure for performing control according to the present invention.

5 is a flowchart showing an adjustment process by the MPU of FIG.

[Explanation of symbols]

10: Laser diode 12: First control current source (voltage / current conversion circuit) 14: High frequency modulation means (high frequency modulation circuit) 16: First control current source (voltage / current conversion circuit) 18: Automatic power control means (automatic power control) Circuit: AP
C circuit) 20: light receiving element for monitor 22: adjusting means (MPU) 24, 26, 28: DA converter 30: AD converter 36, 38: low-pass filter 40, 42, 46: transistor 44: amplifier

Claims (5)

[Claims] 1. A laser diode control method for controlling the intensity of a read beam emitted from a laser diode 10 when reading an optical disk medium, wherein light is emitted by adjusting a first control current source 12 connected in series to the laser diode 10. The threshold current I _th for starting the light emission and the read light emission current I _r for obtaining the specified read power P _r after light emission are detected to obtain the difference current x therebetween, and subsequently the high frequency modulation means 14 connected in series to the laser diode 10. _Is adjusted by the second control current source 16, and a current nx obtained by multiplying the difference current x by a coefficient n for determining the modulation depth is subtracted from the read light emission current I _r to obtain a high frequency modulation current I _hfm. At the same time as the addition, the high frequency modulation current I _hfm is increased, and when the average value of the light emission power reaches the read power P _r , the increase is stopped and fixed. Is automatically subtracted from the read light emission current I _r by the first control current source 12 by subtracting the current nx obtained by multiplying the difference current x by n and flowing to the laser diode 10, and then automatically setting the read power P _r to the set target value. Power control means 18
The control method of the laser diode is characterized in that the first controlled current source 12 is controlled by the output of the laser diode. 2. A laser diode control device for controlling the intensity of a read beam emitted from the laser diode 10 when reading an optical disk medium, wherein the current flowing through the laser diode 10 is adjusted based on a _first setting signal V _1. A first control current source 12 and the laser diode 10 by the first control current source 12.
The high-frequency modulation current I _hfm having a frequency higher than the recording frequency by at least one digit or more, and the magnitude of the high-frequency modulation current I _hfm flowed by the high-frequency modulation device 14 to the second setting signal V. _Second control current source 16 adjusted based on ₂ , monitor light receiving element 20 for detecting light emitting power of laser diode 10, light emission power detection corresponding to target setting signal V ₃ and light receiving current of monitor light receiving element 20. Automatic power control means 1 for controlling the first controlled current source 12 based on the deviation from the signal V _M
8, a threshold current I _th for starting light emission by adjusting the first control current source 12 connected in series to the laser diode 10 and a lead light emission current I _r for obtaining a specified read power P _r after light emission are detected and both are detected. High frequency modulation means 14 connected in series with the laser diode 10
Is adjusted by the second control current source 16, the current nx obtained by multiplying the difference current x by a coefficient n that determines the depth of modulation is added to the current obtained by subtracting the read light emission current I _r , and the high frequency The addition of the modulation current I _hfm is increased, and when the average value of the emission power reaches the read power P _r , the increase is stopped and fixed, and then the read emission current I _r by the first control current source 12 is increased. Current nx obtained by multiplying the differential current x by an integer n
Is subtracted from the laser diode 10 to disconnect the process, and then the first control current source 12 is output by the output of the automatic power control means 18 that sets the read power P _r to the set target value.
A laser diode control device comprising: an adjusting unit 22 for controlling the laser diode. 3. The laser diode control device according to claim 2, wherein the high frequency modulating means 14 converts the pulse signal oscillated at a predetermined frequency into a substantially sinusoidal waveform by a low pass filter. A laser diode control device characterized in that a modulation current is supplied to the laser diode. 4. The laser diode control device according to claim 1, wherein the first and second control current sources 12 and 16 receive a voltage setting signal output from the adjusting means 22 and receive a corresponding current. 2. A laser diode control device, wherein a voltage-current conversion circuit for flowing the above into the laser diode 10 is used. 5. The laser diode control device according to claim 2, wherein the first set signal V ₁ is inputted to the input of the first controlled current source 12 via a first switch SW1, and the second switch is also provided. The automatic light emission power control means 18 via SW2
Of the first switch SW1, the adjusting means 22 adjusts the first control current source 12 with the first switch SW1 turned on and the second switch SW2 turned off.
A laser diode control device for controlling the automatic power control means 18 in a state in which 1 is turned off and the second switch SW2 is turned on.