JP2003273449A - Adjusting method for semiconductor laser driving circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an adjusting method for a semiconductor laser driving circuit capable of ensuring the stability of a signal output upon regeneration. <P>SOLUTION: In an adjusting method for a semiconductor laser driving circuit using a semiconductor laser driven by a driving current comprising a high frequency current superposed on a DC current, an oscillation frequency of the high frequency current is set 1/6 to 1/5 times a relaxation oscillation frequency with the output waveform of the high frequency current set to a rectangular wave in response to the oscillation frequency. Further, the current level of the high frequency current is set such that the peak value of the relaxation oscillation in the state of the high frequency current not superposed on the DC current is two times in the state of the high frequency current superposed on the DC 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 method for adjusting a semiconductor laser driving circuit, which is suitable for application to, for example, an optical pickup of an optical disk device.

[0002]

2. Description of the Related Art Conventionally, for example, in a semiconductor laser used as a light source of an optical pickup of an optical disk device,
For the purpose of reducing so-called return light noise, a semiconductor laser may be driven by a drive current in which a high frequency current is superimposed on a direct current, that is, high frequency superimposition may be performed on the semiconductor laser.

[0003]

In the case of a phase change optical disk, the power (output) required for recording and reproducing by such a semiconductor laser is 5.0 [mW] and 300 [μW] based on the power specification of the phase change optical disk. ]] Has been decided. Therefore, if the coupling of the optical path system (that is, the return rate with respect to the output) is 15%, the power of the semiconductor laser needs to be 33 mW or more.

As described above, since a large power is required at the time of recording on the disc, a high output semiconductor laser is used.

For example, when a semiconductor laser having an output of about 40 [mW], which is sufficiently higher than the recording power of 5.0 [mW], is used, the power of the semiconductor laser is 2.0 when the upper limit of the reproducing power is 0.3 [mW]. It is necessary to set [mW].

Generally, the noise characteristic of a semiconductor laser is obtained by taking the ratio of the power of the semiconductor laser to the light intensity noise per unit frequency (fluctuation of light intensity) and the average light output, as shown in FIG. Relative intensity noise (RIN: Rela)
tive Intensity Noise).

In the characteristic curve of such a semiconductor laser, the value of RIN becomes almost constant from the power value of about 4 [mW]. Therefore, when the semiconductor laser of relatively large power is used, the power value is R at low 2.0 [mW]
There has been a problem that the value of IN becomes large and, as a result, signal noise during reproduction becomes large.

As one method for solving such a problem,
By further reducing the coupling by the optical system during playback,
A method has been proposed in which a semiconductor laser having a relatively high power is used where the RIN value is small. For example, 6.
0 [dB] attenuator (ATT: attenuator) 50
When the transmittance is [%], the reproducing power of the semiconductor laser is 4.0 [mW]. In this case, the current level of the superposed high frequency current increases about 1.2 times.

The reproduction stability of the disk depends not only on the reproduction power of the semiconductor laser but also on the current level of the high frequency current superimposed on the drive current of the semiconductor laser. That is, when reproducing the disc, the reproducing power of the semiconductor laser increases in proportion to the current level of the high frequency current superimposed on the drive current. Therefore, when the reproducing power of the semiconductor laser is higher than a predetermined level, the pits on the optical disc are There is a possibility that the data may be erased by irradiating the laser beam and the recorded data may be erased.

Therefore, it is necessary to prevent the reproduction stability from being impaired by controlling the peak value of the current level of the high frequency current. However, in the level adjustment method currently used, it is necessary to change the semiconductor laser for each type of semiconductor laser. However, there is a problem in that the method of controlling the current level of the high frequency current is still insufficient in practice.

Further, the temperature characteristics of the semiconductor laser are shown in FIG.
Is represented by a characteristic curve in which the horizontal axis represents the optical output and the vertical axis represents the drive current (forward current injected into the semiconductor laser).
For example, characteristic curves F1 to F4 are shown at a temperature of 25 [° C.] or 55 [° C.] and in an on state in which a high frequency current is superimposed or in an off state in which no high frequency current is superimposed. Incidentally, the difference in forward current between the semiconductor lasers in the on state and the off state is called a current offset.

According to these characteristic curves F1 to F4, it can be seen that the higher the temperature, the higher the value of the drive current, and the higher the drive current in the OFF state in which the high frequency current is not superimposed than in the ON state. As described above, the superposition effect of the high-frequency current changes with temperature, which causes a problem that the variation spreads from semiconductor laser to semiconductor laser.

When a semiconductor laser is driven by a driving current on which a high-frequency current is superposed at the time of actually reproducing a disc, the value of RIN inversely proportional to the reproduction power of the semiconductor laser is suppressed to a predetermined value or less, and at the same time, a pit on the optical disc. It is highly desirable if the reproducing power of the semiconductor laser can be suppressed to such an extent that does not disappear.

However, in the conventional semiconductor laser drive circuit, while the value of RIN is sufficiently lowered, at the same time, the peak value of the current level of the high frequency current superimposed on the drive current of the semiconductor laser is adjusted for reproduction. It was very difficult to ensure the stability of the signal output.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a method of adjusting a semiconductor laser drive circuit capable of ensuring the stability of a signal output during reproduction.

[0016]

In order to solve the above problems, the present invention provides a method for adjusting a semiconductor laser drive circuit using a semiconductor laser driven by a drive current in which a high frequency current is superimposed on a direct current. The oscillation frequency is set to 1/6 to 1/5 times the relaxation oscillation frequency, the output waveform of the high frequency current is set to a rectangular wave corresponding to the oscillation frequency, and the current level of the high frequency current is set to the direct current to the high frequency current. Is set so that the peak value of relaxation oscillation is twice as high as that when the high-frequency current is superimposed.

As a result, in the semiconductor laser drive circuit, when the semiconductor laser is driven by the drive current in which the high frequency current is superimposed on the direct current at the time of reproduction, the value of RIN inversely proportional to the reproduction power of the semiconductor laser is suppressed to a predetermined value or less. At the same time, the reproduction power of the semiconductor laser can be suppressed to such an extent that the pits on the optical disk which is the irradiation target of the semiconductor laser do not disappear.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below with reference to the drawings.

(1) Configuration of Semiconductor Laser Driving Circuit According to this Embodiment In FIG. 1, reference numeral 1 denotes the semiconductor laser driving circuit according to this embodiment which is mounted on a read-only optical disk device as a whole. DC current I _{1 of a} predetermined level
The semiconductor laser 2 is driven by the drive current I _{3 obtained} by superimposing the high frequency current I ₂ on.

That is, in the semiconductor laser drive circuit 1, an APC (Automatic Phase Control) circuit 3 for controlling the current level of the direct current I ₁ so that the reproduction power of the laser light emitted from the semiconductor laser 2 is always constant. And a superposed high frequency generation circuit 4 for generating a high frequency current I ₂ which is superposed on the direct current I ₁ .

In addition to the APC circuit 3 and the superposed high frequency generation circuit 4, the semiconductor laser drive circuit 1 further includes
Further, a current measuring circuit 5 for measuring the direct current I ₁ from the output stage of the APC circuit 3 is provided so as to be connected in the APC circuit 3.

In this case, in the APC circuit 3, a current level corresponding to the reproduction power of the laser light outputted from the monitor photodiode 6 for monitoring the reproduction power of the laser light emitted from the semiconductor laser 2 is output. The power detection signal S1 is current-voltage converted in the current-voltage converter 8 including the operational amplifier 7 and the feedback resistor R1, and the power detection voltage signal S2 thus obtained is subjected to the error detection circuit 9
Give to.

The error detecting circuit 9 includes an operational amplifier 10 having an inverting input terminal connected to the output terminal of the operational amplifier 7 of the current-voltage converter 8 via a resistor R2, a feedback resistor R3 connected in parallel to the operational amplifier 10. The operational amplifier 10 has a comparison circuit configuration including a feedback resistor R4 and a capacitor C1 connected in parallel, and a non-inverting input terminal of the operational amplifier 10 is applied with a reference voltage of a predetermined voltage level that can be set from a reference voltage source 11. It

Thus, in the error detection circuit 9, the operational amplifier 10 compares the voltage level of the power detection voltage signal S2 from the current-voltage converter 8 with the voltage level of the reference voltage from the reference voltage source 11, and these levels are compared. Error signal S3 having a voltage level corresponding to the difference (that is, the potential difference)
As a PNP transistor provided in the output stage of the APC circuit 3 via the current measuring circuit 5 (hereinafter, referred to as AP
It is called the C-side transistor) It is sent to the base of TR1.

At this time, the emitter of the APC side transistor TR1 is connected to the cathode terminal of the monitor photodiode 6 via the resistor R5, and the middle point of connection between the resistor R5 and the monitor photodiode 6 is the constant voltage source V.
connected to _cc .

As a result, in the APC circuit 3, the AP
Based on the error signal S3 from the error amplification circuit 9 applied to the base of the C-side transistor TR1, the DC current I ₁ having the voltage level of the error signal S3 can be output from the collector of the APC-side transistor TR1. ing.

Further, the above-mentioned current measuring circuit 5 is an APC.
The side transistor TR1 has a PNP-type transistor (hereinafter referred to as a mirror transistor) TR2 having the same configuration, and the base of the mirror transistor TR2 has an AP.
It is connected to the output stage of the error amplification circuit 9 of the C circuit 3, and its emitter is connected to the connection midpoint of the monitoring photodiode 6 and the constant voltage source V _cc via the resistor R6.
Its collector is grounded via a resistor R7.

As a result, the current measuring circuit 5, based on the error signal S3 from the error amplifier circuit 9 applied to the base of the mirror transistor TR2, has a DC current I of a current level corresponding to the voltage level of the error signal S3. ₁ can be output from the collector of the mirror transistor TR2. This is the mirror transistor TR2
Indicates that the same input / output as the APC side transistor TR1 is performed and the same operation is performed.

On the other hand, in the superposed high frequency generation circuit 4,
A high-frequency oscillator 21 is provided which is capable of freely setting the oscillation frequency by operating the frequency control unit 20 including a variable resistor, and a high-frequency current (HF: High Frequency) I ₂ output from the high-frequency oscillator 21. Is input to the base of the first NPN transistor TR3 of the high frequency current level control unit 22.

In this case, a constant reference voltage is applied from the battery 23 to the base of the second NPN transistor TR4, which forms a differential pair integrally with the first NPN transistor TR3. First and second N
The common emitter of the PN type transistors TR3 and TR4 is
Third NPN type transistor TR5 and the third NP
A level control unit 24 having a variable voltage for adjusting the current level of the high frequency current I ₂ is sequentially connected to the base of the N-type transistor TR5. The emitter of the third NPN transistor TR5 is grounded via the resistor R7.

The collectors of the first and second NPN type transistors TR3 and TR4 are connected to the constant voltage source V _cc either directly or via a resistor R8, and the second
Collector of NPN transistor TR4 and resistor R8
Is the PNP of the output stage of the superposed high frequency generation circuit 4.
The transistor is connected to the base of a type transistor (hereinafter, referred to as a superimposed high frequency side transistor) TR6. The superimposed high-frequency-side transistor 4TR6 constitute a differential pair together with the APC side transistor TR1, its emitter connected to the constant voltage source V _cc through a resistor R9.

As a result, in the superposed high frequency generation circuit 4, the high frequency current I ₂ generated by the high frequency oscillator 21 is generated.
Can be amplified by the high frequency current level control unit 22 and output from the collector of the superimposed high frequency side transistor TR6.

In this semiconductor laser drive circuit 1,
A common collector of the APC side transistor TR1 and the superimposed high frequency side transistor TR6 is grounded via the semiconductor laser 2.

As a result, in the semiconductor laser drive circuit 1, the DC current I ₁ whose current level is adjusted by the APC circuit 3 and the high frequency current I _{2 of} the predetermined frequency and the predetermined current level generated by the superposition high frequency generation circuit 4 are generated. And are superposed and supplied to the semiconductor laser 2 as the drive current I ₃ ,
The semiconductor laser 2 can be lit and driven based on the drive current I ₃ .

In addition to the above configuration, in the semiconductor laser drive circuit 1, a terminal (hereinafter, referred to as the first measurement terminal) connected to the connection midpoint of the mirror transistor TR2 and the resistor R7 in the current measurement circuit 5 is used. By measuring the current value of the collector current of the mirror transistor TR2 via a terminal TP1), the current value of the collector current of the APC side transistor TR1 can be indirectly measured.

The terminal connected to the midpoint of the connection between the third NPN transistor TR3 and the frequency control section 20 in the high frequency current level control section 22 of the superposed high frequency generation circuit 4 (hereinafter referred to as the third measurement terminal). The frequency of the high frequency signal output from the frequency control unit 20 via TP3 can be measured.

Further, the terminal connected to the current control stage of the high frequency signal of the superposed high frequency generation circuit 4 (hereinafter referred to as the second
Of the high frequency current I ₂ generated from the superposed high frequency generation circuit 4 via TP2.

These first to third measuring terminals TP1 to T
The P3 is connected to a personal computer 30 (FIG. 2) described later, and measures the frequency, the current value, and the voltage value in the personal computer 30 and executes various arithmetic processing based on the measurement result. There is.

Actually, the high frequency current I ₂ generated from the high frequency oscillator 21 is a rectangular wave with a duty ratio of 50%, and the oscillation frequency is adjusted according to the operation of the frequency control unit 20. Then, when the differential amplification by the first and second NPN transistors TR3 and TR4 in the high frequency current level control unit 22 of the next stage is performed,
The current level of the high frequency current I ₂ is adjusted according to the operation of the level control unit 24 connected to the NPN transistor TR3.

After this, the superimposed high frequency side transistor TR6
Of the high frequency current I ₂ which is output from the collector, it is superimposed to the DC current I ₁ output from the collector of the APC-side transistor TR1, which is the driving current I ₃ of the semiconductor laser 2
Is output to the semiconductor laser 2.

In the current measuring circuit 5, the current value of the collector current of the mirror transistor TR2 in the current measuring circuit 5 is passed through the first measuring terminal TP1 while the operation of the high frequency oscillator 21 in the superposed high frequency generating circuit 4 is turned off. It is possible to measure the current value of the direct current I ₁ output from the collector of the APC side transistor TR1 during feedback control by the APC loop.

(2) Internal Configuration of Personal Computer 30 FIG. 2 shows the internal configuration of the main body of the personal computer 30. The main body 30A of the personal computer 30 includes a CPU (Central Processin) that controls the entire control.
g Unit) 31 and RO that stores various software
An M (Read Only Memory) 32, a RAM (Random Access Memory) 33 as a work memory of the CPU 31,
A hard disk device 34 in which various data are stored, and C
An interface unit 35 that is an interface for the PU 31 to communicate with the semiconductor laser drive circuit 1 (FIG. 1) via a cable (not shown), an image processing unit 37 to which a display 36 is connected, a keyboard 38, and a mouse 39. And an interface unit 40 connected to
These are connected to each other via a bus 41.

In this case, the CPU 31 sends data (frequency, current value and voltage value) and commands given via the first to third measuring terminals TP1 to TP3 of the semiconductor laser drive circuit 1 via the interface section 35. Various processes are executed based on the fetched data and commands and the software stored in the ROM 32.

As a result of this processing, the CPU 31 screen-displays screen data such as a predetermined graph read from the hard disk device 34 or data such as other programs or commands on the display 36 via the image processing unit 37. It is designed to get you.

In this way, the personal computer 3
0, the first to third parts in the semiconductor laser drive circuit 1
By converting each measurement result obtained through the measurement terminals TP1 to TP3 into a graph or the like on the display 36 and displaying the result on the screen, the operator drives the semiconductor laser while visually checking the graph or the like displayed on the screen. The adjustment items in the circuit 1 can be determined.

(3) Optimal Adjustment of Driving Current of Semiconductor Laser (3-1) Suppression of Peak Value of Reproducing Power of Semiconductor Laser and Mode Hopping First, in FIG. 3, the semiconductor laser driving circuit 1 (FIG. 1)
When the high frequency current I ₂ is output from the superposed high frequency generation circuit 4 to the semiconductor laser 2 to be superimposed on the direct current I ₁ or not (hereinafter, this is referred to as the high frequency superposition ON state or OFF state), the semiconductor The RIN (relative intensity noise) characteristic with respect to the reproduction power of the laser 2 is shown.

The RIN characteristic is represented by a characteristic curve in which the horizontal axis represents the reproducing power of the semiconductor laser 2 and the vertical axis represents the value of RIN. Specifically, the value of the reproducing power of the semiconductor laser 2 is changed in the ON state and the OFF state of the high frequency superposition, respectively.
Characteristic curves F10 and F1 in which the value of RIN corresponding to each 0.2 [mW] is taken from 1.0 [mW] to 10.0 [mW]
It is represented by 1.

According to the RIN characteristic of the semiconductor laser 2, when the reproduction power of the semiconductor laser 2 is relatively small (about 4.0 [mW] or less), the RIN value is higher when the high frequency superposition is turned off. It may become smaller.

At the time of reproduction, the value of RIN is -125 [d
B] When the semiconductor laser 2 is used below, according to the characteristic curves F10 and F11 shown in FIG. 3, it is necessary to be 2.5 [mW] or more in the high frequency superposition off state, and in the high frequency superposition on state. It must be 3.0 mW or more, but in the off state of high frequency superimposition, so-called mode hopping (a phenomenon in which the oscillation wavelength jumps) may occur and noise (mode hopping noise) may occur, so it cannot be normally used.

Therefore, in order to further reduce the coupling by the optical system at the time of reproduction and use the semiconductor laser at a small RIN value, for example, an LED having a transmittance of 50% is used.
(Light Emitting Diode) When attenuated using attenuator,
The value of RIN in the ON state of high frequency superposition is shown in FIG.
It is represented as a characteristic curve F12 in the graph shown in FIG.

In FIG. 4A, the horizontal axis indicates the semiconductor laser 2
Is a graph in which the RIN value is plotted on the right vertical axis and the multiple of the peak value (wave height of the relaxation oscillation frequency) of the high frequency superimposed light power is plotted on the right vertical axis of the reproducing power of. This characteristic curve F12 also has a reproducing power value of the semiconductor laser 2 of 1.0 [m
The value of RIN corresponding to every 0.25 [mW] is taken from W] to 10.0 [mW].

According to this characteristic curve F12, when the reproducing power level of the semiconductor laser 2 is 2.0 [mW], -120
What was [dB] becomes 4.0 [mW] in attenuation, and -1
It can be seen that it is improved to 31 [dB].

The emission waveform at this time is, as shown in FIG. 4A, the reproducing power of the semiconductor laser 2 on the horizontal axis and the peak value of the first pulse of relaxation oscillation corresponding to the reproducing power on the left vertical axis. The characteristic curve F13 is a multiple of (hereinafter, referred to as a peak value). The relaxation oscillation is based on the characteristic that the semiconductor laser 2 starts to emit light after a delay time elapses from the application start time of the drive current I ₃ , repeats oscillation (relaxation oscillation) for a while, and then converges to a steady value. .

With respect to the characteristic curve F13 shown in FIG. 4A, when the average power when the value of the reproducing power of the semiconductor laser 2 is 6.0 [mW] is set to 1, the relaxation oscillation peak value of the reproducing power is 6.0 [mW]. It turns out that it becomes 8 times when.

In FIG. 4 (B), in which parts corresponding to those in FIG. 4 (A) are designated by the same reference numerals, the vertical axis on the left side is a multiple of the peak value of relaxation oscillation (average power at 6.0 [mW]). )
In place of the above, when taking a multiple of the average value of the reproduction power, the peak value of relaxation oscillation becomes 5.5 to 8.0 times when the value of the reproduction power is 3.0 to 6.0 [mW].

If the characteristics of the semiconductor laser 2 and the frequency and current level of the superposed high frequency current I ₂ change, the multiple of the peak value of relaxation oscillation changes and the current level of the high frequency current I ₂ is increased or If the frequency of the current I ₂ is lowered, the peak value of the relaxation oscillation is increased.

The reproducing power of the semiconductor laser 2 is set to 300 [μ
W], and if the peak value of relaxation oscillation is 8 times, 2.4
[MW], which is about half of the recording power of 5.0 [mW] and about 6 of the erasing power of 4.0 [mW].
It becomes 0%.

Next, in FIG. 3 described above, the power value of the semiconductor laser 2 is 4.0 [mW] even in the off state of the high frequency superposition.
From the above, the value of RIN is smaller than -130 [dB], so it can be seen that the high frequency superposition may be turned off as long as mode hopping noise does not occur.

FIG. 5A shows the RIN when the reproducing power of the semiconductor laser 2 is changed and the temperature is swept (start: 25 [° C.], stop: 55 [° C.]) in the off state of high frequency superposition. Shows the characteristics, the power value of the semiconductor laser 2 is 3.0 [mW],
The characteristic curves F15 to F18 at 4.0 [mW], 5.0 [mW] and 6.0 [mW] are shown. According to these characteristic curves F15 to F18, 5.0 to 7.0 at a specific temperature, respectively.
The RIN value of [dB] fluctuates.

On the other hand, in FIG. 5B, the temperature is swept by changing the reproducing power of the semiconductor laser 2 in the ON state of the conventional high frequency superposition (start: 25 [° C.], stop: 55 [° C.]). The RIN characteristic of the semiconductor laser 2 is 3.0 [mW], 4.0 [mW], 5.0 [mW] and 6.0.
The characteristic curves F19 to F22 when [mW] is specified are shown. According to these characteristic curves F19 to F22, the mode hopping noise disappears, but the temperature curve changes depending on the reproducing power of the semiconductor laser 2, and in this example, R
The value of IN may deteriorate by 7.0 [dB]. The peak value of relaxation oscillation is about 8.0 times as shown in FIG. 4 (B) described above.

As described above, according to both graphs of FIGS. 5A and 5B, a current having a current value smaller than the current value at which the semiconductor laser 2 is turned off (hereinafter referred to as LD off current) is driven. It is understood that mode hopping can be suppressed by injecting the current I ₃ into the semiconductor laser 2.

As described above, according to the graphs shown in FIGS. 3 to 5B, the value of RIN is reduced only based on the reproduction power of the semiconductor laser 2, and the drive current I ₃ of the semiconductor laser 2 is reduced. If the semiconductor laser 2 is driven by setting the LD off current to suppress mode hopping, and further suppressing the peak value of relaxation oscillation, R
It can be seen that the IN value can be reduced and the mode hopping can be suppressed at the same time.

(3-2) Reduction of RIN value and suppression of peak value of relaxation oscillation In FIG. 6 (A), the oscillation frequency of the high frequency current I ₂ (hereinafter, referred to as high frequency frequency) is 100 [MHz]. Then, the LD off current as the drive current I ₃ of the semiconductor laser 2 is set to 1.5
It is a graph showing relaxation oscillation when it is set to [mA]. Characteristic curves F23 to F25 are represented for each of a plurality of types of temperatures (25, 40, 55 [° C]).

According to these characteristic curves F23 to F25,
The peak value of relaxation oscillation is four times the average output and twice that at the time of light emission, and is not affected by the temperature characteristics so much, and the light emission delay and the relaxation oscillation frequency are slightly changed.

It can be seen that the peak value of relaxation oscillation can be suppressed to 4.0 times if the setting for driving the semiconductor laser 2 can be used as it is. The lower limit value of the high frequency is twice the transmission band of the reproduction signal, and 140 [MH] if 70 [MHz]
z] or more. If the transmission band of the PD high-frequency amplifier is wide, it saturates, so it is a value that is sufficiently attenuated.
[MHz] or higher is desirable.

In general, relaxation oscillation, which is a characteristic of the semiconductor laser 2, has a hump-shaped waveform attenuated by three pulses (about 2.0 [nS]).
When it is set to 250 [MHz], the resonance energy is attenuated so that it does not affect the subsequent relaxation oscillation. In FIG. 6B, the high frequency frequency is actually 260 [MHz], and the characteristic curves F26 to F29 are shown for each of a plurality of types of temperatures (25, 35, 45, 55 [° C.]), and the relaxation oscillation is shown. Has a peak value of 5 times the average output of the semiconductor laser 2.

FIG. 7 shows relaxation oscillation when the cut-off current is changed. When the current value is set as low as 1.0 [mA], the semiconductor laser 2 is not turned off as shown by the characteristic curve F30, and relaxation is performed. Although the peak value of vibration also becomes smaller, the OFF state becomes shallower and the value of RIN increases. On the other hand, if the current value of the cutoff current is set as high as 2.0 [mA],
As indicated by the characteristic curve F31, the emission of the semiconductor laser 2 is delayed and the peak value of relaxation oscillation is increased, but the value of RIN is decreased.

Therefore, the LD off current of the semiconductor laser 2 is RIN depending on the reproducing power of the semiconductor laser 2 used.
The value of is set to 1.5 [mA], which does not increase relatively.

FIG. 8 is a graph showing the light output characteristics with respect to the drive current (forward current) I ₃ of the semiconductor laser 2, and the characteristic curve F32 in the off state of high frequency superimposition,
Although the linearity (gradient) at the time of light emission is good, the semiconductor laser 2 emits light and does not become zero even if the current is reduced. Therefore, the cutoff is set when the drive current I ₃ of the semiconductor laser 2 is 43.5 [mA] based on the estimation line of the straight line portion of the characteristic curve F32.

When the semiconductor laser 2 is made to emit light with a reproducing power of 6.0 [mW], the driving current (forward current) I ₃ is
It is 48.5 [mA], and the current difference with the cutoff is 5.0.
[MA]. That is, the high frequency current I ₂ has a current value of 5.
The semiconductor laser 2 is cut off if superposed above 0 [mA].

Assuming that the semiconductor laser 2 is in a sufficiently safe off-state of 42 [mA], the LD off-current set value of 1.5 [mA] described above may be added, which is the output power of the semiconductor laser 2. It is not a problem but an operating forward current that is the drive current I ₃ , and therefore it is established even if the characteristics of the semiconductor laser 2 vary.

Characteristic curve F33 in the graph shown in FIG.
Is a case where the reproducing power value of the semiconductor laser 2 is fixed to 6.0 [mW] and the current value of the high frequency current I ₂ is fixed to 5.5 [mA], and the characteristic curve F34 shows the variation due to the reproducing power of the semiconductor laser 2. This is a case where the correction is performed using the current value set for correction (hereinafter, this is referred to as the correction operation current value).

The correction operating current value is {2 × (I _OP
−I _TH ) +1.5} [mA], of which “2”
Is due to the duty ratio of 50% of the high frequency, and becomes a current when the value of the reproducing power of the semiconductor laser 2 in the off state of the high frequency superposition is 12 [mW], and can reduce the value of RIN. Further, I _OP is a drive current value of the semiconductor laser 2 at the time of setting the reproduction power, and I _TH is a current value representing a threshold value at which the reproduction power of the semiconductor laser 2 is estimated to be exhausted (in other words, the semiconductor laser is reversed). 2 is a current value at which the reproduction power suddenly rises) (hereinafter referred to as a threshold current value). Further, “1.5” is the set value of the LD off current of the semiconductor laser 2 described above.

This correction operating current value is an operating point at which the peak value of relaxation oscillation in the off state of high frequency superposition is twice as high as in the on state of high frequency superposition, and the correction operating current value is used. By correcting the variation due to the reproduction power of the semiconductor laser 2, the power value of the semiconductor laser 2 at the time of light emission is doubled, and the value of RIN is reduced without increasing the relaxation oscillation. The peak value can be reliably suppressed to about 4.0 times, which is about half of the conventional value.

FIG. 9 is a comparison of the peak value of relaxation oscillation in the ON state of high frequency superposition between the conventional example and the present embodiment. First, when the offset current in the ON state and the OFF state of the conventional high frequency superposition is 2.0 [mA], the semiconductor laser 2 has a high frequency of 400 [MHz].
When the value of the reproducing power of is 5.0 [mW], the peak value of relaxation oscillation is 8.2 times, which is the maximum (characteristic curve F35).

Secondly, when the setting of the offset current is lowered from 2.0 [mA] to 0.6 [mA] as in the present embodiment, the high frequency frequency is 400 [MHz] and the value of the reproducing power of the semiconductor laser 2 is The peak value of relaxation oscillation is 5.2 times at 4.0 [mW] (characteristic curve F36), but it cannot be turned off at 4.5 [mW] or more, and high frequency superposition is not applied. Third,
When the reproducing power value of the semiconductor laser 2 is fixed at 3.0 [mW] and 5.5 [mA] at a high frequency of 265 [MHz], the peak value of relaxation oscillation becomes 5.2 times at maximum (characteristic curve F
36) corrects using the above-described correction operating current value, the peak value of relaxation oscillation becomes a flattening factor of about 4.0 times (characteristic curve F38).

As described above, firstly, the high frequency is set in the range of 1/6 to 1/5 of the relaxation oscillation frequency,
Secondly, the drive signal, that is, the direct current on which the high frequency is superimposed is set to a rectangular wave, and thirdly, the current level of the high frequency current is set to the correction operating current value, so that the semiconductor laser 2 emits light. The power value doubles, and the RIN value decreases without increasing the relaxation oscillation.
Furthermore, the peak value of relaxation oscillation can be reliably suppressed to about 4.0 times, which is about half of the conventional value. Further, since it is not necessary to adjust the reproduction power of the semiconductor laser 2, there is an advantage that no special adjustment or measurement is required.

(4) Operation and effects of the present embodiment In the above configuration, in the semiconductor laser drive circuit 1, first, the high frequency superposition is turned off, and the reproducing power of the semiconductor laser 2 is made to emit at 300 [μW], The drive current I _OP1 at this time is measured at the measurement terminal TP1.

Then, with the high frequency superposition turned off,
The reproducing power of the semiconductor laser 2 is set to a sufficiently low value of 100 [μW], and the driving current I of the semiconductor laser 2 during light emission is set.
_OP2 is measured at the measurement terminal TP1.

Two drive voltages at this measuring terminal TP1
Flow I_OP1, I_OP2Based on the measurement results of
Threshold current estimated to lose the playback power of laser 2
Value I _THIs given by

[0081]

[Figure 1]

It is calculated as follows.

Thereafter, the output of the high frequency oscillator 31 measured at the measuring terminal TP3 is set to a high frequency frequency of 260 [MHz] by adjusting the variable resistor 30, and this is set to a rectangular wave with a duty ratio of 50 [%]. High frequency current I consisting of
Output as ₂ .

Then, by using the level controller 37 in the superposed high frequency generation circuit 4, the P of the high frequency superposed direct current (that is, the drive current I ₃ ) which is the measurement result of the measurement terminal TP2 is P.
The -P (Peak-to-Peak) value is adjusted so as to be the above-mentioned correction operating current value.

As described above, in the semiconductor laser drive circuit 1,
In the adjustment stage before product shipment, set the high frequency to within 1/6 times to 1/5 times the relaxation oscillation frequency and keep the duty ratio of the high frequency at 50 [%] High-frequency current I with a corresponding rectangular wave
₂ is set, and the current level of the high frequency current I ₂ is set to the correction operation current value.

As a result, the peak value of the relaxation oscillation of the semiconductor laser 2 is lowered (actually to about half of the conventional value) in the case of a sine wave, the margin up to the rated power limit of the semiconductor laser 2 is expanded, and the high frequency current is increased. The current level of I ₂ can be increased more than that of the sine wave, and the semiconductor laser 2
The power value at the time of light emission can be doubled.

Thus, in the semiconductor laser drive circuit 1, when the semiconductor laser 2 is driven by the drive current I ₃ on which the high frequency current is superposed at the time of reproduction, the value of RIN inversely proportional to the reproduction power of the semiconductor laser 2 is set to a predetermined value or less. At the same time, the reproduction peak power of the semiconductor laser 2 can be suppressed to such an extent that the pits on the optical disk do not disappear.

Further, the measurement result of the measurement terminal TP1 is previously stored in the personal computer 30, and the level controller 24 is automatically adjusted based on the measurement result to adjust the measurement result of the measurement terminal TP2. Then, the drive current I ₃ of the semiconductor laser 2 can be automatically adjusted. As a result, it is possible to apply a high frequency superimposition to the DC current I ₁ which is stable with respect to the aging of the semiconductor laser 2.

FIG. 10 shows a case where the temperature characteristics of the semiconductor laser 2 are swept (start: 25 [° C.], stop: 50 [° C.]) in the ON state of the high frequency superposition according to the present embodiment. This corresponds to FIG. 5B described above. In FIG. 10, the power value of the semiconductor laser 2 is 3.0.
[MW], 4.0 [mW], 5.0 [mW] and 6.0 [mW]
The characteristic curves F39 to F42 at the time of are shown.

According to these characteristic curves F39 to F42, in the ON state of the conventional high-frequency superposition, the temperature characteristic which is different from that in the OFF state changes with the average value of the OFF state. At this time, a slight effect of mode hopping remains, but the temperature characteristics are not significantly deteriorated.

FIG. 11 shows the RIN characteristic with respect to the reproducing power of the semiconductor laser 2, showing characteristic curves F43 to F45 in the off state of high frequency superimposition, the conventional case, and the case of the present embodiment, respectively. By comparison, it can be seen that in the case of the characteristic curve F45 according to the present embodiment, the value of RIN can be secured to a practically sufficient level.

According to the above configuration, in the semiconductor laser drive circuit 1, the high frequency of the high frequency current I ₂ is adjusted to ⅙ of the relaxation oscillation frequency at the adjustment stage before product shipment.
While setting the range from 2 times to 1/5 times and maintaining the duty ratio of the high frequency frequency at 50 [%], while setting the high frequency current with a rectangular wave according to the high frequency frequency,
By setting the current level of the high frequency current to the correction operation current value, when the semiconductor laser 2 is driven by the drive current I ₃ on which the high frequency current I ₂ is superimposed at the time of reproduction, the reproduction of the semiconductor laser 2 is performed. RI inversely proportional to power
At the same time as suppressing the value of N to a predetermined value or less, it is possible to suppress the reproduction peak power of the semiconductor laser 2 to the extent that the pits on the optical disk do not disappear, thus ensuring the stability of the signal output during reproduction.

(5) Other Embodiments As described above, in the present embodiment, the oscillation frequency of the high frequency current I ₂ is set to 1/6 to 1/5 times the relaxation oscillation frequency, and the high frequency current I ₂ is set. The case where the output waveform of I ₂ is set to a rectangular wave corresponding to the oscillation frequency has been described. The point is that the semiconductor laser 2 during light emission while maintaining the duty ratio of the oscillation frequency of the high frequency current I ₂ at 50% It is only necessary to improve the power of the so that the noise due to the returning light is not generated.

[0094] In the present embodiment as described above, the current level of the high frequency current I _2, given that is set as the drive current I ₃ of the semiconductor laser 2 in a state of not superimposing a high-frequency current I ₂ to the direct current The case where the difference between the current value and the threshold current value of the semiconductor laser 2 is doubled and the current value at which the semiconductor laser 2 is turned off is set to a value has been described. invention is not limited thereto. in short, the current level of the high frequency current I _2, the state where the peak value of the relaxation oscillation in a state where the DC current I ₁ does not superimpose the high-frequency current I ₂ is superposed the high frequency current I ₂ It is set to double the value, and RI is set within a practically sufficient range.
If it is possible to reduce N and suppress the reproduction peak power of the semiconductor laser 2 at the same time, various other arithmetic processes may be performed.

Further, in the above-mentioned embodiment, the case where the semiconductor laser drive circuit according to the present invention is applied to the read-only optical disk device has been described, but the present invention is not limited to this, and the optical disk for recording and reproducing is described. You may make it apply to an apparatus.

Further, in the above-mentioned embodiment, the semiconductor
Direct current so that the reproducing power of the body laser 2 becomes constant.
I₁APC circuit 3 for controlling the current level of
Flow I _TwoAs shown in FIG. 1, the superposed high frequency generator 4 for generating
Although the case where the configuration is configured has been described, the present invention is not limited to this.
Not limited to this, various other configurations can be widely applied.
Wear.

Further, in the above-described embodiment, when the drive current I ₃ is generated by adding the DC current I ₁ and the high frequency current I ₂ , the APC side transistor TR1 and the superimposed high frequency side forming a differential pair with the transistor TR1. The case where the transistor TR6 is configured has been described.
The present invention is not limited to this, and in short, if the drive current I ₃ can be generated by adding the DC current I ₁ and the high frequency current I ₂ , various other configurations can be widely applied. it can.

[0098]

As described above, according to the present invention, in the adjusting method of the semiconductor laser drive circuit using the semiconductor laser driven by the drive current in which the high frequency current is superimposed on the direct current, the oscillation frequency of the high frequency current is relaxed and oscillated. 1/6 of frequency
~ 1/5 times, the output waveform of the high-frequency current is set to a rectangular wave according to the oscillation frequency, and the current level of the high-frequency current is the peak value of relaxation oscillation without superimposing the high-frequency current on the DC current. When the semiconductor laser is driven by the drive current in which the high frequency current is superimposed on the direct current at the time of reproduction in the semiconductor laser drive circuit, It is possible to suppress the value of RIN, which is inversely proportional to the reproducing power of the semiconductor laser, to a predetermined value or less, and at the same time, to suppress the reproducing peak power of the semiconductor laser to such an extent that the pits on the optical disk that is the irradiation target of the semiconductor laser do not disappear. Thus, it is possible to realize a method of adjusting the semiconductor laser drive circuit, which can ensure the stability of the signal output during reproduction.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a semiconductor laser drive circuit according to an embodiment.

FIG. 2 is a circuit diagram showing a configuration of a personal computer connected to first to third measurement terminals in the semiconductor laser drive circuit according to the present embodiment.

FIG. 3 is a waveform diagram for explaining a RIN characteristic with respect to a reproducing power of a semiconductor laser.

FIG. 4 is a waveform diagram for explaining the relationship between the reproducing power of the semiconductor laser, the RIN characteristic, and the peak value and its average value.

FIG. 5 is a waveform diagram for explaining a relationship between temperature and RIN in an off state and an on state of high frequency superposition.

FIG. 6 is a waveform diagram for explaining relaxation oscillation.

FIG. 7 is a waveform diagram for explaining a relationship between a cutoff current and a peak value in relaxation oscillation.

FIG. 8 is a waveform diagram for explaining a light output characteristic with respect to a driving current of a semiconductor laser.

FIG. 9 is a waveform diagram for explaining comparison of peak values in a high frequency superposition ON state.

FIG. 10: Temperature and RIN in ON state of high frequency superposition
FIG. 6 is a waveform chart for explaining a relationship with.

FIG. 11 is a waveform diagram for explaining the RIN characteristic with respect to the reproduction power of the semiconductor laser.

FIG. 12 is a waveform diagram for explaining noise characteristics of a conventional semiconductor laser.

FIG. 13 is a waveform diagram for explaining temperature characteristics of a conventional semiconductor laser.

[Explanation of symbols]

1 ... Semiconductor laser drive circuit, 2 ... Semiconductor laser, 3
... APC circuit, 4 ... superposed high frequency generation circuit, 5 ... current measurement circuit, TP1 to TP3 ... first to third measurement terminals, 30 ... personal computer, I ₁ ... direct current, I ₂ ... high frequency current, I ₃ ... drive current.

Continued front page    F-term (reference) 5D119 AA20 AA31 BA01 DA05 EC09                       FA05 HA41 HA55 HA58                 5D789 AA20 AA31 BA01 DA05 EC09                       FA05 HA41 HA55 HA58                 5F073 BA04 EA27 GA12 GA24 GA38

Claims (2)

[Claims] 1. A method of adjusting a semiconductor laser drive circuit using a semiconductor laser driven by a drive current in which a high frequency current is superimposed on a direct current, wherein an oscillation frequency of the high frequency current is 1/6 of a relaxation oscillation frequency.
The output waveform of the high-frequency current is set to a rectangular wave corresponding to the oscillation frequency, and the current level of the high-frequency current is relaxed without superimposing the high-frequency current on the DC current. A method for adjusting a semiconductor laser drive circuit, wherein a peak value of vibration is set to be twice as high as that in a state where the high frequency current is superimposed. 2. The current level of the high frequency current is a predetermined current value set as a drive current of the semiconductor laser and a threshold current value of the semiconductor laser in a state where the high frequency current is not superimposed on the direct current. The method for adjusting a semiconductor laser drive circuit according to claim 1, wherein a value obtained by adding a current value at which the semiconductor laser is turned off is added to a value obtained by doubling the difference.