JP2795483B2 - Optical power control circuit for semiconductor light emitting device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical power control circuit of a semiconductor light emitting element in an information recording / reproducing apparatus for an optical disk.

2. Description of the Related Art In an information recording / reproducing apparatus for a write-once (DRAW) type or erasure rewriting (EDRAW) type optical disk, a laser diode which is a semiconductor light emitting element as a light source for emitting a light beam for writing data on the optical disk or reading the written data Is used. In this laser diode optical power control circuit, in order to prevent the C / N of the read signal from deteriorating due to the oscillation mode of the laser diode being changed by the return light from the disk,
A high-frequency current of 100 MHz or more is superimposed on the drive current of the laser diode so that the laser diode oscillates stably against return light (for example, see Japanese Patent Publication No. 59-9086).

Conventionally, the superposition of the high-frequency current has been performed not only in the data reading mode but also in the high-power emission of the data writing mode unless the superposition of the high-frequency current exceeds the maximum rating of the laser diode. However, since the write data and the high-frequency superimposed signal are usually asynchronous, if high-frequency superimposition is performed at the time of data writing, the high-frequency superimposed signal interferes with the data signal to cause cross modulation. As a result, the edge of the write data vibrates in the time axis direction and is recorded, resulting in deterioration of the recording signal.

SUMMARY OF THE INVENTION [Object of the Invention] Accordingly, an object of the present invention is to provide an optical power control circuit of a semiconductor light emitting element which enables stable writing without affecting write data by a high frequency current to be superimposed on a driving current. Aim.

[Constitution of the Invention] A control circuit for controlling the optical power of a semiconductor light-emitting device according to the present invention irradiates a recording medium with a writing light beam or a reading light beam to write and read information data on the recording medium. A control circuit for controlling an optical power of a semiconductor light emitting element for performing a read operation, a means for generating a read drive current according to a read power set value, and a first modulation for modulating a current according to a write power set value by write data. Means for supplying, to the semiconductor light emitting element, a light emitting element drive current obtained by superimposing an output current of the first modulation means on the read drive current; and a means for modulating the write power set value by the write data. (2) a light modulating means, a light detecting means for receiving a part of a light beam emitted from the semiconductor light emitting element, and an output of the second modulating means from an output of the light detecting means. Means for controlling the read drive current to increase or decrease based on a difference between a subtraction effect obtained by subtracting a force and the read power set value, and a high frequency superposition for superposing a high frequency current on the light emitting element drive current only during a read mode period Means, first correction means for extracting a correction current for lowering the bottom power of the writing light beam from the light emitting element driving current during the writing mode period, and adding a correction voltage corresponding to the correction current to the subtraction result. And two correction means.

[Operation of the Invention] In the optical power control circuit for a semiconductor light emitting device according to the present invention, the high frequency current is superimposed on the driving current of the semiconductor light emitting device only in the read mode period, and the superimposition of the high frequency current is prohibited in the write mode period. At the same time, the write drive current of the semiconductor light emitting element is corrected.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.
In the figure, a part of light emitted from a laser diode 1 is guided to a monitor diode 2, and an optical power detection voltage output from the monitor diode 2 passes through a monitor amplifier 3 and is an LPF (low-pass filter) as first averaging means. 4 is supplied. The voltage V ₁ averaged by the LPF 4 becomes an addition input of the adder / subtractor 5. The addition / subtraction output of the addition / subtraction unit 5 is supplied to an inverting input terminal of an operational amplifier OP that forms an integrator 6 together with the capacitor C. A voltage corresponding to the read power set value set by the read power setting circuit 7 is applied to the non-inverting input terminal of the operational amplifier OP. The output voltage of the integrator 6 is converted to a current by a V (voltage) -I (current) converter 8 and supplied to the laser diode 1 via an adder / subtractor 9 as a read drive current.

When writing data, a larger laser power is required than during reading, and the writing power value is set by the writing power setting circuit 10. Voltage corresponding to the write power setting value output from the write power setting circuit 10 is supplied to the switch SW ₁ of the first modulation means is converted into a current by the V-I converter 11. The switch SW ₁ is on the ground side is in read mode period, the write mode period modulates the current corresponding to write power set value by the write data by repeating the ON / OFF operation in accordance with the write data. Output current of the switch SW ₁ is superimposed on the read drive current in the adder-subtracter 9 is supplied to the laser diode 1 as a write drive current.

Further, the adder-subtractor 9, a high frequency current of about 100MHz emanating from the high frequency oscillator 12 are supplied through the switch SW _2. Switch SW ₂ is typically located on (closed) state to an OFF (open) in response from the controller (not shown) to the write gate pulse emitted by the write data section. Thus, the superposition of the high-frequency current on the write drive current of the laser diode 1 is prohibited in the write mode period, and the high-frequency current is superimposed on the read drive current of the laser diode 1 only in the read mode period.

Voltage corresponding to the write power setting value output from the write power setting circuit 10 is supplied to a switch SW ₃ as the second modulation means through the variable resistor VR. The switch SW ₃ is interlocked with the switch SW _1, located on the ground side is in read mode period, the write mode period while modulated by turning on / off the output voltage of the variable resistor VR by the write data
LPF1 as a second averaging means having the same time constant as LPF4
Supply to 3. The voltage V ₃ averaged by the LPF 13 is added to the adder / subtractor 5
Becomes the subtraction input.

And correction current setting circuit 14 for setting a correction current associated with the high-frequency superposition is provided selectively subtracter 9 set correction current in the setting circuit 14 by the switch SW ₄
Is the subtraction input. Switch SW ₄ is interlocked with the switch SW _2, normally in ground side, selects a correction current which is set by the correction current setting circuit 14 by the application of the write gate pulse. That is, in the write mode period, the correction current is extracted from the write drive current.

Also, as will be described later, when aimed at lowering the bottom power of the write power, the correction voltage setting circuit 15 for setting a correction voltage V ₅ for correcting a decrease amount of optical power provided in the write mode Have been. Set correction voltage in this correction voltage setting circuit 15 is supplied to the switch SW _5. Switch SW ₅ is interlocked with the switch SW _2, SW _4, normally in ground side, selects the correction voltage by the application of the write gate pulse. The selected correction voltage is added to the adder / subtractor 5 via the LPF 16 having the same time constant as the LPFs 4 and 13. The addition / subtraction output (V ₁ −V ₃ + V ₅ ) of the adder / subtractor 5 is output to the integrator 6
In the above, a variation with respect to the voltage corresponding to the read power setting value is obtained. In the figure, the switches SW _{1 to} S
Although W ₅ is shown as a mechanical switch for convenience of explanation,
Of course, it can be constituted by a well-known electronic switch circuit. The time constants of the LPFs 4, 13, and 16 are set sufficiently shorter than the response time constant of the APC (auto power control) servo.

Next, the circuit operation of such a configuration will be described with reference to the waveform diagram of FIG. Note that the read / write mode in this circuit is switched according to input write data. That is, the data section of the write data (a) is the write mode period, and the other sections are the read mode period.

First, an operation in a case where superposition of a high-frequency current on a driving current of the laser diode 1 is not considered will be described. It is also assumed that there is no addition input from the LPF 16 to the adder / subtractor 5.

In the read mode, the switches SW ₁ and SW ₃ are both on the ground side, and the read power setting circuit 7 is connected to the laser diode 1.
The read drive current corresponding to the read power set value set in the step (1) is supplied. In this state, the optical power detection voltage detected by the monitor diode 2 is averaged by the LPF 4 via the monitor amplifier 3 and supplied to the adder / subtractor 5. Optical power monitor voltage V ₀ is the output of the monitor amplifier. 3 (b), at the time of reading is substantially constant voltage V _OR, also switch SW ₃
By the output voltage V ₂ (c) is zero, since it is zero also averaged voltage V ₃ by LPF 13, the output voltage V ₄ of that value V _OR is as adder-subtracter 5 (d). Then, the read drive current is increased / decreased (hereinafter, referred to as a control) in accordance with the variation of the output voltage V ₄ (d) with respect to the voltage corresponding to the read power set value.
APC servo is performed), whereby the optical power of the laser diode 1 is kept constant.

In the write mode, when the switches SW ₁ and SW ₃ repeat the on / off operation according to the write data (a), the output voltage V ₀ (b) of the monitor amplifier 3 becomes a constant voltage at the time of reading.
Pulse waveform voltage pulse waveform at the time of writing is superimposed on a V _OR is outputted. By this pulse waveform voltage V ₀ is passed through the LPF 4, FIG. (B) the average voltage as shown by a broken line is obtained as an output voltage V ₁ of the LPF 4. On the other hand, switch SW ₃
As the output voltage V ₂ (c), a voltage corresponding to the write power set value is turned on / off by the write data (a) to obtain a pulse waveform voltage, and this pulse waveform voltage V ₂ passes through the LPF 13 The output voltage of LPF13
Averaging the voltage as shown by a broken line in FIG. (C) is obtained as V _3. Then, by subtracting the average voltages V ₁ above from the average voltage V _3, as the output voltage V ₄ of the adder-subtracter 5 (d), so that the constant voltage V _OR when reading is obtained. That is, the output voltage V ₄ (d) of the adder / subtractor 5 does not change during reading or writing. At the time of writing, the output voltage V ₄ of the adder / subtractor 5 is the same as at the time of reading.
As a matter of course, the read drive current is increased or decreased in accordance with the fluctuation with respect to the voltage corresponding to the read power set value in (d).

Thus, by averaging it after modulating the voltage corresponding to the write power set value by the write data (a), by subtracting the average voltage V ₃ from the averaging voltage V ₁ of the optical power monitor voltage V ₀ , this means that the same constant voltage V _oR obtained as the subtraction voltage V ₄ and when reading during a write, the read mode to the write mode, or with the switching of the reverse can be performed instantaneously, long term Even if the writing power is output over the range, the reading power can be returned to the reading power instantaneously.

Next, a case will be described in which a high-frequency current is superimposed on the drive current of the laser diode 1 in the read mode period and the high-frequency current is not superimposed in the write mode period.

First, in the read mode period, since the switch SW ₂ is in the ON (closed) state, the 100 MHz
The extent of the high-frequency current is to be superimposed is supplied to the adder 9 through the switch SW ₂ to the read driving current of the laser diode 1. As described above, by superimposing the high-frequency current on the drive current of the laser diode 1, the laser diode 1 can stably oscillate even with respect to the return light from the disk.

On the other hand, in the write mode period, the switch SW ₂ is to become off (open) state, so that the superposition of high frequency current to the write drive current the laser diode 1 is inhibited by the application of the write gate pulse. With the superposition of the high-frequency current (P _A ) and without the superposition (P _B ), the optical power of the laser diode 1 differs by ΔP as shown in FIG. 4 As shown in FIG. 4A, the bottom power during writing increases by ΔP from the power during reading. Thereby, the raised by [Delta] V ₀ of the optical power detection voltage V ₀ also corresponding to ΔP, which is the output of the monitor amplifier 3. At this time, the APC servo follows so as to correct the rise ΔV ₀ , and catches up in the servo band. In other words, simply turning on / off the high frequency superposition
When the mode shifts from the read mode to the write mode, or vice versa, it takes time until a certain write power and a certain read power can be emitted.

In order to suppress the fluctuation of the optical power due to the on / off of the high frequency superposition, in the present invention, the high frequency superposition is prohibited and set by the correction current setting circuit 14 at the time of transition from the read mode to the write mode. The correction current is extracted from the write drive current. The value of this correction current is represented by A in the current-optical power characteristic shown in FIG.
By setting a current value corresponding to a point between -C,
As shown in FIG. 7B, the optical power does not change, and the operating point changes from A to C.

As described above, high-frequency superimposition is performed during the data read mode period and high-frequency superimposition is prohibited during the write mode period, so that the oscillation state of the laser diode 1 with respect to return light can be stably maintained during the read mode period. In the writing mode, stable writing can be performed without affecting the recording data of the high-frequency signal. In addition, in the write mode period, by inhibiting the high frequency superposition and extracting the correction current from the write drive current, the fluctuation of the optical power of the laser diode 1 can be prevented beforehand.

By the way, usually, the reading power is set to a somewhat large value within a range that does not cause a thermal change to the optical disc due to the relation with noise. Here, assuming that the bottom power of writing is the same as the reading power, a partial high-temperature portion occurs due to the peak power of writing at the same time as the start of writing, and at this time, the valley portion of the writing pulse train, that is, the bottom power is reduced. The irradiated portion receives heat from the high-temperature portion due to the peak power, so that the temperature of the disk surface during normal reading increases. As a result, there is a possibility that the write state may be reached in a part which is not originally planned, and this may cause an adverse effect such as a blunt edge part of the pulse.

Therefore, when the correction current is extracted, in addition to the correction current, the current for the lowering of the bottom power is also extracted from the write driving current, so that the operating point moves to D and the optical power decreases to P _D. As shown in FIG. 4D, the bottom power at the time of writing can be made lower than the power at the time of reading. As a result, the amount of change in the write power increases, so that the edge of the write data can be clarified. On this occasion,
If the current for the lowering of the bottom power is simply extracted, the optical power detection voltage V ₀ is reduced by the reduced amount, and the APC servo follows so as to compensate for the reduced amount. As shown in parentheses), the optical power changes due to the time constant of the APC servo. Therefore, it has to be added to the correction voltage V ₅ only commensurate with the decrement of the optical power of the laser diode 1 due to withdrawal of bottom power cuts worth of current to the APC servo error signal (V ₁ -V ₃₎ Thus, the stability of the APC servo is maintained, and the bottom power can be made lower than the read power over the write mode period as shown in FIG. 4 (d).

As described above, in the optical power control circuit of the semiconductor light emitting device according to the present invention, the high frequency current is superimposed on the drive current of the semiconductor light emitting device only during the read mode period, and the high frequency current is superimposed during the write mode period. Since the superposition is prohibited and the write drive current of the semiconductor light emitting element is corrected, the stability of the oscillation state with respect to the return light of the semiconductor light emitting element is maintained during the read mode period, and the write data is written during the write mode period. And stable writing can be performed without the influence of the high-frequency current.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram of each part for explaining a circuit operation when high frequency superposition is not considered, and FIG. 3 is a current-optical power characteristic of a laser diode. FIG. 4 is a waveform diagram showing a change in optical power when high-frequency superposition is considered. Description of Signs of Main Parts 1 Laser Diode 2 Monitor Diode 4, 13, 15 Low Pass Filter 6 Integrator 7 Read Power Setting Circuit 10 Write Power Setting Circuit 12 High Frequency Oscillator 14 …… Correction current setting circuit 15 …… Correction voltage setting circuit

Claims (1)

(57) [Claims] 1. A control circuit for controlling the optical power of a semiconductor light emitting element for writing and reading information data on a recording medium by irradiating the recording medium with a writing light beam or a reading light beam. Means for generating a read drive current according to the read power set value; first modulating means for modulating a current according to the write power set value by write data; and an output current of the first modulating means for the read drive current Means for supplying the semiconductor light emitting element with a light emitting element driving current obtained by superimposing the light emitting element on the semiconductor light emitting element; second modulating means for modulating the write power set value by the write data; and one of light beams emitted from the semiconductor light emitting element. A light detection unit that receives light from a light source, and a difference between a subtraction result obtained by subtracting an output of the second modulation unit from an output of the light detection unit and the read power set value. Means for increasing / decreasing the read drive current based on: a high-frequency superimposing means for superimposing a high-frequency current on the light-emitting element drive current only in a read mode period; and Optical power of a semiconductor light emitting device, comprising: first correction means for extracting a correction current corresponding to a reduction in bottom power; and second correction means for adding a correction voltage corresponding to the correction current to the subtraction result. Control circuit.