JPH0636331A - Semiconductor laser control circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To enable high-precision control over a wide band in a semiconductor laser control circuit in which the emission power changes significantly during reproduction and erasure. In a semiconductor laser control circuit for controlling light emission power by a detection signal from a light receiving element for light emission power detection, a reverse bias voltage applied to the light receiving element is changed according to the light emission power of a semiconductor laser. [Effect] When the amount of light incident on the light receiving element is large, the reverse bias applied to the light receiving element is increased to avoid saturation of the light receiving element. When the amount of incident light is small, the reverse bias is reduced to reduce dark current. Therefore, a semiconductor laser control circuit having a wide band and high accuracy can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source control circuit in an optical information recording apparatus provided with a semiconductor laser such as an optical disk device, a laser printer, an optical card drive device, etc., and particularly, during reproduction (reading) and erasing. Time (when erasing)
As described above, the present invention relates to a semiconductor laser control circuit that enables highly accurate control over a wide band in a semiconductor laser control circuit in which the emission power changes significantly.

[0002]

2. Description of the Related Art Conventionally, in an optical information recording apparatus equipped with a semiconductor laser, a drive circuit using a high frequency superimposing circuit has been known in order to suppress reproduction power fluctuations due to the influence of return light from an optical disk during reproduction. Has been. However, the high-frequency superimposing circuit has a problem in that it has a problem in mounting because it is large in volume and also causes an increase in cost.

A semiconductor laser control circuit which does not use such a high frequency superposition circuit requires a control circuit for controlling the emission power of the semiconductor laser. Since such a semiconductor laser control circuit requires several tens of MHz as a control band, the band of each circuit component forming the circuit is also required and a light receiving element (photodiode) for detecting the emission power. Bandwidth is also an issue.

It is known that in order to increase the band of the light receiving element for detecting the emission power, it is necessary to increase the reverse bias voltage applied to this light receiving element. On the other hand,
When the reverse bias voltage is applied, there arises a problem that the dark current of the light receiving element for detecting the emission power increases.

A measurement example of the reverse bias voltage applied to the light emitting power detecting light receiving element and the frequency characteristic of the light emitting power detecting light receiving element will be described below. FIG. 5 is a diagram showing a measurement example of the reverse bias voltage applied to the light receiving element for light emission power detection and its frequency characteristic. In the figure, the horizontal axis represents the reverse bias voltage and the vertical axis represents the frequency.

For example, if the target band of the light receiving element for light emission power detection is 40 MHz, a reverse bias voltage of about 10 V is sufficient when the amount of light incident on the light receiving element for light emission power detection is 1 mW at the time of reading. At times, the amount of light incident on the light receiving element for detecting the emission power becomes 7 mW, so
It is necessary to apply a reverse bias voltage of 0V. As described above, when the target band of the light emitting power detecting light receiving element is increased, it is necessary to change the reverse bias voltage according to the change of the amount of light incident on the light emitting power detecting light receiving element.

However, as mentioned above, dark current increases when the reverse bias voltage is increased. FIG. 6 is a diagram showing a characteristic example of the relationship between the reverse bias voltage of the light receiving element and the dark current. In the figure, the horizontal axis represents the reverse bias voltage (V) and the vertical axis represents the dark current (A).

As shown in FIG. 6, when the reverse bias voltage changes, the dark current also changes. Therefore, the following problems occur. Generally, the semiconductor laser is controlled by the detection current of the light receiving element for detecting the emission power.

If a dark current is included in the detected current, this becomes an offset of the control system, resulting in a large control error. Now, if the reverse bias voltage of the light receiving element for light emission power detection is set to a constant value of 20 V, as shown in FIG.
The dark current Id (A) also becomes constant.

However, the detection output caused by the amount of light incident on the light receiving element for detecting the emission power is 7 mW at the time of erasing and 1 mW at the time of reading. Therefore, the ratio of the dark current to the detection current of the light-emitting power detecting light receiving element during reading increases, and the power control error during reading increases.

Further, when the reverse bias voltage of the light emitting power detecting light receiving element is kept at a constant value of 10 V, there is a 40 MHz band at the time of reading, but at the time of erasing, the light emitting power detecting light receiving element is saturated, so the band Will not exist (does not exist). As described above, in the conventional semiconductor laser control circuit, due to the restriction on the characteristics of the light-emitting power detection light-receiving element, it is not possible to set the common reverse bias voltage at the time of read and erase when the detection currents are different, Further, due to the dark current, an error occurs in the light emission power control system between the reading and the erasing.

[0012]

SUMMARY OF THE INVENTION The present invention solves such inconvenience in the conventional semiconductor laser control circuit, and the reverse bias voltage of the reverse bias voltage is generated during the operation such that the emission power level is different, such as during erase and read. An object of the present invention is to provide a semiconductor laser control circuit in which a control error due to a dark current caused by a change does not occur and a necessary band is sufficiently secured.

[0013]

The present invention is, firstly, a semiconductor laser control circuit in an optical information recording apparatus, which receives a part of light emitted from a semiconductor laser which is a light source, and A light receiving element for detecting the light emitting power, a control means for controlling the light emitting power of the semiconductor laser by a signal detected by the light receiving element, and a driving means for driving the semiconductor laser according to a control signal from the control means. In the semiconductor laser control circuit including, the reverse bias voltage applied to the light receiving element is changed according to the emission power of the semiconductor laser.

Secondly, a semiconductor laser control circuit in the optical information recording apparatus, which receives a part of the light emitted from the semiconductor laser as a light source and detects the light emission power of the semiconductor laser, A semiconductor laser control circuit comprising: a control unit that controls the emission power of a semiconductor laser according to a signal detected by a light receiving element; and a drive unit that drives the semiconductor laser according to a control signal from the control unit. This is a configuration including means for changing the amount of light incident on the light receiving element according to the light emission power of the semiconductor laser.

Thirdly, the second semiconductor laser control circuit includes a filter, a recording timing generation circuit, and an applied voltage control circuit, and controls the amount of light incident on the light receiving element according to the light emission power of the semiconductor laser. It is configured to change.

[0016]

According to the present invention, when the amount of light incident on the light receiving element for light emission power detection is large, the reverse bias applied to the light receiving element is increased to avoid saturation of the light receiving element, and when the amount of incident light is small, the light receiving element is detected. By reducing the reverse bias applied to the semiconductor device to reduce the dark current, a semiconductor laser control circuit having a wide band and good control accuracy is realized even during erasing and reading, which have different emission power levels. Invention). Also, when the reverse bias voltage applied to the light-receiving element for light emission power detection is maintained at a constant value and the amount of light incident on the light-receiving element for light emission power detection is large, the effect of dark current is reduced by reducing the amount of incident light by a filter. By removing it, a wide band, high control accuracy, and high speed semiconductor laser control circuit is realized (the inventions of claims 2 and 3).

[0017]

First Embodiment A semiconductor laser control circuit of the present invention will be described in detail with reference to the drawings. This embodiment corresponds to the invention of claim 1. In the following description, in order to facilitate understanding, the description will be centered on the read and erase times when the emission power levels are remarkably different, but it goes without saying that the write operation can be similarly performed.

FIG. 1 is a functional block diagram showing an embodiment of the main configuration of the semiconductor laser control circuit of the present invention. In the figure, 1 is a semiconductor laser, 2 is a coupling lens, 3 is a beam splitter, 4 is an objective lens, 5 is a light receiving element for reproducing signal monitor, 6 is a light receiving element for detecting emission power, 7 is an optical disk, and 8 is a voltage booster. 9 is a changeover switch, A and B are its terminals, 10 is a changeover switch control unit, 11 is a recording timing generation circuit, 12 is a first I / V conversion amplifier, 13 is a read power control circuit, and 14 is a peak. A power control circuit, 15 is a semiconductor laser drive circuit, 16 is a second I / V conversion amplifier, L is laser light, and V1 and V2 are reverse bias voltages.

Laser light L emitted from the semiconductor laser 1
Passes through the coupling lens 2, becomes parallel light, and is incident on the beam splitter 3. Incident laser light L
Part of is condensed on the optical disk 7 via the objective lens 4.

The condensed laser beam L is reflected by the optical disk 7 and again detected by the reproduction signal monitor light receiving element 5 through the objective lens 4 and the beam splitter 3. The detected intensity of light is converted into an electric signal, and the second I
The signal is supplied from the / V conversion amplifier 16 to a signal detection system (not shown).

At this time, a part of the laser beam L emitted from the semiconductor laser 1 is incident on the light emitting power detecting light receiving element 6 through the beam splitter 3, and the semiconductor laser 1 is detected by the detection signal of the light receiving element 6. Is controlled. Particularly, in the optical disk device, the recording, reproducing, or erasing power must be controlled at different levels.

The structure and operation of the conventional optical pickup device are as described above. Here, the semiconductor laser 1 is detected by the signal detected by the light receiving element 6 for detecting the emission power.
The control means for controlling the light emission power of is composed of a first I / V conversion amplifier 12, a read power control circuit 13, and a peak power control circuit 14.

The driving means for driving the semiconductor laser 1 in response to the control signal from the controlling means is the semiconductor laser driving circuit 15. Not limited to the optical disk device,
In electronic equipment using a semiconductor laser, it is also essential to control the emission power of the semiconductor laser even in a laser printer or an optical card device.

Next, the operation unique to the semiconductor laser control circuit of the present invention will be described. Here, the amount of light incident on the light receiving element 6 for light emission power detection during reading is set to PR,
The amount of light incident on the light receiving element 6 during erasing is PE. When the amount of light incident on the light receiving element 6 is PR, the connection of the changeover switch 9 is changed over to the terminal A side by the control of the changeover switch control section 10 to detect the light emission power.
The reverse bias voltage applied to is set to V1.

On the other hand, when the amount of light incident on the light receiving element 6 is PE, the changeover switch control section 10 controls the connection of the changeover switch 9 to the terminal B side. In this case, the voltage applied to the light receiving element 6 for light emission power detection is
The voltage V1 obtained by boosting the previous voltage V1 by the voltage booster 8.
2 (V2> V1).

Therefore, a highly accurate control circuit can be realized without narrowing the control band of the semiconductor laser. The control operation of the changeover switch control unit 10 in this case is performed by the operation timing signal generated by the recording timing generation circuit 11.

FIG. 2 is a time chart for explaining the operation of the semiconductor laser control circuit of the present invention shown in FIG. In the figure, PE indicates the incident light amount level at the time of erasing, and PR indicates the incident light amount level at the time of reading.

As shown in FIG. 2, in this embodiment,
By switching the reverse bias voltage applied to the light emitting power detection light receiving element 6 at the timing controlled by the output from the recording timing generation circuit 11, that is, at the time of reading and at the time of erasing, when the amount of incident light is large, The reverse bias applied to the element 6 is increased to avoid saturation of the light receiving element 6, and when the amount of incident light is small, the reverse bias applied to the light receiving element 6 is lowered to reduce the dark current. Therefore, the ratio of the dark current to the detected current is kept substantially constant during the reading and the erasing, and the control error is reduced, so that highly accurate control is possible.

[0029]

Second Embodiment A second embodiment of the semiconductor laser control circuit of the present invention will be described in detail. This embodiment corresponds to the invention of claim 2. In the second embodiment, a filter is used, the transmissivity is changed by moving the position of the filter, the reverse bias voltage is kept constant, and the influence of dark current is removed.

FIG. 3 is a functional block diagram showing another embodiment of the essential structure of the semiconductor laser control circuit of the present invention. Reference numerals in the drawing are the same as those in FIG. 1, reference numeral 21 is a filter, and 22 is a filter moving device.

As shown in FIG. 3, a filter 21 is inserted between the beam splitter 3 and the light emitting power detecting light receiving element 6 to reduce the amount of light incident on the light emitting power detecting light receiving element 6. The filter 21 can be moved between a solid line position and a broken line position by the filter moving device 22.

In this case, the filter 21 has a transmittance of (PR / PE) × 100%. First, in the case of PR in which the amount of light incident on the light receiving element 6 for detecting the emission power is small, the filter 21 is placed at the position of the broken line.

In the case of PE with a large amount of incident light, the filter moving device 22 moves the PE to the position indicated by the solid line. By such an operation, the amount of light incident on the light emitting power detection light receiving element 6 is always controlled to a constant state as in the case of PR.

Therefore, the reverse bias voltage is set to a constant value (V
It can be 1). In this way, by keeping the amount of light incident on the light receiving element 6 for detecting the emission power constant, it is possible to widen the dynamic range of the control system. That is, since the band of the light-receiving element 6 for detecting the emission power is realized, a high-speed semiconductor laser control circuit can be obtained. In addition, also in the second embodiment, the filter 2
The timing of movement of 1 is the same as in FIG.

[0035]

Third Embodiment A third embodiment of the semiconductor laser control circuit of the present invention will be described in detail. This embodiment corresponds to the invention of claim 3. In the second embodiment, the position of the filter is physically moved to change the amount of light incident on the light receiving element so that the amount of light incident on the light receiving element becomes constant. In the third embodiment,
By changing the voltage applied to the filter to change the transmittance, the amount of light incident on the light receiving element is made constant.

FIG. 4 is a functional block diagram showing a third embodiment of the essential structure of the semiconductor laser control circuit of the present invention. Reference numerals in the figure are the same as those in FIG. 1, reference numeral 31 is a filter, and reference numeral 32 is an applied voltage control circuit.

As shown in FIG. 4, a filter 31 is inserted between the beam splitter 3 and the light emitting power detecting light receiving element 6 to reduce the amount of light incident on the light emitting power detecting light receiving element 6. The filter 31 is composed of liquid crystal or the like whose transmittance changes when a certain voltage (for example, V3) is applied. The voltage V3 is controlled by the applied voltage control circuit 32.

For example, in the case of PR in which the amount of light incident on the light emitting power detection light receiving element 6 is small, the transmittance of the filter 31 is set to 100% (the applied voltage control circuit 32 does not operate).
In the case of PE with a large amount of incident light, the applied voltage control circuit 32
By applying a certain voltage V3 by the
/ PE) × 100%. By such an operation, as in the case of the second embodiment, the amount of light incident on the light-emission power detecting light-receiving element 6 is always controlled to the same constant state as in the case of PR, so that the reverse bias voltage is changed. It can be set to a constant value (V1).

Since the amount of light incident on the light receiving element 6 for detecting the emission power is constant, it is possible to widen the dynamic range of the control system. In addition, since the operation of changing the transmittance of the liquid crystal filter can be controlled at high speed, it is suitable for higher speed operation as compared with the case of the second embodiment.

By the above-described operation, the band of the light-receiving element 6 for detecting the emission power can be widened, so that a high-speed semiconductor laser control circuit can be obtained. In the third embodiment, the applied voltage control circuit 32 applied to the filter 31 is also used.
The timing of is the same as that of FIG.

[0041]

According to the first aspect of the invention, when the amount of light incident on the light receiving element for detecting the emission power is large, the reverse bias applied to the light receiving element is increased to avoid saturation of the light receiving element, and When the amount of incident light is small, the dark current is reduced by lowering the reverse bias applied to the light receiving element. Therefore, it is possible to realize an accurate semiconductor laser control circuit in a wide band.

According to the second aspect of the present invention, the transmittance of the filter is changed to control the incident light quantity so that the incident light quantity is always constant regardless of whether the incident light quantity is large or small. There is. Thus, if the amount of light incident on the light receiving element for detecting the emission power is always constant, there is no need to change the reverse bias voltage.
The control system can have a wide dynamic range, and the same effect as that of the first aspect of the invention can be obtained.

According to the third aspect of the present invention, the amount of incident light to the light receiving element for detecting the emission power is changed by the liquid crystal filter, so that the amount of incident light is controlled to always be kept at a constant value. Therefore, the same effects as those of the first and second aspects of the present invention can be obtained, and the operation of changing the transmittance of the liquid crystal filter can be controlled at high speed. Can respond.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing an embodiment of a main part configuration of a semiconductor laser control circuit of the present invention.

FIG. 2 is a time chart explaining the operation of the semiconductor laser control circuit of the present invention shown in FIG.

FIG. 3 is a functional block diagram showing another embodiment of the main part configuration of the semiconductor laser control circuit of the present invention.

FIG. 4 is a functional block diagram showing a third embodiment of the main configuration of the semiconductor laser control circuit of the present invention.

FIG. 5 is a diagram showing a measurement example of a reverse bias voltage applied to a light receiving element for light emission power detection and its frequency characteristic.

FIG. 6 is a diagram showing a characteristic example of a relationship between a reverse bias voltage and a dark current of a light receiving element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 semiconductor laser 2 coupling lens 3 beam splitter 4 objective lens 5 light-receiving element for reproducing signal monitor 6 light-receiving element for detecting emission power 7 optical disk 8 voltage booster 9 changeover switch 10 changeover switch control section 11 recording timing generation circuit 12 first I / V conversion amplifier 13 Read power control circuit 14 Peak power control circuit 15 Semiconductor laser drive circuit 16 Second I / V conversion amplifier 21 Filter 22 Filter moving device 31 Filter 32 Applied voltage control circuit

Claims (3)

[Claims] 1. A semiconductor laser control circuit in an optical information recording apparatus, which receives a part of light emitted from a semiconductor laser as a light source and detects a light emission power of the semiconductor laser, and the light receiving element. In the semiconductor laser control circuit, the semiconductor laser control circuit comprises: a control unit that controls the emission power of the semiconductor laser according to the signal detected by the control unit; and a drive unit that drives the semiconductor laser according to the control signal from the control unit. A semiconductor laser control circuit, wherein the reverse bias voltage applied to the light receiving element is changed according to the light emission power of the. 2. A light receiving element, which is a semiconductor laser control circuit in an optical information recording apparatus, receives a part of light emitted from a semiconductor laser which is a light source, and detects the light emission power of the semiconductor laser, and the light receiving element. In the semiconductor laser control circuit, the semiconductor laser control circuit comprises: a control unit that controls the emission power of the semiconductor laser according to the signal detected by the control unit; and a drive unit that drives the semiconductor laser according to the control signal from the control unit. 2. A semiconductor laser control circuit comprising means for changing the amount of light incident on the light receiving element in accordance with the light emission power of. 3. The semiconductor laser control circuit according to claim 2, further comprising a filter, a recording timing generation circuit, and an applied voltage control circuit, wherein the amount of light incident on the light receiving element is changed according to the light emission power of the semiconductor laser. A semiconductor laser control circuit characterized by the above.