JPH06310784A - Driver for semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a driver for a semiconductor laser in which the optical output can be controlled in a short time with respect to a target output and highly accurate control of optical output can be realized. CONSTITUTION:The driver for a semiconductor laser comprises a feedback loops A and B for regulating the driving current of a laser diode 21 roughly and finely, wherein the driving current of the laser diode is regulated to set a target output of the laser diode 21 upon fluctuation of the I-P characteristics of the laser diode 21 due to variation of ambient temperature while controlling the feedback loops A, B simultaneously through a signal processing circuit 29.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser driving device in which the optical output accuracy of a semiconductor laser is improved.

[0002]

2. Description of the Related Art A semiconductor laser is used, for example, as a light source of an optical head for recording / reproducing data on / from a data recording portion of an optical disk. In semiconductor lasers used as the light source of such optical heads, it is important to always keep the optical output relative to the target output constant for stable recording / reproducing of data. As a laser driving device, Japanese Patent Publication No. 1-302
The one disclosed in Japanese Patent No. 788 is known.

FIG. 4 shows a conventional example disclosed in the publication, in which 1 is a laser diode, 2 is a photo diode for monitoring an optical output, 3 and 14 are comparators, and 4 and 13 are A / D converters, respectively. Current source controlled by 10, 15
Reference numeral 5 is a resistor, 6 is a high-speed current switch, 11 and 16 are up / down counters, and 12 is an oscillator.

A feedback loop composed of a laser diode 1, a light output monitoring photodiode 2, a comparator 3, an up / down counter 11, an A / D converter 10, a current source 4, a high speed current switch 6 and a laser diode 1. A and laser diode 1, photodiode 2 for optical output monitoring, comparator 14, up / down counter 16, A / D converter 15, current source 13,
A feedback loop B composed of a high-speed current switch 6 and a laser diode 1 constitutes two negative feedback loops,
Of these, feedback loop A uses laser diode 1
Is roughly adjusted (roughly adjusted), and the feedback B finely adjusts the optical output of the laser diode 1 so that the optical output of the laser diode 1 is finally controlled to be constant. .

[0005]

However, according to the conventional semiconductor laser driving device, in general, the laser diode 1 has a relationship between the forward current I _F and the optical output P _O as shown in FIG. 5 (a). Since the I-P characteristic represented has a temperature characteristic, the forward current I _F required to obtain the same light output changes greatly depending on the change in ambient temperature.

Therefore, a feedback loop B capable of finely adjusting the fluctuation of the forward current I _F due to the change of ambient temperature.
If it is attempted to be absorbed by, it becomes difficult to increase the resolution by the D / A converter 15.

This will be described with reference to FIGS. 5 (a) and 5 (b). Now, assuming that the IP characteristic of the laser diode 1 is a, first, as shown in the period T1, the light output is first performed by the coarse adjustment by the feedback loop A. P ₀ is controlled to P ₀₁ , and then fine adjustment by the feedback loop B is performed to control to the target output P ₀₂ . From this state, when the IP characteristic changes as shown by b due to the increase of the ambient temperature, the feedback loop B further finely adjusts so as to maintain the target output P _02, as shown in the period T2. On the other hand, due to the decrease in ambient temperature, the IP characteristic becomes c
As shown in the period T3, the feedback loop B makes a fine adjustment so as to maintain the target output P ₀₂ .

As a result, as can be seen from the figure, when the I-P characteristic changes due to the change in ambient temperature, these I-
Since the fine adjustment by the feedback loop B is performed so as to maintain the target output P ₀₂ to change the P characteristic, the adjustment range of the forward current I _F responsible in the feedback loop B will extremely broad. This means that I-
When the P characteristic changes, it takes time to control the target output P ₀₂ . Therefore, in order to quickly control to the target output P _02, it is necessary to increase the adjustment width per fine adjustment, but this makes it possible to increase the resolution by the D / A converter 15. However, there is a problem that it is difficult to control the light output with high precision.

The present invention has been made in view of the above circumstances, and provides a semiconductor laser driving device capable of controlling light output with respect to a target output in a short time and realizing highly accurate control of light output. The purpose is to provide.

[0010]

According to the present invention, there is provided a laser diode for generating an optical output, a first feedback loop for coarsely adjusting a drive current of the laser diode, and a fine adjustment for a drive current of the laser diode. The second feedback loop and the first feedback loop and the second feedback loop are simultaneously adjusted by adjusting the driving current of the laser diode for setting the laser diode to a target output when the characteristics of the laser diode change. It is composed of control means for performing while controlling.

[0011]

As a result, according to the present invention, the operation of setting the target output when the characteristic of the laser diode changes is used not only the fine adjustment by the second feedback loop but also the coarse adjustment by the first feedback loop. Therefore, the light output of the laser diode to the target output can be controlled in a short time, and the adjustment range of the second feedback loop can be narrowed.
The adjustment range for each fine adjustment can be reduced, and the resolution can be increased. Therefore, highly accurate control of the light output can be realized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of the same embodiment. In the figure, 21 is a laser diode, 22 is a photodiode for monitoring the optical output of the laser diode 21,
The laser diode 21 has two systems of negative feedback loops, a feedback loop A for performing coarse adjustment (rough adjustment) of the optical output and a feedback loop B for performing fine adjustment (fine adjustment) of the optical output via the photodiode 22. Are connected.

The feedback loop A is a coarse movement D / A.
Converter 23, coarse-motion VI converter 24, IV converter 2
5 and an A / D converter 26, and the feedback loop B includes a fine movement D / A converter 27 and a fine movement VI.
The converter 28, the IV converter 25 and the A / D converter 26 described above are included. In this case, the coarse-motion VI converter 2
Reference numeral 4 denotes resistors R241 to R243 and an operational amplifier OP241.
And a transistor Q241, and a VI converter 28
Is composed of resistors R281 to R283, an operational amplifier OP281 and a transistor Q281, and the IV converter 25 is
It is composed of a resistor R251 and an operational amplifier OP251.

The feedback loop A for roughly adjusting the light output and the feedback loop B for finely adjusting the light output are controlled by the signal processing circuit 29 as described below.

FIG. 2 shows a processing flow of control by the signal processing circuit 29. In this case, k is D / for coarse movement
The indicated value of the A converter 23, l is the indicated value of the fine movement D / A converter 27, m is the output value of the A / D converter 26, and m ₁ is the optical output of the laser diode 21 P ₀₁ (see FIG. 3). ) A / D
The output value of the converter 26, m ₂ is the A / D converter 26 when the optical output of the laser diode 21 is the target output P ₀₂ (see FIG. 3).
Of the target output P ₀₂ , m _u is the upper limit of the allowable range of the variation of the target output P ₀₂ , m _D is the lower limit of the allowable range of the variation of the target output P ₀₂ , and n is the ratio of the resolution of the feedback loop A and the resolution of the feedback loop B. (For example, 3).

First, the operation at the time of starting will be described. In this case, assuming that the IP characteristic of the laser diode 1 is a as shown in FIG. 3A, the operation shown in the period T1 of FIG. 3B is executed. First, the signal processing circuit 29 determines the D / A
The indicated value k of the converter 23 and the indicated value l of the D / A converter 27 are set to zero (step 201). The output value m of the A / D converter 26 and the optical output of the laser diode 21 are P _01.
It is judged whether the relation of the output value m ₁ of the A / D converter 26 at the time (see FIG. 3) is m> m ₁ (step 202). If NO here, coarse adjustment by the feedback loop A is performed. In this case, the indicated value k of the coarse motion D / A converter 23 is increased by +
While repeating ₁ , the operation of determining the relationship of m> m ₁ is repeated (step 203). After that, when the relationship of m> m ₁ is established, the light output of the laser diode 21 is set to P ₀₁ . Then, the command value k of the coarse-motion D / A converter 6 at this time is held.

Next, the output value m of the A / D converter 26 and the optical output of the laser diode 21 are the target output P ₀₂ (see FIG. 3).
It is determined whether the relationship of the output value m ₂ of the A / D converter 26 at this time is m> m ₂ (step 204). If NO here, fine adjustment is performed by the feedback loop B. In this case, the operation of determining the relationship of m> m ₂ is repeated while incrementing the indicated value l of the D / A converter 27 for fine movement by 1 (step 2
05). After that, when the relationship of m> m ₂ is established, the light output of the laser diode 21 is set to the target output P ₀₂ . Then, the instruction value l of the D / A converter 27 for fine movement at this time is stored as l ₀ (step 206).

Next, the APC (auto power control) operation when the IP characteristic of the laser diode 21 changes with the change of the ambient temperature will be described.
In this case, the signal processing circuit 29 uses the laser diode 21.
If the I-P characteristic of No. 2 changes as shown in b and c of FIG. 3A, the output of the A / D converter 26 is set to the lower limit m _D and the upper limit m _U of the allowable range of the variation of the target output P _02. Control to subside during.

First, assuming that the IP characteristic changes from "a" to "b" in FIG. 3A due to an increase in ambient temperature, the optical output P _O of the laser diode 21 due to the forward current I _F02 at this time is: The target output P ₀₂ is greatly reduced to P ₀₂ ′.
In this case, the output value m of the A / D converter 26 and the target output P ₀₂
It is judged whether or not the relation of the lower limit m _D of the allowable range of the variation is m ≧ m _D (step 207). Where P of optical output
_If the drop to ₀₂ 'is large, the output of the A / D converter 26 is smaller than the lower limit m _{D of the} target value, and if NO, then FIG.
The operation indicated by the period T2 is executed. In this case, first, the instruction value l of the fine movement D / A converter 27 is incremented by 1 (step 2
08), the difference (l-l ₀ ) between this indicated value l and l ₀ stored in step 206 described above is n (resolution of feedback loop A / resolution of feedback loop B) (=
It is determined whether it is 3) (step 209).

Here, if NO, the process returns to step 207, and the instruction value l of the fine movement D / A converter 27 of step 208 is incremented by 1 while (l-l _{0 of} step 209).
= N), the operation of determining the relationship is repeated. After that, (l
When the relationship of −l ₀ = n) is established, n (= 3) is subtracted from the instruction value l of the D / A converter 27 for fine movement, and the value is l _0.
At the same time, 1 is added to the indicated value k of the coarse motion D / A converter 23 (step 210). And step 20
7, the operation of determining the relationship of (l-l ₀ = n) is repeated, and the instruction value l of the D / A converter for fine movement 27 becomes (l-l ₀ = n). The indicated value l
Is subtracted from n (= 3) and 1 is added to the indicated value k, and the output value m of the A / D converter 26 is set to the target output P _02.
Will close to the lower limit m _D, then the relationship of m ≧ m _D is satisfied, the light output of the laser diode 21 is controlled to an acceptable range of variation of the target output P _02.

On the other hand, assuming that the IP characteristic changes from a to c in FIG. 3A due to the decrease in ambient temperature, the optical output P _O of the laser diode 21 due to the forward current I _F02 at this time is: The target output P ₀₂ greatly increases to P _{02 ″} . In this case, the relationship between the output value m of the A / D converter 26 and the upper limit m _U of the allowable range of the variation of the target output P ₀₂ is m ≦ m _U.
Is determined (step 211). Here, if the increase of the optical output to P _{02 ″} is large and the output of the A / D converter 26 is larger than the lower limit m _{U of the} target value and NO, then FIG.
The operation indicated by the period T3 is executed. In this case, first, the instruction value l of the D / A converter 27 for fine movement is decremented by 1 (step 2
12) Then, it is judged whether or not the difference (l-l ₀ ) between this indicated value l and l ₀ stored in step 206 described above is n (= resolution of feedback loop A / resolution of feedback loop B) (step 213). ).

Here, if NO, the process returns to step 211, and while the instruction value l of the D / A converter 27 for fine movement of step 212 is decreased by -1, (l ₀ -l of step 213).
= N), the operation of determining the relationship is repeated. After that, (l
_0- l = n) is established, n is added to the instruction value l of the fine movement D / A converter 27 to set the value to l ₀ and the instruction value of the coarse movement D / A converter 23 is set. Subtract 1 from k (step 214). Then, returning to step 211, the operation of determining the relationship (l ₀ −l = n) is repeated, and the instruction value l of the D / A converter 27 for fine movement is (l
Each time _0- l = n), n (=
3) is added and 1 is subtracted from the indicated value k so that the output value m of the A / D converter 26 becomes the upper limit m of the target output P ₀₂ .
Move closer to _U , then in step 211 m ≦ m _U
When the relationship of is satisfied, the optical output of the laser diode 21 is controlled within the allowable range of the variation of the target output P ₀₂ .

Then, the process proceeds to the timer operation of step 215, and after confirming that a predetermined time has passed, step 2
Returning to 07, the above operation is repeated. By executing the above operation by the signal processing circuit 29,
APC is applied so that the optical output of the laser diode 21 is settled between the lower limit and the upper limit of the target output P _{02. In} this case, the APC is not limited to the fine adjustment by the feedback loop B, but also the feedback loop A. Since the coarse adjustment by the feedback loop A is also performed based on the ratio n of the resolution and the resolution of the feedback loop B, the light output to the target output P ₀₂ can be controlled in a short time. Further, as is clear from FIG. 3 (b),
The fine and coarse adjustment by a feedback loop A by the feedback loop B is performed simultaneously, it is possible to narrow the range of adjustment of the forward current I _F responsible feedback loop B, per one time of the fine adjustment The adjustment width can also be reduced, whereby the resolution by the D / A converter 27 can be increased, and highly accurate control of the light output can be realized.

The present invention is not limited to the above-mentioned embodiments, and can be carried out by appropriately modifying it without departing from the scope of the invention.
For example, in the above-described embodiment, steps 210 to 210 in FIG.
Although the APC operation is performed after the startup operation of step 206, the startup operation is omitted and the A
You may make it start from PC operation. Further, in the above-described embodiments, the semiconductor laser used as the light source of the optical head of the optical disk has been described, but the present invention can also be applied to a semiconductor laser used as a light source of a laser printer or optical communication.

[0025]

According to the present invention, the setting operation to the target output when the characteristic of the laser diode is changed uses not only the fine adjustment by the second feedback loop but also the coarse adjustment by the first feedback loop. Therefore, the light output of the laser diode to the target output can be controlled in a short time.

Further, since the adjustment range of the second feedback loop can be narrowed, the adjustment range for each fine adjustment can be reduced, so that the resolution can be increased. It is possible to realize highly accurate control of the light output.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of the embodiment.

FIG. 3 is a diagram for explaining the operation of the embodiment.

FIG. 4 is a diagram showing a schematic configuration of an example of a conventional semiconductor laser driving device.

FIG. 5 is a view for explaining the operation of the semiconductor laser driving device.

[Explanation of symbols]

21 ... Laser diode, 22 ... Photodiode, 2
3 ... D / A converter for coarse movement, 24 ... VI converter for coarse movement,
25 ... IV converter, 26 ... A / D converter, 27 ... fine movement D / A converter, 28 ... fine movement VI converter, 29 ... signal processing circuit.

Claims (2)

[Claims] 1. A laser diode that generates an optical output, a first feedback loop that roughly adjusts the drive current of the laser diode, a second feedback loop that finely adjusts the drive current of the laser diode, and the laser. Control means for adjusting the drive current of the laser diode for setting the target output of the laser diode when the characteristics of the diode change while simultaneously controlling the first feedback loop and the second feedback loop. A semiconductor laser driving device comprising: 2. The initial target output is obtained by the control means performing a coarse adjustment of the drive current of the laser diode by the first feedback loop and then a fine adjustment of the drive current of the laser diode by the second feedback loop. 2. The semiconductor laser driving device according to claim 1, which has a function of setting