JP2009021287A - Light output controller for laser diode - Google Patents

Abstract

Provided is a laser diode light output control device capable of preventing an increase in a current value for driving a laser diode and extending a life against a decrease in light output due to secular change.
An optical output control device for a laser diode is an optical output control device for a laser diode that performs automatic light quantity control by feeding back an optical output of the laser diode, the laser diode, and a driving means for driving the laser diode; A light output detection means for detecting the light output of the laser diode, a drive current detection means for detecting the drive current, a deterioration determination means for determining the deterioration of the laser diode from the light output and the drive current, and based on the determination result The optical output adjustment value generating means for generating the optical output adjustment value of the laser diode, and a signal for controlling the optical output magnitude of the laser diode is output to the driving means by the optical output target value, the optical output adjustment value, and the optical output. Light output control means.
[Selection] Figure 1

Description

  The present invention relates to a light output control device for a laser diode used in a display.

  The laser diode has a characteristic that the drive current for obtaining the same optical output increases with aging. Therefore, the magnitude of the current flowing to the laser is detected, and if the magnitude of the current is below a predetermined reference value, the light output is controlled to be constant, and the drive is performed when the current value reaches the reference value. There has been proposed a method of selecting a control for keeping the current constant (refer to Patent Document 1 below).

FIG. 7 is a block diagram showing a configuration of a conventional laser diode light output control device. The configuration of a conventional light output control device will be briefly described with reference to FIG.
In the conventional laser diode light output control device, the laser diode 3 is driven by the driving means 2. The light output of the laser diode 3 is detected by the light output detection means 5 and input to the light control means 12, and a current command value to the drive means 2 is output to the switching means 9 according to the difference from the light output target value. On the other hand, the current value of the drive means 2 is detected by the current detection means 4 and input to the current control means 8, and the current command value to the drive means 2 is output to the switching means 9 according to the difference from the current target value.

A conventional method for controlling the light output of a laser diode will be described with reference to FIG. FIG. 4A is a graph showing changes in the optical output and current of the laser diode with respect to time in the conventional optical output control method. In this conventional light output control method, as described below, the current itself is controlled in accordance with the magnitude relationship between the current and the reference value.
(A) If the value of the current detection means 4 is smaller than the reference value, the output of the light control means 12 is selected by the switching means 9 and the light output is controlled to match the light output target value. This is generally called APC control.
(B) On the other hand, if the value of the current detection means 4 is larger than the reference value, the output of the current control means 8 is selected by the switching means 9 so that the drive current value matches the current target value. This is generally called ACC control.
As described above, during APC control, the current value gradually increases with the lapse of operation time in order to keep the light output constant. Thereafter, when the current value reaches a certain reference value, the current value is made constant by switching to ACC control.

Japanese Patent Laid-Open No. 10-178229

However, the conventional method can keep the current value constant, but there is a problem that the light output of the laser diode decreases due to deterioration due to secular change, and the light output fluctuates even if the current value is constant. Such a change in light output due to secular change is not preferable because it changes in luminance when used as a light source for a display.
In addition, there is a case where the lifetime of the laser diode is shortened when an attempt is made to increase the luminance by increasing the current value in response to a decrease in light output due to secular change.

  An object of the present invention is to provide a laser diode light output control device capable of preventing an increase in the current value for driving a laser diode and extending its life against a decrease in light output due to secular change. .

In order to solve the above problems, a light output control device according to the present invention is a laser diode light output control device that performs automatic light amount control by feeding back the light output of a laser diode,
A laser diode and driving means for driving the laser diode;
A light output detecting means for detecting a light output of the laser diode;
Drive current detection means for detecting the drive current of the laser diode;
Degradation determination means for determining deterioration of the laser diode from the output of the light output detection means and the output of the drive current detection means;
A light output adjustment value generating means for generating a light output adjustment value of the laser diode based on the determination result of the deterioration determination means;
A light output control means for outputting a signal for controlling the magnitude of the light output of the laser diode to the drive means according to the light output target value, the output of the light output adjustment value generating means, and the output of the light output detection means; Prepared,
Deterioration of the laser diode is determined based on the light output of the laser diode and a drive current, and the light output of the laser diode is changed according to the determination result.

Further, the deterioration determining means includes
The deterioration of the laser diode may be determined by comparing the ratio between the optical output of the laser diode and the drive current with a reference value.

Further, the light output adjustment value generating means
(A) When the ratio between the light output of the laser diode and the drive current is larger than a reference value, a light output adjustment value of 0 is output;
(B) When the ratio between the optical output of the laser diode and the drive current is smaller than a reference value, an optical output adjustment value in an amount proportional to the difference between the ratio of the optical output and the drive current and the reference value is output. To
It is good as well.

Still further, the deterioration determining means includes
The deterioration of the laser diode may be determined using a ratio between the optical output and the drive current in the initial state of the laser diode as a reference value.

Further, the deterioration determining means includes
An increase rate of the optical output with respect to the drive current is calculated based on the optical output of the laser diode and the drive current, and the deterioration rate of the laser diode is determined by comparing the increase rate of the optical output with a reference value. Good.

Further, the light output adjustment value generating means
(A) when the rate of increase of the optical output of the laser diode with respect to the drive current is larger than a reference value, an optical output adjustment value of 0 is output;
(B) When the increase rate of the optical output of the laser diode with respect to the drive current is smaller than a reference value, an optical output adjustment value in an amount proportional to the difference between the increase rate and the reference value is output.
It is good as well.

Still further, the deterioration determining means includes
The deterioration of the laser diode may be determined using an increase rate of the optical output with respect to the drive current in the initial state of the laser diode as a reference value.

The light output adjustment value generating means is
The light output adjustment value may be updated in synchronization with a predetermined timing signal.

  Further, the timing signal may be generated at least at any time point when the circuit of the light output control device is turned on, when the detection of light output of the laser diode is started, or immediately before the circuit is turned off. .

  According to the laser diode light output control device of the present invention, the secular change of the laser diode is determined from the light output detection value and the current detection value, and when this change exceeds a certain value, the target value of the light output By gradually lowering the value, it is possible to prevent an increase in current value due to aging. Further, the lifetime of the laser diode can be extended by reducing the current value by lowering the light output target value. Further, it is possible to make it difficult for the user to notice a change in luminance in display applications by a method of decreasing the light output target value little by little only at the start-up according to the secular change.

  Hereinafter, an optical output control device according to the present invention will be described with reference to the accompanying drawings. In the drawings, substantially the same members are denoted by the same reference numerals.

(Embodiment 1)
FIG. 1 is a block diagram showing a configuration of a laser diode light output control apparatus according to Embodiment 1 of the present invention. This laser diode light output control device includes a light output control means 1, a drive means 2, a laser diode 3, a current detection means 4, a light output detection means 5, a deterioration determination means 6, a light output adjustment value. And generating means 7. The light output control unit 1 acquires a light output target value. The drive unit 2 drives the laser diode 3 by causing a current corresponding to the output of the light output control unit 1 to flow through the laser diode 3. The current detection unit 4 detects the value of the current flowing through the laser diode 3. The light output detection means 5 detects the light output value of the laser diode 3. The deterioration determination unit 6 determines the secular change (deterioration) of the laser diode 3 from the current value detected by the current detection unit 4 and the light output value detected by the light detection unit 5. The light output adjustment value generation means 7 outputs an adjustment value for changing the light output target value according to the output of the deterioration determination means 6. This adjustment value is updated in synchronization with a timing signal generated in accordance with the operation of a display that uses this apparatus as a light source.

FIG. 2 is a block diagram showing a more detailed configuration of the light output control device of FIG. The operation of each component of the laser diode light output control device will be described with reference to FIG.
<Light output control means>
The light output control unit 1 includes an addition circuit 11 and a light control unit 12.
The adder circuit 11 of the light output control means 1 adds the hold signal from the light output adjustment value generation means 7 to the light output target value and uses this as a new light output target value together with the light output detection value of the light output detection means 5. Input to the light control means 12 to perform APC control. Since the hold signal from the light output adjustment value generating means 7 is 0 when it is determined that the laser diode 3 is not deteriorated, the light output target value does not change by addition. On the other hand, when it is determined that the laser diode 3 is deteriorated, the hold signal is negative, so that the optical output target value is reduced by addition.

<Degradation judging means>
The deterioration determining means 6 includes a threshold value subtracting circuit 61, a dividing circuit 62, a subtracting circuit 63, and a determining circuit 64.
The operation of the deterioration determining means 6 will be described. The output (current detection value) of the current detection means 4 enters the division circuit 62 through the threshold value subtraction circuit 61. On the other hand, the output of the light output detection means 5 (light output detection value) also enters the divider circuit 62. Here, the following calculation is performed.
[Increase rate] = light output detection value / (current detection value−threshold current Ith)
Thereby, in the light output characteristics of the laser diode 3 shown in FIG. 5, it is possible to obtain an increase rate (straight line) of the light output with respect to the current after the laser oscillation starts exceeding the threshold current Ith. Then, the subtraction circuit 63 performs deterioration determination by the determination circuit 64 based on the value obtained by subtracting the reference value from the increase rate. When the output of the subtracting circuit 63 is positive, the increase rate of the optical output with respect to the current exceeds the reference value, so it is determined that there is no deterioration, and the output of the determining circuit 64 is “0”. When the output of the subtracting circuit 63 is negative, the rate of increase of the optical output with respect to the current is lower than the reference value, so that it is determined that the deterioration has started, and the output of the determining circuit 64 sets an appropriate coefficient for the output of the subtracting circuit 63 The multiplied value.
Here, for example, the increase rate of the optical output with respect to the drive current in the initial state of the laser diode may be used as the reference value.

  In the above description, the deterioration rate is determined by comparing the increase rate of the optical output with respect to the drive current with the reference value. However, the present invention is not limited to this. Then, deterioration may be determined. In this case, the ratio between the light output and the drive current in the initial state of the laser diode may be used as the reference value.

<Light output adjustment value generating means>
The light output adjustment value generating means 7 includes a hold circuit 71. Regarding the operation of the display using this light output control device as a light source, a timing signal is generated as described later. In the light output adjustment value generating means 7, the output of the deterioration determining means 6 is held by the hold circuit 71 in synchronization with the timing signal, and this hold signal is used as the output of the light output adjustment value generating means 7. As described above, the hold signal is input to the light output control unit 1, calculates a new light output target value, and performs APC control.

The light output adjustment value generation means 7 outputs the light output adjustment value as follows according to the determination result of the deterioration determination means 6.
(A) When the increase rate of the optical output of the laser diode with respect to the drive current is larger than the reference value, an optical output adjustment value of “0” is output.
(B) When the increase rate of the optical output of the laser diode with respect to the drive current is smaller than the reference value, an optical output adjustment value in an amount proportional to the difference between the increase rate and the reference value is output. In this way, when the increase rate is smaller than the reference value, an optical output adjustment value proportional to the difference is output.Therefore, when the increase rate becomes small due to deterioration due to secular change, the light output target value is slightly set. Since it can be lowered step by step, the drive current of the laser diode can be lowered. As a result, the life of the laser diode can be kept long.

<Light output control method>
Next, a series of flows in this light output control device will be described with reference to FIG. FIG. 4B shows changes of the light output, current value, and increase rate with respect to time according to the light output control method of the laser diode of the present invention. This light output control method is characterized in that the control method is changed according to the magnitude relationship between the increase rate of the light output and the reference value.
[1] When the increase rate of the optical output exceeds the reference value (a) When the increase rate of the optical output with respect to the current (slope of the straight line) exceeds the reference value, the output of the determination circuit 64 becomes 0, The adjustment value “0” is held in synchronization with the timing signal.
(B) In this case, since the value input to the adder circuit 11 of the light output control means 1 is 0, the value of the light output target value is directly input to the light control means 12, and the original light output target value is obtained. APC control is performed.

[2] When the increase rate of the light output is below the reference value (a) On the other hand, when the increase rate of the light output with respect to the current (slope of the straight line) is below the reference value, the output of the determination circuit 64 is different. And a negative adjustment value is held in synchronization with the timing signal.
(B) Since the addition amount in the addition circuit 11 is a negative value, the drive means 2 is obtained by subtracting an adjustment value proportional to the difference between the increase rate of the optical output with respect to the current and the reference value from the optical output target value. enter.
(C) Since the value input to the adder circuit 11 of the light output control means 1 is a negative value, a value proportional to the difference between the increase rate of the light output with respect to the current and the reference value is subtracted from the light output target value. Are input to the light control means 12, and APC control is performed with this value. As a result, it is possible to perform an operation of decreasing the light output as the increase rate of the light output with respect to the current decreases from the reference value.
As described above, the light output is controlled to be constant in the range where the increase rate (straight line) of the light output is larger than the reference value. However, if the increase rate falls below the reference value, the light output is adjusted according to the decrease in the increase rate. Can be lowered.

  Next, the timing signal will be described. Since the output of the light output adjustment value generating means 7 is expected to fluctuate somewhat, if it is constantly updated, the light output target value will be constantly fluctuated, resulting in display brightness fluctuations and unsightly. Further, the secular change of the laser diode 3 appears with a relatively long period. Therefore, the timing signal is generated so that the output of the light output adjustment value generating means 7 is once to several times during the activation of the display. Since the adjustment value is held by this timing signal, luminance fluctuation can be suppressed. Furthermore, the adjustment value can be changed in accordance with the aging of the laser diode 3.

6A to 6C show three examples of timing signal generation methods.
FIG. 6A is a schematic diagram showing a method for generating a timing signal at a timing when the display is turned on. In this case, the timing signal can be generated after a predetermined time elapses with a timer or the like after the power is turned on. In this case, the circuit power supply of the light output control device is also turned on at the same time.
FIG. 6B is a schematic diagram showing a method of generating after the light output rises after the display is turned on. A timing signal is generated at the rise of the light output detection signal (at the start of light output detection) indicating that the light output has been detected and rises above a certain level.
FIG. 6C is a schematic diagram illustrating a method for generating a timing signal at the timing when the display is turned off. A timing signal is generated after the power is turned off. The circuit power supply of the light output control device is turned on / off by being delayed by a timer or the like. Thereby, a timing signal can be generated at a desired timing. In this case, after the power of the display is turned off, the circuit power of the light output control device is turned off after a delay time.
As described above, when a timing signal is generated after a certain period of time after the power is turned on, when the optical output rises, or when the power is turned off, the optical output target value is changed only once at the time of startup or during startup. Therefore, it is possible to prevent the user from noticing the luminance change.

(Embodiment 2)
FIG. 3 is a block diagram showing a configuration of a laser diode light output control apparatus according to Embodiment 2 of the present invention. In the light output control apparatus according to the second embodiment, a current control means 8 is further added between the light output control means 1 and the drive means 2 as compared with the light output control apparatus according to the first embodiment of FIG. Is different. The current control means 8 can feed back the current detection value of the current detection means 4 to perform ACC control. Thereby, the current value of the laser diode 3 can be controlled. Therefore, according to the light output control device, in addition to the operation described in the first embodiment, it is possible to suppress a rapid increase in current against a rapid deterioration of the laser diode 3 or the like.

  In the light output control device according to the present invention, the secular change of the laser diode is determined from the light output detection value and the current detection value, and when the secular change exceeds a certain value, the target value of the light output is little by little. By lowering, an increase in current value due to aging can be prevented. Furthermore, the lifetime can be extended by lowering the command value of the light output. Therefore, it is useful as a light output control device for a laser diode used as a light source for a display or the like.

It is a block diagram which shows the structure of the light output control apparatus which concerns on Embodiment 1 of this invention. It is a block diagram which shows the further detailed structure of each structural member of FIG. It is a block diagram which shows the structure of the light output control apparatus which concerns on Embodiment 2 of this invention. (A) is a figure which shows the outline | summary of the conventional light output control method, (b) is a figure which shows the outline | summary of the light output control method in Embodiment 1 of this invention. It is a graph which shows the relationship between the electric current of a laser diode, and optical output. (A)-(c) is the schematic shown about the generation | occurrence | production time of various timing signals. It is a block diagram which shows the structure of the conventional light output control apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light output control means 2 Drive means 3 Laser diode 4 Current detection means 5 Light output detection means 6 Degradation judgment means 7 Light output adjustment value generation means 8 Current control means 9 Switching means 11 Addition circuit 12 Light control means 61 Threshold subtraction Circuit 62 Division circuit 63 Subtraction circuit 64 Determination circuit 71 Hold circuit

Claims (9)

A laser diode light output control device that performs automatic light quantity control by feeding back the light output of the laser diode,
A laser diode and driving means for driving the laser diode;
A light output detecting means for detecting a light output of the laser diode;
Drive current detection means for detecting the drive current of the laser diode;
Degradation determination means for determining deterioration of the laser diode from the output of the light output detection means and the output of the drive current detection means;
A light output adjustment value generating means for generating a light output adjustment value of the laser diode based on the determination result of the deterioration determination means;
A light output control means for outputting a signal for controlling the magnitude of the light output of the laser diode to the drive means according to the light output target value, the output of the light output adjustment value generating means, and the output of the light output detection means; Prepared,
An optical output control device for a laser diode, wherein deterioration of the laser diode is determined based on an optical output of the laser diode and a drive current, and the optical output of the laser diode is changed according to the determination result. The deterioration determining means includes
2. The laser diode light output control device according to claim 1, wherein a deterioration of the laser diode is determined by comparing a ratio between a light output of the laser diode and the drive current with a reference value. 3. The light output adjustment value generating means is
(A) When the ratio between the light output of the laser diode and the drive current is larger than a reference value, a light output adjustment value of 0 is output;
(B) When the ratio between the optical output of the laser diode and the drive current is smaller than a reference value, an optical output adjustment value in an amount proportional to the difference between the ratio of the optical output and the drive current and the reference value is output. To
The light output control device for a laser diode according to claim 2. The deterioration determining means includes
3. The laser diode light output control device according to claim 2, wherein deterioration of the laser diode is determined using a ratio between a light output and a drive current in an initial state of the laser diode as a reference value. 4. The deterioration determining means includes
Calculating an increase rate of the optical output with respect to the drive current based on the optical output of the laser diode and the drive current, and comparing the increase rate of the optical output with a reference value to determine deterioration of the laser diode. 2. The laser diode light output control device according to claim 1, wherein The light output adjustment value generating means is
(A) when the rate of increase of the optical output of the laser diode with respect to the drive current is larger than a reference value, an optical output adjustment value of 0 is output;
(B) When the increase rate of the optical output of the laser diode with respect to the drive current is smaller than a reference value, an optical output adjustment value in an amount proportional to the difference between the increase rate and the reference value is output.
The laser diode light output control device according to claim 5. The deterioration determining means includes
6. The laser diode light output control apparatus according to claim 5, wherein deterioration of the laser diode is determined using a rate of increase of the light output in an initial state of the laser diode with respect to a drive current as a reference value. The light output adjustment value generating means is
2. The laser diode light output control device according to claim 1, wherein the light output adjustment value is updated in synchronization with a predetermined timing signal.   The timing signal is generated at least at any point of time when the circuit of the light output control device is turned on, when the detection of light output of the laser diode is started, or immediately before the circuit is turned off. Item 9. The laser diode light output control device according to Item 8.

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