JPH1070329A - Laser diode-driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser diode driving device of low electric consumption by supplying a constant current to a laser diode, a side flow circuit and a thermoelement driving circuit from a drive current source. SOLUTION: A part of a constant current Io from a drive current source 9 is shunted to a side flow circuit 14, and light output of a laser diode LD 1 is controlled to be constant by increasing and reducing the splitting current. A thermoelement 3 is driven by a current from the drive current source 9, is cooled/heated by the direction of current that flows in the thermoelement 3, and the level of heating/cooling is controlled by the quantity of current. Thus electric consumption is reduced by taking the drive current for the laser diode LD 1 and the thermoelement from the common current source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for maintaining a constant temperature and light output of a laser diode.

[0002]

2. Description of the Related Art In recent years, an optical fiber transmission technique capable of high-speed transmission is being introduced in order to respond to an increasing demand for a broadband service centered on an image. In the optical fiber transmission technology, for example, a high-output laser diode such as an excitation light source of an optical fiber amplifier is used. Since the temperature characteristics and aging characteristics of laser diodes cannot be ignored,
Control to stabilize temperature and light output is indispensable.

FIG. 8 is a diagram showing the structure of a conventional laser diode driving device of this kind. In the figure, 1 is a laser diode (hereinafter abbreviated as LD), 2 is a light receiving element (hereinafter abbreviated as PD) for monitoring the optical output of the laser diode,
3 is a thermoelectric element for controlling the temperature of the LD1, 4 is a thermosensitive element for detecting the temperature of the LD1, 10 is a temperature detection circuit for detecting the difference between the temperature of the laser diode and a specified temperature, 40 is a resistor, and 20 is a comparator. , 16 is a reference current source that is compared with the current flowing through the light receiving element, 13 is an optical output detection circuit that compares the current flowing through the reference current source with the light receiving element 2 and detects a difference between the optical output of the LD 1 and a specified value. Is a transistor, 50 is a push-pull amplifier for driving the thermoelectric element 3, 51 and 52 are transistors, and 53 and 54 are diodes.

The operation will be described. As described above, the LD 1 has a large temperature characteristic and a long-term characteristic, so that temperature stabilization and light output stabilization are essential. Therefore, LD1 comprises PD2 for monitoring the optical output, thermoelectric element 3 for adjusting the temperature of LD1,
The temperature sensing element 4 for detecting the temperature of the LD 1 is incorporated in the same package. The temperature stabilization will be described. The temperature sensing element 4 has a characteristic that the resistance value increases and decreases according to the temperature change of the LD 1 and the voltage dividing ratio with the resistor 40 changes.
The voltage input to 0 changes. The comparator 20 has a specified voltage
The difference between Vref and the output voltage of the temperature sensing element 4 is amplified and input to a push-pull amplifier 50 including transistors 51 to 52 and diodes 53 to 54. The push-pull amplifier 50 supplies the thermoelectric element 3 with a current whose direction changes according to the magnitude relationship between the output voltage of the thermosensitive element 4 and the specified voltage Vref. As a result, the temperature of the LD 1 changes and the temperature sensing element 4
Output voltage also changes. Due to the above negative feedback effect, LD
The temperature of 1 is substantially maintained at the temperature at which the output voltage of the thermosensitive element 4 becomes equal to the specified voltage Vref.

Next, light output stabilization will be described. LD
A part of the light output of No. 1 is received by the PD 2 and input to the light output detection circuit 13. The optical output detection circuit 13 is a reference current source 1
The difference between the currents flowing through the PD 6 and the PD 2, that is, the difference between the specified light output determined by the reference current source 16 and the light output is amplified and input to the base of the transistor 49. The transistor 49 increases the collector current if the light output is smaller than the specified light output, and decreases the collector current if the light output is larger than the specified light output.
Is maintained at a specified light output.

[0006]

Next, consider the power consumption of the conventional laser diode driving device shown in FIG. For example, an LD having a light emission wavelength of 1470 nm used as an excitation light source for an optical fiber amplifier requires a maximum of about 1 A as an LD driving current, and a driving current of the thermoelectric element 3 is also about 1 A at maximum considering an ambient temperature of 0 to 70 ° C. is required. The power supply voltages VCC and VEE in the circuit of FIG.
Considering 5 V, the power consumption of 5 W is necessary for the LD 1 and the transistor 49, and 5 W for the thermoelectric element 3 and the push-pull amplifier 50. Normally, the allowable power consumption of a board on which components are mounted in a communication device is 10 W or less, and the maximum number of excitation light sources for an optical fiber amplifier is one on a single board. There is a problem that the excitation light source cannot be compactly mounted.

Therefore, a first object of the present invention is to obtain a laser diode driving device with low power consumption. A second object is to provide a laser diode driving device capable of controlling light output stabilization and temperature stabilization over a wide range. A third object is to prevent the driving current source of the laser diode driving device from flowing an excessive current that may destroy the laser diode and the thermoelectric element.

[0008]

According to a first aspect of the present invention, there is provided a laser diode driving device comprising: a laser diode for outputting a laser beam; a light receiving element for monitoring an optical output of the laser diode; and a laser diode for monitoring the light receiving element. A light output detection circuit for detecting a difference between the light output and the predetermined light output; a side current circuit for flowing a current supplied to the laser diode based on an output of the light output detection circuit; and detecting a temperature of the laser diode A temperature sensing element, a temperature detection circuit for detecting a difference between a temperature of the laser diode detected by the temperature sensing element and a predetermined temperature, a thermoelectric element for heating or cooling the laser diode according to an applied current and a direction of the current, and a temperature detection. A first current control circuit that controls the amount of current flowing through the thermoelectric element based on the output of the circuit; and
A second current control circuit for controlling the direction of the current flowing through the thermoelectric element; a thermoelectric element driving circuit for driving the thermoelectric element based on the amount of current flowing through the thermoelectric element and the direction of the current; A driving current source for supplying a constant current to the element driving circuit.

A laser diode driving device according to a second aspect of the present invention controls a driving current source based on outputs of a temperature detecting circuit and an optical output detecting circuit.

[0010] In the laser diode driving device according to a third aspect of the present invention, the current source control circuit outputs a current based on a difference from the predetermined level when the output of the optical output detection circuit falls below a predetermined level. A set current generating circuit, and a second set current generating circuit for outputting a current based on a difference between the output of the temperature detecting circuit and the predetermined range when the output of the temperature detecting circuit exceeds the predetermined range. The drive current source outputs the sum of the output current and the output current of the second set current generation circuit, and the drive current source increases the output current based on the output of the current source control circuit.

According to a fourth aspect of the present invention, in the laser diode driving device, the current source control circuit outputs a current based on a difference from the predetermined level when the output of the optical output detection circuit falls below a predetermined level. A set current generating circuit, and a second set current generating circuit for outputting a current based on a difference between the output of the temperature detecting circuit and the predetermined range when the output of the temperature detecting circuit exceeds the predetermined range. The output is compared with the output of the second set current generation circuit, and the drive current source is controlled so as to output the larger current.

A laser diode driving device according to a fifth aspect of the present invention includes a current source monitoring circuit for monitoring an output current of a driving current source, and a comparator for comparing an output of the driving current source control circuit with an output of the current monitoring circuit. And controls the output current of the drive current source to be proportional to the output current of the drive current source control circuit.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. In this embodiment, the power consumption is reduced by taking the drive current of the laser diode and the drive current of the thermoelectric element from a common current source. FIG. 1 is a diagram showing a configuration of a laser diode driving device according to the present embodiment. In the figure, reference numerals 5 to 8 denote first to fourth transistors, respectively, and reference numeral 30 denotes a thermoelectric element drive circuit, which is constituted by first to fourth transistors 5 to 8. A driving current source 9 supplies a constant current Io to the laser diode and thermoelectric element driving circuit.

Reference numeral 11 denotes a first current control circuit which controls the base voltages of the first and second transistors 5 and 6 of the thermoelectric element driving circuit 30. Reference numeral 12 denotes a second current control circuit that controls the base voltages of the third and fourth transistors 7 and 8 of the thermoelectric element drive circuit 30. Reference numeral 14 denotes a side current circuit, which is a voltage-current conversion circuit 32 that generates a current proportional to the output voltage of the optical output detection circuit 13, and amplifies the output current of the voltage-current conversion circuit 32 and is supplied from the drive current source 9. It is composed of a transistor 22 that shunts the constant current Io. The drive current source 9 includes a current source 21 and a current mirror circuit of transistors 17 and 18, and outputs a constant current Ir output from the current source 21.
The constant current Io amplified by the ratio of the emitter widths of the transistors 17 and 18 is output. For the same parts as the conventional example,
The same reference numerals are given.

First, the operation related to the light output stabilizing function will be described. The light output stabilization is performed by dividing a part of the constant current Io supplied from the drive current source 9 to the side current circuit 14 and controlling the LD 1 to keep the light output constant by increasing or decreasing the divided current. That is, the LD 1 emits light by the current supplied from the drive current source 9, and the light is received by the PD 2,
The light receiving current is supplied to the light output detection circuit 13.

The light output detection circuit 13 detects a difference between the current flowing through the PD 2 and the reference current source 16, and if the current of the PD 2 is larger than the current of the reference current source 16, the side current circuit 14
And the drive current of the LD 1 is decreased. When the current of the PD 2 is smaller than the current of the reference current source 16, the current shunted to the side current circuit 14 is reduced.
Increase the drive current of LD1. When the current of the PD 2 is equal to the current of the reference current source 16, the increase and decrease of the current shunted to the bypass circuit 14 and the drive current of the LD 1 are stopped.

For example, when the current of the PD 2 is larger than the current of the reference current source 16, the optical output detection circuit 13 increases the current shunted to the side current circuit 14 and decreases the drive current of the LD 1. Then, the optical output of LD1 decreases and PD2
When the current of the PD2 becomes small, the current of the PD2 becomes the reference current source 16
, The optical output detection circuit 13 reduces the current shunted to the side current circuit 14 and increases the drive current of the LD 1. Then, when the light output of the LD 1 increases and the current of the PD 2 becomes larger than the current of the reference current source 16, the light output detection circuit 13 increases the current shunted to the side current circuit 14 and decreases the drive current of the LD 1. When the current of the PD2 becomes equal to the current of the reference current source 16, the current shunted to the bypass circuit 14 and the drive current of the LD1 are stopped from increasing or decreasing. By the above, L
The light output of D1 is controlled to be constant.

Next, the operation relating to the temperature stabilizing function will be described. The temperature stabilization control drives the thermoelectric element 3 with a current supplied from the driving current source 9, cools or heats the thermoelectric element 3 in the direction of the current flowing through the thermoelectric element 3, and controls the strength of heating / cooling according to the magnitude of the flowing current. It is. The temperature detection circuit 10
The difference between the output voltage of the temperature measuring device D1, for example, the temperature sensing element 4 and the reference voltage corresponding to the reference temperature is output. The first current control circuit 11 controls the base voltages of the first and second transistors 5 and 6 of the thermoelectric element driving circuit 30 based on the output voltage from the temperature detection circuit 10 and controls the amount of current flowing through the thermoelectric element 3. I do. The second current control circuit 12 switches the driving current direction of the thermoelectric element 3 by controlling the base voltages of the third and fourth transistors 7 and 8 of the thermoelectric element driving circuit 30. That is, switching between heating and cooling is performed.

If the output voltage of the temperature detection circuit 10 is 0 V,
That is, if the temperature of the LD 1 is equal to the reference temperature, the first current control circuit 11 applies a base voltage equal to the transistors 5 and 6 of the thermoelectric element drive circuit 30, and the second current control circuit 12 applies the base voltage of the thermoelectric element drive circuit 30. A base voltage equal to transistors 7 and 8 is applied. Since the current flowing through the transistors 5 and 6 and the current flowing through the transistors 7 and 8 are equal,
No current flows through the thermoelectric element, and cooling and heating are not performed. Since the current is supplied from the driving current source 9, the transistors 5, 6 and the transistors 7, 8 of the thermoelectric element driving circuit 30 are used.
Is equal to the output current Io of the drive current source 9.

Next, when the temperature of the LD 1 decreases and the output voltage of the temperature detection circuit 10 increases, the first current control circuit 11
In the state where the sum of the currents flowing through the transistors 5 and 6 of the thermoelectric element driving circuit 30 is equal, the current flowing through the transistor 5 is made smaller than the current flowing through the transistor 6, and
The second current control circuit 12 increases the current flowing through the transistor 7 and reduces the current flowing through the transistor 8 when the sum of the currents flowing through the transistors 7 and 8 of the thermoelectric element driving circuit 30 is equal. The current Io flows through 7, the current stops flowing through the transistor 8, and the current flows in the direction of heating the thermoelectric element, thereby heating the LD1.

Next, when the temperature of the LD 1 rises and the output voltage of the temperature detection circuit 10 decreases, the first current control circuit 11
In the state where the sum of the currents flowing through the transistors 5 and 6 of the thermoelectric element drive circuit 30 is equal, the current flowing through the transistor 5 is made larger than the current flowing through the transistor 6, and
When the second current control circuit 12 increases the current flowing through the transistor 8 of the thermoelectric element driving circuit 30 and decreases the current flowing through the transistor 7, a current I0 flows through the transistor 8 and a current flows through the transistor 7. Then, a current flows in the direction of cooling the thermoelectric element and cools the LD1.

Next, the operation will be described with reference to FIG. FIG.
, The horizontal axis represents the output of the temperature detection circuit 10, the vertical axis is divided into three regions, the first from the bottom is the output current of the drive current source 9, and the second from the bottom is the transistors 5 to 5 of the thermoelectric element drive circuit 30. 8 and the current of the thermoelectric element 3.
8 shows the base voltage. The output voltage of the temperature detection circuit 10 is equal to the temperature of the LD 1 detected by the temperature sensing element 4 and the comparator 20.
Is 0 V when the temperature Trf corresponding to the reference voltage Vref is equal. When the temperature of the LD 1 becomes higher than the specified temperature Trf, generally, the resistance of the temperature-sensitive element 4 decreases, and the output of the temperature detection circuit 10 decreases. In this region, the thermoelectric element 3 is L
The operation mode is the operation mode in which the heat of D1 is taken out and cooled. When the temperature of the LD 1 becomes lower than the specified temperature Trf, the temperature sensing element 4
And the output of the temperature detection circuit 10 rises. In this region, the thermoelectric element 3 is in an operation mode in which heat is applied to the LD 1 to heat it.

The base voltages of the transistors 5 and 6, which are the outputs of the first current control circuit 11, match when the temperature of the LD1 is equal to the specified temperature Trf, and are otherwise proportional to the output voltage of the temperature detection circuit 10. Decrease or increase. Similarly, the base voltages of the transistors 7 and 8, which are the outputs of the second current control circuit 12, match when the temperature of the LD1 is equal to the specified temperature Trf, and otherwise, in proportion to the output voltage of the temperature detection circuit 10. Increase or decrease. Due to the above movement of the base voltages of the transistors 5 to 8, the output current I0 of the driving current source 9 flows through the emitter of the transistor 7 in the heating mode, and conversely, the output of the driving current source 9 flows through the emitter of the transistor 8 in the cooling mode. The current I0 flows.

Considering the operation of the transistors 5 and 6 of the thermoelectric element driving circuit 30 in the heating mode in which the output voltage of the temperature detecting circuit 10 is 0.2 V or more, in this region, the output current I0 of the driving current source 9 is supplied to the transistor 7 in this region. Current flows through the transistor 8. For example, assuming that the resistance of the thermoelectric element 3 is 2Ω and the output current of the constant current source 9 is 1 A, the voltage applied to both ends of the thermoelectric element 3 is 1.0 V. Therefore, when the voltage difference between the transistors 5 and 6 is 1.0 V, the transistor The currents flowing through the emitters 5 and 6 become equal, and at other voltages, the difference between their base voltages, that is, the temperature detection circuit 10
Changes linearly with the output of

The current flowing through the thermoelectric element 3 is
, Which also changes almost linearly with the output of the temperature detection circuit 10. Therefore, when the temperature of the LD 1 decreases, more current flows to the thermoelectric element 3, and the temperature of the LD 1 is kept constant within the range of the control error due to the negative feedback effect. Although the case where the LD 1 is heated has been described in detail, the same operation is performed when cooling the LD 1. As described above, the light output and the temperature of the laser diode are kept constant, and the power consumption can be reduced because the drive current of the laser diode and the drive current of the thermoelectric element are obtained from a common current source. Although the above example has been described using a transistor, the same effect can be obtained by using another field effect transistor or an electronic switch.

Embodiment 2 FIG. This embodiment is different from the first embodiment in that when the driving current source 9 supplies a constant current, the current is insufficient and the optical output cannot be stabilized and the temperature cannot be stabilized. And temperature stabilization. FIG. 3 shows the configuration of the present embodiment. In the figure, 9 is a drive current source, 15 is a current source control circuit, which controls the output current of the drive current source 9. Others are the same as those in FIG. The drive current source 9 includes, for example, a current source 21 that outputs a constant current Ir and transistors 17 and 18.
The drive current source 9 outputs a current obtained by amplifying the output current from the current source control circuit 15 and the constant current Ir by the ratio of the emitter widths of the transistors 17 and 18.

The operation will be described. However, when the drive current source 9 functions as a current source of the constant current Io, the operation is the same as that of the first embodiment, and the description is omitted. Current source control circuit 15
Controls the drive current source 9 to output a constant current Io in a state where the control of the light output stabilization and the temperature stabilization can be performed. However, when the output voltage of the optical output detection circuit 13 is negative and does not reach zero V while the constant current Io is flowing to the LD 1 without flowing the current to the side current circuit 14 (PD from the reference current source).
2 is low), it is not possible to control the light output of the LD 1 to a specified value. Therefore, a light output shortage determination level is provided, and when the output voltage of the light output detection circuit 13 is lower than the light output shortage determination level, the current source control circuit 15 adds the current Io to a current proportional to the light output shortage. The current is controlled to be output to the drive current source 9. Therefore, the drive current of the LD 1 increases and the light output can be stabilized.

If the output voltage of the temperature detection circuit 10 is outside the range of the heating / cooling capability while the constant current Io is flowing through the thermoelectric element 3, the output of the temperature detection circuit 10 becomes a specified value. I can't control it. In view of this, a thermoelectric element underheating determination level is provided, and when the heating is insufficient, that is, when the output voltage of the temperature detection circuit 10 is higher than the thermoelectric element underheating determination level, the current source control circuit 15 determines the current proportional to the heating underheating. To the drive current source 9, and the drive current source 9 outputs a current obtained by amplifying the sum of the current proportional to the insufficient heating and the constant current Ir of the current source 21 by the ratio of the emitter widths of the transistors 17 and 18. . In addition, a thermoelectric element cooling insufficient judgment level is provided, and when the cooling is insufficient, that is, when the output voltage of the temperature detection circuit 10 is larger than the thermoelectric element cooling insufficient judging level, the current source control circuit 15 sets the current proportional to the cooling insufficient. Is output to the drive current source 9, and the drive current source 9 amplifies the sum of the current proportional to the insufficient cooling and the constant current Ir of the current source 21 by the ratio of the emitter widths of the transistors 17 and 18 (the amount of cooling is insufficient). A constant current Io) is output. FIG. 4 shows a thermoelectric element underheating determination level (the output voltage of the temperature detection circuit 10 is +1.1
V) and an insufficient cooling determination level (the output voltage of the temperature detection circuit 10 is -1.1 V), and shows an operation when heating and cooling are insufficient. The output voltage of the temperature detection circuit 10 is ±
The operation when the voltage is within the 1.1V range (the heating / cooling is not insufficient) is the same as that in FIG.

The current source control circuit 15 determines that the temperature of the LD 1 is in the range of insufficient heating / cooling, that is, the output voltage of the temperature detecting circuit 10 in FIG. Below, or underheating judgment level + 1.1V
In this case, the current flowing through the thermoelectric element is limited to a constant current of 1.0 A of the driving current source in FIG. 2, but in this embodiment, as shown in FIG. Even so, the current source control circuit 15 supplies a current proportional to the shortage to the drive current source 9, and the drive current source 9 calculates the sum of the current proportional to the heating / cooling shortage and the constant current Ir of the current source 21 by the transistor 17. , 18 (the insufficient heating / cooling and the constant current Io). Therefore, the drive current of the thermoelectric element increases and temperature stabilization can be achieved.

Embodiment 3 This embodiment shows a specific configuration example of the current source control circuit 15 in the configuration shown in the second embodiment. If the light output is insufficient and the heating or cooling is insufficient, the current source control circuit 15 outputs the current proportional to the sum of the light output insufficient current and the heating or cooling insufficient current. To control. FIG. 5 is a diagram showing a configuration of the current source control circuit 15 and the drive current source 9 according to the present embodiment, wherein 23 of the current source control circuit 15 is a first set current generation circuit, and 24 is a second set current generation circuit. Circuits, 25, 26, 28, 29, 31, 32 are transistors, and 27, 30, 33 are current sources. The configuration of the drive current source 9 is the same as that of the second embodiment shown in FIG. The first set current generation circuit 23 is a current switch composed of transistors 25 and 26 and a current source 27. When the output voltage of the optical output detection circuit 13 becomes lower than the optical output shortage determination level Vref1, the transistor 26 is turned on. Supplies a current proportional to the light output shortage to the drive current source 9. Then, the driving current source 9 outputs a current (light output shortage and constant current Io) obtained by amplifying a current obtained by adding a constant current Ir to a current proportional to the shortage by the ratio of the emitter widths of the transistors 17 and 18. When the output is higher than the light output shortage determination level Vref1, no current flows through the transistor 26, and the drive current source 9 outputs a constant current Io.

The second set current generating circuit 24 includes transistors 28 and 29, a current source 30, and transistors 31 and 32.
And a current source 33 composed of a current source 33 and a current source 33. When the output voltage of the temperature detection circuit 10 becomes lower than the insufficient cooling judgment level Vref2, the current changeover switch composed of the transistors 28 and 29 and the current source 30 supplies the drive current source 9 with a current proportional to the shortage. Supply. The drive current source 9 amplifies a current obtained by adding a constant current Ir to a current proportional to the shortage by the ratio of the emitter widths of the transistors 17 and 18 (light output shortage and constant current I
o) is output. On the other hand, when it is higher than the insufficient cooling determination level Vref2, no current flows through the transistor 29, and the drive current source 9 outputs a constant current Io.

When the output voltage of the temperature detecting circuit 10 becomes higher than the underheating judgment level Vref3, the transistor 31 outputs a current proportional to the shortage when the output voltage of the temperature detecting circuit 10 becomes higher than the heating undercurrent judgment level Vref3. Supply to source 9. Then, the drive current source 9 applies a current obtained by adding a constant current Ir to a current proportional to the shortage, to the transistors 17 and 18.
(A light output shortage and a constant current Io) amplified by the ratio of the emitter width. In addition, the heating insufficient judgment level Vref3
When the voltage becomes lower, no current flows through the transistor 31, and the drive current source 9 outputs a constant current Io.

However, since the outputs of the transistors 26, 29, and 31 are connected and output to the drive current source 9, the current source control circuit 15 outputs the current corresponding to the shortage of the optical output (light of the transistor 26) if the optical output is insufficient and the cooling is insufficient. A current proportional to the sum of the output current) and the current for the insufficient cooling (the output current of the transistor 29) is supplied to the drive current source 9. And the driving current source 9
Outputs a current (light output shortage and constant current Io) obtained by amplifying a current obtained by adding a constant current Ir to a current proportional to the shortage by the ratio of the emitter widths of the transistors 17 and 18. If the light output is insufficient and the heating is insufficient, a current proportional to the sum of the insufficient light output current and the insufficient heating current (the output current of the transistor 31) is supplied to the drive current source 9. And the driving current source 9
Outputs a current (light output shortage and constant current Io) obtained by amplifying a current obtained by adding a constant current Ir to a current proportional to the shortage by the ratio of the emitter widths of the transistors 17 and 18.

As described above, the current source control circuit 15 controls the output current of the drive current source 9 so as to be proportional to the sum of the output currents of the first set current generation circuit and the second set current generation circuit. Light output and operating temperature can be maintained at specified values.

Embodiment 4 FIG. In the third embodiment, if the light output is insufficient and the heating or cooling is insufficient, the drive current source 9 is controlled so as to output a current proportional to the sum of the current for the optical output lack and the current for the heating or cooling insufficient. However, in the present embodiment, the drive current source 9 is controlled so as to output a current proportional to the larger of the light output shortage current and the heating or cooling shortage current. FIG. 6 is a diagram showing a configuration of the current source control circuit 15 and the drive current source 9 according to the present embodiment.
42 is a resistor, 36 and 37 are comparators, 38, 39, 43 to
46 is a transistor. First set current generation circuit 2
Third, the configuration of the second set current generating circuit 24 is described in the third embodiment.
5 is the same as that of FIG. The configuration of the drive current source 9 is the same as that of the second embodiment shown in FIG.

The operation will be described. Comparators 36 and 37
Detects the output current of the first setting current generation circuit 23 and the output current of the second setting current generation circuit 24 from the voltage values generated in the resistors 34 and 35, respectively, and controls the operation mode of the transistors 38 and 39. When the current for the light output shortage, that is, the output current of the first set current generation circuit 23 is larger than the current for the heating or cooling shortage, that is, the output current of the second set current generation circuit 24, the transistor 38 is turned on. Become a resistance 41
As a result, the base voltage of the transistor 43 decreases, and when the transistor 44 is turned on, the output current of the first set current generation circuit 23 is output to the drive current source 9. The drive current source 9 amplifies a current obtained by adding a constant current Ir to a current proportional to the light output shortage of the output of the light output detection circuit 13 by the ratio of the emitter widths of the transistors 17 and 18 (light output shortage). And a constant current Io).

Conversely, when the current for insufficient heating or cooling, ie, the output current of the second set current generating circuit 24, is larger than the current for insufficient light output, ie, the output current of the first set current generating circuit 23. Is that when the transistor 39 is turned on, the base voltage of the transistor 46 is reduced by the resistor 42,
When the transistor 45 is turned on, the output current of the second set current generation circuit 24 is output to the drive current source 9.
That is, a current proportional to the insufficient heating or cooling current is supplied to the drive current source 9 in accordance with the output voltage of the temperature detection circuit 10. The drive current source 9 amplifies a current obtained by adding a constant current Ir to a current proportional to the insufficient heating or cooling current by the ratio of the emitter widths of the transistors 17 and 18 (light output shortage and constant current Io). Is output. As described above, since the drive current source 9 is controlled so as to output a current proportional to the larger of the current for the light output shortage and the current for the heating or cooling shortage, the light output and the operating temperature of the LD 1 are set to the specified values. Can be kept.

Embodiment 5 In the second embodiment, for example, in a transient response state such as when power is turned on, an excessive current
D1 may flow to the thermoelectric element 3 and break it. In the present embodiment, the supply current of the drive current source 9 is monitored to prevent an excessive current from flowing. FIG. 7 is a diagram showing the configuration of the laser diode driving device according to the present embodiment, wherein 47 is a current source monitor circuit, and 48 is a comparator. The rest is the same as FIG. 3 of the second embodiment.

The operation will be described. The drive current source 9 calculates the current from the current source control circuit 15 and the current Ir from the constant current source 21 as follows:
A current amplified by the ratio of the emitter widths of the transistors 17 and 18 is output. Therefore, the maximum output current value of the drive current source 9 is affected by the deviation of the ratio of the emitter width of the transistors 17 and 18 from the design value, the fluctuation of the maximum value of the output current of the current source control circuit 15, and LD in transient state
1. There is a possibility that an excessive current is supplied to the thermoelectric element 3 to destroy it.

Therefore, the current source monitor circuit 47 and the comparator 4
8 is added as shown in FIG.
Monitors the output current of the drive current source 9 and outputs the monitoring result to the comparator 48, which outputs the current source monitor circuit 47
Is compared with the output of the current source control circuit 15 to control the output current of the drive current source 9 to be proportional to the output of the current source control circuit 15. Thus, the drive current source 9 does not flow an excessive current, and the LD 1 and the thermoelectric element 3 are not broken.

[0041]

According to the first aspect of the present invention, the drive current of the laser diode and the drive current of the thermoelectric element are obtained from a common current source, so that the power consumption can be reduced.

According to the second aspect of the present invention, even if the laser diode has insufficient light output or insufficient cooling and heating, the drive current of the laser diode or the drive current of the thermoelectric element is increased, so that the light output stabilization and temperature stabilization are performed over a wide range. Can be achieved.

In the third aspect of the present invention, the current source for driving the laser diode and the thermoelectric element is monitored, and if the current is equal to or more than the specified current, the driving current is reduced. No, LD1, thermoelectric element 3
Without destroying it.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a laser diode driving device according to a first embodiment.

FIG. 2 is an operation explanatory diagram of the laser diode driving device according to the first embodiment.

FIG. 3 is a diagram showing a configuration of a laser diode driving device according to a second embodiment.

FIG. 4 is an operation explanatory diagram of the laser diode driving device according to the second embodiment.

FIG. 5 is a diagram showing a configuration of a drive current source according to a third embodiment.

FIG. 6 is a diagram showing another configuration of the drive current source according to the fourth embodiment.

FIG. 7 is a diagram showing a configuration of a laser diode driving device according to a fifth embodiment.

FIG. 8 is a diagram showing a configuration of a conventional laser diode driving device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 LD (laser diode) 2 PD (photodiode) 3 thermoelectric element 5 to 8 transistor 9 drive current source 10 temperature detection circuit 11 first current control circuit 12 second current control circuit 13 optical output detection circuit 14 side current circuit Reference Signs List 15 current source control circuit 16 reference current source 17, 18 current mirror circuit 20 comparator 21 constant current source 23 first setting current generating circuit 24 second setting current generating circuit 30 thermoelectric element driving circuit 34, 35, 41, 42 Resistance 36, 37 Comparator 38, 39, 43 to 46 Transistor 47 Current source monitor circuit 48 Comparator

Claims (5)

[Claims] 1. A laser diode driving device having the following components: a. A laser diode that outputs laser light, b. A light receiving element for monitoring the light output of the laser diode; c. An optical output detection circuit for detecting a difference between an optical output of the laser diode monitored by the light receiving element and a predetermined optical output; d. A side-current circuit for flowing a current supplied to the laser diode based on an output of the light output detection circuit; e. A temperature sensing element for detecting a temperature of the laser diode; f. A temperature detection circuit for detecting a difference between the temperature of the laser diode detected by the temperature sensing element and a predetermined temperature; g. A thermoelectric element for heating or cooling the laser diode depending on the applied current and the direction of the current; h. A first current control circuit that controls an amount of current flowing through the thermoelectric element based on an output of the temperature detection circuit; i. A second current control circuit that controls a direction of a current flowing through the thermoelectric element based on an output of the temperature detection circuit; j. A thermoelectric element driving circuit for driving the thermoelectric element based on the amount of current flowing through the thermoelectric element and the direction of the current; k. A drive current source for supplying a constant current to the laser diode, the side current circuit, and the thermoelectric element drive circuit. 2. The laser diode driving device according to claim 1, further comprising a current source control circuit that controls the driving current source based on outputs of the temperature detection circuit and the light output detection circuit. 3. The current source control circuit includes: a first set current generation circuit that outputs a current based on a difference from a predetermined level when an output of the optical output detection circuit is lower than a predetermined level; A second set current generating circuit for outputting a current based on a difference from the predetermined range when an output of the detection circuit exceeds a predetermined range, and an output current of the first set current generating circuit and the second set current generating circuit; 3. The laser diode driving device according to claim 2, wherein a sum of output currents of the set current generation circuits is output, and the driving current source increases an output current based on an output of a current source control circuit. 4. The current source control circuit includes: a first set current generation circuit that outputs a current based on a difference from a predetermined level when an output of the optical output detection circuit falls below a predetermined level; A second set current generating circuit for outputting a current based on a difference between the output of the detection circuit and the predetermined range when the output of the detection circuit exceeds the predetermined range; 3. The laser diode driving device according to claim 2, wherein the driving current source is controlled so as to compare an output of the set current generating circuit and output a larger current. 5. A current source monitor circuit for monitoring an output current of the drive current source, and a comparator for comparing an output of the current source control circuit with an output of the current monitor circuit, 5. The laser diode driving device according to claim 2, wherein an output current is controlled so as to be proportional to an output current of the current source control circuit.