JP2002319730A - Temperature control system for laser diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature control system for a laser diode, which can temperature control by a single power source, which has proper temperature control efficiency and low noise level generated in association with the temperature control. SOLUTION: In the temperature control system for the laser diode using a Peltier element, an electric heater is formed on the surface of a ceramic plate for constituting the Peltier element. Thus, cooling control by a thermoelectric semiconductor for constituting the Peltier element or a heating control by the electrothermal heater is selected, in response to the voltage for detecting the temperature of the laser diode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode temperature control system for controlling an oscillation wavelength of a laser diode for converting an electric signal to an optical signal in optical communication, and more particularly to a low-voltage laser diode. The present invention relates to a temperature control method for a laser diode which can control the temperature with a single power supply, has good temperature control efficiency, and has a low noise level generated by the temperature control.

[0002] In Japan, the digital transmission system using electric signals began to be put into practical use in about 1965,
Around 1980, it grew as a main transmission system constituting a trunk line, replacing the analog transmission system.

On the other hand, a digital transmission method using an optical signal is as follows.
At the same time that the digital transmission method using electric signals secured its position as the main transmission method,
In the latter half of the 980s, it became the dominant transmission system on trunk lines.

[0004] Since optical fiber cables are originally broadband, the optical digital transmission system has grown as a system suitable for a large-capacity transmission system in combination with an increase in the speed of an electric-optical conversion element or an optical-electrical conversion element. However, capacity increase by single wavelength transmission is approaching its limit.

On the other hand, with the arrival of the multimedia age,
With the recent rapid spread of the Internet, there is an urgent need to realize an optical digital transmission system having an even larger capacity.

A single-wavelength transmission system for transmitting a single-wavelength optical signal over a single optical fiber cable;
A wavelength-division multiplexing transmission method for multiplexing and transmitting optical signals of a plurality of wavelengths on one optical fiber cable (generally, "W
It is called "DM system". "WDM" stands for "Wavelength Div
Ision Multplexing is an abbreviation that takes the initials. )
Both have been developed in parallel, but under the above-mentioned background, the use of multiple wavelengths in the wavelength division multiplexing transmission system has been spurred in order to cope with a rapid increase in transmission demand.

Furthermore, in order to cope with a sudden increase in required transmission capacity, about 1,500 nanometers (“nano” is 10 ⁻⁹⁾
It is. ) In the nearby wavelength band, it is necessary to perform wavelength multiplexing at wavelength intervals on the order of 0.5 nanometer.

In general, the oscillation wavelength of a laser diode has the characteristic that it varies with the temperature of the laser diode chip, and its temperature coefficient is on the order of 0.1 nanometer / ° C.

Therefore, when wavelength multiplexing is performed at a wavelength interval on the order of about 0.5 nanometer, it is necessary to suppress the temperature of the laser diode chip to a fluctuation of 1 ° C. or less.

In order to control the temperature of the laser diode to the above extent, a laser diode chip is mounted on a ceramic plate in contact with the electrode on the heat absorption side of the Peltier device.
Normally, the temperature of the laser diode is controlled by the direction and value of the current flowing through the Peltier element after bonding.

FIG. 10 is a diagram showing the principle of cooling and heating by a Peltier element, and shows a Peltier element composed of a pair of P-type thermoelectric semiconductors and N-type thermoelectric semiconductors.

In FIG. 10, reference numeral 1 denotes a Peltier element,
Metal electrode 1d that connects one terminal of the N-type thermoelectric semiconductor 1a to one terminal of the N-type thermoelectric semiconductor 1b, the N-type thermoelectric semiconductor 1b, and the N-type thermoelectric semiconductor 1b. Metal electrode 1e formed on one terminal, metal electrode 1f formed on the other terminal of P-type thermoelectric semiconductor 1a, P-type thermoelectric semiconductor 1a and N-type thermoelectric semiconductor 1b
And a ceramic plate 1h arranged on the side where the P-type thermoelectric semiconductor 1a and the N-type thermoelectric semiconductor 1b are not connected.

The P-type thermoelectric semiconductor 1a and the N-type thermoelectric semiconductor 1b are thermoelectric semiconductors usually made of bismuth tellurium as a basic material. The P-type thermoelectric semiconductor 1a, the N-type thermoelectric semiconductor 1b, and the ceramic plate 1g And 1 h is very small.

A battery 3 has a positive electrode connected to the metal electrode 1e and a negative electrode connected to the metal electrode 1f as shown in FIG.

Therefore, the current flows in the direction of the arrow in FIG. That is, electrons move from the P-type thermoelectric semiconductor toward the N-type thermoelectric semiconductor on the metal electrode 1d side, and electrons move from the N-type thermoelectric semiconductor toward the P-type thermoelectric semiconductor on the metal electrodes 1e and 1f. Moving.

The fact that electrons move from the P-type thermoelectric semiconductor to the N-type thermoelectric semiconductor on the metal electrode 1d side means that electrons move from a low energy state to a high energy state. On the 1d side, the vibration energy of the crystal lattice of the surrounding material is absorbed. That is, 1 g of the ceramic plate is cooled.

On the other hand, the fact that electrons move from the N-type thermoelectric semiconductor to the P-type thermoelectric semiconductor on the side of the metal electrodes 1e and 1f means that the electrons shift from a high energy state to a low energy state. Therefore, the metal electrodes 1e and 1
On the f side, the released energy is supplied to the surrounding substances. That is, the ceramic plate 1h is heated.

When the polarity of the battery is reversed from that in FIG. 10, the ceramic plate 1g is heated and the ceramic plate 1h is cooled.

That is, since the heating and cooling of the Peltier element differ depending on the direction of the current, the laser diode chip is die-bonded to one of the ceramic plates, and if the current is switched, the temperature of the laser diode chip is reduced. It can be controlled in any direction. The heating or cooling effect depends on the magnitude of the current, and the Peltier element usually needs to flow on the order of amperes.

A one-stage module in which a plurality of pairs of P-type and N-type thermoelectric semiconductors as shown in FIG. 10 are electrically connected in parallel, and a pair of P-type and N-type thermoelectric semiconductors as shown in FIG. There is a multistage module in which a plurality of modules are serially connected, but the multistage module can increase the temperature difference between the cooling side and the heating side. However, in the case of a multi-stage module, the driving voltage naturally increases.

Therefore, if a Peltier element is used for the temperature control method of the laser diode, there is a possibility that the drive circuit for supplying the current becomes large and the drive circuit generates noise. In this sense, it is important to practically use a laser diode temperature control method that can be miniaturized and generates a low noise level.

[0022]

2. Description of the Related Art FIG. 7 shows a conventional Peltier element driving circuit (part 1) in which a pulse width modulation method (often referred to as "PWM") in which heat absorption and heat generation of a Peltier element are controlled by controlling a duty ratio of a driving pulse. The method is called “P.
"WM" is an abbreviation for "Pulse Width Modulation".)

In FIG. 7, reference numeral 1 denotes a Peltier element;
Is a resistor connected in series to the Peltier element, 101 is an inverter for inverting the logic level of the drive pulse, and 102 to 105 are opened and supplied when the logic level of the supplied pulse is "1", for example. This switch is short-circuited when the pulse logic level is "0".

If the operation of the switch is defined as above, FIG. 8 shows a case where the logic level of the drive pulse is "1". That is, if the logical level of the drive pulse is "1", the logical level of the output of the inverter 101 is "0", so that the switches 103 and 104 are short-circuited and the switches 102 and 105 are open. Peltier current flows in the direction shown by the thin solid line arrow in FIG.

On the other hand, the logic level of the drive pulse is "0"
7, the logical level of the output of the inverter 101 becomes “1”, so that the switches 102 and 105 are short-circuited, and the switches 103 and 104 are opened.
, A Peltier current flows in a direction opposite to the direction indicated by the thin solid arrow.

As described above, when an electric current flows from the N-type thermoelectric semiconductor to the P-type thermoelectric semiconductor, the energy level of electrons at the connection between the P-type thermoelectric semiconductor and the N-type thermoelectric semiconductor is high. To a lower state to absorb the vibrational energy of the surrounding crystal lattice, so that the amount of heat absorbed increases and the temperature decreases.

On the other hand, when a current flows from the P-type thermoelectric semiconductor to the N-type thermoelectric semiconductor, at the connection portion, the energy level of electrons transits from a low state to a high state, and vibration energy is transferred to the surrounding crystal lattice. Increase the temperature as it is supplied.

Therefore, according to the method of controlling the direction of the current of the Peltier element 1 by the driving pulse as described above,
When the duty ratio of the drive pulse is 50%, the increase / decrease in the amount of heat absorbed is balanced, and there is no change in the temperature of the junction. When the duty ratio of the drive pulse is increased / decreased from 50%, the temperature of the connection becomes lower. It rises or falls as the ratio increases or decreases.

Using the above characteristics of the Peltier element, the oscillation wavelength of the laser diode can be stabilized by controlling the duty ratio of the drive pulse by the output of the temperature sensor or the oscillation wavelength sensor of the laser diode. it can.

Further, according to the configuration shown in FIG. 7, the Peltier element driving circuit can be easily formed into a single power supply circuit.

FIG. 8 shows an outline of a method of controlling a Peltier current by a DC input voltage in a conventional Peltier device driving circuit (No. 2).

In FIG. 8, reference numeral 1 denotes a Peltier element;
Is a resistor connected in series to the Peltier element 1, 101 is an inverter for inverting the logic level of the input signal, 11 is
Reference numeral 1 denotes a voltage determination circuit that determines the value of the input voltage and outputs a signal of a logical level “1” or “0”;
8 is a current source whose current is controlled by the value of the input voltage;
Switches 109 and 110 are opened when the logic level of the supplied signal is "1" and short-circuited when the logic level of the supplied signal is "0".

If the operation of the switch is defined as described above, FIG. 8 shows a case where the logic level of the output of the voltage judgment circuit 111 is "1". That is, if the logic level of the output of the voltage determination circuit 111 is “1”, the logic level of the output of the inverter 101 is “0”.
Is short-circuited, and the switch 109 is opened. At this time, a Peltier current flows in a direction indicated by a thin solid line arrow in FIG.

On the other hand, when the logic level of the output of the voltage judgment circuit 111 becomes "0", the logic level of the output of the inverter 101 becomes "1", so that the switch 109 is short-circuited and the switch 110 is opened. 8, a Peltier current flows in a direction opposite to the direction shown by the thin solid line arrow.

Accordingly, one of the switches 109 or 110 is short-circuited depending on whether the input voltage is higher or lower than a predetermined voltage, and the current source 107 or 1 is selected depending on the value of the input voltage.
By controlling the current 08, the amount of heat absorbed by the Peltier element can be controlled.

Then, the oscillation wavelength of the laser diode is stabilized by controlling the value of the input voltage by the output of a temperature sensor thermally connected to the laser diode or the oscillation wavelength sensor of the laser diode. be able to.

Since the direction of the Peltier current is controlled by the DC voltage, the configuration of FIG. 8 has an advantage that the noise level generated is lower than that of the configuration of FIG.

[0038]

However, there are problems in both the configuration of FIG. 7 and the configuration of FIG.

First, the problem of the configuration shown in FIG. 7 is that the level of noise generated is extremely high because an ampere-order current is switched by pulse driving. That is, if the noise generated by the drive circuit of the Peltier element leaks into the circuit for processing the data to be transmitted after being converted into light, it causes a code error in the data. Is modulated by the noise, which again causes a code error. In particular, the effect of noise is large in an electroabsorption optical modulator.

Next, in the case of the configuration shown in FIG. 8, in order to use the Peltier element 1 connected to the ground via the resistor 106, two power supplies of a positive power supply V _CC and a negative power supply V _EE are required. . As described many times, since the drive current of the Peltier device is on the order of amperes, the need for two power supplies means an increase in the size of the drive circuit of the Peltier device.

[0041] Further, the ground instead of the negative power supply V _EE, the voltage of the connection destination of the Peltier element 1 and the resistor 2 (1/2) V _CC
It seems that a single power supply can be used, but (1/2) V
_The circuit that generates _CC also needs to be configured with one power supply capable of flowing in and out of the Peltier current, and eventually becomes a circuit of two power supplies.

In both the configuration of FIG. 7 and the configuration of FIG.
In many cases, a multi-stage module having a large number of stages is used for the purpose of increasing the thermal efficiency.

FIG. 9 shows a configuration in which the heating and cooling Peltier elements are used separately so that the power supply voltage can be reduced.

In FIG. 9, reference numeral 1 denotes a Peltier element, and a first thermoelectric semiconductor section 1c-1 and a second thermoelectric semiconductor section 1c-
2, composed of a ceramic plate 1g and a ceramic plate 1h. Here, the first thermoelectric semiconductor section 1c-1 and the second thermoelectric semiconductor section 1c-2 are a P-type thermoelectric semiconductor 1a, an N-type thermoelectric semiconductor 1b, and a metal electrode 1 according to FIG.
The portions corresponding to d, 1e and 1f are generally formed by electrically connecting a large number of thermoelectric semiconductor pairs in series. Originally, all the thermoelectric semiconductors are connected in series, but in the case of FIG. 9, they are divided into two parts. This is connected to a drive circuit to which a switch for selecting heating or cooling is added in the configuration of FIG. 7 or FIG.
By supplying currents in different directions to c-1 and the second thermoelectric semiconductor section 1c-2, heating or cooling can be selected by one drive circuit and the power supply voltage can be reduced.

However, the above effect can be obtained with a penalty of reducing the heat effect of heating or cooling to half. Conversely, while maintaining the heat effect of heating or cooling, FIG.
When the configuration of the above is applied, naturally, the mounting area is 2
The disadvantage of doubling occurs.

The present invention has been made in view of the above problems, and has
The present invention relates to a diode temperature control method. In particular, the temperature of a laser diode can be controlled with a single low-voltage power supply, the temperature control efficiency is high, and the noise level generated by the temperature control is low. It is intended to provide a control method.

[0047]

According to a first aspect of the present invention, in a temperature control method for a laser diode using a Peltier element, an electric heater is formed on one surface of a ceramic plate constituting the Peltier element, and a laser heater is provided. This is a laser diode temperature control method for selecting either cooling control by the thermoelectric semiconductor constituting the Peltier element or heating control by the electric heater in accordance with the voltage at which the temperature of the diode is detected.

According to the first aspect, an electric heater is formed on one surface of the ceramic plate constituting the Peltier element, and the thermoelectric element constituting the Peltier element is provided in accordance with the voltage detected by detecting the temperature of the laser diode. Since the temperature control of the laser diode is performed by selecting either the cooling control by the semiconductor or the heating control by the electric heater, it is possible to draw out all the cooling capacity of the thermoelectric semiconductor or to reduce the heating capacity of the electric heater. All can be pulled out and a wide temperature control range can be obtained.

According to a second aspect of the present invention, in the laser diode temperature control method according to the first aspect, the electric heater or the thermoelectric semiconductor is divided into a plurality of parts, and the temperature of the laser diode is detected in accordance with a detected voltage. This is a temperature control method of a laser diode for selecting either cooling control by the thermoelectric semiconductor or heating control by the electric heater and variably controlling the number of the thermoelectric semiconductors or the electric heaters to be driven.

According to the second aspect of the invention, the electric heater or the thermoelectric semiconductor is divided into a plurality of parts, and cooling control by the thermoelectric semiconductor or heating by the electric heater is performed in accordance with the detected voltage of the laser diode. Since any one of the controls is selected and the number of the thermoelectric semiconductors or the electric heaters to be driven is variably controlled, the accuracy of the temperature control can be improved and a wide temperature control width can be obtained, and
The voltage for driving the divided thermoelectric semiconductors or the divided electric heaters can be reduced.

According to a third aspect of the present invention, in any one of the first and second aspects of the laser diode temperature control method, an element constituting a circuit for supplying a current to the electric heater is formed by forming the electric heater. This is a method for controlling the temperature of a laser diode mounted on the surface of the ceramic plate.

According to the third aspect of the present invention, since elements constituting a circuit for supplying a current to the electric heater are mounted on the surface of the ceramic plate, heat generation on the ceramic plate increases. If the efficiency improvement or the heating control efficiency can be kept constant, the power supply voltage can be reduced.

[0053]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the technique of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a basic configuration (No. 1) of a composite element of a Peltier element and an electric heater.

In FIG. 1, reference numeral 1c denotes a thermoelectric semiconductor portion, which corresponds to the P-type thermoelectric semiconductor 1a, the N-type thermoelectric semiconductor 1b, and the metal electrodes 1d, 1e and 1f in FIG. Has a large number of thermoelectric semiconductor pairs electrically connected in series. 1g and 1h are ceramic plates.

Reference numeral 5 denotes a laser diode mounted on the ceramic plate 1g by a technique such as die bonding, and reference numeral 6 denotes an electric heater formed on the ceramic plate 1g.

In FIG. 1, wiring for connecting the thermoelectric semiconductor section 1c, the laser diode 5, and the electric heater 6 to a power supply is not shown.

FIG. 2 shows a basic configuration (part 2) of a composite element of a Peltier element and an electric heater.

In FIG. 2, reference numeral 1c denotes a thermoelectric semiconductor portion, and 1g
And 1h, a ceramic plate 5 is a laser diode mounted on the ceramic plate 1g by a technique such as die bonding, and 6 is an electric heater formed on the ceramic plate 1g.

In FIG. 2, wires for connecting the thermoelectric semiconductor section 1c, the laser diode 5, and the electric heater 6 to a power supply are not shown.

The configuration shown in FIG. 1 and the configuration shown in FIG.
Is formed on the upper surface of the ceramic plate 1g or on the side surface of the ceramic plate 1g, but they are exactly the same in that the heating is controlled by forming an electric heater on the ceramic plate 1g. As described above, since the electric heater 6 for heating control is formed on the ceramic plate 1g, the entire thermoelectric semiconductor section 1c can be used for cooling control. That is, the cooling control and the heating control can be performed by using the configuration of FIG. 1 or FIG. 2 while utilizing all the cooling control capabilities of the thermoelectric semiconductor.

The electric heater 6 can be formed by vapor deposition when nichrome or the like is used, and can be formed by printing technology when a thick film resistor is used. or,
In the case of the configuration shown in FIG. 2, it should be noted that since there may be a limit to the thickness of the ceramic plate 1g, selection of design parameters for the electric heater may be slightly restricted.

FIG. 3 shows a driving circuit for the Peltier element and the electric heater corresponding to the configuration of FIG. 1 or FIG.

In FIG. 3, 7-1 to 7-3, 7-1
3 to 7-15 are resistors; 8-1 and 8-5 are comparators that output a signal of a logic level "0" or a logic level "1" according to the magnitude relation of voltages supplied to two input terminals; And 9-5 are power transistors, 7-
19 is a resistor for determining the current of the power transistor 9-1, 7-23 is a resistor for determining the current of the power transistor 9-5, 1 is a Peltier element, and 6 is an electric heater (in the figure, abbreviated simply as "heater"). 7-25 and 7-30 are resistors constituting a resistor voltage dividing circuit for generating a reference voltage to be supplied to the comparators 8-1 and 8-5. .

Here, the voltage at which the temperature of the laser diode is detected (the laser diode and the temperature detecting element are not shown in FIG. 3; the "voltage at which the temperature of the laser diode is detected" is defined as the input voltage. It is assumed that the cooling control is performed by driving the Peltier element when the input voltage is higher than the reference voltage, and the heating control is performed by driving the electric heater when the input voltage is lower than the reference voltage. FIG.
Is shown. Therefore, the reference voltage is supplied to the comparator 8-
1 and the non-inverting input terminal of the comparator 8-5, and the input voltage is supplied to the non-inverting input terminal of the comparator 8-1 and the inverting input terminal of the comparator 8-5.

If the input voltage is higher than the reference voltage, the comparator 8-1 outputs a signal of logic level "1" and the comparator 8-5 outputs a signal of logic level "0". In this case, the Peltier element 1 is driven to perform cooling control.

Conversely, when the input voltage is lower than the reference voltage, the comparator 8-1 outputs a signal of logic level "0", and the comparator 8-5 outputs a signal of logic level "1". Therefore, in this case, the electric heater 6 is driven to perform heating control.

Therefore, the cooling control and the heating control of the laser diode can be performed by using the composite element of the Peltier element and the electric heater having the structure of FIG. 1 or 2 connected to the drive circuit having the structure of FIG. Can be.

FIG. 3 shows a configuration in which one reference voltage is set, and cooling control is performed when the input voltage is higher than the reference voltage, and heating control is performed when the input voltage is lower than the reference voltage. When it is desired to provide a difference between the input voltages for performing the control and the heating control, for example, a reference voltage higher than the reference voltage in FIG. 3 may be supplied to the comparator 8-1. When it is desired to provide an overlap, for example, a reference voltage lower than the reference voltage in FIG.

FIG. 4 shows a configuration of a composite element in which a Peltier element and an electric heater are divided. In this example, the Peltier element and the electric heater are divided into two parts. It should be noted that the example of dividing into two is shown only for the purpose of avoiding complication of the drawing, and it is also possible to divide each into three or more.

In FIG. 4, 1c-1 is a first thermoelectric semiconductor portion, 1c-2 is a second thermoelectric semiconductor portion, 1g and 1h are ceramic plates, and 5 is a technology such as die bonding on a ceramic plate 1g. Laser diode, implemented with
6-1 is a first electric heater formed on the ceramic plate 1g, and 6-2 is a second electric heater formed on the ceramic plate 1g.

In FIG. 4, the first thermoelectric semiconductor section 1c-1, the second thermoelectric semiconductor section 1c-2, the laser diode 5, the first electric heater 6-1 and the second electric heater 6 are also provided. The wiring for connecting -2 to the power supply is not shown. Further, the first thermoelectric semiconductor section 1c-1 and the second thermoelectric semiconductor section 1c-2 are driven independently, and the first electric heater 6-
First, the second electric heater 6-2 is driven independently.

FIG. 5 shows a drive circuit in the case where the Peltier element and the electric heater are divided. Here, although the number of divisions does not match that in FIG. 4, the case where the Peltier element is divided into four and the electric heater is divided into two parts is shown. 4 shows a drive circuit.

In FIG. 5, 7-1 to 7-18 are resistors, and 8-1 to 8-6 are logic level "0" or logic level "1" depending on the magnitude of the voltage supplied to the two input terminals. Comparators for outputting signals, 9-1 to 9-
6, a power transistor; 7-19, a resistor for determining the current of the power transistor 9-1; 7-20, a resistor for determining the current of the power transistor 9-2;
Is a resistor that determines the current of the power transistor 9-3,
7-22 is a resistor for determining the current of the power transistor 9-4, 7-23 is a resistor for determining the current of the power transistor 9-5, and 7-24 is a power transistor 9-.
6 is a resistor for determining the current, 1-1 to 1-4 are Peltier elements divided into four, 6-1 and 6-2 are electric heaters divided into two, and 7-25 to 7-30 are comparators 8-1.
And 8-6, which constitute a resistance voltage dividing circuit for generating a reference voltage to be supplied to the resistors.

Here, when the input voltage at which the temperature of the laser diode is detected is higher than the reference voltage D, the Peltier element is driven to perform cooling control, and when the input voltage is lower than the reference voltage D, the electric heater is driven. FIG. 3 is shown assuming that heating control is performed. Therefore, the reference voltage D is applied to the inverting input terminal of the comparator 8-4 and the comparator 8-5.
, The highest reference voltage A to the inverting input terminal of the comparator 8-1, the second highest reference voltage B to the inverting input terminal of the comparator 8-2, and the third highest reference voltage C Is supplied to the inverting input terminal of the comparator 8-3, and the lowest reference voltage E is supplied to the non-inverting input terminal of the comparator 8-6.

When the input voltage is higher than the reference voltage A, the comparators 8-1 to 8-4 output signals of the logic level "1", and the comparators 8-5 and 8-6.
Outputs a signal of a logic level "0". In this case, all of the Peltier elements 1-1 to 1-4 are driven to perform cooling control. When the input voltage is lower than the reference voltage A and higher than the reference voltage B, the comparators 8-2 to 8-4 output signals of the logic level "1", and the comparators 8-5 and 8-6 output the logic level "1". Since a signal of level "0" is output, in this case, the Peltier elements 1-2 to 1-4 are driven to perform cooling control. Similarly, when the input voltage is lower than the reference voltage B and higher than the reference voltage C, the comparators 8-3 and 8-4 output signals of the logic level "1", and the comparators 8-5 and 8-6.
Outputs a signal of a logic level "0". In this case, the Peltier elements 1-3 and 1-4 are driven to perform cooling control, and the input voltage is lower than the reference voltage C and the reference voltage D
If higher, the comparator 8-4 outputs a signal of logic level "1", and the comparators 8-5 and 8-6
Outputs a signal of logic level "0", and in this case, the Peltier element 1-4 is driven to perform cooling control.

Further, when the input voltage is lower than the reference voltage D and higher than the reference voltage E, the comparators 8-1 to 8-8
-4 outputs a signal of logic level "0", and the comparator 8-5 outputs a signal of logic level "1". In this case, the electric heater 6-1 is driven to perform heating control. When the input voltage is lower than the reference voltage E, the comparators 8-1 to 8-4 output signals of logic level "0", and the comparators 8-5 and 8-6 output signals of logic level "1". In this case, the electric heaters 6-1 and 6-2 are driven to perform heating control.

In other words, according to the configuration of FIG. 5, each of the divided Peltier element and the electric heater can be driven independently, so that the cooling control and the heating control correspond to the voltage at which the temperature of the laser diode is detected. The cooling capacity or the heating capacity can be maximized. That is, the cooling control or the heating control can be performed with high accuracy, and the range of the cooling control or the heating control can be expanded.

Furthermore, since the Peltier element and the electric heater are divided, the driving voltage can be set low.

In the structure shown in FIG. 5, when a specific power transistor is driven, a difference may be provided between input voltages for driving the next power transistor, or a specific power transistor may be driven. Sometimes it is possible to have overlapping input voltages that drive the front and rear power transistors.

FIG. 6 shows a structure in which the elements constituting the electric heater driving circuit are mounted on a ceramic plate, and corresponds to the composite element shown in FIG. 1 and the driving circuit shown in FIG.

In FIG. 6, 1g is a ceramic plate constituting a Peltier element, 5 is a laser diode, 6 is an electric heater, and 9-5 is a power transistor.

That is, the configuration of FIG. 6 is an example in which only the power transistor 9-5 in the drive circuit of the electric heater in FIG. 3 is mounted on the ceramic plate 1g. A technique such as die bonding can be applied as a mounting technique of the power transistor.

In FIG. 6, wirings for connecting the laser diode 5, the electric heater 6, and the power transistor 9-5 to a power supply are not shown.

According to the configuration of FIG. 6, since the power transistor 9-5 for driving the electric heater is mounted on the ceramic plate 1g, the heat generated by the power transistor 9-5 can also be used for heating control. If the heating control efficiency can be improved or the heating control efficiency can be kept constant, the power supply voltage can be reduced.

Although FIG. 6 shows an example in which only the power transistor is mounted on the ceramic plate, it is needless to say that a resistor connected to the power transistor can also be mounted.

It should be noted that the power transistor for driving the Peltier element must not be mounted on the ceramic plate on which the electric heater is formed.
This is because the driving of the Peltier element is performed in the case of the cooling control, and thus the cooling capacity is impaired by mounting the power transistor for driving the Peltier element.

[0088]

As described above in detail, according to the present invention, a laser diode which can control the temperature with a single low-voltage power supply, has a good temperature control efficiency, and has a low noise level generated by the temperature control. Temperature control method can be realized.

That is, according to the first invention, an electric heater is formed on the surface of the ceramic plate constituting the Peltier element, and the thermoelectric element constituting the Peltier element is formed in accordance with the voltage detected by detecting the temperature of the laser diode. Since the temperature control of the laser diode is performed by selecting either the cooling control by the semiconductor or the heating control by the electric heater, it is possible to draw out all the cooling capacity of the thermoelectric semiconductor or to reduce the heating capacity of the electric heater. All can be pulled out, and a wide temperature control range can be obtained. Moreover,
Temperature control is possible with a single power supply.

Further, according to the second invention, the electric heater or the thermoelectric semiconductor is divided into a plurality of parts, and the cooling control by the thermoelectric semiconductor or the electric heater is performed in accordance with the voltage at which the temperature of the laser diode is detected. Since the number of the thermoelectric semiconductors or the number of the electric heaters to be driven is controlled variably by selecting any one of the heating control by, the accuracy of the temperature control can be improved and a wide temperature control width can be obtained, and The voltage for driving the divided thermoelectric semiconductor or the divided electric heater can be reduced. In addition, temperature control is possible with a single power supply.

Further, according to the third aspect of the present invention, since an element constituting a circuit for supplying a current to the electric heater is mounted on the surface of the ceramic plate, the power consumed on the ceramic plate increases. Therefore, the efficiency of heating control can be improved or the power supply voltage can be reduced.

[Brief description of the drawings]

FIG. 1 is a basic configuration of a composite element including a Peltier element and an electric heater (part 1).

FIG. 2 is a basic configuration of a composite element including a Peltier element and an electric heater (part 2).

FIG. 3 is a drive circuit of a Peltier element and an electric heater corresponding to the configuration of FIG. 1 or FIG. 2;

FIG. 4 shows a configuration of a composite element in which a Peltier element and an electric heater are divided.

FIG. 5 is a drive circuit in the case where a Peltier element and an electric heater are divided.

FIG. 6 shows a configuration in which elements constituting an electric heater driving circuit are mounted on a ceramic plate.

FIG. 7 shows a conventional Peltier device driving circuit (No. 1).

FIG. 8 shows a conventional Peltier device driving circuit (No. 2).

FIG. 9 shows a configuration using Peltier elements for heating and heat absorption.

FIG. 10 shows the principle of cooling and heating using a Peltier element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Peltier element 1-1, 1-2, 1-3, 1-4 Peltier element 1a P-type thermoelectric semiconductor 1b N-type thermoelectric semiconductor 1c Thermoelectric semiconductor part 1c-1 First thermoelectric semiconductor part 1c-2 Second 1d, 1e, 1f Metal electrodes 1g, 1h Ceramic plate 3 Battery 5 Laser diode 6 Electric heater 6-1 First electric heater 6-2 Second electric heater 7-1 to 7-30 Resistance 8 -1, 8-2, 8-3, 8-4, 8-5, 8-6 Comparator 9-1, 9-2, 9-3, 9-4, 9-5, 9-6 Power transistor 101 Inverters 102, 103, 104, 105 Switches 106 Resistors 107, 108 Current sources 109, 110 Switches 111 Voltage judgment circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01S 5/022 H01S 5/022

Claims (3)

[Claims] 1. A temperature control method for a laser diode using a Peltier element, wherein an electric heater is formed on one surface of a ceramic plate forming the Peltier element, and the temperature of the laser diode is reduced to a detected voltage. A temperature control method for a laser diode, wherein one of cooling control by a thermoelectric semiconductor constituting the Peltier element and heating control by the electric heater is selected accordingly. 2. The laser diode temperature control method according to claim 1, wherein the electric heater or the thermoelectric semiconductor is divided into a plurality of parts, and the temperature of the laser diode is changed according to a detected voltage. A temperature control method for a laser diode, wherein either cooling control or heating control by the electric heater is selected, and the number of the driven thermoelectric semiconductors or the electric heater is variably controlled. 3. The temperature control method for a laser diode according to claim 1, wherein an element constituting a circuit for supplying a current to the electric heater is a ceramic plate forming the electric heater. A temperature control method for a laser diode characterized by being mounted on the surface of a laser diode.