JPH0575193B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a temperature stabilization device for a semiconductor laser (laser diode; also referred to as LD) that can maintain the operating temperature of the semiconductor laser at a set temperature.

(Prior Art) Semiconductor lasers have recently been used in various devices equipped with optical systems because of their high conversion efficiency of output energy to input energy.
Incidentally, this semiconductor laser has a property that its oscillation frequency and oscillation output change depending on changes in the operating temperature of the semiconductor laser. Therefore, in order to keep the oscillation frequency and oscillation output of the semiconductor laser constant, it is required to maintain the operating temperature of the semiconductor laser at a set temperature.

(Problem to be Solved by the Invention) In order to maintain the set temperature of this semiconductor laser at a predetermined temperature, a temperature control device (see Japanese Patent Application Laid-open No. 1782-1982) having a Peltier element as a thermoelectric effect element is used. It can be considered to be used as a stabilizing device, but in the case of semiconductor lasers, the semiconductor laser itself generates heat due to the injected current. If the thermoelectric effect element is controlled so that the temperature approaches the set temperature, there is a problem in that the operating temperature deviates from the set temperature due to the heat generated by the semiconductor laser.

This problem will be explained in more detail using FIGS. 1 to 6. FIG. 1 shows a control circuit of a temperature control device having a conventional Peltier effect element.
FIG. 2 is a schematic diagram showing a thermoelectric converter _KZ in which a semiconductor laser is attached to the Peltier effect element. The control circuit includes a comparator circuit 1 and a transistor 2 which is configured complementary.
and a Peltier effect type element 3,
The thermoelectric converter K _Z includes a semiconductor laser 4 provided on one side of the Peltier effect element 3, a heat sink 5 provided on the other side, and a thermistor 6 built therein.

The thermistor 6 controls the operating temperature of the semiconductor laser 4.
It has a function of detecting the operating temperature T _T and converting the operating temperature T _T into an operating temperature converted voltage E _T , and this operating temperature converted voltage E _T is input to one terminal of the comparator circuit 1 . A reference voltage E _s corresponding to the set temperature T _s is input to the other terminal of the comparison circuit 1 . Comparison circuit 1
is this reference voltage E _S and its operating temperature conversion voltage E _T
The differential output is outputted to the transistor 2. Transistor 2 is composed of transistor 2a and transistor 2b, and E _T
> E _s (T _T > T _s ), Peltier effect element 3
The energization of the transistor 2 is controlled so that the semiconductor laser 4 is cooled by the Peltier effect element 3, and when E _T <E _s (T _T <T _s ), the semiconductor laser 4 is heated by the Peltier effect element 3. energization of the transistor 2 is controlled, thereby controlling the operating temperature T _T of the semiconductor laser 4 in a direction approaching the set temperature T _s ,
Equilibrium is reached. Let Te be the equilibrium temperature when this equilibrium state is reached.

By the way, the Peltier effect type element 3 has the characteristics shown in FIG. The characteristic diagram shown in FIG. 3 is for the Peltier effect element 3 of KSM-0211 manufactured by Komatsu Electronics. In FIG. 3, the vertical axis shows the amount of heat Q as a thermal load applied to this Peltier effect type element 3, and the horizontal axis shows the equilibrium current I ^e _p flowing through this Peltier effect type element 3.
, and the parameter ΔT is the operating temperature T _T (at this time, T _T = Te) when the equilibrium state is reached and the boundary temperature as the temperature on the heat radiation side of the Peltier effect element 3.
It is the temperature difference from T _h , and ΔT≡Te−T _h . A temperature difference ΔT=0 means that the equilibrium temperature Te is equal to the environmental temperature T _h .

By the way, as is clear from Fig. 3, in the case of a heating element (Q≠0), even if the temperature difference ΔT=0
Even at ℃, in order to dissipate the amount of heat Q,
This means that the equilibrium current I ^e _p flows through the Peltier effect element 3. Here, the operating temperature converted voltage _E T when the operating temperature T _T of the semiconductor laser 4 reaches the equilibrium temperature Te is defined as the equilibrium temperature corresponding voltage Ee. Further, if the voltage _- to ^- current conversion coefficient of the control circuit shown in FIG. Ee= _Es + _I1e /α... ₍ ¹ )

However, I ₁ ^e is the current flowing through the Peltier effect element 3 when trying to control the set temperature T _s and the environmental temperature T _h equally, and at this time, the reference voltage E _s
There is a relationship of E _s = E _h between E h and the environmental temperature corresponding voltage E _h .

Also, as shown in Figure 3, this equilibrium current I ₁ ^e and the amount of heat Q have a linear relationship in the range where the amount of heat Q is small, so if the conversion coefficient is β, the amount of heat Q is Q = β・I ₁ ^e is expressed by (2).

Therefore, using equations (1) and (2), the voltage Ee corresponding to the equilibrium temperature is expressed as Ee=E _s +Q/α·β (3). It should be noted that the fact that equation (3) holds true is also supported by experimental results. FIG. 4 is a diagram plotting the value of the amount of heat Q and the value of the voltage Ee corresponding to the equilibrium temperature obtained through the experiment.

This equation (3) is expressed as follows: When Q=0, if the reference voltage E _s is set equal to the environmental temperature corresponding voltage E _h ,
This shows that Ee= _ES (ΔT=0) because the control circuit performs control so that E _s −E _T =E _T −Ee=0, but when Q≠0, even if Trying to make the set temperature T _s equal to the environmental temperature T _h , E _s =
Even if E _h is set, Ee≠E _s ……(4) shows that. In other words, in the case of a heating element such as the semiconductor laser 4, Equation (3) expresses the equilibrium temperature corresponding voltage Ee corresponding to the equilibrium temperature Te.
does not match the reference voltage E _s corresponding to the set temperature T _s , and in this control circuit, the equilibrium temperature Te will shift with respect to the set temperature T _s . Note that the amount of heat Q is the semiconductor laser 4
The injection current I is proportional to _LD .

By the way, the environmental temperature T _h is not constant;
The set temperature T _S and the environmental temperature T _h
are not necessarily consistent. When the equilibrium temperature Te is different from the environmental temperature T _h (ΔT=Te−T _h ≠0), the Peltier effect element 3 has an equilibrium state as shown in FIG. 3 even when it is not a heating element. current
I ₂ ^e flows.

Figure 5 shows the relationship between ΔT=Te−T _h and equilibrium current I ₂ ^e when Q=0 for Peltier effect element 3.
The voltage Ee corresponding to the equilibrium temperature is calculated by the equation I ₂ ^e = α・(Ee−E _S ), Ee=E _s + I ₂ ^e /α (5) Here, the equilibrium temperature Te and In areas where the temperature difference ΔT from the environmental temperature T _h is small (ΔT≦15℃), the temperature difference ΔT
and the equilibrium current I ₂ ^e have a linear relationship.

Therefore, the temperature difference ΔT is ΔT=−γ·I ₂ ^e ……(6) However, the direction of flow of the equilibrium current I ₂ ^e flowing through the Peltier effect element 3 is correct when it flows in the direction to cool the sample. and γ is the conversion coefficient.

Using this equation (6), we transform equation (5) and express the voltage corresponding to the equilibrium temperature Ee as a function of the temperature difference ΔT, Ee=E _s −1/α・γ・ΔT ……(7) Become.

Therefore, using the circuit shown in Figure 1,
Equilibrium temperature corresponding voltage corresponding to equilibrium temperature Te when set temperature T _s and environmental temperature T _h do not match
Ee does not match the reference voltage _Es , and the difference "Ee- _Es " causes the equilibrium temperature Te to shift with respect to the set temperature _Ts by an amount proportional to ΔT. FIG. 6 is a graph showing this fact confirmed through experiments.

In other words, even if the set temperature T _s is constant, if the environmental temperature T _h changes, the temperature difference ΔT will change.
The equilibrium temperature Te will change under the influence of the environmental temperature T _h , and the operating temperature T _T will not be constant.

Next, if it is a heating element and the environmental temperature T _h and the set temperature T _S do not match, the equilibrium current I ^e _p
is expressed by I ^e _p =I ₁ ^e +I ₂ ^e =Q/β−ΔT/γ (8) according to the principle of superposition.

Transforming this equation (8) using equation (1), Ee−E _s = I ^e / _p / α = Q / α・β − ΔT / α・γ, and Ee = E _s Q / α・β −ΔT/α・γ……(9) is obtained.

As is clear from equation (9), as a means to bring the equilibrium temperature Te closer to the set temperature _Ts , regardless of Q and ΔT, the voltage-to-current conversion coefficient (also called current amplification factor) α should be made as large as possible. is possible. However, when this voltage/current conversion coefficient α is increased, overshoot occurs in proportion to the size of α, and on the contrary, the problem arises that the operating temperature T _T is not stable.

(Object of the Invention) An object of the present invention is to control a thermoelectric effect element in appropriate response to changes in the amount of heat generated by a semiconductor laser and changes in the environmental temperature around the semiconductor laser, thereby controlling the operating temperature of the semiconductor laser. An object of the present invention is to provide a temperature stabilizing device for a semiconductor laser that can always maintain the temperature at a set temperature.

(Means for Solving the Problems) The present invention is characterized in that, in a semiconductor laser temperature stabilization device that operates a semiconductor laser at a predetermined set temperature, a current supply source that supplies injection current to the semiconductor laser; a calorific value detection unit that detects the calorific value based on the injection current of the semiconductor laser;
an operating temperature detection section that is provided in the semiconductor laser and detects its operating temperature; an environmental temperature detection section that detects the environmental temperature around the semiconductor laser;
The thermoelectric effect element that transfers heat to and from the semiconductor laser, the output of its operating temperature detection section, and the output of its environmental temperature detection section are input, and the difference between its operating temperature and its environment temperature is determined. A difference correction output generation circuit that generates a difference correction output to correct the deviation between the operating temperature and its set temperature, and the output of its heat generation detection section are input, and the output of the heat generation amount detection section is inputted. A heat generation correction output generation circuit that generates a heat generation correction output to correct the deviation between the operating temperature and its set temperature based on the set temperature, and a reference voltage corresponding to the set temperature is applied, and the difference correction is performed. The reference voltage is corrected based on the difference correction output of the output generation circuit and the heat generation correction output of the output generation circuit for heat generation, and the correction reference voltage and its operation are corrected. and a control section that compares the output of the temperature detection section and controls the thermoelectric effect element so that its operating temperature matches the set temperature.

(Function) According to the present invention, the difference correction output generation circuit generates the difference correction output between the operating temperature and the environmental temperature, and the heat generation correction output generation circuit generates the heat generation correction output. The output for correcting the heat content and the output for correcting the difference are input to the control unit, and the control unit corrects the reference voltage corresponding to the set temperature based on the output for difference correction and the output for heat content correction. , outputs a corrected reference voltage. Then, the control section compares this corrected reference voltage with the output of the operating temperature detection section and controls the thermoelectric effect element so that its operating temperature matches the set temperature.

(Example) Examples of the present invention will be described below with reference to the drawings.

Figure 7 shows the reference voltage E _s1 corresponding to the set temperature T _s .
is applied, and the difference correction output generation circuit _K1 described later
The reference voltage E s1 is corrected to obtain the corrected reference voltage E _s2 (described later) based on the difference correction output E _c ″ of the output circuit K ₂ and the output E _{c ′} of the output generation circuit K _{2 (described later)} . The corrected reference voltage E _s2 is compared with the output of the operating temperature detection section, _and the operating temperature _T
7 shows the configuration of a control section K3 that controls the thermoelectric effect element 3 so that the values coincide with each other. In FIG. 7, 10 is an operational amplifier. This operational amplifier 1
A reference voltage E _s1 corresponding to the set temperature T _s is input to one terminal of the 0 terminal. A correction voltage E _c as a correction output is input to the other terminal of the operational amplifier 10 . This correction voltage E _c is a physical quantity proportional to the amount of heat Q of the semiconductor laser 4 and the temperature difference ΔT between the environmental temperature T _h and the set temperature T _s , and its correction output generation circuit will be described later. operational amplifier 1
0 is the difference between the reference voltage E _s1 and the correction voltage E _c ``E _s1 −
A corrected reference voltage E _s2 corresponding to "E _c " is outputted to the other terminal of the comparator circuit 1. The comparator circuit 1 compares the _operating temperature conversion voltage _E
and the operating temperature is controlled by the transistor 2.
The energization of the Peltier effect element 3 is controlled so that T _T reaches an equilibrium state.

Assuming that the operating temperature T _T reaches an equilibrium state through this control, equation (9) uses the corrected reference voltage E _s2 as Ee=E _s2 Q/α・β−ΔT/α・γ... It can be expressed as (10).

Since E _s2 =E _s1 −E _c , equation (10) can be transformed into the following equation: Ee=E _s1 −E _c Q/α・β−ΔT/α・γ (11).

In order for the equilibrium temperature Te to match the set temperature T _s ,
The difference between the reference voltage E _s1 and the equilibrium temperature corresponding voltage Ee must be "0".

Under this condition, if we transform equation (11), we get E _{c =} Q/α・β−ΔT/α from the equation Ee−E _s1 −E c Q/α・β−ΔT/α・γ=0・γ ……(12) Obtain the formula.

Therefore, in equation (12), E _c ′=Q/α・β ……(13) E _c ″=−ΔT/α・γ ……(14)

That is, E _c =E _c ′+E _c ″.

This symbol E _c ′ physically represents the correction voltage as the output for correcting the heat generation component, which is required to correct the deviation between the operating temperature T _T and the set temperature T _s based on the heat generation component of the semiconductor laser 4. The symbol E _c ″ means,
Physically, it means a difference correction voltage as a difference correction output for correcting the operating temperature T _T and the set temperature T _s based on the difference between the operating temperature T _T and the set temperature T _s . Therefore, this correction voltage E _c ′,
If E _c ″ is added as the control voltage E _c , the equilibrium temperature Te when the operating temperature T _T reaches an equilibrium state is set as the set temperature.
This means that it can be matched to T _s .

FIG. 8 shows an embodiment of the heating component correction generation circuit _K2 that generates the heating component correction voltage E _c '. Since the heat generation amount Q of the semiconductor laser 4 is proportional to the injection current _ILD as shown in FIG _. A fixed resistor R _F is provided in the middle of the series circuit, and the fact that the potential drop V is proportional to the injected current is utilized.

Expressing this using a mathematical formula, from Q=C・I _LD and V= _RF・I _LD , V= _RF・Q/C (15). However, symbol C is a conversion coefficient.

This voltage V is input to one terminal of the operational amplifier 11, and the variable resistor R _v connected to the operational amplifier 12
The amplification factor m is adjusted accordingly.

Since the output voltage output from the operational amplifier 12 is used as the heat generation compensation voltage E _c ',
E _c ′=mV, and from this equation, equations (13), and (15), the amplification factor m becomes m=C/R・1/α・β...(16). In this equation (16), all the physical quantities included in the terms on the right side can be regarded as constants, so the amplification factor m is uniquely determined.

Since the amplification factor m is m<1 and non-inverting amplification cannot be performed directly, in the embodiment, inverting amplification is performed twice.

FIG. 10 shows an embodiment of the difference correction output generation circuit _K1 that generates the difference correction voltage E _c ″.

In FIG. 10, 13 and 14 are thermistors, the thermistor 13 is built into the semiconductor laser 4, and the thermistor 14 is attached to the heat sink 5. The thermistor 13 functions as an operating temperature detection section that detects the operating temperature T _T of the semiconductor laser 4 . The thermistor 14 is connected to the ambient temperature
It functions as an environmental temperature detection section that detects T _h .
Detection outputs E _T1 and E _T1 detected by the thermistors 13 and 14 are input to an operational amplifier 17 via temperature-voltage conversion circuits 15 and 16, respectively. This operational amplifier 17 has a function of generating a voltage V _D proportional to the temperature difference ΔT.

Here, if the temperature/voltage conversion coefficient is expressed by the symbol n, the relationship between ΔT and voltage V _D can be expressed by the following formula: V _D =n·ΔT (17).

Therefore, if we decide to adjust the amplification factor m' by the variable resistor R _v ' connected to the operational amplifier 17, E _c ''=-ΔT/α・γ=m′・V _D =m′・n・ΔT Therefore, the amplification factor m′ is m′=−ΔT/n・α・γ……(18) Therefore, these correction output generation circuits K ₁ , K ₂
is connected to the control unit _K3 shown in FIG. 7 to constitute a semiconductor laser temperature stabilization device shown in FIG. 11,
By adjusting the amplification factors m and m', the operating temperature T T becomes the set temperature T _s regardless of the heat generation amount Q of the semiconductor laser 4 and the temperature difference _ΔT between the environmental temperature T _h and the operating temperature T _T
can be matched.

By the way, the temperature difference ΔT is linear only where ΔT is small, and if the temperature difference ΔT between the set temperature T _s and the environmental temperature T _h is too large, it cannot be considered linear (see FIG. 5).

In this case, the Peltier effect type elements 3 are provided in two stages. FIG. 12 shows this Peltier effect type element 3.
This figure shows the configuration of a thermoelectric converter K _z ' provided in two stages, where 18 is the first Peltier effect element, 19 is the second
The Peltier effect element 20 indicates a heat conductor. The thermal conductor 20 is the first Peltier effect element 18
A thermistor 21 is provided between the thermal conductor 20 and the second Peltier effect element 19 . This thermistor 21 is a thermal conductor 2
It has a function of detecting the temperature T _h ' of 0. this temperature
T _h ' has an intermediate value between the environmental temperature T _h and the operating temperature T _T , and this temperature T _h ' is treated as the environmental temperature T _h of the first Peltier effect element. Then, a temperature stabilizing device for a semiconductor laser shown in FIG. 13 is constructed. This temperature stabilizing device for a semiconductor laser includes a transistor 2' for controlling a Peltier effect element 19 and a comparator circuit 1'. A reference voltage E _s1 is applied to one terminal of the comparison circuit 1', and an environmental temperature corresponding voltage E _T2 ' output from the thermistor 21 is applied to the other terminal. Then, this environmental temperature corresponding voltage E _T2 ′ and the reference voltage E _s1 are compared, and the transistor 2 ′ is controlled based on the output of the difference, and the environmental temperature T _h
is controlled so that it approaches the temperature T _h ′. Also, the difference correction output E _c ″ is generated based on this temperature T _h ′ and the operating temperature _TT . Then, if this temperature T _h ′ is kept as close to the operating temperature _TT as possible,
Since ΔT=T _T −T _h ′ can be made small,
The first Peltier effect element 18 can be controlled in a linear region. Further, since the second Peltier effect element 19 can reduce changes in the environmental temperature T _h , the operating temperature T _T can be further maintained at the set temperature T _s .

In the above embodiments, a case has been described in which a Peltier effect type element is used as a thermoelectric effect type element, but a Thomson effect type element can also be used as a thermoelectric effect type element.

(Effects of the Invention) The present invention provides a current supply source that supplies injection current to a semiconductor laser, a heat generation amount detection section that detects the amount of heat generated based on the injection current of the semiconductor laser, and a heat generation amount detection section that is provided in the semiconductor laser and operates. An operating temperature detection section that detects temperature, an environmental temperature detection section that detects the environmental temperature around the semiconductor laser, a thermoelectric effect element that transfers heat between the semiconductor laser, and the operation temperature detection section. and the output of its environmental temperature detection section are input, and a difference correction output is generated based on the difference between the operating temperature and the environment temperature to correct the deviation between the operating temperature and the set temperature. The output of the output generation circuit and its heat generation detection section is input, and the heat generation circuit generates a heat generation correction output to correct the deviation between the operating temperature and the set temperature based on the heat generation of the semiconductor laser. A correction output generation circuit and a reference voltage corresponding to its set temperature are applied, and based on the difference correction output of the difference correction output generation circuit and the heat generation correction output of the heat generation correction output generation circuit. , corrects the reference voltage and outputs a corrected reference voltage, compares this corrected reference voltage with the output of its operating temperature detection section, and controls the thermoelectric effect element so that its operating temperature matches the set temperature. It is characterized by having a control section that controls the thermoelectric effect element in response to changes in the amount of heat generated by the semiconductor laser and changes in the environmental temperature around the semiconductor laser, thereby controlling the thermoelectric effect element. This has the effect that the operating temperature can always be kept at the set temperature.

The first thermoelectric effect element can be controlled in a linear region. Further, since changes in the environmental temperature can be reduced by the second thermoelectric effect element, the operating temperature can be further maintained at the set temperature.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a control circuit when a temperature stabilizing device for a semiconductor laser is configured using a temperature control device having a conventional Peltier effect element.
The figure is a configuration diagram showing a thermoelectric converter constructed by attaching a semiconductor laser to the Peltier effect element, Figure 3 is a characteristic diagram of the Peltier effect element showing the relationship between the amount of heat and the equilibrium current, and Figure 4 is a diagram showing the characteristics of the Peltier effect element. Figure 5, which is a diagram plotting the value of the amount of heat obtained through experiments and the value of the voltage corresponding to the equilibrium temperature, shows the Peltier effect type when the equilibrium temperature and the environmental temperature are different when the heat generating element is not used. A diagram showing the characteristics of the balanced current flowing through the device, FIG. 6 is a diagram showing experimental results when a Peltier effect device is controlled using the control circuit shown in FIG. 1, and FIG. 7 is a diagram showing the semiconductor laser according to the present invention. FIG. 8 is a configuration diagram of an output generation circuit for heat generation correction according to the present invention, and FIG. 9 is a circuit diagram showing a control section of a temperature stabilizing device of a semiconductor laser according to the present invention. A characteristic diagram showing the relationship between the amount of heat and the injection current of a semiconductor laser, FIG. 10 is a configuration diagram of a differential correction output generation circuit according to the present invention, and FIG. 11 is a diagram of a temperature stabilization device for a semiconductor laser according to the present invention. FIG. 12 is a circuit diagram showing the overall configuration, FIG. 12 is a diagram showing another configuration of the thermoelectric converter used in the semiconductor laser temperature stabilization device according to the present invention, and FIG. 13 is a circuit diagram of the semiconductor laser used in the thermoelectric converter. FIG. 2 is a circuit diagram showing the overall configuration of the temperature stabilization device. 3...Thermoelectric effect element, 4...Semiconductor laser, 9...Injection current supply source, 13...Operating temperature detection section (thermistor), 14...Environmental temperature detection section (thermistor), _K1 ...Differential correction output generation circuit for
K ₂ ... Output generation circuit for heat generation compensation, K ₃ ... Control section, T _h ... Environmental temperature, T _T ... Operating temperature, T _s ...
Set temperature, E _s , E _s1 ... Reference voltage, E _s2 ... Correction reference voltage, E c ′ ... Output for heat generation correction, E _{c '} ' ... Output for difference correction.

Claims (1)

[Scope of Claims] 1. A semiconductor laser temperature stabilization device that operates a semiconductor laser at a predetermined set temperature, comprising: a current supply source that supplies injection current to the semiconductor laser; and a heat generation amount based on the injection current of the semiconductor laser. an operating temperature detection section that is provided on the semiconductor laser and detects its operating temperature; an environmental temperature detection section that detects the environmental temperature around the semiconductor laser; A thermoelectric effect element that transfers heat between a difference correction output generation circuit that generates a difference correction output for correcting deviation from the set temperature; and an output of the heat generation amount detection section is inputted, and the operating temperature is adjusted based on the heat generation amount of the semiconductor laser. a heating component correction output generation circuit that generates a heating component correction output for correcting a deviation between the temperature and the set temperature; and a reference voltage corresponding to the set temperature is applied;
correcting the reference voltage and outputting a corrected reference voltage based on the difference correction output of the difference correction output generation circuit and the heat generation correction output of the heat generation correction output generation circuit; and a control section that compares the output of the operating temperature detection section and controls the thermoelectric effect element so that the operating temperature matches the set temperature. Device. 2. The thermoelectric effect element is a first thermoelectric effect element that is in contact with the semiconductor laser and directly exchanges heat with the semiconductor laser, and a first thermoelectric effect element that exchanges heat between the first thermoelectric effect element and the atmosphere. a second thermoelectric effect element;
2. The semiconductor laser temperature stabilization device according to claim 1, wherein the device is configured to detect the temperature between the thermoelectric effect element and the second thermoelectric effect element.