JP2006114774A - Wavelength stabilizing semiconductor laser equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength stabilizing semiconductor laser equipment with a control performance of wavelength kept stabilized even if drive current varies because a semiconductor laser deteriorates. <P>SOLUTION: The equipment comprises a power controller 6 controlling the drive current of a semiconductor laser 2 so that optical output power may become constant; and a heating controller 9 controlling the temperature of the semiconductor laser 2 so that drive voltage may become its target value by fixing the target value of the drive voltage, based on the drive current controlled by the power controller 6 on the basis of a property between the drive current and the drive voltage at a constant condition of optical output wavelength kept in advance. Although the oscillation wavelength of the optical resonator of the semiconductor laser 2 varies by carrier density variation depending on the drive current, and refractive index variation based on temperature optical effect depending on temperature, when the drive current varies because the semiconductor laser 2 deteriorates, the control performance of the wavelength stabilization can be kept by controlling to an optimal drive voltage considering its drive current variation for controlling the optical output wavelength constant. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wavelength-stabilized semiconductor laser device that stabilizes the optical output wavelength of a semiconductor laser regardless of changes over time.

  As a conventional wavelength-stabilized semiconductor laser device, a first control device that controls the drive current so that the optical output power of the semiconductor laser is constant, a temperature detector that detects the temperature of the heat sink on which the semiconductor laser is mounted, In order to correct the temperature error between the active layer of the semiconductor laser and the temperature detector, power consumption is obtained from the drive current and terminal voltage of the semiconductor laser, and the set temperature is corrected according to the obtained power consumption. And a third control device for controlling the Peltier element capable of heating and cooling the semiconductor laser so that the temperature detected by the temperature detector becomes the set temperature corrected by the second control device. (For example, refer to Patent Document 1).

Next, the operation will be described.
The driving current of the semiconductor laser is controlled by the first controller so that the optical output power becomes constant. The temperature of the heat sink on which the semiconductor laser is mounted is feedback controlled by the third control device using the temperature detected by the temperature detector mounted on the heat sink. The temperature error between the temperature of the temperature detector and the temperature of the active layer of the semiconductor laser is proportional to the power consumption of the semiconductor laser if the thermal resistance from the active layer of the semiconductor laser to the heat sink is constant and there is no heat flow from the outside. I think that. In the second control device, the power consumption is obtained from the drive current and the terminal voltage of the semiconductor laser, the set temperature is corrected by the power consumption, and the result is output to the third control device as the target temperature value. In particular, the temperature of the active layer of the semiconductor laser is kept constant, and the light output wavelength is stabilized.

JP-A-6-2839797

Since the conventional wavelength-stabilized semiconductor laser device is configured as described above, the optical output wavelength is stabilized by keeping the temperature of the active layer of the semiconductor laser constant, but the semiconductor laser deteriorates. Even if the drive current changes, the target temperature value is basically only corrected for the temperature error between the temperature of the temperature detector and the temperature of the active layer of the semiconductor laser. Therefore, there is a problem that the light output wavelength slightly shifts due to a change in carrier density according to a change in driving current, and the control performance is lowered in stabilizing the wavelength.
Further, there is a problem that the configuration becomes complicated by using the temperature detector.
Furthermore, a temperature difference is generated between the semiconductor laser and the heat sink in order to perform temperature stabilization by measuring the temperature on the heat sink that is some distance away from the semiconductor laser. The temperature difference between the semiconductor laser and the temperature detector can be approximated in proportion to the power consumption of the semiconductor laser when there is no heat flow from the outside to the top surface of the Peltier element. When there is a heat inflow, a temperature distribution change on the Peltier element surface according to the amount of heat occurs, and there is a problem that wavelength deviation occurs due to deviation from proportional approximation.

  Further, in Patent Document 1, a several millimeter square Peltier element for heating and cooling is mounted in a ceramic package generally used as a semiconductor laser device, and a laser chip, a thermistor, and the like are mounted on the Peltier element. The one with is shown. In this semiconductor laser device, the temperature on the Peltier element is controlled to be constant, and the temperature between the outside and the upper surface of the Peltier element is a kind of thermostat that is thermally insulated with air, so that the temperature on the Peltier element is kept constant. As a result, the amount of heat inflow is stabilized to some extent, so that the temperature error between the temperature of the thermistor and the temperature of the active layer of the laser chip can be proportionally approximated by the power consumption of the laser chip.

However, a module in which a Peltier element and a temperature detector are mounted generally has an expensive member, and there is a problem that cost reduction is difficult.
Further, the temperature stabilization control using the Peltier element has a problem that it is difficult to reduce the power consumption because a large power consumption is required because the efficiency of the Peltier element is low.
Furthermore, the response of the Peltier element is usually slow, and there is a problem that a control time in seconds is required.
Furthermore, in the case of a general Peltier-less optical module that does not use a Peltier element, a CAN type (CAN PACKAGE) low-priced package is used, but it is difficult to mount a temperature detector because the number of pins is limited. . If the temperature detector is mounted on the heat sink inside the Peltier-less optical module, the temperature detector, the active layer of the semiconductor laser, This temperature difference deviates from the proportional relationship with the power consumption of the semiconductor laser, and there is a problem that wavelength fluctuation occurs.

  The present invention has been made to solve the above-described problems. Even when the driving current changes due to deterioration of the semiconductor laser, the optimum optical output wavelength is taken into consideration in order to keep the optical output wavelength constant. An object of the present invention is to obtain a wavelength-stabilized semiconductor laser device that controls the drive voltage and improves the control performance of wavelength stabilization.

  The wavelength-stabilized semiconductor laser device according to the present invention determines a drive voltage target value corresponding to the drive current to the semiconductor laser based on the relationship used as a reference for the drive current and the drive voltage, and drives the drive voltage to the semiconductor laser. The temperature of the semiconductor laser is controlled so that becomes the target value.

According to the present invention, the oscillation wavelength of the optical resonator of the semiconductor laser changes due to the refractive index change due to the carrier density change depending on the drive current and the refractive index change due to the temperature optical effect depending on the temperature. When the drive current changes due to deterioration, it can be controlled to the optimum drive voltage (temperature) taking into account the change of the drive current in order to control the optical output wavelength constant, that is, carrier density change and temperature Both optical effects can be optimally controlled, and the control performance of wavelength stabilization can be improved.
Further, the configuration can be simplified without using a temperature detector.
Furthermore, since temperature is not detected when the optical output wavelength is controlled to be constant, there is no need to consider temperature distribution changes and the like, and there is an effect that deterioration of control performance can be prevented in stabilizing the wavelength.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a wavelength-stabilized semiconductor laser device according to Embodiment 1 of the present invention. In the figure, the semiconductor laser device 1 outputs light by passing a drive current, and light changes with temperature change of the active layer. A semiconductor laser 2 whose output wavelength varies, a heating element 3 provided in the vicinity of the semiconductor laser 2 to change the heat generation amount according to the amount of supplied current, and to control the temperature of the active layer of the semiconductor laser 2, and a photodiode And a light receiver (light output power detector) 4 that receives a part of the light output from the semiconductor laser 2 and converts it into a current signal.
FIG. 2 is a perspective view showing the appearance of the semiconductor laser device. In FIG. 2, a semiconductor laser driving current electrode 2a to which a driving current is input is integrated on a chip of the semiconductor laser 2 in the form of a thin film. The active layer 2b that outputs light according to the input of the drive current is integrated. Further, on the chip of the semiconductor laser 2, a thin film heater composed of a resistor as a heating element 3 is integrated in the vicinity of the active layer 2 b, and a heating element supply current electrode 3 a is integrated in a thin film shape.

In FIG. 1, a power monitor (light output power detector) 5 converts a current signal from the light receiver 4 into a light output power signal that is easy to handle. For example, it is configured by an impedance conversion circuit that converts a current signal input from the light receiver 4 into a voltage signal indicating optical output power, and linear conversion that linearly converts the current signal into a voltage signal may be used. A log conversion that weights a weak current signal may be used.
The power control unit (drive current control unit) 6 controls the drive current to the semiconductor laser 2 so that the optical output power signal input from the power monitor 5 is constant. The current monitor (drive current detector) 7 detects the drive current supplied to the semiconductor laser 2, and the voltage monitor (drive voltage detector) 8 detects the drive voltage supplied to the semiconductor laser 2. .
The heat generation control unit (temperature control unit) 9 is driven according to the drive current detected by the current monitor 7 based on the drive current versus drive voltage characteristics under a predetermined condition of the optical output wavelength of the semiconductor laser 2 held in advance. The target value of the voltage is determined, the supply current to the heating element 3 is controlled so that the drive voltage detected by the voltage monitor 8 becomes the target value, and the temperature of the active layer 2b of the semiconductor laser 2 is controlled. is there.

Next, the operation will be described.
In FIG. 1, the semiconductor laser 2 outputs light when a drive current supplied from the power control unit 6 flows. The light receiver 4 receives a part of the light output and converts it into a current signal. That is, the optical output power generated from the semiconductor laser 2 is converted into a current signal. The power monitor 5 converts the current signal into an optical output power signal and outputs it to the power control unit 6. The power control unit 6 controls the drive current so that the input optical output power signal is constant, that is, the optical output power generated from the semiconductor laser 2 is constant, and supplies it to the semiconductor laser 2. . For example, when the semiconductor laser 2 deteriorates due to a change over time or when the environmental temperature changes, the optical output power is controlled to be constant by changing the drive current.

The current monitor 7 detects the drive current, and the voltage monitor 8 detects the drive voltage to the semiconductor laser 2 at that time and outputs it to the heat generation control unit 9.
The heat generation control unit 9 determines a target value of the driving voltage of the semiconductor laser 2 according to the driving current detected by the current monitor 8, and the heating element 3 so that the driving voltage detected by the voltage monitor 9 becomes the target value. To control the temperature of the active layer 2b of the semiconductor laser 2.
As the heating element 3, for example, as shown in FIG. 2, a heating element integrated as a thin film heater made of a resistor is used in the vicinity of the active layer 2 b on the chip of the semiconductor laser 2. In this thin film heater, the amount of heat generated varies depending on the magnitude of the supplied current, and the temperature of the active layer 2b of the semiconductor laser 2 can be controlled. Such a thin film heater on the chip of the semiconductor laser 2 is low in cost, has high thermal efficiency, can reduce power consumption, and can increase the operating speed of wavelength control.

3 and 4 are characteristic diagrams showing drive current versus optical output power characteristics and drive current versus drive voltage characteristics.
The target value of the drive voltage corresponding to the drive current in the heat generation control unit 9 is determined using drive current versus drive voltage characteristics under a constant condition of the light output wavelength of the semiconductor laser 2 as shown in FIG. That is, in FIG. 3, when the optical output power is controlled to be constant Pc and the optical output wavelength is controlled to be constant λc, when the drive current detected by the current monitor 7 is Ic, the optical output wavelength at that time The target value of the driving voltage for stabilizing at constant λc is determined as Vc using the driving current vs. driving voltage characteristic.
Further, for example, when the semiconductor laser 2 deteriorates due to a change over time or the environmental temperature changes, as shown in FIG. 4, the optical output power is controlled at a constant Pc and the optical output wavelength is controlled at a constant λc. The drive current detected by the current monitor 7 changes from Ic to Ic + α. At that time, the target value of the drive voltage for stabilizing the optical output wavelength at a constant λc, and the drive current vs. drive voltage characteristic And determined as Vc + β.
The characteristics of the two lines in FIGS. 3 and 4 are drive current versus drive voltage characteristics under a constant condition of the optical output power Pc.

In general, the oscillation wavelength of an optical resonator of a semiconductor laser changes due to a refractive index change due to a carrier density change depending on a drive current and a refractive index change due to a temperature optical effect depending on temperature. In the first embodiment, the heat generation control unit 9 holds the drive current versus drive voltage characteristic under a constant condition of the light output wavelength in a state including temperature change and carrier density change, and drive according to the drive current at that time By controlling the temperature of the semiconductor laser 2 so as to reach the target value of the voltage, when the semiconductor laser 2 deteriorates and the drive current changes, the change in the drive current is controlled in order to keep the optical output wavelength constant. It is possible to control to the optimum driving voltage (temperature) in consideration, that is, it is possible to optimally control both the carrier density change and the temperature optical effect, and it is possible to improve the control performance of wavelength stabilization.
The drive current vs. drive voltage characteristics as shown in FIG. 3 and FIG. 4 may be acquired in advance for each semiconductor laser 2 and held and referred to by the heat generation control unit 9 as a data table. Alternatively, the heat generation control unit 9 may obtain and obtain a relational expression that holds true. The simplest data acquisition method is to change the temperature as a parameter and acquire the drive current vs. drive voltage characteristics.

In the first embodiment, as shown in FIG. 2, a thin film heater composed of a resistor is integrated as a heating element 3 in the vicinity of the active layer 2b on the chip of the semiconductor laser 2. A diode may be integrated instead of a resistor as the heating element 3. In this case, since the semiconductor laser 2 itself is composed of a semiconductor, it is easy to form a diode in the immediate vicinity of the active layer 2b. By integrating on the chip, the heating element 3 can be formed at a low cost and in the immediate vicinity of the active layer 2b of the semiconductor laser 2, so that the thermal efficiency is high, the power consumption can be reduced, and the operation speed of the wavelength control is increased. Can be fast. Furthermore, since the semiconductor laser device 1 can be formed in a small size, the semiconductor laser device 1 can be downsized.
In the first embodiment, the heating element 3 is used for the semiconductor laser device 1. However, if a temperature controller having a cooling function such as a Peltier element can be realized at a small size and low cost, the heating element 3 It may be used instead.

As described above, according to the first embodiment, the target value of the drive voltage corresponding to the drive current to the semiconductor laser 2 is determined based on the drive current versus drive voltage characteristics under a constant condition of the optical output wavelength. Since the temperature of the semiconductor laser 2 is controlled so that the drive voltage to the semiconductor laser 2 becomes the target value, the optical output wavelength is made constant when the semiconductor laser 2 deteriorates and the drive current changes. It is possible to control to the optimum driving voltage (temperature) in consideration of the change of the driving current in the control, that is, to control both the carrier density change and the temperature optical effect optimally, and to stabilize the wavelength. Control performance can be improved.
Further, the configuration can be simplified without using a temperature detector.
Further, since the temperature is not detected when the optical output wavelength is controlled to be constant, it is not necessary to consider the temperature distribution change and the like, and it is possible to prevent the control performance from degrading upon stabilizing the wavelength.
Furthermore, since the heating element 3 is used, the cost can be reduced, the power consumption can be increased, and the responsiveness can be increased as compared with the case where a Peltier element or the like is used. The semiconductor laser 2 can be reduced in size.
Furthermore, since the heating element 3 is used without using the temperature detector, an inexpensive module package such as a CAN type can be applied, and the cost can be further reduced.
Furthermore, since the heating element 3 is formed by forming a thin film heater made of a resistor on the chip of the semiconductor laser 2, the thin film heater on the chip is low in cost, has high thermal efficiency, can reduce power consumption, and can control wavelength. The operation speed can be increased. Furthermore, since the semiconductor laser device 1 can be formed in a small size, the semiconductor laser device 1 can be downsized.

Embodiment 2. FIG.
FIG. 5 is a perspective view showing the appearance of the semiconductor laser device according to the second embodiment of the present invention. In the figure, the semiconductor laser 2 is mounted on the heat sink 11, and the heating element 12 and the heating element supply current electrode 12a are arranged. It is a thing. Other configurations are the same as those in FIG.

Next, the operation will be described.
In the first embodiment, the heating element 3 and the heating element supply current electrode 3a are integrated in the form of a thin film on the chip of the semiconductor laser 2. However, in the second embodiment, the semiconductor laser 2 is mounted on the chip. A heating element 12 and a heating element supply current electrode 12a are arranged on a heat sink 11 to be mounted.
As described above, even if the heating element 12 is disposed on the heat sink 11, if the heating element 12 is disposed near the active layer 2 b of the semiconductor laser 2, the control performance can be maintained.

  As described above, according to the second embodiment, since the heating element 12 is disposed on the heat sink 11 of the semiconductor laser device 1, the heating element 3 and the heating element supply current electrode 3a are provided on the chip of the semiconductor laser 2. The configuration of the semiconductor laser 2 can be simplified without integration. Further, if the heating element 12 is formed of a thin film heater made of a resistor, the cost can be reduced, the thermal efficiency is high, the power consumption can be reduced, and the operation speed of wavelength control can be increased. Further, since the semiconductor laser device can be formed in a small size, the semiconductor laser device can be downsized.

Embodiment 3 FIG.
6 is a block diagram showing a wavelength-stabilized semiconductor laser device according to Embodiment 3 of the present invention. In the figure, a cooler 21 controls the temperature of the active layer of the semiconductor laser 2 by cooling. The cooling control unit (temperature control unit) 22 supplies a control current to the cooler 21 in accordance with the supply current from the heat generation control unit 9 and controls the cooling amount of the cooler 21.
FIG. 7 is a perspective view showing the appearance of the semiconductor laser device. In the figure, the cooler 21 is disposed under the heat sink 11 on which the semiconductor laser 2 shown in FIG. 2 is mounted, and includes three plates including hatched portions. And a Peltier element supply current electrode 21b disposed on the lowermost plate of the Peltier element 21a. Other configurations are the same as those in FIG.

Next, the operation will be described.
In the first embodiment and the second embodiment, the temperature control of the active layer 2b of the semiconductor laser 2 is performed only by controlling the heating element 3. However, in the third embodiment, the active layer 2b of the semiconductor laser 2 is controlled. Is controlled by the heating element 3 and the cooler 21, and the temperature of the entire semiconductor laser 2 is controlled in a low region.
In FIG. 6, the cooling control unit 22 supplies a control current to the cooler 21 according to the supply current from the heat generation control unit 9, and controls the cooling amount of the cooler 21.
As shown in FIG. 7, when the Peltier element 21 a is used as the cooler 21, the semiconductor laser 2 is cooled according to the current supplied to the Peltier element supply current electrode 21 b under the control of the cooling device 22.
In general, it is known that a semiconductor laser has a lower failure rate as the operating temperature is lower, and lowering the control target temperature is effective for ensuring reliability. In recent years, semiconductor lasers capable of operating at high temperatures have been put into practical use, but reliability can be improved by combination with the cooler 21.
The Peltier element 21a is operated according to the control current. However, the Peltier element 21a may be controlled to be turned on only when the supply current to the heating element 3 becomes a certain value or less.
Moreover, you may use a radiation fin instead of the Peltier device 21a as the cooler 21. FIG.

  As described above, according to the third embodiment, since the cooler 21 is used in addition to the heating element 3, the controlled target temperature can be set low, and the failure rate of the semiconductor laser device 1 can be set. Can be lowered.

1 is a block diagram showing a wavelength stabilized semiconductor laser device according to a first embodiment of the present invention. It is a perspective view which shows the external appearance of a semiconductor laser apparatus. It is a characteristic view which shows a drive current versus optical output power characteristic and a drive current versus drive voltage characteristic. It is a characteristic view which shows a drive current versus optical output power characteristic and a drive current versus drive voltage characteristic. It is a perspective view which shows the external appearance of the semiconductor laser apparatus by Embodiment 2 of this invention. It is a block diagram which shows the wavelength stabilization semiconductor laser apparatus by Embodiment 3 of this invention. It is a perspective view which shows the external appearance of a semiconductor laser apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Semiconductor laser apparatus, 2 Semiconductor laser, 2a Semiconductor laser drive current electrode, 2b Active layer, 3,12 Heat generating body, 3a, 12a Heating body supply current electrode, 4 Light receiver (light output power detection part), 5 Power monitor ( Optical output power detection unit), 6 Power control unit (drive current control unit), 7 Current monitor (drive current detection unit), 8 Voltage monitor (drive voltage detection unit), 9 Heat generation control unit (temperature control unit), 11 Heat sink , 21 cooler, 21a Peltier element, 21b Peltier element supply current electrode, 22 cooling controller (temperature controller).

Claims (6)

A semiconductor laser whose relationship between the drive current and the drive voltage is known, and
An optical output power detector for detecting the optical output power of the semiconductor laser;
A drive current control unit for controlling the drive current of the semiconductor laser so that the light output power detected by the light output power detection unit is constant;
A drive current detector for detecting a drive current supplied from the drive current controller to the semiconductor laser;
A drive voltage detector for detecting a drive voltage supplied from the drive current controller to the semiconductor laser;
Based on the relationship between the drive current and the drive voltage as a reference, a target value of the drive voltage corresponding to the drive current detected by the drive current detector is determined, and the drive voltage detected by the drive voltage detector is A wavelength-stabilized semiconductor laser device comprising: a temperature control unit that controls the temperature of the semiconductor laser so as to achieve the target value. The temperature controller
2. The wavelength-stabilized semiconductor laser device according to claim 1, wherein the temperature of the semiconductor laser is controlled by changing the amount of heat generated by the heating element. The heating element
3. The wavelength-stabilized semiconductor laser device according to claim 2, wherein the resistor is a resistor integrated on a semiconductor laser chip. The heating element
3. A wavelength-stabilized semiconductor laser device according to claim 2, wherein the wavelength-stabilized semiconductor laser device is a diode integrated on a semiconductor laser chip. The heating element
3. The wavelength-stabilized semiconductor laser device according to claim 2, wherein the wavelength-stabilized semiconductor laser device is disposed on a heat sink on which the semiconductor laser is mounted. The temperature controller
2. The wavelength-stabilized semiconductor laser device according to claim 1, wherein the temperature of the semiconductor laser is controlled by a change in the amount of heat generated by the heating element and a change in the amount of cooling by the cooler.

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