JPS63136584A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser device having high interchangeability and excellent wavelength controllability even in long-term usage by mounting a photodetector, sensibility of which monotonously depends upon a wavelength, and controlling an operating temperature so that the ratio of an output from the photodetector to an output from a photodetector, sensibility of which does not depend upon the wavelength, is kept constant. CONSTITUTION:An output A from a photodetector, a detecting output of which does not depend upon a wavelength, is compared with reference voltage 14, and the driving currents of a laser are controlled so that an oscillation output is held constant by an output from an error amplifier 15. On the other hand, an output B/A from a divider 11 is compared with reference voltage 17 to a set wavelength, the driving currents of an electronic type cooling heating element are controlled by an output from an error amplifier 18, and a temperature is controlled. Accordingly, when the operating temperature of the semiconductor laser is controlled so that the ratio of an output from the photodetector to the output from the photodetector, sensibility of which does not depend upon the wavelength, is kept constant, the oscillation wavelength of the semiconductor laser can be held constant with out being subject to the effect on an output from the semiconductor laser.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Field of Industrial Application) The present invention relates to a semiconductor laser device, and particularly to a semiconductor laser device whose oscillation wavelength can be controlled to a constant value.

(Prior art) In general, in semiconductor lasers, in order to prevent damage to the laser due to excessive output and to ensure stable operation, the oscillation output light intensity is monitored, the value is compared with a standard 1st shift, and the laser Oscillation output control is required to control the drive current. In addition, semiconductor lasers can be used for optical communication through optical fibers.
Furthermore, when used for measurement purposes such as measuring light transmittance, wavelength control is required in addition to oscillation output control.

FIG. 9 shows the change in the oscillation wavelength when the temperature is changed while the drive current is controlled to keep the oscillation output of the GaAIAs semiconductor laser constant.

Conventionally, in order to keep the oscillation wavelength constant, an indirect method has been used in which the temperature of the entire package is kept constant while the current is controlled so that the output intensity is constant.

FIG. 10 shows an example of a semiconductor laser device used for such a purpose. This device uses semiconductor laser pellets (6
6) is mounted on a pellet carrier (67), and this carrier is mounted on an electronic cooling and heating device (68) that utilizes the Seebeck effect. Sensors (6) for temperature measurement are fixed to the pellet carrier. A photodiode (70) is installed for the light emitted from the end face opposite to the light output end face of the semiconductor laser pellet (66), and the intensity of the oscillated output light is monitored by this. The whole is housed in one airtight package (71), and a sink (72) is attached to the package for heat radiation of the electronic cooling/heating device 2 (68).

In order to stabilize the oscillation output, the detection output of the monitor photodiode is connected to the reference voltage (73) by an error amplifier (73).
Δ), and the pellet drive current is controlled by the output of this error amplifier (73). Hey, this keeps the light output constant. On the other hand, in order to stabilize the temperature, the output of the temperature 1 degree sensor (69) is compared with the reference voltage (76) by an error amplifier (75), and the output of this error amplifier (75) is used to determine the temperature of the electronic cooling/heating device ( 68).

That is, the stabilization ff1l control of the oscillation wavelength of the semiconductor laser is performed by keeping the optical output constant based on feedback from the output light intensity monitor and keeping the package temperature constant.

(Problems to be Solved by the Invention) Generally, the temperature characteristics of the oscillation wavelength of a semiconductor laser differ significantly from pellet to pellet. For this reason, in the above-mentioned method of controlling the excavation wavelength by temperature stabilization, it is necessary to accurately measure the oscillation wavelength of each laser using a spectrometer, etc., to determine the pellet carrier temperature that provides the desired wavelength, and then perform temperature control. be.

FIG. 11 shows the change in the oscillation wavelength when the drive current is changed while keeping the temperature of the pellet carrier constant. this is,
Due to thermal resistance between the pellet and pellet carrier, for example, in a state where the drive current changes even if the temperature is kept constant,
This shows that the temperature of the junction changes and the oscillation wavelength changes. Further, when the semiconductor laser is operated with a constant optical output, the driving current changes with time as shown in FIG. 12 due to deterioration of the pellet itself. Therefore, the drive current required to operate at a constant optical output increases with time.

Therefore, the above method of keeping the optical output constant and the package temperature constant cannot compensate for the oscillation wavelength caused by fluctuations in the operating point of the semiconductor laser pellet over a long period of time. Furthermore, even if the laser drive current is constant, if the package temperature or degree fluctuates widely, there will be an instantaneous temperature difference between the pellet light emitting part and the temperature detection part of the pellet carrier, causing a shift in the oscillation wavelength. Ru.

In other words, in the conventional technology, it is necessary to set the operating temperature for each semiconductor laser to obtain the desired wavelength, resulting in poor device compatibility. This is an indirect method of controlling the oscillation wavelength of a semiconductor laser, and cannot cope with fluctuations in the temperature-wavelength characteristics of a pellet that is exposed to long-term operation. Another drawback is that it cannot respond to instantaneous fluctuations in the excavation wavelength due to significant changes in the operating environment.

The present invention provides a semiconductor laser device that is simpler, has high compatibility between semiconductor lasers, and has good wavelength control properties even when used for a long time.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a semiconductor laser and a semiconductor laser that receives a portion of the output light of the semiconductor laser in a controlled wavelength band in which the sensitivity depends on the wavelength. a first photodetector whose sensitivity monotonically depends on the wavelength in a controlled wavelength band that receives a portion of the output light of the semiconductor laser; and the first and second photodetectors. An operational amplifier that determines the ratio of the outputs of the amplifier, an error amplifier that determines the deviation of the output of this operational amplifier from a reference value, and a semiconductor laser temperature that is driven by the output of this error amplifier so that the output of the error amplifier is constant. This is a semiconductor laser device characterized by comprising a temperature control device for raising and lowering the temperature, and means for passing a current through the semiconductor laser.

Furthermore, the photodetector includes a semiconductor laser, a photodetector whose sensitivity does not depend on the wavelength for receiving a portion of the output light of the semiconductor laser, and a filter whose transmittance changes monotonically with respect to the wavelength in the measurement range of the wavelength. A means for inserting and removing at a predetermined cycle on the front of the device, and a means for synchronously inspecting the output of the photodetector according to the cycle of double insertion and obtaining the output of the photodetector with and without a filter. , an operational amplifier that calculates the ratio of the output of the photodetector with and without a filter, an error amplifier that calculates the deviation of the output of this operational amplifier from a reference value, and This semiconductor laser device is characterized in that it is equipped with a temperature control device for raising and lowering the temperature of a semiconductor laser driven by the output so that the output of an error amplifier becomes constant, and means for flowing a current through the semiconductor laser.

(Function) Since it has a photodetector whose sensitivity depends monotonically on the wavelength, the detection output of the detector corresponds one-to-one with the excavation wavelength of the semiconductor laser. Therefore, if the operating temperature of the semiconductor laser is controlled so that the ratio between the output of this photodetector and the output of a photodetector whose sensitivity does not depend on wavelength is constant, it will not be affected by the driving current of the semiconductor laser. It becomes possible to keep the excavation wavelength of the semiconductor laser constant. In particular, since temperature control is performed using a component corresponding to the optical output that is related to the drive current and reflects the junction temperature, it is possible to achieve more accurate wavelength control over a long period of time than in the prior art.

<Embodiment> A semiconductor laser device according to an embodiment of the present invention will be described with reference to FIG.

A semiconductor laser pellet (1) is fixed to a pellet carrier (2) made of a metal with good thermal conductivity, and the pellet carrier (2) is fixed to an electronic cooling/heating element (3).These parts All are housed in an airtight package (4).The laser output light is transmitted through a lens (
After the parallel beam is made into parallel light in step 5), a part of it is taken out by a beam splitter (6). This light is split into two by a beam splitter (7), one is passed through a photodetector (8) whose sensitivity is independent of wavelength, and the other is passed through an optical filter (9) whose transmittance varies monotonically with wavelength. The light is respectively incident on a photodetector (10) whose sensitivity is independent of wavelength. Hey, optical filter (9) and photodetector (1)
0) constitutes a photodetector whose sensitivity is wavelength dependent. The outputs A and B of each photodetector (8) (10) are divided by the divider (
The ratio B/A is determined in step 11). Figure 2a shows the transmittance characteristics (
12), and Figure a shows the dependence (13) of the output B/A of the divider (11) on wavelength. B/A represents a characteristic obtained by multiplying the filter transmittance by a constant.

Now, the output A of the photodetector, whose detection output does not depend on the wavelength, is compared with the reference voltage (14), and the laser drive current is controlled by the output of the error amplifier (15) so that the oscillation output is constant. , the output B/A of the divider (11) is compared with the reference voltage (17) for the set wavelength (16), and the drive current of the electronic cooling/heating element is controlled by the output of the error amplifier (18) to control the temperature. do.

As described above, since the present invention includes a photodetector whose sensitivity monotonically depends on wavelength, the detection output of the detector has a one-to-one correspondence with the oscillation wavelength of the semiconductor laser. Therefore, if the operating temperature of the semiconductor laser is controlled so that the ratio between the output of this photodetector and the output of a photodetector whose sensitivity does not depend on wavelength is constant, the output of the semiconductor laser will not be affected. The oscillation wavelength of the semiconductor laser can be kept constant. In particular, temperature control is performed using a component corresponding to the optical output that is related to the drive current and reflects the junction temperature.
More accurate wavelength control than conventional technology becomes possible over a long period of time.

FIG. 3 shows the temperature characteristics of the oscillation wavelength of the semiconductor laser device of the above-described embodiment in comparison with that of the prior art. FIG. 3a shows the prior art, and the same figure shows the case of the present invention. Changes in oscillation wavelength (51) in response to outside temperature changes (50) in a conventional method for stabilizing the temperature of pellet carriers
observed fluctuations in the oscillation wavelength due to mode hopping when the temperature suddenly changes (52). On the other hand, in the semiconductor laser technology of the present invention, no change was observed in the oscillation wavelength (54) with respect to the change in outside temperature (53).

In the above-described embodiment, the laser beam is once converted into parallel light and then incident on the photodetector, but it is of course possible to perform wavelength control in the same way even if the laser beam remains as divergent light.

Next, another embodiment of the invention will be described with reference to FIG. In this embodiment, instead of using two photodetectors,
A rotating optical chopper having one photodetector and a filter is used, and the oscillation wavelength of the semiconductor laser can be stabilized in the same manner as in the above embodiment.

The semiconductor laser pellet (19) is fixed to a pellet carrier (20) made of a metal with good thermal conductivity.
The pellet carrier is fixed on the electronic cooling and heating element (21). All these parts are housed in an airtight package (22). After the laser output light is made into parallel light by a lens (23), it is sent to a beam splitter (24).
) a part of it is extracted. Further, the light passes through a rotating optical chopper (25) and enters a photodetector (26).The output C of the photodetector (26) is transmitted through two synchronous waveform filters (26).
27) and (28).

FIG. 5 is a cross-sectional view of the rotary optical chopper (25), which includes an optical filter portion (29) and a transmitting portion (30) whose transmittance changes monotonically with respect to wavelength. The output C of the photodetector (26) corresponding to the filter part and transmission part of this optical chopper shows a pulse output as shown in FIG. 6a. This output pulse C has no filter j
The output of the photodetector (31) in the first case and the output (32) of the photodetector with the filter appear alternately. Pulses D and E are generated from a synchronous pulse generator (33) for detecting rain detection output in synchronization with the rotation of the optical chopper. Pulse 01E
In line with the light transmitting part of the optical chopper and part of the filter,
The pulses are as shown in Fig. 6bSc, and are input to the synchronous detectors (27) and (28), respectively, and the synchronous detectors (27) and (28) each output the photodetection output without a filter ( 31) and the photodetector (32) with a filter are selectively taken out and smoothed.

Here, optical detection without a filter (synchronous detector (
27) ') Output A and light detection with filter (
The ratio B/A of the output signal of the synchronous detector (28) is obtained by a divider (60). The output A of the photodetector, whose detection output does not depend on the wavelength, is compared with a reference voltage (35), and the laser drive current is controlled by the output J of the error amplifier (34) so that the oscillation output is constant.

On the other hand, the output B/A of the divider (60) is compared with a reference voltage (61) for a set wavelength, and the drive current of the electronic cooling/heating element is controlled by the output of the error amplifier (62) to control the temperature. In this way, the oscillation wavelength of the semiconductor laser is stabilized as in the above embodiment.

Next, an embodiment in which a photodetector is enclosed in an airtight package will be described with reference to FIG.

That is, in this embodiment, the laser pellet 38) is fixed to a pellet carrier (39) with good thermal conductivity, and this pellet carrier (39) is fixed to the electronic cooling/heating element (40). .

A 3i photodiode (41) is fixed to the pellet carrier (39) as two photodetectors, one whose sensitivity does not depend on the wavelength and one whose sensitivity depends on the wavelength, and which are formed on the same substrate. The emitted light from the end face of is incident. As shown in the cross-sectional groove path in Figure 7, this photodiode is made of a dielectric multilayer film or colored glass on one surface of the two photodiodes, and has a transmittance that varies with wavelength within the wavelength control range of the laser. It is made up of three optical filter films (48) that change monotonically. That is, an n1i (43) is formed by impurity diffusion on a high resistance 3i substrate (42), an AU electrode (44) is formed thereon, and a p' layer (45) is further divided into two regions by impurity diffusion. ), (46) are formed, S
! Protection of 02! 1! (47) is formed on both surfaces, and then an optical filter is formed only on one surface. Note that (49) is the A1 electrode.

In particular, in this embodiment, a photodetector whose sensitivity is wavelength dependent and a photodetector which is independent are housed in a hermetic package;
Since the emitted light from the end face opposite to the emission end face of the laser pellet is incident on each of them, the configuration of the optical system that guides the light to the photodetector is simplified, and the semiconductor laser device is thereby made more compact. Further, although two photodiodes are formed on the same substrate, it is of course possible to use individual photodiodes. In addition, the photodetector is not limited to the 3i photodiode, and other photodetectors such as a small Ge photodiode may be used with sensitivity adjusted to the wavelength of the laser.

Incidentally, in the above embodiment, optical output control (controlling the drive current of the semiconductor laser) is performed simultaneously with temperature control, but the oscillation wavelength can be sufficiently stabilized by temperature control alone.

[Effects of the Invention] As described above, according to the semiconductor laser device shown in the present invention,
Stabilization of the oscillation wavelength of a semiconductor laser can be achieved with high precision using a simple device.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a semiconductor laser device according to an embodiment of the present invention, and FIG. 2 is a diagram showing transmittance characteristics of an optical filter for giving a light output detector a monotonous sensitivity dependence with respect to wavelength. FIG. 3 is a diagram showing the temperature change characteristics of the oscillation wavelength in the semiconductor laser device of the present invention and the conventional device, FIG. 4 is a diagram showing another embodiment of the semiconductor laser device of the present invention, and FIG. 5 is a diagram of the optical chopper. 6 is a diagram showing the output waveform of the photodetector, FIG. 7 is a diagram showing another embodiment of the semiconductor laser device of the present invention, FIG. 8 is a sectional view of the photodiode, and FIG. 9 is a diagram showing the structure of the photodiode. A diagram showing the change in the emission wavelength when the oscillation output of the semiconductor laser is constant and the package temperature is changed. Figure 10 is a diagram showing a conventional semiconductor laser device. Figure 11 is a diagram showing the change in the emission wavelength when the package temperature of the semiconductor laser is constant. , is a diagram showing changes over time when the drive current is changed. (1)... Semiconductor laser pellet, (2)... Pellet carrier, (3)... Electronic cooling/heating element, (4)... Airtight package, (8), (1)... A photodetector whose sensitivity does not depend on wavelength, (9)...optical filter, (11)...divider,

Claims (8)

[Claims] (1) a semiconductor laser, a first photodetector whose sensitivity does not depend on wavelength in the control wavelength band of the semiconductor laser light that receives a portion of the output light of the semiconductor laser, and the output light of the semiconductor laser; a second photodetector whose sensitivity monotonically depends on the wavelength in the controlled wavelength band that receives a portion of the light; an operational amplifier that determines the ratio of the outputs of the first and second photodetectors; an error amplifier that determines the deviation of the output of the operational amplifier from a reference value; a temperature control device that is driven by the output of the error amplifier and increases or decreases the temperature of the semiconductor laser so that the output of the error amplifier becomes constant; 1. A semiconductor laser device comprising: means for passing a current through the semiconductor laser. (2) The semiconductor laser device according to claim 1, wherein the temperature control device includes a Peltier element. (3) The first photodetector includes a photodetecting element whose sensitivity does not depend on the wavelength in the wavelength measurement range, and a photodetection element installed in front of the photodetection element whose transmittance is monotonous with the wavelength in the wavelength measurement range. 2. The semiconductor laser device according to claim 1, further comprising a filter. (4) The means for passing a current through the semiconductor laser includes the first
an error amplifier for determining the deviation between the output of the photodetector and a predetermined reference value; and an error amplifier for driving the output of the error amplifier to increase or decrease the current of the semiconductor laser so that the output of the error amplifier is constant. 2. The semiconductor laser device according to claim 1, further comprising a current control device. (5) A dielectric multilayer film or colored glass is formed on one surface of two photodiodes whose sensitivity does not depend on wavelength in the control wavelength band of the semiconductor laser beam formed on the same substrate. The semiconductor according to claim 1, characterized in that a thin film filter that monotonically changes is formed as the second photodetector, and the other without a filter is used as the first photodetector. laser equipment. (6) A semiconductor laser, a photodetector whose sensitivity does not depend on the wavelength for receiving a portion of the output light of the semiconductor laser, and a filter whose transmittance changes monotonically with respect to the wavelength in the measurement range of the wavelength. means for inserting and removing at a predetermined period in front of the detector; means for synchronously detecting the output of the photodetector in accordance with the period of the insertion and removal, and obtaining the output of the photodetector with and without a filter; An operational amplifier that calculates the ratio of the output of the photodetector when there is a filter and the output of the photodetector when there is no filter, an error amplifier that calculates the deviation of the output of this operational amplifier from a reference value, and the output of this error amplifier. A semiconductor laser device comprising: a temperature control device for increasing or decreasing the temperature of the semiconductor laser so that the output of the driven error amplifier becomes constant; and means for flowing a current through the semiconductor laser. (7) The semiconductor laser device according to claim 6, wherein the temperature control device includes a Peltier element. (8) The means for passing a current through the semiconductor laser includes an error amplifier that determines the deviation from the output of the photodetector when the filter is provided and a predetermined reference value, and an error amplifier that is driven by the output of the error amplifier. 7. The semiconductor laser device according to claim 6, further comprising a current control device for increasing and decreasing the current of the semiconductor laser so that the output is constant.