JP2003179298A - Semiconductor laser module and its designing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser module in which current dependency and temperature dependency are suppressed. <P>SOLUTION: The semiconductor laser module A<SB>1</SB>comprises a semiconductor laser element 5 having a diffraction grating arranged in the vicinity of an active layer, an optical fiber 8 for transmitting light emitted from the semiconductor laser element 5, and a Peltier module 2 for regulating the temperature of the semiconductor laser element 5, wherein the semiconductor laser element 5 and the Peltier module 2 are connected electrically in series and the wavelength of light emitted from the semiconductor laser element 5 is substantially constant in the working region of driving current of the semiconductor laser element 5. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser module, more specifically, a laser element which can be cooled by its own driving current is incorporated, whereby the temperature dependence of the oscillation wavelength of the laser element and the current dependence thereof. The present invention relates to a semiconductor laser module that is designed to suppress the characteristics and is useful as a pumping light source for, for example, a Raman amplifier.

The present invention also relates to a design method for exhibiting optimum light output characteristics with minimum power consumption when designing a semiconductor laser module driven by a constant power supply voltage.

[0003]

2. Description of the Related Art Wavelength Division Mu
The ltiplexing (WDM) communication system has been developed as an optical communication system for transmitting a plurality of signal lights. In this system, an optical amplifier is arranged at a predetermined position of an optical line, a laser module incorporating a Fabry-Perot type semiconductor laser device is connected to the optical amplifier, and an excitation laser beam having a predetermined oscillation spectrum is emitted from this laser module. Is incident on the optical amplifier, the optical signal attenuated in the transmission process of the upstream line is amplified, and the optically amplified signal light is transmitted again to the downstream line.

At present, an Er-doped fiber amplifier (EDFA) is widely used as an optical amplifier in this system. This EDFA performs stimulated emission type optical amplification, Er ions are excited by the excitation laser light incident from the laser module, and a flat gain wavelength band defined by the energy level is expressed in the EDFA.
Then, the signal light of the wavelength included in this flat gain wavelength band is optically amplified.

ED for performing such stimulated emission type optical amplification
In FA, the practical gain wavelength band involved in optical amplification of signal light is 1530 to 1610 nm due to its flatness.
It is a degree. That is, when the EDFA is used, the signal light that can be optically amplified by the system is limited to the one whose wavelength is within the above band. On the other hand, a Raman amplification method has been conventionally known as an optical amplification method for signal light. Since this amplification system has a feature that it can optically amplify a signal light of a wider band than the case of the above-mentioned EDFA amplifier, the expectation for its application to an optical communication system is increasing in recent years.

In this Raman amplification system, when a laser beam (excitation laser beam) having an extremely high optical power is incident on an optical fiber, stimulated Raman scattering occurs in this optical fiber, and the wavelength of the excitation laser beam is about 100 nm. Phenomenon in which a gain appears on a relatively long wavelength side, and when a signal light having a wavelength included in the wavelength band that gives the above-mentioned gain is incident on an optical fiber in such an excited state, the signal light is optically amplified. Is an optical amplification method that utilizes the.

This Raman amplification system is based on the above-mentioned EDFA.
Unlike the above case, since the optical fiber (optical line) itself can be used as the amplification medium without using a special optical fiber, it can be directly applied to the existing optical line. That is, unlike the case of EDFA,
It is possible to reduce the number of relay points for optical amplification in the entire optical line, which can simplify the maintenance management of the entire system and reduce the construction cost and maintenance cost of the entire system.
At the same time, it has the advantage of increasing the reliability of the entire system. Then, application of this Raman amplification method to a submarine optical communication cable system has begun to be studied.

By the way, the laser module incorporated in the above-mentioned system as an excitation light source usually contains a Peltier module in a package, and a Fabry-Perot type semiconductor laser element is further arranged thereon.
It has a structure in which the emission end face of the laser element and an optical fiber are optically coupled. Then, the laser element is driven with a predetermined drive current and a drive voltage, and laser light having a predetermined wavelength determined by the laser element is output as excitation light.

In this case, the excitation light is mainly
The following characteristics are required. First of all, even if the driving current of the laser element or the environmental temperature changes, the oscillation wavelength does not change and the oscillation wavelength is stable in a predetermined oscillation spectrum. In particular, Raman amplification has a characteristic that a gain appears on the long wavelength side of the pumping light wavelength by a predetermined amount, so that it is very important that the pumping light wavelength is stable. In response to such requirements, for example, in the case of a laser module for a Raman amplifier, a fiber grating (FB
G) is formed to realize high wavelength stability.

However, in the case of this laser module with an FBG, noise is inevitably generated due to the resonance between the FBG and the reflection end face of the laser element, and it is impossible in principle to eliminate this noise. Therefore, it is not preferable to incorporate the above-mentioned laser module with an FBG as a pumping light source of a Raman amplifier which requires that pumping light has low noise (low RIN).

The second requirement is to increase the output power of the excitation light. This requirement can be realized by increasing the drive current of the laser element. However, as the drive current increases, the laser element itself generates heat and its optical output decreases, and at the same time, the oscillation wavelength shifts to the long wavelength side. The occurrence of such a situation is extremely inconvenient for a laser module for a Raman amplifier, which is strongly required to have high output and wavelength stability.

To solve such a problem, usually, a temperature detecting element such as a thermistor is arranged in the laser element, the temperature of the laser element is measured, and the driving power supply of the laser element is determined based on the temperature signal. The Peltier module driving power supply of another system supplies a current of a predetermined value to the Peltier module to drive the Peltier module, thereby cooling the laser element and maintaining the laser element at a predetermined temperature. There is.

[0013]

By the way, the Raman amplification system has begun to be adopted in submarine optical communication cable systems. The laser module incorporated in this system usually has a structure in which no Peltier module is arranged. If the Peltier module is incorporated, the current consumption of the laser module is the sum of the drive current of the laser element and the drive current of the Peltier module. However, since the driving power of the laser module is transmitted from a long distance, large current transmission cannot be performed due to the resistance loss of the power transmission cable. As a result, the supply current to the laser module must be limited, and the Peltier module is not installed.

From the above, the laser module used as the pumping light source for the seabed, especially the oscillation wavelength of 1
In the case of a laser module of 300 to 1550 nm band, when a large driving current is applied to the laser element in order to increase the output power, heat is generated and the optical output is reduced, which makes it difficult to achieve the high output power. Is. Further, in order to reduce the noise, if the wavelength stabilization process of the output light is not performed, that is, the FBG is used, the wavelength of the output light shifts to the long wavelength side, and the wavelength stabilization of the pump light is not possible. It was difficult.

The present invention solves the above-mentioned problems, makes it possible to reduce the current to be supplied, suppresses the power consumption, and is excellent in wavelength stability of output light and low noise. For the purpose of providing. Moreover, it aims at providing the design method of such a semiconductor laser module.

[0016]

In order to achieve the above-mentioned object, in the present invention, a semiconductor laser device in which a diffraction grating is arranged in the vicinity of an active layer, and a light emitted from the semiconductor laser device are transmitted. Optical fiber and a Peltier module for adjusting the temperature of the semiconductor laser element, the semiconductor laser element and the Peltier module are electrically connected in series, and the emitted light from the semiconductor laser element. Provided is a semiconductor laser module, wherein the wavelength is set to be substantially constant within a usage region of the drive current of the semiconductor laser device.

In the present invention, the semiconductor laser device and the Peltier module are electrically connected in series,
When designing a semiconductor laser module that is driven with a constant power supply voltage, the drive current and drive voltage of the semiconductor laser device at the time of maximum output drive are I _max and V _LD , respectively, and the power supply voltage is E, Further, when the drive current and drive voltage of the Peltier module are I _PE and V _PE , respectively, 0.8E <V _PE + V _LD <E, I _PE = I _max , preferably 0 There is provided a method for designing a semiconductor laser module, characterized in that the shape, the number of logarithms, and the arrangement of the Peltier elements in the Peltier module are designed so as to satisfy 0.9E <V _PE + V _LD <E.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An example A ₁ of a laser module of the present invention is shown in FIG. 1 as a schematic view. In this laser module, a Peltier module 2 including a plurality of Peltier elements 2c sandwiched between an upper plate 2a and a lower plate 2b made of Al ₂ O ₃ , for example, is arranged on the inner bottom surface of a package 1 made of ceramics. There is. The Peltier module 2 includes a pair of P-type and N-type Peltier elements,
A plurality of pairs are electrically connected in series.

A base 3 made of, for example, a Cu--W alloy is arranged on the upper plate 2a, and a heat sink 4 having a semiconductor laser element 5 to be described later mounted thereon is further arranged thereon. A carrier-attached photodiode 6 for current monitoring is arranged on the back side of the laser element 5, and further, on the front side of the laser element 5, an optical fiber 8 is provided via a first lens 7a and a second lens 7b. Are optically coupled to each other.

Another example A ₂ of the laser module of the present invention is shown in FIG. The Peltier module ₂ in the laser module A ₂ has a structure in which two modules 2A and 2B each formed by connecting a plurality of pairs of Peltier elements in series are electrically connected in parallel. These laser modules A ₁ and A ₂ have the following features.

(1) The incorporated laser element 5 is
A diffraction grating is formed near the active layer. (2) The laser element 5 and the Peltier module 2 are electrically connected in series, and the drive current of the laser element 5 directly functions as the drive current of the Peltier module.

First, FIG. 3 shows an example B of the layer structure of the laser element 5 manufactured using the InP semiconductor material. In this laser device 5, a lower clad layer 5b made of n-InP that also serves as a buffer layer and a lower clad layer is formed on the (100) plane of the n-InP substrate 5a, and InGaA.
An active layer 5c having a layer structure in which a multiple quantum well structure made of sP is sandwiched between GRIN-SCH layers made of InGaAsP, and a spacer layer 5d described later made of p-InP,
Upper clad layer 5e made of p-InP, InGaAs
A cap layer 5f made of P is sequentially stacked.

In the spacer layer 5d, for example, p-InGa having a thickness of 20 nm and a period of about 230 nm is used.
A diffraction grating 5g made of As is formed. Since this diffraction grating 5g has an optical feedback function and a wavelength selection characteristic,
This layer structure has a function of emitting light by itself and a function of emitting laser light having a specific wavelength defined by the period of the diffraction grating.

A spacer layer 5d including the diffraction grating 5g,
The active layer 5c and the upper part of the lower clad layer 5b are processed into a mesa stripe shape, and a p-InP layer 5h and an n-InP layer 5i are sequentially stacked on both sides thereof to form a current blocking layer. Further, a p-type electrode 5j is formed on the cap layer 5f, and an n-type electrode 5k is formed on the back surface of the substrate 5a.

On both end faces of this layer structure B, as shown in FIG.
As shown in, a pair of reflection films 5l and 5m are formed. That is, one end surface of the layer structure B has a reflectance of 80
% Reflection film 5l is formed to form the rear end surface of the laser element 5, and the other end surface is formed with a reflection film 5m having a reflectance of 1 to 5% to form the front end surface of the laser element 5. is doing.

This laser element 5 is premised to be used as a pumping light source of a Raman amplifier, its oscillation wavelength is 1300 to 1550 nm, and its cavity length (L) is set to 800 to 3200 μm. When a drive current is injected into the active layer 5c, laser light oscillates in the active layer, the laser light is excited in the resonator and emitted from the front end face as shown by the arrow in FIG.

Here, the mode interval (Δλ) of the longitudinal mode in the excitation light generated by the resonator is expressed by the following equation: Δλ = λ ₀ ² / (2nL) (λ ₀ is the oscillation wavelength of the excitation light, n is the resonator Effective refractive index of
L represents the resonator length).

Now, the oscillation wavelength (λ ₀ ) of the excitation light is 1480n
m, effective refractive index (n) 3.5, resonator length (L) 800
If it is μm, the mode interval (Δλ) of the longitudinal mode is about 0.39 nm. In addition, the resonator length (L) is 3200μ
At m, the mode interval (Δλ) is about 0.1 nm.
On the other hand, the diffraction grating 5g located on the reflection film 5m side above the active layer selects a predetermined longitudinal mode according to its Bragg wavelength. The wavelength selection characteristic of the diffraction grating at that time draws a spectrum curve as shown in FIG.

In the laser element 5, by setting the period of the diffraction grating 5g and the cavity length (L) to appropriate values, the spectral intensity (Pmax) of the peak value in the spectrum curve of FIG. 5 is 3 dB lower. It is designed so that a plurality of (three in the figure) longitudinal modes are included in the wavelength interval that gives the spectral intensity. Therefore, this laser element 5 oscillates in a multi-longitudinal mode and can emit laser light having a high optical output in a state in which the peak value of the spectrum intensity is suppressed, as compared with a laser element which oscillates in a single longitudinal mode.

This is an advantageous characteristic for the pumping light source of the Raman amplifier. That is, in the case of a Raman amplifier, in order to increase the Raman gain, it is preferable to increase the optical output of the pump light, but at that time, if the peak value of the optical output is high, stimulated Brillouin scattering occurs and noise is generated. Will increase. However, in the case of this laser device 5, the peak value of the light output can be set to be lower than the threshold value at which stimulated Brillouin scattering occurs, and the light output of the excitation light can be increased as a whole. This is because a large Raman gain can be obtained.

Further, since the laser element 5 oscillates in the multi-longitudinal mode, the following effects can be obtained. For example, Raman amplification is realized by matching the polarization direction of the signal light with the polarization direction of the pumping light. For that purpose, it is preferable to depolarize the pumping light. In order to realize this, for example, a method of combining two or more polarized waves with orthogonal polarization or a method of propagating pumping light into a polarization maintaining fiber with the polarization plane and the polarization maintaining axis at 45 ° is adopted. can do. In the latter method using the polarization maintaining fiber, the length of the polarization maintaining fiber can be shortened as the spectrum width of the pumping light is wider. In the present embodiment, the pumping light from the laser element 5 has a multi-longitudinal mode, so that the length of the polarization maintaining fiber used can be shortened. As a result, downsizing of Raman amplification is realized. Further, as the number of longitudinal modes increases, the coherence length becomes shorter, the degree of polarization (DOP: Degree Of Polarization) becomes smaller, and the polarization dependence can be eliminated.
The Raman amplifier can be simplified and downsized.

Further, since the laser element 5 has the diffraction grating formed in the resonator, the laser element 5 has an extremely excellent noise characteristic as compared with the above-mentioned laser module with FGB. As described above, the laser module of the present invention uses the laser element having the built-in diffraction grating in the vicinity of the active layer as a light source, and therefore its excitation light exhibits the above-mentioned characteristics,
It is effective as a pumping light source for Raman amplifiers.

Although the diffraction grating 5 partially formed on the reflective film 5m side is used here, the reflective film 5 is used.
It may be formed on the 1 side or may be formed on the entire region in the light propagation direction. By the way, in the laser element 5 incorporated in the laser module of the present invention, when the environmental temperature rises or the drive current increases,
As the refractive index of the diffraction grating 5g changes, its oscillation wavelength monotonically shifts to the long wavelength side.

For example, when the environmental temperature changes, the oscillation wavelength of the laser element 5 changes as shown in FIG. For comparison, the behavior of a normal Fabry-Perot type laser device made of InP-based material is also shown in FIG. As is apparent from FIG. 6, the laser element 5 according to the present invention also has temperature dependence, but compared to a normal Fabry-Perot type laser element, the oscillation wavelength of the laser element 5 is closer to the long wavelength side. The shift amount is small, and the value is about 0.1 nm / ° C.

FIG. 7 shows the relationship between the drive current and the oscillation wavelength. As is apparent from FIG. 7, the laser element 5 according to the present invention also has current dependency, but the shift amount is very small as compared with a normal Fabry-Perot type laser element, and is about 0.003 nm / mA. It is a degree. In any case,
Laser element 5 incorporated in the laser module of the present invention
However, when this laser module is used as, for example, a pumping light source for a Raman amplifier, its oscillation wavelength is different from that of the built-in laser element. It is desirable to minimize the temperature dependence and the current dependence of the above, or to make them zero.

Therefore, in the present invention, the laser module is provided with the following second feature. That is, in the case of this laser module, as shown in FIG. 8, the Peltier module 2 and the laser element 5 are connected in series. That is, the input end of the laser element 5 is connected to one of the lead pins 9a formed in the package 1, the output end thereof is connected to the input end of the Peltier module 2, and the output end of the Peltier module 2 is It is connected to another lead pin 9b.

Therefore, in this laser module A, the drive current of the laser element 5 simultaneously functions as the drive current of the Peltier module 2. However, laser element 5
Peltier module 2 when the drive current to the
Must be connected to cool the laser element 5. Note that, in FIG. 8, the photodiode 6 is connected to another lead pin and is driven by a power supply of another system.

In the case of these laser modules A ₁ and A ₂ , when the drive current to the laser element 5 is increased in order to increase the output of pumping light, the oscillation wavelength from the laser element 5 shifts to the long wavelength side. However, since the large drive current also drives the Peltier module 2,
The amount of heat absorbed by the Peltier module 2 also increases, and as a result, the cooling effect on the laser element 5 also increases,
The temperature of the laser element 5 drops. That is, the laser element 5
It is possible to suppress the oscillation wavelength from becoming longer. Therefore, if the driving condition of the Peltier module is set so that the wavelength of the output light of the laser device becomes constant even if the driving current to the laser device 5 increases, the oscillation wavelength will be approximately within the driving condition of the laser device. It is possible to keep it constant.

Here, in order to keep the wavelength of the light output from the laser element 5 constant within a predetermined drive current range with the above-described configuration, parameter fitting is performed on the laser element 5 and the Peltier module 2. Need to be told. That is, when the drive current dependency is ignored, the temperature of the laser element 5 may be kept constant in order to keep the wavelength of light constant. This means that, in terms of heat quantity, the following relational expression is satisfied within a predetermined drive current range.

(Heat generation amount Q _LD of laser element 5) = (Heat absorption amount Q _PE of Peltier module 2) (1) However, strictly speaking, the wavelength of the light output from the laser element 5 is There is not only temperature dependence but also drive current dependence (both wavelengths increase monotonically with increase in drive current).

Therefore, the driving current dependency can be canceled.
In order to increase the driving current, the laser element 5
It is preferable that the temperature of is gradually decreased. this is
When the amount of heat is set, the following relational expression is satisfied within the specified drive current range.
It means being done. Q_LD<Q_PE            ... (2) FIG. 9 is a schematic diagram showing the thermal characteristics of the Peltier module 2.
It's rough. As shown in FIG. 9, the Peltier module 2
As the parameters that determine the thermal characteristics of the
Calorie Q_PEAnd the temperature of the upper and lower surfaces of the Peltier module 2
There is a difference ΔT, and if two of these parameters are decided
Another parameter is decided. In addition, drive current I
I₁, I₂, I₃... and increase, ΔT and Q_PEOff
Piece ΔT_max, Q _{PE, max}Have a relationship to increase.

In this embodiment, the drive current I of the Peltier module 2 is the same as the drive current of the laser element 5, and the heat absorption amount Q _PE is a predetermined value that satisfies the above equation (1) or (2). Need to take. Under these conditions, the number of pairs of Peltier elements of the Peltier module 2, the area of the upper surface and the lower surface of the Peltier module 2 are set so that Q _PE and ΔT have predetermined values that match the heat generation characteristics of the laser element 5 for a predetermined drive current I. The wavelength of the output light of the laser element can be made constant by appropriately setting the material, the arrangement of the Peltier element, and the like.

In the laser module A of the present invention, the fluctuation of the oscillation wavelength is within ± 1 nm by relying on the above-mentioned design criteria in the use range of the drive current of the laser element 5, preferably in the whole range. Can be regulated. Next, a method of designing the semiconductor laser module of the present invention will be described. This design method is incorporated as long as it is a semiconductor laser module of a type in which a semiconductor laser device and a Peltier module are connected in series, and the laser module operates at a constant power supply voltage (E). It can be applied regardless of the type of the semiconductor laser device.

First, the semiconductor laser element used is the maximum light source.
Drive current (I _maxAnd drive)
Voltage (V_LDIs set as a characteristic of the laser device.
It is given uniquely in the timing. And give this
In order to keep the laser element in this state,
The module is designed.

In this case, since the laser element and the Peltier module are connected in series, the driving current (I _PE ) of the Peltier module is the driving current (I _PE ) of the laser element.
must be equivalent to _max ). That is, I _PE
= I _max is designed. In addition, the drive voltage (referred to as V _PE ) of the Peltier module when the drive current of the Peltier module is I _PE must be V _PE ≦ E−V _LD .

That is, in order to drive the laser device with the maximum light output, the Peltier module has I _PE = I _max.
It is necessary that V _PE be designed to be driven at a value close to the maximum value in the range that does not exceed the (E−V _LD ) value. This can be realized by appropriately selecting the shape, logarithm, arrangement, etc. of the Peltier elements that form the Peltier module. One example is shown below.

Length 0.64 mm, width 0.64 mm, height 0.82 m
Seebeck coefficient of 2.0 × 10 ⁻⁴ V / in a cubic bulk of m
K, performance index 2.8 × 10 ^-3 V / K, resistivity 1.1 × 10
A Peltier device having a ^-5 Ωm and a thermal conductivity of 1.3 W / K / m was prepared. The Peltier device was connected in series in the logarithm shown in Table ₁ to assemble the laser module A ₁ shown in FIG. In addition, a group 2 of 25 pairs of Peltier elements connected in series
Two laser modules A and 2B were connected in parallel to assemble the laser module A ₂ shown in FIG.

Then, the laser modules A ₁ and A ₂ were driven while the power supply voltage was kept constant at E = 5 volts. Table 1 shows the driving conditions of the laser element and the Peltier module at this time.

[0049]

[Table 1]

As is clear from Table 1, the driving voltage and driving current of the Peltier module can be changed by changing the logarithm used and the arrangement of the Peltier device. Therefore, if I _{max of} the laser element and V _LD at that time are determined, V _{PE of} the Peltier module driven by the I _max value is determined.
And the logarithm and arrangement of the Peltier elements can be selected accordingly.

And assembled by such a design concept
The laser module has low power consumption, and
The light output characteristics of the laser device will be maximized.
In the actual design, set the margin of the power supply voltage during driving.
Considering total voltage V_LD+ V_PETo 0.8E <V_LD+ V_PE
<E, preferably 0.9E <V_LD+ V
_PEIt is desirable to set so as to satisfy <E.

[0052]

EXAMPLES (1) Laser device The laser device shown in FIGS. 3 and 4 was manufactured from an InP-based material. In the case of this laser device, the diffraction grating 5g is p-InG.
It is made of aAsP and has a thickness of 20 nm and a period of about 230 nm. This laser element has a cavity length of 1500μ.
m, and oscillates in the 1480 nm band. The power consumption is 0.75W when the driving current is 500mA,
When the drive current is 800mA, it is 1.4W, 20% of power consumption is converted to light, and the rest is consumed as heat.

(2) Assembly of Laser Module The laser module A ₁ shown in FIG. ₁ was assembled using the above laser device. At that time, the laser element 5 and the Peltier module 2 were connected in series as shown in FIG. At this time, the Peltier module 2 has 32 pairs of Peltier elements having a size of 8 mm × 12 mm × 1.65 mmt, and the maximum heat absorption amount (Q _{PE max} ) when there is no temperature difference between the upper surface and the lower surface. Was 10 W, the current value (I) at that time was 4.7 A, and the maximum temperature difference (ΔT _max ) between the upper surface and the lower surface when there was no heat absorption was 95 ° C. For comparison, the above-mentioned Fabry-Perot type laser element was used as a laser element, and a laser module without a Peltier module was also assembled.

(3) The laser module was driven with the characteristic environmental temperature set to 45 ° C. The driving current was changed and the oscillation wavelength of the excitation light at that time was measured. The results are shown in Fig. 9. An approximate expression of the oscillation wavelength (y) and the drive current (x) in each case is shown in the figure. As is clear from FIG. 9, in the laser module of the present invention, the amount of shift of the oscillation wavelength to the long wavelength side is small even if the drive current is large, and the current dependence is significantly reduced.

The output from the optical fiber of the laser module was measured while keeping the ambient temperature at 45 ° C. and changing the drive current. The results are shown in Fig. 10. As is apparent from FIG. 10, the output of the laser module of the present invention is significantly higher than that of the laser module of the comparative example. This indicates that the larger the driving current, the stronger the cooling effect of the Peltier module and the lower the temperature of the laser element.

[0056]

As is apparent from the above description, in the laser module of the present invention, the incorporated laser element has a built-in diffraction grating having an optical feedback function and wavelength selection characteristics in the vicinity of the active layer. Therefore, the wavelength stability itself is excellent. At the same time, since the laser element and the Peltier module are connected in series, the drive current of the laser element immediately functions as the drive current of the Peltier module, and as a result, the laser element can cool itself with its own drive current. Therefore, the shift of the oscillation wavelength to the long wavelength side is suppressed, and high output driving becomes possible.

Therefore, the laser module of the present invention has a high output and excellent wavelength stability, and is useful as a pumping light source for a Raman amplifier. Moreover, since it consumes less power, it can be used as a pumping light source for a submarine optical communication cable system. It is valid. Further, according to the designing method of the present invention, it is possible to manufacture a laser module that can reduce power consumption under a constant power supply voltage and exhibit optimum light output characteristics.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example A ₁ of a laser module of the present invention.

FIG. 2 is a schematic sectional view showing an example A ₂ of another laser module of the present invention.

FIG. 3 is a partially cutaway perspective view showing a layer structure example B of a laser element 5 to be incorporated.

FIG. 4 is a sectional view of a laser device 5.

5 is an example of a spectrum diagram of laser light from a laser element 5. FIG.

FIG. 6 is a graph showing the relationship between the environmental temperature of the laser device 5 and the oscillation wavelength.

FIG. 7 is a graph showing the relationship between the drive current of the laser element 5 and the oscillation wavelength.

FIG. 8 is a schematic diagram showing a connection state of the laser element 5 and the Peltier module 2 in the laser module of the present invention.

FIG. 9 is a schematic diagram showing thermal characteristics of a Peltier module.

FIG. 10 is a graph showing the relationship between the drive current of the laser module and the oscillation wavelength.

FIG. 11 is a graph showing the relationship between the drive current of the laser module and the fiber output.

[Explanation of symbols]

1 package 2 Peltier module 3 base 4 heat sink 5 Laser device 5a substrate (n-InP) 5b Lower clad layer (n-InP) 5c active layer 5d spacer layer (p-InP) 5e Upper clad layer (p-InP) 5f Cap layer (InGaAsP) 5g diffraction grating (p-InGaAs) 5h p-InP layer (current blocking layer) 5 in-InP layer (current blocking layer) 5j p-type electrode 5k n-type electrode 6 photodiodes 7a first lens 7b Second lens 8 optical fibers 9a, 9b Lead pin

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Claims (7)

[Claims] 1. A semiconductor laser device having a diffraction grating arranged in the vicinity of an active layer, an optical fiber for transmitting light emitted from the semiconductor laser device, and a Peltier module for controlling the temperature of the semiconductor laser device. The semiconductor laser device and the Peltier module are electrically connected in series, and the wavelength of the emitted light from the semiconductor laser device is substantially constant within the use region of the drive current of the semiconductor laser device. A semiconductor laser module characterized in that 2. The semiconductor laser device includes a laser beam including a plurality of longitudinal modes between an optical output having a maximum peak value in a spectrum curve of its emitted light and an optical output 3 dB lower than the optical output. The semiconductor laser module according to claim 1, which emits a laser beam. 3. The semiconductor laser module according to claim 1, wherein the maximum value of the drive current is any value of 300 mA or more. 4. The semiconductor laser module according to claim 1, which is used as an optical amplifier for a submarine optical communication cable. 5. The semiconductor laser module according to claim 1, which is used as a pumping light source for a Raman amplifier. 6. When designing a semiconductor laser module in which a semiconductor laser device and a Peltier module are electrically connected in series and driven by a constant power supply voltage, a drive current of the semiconductor laser device at the maximum output drive time. And drive voltage are I _max and V _LD , respectively, the power supply voltage is E, and the drive current and drive voltage of the Peltier module are I _PE and V _PE , respectively, 0.8E < A method of designing a semiconductor laser module, characterized in that the shape, the number of logarithms, and the arrangement of the Peltier elements in the Peltier module are designed so as to satisfy V _PE + V _LD <E, I _PE = I _max . 7. The method of designing a semiconductor laser module according to claim 6, wherein the relationship of 0.9E <V _PE + V _LD <E is satisfied.