JP2003060317A - Semiconductor laser module and semiconductor laser device having optical feedback function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser module for emitting an exciting laser beam having improved temporal stability. SOLUTION: In the semiconductor laser module A, a semiconductor laser device B1 is optically coupled to an element 5a having an optical feedback function, and the semiconductor laser device B1 has a layer structure A formed on a GaAs substrate, and the layer structure A has an active layer provided with a well layer, consisting of a semiconductor material containing Ga and As, and a barrier layer surrounding the well layer. In the semiconductor laser module A, a longitudinal mode oscillates in a multi-mode, and the thickness of the well layer in the active layer is >=10 nm.

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 and a semiconductor laser device having an optical feedback function,
More specifically, the present invention relates to a semiconductor laser module having an optical feedback function, in which a laser beam to be output is in a wavelength range of 940 to 990 nm and an optical output of the laser beam is temporally stable.

[0002]

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, for example, an Er-doped optical fiber amplifier (EDFA) is arranged at a predetermined position of an optical line, a pumping laser module having a semiconductor laser element as a pumping light source is connected thereto, and pumping laser light is emitted from this laser module. The E
The signal light incident on the DFA and optically amplified from the signal light source is optically amplified, whereby the optically amplified signal light is again transmitted to the downstream side.

In this case, for the semiconductor laser device incorporated in the laser module, the injection current value is changed by following the fluctuation of the optical output of the signal light source.
Measures are taken to control the optical output of the excitation laser light. In the case of a semiconductor laser device having an oscillation wavelength in the wavelength range of 1480 nm, the EDFA has a wide gain band, and therefore the above-mentioned treatment is effective. However, in the case of a semiconductor laser device having an oscillation wavelength in the wavelength range of 980 nm, the above-mentioned treatment cannot be adopted because the gain band in the EDFA is narrow.

Therefore, the oscillation wavelength is 980 nm.
When a laser module is constructed using semiconductor laser elements in the wavelength range, it is necessary to specify the wavelength of the pumping laser light from the semiconductor laser element to the wavelength corresponding to the narrow gain band. Therefore, the emission end face (front end face) of the semiconductor laser element, which is the light source, has a wavelength selection function such as a fiber Bragg grating having a predetermined reflection bandwidth, and at the same time optically couples an element having an optical feedback function. It has been studied to specify the wavelength of the excitation laser light emitted from the laser module within, for example, the reflection bandwidth of the fiber Bragg grating and stabilize the wavelength by forming the optical feedback structure.

However, in the case of a GaAs-based laser device, which is a typical semiconductor laser device with an oscillation wavelength in the 980 nm wavelength range, when the laser module is assembled by optical coupling with the fiber Bragg grating, the wavelength of the excitation laser light obtained. Although it is within the reflection bandwidth of the fiber Bragg grating, for example, if the injection current to the laser element fluctuates, a slight mechanical vibration is applied to the laser module, or the arrangement of the optical fiber with respect to the laser module changes, However, there is a problem in that the excitation laser light obtained from the laser module contains noise.

This is considered to be because, in the case of a GaAs laser device, the oscillation longitudinal mode is likely to be a single mode, and its optical output easily fluctuates on the order of several percent. Considering that it is standardized that the fluctuation of the optical output of the excitation laser beam emitted from the laser module is usually 0.5% or less, the above-mentioned problem is inconvenient.

Therefore, in the above laser module, in order to obtain stable laser light for excitation within the reflection bandwidth of the fiber Bragg grating,
It is considered that the oscillation laser light of the GaAs-based laser element that is the light source needs to be multimode.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems when a laser module is assembled by optically coupling a GaAs laser element having an oscillation wavelength in the wavelength range of 980 nm and a fiber Bragg grating for pumping. It is an object of the present invention to provide a semiconductor laser module in which the wavelength of laser light is within the reflection bandwidth of the fiber Bragg grating and is stable over time, and the generation of noise is suppressed. Specifically, it oscillates multi-mode excitation laser light within the reflection bandwidth of an element that has an optical feedback function such as a fiber Bragg grating, and the optical output of the excitation laser light is stable over time at a specific wavelength. A laser module is provided. Further, a semiconductor laser device that can be used as a pumping light source is provided because it has an optical feedback function by itself.

[0009]

In order to achieve the above object, in the present invention, a layer structure having a well layer made of a semiconductor material containing at least Ga and As and an active layer having a barrier layer surrounding the well layer is formed. Is formed on a GaAs substrate, and is used as a pumping light source in which a semiconductor laser element in which light resonates in parallel with the substrate and an element having an optical feedback function are optically coupled. The longitudinal mode oscillates in multimode, and the thickness of the well layer in the active layer is 10 nm.
A semiconductor laser module having the above is provided.

Further, in the present invention, at least the active layer of the semiconductor laser device is doped with an impurity, particularly an n-type impurity suitable for Si, and / or an n-type clad of the layer structure. The layer is doped with n-type impurities, preferably Si.
Further, in the quantum well structure, there is provided a semiconductor laser module in which the well layer is preferably thicker than the barrier layer.

Further, in the present invention, a layer structure having an active layer of a quantum well structure made of a semiconductor material containing at least Ga and As is formed on a GaAs substrate, and the well in the active layer of the semiconductor laser device is formed. Provided is a semiconductor laser module having a thick layer and forming an element having an optical feedback function by forming a grating near the active layer.

When the length of the resonator in which light resonates parallel to the substrate in the semiconductor laser device is L (μm), the optical output of the semiconductor laser module is L.
Provided is a semiconductor laser module of × 0.1 mW / μm or more.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The semiconductor laser module of the present invention is constructed by optically coupling a semiconductor laser element described later and an element having an optical feedback function, and the element used at that time has a wavelength selection function. And, as long as it exhibits a specific reflectance for a specific wavelength, it may be anything, for example,
A fiber Bragg grating (FBG), a dielectric multilayer filter, a distributed black reflector (DBR), etc. can be mentioned.

FIG. 1 shows an example A of the laser module of the present invention.
Shown in. In this laser module A, a Peltier module 2 for cooling a laser element B ₁ described later is arranged on a bottom plate 1a of a package 1, and a base material 3 made of, for example, Kovar is arranged on the Peltier module 2. ing. A laser element B ₁ is arranged on a base material 3 via a chip carrier 4, and an optical fiber 5 having a fiber Bragg grating 5a is optically coupled in a state where the optical axis is aligned with the laser element B _1. ing.

The optical fiber 5 is fixed on the base material 3 by a fiber fixing member 6, and the emitting end side of the optical fiber 5 is sealed in the cylindrical hole portion 1b of the package 1 through a sleeve 7 which is hermetically attached. Is derived from. Also,
A photodiode 8 is arranged on the back side of the laser element B ₁ so that the magnitude of the optical output of the laser module can be monitored.

In order to increase the optical coupling efficiency between the laser element and the optical fiber, it is preferable to use an optical fiber whose tip has a lens shape.
Even if the tip is not in the shape of a lens, the optical coupling efficiency between the two can be increased by interposing a lens in the middle. When a wedge-shaped optical fiber is used as the optical fiber, the assembled laser module has high optical coupling efficiency, the number of parts required for the assembly is reduced, and the total manufacturing cost is reduced.

An example B ₁ of the laser device of the present invention incorporated in this laser module A is shown in FIG. The laser element B ₁ has an upper portion in the shape of a ridge waveguide and has a predetermined cavity length (L) as a whole. And n-G
A layer structure C, which will be described later, is formed on the substrate 10 made of aAs, and the back surface of the substrate 10 is made of, for example, AuGeNi / Au.
And a protective film 13 made of, for example, silicon nitride (SiNx) is formed on the upper surface of the layer structure C.
Via the upper electrode 14 made of, for example, Ti / Pt / Au
Are formed.

The layer structure C is composed of an epitaxial crystal growth layer of a semiconductor material containing at least Ga and As, and the waveguide direction in the resonator is the n-GaAs substrate 10.
Parallel to the surface of. This layer structure C is specifically
For example, a lower clad layer 15 made of n-AlGaAs,
Lower GRIN-SCH made of, for example, i-AlGaAs
The layer 16a, an active layer 17 described later, for example, i-AlGaA
an upper GRIN-SCH layer 16b of s, eg p-
The upper clad layer 18 made of AlGaAs and the cap layer 19 made of p-GaAs, for example, are laminated in this order.

The protective film 13 formed by covering the upper surface of the layer structure C does not cover a part of the upper surface of the ridge waveguide. The upper electrode 14 is in direct contact with the cap layer 19 exposed from the non-covered portion of the protective film 13, and an injection current can be supplied from here to the active layer 17 of the layer structure C. Then, the emitting end face (front end face) is covered with a dielectric film (not shown) having a reflectance of 5%, and the other end face (rear end face) is a dielectric film (not shown) having a reflectance of 92%, for example. The optical output of the laser light oscillated by the resonator can be efficiently extracted.

Here, the active layer 17 is formed of one or more well layers and barrier layers surrounding the well layers. Especially,
From the viewpoint of the temporal stability of the excitation laser light from the laser module A, a quantum well structure having one well layer and barrier layers on both sides thereof is preferable. The well layer is usually In, for example, when the oscillation wavelength is 980 nm.
GaAs, GaAsSb, InGaAsSb, InGa
It is formed of AsP, InGaAsSbP, GaAsSbP, etc., but if the oscillation wavelength is in the 870 nm wavelength range, i-G
It may be formed of aAs. Further, the barrier layer is usually formed of i-InGaAs when the oscillation wavelength is in the wavelength range of 980 nm, but may be formed of another semiconductor material described above in relation to the oscillation wavelength.

This semiconductor laser device is characterized in that the above layer structure C satisfies the following conditions. (1) First condition: First, the well layer is thicker than the conventional one. Specifically, it is 10 nm or more. This is a basic and essential condition. In that case, it goes without saying that the upper limit of the thickness of the well layer is limited by the critical film thickness of the semiconductor material used for forming the well layer.
The upper limit is about 20 nm.

When the injection current from the upper electrode 14 is equal to or more than the threshold current (Ith), the laser device of the present invention having such a layer structure C emits a laser beam in the wavelength region of 940 to 980 nm at the front end. It oscillates from the surface. Then, the laser light for excitation from the laser module in which this laser element is incorporated, by the interaction with the optical feedback function described later,
It becomes a multimode composed of a plurality of longitudinal modes with a predetermined Fabry-Perot interval, and its temporal fluctuation is suppressed and its spectrum is temporally stabilized.

Incidentally, in the conventional research trend in GaAs laser devices, it has been pursued to make the thickness of the well layer substantially thinner than 10 nm in order to control the gain spectrum in the laser device. However, even if a fiber Bragg grating (FBG) is optically coupled to such a laser device to assemble a laser module, the feedback light from the fiber Bragg grating is converted into a single mode, and the excitation laser light output from the laser module is generated. The spectrum of 1 showed a tendency to fluctuate and become unstable.

The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and, contrary to the conventional method, when the thickness of the well layer in the laser element is increased to 10 nm or more, it is incorporated. The laser light for excitation from the laser module with an FBG has been made into a multi-mode, and it has been found that the temporal stability thereof is improved. As a result of further research, the above-mentioned first condition in the layer structure C has been established. I did.

(2) Second condition: On the assumption that the above first condition is satisfied, at least one of the quantum well structures is
That is, the layer is doped with impurities. In that case, the impurities may be doped in either the well layer or the barrier layer, or may be doped in both the well layer and the barrier layer. Further, the plurality of well layers or the plurality of barrier layers may be doped. The doping may be homogeneous or variable (eg, graded doping or some combination of doped and undoped layers). In either case, carriers are stored in the well layer.

When the active layer is doped with an impurity in any of the above-mentioned modes, the laser light for excitation from the laser module incorporating the laser element has little fluctuation with time and is further stabilized. improves. In that case, as the impurities, either n-type impurities or p-type impurities can be used. As the n-type impurity, for example, one kind or two or more kinds of Si, S, Se can be used, and as the p-type impurity, for example, Be, M
One or two or more of g and Zn can be used.

When at least one layer of these impurities is doped with n-type impurities, and particularly Si, among them, the oscillated laser beam from the laser element surely becomes multimode, and the laser module incorporating the laser element. This is preferable because the temporal fluctuation of the excitation laser light from the is reliably suppressed and stabilized. In that case,
The doping concentration of Si into the well layer is 1 × 10 ¹⁶ / cm ³ to
When it is set to 5 × 10 ¹⁶ / cm ³ , the above-mentioned effects are remarkably exhibited and it is effective. Si doping concentration is 1 × 10
If it is lower than ¹⁶ / cm ³ , the above effect is not sufficiently expressed, and if the doping concentration is higher than 5 × 10 ¹⁶ / cm ³ , the purity of the well layer and the barrier layer is lowered, and The function as a well layer will be lost.

(3) Third condition: One or more layers which are located above or below the active layer and confine the laser light generated in the active layer on the assumption that the above-mentioned first condition is satisfied. One of the layers is doped with impurities. These layers are optical confinement layers (eg GRIN
-SCH layer) and / or clad layer.

In the case of the laser device B ₁ shown in FIG. 2, specifically, the lower cladding layer 1 made of n-AlGaAs is used.
5. Lower GRIN-SCH layer 16a made of i-AlGaAs, upper GRIN-SC layer made of i-AlGaAs
Any or all of the H layer 16b and the upper clad layer 18 made of p-AlGaAs are doped with impurities.

In particular, when the cladding layer, or the n-type lower cladding layer, is doped with Si, which is an n-type impurity, it is possible to reliably realize multimode oscillation laser light, which is preferable. . In that case, the doping concentration of Si is preferably about 1 × 10 ¹⁷ / cm ³ to 4 × 10 ¹⁷ / cm ³ . More preferably 2 × 10 ¹⁷ / cm ³ to 4
× 10 ¹⁷ / cm ³ .

In the case of the laser device B ₁ , the first condition among the above three conditions must be satisfied as an indispensable condition. This is because it becomes impossible to realize the temporal stability of the excitation laser light from the assembled laser module. In addition, if either or both of the second condition and the third condition are satisfied, the temporal stability of the excitation laser light is improved as compared with the case of only the first condition, which is preferable. is there. In particular, when both conditions are satisfied, that is, when the first to third conditions are all satisfied, the temporal stability of the excitation laser light is significantly improved, which is more preferable.

The laser device B ₁ has the following characteristics. This will be explained below. Prior to the explanation, the threshold current (Ith) and spontaneous emission (Ath)
mplifiedSpantaneous Emission (ASE) spectrum and the spectrum width (Δλ) of the ASE spectrum are defined.

[0033] When the plots light output (L _OPT) of the laser element actuated by the driving current (I) To graph L _OPT -I, above a certain current value (I _A), the light output is a current value It increases linearly with (I). This graph is shown in Figure 3.
Shown in. The straight line fits the segment of the linear characteristic described above. Then, (when L _{OP T} = 0) I-axis defines the value of the current is cut off the straight line and a threshold current (Ith).

First, the threshold current (I
When a current having a value (I) smaller than th) is injected, the laser element emits spontaneous emission light. ASE (Am
Select the spontaneous emission light from the emission end face (front end face) based on plified Spontaneous Emmision (ASE), take the optical output on the vertical axis and the wavelength on the horizontal axis, and select the spontaneous emission light from the envelope of the optical output of each mode. Draw the spectrum curve of. The resulting spectral curve is typically as shown in FIG. 4, becomes asymmetric curve having the maximum output of the optical output (P _O), and the longitudinal mode of the plurality of Fabry-Perot type in this curve Is included.

In this spectrum curve, first, the points (S ₁ , S ₂ ) on the spectrum curve showing the optical output (P ₁ ) which is 3 dB lower than the maximum output (P _O ) are grasped, and then each point S. ₁ , the wavelength of the spontaneous emission light corresponding to S ₂ (λ ₁ ,
λ ₂ and the unit is nm). From point S ₁ to point S ₂
Here, the spectral width of the spontaneous emission light is defined as Δλ. And it is the maximum power of the spectral curve (P
_O ) and the range of the outputs (P ₁ , P ₂ ) on both sides which is 3 dB lower than that. As is clear from the figure, Δλ is (λ ₂
It is equivalent to −λ ₁ ).

When the laser element B ₁ satisfies the first condition and the injection current (I) satisfies the relationship of 0.2 ≦ I / Ith ≦ 0.8, the laser element B ₁ is Is I
All of the values have the characteristic of emitting spontaneous emission light such that the Δλ value is 15 nm or more.
Here, when the Δλ value is smaller than 15 nm, when the laser element is driven by an injection current of Ith value or more to oscillate the laser light, the longitudinal mode (FP) included in the Δλ value is generated. The number of modes will decrease. Then, for example, when a laser module is assembled by optically coupling a fiber Bragg grating to the laser element and driving it, the excitation laser light from that is in a state in which single mode or single mode and multimode alternate temporally, The light output becomes unstable and noise is generated.

However, when the Δλ value is larger than 15 nm, the number of longitudinal modes included in the Δλ value is large in the spectrum curve of the laser light oscillated from the laser element B ₁ , and the oscillated laser light is always multi-mode. The mode has been changed. Therefore, the excitation laser light obtained from the laser module described above is within the reflection bandwidth of the fiber Bragg grating even if the optical fiber is moved during module operation or if some disturbance such as mechanical vibration of the module is received. And keep a stable state. That is, the destabilization of the excitation laser light is significantly suppressed.

Here, the reason why the oscillation laser beam of the laser element B ₁ exhibits the above-mentioned characteristics is that the thickness of the well layer is basically set to 10 nm or more (first condition). That is, it can be considered that the thickness of the well layer can be defined as a factor that influences the magnitude of the above-mentioned Δλ value and also controls it. If this thickness is thinner than 10 nm, the Δλ value at the time of ASE becomes smaller than 15 nm, and it becomes difficult to realize multimode oscillation laser light.
As a result, the pumping laser light from the laser module fluctuates and its temporal stability deteriorates.

In the case of the laser device B ₁ , the shape of the spectrum curve of spontaneous emission light at the time of ASE changes variously depending on the relation between the first condition to the third condition described above, but the changing shape is For convenience, they can be distinguished as follows. This will be explained below. First, in the case of a conventional laser device that does not satisfy any of the first to third conditions, the spectrum curve of spontaneous emission light during ASE tends to have a shape as shown in FIG. . That is, the shape of the spectrum curve near the maximum intensity of the light output is likely to be slightly concave as shown by the mark ↔ in the figure. The type of spectrum curve exhibiting such a tendency is hereinafter referred to as type 1.

ASE in the case of a laser device which does not satisfy the first condition and the second condition but satisfies only the third condition.
The spectral curve of spontaneous emission light at time tends to be
It tends to have the shape shown in FIG. That is, the shape of the spectrum curve near the maximum intensity of the light output tends to be slightly convex as shown by the circle in the figure. The type of spectral curve that shows this tendency is
Type 2

The first condition is always satisfied and either one of the second condition and the third condition is satisfied, or both the second condition and the third condition are satisfied. In the case of the laser element B ₁ which is not provided, the spectrum curve of the spontaneous emission light at the time of ASE tends to have a shape as shown in FIG. That is, the shape of the spectrum curve in the vicinity of the maximum intensity of the light output tends to be a rounded convex shape over the location of the maximum intensity, as shown by ∘ marks in the figure. The type of spectrum curve showing such a tendency is hereinafter referred to as type 3.

In the case of the laser device B ₁ satisfying the first condition to the third condition at the same time, the spectrum curve of spontaneous emission light at the time of ASE tends to have a shape as shown in FIG. Cheap. That is, type 2 and type 3
Is a composite shape, and the entire shape is a rounded convex shape that straddles a portion of maximum intensity, and at the same time, the shape of the spectrum curve near the maximum intensity tends to be a convex shape. The type of spectrum curve showing such a tendency is hereinafter referred to as type 4.

That is, the laser device B ₁ has a characteristic that, when a spectrum curve of spontaneous emission light at the time of ASE is drawn, the spectrum curve shows either type 3 or type 4. From a different point of view, the laser element that draws the spectrum curve of spontaneous emission light at the time of ASE and shows the shape of type 3 or type 4 is the laser element B ₁ satisfying at least the above-mentioned first condition. . Therefore, the pumping laser light from the laser module assembled using it has good temporal stability. That is, it is possible to determine from the spectrum curve of spontaneous emission light at the time of ASE whether the laser element is effective for the temporal stability of the excitation laser light.

The laser element B ₁ preferably has the following characteristics. It will be described with reference to FIG. First, laser light is oscillated from the laser element B ₁ .
Here, it is assumed that the longitudinal direction of the laser element B ₁ (laser light emission direction) is the x-axis direction, the thickness direction, that is, the stacking direction in the layer structure C is the z-axis direction, and the width direction is the y-axis direction. Then, the description will be made focusing on the z-axis direction component of the emitted light.

The emitted light is the laser element B.₁Exit from the optical axis
Far-field pattern (FFP) on the plane orthogonal to
Occurs. The maximum z-axis component of this far field image (FFP) is
Output P ₀Is a light output distribution curve having. This and
Half the output level (1 / 2P₀) Place in the far field
Two points were found along the vertical (z-axis) direction of the FFP.
In addition, the light emitted from the front end face of the laser element is
A spread angle θ for each of the points is observed.

The angle θ is a full-width half angle (full-width half angle).
also known as the maximum angle). because,
This angle is formed between the front end face and the entire width between two points on the vertical axis which is half the power level. The laser device B ₁ has the above-mentioned spread angle θ of 25 °.
The following is preferable. This spread angle θ is 25 °
By the following, the laser element B ₁ has a sufficiently high coupling efficiency with the optical fiber, and not only can the optical output at the fiber end be increased, but also the optical confinement coefficient in the active layer becomes sufficiently small. Therefore, it is highly efficient.

Although the above description has been made in the case of the ridge waveguide type laser device, the laser device B ₁ is not limited to such a structure, and the layer structure satisfying the above-mentioned first condition. Self-aligned (SA
It may have an S-type) structure. As mentioned above,
The laser element B ₁ is incorporated in the package together with the element 5a having an optical feedback function, which is external to the semiconductor chip on which the element B ₁ is formed. However, the present invention is equally applicable to a laser device in which an element having an optical feedback function is integrated on a semiconductor chip as a laser resonator.

The laser device of the present invention provided with such an element having an integrated optical feedback function will be described.
FIG. 1 is a partially cutaway perspective view showing an example B ₂ of this laser device.
It shows in 0. This laser device B ₂ has a spacer layer 20 interposed between the upper GRIN-SCH layer 16 b and the upper clad layer 18 in the layer structure C of the laser device B ₁ shown in FIG. A current blocking layer 22 is formed by arranging a grating 21 with a predetermined period on the active layer 17 and stacking a p-type layer 22a and an n-type layer 22b on both sides of the active layer 17.

The laser element B ₂ has the grating 21 as an element having the optical feedback function and the wavelength selection characteristic in the vicinity of the active layer 17, so that the laser element B ₂ itself has the optical feedback function. A laser beam having a specific wavelength defined by the reflection bandwidth of 21 is output. In that case, the active layer 17 satisfies at least the above-mentioned first condition, and by satisfying the second condition and the third condition, the laser light from the laser element B ₂ can be changed as shown in FIG. Similar to the case of the laser module of the present invention shown,
It is in multi-mode, and its optical output is in a state with little temporal fluctuation.

That is, this laser element B ₂ can exhibit the same function as the laser module A shown in FIG. 1 by itself. As a matter of course, the laser module shown in FIG. 1 can be assembled by using the laser element B ₂ as a light source. The maximum optical output of the semiconductor laser module in the present invention is L × 0.1 mW / μm or more, more preferably L × 0.25 mW / μm or more. Here, L is the length (unit: μm) of the resonator of the semiconductor laser device used in the present invention. From the above relationship, the maximum optical output of the semiconductor laser module of the present invention is 80 mW, and more preferably 200 mW when the cavity length is 800 μm. The resonator length is 1200 μm
The maximum light output is 120mW, more preferably 300
mW, and the maximum optical output when the resonator length (L) is 1800 μm is 180 mW, more preferably 450 mW.

[0051]

[Example] 1. Manufacturing of Laser Element B ₁ Each layer shown in Tables 1 and 2 was formed on a substrate made of n-GaAs to form a layer structure C shown in FIG. A ridge waveguide having a width of 4 μm and a height of 1.2 μm is formed on the upper surface of the formed layer structure by applying photolithography technology and etching technology, and then a protective film made of SiN 1 is formed thereon.
Formed 3.

Then, the back surface of the substrate 10 is polished to form the lower electrode 12 made of AuGeNi / Au, and a part of the protective film on the upper surface of the cap layer 19 is removed. The upper electrode 14 made of / Pt / Au was formed. Then, the substrate is cleaved to form a bar having a resonator length (L) of 800 μm, and a low reflection film made of SiN and having a reflectance of 0.8% is formed on one end face to form a front end face. On the other end face, a highly reflective film made of SiO ₂ / Si having a reflectance of 92% was formed to form a rear end face.
Finally, the bar was processed into chips to manufacture the laser device B ₁ shown in FIG.

[0053]

[Table 1]

[0054]

[Table 2]

A schematic diagram of the conduction band of the laser device 1 is shown in FIG. 11, and a schematic diagram of the conduction band of the laser device 4 is shown in FIG. All the numbers in the figure indicate the respective layers shown in FIG.

2. Laser element characteristics AQ6317 is used for the laser elements shown in Tables 1 and 2.
ASE spontaneous emission light was emitted using (Optical Spectrum Analyzer manufactured by ANDO), each spectrum curve was obtained, and the shape thereof was observed. The results are shown in Table 3. Further, each laser element was made to oscillate, and the far-field image of the oscillated laser light was measured using a photodiode to obtain the vertical spread angle θ corresponding to the half-value width of the spectrum curve. The results are also shown in Table 3.

[0057]

[Table 3]

For the laser element 1, the laser element 3, and the laser element 4, the injection current (I) is changed to emit spontaneous emission light, and the respective spectral curves are drawn.
The spectral width (Δλ value) shown between two wavelengths in the case of an output that is 3 dB lower than the maximum output (P ₀ ) was obtained.
Then, the I / Ith value and the spectrum width (Δλ value) were plotted. The results are shown in Fig. 13.

From the above results, the following is clear. (1) First, as is clear from FIG. 13, the laser elements 1, 3 and 4 all oscillate when the I / Ith value is 1 or more, that is, when the injection current is equal to or more than the threshold current. However, in the region of the injection current of I value that spontaneous emission light emits, in the case of the laser device 1, the I value is Ith.
Spectral width (Δλ value) in spontaneous emission that decreases substantially linearly with increasing value
have.

On the contrary, the spectral width (Δλ value) of the laser element 4 remains substantially the same value at I / Ith values between 0.2 and 0.6, and I / Ith As the value increases from 0.6 to about 1.0, it decreases toward zero with a large slope. The laser device 3 also exhibits substantially the same behavior as the laser device 4, but has two prominent stages with a reduced spectral width (Δλ value), and there is a flat region between the stages. The first reduction stage is relatively small and has an I / Ith value of 0.2 to about 0.4.
It's happening between increasing. The second reduction stage is large and is occurring while the I / Ith value increases from 0.8 to about 1.05. The flat region occurs when the I / Ith value is between about 0.4 and about 0.8, and the spectral width Δλ in that case is substantially constant.

(2) In any case, in the case of the laser element 3 and the laser element 4, a wide range of I / Ith values (0.4 and 0.
(Between 8), the Δλ value shows a stable value.
This means that even if the I value fluctuates within this range, the shape of the spectrum curve of the spontaneous emission light changes only slightly and is stable. this is,
It is considered that this is an index that gives advance notice of the stability of the oscillated laser light when driven with an injection current (I) larger than the threshold.

Then, Δ of the laser elements 3 and 4
When the λ value is compared, the I / Ith value between 0.2 and 0.9 (that is, the flat region) shows a larger value in the case of the laser element 4, which means that It is considered that the element 4 suggests that the driving stability is superior.

(3) Referring to Table 1, Table 2 and Table 3, in the case of the laser device 1 having the quantum well structure of the double-layer structure with the well layer thickness of 7 nm, the spontaneous emission The shape of the spectrum curve is type 1, and its Δ
Although the λ value changes as shown in FIG. 13, in the laser device 3 in which the first condition is satisfied by increasing the thickness of the well layer to 12 nm and the quantum well structure has a single-layer structure, the spectrum is The shape of the curve changes to type 3, and the Δλ value is stable.

Then, in the case of the laser device 4 satisfying both the second condition and the third condition while satisfying the first condition, the shape of the spectrum curve is type 4, and the Δλ value is also It has stabilized at a high level.

(4) That is, when the thickness of the well layer is increased, the shape of the spectrum curve of spontaneous emission light changes to type 3, and at the same time, the Δλ value is stabilized in a wide range of I / Ith value. Then, assuming that the above first condition is satisfied,
Further, Si doping is performed on the well layer (satisfaction of the second condition), and Si doping is performed on the n-type cladding layer at a high concentration of 3 × 10 ¹⁷ / cm ³ (satisfaction of the third condition), and spontaneous emission is performed. The shape of the spectrum curve of light is type 2 and type 3.
It has been revealed that the shape changes to a type 4 in which the two are combined, that is, type 4, and at the same time, the Δλ value stabilizes at a high level in a wide range of the I / Ith value.

The above description is for the case of a laser device having a front end face reflectance of 0.8%. However, the front end face reflectance is changed within the range of 0.5 to 15%. It was confirmed that each laser element exhibited the same characteristics as described above even in the case of the above. Further, although the n-type substrate is used as the substrate in the embodiment, similar characteristics can be obtained even if the substrate is p-type. However, in that case, the conductivity type of each layer in the layer structure C is opposite to that in the embodiment.

3. Assembling the laser module Among the laser elements shown in Table 1 and Table 2, the laser element 1 and the laser element 4 are selected, and each of them is optically coupled with the optical fiber in which the fiber Bragg grating is formed through the lens. The laser module A shown in FIG. 1 was assembled.

A device incorporating the laser element 1 is referred to as device A ₁ (conventional device), and a device incorporating the laser element 4 is referred to as device A ₂ (example device). The fiber Bragg grating optically coupled to the laser element 1 has a reflectance of 7%, a reflection bandwidth of 1.5 nm, and a central wavelength of 979n.
The fiber Bragg grating, which is designed to have a wavelength selection characteristic of m, is optically coupled to the laser element 4 and has a reflectance of 7%, a reflection bandwidth of 1.5 nm, and a center wavelength of 976 nm. Is designed to be.

4. Performance of Laser Module (1) Time Stability of Excitation Laser Light A current of 250 mA was injected into the devices A ₁ and A ₂ to emit the excitation laser light. Then, the optical output (Pf) of the laser light is measured by a system including a Lightwave multimeter 8153A (manufactured by Azirendo), Power Sensor Module 81533B (manufactured by Azirendo), and Optical Head 81525A, and monitor light intensity (Im). ADVANTEST Digi
tal Electrometer R8240 (manufactured by Advantest) and IL
X Lightwave Laser Diode Controller LDC-3744B (I
LX Lightwave). Then, over a time interval of about 1 minute, Pf and Im
The rate of change (%) in the measured value was calculated at 0.4 second intervals.

[0070] The results of the case of the apparatus A ₁ in FIG. 14, device A ₂
The results in the case of are shown in FIG. 14 and 15
As is clear from the comparison, the device A ₂ is significantly superior to the device A ₁ in the temporal stability of the oscillated laser light.

(2) Stability of oscillated laser light with respect to drive current value The drive current to the devices A ₁ and A ₂ is 5 mA from the threshold value Ith.
The light output (Pf) of the excitation laser light and the change rate (%) of the monitor light intensity (Im) were calculated by the measurement system used in (1) each time. Device A
Figure 16 results in the case of _1, Fig. 1 the results when the device A ₂
7 shows. As is clear from comparison between FIG. 16 and FIG. 17, in the case of the device A ₁ , when the drive current changes, Pf, Im
Shows a large fluctuation, but in the case of the device A ₂ , it does not fluctuate at all, and this device oscillates a very stable excitation laser beam even if the drive current changes. Figure 1
6 and FIG. 17, it can be seen that the maximum allowable change rate is 0.5%.

(3) Time stability of spectrum of excitation laser light A driving current of 250 mA was injected into the devices A ₁ and A ₂ to emit the excitation laser light. Then, the spectra at the start of driving and 10 seconds, 20 seconds, 30 seconds, and 40 seconds after that were observed. The results, in the case of the apparatus A ₁ in FIGS. 18 to 22, in the case of device A ₂ 23 to 27
It was shown to.

From the above results, the following is clear. Comparing the spectrum diagrams (FIGS. 18 and 23) of the excitation laser light immediately after the device A ₁ and the device A ₂ are driven,
In the case of the device A ₁ , the center wavelength thereof oscillates in the single longitudinal mode in the vicinity of the center wavelength (979 nm) of the fiber Bragg grating. On the contrary, in the case of the device A ₂ , the central wavelength of the fiber Bragg grating (97
The multi-longitudinal mode oscillates around 6 nm).

The oscillation laser beam of the device A ₁ has its oscillation spectrum fluctuated as time passes. However, in the case of the device A ₂ , even after the driving time has elapsed, the oscillation spectrum of the device A ₂ is at the start point of driving (see
It is substantially the same as the case of 8). That is, the device A ₂ emits the excitation laser light excellent in time stability.

(4) Relation between optical output and state of optical fiber In the apparatus A ₂ , the optical fiber was oscillated with the diameter of about 100 mm for 3 turns. The oscillation spectrum at that time is shown in FIG. Then, the optical fiber was rewound from the above-mentioned wound state to a wound state of 3 turns with a diameter of about 100 mm, and laser oscillation was performed under the same conditions. The oscillation spectrum at that time is shown in FIG.

As is apparent from FIGS. 28 and 29, even if the winding state of the optical fiber changes, the oscillation spectrum of the excitation laser beam from the device A ₂ does not change. On the other hand, in the device A ₁ , the optical fiber with a diameter of 100 mm is 5
Laser oscillation was performed in the turned state. The oscillation spectrum at that time was multimode oscillation as shown in FIG.

Next, the optical fiber was rewound from the above-mentioned wound state to a wound state of 4 turns with a diameter of 100 mm, and laser oscillation was performed under the same conditions. The oscillation spectrum at that time is shown in FIG. As is clear from comparison between FIG. 30 and FIG. 31, in the case of the device A ₁ , when the winding state of the optical fiber changes, the oscillation spectrum of the excitation laser light changes.

As described above, in the device A ₂ , the excitation laser light emitted is stable regardless of the winding state of the optical fiber, or more generally, whatever the optical fiber is. It has been found.

[0079]

As is apparent from the above description, in the laser module of the present invention, the well layer has a thickness of 10 nm or more, which is thicker than the conventional one, and the well layer is doped with impurities. Since the layer is doped with an n-type impurity, the oscillation laser light is assembled by optically coupling a laser element that multimodes and a fiber Bragg grating. Is excellent. Further, the excitation laser light emitted is stable even if the drive current of the laser element fluctuates. Further, even if the winding state of the optical fiber is changed, for example, the exciting laser light emitted is stable and has high practical reliability.

[Brief description of drawings]

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

FIG. 2 is a perspective view showing an example B ₁ of the laser device of the present invention.

FIG. 3 is a graph for defining a threshold current of a laser device.

FIG. 4 is a graph showing a spectrum curve of spontaneous emission light.

FIG. 5 is a spectrum curve diagram of type 1 in spontaneous emission light of a laser device.

FIG. 6 is a spectrum curve diagram of type 2 in spontaneous emission light of a laser device.

FIG. 7 is a spectrum curve diagram of type 3 in spontaneous emission light of a laser device.

FIG. 8 is a spectrum curve diagram of type 4 in spontaneous emission light of a laser device.

FIG. 9 is an explanatory diagram for explaining a spread angle θ of a far field image.

FIG. 10 is a partially cutaway perspective view showing an example B ₂ of the semiconductor laser device of the present invention.

FIG. 11 is a schematic diagram of a conduction band of laser elements 1 and 2.

FIG. 12 is a schematic diagram of a conduction band of the laser device 4.

FIG. 13 is a graph showing the relationship between the I / Ith value and the spectral width (Δλ) in the laser device.

FIG. 14 is a graph showing a Pf change rate and an Im change rate of device A.

FIG. 15 is a graph showing the Pf change rate and the Im change rate of device B.

16 is a graph showing Pf and Im change rates with respect to the drive current of device A. FIG.

FIG. 17 is a graph showing Pf and Im change rates with respect to the drive current of device B.

FIG. 18 is a spectrum diagram of excitation laser light at the start of driving the device A.

FIG. 19 is a spectrum diagram of the excitation laser light after 10 seconds have elapsed from the start of driving the device A.

FIG. 20 is a spectrum diagram of a laser beam for excitation after 20 seconds have elapsed from the start of driving the device A.

FIG. 21 is a spectrum diagram of the excitation laser light after 30 seconds have elapsed from the start of driving the device A.

FIG. 22 is a spectrum diagram of a laser beam for excitation 40 seconds after the driving of the device A is started.

FIG. 23 is a spectrum diagram of a laser beam for excitation at the start of driving the device B.

FIG. 24 is a spectrum diagram of excitation laser light after 10 seconds have elapsed from the start of driving the device B.

FIG. 25 is a spectrum diagram of the excitation laser light after 20 seconds have elapsed from the start of driving the device B.

FIG. 26 is a spectrum diagram of excitation laser light after 30 seconds have elapsed from the start of driving the device B.

FIG. 27 is a spectrum diagram of the excitation laser light 40 seconds after the start of driving the device B.

FIG. 28 is a spectrum diagram of the excitation laser light of the device A when the optical fiber has a diameter of 100 mm and is wound in three turns.

FIG. 29 is a spectrum diagram of the excitation laser light of the device A when the optical fiber is changed to a wound state of 100 mm in diameter and 3 turns.

FIG. 30 is a spectrum diagram of the excitation laser light of the device B when the optical fiber has a diameter of 100 mm and is wound for 5 turns.

FIG. 31: Optical fiber 100 mm in diameter 5 turns to 4
FIG. 6 is a spectrum diagram of the excitation laser light of the device B when changed to a wound state of a turn.

[Explanation of symbols]

1 package 1a Package 10 bottom plate 1b Package 10 cylindrical hole 2 Peltier module 3 base materials 4 chip carrier 5 optical fiber 5a Fiber Bragg grating 6 Fiber fixing member 7 sleeve 10 substrates 12 Lower electrode 13 Protective film 14 Upper electrode C layer structure 15 Lower clad layer 16a Lower GRIN-SCH layer 17 Quantum well structure active layer 16b Upper GRIN-SCH layer 18 Upper clad layer 19 Cap layer 20 Spacer layer 21 Grating 22 Current blocking layer

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5F073 AA13 AA63 AB25 AB28 AB29                       BA01 BA09 CA04 CA07 CB13                       CB19 EA01 EA03 FA06

Claims (17)

[Claims] 1. A layer structure having a well layer made of a semiconductor material containing at least Ga and As and an active layer having a barrier layer surrounding the well layer is formed on a GaAs substrate, and light resonates parallel to the substrate. In a semiconductor laser module used for a pumping light source in which a semiconductor laser element and an element having an optical feedback function are optically coupled, the semiconductor laser module oscillates in a longitudinal mode in a multimode, and a well layer in the active layer. A semiconductor laser module having a thickness of 10 nm or more. 2. The semiconductor laser module according to claim 1, wherein at least the active layer is doped with impurities. 3. The impurity is an n-type impurity.
Semiconductor laser module. 4. The semiconductor laser module according to claim 3, wherein the n-type impurity is Si. 5. The doping concentration of Si is 1 × 10 ^16.
/ Cm ^{3 to} 5 × 10 ¹⁸ / cm ³ The semiconductor laser module according to claim 4. 6. The semiconductor laser module according to claim 1, wherein the n-type clad layer having the layer structure is doped with at least Si. 7. The semiconductor laser module according to claim 1, wherein the number of well layers in the active layer is one. 8. The semiconductor laser module according to claim 1, wherein the well layer has a thickness greater than that of the barrier layer. 9. The semiconductor material forming the active layer is G
aAs, InGaAs, GaAsSb, or InGa
The semiconductor laser module according to claim 1, which is AsSb. 10. The semiconductor laser module according to claim 1, wherein an oscillation wavelength of oscillation laser light of the semiconductor laser element is 940 to 990 nm. 11. The semiconductor laser device is either a ridge waveguide type or a self-aligned type.
0 of the semiconductor laser modules. 12. The semiconductor laser module according to claim 1, wherein a divergence angle in a vertical direction in a half value width of a light output distribution curve of the oscillation laser light of the semiconductor laser element is 25 ° or less. 13. The semiconductor laser device has the following formula:
Spectral curve of spontaneous emission light emitted when a current satisfying the relation of 2 ≦ I / Ith ≦ 0.8 (wherein I is an injection current and Ith is an injection current when starting laser oscillation) is injected. 2. The spectral width of a portion exhibiting an intensity of 3 dB lower than the maximum intensity is 15 nm or more.
2. A semiconductor laser module according to any one of 2. 14. The element having the optical feedback function includes a fiber Bragg grating, a dielectric multilayer film filter,
Or a distributed Bragg reflector.
13. The semiconductor laser module according to any one of 13. 15. The semiconductor laser module according to claim 1, wherein the element having an optical feedback function is a fiber Bragg grating formed in a wedge-shaped optical fiber. 16. The semiconductor laser module according to claim 1, wherein an element having the optical feedback function is formed by forming a grating near the active layer in the semiconductor laser element. 17. When the length of a resonator in which light resonates parallel to the substrate in the semiconductor laser device is L (μm), the optical output of the semiconductor laser module is L ×.
The semiconductor laser module according to any one of claims 1 to 16, which has a power density of 0.1 mW / µm or more.