JP2002368341A - Semiconductor laser element and exciting light source using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser element that can realize high optical output operation and an optical fiber amplifier using the same. SOLUTION: This semiconductor laser element is provided with an MQW structure including more than one well layer and more than one barrier, and an active layer 4 having a resonator of 800 μm or more. The active layer 4 is provided with a doped area 8 including at least one well layer and at least one barrier layer adjacent to the well layer. The entire active area comprised of all well and active layers may be doped. Upper and lower optical containment layers 3A and 3B of about 20 nm-50 nm in thickness are adjacent to the active layer 4. An optical fiber amplifier incorporating the semiconductor laser element is disclosed, and it is arranged on a cooler and includes the semiconductor laser element packaged within a package, and the light incident end face of an optical fiber is optically connected with the light output end face.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multiple quantum well (mult)
The present invention relates to a semiconductor laser device having an active layer (light emitting region) having an iple quantum well (MQW) structure.
More specifically, the present invention relates to an MQW semiconductor laser device having a high carrier injection efficiency and realizing a high light output operation. The present invention also relates to an excitation light source using the same.

[0002]

2. Description of the Related Art A semiconductor laser device having an MQW structure as an active layer (light emitting region) oscillates at a lower threshold current and can operate at a higher light output than a semiconductor laser device having a bulk active layer. It has been known. FIG. 1 shows an example of a cross-sectional structure of such a known MQW laser device.
(A).

The laser device shown in FIG. 1A is composed of a large number of semiconductor layers formed on a semiconductor substrate, which is illustratively an n-type semiconductor, using a known method. The various layers are n
Type lower cladding layer 2A, undoped lower optical confinement layer 3A, active layer 4, undoped upper optical confinement layer 3
B, a p-type upper cladding layer 2 </ b> B, and a p-type cap layer 5. These layers are sequentially formed on the substrate 1 by any of known epitaxial crystal growth methods such as a metal organic chemical vapor deposition (MOCVD) method.
Further, an n-type lower electrode 6A is formed on the lower surface of the substrate 1, and a p-type upper electrode is formed on the cap layer 5.

As shown in FIG. 1A, the active layer 4
The adjacent light confinement layers 3A and 3B are formed in a long mesa structure using a conventional photolithography technique. Next, the p-type semiconductor layer 7A and the n-type semiconductor layer 7B for current narrowing are used to inject a current into a narrow region during driving.
It is formed adjacent to the mesa structure. The obtained structure is then cleaved and formed on _one cleavage plane, and has a predetermined length having a front end face (S ₁ ) used for light emission and a rear end face (S ₂ ) formed on the opposite cleavage plane. Laser element having a cavity length (L) of The front end face S1 has a low reflection film for promoting light emission from the front face of the resonator, and the rear end face has a high reflection film for suppressing light emission from the back face.

It is known that the active layer 4 is designed to have an MQW structure consisting essentially of a heterojunction of alternating well layers of semiconductor material. Each heterojunction is composed of a pair of semiconductor layers, that is, a well layer having a narrow band gap energy and a barrier layer. The bandgap energy of the barrier layer is wider than that of the well layer. Various sub-layers in MQW structure
Have a thickness of several nm.

Each of the lower and upper light confinement layers 3A and 3B adjacent to the active layer 4 enhances the confinement of the laser light generated in the active layer 4, thereby increasing the external differential quantum efficiency of the laser device and increasing the light output. To achieve operation, it is designed to have an isolated confinement heterojunction structure (SCH). The laser device of FIG. 1A is arranged in a package and used as a signal light source of an optical communication system or an erbium-doped fiber amplifier (EDF).
It is known that a laser module suitable as a light source for exciting an optical fiber amplifier such as A) or a Raman amplifier can be assembled. Within the package, the laser element is thermally coupled to a cooling element comprising a Peltier element. In addition, the package is equipped with known elements to monitor and control the heat generated and the light output and to ensure good optical coupling of the laser output to the optical fiber.

In recent years, the rapid growth of the Internet and other communication systems has led to the development of optical fiber wavelength division multiplexing (WDM) systems in order to provide increased data transmission capacity in those systems.
In order to provide an optical fiber amplifier that operates at a high output so as to meet the demand for an increased number of channels, a pumping laser device having a high optical output coupled to an optical fiber is required. Pumping lasers for optical fiber amplifiers are required to be constantly optically coupled to an optical fiber at a higher optical output, and to be driven stably with a narrow spectral width in order to use the laser in an optical fiber Raman amplifier.

[0008] One method of realizing a high-power pumped laser device with MQW is to increase the cavity length (L). Increasing the cavity length reduces both the electrical resistance and the thermal resistance of the laser element. This further increases the saturation drive current Isat at which the maximum light output occurs. This is because light output saturation due to heat is suppressed. However, when the reflectivity of the output end face is constant, increasing L increases the external differential quantum efficiency, as shown in FIG. 1B. As is clear from FIG. 1B, the output-current curve is relatively low from the beginning for a long-cavity laser device. As described above, since the external differential quantum efficiency decreases as the cavity length increases, it is disadvantageous to use a long cavity laser element for high light output operation at a certain drive current.

This problem can be alleviated to some extent by reducing the reflectivity at the output end face. However, if the reflectance of the output end face of the laser element is made smaller than a certain value, the differential quantum efficiency of the laser element is reduced, and the maximum light output is reduced. The reported mechanisms for such degradation include leakage of carriers from the MQW structure to the optical confinement and cladding layers, increased light absorption and recombination loss due to this carrier leakage, and non- Includes homogeneous hole injection.

In a low-power, short-cavity laser device, GR
The IN-SCH structure is known to be effective. A continuous GRIN structure or a multi-layer GRIN structure has been reported to achieve low threshold current operation.
For high power laser devices, the reported results are 2
It shows that the GRIN structure of the stage has the advantage of high light output.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a new and improved semiconductor laser device which avoids the above-mentioned problem of limiting the high light output operation of the above laser device. In particular, the laser device of the present invention is useful as a pumping light source having high carrier injection efficiency for an optical fiber amplifier. According to the present invention, high carrier injection can be realized without increasing reactive current.
Light output can be increased as compared with other laser devices having a structure.

[0012]

In order to achieve the above-mentioned object, according to the present invention, there is provided an optical confinement layer arranged on an active layer of an MQW structure having a plurality of well layers and a plurality of barrier layers. A cavity length of at least 800 nm, and at least one well layer in the active layer and at least one barrier layer adjacent to the well layer are doped with impurities. In addition, a semiconductor laser device is provided, wherein the thickness of the light confinement layer is 20 to 50 nm.

Further, in the present invention, the semiconductor laser element is disposed in a package having a cooling element, an optical lens, and a photodetector, and an optical fiber is coupled to an optical output end face of the semiconductor laser element. A pumping device for an optical fiber amplifier is provided.

[0014]

DETAILED DESCRIPTION OF THE INVENTION In one aspect, the present invention is directed to a laser structure (also referred to as a laser element) having the capability to produce high light output. The laser device of the present invention preferably has the layer structure shown in the cross-sectional structure example of FIG. M of the active layer 4 of the present invention
The QW structure (not shown in FIG. 1A) is sandwiched between adjacent light confinement layers 3A and 3B. In relation to the purpose of manufacturing a high-power laser element, a laser element having a cavity length (L) of 800 μm or more is particularly useful among the types shown in FIG.

One possible way to obtain higher light output from a semiconductor laser device having an MQW active layer is to sandwich a non-doped well layer between barrier layers having an n-type dopant such as Se or S. is there. This so-called modulation doping of the barrier layer is thereby controlled by the MQW
The internal loss of the structure is suppressed, thereby enabling a high light output operation.

However, in the case of MOCVD, it is necessary to selectively dope only the barrier layer with an n-type dopant, so that it is very difficult to form this type of modulation-doped structure in the active layer. is there. For example, when the n-type dopant is S, S diffuses from the barrier layer to the adjacent well layer at the temperature at the time of device manufacture. Similarly, when Se is used, the well-known memory effect of Se occurs during the crystal growth and results in well layers being included. Completely interrupting the crystal growth process creates interface states and limits the light output of the device.

FIG. 2 shows an example of an energy band diagram of the conduction band and the valence band of the laser device of the present invention. FIG. 2 shows the band gap between the conduction band and the valence band, and shows a lower optical confinement layer 3A, an active layer 4, an upper optical confinement layer 3B, and an upper clad layer 2B on the lower clad layer 2A.
Are formed in this order. As shown in FIG. 2, the active layer 4 comprises an alternating heterojunction of a well layer 4A and a barrier layer 4B, thereby providing an MQW structure having five wells. Light confinement layer 3 disposed between active layer 4 and cladding layers 2A and 2B
A and 3B are formed such that their compositions and thicknesses are symmetrical with respect to the active layer 4. Each of the light confinement layers 3A and 3B has a number of steps in each energy band as shown in FIG.

As shown in FIG. 2, the band gap is
It is smallest in the well of the MQW structure of the active layer 4, larger in the MQW barrier layer, larger in the optical confinement layer, and largest in the cladding layer. A first basic feature of the laser device of the present invention is that a dopant is introduced into at least one well layer 4A of the active layer 4 and a barrier layer 4B adjacent thereto, thereby forming a doped region 8. That is. FIG. 3 (c) shows a doped region 8 having only one barrier layer and well layer, but according to the present invention, the doped region 8 may have any number of pairs of well layers and barrier layers. FIG. 3 (b), which may be unfolded. In fact, according to the invention, the entire active layer may be included in the doped region 8. The present inventors have measured that increasing the doped region in all active layers reduces the series resistance and thermal resistance of the laser device. Reduction of series resistance and thermal resistance reduces heat generation and increases maximum light output.

The dopant used to form the doped region 8 is preferably an n-type impurity such as S and Si, or a combination thereof. Doping concentration is 1 × 1
It is preferable to set to about 0 ^{17 to} 3 × 10 ¹⁸ cm ⁻³ .
We do not obtain the aforementioned benefit of creating a doped region 8 in the active layer 4 if the doping concentration is lower than about 1 × 10 ¹⁷ cm ⁻³ , so that the light output is intended. That strengthening will not be realized. On the other hand, we have a doping concentration of about 3 ×
It has been found that, when it is higher than 10 ¹⁸ cm ^-3 , the crystallinity of the active layer 4 is degraded, causing a similar increase in non-light-emitting components. This limits the high power operation of the resulting laser device.

While an n-type dopant is preferred, the dopant used in the present invention may be replaced by a p-type dopant. In this case, the p-type dopant may be any one of Be, Mg, and Zn, or a combination thereof.
Another important feature of the present invention is that the light confinement layers 3A and 3B shown in FIG.
That is, they are arranged so as to be set within the range of 0 nm. If the thickness of the optical confinement layers 3A and 3B is thinner than 20 nm, the obtained optical output can reach saturation with a low drive current due to overflow of electrons. On the other hand, when the thickness of the optical confinement layer is 50 nm or more, the DC resistance of the laser device increases. This causes significant heat generation, which can also cause light output saturation due to thermal saturation.

The light confinement layers 3A and 3B form a heterojunction with the active layer 4. Similarly, the optical confinement layer further forms a heterojunction with the upper and lower cladding layers 2B and 2A. The band gap energy of the cladding layers 2B and 2A is larger than the band gap energy of the active layer 4.
As shown in FIG. 2, the light confinement layer 3B, the minimum bandgap energy E ₁ of 3A, the difference between the maximum band gap energy E ₂ of the optical confinement layer is preferably about 90meV more.

As shown in FIG. 2, the optical confinement layers 3A,
3B, for example, a sublayer 3B₁, 3B_Two, ...
... 3B_n, And 3A₁, 3A_Two, ..... 3A_nof
As described above, it is preferable to configure with three or more constituent layers. Book
According to the invention, the band gap of each of these constituent layers is provided.
As shown in FIG. 2 and FIG.
It increases stepwise as it gets farther from the active layer 4. Figure
3 is a constituent layer 3B₁, 3B_Two, ..... 3B_nComposed of
Of the step of the band gap of the confined light confinement layer 3B
Series of points A in the part₁, A_Two, .... A_n, A₀Shows
are doing. Point A ₀Is the light confinement layer 3B_nAnd adjacent to it
Note that the step is formed between the cladding layers 2B.
I want to be watched. FIG. 3A shows the layer 3B.₁And it
In the band gap energy between adjacent active layers 4
Point A located on stairs₀'It is shown. Point A₀’,
A₁, A_Two, .... A_nAnd A₀Is a band group
Define the envelope of the cap energy (hereinafter this envelope
Is referred to as a band gap energy ray). This
The bandgap energy ray of is straight or
Is continuous and upward as shown by the broken line in FIG.
Or a downward curved shape. This
The upward or downward curved shape of
It may be a lock.

[0023] For FIG. 3 (a), thus, to have a linear shape as a whole a band gap energy rays, a band gap energy rays intersect at the band gap energy beam and the point A _n of the layer 3B _n. In this case, the light confinement layer 3B is said to have a linear GRIN-SCH structure. As already pointed out, the light confinement layer 3A,
3B is not limited to only the three-layer structure example. It is preferred to increase the number of sub-layers. However, increasing the number of layers requires careful control of the composition of each layer-if even one of them deviates from certain lattice-matching conditions, crystal degradation will occur, which will cause laser operation due to crystal defects. It is feared that it deteriorates.

The laser element of the present invention is preferably formed so that each of the well layers 4A has a compressive strain of about 0.5 and about 1.5% with respect to the substrate 1.
Further, the laser device of the present invention is preferably formed so that each of the barrier layers 4B has a tensile strain in order to compensate for the compressive strain of the well layer 4A. In particular, the laser device of the present invention is formed so that the barrier layer 4B has a tensile strain in order to compensate for a compressive strain larger than 1.5% of the well layer 4A.

As pointed out above, the laser device of the present invention preferably has a cavity length (L) of about 800 μm or more. More preferably, L is greater than about 1000 μm. When the cavity length is shorter than about 800 μm, the electric resistance and the thermal impedance of the laser element become larger, and the saturation current is reduced. This is because thermal saturation suppresses the saturation current. Thus, the resonator length is about 800 μm
If shorter, the benefits of the present invention will not be fully realized. For example, when a relatively long resonator having a cavity length of about 800 μm or more is used, the reflectance of the front end face of the laser element is about 5%.
Hereinafter, it is preferable that the reflectance of the rear end face is 90% or more. Forming a low-reflection coating on the front end face of the laser device reduces the external quantum efficiency that would otherwise occur based on the reduced mirror loss to total loss caused by the use of a longer cavity. Compensate for the decrease. For a laser device having a cavity length of 1000 μm or more, it is preferable that the low reflection film has a reflectance of about 1.5%.

Next, an example of the laser component of the present invention will be described with reference to FIG. This laser component 40 is package 1
The laser element 41 is hermetically sealed in the area 0. The laser element 41 is arranged on the cooling element 9 composed of a number of Peltier elements 9a. The collimator lens 11a is arranged close to the output end face of the laser element 41, and the light focusing or light focusing lens 11b is arranged near the wall of the package 10. The optical fiber 12 is connected to the lens 1 so that the light from the laser element 41 is optically coupled to the optical fiber 12.
1b, and is disposed at the front of the package 10. The photodiode 13 is arranged close to the rear end face of the laser element 41 and monitors the light output from the element. An isolator 14 is disposed between the collimator lens 11a and the lens 11b, and suppresses return light from the optical fiber.

Preferably, the optical fiber 12 has an optical fiber grating 12b formed on its central core 12a.
Having. The reflection bandwidth of the fiber grating 12b is preferably about 3 nm or less. (This reflection bandwidth corresponds to the reflection spectrum of the fiber grating 12b.
full width of half maximums (FWHM)). More preferably, the reflection bandwidth of the fiber grating is set to about 2 nm or less, and even more preferably to about 1.5 nm or less. However, the reflection bandwidth of the fiber grating 12b should be larger than the longitudinal mode wavelength interval of the light from the laser element 8. By setting the bandwidth of the grating in this way, the longitudinal mode kink in the current-light output characteristics of the laser light from the optical fiber 12 is reduced or eliminated, and at the same time,
Multiplexing can be enhanced by narrowing the spectrum width of light. The laser module of the present invention of FIG. 4 achieves higher output and operates more stably than known laser modules.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A number of semiconductor laser devices according to the present invention having a wavelength of 1480 nm and the layer structure shown in FIG. 1A were manufactured as follows, and the parameters were changed while changing various parameters of the manufactured devices. And the relationship between laser characteristics were analyzed. Effect of Impurity Doping on Active Layer An n-type cladding layer 2A made of n-type InP was formed on the substrate 1 of n-type InP. As shown in FIG. 3B, a lower light confinement layer 3A was formed on the lower clad layer 2A. The lower light confinement layer 3A has the following G
Manufactured in undoped InGaAsP-based semiconductor material with RIN-SCH structure: first layer 3A ₂ , λg = 1.1 μ
m, thickness 20 nm; and second layer 3A ₁ , λg = 1.2 μm
m and a thickness of 20 nm.

As will be described in detail below, an active layer 4 was then formed on the lower optical confinement layer 3A. Next, a first layer 3B ₁ , λg = 1.2 μm and a thickness of 20 nm are formed thereon.
Then, an upper optical confinement layer 3B of InGaAsP having a thickness of 20 nm and a second layer 3B ₂ , λg = 1.1 μm was formed. Thus, the upper and lower light confinement layers 3A, 3A
B was manufactured to be symmetric with respect to the active layer 4.

Each of the MQW active layers 4 has a thickness of 4 nm.
And made of InGaAsP5Formed of 4A wells
Was. Each of the well layers has a thickness of 10 nm and is made of InGaAs.
It was surrounded by a barrier layer made of P (λg = 1.2 μm). This
MQW active layer structure has 1% compressive strain in each well
It was formed to have. n-type dopant Se is MQW
Injected into the layer group of the active layer,
Region 8 was formed: a first set of devices was formed with a well layer 4A and a barrier.
All the wall layers 4B have a dopant concentration of 5 × 10¹⁷cm^-8And all
All MQW layers were manufactured by doping (FIG. 3 (b)
This case is referred to as “full doping”). Elementary
The second set of children consists of a central well layer 4A and
Only one pair of one adjacent barrier layer 4B has 5 × 1
0 ¹⁷cm^-8Manufactured by doping with dopant concentration
(In this case, shown in FIG.
). Further, an undoped active layer 4 is provided as a comparative example.
The device set was manufactured (hereinafter referred to as “undoped”).
Say).

Thereafter, a mesa structure is formed on each element by using ordinary photolithography and etching techniques.
Next, a p-type current blocking layer 7A and an n-type current blocking layer 7B for current constriction were formed in a region close to the obtained mesa. Next, an upper cladding layer 2B made of p-type InP is formed on the upper optical confinement layer 3B,
A contact layer 5 made of p-type InGaAsP was formed thereon. Next, a p-type upper electrode was formed on the contact layer, and the back surface of the substrate 1 was polished. An n-type electrode 6A was formed on the polished surface obtained.

The resulting structure is then cleaved and
The cavity length (L) is set to 000 μm, a low reflection film (reflectance 1%) is formed on the front end face S1, and a high reflection film (reflectance 95%) is formed on the rear end face S2. Completed. For three different types of laser devices, the maximum light output (Pmax) during current driving was measured. The results obtained are also summarized in Table 1 below.

[0033]

[Table 1]

Table 1 compares the maximum optical power Pmax for three types of laser devices having different doping states and a cavity length of 1000 μm. From Table 1,
It can be seen that high light output driving is achieved when all the well layers and barrier layers of the active layer are doped. Next, the relationship between Pmax and n-type (Se) doping concentration was investigated for fully doped devices. The laser device used in this study had the same structure as that described above, except that the cavity length (L) was set to 1300 μm. The results are shown in FIG.

As shown in FIG. 5, the Pmax value is
When the Se doping concentration is set to 1 × 10 ¹⁸ cm ⁻³ , a distinct maximum value of about 400 mW is reached for the investigated device. At lower or higher dopant concentrations, the effect of doping is relatively diminished. Thus, according to the present invention, the optimized value of the doping concentration in the active layer is set to maximize the Pmax value.

Investigation of GRIN-SCH Structure Thickness As described above, except that the GRIN-SCH structure of the optical confinement layer was changed to investigate how the difference in thickness affects the laser output. A laser device was manufactured in the same manner. The resonator length of the laser element used in the investigation was set to 1300 μm. As described above, the upper light confinement layer 3B and the lower light confinement layer 3A respectively
It has a two-layer structure having constituent layers 3B ₁ , 3B ₂ and 3A ₁ , 3A ₂ . For this part of the study, each active layer of the device was fully doped (Se doping concentration 1 × 1
0 ¹⁸ cm ^-3 ).

The Pmax value of the obtained laser device was measured, and the result is shown in FIG. Again, the data is about 400 mW for a light confinement layer thickness of about 40 nm.
Shows a very clear maximum value. FIG. 6 (a)
Indicates that when the thickness of the optical confinement layer is in the range of about 20 to 50 nm, an optical output drive higher than 360 mW was obtained.

[0038]The relationship between Pmax and the number of steps in the optical confinement layer
Engagement investigation Next, for the fully doped device, Pmax and the light confinement layer
The relationship with the number of stairs inside was investigated. FIG. 6B shows light.
Numerous band gap steps in the confinement layers 3A and 3B
1 shows a structure having the same. The light confinement layer 3A is made of undoped I
Made of nGaAsP-based semiconductor material, formed in the following order
(1) Layer 3A₆, Λg = 0.95 μm, thickness 8 nm; (2)
Layer 3A_Five, Λg = 1.0 μm, thickness 7 nm; (3) Layer 3
A_Four, Λg = 1.05 μm, thickness 7 nm; (4) Layer 3A _Three,
λg = 1.1 μm, thickness 6 nm; (5) Layer 3A_Two, Λg =
1.15 μm, thickness 6 nm; and (6) layer 3A₁, Λg =
1.2 μm, thickness 6 nm.

Next, an active layer 4 described later was formed on the lower light confinement layer 3A. Next, an upper optical confinement layer 3B was formed thereon by successively forming the following undoped InGaAsP layers: (1) layer 3B ₁ , λg = 1.2 μm, thickness 6 nm; (2) layer 3B ₂ , Λg = 1.15 μm, thickness 6 nm; (3) Layer 3
B ₃ , λg = 1.1 μm, thickness 6 nm; (4) Layer 3B ₄ , λ
g = 1.05 μm, thickness 7 nm; (5) Layer 3B ₅ , λg =
1.0 μm, thickness 7 nm; and (6) layer 3B ₆ , λg =
0.95 μm, thickness 8 nm. Thus, the upper and lower light confinement layers were fabricated to be symmetric about the active layer.

The active layer 4 has a thickness of 4 nm, and is formed with five wells 4A made of InGaAsP. Each of the well layers is formed of InGaAsP (λg
= 1.2 μm) and is surrounded by a barrier layer 4B having a thickness of 10 nm. All of the MQW active layer structure is formed to have a compressive strain of 1%, was also "Furudopu" in dopant concentration 5 × 10 ¹⁸ cm ^-8 to all the well layer 4A and the barrier layer 4B. The resonator length (L) is 1300 μm.

FIG. 6C shows the relationship between Pmax and the number of steps of the light confinement layer. It is clear that Pmax increases as the number of steps in the laser element increases, both when the active layer is doped and when it is undoped. According to a preferred embodiment of the present invention, the light confinement layer has at least three steps to increase Pmax. The data shown in FIG. 6 (c) was obtained by forming a light confinement layer as described above, but by changing the number of steps in the layer. In each example, the entire thickness of the light confinement layers 3A and 3B was about 40 nm. FIG. 6 (c) again shows that active doping increases the Pmax value as compared to the undoped device.

The band gap of the outermost light confinement layer
Between the energy (E ₂ ) and the innermost light confinement layer (E ₁ )
Investigation of the difference between the band gap energy and the band gap energy difference between the outermost light confinement layer and the innermost light confinement layer (E ₂ −E ₁ ). Then, a fully-doped laser device in which the cavity length was set to 1300 μm and the Se doping concentration of the active layer was set to 5 × 10 ¹⁷ cm ⁻³ was manufactured. Further, a laser device in which E ₂ −E ₁ = 0 was also manufactured.

The Pmax values of these laser elements were measured, and the results are shown in FIG. To determine the light output at saturation drive current (saturation current), the optical output of the laser device - current characteristics are also measured, and the results, the form of a graph of the saturation current as a function of E ₂ -E ₁ value Is shown in FIG. Figure 7 shows the optical output increases as E ₂ -E ₁ value increases. When E ₂ -E ₁ value is about 90meV or more, a high light output than 360mW was obtained. In the device under investigation, output saturation occurred at about 400 mW. 8, 90 meV of E ₂ -E ₁
Has a saturation current higher than about 1200 mA, which indicates that it can be driven with a large injection current, in other words, a high maximum light output can be obtained.

Although the embodiment has a 1480 nm laser device, it will be apparent to those skilled in the art that the present invention is not limited to such a laser device. In particular, it will be appreciated that the devices of the present invention are also particularly useful as pumping sources for Raman amplifiers operating in the 1200-1550 nm band. Also, while the invention has been described with respect to an example of an InGaAsP-based laser device on an InP substrate, the invention is not limited to such a structure;
AsP laser device and AlGa on GaAs substrate
It will be apparent to those skilled in the art that it has applicability to InP, AlGaInNAsP or GaInAsP based laser devices. Further, those skilled in the art will appreciate that the substrate may be changed to a p-type substrate.

[0045]

According to the laser device of the present invention, the carrier injection efficiency is high, and the light confinement effect of the light confinement layer in the process of high light output operation is large. Therefore, the laser device is effectively used as a light source for a pumping optical fiber amplifier. Available. Accordingly, the laser device of the present invention is particularly useful as a light source for use in modern systems under severe demands of W-level light output operation, such as, for example, erbium-doped fiber amplifiers and / or Raman amplifiers. Are suitable.

Although the invention has been described with respect to particular embodiments thereof, those skilled in the art will recognize that other modifications may be made without departing from the spirit of the invention. Therefore, the present invention should be construed as limited only by the appended claims.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view of a semiconductor laser device. (B) is a graph showing the optical output as a function of the drive current and the cavity length of the conventional device.

FIG. 2 shows an example of a laser structure according to an embodiment of the present invention;
FIG. 4 is an energy band diagram showing band gap energies of a W active layer and a light confinement layer and a cladding layer adjacent thereto.

FIG. 3A is an energy band diagram showing a band gap energy for a layer group between a cladding layer and an active layer according to an example of the present invention. (B) is an energy band diagram showing a fully doped active layer according to an example of the present invention and showing a band gap energy for a layer group in a laser device of the present invention located between cladding layers. (C) is an energy band diagram showing the band gap energy of the layer group in the laser device of the present invention located between the cladding layers, and showing the centrally doped active layer according to an example of the present invention.

FIG. 4 is a schematic sectional view of an example of the laser module of the present invention.

FIG. 5 is a graph showing the maximum laser light output (Pmax) as a function of the Se doping concentration in the active MQW layer of the present invention for a fully doped device having a cavity length of 1300 μm.

FIG. 6 (a) shows a 13 × 10 ¹⁸ cm ⁻³ doping concentration.
5 is a graph showing the maximum light output (Pmax) as a function of the thickness of the light confinement layer in a fully doped laser structure of the present invention having a cavity length of 00 μm. (B) In a laser structure according to another embodiment of the present invention having a fully doped active layer, M
FIG. 4 is an energy band diagram showing band gap energies of a light confinement layer and a cladding layer adjacent to a QW active layer. Also, (c) is a graph showing the relationship between Pmax and the number of steps in the light confinement layer, comparing the undoped and active layer doped active layers.

FIG. 7: 1300 μ at a doping concentration of 1 × 10 ¹⁷ cm ⁻³
A function of the energy difference between the bandgap energy of the outermost light confinement layer (E ₂ ) and the bandgap energy of the innermost light confinement layer (E ₁ ) in an example of a fully doped laser structure of the present invention having a cavity length of m 7 is a graph showing a maximum light output (Pmax) as a graph.

[8] In the laser device of the example, the band gap energy of the outermost optical confinement layer saturation current when the light output is saturated (E ₂₎ and the innermost optical confinement layer band gap energy of the (E ₁₎ 4 is a graph shown as a function of the energy difference between them.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2A Lower cladding layer 2B Upper cladding layer 3A Lower light confinement layer 3B Upper light confinement layer 4 Active layer 4A Well layer 4B Barrier layer 5 Contact layer 6A Lower electrode 6B Upper electrode 7A P-type semiconductor layer 7B N-type semiconductor layer 9 Cooling Element 9a Peltier element 10 Housing 11a Collimator lens 11b Condensing lens 12 Optical fiber 12a Core 12b Fiber grating 13 Photodetector 14 Isolator 40 Optical component 41 Semiconductor laser element

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tsuyoshi Saito 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd. (72) Inventor Satoshi Irino 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Inventor Ryuichiro Minato 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. F-term (reference) 5F073 AA22 AA46 AA74 AB27 AB28 AB30 BA01 CA12 CB02 CB13 DA05 DA21 DA31 EA24 FA01 FA06 FA25 FA29

Claims (19)

[Claims] 1. A plurality of individual well layers, each formed between adjacent barrier layers, wherein at least one of said well layers and at least one of said barrier layers are doped and have a thickness of 800 μm or more. A semiconductor laser device comprising: an active layer having a multiple quantum well structure having a cavity length; and upper and lower optical confinement layers adjacent to the active layer. 2. The optical confinement layer having a thickness of 2
2. The semiconductor laser device according to claim 1, which has a thickness of 0 to 50 nm. 3. The method according to claim 1, wherein the at least one well layer and the at least one barrier layer have a concentration of 1 × with an n-type dopant.
The semiconductor laser device according to claim 1, wherein the semiconductor laser device is doped with 10 ^{17 to} 3 × 10 ¹⁸ cm ⁻³ . 4. The semiconductor laser device according to claim 3, wherein said n-type dopant is selected from the group consisting of Se, S and Si. 5. The semiconductor laser device according to claim 1, wherein said cavity length is longer than 1000 μm. 6. The semiconductor laser device according to claim 1, wherein a plurality of well layers and adjacent barrier layers are doped. 7. The semiconductor laser device according to claim 6, wherein all the well layers and all the barrier layers are doped. 8. The light confinement layer is formed of a plurality of layers having different band gap energies.
7. The semiconductor laser device according to any one of 7. 9. The semiconductor laser device according to claim 8, wherein the band gap energy increases stepwise from the active layer to the end surface of the adjacent optical confinement layer. 10. The method according to claim 1, wherein upper and lower cladding layers are formed adjacent to the light confinement layer, and the band gap energies of the cladding layers are larger than any of the band gap energies of the active layer and the light confinement layer adjacent thereto. Item 10. The semiconductor laser device according to any one of Items 1 to 9. 11. The semiconductor laser device according to claim 1, wherein a band gap energy at a boundary between adjacent various layers is determined by a band gap envelope, and said band gap envelope is a straight line. 12. The semiconductor according to claim 1, wherein the band gap energy at the boundary between the various adjacent layers is determined by a band gap envelope, and the band gap envelope is a curve (up or down). Laser element. 13. The semiconductor laser device according to claim 12, wherein said curve is substantially parabolic. 14. The semiconductor laser device according to claim 1, wherein said well layer has a compressive strain of 0.5 to 1.5%. 15. The semiconductor laser device according to claim 1, wherein the emission end face of the resonator has a reflectance of less than 5%, and the rear end face has a reflectance of more than 90%. 16. The wavelength of emitted light is 1200 to 1550.
The semiconductor laser device according to any one of claims 1 to 15, which has a value of nm (between). 17. A laser component incorporating the semiconductor laser device according to claim 1, further comprising at least one lens for optically coupling an output of said semiconductor laser device to an end face of an optical fiber. A laser component comprising: the semiconductor laser element; and the semiconductor laser element is thermally coupled to a cooling element. 18. The laser component according to claim 17, wherein a grating is formed inside the optical fiber, and the grating has a bandwidth of 3 nm or less. 19. A stepped upper and lower light confinement layer, each having a thickness of 20-50 nm, and a plurality of individual well layers formed between adjacent barrier layers, each having a length of more than 800 μm. A semiconductor laser device having a multiple quantum well structure having a cavity length and an active layer disposed between the optical confinement layers, wherein the number of stages of the optical confinement layer is at least three. Characteristic semiconductor laser device.