JP2003158341A - Semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser element of a quantum well structure wherein a section of a radiation beam is made almost genuine circular and junction efficiency with an optical fiber can be improved. SOLUTION: A quantum well layer 7 is formed in an almost central part of an InP substrate 1, and constriction layers 8 are formed on both a right side and a left side of the layer 7, which is constituted of a lamination structure provided with an N-type clad layer 2, a light confining layer 23, an active layer 24, a light confining layer 25 and a P-type clad layer 6. The total thicknesses of the active layer 24 and the light confining layers 23, 25 is made at least 1000 Åand at most 2000 Å, a light confining coefficient is made small, oozing-out amount wherein a light which is confined in the active layer 24 and activated is oozed out to the clad layers 2, 6 sides is increased, a spreading angle of a beam in a vertical direction which is cast from the active layer 24 and oozing-out parts is made small, and a beam of a pattern mode which is an almost genuine circle is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device having a quantum well structure.

[0002]

2. Description of the Related Art Quantum well semiconductor laser devices have been widely used as a light source for optical communication, and the structure of a quantum well semiconductor laser device having a typical buried waveguide of this type is shown in FIG. ing.

In the figure, a quantum well layer 7 is formed in the central portion of an N-type InP substrate 1, and confinement layers 8 are formed on both left and right sides of the quantum well layer 7. The quantum well layer 7
Is an optical confinement layer (GRIN-
SCH region 3), an active layer 4, an optical confinement layer 5, and a P-type clad layer 6 made of InP, which are laminated in this order. The optical confinement layers 3 and 5 have four different compositions of GaI.
nAsP layer, that is, four kinds of GaInAsP having band gap wavelength λg of 1.05, 1.10, 1.20 and 1.30 μm and a thickness of 300 Å each.
Has a function of confining light in the active layer 4 from the upper and lower sides by changing the refractive index in a stepwise manner.

The active layer 4 has a bandgap wavelength λg of 1.
A well layer made of GaInAsP having a thickness of 55 μm and a thickness of 65 Å and a bandgap wavelength λg of 1.30 μm
And a barrier layer made of GaInAsP having a thickness of 80Å and an MQW active layer having 5 wells.

When manufacturing the semiconductor laser device having the quantum well structure, N is formed on the entire upper surface of the InP substrate 1.
The type clad layer 2, the optical confinement layer 3, the active layer 4, the optical confinement layer 5, and the P type clad layer 6 are laminated and formed, after which the quantum well width L is left to be about 2 μm to form a mesa stripe shape. Then, the left and right sides thereof are removed by etching, and the P-type InP layer 9 and the N-type InP layer 10 are regrown in the removed portions to form the constricted layer 8 and the active layer 4 and the constricted layer 8 are formed. The P-type clad layer 11 made of InP is grown on the formed upper side, and thereafter, the N-side electrode 12 is formed on the lower surface side and the P-side electrode 13 is formed on the upper surface side.

When driving a semiconductor laser device of this type, a positive power supply voltage is applied to the P-side electrode 13 and N is applied.
The negative side of the power supply voltage is connected to the side electrode 12. Since the current flowing from the P-side electrode 13 to the N-side electrode 12 does not flow in the constriction layer 8, it flows concentratedly in the quantum well layer 7, which excites the active layer 4 and excites the active layer 4. The light source light is emitted from one end surface of the active layer 4 (usually, reflective films having different reflectances are formed on both end sides of the active layer 4, and the power of the light excited in the active layer 4 has Light source light is emitted from the end face side when it exceeds the smaller threshold).

[0007]

However, when manufacturing a semiconductor laser device of this type, it is unavoidable that the cross-sectional shape of the active layer 4 is rectangular, and therefore the active layer 4 emits light. The divergence angle of the beam in the vertical direction is larger than the divergence angle of the beam in the horizontal direction (parallel direction) of the active layer 4. For example, in the conventional semiconductor laser, the divergence angle of the beam in the vertical direction of the active layer 4 is 3
Since the divergence angle of the horizontal beam of the active layer 4 is about 25 ° and the divergence angle of the vertical beam is large, the cross-sectional shape of the beam emitted from the active layer 4 becomes elliptic, and the semiconductor laser When light is introduced from the element to the optical fiber having a circular core, there is a problem that the coupling efficiency of the light is deteriorated.

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to make the spread pattern of the beam emitted from the active layer into a substantially circular shape so as to enhance the coupling efficiency to the optical fiber. It is to provide a semiconductor laser device.

[0009]

In order to achieve the above object, the present invention is constructed as follows. That is, the first aspect of the invention is to provide a plurality of Ga _1-X In _X A on the InP substrate.
In an embedded semiconductor laser device having an active layer including multiple quantum wells composed of a s _{1 -Y} P _Y well layer and a barrier layer, and an optical confinement layer sandwiching the active layer in a sandwich form from the upper and lower sides, one of upper and lower light The confinement layer is thinner than the active layer, and the total thickness of the active layer and the upper and lower optical confinement layers is set to 1000 Å or more and 2000 Å or less.

Further, a second invention is characterized in that, in the one having the structure of the first invention, the semiconductor laser device is for an excitation light source and is used by being optically coupled with an optical fiber. .

Further, a third invention is the one having the constitution of the second invention, wherein the excitation band wavelength is 1.48 μm.
The feature is that it is made into a belt.

[0012]

In the present invention having the above-mentioned structure, the total thickness of the active layer and the light confining layers above and below the active layer is reduced to 2000 Å or less, so that the light confining coefficient is reduced and the light excited in the active layer is reduced. Energy seeps out from the active layer to the cladding layer side outside the optical confinement layer. This bleeding amount becomes maximum in the middle part of the width of the quantum well.As a result, the light emitting surface with the bleeding region on the clad layer side is close to a circle, which makes The divergence angles of the beams in the horizontal direction are substantially equal, and a beam having a mode pattern close to a circle is output as the light source light.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. The same parts as those of the conventional example are designated by the same reference numerals,
The duplicate description will be omitted. FIG. 1 shows an embodiment of a semiconductor laser device according to the present invention. The semiconductor laser device of this embodiment also has a quantum well structure like the conventional example, and has a quantum well layer 7 and a constriction layer 8. Then, these layers formed on the InP substrate 1 are MO-CVD.
(Metal-Organic Chemical V
It is formed by utilizing vapor phase growth or the like according to apor Deposition). The quantum well layer 7 in this embodiment is similar to the conventional example in that the N-type cladding layer 2, the optical confinement layer 23, the active layer 24 and the optical confinement layer 2 are formed on the InP substrate 1.
5 and the P-type clad layer 6 are laminated. The first characteristic of this embodiment different from the conventional example is that the total thickness of the optical confinement layers 23 and 25 and the active layer 24 is 2000.
Å The second feature is that the optical confinement layer 2
The thickness of 3, 25 is smaller than the thickness of the active layer 24, and other configurations are the same as those of the conventional example.

1.48 μm for semiconductor laser as excitation light source
When operating in the excitation band wavelength of the band, the beam power as the excitation light source is larger than the beam power for communication, and in order to operate in the excitation band wavelength of the 1.48 μm band for the excitation light source, the active layer is The total thickness of the upper and lower optical confinement layers needs to be 1.48 μm for this excitation light source.
The lower limit thickness of the sum, which is naturally determined when operating at the excitation band wavelength of the band, is 1000 Å (Å).

The optical confinement layer 23 is composed of two types of GaInAsP having band gap wavelengths λg of 1.20 μm and 1.30 μm and having different layer thicknesses of 200 Å, and the optical confinement layer 25 is also the same. It is composed. As in the conventional example, the active layer 24 is made of GaInA having a bandgap wavelength λg of 1.55 μm and a layer thickness of 65Å.
Well layer of sP and band gap wavelength of 1.30 μm
And consists of a GaInAsP barrier layer with a layer thickness of 80Å,
The number of wells is 5. In this embodiment, the optical confinement layer 23 has a layer thickness of 400Å and the active layer 24 has a layer thickness of 645.
Å, the thickness of the light confinement layer 25 is 400 Å,
The total thickness of the light confinement layer 23, the active layer 24, and the light confinement layer 25 is 1445Å, which is thinner than the conventional example of 3045Å.

When the semiconductor laser device of this embodiment is driven, the current flowing between the electrodes 12 and 13 is concentrated in the quantum well layer 7 to excite the light confined in the active layer 24, and the light in the active layer 24 is excited. The energy is increased, but at this time, the light confinement layers 23 and 25 are thinned to reduce the light confinement coefficient, and as a result, the clad layer 2 for the light confined in the active layer 25 and activated. The exudation to 6 becomes larger. The amount of light bleeding into the cladding layers 2 and 6 is the largest at the center of the width L of the quantum well, and the amount of bleeding gradually decreases toward both ends.
The cross-sectional shape of the light emission including the active layer 24 and the bleeding portions of the clad layers 2 and 6 is almost a circle, and the divergence angle of the beam emitted from the active layer 24 and the light bleeding portion is vertical. The angle becomes substantially the same in the horizontal and horizontal directions, and the light is output as light in a substantially circular mode pattern.

The present inventor manufactured the semiconductor laser device of this embodiment and measured the divergence angle of the emitted beam, and obtained the measurement results shown in FIG. According to this, 50m
The divergence angle in the vertical direction when the radiant power of W is 25.0 °
((B) in the figure), and the horizontal spread angle is 2
It was 5.4 ° ((a) in the figure), and a radiation beam pattern that was almost a perfect circle could be created.

FIG. 3 shows the semiconductor laser device of this embodiment as an AR.
FIG. 6 shows output characteristics of a device in which an optical fiber is coupled to a laser diode having an HR coating and a cavity length of 1 mm to form a module. According to this, when the driving current is 1 A, the end light output of the optical fiber is 128 m.
A high output of W, which can be used as an excitation light source, was obtained, and the coupling efficiency between the semiconductor laser device and the optical fiber at this time was 70%. The excitation band wavelength of the semiconductor laser at this time is 1.48 μm band when the emission wavelength is calculated from the layer thicknesses of the well layer and the barrier layer of the active layer and the band gap wavelength of each layer. When the coupling efficiency between the semiconductor laser device and the optical fiber of the conventional example was examined in the same manner, the coupling efficiency was about 50%, and this example can improve the coupling efficiency by about 20% as compared with the conventional example. I was able to.

The present invention is not limited to the above-mentioned embodiment, and various embodiments can be adopted. For example, in the above embodiment, the total thickness of the light confinement layers 23 and 25 and the active layer 24 is set to 1445Å, but the total thickness is 200
It should be 0 Å or less. The present inventor has
25, the relationship between the total thickness of the active layer 24 and the active layer 24 and the divergence angle of the outgoing beam due to the bleeding of light into the clad layer was examined by experiments. When the total thickness exceeds 2000 Å The amount of light was almost gone, and the beam emission pattern was almost elliptical, and no improvement in the characteristics of the coupling efficiency with the optical fiber could be obtained. However, as the total thickness fell below 2000 Å, the amount of light bleeded out. It was confirmed that the output beam pattern was gradually increased in size, and the shape of the output beam pattern was changed from an elliptical shape to a circular shape, so that the coupling efficiency with the optical fiber could be improved.

Further, in the above embodiment, the active layer 24 and the light confining layers 23, 25 are made to have the same thickness as the conventional example, and the light confining layers 23, 25 are thinned.
Although the total thickness of 25 is reduced (in the present embodiment, the thickness of the light confinement layers 23 and 25 is smaller than that of the active layer 24), of course, the thickness of the active layer 24 together with the light confinement layers 23 and 25 is reduced. May be thin.

[0021]

According to the present invention, the total thickness of the active layer of the quantum well and the optical confinement layers on the upper and lower sides of the active layer is 2000.
Since it is less than or equal to Å, this total becomes thin, the optical confinement coefficient becomes small, and the amount of light confined in the active layer and activated becomes large in the clad layer. In particular, by making the thickness of one of the upper and lower light confinement layers that sandwich the active layer smaller than the thickness of the active layer, the light confinement layer can be made significantly thinner than the conventional example, and the light bleeding effect can be obtained. In addition, it becomes easy to make the total thickness of the active layer and the light confinement layers on the upper and lower sides of this active layer 2000 Å or less. The thin structure, in which the total thickness of the active layer and the light confinement layers on the upper and lower sides of the active layer is 2000 Å or less, reduces the vertical divergence angle of the beam emitted from the semiconductor laser device, thereby increasing the vertical and horizontal directions. Since the beams can be output as circular mode pattern beams having substantially the same divergence angle, the coupling efficiency with respect to the optical fiber can be significantly improved.

In particular, when emitting a high-power beam for an excitation light source, if the total thickness of the active layer and the optical confinement layers on the upper and lower sides of this active layer is large, the beam pattern of the emitted beam becomes an elliptical pattern. However, as in the present invention, the total thickness of the active layer and the optical confinement layers on the upper and lower sides of the active layer is reduced to 2000 Å or less, so that a high-power launch beam for an excitation light source is also excellent. This has the effect of obtaining a circular mode beam pattern.

[Brief description of drawings]

FIG. 1 is a sectional configuration diagram of an embodiment of a semiconductor laser device according to the present invention.

FIG. 2 is a graph of a beam divergence angle of the semiconductor laser device of the example.

FIG. 3 is an output characteristic graph of a module incorporating the semiconductor laser device of the same example.

FIG. 4 is a cross-sectional view of a conventional semiconductor laser device having a quantum well structure.

[Explanation of symbols]

1 InP substrate 2 N-type clad layer 6,11 P-type clad layer 7 Quantum well layer 8 Constriction layer 9 P-type InP layer 10 N-type InP layer 23,25 Optical confinement layer 24 Active layer

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshio Kikuta             2-6-1, Marunouchi, Chiyoda-ku, Tokyo             Kawa Electric Industry Co., Ltd. F term (reference) 5F073 AA22 AA45 AA74 AA76 AA83                       AA89 AB28 BA03 CA12 DA05                       EA20 EA24 EA29

Claims (3)

[Claims] 1. A plurality of Ga _1-X In _X on an InP substrate.
In an embedded semiconductor laser device having an active layer including a multi-quantum well composed of an As _1-Y P _Y well layer and a barrier layer, and an optical confinement layer sandwiching the active layer in a sandwich shape from the upper and lower sides, one of upper and lower light A semiconductor laser device, wherein the confinement layer is thinner than the active layer, and the total thickness of the active layer and the upper and lower optical confinement layers is set to 1000 Å or more and 2000 Å or less. 2. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is for an excitation light source and is used by being optically coupled with an optical fiber. 3. The semiconductor laser device according to claim 2, wherein the excitation band wavelength is set to 1.48 μm band.