JP3027044B2 - Semiconductor distributed feedback laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor distributed feedback laser device (GC-DFB) using distributed light feedback by gain coupling.
-LD).

[0002]

2. Description of the Related Art As one structure for obtaining light distribution feedback by gain coupling, a structure in which a light absorption layer is provided periodically along the optical axis direction of an active layer is known as Roki, Nakano Yoshiaki, Tada Kunio,
20th International Conference on
Y. Luo, Y. Nakano and K. Tada, "Fabrication and Solid State Devices and Materials, Extended Abstracts, pp. 327-330.
Characteristics of aGain-Coupled Distributed Fee
dback Laser Diode ", Extended Abstracts of the 20th
(1988 International) Conference on the Solid Stat
e Devices and Materials, Tokyo, pp.327-330). A further improved structure is disclosed in the specification and drawings of a patent application filed by the present applicant, Japanese Patent Application No. 3-181209 (hereinafter referred to as "the prior application").

[0003]

In the conventional structure, when a semiconductor having a forbidden band width equal to or smaller than that of the active layer is used as the light absorbing layer, absorption saturation occurs at a high light output, and the absorption coefficient of the light absorbing layer is reduced. May drop. Since the magnitude of the gain coupling is proportional to the absorption coefficient of the light absorbing layer, if such a phenomenon occurs, the gain coupling will also be reduced. In an extreme case, the light absorption layer may be transparent and the gain coupling may not work. Even if not extremely extreme, there is a possibility that the characteristics of the optical output with respect to the current injected into the active layer become nonlinear.

An object of the present invention is to solve such a problem and to provide a semiconductor distributed feedback laser device having a structure capable of controlling absorption saturation of a light absorption layer.

[0005]

The semiconductor distributed feedback laser device according to the present invention is provided with a light absorbing layer for periodically absorbing stimulated emission light of the active layer along the optical axis direction of the active layer.
A means for providing a p-type layer and an n-type layer in contact with the light absorbing layer and applying a bias voltage different from the bias voltage accompanying the current injection to the active layer between the p-type layer and the n-type layer is provided. It is characterized by being provided.

[0006] The p-type layer and the n-type layer may be arranged with the light absorbing layer interposed therebetween, and one may be laminated on the light absorbing layer and the other may be formed so as to embed them. By using at least one of the p-type layer and the n-type layer, a layer structure combined with a refractive index and a shape that substantially cancels the periodic change in the refractive index of the light absorbing layer can be provided. In particular, in the case of a structure in which the light absorption layer is sandwiched between the p-type layer and the n-type layer,
It is preferable to set the refractive index in combination with the mold layer.

The means for applying a bias voltage preferably includes a reverse bias means for eliminating carriers in the light absorbing layer to prevent the absorption saturation. Separately or together with this, a forward bias means for injecting carriers into the light absorbing layer to suppress its absorption coefficient may be included.

[0008]

When a reverse bias is applied to the light absorbing layer, carriers generated in the light absorbing layer can be efficiently eliminated from the layer, and absorption saturation can be prevented. Therefore, the magnitude of the gain coupling can be maintained up to a high output. Further, when a forward bias is applied to the light absorbing layer, absorption saturation is likely to occur, so that the absorption coefficient of the light absorbing layer can be suppressed and the gain coupling coefficient can be controlled.

As the light absorbing layer, a layer in which the absorption coefficient of a layer formed to have a substantially uniform thickness is periodically changed is also possible. However, practically, it is preferable that the light absorbing layer itself is provided periodically. In that case, as shown in the specification and drawings of the previous application, a low refractive index layer and an intermediate refractive index layer are provided corresponding to the shape of the light absorbing layer, and the refractive index generated by the distribution of the light absorbing layer. The distribution can be offset. This is effective when it is desired to remove the refractive index coupling component. Although such a low refractive index layer and an intermediate refractive index layer can be provided separately from the p-type layer and the n-type layer according to the present invention, at least one of the p-type layer and the n-type layer may be used. it can. In particular, in the case of a structure sandwiching a light absorption layer, it is preferable to use each of them as a low refractive index layer and an intermediate refractive index layer.

[0010]

FIG. 1 is a perspective view showing a semiconductor distributed feedback laser device according to a first embodiment of the present invention, and FIG. 2 is a diagram showing current and voltage directions in a cross section transverse to the optical axis direction. FIG.
Here, a part is cut away to show the internal structure.
This embodiment uses a structure shown in the specification and drawings of the previous application, that is, a structure in which a low refractive index layer and an intermediate refractive index layer are combined so as to cancel out the refractive index coupling component due to the light absorbing layer. A bias voltage can be applied to the absorption layer.

That is, this laser device has a multiple quantum well active layer 3 for generating stimulated emission light by current injection, and periodically absorbs the stimulated emission light generated by this active layer 3 in the optical axis direction. And a light absorption layer 6 for giving a light distribution feedback by gain coupling to the stimulated emission light.

The features of this embodiment are as follows.
It has an intermediate refractive index layer 7 as a p-type layer in contact with the light absorbing layer 6, a low refractive index layer 5 and a cladding layer 4 as an n-type layer, and a bias voltage different from a bias voltage accompanying current injection into the active layer 3. Is applied between the intermediate refractive index layer 7 and the low refractive index layer 5 and the cladding layer 4 by connecting the intermediate refractive index layer 7 to the electrode 10 via the p-type cladding layer 8 and the p-type contact layer 9. The low refractive index layer 5 and the cladding layer 4 are connected to the electrode 14 via the n-type buried layer 12 and the n-type contact layer 13.

To manufacture this laser device, first, a p-type cladding layer 2 is formed on a p-type substrate 1 having a (100) crystal plane.
And an undoped active layer 3, an n-type cladding layer 4, an n-type low refractive index layer 5, and an undoped light absorbing layer 6 are crystal-grown, and the light absorbing layer 6 and the low refractive index layer are subjected to interference exposure and wet etching or dry etching. 5 is formed with an uneven shape. Next, the p-type intermediate refractive index layer 7 is grown by a metal organic chemical vapor deposition method or the like. Here, the film thickness and composition of the low refractive index layer 5 and the intermediate refractive index layer 7 are selected so as to cancel the component of the refractive index coupling generated due to the uneven shape of the light absorbing layer 6. Subsequently, a p-type cladding layer 8 and a p-type contact layer 9 are grown. Thereafter, mesa etching is performed up to the cladding layer 2, and the n-type buried layer 12 and the n-type contact layer 13 are selectively grown. Further, electrodes 10, 11, and 14 are formed on the surface of the p-type contact layer 9, the back surface of the substrate 1, and the surface of the n-type contact layer 13, respectively. It is desirable to provide a non-reflective coating or a window structure on both end surfaces of the element to reduce the reflectance.

In this structure, a current for laser oscillation is injected from the substrate 1 into the active layer 3 via the cladding layer 2, and further flows through the path of the cladding layer 4, the buried layer 12 and the contact layer 13. . A bias voltage applied to the light absorbing layer 6 is applied from the contact layer 9 to the intermediate refractive index layer 7 via the cladding layer 8 and from the contact layer 13 to the cladding layer 4 and the low refractive index layer 5 via the burying layer 12. Is done.

An example of the composition of each layer in the case of the InP system is shown below.

1 substrate p-InP 2 clad layer p-InP 3 active layer i-InGaAsP (λ _g = 1.3
μm) and i-InGaAs multiple quantum well structure equivalent λ _g = 1.55 μm 4 cladding layer n-InP 5 low refractive index layer n-InGaAsP (λ _g = 1.1
μm) 6 light absorbing layer i-InGaAs 7 intermediate refractive index layer p-InGaAsP (λ _g = 1.3
μm) 8 cladding layer p-InP 9 contact layer p-InGaAs 10 electrode Cr / Au 11 electrode Cr / Au 12 buried layer n-InP 13 contact layer n-InGaAs 14 electrode AuGeNi / Au where InGaAs and InGaAsP are InP It is lattice matched, lambda _g denotes a wavelength of light corresponding to the forbidden band width.

FIG. 3 is a perspective view showing a semiconductor distributed feedback laser device according to a second embodiment of the present invention, and FIG. 4 is a diagram showing current and voltage directions in a cross section transverse to the optical axis direction. In FIG. 3, a part is cut away as in FIG.

In the first embodiment, p is set so as to sandwich the light absorbing layer.
The mold layer and the n-type layer were laminated. On the other hand, in the second embodiment, one of the p-type layer and the n-type layer is laminated on the light absorbing layer, and the other is embedded with the light absorbing layer.

That is, the feature of this embodiment is that the intermediate refractive index layer 7 and the low refractive index layer 25 are arranged as a p-type layer in contact with the light absorbing layer 6 with the light absorbing layer 6 interposed therebetween.
And a buried layer 12 as an n-type layer, and a bias voltage different from the bias voltage accompanying the current injection into the multiple quantum well active layer 3 is applied to the intermediate refractive index layer 7, the low refractive index layer 25, and the buried layer. As a means for applying a voltage between the first electrode 12 and the first electrode 12 via the p-type cladding layer 8 and the p-type contact layer 9,
0, and the buried layer 12 is connected to the electrode 14 via the n-type contact layer 13.

In order to manufacture this laser device, first, an n-type cladding layer 22, an undoped active layer 3, a p-type cladding layer 24, a p-type cladding layer 24 are formed on an n-type substrate 21 having a (100) crystal plane.
The low-refractive index layer 25 and the undoped light absorbing layer 6 are crystal-grown, and the light absorbing layer 6 and the low refractive index layer 2 are subjected to interference exposure and wet etching or dry etching.
5 is formed with an uneven shape. Next, the p-type intermediate refractive index layer 7 is grown by a metal organic chemical vapor deposition method or the like. here,
The thickness and composition of the low-refractive-index layer 25 and the intermediate-refractive-index layer 7 are selected so as to cancel out the components of the refractive index coupling generated due to the uneven shape of the light absorbing layer 6. Then p
A type cladding layer 8 and a p-type contact layer 9 are grown.
Thereafter, mesa etching is performed up to the cladding layer 24, and the n-type buried layer 12 and the n-type contact layer 13 are selectively grown.
Further, electrodes 10, 31 and 1 are respectively provided on the surface of the contact layer 9, the back surface of the substrate 21 and the surface of the contact layer 13.
4 is formed. It is desirable to provide a non-reflective coating or a window structure on both end surfaces of the element to reduce the reflectance.

In this structure, a current for laser oscillation is injected from the contact layer 9 into the active layer 3 via the cladding layer 8, the intermediate refractive index layer 7, the low refractive index layer 25 and the cladding layer 24, and From the cladding layer 22 to the substrate 2
Flow on the path to 1. The bias voltage to the light absorbing layer 6 is
The voltage is applied from the contact layer 9 to the intermediate refractive index layer 7 and the low refractive index layer 25 via the cladding layer 8, and from the contact layer 13 to the buried layer 12.

An example of the composition of each layer in the case of the InP system is shown below.

21 substrate n-InP 22 clad layer n-InP 3 active layer i-InGaAsP (λ _g = 1.3
μm) and i-InGaAs multiple quantum well structure equivalent λ _g = 1.55 μm 24 cladding layer p-InP 25 low refractive index layer p-InGaAsP (λ _g = 1.
1 μm) 6 light absorbing layer i-InGaAs 7 intermediate refractive index layer p-InGaAsP (λ _g = 1.3
8 m clad layer p-InP 9 contact layer p-InGaAs 10 electrode Cr / Au 31 electrode AuGeNi / Au 12 buried layer n-InP 13 contact layer n-InGaAs 14 electrode AuGeNi / Au However, InGaAs and InGaAsP are InP. It is lattice matched, lambda _g denotes a wavelength of light corresponding to the forbidden band width.

In the above embodiment, in order to obtain the light distribution feedback by only the gain coupling component, the refractive index coupling component is suppressed by combining the light absorbing layer with the low refractive index layer and the intermediate refractive index layer. However, depending on the application, the refractive index coupling component may be left in some cases. In that case, it is not necessary to combine a low refractive index layer and an intermediate refractive index layer.

In the above description, a basic structure example is shown. However, an internal current confinement layer or the like may be added to efficiently inject a current into the active layer. A single quantum well or a mixed crystal may be used as the active layer, and a quantum well structure may be used as the light absorbing layer. The present invention can be implemented even if the p-type and the n-type are exchanged. Further, the present invention can be similarly implemented using other materials such as GaAs.

[0026]

As described above, the semiconductor distributed feedback laser device of the present invention can efficiently eliminate carriers generated in the light absorbing layer by applying a reverse bias to the light absorbing layer. Therefore, absorption saturation can be prevented, and the magnitude of gain coupling can be maintained up to high output. Therefore, it is possible to sufficiently bring out the advantages of gain coupling such as excellent single mode characteristics to a high output, and it can also be used in fields requiring linearity of current-to-optical output characteristics such as modulation operation. Become like

Further, when a forward bias is applied to the light absorbing layer, the gain coupling coefficient can be controlled by positively causing absorption saturation and controlling and suppressing the absorption coefficient of the light absorbing layer.
Such a method of use can be used not only for optimizing the gain coupling coefficient, but also for generating a short pulse.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a semiconductor distributed feedback laser device according to a first embodiment of the present invention, with a part cut away to show the internal structure.

FIG. 2 is a diagram showing current and voltage directions in a cross section of the first embodiment which crosses the optical axis direction.

FIG. 3 is a perspective view showing a semiconductor distributed feedback laser device according to a second embodiment of the present invention, with a portion cut away to show the internal structure.

FIG. 4 is a diagram showing current and voltage directions in a cross section transverse to the optical axis direction of the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 21 Substrate 2, 4, 22, 24 Cladding layer 3 Active layer 5, 25 Low refractive index layer 6 Light absorption layer 7 Intermediate refractive index layer 8 Cladding layer 9, 13 Contact layer 10, 11, 14, 31 Electrode 12 embedding Layer

────────────────────────────────────────────────── (5) References JP-A-3-35581 (JP, A) JP-A-62-173786 (JP, A) JP-A-62-84583 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) H01S 5/00 JICST file (JOIS)

Claims (6)

(57) [Claims] 1. An active layer for generating stimulated emission light by current injection, and a light distribution feedback by gain coupling to the stimulated emission light generated by the active layer periodically in the optical axis direction. A distributed absorption laser device having a light absorbing layer for providing a p-type layer and an n-type layer in contact with the light absorbing layer, and applying a bias voltage different from the bias voltage accompanying the current injection to the semiconductor device. A semiconductor distributed feedback laser device characterized by comprising means for applying a voltage between a p-type layer and an n-type layer. 2. The semiconductor distributed feedback laser device according to claim 1, wherein the p-type layer and the n-type layer are arranged with the light absorbing layer interposed therebetween. 3. The distributed feedback laser device according to claim 1, wherein one of the p-type layer and the n-type layer is stacked on the light absorption layer, and the other is formed as a layer burying the light absorption layer. 4. A light-absorbing layer having a layer structure combined with a refractive index and a shape such that the periodic change of the refractive index of the light-absorbing layer is substantially canceled, and at least a part of the layer structure includes the p-type layer and the n-type. 4. The semiconductor distributed feedback laser device according to claim 1, wherein the laser is formed by at least one of the layers. 5. The semiconductor distributed feedback laser device according to claim 1, wherein said applying means includes a reverse bias means for preventing absorption saturation by eliminating carriers in the light absorbing layer. 6. The semiconductor distributed feedback laser device according to claim 1, wherein the means for applying includes a forward bias means for injecting carriers into the light absorbing layer to suppress the absorption coefficient.