Semiconductor optical integrated device

Abstract

The semiconductor optical integrated element of the present disclosure is a semiconductor optical integrated element comprising: a laser diode section (101) having a first optical waveguide (20) and generating laser light; a separation section (102) connected to the laser diode section (101) and having a second optical waveguide (21) including a first core layer (2) that propagates the laser light emitted from the laser diode section (101); and an optical modulator section (103) having a third optical waveguide (22) connected to the separation section (102) and including a second core layer (3) that absorbs a portion of the laser light emitted from the separation section, wherein the third optical waveguide (22) has a constant thickness in a direction perpendicular to the surface of the substrate on which the optical modulator section (103) is formed, and the proportion of the second core layer (3) in a cross section of the third optical waveguide (22) perpendicular to the laser light propagation direction increases from the incident side to the output side of the laser light. This makes it possible to reduce the concentration of optical absorption current in the vicinity of the incident end face of the optical modulator section (103) compared to the conventional technique, thereby making it possible to obtain a semiconductor optical integrated device in which the occurrence of deterioration in characteristics is suppressed.

Description

[Technical field]

[0001] The present disclosure relates to a semiconductor optical integrated device. [Background technology]

[0002] As an example of a conventional semiconductor optical integrated element, a semiconductor optical integrated element is known in which the optical waveguide of the optical modulator section and the optical waveguide of the separation section between the laser diode and the optical modulator section have the same layer structure along the optical axis direction, i.e., the cross-sectional shape with respect to the optical axis is the same. In addition, in order to reduce the concentration of the optical absorption current near the light incident end face of the optical modulator section, for example, Patent Document 1 discloses a technology in which a non-doped layer is introduced into the optical modulator section and the thickness of the layer is made thicker on the light incident side and thinner on the light output side, thereby reducing the concentration of the optical absorption current at the light incident end face. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-24289 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology disclosed in Patent Document 1 aims to suppress the light absorption current by reducing the applied reverse bias voltage by the non-doped layer, but does not suppress the intensity of the light incident on the light absorption layer itself. In addition, since the intensity of the light emitted from the laser diode is strongest near the center in the optical axis direction, the light absorption current near the light incident end face cannot be suppressed completely in the optical modulator section having the light absorption layer disposed near the center in the optical axis direction on the light incident end face, and the light absorption current is likely to concentrate in a small area. In other words, the conventional semiconductor optical integrated element has a problem that the light absorption current is concentrated in a small area near the light incident end face of the optical modulator section because light with high intensity is incident on the light absorption layer, which may cause the characteristics of the semiconductor optical integrated element to deteriorate. [Means for solving the problem]

[0005] The semiconductor optical integrated device according to the present disclosure comprises: The laser diode section has a first optical waveguide and generates laser light, a separation section connected to the laser diode section and having a second optical waveguide including a first core layer that propagates the laser light emitted from the laser diode section, and an optical modulator section has a third optical waveguide connected to the separation section and including a second core layer that absorbs a part of the laser light emitted from the separation section, the third optical waveguide having a constant thickness in a direction perpendicular to the surface of the substrate on which the optical modulator section is formed, and the proportion of the second core layer in a cross section of the third optical waveguide perpendicular to the laser light propagation direction increases from the incident side to the output side of the laser light. and at an incident end face of the optical modulator section, the third optical waveguide has the first core layer or a third core layer which does not contribute to absorbing the laser light. It is a semiconductor optical integrated device. Effect of the Invention

[0006] According to the present disclosure, the concentration of optical absorption current near the incident end face of the optical modulator section can be reduced compared to the conventional art, thereby providing a semiconductor optical integrated device in which the occurrence of characteristic degradation is suppressed. [Brief description of the drawings]

[0007] [Figure 1] 1 is a schematic top view of a semiconductor optical integrated device according to a first embodiment. [Diagram 2] 1 is a schematic cross-sectional view taken along line GG of a semiconductor optical integrated device according to a first embodiment. [Diagram 3] 2 is a schematic cross-sectional view taken along line AA of the semiconductor optical integrated device according to the first embodiment. FIG. [Figure 4] 2A and 2B are a schematic cross-sectional view and a schematic cross-sectional view taken along line BB and CC of the semiconductor optical integrated device according to the first embodiment. [Diagram 5] 1 is a schematic DD cross-sectional view of a semiconductor optical integrated device according to a first embodiment. [Figure 6] 1 is a schematic EE cross-sectional view of a semiconductor optical integrated device according to a first embodiment. [Figure 7]FF cross-sectional view of a semiconductor optical integrated device according to a first embodiment. [Figure 8] FIG. 6 is a schematic DD cross-sectional view of a semiconductor optical integrated device according to a second embodiment. [Figure 9] FIG. 11 is a schematic EE cross-sectional view of a semiconductor optical integrated device according to a second embodiment. [Figure 10] FIG. 5 is a schematic cross-sectional view taken along line G-G of a semiconductor optical integrated device according to a second embodiment. [Figure 11] FIG. 11 is a schematic top view showing a semiconductor optical integrated device according to a third embodiment. [Figure 12] FIG. 11 is a schematic cross-sectional view taken along the line BB of a semiconductor optical integrated device according to a third embodiment. [Figure 13] FIG. 11 is a schematic cross-sectional view taken along line CC of a semiconductor optical integrated device according to a third embodiment. [Figure 14] FIG. 11 is a schematic HH sectional view of a semiconductor optical integrated device according to a third embodiment. [Figure 15] FIG. 11 is a schematic DD cross-sectional view of a semiconductor optical integrated device according to a third embodiment. [Figure 16] FIG. 11 is a schematic EE cross-sectional view of a semiconductor optical integrated device according to a third embodiment. [Figure 17] FIG. 2 is a schematic cross-sectional view of a semiconductor optical integrated device according to a third embodiment. [Figure 18] FIG. 11 is a schematic cross-sectional view taken along line BB of a semiconductor optical integrated device according to a fourth embodiment. [Figure 19] FIG. 11 is a schematic cross-sectional view taken along line CC of a semiconductor optical integrated device according to a fourth embodiment. [Figure 20] FIG. 11 is a schematic cross-sectional view of a JJ of a semiconductor optical integrated device according to a fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] An example of a semiconductor optical integrated device according to the present disclosure will be described below, but the present disclosure is not limited to the embodiment described below, and can be modified as desired without departing from the scope of the present disclosure. For convenience, repeated explanations may be omitted.

[0009] Embodiment 1 FIG. 1 is a schematic top view of a semiconductor optical integrated device according to the first embodiment. FIG. 2 is a schematic GG cross-sectional view of the semiconductor optical integrated device according to the first embodiment shown in FIG. 1. FIG. 3 is a schematic AA cross-sectional view of the semiconductor optical integrated device according to the first embodiment shown in FIG. 1. FIG. 4 is a schematic BB cross-sectional view (and a schematic CC cross-sectional view) of the semiconductor optical integrated device according to the first embodiment shown in FIG. 1. FIG. 5 is a schematic DD cross-sectional view of the semiconductor optical integrated device according to the first embodiment shown in FIG. 1. FIG. 6 is a schematic EE cross-sectional view of the semiconductor optical integrated device according to the first embodiment shown in FIG. 1. FIG. 7 is a schematic FF cross-sectional view of the optical modulator section 103 of the semiconductor optical integrated device according to the first embodiment shown in FIGS. 5 and 6. As shown in Figures 1 and 2, the semiconductor optical integrated device of embodiment 1 has a laser diode section 101 that generates laser light, an optical modulator section 103 that modulates the laser light generated from the laser diode section 101, and a separation section 102 that electrically separates the laser diode section 101 and the optical modulator section 103.

[0010] As shown in Figs. 2 and 3, the laser diode section 101 is configured by stacking an n-type InP first cladding layer 4, a laser diode section core layer 1, a p-type InP first cladding layer 6, a diffraction grating 8, and an n-type InP fourth cladding layer 9 on one surface of an n-type InP substrate 12. Here, unless otherwise specified, the direction of the surface on which the semiconductor layers of the n-type InP substrate 12 are stacked is referred to as the upward direction, and the surface perpendicular to the upward direction and the propagation direction of the laser light is referred to as the side. The first optical waveguide 20 shown in Fig. 1 refers to an optical waveguide including the n-type InP first cladding layer 4, the laser diode section core layer 1, and the p-type InP first cladding layer 6. Both side portions of the laser diode section core layer 1 through which the laser light propagates are buried with a semiconductor burying layer 13 to form a buried structure. The semiconductor burying layer 13 may be configured of p-type InP and n-type InP, or a semiconductor such as Fe-doped InP may be used. A p-type first contact layer 10 is laminated on the upper surfaces of the n-type InP fourth cladding layer 9 and the semiconductor buried layer 13, and a protective passivation film 14 is formed on the upper surface of the p-type first contact layer 10. Furthermore, an electrode 16 serving as an anode electrode is formed on the protective passivation film 14, and the electrode 16 and the p-type first contact layer 10 are electrically connected through an opening formed in the protective passivation film 14. A first electrode 11 serving as a cathode electrode is provided on the lower surface side, which is the other surface of the n-type InP substrate 12, and the first electrode 11 and the n-type InP substrate 12 are electrically connected.

[0011] As shown in FIG. 2 and FIG. 4, the separation section 102 is configured by a structure in which an n-type InP second cladding layer 5, a first waveguide core layer 2, and a p-type InP second cladding layer 7 are laminated on an n-type InP substrate 12. The second optical waveguide 21 shown in FIG. 1 indicates an optical waveguide including an n-type InP second cladding layer 5, a first waveguide core layer 2, and a p-type InP second cladding layer 7. Both side portions of the first waveguide core layer 2 are buried with a semiconductor burying layer 13 to form a buried structure. A p-type first contact layer 10 is laminated on the upper surfaces of the p-type InP second cladding layer 7 and the semiconductor burying layer 13, and a protective passivation film 14 is formed on the upper surface of the p-type first contact layer 10. A first electrode 11, which is a cathode electrode, is provided on the lower surface side, which is the other surface of the n-type InP substrate 12. The second optical waveguide may have a high mesa ridge structure.

[0012] As shown in Figs. 1, 2, 5, 6 and 7, the optical modulator section 103 is configured by stacking an n-type InP second cladding layer 5, an optical modulator section core layer 3 and a first waveguide core layer 2, and a p-type InP second cladding layer 7 on an n-type InP substrate 12. The third optical waveguide 22 shown in Fig. 1 indicates an optical waveguide including the n-type InP second cladding layer 5, an optical modulator section core layer 3 and a first waveguide core layer 2, and a p-type InP second cladding layer 7. Both side portions of the third optical waveguide 22 are buried by the semiconductor burying layer 13, as are both side portions of the first waveguide core layer 2. A p-type first contact layer 10 is stacked on the upper surfaces of the p-type InP second cladding layer 7 and the semiconductor burying layer 13, and a protective passivation film 14 is formed on the upper surface of the p-type first contact layer 10. Furthermore, an electrode 16, which is an anode electrode, is formed on the protective passivation film 14, and the electrode 17 and the p-type first contact layer 10 are electrically connected through an opening formed in the protective passivation film 14. A first electrode 11 is provided on the lower surface side of the n-type InP substrate 12 and is electrically connected to the n-type InP substrate 12. The third optical waveguide 22 may have a high mesa ridge structure. As shown in FIG. 6, the optical modulator section 103 has a structure in which the distance between the side surfaces of the first waveguide core layer 2, that is, the width of the first waveguide core layer 2 in the traveling direction of the laser light, narrows from the laser light incident side connected to the separation section 102 toward the laser light output end face 19 side. On the other hand, since the width of the third optical waveguide 22 in the traveling direction of the laser light is constant, the width of the optical modulator section core layer 3 widens toward the traveling direction of the laser light in response to the narrowing of the width of the first waveguide core layer 2 in the traveling direction of the laser light. In addition, in FIG. 6, the width of the first waveguide core layer 2 is shown to be continuously narrowed from the laser light incident side toward the laser light output end face 19 side, but it may be formed in a stepped staircase shape, or may be a combination of a continuous structure and a stepped structure.

[0013] Next, the basic operation of the above-mentioned semiconductor optical integrated device will be described. When a forward current is applied to the laser diode section 101, laser oscillation occurs and laser light is emitted from the laser diode section 101. This laser light enters the separator section 102, propagates through the optical modulator section 103, The laser light is emitted to the outside from the emission end surface 19. The laser diode section 101 is configured, for example, with a distributed feedback laser structure. The distributed feedback laser structure is provided with a diffraction grating 8, which allows laser light with single-mode oscillation to be obtained. The optical modulator section 103 is an electroabsorption modulator that controls the amount of light absorption by an electric field, and the amount of light absorption increases when a reverse bias voltage is applied. In other words, the input laser light is modulated depending on the magnitude of the voltage applied to the optical modulator section 103. When light is absorbed, the absorbed light is converted into carriers, and a current flows as a photocurrent.

[0014] Next, more specific operations and effects of the semiconductor optical integrated device according to the first embodiment will be described. First, regarding the fact that the optical absorption current is concentrated near the incident end face of the optical modulator section where the optical intensity is the highest, it is possible to suppress the optical absorption current from concentrating in a minute region by reducing the amount of light absorption near the incident end face of the optical modulator section. Specifically, it is conceivable to reduce the intensity of light incident on the optical modulator section core layer where optical absorption occurs at the incident end face of the optical modulator section where the optical intensity is high. Here, since optical absorption by the optical modulator section core layer occurs in the axial direction of the optical waveguide inside the optical modulator section, the relationship between the optical waveguide length from the light incident end and the optical intensity is expressed by the following formula (1). P(x)=P(0)exp(-Γαx) (1) Γ is the optical confinement coefficient of the core layer of the optical modulator section, α is the absorption coefficient of the core layer of the optical modulator section, x is the optical waveguide length from the light input end, and P(0) is the intensity of the incident light. In other words, when Γ and α are constants with respect to x, the incident light exponentially decreases from the input end of the optical waveguide toward the output direction. In other words, the amount of light absorbed at a certain x also exponentially decreases from the input end of the optical waveguide toward the output direction. Therefore, in the optical waveguide of an electroabsorption (EA) modulator, by making Γ small on the input side where the light intensity is high and making Γ continuously larger toward the output side, it is possible to reduce the optical absorption current on the input side where the light intensity is high. This makes it possible to approach the direction in which the amount of light absorbed per unit area is averaged in the optical axis direction, and the increase in the optical absorption current density on the input side can be suppressed compared to the conventional method.

[0015] In the semiconductor optical integrated device according to the first embodiment, the third optical waveguide 22 of the optical modulator section 103 has both side portions of the first waveguide core layer 2, which does not function as an optical absorption layer, embedded with the optical modulator section core layer 3, which functions as an optical absorption layer, as shown in FIG. 5, FIG. 6, and FIG. 7. In addition, in the vertical cross section of the third optical waveguide 22 relative to the optical axis, the ratio of the cross-sectional area of ​​the optical modulator section core layer 3 increases from the light incident side toward the light output side. In other words, the ratio of the light incident into the third optical waveguide 22 that is applied to the optical modulator section core layer 3 increases from the light incident side toward the light output side, which means that the substantial optical confinement factor Γ of the third optical waveguide 22 increases from the light incident side toward the light output side. Since the amount of light absorption is correlated with the optical confinement factor Γ, in the third optical waveguide 22 configured in this manner, the amount of light absorption on the input end face 23 side can be suppressed compared to the light output end face side while keeping the thickness of the third optical waveguide 22 constant. Here, the term "keep the thickness constant" means that the thickness does not have to be changed as a design intent. In other words, it does not mean that the thickness is strictly constant, but includes the case where the thickness is approximately constant. As a specific example of the first waveguide core layer 2 and the optical modulator core layer 3, for example, the total width of the first waveguide core layer 2 and the optical modulator core layer 3 is about 2 μm, the width of the first waveguide core layer 2 on the side of the incident end face 23 is about 2 μm, and the width of the first waveguide core layer 2 on the side of the exit end face is about 0.4 μm. The width of the first waveguide core layer 2 of the optical modulator section 103 may be not only a tapered shape that narrows continuously from the light incident side to the light emitting side, but also a stepped shape that narrows in a stepped manner. The first waveguide core layer 2 of the optical modulator section 103 may be extended to the end face of the semiconductor optical integrated device. The first waveguide core layer 2 of the optical modulator section 103 may be grown together with the optical waveguide layer of the separation section 102, or may be grown separately. The semiconductor buried layer 13 may be made of p-type InP and n-type InP, or may use a semiconductor such as Fe-doped InP. The laser diode section core layer 1 of the laser diode section 101 is made of, for example, an InGaAsP-based multiple quantum well layer, and the band gap wavelength of the multiple quantum well layer is about 1.2 to 1.6 μm. The band gap wavelength of the first waveguide core layer 2 of the separation section 102 and the optical modulator section 103 may be set to be shorter than the laser wavelength oscillated from the laser diode section 101, for example, about 0.9 to 1.5 μm. The band gap wavelength of the optical modulator section core layer 3 of the optical modulator section 103 may be set to be shorter than the laser wavelength oscillated from the laser diode section 101, for example, about 0.9 to 1.5 μm, which is composed of an InGaAsP-based multiple quantum well layer. The band gap wavelength of the optical modulator section core layer 3 may be constant from the light incident side to the light emitting side, or may be lengthened continuously or stepwise. The laser diode section core layer 1 and the optical modulator section core layer 3 may be formed by applying a selective growth technique, or may be formed separately by Butt-Joint growth.

[0016] Next, a method for manufacturing the semiconductor optical integrated device according to the first embodiment will be described. In the region where the laser diode section 101 is to be formed, an n-type InP first cladding layer 4, a laser diode section core layer 1, a p-type InP first cladding layer 6, a diffraction grating 8, and an n-type InP fourth cladding layer 9 are laminated on an n-type InP substrate 12. In the region where the separation section 102 and the optical modulator section 103 are to be formed, an n-type InP second cladding layer 5 and a first waveguide core layer 2 are laminated on an n-type InP substrate 12. Then, an insulating film is formed on the upper surface of the first waveguide core layer 2, and the insulating film is patterned so that the insulating film remains in a shape corresponding to the first waveguide core layer 2 shown in FIG. 7. Using the insulating film as an etching mask, an etching technique such as dry etching is used to etch the first waveguide core layer 2 of the optical modulator section 103, thereby forming the first waveguide core layer 2 in the shape shown in FIG. 7. Next, both side portions of the first waveguide core layer 2 of the optical modulator section 103 are embedded with the optical modulator section core layer 3. After that, the insulating film used as the etching mask is removed, and the separation section 102 and the p-type InP second cladding layer 7 of the optical modulator section 103 are laminated. Next, an insulating film is formed on the upper surfaces of the n-type InP fourth cladding layer 9 of the laser diode section 101, the p-type InP second cladding layer 7 of the separation section 102, and the p-type InP second cladding layer 7 of the optical modulator section 103, and the insulating film is patterned into shapes corresponding to the ridge structures of the first optical waveguide 20, the second optical waveguide 21, and the third optical waveguide 22, respectively. Using the insulating film as an etching mask, the ridge structures of the first optical waveguide 20, the second optical waveguide 21, and the third optical waveguide 22 are formed by using an etching technique such as dry etching. Next, both side portions of the ridge structure of the laser diode section 101, the separator section 102, and the optical modulator section 103 are buried with a semiconductor burying layer 13. The semiconductor burying layer 13 may be composed of p-type InP and n-type InP, or a semiconductor such as Fe-doped InP may be used. Thereafter, the insulating film is removed, and the p-type first contact layer 10 is laminated. Next, a protective passivation film 14 is formed on the upper surface of the p-type first contact layer 10. An opening is formed in the protective passivation film 14 on the upper surface of the laser diode section 101, and an electrode 16 electrically connected to the p-type first contact layer 10 is formed.Also, an opening is formed in the protective passivation film 14 on the upper surface of the optical modulator section 103, and an electrode 17 electrically connected to the p-type first contact layer 10 and a bonding pad 18 electrically connected to the electrode 17 are formed.

[0017] As described above, the semiconductor optical integrated device according to the first embodiment has a structure in which the thickness of the third optical waveguide 22 of the optical modulator section 103 is constant, and both side surfaces of the first waveguide core layer 2, which does not function as an optical absorption layer, are embedded with the optical modulator section core layer 3, which functions as an optical absorption layer. That is, the optical modulator section core layer 3 is provided at a position sandwiching the first waveguide core layer 2 from the sides in the propagation direction of the laser light. Furthermore, the ratio of the cross-sectional area of ​​the optical modulator section core layer 3 to the vertical cross section of the third optical waveguide 22 with respect to the optical axis increases from the incident side to the output side of the light. The semiconductor optical integrated device configured in this manner can suppress the amount of light absorption on the light incident end face 23 side compared to the light emitting end face 19 side, while keeping the thickness of the third optical waveguide 22 constant.

[0018] Therefore, by applying the semiconductor optical integrated element shown in the first embodiment, it is possible to prevent light with high intensity from being incident on the optical absorption layer in the vicinity of the incident end face 23 of the optical modulator section, so that it is possible to provide a semiconductor optical integrated element that prevents characteristic degradation caused by the optical absorption current being concentrated in a small area.

[0019] Embodiment 2 The semiconductor optical integrated device according to the second embodiment is described below. Since the configuration of the semiconductor optical integrated device according to the second embodiment is the same as that of the first embodiment except for the structure of the optical modulator section 103, the following mainly describes the differences from the first embodiment, and may omit overlapping parts.

[0020] A schematic top view of the semiconductor optical integrated device according to the second embodiment is similar to Fig. 1. Fig. 8 is a schematic DD cross-sectional view of the semiconductor optical integrated device according to the second embodiment shown in Fig. 1. Fig. 9 is a schematic EE cross-sectional view of the semiconductor optical integrated device according to the second embodiment shown in Fig. 1. Fig. 10 is a schematic GG cross-sectional view of the optical modulator section 103 of the semiconductor optical integrated device according to the second embodiment shown in Fig. 1. 8 to 10, the optical modulator section 103 of the semiconductor optical integrated device according to the second embodiment is configured to have a structure in which an n-type InP second cladding layer 5, a first waveguide core layer 2, an optical modulator section core layer 3, and a p-type InP second cladding layer 7 are laminated on an n-type InP substrate 12. The first waveguide core layer 2 has a structure in which the thickness in the lamination direction of the third optical waveguide 22, that is, the thickness in the vertical direction, is continuously reduced from the laser light incident side toward the laser light output end face 19 side. On the other hand, since the thickness of the third optical waveguide 22 is constant, the thickness of the optical modulator section core layer 3 is structured to be thicker toward the laser light traveling direction in response to the thickness of the first waveguide core layer 2 being thinner in the laser light traveling direction. Although the thickness of the first waveguide core layer 2 and the optical modulator core layer 3 is shown to change continuously along the traveling direction of the laser light, they may be formed in a stepped shape, or may be a combination of a continuous structure and a stepped structure. Also, the order of laminating the first waveguide core layer 2 and the optical modulator core layer 3 may be reversed.

[0021] As described above, the semiconductor optical integrated device according to the second embodiment has a structure in which the first waveguide core layer 2, which does not function as a light absorption layer, and the optical modulator core layer 3 are stacked vertically while the thickness of the third optical waveguide 22 of the optical modulator section 103 is constant. Furthermore, the thickness of the optical modulator core layer 3 increases in the traveling direction of the laser light. In other words, the ratio of the cross-sectional area of ​​the optical modulator core layer 3 to the vertical cross section of the third optical waveguide 22 relative to the optical axis increases from the incident side toward the exit side of the light. The semiconductor optical integrated device configured in this manner can suppress the amount of light absorption on the light incident end face 23 side compared to the light emitting end face 19 side, while keeping the thickness of the third optical waveguide 22 constant.

[0022] Therefore, by applying the semiconductor optical integrated element shown in the second embodiment, similarly to the first embodiment, it is possible to suppress the incidence of light with high intensity on the optical absorption layer in the vicinity of the incident end face 23 of the optical modulator section, and thus it is possible to provide a semiconductor optical integrated element which prevents the deterioration of characteristics caused by the concentration of the optical absorption current in a minute region.

[0023] Embodiment 3 The semiconductor optical integrated device according to the third embodiment is described below. The configuration of the semiconductor optical integrated device according to the third embodiment is different from that of the first embodiment in the structures of the separation section 102 and the optical modulator section 103. Differences from the first embodiment are mainly described, and overlapping parts may be omitted.

[0024] FIG. 11 is a schematic top view showing a semiconductor optical integrated device according to the third embodiment. FIG. 12 is a schematic cross-sectional view taken along line BB of the separation unit 102 shown in FIG. 11 of the semiconductor optical integrated device according to the third embodiment. FIG. 13 is a schematic cross-sectional view taken along line CC of the separation unit 102 shown in FIG. 11 of the semiconductor optical integrated device according to the third embodiment. FIG. 14 is a schematic cross-sectional view taken along line HH of the separation unit 102 shown in FIGS. 12 and 13 of the semiconductor optical integrated device according to the third embodiment. FIG. 15 is a schematic cross-sectional view taken along line DD of the optical modulator unit 103 shown in FIG. 11 of the semiconductor optical integrated device according to the third embodiment. FIG. 16 is a schematic cross-sectional view taken along line EE of the optical modulator unit 103 shown in FIG. 11 of the semiconductor optical integrated device according to the third embodiment. FIG. 17 is a schematic cross-sectional view taken along line II of the optical modulator unit 103 shown in FIGS. 15 and 16 of the semiconductor optical integrated device according to the third embodiment. First, as shown in Fig. 11 to Fig. 14, the separation section 102 of the semiconductor optical integrated device according to the third embodiment has a structure in which the width of the second optical waveguide 21 in the laser light propagation direction becomes wider toward the laser light propagation direction. Also, as shown in Fig. 15 to Fig. 17, the optical modulator section 103 of the semiconductor optical integrated device according to the third embodiment has a structure in which the width of the third optical waveguide 22 in the laser light propagation direction becomes narrower toward the laser light propagation direction. However, the third optical waveguide 22 has a constant height, and an optical modulator section core layer 3 with a constant width is formed in the center along the laser light propagation direction, and both side surfaces of the optical modulator section core layer 3 are embedded with the first waveguide core layer 2. Furthermore, the width of the first waveguide core layer 2 embedded in both side surfaces of the optical modulator section core layer 3 becomes narrower along the laser light propagation direction. In addition, in FIG. 17, the width of the first waveguide core layer 2 is shown to be continuously narrowed along the traveling direction of the laser light, but it may be formed in a stepped shape having steps, or may be a combination of a continuous structure and a stepped structure.

[0025] As described above, in the semiconductor optical integrated device according to the third embodiment, the width of the second optical waveguide 21 of the separation section 102 becomes wider from the light incident side toward the light exit side. As a result, compared to the case where the width of the second optical waveguide 21 is constant, the optical confinement factor Γ at the incident end face 23 of the optical modulator section 103 can be reduced, and the optical intensity per unit area can be reduced. In addition, the width of the first waveguide core layer 2 of the optical modulator section 103 becomes narrower from the light incident side toward the light exit side. As a result, the optical confinement factor Γ of the optical modulator section core layer 3 can be increased from the light incident side toward the light exit side. Therefore, the laser light can be reduced in intensity by passing through the separation section 102, and further, in the optical modulator section 103, the amount of light absorption on the incident end face 23 side can be suppressed compared to the light exit end face 19 side. As a result, compared to the conventional semiconductor optical integrated device, the concentration of the optical absorption current in the vicinity of the incident end face 23 of the optical modulator section 103 can be reduced.

[0026] As described above, in the semiconductor optical integrated device according to the third embodiment, the width of the second optical waveguide 21 of the separation section 102 becomes wider from the light incident side toward the light exit side. Furthermore, the width of the first waveguide core layer 2 of the optical modulator section 103 becomes narrower from the light incident side toward the light exit side, and the ratio of the cross-sectional area of ​​the optical modulator section core layer 3 to the vertical cross section of the third optical waveguide 22 relative to the optical axis becomes larger from the light incident side toward the light exit side. The semiconductor optical integrated device configured in this manner can suppress the amount of light absorption on the light incident end face 23 side compared to the light emitting end face 19 side, while keeping the thickness of the third optical waveguide 22 constant.

[0027] Therefore, by applying the semiconductor optical integrated element shown in the third embodiment, similarly to the first embodiment, it is possible to suppress the incidence of light with high intensity on the optical absorption layer in the vicinity of the incident end face 23 of the optical modulator section, and thus it is possible to provide a semiconductor optical integrated element which prevents the deterioration of characteristics caused by the concentration of the optical absorption current in a minute region.

[0028] Embodiment 4 The semiconductor optical integrated device according to the fourth embodiment is described below. Since the configuration of the semiconductor optical integrated device according to the fourth embodiment is the same as that of the third embodiment except for the structure of the separation unit 102, the following mainly describes the differences from the third embodiment, and may omit overlapping parts.

[0029] A schematic top view of the semiconductor optical integrated device according to the fourth embodiment is similar to Fig. 11. Fig. 18 is a schematic cross-sectional view taken along line BB of the separation unit 102 of the semiconductor optical integrated device according to the fourth embodiment shown in Fig. 11. Fig. 19 is a schematic cross-sectional view taken along line CC of the separation unit 102 of the semiconductor optical integrated device according to the fourth embodiment shown in Fig. 11. Fig. 20 is a schematic cross-sectional view taken along line JJ of the separation unit 102 of the semiconductor optical integrated device according to the fourth embodiment shown in Figs. 18 and 19. In the semiconductor optical integrated device according to the fourth embodiment, the separator 102 is configured to have a structure in which an n-type InP second cladding layer 5, a first waveguide core layer 2 and a second waveguide core layer 15, and a p-type InP second cladding layer 7 are laminated on an n-type InP substrate 12. A first electrode 11, which is a cathode electrode, is provided on the lower surface of the n-type InP substrate 12, and the first electrode 11 and the n-type InP substrate 12 are electrically connected. The second optical waveguide 21 shown in FIG. 11 indicates an optical waveguide including the n-type InP second cladding layer 5, the first waveguide core layer 2 and the second waveguide core layer 15, and the p-type InP second cladding layer 7.

[0030] The width of the first waveguide core layer 2 of the separation section 102 is continuously narrowed from the incident side of the laser light toward the emission side. The width of the first waveguide core layer 2 of the separation section 102 may be a stepped shape having a step-like narrowing shape, instead of a tapered shape having a step-like narrowing shape, from the incident side of the light toward the emission side. The width of the second waveguide core layer 15 of the separation section 102 is continuously widened. The width of the second waveguide core layer 15 may be a stepped shape having a step-like widening shape, instead of an inverse tapered shape having a step-like widening shape, from the incident side of the light toward the emission side. Here, the semiconductor constituting the first waveguide core layer 2 and the semiconductor constituting the second waveguide core layer 15 are semiconductors having different band gap wavelengths, so that the beam diameter of the laser light passing through the second optical waveguide 21 can be controlled. For example, the first waveguide core layer 2 is made of an InGaAsP-based material having a bandgap wavelength of about 0.9 to 1.5 μm, and the second waveguide core layer 15 is made of an InP-based material having a bandgap wavelength of about 0.9 to 1.0 μm, thereby making it possible to change the spreading and coupling of the laser light.

[0031] As described above, in the semiconductor optical integrated device according to the fourth embodiment, the width of the second optical waveguide 21 of the separation section 102 becomes wider from the light incident side toward the light emitting side, as in the case of the forty-third embodiment. In addition, it is possible to apply the first waveguide core layer 2 and the second waveguide core layer 15 using semiconductors having different band gap wavelengths. As a result, compared to the case where the width of the second optical waveguide 21 is constant, the optical confinement factor Γ at the incident end face 23 of the optical modulator section 103 can be reduced, the light intensity per unit area can be reduced, and it is possible to couple the laser light more efficiently than in the third embodiment and make it incident on the optical modulator section 103. As a result, it is possible to couple the laser light more efficiently than in the third embodiment, while reducing the concentration of the optical absorption current in the vicinity of the incident end face 23 of the optical modulator section 103 compared to the conventional semiconductor optical integrated device.

[0032] As described above, in the semiconductor optical integrated device according to the fourth embodiment, the width of the first waveguide core layer 2 of the separation section 102 narrows from the incident side to the output side of the laser light, and the width of the second waveguide core layer 15 continuously widens. In addition, the semiconductors constituting the first waveguide core layer 2 and the semiconductors constituting the second waveguide core layer 15 are semiconductors having different band gap wavelengths. This makes it possible to couple the laser light more efficiently than in the third embodiment and input it to the optical modulator section 103. Furthermore, as in the third embodiment, the width of the first waveguide core layer 2 of the optical modulator section 103 narrows from the incident side to the output side of the light, and the ratio of the cross-sectional area of ​​the optical modulator section core layer 3 to the vertical cross section of the third optical waveguide 22 relative to the optical axis increases from the incident side to the output side of the light. The semiconductor optical integrated device configured in this manner can suppress the amount of light absorption on the light incident end face 23 side compared to the light emitting end face 19 side while keeping the thickness of the third optical waveguide 22 constant, and can couple laser light more efficiently than in the third embodiment.

[0033] Therefore, by applying the semiconductor optical integrated element shown in the fourth embodiment, as in the third embodiment, it is possible to suppress the incidence of light with high intensity on the optical absorption layer in the vicinity of the incident end face 23 of the optical modulator section, thereby preventing the deterioration of characteristics caused by the optical absorption current concentrating in a minute region, and furthermore, it is possible to provide a semiconductor optical integrated element capable of efficient coupling of laser light. [Explanation of symbols]

[0034] 1 Laser diode core layer 2. First waveguide core layer 3 Optical modulator core layer 4 n-type InP first cladding layer 5 n-type InP second cladding layer 6 p-type InP first cladding layer 7 p-type InP second cladding layer 8. Diffraction Grating 9 n-type InP fourth cladding layer 10 p-type first contact layer 11 1st electrode 12 n-type InP substrate 13 Semiconductor buried layer 14 Protective passivation film 15 Second waveguide core layer 16 electrodes 17 electrodes 18 Bonding Pads 19 Output end face 20 First optical waveguide 21 Second optical waveguide 22 Third optical waveguide 23 Incidence end face 101 Laser diode section 102 Separation part 103 Optical Modulator Section

Claims

1. a laser diode portion having a first optical waveguide and generating a laser beam; a separation section connected to the laser diode section and having a second optical waveguide including a first core layer through which a laser beam emitted from the laser diode section propagates; an optical modulator section having a third optical waveguide connected to the separation section and including a second core layer that absorbs a part of the laser light emitted from the separation section; Equipped with the third optical waveguide has a constant thickness in a direction perpendicular to a surface of a substrate on which the optical modulator section is formed, a ratio of the second core layer in a cross section of the third optical waveguide perpendicular to a laser light propagation direction increases from an incident side toward an exit side of the laser light, At an incident end surface of the optical modulator section, the third optical waveguide has the first core layer or a third core layer which does not contribute to absorbing laser light. Semiconductor optical integrated device.

2. the third optical waveguide includes the first core layer and the second core layer, the second core layer is provided at a position sandwiching the first core layer from the side in a propagation direction of laser light, a width of the first core layer sandwiched between the second core layers narrows from the laser light incident side toward the laser light exit side; 2. The semiconductor optical integrated device according to claim 1.

3. the second core layer has a thickness in a direction perpendicular to a surface of the substrate on which the optical modulator section is formed, the thickness increasing from the laser light incident side toward the laser light exit side; 2. The semiconductor optical integrated device according to claim 1.

4. the second optical waveguide has a width in a direction perpendicular to a propagation direction of the laser light and parallel to a surface of the substrate on which the separation unit is formed, the width increasing from an incident side to an exit side of the laser light, the third optical waveguide includes the third core layer, and a width in a direction perpendicular to a propagation direction of the laser light and parallel to a surface of the substrate on which the separation section is formed becomes narrower from an incident side to an exit side of the laser light, the third core layer is provided at a position sandwiching the second core layer from the sides in a propagation direction of the laser light, and the width of the third core layer is narrowed from the incident side toward the output side of the laser light.

2. The semiconductor optical integrated device according to claim 1.

5. the second optical waveguide includes a fourth core layer having a band gap wavelength different from that of the first core layer, the first core layer has a width that is perpendicular to a propagation direction of the laser light and parallel to a surface of the substrate on which the separation portion is formed, the width of the first core layer narrowing from an incident side to an exit side of the laser light, the fourth core layer is provided at a position sandwiching the first core layer from the side in the propagation direction of the laser light, and the width of the fourth core layer increases from the incident side toward the output side of the laser light.

5. The semiconductor optical integrated device according to claim 4.

6. The band gap wavelength of the second core layer is longer on the laser light emission side than on the laser light incidence side.

6. The semiconductor optical integrated device according to claim 1.

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