Optical semiconductor device

Abstract

To suppress pattern effects in a semiconductor optical amplifier.SOLUTION: An optical semiconductor device includes a core-shaped active layer 103 formed by semiconductor layers 103a, 103b, 103c, 103d made of compound semiconductors formed on a substrate 101. The optical confinement coefficient of an optical waveguide, with the active layer 103 as its core, is reduced from an optical input position to an optical output position. For example, the semiconductor layers 103a, 103b, 103c, 103d are formed by stacking at multiple locations on the substrate 101, and the number of stacked semiconductor layers 103a, 103b, 103c, 103d gradually decreases from the optical input position to the optical output position.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present invention relates to an optical semiconductor element. [Background technology]

[0002] BACKGROUND ART Semiconductor optical amplifiers (SOAs) are used in optical communications such as those on the Internet (Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Jui-Pin Wu et al., "Low-Pattern-Dependence Prechirp Optical Modulation by Using Saturation Behaviors of SOA-Integrated EMA", Journal of Lightwave Technology, vol. 31, no. 23, pp. 3651-3657, 2013. Summary of the Invention [Problem to be solved by the invention]

[0004] The pattern effect is a problem with this SOA. When the optical output of the SOA increases and approaches saturation, the SOA is no longer able to keep up with the rapidly changing input light, and the waveform of the output light from the SOA is distorted, a phenomenon known as the pattern effect.

[0005] For example, when "1" and "0" signals corresponding to 10 dBm and 0 dBm are input, the output light is amplified to 18 dBm and 10 dBm because the gain of the two signals is different, causing problems such as a change in the extinction ratio of the optical waveform before input to the SOA (10 dB → 8 dB).

[0006] The present invention has been made to solve the above problems, and has as its object to suppress the pattern effect in a semiconductor optical amplifier. [Means for solving the problem]

[0007] The optical semiconductor element according to the present invention comprises a core-shaped active layer made of a semiconductor layer made of a compound semiconductor formed on a substrate, and the optical confinement factor of the optical waveguide having the active layer as the core is made smaller from the optical input position to the optical output position.

[0008] In the optical semiconductor element, the semiconductor layers are stacked at a plurality of locations on the substrate, and the number of stacked semiconductor layers gradually decreases from the light input position to the light output position.

[0009] In one configuration example of the optical semiconductor device, the active layer has a multiple quantum well structure, and each of the semiconductor layers is a well layer of the multiple quantum well structure.

[0010] In one configuration example of the optical semiconductor device, each of the semiconductor layers has a multiple quantum well structure.

[0011] In one configuration example of the optical semiconductor element, the conduction band offset between the well layer and the barrier layer in each semiconductor layer is made smaller as the semiconductor layer is farther from the substrate.

[0012] In the above-described exemplary configuration of the optical semiconductor element, the width of the active layer gradually increases in plan view from the light input position to the light output position. [Effects of the Invention]

[0013] As described above, according to the present invention, the optical confinement factor of the optical waveguide having the active layer as its core decreases from the optical input position to the optical output position, thereby suppressing the pattern effect in the semiconductor optical amplifier. [Brief explanation of the drawings]

[0014] [Figure 1A]FIG. 1A is a cross-sectional view showing the configuration of an optical semiconductor element according to an embodiment of the present invention. [Figure 1B] FIG. 1B is a cross-sectional view showing the configuration of an optical semiconductor element according to an embodiment of the present invention. [Figure 2] FIG. 2 is a characteristic diagram showing the relationship between the input light intensity and the gain for an SOA for each optical confinement factor Γ. [Figure 3] FIG. 3 is a characteristic diagram showing the relationship between the number of stacked semiconductor layers and the optical confinement factor. [Figure 4] FIG. 4 is a distribution diagram showing the distribution of light intensity in the cross section of the active layer 103 at positions (a), (b), (c), and (d) in FIG. 1A. [Figure 5] FIG. 5 is a characteristic diagram showing the relationship between the width of the active layer and the optical confinement factor. [Figure 6] FIG. 6 is a characteristic diagram showing the relationship between the width of the active layer and the optical confinement factor per width of one semiconductor layer. [Figure 7] FIG. 7 is a distribution diagram showing the distribution of light intensity in the cross section of the active layer 103 when the width of the active layer 103 is set to 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, and 8 μm. [Figure 8] FIG. 8 is a characteristic diagram showing the relationship between the width of the active layer 103 and the optical confinement factor when the number of stacked semiconductor layers is changed. [Figure 9] FIG. 9 is a characteristic diagram showing the change in the optical confinement factor per width of one semiconductor layer when the number of stacked semiconductor layers is changed. DETAILED DESCRIPTION OF THE INVENTION

[0015] An optical semiconductor device according to an embodiment of the present invention will be described below with reference to Figures 1A and 1B. Figure 1A shows a cross section parallel to the waveguide direction, and Figure 1B shows a cross section perpendicular to the waveguide direction at position (a) in Figure 1A.

[0016] This optical semiconductor device includes a core-shaped active layer 103 made of semiconductor layers 103a, 103b, 103c, and 103d made of compound semiconductors formed on a substrate 101. In this example, the active layer 103 is provided on a lower cladding layer 102, and an upper cladding layer 104 is provided on the active layer 103. Furthermore, the optical confinement factor of the optical waveguide having the active layer 103 as its core decreases from the optical input position to the optical output position. Note that, although not shown, on the paper surface of FIG. 1A, the optical input position is on the left and the optical output position is on the right.

[0017] This optical semiconductor device is a semiconductor optical amplifier (SOA). The saturated output power P sat can be expressed by the following formula:

[0018]

number

[0019] W is the width of the active layer 103, d a is the thickness of the active layer 103, Γ is the optical confinement factor, A is the differential gain, and τ is the carrier lifetime. As shown in FIG. 2, by lowering the optical confinement factor Γ, the absolute amount of gain in the SOA decreases, but the saturated gain can be increased. In the optical semiconductor device according to the embodiment, the optical confinement factor Γ is gradually reduced from the optical input position to the optical output position, thereby suppressing the decrease in the absolute amount of gain throughout the SOA while increasing the saturated gain, thereby suppressing the pattern effect in the SOA.

[0020] For example, semiconductor layers 103a, 103b, 103c, and 103d are stacked in multiple locations on substrate 101, and the number of stacked semiconductor layers 103a, 103b, 103c, and 103d gradually decreases from the light input position to the light output position. For example, in first region 131 on the light input position side, four layers, semiconductor layer 103a, semiconductor layer 103b, semiconductor layer 103c, and semiconductor layer 103d, are stacked. In second region 132, which is adjacent to first region 131 on the light output position side, three layers, semiconductor layer 103a, semiconductor layer 103b, and semiconductor layer 103c, are stacked. In third region 133, which is adjacent to second region 132 on the light output position side, two layers, semiconductor layer 103a and semiconductor layer 103b, are stacked.

[0021] As shown in FIG. 3, the optical confinement factor can be increased by increasing the number of layers. In other words, the optical confinement factor can be decreased by decreasing the number of layers. More specifically, by decreasing the number of layers, the optical confinement factor per width of one semiconductor layer of the optical waveguide having the active layer 103 as its core can be decreased from the optical input position to the optical output position. Therefore, as described above, by decreasing the number of layers from the optical input position to the optical output position, the optical confinement factor can be decreased toward the optical output position. Note that the number of layers is not limited to four, and can be at least two layers, or five or more layers.

[0022] 4 shows the distribution of light intensity in the cross section of the active layer 103 at positions (a), (b), (c), and (d) in FIG. 1A. Note that this example illustrates a configuration in which the width of the active layer 103 gradually increases in plan view from the light input position to the light output position. Light is confined in the active layer 103 at all positions.

[0023] The active layer 103 may have a multiple quantum well structure, and each of the semiconductor layers 103a, 103b, 103c, and 103d may be a well layer of the multiple quantum well structure. For example, the active layer 103 may have a multiple quantum well structure in which semiconductor layers 103a, 103b, 103c, and 103d, which are well layers made of undoped i-InAlGaAs, and barrier layers made of InAlGaAs are alternately stacked.

[0024] Each of the semiconductor layers 103a, 103b, 103c, and 103d may have a multiple quantum well structure. Each of the semiconductor layers 103a, 103b, 103c, and 103d may have a multiple quantum well structure in which well layers made of undoped i-InAlGaAs and barrier layers made of InAlGaAs are alternately stacked. An InP layer may be provided between each of the semiconductor layers 103a, 103b, 103c, and 103d.

[0025] In this case, the conduction band offset between the well layer and the barrier layer in each of the semiconductor layers 103a, 103b, 103c, and 103d can be made smaller as the semiconductor layers 103a, 103b, 103c, and 103d are further away from the substrate 101. For example, the conduction band offset can be set as follows: semiconductor layer 103a > semiconductor layer 103b > semiconductor layer 103c > semiconductor layer 103d. Increasing the conduction band offset strengthens the electron confinement, resulting in a larger gain. As mentioned above, lowering the optical confinement factor Γ reduces the absolute amount of gain in the SOA. However, the above-described configuration can suppress the decrease in gain on the side of the optical output position where the number of layers is reduced.

[0026] Next, we will explain the effect of gradually increasing the width of the active layer 103 in a planar view from the light input position to the light output position. Increasing the width of the active layer 103 can reduce the optical confinement factor per width of one semiconductor layer of the optical waveguide with the active layer 103 as the core. As the width of the active layer 103 is increased, the optical confinement factor of the entire optical waveguide formed by the active layer 103 increases, as shown in Figure 5. However, as shown in Figure 6, the optical confinement factor per width of one semiconductor layer decreases as the width is increased. Figure 7 shows the distribution of optical intensity in the cross section of the active layer 103 when the width of the active layer 103 is set to 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, and 8 μm.

[0027] The above relationship also changes depending on the number of stacked semiconductor layers. Fig. 8 shows the relationship between the width of the active layer 103 and the optical confinement factor when the number of stacked semiconductor layers is changed. Fig. 9 also shows the change in the optical confinement factor per width of one semiconductor layer when the number of stacked semiconductor layers is changed. In Figs. 8 and 9, (a) shows the number of stacked layers is 4, (b) shows the number of stacked layers is 3, (c) shows the number of stacked layers is 2, and (d) shows the number of stacked layers is 1. The greater the number of stacked semiconductor layers, the greater the effect of reducing the optical confinement factor per width of one semiconductor layer by widening the width.

[0028] As described above, according to the present invention, for example, by gradually reducing the number of stacked semiconductor layers constituting the active layer, the optical confinement factor of the optical waveguide having the active layer as its core decreases from the optical input position to the optical output position, thereby making it possible to suppress the pattern effect in the semiconductor optical amplifier.

[0029] The present invention is not limited to the above-described embodiments, and it is apparent that many modifications and combinations can be made by a person skilled in the art within the technical spirit of the present invention. For example, although the above-described embodiment has cladding layers above and below the active layer, the present invention is not limited to this. For example, an optical confinement layer can be provided between the cladding layer and the active layer to form a separate confined heterostructure (SCH). [Explanation of symbols]

[0030] 101...substrate, 102...lower cladding layer, 103...active layer, 103a, 103b, 103c, 103d...semiconductor layers, 104...upper cladding layer, 131...first region, 132...second region, 133...third region.

Claims

1. a core-shaped active layer made of a semiconductor layer made of a compound semiconductor formed on a substrate; The optical confinement factor of the optical waveguide having the active layer as a core is made smaller from the optical input position to the optical output position. Optical semiconductor element.

2. 2. The optical semiconductor device according to claim 1, the semiconductor layer is formed by laminating at a plurality of locations on the substrate, The number of stacked semiconductor layers gradually decreases from the light input position to the light output position. Optical semiconductor element.

3. 3. The optical semiconductor device according to claim 2, the active layer has a multiple quantum well structure, Each of the semiconductor layers is a well layer of a multiple quantum well structure. Optical semiconductor element.

4. 3. The optical semiconductor device according to claim 2, Each of the semiconductor layers has a multiple quantum well structure. Optical semiconductor element.

5. 5. The optical semiconductor device according to claim 4, The conduction band offset between the well layer and the barrier layer in each of the semiconductor layers is smaller in the semiconductor layer farther from the substrate. Optical semiconductor element.

6. The optical semiconductor device according to any one of claims 1 to 5, The width of the active layer gradually increases from the light input position to the light output position in a plan view. Optical semiconductor element.

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