Light-emitting devices

Abstract

This light-emitting device is provided with: a wave guide-type light-emitting element (102) formed on a cladding layer (101); a core (104) formed on the cladding layer (101) and constituting a port (103) opposite to an output port of the light-emitting element (102); and a light absorption layer (105) formed on the core (104) in a state of being in contact therewith. The core (104) is composed of a group III-V compound semiconductor such as InP. The core (104) is composed of a group III-V compound semiconductor that can guide (transmit) light (laser beam) outputted from the light-emitting element (102). The light absorption layer (105) is composed of a group III-V compound semiconductor, such as InGaAs, having a refractive index higher than that of the core (104). The group III-V compound semiconductor having the higher refractive index has an absorption coefficient with respect to light transmitted through the core (104) (light emitted from the light-emitting element (102)).

Description

[Technical Field]

[0001] The present invention relates to a light-emitting device comprising a light-emitting element. [Background technology]

[0002] The explosive growth in network traffic accompanying the spread of the Internet has led to a continuous increase in the speed and capacity of optical fiber transmission. Semiconductor lasers are used in light-emitting devices such as optical transceivers used in optical communications, and have continued to develop as light source devices supporting optical fiber communications. For example, a light-emitting device may be configured as shown in FIGS. 10A, 10B, and 10C. The light-emitting device includes a semiconductor laser 302 formed on a cladding layer 301, an output port 303 formed by a first core 305, and an unwanted port 304 formed by a second core 306.

[0003] The semiconductor laser 302 includes a compound semiconductor layer 321 such as InP and a core-shaped active layer 322 embedded in the compound semiconductor layer 321. The active layer 322 also includes an n-semiconductor layer 323 and a p-semiconductor layer 324 formed in an optical waveguide formed by the active layer 322, sandwiching the active layer 322 in a direction perpendicular to the waveguide direction. The n-semiconductor layer 323 is made of a compound semiconductor doped with n-type impurities, and the p-semiconductor layer 324 is made of a compound semiconductor doped with p-type impurities. The region of the compound semiconductor layer 321 where the active layer 322 is embedded is non-doped. An n-electrode 327 and a p-electrode 328 are ohmically connected to the n-semiconductor layer 323 and the p-semiconductor layer 324 via an n-contact layer 325 and a p-contact layer 326.

[0004] The semiconductor laser 302 configured in this manner is a semiconductor laser with a diffraction grating as a distributed Bragg reflector structure (resonator). Laser oscillation is obtained by injecting a current into the active layer 322 of the semiconductor laser 302 via the n-electrode 327 and the p-electrode 328. The laser light generated by this laser oscillation is guided (output) to the output port 303 and the unwanted port 304.

[0005] In this way, the light generated by the semiconductor laser is emitted from both ends of the semiconductor laser. In this type of semiconductor laser, it is common to extract light from one side (output port), so the light emitted from the side not used for extraction (unwanted port) is emitted into the spatial-optical integrated circuit as stray light, and some of it is reflected back into the semiconductor laser as light.

[0006] It is known that the generation of such stray light can cause optical crosstalk within optical integrated circuits, and that the generation of reflected light can destabilize the operation of semiconductor lasers (Non-Patent Document 1).

[0007] Therefore, reducing the light emitted from the unnecessary ports, i.e., optical termination, is essential for stable operation of the semiconductor laser. For such optical termination, a conventional technique is used, as shown in Fig. 11, in which light emitted from the unnecessary port 304 by the second core 306a is coupled to an optical waveguide 307 made of a highly p-doped Si core 308, and the light is absorbed by free carrier absorption. The second core 306a is configured so that its width becomes narrower as it moves away from the semiconductor laser 302, and the Si core 308 is configured so that its width becomes narrower as it approaches the coupling point with the second core 306a. Another method used for optical termination is to optically wire the optical waveguide constituting the unnecessary port in a spiral shape in a plan view and gradually release the light into space. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] S. Gomez1 et al., "High coherence collapse of a hybrid III-V / Si semiconductor laser with a large quality factor", Journal of Physics: Photonics, vol. 2, 025005, 2020. Summary of the Invention [Problem to be solved by the invention]

[0009] However, in order to suppress the stray light mentioned above, the optical absorption by free carrier absorption requires the optical waveguide that constitutes the optical terminal to be long, which increases the area occupied by the optical transceiver and hinders the miniaturization of the device. Also, when coupling a Si optical waveguide to an unnecessary port, optical reflection occurs during coupling, which causes problems by returning light to the semiconductor laser.

[0010] The present invention has been made to solve the above problems, and has as its object to reduce the amount of light output to unnecessary ports without hindering miniaturization. [Means for solving the problem]

[0011] The light-emitting device according to the present invention comprises a waveguide-type light-emitting element formed on a cladding layer, a core made of a III-V compound semiconductor formed on the cladding layer and constituting a port opposite to the output port of the light-emitting element, and a light-absorbing layer made of a III-V compound semiconductor having a refractive index higher than that of the core and formed on and in contact with the core. [Effects of the Invention]

[0012] As described above, according to the present invention, a light absorption layer made of a III-V compound semiconductor having a higher refractive index than the core is provided on the core constituting the port opposite the output port, so that the light output to the unnecessary port can be reduced without hindering miniaturization. [Brief explanation of the drawings]

[0013] [Figure 1A] FIG. 1A is a plan view showing the configuration of a light-emitting device according to an embodiment of the present invention. [Figure 1B] FIG. 1B is a cross-sectional view showing a partial configuration of a light-emitting device according to an embodiment of the present invention. [Figure 1C]FIG. 1C is a cross-sectional view showing a partial configuration of a light-emitting device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view showing the configuration of another light-emitting device according to an embodiment of the present invention. [Figure 3] FIG. 3 is a plan view showing the configuration of another light-emitting device according to an embodiment of the present invention. [Figure 4A] FIG. 4A is a plan view showing the configuration of another light-emitting device according to an embodiment of the present invention. [Figure 4B] FIG. 4B is a cross-sectional view showing a partial configuration of another light-emitting device according to an embodiment of the present invention. [Figure 5A] FIG. 5A is a diagram illustrating conditions used to calculate the amount of transmitted light and the amount of reflected light of light emitted to a conventional unnecessary port. [Figure 5B] FIG. 5B is an explanatory diagram for explaining the conditions used to calculate the amount of transmitted light and the amount of reflected light of light emitted to a conventional unnecessary port. [Figure 6A] FIG. 6A is an explanatory diagram for explaining conditions used to calculate the amount of transmitted light and the amount of reflected light of light emitted to an optical terminator constituting a light emitting device according to an embodiment. [Figure 6B] FIG. 6B is an explanatory diagram for explaining conditions used to calculate the amount of transmitted light and the amount of reflected light of light emitted to an optical terminator constituting the light emitting device according to the embodiment. [Figure 7A] FIG. 7A is an explanatory diagram for explaining the conditions used to calculate the amount of transmitted light and the amount of reflected light of light emitted to a conventional optical terminator. [Figure 7B] FIG. 7B is an explanatory diagram for explaining the conditions used to calculate the amount of transmitted light and the amount of reflected light of light emitted to a conventional optical terminator. [Figure 8A] FIG. 8A is a distribution diagram of the amount of transmitted light and the amount of reflected light of light emitted to a conventional unnecessary port. [Figure 8B] FIG. 8B is a distribution diagram of the amount of transmitted light and the amount of reflected light of emitted light to an optical terminator constituting the light emitting device according to the embodiment. [Figure 8C]FIG. 8C is a distribution diagram of the amount of transmitted light and the amount of reflected light of light emitted to a conventional optical terminator. [Figure 9] FIG. 9 is a characteristic diagram showing the amount of transmitted light and the amount of reflected light of emitted light in each configuration. [Figure 10A] FIG. 10A is a plan view showing the configuration of a conventional light-emitting device. [Figure 10B] FIG. 10B is a cross-sectional view showing a partial configuration of a conventional light-emitting device. [Figure 10C] FIG. 10C is a cross-sectional view showing a partial configuration of a conventional light-emitting device. [Figure 11] FIG. 11 is a plan view showing the configuration of a conventional light-emitting device. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, a light-emitting device according to an embodiment of the present invention will be described with reference to Figures 1A, 1B, and 1C. Figure 1B shows a cross section taken along line aa' in Figure 1A. Figure 1C shows a cross section taken along line bb' in Figure 1A.

[0015] This light-emitting device comprises a waveguide-type light-emitting element 102 formed on a cladding layer 101, a core 104 formed on the cladding layer 101 and constituting a port 103 opposite the output port of the light-emitting element 102, and a light-absorbing layer 105 formed on and in contact with the core 104.

[0016] The cladding layer 101 can be made of an insulating material such as silicon oxide. The core 104 is made of a III-V compound semiconductor such as InP. The core 104 is made of a III-V compound semiconductor that can guide (transmit) the light (laser light) output from the light emitting element 102.

[0017] The light absorption layer 105 is made of a III-V compound semiconductor, such as InGaAs, having a higher refractive index than the core 104. A III-V compound semiconductor with a higher refractive index has an absorption coefficient for light that passes through the core 104 (light output from the light emitting element 102). In the region where the light absorption layer 105 is formed, the core 104 and the light absorption layer 105 have the same shape in a planar view.

[0018] 1B and 1C, the upper cladding of the light emitting element 102, the core 104, and the light absorbing layer 105 is omitted, but the upper cladding can be made of an insulating material such as silicon oxide, similar to the cladding layer 101. The upper cladding can also be air.

[0019] Light emitting element 102 is, for example, a well-known lateral current injection type semiconductor laser, and first includes a core-shaped active layer 122 embedded in a compound semiconductor layer 121 such as InP. Also, an n-semiconductor layer 123 and a p-semiconductor layer 124 are formed in the optical waveguide formed by active layer 122, sandwiching active layer 122 in a direction perpendicular to the waveguide direction. In this example, n-semiconductor layer 123 and p-semiconductor layer 124 are arranged to sandwich active layer 122 in a direction parallel to the plane of cladding layer 101 (lateral current injection type).

[0020] The n-semiconductor layer 123 is made of a III-V compound semiconductor (InP) doped with n-type impurities, and the p-semiconductor layer 124 is made of a III-V compound semiconductor (InP) doped with p-type impurities. These are formed by doping the corresponding impurities into the compound semiconductor layer 121. The region of the compound semiconductor layer 121 where the active layer 122 is buried is non-doped.

[0021] Furthermore, n-electrode 127 and p-electrode 128 are in ohmic contact with n-semiconductor layer 123 and p-semiconductor layer 124 via n-contact layer 125 and p-contact layer 126. N-contact layer 125 and p-contact layer 126 are made of a III-V compound semiconductor (InGaAs) doped with corresponding impurities at high concentrations. Light-emitting element 102 configured in this manner serves as a semiconductor laser in which the diffraction grating formed on active layer 122 has a distributed Bragg reflection structure.

[0022] Laser oscillation is obtained by injecting a current into active layer 122 of light emitting element 102 constituting this semiconductor laser via n-electrode 127 and p-electrode 128. Laser light generated by this laser oscillation is guided (output) to port 103, which is formed by an output port (not shown) and core 104. Port 103 is generally called an unwanted port, but in this embodiment, port 103 serves as an optical terminator.

[0023] In the above description, the light emitting element 102 has a current injection structure of a so-called lateral current injection type, but the present invention is not limited to this and may have a current injection structure of a vertical current injection type.

[0024] According to the embodiment, light emitted to port 103, which is called an unwanted port, is mode-coupled to light absorption layer 105 formed on core 104 and propagates while being optically absorbed by light absorption layer 105. As a result, it is possible to reduce reflection on light-emitting element 102 and stray light into the optical integrated circuit. For example, InGaAs used as a contact layer of an InP-based semiconductor laser constituting light-emitting element 102 has a high absorption coefficient in the communication wavelength band, so that it is possible to reduce the light output without lengthening port 103.

[0025] 2, the port 103a can be configured by a core 104a whose width narrows with increasing distance from the light emitting element 102 in the waveguide direction. In this case, the light absorbing layer 105a formed on and in contact with the core 104a can also narrow with increasing distance from the light emitting element 102 in the waveguide direction.

[0026] 3, the port 103b can be configured by the core 104b and the light absorbing layer 105b with the bend 106. The core 104b and the light absorbing layer 105b change their waveguiding direction at the bend 106. In this example, the core 104b and the light absorbing layer 105b change their waveguiding direction to the right at the bend 106 in a plan view.

[0027] 4A and 4B, the port 103c can be configured by a core 104c and a light absorption layer 105c having substantially the same width as the light emitting element 102. For example, the core 104c has the same width as the compound semiconductor layer 121. Note that FIG. 4B shows a cross section taken along line aa' in FIG. 4A.

[0028] Next, we will explain the results of a simulation of the amount of transmitted and reflected light emitted to the unnecessary ports that make up the optical terminator. In this simulation, we first performed a conventional configuration, as shown in Figure 5A, in which the optical waveguide of the unnecessary port was composed of a core made of InP and a cladding made of SiO2, and the cross-sectional shape of the core was set to be 1.5 μm wide and 0.34 μm thick.

[0029] As a configuration according to the embodiment, as shown in FIG. 6A, the optical waveguide of the optical terminator (unnecessary port) is composed of a core made of InP, an InGaAs light absorption layer formed on the upper surface of the core, and a cladding made of SiO2, and the cross-sectional shape of the core is 1.5 μm in width and 0.34 μm in thickness, and the cross-sectional shape of the light absorption layer is 1.5 μm in width and 0.05 μm in thickness.

[0030] As a comparison, as shown in Figure 7A, an optical terminator (unwanted port) was constructed with an InP core, a Si core placed below the core, and a cladding made of SiO2. The cross-sectional shape of the core was 0.1 to 1.5 μm wide and 0.34 μm thick, and the cross-sectional shape of the Si core was 0.1 to 0.44 μm wide and 0.22 μm thick. The Si core was highly p-doped.

[0031] In all configurations, as shown in Figures 5B, 6B, and 7B, the position x = 0 μm in the waveguide direction was the light incident position, x = -5.0 μm was the reflectance monitor position, x = 50 μm was the transmittance monitor position, and x = 100 μm was the stray light monitor position. Note that the position x = 60 μm in the waveguide direction is the waveguide end.

[0032] FIG. 8A shows the distribution of the amount of transmitted light and the amount of reflected light of light emitted to a conventional undesired port under the condition of FIG. 5A. FIG. 8B shows the distribution of the amount of transmitted light and the amount of reflected light of light emitted to an optical terminator configured according to an embodiment under the condition of FIG. 6A. FIG. 8C shows the distribution of the amount of transmitted light and the amount of reflected light of light emitted to an optical terminator including a conventional Si core under the condition of FIG. 7A. FIG. 9 shows a summary of these results. In FIG. 9, white circles indicate the amount of transmitted light and the amount of reflected light of light emitted to a conventional undesired port, black circles indicate the amount of transmitted light and the amount of reflected light of light emitted to an optical terminator configured according to an embodiment, and black triangles indicate the amount of transmitted light and the amount of reflected light of light emitted to an optical terminator including a conventional Si core. In FIG. 9, (a) indicates the amount of reflected light, and (b) indicates the amount of stray light.

[0033] As is clear from these results, the amount of reflected light is reduced in the optical terminator configured according to the embodiment. In this example, the amount of reflected light is reduced by more than 40 dB. Furthermore, compared to when a highly p-doped Si core is used, the optical terminator configured according to the embodiment can be reduced in overall length by more than half.

[0034] As described above, according to the present invention, a light absorption layer made of a III-V compound semiconductor having a higher refractive index than the core is provided on the core constituting the port opposite the output port, so that it is possible to reduce the light output to unnecessary ports without hindering miniaturization.

[0035] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention. [Explanation of symbols]

[0036] 101...cladding layer, 102...light-emitting element, 103...port, 104...core, 105...light-absorbing layer, 121...compound semiconductor layer, 122...active layer, 123...n semiconductor layer, 124...p semiconductor layer, 125...n contact layer, 126...p contact layer, 127...n electrode, 128...p electrode.

Claims

1. a waveguide-type light-emitting element formed on the cladding layer; a core made of a III-V compound semiconductor formed on the cladding layer and constituting a port opposite to an output port of the light emitting device; a light absorbing layer formed on and in contact with the core, the light absorbing layer being made of a III-V group compound semiconductor having a refractive index higher than that of the core; Equipped with In the region where the light absorbing layer is formed, the core and the light absorbing layer have the same shape in a plan view, The light-emitting device is characterized in that the width of the core narrows as it moves away from the light-emitting element in the waveguiding direction.

2. A waveguide-type light-emitting element formed on a cladding layer; a core made of a III-V compound semiconductor formed on the cladding layer and constituting a port opposite to an output port of the light emitting device; a light absorbing layer formed on and in contact with the core, the light absorbing layer being made of a III-V group compound semiconductor having a refractive index higher than that of the core; Equipped with In the region where the light absorbing layer is formed, the core and the light absorbing layer have the same shape in a plan view, A light-emitting device, wherein the core has a bent portion.

3. A waveguide-type light-emitting element formed on a cladding layer; a core made of a III-V compound semiconductor formed on the cladding layer and constituting a port opposite to an output port of the light emitting device; a light absorbing layer formed on and in contact with the core, the light absorbing layer being made of a III-V group compound semiconductor having a refractive index higher than that of the core; Equipped with In the region where the light absorbing layer is formed, the core and the light absorbing layer have the same shape in a plan view, The light-emitting device is characterized in that the core has substantially the same width as the light-emitting element.

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