Semiconductor optical element

Abstract

This semiconductor optical element comprises an optical modulator (151), a first optical waveguide (152), and a second optical waveguide (153) that are formed on a Si substrate (101). The second optical waveguide (153) comprises a second core (131), a third semiconductor layer (132), a fourth semiconductor layer (133), a third electrode (134), and a fourth electrode (135). The second optical waveguide (153) is optically connected to the first optical waveguide (152) and is a resistive load connected to the optical modulator (151).

Description

semiconductor optical device

[0001] The present invention relates to a semiconductor optical device.

[0002] In datacenter networks, there is a demand for smaller, lower-cost, and lower-power optical transceivers. In recent years, technologies have been developed to integrate high-speed semiconductor optical modulators, light sources, and SOA (semiconductor optical amplifiers) on inexpensive silicon substrates. For example, there is a technology that uses a thin-film optical modulator made of III-V compound semiconductors to achieve both high-speed and low-voltage operation, and integrates it on a silicon substrate together with a thin-film laser (Non-Patent Document 1). These elements can be integrated with low-loss optical waveguides on a silicon substrate made of silicon, silicon nitride, silicon oxynitride, or silicon on an Si substrate to form an optical integrated circuit.

[0003] The optical modulator disclosed in Non-Patent Document 1 includes a p-type InP layer and an n-type InP layer sandwiching a core-shaped active layer, and electrodes are formed on each of the p-type InP layer and the n-type InP layer. In general, the electrode connected to the p-type InP layer serves as a ground terminal, and the electrode connected to the n-type InP layer serves as a signal terminal to operate the optical modulator.

[0004] This optical modulator can be represented by a solid-line equivalent circuit consisting of substrate capacitance Csi, substrate resistance Rsi, junction capacitance Cj, element series resistance Rs, diode resistance Rj, and electrode capacitance Cp, as shown in Figure 8. It is known that the 3-dB bandwidth of the optical modulator can be improved by connecting a load resistor Load between the two electrodes, as shown by the dotted line in this equivalent circuit.

[0005] T. Hiraki et al., "Over-67-GHz-Bandwidth Membrane InGaAlAs Electro-Absorption Modulator Integrated With DFB Laser on Si Platform", Journal of Lightwave Technology, vol. 41, no. 3, pp. 880-887, 2023.

[0006] Generally, the load resistor is mounted outside the chip on which the optical modulator is formed and connected to the electrodes of the optical modulator. However, this configuration increases the mounting cost. While there is also a configuration in which the load resistor is integrated on the chip, this generally requires a multi-layer wiring process to form metal wiring and resistors in layers sufficiently distant from the optical modulator to avoid interference with the guided light, which increases the cost of the process after the optical modulator is formed.

[0007] The present invention has been made to solve the above problems, and has as its object to connect a load resistor while suppressing increases in manufacturing costs and improving the 3-dB bandwidth of an optical modulator.

[0008] The semiconductor optical device according to the present invention comprises an optical modulator including: an insulating layer formed on a Si substrate; an active layer made of a compound semiconductor formed on the insulating layer and extending in the light propagation direction; a first p-type semiconductor layer and a second n-type semiconductor layer made of a compound semiconductor different from the active layer and formed on the insulating layer in a direction perpendicular to the light propagation direction, with the active layer sandwiched between them; a first electrode formed on the first semiconductor layer and extending in the light propagation direction to connect to the first semiconductor layer; and a second electrode formed on the second semiconductor layer and extending in the light propagation direction to connect to the second semiconductor layer; a first core formed on the insulating layer, continuous with the optical modulator, and made of a compound semiconductor and extending in the light propagation direction, and a cladding layer formed to cover the first core, a second core made of an n-type or p-type compound semiconductor formed on an insulating layer so as to be continuous with the first optical waveguide and extend in the light propagation direction; a third semiconductor layer and a fourth semiconductor layer formed on the insulating layer on either side of the second core in a direction perpendicular to the light propagation direction and made of a compound semiconductor different from that of the second core and having the same conductivity type as the second core; a third electrode formed on the third semiconductor layer so as to extend in the light propagation direction, connected to the third semiconductor layer, and at the same potential as the first electrode; and a fourth electrode formed on the fourth semiconductor layer so as to extend in the light propagation direction, connected to the fourth semiconductor layer, and at the same potential as the second electrode, the second optical waveguide being optically connected to the first optical waveguide and serving as a load resistor connected to the optical modulator.

[0009] The semiconductor optical device according to the present invention includes an optical modulator including an insulating layer formed on a Si substrate, an active layer made of a compound semiconductor formed on the insulating layer and extending in the light propagation direction, a first p-type semiconductor layer and a second n-type semiconductor layer made of a compound semiconductor different from the active layer and formed on the insulating layer in a direction perpendicular to the light propagation direction, a first electrode formed on the first semiconductor layer and extending in the light propagation direction to connect to the first semiconductor layer, and a second electrode formed on the second semiconductor layer and extending in the light propagation direction to connect to the second semiconductor layer; a first Si slab layer and a second Si slab layer formed on the insulating layer in a direction perpendicular to the light propagation direction, with the Si core sandwiched therebetween; a third electrode formed on the first Si slab layer, extending in the light propagation direction, connected to the first Si slab layer and at the same potential as the first electrode; and a fourth electrode formed on the second Si slab layer, extending in the light propagation direction, and at the same potential as the second electrode connected to the second Si slab layer. The Si core, the first Si slab layer, and the second Si slab layer are n-type and optically connected to the optical modulator, and a Si optical waveguide serving as a load resistor connected to the optical modulator is provided.

[0010] As described above, according to the present invention, an optical waveguide that is optically connected to an optical modulator and electrically connected to the optical modulator as a load resistor is integrated, so that the load resistor can be connected while suppressing increases in manufacturing costs, and the 3-dB bandwidth of the optical modulator can be improved.

[0011] FIG. 1 is a diagram showing the configuration of a semiconductor optical device according to a first embodiment of the present invention. FIG. 2 is a diagram showing the configuration of another semiconductor optical device according to the first embodiment of the present invention. FIG. 3A is a characteristics diagram showing the results of calculating the change in frequency response of an optical modulator 151 depending on the resistance value of a second optical waveguide 153. FIG. 3B is a characteristics diagram showing the results of calculating the resistance value when a second optical waveguide 153 is formed with a donor density of a second semiconductor layer 105 made of n-type InP constituting the optical modulator 151. FIG. 4 is a diagram showing the configuration of another semiconductor optical device according to the first embodiment of the present invention. FIG. 5 is a diagram showing the configuration of a semiconductor optical device according to a second embodiment of the present invention. FIG. 6 is a diagram showing the configuration of a semiconductor optical device according to a third embodiment of the present invention. FIG. 7 is a diagram showing the configuration of another semiconductor optical device according to the third embodiment of the present invention. FIG. 8 is a circuit diagram showing an equivalent circuit of an optical modulator.

[0012] Hereinafter, a semiconductor optical device according to an embodiment of the present invention will be described.

[0013] First Embodiment First, a semiconductor optical device according to a first embodiment of the present invention will be described with reference to Fig. 1. This semiconductor optical device includes an optical modulator 151, a first optical waveguide 152, and a second optical waveguide 153 formed on a Si substrate 101. The optical modulator 151, the first optical waveguide 152, and the second optical waveguide 153 can have the same width in a direction parallel to the surface of the Si substrate 101 and perpendicular to the direction of light propagation, for example.

[0014] The optical modulator 151 includes an insulating layer 102 , an active layer 103 , a first semiconductor layer 104 , a second semiconductor layer 105 , a first electrode 106 , and a second electrode 107 .

[0015] The insulating layer 102 is formed on the Si substrate 101, and the active layer 103 is formed on the insulating layer 102. The insulating layer 102 can be made of, for example, SiO2. The active layer 103 is made of a compound semiconductor and extends in the direction of light propagation. The active layer 103 can have a bulk structure made of, for example, InGaAsP. The active layer 103 can also be a multi-quantum well (MQW) made of InGaAsP / InGaAsP or an MQW made of InGaAs / InP. A double heterostructure can also be formed by forming semiconductor layers made of InP, whose energy gap is larger than that of the material of the barrier layer of the MQW, below and above the active layer.

[0016] The first semiconductor layer 104 and the second semiconductor layer 105 are formed on the insulating layer 102 and are arranged in a direction perpendicular to the light propagation direction, with the active layer 103 sandwiched between them. The first semiconductor layer 104 and the second semiconductor layer 105 are each arranged in contact with the active layer 103. The first semiconductor layer 104 and the second semiconductor layer 105 are made of a compound semiconductor different from that of the active layer 103. The first semiconductor layer 104 is p-type, and the second semiconductor layer 105 is n-type. The first semiconductor layer 104 and the second semiconductor layer 105 can be made of, for example, InP.

[0017] A first electrode 106 is connected to the top of the first semiconductor layer 104, and a second electrode 107 is connected to the top of the second semiconductor layer 105. The first electrode 106 is formed on the first semiconductor layer 104 and extends in the light propagation direction. The second electrode 107 is formed on the second semiconductor layer 105 and extends in the light propagation direction.

[0018] The first optical waveguide 152 includes a first core 121 made of a compound semiconductor formed on the insulating layer 102 so as to extend in the light propagation direction, continuous with the optical modulator 151, and a clad layer 122 formed to cover the first core 121. The first optical waveguide 152 is optically connected to the optical modulator 151. The first optical waveguide 152 is a so-called channel-type optical waveguide using the first core 121.

[0019] The second optical waveguide 153 includes a second core 131, a third semiconductor layer 132, a fourth semiconductor layer 133, a third electrode 134, and a fourth electrode 135. The second optical waveguide 153 is optically connected to the first optical waveguide 152 and serves as a load resistor connected to the optical modulator 151.

[0020] The second core 131 is formed so as to extend in the light propagation direction on the insulating layer 102, continuing from the first optical waveguide 152. The second core 131 is made of an n-type or p-type compound semiconductor.

[0021] The third semiconductor layer 132 and the fourth semiconductor layer 133 are formed on the insulating layer 102 in a direction perpendicular to the light propagation direction, sandwiching the second core 131 therebetween. The third semiconductor layer 132 and the fourth semiconductor layer 133 are made of a compound semiconductor different from that of the second core 131. The third semiconductor layer 132 and the fourth semiconductor layer 133 may be made of InP, for example. The third semiconductor layer 132 and the fourth semiconductor layer 133 have the same conductivity type as the second core 131. The second core 131 is sandwiched above and below by layers made of the same semiconductor as the third semiconductor layer 132 and the fourth semiconductor layer 133, forming a buried core structure.

[0022] The third electrode 134 is formed on the third semiconductor layer 132 and extends in the light propagation direction. The third electrode 134 is connected to the third semiconductor layer 132 and has the same potential as the first electrode 106. The fourth electrode 135 is formed on the fourth semiconductor layer 133 and extends in the light propagation direction. The fourth electrode 135 is connected to the fourth semiconductor layer 133 and has the same potential as the second electrode 107. Protective insulating layers 108 are formed on the optical modulator 151 between the first electrode 106 and the second electrode 107, on the first optical waveguide 152 between the third electrode 134 and the fourth electrode 135, and on the second optical waveguide 153 between the third electrode 134 and the fourth electrode 135.

[0023] Furthermore, in the semiconductor optical device according to the first embodiment, the first core 121 and the second core 131 are formed from portions of the active layer 103 that extend in the light propagation direction. The cladding layer 122 can be formed from the same compound semiconductor as the first semiconductor layer 104 and the second semiconductor layer 105. The third semiconductor layer 132 and the fourth semiconductor layer 133 are formed from the same compound semiconductor as the first semiconductor layer 104 and the second semiconductor layer 105. The first electrode 106 and the third electrode 134 are common to each other, and the second electrode 107 and the fourth electrode 135 are common to each other.

[0024] As described above, the second core 131 of the second optical waveguide 153 is formed from an extended portion of the active layer 103 of the optical modulator 151, and the third semiconductor layer 132 and the fourth semiconductor layer 133 are formed from extended portions of the first semiconductor layer 104 and the second semiconductor layer 105, respectively, and the entire structure is n-type or p-type. Even if the second core 131 has an MQW structure, it is possible to disorder the MQW by, for example, converting it to n-type by Si ion implantation. This shortens only the absorption edge wavelength of the second core 131, significantly reducing the loss caused by the absorption of light transmitted through the second optical waveguide 153 by the second core 131. Furthermore, because donors have lower free carrier absorption in InP-based materials than acceptors, the second optical waveguide 153 is preferably n-type.

[0025] Although not shown, the input end of the optical modulator 151 on the side to which the first optical waveguide 152 is not connected can be optically connected to a Si optical waveguide via a mode conversion section with a tapered core formed continuously with the active layer 103. Furthermore, the output end of the second optical waveguide 153 on the side to which the first optical waveguide 152 is not connected can be optically connected to a Si optical waveguide via a mode conversion section with a tapered core formed continuously with the second core 131.

[0026] With this configuration, when a reverse bias voltage is applied to the first electrode 106 and the second electrode 107 of the optical modulator 151, the second optical waveguide 153 to which the third electrode 134 and the fourth electrode 135, which are at the same potential, are connected functions as a resistor that allows a current to flow through the third semiconductor layer 132, the second core 131, and the fourth semiconductor layer 133. Even in an n-type or p-type state, the optical confinement by the second core 131 is maintained, so the optical modulation signal passes through the second optical waveguide 153 and is coupled to the Si optical waveguide via the mode conversion section made of the tapered core on the output side.

[0027] 2, the first optical waveguide 152 can be composed of a first core 121a made of an undoped compound semiconductor such as InP and a cladding layer 122a made of SiO. Fabrication is easy if the thickness of the cladding layer 122 is the same as that of the first semiconductor layer 104 and the second semiconductor layer 105, and the width of the first core 121a is set to a core width that allows highly efficient coupling with the active layer 103. This configuration makes it easy to separate the optical modulator 151 and the second optical waveguide 153.

[0028] 3A shows the results of calculating the change in frequency response of the optical modulator 151 depending on the resistance value of the second optical waveguide 153. This calculation shows the E-O response calculation results when the parameters of the equivalent circuit described with reference to FIG. 8 are: substrate capacitance Csi = 6 fF, substrate resistance Rsi = 1.7 kΩ, junction capacitance Cj = 50 fF, element series resistance Rs = 20 Ω, diode resistance Rj = 3 kΩ, and electrode capacitance Cp = 16 fF, and the value of the load resistance connected in parallel to the electrode capacitance Cp is changed. The smaller the resistance, the greater the 3-dB bandwidth. The bandwidth, which was about 40 GHz without resistance, becomes a bandwidth of 50 GHz or more by connecting a resistor of 100 Ω or less.

[0029] 3B shows the calculation results of the resistance value when the second optical waveguide 153 is formed with a donor density of the second semiconductor layer 105 made of n-type InP that constitutes the optical modulator 151. A representative experimental value was used for the resistivity of the n-type InP. For simplicity, the resistivity of the second core 131 formed by the extension of the active layer 103 was also set to the same as the resistivity of the n-type InP in this calculation. However, since the area that the second core 131 occupies in the entire second optical waveguide 153 is small, this does not have a significant effect.

[0030] L on the horizontal axis represents the length of the second optical waveguide 153, and W represents the width between the third electrode 134 and the fourth electrode 135 of the second optical waveguide 153. The thicknesses of the third semiconductor layer 132 and the fourth semiconductor layer 133 were set to 340 nm. Calculation results indicated that a resistance of 100 Ω or less can be achieved with dimensions of W: 30 μm or less and L: 15 μm or less. While the semiconductor optical device according to the embodiment can achieve a broadband by reducing the resistance value, increasing the current flowing through the resistor increases power consumption. Therefore, a resistance value that ensures the minimum necessary bandwidth is required. Furthermore, the electrode dimensions can be designed not only to achieve the desired resistance value but also within a range that can be considered as a lumped-constant electrode.

[0031] 4, the first optical waveguide 152 and the second optical waveguide 153 can be arranged at two locations in the light propagation direction so as to sandwich the optical modulator 151. The second optical waveguide 153 generates heat when a current flows through it, but by arranging them at two locations as described above, it is expected that the temperature change in the active layer 103 of the optical modulator 151 can be made uniform.

[0032] Second Embodiment Next, a semiconductor optical device according to a second embodiment of the present invention will be described with reference to Fig. 5. This semiconductor optical device includes an optical modulator 151, a first optical waveguide 152, and a second optical waveguide 153 formed on a Si substrate 101. The optical modulator 151, the first optical waveguide 152, and the second optical waveguide 153 can have the same width in a direction parallel to the surface of the Si substrate 101 and perpendicular to the direction of light propagation, for example.

[0033] The optical modulator 151 includes an insulating layer 102 , an active layer 103 , a first semiconductor layer 104 , a second semiconductor layer 105 , a first electrode 106 , and a second electrode 107 .

[0034] The insulating layer 102 is formed on the Si substrate 101, and the active layer 103 is formed on the insulating layer 102. The active layer 103 is made of a compound semiconductor and is formed to extend in the light propagation direction.

[0035] The first semiconductor layer 104 and the second semiconductor layer 105 are formed on the insulating layer 102 and are arranged in a direction perpendicular to the light propagation direction, sandwiching the active layer 103. The first semiconductor layer 104 and the second semiconductor layer 105 are made of a compound semiconductor different from that of the active layer 103. The first semiconductor layer 104 is p-type, and the second semiconductor layer 105 is n-type.

[0036] A first electrode 106 is connected to the top of the first semiconductor layer 104, and a second electrode 107 is connected to the top of the second semiconductor layer 105. The first electrode 106 is formed on the first semiconductor layer 104 and extends in the light propagation direction. The second electrode 107 is formed on the second semiconductor layer 105 and extends in the light propagation direction.

[0037] The first optical waveguide 152 includes a first core 121a made of a compound semiconductor and formed on the insulating layer 102 so as to extend in the light propagation direction, continuous with the optical modulator 151, and a cladding layer 122a made of SiO formed to cover the first core 121a. The first optical waveguide 152 is optically connected to the optical modulator 151.

[0038] The second optical waveguide 153 includes a second core 131, a third semiconductor layer 132, a fourth semiconductor layer 133, a third electrode 134, and a fourth electrode 135. The second optical waveguide 153 is optically connected to the first optical waveguide 152 and serves as a load resistor connected to the optical modulator 151.

[0039] The second core 131 is formed so as to extend in the light propagation direction on the insulating layer 102, continuing from the first optical waveguide 152. The second core 131 is made of an n-type or p-type compound semiconductor.

[0040] The third semiconductor layer 132 and the fourth semiconductor layer 133 are formed on the insulating layer 102 in a direction perpendicular to the light propagation direction, sandwiching the second core 131 therebetween. The third semiconductor layer 132 and the fourth semiconductor layer 133 are made of a compound semiconductor different from that of the second core 131. The third semiconductor layer 132 and the fourth semiconductor layer 133 have the same conductivity type as the second core 131. The second core 131 is sandwiched above and below by layers made of the same semiconductor as the third semiconductor layer 132 and the fourth semiconductor layer 133, forming a buried core structure.

[0041] The third electrode 134 is formed on the third semiconductor layer 132 and extends in the light propagation direction. The third electrode 134 is connected to the third semiconductor layer 132 and has the same potential as the first electrode 106. The fourth electrode 135 is formed on the fourth semiconductor layer 133 and extends in the light propagation direction. The fourth electrode 135 is connected to the fourth semiconductor layer 133 and has the same potential as the second electrode 107.

[0042] In addition, in this semiconductor optical device, the second core 131 has the same configuration as the active layer 103. Furthermore, the third semiconductor layer 132 and the fourth semiconductor layer 133 are made of the same compound semiconductor as the first semiconductor layer 104 and the second semiconductor layer 105. Furthermore, the first electrode 106 and the third electrode 134 are common to each other, and the second electrode 107 and the fourth electrode 135 are common to each other.

[0043] The above-described configuration is the same as that of the first embodiment. In the second embodiment, a third core 109 is further provided on the Si substrate 101 side of the first core 121 a and the second core 131. The third core 109 is made of, for example, Si and is embedded in the insulating layer 102. The third core 109 is arranged so as to be optically coupled to the first core 121 a and the second core 131. The third core 109 has a tapered structure in which the core width gradually increases from the optical modulator 151 side to the second optical waveguide 153 side.

[0044] From the optical modulator 151, through the first optical waveguide 152, and the second optical waveguide 153, the guided light is gradually coupled from the first core 121a to the third core 109. In the second optical waveguide 153, the core width of the third core 109 is wider, and most of the light intensity is confined in the third core 109. This makes it possible to reduce absorption by the second core 131 of the second optical waveguide 153 and free carrier absorption. Note that the third core 109 is not limited to Si, and can be made of various semiconductor materials, dielectric materials such as SiN and SiON, or nonlinear crystals such as lithium niobate (LiNbO).

[0045] Third Embodiment Next, a semiconductor optical device according to a third embodiment of the present invention will be described with reference to Fig. 6. This semiconductor optical device includes an optical modulator 151 and a Si optical waveguide 154 formed on a Si substrate 101.

[0046] The optical modulator 151 includes an insulating layer 102, an active layer 103, a first semiconductor layer 104, a second semiconductor layer 105, a first electrode 106, and a second electrode 107. These components are similar to those in the first and second embodiments described above, and therefore will not be described in detail.

[0047] In the third embodiment, a Si optical waveguide 154 including a Si core 141, a first Si slab layer 142, a second Si slab layer 143, a third electrode 144, and a fourth electrode 145 serves as a load resistor connected to an optical modulator 151. The Si core 141, the first Si slab layer 142, and the second Si slab layer 143 are of n-type.

[0048] The Si core 141 is adjacent to the optical modulator 151 in the light propagation direction and is formed on the insulating layer 102 to extend in the light propagation direction. The first Si slab layer 142 and the second Si slab layer 143 are formed on the insulating layer 102 in a direction perpendicular to the light propagation direction, sandwiching the Si core 141. The Si optical waveguide 154 is a so-called rib-type optical waveguide that includes the first Si slab layer 142 and the second Si slab layer 143.

[0049] The third electrode 144 is formed on the first Si slab layer 142, extending in the light propagation direction, and connected to the first Si slab layer 142. The third electrode 144 has the same potential as the first electrode 106. The third electrode 144 is formed on the contact portion 142a of the first Si slab layer 142. The fourth electrode 145 is formed on the second Si slab layer 143, extending in the light propagation direction, and connected to the second Si slab layer 143. The fourth electrode 145 has the same potential as the second electrode. The fourth electrode 145 is formed on the contact portion 143a of the second Si slab layer 143.

[0050] A protective insulating layer 108 is formed on the optical modulator 151 between the first electrode 106 and the second electrode 107 and on the Si optical waveguide 154 between the third electrode 144 and the fourth electrode 145.

[0051] 6C, near the boundary between the optical modulator 151 and the Si optical waveguide 154, the Si core 141 is tapered so that the core width becomes smaller as it approaches the optical modulator 151. Furthermore, above the tapered Si core 141, a mode conversion section 103' is provided, into which the active layer 103 extends. The mode conversion section 103' is tapered so that the core width becomes smaller as it moves away from the optical modulator 151.

[0052] 7, an MQW active layer 103a can be formed across the entire optical modulator 151 in the width direction, which is parallel to the surface of the Si substrate 101 and perpendicular to the light propagation direction, and a p-type region 104a and an n-type region 105a can be formed to sandwich an optical confinement region in the center of the width direction. In this case, the Si core 141 can be extended toward the optical modulator 151, thereby providing an extension portion 141a formed continuously with the Si core 141. The extension portion 141a is formed on the Si substrate 101 side of the active layer 103a. The extension portion 141a is positioned so as to be optically coupled to the active layer 103a.

[0053] By providing the extension portion 141a, the region of the active layer 103a that overlaps with the extension portion 141a in the stacking direction (thickness direction) can be used as an optical confinement region. In the region where the extension portion 141a is formed, the extension portion 141a and the active layer 103a are optically coupled to form a waveguide mode.

[0054] Although not shown, the input end of the optical modulator 151 on the side to which the Si optical waveguide 154 is not connected can be optically connected to the Si optical waveguide via a mode conversion section with a tapered core formed continuously with the active layer 103. Furthermore, the output end of the Si optical waveguide 154 on the side to which the optical modulator 151 is not connected can be optically connected to the Si optical waveguide via a mode conversion section with a tapered core formed continuously with the Si core 141.

[0055] With this configuration, when a reverse bias voltage is applied to the first electrode 106 and the second electrode 107 of the optical modulator 151, the Si optical waveguide 154 to which the third electrode 144 and the fourth electrode 145, which are at the same potential, are connected functions as a resistor that allows a current to flow through the first Si slab layer 142, the Si core 141, and the second Si slab layer 143. Since the optical confinement by the Si core 141 is maintained, the optical modulation signal passes through the Si optical waveguide 154 and is coupled to the Si optical waveguide via the mode conversion section made of the tapered core on the output side.

[0056] In each of the above-described embodiments, the compound semiconductor is not limited to InP, but may be InGaAs, InAlAs, AlGaAs, InGaAsP, InGaAlAs, or the like.

[0057] As described above, according to the embodiment of the present invention, an optical waveguide that is optically connected to an optical modulator and electrically connected to the optical modulator as a load resistor is integrated, so that the load resistor can be connected while suppressing increases in manufacturing costs, and the 3-dB bandwidth of the optical modulator can be improved.

[0058] 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.

[0059] 101...Si substrate, 102...insulating layer, 103...active layer, 104...first semiconductor layer, 105...second semiconductor layer, 106...first electrode, 107...second electrode, 108...protective insulating layer, 121...first core, 122...clad layer, 131...second core, 132...third semiconductor layer, 133...fourth semiconductor layer, 134...third electrode, 135...fourth electrode, 151...optical modulator, 152...first optical waveguide, 153...second optical waveguide.

Claims

an active layer made of a compound semiconductor and formed on the insulating layer to extend in the direction of light propagation; a first p-type semiconductor layer and a second n-type semiconductor layer made of a compound semiconductor different from the active layer and formed on the insulating layer in a direction perpendicular to the direction of light propagation, with the active layer sandwiched between them; a first electrode formed on the first semiconductor layer to extend in the direction of light propagation and connect to the first semiconductor layer; and a second electrode formed on the second semiconductor layer to extend in the direction of light propagation and connect to the second semiconductor layer; an optical modulator comprising: a first core made of a compound semiconductor and formed on the insulating layer to extend in the direction of light propagation, continuous with the optical modulator; a third semiconductor layer and a fourth semiconductor layer, which are formed on the insulating layer on either side of the second core in a direction perpendicular to the light propagation direction, and which are made of a compound semiconductor different from that of the second core and have the same conductivity type as the second core; a third electrode, which is formed on the third semiconductor layer and extends in the light propagation direction, is connected to the third semiconductor layer, and has the same potential as the first electrode; and a fourth electrode, which is formed on the fourth semiconductor layer and extends in the light propagation direction, is connected to the fourth semiconductor layer, and has the same potential as the second electrode, and which is optically connected to the first optical waveguide and serves as a load resistor connected to the optical modulator.

2. A semiconductor optical device according to claim 1, wherein the first core and the second core are made of portions of the active layer extending in the light propagation direction, the cladding layer is made of the same compound semiconductor as the first semiconductor layer and the second semiconductor layer, the third semiconductor layer and the fourth semiconductor layer are made of the same compound semiconductor as the first semiconductor layer and the second semiconductor layer, the first electrode and the third electrode are common, and the second electrode and the fourth electrode are common.

3. A semiconductor optical device according to claim 1, wherein the first core is made of an undoped compound semiconductor, and the third semiconductor layer and the fourth semiconductor layer are made of the same compound semiconductor as the first semiconductor layer and the second semiconductor layer.

4. A semiconductor optical device according to any one of claims 1 to 3, further comprising a third core formed on the Si substrate side of said first core and said second core. an active layer made of a compound semiconductor and formed on the insulating layer to extend in the direction of light propagation; a first p-type semiconductor layer and a second n-type semiconductor layer made of a compound semiconductor different from the active layer and formed on the insulating layer in a direction perpendicular to the direction of light propagation, with the active layer sandwiched between them; a first electrode formed on the first semiconductor layer to extend in the direction of light propagation and connect to the first semiconductor layer; and a second electrode formed on the second semiconductor layer to extend in the direction of light propagation and connect to the second semiconductor layer; a Si core adjacent to the optical modulator in the direction of light propagation, formed on the insulating layer to extend in the direction of light propagation; first and second Si slab layers formed on the insulating layer to sandwich the Si core in a direction perpendicular to the direction of light propagation; a fourth electrode formed on the second Si slab layer extending in the light propagation direction and connected to the second Si slab layer, the fourth electrode having the same potential as the second electrode, wherein the Si core, the first Si slab layer, and the second Si slab layer are n-type and optically connected to the optical modulator, and a Si optical waveguide serving as a load resistor connected to the optical modulator.

6. A semiconductor optical device according to claim 5, further comprising an extension portion formed continuously with said Si core and on the Si substrate side of said active layer.

Images