Semiconductor optical integrated element

Abstract

A semiconductor optical integrated element (500, 600, 700, 750) according to the present disclosure comprises: a semiconductor laser unit (2) that is formed on a substrate (1) and that comprises a semiconductor laser; and an optical modulation unit (20) that is formed on the substrate (1) and that comprises a first optical modulation unit (5) having one end (5a) connected to one end (2a) of the semiconductor laser unit (2) via a first passive waveguide (3), and a second optical modulation unit (6) having one end (6a) connected to the other end (2b) of the semiconductor laser unit (2) via a second passive waveguide (4).

Description

semiconductor optical integrated device

[0001] The present disclosure relates to semiconductor integrated optical devices.

[0002] The spread of mobile communication devices such as smartphones and the diversification of data services due to the expansion of cloud services have led to a rapid increase in communication traffic in recent years, which has led to demand for even faster and larger capacity optical communication systems.

[0003] A Mach-Zehnder (MZ) type semiconductor modulator (hereinafter referred to as an MZ type semiconductor optical modulator) can be made smaller and consume less power than conventional LN optical modulators that use an LN waveguide made of a dielectric material such as lithium niobate (LiNbO3), and is therefore an important key device for increasing the capacity of optical communication systems.

[0004] The MZ-type semiconductor optical modulator utilizes the Quantum Confined Stark Effect (QCSE) that is unique to the quantum well structure, and therefore the change in refractive index when a voltage is applied is greater than that of an LN waveguide, making it possible to miniaturize the device and reduce power consumption.

[0005] In addition, semiconductor optical integrated devices that integrate a semiconductor laser and an MZ-type semiconductor optical modulator have also been developed. Compared to configurations in which individual elements are combined using lenses or the like, semiconductor optical integrated devices can be made smaller and have higher output.

[0006] However, in a semiconductor optical integrated element in which a semiconductor laser and an MZ-type semiconductor optical modulator are arranged in a straight line, the length of the semiconductor laser is about 500 μm and the length of the MZ-type semiconductor optical modulator is about 4 mm, which causes a problem that the length of the semiconductor optical integrated element in the longitudinal direction is long. In order to shorten the length of the semiconductor optical integrated element in the longitudinal direction, for example, Patent Document 1 proposes a configuration in which the semiconductor laser and the MZ-type semiconductor modulator are folded back.

[0007] JP 2012-74411 A

[0008] However, in the optical semiconductor element described in Patent Document 1, the laser light emitted from the semiconductor laser is split into two by the first optical coupler and then output to the first phase modulation section and the second phase modulation section of the MZ-type semiconductor optical modulator, so there remains the problem that the length of the element in the longitudinal direction cannot be sufficiently shortened.

[0009] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a semiconductor optical integrated element that integrates a semiconductor laser and an MZ-type semiconductor optical modulator and has a configuration in which the length in the longitudinal direction is further shortened.

[0010] The semiconductor optical integrated device according to the present disclosure comprises: a semiconductor laser section formed on a substrate and consisting of a semiconductor laser; and an optical modulation section formed on the substrate and consisting of a first optical modulation section having one end connected to one end of the semiconductor laser section via a first passive waveguide, and a second optical modulation section having one end connected to the other end of the semiconductor laser section via a second passive waveguide.

[0011] According to the semiconductor optical integrated element of the present disclosure, the laser light emitted from the semiconductor laser portion is output to the optical modulation portion without being branched, thereby achieving the effect of obtaining a semiconductor optical integrated element having a configuration in which the length in the longitudinal direction is further shortened.

[0012] FIG. 1 is a top view showing the configuration of a semiconductor optical integrated device according to a first embodiment. FIG. 2 is a cross-sectional view of a semiconductor laser section in the semiconductor optical integrated device according to the first embodiment. FIG. 3 is a cross-sectional view of an optical modulation section in the semiconductor optical integrated device according to the first embodiment. FIG. 4 is a cross-sectional view of a passive waveguide in the semiconductor optical integrated device according to the first embodiment. FIG. 5 is a top view showing the configuration of a semiconductor optical integrated device according to a modification of the first embodiment. FIG. 6 is a top view showing the configuration of a combination of the semiconductor optical integrated device according to the first embodiment and a driver circuit for generating an RF signal. FIG. 7 is a top view showing the configuration of a semiconductor optical integrated device according to a second embodiment. FIG. 8 is a top view showing the configuration of a semiconductor optical integrated device according to a third embodiment. FIG. 9 is a top view showing the configuration of a semiconductor optical integrated device according to a modification of the third embodiment. FIG. 10 is a top view showing the configuration of a semiconductor optical integrated device according to a fourth embodiment. FIG. 11 is a cross-sectional view of a monitor light-receiving section in the semiconductor optical integrated device according to the fourth embodiment.

[0013] First Embodiment Fig. 1 is a top view showing the configuration of a semiconductor optical integrated device 500 according to a first embodiment.

[0014] <Configuration of Semiconductor Optical Integrated Device According to First Embodiment> The semiconductor optical integrated device 500 according to the first embodiment includes a semiconductor laser section 2 formed on a semiconductor substrate 1 and made of a semiconductor laser, a first passive waveguide 3 having one end connected to one end 2a of the semiconductor laser section 2, a second passive waveguide 4 having one end connected to the other end 2b of the semiconductor laser section 2, a first optical modulation section 5 having one end 5a connected to the other end of the first passive waveguide 3, and a second passive waveguide 5a. a second optical modulation section 6 having one end 6a connected to the other end of the first passive waveguide 4; a third passive waveguide 7 having one end connected to the other end 5b of the first optical modulation section 5; a fourth passive waveguide 8 having one end connected to the other end 6b of the second optical modulation section 6; an optical multiplexing section 9 having one end 9a connected to the other end of the third passive waveguide 7 and the other end of the fourth passive waveguide 8; and an optical output section 10 having the other end 9b of the optical multiplexing section 9 connected.

[0015] The optical modulation section 20 is composed of a pair of a first optical modulation section 5 and a second optical modulation section 6. The semiconductor laser section 2 is disposed in a position facing the optical modulation section 20. The longitudinal direction of the semiconductor laser section 2 and the longitudinal directions of the first optical modulation section 5 and the second optical modulation section 6 are parallel to each other. The first passive waveguide 3 to the fourth passive waveguide 8 are collectively referred to as passive waveguides 30. Note that a substrate other than the semiconductor substrate 1 may be used.

[0016] The structures and manufacturing methods of the semiconductor laser section 2, the optical modulation section 20, and the passive waveguide 30 that constitute the semiconductor optical integrated device 500 will be described below.

[0017] <Structure of Semiconductor Laser Portion> The semiconductor laser portion 2 will be described with reference to FIG. 2, which shows a cross-sectional view taken along a plane perpendicular to the light propagation direction. the semiconductor laser section 2 is composed of: a part of the n-type lower cladding layer 41 formed on the semiconductor substrate 1; a gain core layer 42; a high mesa structure 55 in which a part of the p-type upper cladding layer 43 is formed in a stripe shape; a current blocking layer 45 consisting of a p-type current blocking layer 45 a and an n-type current blocking layer 45 b formed on the n-type lower cladding layer 41 on both sides of the stripe-shaped high mesa structure 55; a remaining part of the p-type upper cladding layer 43 and a p-type contact layer 46 formed on the upper surfaces of the high mesa structure 55 and the current blocking layer 45; a laser section electrode 47 formed on the upper surface of the p-type contact layer 46; a protective insulating film 48 covering at least the side portions of the high mesa structure 55 and the surface of the p-type contact layer 46 that is not covered by the laser section electrode 47; an n-type contact layer 49 formed on the n-type lower cladding layer 41 at a distance from the high mesa structure 55; and a lower electrode 50 provided on the n-type contact layer 49.

[0018] The gain core layer 42 is a semiconductor layer that has the function of amplifying light. The n-type lower cladding layer 41 and the p-type upper cladding layer 43 are made of semiconductor layers with a lower refractive index than the gain core layer 42 in order to confine light in the gain core layer 42.

[0019] The p-type contact layer 46 is made of a semiconductor layer having a lower resistance than the p-type upper cladding layer 43 in order to reduce the resistance when a current is injected from the laser portion electrode 47 into the semiconductor layer.

[0020] The current blocking layer 45 is made of a material and structure that does not allow current to flow, and functions as a semiconductor layer for concentrating current in the gain core layer 42. In the example of the semiconductor laser section 2 shown in Figure 2, the current blocking layer 45 is made of two layers: a p-type current blocking layer 45a and an n-type current blocking layer 45b formed inside the p-type current blocking layer 45a and having an end that is not in contact with the gain core layer 42.

[0021] The protective insulating film 48 is made of an insulating material such as an inorganic insulating film, an oxide film, a nitride film, or an organic insulating film, such as benzocyclobutene (BCB). The protective insulating film 48 has the function of preventing the semiconductor from being oxidized or altered by oxygen, water, etc. in the atmosphere.

[0022] The semiconductor laser section 2 shown in the first embodiment has a buried structure in which a current blocking layer 45 is formed on the sidewall of the gain core layer 42, that is, on the side surface of the high mesa structure 55. In the buried structure, heat generated in the gain core layer 42 is diffused via the current blocking layer 45, and a decrease in gain due to a rise in temperature of the gain core layer 42 can be suppressed, thereby enabling high output power.

[0023] <Method of Manufacturing Semiconductor Laser Portion> The following describes a method of manufacturing the semiconductor laser portion 2. For example, on the semiconductor substrate 1 made of an InP substrate having a (100) plane of semiconductor crystal orientation as the substrate surface, an n-type InP layer having a thickness of 2000 nm that constitutes the n-type lower cladding layer 41, a multi-quantum well layer made of AlGaInAs with a total thickness of 100 nm that serves as the gain core layer 42 of the semiconductor laser portion 2, and a p-type InP layer having a thickness of 2000 nm that constitutes the p-type upper cladding layer 43 are epitaxially grown in this order using metal organic chemical vapor deposition (MOCVD).

[0024] The multiple quantum well layers constituting the gain core layer 42 are composed of repeated pairs of well layers that contribute to light emission and barrier layers that have a larger band gap than the well layers. The gain core layer 42 is composed of, for example, eight pairs of multiple quantum well layers. The n-type lower cladding layer 41 formed by the above-mentioned epitaxial crystal growth can be used in common as the n-type lower cladding layer of the optical modulation section 20 and the passive waveguide 30, which will be described later.

[0025] <Structure of Light Modulation Section> The light modulation section 20 will be described with reference to FIG. 3, which shows a cross-sectional view taken along a plane perpendicular to the propagation direction of light.

[0026] The optical modulation section 20 is composed of a part of an n-type lower cladding layer 61 formed on the semiconductor substrate 1, an optical modulation core layer 62, a p-type upper cladding layer 63, a high mesa structure 65 in which a p-type contact layer 64 is formed in a stripe shape, an optical modulation section electrode 67 formed on the upper surface of the p-type contact layer 64, a protective insulating film 68 covering at least the side portion of the high mesa structure 65, an n-type contact layer 69 formed on the n-type lower cladding layer 61 at a distance from the high mesa structure 65, and a lower electrode 70 provided on the n-type contact layer 69.

[0027] The light modulation core layer 62 is a semiconductor layer that has the function of changing the phase of propagating light by changing the refractive index when a reverse bias is applied. The p-type upper cladding layer 63 is made of a semiconductor layer with a lower refractive index than the light modulation core layer 62 in order to confine light in the light modulation core layer 62.

[0028] The p-type contact layer 64 is made of a semiconductor layer having a lower resistance than the p-type upper cladding layer 63 in order to reduce the resistance when a voltage is applied from the optical modulation electrode 67 to the semiconductor layer.

[0029] The protective insulating film 68 is made of an insulating material such as an inorganic insulating film, an oxide film, a nitride film, or an organic insulating film, such as BCB, etc. The protective insulating film 68 has the function of preventing the semiconductor from being oxidized or altered by oxygen, water, etc. in the atmosphere.

[0030] The optical modulation section 20 shown in the first embodiment is configured with a high mesa structure 65 obtained by etching from the p-type contact layer 64 to a part of the n-type lower cladding layer 61 by RIE or the like.

[0031] In the high mesa structure 65, the difference in refractive index between the light modulation core layer 62 and the etched region is large, so that light can be tightly confined in the light modulation core layer 62. When the refractive index of the light modulation core layer 62 changes due to the high mesa structure 65, the amount of phase change of light increases, so high modulation efficiency can be obtained.

[0032] <Method of Manufacturing Optical Modulation Section> The following describes a method of manufacturing the optical modulation section 20. On the surface of the epitaxially grown n-type lower cladding layer 61, a multiple quantum well layer made of AlGaInAs with a total layer thickness of 300 nm that constitutes the optical modulation core layer 62, a p-type InP layer with a layer thickness of 2000 nm that constitutes the p-type upper cladding layer 63, and a p-type InGaAs layer with a layer thickness of 300 nm that constitutes the p-type contact layer 64 are sequentially grown by epitaxial crystal growth.

[0033] After the epitaxial crystal growth, each semiconductor layer is selectively etched by RIE or the like to form a high mesa structure 65. On the p-type contact layer 64, an optical modulation section electrode 67 made of a metal such as Ti, Au, Pt, Nb, or Ni, and a 300 nm-thick SiO film constituting a protective insulating film 68 for protecting the semiconductor surface are formed by a film formation method such as CVD.

[0034] <Function of Passive Waveguide> The passive waveguide 30 functions as a waveguide for connecting the respective element portions formed on the semiconductor substrate 1 .

[0035] 4, which shows a cross-sectional view of the passive waveguide 30 taken along a plane perpendicular to the light propagation direction. The passive waveguide 30 is composed of a high mesa structure 85 in which a part of an n-type lower cladding layer 81, a waveguide core layer 82, and an i-type upper cladding layer 83 are formed on a semiconductor substrate 1 in a striped pattern, and a protective insulating film 88 that covers at least the top and side surfaces of the high mesa structure 85.

[0036] The passive waveguide 30 in the semiconductor optical integrated device 500 according to the first embodiment has a high mesa structure 85 formed by etching the i-type upper cladding layer 83 through a portion of the n-type lower cladding layer 81 by RIE or the like. To connect the semiconductor laser section 2 and the optical modulation section 20, the passive waveguide 30 connecting them must have a curved region (hereinafter referred to as the curved portion) in part. In order to suppress optical loss in the curved portion of the passive waveguide 30, it is preferable to apply a high mesa structure 85 to the passive waveguide 30, which can tightly confine light within the waveguide core layer 82.

[0037] The i-type upper cladding layer 83 is made of a semiconductor layer having a lower refractive index than the waveguide core layer 82 in order to confine light in the waveguide core layer 82 .

[0038] The protective insulating film 88 is made of an insulating material such as an inorganic insulating film, an oxide film, a nitride film, or an organic insulating film, such as BCB, etc. The protective insulating film 88 has the function of preventing the semiconductor from being oxidized or altered by oxygen, water, etc. in the atmosphere.

[0039] The waveguide core layer 82 may have the same structure as the optical modulation core layer 62 of the optical modulation section 20. In this way, the semiconductor optical integrated device 500 can be configured with two types of core layers: the gain core layer 42 of the semiconductor laser section 2 and the optical modulation core layer 62 of the optical modulation section 20 and the passive waveguide 30.

[0040] Since the passive waveguide 30 does not have the function of changing the intensity and phase of light, it does not require a structure for applying the necessary current or voltage to electrodes, contact layers, etc.

[0041] <Method for Manufacturing Passive Waveguide> The following describes a method for manufacturing the passive waveguide 30. On the surface of the n-type lower cladding layer 81 epitaxially grown during the formation of the semiconductor laser portion 2, a multi-quantum well layer made of AlGaInAs with a total layer thickness of 300 nm constituting the waveguide core layer 82, and an i-type InP layer with a layer thickness of 2000 nm constituting the i-type upper cladding layer 83 are sequentially grown by epitaxial crystal growth.

[0042] After the epitaxial crystal growth, each semiconductor layer is selectively etched by RIE or the like to form a high mesa structure 85. A 300 nm thick SiO film that constitutes a protective insulating film 88 for protecting the semiconductor surface is formed by a film formation method such as CVD.

[0043] <Operation of the semiconductor optical integrated device according to the first embodiment> The operation of the semiconductor optical integrated device 500 according to the first embodiment will be described below. The laser light emitted from one end 2a of the semiconductor laser portion 2 propagates through the first passive waveguide 3 and enters the first optical modulation portion 5 from one end 5a of the first optical modulation portion 5. In the first optical modulation portion 5, an RF electrical signal is applied to the optical modulation portion electrode 67, and the refractive index of the waveguide changes, thereby changing the phase of the light passing through the first optical modulation portion 5.

[0044] On the other hand, the laser light emitted from the other end 2b of the semiconductor laser unit 2 propagates through the second passive waveguide 4 and enters the second optical modulation unit 6 from one end 6a of the second optical modulation unit 6. In the second optical modulation unit 6, an RF electrical signal is applied to the optical modulation unit electrode 67, and the refractive index of the waveguide changes, thereby changing the phase of the light passing through the second optical modulation unit 6.

[0045] The light that has been phase-modulated in the first optical modulation section 5 and the second optical modulation section 6 of the optical modulation section 20 enters the optical multiplexing section 9 via the third passive waveguide 7 and the fourth passive waveguide 8, respectively, where it is multiplexed into one intensity-modulated signal and emitted from the optical output section 10 to the outside of the semiconductor optical integrated device 500.

[0046] <Function of the semiconductor optical integrated device according to the first embodiment> The laser light output from both ends of the semiconductor laser section 2 propagates through the passive waveguide 30, is input to the first optical modulation section 5 and the second optical modulation section 6, and is multiplexed by the optical multiplexing section 9 before being output.

[0047] In the optical modulation section 20, an RF electrical signal is applied to the optical modulation section electrode 67, which changes the refractive index of the waveguide and the phase of the light passing through the waveguide, thereby changing the intensity of the optical output combined by the optical combining section 9 and generating an intensity-modulated signal.

[0048] For example, an intensity modulation signal can be generated by applying the same reverse bias voltage of about several volts to the optical modulation section electrodes 67 of the first optical modulation section 5 and the second optical modulation section 6, and then applying an RF electrical signal that applies a reverse voltage (push-pull) to each of the first optical modulation section 5 and the second optical modulation section 6.

[0049] <Characteristics of the semiconductor optical integrated device according to the first embodiment> In the optical semiconductor device described in Patent Document 1, the laser light output from the semiconductor laser unit is branched by a branching unit, and each laser light is input to each modulation unit. On the other hand, the semiconductor optical integrated device according to the first embodiment is characterized in that two laser lights output from both ends of the semiconductor laser unit 2, respectively, are directly input to the optical modulation unit 20.

[0050] <Effects of the semiconductor optical integrated element according to the first embodiment> According to the semiconductor optical integrated element according to the first embodiment, when laser light is output from the semiconductor laser section to the optical modulation section, there is no need to provide a branch section in the passive waveguide, which makes it possible to shorten the chip length. Furthermore, since there is no branch section in the passive waveguide, no loss due to the branch section occurs, which has the effect of providing a semiconductor optical integrated element with increased optical output.

[0051] Modification of First Embodiment <Features of a Semiconductor Optical Integrated Device According to a Modification of First Embodiment> Fig. 5 is a top view showing the configuration of a semiconductor optical integrated device 550 according to a modification of the first embodiment. The semiconductor optical integrated device 500 according to the first embodiment shown in Fig. 1 uses laser light output from a single semiconductor laser portion 2. On the other hand, the semiconductor optical integrated device 550 according to the modification of the first embodiment is characterized in that it is configured with two semiconductor laser portions, namely, a first semiconductor laser portion 22 consisting of a first semiconductor laser and a second semiconductor laser portion 23 consisting of a second semiconductor laser.

[0052] The first semiconductor laser unit 22 is disposed in parallel to the first optical modulation unit 5 at a position opposite to the first optical modulation unit 5. The second semiconductor laser unit 23 is disposed in parallel to the second optical modulation unit 6 at a position opposite to the second optical modulation unit 6.

[0053] <Configuration of Semiconductor Optical Integrated Device According to Modification of First Embodiment> A semiconductor optical integrated device 550 according to a modification of the first embodiment includes, provided on a semiconductor substrate 1, a first semiconductor laser portion 22 made of a first semiconductor laser, a second semiconductor laser portion 23 made of a second semiconductor laser, a first passive waveguide 3 having one end connected to one end 22a of the first semiconductor laser portion 22, a second passive waveguide 4 having one end connected to one end 23a of the second semiconductor laser portion 23, and a second passive waveguide 5 having one end 5a connected to the other end of the first passive waveguide 3. the second optical modulation section 6 having one end 6a connected to the other end of the second passive waveguide 4; a third passive waveguide 7 having one end connected to the other end 5b of the first optical modulation section 5; a fourth passive waveguide 8 having one end connected to the other end 6b of the second optical modulation section 6; an optical multiplexing section 9 having one end 9a connected to the other end of the third passive waveguide 7 and the other end of the fourth passive waveguide 8; and an optical output section 10 connected to the other end 9b of the optical multiplexing section 9.

[0054] The cross-sectional structures of the first semiconductor laser portion 22 and the second semiconductor laser portion 23 are the same as the cross-sectional structure of the semiconductor laser portion 2 of the first embodiment, and therefore, description thereof will be omitted.

[0055] <Effects of the semiconductor optical integrated element according to the modification of the first embodiment> As described above, according to the semiconductor optical integrated element according to the modification of the first embodiment, as described above, the two semiconductor laser portions, the first semiconductor laser portion and the second semiconductor laser portion, are arranged in parallel at positions facing the first optical modulation portion and the second optical modulation portion that constitute the optical modulation portion, respectively. Therefore, similar to the first embodiment, when outputting laser light from the semiconductor laser portion to the optical modulation portion, there is no need to provide a branch portion in the passive waveguide, which enables the chip length to be shortened. Furthermore, since there is no branch portion in the passive waveguide, no loss due to the branch portion occurs, and therefore, an effect is achieved in which a semiconductor optical integrated element with increased optical output is obtained.

[0056] <Combination of Semiconductor Optical Integrated Device According to First Embodiment and Driver Circuit> When driving the semiconductor optical integrated device 500 according to the first embodiment, it is used in combination with a driver circuit 90 for generating an RF signal, as shown in FIG.

[0057] An electrode pad 91 for RF signal output is arranged on a driver circuit 90 for generating an RF signal, and is connected by a wire 92 or the like to an RF signal input wiring section 93 formed on the semiconductor optical integrated device 500, and an RF signal is applied to the optical modulation section 20. The RF signal propagating through the optical modulation section 20 is attenuated to some extent during propagation and reaches the terminal end of the optical modulation section 20. By arranging a termination resistor 94 at the terminal end of the optical modulation section 20, which has a resistance value that matches the impedance of the optical modulation section 20, unnecessary reflection at the terminal end of the RF signal can be suppressed.

[0058] <Effect of Combining the Semiconductor Optical Integrated Element and Driver Circuit According to the First Embodiment> According to the configuration of the combination of the semiconductor optical integrated element 500 and the driver circuit 90 according to the first embodiment, the first optical modulation section 5 and the second optical modulation section 6 are arranged in parallel and facing each other, so that attenuation of the RF electrical signal output from the driver circuit 90 for generating an RF signal is relatively suppressed, thereby achieving the effect of enabling the semiconductor optical integrated element 500 to have a broadband.

[0059] Furthermore, since the termination resistor 94 provided to suppress reflection of the RF signal at the termination side of the optical modulation section 20 can be arranged using short wiring, the generation of excess stray capacitance and the like can be suppressed, thereby achieving the effect of enabling the semiconductor optical integrated element 500 to have a wider bandwidth.

[0060] Second Embodiment <Features of the Semiconductor Optical Integrated Device According to the Second Embodiment> Fig. 7 is a top view showing the configuration of a semiconductor optical integrated device 600 according to the second embodiment. The semiconductor optical integrated device 600 according to the second embodiment is characterized in that, in addition to the configuration of the semiconductor optical integrated device 500 according to the first embodiment, a first optical amplification section 100 and a first phase adjustment section 110 are provided in the first passive waveguide 3, and a second optical amplification section 101 and a second phase adjustment section 111 are provided in the second passive waveguide 4. Hereinafter, the first optical amplification section 100 and the second optical amplification section 101 will be collectively referred to as optical amplification sections, and the first phase adjustment section 110 and the second phase adjustment section 111 will be collectively referred to as phase adjustment sections.

[0061] <Function of Phase Adjustment Unit> The phase adjustment unit has the function of adjusting the phase of propagating light by changing the refractive index of the phase adjustment unit core layer (not shown) by applying a current. In the semiconductor optical integrated device 600 according to the second embodiment, the optical intensity of the output light is determined based on the relative phase relationship of each modulated light when multiplexed in the optical multiplexer 9. For example, if the relative phase difference between each modulated light is set to zero, the optical output is maximized. On the other hand, if the relative phase difference between each modulated light is set to 180 degrees, the optical output is zero. Furthermore, if the relative phase difference between each modulated light is set to 90 degrees, the optical output is halved.

[0062] For example, by applying an RF electrical signal that applies a reverse voltage (push-pull) to each optical modulation section while setting the relative phase difference between each modulated light to 90 degrees and the optical output to 1 / 2, it becomes possible to output any intensity-modulated signal light with an optical output intensity between 0 and 1, with the optical output intensity at 1 / 2 as the center.

[0063] <Function of Optical Amplification Section> The optical amplification section can amplify light by applying a current, and therefore can increase the optical intensity of the output light of the semiconductor optical integrated device 600 .

[0064] If the intensities of the laser beams output from both ends of the semiconductor laser unit are different, a problem occurs in that the extinction ratio deteriorates when the beams are combined in the optical multiplexer 9. To improve this problem, the optical amplifier adjusts the optical intensities of the modulated beams combined in the optical multiplexer 9 so that they are the same, thereby making it possible to suppress deterioration of the extinction ratio.

[0065] The semiconductor optical integrated device 600 according to the second embodiment may be configured such that either one or both of the first optical amplification section 100 and the first phase adjustment section 110 are provided in the first passive waveguide 3 connected to one end 2 a of the semiconductor laser section 2, and either one or both of the second optical amplification section 101 and the second phase adjustment section 111 are provided in the second passive waveguide 4 connected to the other end 2 b of the semiconductor laser section 2.

[0066] Furthermore, instead of the semiconductor optical integrated device 500 according to the first embodiment, the present invention may be applied to a semiconductor optical integrated device 550 according to a modified example of the first embodiment, in which either one or both of the first optical amplification section 100 and the first phase adjustment section 110 are provided in the first passive waveguide 3 connected to one end 22 a of the first semiconductor laser section 22, and either one or both of the second optical amplification section 101 and the second phase adjustment section 111 are provided in the second passive waveguide 4 connected to one end 23 a of the second semiconductor laser section 23.

[0067] <Effects of the semiconductor optical integrated element according to the second embodiment> As described above, the semiconductor optical integrated element according to the second embodiment has a first optical amplification section and a first phase adjustment section provided in the first passive waveguide, and a second optical amplification section and a second phase adjustment section provided in the second passive waveguide, thereby achieving the effect of obtaining a semiconductor optical integrated element that is capable of outputting intensity-modulated signal light with an optical output intensity of any value between 0 and 1 and that is also capable of increasing the optical intensity of the output light.

[0068] Third Embodiment <Features of the Semiconductor Optical Integrated Device According to the Third Embodiment> Fig. 8 is a top view showing the configuration of a semiconductor optical integrated device 700 according to the third embodiment. The semiconductor optical integrated device 700 according to the third embodiment has a basic configuration in common with the semiconductor optical integrated device 500 according to the first embodiment, but is characterized in that the waveguide length L1 of the first passive waveguide 120 and the waveguide length L2 of the second passive waveguide 121 are equal.

[0069] By making the waveguide length L1 of the first passive waveguide 120 and the waveguide length L2 of the second passive waveguide 121 equal, it is possible to make the propagation losses of the passive waveguides equal, thereby suppressing deterioration of the extinction ratio. Another effect is that a stable optical output can be obtained even if the wavelength of the laser light output from the semiconductor laser unit 2 fluctuates.

[0070] In addition to making the lengths of the above-mentioned waveguides equal, if the equivalent refractive indexes of the passive waveguides are also made equal, for example, if the optical multiplexing unit 9 is a 2×1 MMI (Multi-Mode Interference), the phases of the light multiplexed in the optical multiplexing unit 9 will match in principle, and the maximum output light, that is, output light with a light intensity of 1, will be output.

[0071] When the optical multiplexer 9 is a 2x2 MMI, the optical intensity of each output port is 1 / 2. Therefore, with 1 / 2 optical intensity as the center value, an intensity-modulated signal with an optical intensity ranging from 0 to 1 can be output by applying an RF signal. Therefore, with a 2x1 MMI, phase adjustment is required to set the center value of the optical intensity to 1 / 2, but with a 2x2 MMI, phase adjustment is not required in principle.

[0072] In the case where the semiconductor optical integrated device 700 according to the third embodiment has the same basic configuration as the semiconductor optical integrated device 600 according to the second embodiment, the device may be configured as follows.

[0073] When the first optical amplifier 100 is provided in the first passive waveguide 3 of the semiconductor optical integrated device 700 and the second optical amplifier 101 is provided in the second passive waveguide 4, the total length of the first passive waveguide 3 and the first optical amplifier 100 needs to be equal to the total length of the second passive waveguide 4 and the second optical amplifier 101.

[0074] When the first phase adjustment section 110 is provided in the first passive waveguide 3 and the second phase adjustment section 111 is provided in the second passive waveguide 4 of the semiconductor optical integrated device 700, the total length of the first passive waveguide 3 and the first phase adjustment section 110 should be equal to the total length of the second passive waveguide 4 and the second phase adjustment section 111.

[0075] When the first passive waveguide 3 of the semiconductor optical integrated device 700 is provided with the first optical amplification section 100 and the first phase adjustment section 110, and the second passive waveguide 4 is provided with the second optical amplification section 101 and the second phase adjustment section 111, the total length of the first passive waveguide 3, the first optical amplification section 100, and the first phase adjustment section 110 should be equal to the total length of the second passive waveguide 4, the second optical amplification section 101, and the second phase adjustment section 111.

[0076] <Effects of Semiconductor Optical Integrated Device According to Third Embodiment> As described above, according to the semiconductor optical integrated device according to the third embodiment, the waveguide length of the first passive waveguide and the waveguide length of the second passive waveguide are made equal, and therefore it is possible to suppress deterioration of the extinction ratio, and it is possible to obtain an effect of obtaining a semiconductor optical integrated device that can achieve stable optical output even when the wavelength of the laser light output from the semiconductor laser unit fluctuates.

[0077] Modification of Third Embodiment <Features of a Semiconductor Optical Integrated Device According to a Modification of Third Embodiment> Fig. 9 is a top view showing the configuration of a semiconductor optical integrated device 750 according to a modification of the third embodiment. The semiconductor optical integrated device 750 according to the modification of the third embodiment is characterized in that the number N1 of curved portions C1 of the first passive waveguide 130 is equal to the number N2 of curved portions C2 of the second passive waveguide 131. Note that in Fig. 9, for convenience, each curved portion is drawn as if the passive waveguide is bent at a right angle.

[0078] <Effects of the semiconductor optical integrated element according to the modification of the third embodiment> As described above, the semiconductor optical integrated element according to the modification of the third embodiment has the above-mentioned configuration, which makes it possible to equalize the radiation loss due to the curved portions between the first passive waveguide and the second passive waveguide, thereby achieving the effect of obtaining a semiconductor optical integrated element that can suppress deterioration of the extinction ratio.

[0079] Fourth Embodiment <Features of the Semiconductor Optical Integrated Device According to the Fourth Embodiment> Fig. 10 is a top view showing the configuration of a semiconductor optical integrated device 800 according to the fourth embodiment. The semiconductor optical integrated device 800 according to the fourth embodiment is characterized in that, in addition to the configuration of the semiconductor optical integrated device 550 according to the modified example of the first embodiment, a first monitor light-receiving portion 171 is provided at the other end 151b of the first semiconductor laser portion 151, and a second monitor light-receiving portion 172 is provided at the other end 152b of the second semiconductor laser portion 152. In the following description, the first monitor light-receiving portion 171 and the second monitor light-receiving portion 172 are collectively referred to as a monitor light-receiving portion 173.

[0080] The semiconductor optical integrated device 800 according to the fourth embodiment includes a first semiconductor laser portion 151 formed on a semiconductor substrate 1 and consisting of a first semiconductor laser, a second semiconductor laser portion 152 formed on a second semiconductor laser, a first passive waveguide 3 having one end connected to one end 151 a of the first semiconductor laser portion 151, a first monitor light receiving portion 171 connected to the other end 151 b of the first semiconductor laser portion 151, a second passive waveguide 4 having one end connected to one end 152 a of the second semiconductor laser portion 152, and a second passive waveguide 5 having one end connected to the other end 151 b of the second semiconductor laser portion 152. 2b, a first optical modulation section 5 having one end 5a connected to the other end of the first passive waveguide 3, a second optical modulation section 6 having one end 6a connected to the other end of the second passive waveguide 4, a third passive waveguide 7 having one end connected to the other end 5b of the first optical modulation section 5, a fourth passive waveguide 8 having one end connected to the other end 6b of the second optical modulation section 6, an optical multiplexing section 9 having one end 9a connected to the other end of the third passive waveguide 7 and the other end of the fourth passive waveguide 8, and an optical output section 10 having the other end 9b of the optical multiplexing section 9 connected.

[0081] Due to variations in characteristics among the multiple semiconductor laser portions formed on the semiconductor substrate 1, a problem may occur in which the optical output intensities of the semiconductor laser portions differ even when the same current value is applied to each semiconductor laser portion. In the semiconductor optical integrated device 800 according to the fourth embodiment, by providing a monitor light receiving portion for each semiconductor laser portion 151, 152, the optical output intensities of the semiconductor laser portions 151, 152 can be monitored and the current values ​​applied to the semiconductor laser portions 151, 152 can be individually adjusted to make the optical output intensities the same. As a result, deterioration of the extinction ratio of the semiconductor optical integrated device can be suppressed.

[0082] 11 is a cross-sectional view of the monitor light-receiving section 173 in the semiconductor optical integrated device 800 according to the fourth embodiment. Note that Fig. 11 shows a cross-sectional view of the monitor light-receiving section 173 taken along a plane perpendicular to the propagation direction of light.

[0083] The monitor light receiving section 173 is composed of a part of the n-type lower cladding layer 161 formed on the semiconductor substrate 1, a light absorbing core layer 162, a p-type upper cladding layer 163, a high mesa structure 165 in which the p-type contact layer 164 is formed in a stripe shape, a light receiving section electrode 167 formed on the upper surface of the p-type contact layer 164, a protective insulating film 168 covering at least the side portion of the high mesa structure 165, an n-type contact layer 169 formed on the n-type lower cladding layer 161 at a distance from the high mesa structure 165, and a lower electrode 170 provided on the n-type contact layer 169.

[0084] The optical absorption core layer 162 has the same structure as the gain core layer 42 formed in the first semiconductor laser portion 22 and the second semiconductor laser portion 23 of the semiconductor optical integrated device 550 according to the modified example of the first embodiment. However, it does not have a buried structure like the semiconductor laser portion, but has a high mesa structure 165 similar to the optical modulation portion 20.

[0085] In the semiconductor laser section, a forward current is applied to amplify the light propagating therein, and therefore the core layer is particularly called a gain core layer 42. The core layer of the monitor light-receiving section 173 in the fourth embodiment is the same as that of the semiconductor laser section, but since it is a core layer for absorbing light, it is particularly called a light absorption core layer 162 in the fourth embodiment.

[0086] The light absorbing core layer 162 has the function of passing a photocurrent proportional to the intensity of incident light when a reverse bias is applied. The n-type lower cladding layer 161 and the p-type upper cladding layer 163 are made of semiconductor layers with a lower refractive index than the light absorbing core layer 162 in order to confine light in the light absorbing core layer 162. The p-type contact layer 164 is made of a semiconductor layer with a lower resistance than the p-type upper cladding layer 163 in order to reduce resistance.

[0087] The protective insulating film 168 is made of an insulating material such as an inorganic insulating film, an oxide film, a nitride film, or an organic insulating film, such as BCB, etc. The protective insulating film 168 has the function of preventing the semiconductor from being oxidized or altered by oxygen, water, etc. in the atmosphere.

[0088] <Method for Manufacturing Monitor Light-Receiving Section> The following describes a method for manufacturing the monitor light-receiving section 173. On the semiconductor substrate 1, the following are epitaxially grown in sequence by MOCVD: n-type lower cladding layer 161 made of an n-type InP layer with a layer thickness of 2000 nm; light-absorbing core layer 162 made of an AlGaInAs multiple quantum well layer with a total layer thickness of 100 nm; p-type upper cladding layer 163 made of a p-type InP layer with a layer thickness of 2000 nm; and p-type contact layer 164 made of a p-type InGaAs layer with a layer thickness of 300 nm.

[0089] After epitaxial crystal growth, each semiconductor layer is selectively etched by RIE or the like to form a high mesa structure 165. A light-receiving electrode 167 made of a metal such as Ti, Au, Pt, Nb, or Ni is formed on the p-type contact layer 164, and a 300-nm-thick SiO film that constitutes a protective insulating film 168 for protecting the semiconductor surface is formed by a film-forming method such as CVD.

[0090] In the above-mentioned configuration, the multiple quantum well layer of the light absorption core layer 162 is composed of repeated pairs of well layers that contribute to light absorption and barrier layers whose band gap is larger than that of the well layers, for example, 8 pairs. In the above-mentioned configuration, the n-type lower cladding layer 161 can be common to the n-type lower cladding layer of the semiconductor laser section and the passive waveguide.

[0091] <Effects of the semiconductor optical integrated element according to the fourth embodiment> As described above, in the semiconductor optical integrated element according to the fourth embodiment, by arranging a monitor light receiving unit in each semiconductor laser portion, the optical output intensity of each semiconductor laser portion can be monitored, and by individually adjusting the current value applied to each semiconductor laser portion, the optical output intensity can be made uniform, thereby achieving the effect of obtaining a semiconductor optical integrated element that can suppress deterioration of the extinction ratio.

[0092] Although the present disclosure describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations.

[0093] Therefore, countless variations not illustrated are conceivable within the scope of the technology of the present disclosure, including, for example, cases where at least one component is modified, added, or omitted, and even cases where at least one component is extracted and combined with a component of another embodiment.

[0094] 1 semiconductor substrate, 2 semiconductor laser section, 2a, 5a, 6a, 9a, 22a, 23a, 151a, 152a one end, 2b, 5b, 6b, 9b, 151b, 152b other end, 3, 120, 130 first passive waveguide, 4, 121, 131 second passive waveguide, 5 first optical modulation section, 6 second optical modulation section, 7 third passive waveguide, 8 fourth passive waveguide, 9 optical multiplexing section, 10 optical output section, 20 optical modulation section, 22, 151 first semiconductor laser section, 23, 152 second semiconductor laser section, 30 passive waveguide, 41, 61, 81, 161 n-type lower cladding layer, 42 gain core layer, 43, 63, 163 p-type upper cladding layer, 45 Current blocking layer, 45a p-type current blocking layer, 45b n-type current blocking layer, 46, 64, 164 p-type contact layer, 47 laser section electrode, 48, 68, 88, 168 protective insulating film, 49, 69, 169 n-type contact layer, 50, 70, 170 lower electrode, 55, 65, 85, 165 high mesa structure, 62 optical modulation core layer, 67 optical modulation section electrode, 83 i-type upper clad layer, 90 driver circuit, 91 electrode pad, 92 wire, 93 RF signal input wiring section, 94 termination resistor, 100 first optical amplification section, 101 second optical amplification section, 110 first phase adjustment section, 111 second phase adjustment section, 162 light absorption core layer, 167 light receiving section electrode, 171 first monitor light receiving section, 172 Second monitor light receiving portion, 173 Monitor light receiving portion, 500, 550, 600, 700, 750, 800 Semiconductor optical integrated element, C1, C2 Curved portion, L1, L2 Waveguide length

Claims

1. A semiconductor optical integrated device comprising: a semiconductor laser section formed on a substrate and consisting of a semiconductor laser; and an optical modulation section formed on the substrate and consisting of a first optical modulation section having one end connected to one end of the semiconductor laser section via a first passive waveguide, and a second optical modulation section having one end connected to the other end of the semiconductor laser section via a second passive waveguide.

2. The semiconductor optical integrated device according to claim 1, wherein the longitudinal direction of said semiconductor laser section is parallel to the longitudinal directions of said first optical modulation section and said second optical modulation section.

3. A semiconductor optical integrated device according to claim 1 or 2, characterized in that either one or both of a first optical amplification section and a first phase adjustment section are provided in the first passive waveguide connected to one end of the semiconductor laser section, and either one or both of a second optical amplification section and a second phase adjustment section are provided in the second passive waveguide connected to the other end of the semiconductor laser section.

4. A semiconductor optical integrated device comprising: a first semiconductor laser section formed on a substrate and consisting of a first semiconductor laser; a second semiconductor laser section formed on a substrate and consisting of a second semiconductor laser; and an optical modulation section formed on the substrate, one end of which is connected to one end of the first semiconductor laser section via a first passive waveguide and arranged in a position facing the first semiconductor laser section, and a second optical modulation section one end of which is connected to one end of the second semiconductor laser section via a second passive waveguide and arranged in a position facing the second semiconductor laser section.

5. A semiconductor optical integrated device according to claim 4, characterized in that the longitudinal direction of the first semiconductor laser section and the longitudinal direction of the first optical modulation section are parallel, and the longitudinal direction of the second semiconductor laser section and the longitudinal direction of the second optical modulation section are parallel.

6. A semiconductor optical integrated device according to claim 4 or 5, characterized in that either one or both of a first optical amplification section and a first phase adjustment section are provided in the first passive waveguide connected to one end of the first semiconductor laser section, and either one or both of a second optical amplification section and a second phase adjustment section are provided in the second passive waveguide connected to one end of the second semiconductor laser section.

7. A semiconductor optical integrated device according to any one of claims 1, 2, 4 and 5, characterized in that the waveguide length L1 of said first passive waveguide and the waveguide length L2 of said second passive waveguide are equal.

8. When the first optical amplifier is provided in the first passive waveguide and the second optical amplifier is provided in the second passive waveguide, the total length of the first passive waveguide and the first optical amplifier is equal to the total length of the second passive waveguide and the second optical amplifier, and when the first phase adjustment unit is provided in the first passive waveguide and the second phase adjustment unit is provided in the second passive waveguide, the total length of the first passive waveguide and the first phase adjustment unit is equal to the total length of the second passive waveguide.

7. The semiconductor optical integrated device according to claim 3, wherein when the first optical amplifier and the first phase adjuster are provided in the first passive waveguide and the second optical amplifier and the second phase adjuster are provided in the second passive waveguide, respectively, the total length of the first passive waveguide, the first optical amplifier, and the first phase adjuster is equal to the total length of the second passive waveguide, the second optical amplifier, and the second phase adjuster.

9. A semiconductor optical integrated device according to any one of claims 4 to 6, further comprising: a first monitor light receiving section connected to the other end of the first semiconductor laser section and receiving the optical output of the first semiconductor laser; and a second monitor light receiving section connected to the other end of the second semiconductor laser section and receiving the optical output of the second semiconductor laser.

10. A semiconductor optical integrated device according to any one of claims 1 to 9, characterized in that the number of curved portions C1 of the first passive waveguide is equal to the number of curved portions C2 of the second passive waveguide.

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