Semiconductor optical integrated devices

Abstract

The semiconductor optical integrated element based on this disclosure comprises: a semiconductor substrate (10); a first optical amplifier (200) that amplifies signal light input from a first end face (10a) along an optical waveguide; a first passive optical waveguide (203) that guides the amplified signal light in a direction different from the direction of the optical waveguide; an optical splitter (204) that splits the guided signal light into multiple signal lights; a phase modulator (202) connected to the first passive optical waveguide (203) that modulates the multiple signal lights in different directions; a second passive optical waveguide (206) that guides the phase-modulated signal light from different directions toward the direction of the optical waveguide; an optical synthesizer (205) that combines the phase-modulated multiple signal lights into a single signal light; and a second optical amplifier (201) that amplifies the signal light guided by the second passive optical waveguide (206) along the direction of the optical waveguide, with a saturated light output less than that of the first optical amplifier (200).

Description

Technical Field

[0001] This disclosure relates to a semiconductor optical integrated device. Background Technology

[0002] The proliferation of mobile communication terminals such as smartphones and the diversification of cloud data services have led to a rapid increase in communication traffic. Consequently, not only are trunk optical communication networks connecting major cities required, but also short-distance optical communication networks between cities and data centers are demanding higher speeds and larger capacities.

[0003] For transmitting large amounts of communication data, optical transceivers capable of coherent phase modulation with multi-value modulation are effective, and Mach-Zehnder type phase modulation elements capable of generating optical modulation signals at high speed have attracted much attention.

[0004] Furthermore, miniaturization and low power consumption are required in optical transceivers. Therefore, using phase modulation elements made of semiconductor materials is effective in replacing phase modulation elements made of dielectric materials such as lithium niobate (LiNbO3). Moreover, further miniaturization can be achieved by integrating laser elements, optical amplification elements that amplify signal light, and other components onto the same semiconductor substrate, thus increasing the expectation for semiconductor optical integrated devices.

[0005] Patent Document 1: Japanese Patent No. 5497678

[0006] Patent Document 2: Japanese Patent No. 5144306

[0007] Patent Document 3: International Publication No. 2018 / 117077

[0008] Non-patent document 1: N.Kikuchi et al., "High-speed InP-based Mach-ZehnderModulator for Advanced Modulation Formats", Compound Semiconductor IntegratedCircuit Symposium, Oct. 2012. Summary of the Invention

[0009] The problem the invention aims to solve

[0010] To obtain small and low-power semiconductor optical integrated devices, it is desirable to integrate phase modulation elements and optical amplification elements on an InP (indium phosphide) substrate. In this case, by forming an optical waveguide for the phase modulation element along the [0-11] plane direction axis, which is the crystal plane orientation, high modulation efficiency can be obtained, thus enabling miniaturization of semiconductor optical integrated devices.

[0011] Furthermore, in the path of light propagation from the light input section to the light output section, high optical gain can be obtained by placing the optical amplification element in the pre-stage and post-stage of the phase modulation element, respectively, thereby enabling low power consumption of the optical integrated element. However, there is a problem that the modulation signal is distorted and the desired optical modulation signal cannot be obtained.

[0012] This disclosure was made to solve the problems described above, and aims to provide a semiconductor optical integrated device with high phase modulation efficiency and the ability to obtain modulated optical signals with low distortion.

[0013] Solution for solving the problem

[0014] The semiconductor optical integrated element disclosed herein is a semiconductor optical integrated element that amplifies signal light input to a semiconductor substrate. The semiconductor optical integrated element comprises: a light input section disposed grounded to a first end face of the semiconductor substrate, for inputting the signal light; a first optical amplifier disposed on the semiconductor substrate and in contact with the light input section, for amplifying the signal light input from the contacted light input section along an optical waveguide; a passive optical waveguide section disposed on the semiconductor substrate, for propagating the signal light amplified by the first optical amplifier in a light propagation direction different from the direction of the optical waveguide; and a phase modulator disposed on the semiconductor substrate for modulating the passive optical waveguide. The signal light propagating in the optical waveguide is phase-modulated; a second optical amplifier, disposed on the semiconductor substrate, amplifies the signal light propagating in the light propagation direction by the passive optical waveguide and whose phase is modulated by the phase modulator along a direction of the optical waveguide different from the light propagation direction; and an optical output section, grounded to a first end face of the semiconductor substrate, in contact with the second optical amplifier, outputting the signal light amplified by the contacted second optical amplifier along a direction of the optical waveguide different from the light propagation direction, wherein the optical waveguide length of the second optical amplifier in contact with the optical output section is shorter than the optical waveguide length of the first optical amplifier.

[0015] The effects of the invention

[0016] According to the semiconductor optical integrated element based on this disclosure, the optical waveguides of the first optical amplifier and the second optical amplifier are configured such that their directions are different from those of the optical waveguide of the phase modulator, and the second optical amplifier configured on the optical output side has a smaller saturation light output than the first optical amplifier configured on the optical input side. Therefore, it achieves the effect of high phase modulation efficiency and low distortion of the modulated optical signal. Attached Figure Description

[0017] Figure 1 This is a top view showing a semiconductor optical integrated device based on Embodiment 1.

[0018] Figure 2 This is a top view showing a modified example of the semiconductor optical integrated device based on Embodiment 1.

[0019] Figure 3 This is a cross-sectional view showing the optical amplifier in the semiconductor optical integrated device based on Embodiment 1.

[0020] Figure 4 This is a cross-sectional view showing the phase modulator in the semiconductor optical integrated device based on Embodiment 1.

[0021] Figure 5 This is a cross-sectional view showing the phase modulator in the semiconductor optical integrated device based on Embodiment 1.

[0022] Figure 6 This is a cross-sectional view showing a passive optical waveguide in a semiconductor optical integrated device based on Embodiment 1.

[0023] Figure 7 This is a top view showing a semiconductor optical integrated device based on Embodiment 2.

[0024] Figure 8 This is a top view showing a modified example of a semiconductor optical integrated device based on Embodiment 2.

[0025] Figure 9 This is a cross-sectional view showing the optical amplifier in the semiconductor optical integrated device based on Embodiment 2.

[0026] Figure 10 This is a cross-sectional view showing the optical amplifier in the semiconductor optical integrated device based on Embodiment 2.

[0027] Figure 11 This is a diagram showing the energy band diagram of the multi-quantum-well structure of the optical amplifier in the semiconductor optical integrated device based on Embodiment 2.

[0028] Figure 12 This is a diagram showing the energy band diagram of the multi-quantum-well structure of the optical amplifier in the semiconductor optical integrated device based on Embodiment 2.

[0029] (Explanation of reference numerals in the attached diagram)

[0030] 10: Semiconductor substrate; 10a: First end face; 10b: Second end face; 11: Lower cladding layer; 12: Gain core layer; 13, 21, 31: Upper cladding layer; 14, 22: Contact layer; 15: Current blocking layer; 16: Electrode for optical amplifier; 17, 24, 32: Protective insulating film; 20: Modulation core layer; 23: Electrode for phase modulator; 30: Optical waveguide core layer; 40: Optical input section; 41: Optical output section; 50, 51: Anti-reflective coating; 55: First gain core layer; 56: Second gain core layer; 60: Embedded structure 70: Mesa-type structure; 80: Ridge-type structure; 90: Mesa-type structure for passive optical waveguides; 100, 110, 150, 160: Semiconductor optical integrated devices; 200, 300: First optical amplifier; 201, 301: Second optical amplifier; 202: Phase modulator; 203: First passive optical waveguide; 204: Optical splitter; 205: Optical combiner; 206: Second passive optical waveguide; 400, 410: Multiple quantum well structure; 411: Conductor band; 412: Valence band; 421: Well layer; 422: Barrier layer Detailed Implementation

[0031] Implementation method 1.

[0032] Figure 1 The image shows a top view of a semiconductor optical integrated device 100 based on Embodiment 1.

[0033] The semiconductor optical integrated element 100 based on Embodiment 1 integrates the following components on the surface of a semiconductor substrate 10 formed using group IV semiconductors, group III-V compound semiconductors, group II-VI compound semiconductors, or semiconductors composed of mixed crystals thereof: a first optical amplifier 200 and a second optical amplifier 201, which have the function of amplifying the intensity of light; a phase modulator 202, which has the function of changing the phase of light; a first passive optical waveguide 203, which connects the first optical amplifier 200 and the phase modulator 202 and has the function of propagating light; and a second passive optical waveguide 206, which connects the phase modulator 202 and the second optical amplifier 201 and has the function of propagating light.

[0034] The light input section 40 of the semiconductor optical integrated element 100 is disposed on a first end face 10a, which has been formed into a flat surface by methods such as cleaving or etching. A first optical amplifier 200 is disposed such that one end is connected to the light input section 40. In other words, the end of the first optical amplifier 200 facing the first end face 10a functions as the light input section 40. Furthermore, the aforementioned first end face 10a refers to the side surface of the semiconductor optical integrated element 100.

[0035] Since one end of the first optical amplifier 200 is connected to the first end face 10a, there is no need to set up a passive optical waveguide to guide the signal light from the first end face 10a to the first optical amplifier 200. Therefore, it can achieve the effect of high output of the amplified signal light even with low power consumption.

[0036] Similarly, the second optical amplifier 201 is configured to connect with the light output section 41 disposed on the first end face 10a. In other words, the end of the second optical amplifier 201 facing the first end face 10a functions as the light output section 41.

[0037] The length of the optical amplification region in the second optical amplifier 201, i.e., the optical waveguide length L2 of the second optical amplifier 201, is shorter than the length of the optical amplification region in the first optical amplifier 200, i.e., the optical waveguide length L1 of the first optical amplifier 200. That is, the relationship L1>L2 holds true.

[0038] The technical significance of making the optical waveguide length L2 of the second optical amplifier 201 shorter than the optical waveguide length L1 of the first optical amplifier 200 will be described later.

[0039] Similar to the configuration of the first optical amplifier 200, one end of the second optical amplifier 201 is connected to the first end face 10a. Therefore, there is no need to set up a passive optical waveguide to guide the signal light from the second optical amplifier 201 to the first end face 10a. Thus, the amplified signal light can be amplified with high output even with low power consumption.

[0040] The light propagation direction of the first optical amplifier 200 and the light propagation direction of the second optical amplifier 201 are along the

[011] plane direction axis, which is the crystal plane orientation of the semiconductor. On the other hand, the light propagation direction of the phase modulator 202 is along the [0-11] plane direction axis, which is the crystal plane orientation of the semiconductor.

[0041] That is, the propagation directions of the light from the first optical amplifier 200 and the second optical amplifier 201 are 90° out of phase with the propagation direction of the light from the phase modulator 202.

[0042] An anti-reflective coating 50 is formed on the first end face 10a, which is provided with a light input section 40 and a light output section 41, to cover the light input section 40 and the light output section 41. This anti-reflective coating 50 can prevent the reflected light amplified in the first optical amplifier 200 or the second optical amplifier 201 from interfering with the signal light, thereby suppressing the distortion of the optical modulation signal.

[0043] First, regarding the construction of the first optical amplifier 200 and the second optical amplifier 201, a cross-sectional view showing a plane orthogonal to the direction of light propagation is used. Figure 3 Please provide an explanation.

[0044] The gain core layer 12 is a semiconductor layer that amplifies the input light by injecting current. The lower cladding layer 11 and upper cladding layer 13, respectively disposed above and below the gain core layer 12, are composed of semiconductor layers with a refractive index lower than that of the gain core layer 12, so as to confine the light within the gain core layer 12.

[0045] In order to reduce the resistance when injecting current from the optical amplifier electrode 16 to the lower semiconductor layers, the contact layer 14 is composed of a semiconductor layer with a lower resistance than the upper cladding layer 13.

[0046] The current blocking layer 15 is made of a structure or material that prevents current flow and is a semiconductor layer used to concentrate current in the gain core layer 12. Furthermore, in Figure 3 In the example of the current blocking layer 15, a three-layer structure of a first current blocking layer 15a, a second current blocking layer 15b, and a third current blocking layer 15c is shown. However, the structure of the current blocking layer 15 is not limited to this three-layer structure, as long as it is a semiconductor layer with the function of blocking current.

[0047] The protective insulating film 17 is composed of inorganic insulating films such as oxide films and nitride films, or organic insulating films such as benzocyclobutene (BCB), and is used to prevent the semiconductor layers from being oxidized or deteriorated due to oxygen and water in the atmosphere.

[0048] The first optical amplifier 200 and the second optical amplifier 201, which constitute part of the semiconductor optical integrated element 100 based on Embodiment 1, are composed of an embedded structure 60 in which a current blocking layer 15 is formed on the sidewall of the gain core layer 12. The embedded structure 60 functions as an optical waveguide.

[0049] In the embedded structure 60, the heat generated in the gain core layer 12 is diffused through the current blocking layer 15, which can suppress the gain reduction caused by the temperature rise of the gain core layer 12, thus achieving the effect of enabling the semiconductor optical integrated device 100 to have high output.

[0050] Next, details of the manufacturing methods for the first optical amplifier 200 and the second optical amplifier 201 will be described.

[0051] For example, on a semiconductor substrate 10 composed of an InP substrate with the (100) plane of semiconductor crystal orientation as the substrate surface, metal-organic chemical vapor deposition (MOCVD) is used to epitaxially grow an n-type InP layer with a thickness of 2000 nm that becomes the lower cladding layer 11, a multi-quantum well structure 400 composed of AlGaInAs with a total thickness of 100 nm that functions as the gain core layer 12 of the first optical amplifier 200 and the second optical amplifier 201, and a p-type InP layer with a thickness of 500 nm that becomes part of the upper cladding layer 13.

[0052] Here, the multiple quantum well structure 400 is constructed by repeating pairs of well layers 421 that facilitate light amplification and barrier layers 422 with band gaps larger than those of the well layers 421. In the first optical amplifier 200 and the second optical amplifier 201, for example, eight pairs of well layers 421 and barrier layers 422 in the multiple quantum well structure 400 are provided. The multiple quantum well structure 400 will be described in detail later.

[0053] Furthermore, the lower cladding 11 epitaxially grown in this process can also serve as the lower cladding 11 of the phase modulator 202, the first passive optical waveguide 203, and the second passive optical waveguide 206, as described later.

[0054] Next, using photolithography and etching techniques such as RIE (Reactive Ion Etching), the p-type InP layer, which is part of the upper cladding 13, the gain core layer 12, and the n-type InP layer, which is part of the lower cladding 11, are etched in a manner that preserves the areas where the first optical amplifier 200 and the second optical amplifier 201 are to be formed, in order to form a ridge structure.

[0055] This ridge structure is formed such that the direction of light propagation is along the

[011] plane orientation axis, which is the crystal plane orientation of the semiconductor. In addition, the optical waveguide length L1 along the

[011] plane orientation axis in the ridge structure of the first optical amplifier 200 is set to 500 μm and the optical waveguide width is set to 2 μm. The optical waveguide length L2 along the

[011] plane orientation axis, which is the crystal plane orientation of the semiconductor, in the ridge structure of the second optical amplifier 201 is set to 300 μm and the optical waveguide width is set to 2 μm. This allows the optical waveguide length L2 of the second optical amplifier 201 to be shorter than the optical waveguide length L1 of the first optical amplifier 200.

[0056] The saturated light output of the first optical amplifier 200 and the second optical amplifier 201 is proportional to the input power. Therefore, by setting the optical waveguide length L2 of the second optical amplifier 201 to be shorter than the optical waveguide length L1 of the first optical amplifier 200 as described above, it is possible to achieve a structure in which the saturated light output of the second optical amplifier 201 is smaller than that of the first optical amplifier 200.

[0057] Therefore, although the signal light that gains gain in the optical amplifier that performs optical amplification under large saturation light output is distorted in phase, by applying the structure described above in which the optical waveguide length L2 of the second optical amplifier 201 is shorter than the optical waveguide length L1 of the first optical amplifier 200, a modulated optical signal with less distortion can be obtained from the light output section 41 in the semiconductor optical integrated device 100 based on Embodiment 1.

[0058] Next, in order to establish an embedded structure 60 in which a current blocking layer 15 is formed on the sidewall of the gain core layer 12, a current blocking layer 15 with a layer thickness that matches the height of the ridge structure is formed by epitaxial growth.

[0059] Here, when the current blocking layer 15 is formed in a ridge structure along the [0-11] plane orientation which is the crystal plane orientation of the semiconductor, the crystal growth rate is fast when epitaxially growing towards the (111) plane exposed on the ridge, making it difficult to form a flat current blocking layer 15 on the sidewall of the ridge. As a result, the current cannot be sufficiently concentrated in the gain core layer 12, and the desired light output may not be obtained.

[0060] On the other hand, in the semiconductor optical integrated device 100 based on the present disclosure, the optical waveguide formed by the ridge structure of the first optical amplifier 200 and the second optical amplifier 201 and the embedded structure 60 is formed along the

[011] plane direction axis which is the crystal plane orientation of the semiconductor. As a result, the (111) plane is not exposed at the ridge, so a flat current blocking layer 15 with high current concentration effect can be formed. As a result, high light output can be obtained with low power consumption.

[0061] In the current blocking layer 15, a stacked structure formed by repeatedly stacking a p-type semiconductor layer-n-p-type semiconductor layer or a semi-insulating semiconductor such as an Fe-doped InP layer can be used.

[0062] For example, when the height of the ridge is 700 nm, a three-layer structure consisting of a first current blocking layer 15a composed of a p-type InP layer with a thickness of 100 nm, a second current blocking layer 15b composed of an n-type InP layer with a thickness of 500 nm, and a third current blocking layer 15c composed of a p-type InP layer with a thickness of 500 nm is epitaxially grown from the semiconductor substrate 10 side, thereby forming the current blocking layer 15.

[0063] Next, a 1500 nm thick p-type InP layer, which becomes the upper cladding layer 13, and a 300 nm thick p-type InGaAs layer, which becomes the contact layer 14, are formed by epitaxial growth.

[0064] Furthermore, an electrode 16 for an optical amplifier, composed of metals such as Ti, Au, Pt, Nb, and Ni, is formed on the contact layer 14.

[0065] Furthermore, to prevent deterioration of the semiconductor layer due to oxidation, a protective insulating film 17 composed of silicon dioxide (SiO2) with a thickness of 300 nm is formed using methods such as CVD (Chemical Vapor Deposition), thereby completing a process that achieves a protective insulating film 17 with properties such as... Figure 3 The first optical amplifier 200 and the second optical amplifier 201 are shown in an embedded structure 60 with current blocking layers 15 formed on the sidewalls of the gain core layer 12.

[0066] Next, regarding the phase modulator 202, a cross-sectional view is used, representing a plane orthogonal to the direction of light propagation. Figure 4 and Figure 5 Please provide an explanation.

[0067] Phase modulator 202 applies a voltage to modulation core layer 20 to change the refractive index of signal light that has been amplified by first optical amplifier 200 and guided by first passive optical waveguide 203 in a direction different from the direction of optical waveguide of phase modulator 202, thereby changing the phase and thus performing phase modulation.

[0068] The modulation core layer 20 is a semiconductor layer that changes the phase of propagating light by changing its refractive index when a voltage is applied, and it is formed on the lower cladding layer 11 described above. In order to confine the light within the modulation core layer 20, the upper cladding layer 21 is composed of a semiconductor layer with a refractive index lower than that of the modulation core layer 20.

[0069] In order to reduce the resistance when applying voltage from the phase modulator electrode 23 to each semiconductor layer, the contact layer 22 is composed of a semiconductor layer with a lower resistance than the upper cladding layer 21.

[0070] The protective insulating film 24 is composed of insulating materials such as inorganic insulating films such as oxide films and nitride films, or organic insulating films such as benzocyclobutene (BCB). It is an insulating film used to prevent the semiconductor layers from being oxidized or deteriorated due to oxygen and water in the atmosphere.

[0071] The phase modulator 202, which constitutes part of the semiconductor optical integrated element 100 based on Embodiment 1, is preferably used in... Figure 4 The high platform type structure 70 shown Figure 5The ridge structure 80 shown is any of the structures in the ridge structure 70, which is formed by etching a portion from the contact layer 22 to the lower cladding layer 11 except for the light propagation area, by means of RIE or the like. The ridge structure 80 is formed by etching a portion from the contact layer 22 to the upper cladding layer 21.

[0072] exist Figure 4 In the high-platform structure 70 shown, the refractive index difference between the modulation core layer 20 and the etched area is large, thus enabling strong confinement of light within the modulation core layer 20. Consequently, when the refractive index of the modulation core layer 20 changes, the phase change of the light increases, resulting in high phase modulation efficiency.

[0073] On the other hand, Figure 5 In the ridge structure 80 shown, the sidewalls of the modulation core layer 20 are not exposed, thus suppressing damage to the crystal surface caused by etching or deterioration caused by oxidation. Therefore, it has the effect of reducing the characteristic deviation of the phase modulator 202 and improving its long-term reliability.

[0074] The following describes the manufacturing method of the phase modulator 202.

[0075] On the lower cladding 11 epitaxially grown during the formation of the first optical amplifier 200 and the second optical amplifier 201, a multi-quantum well structure 400 consisting of AlGaInAs (aluminium gallium indium arsenide) with a total layer thickness of 300 nm, which becomes the modulation core layer 20, a p-type InP layer with a layer thickness of 1800 nm that becomes the upper cladding 21, and a p-type InGaAs (indium gallium arsenide) layer with a layer thickness of 300 nm that becomes the contact layer 22 are epitaxially grown.

[0076] Next, in order to form Figure 4 High platform type structure 70 or Figure 5 The ridge structure 80 is selectively etched by etching methods such as RIE, and a 300nm thick SiO2 film, consisting of a phase modulator electrode 23 made of metals such as Ti, Au, Pt, Nb, and Ni, and a protective insulating film 24 that serves to protect the surface of the semiconductor layer, is formed by CVD or other methods.

[0077] In the aforementioned manufacturing process, the phase modulator 202, which has an optical waveguide composed of a mesa-type structure 70 or a ridge-type structure 80, is formed such that the direction of light propagation is along the [0-11] plane orientation axis, which is the crystal plane orientation of the semiconductor. When a voltage is applied to the modulation core layer 20 of the phase modulator 202, the refractive index of the modulation core layer 20 changes due to electro-optic effects such as the Pockels effect, Kerr effect, and quantum confinement Stark effect. When the phase modulator 202 is formed along the light propagation direction, i.e., the direction of the optical waveguide, which is the crystal plane orientation of the semiconductor, the directions of the refractive index changes caused by the Pockels effect and the quantum confinement Stark effect become the same and overlap each other, thus achieving high phase modulation efficiency.

[0078] Next, regarding the first passive optical waveguide 203, a cross-sectional view is used on a plane orthogonal to the direction of light propagation. Figure 6 To enable light to propagate without loss, the optical waveguide core layer 30 is composed of a semiconductor layer with a bandgap energy greater than the photon energy hν of the signal light, and is formed on the lower cladding layer 11.

[0079] The upper cladding layer 31, in order to enclose light within the optical waveguide core layer 30, is composed of a semiconductor layer with a refractive index lower than that of the optical waveguide core layer 30. The protective insulating film 32 is composed of insulating materials such as inorganic insulating films (e.g., oxide films or nitride films) or organic insulating films (e.g., benzocyclobutene (BCB)), and is used to prevent oxidation or deterioration of the semiconductor layers due to the influence of oxygen and water in the atmosphere.

[0080] The first passive optical waveguide 203 does not have the function of changing the intensity and phase of light, so it can also be devoid of electrodes, contact layers, or other structures used to apply current or voltage.

[0081] The first passive optical waveguide 203, which constitutes part of the semiconductor optical integrated element 100 based on Embodiment 1, is configured as a passive optical waveguide high-platform structure 90 formed by etching a portion from the upper cladding 31 to the lower cladding 11 by means of RIE method or the like.

[0082] The direction axis of the propagating light of the first optical amplifier 200 is orthogonal to that of the phase modulator 202, therefore the first passive optical waveguide 203 connecting them requires a curved region. In order to suppress optical loss of the optical waveguide in the curved region, the first passive optical waveguide 203 is preferably a passive optical waveguide with a high-platform structure 90 that strongly seals the light.

[0083] In addition, such as Figure 1As shown, a portion of the first passive optical waveguide 203 may also include an optical splitter 204, which is composed of a multi-mode interference waveguide (MMI) or a directional coupler.

[0084] In this case, a Mach-Zehnder type modulator can be used as a phase modulator 202 inside the semiconductor optical integrated element 100, which can help to miniaturize the optical transceiver.

[0085] Next, details of the manufacturing method of the first passive optical waveguide 203 will be described. Furthermore, the manufacturing method of the second passive optical waveguide 206, described later, is the same.

[0086] On the lower cladding 11 epitaxially grown during the formation of the first optical amplifier 200 and the second optical amplifier 201, an i-type InGaAsP (Indium Gallium Arsenide Phosphide) layer with a thickness of 100 nm, which becomes the optical waveguide core layer 30, and an i-type InP layer with a thickness of 2000 nm, which becomes the upper cladding 31, are epitaxially grown.

[0087] Next, as Figure 6 As shown, a passive optical waveguide high-platform structure 90 is formed by etching the semiconductor layer using methods such as RIE, and a SiO2 film with a thickness of 300 nm is formed as a protective insulating film 32 using methods such as CVD. This protective insulating film 32 is used to protect the surfaces of each semiconductor layer exposed by etching.

[0088] In addition, such as Figure 1 As shown, a portion of the first passive optical waveguide 203 may also include an optical splitter 204 and an optical combiner 205 based on a multi-mode interference waveguide (MMI) or a directional coupler. In this case, a Mach-Zehnder modulator can be easily constructed inside the semiconductor optical integrated element 100, thus contributing to the miniaturization of the optical transceiver.

[0089] The second passive optical waveguide 206, which constitutes part of the semiconductor optical integrated element 100 based on Embodiment 1, is similarly configured as the first passive optical waveguide 203 to be a passive optical waveguide with a high-platform structure 90 formed by etching a portion from the upper cladding 31 to the lower cladding 11 by the RIE method or the like.

[0090] Since the phase modulator 202 is orthogonal to the direction axis of the propagating light of the second optical amplifier 201, the second passive optical waveguide 206 connecting them requires a curved region. In order to suppress optical losses in the curved region, similar to the first passive optical waveguide 203, the second passive optical waveguide 206 is preferably a passive optical waveguide with a high-platform structure 90 that strongly seals the light.

[0091] In addition, such as Figure 1 As shown, when an optical splitter 204 is provided in a part of the first passive optical waveguide 203, in order to combine the multiple branched signal beams into a single signal beam, an optical combiner 205 based on a multimode interference waveguide or directional coupler is provided in a part of the second passive optical waveguide 206.

[0092] Next, from the semiconductor wafer on which multiple semiconductor optical integrated elements 100 are formed, chip separation methods such as cleaving or etching are used to separate the semiconductor optical integrated elements 100 into individual chips so that one end of the first optical amplifier 200 and the second optical amplifier 201 are exposed on the first end face 10a, that is, one end of the first optical amplifier 200 and the second optical amplifier 201 are both connected to the first end face 10a.

[0093] In this chip separation process, the portion of the first optical amplifier 200 exposed on the first end face 10a becomes the light input section 40, and the portion of the second optical amplifier 201 exposed on the first end face 10a becomes the light output section 41. Furthermore, the light input section 40 is one end of the first optical amplifier 200, and the light output section 41 is one end of the second optical amplifier 201.

[0094] An anti-reflective coating 50 is formed on the first end face 10a using a vapor deposition or sputtering method to cover the light input section 40 and the light output section 41. The anti-reflective coating 50 is configured as a layer structure with zero light reflectivity on the first end face 10a by means of a stacked structure of an insulating film composed of oxide films or nitride films of Si, Al, Ta, Nb, etc.

[0095] For example, as described in Patent Document 3, when the optical amplification element is not connected to the end face but is formed inside the chip, a new optical waveguide is required between the optical amplification element and the optical input section, and between the optical amplification element and the optical output section. In this optical waveguide, the core layers of the optical amplification element and the optical waveguide are composed of different refractive indices or film thicknesses, so the interface between the two is optically discontinuous. As a result, part of the signal light is reflected at the interface, generating reflected light that propagates in the opposite direction. The reflected light re-enters the optical amplification element and is amplified, interfering with the signal light, thus causing an undesirable situation that leads to distortion of the optical modulation signal.

[0096] On the other hand, according to the semiconductor optical integrated element 100 based on the present disclosure, at the part of the first optical amplifier 200 and the second optical amplifier 201 that is in contact with the first end face 10a, a structure with zero reflectivity can be realized by the non-reflective coating 50. Therefore, there will be no interference between the amplified reflected light and the signal light, and as a result, the distortion of the optical modulation signal can be suppressed.

[0097] The above explains Figure 1 The semiconductor optical integrated element 100 shown. Figure 2 It means as Figure 1 A top view of a modified example of the semiconductor optical integrated element 100, specifically the semiconductor optical integrated element 110.

[0098] The difference between the semiconductor optical integrated element 100 and the semiconductor optical integrated element 110 is that, in the semiconductor optical integrated element 100, the light input portion 40 and the light output portion 41 are disposed on the same side surface, i.e., the first end surface 10a side, while in the modified semiconductor optical integrated element 110, the light output portion 41 is disposed on the second end surface 10b side facing the first end surface 10a where the light input portion 40 is disposed. An anti-reflective coating 51 is formed on the opposing second end surface 10b. The structure of the anti-reflective coating 51 is the same as that of the anti-reflective coating 50 described above. Other structures are the same as those of the semiconductor optical integrated element 100.

[0099] Since one end of the second optical amplifier 201 is connected to the second end face 10b, there is no need to set up a passive optical waveguide to guide the signal light from the second optical amplifier 201 to the first end face 10a. Therefore, it can achieve the effect of high output of the amplified signal light even with low power consumption.

[0100] According to the structure of the semiconductor optical integrated element 110 as a variant, a light output section 41 is provided on the second end face 10b side facing the side face where the light input section 40 is provided. Therefore, light output can be taken out from the opposing second end face 10b side. Thus, while achieving the same effect as the semiconductor optical integrated element 100, the flexibility of the semiconductor optical integrated element configuration is improved.

[0101] Furthermore, the above description describes the minimum elements required for the operation of the first optical amplifier 200, the second optical amplifier 201, and the phase modulator 202, but ultimately wiring electrodes, wire bonding electrode pads, electrode protective films, etc. are also formed as needed.

[0102] In addition, the order of manufacturing processes for each structure can be changed, and the semiconductor layers, insulating films, electrodes, etc. are not limited to the materials mentioned above. Other materials can be used as long as they can realize the structure of the semiconductor optical integrated elements 100 and 110 disclosed herein.

[0103] In the above, based on the semiconductor optical integrated element of Embodiment 1, the optical waveguides of the first optical amplifier 200 and the second optical amplifier 201 are configured such that their directions are different from the direction of the optical waveguide of the phase modulator 202, and the optical waveguide length L2 of the second optical amplifier 201 is set to be shorter than the optical waveguide length L1 of the first optical amplifier 200. As a result, the saturation light output of the second optical amplifier 201 is smaller than that of the first optical amplifier 200, thus achieving the effect of high phase modulation efficiency and obtaining a modulated optical signal with less distortion.

[0104] Furthermore, according to the semiconductor optical integrated device based on Embodiment 1, the first optical amplifier 200 is configured to be connected to the first end face 10a, and the second optical amplifier 201 is configured to be connected to either the first end face 10a or the second end face 10b. Therefore, it also achieves the effect of achieving high output of the amplified signal light even with low power consumption.

[0105] Implementation method 2.

[0106] Figure 7 The image shows a top view of the semiconductor optical integrated device 150 based on Embodiment 2. Figure 8 The image shows a top view of a semiconductor optical integrated element 160, which is a modified example of the semiconductor optical integrated element 150.

[0107] Figure 7 The semiconductor optical integrated element 150 shown is Figure 8 The difference in the construction of the semiconductor optical integrated element 160 shown is that, in the semiconductor optical integrated element 150, similar to the semiconductor optical integrated element 100 based on Embodiment 1, the optical waveguide length L2 of the second optical amplifier 301 is shorter than the optical waveguide length L1 of the first optical amplifier 300. In contrast, in the semiconductor optical integrated element 160 as a variant, the optical waveguide length of the second optical amplifier 301 is the same as the optical waveguide length L1 of the first optical amplifier 300, that is, the optical waveguide length of both is L1.

[0108] In the semiconductor optical integrated device 150 based on Embodiment 2, the total number of well layers 421 in the multi-quantum well structure 400 constituting the first gain core layer 55 of the first optical amplifier 300 and the multi-quantum well structure 410 constituting the second gain core layer 56 of the second optical amplifier 301 is greater than the total number of well layers 421 constituting the multi-quantum well structure 400 constituting the first gain core layer 55 of the first optical amplifier 300 which is grounded to the first end face 10a of the light input section 40. This is a difference from the semiconductor optical integrated device 100 based on Embodiment 1.

[0109] Similar to the semiconductor optical integrated element 100 based on Embodiment 1, the light propagation direction of the first optical amplifier 300 and the second optical amplifier 301 is along the direction of the

[011] plane direction axis, which is the crystal plane orientation of the semiconductor, and the light propagation direction of the phase modulator 202 is along the direction of the [0-11] plane direction axis, which is the crystal plane orientation of the semiconductor.

[0110] The structure other than the first optical amplifier 300 and the second optical amplifier 301 is the same as the component structure shown in Embodiment 1, and therefore will be omitted in the following description.

[0111] Figure 9 The image shows a cross-sectional view of a first optical amplifier 300, which forms part of the structure of the semiconductor optical integrated element 150 based on Embodiment 2, on a plane orthogonal to the direction of light propagation. Figure 10 The figure shows a cross-sectional view of the second optical amplifier 301 on a plane orthogonal to the direction of light propagation.

[0112] The total number of well layers 421 in the multi-quantum well structure 400 constituting the first gain core layer 55 of the first optical amplifier 300 is set to be less than the total number of well layers 421 in the multi-quantum well structure 410 constituting the second gain core layer 56 of the second optical amplifier 301.

[0113] Figure 11 The diagram shows an energy band diagram of a multi-quantum well structure 400 comprising a first gain core layer 55 and six well layers 421, including adjacent regions, that constitutes the first optical amplifier 300. Figure 12 The diagram shows an energy band diagram of a multi-quantum well structure 410 comprising eight layers, including adjacent regions, of the second gain core layer 56 and well layers 421 that constitute the second optical amplifier 301.

[0114] exist Figure 11 and Figure 12 In the energy band diagram, the upper line represents the conduction band 411 of each semiconductor layer, and the lower line represents the valence band 412 of each semiconductor layer. Figure 11 The energy band diagram shows that the multi-quantum well structure 400 constituting the first gain core layer 55 is composed of six alternately formed well layers 421 and seven barrier layers 422. The multi-quantum well structure 400 is connected to the lower cladding layer 11 and the upper cladding layer 13.

[0115] Figure 12 The energy band diagram shows that the multi-quantum well structure 410 constituting the second gain core layer 56 is composed of eight alternately formed well layers 421 and nine barrier layers 422. The multi-quantum well structure 410 is connected to the lower cladding layer 11 and the upper cladding layer 13.

[0116] Generally, the gain in an optical amplifier is increased by increasing the optical confinement factor to the gain core. On the other hand, the saturated light output is proportional to the power input to the optical amplifier; therefore, a low optical confinement factor to the gain core results in a high saturated light output. Furthermore, the more quantum well layers in a multi-quantum-well structure, the higher the optical confinement factor to the gain core becomes, thus resulting in a lower saturated light output.

[0117] Therefore, by making the total number of well layers 421 in the multi-quantum well structure 410 constituting the second gain core layer 56 of the second optical amplifier 301 greater than the total number of well layers 421 in the multi-quantum well structure 400 constituting the first gain core layer 55 of the first optical amplifier 300, it is possible to achieve a structure with a smaller saturation light output of the second optical amplifier 301, resulting in a modulated optical signal with less distortion.

[0118] exist Figure 8 In the semiconductor optical integrated element 160 shown as a modified example of the semiconductor optical integrated element 150, as described above, the optical waveguide length of the second optical amplifier 301 is the same as the optical waveguide length L1 of the first optical amplifier 300.

[0119] In the semiconductor optical integrated element 160, it is also designed such that the saturated light output of the second optical amplifier 301 is less than the saturated light output of the first optical amplifier 300. Therefore, by applying the design of the multi-quantum well structures 400 and 410 of the first gain core layer 55 and the second gain core layer 56, that is, by making the total number of well layers 421 of the multi-quantum well structure 410 constituting the second gain core layer 56 of the second optical amplifier 301 greater than the total number of well layers 421 of the multi-quantum well structure 400 constituting the first gain core layer 55 of the first optical amplifier 300, even if the optical waveguide length of the first optical amplifier 300 and the optical waveguide length of the second optical amplifier 301 are the same, it is possible to achieve a structure with a smaller saturated light output of the second optical amplifier 301.

[0120] As an example of a semiconductor optical integrated element 160, for instance, if the total number of well layers 421 of the multi-quantum-well construction 400 constituting the first gain core layer 55 of the first optical amplifier 300 is as follows: Figure 11 The band structure is set to 6 layers as shown in the diagram. On the other hand, the total number of well layers 421 of the multi-quantum well structure 410 constituting the second gain core layer 56 of the second optical amplifier 301 is as follows: Figure 12 If the band structure is set to 8 layers as shown in the diagram, it is possible to achieve a structure in which the second optical amplifier 301, which has a larger total number of well layers 421 than the first optical amplifier 300, has a smaller saturation light output. As a result, a modulated optical signal with less distortion can be obtained.

[0121] In the semiconductor optical integrated device 160, in addition to achieving the same effect as the semiconductor optical integrated device 150, the design of the semiconductor optical integrated device is made easier by making the optical waveguide lengths of the first optical amplifier 300 and the second optical amplifier 301 the same.

[0122] Based on the semiconductor optical integrated element 150 and semiconductor optical integrated element 160 of Embodiment 2, the optical waveguides of the first optical amplifier 300 and the second optical amplifier 301 are configured such that their directions are different from the optical waveguide direction of the phase modulator 202. Furthermore, the total number of well layers 421 in the multi-quantum well structure 410 constituting the second gain core layer 56 of the second optical amplifier 301 is set such that the total number of well layers 421 in the multi-quantum well structure 400 constituting the first gain core layer 55 of the first optical amplifier 300 is greater than the total number of well layers 421 in the first gain core layer 55 of the first optical amplifier 300. Therefore, it is easy to make the saturation light output of the second optical amplifier 301 less than the saturation light output of the first optical amplifier 300, thus achieving the effect of high phase modulation efficiency and obtaining a modulated optical signal with less distortion.

[0123] This disclosure describes various exemplary embodiments and examples, but the various features, methods, and functions described in one or more embodiments are not limited to the application of a particular embodiment and can be applied to the embodiments individually or in various combinations.

[0124] Therefore, numerous variations not illustrated are conceivable within the scope of the technology disclosed in this application. These include variations of at least one structural element, additions, omissions, and extraction of at least one structural element combined with structural elements from other embodiments.

Claims

1. A semiconductor optical integrated device for amplifying signal light input to a semiconductor substrate, characterized in that it comprises: The light input section is grounded to the first end face of the semiconductor substrate and inputs the signal light. A first optical amplifier is disposed on the semiconductor substrate and in contact with the optical input section, and amplifies the signal light input from the contacted optical input section along the optical waveguide; A passive optical waveguide is disposed on the semiconductor substrate to propagate the signal light amplified by the first optical amplifier in a light propagation direction different from that of the optical waveguide. A phase modulator is disposed on the semiconductor substrate to perform phase modulation on the signal light propagating in the passive optical waveguide. A second optical amplifier is disposed on the semiconductor substrate, which amplifies the signal light propagated by the passive optical waveguide in the direction of light propagation and whose phase has been modulated by the phase modulator along the direction of the optical waveguide, which is different from the direction of light propagation. as well as The light output section is grounded to the first end face of the semiconductor substrate, contacts the second optical amplifier, and outputs the signal light amplified by the second optical amplifier along a direction different from the light propagation direction of the optical waveguide. The waveguide length of the second optical amplifier that is in contact with the optical output section is shorter than the waveguide length of the first optical amplifier.

2. The semiconductor optical integrated device according to claim 1, characterized in that, The optical blockage coefficient of the second optical amplifier is greater than that of the first optical amplifier. The first gain core layer of the first optical amplifier and the second gain core layer of the second optical amplifier are each constructed from multiple quantum wells, and the total number of well layers in the multiple quantum well construction constituting the second gain core layer is greater than the total number of well layers in the multiple quantum well construction constituting the first gain core layer.

3. The semiconductor optical integrated device according to claim 1 or 2, characterized in that, The direction of the optical waveguide of the first optical amplifier is the [011] plane orientation axis as the crystal plane orientation, and the different light propagation directions are the [0-11] plane orientation axes as the crystal plane orientation.

4. The semiconductor optical integrated device according to any one of claims 1 to 3, characterized in that, The optical waveguides of the first optical amplifier and the second optical amplifier are respectively embedded structures with current blocking layers formed on the sidewalls of the gain core layer.

5. The semiconductor optical integrated element according to any one of claims 1 to 4, characterized in that, A non-reflective coating is provided on the first end face.

6. A semiconductor optical integrated element having a first end face and a second end face facing the first end face, characterized in that it comprises: Semiconductor substrate; A first optical amplifier is disposed on the semiconductor substrate, with one end connected to the first end face, and amplifies the signal light input from the first end face along the optical waveguide; A first passive optical waveguide is disposed on the semiconductor substrate and connected to the other end of the first optical amplifier to guide the amplified signal light in a direction different from that of the optical waveguide. An optical splitter, disposed in the first passive optical waveguide, splits the signal light of the guided wave into multiple signal lights; A phase modulator is disposed on the semiconductor substrate and connected to the first passive optical waveguide, which has multiple branches, to perform phase modulation on the multiple signal lights along the different directions. A second passive optical waveguide is disposed on the semiconductor substrate, with one end connected to the phase modulator, and guides the phase-modulated signal light from the different directions toward the optical waveguide. An optical combiner, disposed in the second passive optical waveguide, combines multiple phase-modulated signal beams into a single signal beam; as well as A second optical amplifier is disposed on the semiconductor substrate with one end connected to the other end of the second passive optical waveguide and the other end connected to either the first end face or the second end face. It amplifies the signal light guided by the second passive optical waveguide along the direction of the waveguide and outputs the amplified signal light to the outside. The optical blockage coefficient of the second optical amplifier is greater than that of the first optical amplifier. The optical waveguide lengths of the first optical amplifier and the second optical amplifier are the same. The first gain core layer of the first optical amplifier and the second gain core layer of the second optical amplifier are each constructed from multiple quantum wells, and the total number of quantum wells constituting the second gain core layer is greater than the total number of quantum wells constituting the first gain core layer.

7. A semiconductor optical integrated element having a first end face and a second end face facing the first end face, characterized in that it comprises: Semiconductor substrate; A first optical amplifier is disposed on the semiconductor substrate, with one end connected to the first end face, and amplifies the signal light input from the first end face along the optical waveguide; A first passive optical waveguide is disposed on the semiconductor substrate and connected to the other end of the first optical amplifier to guide the amplified signal light in a direction different from that of the optical waveguide. An optical splitter, disposed in the first passive optical waveguide, splits the signal light of the guided wave into multiple signal lights; A phase modulator is disposed on the semiconductor substrate and connected to the first passive optical waveguide, which has multiple branches, to perform phase modulation on the multiple signal lights along the different directions. A second passive optical waveguide is disposed on the semiconductor substrate, with one end connected to the phase modulator, and guides the phase-modulated signal light from the different directions toward the optical waveguide. An optical combiner, disposed in the second passive optical waveguide, combines multiple phase-modulated signal beams into a single signal beam; as well as A second optical amplifier is disposed on the semiconductor substrate with one end connected to the other end of the second passive optical waveguide and the other end connected to either the first end face or the second end face. It amplifies the signal light guided by the second passive optical waveguide along the direction of the waveguide and outputs the amplified signal light to the outside. The optical blockage coefficient of the second optical amplifier is greater than that of the first optical amplifier. The optical waveguide length of the second optical amplifier is shorter than that of the first optical amplifier. The first gain core layer of the first optical amplifier and the second gain core layer of the second optical amplifier are respectively constructed from multiple quantum wells, and the total number of well layers in the multiple quantum well construction constituting the second gain core layer is greater than the total number of well layers in the multiple quantum well construction constituting the first gain core layer.

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