Semiconductor optical phase modulator and method of inspecting the same

Abstract

The semiconductor optical phase modulator (1) includes: an optical phase modulation element (3); a first semiconductor optical amplifier (40) for amplifying light input to the optical phase modulation element (3); and a second semiconductor optical amplifier (50) for amplifying the modulation signal light output from the optical phase modulation element (3). The optical input terminal of the semiconductor optical phase modulator (1) is the optical input end face (40a) of the first semiconductor optical amplifier (40). The optical output terminal of the semiconductor optical phase modulator (1) is the optical output end face (50a) of the second semiconductor optical amplifier (50).

Description

Technical Field

[0001] This disclosure relates to semiconductor optical phase modulators and methods for inspecting them. Background Technology

[0002] Japanese Patent No. 6541898 (Patent Document 1) discloses an optical phase modulator. The optical phase modulator includes a QPSK phase modulator, a first semiconductor optical amplifier disposed at the input of the QPSK phase modulator, and a second semiconductor optical amplifier disposed at the output of the QPSK phase modulator.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent No. 6541898 Summary of the Invention

[0006] To input light into the optical phase modulator, the optical input end of the optical phase modulator is optically coupled to the input fiber. To transmit the modulated signal light generated by the optical phase modulator, the optical output end of the optical phase modulator is optically coupled to the output fiber. However, in the optical phase modulator disclosed in Patent Document 1, an input passive waveguide is formed between the optical input end of the optical phase modulator and the first semiconductor optical amplifier, and an output passive waveguide is formed between the optical output end of the optical phase modulator and the second semiconductor optical amplifier. The optical blockage coefficients of both the input and output passive waveguides are greater than those of the first and second semiconductor optical amplifiers. The mode field diameters of the light in both the input and output passive waveguides are small, resulting in large optical coupling losses between the optical phase modulator and the input fiber, and between the optical phase modulator and the output fiber.

[0007] Furthermore, Patent Document 1 discloses a method for inspecting an optical phase modulator as follows: A test light source and an input optical fiber are configured at the optical input end of the optical phase modulator. An output optical fiber and a power meter are configured at the optical output end of the optical phase modulator. Light emitted from the light source is incident on the optical phase modulator via the input optical fiber. Light output from the optical phase modulator is incident on the power meter via the output optical fiber. If the output of the power meter is above the reference output, the optical phase modulator is determined to be a qualified product. Conversely, if the output of the power meter is below the reference output, the optical phase modulator is determined to be a defective product. In this method of inspecting an optical phase modulator, it is necessary to accurately align the input and output optical fibers with the optical phase modulator. However, a significant amount of time is spent on aligning the input and output optical fibers with the optical phase modulator.

[0008] The first aspect of this disclosure aims to provide a semiconductor optical phase modulator capable of reducing optical coupling losses with optical fibers. The second aspect of this disclosure aims to provide a method for inspecting semiconductor optical phase modulators that can shorten the inspection time.

[0009] The disclosed semiconductor optical phase modulator includes: an optical phase modulation element; a first semiconductor optical amplifier for amplifying light input to the optical phase modulation element; and a second semiconductor optical amplifier for amplifying modulated signal light output from the optical phase modulation element. The first semiconductor optical amplifier includes a first core layer having a first multi-quantum well structure. The optical phase modulation element includes a second core layer having a second multi-quantum well structure. The second semiconductor optical amplifier includes a third core layer having a third multi-quantum well structure. The first thickness of the first core layer is less than the second thickness of the second core layer. The number of first well layers in the first multi-quantum well structure is less than the number of second well layers in the second multi-quantum well structure. The third thickness of the third core layer is less than the second thickness of the second core layer. The number of third well layers in the third multi-quantum well structure is less than the number of second well layers in the second multi-quantum well structure. The optical input terminal of the semiconductor optical phase modulator is the optical input end face of the first semiconductor optical amplifier. The optical output terminal of the semiconductor optical phase modulator is the optical output end face of the second semiconductor optical amplifier.

[0010] The inspection method for the semiconductor optical phase modulator disclosed herein includes: applying a positive bias voltage to one of the first semiconductor optical amplifier and the second semiconductor optical amplifier, emitting inspection light from one of the first semiconductor optical amplifier and the second semiconductor optical amplifier; applying a reverse bias voltage to the other of the first semiconductor optical amplifier and the second semiconductor optical amplifier; and comparing the intensity of the inspection light detected in the other of the first semiconductor optical amplifier and the intensity of the reference light.

[0011] Therefore, the optical blockage coefficient of the first semiconductor optical amplifier is smaller than that of the optical phase modulation element, and the optical blockage coefficient of the second semiconductor optical amplifier is also smaller than that of the optical phase modulation element. The mode field diameter of the light in both the first and second semiconductor optical amplifiers increases. The optical coupling loss between the semiconductor optical phase modulator and the input fiber, and between the semiconductor optical phase modulator and the output fiber, can be reduced.

[0012] In the inspection method for semiconductor optical phase modulators disclosed herein, it is not necessary to prepare the inspection light source, input optical fiber, output optical fiber, and power meter independently of the semiconductor optical phase modulator, nor is it necessary to align the inspection light source, input optical fiber, output optical fiber, and power meter with the semiconductor optical phase modulator. Therefore, the inspection time for semiconductor optical phase modulators can be shortened according to the inspection method of this disclosure. Attached Figure Description

[0013] Figure 1 This is a schematic top view of the semiconductor optical phase modulator of Embodiment 1.

[0014] Figure 2 This is a schematic cross-sectional view of the passive waveguide of the semiconductor optical phase modulator according to Embodiment 1.

[0015] Figure 3 This is a schematic cross-sectional view of the optical beam splitter and optical coupler of the semiconductor optical phase modulator of Embodiment 1.

[0016] Figure 4 This is a schematic cross-sectional view of the phase modulation section and the phase adjustment section of the semiconductor optical phase modulator according to Embodiment 1.

[0017] Figure 5 This is a schematic cross-sectional view of the first semiconductor optical amplifier of the semiconductor optical phase modulator of Embodiment 1.

[0018] Figure 6 This is a schematic cross-sectional view of the second semiconductor optical amplifier of the semiconductor optical phase modulator of Embodiment 1.

[0019] Figure 7 This is a control block diagram of the semiconductor optical phase modulation device according to Embodiment 1.

[0020] Figure 8 This is a flowchart illustrating the inspection method of the semiconductor optical phase modulator according to Embodiment 1.

[0021] Figure 9 This is a schematic top view of the semiconductor optical phase modulator of Embodiment 2.

[0022] Figure 10 This is a schematic cross-sectional view of a monitor photodiode of the semiconductor optical phase modulator of Embodiment 2.

[0023] Figure 11 This is a schematic cross-sectional view of a monitor photodiode of the semiconductor optical phase modulator of Embodiment 2.

[0024] Figure 12 This is a flowchart illustrating the inspection method of the semiconductor optical phase modulator according to Embodiment 2.

[0025] Figure 13 This is a schematic top view of the semiconductor optical phase modulator of Embodiment 3.

[0026] Figure 14 This is a schematic cross-sectional view of the third semiconductor optical amplifier of the semiconductor optical phase modulator in Embodiment 3.

[0027] Figure 15This is a flowchart illustrating the inspection method of the semiconductor optical phase modulator according to Embodiment 3.

[0028] (Symbol Explanation)

[0029] 1, 1b, 1c: Semiconductor optical phase modulator; 2: Optical phase modulation device; 3: Optical phase modulation element; 5a: Input fiber; 5b: Output fiber; 7: Controller; 9: Substrate; 9a: First end face; 9b: Second end face; 10: Parent Mach-Zehnder interferometer; 11, 12: First branch waveguide; 13, 23: Optical beam splitter; 14, 24: Optical coupler; 17, 18: Parent phase adjustment section; 20: Child Mach-Zehnder interferometer; 21, 22: Second branch waveguide; 25, 26: Phase modulation section; 27, 28: Child phase adjustment section; 31, 41, 51, 61, 71, 81: Lower cladding; 32, 42, 52, 82: Core layer; 33, 33b, 43, 53, 63, 73, 83: Upper cladding Layers; 34, 44a, 44b, 54a, 54b, 64a, 64b, 74a, 74b, 84a, 84b: Contact layers; 36, 46a, 46b, 56a, 56b, 66a, 66b, 76a, 76b, 86a, 86b: Electrodes; 37: Insulating protective layer; 39, 49: Optical waveguides; 40: First semiconductor optical amplifier; 40a: Optical input end face; 45, 55, 65, 75, 85: Current blocking layers; 45a, 55a, 85a: P-type semiconductor layers; 45b, 55b, 85b: N-type semiconductor layers; 50: Second semiconductor optical amplifier; 50a: Optical output end face; 60, 70: Photodiodes for monitors; 62, 72: Light absorption layers; 80: Third semiconductor optical amplifier. Detailed Implementation

[0030] The embodiments of this disclosure will be described below. Furthermore, the same reference numerals will be used for the same structures, and their descriptions will not be repeated.

[0031] Implementation method 1.

[0032] Reference Figures 1 to 6 The semiconductor optical phase modulator 1 of Embodiment 1 is described below. The semiconductor optical phase modulator 1 mainly includes an optical phase modulation element 3, a first semiconductor optical amplifier 40, a second semiconductor optical amplifier 50, and a substrate 9.

[0033] The substrate 9 is, for example, a semiconductor substrate such as an InP substrate. The substrate 9 includes a first end face 9a and a second end face 9b. The second end face 9b may also be located on the side opposite to the first end face 9a. An optical phase modulation element 3, a first semiconductor optical amplifier 40, and a second semiconductor optical amplifier 50 are formed on the substrate 9.

[0034] The optical phase modulation element 3 is, for example, an IQ (In-phase Quadrature) optical modulation unit capable of four-phase shift modulation (QPSK). The optical phase modulation element 3 includes a parent Mach-Zehnder interferometer 10, two child Mach-Zehnder interferometers 20, phase modulation units 25 and 26, a parent phase adjustment unit 17 and 18, and child phase adjustment units 27 and 28. The parent Mach-Zehnder interferometer 10, the two child Mach-Zehnder interferometers 20, the phase modulation unit 25 and 26, the parent phase adjustment unit 17 and 18, and the child phase adjustment units 27 and 28 may also include a common core layer (core layers 32, 42, and 52) in terms of material and layer structure.

[0035] The Mach-Zehnder interferometer 10 includes two first-branch waveguides 11 and 12, an optical beam splitter 13, and an optical coupler 14.

[0036] like Figure 2 As shown, the first branch waveguides 11 and 12 respectively include a lower cladding 31, a core layer 32, and an upper cladding 33. The first branch waveguides 11 and 12 may also include an insulating protective layer 37.

[0037] A lower cladding layer 31 is formed on the substrate 9. The lower cladding layer 31 is, for example, an n-type InP layer. A core layer 32 is formed on the lower cladding layer 31. The refractive index of the core layer 32 is greater than that of the lower cladding layer 31 and greater than that of the upper cladding layer 33. The core layer 32 is, for example, formed of a semiconductor material such as AlGaInAs. The core layer 32 has, for example, a multiple quantum well (MQW) structure. An upper cladding layer 33 is formed on the core layer 32. The upper cladding layer 33 is, for example, an i-type InP layer. The first branch waveguides 11 and 12 each have a mesa structure.

[0038] An insulating protective layer 37 is formed on the raised platform structure. Specifically, the insulating protective layer 37 is formed on the upper surface and sides of the upper cladding layer 33, the sides of the core layer 32, and the lower cladding layer 31. The insulating protective layer 37 is formed of an inorganic insulating material such as silicon oxide or silicon nitride, or an organic insulating material such as benzocyclobutene (BCB). The insulating protective layer 37 prevents the semiconductor optical phase modulator 1 from contacting oxygen or water contained in the surrounding atmosphere of the semiconductor optical phase modulator 1, thus preventing oxidation or deterioration.

[0039] An optical beamsplitter 13 is formed between the two first branch waveguides 11 and 12 and the first semiconductor optical amplifier 40. The optical beamsplitter 13 splits the light amplified by the first semiconductor optical amplifier 40 and outputs it to the two first branch waveguides 11 and 12. Figure 3As shown, the optical beamsplitter 13, like the first branch waveguides 11 and 12, includes a lower cladding 31, a core layer 32, and an upper cladding 33. The optical beamsplitter 13 is formed of the same material as the first branch waveguides 11 and 12 and has the same layered structure. The optical beamsplitter 13 is, for example, a multimode interference (MMI) beamsplitter. The optical beamsplitter 13 is, for example, a 2×2 MMI beamsplitter. The width of the core layer 32 of the optical beamsplitter 13 is greater than the width of the core layer 32 of each of the two first branch waveguides 11 and 12.

[0040] The two output ports of the optical beamsplitter 13 are connected to the two first branch waveguides 11 and 12. One of the two input ports of the optical beamsplitter 13 is optically coupled to the first semiconductor optical amplifier 40. Specifically, the optical waveguide 39 is connected to one of the two input ports of the optical beamsplitter 13 and the first semiconductor optical amplifier 40. The optical waveguide 39 has the same structure as the first branch waveguides 11 and 12.

[0041] An optical coupler 14 is formed between the two first branch waveguides 11 and 12 and the second semiconductor optical amplifier 50. The optical coupler 14 combines the light transmitted in the two first branch waveguides 11 and 12 and outputs it towards the second semiconductor optical amplifier 50. Figure 3 As shown, the optical coupler 14 is constructed in the same manner as the optical beamsplitter 13. The optical coupler 14 is formed of the same material as the optical beamsplitter 13 and the second branch waveguide, and has the same layered structure. The optical coupler 14 is, for example, an MMI coupler. The optical coupler 14 is, for example, a 2×2 MMI coupler. The width of the core layer 32 of the optical coupler 14 is greater than the width of the core layer 32 of each of the two first branch waveguides 11 and 12.

[0042] The two input ports of the optical coupler 14 are connected to the two first branch waveguides 11 and 12. One of the two output ports of the optical coupler 14 is optically coupled to the second semiconductor optical amplifier 50. Specifically, the optical waveguide 49 is connected to one of the two output ports of the optical coupler 14 and the second semiconductor optical amplifier 50. The optical waveguide 49 has the same structure as the first branch waveguides 11 and 12.

[0043] Two sub-Mach-Zehnder interferometers 20 are respectively connected to two first branch waveguides 11 and 12. The sub-Mach-Zehnder interferometer 20 connected to the first branch waveguide 11 and the phase modulation sections 25 and 26 constitute, for example, a Mach-Zehnder type optical phase modulator for the I channel. The sub-Mach-Zehnder interferometer 20 connected to the first branch waveguide 12 and the phase modulation sections 25 and 26 constitute, for example, a Mach-Zehnder type optical phase modulator for the Q channel. The sub-Mach-Zehnder interferometer 20 includes two second branch waveguides 21 and 22, an optical beamsplitter 23, and an optical coupler 24.

[0044] like Figure 2 As shown, the second branch waveguides 21 and 22 have the same structure as the first branch waveguides 11 and 12, respectively. The second branch waveguides 21 and 22 are formed of the same material as the first branch waveguides 11 and 12 and have the same layered structure.

[0045] An optical beamsplitter 23 is formed between the two second-branch waveguides 21 and 22 and the optical beamsplitter 13. The optical beamsplitter 23 further splits the light that has been split by the optical beamsplitter 13 and outputs it to the two second-branch waveguides 21 and 22. For example... Figure 3 As shown, optical beamsplitter 23 is constructed in the same manner as optical beamsplitter 13. Optical beamsplitter 23 is, for example, an MMI beamsplitter. Optical beamsplitter 23 is, for example, a 2×2 MMI beamsplitter. The two output ports of optical beamsplitter 23 are connected to two second branch waveguides 21 and 22. One of the two input ports of optical beamsplitter 23 is connected to one of the two first branch waveguides 11 and 12.

[0046] Optical coupler 24 is formed between the two second branch waveguides 21 and 22 and optical coupler 14. Optical coupler 24 combines the light transmitted in the two second branch waveguides 21 and 22 and outputs it towards optical coupler 14. Figure 3 As shown, optical coupler 24 is configured similarly to optical coupler 14. Optical coupler 24 is, for example, an MMI coupler. Optical coupler 24 is, for example, a 2×2 MMI coupler. The two input ports of optical coupler 24 are connected to two second branch waveguides 21 and 22. One of the two output ports of optical coupler 24 is connected to one of the two first branch waveguides 11 and 12.

[0047] Phase modulation units 25 and 26 are disposed on the two second branch waveguides 21 and 22. Specifically, phase modulation unit 25 is disposed on second branch waveguide 21. Phase modulation unit 26 is disposed on second branch waveguide 22. Figure 4 As shown, phase modulation units 25 and 26, in addition to a lower cladding layer 31, a core layer 32, and an upper cladding layer 33b, also include a contact layer 34 and an electrode 36. Phase modulation units 25 and 26 may also include an insulating protective layer 37. The upper cladding layer 33b of the phase modulation units 25 and 26 is, for example, a p-type InP layer. The contact layer 34 is, for example, a p-type InGaAs layer, an AuZn layer, or an AuBe layer. The electrode 36 is, for example, formed of a metal such as Ti, Au, Pt, Nb, or Ni. Phase modulation units 25 and 26, for example, have a mesa structure.

[0048] An insulating protective layer 37 is formed on the raised platform structure. Specifically, the insulating protective layer 37 is formed on the side of the contact layer 34, the side of the upper cladding layer 33b, the side of the core layer 32, and the lower cladding layer 31.

[0049] Parent phase adjustment units 17 and 18 are disposed on the two first branch waveguides 11 and 12. Specifically, parent phase adjustment unit 17 is disposed on the first branch waveguide 11. Parent phase adjustment unit 18 is disposed on the first branch waveguide 12. Figure 4 As shown, the parent phase adjustment units 17 and 18 have the same structure as the phase modulation units 25 and 26. The parent phase adjustment units 17 and 18 are formed of the same material as the phase modulation units 25 and 26 and have the same layer structure. For example, the phase provided to the I-channel optical signal and the Q-channel optical signal is adjusted in the parent phase adjustment units 17 and 18 in such a way that the phase difference between the I-channel optical signal output from the first branch waveguide 11 and the Q-channel optical signal output from the first branch waveguide 12 is π / 2 at the input port of the optical coupler 14.

[0050] Sub-phase adjustment units 27 and 28 are disposed on the two second branch waveguides 21 and 22. Specifically, sub-phase adjustment unit 27 is disposed on second branch waveguide 21. Sub-phase adjustment unit 28 is disposed on second branch waveguide 22. Figure 4 As shown, the sub-phase adjustment units 27 and 28 have the same structure as the phase modulation units 25 and 26. The sub-phase adjustment units 27 and 28 are formed of the same material as the phase modulation units 25 and 26 and have the same layer structure.

[0051] A first semiconductor optical amplifier 40 is formed between the optical phase modulation element 3 and the first end face 9a of the substrate 9. The optical input end of the semiconductor optical phase modulator 1 is the optical input end face 40a of the first semiconductor optical amplifier 40. The first semiconductor optical amplifier 40 is optically coupled to the input optical fiber 5a. The optical input end face 40a of the first semiconductor optical amplifier 40 may also be on the same surface as the first end face 9a of the substrate 9. The first semiconductor optical amplifier 40 amplifies the light input to the optical phase modulation element 3.

[0052] like Figure 5 As shown, the first semiconductor optical amplifier 40 includes a lower cladding layer 41, a core layer 42, an upper cladding layer 43, a current blocking layer 45, contact layers 44a and 44b, and electrodes 46a and 46b. The first semiconductor optical amplifier 40 may also include an insulating protective layer 37.

[0053] A lower cladding layer 41 is formed on the substrate 9. The lower cladding layer 41 is, for example, an n-type InP layer. A core layer 42 is formed on the lower cladding layer 41. The refractive index of the core layer 42 is greater than that of the lower cladding layer 41 and greater than that of the upper cladding layer 43. The core layer 42 is, for example, formed of a semiconductor material such as AlGaInAs. The core layer 42 has, for example, a multiple quantum well (MQW) structure. The thickness of the core layer 42 of the first semiconductor optical amplifier 40 is less than the thickness of the core layer 32 of the optical phase modulation element 3. The number of well layers in the core layer 42 of the first semiconductor optical amplifier 40 is less than the number of well layers in the core layer 32 of the optical phase modulation element 3. Therefore, the optical blocking factor of the first semiconductor optical amplifier 40 is less than that of the optical blocking factor of the optical phase modulation element 3. The upper cladding layer 43 is, for example, a p-type InP layer. The first semiconductor optical amplifier 40 has, for example, a mesa structure.

[0054] A current blocking layer 45 is formed on both sides of the core layer 42. The current blocking layer 45 concentrates the current flowing between the electrodes 46a and 46b into the core layer 42. The current blocking layer 45 may include, for example, a p-type semiconductor layer 45a such as p-type InP and an n-type semiconductor layer 45b such as n-type InP. The current blocking layer 45 may also be a semi-insulating layer such as an InP layer with added Fe. The contact layers 44a and 44b may be, for example, an n-type InGaAs layer, an AuZn layer, or an AuBe layer. The electrodes 46a and 46b may be formed of, for example, a metal such as Ti, Au, Pt, Nb, or Ni.

[0055] An insulating protective layer 37 is formed on the raised platform structure. Specifically, the insulating protective layer 37 is formed on the contact layers 44a and 44b, on the side of the upper cladding layer 43, on the side of the current blocking layer 45, and on the lower cladding layer 41.

[0056] The second semiconductor optical amplifier 50 is formed between the optical phase modulation element 3 and the second end face 9b of the substrate 9. The optical output end of the semiconductor optical phase modulator 1 is the optical output end face 50a of the second semiconductor optical amplifier 50. The second semiconductor optical amplifier 50 is optically coupled to the output optical fiber 5b. The optical output end face 50a of the second semiconductor optical amplifier 50 may also be on the same surface as the second end face 9b of the substrate 9. The second semiconductor optical amplifier 50 amplifies the modulation signal light output from the optical phase modulation element 3.

[0057] The second semiconductor optical amplifier 50 is configured in the same way as the first semiconductor optical amplifier 40. Specifically, as follows: Figure 6As shown, the second semiconductor optical amplifier 50 includes a lower cladding layer 51, a core layer 52, an upper cladding layer 53, a current blocking layer 55, contact layers 54a and 54b, and electrodes 56a and 56b. The current blocking layer 55 may include, for example, a p-type semiconductor layer 55a such as p-type InP, and an n-type semiconductor layer 55b such as n-type InP. The current blocking layer 55 may also be a semi-insulating layer such as an InP layer with added Fe. The second semiconductor optical amplifier 50 may also include an insulating protective layer 37. The core layer 42 of the first semiconductor optical amplifier 40 and the core layer 52 of the second semiconductor optical amplifier 50 may also be formed of the same material and have the same layer structure.

[0058] The thickness of the core layer 52 of the second semiconductor optical amplifier 50 is less than the thickness of the core layer 32 of the optical phase modulation element 3. The number of well layers in the core layer 52 of the second semiconductor optical amplifier 50 is less than the number of well layers in the core layer 32 of the optical phase modulation element 3. Therefore, the optical blocking factor of the core layer 52 of the second semiconductor optical amplifier 50 is less than the optical blocking factor of the core layer 32 of the optical phase modulation element 3.

[0059] The second length of the second semiconductor optical amplifier 50 may also be shorter than the first length of the first semiconductor optical amplifier 40. In this specification, the first length of the first semiconductor optical amplifier 40 means the length between the optical input end face 40a and the optical output end face of the first semiconductor optical amplifier 40, and the second length of the second semiconductor optical amplifier 50 means the length between the optical input end face and the optical output end face 50a of the second semiconductor optical amplifier 50.

[0060] Generally, the carrier density within a semiconductor optical amplifier varies depending on the intensity distribution of the light incident on it. The intensity distribution of the light incident on the semiconductor optical amplifier refers to the intensity distribution of the light in a cross-section perpendicular to its direction of travel. Variations in the carrier density within the semiconductor optical amplifier cause variations in its refractive index, resulting in phase distortion in the light amplified by the amplifier. By making the second length of the second semiconductor optical amplifier 50, into which more intense light is incident, shorter than the first length of the first semiconductor optical amplifier 40, the phase distortion caused by the second semiconductor optical amplifier 50 on the modulated signal light output from the optical phase modulation element 3 can be reduced.

[0061] Reference Figure 7The optical phase modulation device 2 includes a semiconductor optical phase modulator 1 and a controller 7. The semiconductor optical phase modulator 1 is connected to the controller 7. The controller 7 can control the voltage applied to the phase modulation units 25 and 26, the voltage applied to the parent phase adjustment units 17 and 18, the voltage applied to the child phase adjustment units 27 and 28, the current injected into the first semiconductor optical amplifier 40, the current injected into the second semiconductor optical amplifier 50, the voltage applied to the first semiconductor optical amplifier 40, and the voltage applied to the second semiconductor optical amplifier 50. The controller 7 can compare the intensity of the test light detected in the other of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50 with the reference light intensity to determine whether the semiconductor optical phase modulator 1 is a qualified product. The controller 7 is, for example, a microcomputer or electronic circuit including a processor.

[0062] The operation of the semiconductor optical phase modulator 1 in this embodiment will be explained.

[0063] The first semiconductor optical amplifier 40 amplifies the light input to the semiconductor optical phase modulator 1. A high-frequency electrical signal is applied to the phase modulation sections 25 and 26, causing a change in the refractive index of the core layer 32 of the phase modulation sections 25 and 26. The sub-Mach-Zehnder interferometer 20, connected to the first branch waveguide 11, outputs an I-channel optical signal. The sub-Mach-Zehnder interferometer 20, connected to the first branch waveguide 12, outputs a Q-channel optical signal. The optical coupler 14 combines the I-channel and Q-channel optical signals. The optical phase modulation element 3 outputs the modulated signal light towards the second semiconductor optical amplifier 50. The second semiconductor optical amplifier 50 amplifies the modulated signal light. Thus, the semiconductor optical phase modulator 1 outputs the modulated signal light.

[0064] Reference Figure 8 This describes the inspection method for the semiconductor optical phase modulator 1 according to Embodiment 1.

[0065] The inspection method for the semiconductor optical phase modulator 1 according to this embodiment includes: emitting inspection light from one of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50 (S1); applying a reverse bias voltage to the other of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50 (S2); and comparing the intensity of the inspection light detected in the other of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50 with the intensity of a reference light (S5). When the semiconductor optical phase modulator 1 includes parent phase adjustment units 17 and 18 and child phase adjustment units 27 and 28, the inspection method for the semiconductor optical phase modulator 1 according to this embodiment further includes: adjusting the voltage applied to the child phase adjustment units 27 and 28 (S3); and adjusting the voltage applied to the parent phase adjustment units 17 and 18 (S4).

[0066] In step S1, for example, a positive bias voltage is applied to one of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50. One of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50 emits amplified natural emission light (ASE light). This ASE light is used as inspection light, and one of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50 functions as the light source for the inspection light.

[0067] In step S2, a reverse bias voltage is applied to the other side of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50. The other side of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50 functions as a photodiode for detecting the intensity of the inspection light. Steps S2 and S1 can be performed either first or last.

[0068] In step S3, the voltage applied to the sub-phase adjustment units 27 and 28 is adjusted. For example, the controller 7 adjusts the voltage applied to the sub-phase adjustment units 27 and 28 in a way that maximizes the intensity of the inspection light detected by the other of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50.

[0069] In step S4, the voltage applied to the parent phase adjustment units 17 and 18 is adjusted. For example, the controller 7 adjusts the voltage applied to the parent phase adjustment units 17 and 18 in a way that maximizes the intensity of the inspection light detected by the other of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50. Steps S3 and S4 can also be repeated.

[0070] In step S5, the controller 7 compares the intensity of the inspection light detected in the other of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50 with the intensity of the reference light. For example, when the intensity of the inspection light is greater than or equal to the intensity of the reference light, the controller 7 determines that the semiconductor optical phase modulator 1 is a qualified product. Conversely, when the intensity of the inspection light is less than the intensity of the reference light, the controller 7 determines that the semiconductor optical phase modulator 1 is a defective product.

[0071] The effectiveness of the semiconductor optical phase modulator 1 and its inspection method in this embodiment will be explained.

[0072] The semiconductor optical phase modulator 1 of this embodiment includes: an optical phase modulation element 3; a first semiconductor optical amplifier 40 for amplifying light input to the optical phase modulation element 3; and a second semiconductor optical amplifier 50 for amplifying modulation signal light output from the optical phase modulation element 3. The first semiconductor optical amplifier 40 includes a first core layer (core layer 42) having a first multi-quantum well structure. The optical phase modulation element 3 includes a second core layer (core layer 32) having a second multi-quantum well structure. The second semiconductor optical amplifier 50 includes a third core layer (core layer 52) having a third multi-quantum well structure. The first thickness of the first core layer is less than the second thickness of the second core layer. The number of first well layers in the first multi-quantum well structure is less than the number of second well layers in the second multi-quantum well structure. The third thickness of the third core layer is less than the second thickness of the second core layer. The number of third well layers in the third multi-quantum well structure is less than the number of second well layers in the second multi-quantum well structure. The optical input terminal of the semiconductor optical phase modulator 1 is the optical input end face 40a of the first semiconductor optical amplifier 40. The optical output terminal of the semiconductor optical phase modulator 1 is the optical output end face 50a of the second semiconductor optical amplifier 50.

[0073] Therefore, the optical blockage coefficient of the first semiconductor optical amplifier 40 is smaller than that of the optical phase modulation element 3, and the optical blockage coefficient of the second semiconductor optical amplifier 50 is also smaller than that of the optical phase modulation element 3. The mode field diameter of the light in both the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50 is increased. The optical coupling loss between the semiconductor optical phase modulator 1 and the input fiber 5a, and the optical coupling loss between the semiconductor optical phase modulator 1 and the output fiber 5b, can be reduced.

[0074] The semiconductor optical phase modulator 1 of this embodiment further includes a substrate 9 on which an optical phase modulation element 3, a first semiconductor optical amplifier 40, and a second semiconductor optical amplifier 50 are mounted. The optical input end face 40a of the first semiconductor optical amplifier 40 is on the same side as the first end face 9a of the substrate 9. The optical output end face 50a of the second semiconductor optical amplifier 50 is on the same side as the second end face 9b of the substrate 9, which is different from the first end face 9a. Therefore, the optical coupling loss between the semiconductor optical phase modulator 1 and the input optical fiber 5a and the optical coupling loss between the semiconductor optical phase modulator 1 and the output optical fiber 5b can be reduced.

[0075] In the semiconductor optical phase modulator 1 of this embodiment, the second length of the second semiconductor optical amplifier 50 is shorter than the first length of the first semiconductor optical amplifier 40. Therefore, the phase distortion caused by the second semiconductor optical amplifier 50 to the modulated signal light output from the optical phase modulation element 3 can be reduced. The semiconductor optical phase modulator 1 can output phase-modulated signal light of higher quality.

[0076] In the semiconductor optical phase modulator 1 of this embodiment, the first core layer (core layer 42) and the third core layer (core layer 52) are formed of the same material and have the same layer structure. Therefore, the core layers of the semiconductor optical phase modulator 1 are formed of two core materials. The number of core layer types in the semiconductor optical phase modulator 1 is reduced, thus lowering the cost of the semiconductor optical phase modulator 1.

[0077] In the semiconductor optical phase modulator 1 of this embodiment, the optical phase modulation element 3 includes a parent Mach-Zehnder interferometer 10, two child Mach-Zehnder interferometers 20, and phase modulation units 25 and 26. The parent Mach-Zehnder interferometer 10 includes two first branch waveguides 11 and 12. The two child Mach-Zehnder interferometers 20 are respectively connected to the two first branch waveguides 11 and 12, and each child Mach-Zehnder interferometer 20 includes two second branch waveguides 21 and 22. The phase modulation units 25 and 26 are disposed on the two second branch waveguides 21 and 22. Therefore, the semiconductor optical phase modulator 1 can output a multi-valued phase modulation signal such as QPSK.

[0078] In the semiconductor optical phase modulator 1 of this embodiment, the optical phase modulation element 3 further includes parent phase adjustment units 17 and 18, and child phase adjustment units 27 and 28. The parent phase adjustment units 17 and 18 are disposed on two first branch waveguides 11 and 12. The child phase adjustment units 27 and 28 are disposed on two second branch waveguides 21 and 22. Therefore, the semiconductor optical phase modulator 1 can output a higher quality multi-valued phase modulation signal.

[0079] The inspection method of the semiconductor optical phase modulator 1 in this embodiment includes: applying a positive bias voltage to one of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50, emitting inspection light from one of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50 (S1); applying a reverse bias voltage to the other of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50 (S2); and comparing the intensity of the inspection light detected in the other of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50 with the intensity of the reference light (S5).

[0080] In the inspection method of the semiconductor optical phase modulator 1 of this embodiment, it is not necessary to prepare the inspection light source, input optical fiber, output optical fiber, and power meter independently of the semiconductor optical phase modulator 1, nor is it necessary to align the inspection light source, input optical fiber, output optical fiber, and power meter with the semiconductor optical phase modulator 1. Therefore, the inspection time of the semiconductor optical phase modulator 1 can be shortened.

[0081] Implementation method 2.

[0082] Reference Figures 9 to 12The semiconductor optical phase modulator 1b of Embodiment 2 will be described. The semiconductor optical phase modulator 1b of this embodiment has the same structure as the semiconductor optical phase modulator 1 of Embodiment 1, but differs mainly in the following aspects.

[0083] Reference Figure 9 The semiconductor optical phase modulator 1b also includes a monitor photodiode 60 and a monitor photodiode 70. The monitor photodiode 60 is optically coupled to the other of the two output ports of the optocoupler 14. The monitor photodiode 70 is optically coupled to the other of the two output ports of the optocoupler 24.

[0084] Reference Figure 10 The monitor photodiode 60 includes a lower cladding layer 61, a light-absorbing layer 62, an upper cladding layer 63, contact layers 64a and 64b, and electrodes 66a and 66b. The monitor photodiode 60 may also include an insulating protective layer 37.

[0085] A lower cladding layer 61 is formed on the substrate 9. The lower cladding layer 61 is, for example, an n-type InP layer. The refractive index of the light-absorbing layer 62 is greater than that of the lower cladding layer 61 and greater than that of the upper cladding layer 63. The light-absorbing layer 62 is, for example, formed of a semiconductor material such as AlGaInAs. The light-absorbing layer 62 has, for example, a multiple quantum well (MQW) structure. The light-absorbing layer 62 of the monitor photodiode 60 can also be formed of the same material as the core layer 42 of the first semiconductor optical amplifier 40 and the core layer 52 of the second semiconductor optical amplifier 50, and has the same layer structure. The upper cladding layer 63 is, for example, a p-type InP layer. The monitor photodiode 60 has, for example, a mesa structure.

[0086] Contact layers 64a and 64b are, for example, n-type InGaAs layers, AuZn layers, or AuBe layers. Electrodes 66a and 66b are formed of, for example, metals such as Ti, Au, Pt, Nb, or Ni. An insulating protective layer 37 is formed on the raised platform structure. Specifically, the insulating protective layer 37 is formed on the contact layers 64a and 64b, on the side surface of the upper cladding 63, and on the lower cladding 61.

[0087] Reference Figure 11The monitor photodiode 70 has the same structure as the monitor photodiode 60. Specifically, the monitor photodiode 70 includes a lower cladding layer 71, a light-absorbing layer 72, an upper cladding layer 73, contact layers 74a and 74b, and electrodes 76a and 76b. The monitor photodiode 70 may also include an insulating protective layer 37. The light-absorbing layer 72 of the monitor photodiode 70 is formed of the same material as the light-absorbing layer 62 of the monitor photodiode 60 and has the same layer structure. The light-absorbing layer 72 of the monitor photodiode 70 may also be formed of the same material as the core layer 42 of the first semiconductor optical amplifier 40 and the core layer 52 of the second semiconductor optical amplifier 50, and have the same layer structure.

[0088] Reference Figure 7 The optical phase modulation device 2 in this embodiment is the same as the optical phase modulation device 2 in Embodiment 1, but it is equipped with a semiconductor optical phase modulator 1b instead of the semiconductor optical phase modulator 1. The controller 7 can receive signals related to the intensity of the inspected light from the monitor photodiodes 60 and 70.

[0089] Reference Figure 12 This section describes the inspection method for the semiconductor optical phase modulator 1b according to Embodiment 2. The inspection method for the semiconductor optical phase modulator 1b in this embodiment includes the same steps as the inspection method for the semiconductor optical phase modulator 1 in Embodiment 1, but differs mainly in the following aspects. The inspection method for the semiconductor optical phase modulator 1b in this embodiment further includes applying a reverse bias voltage to the monitor photodiodes 60 and 70 (S12). In the inspection method for the semiconductor optical phase modulator 1b in this embodiment, after adjusting the voltage applied to the parent phase adjustment units 17 and 18 (S4), a reverse bias voltage is applied to the other side of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50 (S2).

[0090] Specifically, step S1 in this embodiment is the same as step S1 in the previous embodiment. One of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50 functions as a light source for checking light.

[0091] In step S12, a reverse bias voltage is applied to the monitor photodiodes 60 and 70. The monitor photodiodes 60 and 70 can detect inspection light emitted from either the first semiconductor optical amplifier 40 or the second semiconductor optical amplifier 50.

[0092] In step S3, the voltage applied to the sub-phase adjustment units 27 and 28 is adjusted. For example, the controller 7 adjusts the voltage applied to the sub-phase adjustment units 27 and 28 in a way that maximizes the intensity of the inspection light detected by the monitor photodiode 70.

[0093] In step S4, the voltage applied to the parent phase adjustment units 17 and 18 is adjusted. For example, the controller 7 adjusts the voltage applied to the parent phase adjustment units 17 and 18 in a way that maximizes the intensity of the inspection light detected by the monitor photodiode 60.

[0094] Step S2 is performed after step S4. In step S2, a reverse bias voltage is applied to the other side of the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50. Therefore, the first semiconductor optical amplifier 40 and the other side of the second semiconductor optical amplifier 50 function as photodiodes for detecting and checking light.

[0095] Step S5 follows step S2. Step S5 in this embodiment is the same as step S5 in the other embodiment.

[0096] The effects of the semiconductor optical phase modulator 1b in this embodiment will be explained.

[0097] The semiconductor optical phase modulator 1b of this embodiment also includes a first monitor photodiode (monitor photodiode 60) and a second monitor photodiode (monitor photodiode 70). The parent Mach-Zehnder interferometer 10 includes a first 2×2 optical coupler (optical coupler 14) containing a first optical output port and a second optical output port. The first optical output port is optically coupled to the second semiconductor optical amplifier 50. The second optical output port is optically coupled to the first monitor photodiode. The two child Mach-Zehnder interferometers 20 each include a second 2×2 optical coupler (optical coupler 24) containing a third optical output port and a fourth optical output port. The third optical output port is connected to one of the two first branch waveguides 11 and 12 of the parent Mach-Zehnder interferometer 10. The fourth optical output port is optically coupled to the second monitor photodiode.

[0098] Therefore, the parent phase adjustment units 17 and 18 can be adjusted according to the intensity of the detection light detected by the first monitor photodiode (monitor photodiode 60). The child phase adjustment units 27 and 28 can be adjusted according to the intensity of the detection light detected by the second monitor photodiode (monitor photodiode 70). The parent phase adjustment units 17 and 18 and the child phase adjustment units 27 and 28 can be adjusted independently of each other. The parent phase adjustment units 17 and 18 can adjust the optical path length of the two first branch waveguides 11 and 12 more accurately, and the child phase adjustment units 27 and 28 can adjust the optical path length of the two second branch waveguides 21 and 22 more accurately. The semiconductor optical phase modulator 1b can output higher quality phase modulated signal light.

[0099] In the semiconductor optical phase modulator 1b of this embodiment, the first monitor photodiode (monitor photodiode 60) includes a first light-absorbing layer (light-absorbing layer 62) having a fourth multiple quantum well structure. The second monitor photodiode (monitor photodiode 70) includes a second light-absorbing layer (light-absorbing layer 72) having a fifth multiple quantum well structure. The first core layer (core layer 42), the third core layer (core layer 52), the first light-absorbing layer, and the second light-absorbing layer are formed of the same material and have the same layer structure. Therefore, the variety of core layers and light-absorbing layers in the semiconductor optical phase modulator 1b is reduced. The cost of the semiconductor optical phase modulator 1b can be reduced.

[0100] Implementation method 3.

[0101] Reference Figure 13 as well as Figure 14 The semiconductor optical phase modulator 1c of Embodiment 3 will be described. The semiconductor optical phase modulator 1c of this embodiment has the same structure as the semiconductor optical phase modulator 1 of Embodiment 1, but differs mainly in the following aspects.

[0102] The semiconductor optical phase modulator 1c also includes a third semiconductor optical amplifier 80. The other of the two input ports of the optical beam splitter 23 is optically coupled to the third semiconductor optical amplifier 80.

[0103] The third semiconductor optical amplifier 80 is configured in the same way as the first semiconductor optical amplifier 40 and the second semiconductor optical amplifier 50. Specifically, as follows: Figure 14 As shown, the third semiconductor optical amplifier 80 includes a lower cladding layer 81, a core layer 82, an upper cladding layer 83, a current blocking layer 85, contact layers 84a and 84b, and electrodes 86a and 86b. The current blocking layer 85 may include, for example, a p-type semiconductor layer 85a such as p-type InP and an n-type semiconductor layer 85b such as n-type InP. The current blocking layer 85 may also be a semi-insulating layer such as an InP layer with added Fe. The third semiconductor optical amplifier 80 may also include an insulating protective layer 37. The core layer 82 of the third semiconductor optical amplifier 80 may also be formed of the same material as the core layer 42 of the first semiconductor optical amplifier 40 and the core layer 52 of the second semiconductor optical amplifier 50, and have the same layer structure.

[0104] Reference Figure 15 The following describes the inspection method for the semiconductor optical phase modulator 1c according to Embodiment 3. The inspection method for the semiconductor optical phase modulator 1c in this embodiment has the same steps as the inspection method for the semiconductor optical phase modulator 1 in Embodiment 1, but differs mainly in the following aspects.

[0105] Reference Figure 7The optical phase modulation device 2 in this embodiment is the same as the optical phase modulation device 2 in Embodiment 1, but instead of the semiconductor optical phase modulator 1, it is equipped with a semiconductor optical phase modulator 1c. Furthermore, the controller 7 can control the current injected into the third semiconductor optical amplifier 80.

[0106] The inspection method of the semiconductor optical phase modulator 1c according to this embodiment includes: emitting a first inspection light from a first semiconductor optical amplifier 40 and emitting a second inspection light from a third semiconductor optical amplifier 80 (S21); applying a reverse bias voltage to a second semiconductor optical amplifier 50 (S22); and comparing the intensity of the inspection light detected in the second semiconductor optical amplifier 50 with the intensity of a reference light (S25). The intensity of the inspection light is the sum of the first intensity of the first inspection light and the second intensity of the second inspection light. When the semiconductor optical phase modulator 1c has parent phase adjustment units 17 and 18 and child phase adjustment units 27 and 28, the inspection method of the semiconductor optical phase modulator 1c according to this embodiment further includes: adjusting the voltage applied to the child phase adjustment units 27 and 28 (S3); and adjusting the voltage applied to the parent phase adjustment units 17 and 18 (S4).

[0107] Specifically, in step S21, a positive bias voltage is applied to the first semiconductor optical amplifier 40 and the third semiconductor optical amplifier 80. The first semiconductor optical amplifier 40 and the third semiconductor optical amplifier 80 output ASE light. The ASE light emitted from the first semiconductor optical amplifier 40 is used as the first inspection light, and the first semiconductor optical amplifier 40 functions as the first source of the first inspection light. The ASE light emitted from the third semiconductor optical amplifier 80 is used as the second inspection light, and the third semiconductor optical amplifier 80 functions as the second source of the second inspection light.

[0108] In step S22, a reverse bias voltage is applied to the second semiconductor optical amplifier 50. The second semiconductor optical amplifier 50 functions as a photodiode for detecting the intensity of the inspection light. The intensity of the inspection light is the sum of the first intensity of the first inspection light and the second intensity of the second inspection light.

[0109] In step S3, the voltage applied to the sub-phase adjustment units 27 and 28 is adjusted. Specifically, the controller 7 adjusts the voltage applied to the sub-phase adjustment units 27 and 28 in a manner that maximizes the intensity of the inspection light detected by the second semiconductor optical amplifier 50.

[0110] In step S4, the voltage applied to the parent phase adjustment units 17 and 18 is adjusted. Specifically, the controller 7 adjusts the voltage applied to the parent phase adjustment units 17 and 18 in a manner that maximizes the intensity of the inspection light detected by the second semiconductor optical amplifier 50. Steps S3 and S4 can also be repeated.

[0111] In step S25, the controller 7 compares the intensity of the inspection light detected in the second semiconductor optical amplifier 50 with the intensity of the reference light. For example, if the intensity of the inspection light is greater than or equal to the intensity of the reference light, the controller 7 determines that the semiconductor optical phase modulator 1c is a qualified product. Conversely, if the intensity of the inspection light is less than the intensity of the reference light, the controller 7 determines that the semiconductor optical phase modulator 1c is a defective product.

[0112] The effectiveness of the semiconductor optical phase modulator 1c and its inspection method in this embodiment is explained.

[0113] The semiconductor optical phase modulator 1c of this embodiment also includes a third semiconductor optical amplifier 80. The two sub-Mach-Zehnder interferometers 20 each include a second 2×2 optical beamsplitter (optical beamsplitter 23) containing a third optical input port and a fourth optical input port. The third optical input port is connected to one of the two first branch waveguides 11 and 12 of the parent Mach-Zehnder interferometer 10. The fourth optical input port is optically coupled to the third semiconductor optical amplifier 80.

[0114] The inspection light is supplied not only from the first semiconductor optical amplifier 40 but also from the third semiconductor optical amplifier 80. The intensity of the inspection light detected in the second semiconductor optical amplifier 50, which can function as a photodiode, is increased. The semiconductor optical phase modulator 1c can be inspected with higher precision.

[0115] The inspection method for the semiconductor optical phase modulator 1c according to this embodiment includes: applying a positive bias voltage to a first semiconductor optical amplifier 40 and a third semiconductor optical amplifier 80, emitting a first inspection light from the first semiconductor optical amplifier 40, and emitting a second inspection light from the third semiconductor optical amplifier 80 (S21); applying a reverse bias voltage to a second semiconductor optical amplifier 50 (S22); and comparing the intensity of the inspection light detected in the second semiconductor optical amplifier 50 with the intensity of a reference light (S25). The intensity of the inspection light is the sum of the first intensity of the first inspection light and the second intensity of the second inspection light.

[0116] The inspection light is supplied not only from the first semiconductor optical amplifier 40 but also from the third semiconductor optical amplifier 80. The intensity of the inspection light detected in the second semiconductor optical amplifier 50, which can function as a photodiode, is increased. The semiconductor optical phase modulator 1c can be inspected with higher precision.

[0117] The embodiments 1 to 3 disclosed herein are merely illustrative in all respects and should not be considered limiting. At least two of the embodiments 1 to 3 disclosed herein may be combined, provided there is no contradiction. The scope of this disclosure is not defined by the foregoing description but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A semiconductor optical phase modulator, comprising: Optical phase modulation element; A first semiconductor optical amplifier amplifies the light input to the optical phase modulation element; The second semiconductor optical amplifier amplifies the modulated signal light output from the optical phase modulation element; The first monitor uses a photodiode; as well as The second monitor uses a photodiode. in, The first semiconductor optical amplifier includes a first core layer having a first multi-quantum-well structure. The optical phase modulation element includes a second core layer having a second multiple quantum well structure. The second semiconductor optical amplifier includes a third core layer having a third multi-quantum-well structure. The first thickness of the first core layer is less than the second thickness of the second core layer. The first multi-quantum well structure has fewer first well layers than the second multi-quantum well structure. The third thickness of the third core layer is less than the second thickness of the second core layer. The third multi-quantum well structure has fewer third well layers than the second multi-quantum well structure. The optical input terminal of the semiconductor optical phase modulator is the optical input terminal face of the first semiconductor optical amplifier. The optical output terminal of the semiconductor optical phase modulator is the optical output terminal face of the second semiconductor optical amplifier. The optical phase modulation element includes a parent Mach-Zehnder interferometer, two child Mach-Zehnder interferometers, a phase modulation unit, a parent phase adjustment unit, and child phase adjustment units. The parent Mach-Zehnder interferometer includes two first-branch waveguides and a first 2×2 optical coupler containing a first optical output port and a second optical output port. The two sub-Mach-Zehnder interferometers are respectively inserted and connected to the two first branch waveguides, and each of the two sub-Mach-Zehnder interferometers includes two second branch waveguides and a second 2×2 optical coupler containing a third optical output port and a fourth optical output port. The first semiconductor optical amplifier is connected to the parent Mach-Zehnder interferometer. The phase modulation section is disposed on the two second branch waveguides. The parent phase adjustment section is located in the two first branch waveguides. The sub-phase adjustment section is disposed on the two second branch waveguides. The first optical output port is optically coupled to the second semiconductor optical amplifier. The second optical output port is optically coupled to the photodiode of the first monitor. The two third optical output ports are respectively connected to the two first branch waveguides of the parent Mach-Zehnder interferometer. The two fourth optical output ports are optically coupled to different photodiodes for the second monitor.

2. The semiconductor optical phase modulator according to claim 1, wherein, It also includes a substrate equipped with the aforementioned optical phase modulation element, the first semiconductor optical amplifier, and the second semiconductor optical amplifier. The light input end face of the first semiconductor optical amplifier is on the same plane as the first end face of the substrate. The light output end face of the second semiconductor optical amplifier is on the same side as the second end face of the substrate, which is different from the first end face.

3. The semiconductor optical phase modulator according to claim 1 or 2, wherein, The length of the second semiconductor optical amplifier is shorter than the length of the first semiconductor optical amplifier.

4. The semiconductor optical phase modulator according to claim 1 or 2, wherein, The first core layer and the third core layer are formed of the same material and have the same layer structure.

5. The semiconductor optical phase modulator according to claim 1 or 2, wherein, The first monitor photodiode includes a first light-absorbing layer having a fourth multiple quantum well structure. The second monitor photodiode includes a second light-absorbing layer having a fifth multiple quantum well structure. The first core layer, the third core layer, the first light-absorbing layer, and the second light-absorbing layer are formed of the same material and have the same layer structure.

6. The semiconductor optical phase modulator according to claim 1 or 2, wherein, It also features a third semiconductor optical amplifier. The two sub-Mach-Zehnder interferometers each include a second 2×2 optical beamsplitter containing a third optical input port and a fourth optical input port. The third optical input port is optically coupled to one of the two first-branch waveguides of the parent Mach-Zehnder interferometer. The fourth optical input port is optically coupled to the third semiconductor optical amplifier.

7. A method for inspecting a semiconductor optical phase modulator according to any one of claims 1 to 6, comprising: A positive bias voltage is applied to one of the first semiconductor optical amplifier and the second semiconductor optical amplifier, and inspection light is emitted from the one of the first semiconductor optical amplifier and the second semiconductor optical amplifier. A reverse bias voltage is applied to the other side of the first semiconductor optical amplifier and the second semiconductor optical amplifier; as well as The intensity of the test light detected in the first semiconductor optical amplifier and the other of the second semiconductor optical amplifier are compared with the intensity of the reference light.

8. A method for inspecting a semiconductor optical phase modulator as described in claim 6, comprising: A positive bias voltage is applied to the first semiconductor optical amplifier and the third semiconductor optical amplifier, a first inspection light is emitted from the first semiconductor optical amplifier, and a second inspection light is emitted from the third semiconductor optical amplifier; A reverse bias voltage is applied to the second semiconductor optical amplifier; as well as The intensity of the test light detected in the second semiconductor optical amplifier is compared with the intensity of the reference light. The intensity of the inspection light is the sum of the first intensity of the first inspection light and the second intensity of the second inspection light.

9. A semiconductor optical phase modulator, comprising: Optical phase modulation element; A first semiconductor optical amplifier amplifies the light input to the optical phase modulation element; A second semiconductor optical amplifier amplifies the modulated signal light output from the optical phase modulation element; and Third semiconductor optical amplifier in, The first semiconductor optical amplifier includes a first core layer having a first multi-quantum-well structure. The optical phase modulation element includes a second core layer having a second multiple quantum well structure. The second semiconductor optical amplifier includes a third core layer having a third multi-quantum-well structure. The first thickness of the first core layer is less than the second thickness of the second core layer. The first multi-quantum well structure has fewer first well layers than the second multi-quantum well structure. The third thickness of the third core layer is less than the second thickness of the second core layer. The third multi-quantum well structure has fewer third well layers than the second multi-quantum well structure. The optical input terminal of the semiconductor optical phase modulator is the optical input terminal face of the first semiconductor optical amplifier. The optical output terminal of the semiconductor optical phase modulator is the optical output terminal face of the second semiconductor optical amplifier. The optical phase modulation element includes a parent Mach-Zehnder interferometer, two child Mach-Zehnder interferometers, and a phase modulation unit. The parent Mach-Zehnder interferometer includes two first-branch waveguides and a first 2×2 optical coupler containing a first optical output port and a second optical output port. The two sub-Mach-Zehnder interferometers are respectively inserted and connected to the two first branch waveguides, and the two sub-Mach-Zehnder interferometers each include two second branch waveguides and a second 2×2 optical beam splitter containing a third optical input port and a fourth optical input port. The first semiconductor optical amplifier is connected to the parent Mach-Zehnder interferometer. The phase modulation section is disposed on the two second branch waveguides. The first optical output port is optically coupled to the second semiconductor optical amplifier. The two third optical input ports are optically coupled to the two first branch waveguides of the parent Mach-Zehnder interferometer, respectively. The two fourth optical input ports are optically coupled to different third semiconductor optical amplifiers, respectively.

10. A method for inspecting a semiconductor optical phase modulator, wherein, The semiconductor optical phase modulator includes: Optical phase modulation element; A first semiconductor optical amplifier amplifies the light input to the optical phase modulation element; and The second semiconductor optical amplifier amplifies the modulated signal light output from the optical phase modulation element. The first semiconductor optical amplifier includes a first core layer having a first multi-quantum-well structure. The optical phase modulation element includes a second core layer having a second multiple quantum well structure. The second semiconductor optical amplifier includes a third core layer having a third multi-quantum-well structure. The first thickness of the first core layer is less than the second thickness of the second core layer. The first multi-quantum well structure has fewer first well layers than the second multi-quantum well structure. The third thickness of the third core layer is less than the second thickness of the second core layer. The third multi-quantum well structure has fewer third well layers than the second multi-quantum well structure. The optical input terminal of the semiconductor optical phase modulator is the optical input terminal face of the first semiconductor optical amplifier. The optical output terminal of the semiconductor optical phase modulator is the optical output terminal face of the second semiconductor optical amplifier. The inspection method includes: A positive bias voltage is applied to one of the first semiconductor optical amplifier and the second semiconductor optical amplifier, and inspection light is emitted from the one of the first semiconductor optical amplifier and the second semiconductor optical amplifier. A reverse bias voltage is applied to the other side of the first semiconductor optical amplifier and the second semiconductor optical amplifier; as well as The intensity of the test light detected in the first semiconductor optical amplifier and the other of the second semiconductor optical amplifier are compared with the intensity of the reference light.

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