Optical modulator and method for manufacturing optical modulator

Abstract

The invention provides an optical modulator and a method for manufacturing the optical modulator, which can reduce the intensity of light input to each waveguide of a Mach-Zehnder modulator. The optical modulator is provided with: a first Mach-Zehnder modulation unit having a first waveguide and a second waveguide; a second Mach-Zehnder modulation unit having a third waveguide and a fourth waveguide; and a third Mach-Zehnder modulation unit optically coupled to the first Mach-Zehnder modulation unit and the second Mach-Zehnder modulation unit. The third Mach-Zehnder modulation unit is provided with: a fifth waveguide having an input end optically coupled to the output end of the first waveguide; a sixth waveguide having an input end optically coupled with the output end of the second waveguide; a seventh waveguide having an input end optically coupled with the output end of the third waveguide; and an eighth waveguide having an input end optically coupled to the output end of the fourth waveguide.

Description

Technical Field

[0001] The present disclosure relates to an optical modulator and a method for manufacturing the optical modulator. Background Art

[0002] Patent document 1 discloses an optical modulator. The optical modulator includes a first Mach-Zehnder modulation unit and a second Mach-Zehnder modulation unit. The first Mach-Zehnder modulation unit includes a first waveguide and a second waveguide. The second Mach-Zehnder modulation unit includes a third waveguide and a fourth waveguide. The output ends of the first waveguide and the second waveguide are optically coupled to a fifth waveguide via an optical coupler. The output ends of the third waveguide and the fourth waveguide are optically coupled to a sixth waveguide via an optical coupler.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2021-33042

[0006] Patent Document 2: U.S. Patent No. 9069223 Summary of the invention

[0007] Problems to be solved by the invention

[0008] In the optical modulator of Patent Document 1, light from an input waveguide propagates in a first waveguide and a second waveguide, and the light propagating in each waveguide is synthesized by an optical coupler. Similarly, light from an input waveguide propagates in a third waveguide and a fourth waveguide, and the light propagating in each waveguide is synthesized by an optical coupler. Then, the light synthesized by the optical coupler is guided to a fifth waveguide and a sixth waveguide. In this case, the intensity of the light propagating in the fifth waveguide is the sum of the intensity of the light propagating in the first waveguide and the intensity of the light propagating in the second waveguide. The intensity of the light propagating in the sixth waveguide is the sum of the intensity of the light propagating in the third waveguide and the intensity of the light propagating in the fourth waveguide. Therefore, in the case of using a Mach-Zehnder modulation section having a fifth waveguide and a sixth waveguide, the intensity of the light input to each waveguide of the Mach-Zehnder modulation section is higher than the intensity of the light propagating in each waveguide from the first waveguide to the fourth waveguide.

[0009] The present disclosure provides an optical modulator capable of reducing the intensity of light input to each waveguide of a Mach-Zehnder modulation section and a method for manufacturing the optical modulator.

[0010] Methods used to solve problems

[0011] An optical modulator according to one aspect of the present disclosure comprises: a first Mach-Zehnder modulation section having a first waveguide and a second waveguide; a second Mach-Zehnder modulation section having a third waveguide and a fourth waveguide; a third Mach-Zehnder modulation section optically coupled to the first Mach-Zehnder modulation section and the second Mach-Zehnder modulation section; and an optical coupler optically coupled to the third Mach-Zehnder modulation section, wherein the third Mach-Zehnder modulation section comprises: a fifth waveguide having an input end optically coupled to an output end of the first waveguide; and a third Mach-Zehnder modulation section optically coupled to the output end of the first waveguide. a sixth waveguide having an input end optically coupled to the output end of the second waveguide; a seventh waveguide having an input end optically coupled to the output end of the third waveguide; an eighth waveguide having an input end optically coupled to the output end of the fourth waveguide; a first electrode connected to the fifth waveguide and the sixth waveguide; and a second electrode connected to the seventh waveguide and the eighth waveguide, the optical coupler being optically coupled to the output ends of the fifth waveguide, the sixth waveguide, the seventh waveguide and the eighth waveguide.

[0012] Effects of the Invention

[0013] According to the present disclosure, an optical modulator capable of reducing the intensity of light input to each waveguide of a Mach-Zehnder modulation section and a method for manufacturing the optical modulator are provided.

[0014] Description of Reference Numerals

[0015] Figure 1 It is a top view schematically showing a light modulator according to one embodiment.

[0016] Figure 2 is along Figure 1 Cross-sectional view along line II-II.

[0017] Figure 3 is along Figure 1 Cross-sectional view along line III-III.

[0018] Figure 4 This is a diagram showing the relationship between the intensity of light propagating in a waveguide and the voltage that can be applied to an electrode connected to the waveguide.

[0019] Figure 5 : is a flowchart showing a method for manufacturing the optical modulator according to the present embodiment.

[0020] Description of Reference Numerals

[0021] 1: optical modulator;

[0022] 11: substrate;

[0023] 11a: first end;

[0024] 11c: main surface;

[0025] 12: first semiconductor layer;

[0026] 13: core layer;

[0027] 14: second semiconductor layer;

[0028] 15: third semiconductor layer;

[0029] 16: fourth semiconductor layer;

[0030] 17: fourth semiconductor layer;

[0031] 18: resin layer;

[0032] 19: resin layer;

[0033] 20: Insulation film;

[0034] 21: Insulating film;

[0035] 22: sixth semiconductor layer;

[0036] 23: core layer;

[0037] 24: seventh semiconductor layer;

[0038] C1: optical filter;

[0039] C2: Optocoupler;

[0040] C3: Optocoupler;

[0041] C4: Optocoupler;

[0042] C5: Optocoupler;

[0043] C6: Optocoupler;

[0044] C7: Optocoupler;

[0045] C8: Optocoupler;

[0046] C9: Optocoupler;

[0047] C9a: optical coupler (first optical coupler);

[0048] C9b: optical coupler (second optical coupler);

[0049] C9c: optical coupler (third optical coupler);

[0050] E1a: electrode (third electrode);

[0051] E1b: Wiring;

[0052] E1c: electrode pad;

[0053] E2a: electrode (fourth electrode);

[0054] E2b: Wiring;

[0055] E2c: electrode pad;

[0056] E3a: electrode (fifth electrode);

[0057] E3b: Wiring;

[0058] E3c: electrode pad;

[0059] E4a: electrode (sixth electrode);

[0060] E4b: Wiring;

[0061] E4c: electrode pad;

[0062] E5a: electrode (first electrode);

[0063] E5b: Wiring;

[0064] E5c: electrode pad;

[0065] E6a: electrode (second electrode);

[0066] E6b: Wiring;

[0067] E6c: electrode pad;

[0068] E7: ground electrode;

[0069] G1: curve graph;

[0070] M1: first light modulation unit;

[0071] M2: second optical modulation unit;

[0072] MZ1: The first Mach-Zehnder modulation unit;

[0073] MZ2: Second Mach-Zehnder modulation unit;

[0074] MZ3: The third Mach-Zehnder modulation unit;

[0075] P1: input port;

[0076] P2: first output port;

[0077] P3: second output port;

[0078] W1: input waveguide;

[0079] W2: waveguide;

[0080] W3: waveguide;

[0081] W4: waveguide;

[0082] W5: waveguide;

[0083] W6: waveguide;

[0084] W7: waveguide;

[0085] W8: waveguide;

[0086] W9a: first output waveguide;

[0087] W9b: second output waveguide;

[0088] W10: waveguide (first waveguide);

[0089] W11: waveguide (second waveguide);

[0090] W12: waveguide (third waveguide);

[0091] W13: waveguide (fourth waveguide);

[0092] W14: waveguide (fifth waveguide);

[0093] W15: waveguide (sixth waveguide);

[0094] W16: waveguide (the seventh waveguide);

[0095] W17: waveguide (eighth waveguide);

[0096] W18: waveguide (ninth waveguide);

[0097] W19: waveguide;

[0098] W20: waveguide;

[0099] W21: Waveguide. DETAILED DESCRIPTION

[0100] [Description of Embodiments of the Present Disclosure]

[0101] First, the contents of the embodiments of the present disclosure will be listed and described.

[0102] (1) An optical modulator according to one embodiment includes: a first Mach-Zehnder modulator having a first waveguide and a second waveguide; a second Mach-Zehnder modulator having a third waveguide and a fourth waveguide; a third Mach-Zehnder modulator optically coupled to the first Mach-Zehnder modulator and the second Mach-Zehnder modulator; and an optical coupler optically coupled to the third Mach-Zehnder modulator, the third Mach-Zehnder modulator including: a fifth waveguide having an input end optically coupled to an output end of the first waveguide; a sixth waveguide having an input end optically coupled to an output end of the second waveguide; a seventh waveguide having an input end optically coupled to an output end of the third waveguide; and an eighth waveguide having an input end optically coupled to an output end of the fourth waveguide; a first electrode connected to the fifth waveguide and the sixth waveguide; and a second electrode connected to the seventh waveguide and the eighth waveguide, the optical coupler optically coupled to the output ends of the fifth waveguide, the sixth waveguide, the seventh waveguide, and the eighth waveguide.

[0103] According to the optical modulator of this embodiment, the intensity of light input to each waveguide of the third Mach-Zehnder modulation unit (each of the fifth waveguide to the eighth waveguide) can be reduced.

[0104] (2) In addition to the above (1), the optical modulator may further include a ninth waveguide connecting the output end of the first waveguide and the input end of the fifth waveguide, the upper cladding of the ninth waveguide includes a semiconductor layer of the first conductivity type, and the upper cladding of each of the first waveguide and the fifth waveguide includes a semiconductor layer of the second conductivity type.

[0105] (3) In the above (1) or (2), the optical coupler may include: a first optical coupler optically coupled to the output end of the fifth waveguide and the output end of the sixth waveguide; a second optical coupler optically coupled to the output end of the seventh waveguide and the output end of the eighth waveguide; and a third optical coupler optically coupled to the first optical coupler and the second optical coupler.

[0106] (4) The manufacturing method of the optical modulator involved in this embodiment includes the following steps: preparing an optical modulator described in any one of (1) to (3) above, wherein the optical modulator also has: a third electrode connected to the first waveguide, a fourth electrode connected to the second waveguide, a fifth electrode connected to the third waveguide, and a sixth electrode connected to the fourth waveguide; adjusting the voltage applied to the third electrode and the fourth electrode; adjusting the voltage applied to the fifth electrode and the sixth electrode; adjusting the voltage applied to the first electrode based on the adjustment result of the voltage applied to the third electrode and the fourth electrode; adjusting the voltage applied to the second electrode based on the adjustment result of the voltage applied to the fifth electrode and the sixth electrode; adjusting the voltage applied to the third electrode and the fourth electrode based on the adjustment result of the voltage applied to the first electrode; and adjusting the voltage applied to the fifth electrode and the sixth electrode based on the adjustment result of the voltage applied to the second electrode.

[0107] [Details of the embodiments of the present disclosure]

[0108] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the accompanying drawings, the same reference numerals are used for the same or equivalent elements, and repeated descriptions are omitted. In the accompanying drawings, the X-axis direction, the Y-axis direction, and the Z-axis direction that intersect each other are indicated as needed. The X-axis direction, the Y-axis direction, and the Z-axis direction are, for example, orthogonal to each other.

[0109] Figure 1 Schematically showing a top view of the optical modulator involved in the present embodiment. The optical modulator 1 can, for example, modulate the intensity of light or the phase of light in optical communication to generate a modulated signal. The optical modulator 1 may also include an input port P1, a substrate 11, an input waveguide W1, a waveguide W2, a waveguide W3, a waveguide W4, a waveguide W5, a waveguide W6, a waveguide W7, a waveguide W8, an optical filter C1, an optical coupler C2, an optical coupler C3, an optical coupler C4, an optical coupler C5, an optical coupler C6, an optical coupler C7, an optical coupler C8, an optical coupler C9, a first optical modulation unit M1, a second optical modulation unit M2, a first output waveguide W9a, a first output port P2, a second output waveguide W9b, and a second output port P3. The optical modulator 1 may not include the optical coupler C4, the optical coupler C7, the optical coupler C8, the second optical modulation unit M2, the second output waveguide W9b, and the second output port P3.

[0110] The substrate 11 extends in the X-axis direction and the Y-axis direction. When viewed from the Z-axis direction, the substrate 11 may also be substantially rectangular. When viewed from the Z-axis direction, an input port P1 is provided at the first end 11a of the substrate 11 in the X-axis direction. The input port P1 is located at the center of the first end 11a of the substrate 11 in the Y-axis direction.

[0111] An input waveguide W1 is provided on the substrate 11. The input end of the input waveguide W1 is connected to the input port P1. For example, the input end of the input waveguide W1 is the input port P1. The output end of the input waveguide W1 is optically coupled to the input end of the optical filter C1. The output end of the optical filter C1 is optically coupled to the input end of the waveguide W2. The optical filter C1 is, for example, a coupler with one input and one output. The output end of the waveguide W2 is optically coupled to the input end of the optical coupler C2. The output end of the optical coupler C2 is optically coupled to the input end of the waveguide W3 and the input end of the waveguide W4. The optical coupler C2 is, for example, an MMI (Multi-Mode Interface) coupler with one input and two outputs.

[0112] The output end of waveguide W3 is optically coupled to the input end of optical coupler C3. The two output ends of optical coupler C3 are optically coupled to the input end of waveguide W5 and the input end of waveguide W6, respectively. The output end of waveguide W4 is optically coupled to the input end of optical coupler C4. The two output ends of optical coupler C4 are optically coupled to the input end of waveguide W7 and the input end of waveguide W8, respectively. Optical coupler C3 and optical coupler C4 are, for example, MMI couplers with one input and two outputs.

[0113] The output end of waveguide W5 is optically coupled to the input end of optical coupler C5. The output end of waveguide W6 is optically coupled to the input end of optical coupler C6. The output end of waveguide W7 is optically coupled to the input end of optical coupler C7. The output end of waveguide W8 is optically coupled to the input end of optical coupler C8.

[0114] The first optical modulator M1 and the second optical modulator M2 are provided on the substrate 11. The first optical modulator M1 and the second optical modulator M2 are configured to sandwich the input waveguide W1 in the Y-axis direction. The first optical modulator M1 and the second optical modulator M2 are, for example, IQ optical modulators. The first optical modulator M1 and the second optical modulator M2 each include a first Mach-Zehnder modulator MZ1, a second Mach-Zehnder modulator MZ2, and a third Mach-Zehnder modulator MZ3.

[0115] The first Mach-Zehnder modulation section MZ1 has a waveguide W10 (first waveguide), a waveguide W11 (second waveguide), an electrode E1a (third electrode), and an electrode E2a (fourth electrode). The waveguide W10 and the waveguide W11 are respectively the first branch waveguide and the second branch waveguide of the first Mach-Zehnder modulation section MZ1. The waveguide W10 and the waveguide W11 are arranged on the substrate 11 and have a height in the Z-axis direction. The input end of the waveguide W10 and the input end of the waveguide W11 are respectively optically coupled to the two output ends of the optical coupler C5. The optical coupler C5 is, for example, an MMI coupler with one input and two outputs.

[0116] The electrode E1a is connected to the waveguide W10. The electrode E1a is provided on the waveguide W10. The electrode E1a applies a voltage to the waveguide W10. The electrode E1a is electrically connected to the electrode pad E1c via the wiring E1b. A voltage is applied to the electrode pad E1c by a power source (not shown).

[0117] The electrode E2a is connected to the waveguide W11. The electrode E2a is provided on the waveguide W11. The electrode E2a applies a voltage to the waveguide W11. The electrode E2a is electrically connected to the electrode pad E2c via the wiring E2b. A voltage is applied to the electrode pad E2c by a power source (not shown).

[0118] The second Mach-Zehnder modulation section MZ2 has a waveguide W12 (third waveguide), a waveguide W13 (fourth waveguide), an electrode E3a (fifth electrode), and an electrode E4a (sixth electrode). The waveguide W12 and the waveguide W13 are respectively the first branch waveguide and the second branch waveguide of the second Mach-Zehnder modulation section MZ2. The waveguide W12 and the waveguide W13 are arranged on the substrate 11 and have a height in the Z-axis direction. The input end of the waveguide W12 and the input end of the waveguide W13 are respectively optically coupled to the two output ends of the optical coupler C6. The optical coupler C6 is, for example, an MMI coupler with one input and two outputs.

[0119] The electrode E3a is connected to the waveguide W12. The electrode E3a is provided on the waveguide W12. The electrode E3a applies a voltage to the waveguide W12. The electrode E3a is electrically connected to the electrode pad E3c via the wiring E3b. A voltage is applied to the electrode pad E3c by a power source (not shown).

[0120] The electrode E4a is connected to the waveguide W13. The electrode E4a is provided on the waveguide W13. The electrode E4a applies a voltage to the waveguide W13. The electrode E4a is electrically connected to the electrode pad E4c via the wiring E4b. A voltage is applied to the electrode pad E4c by a power source (not shown).

[0121] The third Mach-Zehnder modulation unit MZ3 has a waveguide W14 (fifth waveguide), a waveguide W15 (sixth waveguide), a waveguide W16 (seventh waveguide), a waveguide W17 (eighth waveguide), an electrode E5a (first electrode), and an electrode E6a (second electrode). The waveguide W14 and the waveguide W15 are spaced apart from each other and extend. The waveguide W16 and the waveguide W17 are spaced apart from each other and extend. The waveguide W14 and the waveguide W15 function as a first branch waveguide of the third Mach-Zehnder modulation unit MZ3. The waveguide W16 and the waveguide W17 function as a second branch waveguide of the third Mach-Zehnder modulation unit MZ3. The waveguide W14, the waveguide W15, the waveguide W16, and the waveguide W17 are provided on the substrate 11 and have a height in the Z-axis direction.

[0122] The input end of waveguide W14 is optically coupled to the output end of waveguide W10. The input end of waveguide W15 is optically coupled to the output end of waveguide W11.

[0123] The input end of waveguide W16 is optically coupled to the output end of waveguide W12. The input end of waveguide W17 is optically coupled to the output end of waveguide W13.

[0124] The electrode E5a is connected to the waveguide W14 and the waveguide W15. The electrode E5a includes a first portion E5a1 provided on the waveguide W14, a second portion E5a2 provided on the waveguide W15, and a third portion E5a3 connecting the first portion and the second portion. The electrode E5a applies a voltage to the waveguide W14 and the waveguide W15. The electrode E5a is electrically connected to the electrode pad E5c via the wiring E5b. A voltage is applied to the electrode pad E5c by a power supply (not shown).

[0125] The electrode E6a is connected to the waveguide W16 and the waveguide W17. The electrode E6a includes a first portion E6a1 provided on the waveguide W16, a second portion E6a2 provided on the waveguide W17, and a third portion (not shown) connecting the first portion and the second portion. The electrode E6a applies a voltage to the waveguide W16 and the waveguide W17. The electrode E6a is electrically connected to the electrode pad E6c via the wiring E6b. A voltage is applied to the electrode pad E6c by a power supply (not shown).

[0126] Reference Figure 2 , the structures of waveguide W14, waveguide W15, waveguide W16, and waveguide W17 are further described in detail. Figure 2 is along Figure 1 The cross-sectional view of the II-II line. Figure 2 , cross sections of waveguide W14, waveguide W15, waveguide W16, and waveguide W17 are shown.

[0127] like Figure 2As shown, waveguide W14, waveguide W15, waveguide W16, and waveguide W17 each have an n-type (first conductive type) first semiconductor layer 12 arranged on a substrate 11, a core layer 13 arranged on the first semiconductor layer 12, a p-type (second conductive type) second semiconductor layer 14 arranged on the core layer 13, and a third semiconductor layer 15 arranged on the second semiconductor layer 14.

[0128] In the present embodiment, the fourth semiconductor layer 16 and the fourth semiconductor layer 17 are provided on the main surface 11c of the substrate 11 so as to be spaced apart from each other in the Y-axis direction. The fourth semiconductor layer 16 is provided between the main surface 11c and the first semiconductor layer 12 of the waveguide W14 and the first semiconductor layer 12 of the waveguide W15. The fourth semiconductor layer 17 is provided between the main surface 11c and the first semiconductor layer 12 of the waveguide W16 and the first semiconductor layer 12 of the waveguide W17. On the main surface 11c of the substrate 11, the fourth semiconductor layer 16, the fourth semiconductor layer 17, the first semiconductor layer 12, the core layer 13, the second semiconductor layer 14, and the third semiconductor layer 15 are provided in this order.

[0129] The first semiconductor layer 12 constitutes the lower cladding of each of the waveguides W14, W15, W16, and W17. The second semiconductor layer 14 constitutes the upper cladding of each of the waveguides W14, W15, W16, and W17. The third semiconductor layer 15 constitutes the upper contact of each of the waveguides W14, W15, W16, and W17. The fourth semiconductor layer 16 and the fourth semiconductor layer 17 constitute the lower contact of each of the waveguides W14, W15, W16, and W17. The core layer 13 of the waveguide W14, the core layer 13 of the waveguide W15, the core layer 13 of the waveguide W16, and the core layer 13 of the waveguide W17 are arranged to be spaced apart from each other in the Y-axis direction.

[0130] The substrate 11 is, for example, a semi-insulating semiconductor substrate. The substrate 11 includes a III-V compound semiconductor doped with an insulating dopant. The substrate 11 includes, for example, indium phosphide (InP) doped with iron (Fe).

[0131] The first semiconductor layer 12 includes a III-V compound semiconductor doped with an n-type dopant. The first semiconductor layer 12 includes, for example, InP doped with silicon (Si). The second semiconductor layer 14 includes a III-V compound semiconductor doped with a p-type dopant. The second semiconductor layer 14 includes, for example, indium gallium arsenide (InGaAs) or InP doped with zinc (Zn). The third semiconductor layer 15 includes a III-V compound semiconductor doped with a p-type dopant. The third semiconductor layer 15 has a p-type dopant concentration higher than the p-type dopant concentration of the second semiconductor layer 14. The third semiconductor layer 15 may also include a semiconductor material different from the semiconductor material of the second semiconductor layer 14. The third semiconductor layer 15 includes, for example, InGaAs or InP doped with silicon (Si). The fourth semiconductor layer 16 and the fourth semiconductor layer 17 include a III-V compound semiconductor doped with an n-type dopant. The fourth semiconductor layer 16 and the fourth semiconductor layer 17 have an n-type dopant concentration higher than the n-type dopant concentration of the first semiconductor layer 12. The fourth semiconductor layers 16 and 17 include, for example, InP doped with silicon (Si).

[0132] The core layer 13 is an i-type semiconductor layer, that is, an undoped semiconductor layer. The core layer 13 may have a multi-quantum well structure. The core layer 13 includes, for example, a III-V compound semiconductor of the aluminum gallium indium arsenide (AlGaInAs) system.

[0133] Resin layers 18 and 19 and insulating films 20 and 21 are also provided on the main surface 11c of the substrate 11. The resin layer 18 is provided on the main surface 11c. The resin layer 18 is provided to fill the waveguides W14, W15, W16, W17 and the fourth semiconductor layer 16 and the fourth semiconductor layer 17. That is, the waveguides W14, W15, W16, W17 and the fourth semiconductor layer 16 and the fourth semiconductor layer 17 are covered by the resin layer 18. The insulating film 20 is provided on the resin layer 18. The resin layer 19 is provided on the insulating film 20. The resin layer 19 is provided to fill the electrode E5a and the electrode E6a. That is, the electrode E5a and the electrode E6a are covered by the resin layer 19. The insulating film 21 is provided on the resin layer 19.

[0134] The resin layers 18 and 19 include, for example, benzocyclobutene (BCB). The insulating films 20 and 21 are, for example, protective films including inorganic materials. The insulating films 20 and 21 are, for example, protective films including silicon oxide (SiO2). Alternatively, the insulating films 20 and 21 may also be protective films including silicon oxynitride (SiON).

[0135] The third semiconductor layer 15 and the second semiconductor layer 14 of the waveguide W14 are connected to an electrode E5a. Similarly, the third semiconductor layer 15 and the second semiconductor layer 14 of the waveguide W15 are connected to an electrode E5a. The electrode E5a is in ohmic contact with each corresponding third semiconductor layer 15. The electrode E5a includes, for example, a platinum (Pt) layer, a titanium (Ti) layer, and a gold (Au) layer.

[0136] As described above, the wiring E5b is connected to the electrode E5a. Figure 2 As shown, the wiring E5b is connected to the electrode E5a through the resin layer 19 and the insulating film 21. The wiring E5b includes, for example, a titanium tungsten (TiW) layer, a Pt layer, and an Au layer.

[0137] A ground electrode (not shown) is provided at a position separated from the waveguide W14 and the waveguide W15 and on the fourth semiconductor layer 16. The ground electrode includes, for example, an alloy layer of Au, germanium (Ge), and nickel (Ni), a Ti layer, a Pt layer, and an Au layer. The ground electrode is electrically connected to the fourth semiconductor layer 16.

[0138] The third semiconductor layer 15 and the second semiconductor layer 14 of the waveguide W16 are connected to an electrode E6a. Similarly, the third semiconductor layer 15 and the second semiconductor layer 14 of the waveguide W17 are connected to an electrode E6a. The electrode E6a is in ohmic contact with each corresponding third semiconductor layer 15. The electrode E6a includes, for example, a platinum (Pt) layer, a titanium (Ti) layer, and a gold (Au) layer.

[0139] As described above, the wiring E6b is connected to the electrode E6a. Although not shown in the figure, the wiring E6b penetrates the resin layer 19 and the insulating film 21 and is connected to the electrode E6a in the same manner as the wiring E5b. The wiring E6b includes, for example, a titanium tungsten (TiW) layer, a Pt layer, and an Au layer.

[0140] A ground electrode E7 is provided at a position separated from the waveguides W16 and W17 and on the fourth semiconductor layer 17. The ground electrode E7 includes, for example, an alloy layer of Au, germanium (Ge), and nickel (Ni), a Ti layer, a Pt layer, and an Au layer. The ground electrode E7 is electrically connected to the fourth semiconductor layer 17.

[0141] In the third Mach-Zehnder modulation section MZ3, a voltage is applied between the electrode E5a and the ground electrode and between the electrode E6a and the ground electrode E7. For example, a DC reverse bias voltage and an AC voltage are superimposed and applied between the electrode E5a and the ground electrode and between the electrode E6a and the ground electrode E7. As a result, an electrical signal propagates between the electrode E5a and the ground electrode and between the electrode E6a and the ground electrode E7. The refractive index of the waveguide W14, the waveguide W15, the waveguide W16, and the waveguide W17 changes due to the electrical signal. As a result, the phase of the light propagating in the waveguide W14, the waveguide W15, the waveguide W16, and the waveguide W17 is modulated.

[0142] In this embodiment, the waveguide W10 and the waveguide W11 have the same structure as the waveguide W14 and the waveguide W15. That is, each of the waveguide W10 and the waveguide W11 includes an n-type first semiconductor layer 12 provided on the substrate 11, a core layer 13 provided on the first semiconductor layer 12, a p-type second semiconductor layer 14 provided on the core layer 13, and a third semiconductor layer 15 provided on the second semiconductor layer 14.

[0143] In this embodiment, the waveguide W12 and the waveguide W13 have the same structure as the waveguide W16 and the waveguide W17. That is, each of the waveguide W12 and the waveguide W13 includes an n-type first semiconductor layer 12 provided on the substrate 11, a core layer 13 provided on the first semiconductor layer 12, a p-type second semiconductor layer 14 provided on the core layer 13, and a third semiconductor layer 15 provided on the second semiconductor layer 14.

[0144] Although not shown in the figure, the electrode E1a is connected to the third semiconductor layer 15 and the second semiconductor layer 14 of the waveguide W10. The electrode E1a is in ohmic contact with the third semiconductor layer 15 of the waveguide W10. Similarly, the electrode E2a is connected to the third semiconductor layer 15 and the second semiconductor layer 14 of the waveguide W11. The electrode E2a is in ohmic contact with the third semiconductor layer 15 of the waveguide W11. The electrode E1a and the electrode E2a include, for example, a platinum (Pt) layer, a titanium (Ti) layer, and a gold (Au) layer.

[0145] Electrodes (not shown) are provided at positions separated from the waveguides W10 and W11 and on the fourth semiconductor layer 16. The electrodes include, for example, an alloy layer of Au, germanium (Ge), and nickel (Ni), a Ti layer, a Pt layer, and an Au layer. The electrodes are electrically connected to the fourth semiconductor layer 16.

[0146] In the first Mach-Zehnder modulation section MZ1, a voltage is applied between the electrode E1a and the electrode E2a and an electrode not shown in the figure. For example, a DC reverse bias voltage and an AC voltage are superimposed and applied between the electrode E1a and the electrode E2a and an electrode not shown in the figure. As a result, an electrical signal propagates between the electrode E1a and the electrode E2a and an electrode not shown in the figure. The refractive index of the waveguide W10 and the waveguide W11 changes due to the electrical signal. As a result, the phase of the light propagating in the waveguide W10 and the waveguide W11 is modulated.

[0147] Although not shown in the figure, the electrode E3a is connected to the third semiconductor layer 15 and the second semiconductor layer 14 of the waveguide W12. The electrode E3a is in ohmic contact with the third semiconductor layer 15 of the waveguide W12. Similarly, the electrode E4a is connected to the third semiconductor layer 15 and the second semiconductor layer 14 of the waveguide W13. The electrode E4a is in ohmic contact with the third semiconductor layer 15 of the waveguide W13. The electrode E3a and the electrode E4a include, for example, a platinum (Pt) layer, a titanium (Ti) layer, and a gold (Au) layer.

[0148] Electrodes (not shown) are provided at positions separated from the waveguides W12 and W13 and on the fourth semiconductor layer 17. The electrodes include, for example, an alloy layer of Au, germanium (Ge), and nickel (Ni), a Ti layer, a Pt layer, and an Au layer. The electrodes are electrically connected to the fourth semiconductor layer 17.

[0149] In the second Mach-Zehnder modulation section MZ2, a voltage is applied between the electrode E3a and the electrode E4a and an electrode not shown in the figure. For example, a DC reverse bias voltage and an AC voltage are superimposed and applied between the electrode E3a and the electrode E4a and an electrode not shown in the figure. As a result, an electrical signal propagates between the electrode E3a and the electrode E4a and an electrode not shown in the figure. The refractive index of the waveguide W12 and the waveguide W13 changes due to the electrical signal. As a result, the phase of the light propagating in the waveguide W12 and the waveguide W13 is modulated.

[0150] Refer again Figure 1 In this embodiment, the optical coupler C9 includes an optical coupler C9a (first optical coupler), an optical coupler C9b (second optical coupler), and an optical coupler C9c (third optical coupler). The optical coupler C9a, the optical coupler C9b, and the optical coupler C9c are arranged at a position closer to the first end 11a of the substrate 11 than the third Mach-Zehnder modulation unit MZ3 in the X-axis direction.

[0151] The optical coupler C9a is optically coupled to the output end of the waveguide W14 and the output end of the waveguide W15. Specifically, the output end of the waveguide W14 and the output end of the waveguide W15 are optically coupled to the two input ends of the optical coupler C9a, respectively.

[0152] The optical coupler C9b is optically coupled to the output end of the waveguide W16 and the output end of the waveguide W17. Specifically, the output end of the waveguide W16 and the output end of the waveguide W17 are optically coupled to the two input ends of the optical coupler C9b, respectively.

[0153] The output end of the optical coupler C9a and the output end of the optical coupler C9b are optically coupled to the two input ends of the optical coupler C9c, respectively. That is, the optical coupler C9c is optically coupled to the optical coupler C9a and the optical coupler C9b. The optical coupler C9a and the optical coupler C9b are, for example, MMI couplers with two inputs and one output.

[0154] In this embodiment, in the first optical modulation unit M1, two first output waveguides W9a are optically coupled to the two output ends of the optical coupler C9c, respectively. In the second optical modulation unit M2, two second output waveguides W9b are optically coupled to the two output ends of the optical coupler C9c, respectively. The optical coupler C9c is, for example, an MMI coupler with two inputs and two outputs. The two first output waveguides W9a are connected to the two first output ports P2, respectively. For example, the output ends of the first output waveguide W9a are each the first output port P2. The two second output waveguides W9b are connected to the two second output ports P3, respectively. For example, the output ends of the second output waveguide W9b are each the second output port P3.

[0155] The first output port P2 and the second output port P3 are provided at the first end 11a of the substrate 11 in the X-axis direction. The first output port P2 and the second output port P3 are provided to sandwich the input port P1 in the Y-axis direction.

[0156] Next, refer to Figure 3 , the connection method of the waveguide W10, waveguide W11, waveguide W12, waveguide W13 and the corresponding waveguide W14, waveguide W15, waveguide W16, waveguide W17 in this embodiment is further described in detail.

[0157] In this embodiment, the first optical modulator M1 and the second optical modulator M2 also have a waveguide W18 (ninth waveguide), waveguide W19, waveguide W20, and waveguide W21 connecting waveguide W10, waveguide W11, waveguide W12, waveguide W13 and the corresponding waveguides W14, waveguide W15, waveguide W16, and waveguide W17. Figure 3 is along Figure 1 The cross-sectional view of the III-III line. Figure 3 In FIG, cross sections of waveguide W10, waveguide W14, and waveguide W18 are shown. Figure 3In FIG. 1 , structures (electrodes, etc.) on the waveguides W10 , W14 , and W18 are omitted. The waveguides W18 , W19 , W20 , and W21 are provided on the substrate 11 and have a height in the Z-axis direction.

[0158] Waveguide W18 connects the output end of waveguide W10 and the input end of waveguide W14. Specifically, the input end of waveguide W18 is connected to the output end of waveguide W10, and the output end of waveguide W18 is connected to the input end of waveguide W14. Thus, the output end of waveguide W10 is optically coupled to the input end of waveguide W14. The output end of waveguide W10 is optically coupled to the input end of waveguide W14 via waveguide W18. That is, the output end of waveguide W10 and the input end of waveguide W14 are optically coupled without an optical coupler. The length of waveguide W18 can be greater than 10 μm, or less than 2000 μm. In this embodiment, the length of waveguide W18 is specified by the length in the X-axis direction.

[0159] like Figure 3 As shown, the waveguide W18 includes an n-type sixth semiconductor layer 22 provided on the fourth semiconductor layer 16, a core layer 23 provided on the sixth semiconductor layer 22, and an n-type seventh semiconductor layer 24 provided on the core layer 23. No electrode is connected to the waveguide W18.

[0160] The sixth semiconductor layer 22 constitutes the lower cladding layer of the waveguide W18. The seventh semiconductor layer 24 constitutes the upper cladding layer of the waveguide W18. The sixth semiconductor layer 22 and the seventh semiconductor layer 24 include a III-V compound semiconductor doped with an n-type dopant. The sixth semiconductor layer 22 and the seventh semiconductor layer 24 include, for example, InP doped with silicon (Si).

[0161] As described above, the seventh semiconductor layer 24 is an n-type semiconductor layer, and the third semiconductor layer 15 is a p-type semiconductor layer. That is, the upper cladding layers of the waveguide W10, the upper cladding layers of the waveguide W14, and the upper cladding layers of the waveguide W18 are composed of semiconductor layers of different conductivity types.

[0162] The core layer 23 is an i-type semiconductor layer, that is, an undoped semiconductor layer. The core layer 23 may have a multi-quantum well structure. The core layer 23 includes, for example, a III-V compound semiconductor of the aluminum gallium indium arsenide (AlGaInAs) system.

[0163] Waveguide W19 connects the output end of waveguide W11 and the input end of waveguide W15. Specifically, the input end of waveguide W19 is connected to the output end of waveguide W11, and the output end of waveguide W19 is connected to the input end of waveguide W15. Thus, the output end of waveguide W11 is optically coupled to the input end of waveguide W15 via waveguide W19. That is, the output end of waveguide W11 and the input end of waveguide W15 are optically coupled without an optical coupler. The length of waveguide W19 may also be the same as the length of waveguide W18. In this embodiment, the length of waveguide W19 is specified by the length in the X-axis direction.

[0164] Waveguide W20 connects the output end of waveguide W12 and the input end of waveguide W16. Specifically, the input end of waveguide W20 is connected to the output end of waveguide W12, and the output end of waveguide W20 is connected to the input end of waveguide W16. Thus, the output end of waveguide W12 is optically coupled to the input end of waveguide W16 via waveguide W20. That is, the output end of waveguide W12 is optically coupled to the input end of waveguide W16 without an optical coupler. The length of waveguide W20 may also be the same as the length of waveguide W18. In this embodiment, the length of waveguide W20 is specified by the length in the X-axis direction.

[0165] Waveguide W21 connects the output end of waveguide W13 and the input end of waveguide W17. Specifically, the input end of waveguide W21 is connected to the output end of waveguide W13, and the output end of waveguide W21 is connected to the input end of waveguide W17. Thus, the output end of waveguide W13 is optically coupled to the input end of waveguide W17 via waveguide W21. That is, the output end of waveguide W13 is optically coupled to the input end of waveguide W17 without an optical coupler. The length of waveguide W21 may also be the same as the length of waveguide W18. In this embodiment, the length of waveguide W21 is specified by the length in the X-axis direction.

[0166] In the present embodiment, the waveguide W19, the waveguide W20, and the waveguide W21 have the same structure as the waveguide W18. That is, the waveguide W19 includes an n-type sixth semiconductor layer 22 provided on the fourth semiconductor layer 16, a core layer 23 provided on the sixth semiconductor layer 22, and an n-type seventh semiconductor layer 24 provided on the core layer 23. The waveguide W20 and the waveguide W21 each include an n-type sixth semiconductor layer 22 provided on the fourth semiconductor layer 17, a core layer 23 provided on the sixth semiconductor layer 22, and an n-type seventh semiconductor layer 24 provided on the core layer 23.

[0167] Therefore, the upper cladding of the waveguide W11, the upper cladding of the waveguide W15, and the upper cladding of the waveguide W19 are composed of semiconductor layers of different conductivity types. The upper cladding of the waveguide W12, the upper cladding of the waveguide W16, and the upper cladding of the waveguide W20 are composed of semiconductor layers of different conductivity types. The upper cladding of the waveguide W13, the upper cladding of the waveguide W17, and the upper cladding of the waveguide W21 are composed of semiconductor layers of different conductivity types.

[0168] In the optical modulator 1 of the present embodiment, the waveguide W14 has an input end optically coupled to the output end of the waveguide W10. The waveguide W15 has an input end optically coupled to the output end of the waveguide W11. The waveguide W16 has an input end optically coupled to the output end of the waveguide W12. The waveguide W17 has an input end optically coupled to the output end of the waveguide W13. That is, the waveguide W10 and the waveguide W14 are optically coupled to each other in a one-to-one relationship. The waveguide W11 and the waveguide W15 are optically coupled to each other in a one-to-one relationship. The waveguide W12 and the waveguide W16 are optically coupled to each other in a one-to-one relationship. The waveguide W13 and the waveguide W17 are optically coupled to each other in a one-to-one relationship. Therefore, the intensity of light propagating through each waveguide of waveguide W10, waveguide W11, waveguide W12, and waveguide W13 can be made equal to the intensity of light propagating through each waveguide of waveguide W14, waveguide W15, waveguide W16, and waveguide W17. As a result, the intensity of light input to each waveguide W14, waveguide W15, waveguide W16, and waveguide W17 of the third Mach-Zehnder modulation unit MZ3 can be reduced.

[0169] The magnitude of the voltage that can be applied to the waveguide depends on the intensity of the light propagating in the waveguide. Specifically, if the intensity of the light propagating in the waveguide decreases, the voltage that can be applied to the electrode connected to the waveguide increases. Figure 4 , the relationship between the intensity of light propagating in a waveguide and the voltage that can be applied to an electrode connected to the waveguide is described in further detail. Figure 4 This is a graph showing the relationship between the intensity of light propagating in a waveguide and the voltage that can be applied to an electrode connected to the waveguide. The vertical axis is the intensity of light (dBm) and the horizontal axis is the voltage (V).

[0170] exist Figure 4 In FIG. 1 , a graph G1 shows the relationship between the intensity of light having a wavelength of 1530 nm and the maximum voltage that can be applied to an electrode connected to the waveguide when the light propagates in the waveguide at the intensity.

[0171] As shown in the graph G1, if the intensity of light decreases, the maximum voltage that can be applied to the electrode increases. For example, if the intensity of light decreases by 3 dBm, the maximum voltage that can be applied to the electrode increases by about 1 V. Therefore, if the intensity of light propagating in the waveguide can be reduced, the voltage applied to the electrode connected to the waveguide can be increased, thereby expanding the phase range that can be modulated.

[0172] As described above, in the optical modulator 1, the intensity of light input to each waveguide W14, waveguide W15, waveguide W16, and waveguide W17 of the third Mach-Zehnder modulation section MZ3 can be reduced. Therefore, in the optical modulator 1, compared with the optical modulator in which the third Mach-Zehnder modulation section has two branch waveguides, the modulatable phase can be expanded in the third Mach-Zehnder modulation section MZ3. Alternatively, in the optical modulator 1, the intensity of light incident on the input waveguide W1 can be increased while maintaining the modulatable phase range in the same state as the above-mentioned optical modulator. As a result, in the optical modulator 1, the intensity of the output light can be increased.

[0173] Next, refer to Figure 5 , a method for manufacturing the optical modulator involved in this embodiment is described. Figure 5 1 is a flowchart showing a method for manufacturing the optical modulator according to the present embodiment. The optical modulator 1 can be manufactured as follows.

[0174] First, the optical modulator 1 is prepared (step S1). Each waveguide included in the optical modulator 1 can be formed by processing a semiconductor stack by photolithography and etching. Each electrode included in the optical modulator 1 can be formed by lift-off.

[0175] Next, the voltage applied to the electrodes E1a and E2a is adjusted (step S2). In step S2, the voltage applied to the electrodes E1a and E2a is adjusted so that the intensity of the output light at the first output port P2 and the second output port P3 is maximized.

[0176] In the present manufacturing method, the voltages applied to the electrodes E1a and E2a are adjusted, for example, as follows. First, the voltage applied to the electrode E1a is adjusted. At this time, the voltage applied to the electrode E2a is fixed. The voltage applied to the electrode E2a is fixed to 0 V, for example. Next, while changing the value of the voltage applied to the electrode E1a within a predetermined range, the intensity of the output light is measured. The above range is set to, for example, not less than -15 V and not more than 0 V. Next, the voltage value corresponding to the maximum intensity among the measured output light intensities is recorded.

[0177] Next, the voltage applied to the electrode E2a is adjusted in the same manner as the method for adjusting the voltage applied to the electrode E1a. Then, the absolute value of the voltage value recorded in the electrode E1a is compared with the absolute value of the voltage value recorded in the electrode E2a. The voltage value with a smaller absolute value is set as the voltage applied to the corresponding electrode, and the voltage applied to the other electrode is set to 0V. For example, when the absolute value of the voltage value recorded in the electrode E1a is smaller than the absolute value of the voltage value recorded in the electrode E2a, the voltage applied to the electrode E1a is set to the recorded voltage value, and the voltage applied to the electrode E2a is set to 0V.

[0178] It should be noted that in step S2, the voltage applied to the electrodes E3a, E4a, and E6a is fixed to the extinction voltage, and the voltage applied to the electrode E5a is fixed. The extinction voltage is set to, for example, -18 V. The voltage applied to the electrode E5a is fixed to, for example, 0 V.

[0179] Next, the voltage applied to the electrode E3a and the electrode E4a is adjusted (step S3). In step S3, the voltage applied to the electrode E3a and the electrode E4a is adjusted so that the intensity of the output light at the first output port P2 and the second output port P3 is maximized. In the present manufacturing method, for example, the voltage applied to the electrode E3a and the electrode E4a is adjusted in the same manner as step S2 in which the voltage applied to the electrode E1a and the electrode E2a is adjusted.

[0180] Next, based on the adjustment results of the voltages applied to the electrodes E1a, E2a, E3a, and E4a (the results of steps S2 and S3), the voltages applied to the electrodes E5a and E6a are adjusted (step S4). In step S4, based on the adjustment results of the voltages applied to the electrodes E1a, E2a, E3a, and E4a, the voltages applied to the electrodes E5a and E6a are adjusted so that the intensity of the output light at the first output port P2 and the second output port P3 is maximized.

[0181] In the present manufacturing method, the voltage applied to the electrode E5a and the electrode E6a is adjusted, for example, as follows. First, the voltage applied to the electrode E5a is adjusted. At this time, the voltage applied to the electrode E6a is fixed. The voltage applied to the electrode E6a is fixed to 0V, for example. Next, while changing the value of the voltage applied to the electrode E5a within a predetermined range, the intensity of the output light is measured. The above range is set to, for example, above -15V and below 0V. Next, the voltage value corresponding to the maximum intensity among the measured output light intensities is recorded.

[0182] Next, the voltage applied to electrode E6a is adjusted in the same manner as the method for adjusting the voltage applied to electrode E5a. Then, the absolute value of the voltage value recorded in electrode E5a is compared with the absolute value of the voltage value recorded in electrode E6a. The voltage value with a smaller absolute value is set as the voltage applied to the corresponding electrode, and the voltage applied to the other electrode is set to 0V. For example, when the absolute value of the voltage value recorded in electrode E5a is smaller than the absolute value of the voltage value recorded in electrode E6a, the voltage applied to electrode E5a is set to the recorded voltage value, and the voltage applied to electrode E6a is set to 0V. It should be noted that in step S4, the voltages applied to electrode E1a, electrode E2a, electrode E3a, and electrode E4a are set to voltages based on the adjustment results in steps S2 and S3, respectively.

[0183] Next, based on the result of adjusting the voltage applied to the electrodes E5a and E6a, the voltage applied to the electrodes E1a and E2a or the voltage applied to the electrodes E3a and E4a is adjusted again (step S5). In step S5, based on the result of adjusting the voltage applied to the electrodes E5a and E6a, the voltage applied to the electrodes E1a and E2a or the voltage applied to the electrodes E3a and E4a is adjusted again in such a way that the intensity of the output light at the first output port P2 and the second output port P3 is maximized.

[0184] In the present manufacturing method, for example, the voltage applied to the electrodes E1a and E2a or the voltage applied to the electrodes E3a and E4a is readjusted as follows: When the voltage applied to the electrode E5a is set to the voltage value recorded in step S4 and the voltage applied to the electrode E6a is set to 0 V, the voltage applied to the electrodes E1a and E2a is readjusted.

[0185] Specifically, in electrode E1a and electrode E2a, the electrodes set to the voltage values ​​recorded in step S2 are adjusted again. For example, in step S2, when the voltage applied to electrode E1a is set to the recorded voltage value and the voltage applied to electrode E2a is set to 0V, the voltage applied to electrode E1a is adjusted again. In this case, first, while changing the voltage value applied to electrode E1a within a predetermined range, the intensity of the output light is measured again. At this time, the voltages applied to electrode E2a, electrode E3a, and electrode E4a are set to the voltages adjusted in steps S2 and S3, respectively. The above range is set to the same range as step S2, for example. Next, the voltage corresponding to the maximum intensity among the measured output light intensities is set as the voltage applied to electrode E1a.

[0186] On the other hand, when the voltage applied to the electrode E5a is set to 0 V and the voltage applied to the electrode E6a is set to the voltage value recorded in step S4, the voltage applied to the electrodes E3a and E4a is adjusted again in the same manner as the above method. That is, in step S5, the voltage applied to the electrodes E5a and E6a corresponding to the electrodes to which the voltage values ​​recorded in step S4 are set is adjusted again.

[0187] According to the present manufacturing method, it is possible to provide the optical modulator 1 capable of reducing the intensity of light input to each of the waveguides W14 , W15 , W16 , and W17 of the third Mach-Zehnder modulator MZ3 .

[0188] In the optical modulator 1, a voltage is applied to the waveguides W14 and W15 via the electrode E5a, and a voltage is applied to the waveguides W16 and W17 via the electrode E6a. In this case, if the optical modulator 1 is manufactured without going through the above-mentioned step S5, even if the same voltage is applied to the waveguides W14 and W15, the modulation amount of the phase of the light propagating in the waveguides W14 and W15 may be different due to individual differences between the waveguides. The same is true for the waveguides W16 and W17.

[0189] In the present manufacturing method, after the voltage applied to the electrode E5a and the electrode E6a is adjusted, the voltage applied to the electrode E1a and the electrode E2a or the voltage applied to the electrode E3a and the electrode E4a is adjusted again based on the result of the adjustment. Therefore, by re-adjusting the voltage applied to the electrode E1a and the electrode E2a, the difference in the modulation amount of the phase of light due to the individual difference between the waveguide W14 and the waveguide W15 is eliminated. Similarly, by re-adjusting the voltage applied to the electrode E3a and the electrode E4a, the difference in the modulation amount of the phase of light due to the individual difference between the waveguide W16 and the waveguide W17 is eliminated. As a result, according to the present manufacturing method, it is possible to suppress the occurrence of deviations in the modulation amount of the phase of light between the waveguide W14 and the waveguide W15 and the modulation amount of the phase of light between the waveguide W16 and the waveguide W17.

[0190] As mentioned above, although the preferred embodiment of this disclosure was described in detail, this disclosure is not limited to the above embodiment.

[0191] In the above embodiment, the third semiconductor layer 15 is a p-type semiconductor layer, and the seventh semiconductor layer 24 is an n-type semiconductor layer. However, the combination of the conductivity type of the third semiconductor layer 15 and the conductivity type of the seventh semiconductor layer 24 is not limited to the above combination. That is, the third semiconductor layer 15 may also be an n-type semiconductor layer, and the seventh semiconductor layer 24 may also be a p-type semiconductor layer.

[0192] In the above-mentioned embodiment, the waveguide W19, the waveguide W20, and the waveguide W21 have the same structure as the waveguide W18. However, the structures of the waveguide W19, the waveguide W20, and the waveguide W21 are not limited to the above-mentioned structures. That is, the waveguide W19, the waveguide W20, and the waveguide W21 may also have a structure different from that of the waveguide W18.

[0193] In the above-mentioned embodiment, the output end of waveguide W10 is optically coupled to the input end of waveguide W14 via waveguide W18. The output end of waveguide W11 is optically coupled to the input end of waveguide W15 via waveguide W19. The output end of waveguide W12 is optically coupled to the input end of waveguide W16 via waveguide W20. The output end of waveguide W13 is optically coupled to the input end of waveguide W17 via waveguide W21.

[0194] However, the connection method of waveguide W10, waveguide W11, waveguide W12, waveguide W13 and corresponding waveguide W14, waveguide W15, waveguide W16, waveguide W17 is not limited to the above method. For example, the optical modulator 1 may not have at least one of waveguide W18, waveguide W19, waveguide W20, and waveguide W21. In the case where the optical modulator 1 does not have waveguide W18, the output end of waveguide W10 may be directly connected to the input end of waveguide W14. Similarly, the output end of waveguide W11 may be directly connected to the input end of waveguide W15, the output end of waveguide W12 may be directly connected to the input end of waveguide W16, and the output end of waveguide W13 may be directly connected to the input end of waveguide W17.

[0195] In the above-mentioned embodiment, the optical coupler C9 includes the optical coupler C9a, the optical coupler C9b, and the optical coupler C9c. However, the optical coupler C9 only needs to be optically coupled to the output end of the waveguide W14, the output end of the waveguide W15, the output end of the waveguide W16, and the output end of the waveguide W17, and may not include the optical coupler C9a, the optical coupler C9b, and the optical coupler C9c. In this case, the output end of the waveguide W14, the output end of the waveguide W15, the output end of the waveguide W16, and the output end of the waveguide W17 may be optically coupled to the input end of the optical coupler C9. That is, the optical coupler C9 may be an MMI coupler with four inputs and two outputs.

[0196] In the above-mentioned manufacturing method, the voltages applied to the electrodes E1a, E2a, E3a, E4a, E5a, and E6a are adjusted in such a manner that the intensity of the output light at the first output port P2 and the second output port P3 is maximized. However, the voltages applied to the electrodes E1a, E2a, E3a, E4a, E5a, and E6a may not be adjusted in such a manner that the intensity of the output light is maximized.

[0197] For example, the voltages applied to the electrodes E1a, E2a, E3a, E4a, E5a, and E6a may be adjusted so that the intensity of the output light at the first output port P2 and the second output port P3 is minimized. Alternatively, the voltages applied to the electrodes E1a, E2a, E3a, E4a, E5a, and E6a may be adjusted so that the intensity of the output light at the first output port P2 and the second output port P3 is a predetermined value.

[0198] In these cases, in step S2, the voltage applied to the electrodes E1a and E2a may be adjusted so that the intensity of the output light at the first output port P2 and the second output port P3 is minimized or a predetermined value. In step S3, the voltage applied to the electrodes E3a and E4a may be adjusted so that the intensity of the output light at the first output port P2 and the second output port P3 is minimized or a predetermined value. In step S4, based on the adjustment result of the voltage applied to the electrodes E1a, the electrodes E2a, the electrodes E3a, and the electrodes E4a, the voltage applied to the electrodes E5a and E6a may be adjusted so that the intensity of the output light at the first output port P2 and the second output port P3 is minimized or a predetermined value. Alternatively, in step S5, based on the adjustment result of the voltage applied to electrodes E5a and E6a, the voltage applied to electrodes E1a and E2a or the voltage applied to electrodes E3a and E4a is adjusted again in such a manner that the intensity of the output light at the first output port P2 and the second output port P3 is minimized or reaches a predetermined value.

[0199] The embodiments disclosed this time should be considered as illustrative in all aspects and not restrictive. The scope of the present invention is indicated by the claims rather than the above meaning, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. An optical modulator, wherein: The optical modulator comprises: A first Mach-Zehnder modulation section having a first waveguide and a second waveguide; A second Mach-Zehnder modulation section having a third waveguide and a fourth waveguide; a third Mach-Zehnder modulation section optically coupled to the first Mach-Zehnder modulation section and the second Mach-Zehnder modulation section; and an optical coupler optically coupled to the third Mach-Zehnder modulation unit, The third Mach-Zehnder modulation unit comprises: a fifth waveguide having an input end optically coupled to the output end of the first waveguide; a sixth waveguide having an input end optically coupled to the output end of the second waveguide; a seventh waveguide having an input end optically coupled to the output end of the third waveguide; an eighth waveguide having an input end optically coupled to the output end of the fourth waveguide; A first electrode connected to the fifth waveguide and the sixth waveguide; as well as a second electrode connected to the seventh waveguide and the eighth waveguide, The optical coupler is optically coupled to an output end of the fifth waveguide, an output end of the sixth waveguide, an output end of the seventh waveguide, and an output end of the eighth waveguide.

2. The optical modulator according to claim 1, wherein The optical modulator further includes a ninth waveguide connecting the output end of the first waveguide and the input end of the fifth waveguide. The upper cladding layer of the ninth waveguide includes a semiconductor layer of the first conductivity type, The upper cladding layers of each of the first waveguide and the fifth waveguide include a semiconductor layer of the second conductivity type.

3. The optical modulator according to claim 1 or 2, wherein: The optical coupler comprises: a first optical coupler optically coupled to the output end of the fifth waveguide and the output end of the sixth waveguide; a second optical coupler optically coupled to the output end of the seventh waveguide and the output end of the eighth waveguide; as well as The third optical coupler is optically coupled to the first optical coupler and the second optical coupler.

4. A method for manufacturing an optical modulator, wherein: The manufacturing method of the optical modulator comprises the following steps: A light modulator according to claim 1 or 2 is prepared, wherein the light modulator further comprises: a third electrode connected to the first waveguide; a fourth electrode connected to the second waveguide; a fifth electrode connected to the third waveguide; and a sixth electrode connected to the fourth waveguide; adjusting the voltage applied to the third electrode and the fourth electrode; adjusting the voltage applied to the fifth electrode and the sixth electrode; adjusting the voltages applied to the first electrode and the second electrode based on the adjustment results of the voltages applied to the third electrode, the fourth electrode, the fifth electrode, and the sixth electrode; as well as Based on the adjustment result of the voltage applied to the first electrode and the second electrode, the voltage applied to the third electrode and the fourth electrode, or the voltage applied to the fifth electrode and the sixth electrode is adjusted again.

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