Mach-Zehnder modulator and optical modulation module

Abstract

The present invention provides a Mach-Zehnder modulator and optical modulation module capable of reducing stray light. [Solution] A Mach-Zehnder modulator comprising a first input waveguide and a second input waveguide, a first output waveguide and a second output waveguide, and a first multiplexer, wherein light is input from the first input waveguide and the second input waveguide to the first multiplexer, and the light is output from the first multiplexer to the first output waveguide and the second output waveguide, and the light absorption rate of the second output waveguide is higher than the light absorption rate of the first output waveguide.

Description

[Technical Field]

[0001] This disclosure relates to a Mach-Zehnder modulator and an optical modulation module. [Background technology]

[0002] Mach-Zehnder modulators are known (Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-008275 [Patent Document 2] Japanese Patent Publication No. 2014-164243 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In a Mach-Zehnder modulator, light guided by two branched waveguides is combined at the multiplexing section. The light can be modulated according to the optical path difference between the two waveguides. However, unwanted light can be emitted from the waveguides, resulting in stray light. When stray light propagates within the modulator, it can cause deterioration of the extinction ratio and interference with the signal light. Therefore, the objective is to provide a Mach-Zehnder modulator that can reduce stray light. [Means for solving the problem]

[0005] The Mach-Zehnder modulator according to this disclosure comprises a first input waveguide and a second input waveguide, a first output waveguide and a second output waveguide, and a first multiplexer, wherein light is input from the first input waveguide and the second input waveguide to the first multiplexer, and the light is output from the first multiplexer to the first output waveguide and the second output waveguide, and the light absorption rate of the second output waveguide is higher than the light absorption rate of the first output waveguide. [Effects of the Invention]

[0006] According to the present disclosure, it is possible to provide a Mach-Zehnder modulator and an optical modulation module capable of reducing stray light.

Brief Description of the Drawings

[0007] [Figure 1] FIG. 1 is a plan view illustrating a Mach-Zehnder modulator according to the first embodiment. [Figure 2] FIG. 2 is a plan view illustrating a Mach-Zehnder modulator. [Figure 3A] FIG. 3A is a cross-sectional view taken along line A-A of FIG. 2. [Figure 3B] FIG. 3B is a cross-sectional view taken along line B-B of FIG. 2. [Figure 4] FIG. 4 is a cross-sectional view illustrating a Mach-Zehnder modulator according to the second embodiment. [Figure 5] FIG. 5 is a schematic view illustrating an optical modulation module according to the third embodiment.

Modes for Carrying Out the Invention

[0008] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0009] One aspect of the present disclosure includes (1) a first input waveguide, a second input waveguide, a first output waveguide, a second output waveguide, and a first combiner. Light is input from the first input waveguide and the second input waveguide to the first combiner, and the light is output from the first combiner to the first output waveguide and the second output waveguide. The light absorption rate of the second output waveguide is higher than that of the first output waveguide. Since light is absorbed in the second output waveguide, stray light can be reduced. (2) In the above (1), the first input waveguide, the second input waveguide, the first output waveguide, and the second output waveguide have a first semiconductor layer, a core layer, and a second semiconductor layer. The first semiconductor layer, the core layer, and the second semiconductor layer are laminated in order to form a waveguide mesa. Ions may be implanted into the core layer of the second output waveguide. The core layer of the second output waveguide has a higher absorption rate than the core layer of the first output waveguide. The light propagating through the second output waveguide is absorbed by the core layer. Stray light can be reduced. (3) In the above (2), a first electrode and a second electrode are provided. The first electrode is electrically connected to the first semiconductor layer, and the second electrode may be electrically connected to the second semiconductor layer of each of the first input waveguide and the second input waveguide. By applying a voltage, the phase of light can be adjusted. Even without applying a voltage to the second output waveguide, the light is absorbed by the core layer. Stray light can be reduced. (4) In the above (2) or (3), the concentration of the ions may be 1×10 17 cm -3 or more and 5×10 19 cm -3 or less. Since the light is absorbed, stray light can be reduced. (5) In any of the above (1) to (4), a metal film covering the surface of the second output waveguide may be provided. The light propagating through the second output waveguide is absorbed by the metal film. Stray light can be reduced. (6) In the above (5), the first input waveguide, the second input waveguide, the first output waveguide, and the second output waveguide have a first semiconductor layer, a core layer, and a second semiconductor layer. The first semiconductor layer, the core layer, and the second semiconductor layer are laminated in order to form a waveguide mesa. The metal film may contact the side surface and the upper surface of the waveguide mesa of the second output waveguide. Stray light can be reduced. (7) In the above (5) or (6), the device comprises a first electrode and a second electrode, wherein the first electrode is electrically connected to the first semiconductor layer, and the second electrode is electrically connected to the second semiconductor layer of the first input waveguide and the second input waveguide, and the metal film may be spaced apart from the first electrode and the second electrode. The phase of the light can be adjusted by applying a voltage. The light propagating through the second output waveguide is absorbed by the metal film. Stray light can be reduced. (8) In (2) or (6) above, the first semiconductor layer may have a first conductivity type and the second semiconductor layer may have a second conductivity type. A pin junction is formed in the waveguide mesa. (9) In (3) and (7) above, a third electrode may be provided in the first output waveguide. The phase of the light can be adjusted by applying a voltage. Light is absorbed even without applying a voltage to the second output waveguide. Stray light can be reduced. (10) In any of (1) to (9) above, the system comprises a first Mach-Zehnder modulator, a second Mach-Zehnder modulator, and a second multiplexer, wherein the first Mach-Zehnder modulator and the second Mach-Zehnder modulator each have a first input waveguide and a second input waveguide, a first output waveguide and a second output waveguide, and a first multiplexer, and the light is input from the first output waveguide of the first Mach-Zehnder modulator and the first output waveguide of the second Mach-Zehnder modulator to the second multiplexer, and the second output waveguide of the first Mach-Zehnder modulator and the second output waveguide of the second Mach-Zehnder modulator do not have to be optically coupled to the second multiplexer. Stray light can be reduced in the first Mach-Zehnder modulator and the second Mach-Zehnder modulator. (11) In the above (10), a third output waveguide and a fourth output waveguide may be provided, and the light may be output from the second multiplexer to the third output waveguide and the fourth output waveguide. Stray light can be reduced. Light modulated by the first Mach-Zehnder modulator and the second Mach-Zehnder modulator is output from the third output waveguide and the fourth output waveguide. (12) A modulator chip comprising an optical component, wherein the modulator chip has a first Mach-Zehnder modulator and a second Mach-Zehnder modulator, the optical component is provided outside the modulator chip, the first Mach-Zehnder modulator and the second Mach-Zehnder modulator each have a first input waveguide and a second input waveguide, a first output waveguide and a second output waveguide, and a first multiplexer, the modulator chip having a second multiplexer, a third output waveguide, and a fourth output waveguide, the second output waveguide of the first Mach-Zehnder modulator and the second output waveguide of the second Mach-Zehnder modulator The waveguide is not optically coupled to the second multiplexer, the light absorption rate of the second output waveguide is higher than that of the first output waveguide, light is input from the first input waveguide and the second input waveguide to the first multiplexer, the light is output from the first multiplexer to the first output waveguide and the second output waveguide, the light is input from the first output waveguide to the second multiplexer, the light is output from the second multiplexer to the third output waveguide and the fourth output waveguide, and the light is output from the third output waveguide and the fourth output waveguide towards the optical components in this optical modulation module. Stray light can be reduced.

[0010] [Details of the embodiments of this disclosure] Specific examples of Mach-Zehnder modulators and optical modulation modules according to embodiments of this disclosure will be described below with reference to the drawings. However, this disclosure is not limited to these examples and is intended to include all modifications within the meaning and scope of the claims as indicated by the claims.

[0011] <First Embodiment> Figure 1 is a plan view illustrating a Mach-Zehnder modulator 100 according to a first embodiment. The Mach-Zehnder modulator 100 includes a Mach-Zehnder modulator 10 and a Mach-Zehnder modulator 12. The Mach-Zehnder modulator 10 and the Mach-Zehnder modulator 12 are integrated on a single chip. Two ends of the Mach-Zehnder modulator 100 are parallel in the X-axis direction. The other two ends are parallel in the Y-axis direction. The Z-axis direction is the normal direction to the top surface of the Mach-Zehnder modulator 100. The X-axis, Y-axis, and Z-axis directions are orthogonal to each other.

[0012] Mach-Zehnder modulator 10 is a parent Mach-Zehnder modulator and includes Mach-Zehnder modulator 14 (first Mach-Zehnder modulator) and Mach-Zehnder modulator 15 (second Mach-Zehnder modulator). Mach-Zehnder modulator 12 is a parent Mach-Zehnder modulator and includes Mach-Zehnder modulator 16 (first Mach-Zehnder modulator) and Mach-Zehnder modulator 18 (second Mach-Zehnder modulator). Mach-Zehnder modulators 14, 15, 16, and 18 are child Mach-Zehnder modulators. Mach-Zehnder modulators 14, 15, 16, and 18 are aligned in the Y-axis direction.

[0013] The Mach-Zehnder modulator 100 includes waveguides 20, 21, 22, a multiplexer 40 (second multiplexer / demultiplexer), waveguide 41 (third output waveguide), waveguide 42 (fourth output waveguide), a multiplexer 47 (second multiplexer / demultiplexer), waveguide 48 (third output waveguide), and waveguide 49 (fourth output waveguide). Waveguide 20 is the input waveguide of the Mach-Zehnder modulator 100. Waveguides 41, 42, 48, and 49 are output waveguides.

[0014] Waveguides 20, 41, 42, 48, and 49 extend to one end of the Mach-Zehnder modulator 100 in the X-axis direction.

[0015] The waveguide of a Mach-Zehnder modulator is an arm waveguide with a mesa shape protruding in the Z-axis direction. The multiplexer is a 2-input, 2-output (2x2) coupler, such as a multi-mode interference (MMI).

[0016] Waveguide 20 extends in the X-axis direction from one end of the Mach-Zehnder modulator 100. Waveguides 21 and 22 branch off from waveguide 20. Waveguides 23 and 24 branch off from waveguide 21. Mach-Zehnder modulators 14 and 15 are connected in parallel between waveguide 21 and the multiplexer 40.

[0017] The Mach-Zehnder modulator 14 includes a waveguide 23, a waveguide 27 (first input waveguide), a waveguide 28 (second input waveguide), a waveguide 30 (first output waveguide), a waveguide 31 (second output waveguide), a multiplexer 29 (first multiplexer), electrodes 32, 33, 34, 35, and 36 (third electrode). Waveguide 23 is the input waveguide for the Mach-Zehnder modulator 14. Waveguides 27 and 28 branch off from waveguide 23. Waveguides 27 and 28 are parallel in the X-axis direction.

[0018] Waveguides 27 and 28 are input waveguides for the multiplexer 29 and are optically coupled to the input terminals of the multiplexer 29. Waveguides 30 and 31 are output waveguides for the multiplexer 29 and are optically coupled to the output terminals of the multiplexer 29.

[0019] Electrodes 32 and 33 are provided in waveguide 27. Electrodes 34 and 35 are provided in waveguide 28. Electrodes 32 and 34 are modulation electrodes. Electrodes 33 and 35 are phase adjustment electrodes. Electrode 36 is provided in waveguide 30. In Figure 1, electrodes not shown are provided at positions separated from the waveguides.

[0020] The Mach-Zehnder modulator 15 has the same configuration as the Mach-Zehnder modulator 14. Two waveguides branch off from waveguide 24. These two waveguides are optically coupled to the input terminal of the multiplexer 37 (first multiplexer). Waveguides 38 (first output waveguide) and 39 (second output waveguide) are optically coupled to the output terminal of the multiplexer 37.

[0021] Waveguides 30 and 38 are optically coupled to the input terminals of the multiplexer 40. Waveguides 41 and 42 are optically coupled to the output terminals of the multiplexer 40. Waveguides 41 and 42 are the output waveguides of the Mach-Zehnder modulator 100 and extend from the multiplexer 40 to the ends of the Mach-Zehnder modulator 100. Waveguides 31 and 39 are not coupled to the multiplexer 40 and do not reach the ends of the Mach-Zehnder modulator 100.

[0022] Mach-Zehnder modulator 12 has the same configuration as Mach-Zehnder modulator 10. Mach-Zehnder modulators 16 and 18 are connected in parallel between waveguide 22 and multiplexer 47. Waveguides 25 and 26 branch off from waveguide 22. Waveguide 25 is included in Mach-Zehnder modulator 16. Waveguide 26 is included in Mach-Zehnder modulator 18. Waveguide 43 (first output waveguide) of Mach-Zehnder modulator 16 and waveguide 45 (first output waveguide) of Mach-Zehnder modulator 18 are optically coupled to the input terminals of multiplexer 47. Waveguides 48 and 49 are optically coupled to the output terminals of multiplexer 47 and extend to the end of Mach-Zehnder modulator 100. The waveguide 44 (second output waveguide) of the Mach-Zehnder modulator 16 and the waveguide 46 (second output waveguide) of the Mach-Zehnder modulator 18 are not coupled to the multiplexer 47 and do not reach the end of the Mach-Zehnder modulator 100.

[0023] FIG. 2 is a plan view illustrating the Mach-Zehnder modulator 14, with an enlargement near the multiplexer 29. The waveguide 27 and the waveguide 28 extend longer than the portion illustrated in FIG. 2 and are coupled to the waveguide 23 shown in FIG. 1. The waveguide 30 extends longer than the portion illustrated in FIG. 2 and is coupled to the multiplexer 40 shown in FIG. 1. The waveguide 31 is shorter than the waveguide 27, the waveguide 28, and the waveguide 30 and terminates within FIG. 2. The length L1 of the waveguide 31 is, for example, 0.5 mm.

[0024] FIG. 3A is a cross-sectional view taken along the line A-A of FIG. 2, illustrating a cross-section including the waveguide 30. FIG. 3B is a cross-sectional view taken along the line B-B of FIG. 2, illustrating a cross-section including the waveguide 31. As shown in FIGS. 3A and 3B, the Mach-Zehnder modulator 100 includes a substrate 50, a cladding layer 52 (first semiconductor layer), a core layer 54, a cladding layer 56 (second semiconductor layer), and a contact layer 58 (second semiconductor layer). The cladding layer 52 is provided on the upper surface of the substrate 50. A part of the cladding layer 52 protrudes in the Z-axis direction. The core layer 54, the cladding layer 56, and the contact layer 58 are laminated on the protruding portion.

[0025] The substrate 50 is, for example, a semi-insulating semiconductor substrate. The substrate 50 is formed of, for example, indium phosphide (InP) doped with iron (Fe). The dopant concentration is, for example, 1×10 17 cm -3 or more and 1×10 18 cm -3 or less. The cladding layer 52 is formed of, for example, n-type (first conductivity type) indium phosphide (n-InP). The cladding layer 52 is doped with, for example, silicon (Si) as an n-type dopant. The dopant concentration is, for example, 1×10 18 cm -3 or more and 1×10 19 cm -3 or less.

[0026] The core layer 54 has, for example, a multiple quantum well structure (MQW) and includes multiple well layers and multiple barrier layers. The well layers and barrier layers are stacked alternately. The well layers and barrier layers are formed of, for example, undoped aluminum gallium arsenide (AlGaInAs).

[0027] The cladding layer 56 is formed of, for example, p-type (second conductivity type) indium phosphide (p-InP). The cladding layer 56 is doped with, for example, zinc (Zn) as a p-type dopant. The dopant concentration is, for example, 1 × 10⁻⁶. 17 cm -3 The above 2 x 10 18 cm -3 The following applies: The contact layer 58 is formed of, for example, p-type indium gallium arsenide (p-InGaAs). A pin (positive-intrinsic-negative) junction is formed in the waveguide mesa. A voltage is applied to the core layer 54 by applying a voltage. The dopant concentration of the contact layer 58 is, for example, 1 × 10⁻¹⁶. 18 cm -3 The above 1 x 10 19 cm -3 The following applies: The contact layer 58 and the cladding layer 56 contain protons (H + Ions such as ) may be implanted. The cladding layer 52 may be p-type (first conductivity type), and the cladding layer 56 and contact layer 58 may be n-type (second conductivity type).

[0028] As shown in Figure 3A, the protrusions of the cladding layer 52, the core layer 54, the cladding layer 56, and the contact layer 58 form a mesa-shaped waveguide 30. The insulating film 60 covers the sides and top of the waveguide 30 and the top of the cladding layer 52. The insulating film 60 is made of, for example, silicon nitride (SiN).

[0029] An opening is provided in the insulating film 60 in the portion covering the upper surface of the waveguide 30. An electrode 36 (second electrode) is provided in this opening. Electrode 36 is a p electrode and is electrically connected to the contact layer 58. Electrode 36 is made of metal. An opening is provided in the insulating film 60 in the portion covering the cladding layer 52. Electrode 62 (first electrode) is provided in this opening. Electrode 62 is an n electrode and is electrically connected to the cladding layer 52. Electrode 62 is made of, for example, an alloy of gold (Au) and germanium (Ge) (AuGe alloy). Electrode 36 may or may not be provided in the contact layer 58 of the output waveguide (waveguide 30, etc.). Electrode 62 may or may not be provided in the cladding layer 52 of the output waveguide.

[0030] Waveguides other than waveguides 31, 39, 44, and 46 have the same configuration as waveguide 30.

[0031] As shown in Figure 3B, the protrusions of the cladding layer 52, the core layer 54, the cladding layer 56, and the contact layer 58 form a mesa-shaped waveguide 31. The insulating film 60 covers the sides and top surface of the waveguide 31 and the top surface of the cladding layer 52. No electrodes are provided in the waveguide 31.

[0032] The core layer 54 of the waveguide 31 contains protons (H + Ions such as ) are implanted. The ion concentration is, for example, 1 × 10⁻¹⁰. 17 cm -3 The above 5 x 10 19 cm -3 The following is the case: Defects are generated in the core layer 54 of waveguide 31 by ion implantation. The core layer 54 of waveguide 31 has more crystal defects than the core layer 54 of waveguide 30. Due to these defects, the light absorption rate in the core layer 54 of waveguide 31 is higher than that in the core layer 54 of waveguide 30.

[0033] Waveguides 39, 44, and 46 have the same configuration as waveguide 31. Protons are injected into the core layer 54 of each of waveguides 39, 44, and 46.

[0034] The ends of waveguide 20 function as input ports. The ends of waveguides 41, 42, 48, and 49 function as output ports. Light is incident on waveguide 20 from an external light source. The light propagates through waveguide 20 and then branches off into waveguides 21 and 22. The light propagating through waveguide 21 branches off into waveguides 23 and 24.

[0035] Light propagating through waveguide 23 is input to the Mach-Zehnder modulator 14 and propagates through waveguides 27 and 28. The light is modulated by applying voltage to electrodes 32 and 34. The phase of the light is adjusted by applying voltage to electrodes 33 and 35.

[0036] The modulated light enters the multiplexer 29, splits into waveguides 30 and 31, and exits from the multiplexer 29. The light propagating through waveguide 30 enters the multiplexer 40. The output light of the Mach-Zehnder modulator 15 propagates through waveguide 38 and enters the multiplexer 40. The output light of the Mach-Zehnder modulator 14 and the output light of the Mach-Zehnder modulator 15 are combined in the multiplexer 40. The combined light splits into waveguides 41 and 42 and exits to the outside of the Mach-Zehnder modulator 100.

[0037] Because the core layer 54 of waveguide 31 has a high absorption rate, light propagating through waveguide 31 is absorbed by the core layer 54. At the end of waveguide 31 opposite the multiplexer 29, the light is reflected and travels back and forth through waveguide 31. The light attenuates as it propagates through waveguide 31. Therefore, it is difficult for light to be emitted from waveguide 31. Light propagating through waveguide 39 is absorbed by the core layer 54. Because unwanted light is absorbed in waveguides 31 and 39, stray light can be reduced.

[0038] Light is modulated in Mach-Zehnder modulators 16 and 18. The output light from Mach-Zehnder modulator 16 propagates through waveguide 43 and is incident on multiplexer 47. The output light from Mach-Zehnder modulator 18 propagates through waveguide 45 and is incident on multiplexer 47. The output light propagates through waveguides 48 and 49 and is emitted. Light propagating through waveguide 46 and light propagating through waveguide 44 is absorbed by core layer 54. Light is less likely to be emitted from waveguides 44 and 46, and stray light can be reduced.

[0039] (Manufacturing method) For example, a cladding layer 52, a core layer 54, a cladding layer 56, and a contact layer 58 are epitaxially grown on the upper surface of a substrate 50 using metal-organic chemical vapor deposition (MOCVD). A mask is provided, and openings are made in the mask in the portions corresponding to waveguides 31, 39, 44, and 46. After forming the openings in the mask, ions are implanted. The proton concentration profile can be controlled by the ion implantation energy and the ion dose. For example, ion implantation is performed so that the proton concentration peak is located in the core layer 54. After ion implantation, the mask is removed. After ion implantation, heat treatment may be performed. The heat treatment temperature is, for example, 300°C to 500°C. The time is, for example, 60 minutes to 120 minutes.

[0040] Waveguides are formed by etching. An insulating film 60 is deposited by plasma CVD (PECVD: Plasma Enhanced CVD) or the like. Electrodes are formed by vacuum deposition and lift-off. The Mach-Zehnder modulator 100 is formed through the above steps.

[0041] According to the first embodiment, waveguides 27, 28, 30, and 31 of the Mach-Zehnder modulator 14 are optically coupled to a multiplexer 29. Light is input to the multiplexer 29 from waveguides 27 and 28, and light is output from the multiplexer 29 to waveguides 30 and 31. Light propagating through waveguide 30 is emitted to the outside. The light absorption rate of waveguide 31 is higher than that of waveguide 31. Light propagating through waveguide 31 is absorbed and attenuated in waveguide 31. Light is less likely to be emitted from waveguide 31, and stray light can be reduced.

[0042] As shown in Figures 3A and 3B, the waveguide consists of an n-type cladding layer 52, a core layer 54, a p-type cladding layer 56, and a contact layer 58. The core layer 54 is, for example, MQW. Light is distributed and propagates through the core layer 54. Ions are implanted into the core layer 54 of waveguides 31, 39, 44, and 46 to create defects. This increases the light absorption rate of the core layer 54. Stray light can be reduced.

[0043] As shown in Figure 1, electrodes are provided in waveguides 27, 28, and 30. By applying a voltage to the electrodes in waveguides 27, 28, and 30, it is possible to control the modulation and phase of light, and also control the extinction ratio. Ion implantation increases the light absorption rate of the core layer 54 of waveguides 31, 39, 44, and 46. By reducing stray light, interference between stray light and output light is less likely to occur. The extinction ratio is less likely to deteriorate. Electrodes do not need to be provided in the contact layer 58 of waveguides 31, 39, 44, and 46. Waveguide 31 has a high light absorption rate even without applying a voltage.

[0044] The concentration of ions injected into the core layer 54 is, for example, 1 × 10⁻⁶. 17 cm -3 The above 5 x 10 19 cm -3The following is possible: The light absorption rate of the core layer 54 can be increased. For example, protons are injected into the core layer 54 from the Z-axis direction. Ions are distributed in the contact layer 58, cladding layer 56, and core layer 54. The ion acceleration voltage and other parameters are controlled so that the concentration in the core layer 54 reaches a desired level. If the cladding layer 52 is p-type, the ions may be distributed in the cladding layer 52.

[0045] Ions may also be implanted into the p-type cladding layer 56 and contact layer 58 of waveguides other than waveguides 31, 39, 44, and 46. This can reduce light absorption by the p-type semiconductor layer. In the waveguide mesa, the p-type contact layer 58 and cladding layer 56, the undoped core layer 54, and the n-type cladding layer 52 form a PIN junction. A voltage can be selectively applied to the core layer 54. On the other hand, by implanting ions into the core layer 54 of waveguides 31, 39, 44, and 46, the absorption rate can be increased, allowing light to be absorbed.

[0046] As shown in Figure 1, the waveguide 31 is not connected to the multiplexer 40 but is terminated. Light incident on the waveguide 31 from the multiplexer 29 is reflected at the end of the waveguide 31 and travels back and forth along the waveguide 31. During the round trip, the light is absorbed by the core layer 54. Stray light can be reduced. The propagation loss of the ion-implanted core layer 54 is, for example, 40 dB / mm. If the length L1 of the waveguide 31 is 0.5 mm, the light traveling back and forth along the waveguide 31 is attenuated by 40 dB. Stray light can be effectively reduced. By increasing the length of the waveguide 31, the light is attenuated further.

[0047] The Mach-Zehnder modulator 100 includes four Mach-Zehnder modulators 14, 15, 16, and 18. The four Mach-Zehnder modulators have the same configuration. Modulated light is output from waveguides 41, 42, 48, and 49. Ions are implanted into the core layer 54 of waveguides 31, 39, 44, and 46 to increase their absorption rate. This reduces stray light within the Mach-Zehnder modulator 100. In Mach-Zehnder modulator 14, waveguides 27 and 28 are paired. By applying a voltage to the electrodes, the light propagating through these waveguides is modulated. In Mach-Zehnder modulator 10, waveguides 30 and 38 are paired. By applying a voltage to electrode 36, the phase of the light is adjusted. Electrodes may or may not be provided in waveguides 30, 38, 43, and 45. It is sufficient that light can propagate from waveguides 30, 38, 43, and 45 to the multiplexer.

[0048] The number of Mach-Zehnder modulators in the Mach-Zehnder modulator 100 may be four or less, or four or more.

[0049] <Second Embodiment> Figure 4 is a cross-sectional view illustrating a Mach-Zehnder modulator according to the second embodiment, showing a cross-section including the waveguide 31. The same configuration as in the first embodiment will not be described.

[0050] As shown in Figure 4, the waveguide 31 has a cladding layer 52, a core layer 54, and a cladding layer 56. A contact layer 58 is not provided in waveguide 31, but is provided in waveguide 30 and the like. The upper surface of waveguide 31 is the surface of the cladding layer 56. The side surfaces of waveguide 31 are formed by the cladding layer 52, the core layer 54, and the cladding layer 56.

[0051] The metal film 64 covers the surface of the waveguide 31 and is in contact with the top and side surfaces of the waveguide 31. Waveguides 39, 44, and 46 are also covered with the metal film 64. The metal film 64 is made of, for example, an AuGe alloy. The Ge composition ratio of the metal film 64 is, for example, 12 wt%. The metal film 64 is spaced apart from the electrodes and is not connected to them.

[0052] According to the second embodiment, the metal film 64 covers waveguides 31, 39, 44, and 46. Light propagating through these waveguides is absorbed by the metal film 64. Stray light can be reduced.

[0053] The metal film 64 is in contact with the cladding layer 52, the core layer 54, and the cladding layer 56. Light propagating through the waveguide is easily absorbed by the metal film 64. The length L1 of the waveguide 31, for example, is 0.1 mm. During round trip travel through the waveguide, the light is attenuated by more than 40 dB. Stray light can be effectively reduced.

[0054] The metal film 64 is spaced apart from the electrodes, and no voltage is applied to it. When modulating light, a voltage is applied to the electrodes. Stray light can be reduced while modulating light. The metal film 64 can be made of any metal, for example, the same material as the electrode 62. The electrode 62 and the metal film 64 can be deposited simultaneously. Ions may be implanted into the core layer 54, and the waveguide may be covered with the metal film 64.

[0055] <Third Embodiment> Figure 5 is a schematic diagram illustrating an optical modulation module 300 according to the third embodiment. The same configuration as in the first or second embodiment will not be described. The dashed lines in Figure 5 represent light.

[0056] As shown in Figure 5, the optical modulation module 300 has a Mach-Zehnder modulator 100, a base 70, and a flexible printed circuit board 72. Inside the base 70 are the Mach-Zehnder modulator 100, a temperature control element 71, a driver IC (Integrated Circuit) 73, lenses 77, 80, 83, photodiodes 78, 79, mirrors 75, 76, 82, a polarization rotor 81, and a polarization combiner 84.

[0057] The Mach-Zehnder modulator 100 is a modulator chip, with Mach-Zehnder modulators 10 and 12 integrated on a single chip. Waveguides 31, 39, 44, and 46 of the Mach-Zehnder modulator 100 are not coupled to a multiplexer. Ions may be implanted into the core layer 54 of these waveguides. These waveguides may be covered with a metal film 64.

[0058] The flexible printed circuit board 72 is located outside the base 70 and is mounted on the base 70. The flexible printed circuit board 72 is electrically connected to the driver IC 73. The driver IC 73 is electrically connected to the electrodes of the Mach-Zehnder modulator 100 via wiring 74. The temperature control element 71 is, for example, a Peltier element and regulates the temperature inside the base 70.

[0059] Optically coupled to the optical modulation module 300 is an optical fiber (not shown). Light is input to the optical modulation module 300 from the input optical fiber. The input light is reflected by mirrors 75 and 76 and then focused by lens 77. The focused light is input to the Mach-Zehnder modulator 100.

[0060] Light propagates through the waveguide of the Mach-Zehnder modulator 100. Modulation of the light is performed by applying a voltage from the driver IC 73. The modulated light is output from the Mach-Zehnder modulator 100. The Mach-Zehnder modulator 10 outputs, for example, Y polarization. The Mach-Zehnder modulator 12 outputs, for example, X polarization.

[0061] The Mach-Zehnder modulator 10 outputs two beams of light. One of the two output beams is input to the photodiode 78. The other output beam is focused by the lens 80 and input to the polarization rotor 81. The polarization direction of the light is rotated in the polarization rotor 81. The light is reflected by the mirror 82 and input to the polarization combiner 84.

[0062] The Mach-Zehnder modulator 12 outputs two beams of light. One of the two output beams is input to the photodiode 79. The other output beam is focused by the lens 83 and then input to the polarization combiner 84. The combined beam of light from the polarization combiner 84 is output from the optical modulation module 300.

[0063] According to the third embodiment, light is absorbed in waveguides 31, 39, 44, and 46 of the Mach-Zehnder modulator 100. Because the light is absorbed in the waveguides, it is less likely to be radiated outside the waveguides. Stray light can be reduced.

[0064] Reducing stray light inside the Mach-Zehnder modulator 100 makes it less likely for the extinction ratio to worsen and for interference between signal light and stray light to occur. Because unwanted light is not emitted outside the Mach-Zehnder modulator 100 and the light is absorbed by the waveguide of the Mach-Zehnder modulator 100, stray light within the base 70 can be reduced. The effect of stray light on optical components such as photodiodes, polarization rotors 81, and polarization combiners 84 is reduced. Crosstalk and other issues become less likely to occur.

[0065] Although embodiments of this disclosure have been described in detail above, this disclosure is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of this disclosure as described in the claims. [Explanation of Symbols]

[0066] 10, 12, 14, 15, 16, 18, 100 Mach-Zehnder modulators Waveguides 20, 21, 22, 23, 24, 25, 26, 27, 28, 30, 31, 38, 39, 41, 42, 43, 44, 45, 46, 48, 49 29, 37, 40, 47 multiplexer 32, 33, 34, 36, 62 electrodes 50 circuit boards 52, 56 Clad layer 54 core layers 58 Contact Layer 60 insulating film 64 Metal film 70 Base 71 Temperature control element 72 Flexible Printed Circuit Boards 73 Driver ICs 74 Wiring 75, 76, 82 Miller 77, 80, 83 lenses 78, 79 Photodiode 81 Polarization Rotor 84 Polarization combiner 300 Optical Modulation Modules

Claims

1. A first input waveguide and a second input waveguide, A first output waveguide and a second output waveguide, It is equipped with a first wave combiner, Light is input to the first multiplexer from the first input waveguide and the second input waveguide. The light is output from the first multiplexer to the first output waveguide and the second output waveguide. A Mach-Zehnder modulator in which the optical absorption rate of the second output waveguide is higher than that of the first output waveguide.

2. The first input waveguide, the second input waveguide, the first output waveguide, and the second output waveguide each have a first semiconductor layer, a core layer, and a second semiconductor layer. The first semiconductor layer, the core layer, and the second semiconductor layer are stacked in order to form a waveguide mesa. The Mach-Zehnder modulator according to claim 1, wherein ions are implanted in the core layer of the second output waveguide.

3. First electrode and It comprises a second electrode and The first electrode is electrically connected to the first semiconductor layer, The Mach-Zehnder modulator according to claim 2, wherein the second electrode is electrically connected to the second semiconductor layer of the first input waveguide and the second input waveguide, respectively.

4. The concentration of the aforementioned ions is 1 × 10 １７ cm －３ The above 5 x 10 １９ cm －３ The Mach-Zehnder modulator according to claim 2, which is as follows:

5. The Mach-Zehnder modulator according to claim 1, further comprising a metal film covering the surface of the second output waveguide.

6. The first input waveguide, the second input waveguide, the first output waveguide, and the second output waveguide each have a first semiconductor layer, a core layer, and a second semiconductor layer. The first semiconductor layer, the core layer, and the second semiconductor layer are stacked in order to form a waveguide mesa. The Mach-Zehnder modulator according to claim 5, wherein the metal film is in contact with the side and top surfaces of the waveguide mesa of the second output waveguide.

7. First electrode and It comprises a second electrode and The first electrode is electrically connected to the first semiconductor layer, The second electrode is electrically connected to the second semiconductor layer of the first input waveguide and the second input waveguide, The Mach-Zehnder modulator according to claim 6, wherein the metal film is spaced apart from the first electrode and the second electrode.

8. The first semiconductor layer has a first conductivity type, The Mach-Zehnder modulator according to claim 2 or claim 6, wherein the second semiconductor layer has a second conductivity type.

9. The Mach-Zehnder modulator according to claim 3 or claim 7, further comprising a third electrode provided in the first output waveguide.

10. First Mach-Zehnder modulator, The second Mach-Zehnder modulator, It is equipped with a second wave combiner, The first Mach-Zehnder modulator and the second Mach-Zehnder modulator are, The first input waveguide and the second input waveguide, The first output waveguide and the second output waveguide, The first multiplexer and, The light is input to the second multiplexer from the first output waveguide of the first Mach-Zehnder modulator and the first output waveguide of the second Mach-Zehnder modulator. The Mach-Zehnder modulator according to claim 1 or claim 2, wherein the second output waveguide of the first Mach-Zehnder modulator and the second output waveguide of the second Mach-Zehnder modulator are not optically coupled to the second multiplexer.

11. It comprises a third output waveguide and a fourth output waveguide, The Mach-Zehnder modulator according to claim 10, wherein the light is output from the second multiplexer to the third output waveguide and the fourth output waveguide.

12. modulator chip, It comprises optical components, The modulator chip includes a first Mach-Zehnder modulator and a second Mach-Zehnder modulator. The optical component is provided outside the modulator chip. The first Mach-Zehnder modulator and the second Mach-Zehnder modulator are, A first input waveguide and a second input waveguide, A first output waveguide and a second output waveguide, It has a first wave combiner, The modulator chip has a second multiplexer, a third output waveguide, and a fourth output waveguide. The second output waveguide of the first Mach-Zehnder modulator and the second output waveguide of the second Mach-Zehnder modulator are not optically coupled to the second multiplexer. The optical absorption rate of the second output waveguide is higher than that of the first output waveguide. Light is input to the first multiplexer from the first input waveguide and the second input waveguide. The light is output from the first multiplexer to the first output waveguide and the second output waveguide. The light is input from the first output waveguide to the second multiplexer, The light is output from the second multiplexer to the third output waveguide and the fourth output waveguide. An optical modulation module in which the light is output from the third output waveguide and the fourth output waveguide toward the optical component.

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