Phase adjuster

Abstract

To provide a phase adjuster with which, while suppressing the size in a prescribed direction of each of a plurality of waveguides, it is possible to add a phase difference to light propagating through the plurality of waveguides.SOLUTION: A phase adjuster for adjusting the phases of multiple rays of incident light comprises: a first optical path L1 formed extending along a prescribed direction Da and which first light among the multiple rays of light propagates through; and a second optical path L2 formed facing the first optical path and extending along a prescribed direction and which second light different from the first light among the multiple rays of light propagates through. The first optical path and the second optical path have a region formed from materials mutually differing in the refractive index of light.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a phase adjuster. [Background technology]

[0002] A passive phase adjuster is known that adjusts the phase of each of two incident lights depending on the difference in the shape of the two waveguides through which the two incident lights propagate (see, for example, Non-Patent Document 1). The phase adjuster described in Non-Patent Document 1 adjusts the phase difference between two lights propagating through two waveguides.

[0003] Here, the direction in which light propagates in the waveguide is the predetermined direction, and the predetermined direction intersecting the predetermined direction is the width direction. The phase adjuster described in Non-Patent Document 1 has an expanded portion in which the size of the width direction of each of the two waveguides gradually increases along the predetermined direction, and the size of the expanded portion of one waveguide in the width direction is larger than the size of the expanded portion of the other waveguide in the width direction. The phase adjuster described in Non-Patent Document 1 makes it possible to impart a phase difference between light propagating in one waveguide and light propagating in the other waveguide by the difference in effective refractive index of the two waveguides caused by the difference in the size of the expanded portions of the two waveguides in the width direction. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Ultra-Broadband Mode Converter and Multiplexer Based on Sub-Wavelength Structures Volume 10, Number 2, April 2018 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, the phase difference that can be imparted to the light propagating through the two waveguides is equal to the difference between the effective refractive indices of the two waveguides multiplied by the size of the waveguide in the predetermined direction when the two waveguides are equal to each other. Therefore, the greater the difference between the effective refractive indices of the two waveguides, the greater the phase difference that can be imparted to the light propagating through the two waveguides. The greater the widthwise size of each of the two waveguides, the greater the effective refractive index of each of the two waveguides.

[0006] However, the rate of increase in the effective refractive index relative to the rate of increase in the width direction of the waveguide becomes smaller as the width direction of the waveguide increases. In other words, the rate of increase in the effective refractive index relative to the rate of increase in the width direction of the waveguide becomes slower as the width direction of the waveguide increases. For this reason, even if a difference in the effective refractive index is generated between the two waveguides by the difference in the width direction of the enlarged portions of the two waveguides as in the phase shifter described in Non-Patent Document 1, it is difficult to increase the difference in the effective refractive index between the two waveguides.

[0007] Therefore, when a phase difference is applied to light propagating through two waveguides by the difference in the width direction of the enlarged portions of the two waveguides, the larger the phase difference to be applied, the larger the size of each of the two waveguides in a predetermined direction must be. However, if the size of the waveguide in the predetermined direction is increased, the size of the phase shifter in the predetermined direction also increases, which is not preferable. This problem was discovered through extensive research by the inventors.

[0008] An object of the present disclosure is to provide a phase adjuster capable of imparting a phase difference to light propagating through a plurality of waveguides while suppressing the size of each of the plurality of waveguides in a predetermined direction. [Means for solving the problem]

[0009] According to one aspect of the disclosure, A phase adjuster for adjusting phases of a plurality of incident light beams, A first optical path (L1) extending along a predetermined direction (Da) and through which a first light beam of the plurality of light beams propagates; a second optical path (L2) formed to extend along a predetermined direction opposite to the first optical path, through which a second light different from the first light among the plurality of light beams propagates; The first optical path and the second optical path have portions formed of materials having different optical refractive indices.

[0010] According to this, a phase difference can be given between the first light propagating through the first optical path and the second light propagating through the second optical path by a portion formed of a member having a different refractive index between the first light propagating through the first optical path and the second light propagating through the second optical path. Therefore, it is easier to suppress the size of each of the first optical path and the second optical path in a predetermined direction compared to a formation in which a phase difference is given between the first light propagating through the first optical path and the second light propagating through the second optical path by a difference in the shape of each of the first optical path and the second optical path. Therefore, a phase difference can be given between the first light propagating through the first optical path and the second light propagating through the second optical path while suppressing the size of each of the first optical path and the second optical path in the predetermined direction.

[0011] Note that the reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and specific components described in the embodiments described below. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a diagram illustrating a state in which a phase adjuster according to a first embodiment is applied. [Diagram 2] FIG. 2 is a top view of the phase adjuster according to the first embodiment. [Diagram 3] FIG. 2 is a cross-sectional view taken along line III-III shown in FIG. [Figure 4] 1 is a diagram showing the difference in effective refractive index of light between a core layer made of silicon nitride and a core layer made of silicon. [Diagram 5] 1A and 1B are diagrams for explaining changes in the phase of light propagating through an optical path. [Figure 6] 1A and 1B are diagrams for explaining changes in the phase of light propagating through an optical path. [Figure 7]FIG. 1 is a diagram for explaining that it is possible to impart a phase difference to light propagating through two optical paths. [Figure 8] FIG. 4 is a top view of the comparison phase adjuster. [Figure 9] FIG. 13 is a diagram showing the relationship between the rate of increase in the core width and the rate of increase in the effective refractive index of light. [Figure 10] FIG. 1 is a diagram illustrating a phase adjuster that imparts a phase difference to light by using two optical paths having members with different effective refractive indices of light. [Figure 11] FIG. 2 is a diagram showing a first optical path and a second optical path according to the first embodiment. [Figure 12] FIG. 13 is a diagram showing the effective refractive index difference between two core layers formed of different materials. [Figure 13] FIG. 4 is a table showing components and core lengths of the phase adjustment units of the phase adjuster according to the first embodiment and the comparative phase adjuster. [Figure 14] 11 is a diagram showing the relationship between the deviation of the core width and the error of the phase difference. FIG. [Figure 15] FIG. 4 is a top view of a phase adjuster according to a first modified example of the first embodiment. [Figure 16] FIG. 4 is a top view of a phase adjuster according to a second modification of the first embodiment. [Figure 17] FIG. 13 is a top view of a phase adjuster according to a third modification of the first embodiment. [Figure 18] FIG. 13 is a top view of a phase adjuster according to a fourth modification of the first embodiment. [Figure 19] FIG. 11 is a diagram illustrating a state in which a phase adjuster according to a second embodiment is applied. [Figure 20] FIG. 11 is a top view of a phase adjuster according to a third embodiment. [Figure 21] 1 is a diagram showing the difference in effective refractive index of light between a core layer made of silicon nitride and a core layer made of silicon. [Figure 22] FIG. 13 is a graph showing the rate of increase in the effective refractive index of light relative to the rate of increase in the core width. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments of the present disclosure will be described with reference to the drawings. In the following embodiments, the same reference numerals are used for parts that are the same as or equivalent to those described in the preceding embodiments, and the description thereof may be omitted. In addition, in the embodiments, when only a part of the components is described, the components described in the preceding embodiments can be applied to the other parts of the components. In the following embodiments, each embodiment can be partially combined with each other, even if not specifically stated, as long as it does not cause any trouble in combination.

[0014] (First embodiment) The phase adjuster 1 of this embodiment will be described with reference to Figs. 1 to 14. The phase adjuster 1 of this embodiment is disposed, for example, between an input-side multiplexer Mi and an output-side multiplexer Mo, and is used to adjust the phases of two lights input from the input-side multiplexer Mi to the phase adjuster 1, and output the two adjusted lights to the output-side multiplexer Mo. The phase adjuster 1, for example, shifts the phases of two lights input from the input-side multiplexer Mi in a phase-aligned state, and outputs the lights to the output-side multiplexer Mo. Alternatively, the phase adjuster 1 may adjust the phases of two lights input from the input-side multiplexer Mi in a phase-shifted state so that they are aligned, and output the lights to the output-side multiplexer Mo.

[0015] As shown in Fig. 2 and Fig. 3, the phase shifter 1 of this embodiment includes a silicon substrate 2, three clad layers 3a, 3b, and 3c, and six core layers 10, 20, 30, 40, 50, and 60. The three clad layers 3a, 3b, and 3c and the six core layers 10, 20, 30, 40, 50, and 60 are stacked on the silicon substrate 2. Specifically, the phase shifter 1 includes a first clad layer 3a formed on the silicon substrate 2, and a second clad layer 3b, a third core layer 30, and a fourth core layer 40 formed on the first clad layer 3a. The phase shifter 1 also includes a first core layer 10, a second core layer 20, a fifth core layer 50, and a sixth core layer 60 formed on the second clad layer 3b. In the following, the first cladding layer 3a, the second cladding layer 3b, and the third cladding layer 3c may be referred to as the first cladding layer 3a to the third cladding layer 3c. Also, the first core layer 10, the second core layer 20, the third core layer 30, the fourth core layer 40, the fifth core layer 50, and the sixth core layer 60 may be referred to as the first core layer 10 to the sixth core layer 60. Also, the second cladding layer 3b and the third cladding layer 3c are omitted in Figures 1 and 2.

[0016] The first core layer 10 to the sixth core layer 60 have a higher refractive index than the first cladding layer 3a to the third cladding layer 3c. Therefore, the first core layer 10 to the sixth core layer 60 function as a waveguide that guides two lights incident from the input-side multiplexer Mi to the output-side multiplexer Mo in the phase shifter 1.

[0017] 1 etc., a direction along which two light beams propagate in phase adjuster 1 is referred to as a first direction Da. A direction in which phase adjuster 1 emits light in first direction Da is referred to as an emission direction Da1, and a direction opposite to emission direction Da1 is referred to as a reverse emission direction Da2.

[0018] As shown in FIG. 3 etc., the direction in which the first cladding layer 3a to the third cladding layer 3c are stacked is defined as a second direction Db, and the direction perpendicular to the first direction Da and the second direction Db is defined as a third direction Dc.

[0019] As shown in FIG. 2 and FIG. 3, the first cladding layer 3a is formed in a cube shape with the first direction Da as the longitudinal direction. The second cladding layer 3b, the third core layer 30, and the fourth core layer 40 are formed on the first cladding layer 3a. The second cladding layer 3b is formed on the first cladding layer 3a except for the portions where the third core layer 30 and the fourth core layer 40 are formed. The first core layer 10, the second core layer 20, the fifth core layer 50, and the sixth core layer 60 are formed on the second cladding layer 3b. The third cladding layer 3c is formed on the second cladding layer 3b, and is formed on the portions where the first core layer 10, the second core layer 20, the fifth core layer 50, and the sixth core layer 60 are formed.

[0020] The first cladding layer 3a, the second cladding layer 3b and the third cladding layer 3c are formed of, for example, silicon oxide, ie, SiO2, which is an insulator.

[0021] The first core layer 10, the second core layer 20, the fifth core layer 50 and the sixth core layer 60 are formed on the second cladding layer 3b. The third core layer 30 and the fourth core layer 40 are formed on the first cladding layer 3a. The first core layer 10 to the sixth core layer 60 are formed in a thin flat shape in which the size in the second direction Db is smaller than the size in the first direction Da and the third direction Dc. That is, the first core layer 10 to the sixth core layer 60 are formed as a strip-type waveguide. The first core layer 10 to the sixth core layer 60 of this embodiment are significantly smaller in size in the second direction Db than the size in the first direction Da and the third direction Dc. Hereinafter, the size of each of the first core layer 10 to the sixth core layer 60 in the first direction Da may be referred to as the core length, the size of each of the first core layer 10 to the sixth core layer 60 in the second direction Db may be referred to as the core thickness, and the size of each of the first core layer 10 to the sixth core layer 60 in the third direction Dc may be referred to as the core width.

[0022] As shown in Fig. 2, the first core layer 10, the third core layer 30, and the fifth core layer 50 are formed at the same position in the third direction Dc. The first core layer 10, the third core layer 30, and the fifth core layer 50 are arranged in this order along the emission direction Da1. However, as shown in Fig. 3, the first core layer 10 and the fifth core layer 50 are arranged at positions shifted from the third core layer 30 in the second direction Db.

[0023] 2, the second core layer 20, the fourth core layer 40, and the sixth core layer 60 are aligned in the third direction Dc. The second core layer 20, the fourth core layer 40, and the sixth core layer 60 are arranged in this order along the emission direction Da1. However, although not shown, the second core layer 20 and the sixth core layer 60 are arranged so that their positions in the second direction Db are shifted from the fourth core layer 40.

[0024] Moreover, the first core layer 10, the third core layer 30, and the fifth core layer 50 face the second core layer 20, the fourth core layer 40, and the sixth core layer 60 at a distance from each other in the third direction Dc. Specifically, the first core layer 10 faces the second core layer 20 in the third direction Dc. Moreover, the third core layer 30 faces the fourth core layer 40 in the third direction Dc. And the fifth core layer 50 faces the sixth core layer 60 in the third direction Dc. The third direction Dc in this embodiment corresponds to the facing direction.

[0025] The first core layer 10, the third core layer 30, and the fifth core layer 50 thus formed function as a first optical path L1 along which the first light, which is one of the two lights incident from the input-side multiplexer Mi, propagates. The second core layer 20, the fourth core layer 40, and the sixth core layer 60 function as a second optical path L2 along which the second light, which is the other of the two lights incident from the input-side multiplexer Mi, propagates. The first optical path L1 formed by the first core layer 10, the third core layer 30, and the fifth core layer 50 and the second optical path L2 formed by the second core layer 20, the fourth core layer 40, and the sixth core layer 60 are formed to extend along a first direction Da, which is a predetermined direction. The first optical path L1 and the second optical path L2 have portions formed of members having mutually different optical refractive indices.

[0026] Specifically, the first core layer 10, the second core layer 20, the fifth core layer 50 and the sixth core layer 60 are formed of silicon nitride, i.e., silicon nitride, SiN. In contrast, the third core layer 30 and the fourth core layer 40 are formed of silicon, i.e., Si, which has a different refractive index of light from that of silicon nitride. As shown in FIG. 4, silicon nitride and silicon have different effective refractive indices of light. Specifically, under the same core width condition, silicon has a larger effective refractive index of light than silicon nitride. In FIG. 4, the solid line indicates the effective refractive index of light of silicon, and the dashed line indicates the effective refractive index of light of silicon nitride.

[0027] That is, the first optical path L1 has a first core layer 10, a fifth core layer 50, and a third core layer 30 formed of a material having a different optical refractive index from the first core layer 10 and the fifth core layer 50. The second optical path L2 has a second core layer 20, a sixth core layer 60, and a fourth core layer 40 formed of a material having a different optical refractive index from the second core layer 20 and the sixth core layer 60. The first core layer 10, the second core layer 20, the fifth core layer 50, and the sixth core layer 60 are formed of the same material, silicon nitride. The second core layer 20 and the fourth core layer 40 are formed of the same material, silicon.

[0028] First, the first core layer 10, the third core layer 30, and the fifth core layer 50 which constitute the first optical path L1 will be described.

[0029] As shown in FIG. 2, the first core layer 10 includes a first incident portion 11, a first extension portion 12, a first propagation portion 13, and a first contraction portion 14. The first incident portion 11, the first extension portion 12, the first propagation portion 13, and the first contraction portion 14 are formed in this order along the emission direction Da1. The first core layer 10 has a constant core thickness of 0.40 μm from the end portion on the emission reverse direction Da2 side to the end portion on the emission direction Da1 side. In contrast, the first core layer 10 has different core widths depending on the first incident portion 11, the first extension portion 12, the first propagation portion 13, and the first contraction portion 14.

[0030] The first incident portion 11 is a portion optically coupled to the input-side multiplexer Mi, and guides the first light propagating from the input-side multiplexer Mi in the output direction Da1. The first incident portion 11 has a constant core width from the end portion on the output reverse direction Da2 side to the end portion on the output direction Da1 side. Specifically, the first incident portion 11 is formed with a core width of 1.0 μm. In this embodiment, the first incident portion 11 corresponds to the first input portion.

[0031] The first extension section 12 is a section through which the first light propagates from the first entrance section 11. The first extension section 12 has a core width that gradually expands along the emission direction Da1 from the end on the emission reverse direction Da2 side to the end on the emission direction Da1 side. Specifically, the core width of the first extension section 12 is 1.0 μm at the end on the emission reverse direction Da2 side and 2.0 μm at the end on the emission direction Da1 side. The first extension section 12 is also formed with a core length of 20 μm.

[0032] The first propagation section 13 is a section through which the first light propagates from the first extension section 12, and guides the first light propagated from the first extension section 12 in the emission direction Da1. The first propagation section 13 has a constant core width from the end on the emission reverse direction Da2 side to the end on the emission direction Da1 side, and is large enough to allow the first light to propagate in a high-order mode. Specifically, as shown in FIG. 4, the first propagation section 13 made of silicon nitride has a core width of 2.0 μm, which is included in the blunt region R that can significantly reduce the increase rate of the effective refractive index of light relative to the increase rate of the core width. The first propagation section 13 is also formed with a core length of 10 μm.

[0033] The first reduction section 14 is a section that optically couples the first core layer 10 to the third core layer 30, and is a section that transitions the first light propagated to the first propagation section 13 to the third core layer 30. The first reduction section 14 has a core width that gradually decreases along the emission direction Da1 from the end on the emission reverse direction Da2 side to the end on the emission direction Da1 side. Specifically, the core width of the first reduction section 14 is 2.0 μm at the end on the emission reverse direction Da2 side, and 0.15 μm at the end on the emission direction Da1 side (not shown). The core width at the end on the emission direction Da1 side of the first reduction section 14 is as small as possible in the manufacturing process used. The first reduction section 14 is formed with a core length of 35 μm.

[0034] Moreover, the first reduced portion 14 is formed so that the emission direction Da1 side overlaps with a third expanded portion 31 (to be described later) of the third core layer 30 in the second direction Db.

[0035] The third core layer 30 is formed apart from the first core layer 10 and the fifth core layer 50 in the second direction Db. The third core layer 30 also includes a third expansion section 31, a third propagation section 32, and a third contraction section 33. The third expansion section 31, the third propagation section 32, and the third contraction section 33 are formed in this order in series along the emission direction Da1. The third core layer 30 has a constant core thickness of 0.21 μm from the end on the emission reverse direction Da2 side to the end on the emission direction Da1 side. In contrast, the third core layer 30 has a core width that differs depending on the third expansion section 31, the third propagation section 32, and the third contraction section 33.

[0036] The third extension 31 is a portion optically coupled to the first reduction section 14, and guides the first light propagating from the first reduction section 14 in the emission direction Da1. The third extension 31 has a core width that gradually expands along the emission direction Da1 from the end on the emission reverse direction Da2 side to the end on the emission direction Da1 side. Specifically, the core width of the third extension 31 is 0.15 μm at the end on the emission reverse direction Da2 side (not shown) and 2.0 μm at the end on the emission direction Da1 side. The core width at the end on the emission reverse direction Da2 side of the third extension 31 is as small as possible in the manufacturing process used. The third extension 31 is formed with a core length of 35 μm.

[0037] The third propagation section 32 is a section through which the first light propagates from the third extension section 31, and guides the first light propagated from the third extension section 31 in the emission direction Da1. The third propagation section 32 has a constant core width from the end on the emission reverse direction Da2 side to the end on the emission direction Da1 side, and is large enough to allow the first light to propagate in a high-order mode. Specifically, as shown in FIG. 4, the third propagation section 32 made of silicon has a core width of 2.0 μm included in the blunt region R that can significantly reduce the increase rate of the effective refractive index of light relative to the increase rate of the core width. The third propagation section 32 has a core width equal to that of the first propagation section 13.

[0038] Note that "the core width of the third propagation section 32 is equal to the core width of the first propagation section 13" does not mean that the core width of the third propagation section 32 and the core width of the first propagation section 13 are completely equal in the strict sense, but also includes a slight difference in size due to manufacturing errors, etc. The term "equal" has the same meaning in the description of the shapes of each component of the phase shifter 1 described later.

[0039] Moreover, the third propagation section 32 has a core length greater than the core length of the first propagation section 13. Specifically, the third propagation section 32 is formed to have a core length of 10.35 μm, which is 0.35 μm greater than the core length of the first propagation section 13. Note that in FIG. 2 and other figures, the difference of 0.35 μm between the core lengths of the first propagation section 13 and the third propagation section 32 is exaggerated to make the difference easier to understand.

[0040] The third reduction section 33 is a section that optically couples the third core layer 30 to the fifth core layer 50, and is a section that transitions the first light propagated from the third propagation section 32 to the fifth core layer 50. The third reduction section 33 has a core width that gradually decreases along the emission direction Da1 from the end on the emission reverse direction Da2 side to the end on the emission direction Da1 side. Specifically, the core width of the third reduction section 33 is 2.0 μm at the end on the emission reverse direction Da2 side, and 0.15 μm at the end on the emission direction Da1 side (not shown). The core width of the third reduction section 33 at the end on the emission direction Da1 side is as small as possible in the manufacturing process used. The third reduction section 33 is formed with a core length of 35 μm.

[0041] The third reduced portion 33 is formed so that its emission direction Da1 side overlaps with a fifth expanded portion 51 (to be described later) of the fifth core layer 50 in the second direction Db.

[0042] The fifth core layer 50 includes a fifth extension portion 51 and a fifth emission portion 52. The fifth extension portion 51 and the fifth emission portion 52 are formed in this order in series along the emission direction Da1. The fifth core layer 50 has a constant core thickness of 0.40 μm from the end portion on the emission reverse direction Da2 side to the end portion on the emission direction Da1 side. In contrast, the fifth core layer 50 has a core width that differs between the fifth extension portion 51 and the fifth emission portion 52.

[0043] The fifth extension 51 is a portion optically coupled to the third reduction section 33, and guides the first light propagating from the third reduction section 33 in the emission direction Da1. The fifth extension 51 has a core width gradually expanding along the emission direction Da1 from the end on the emission reverse direction Da2 side to the end on the emission direction Da1 side. Specifically, the core width of the fifth extension 51 is 0.15 μm at the end on the emission reverse direction Da2 side (not shown) and 1.0 μm at the end on the emission direction Da1 side. The core width at the end on the emission reverse direction Da2 side of the fifth extension 51 is as small as possible in the manufacturing process used. The fifth extension 51 is formed with a core length of 15 μm.

[0044] The fifth exit section 52 is a section through which the first light propagates from the fifth extension section 51, and guides the first light propagated from the fifth extension section 51 to the output-side multiplexer Mo. The fifth exit section 52 has an end on the output direction Da1 side optically coupled to the output-side multiplexer Mo. The fifth exit section 52 has a constant core width from the end on the output reverse direction Da2 side to the end on the output direction Da1 side, and is formed smaller than the first propagation section 13 and the third propagation section 32. Specifically, the fifth exit section 52 is formed with a core width of 1.0 μm. The fifth exit section 52 has the same core width as the first entrance section 11. In this embodiment, the fifth exit section 52 corresponds to the first output section.

[0045] The above is a description of the first core layer 10, the third core layer 30, and the fifth core layer 50 that constitute the first optical path L1. Next, a description will be given of the second core layer 20, the fourth core layer 40, and the sixth core layer 60 that constitute the second optical path L2.

[0046] The second core layer 20 includes a second incident portion 21, a second expansion portion 22, a second propagation portion 23, and a second contraction portion 24. The second incident portion 21, the second expansion portion 22, the second propagation portion 23, and the second contraction portion 24 are formed in this order along the emission direction Da1. The second core layer 20 has a constant core thickness of 0.40 μm from the end portion on the emission reverse direction Da2 side to the end portion on the emission direction Da1 side. In contrast, the second core layer 20 has a core width that differs depending on the second incident portion 21, the second expansion portion 22, the second propagation portion 23, and the second contraction portion 24.

[0047] Moreover, the second core layer 20 has a shape similar to that of the first core layer 10. Specifically, in the second core layer 20, the second entrance portion 21 is formed in the same shape as the first entrance portion 11, the second expansion portion 22 is formed in the same shape as the first expansion portion 12, and the second contraction portion 24 is formed in the same shape as the first contraction portion 14. In contrast, in the second core layer 20, the second propagation portion 23 is formed in a shape different from that of the first propagation portion 13. Specifically, the second propagation portion 23 has a different core length from that of the first propagation portion 13. That is, the first core layer 10 and the second core layer 20 are formed in the same shape except for the core length of the first propagation portion 13 and the core length of the second propagation portion 23. For this reason, in the following description of the second entrance portion 21, the second expansion portion 22, the second propagation portion 23, and the second contraction portion 24, the description of the sizes is partially omitted.

[0048] The second incident portion 21 is a portion optically coupled to the input-side multiplexer Mi, and guides the second light propagating from the input-side multiplexer Mi in the output direction Da1. The second incident portion 21 has a constant core width from its end on the output reverse direction Da2 side to its end on the output direction Da1 side. In this embodiment, the second incident portion 21 corresponds to the second input portion.

[0049] The second extension portion 22 is a portion through which the second light propagates from the second incident portion 21. In the second extension portion 22, the core width from the end portion on the side of the reverse emission direction Da2 to the end portion on the side of the emission direction Da1 gradually expands along the emission direction Da1.

[0050] The second propagation section 23 is a section through which the second light propagates from the second extension section 22, and guides the second light propagated from the second extension section 22 in the emission direction Da1. The second propagation section 23 has a constant core width from the end on the emission reverse direction Da2 side to the end on the emission direction Da1 side, and is large enough to allow the second light to propagate in a high-order mode. Specifically, the second propagation section 23 made of silicon nitride has a core width of 2.0 μm, which is included in the blunt region R that can significantly reduce the increase rate of the effective refractive index of light relative to the increase rate of the core width, as shown in FIG. 4.

[0051] Further, the second propagation section 23 has a core length greater than the core length of the first propagation section 13. Specifically, the second propagation section 23 is formed to have a core length of 10.35 μm, which is 0.35 μm greater than the core length of the first propagation section 13. The second propagation section 23 is formed to have a core length equal to the core length of the third propagation section 32. Note that in FIG. 2 and other figures, the difference of 0.35 μm between the core lengths of the second propagation section 23 and the first propagation section 13 is illustrated in an exaggerated manner to make the difference easier to understand.

[0052] The second contraction section 24 is a section that optically couples the second core layer 20 to the fourth core layer 40, and is a section that transitions the second light propagated to the second propagation section 23 to the fourth core layer 40. The second contraction section 24 has a core width that gradually decreases along the output direction Da1 from an end on the output reverse direction Da2 side to an end on the output direction Da1 side. In addition, the second contraction section 24 is formed so that the output direction Da1 side overlaps with a fourth extension section 41 (described later) of the fourth core layer 40 in the second direction Db.

[0053] The fourth core layer 40 includes a fourth extension section 41, a fourth propagation section 42, and a fourth contraction section 43. The fourth extension section 41, the fourth propagation section 42, and the fourth contraction section 43 are formed in series in this order along the emission direction Da1. The fourth core layer 40 has a constant core thickness of 0.21 μm from the end on the emission reverse direction Da2 side to the end on the emission direction Da1 side. In contrast, the fourth core layer 40 has different core widths depending on the fourth extension section 41, the fourth propagation section 42, and the fourth contraction section 43.

[0054] Moreover, the fourth core layer 40 has a shape similar to that of the third core layer 30. Specifically, in the fourth core layer 40, the fourth expansion portion 41 is formed in the same shape as the third expansion portion 31, and the fourth contraction portion 43 is formed in the same shape as the third contraction portion 33. In contrast, in the fourth core layer 40, the fourth propagation portion 42 is formed in a shape different from that of the third propagation portion 32. Specifically, the fourth propagation portion 42 has a different core length from that of the third propagation portion 32. That is, the third core layer 30 and the fourth core layer 40 are formed in the same shape except for the core length of the third propagation portion 32 and the core length of the fourth propagation portion 42. For this reason, in the following description of the fourth expansion portion 41, the fourth propagation portion 42, and the fourth contraction portion 43, the description of the sizes is partially omitted.

[0055] The fourth extension section 41 is a portion optically coupled to the second reduction section 24, and guides the second light propagating from the second reduction section 24 in the emission direction Da1. The fourth extension section 41 has a core width that gradually expands along the emission direction Da1 from its end on the emission reverse direction Da2 side to its end on the emission direction Da1 side.

[0056] The fourth propagation section 42 is a section through which the first light propagates from the fourth extension section 41, and guides the first light propagated from the fourth extension section 41 in the emission direction Da1. The fourth propagation section 42 has a constant core width from the end on the emission reverse direction Da2 side to the end on the emission direction Da1 side, and is large enough to allow the first light to propagate in a high-order mode. Specifically, the fourth propagation section 42 made of silicon has a core width of 2.0 μm, which is included in the blunt region R that can significantly reduce the increase rate of the effective refractive index of light relative to the increase rate of the core width, as shown in FIG.

[0057] Moreover, the fourth propagation section 42 has a core length shorter than the core length of the second propagation section 23. Specifically, the fourth propagation section 42 is formed to have a core length of 10 μm, which is shorter than the core length of the second propagation section 23 by 0.35 μm. Moreover, the fourth propagation section 42 is formed to have a core length equal to the core length of the first propagation section 13.

[0058] The fourth reduction section 43 is a section that optically couples the fourth core layer 40 to the sixth core layer 60, and is a section that transitions the second light propagated from the fourth propagation section 42 to the sixth core layer 60. The fourth reduction section 43 has a core width that gradually decreases along the emission direction Da1 from an end on the emission reverse direction Da2 side to an end on the emission direction Da1 side. In addition, the fourth reduction section 43 is formed so that the emission direction Da1 side overlaps with a sixth extension section 61 (described later) of the sixth core layer 60 in the second direction Db.

[0059] The sixth core layer 60 includes a sixth extension portion 61 and a sixth emission portion 62. The sixth extension portion 61 and the sixth emission portion 62 are formed in this order in series along the emission direction Da1. The sixth core layer 60 has a constant core thickness of 0.40 μm from the end on the emission reverse direction Da2 side to the end on the emission direction Da1 side. In contrast, the sixth core layer 60 has a core width that differs between the sixth extension portion 61 and the sixth emission portion 62.

[0060] The sixth extension section 61 is a portion optically coupled to the fourth reduction section 43, and guides the second light propagating from the fourth reduction section 43 in the emission direction Da1. The sixth extension section 61 has a core width that gradually expands along the emission direction Da1 from its end on the opposite emission direction Da2 side to its end on the emission direction Da1 side.

[0061] The sixth exit section 62 is a section through which the second light propagates from the sixth extension section 61, and guides the second light propagated from the sixth extension section 61 to the output-side multiplexer Mo. The sixth exit section 62 has an end on the output direction Da1 side optically coupled to the output-side multiplexer Mo. The sixth exit section 62 has a constant core width from its end on the output reverse direction Da2 side to its end on the output direction Da1 side, and is formed smaller than the second propagation section 23 and the fourth propagation section 42. In this embodiment, the sixth exit section 62 corresponds to the second output section.

[0062] When the first core layer 10, the second core layer 20, the third core layer 30 and the fourth core layer 40 are formed in this manner, the first core layer 10 has a smaller core length than the third core layer 30 by the difference between the core lengths of the first propagation section 13 and the third propagation section 32. The second core layer 20 has a larger core length than the fourth core layer 40 by the difference between the core lengths of the second propagation section 23 and the fourth propagation section 42. The difference between the core lengths of the first propagation section 13 and the third propagation section 32 is equal to the difference between the core lengths of the second propagation section 23 and the fourth propagation section 42. In other words, the sum of the core lengths of the first propagation section 13 and the third propagation section 32 is equal to the sum of the core lengths of the second propagation section 23 and the fourth propagation section 42.

[0063] In addition, the material and shape of the portion of the first optical path L1 different from the first propagation section 13 and the third propagation section 32 are the same as the material and shape of the portion of the second optical path L2 different from the second propagation section 23 and the fourth propagation section 42. The first optical path L1 and the second optical path L2 have the same size in the first direction Da. Here, the shape of the portion of the first optical path L1 different from the first propagation section 13 and the third propagation section 32 is the same as the shape of the portion of the second optical path L2 different from the second propagation section 23 and the fourth propagation section 42 includes the meaning that the size of the portion of the first optical path L1 different from the first propagation section 13 and the third propagation section 32 in the first optical path L1 in the first direction Da is equal to the size of the portion of the second optical path L2 different from the second propagation section 23 and the fourth propagation section 42 in the first optical path L2 in the first direction Da.

[0064] The first entrance portion 11, the second entrance portion 21, the fifth exit portion 52 and the sixth exit portion 62 are formed of the same material, that is, silicon nitride.

[0065] Here, the input side multiplexer Mi and output side multiplexer Mo to which the phase shifter 1 of this embodiment is connected are formed of silicon nitride, which is the same material as the first entrance portion 11, the second entrance portion 21, the fifth exit portion 52, and the sixth exit portion 62. For this reason, the phase shifter 1 is capable of directly connecting the first entrance portion 11 and the second entrance portion 21 to the input side multiplexer Mi, and is capable of directly connecting the fifth exit portion 52 and the sixth exit portion 62 to the output side multiplexer Mo.

[0066] In this embodiment, the first propagation section 13 functions as a 1-1 waveguide, and the third propagation section 32 functions as a 1-2 waveguide. The second propagation section 23 functions as a 2-1 waveguide, and the fourth propagation section 42 functions as a 2-2 waveguide.

[0067] To manufacture the phase shifter 1 of this embodiment, first, a silicon substrate 2 is prepared, and a first clad layer 3a is formed on the silicon substrate 2. Then, a third core layer 30 and a fourth core layer 40 are formed on the first clad layer 3a by patterning. After that, a second clad layer 3b is formed on the third core layer 30, the fourth core layer 40, and a portion of the first clad layer 3a where the third core layer 30 and the fourth core layer 40 are not formed. As a result, the third core layer 30 and the fourth core layer 40 are covered with the second clad layer 3b. Then, unnecessary portions of the second clad layer 3b formed on the third core layer 30 and the fourth core layer 40 are removed by, for example, CMP (Chemical Mechanical Polish).

[0068] Thereafter, the first core layer 10, the second core layer 20, the fifth core layer 50, and the sixth core layer 60 are formed on the second clad layer 3b by patterning. Then, the third clad layer 3c is formed on the first core layer 10, the second core layer 20, the fifth core layer 50, the sixth core layer 60, and the second clad layer 3b in the portions where the first core layer 10, the second core layer 20, the fifth core layer 50, and the sixth core layer 60 are not formed. As a result, the first core layer 10, the second core layer 20, the fifth core layer 50, and the sixth core layer 60 are covered with the third clad layer 3c.

[0069] Thereafter, unnecessary portions of the third cladding layer 3c formed on the first core layer 10, the second core layer 20, the fifth core layer 50, and the sixth core layer 60 are removed by, for example, CMP. This completes the manufacture of the above-mentioned phase shifter 1 in which the first cladding layer 3a to the third cladding layer 3c and the first core layer 10 to the sixth core layer 60 are formed on the silicon substrate 2.

[0070] Next, an operation of the phase adjuster 1 of this embodiment will be described. In the phase adjuster 1 of this embodiment, when a first light is propagated from the input-side multiplexer Mi to the first incident portion 11 of the first core layer 10, the first light propagates through the first extension portion 12 and the first propagation portion 13 along the output direction Da1, and is propagated from the first propagation portion 13 to the first reduction portion 14.

[0071] The first reduced portion 14 has a core width that is smaller along the emission direction Da1. Therefore, in the first reduced portion 14, the confinement of light when the laser light propagates gradually weakens along the emission direction Da1. Therefore, the first light propagating through the first reduced portion 14 is gradually transferred to the third extension portion 31 of the third core layer 30. The first reduced portion 14 and the third extension portion 31 function as a converter that transfers the first light from the first core layer 10 to the third core layer 30.

[0072] Then, the first light that has been transitioned to the third extension portion 31 is propagated along the emission direction Da1, and is propagated from the third extension portion 31 to the third contraction portion 33 via the third propagation portion 32.

[0073] The third narrowing portion 33 has a core width that is narrowed along the emission direction Da1. Therefore, in the third narrowing portion 33, the confinement of light when the laser light propagates gradually weakens along the emission direction Da1. Therefore, the first light propagating through the third narrowing portion 33 is gradually transferred to the fifth extension portion 51 of the fifth core layer 50. The third narrowing portion 33 and the fifth extension portion 51 function as a converter that transfers the first light from the third core layer 30 to the fifth core layer 50.

[0074] Then, the first light transitioned to the fifth extension section 51 propagates along the output direction Da1, and propagates from the fifth extension section 51 to the fifth output section 52. Then, the first light propagated to the fifth output section 52 propagates along the output direction Da1, and propagates to the output-side multiplexer Mo.

[0075] In addition, in the phase adjuster 1, when the second light is propagated from the input side multiplexer Mi to the second incident portion 21 of the second core layer 20, the second light propagates through the second extension portion 22 and the second propagation portion 23 along the output direction Da1, and is propagated from the second propagation portion 23 to the second reduction portion 24.

[0076] The second reduced portion 24 has a core width that is smaller along the emission direction Da1. Therefore, in the second reduced portion 24, the confinement of light when the laser light propagates gradually weakens along the emission direction Da1. Therefore, the second light propagating through the second reduced portion 24 is gradually transferred to the fourth extension portion 41 of the fourth core layer 40. The second reduced portion 24 and the fourth extension portion 41 function as a converter that transfers the second light from the second core layer 20 to the fourth core layer 40.

[0077] Then, the second light that has been transitioned to the fourth extension portion 41 is propagated along the emission direction Da1, and is propagated from the fourth extension portion 41 to the fourth contraction portion 43 via the fourth propagation portion .

[0078] The fourth reduced portion 43 has a core width that is narrowed along the emission direction Da1. Therefore, in the fourth reduced portion 43, the confinement of light when the laser light propagates gradually weakens along the emission direction Da1. Therefore, the second light propagating through the fourth reduced portion 43 is gradually transitioned to the sixth extended portion 61 of the sixth core layer 60. The fourth reduced portion 43 and the sixth extended portion 61 function as a converter that transitions the second light from the fourth core layer 40 to the sixth core layer 60.

[0079] Then, the second light transitioned to the sixth extension portion 61 propagates along the output direction Da1, and propagates from the sixth extension portion 61 to the sixth output portion 62. Then, the second light propagated to the sixth output portion 62 propagates along the output direction Da1, and propagates to the output-side multiplexer Mo.

[0080] In this manner, the phase adjuster 1 in which the first light propagates through the first optical path L1 and the second light propagates through the second optical path L2 changes the phase of the first light and the phase of the second light when propagating through the first optical path L1 and the second optical path L2, respectively. Therefore, the phase adjuster 1 can arbitrarily adjust the phases of the first light propagating through the first optical path L1 and the second light propagating through the second optical path L2, and provide a phase difference between the first light output from the first optical path L1 and the second light output from the second optical path L2. When the wavelengths of the first light and the second light are each 1550 nm, the phase adjuster 1 of this embodiment can provide a phase difference of 90° between the first light output from the first optical path L1 and the second light output from the second optical path L2 by the above configuration.

[0081] Here, in explaining the change in the phase of light propagating through the first optical path L1 and the second optical path L2, the change in the phase of light will first be explained using the optical path X shown in Figures 5 and 6. The optical path X shown in Figures 5 and 6 has a clad layer LC around it, whose refractive index is smaller than that of the optical path X. The propagation constant β of the light propagating through the optical path X can be calculated by the following formula 1.

[0082] (Number 1) β=k×n eff =2π / λ×n eff Here, k in the formula 1 is the wave number of light. eff is the effective refractive index of the light on the optical path X. In addition, λ in Equation 1 is the wavelength of the light.

[0083] The change in phase φ of light propagating along the optical path X can be calculated using the propagation constant β from the following equation 2.

[0084] (Number 2) φ=βL=2π / λ×n eff ×L Here, L in Equation 2 is the path length of the optical path X, and corresponds to the size of the phase adjuster 1 of the present embodiment in the first direction Da.

[0085] As shown in Equation 2, the phase of light is λ / n eff When the light travels a distance of , the phase rotates by 2π. The effective refractive index of light is affected by the size of the optical path X. Specifically, the effective refractive index of light is affected by the thickness t, which is the size of the optical path X in the direction corresponding to the second direction Db in the phase adjuster 1 of this embodiment, and the width w, which is the size of the optical path X in the direction corresponding to the third direction Dc. Therefore, when there are two optical paths X, the change in the phase φ of each of the lights propagating through the two optical paths X can be calculated by the above formula 2.

[0086] For this reason, the phase difference Δφ occurring between the light propagating through the first comparison optical path CL1 and the light propagating through the second comparison optical path CL2 shown in Fig. 7 can be calculated by the following Equation 3. The first comparison optical path CL1 and the second comparison optical path CL2 are formed of the same material having the same refractive index.

[0087] (Number 3) Δφ=2π / λ((n eff1 ×L1)-(n eff2 ×L2)) Here, L1 in the formula 3 is the path length of the first comparative optical path CL1, and corresponds to the size in the first direction Da of the phase adjuster 1 of the present embodiment. eff1 is the effective refractive index of the light in the first comparative optical path CL1. Furthermore, L2 in Equation 3 is the path length of the second comparative optical path CL2, and corresponds to the size in the first direction Da in the phase shifter 1 of this embodiment. Furthermore, n eff2 is the effective refractive index of the light in the second comparative optical path CL2.

[0088] In this way, by utilizing the difference in effective refractive index and the difference in path length between the first comparison optical path CL1 and the second comparison optical path CL2, a phase difference can be imparted between the light exiting from the first comparison optical path CL1 and the light exiting from the second comparison optical path CL2.

[0089] As described above, the effective refractive index of light is affected by the thickness and width of each of the first and second comparative optical paths CL1 and CL2. Therefore, the comparative phase adjuster 100 having the third and fourth comparative optical paths CL3 and CL4 shown in Fig. 8 can impart a phase difference Δφ between two lights propagating through two optical paths by the third and fourth comparative optical paths CL3 and CL4 having portions with different widths.

[0090] The third comparative optical path CL3 and the fourth comparative optical path CL4 have a first region I portion expanding along the first direction Da and a third region III portion contracting along the first direction Da, like the first core layer 10 and the second core layer 20 of this embodiment. The third comparative optical path CL3 has a size in the third direction Dc of a width w u The fourth comparative optical path CL4 has a second region II portion extending from the first direction Da to the third direction Dc, and has a path length L3 in the first direction Da. L and has a second region II portion extending from the first direction Da to the second direction Da, and is formed with a path length L4. The third comparative optical path CL3 and the fourth comparative optical path CL4 have the same path length. The third comparative optical path CL3 and the fourth comparative optical path CL4 are formed of the same material, that is, have the same refractive index.

[0091] The width w of the third comparative optical path CL3 u is the width w of the fourth comparative optical path CL4 L When the third comparative optical path CL3 and the fourth comparative optical path CL4 are configured in this manner, the phase difference Δφ imparted between the light propagating through the third comparative optical path CL3 and the light propagating through the fourth comparative optical path CL4 can be calculated by the following formula 4.

[0092] (Number 4) Δφ=(φ I_3 -φ I_4 )+(φ II_3 -φ II_4 )+(φ III_3 -φ III_4 ) Here, (φ I_3 -φI_4 ) represents a phase difference given between the light propagating through the third comparative optical path CL3 and the light propagating through the fourth comparative optical path CL4 in the first region I portion in the third comparative optical path CL3 and the fourth comparative optical path CL4. II_3 -φ II_4 ) represents a phase difference given between the light propagating through the third comparative optical path CL3 and the light propagating through the fourth comparative optical path CL4 in the second region II portion in the third comparative optical path CL3 and the fourth comparative optical path CL4. III_3 -φ III_4 ) indicates a phase difference imparted between the light propagating through the third comparative optical path CL3 and the light propagating through the fourth comparative optical path CL4 in the third region III portion in the third comparative optical path CL3 and the fourth comparative optical path CL4.

[0093] In addition, the third comparative optical path CL3 and the fourth comparative optical path CL4 have different widthwise sizes in the first region I, the second region II, and the third region III of the third comparative optical path CL3 and the fourth comparative optical path CL4, so that in the third comparative optical path CL3 and the fourth comparative optical path CL4, a difference occurs in the effective refractive index of light in the first region I, the second region II, and the third region III of the third comparative optical path CL3 and the fourth comparative optical path CL4.

[0094] The effective refractive index n eff3 The effective refractive index of the light in the fourth comparative optical path CL4 is n eff4 In this case, as shown in the above-mentioned formula 3, the phase difference Δφ imparted between the light propagating through the third comparative optical path CL3 and the light propagating through the fourth comparative optical path CL4 can be calculated by the following formula 5.

[0095] (Number 5) Δφ=2π / λ((n eff3 ×L3)-(n eff4 ×L4)) As described above, the third comparative optical path CL3 and the fourth comparative optical path CL4 have the same path length. Therefore, the above formula 5 can be replaced with the following formula 6.

[0096] (Number 6) Δφ=2π / λ×L3(n eff3 -n eff4 )=2π / λ×L4(n eff3 -n eff4 ) Generally, the rate of increase in the effective refractive index of light relative to the rate of increase in the width direction of the optical waveguide, i.e., the size in the third direction Dc, decreases as the size of the optical waveguide in the third direction Dc increases, as shown in Fig. 9. That is, the rate of increase in the effective refractive index of light relative to the rate of increase in the size of the optical waveguide in the third direction Dc decreases as the size of the optical waveguide in the third direction Dc increases.

[0097] For example, the size of the third direction Dc of the optical waveguide is a size that allows light to propagate in a high-order mode, as in the first propagation section 13, the second propagation section 23, the third propagation section 32, and the fourth propagation section 42 of this embodiment. In this case, the size of the third direction Dc of these propagation sections 13, 23, 32, and 42 becomes a blunt region R where the increase rate of the effective refractive index of light becomes blunt, as shown in FIG. 9. Therefore, even if a difference in the effective refractive index of light is generated in the blunt region R where the increase rate of the effective refractive index of light becomes blunt, it is difficult to increase the difference in the effective refractive index of light. Therefore, as can be seen from the above formula 6, the larger the required phase difference Δφ, the larger the required path length of the optical waveguide. However, if the path length of the optical waveguide, i.e., the size in the first direction Da, is increased, the size of the first direction Da of the phase shifter 1 becomes large, which is not preferable.

[0098] Furthermore, as the size of the optical waveguide in the first direction Da is increased, the error in the phase difference Δφ tends to increase due to dimensional errors caused by manufacturing errors in the first direction Da of the optical waveguide, i.e., the influence caused by manufacturing errors becomes greater.

[0099] Therefore, the inventors have considered imparting a phase difference between the lights propagating through the two optical waveguides by using members having different optical refractive indices for the two optical waveguides. Below, a method of imparting a phase difference between the lights propagating through these two optical paths will be described using a fifth comparative optical path CL5 and a sixth comparative optical path CL6 which are schematic diagrams of two optical waveguides having members having different optical refractive indices as shown in Fig. 10.

[0100] The fifth comparative optical path CL5 and the sixth comparative optical path CL6 each have an entrance region A into which light is incident, wide regions B to D formed with widths at which the rate of increase in the effective refractive index of light becomes slower, and an exit region E from which light exits. The width w2 of the wide regions B to D is formed larger than the width w1 of the entrance region A and the exit region E.

[0101] In the fifth comparative optical path CL5 and the sixth comparative optical path CL6, the wide region B and the wide region D are formed of the same material, and the refractive indexes of the light are equal. In contrast, the wide region C of the fifth comparative optical path CL5 and the sixth comparative optical path CL6 is formed of a material having a different refractive index. In Fig. 10, the different materials are shown with different hatching to make the differences between the materials easier to understand.

[0102] The phase φ of the light emitted from the fifth comparative optical path CL5 out5 can be calculated using the following formula 7.

[0103] (Number 7) φ out5 =φ in5 +φ A_5 +φ B_5 +φ C_5 +φ D_5 +φ E_5 Here, φ in Equation 7 in5 is the phase of the light incident on the fifth comparative optical path CL5. A_5 , φ B_5 , φ C_5 , φ D_5 , φ E_5is the amount of change in phase that occurs when the light propagates through the entrance region A, the wide regions B to D, and the exit region E of the fifth comparative optical path CL5.

[0104] In addition, the phase φ of the light emitted from the sixth comparative optical path CL6 out6 can be calculated using the following formula 8.

[0105] (Number 8) φ out6 =φ in6 +φ A_6 +φ B_6 +φ C_6 +φ D_6 +φ E_6 Here, φ in Equation 8 in6 is the phase of the light incident on the sixth comparative optical path CL6. A_6 , φ B_6 , φ C_6 , φ D_6 , φ E_6 is the amount of change in phase that occurs when the light propagates through the entrance region A, the wide regions B to D, and the exit region E of the sixth comparative optical path CL6.

[0106] Here, the entrance area A, the wide area B, the wide area D, and the exit area E of each of the fifth comparative optical path CL5 and the sixth comparative optical path CL6 are formed of the same material and have the same shape. A_5 and φ A_6 are equal. B_5 and φ B_6 are equal. D_5 and φ D_6 are equal. E_5 and φ E_6 are equal.

[0107] In contrast, the wide regions C of the fifth and sixth comparative optical paths CL5 and CL6 have the same shape, but are made of materials with different optical refractive indices. C_5 and φ C_6 is different.

[0108] Therefore, the phase difference Δφ imparted between the light propagating through the fifth comparative optical path CL5 and the light propagating through the sixth comparative optical path CL6 can be calculated by the following formula 9.

[0109] (Number 9) Δφ=φ out5 -φ out6 =(φ in5 -φ in6 )+(φ C_5 -φ C_6 ) Here, (φ in5 -φ in6 ) represents the phase difference between the light beams incident on the fifth comparative optical path CL5 and the sixth comparative optical path CL6. C_5 -φ C_6 ) indicates the phase difference of the light newly imparted in the wide region C of each of the fifth comparative optical path CL5 and the sixth comparative optical path CL6.

[0110] In this way, by using materials having different optical refractive indices, a phase difference can be imparted to two lights propagating through two optical waveguides. For this reason, in the phase adjuster 1 of this embodiment, the first optical path L1 and the second optical path L2 are formed by including silicon nitride and silicon, which have different optical refractive indices.

[0111] Next, to show the effect of the phase adjuster 1 of this embodiment, it will be compared with the comparative phase adjuster 100 shown in FIG. 7. As described above, in the comparative phase adjuster 100, the third comparative optical path CL3 and the fourth comparative optical path CL4 are formed of the same material, that is, they are made of materials having the same refractive index. In addition, in the comparative phase adjuster 100, the width w u is the width w of the fourth comparison optical path CL4 L The third comparative optical path CL3 and the fourth comparative optical path CL4 have the same path length. The comparative phase adjuster 100 can impart a phase difference Δφ, which can be calculated by the above formula 6, between the light propagating through the third comparative optical path CL3 and the light propagating through the fourth comparative optical path CL4.

[0112] Here, in order to compare the phase adjuster 1 of the present embodiment with the comparative phase adjuster 100, the comparative phase adjuster 100 is configured to be able to give a phase difference of 90° between the light emitted from the third comparative optical path CL3 and the light emitted from the fourth comparative optical path CL4. In this case, the width w u is formed to have a core width of 2.0 μm, which is the same as the core widths of the first propagation portion 13, the second propagation portion 23, the third propagation portion 32, and the fourth propagation portion 42. Then, the width w L is formed with a size of 1.8 μm which is different from 2.0 μm.

[0113] Moreover, the size in the first direction Da of the first region I and the third region III of each of the third comparative optical path CL3 and the fourth comparative optical path CL4 is 20 μm, which is the same as the core length of each of the first extension section 12 and the second extension section 22. In such a configuration, in order to impart a phase difference of 90° between the light emitted from the third comparative optical path CL3 and the light emitted from the fourth comparative optical path CL4, the size in the first direction Da of the second region II of each of the third comparative optical path CL3 and the fourth comparative optical path CL4 needs to be 98 μm.

[0114] The comparative phase adjuster 100 thus configured provides a phase difference of 90° between the light emitted from the third comparative optical path CL3 and the light emitted from the fourth comparative optical path CL4 due to the difference in the shape of the second region II portion of each of the third comparative optical path CL3 and the fourth comparative optical path CL4. u and the width w of the fourth comparison optical path CL4 L A phase difference of 90° is provided between the light exiting from the third comparative optical path CL3 and the light exiting from the fourth comparative optical path CL4 due to a difference in the effective refractive index of the light generated by the difference between these. In the comparative phase adjuster 100, the second region II portions of the third comparative optical path CL3 and the fourth comparative optical path CL4 serve as phase adjustment sections that provide a phase difference between the light exiting from the third comparative optical path CL3 and the light exiting from the fourth comparative optical path CL4.

[0115] In contrast, in the phase adjuster 1 of the present embodiment, as shown in Fig. 11, the first entrance portion 11 of the first optical path L1 is identical in shape and material to the second entrance portion 21 of the second optical path L2, and the first extension portion 12 of the first optical path L1 is identical in shape and material to the second extension portion 22 of the second optical path L2. In addition, in the phase adjuster 1, the first contraction portion 14 of the first optical path L1 is identical in shape and material to the second contraction portion 24 of the second optical path L2, and the third extension portion 31 of the first optical path L1 is identical in shape and material to the fourth extension portion 41 of the second optical path L2. In addition, in the phase adjuster 1, the third contraction portion 33 of the first optical path L1 is identical in shape and material to the fourth contraction portion 43 of the second optical path L2, and the fifth extension portion 51 of the first optical path L1 is identical in shape and material to the sixth extension portion 61 of the second optical path L2. Furthermore, in the phase adjuster 1, the fifth extension portion 51 of the first optical path L1 has the same shape and material as the sixth extension portion 61 of the second optical path L2, and the fifth exit portion 52 of the first optical path L1 has the same shape and material as the sixth exit portion 62 of the second optical path L2.

[0116] However, in the phase adjuster 1, the first propagation section 13 of the first optical path L1 and the second propagation section 23 of the second optical path L2 are made of the same material, but have different core lengths. Also, in the phase adjuster 1, the third propagation section 32 of the first optical path L1 and the fourth propagation section 42 of the second optical path L2 are made of the same material, but have different core lengths.

[0117] The phase adjuster 1 thus configured provides a phase difference between the first light propagating through the first propagation section 13 and the second light propagating through the second propagation section 23 due to the difference in core length between the first propagation section 13 of the first optical path L1 and the second propagation section 23 of the second optical path L2. Specifically, in the second propagation section 23, which has a core length larger than that of the first propagation section 13, a portion having a size in the first direction Da larger than that of the first propagation section 13 provides a phase difference between the first light and the second light. More specifically, in the second propagation section 23, a portion having a size in the first direction Da larger than that of the first propagation section 13 by 0.35 μm provides a phase difference between the first light and the second light. In the phase adjuster 1 of this embodiment, a portion of the second propagation section 23 having a size larger than that of the first propagation section 13 by 0.35 μm serves as a phase adjuster that provides a phase difference between the first light and the second light. In the following, the portion of the second propagation section 23 that gives a phase difference between the first light and the second light will also be referred to as a first phase adjustment section 71.

[0118] In addition, the phase adjuster 1 provides a phase difference between the first light propagating through the third propagation section 32 and the second light propagating through the fourth propagation section 42 due to the difference in core length between the third propagation section 32 of the first optical path L1 and the fourth propagation section 42 of the second optical path L2. Specifically, in the third propagation section 32, which has a larger size in the first direction Da than the fourth propagation section 42, a portion having a larger size in the first direction Da than the fourth propagation section 42 provides a phase difference between the first light and the second light. More specifically, in the third propagation section 32, a portion having a size in the first direction Da that is 0.35 μm larger than the fourth propagation section 42 provides a phase difference between the first light and the second light. In the phase adjuster 1 of this embodiment, a portion of the third propagation section 32 that is 0.35 μm larger than the fourth propagation section 42 serves as a phase adjuster that provides a phase difference between the first light and the second light. In the following, the portion of the third propagation section 32 that provides a phase difference between the first light and the second light will also be referred to as a second phase adjustment section 72.

[0119] In the phase adjuster 1 of this embodiment, the first optical path L1 and the second optical path L2 are identical in material and shape to each other except for the first phase adjuster 71 and the second phase adjuster 72. The phase adjuster 1 can adjust the phase difference provided between the first light and the second light by adjusting the size of the first direction Da of each of the first phase adjuster 71 and the second phase adjuster 72. For example, when the size of the first direction Da of each of the first phase adjuster 71 and the second phase adjuster 72 is increased from 0.35 μm to 0.65 μm, a phase difference of 180° can be provided between the first light output from the first optical path L1 and the second light output from the second optical path L2.

[0120] Here, the first core layer 10 including the first propagation portion 13 is made of silicon nitride. Also, the fourth core layer 40 including the fourth propagation portion 42 having the same core length as the first propagation portion 13 is made of silicon, which is a material different from the material forming the first core layer 10.

[0121] The second core layer 20 including the second propagation portion 23 is made of silicon nitride. The third core layer 30 including the third propagation portion 32 having the same core length as the second propagation portion 23 is made of silicon, which is a material different from the material forming the second core layer 20.

[0122] Silicon nitride and silicon have different optical refractive indices when the core width is the same, as shown in Fig. 4. Therefore, as shown in Fig. 12, an effective refractive index difference Δn eff As a result, an effective refractive index difference Δn eff It is possible to impart a phase difference according to the

[0123] In addition, between the second propagation portion 23 and the third propagation portion 32, there is an effective refractive index difference Δn effAs a result, an effective refractive index difference Δn eff It is possible to impart a phase difference according to the

[0124] In FIG. 12, the solid line indicates the effective refractive index of silicon, and the dashed line indicates the effective refractive index of silicon nitride.

[0125] As described above, in the first optical path L1, the members and shapes of the portions different from the first propagation section 13 and the third propagation section 32 are the same as the members and shapes of the portions different from the second propagation section 23 and the fourth propagation section 42 in the second optical path L2. Here, the portions different from the first propagation section 13 and the third propagation section 32 in the first optical path L1 are referred to as non-propagation portions in the first optical path L1, and the portions different from the second propagation section 23 and the fourth propagation section 42 in the second optical path L2 are referred to as non-propagation portions in the second optical path L2.

[0126] In the first optical path L1, the material and shape of the non-propagation portion in the first optical path L1 are the same as the material and shape of the non-propagation portion in the second optical path L2. Therefore, the product of the size in the first direction Da of the non-propagation portion in the first optical path L1 and the effective refractive index of light is the same as the product of the size in the first direction Da of the non-propagation portion in the second optical path L2 and the effective refractive index of light.

[0127] Incidentally, a change in the phase of the first light propagating through a portion other than the propagation direction in the first optical path L1 can be calculated by multiplying the magnitude of the portion other than the propagation direction in the first direction Da in the first optical path L1 and the effective refractive index of the light, using the above-mentioned formula 2. Also, a change in the phase of the second light propagating through a portion other than the propagation direction in the second optical path L2 can be calculated by multiplying the magnitude of the portion other than the propagation direction in the first direction Da in the second optical path L2 and the effective refractive index of the light, using the above-mentioned formula 2.

[0128] Therefore, the phase change of the first light propagating through the portion other than the propagation in the first optical path L1, which has the same material and shape, and the phase change of the second light propagating through the portion other than the propagation in the second optical path L2, are equal to each other.

[0129] 13 shows a table summarizing the components and core lengths of the phase adjustment units of the phase adjuster 1 and the comparative phase adjuster 100 of this embodiment. As shown in FIG. 13, the first phase adjustment unit 71 and the second phase adjustment unit 72 of the phase adjuster 1 of this embodiment have core lengths significantly shorter than the second region II portions of the third comparison optical path CL3 and the fourth comparison optical path CL4, which are the phase adjustment units of the comparative phase adjuster 100. This allows the phase adjuster 1 to make the core lengths of the first optical path L1 and the second optical path L2 significantly shorter than the core lengths of the third comparison optical path CL3 and the fourth comparison optical path CL4 of the comparative phase adjuster 100.

[0130] Furthermore, in the phase adjuster 1 of this embodiment, the core widths of the first phase adjuster 71 and the second phase adjuster 72 are formed to be 2.0 μm included in the blunt region R that can significantly reduce the increase rate of the effective refractive index of light relative to the increase rate of the core width. Therefore, even if the core widths of the first phase adjuster 71 and the second phase adjuster 72 deviate from the design value due to manufacturing errors, the influence of the effective refractive index of light deviating from the design value can be suppressed.

[0131] Furthermore, in the comparative phase adjuster 100, the core width of the second region II portion of the third comparative optical path CL3 is formed to be 2.0 μm included in the blunt region R, and the core width of the second region II portion of the fourth comparative optical path CL4 is formed to be 2.8 μm included in the blunt region R. Therefore, even if the core widths of the second region II portions of each of the third comparative optical path CL3 and the fourth comparative optical path CL4 deviate from the design value due to manufacturing errors, it is possible to suppress the influence of the effective refractive index of light deviating from the design value.

[0132] However, the phase difference that the comparative phase adjuster 100 imparts between the light propagating through the third comparative optical path CL3 and the light propagating through the fourth comparative optical path CL4 is proportional to the core length of the second region II portion of each of the third comparative optical path CL3 and the fourth comparative optical path CL4, as shown in the above-mentioned equation 6.

[0133] Here, the second region II portions of the third comparison optical path CL3 and the fourth comparison optical path CL4 of the comparison phase adjuster 100 are much larger than the core lengths of the first phase adjuster 71 and the second phase adjuster 72 of the phase adjuster 1 of this embodiment. Therefore, in the comparison phase adjuster 100, when the core widths of the second region II portions of the third comparison optical path CL3 and the fourth comparison optical path CL4 deviate from the design values, the influence on the phase difference to be applied becomes large. In other words, the comparative phase adjuster 100 is relatively affected by manufacturing errors.

[0134] 14 shows the effect on the phase difference to be applied when the core width deviates from the design value due to manufacturing errors in phase adjuster 1 of this embodiment and comparative phase adjuster 100. In FIG. 14, the solid line indicates the phase difference deviation due to manufacturing errors in phase adjuster 1 of this embodiment, and the dashed line indicates the phase difference deviation due to manufacturing errors in comparative phase adjuster 100.

[0135] 14, when the core width of the second region II portion of the third comparison optical path CL3 of the comparison phase shifter 100 deviates from 2.0 μm due to a manufacturing error, the phase difference to be imparted increases from the design value of 90° as the core width decreases from the design value. Also, the phase difference to be imparted decreases from the design value of 90° as the core width of the second region II portion of the third comparison optical path CL3 increases from the design value.

[0136] In contrast, even if the core widths of first phase adjustment unit 71 and second phase adjustment unit 72 of phase adjuster 1 of the present embodiment deviate from 2.0 μm due to manufacturing errors, the phase difference to be imparted remains almost unchanged from the design value of 90°. That is, phase adjuster 1 can suppress the influence of manufacturing errors in the core widths of first phase adjustment unit 71 and second phase adjustment unit 72.

[0137] As described above, the phase adjuster 1 includes the first optical path L1 extending along the first direction Da and through which the first light propagates, and the second optical path L2 extending along the first direction Da and through which the second light propagates. The first optical path L1 includes the third core layer 30 formed of a member having a refractive index different from that of the second core layer 20 of the second optical path L2, and the first core layer 10 formed of a member having a refractive index different from that of the fourth core layer 40 of the second optical path L2.

[0138] According to this, the first core layer 10 and the fourth core layer 40, which are formed from materials having different optical refractive indices, and the second core layer 20 and the third core layer 30, can impart a phase difference between the first light propagating through the first optical path L1 and the second light propagating through the second optical path L2.

[0139] For this reason, it is easier to suppress the magnitude of the first direction Da of each of the first optical path L1 and the second optical path L2 than in a configuration in which a phase difference is provided between the first light propagating through the first optical path L1 and the second light propagating through the second optical path L2 due to the difference in the shapes of the first optical path L1 and the second optical path L2. Therefore, it is possible to provide a phase difference between the first light propagating through the first optical path L1 and the second light propagating through the second optical path L2 while suppressing the magnitude of the first direction Da of each of the first optical path L1 and the second optical path L2.

[0140] Furthermore, according to the above embodiment, the following effects can be obtained.

[0141] (1) In the above embodiment, the first optical path L1 includes the first propagation section 13 and the third propagation section 32 formed of members having different optical refractive indices. The second optical path L2 includes the second propagation section 23 having a different optical refractive index from the third propagation section 32 and a different optical refractive index from the fourth propagation section 42, and also includes the fourth propagation section 42 having a different optical refractive index from the first propagation section 13.

[0142] According to this, the first propagation section 13 can impart a phase difference between the first light and the second light between the fourth propagation section 42 and the first propagation section 13 based on the difference in effective refractive index between the light of the first propagation section 13 and the fourth propagation section 42. In addition, the third propagation section 32 can impart a phase difference between the first light and the second light between the second propagation section 23 and the third propagation section 32 based on the difference in effective refractive index between the light of the third propagation section 32 and the second propagation section 23.

[0143] Therefore, compared to a case where the first optical path L1 and the second optical path L2 are each formed by one member to provide a phase difference between the first light and the second light, it is easier to reduce the size of each of the first optical path L1 and the second optical path L2 in a predetermined direction. Therefore, it is easier to increase the phase difference provided between the first light and the second light while reducing the size of each of the first optical path L1 and the second optical path L2 in the predetermined direction.

[0144] (2) In the above embodiment, the first propagation section 13 is formed of the same material as the second propagation section 23, and has the same core width as the core width of the second propagation section 23, but has a core length different from the core length of the second propagation section 23. The third propagation section 32 is formed of the same material as the fourth propagation section 42, and has the same core width as the core width of the fourth propagation section 42, but has a core length different from the core length of the fourth propagation section 42.

[0145] This makes it possible to provide a phase difference between the first light and the second light according to the difference in core length between the first propagation section 13 and the second propagation section 23, both of which are made of the same material. Furthermore, it is possible to provide a phase difference between the first light and the second light according to the difference in core length between the third propagation section 32 and the fourth propagation section 42, both of which are made of the same material.

[0146] (3) In the above embodiment, the first propagation section 13 and the third propagation section 32 have core widths set to a size that allows the first light to propagate in a higher-order mode. The second propagation section 23 and the fourth propagation section 42 have core widths set to a size that allows the second light to propagate in a higher-order mode.

[0147] As described above, the increase rate of the effective refractive index of light relative to the increase rate of the core width of each of the first propagation section 13 and the third propagation section 32 decreases as the core width of each of the first propagation section 13 and the third propagation section 32 increases. That is, the increase rate of the effective refractive index of light relative to the increase rate of the core width of each of the first propagation section 13 and the third propagation section 32 decreases as the core width of each of the first propagation section 13 and the third propagation section 32 increases. When the core width of each of the first propagation section 13 and the third propagation section 32 is large enough to propagate in a higher-order mode, the increase rate of the effective refractive index of light relative to the increase rate of the core width of each of the first propagation section 13 and the third propagation section 32 is very small.

[0148] Moreover, the rate of increase of the effective refractive index of light with respect to the rate of increase of the core width of each of the second propagation section 23 and the fourth propagation section 42 decreases as the core width of each of the second propagation section 23 and the fourth propagation section 42 increases. That is, the rate of increase of the effective refractive index of light with respect to the rate of increase of the size of each of the second propagation section 23 and the fourth propagation section 42 in the third direction Dc decreases as the core width of each of the second propagation section 23 and the fourth propagation section 42 increases. And, when the core width of each of the second propagation section 23 and the fourth propagation section 42 is large enough to propagate in a higher-order mode, the rate of increase of the effective refractive index of light with respect to the rate of increase of the core width of each of the second propagation section 23 and the fourth propagation section 42 is very small.

[0149] Here, the first propagation section 13 and the third propagation section 32, and the second propagation section 23 and the fourth propagation section 42 are sections that impart a phase difference between the first light and the second light.

[0150] In this embodiment, the core widths of the first propagation section 13, the third propagation section 32, the second propagation section 23, and the fourth propagation section 42 are set to a size that allows the first light and the second light to propagate in a high-order mode. This makes it easy to reduce the error in the effective refractive index of light due to the manufacturing error in the core widths of the first propagation section 13, the third propagation section 32, the second propagation section 23, and the fourth propagation section 42. Therefore, it is possible to reduce the error in the phase difference caused by the manufacturing error when providing the first light and the second light with a phase difference according to the difference in core length between the first propagation section 13 and the second propagation section 23. It is also possible to reduce the error in the phase difference caused by the manufacturing error when providing the first light and the second light with a phase difference according to the difference in core length between the third propagation section 32 and the fourth propagation section 42.

[0151] (4) In the above embodiment, the materials and shapes of the parts of the first optical path L1 that are different from the first propagation section 13 and the third propagation section 32 in the first optical path L1 are the same as the materials and shapes of the parts of the first optical path L1 that are different from the second propagation section 23 and the fourth propagation section 42 in the second optical path L2.

[0152] According to this, the portions in the first optical path L1 and the second optical path L2 that impart a phase difference between the first light and the second light can be limited to the first propagation section 13 and the third propagation section 32, and the second propagation section 23 and the fourth propagation section 42. In other words, the portions that impart a phase difference between the first light and the second light can be portions that can reduce an error in the phase difference imparted between the first light and the second light due to a manufacturing error. Therefore, the influence of a manufacturing error on the phase difference imparted by the phase adjuster 1 between the first light and the second light can be further reduced.

[0153] (5) In the above embodiment, the third propagation section 32 has a core length greater than the core length of the first propagation section 13. The fourth propagation section 42 has a core length smaller than the core length of the second propagation section 23.

[0154] This makes it possible to make the sum of the core length of the first propagation section 13 and the core length of the third propagation section 32 closer to the sum of the core length of the second propagation section 23 and the fourth propagation section 42. This makes it possible to easily make the sizes of the first optical path L1 and the second optical path L2 in the first direction Da closer to each other.

[0155] Incidentally, when the phase adjuster 1, in which the first optical path L1 and the second optical path L2 have different sizes in the first direction Da, is mounted in an optical IC chip including optical components other than the phase adjuster 1, the positions of the first direction Da of the inlet and outlet of light in the first optical path L1 and the second optical path L2 are made to coincide with each other. In this case, if the optical path having the shorter path length of the first optical path L1 or the second optical path L2 is entirely formed in a straight line, the optical path having the longer path length cannot be entirely formed in a straight line, and it is necessary to form a part of it in a curved line. Then, when mounting an optical component other than the phase adjuster 1 in the optical IC chip, it is necessary to provide a detour around the curved part. In this case, since it is necessary to secure a distance between the optical path having a curved shape and the optical component, the mounting position of the optical component is limited, making it difficult to mount the optical component.

[0156] In contrast, according to the phase adjuster 1 of the present embodiment in which the sizes of the first optical path L1 and the second optical path L2 in the first direction Da can be easily made closer to each other, the distance between the first optical path L1 and the optical component and the distance between the second optical path L2 and the optical component can be easily made closer to each other. Therefore, the mounting position of the optical component is less likely to be restricted, and the optical component can be easily mounted.

[0157] (6) In the above embodiment, the sum of the core length of the first propagation section 13 and the core length of the third propagation section 32 is equal to the sum of the core length of the second propagation section 23 and the core length of the fourth propagation section 42.

[0158] This allows the first optical path L1 and the second optical path L2 to have the same size in a given direction. Therefore, when the first optical path L1 and the second optical path L2 are formed linearly as in the phase adjuster 1 of this embodiment, the positions of the first direction Da of the inlet and the outlet of the light propagating through the first optical path L1 and the second optical path L2 can be made to coincide. Then, when the phase adjuster 1 is mounted in an optical IC chip including optical components other than the phase adjuster 1, the distance between the first optical path L1 and the second optical path L2 and the optical components can be made even closer, making it easier to mount the optical components.

[0159] (7) In the above embodiment, the product of the magnitude of the first direction Da of the non-propagation portion in the first optical path L1 and the effective refractive index of light is the same as the product of the first direction Da of the non-propagation portion in the second optical path L2 and the effective refractive index of light.

[0160] According to this, the amount of change in phase when the first light propagates through the portion other than the propagation in the first optical path L1 can be made equal to the amount of change in phase when the second light propagates through the portion other than the propagation in the second optical path L2. Therefore, the portion that imparts a phase difference between the first light and the second light in the first optical path L1 and the second optical path L2 can be limited to the first propagation section 13 and the third propagation section 32, and the second propagation section 23 and the fourth propagation section 42. In other words, the portion that imparts a phase difference between the first light and the second light can be a portion that can reduce the error of the phase difference imparted between the first light and the second light due to the manufacturing error. Therefore, the influence of the manufacturing error on the phase difference imparted by the phase adjuster 1 between the first light and the second light can be reduced.

[0161] (8) In the above embodiment, the first optical path L1 has a first entrance portion 11 into which the first light is incident and a fifth exit portion 52 from which the first light is emitted. The second optical path L2 has a second entrance portion 21 into which the second light is incident and a sixth exit portion 62 from which the second light is emitted. The first entrance portion 11, the second entrance portion 21, the fifth exit portion 52, and the sixth exit portion 62 are formed of the same member.

[0162] According to this, when the input side multiplexer Mi that inputs the first light and the second light to the phase shifter 1 and the output side multiplexer Mo that receives the first light and the second light output from the phase shifter 1 are made of the same material, the phase shifter 1 can be applied without using another material converter.

[0163] (9) In the above embodiment, the first optical path L1 and the second optical path L2 are formed of silicon and silicon nitride.

[0164] As described above, silicon and silicon nitride are materials having a characteristic of having a blunt region R where the rate of increase of the effective refractive index of light becomes significantly smaller with respect to the rate of increase of the core width. Therefore, according to the present embodiment in which the first optical path L1 and the second optical path L2 are formed of silicon and silicon nitride, the effective refractive index of light can be made less susceptible to the effects of manufacturing errors in the core widths of the first propagation section 13 and the third propagation section 32. In addition, the effective refractive index of light can be made less susceptible to the effects of manufacturing errors in the core widths of the second propagation section 23 and the fourth propagation section 42.

[0165] (First modified example of the first embodiment) In the above-described first embodiment, an example has been described in which the core width of the first entrance portion 11 and the core width of the fifth exit portion 52 are smaller than the core widths of the first propagation portion 13 and the third propagation portion 32, but the present invention is not limited to this. Also, in the above-described first embodiment, an example has been described in which the core width of the second entrance portion 21 and the core width of the sixth exit portion 62 are smaller than the core widths of the second propagation portion 23 and the fourth propagation portion 42, but the present invention is not limited to this.

[0166] 15, the first core layer 10 may not have the first extension portion 12, and the core width of the first entrance portion 11 may be formed equal to the core width of the first propagation portion 13. The fifth core layer 50 may be formed such that the core width of the fifth exit portion 52 is equal to the core width of the third propagation portion 32. Although not shown, the core width of the first entrance portion 11 may be formed larger than the core width of the first propagation portion 13, and the core width of the fifth exit portion 52 may be formed larger than the core width of the third propagation portion 32.

[0167] 15, the second core layer 20 may not have the second extension portion 22, and the core width of the second entrance portion 21 may be formed equal to the core width of the second propagation portion 23. The sixth core layer 60 may be formed such that the core width of the sixth exit portion 62 is equal to the core width of the fourth propagation portion 42. Although not shown, the core width of the second entrance portion 21 may be formed larger than the core width of the second propagation portion 23, and the core width of the sixth exit portion 62 may be formed larger than the core width of the fourth propagation portion 42.

[0168] (Second modified example of the first embodiment) In the above-described first embodiment, an example in which the core width of the first propagation section 13 and the core width of the third propagation section 32 are formed to be equal has been described, but the present invention is not limited to this. Also, in the above-described first embodiment, an example in which the core width of the second propagation section 23 and the core width of the fourth propagation section 42 are formed to be equal has been described, but the present invention is not limited to this.

[0169] For example, as shown in Fig. 16, the core width of the first propagation section 13 may be formed to be larger than the core width of the third propagation section 32. Also, as shown in Fig. 16, the core width of the second propagation section 23 may be formed to be larger than the core width of the fourth propagation section 42.

[0170] (Third modified example of the first embodiment) In the above-described first embodiment, an example has been described in which the phase adjuster 1 has two optical paths, that is, the first optical path L1 and the second optical path L2, but the present invention is not limited to this.

[0171] For example, as shown in FIG. 17, the phase adjuster 1 may have another optical path L5 in addition to the first optical path L1 and the second optical path L2, or may have four or more optical paths (not shown).

[0172] (Fourth Modification of the First Embodiment) In the above-described first embodiment, an example in which one phase adjustment unit is provided in each of the first optical path L1 and the second optical path L2 has been described, but the present invention is not limited to this.

[0173] For example, as shown in FIG. 18, the first optical path L1 may be formed by two consecutive sets of the first core layer 10, the third core layer 30, and the fifth core layer 50, or may be formed by three or more consecutive sets, not shown. The second optical path L2 may be formed by two consecutive sets of the second core layer 20, the fourth core layer 40, and the sixth core layer 60, or may be formed by three or more consecutive sets, not shown. When the first optical path L1 is formed by two consecutive sets of the first core layer 10, the third core layer 30, and the fifth core layer 50, and the second optical path L2 is formed by two consecutive sets of the second core layer 20, the fourth core layer 40, and the sixth core layer 60, two phase adjustment units are provided in each of the first optical path L1 and the second optical path L2.

[0174] (Fifth modified example of the first embodiment) In the above-described first embodiment, an example was described in which the first core layer 10, the second core layer 20, the fifth core layer 50 and the sixth core layer 60 are formed of silicon nitride, and the third core layer 30 and the fourth core layer 40 are formed of silicon, but this is not limited to this.

[0175] For example, the first core layer 10, the second core layer 20, the fifth core layer 50 and the sixth core layer 60 may be formed of silicon, and the third core layer 30 and the fourth core layer 40 may be formed of silicon nitride.

[0176] (Sixth Modification of the First Embodiment) In the above-described first embodiment, an example in which the first core layer 10 to the sixth core layer 60 are formed as strip-type waveguides has been described, but the present invention is not limited to this.

[0177] For example, the first core layer 10 to the sixth core layer 60 may be formed as a ridge-type waveguide having a convex cross-sectional shape perpendicular to the first direction Da.

[0178] Second embodiment Next, the second embodiment will be described with reference to FIG. 19. In this embodiment, the configurations of the first optical path L1 and the second optical path L2 are different from those of the first embodiment. The rest is the same as the first embodiment. Therefore, in this embodiment, the parts different from the first embodiment will be mainly described, and the description of the parts similar to the first embodiment may be omitted.

[0179] 19, the first optical path L1 of the present embodiment does not have a fifth core layer 50, unlike the first embodiment. In this case, the third reduction section 33 in the third core layer 30 functions as a first output section that guides the first light propagated from the third propagation section 32 to the output-side multiplexer Mo.

[0180] Moreover, the second optical path L2 of the present embodiment does not have the sixth core layer 60, unlike the first embodiment. In this case, the fourth reduction section 43 in the fourth core layer 40 functions as a second output section that guides the second light propagated from the fourth propagation section 42 to the output-side multiplexer Mo.

[0181] When the first optical path L1 and the second optical path L2 are formed in this manner, the first entrance portion 11 and the second entrance portion 21 are made of the same material, silicon nitride. The third reduction portion 33 and the fourth reduction portion 43 are made of the same material, silicon. The first entrance portion 11 and the second entrance portion 21, and the third reduction portion 33 and the fourth reduction portion 43 are made of materials with different optical refractive indices.

[0182] The reason why the first optical path L1 and the second optical path L2 are formed in this manner will be described below.

[0183] The input side multiplexer Mi to which the phase shifter 1 of this embodiment is connected is made of silicon nitride. In contrast, the output side multiplexer Mo is made of silicon, unlike the first embodiment. That is, the phase shifter 1 of this embodiment is connected to multiplexers Mi and Mo made of different materials on the input and output sides.

[0184] For this reason, the phase shifter 1 of this embodiment is capable of directly connecting the first incident section 11 and the second incident section 21 to the input side multiplexer Mi, and is capable of directly connecting the third reduction section 33 and the fourth reduction section 43 to the output side multiplexer Mo.

[0185] As described above, the first optical path L1 of this embodiment has the first entrance portion 11 into which the first light is incident, and the third reduction portion 33 from which the first light is emitted. The second optical path L2 has the second entrance portion 21 into which the second light is incident, and the second reduction portion 24 from which the second light is emitted. The first entrance portion 11 and the second entrance portion 21 are formed of the same material. The third reduction portion 33 and the fourth reduction portion 43 are formed of the same material, but are formed of a different material from the first entrance portion 11 and the second entrance portion 21.

[0186] According to this, when the input-side multiplexer Mi and the output-side multiplexer Mo connected to the phase shifter 1 are formed of different materials, it is possible to eliminate the need for a material converter for connecting the phase shifter 1 to the input-side multiplexer Mi and the output-side multiplexer Mo. In other words, the phase shifter 1 can also be used as a material converter.

[0187] Third embodiment Next, the third embodiment will be described with reference to Figs. 20 to 22. In this embodiment, the core widths of the first entrance section 11, the first propagation section 13, the third propagation section 32, and the fifth exit section 52 are different from those of the first embodiment. In addition, in this embodiment, the core widths of the second entrance section 21, the second propagation section 23, the fourth propagation section 42, and the sixth exit section 62 are different from those of the first embodiment. Other than that, this embodiment is similar to the first embodiment. Therefore, in this embodiment, the parts different from the first embodiment will be mainly described, and the description of the parts similar to those of the first embodiment may be omitted.

[0188] 20, the first entrance portion 11 and the fifth exit portion 52 in this embodiment are formed to have a core width of 1.0 μm. The core width of the first propagation portion 13 is formed to be 1.24 μm. The core width of the third propagation portion 32 is formed to be larger than the core width of the first propagation portion 13. Specifically, the core width of the third propagation portion 32 is formed to be 1.45 μm.

[0189] In this embodiment, the second input portion 21 and the sixth output portion 62 are formed to have a core width of 1.0 μm. The second propagation portion 23 is formed to have a core width of 1.4 μm. The fourth propagation portion 42 is formed to have a core width larger than the core width of the second propagation portion 23. Specifically, the fourth propagation portion 42 is formed to have a core width of 1.45 μm.

[0190] The reason why the core width of the third propagation section 32 is formed larger than the core width of the first propagation section 13 and the core width of the fourth propagation section 42 is formed larger than the core width of the second propagation section 23 will be explained below.

[0191] As described above, the third core layer 30 including the third propagation portion 32 and the fourth core layer 40 including the fourth propagation portion 42 are made of silicon. In contrast, the first core layer 10 including the first propagation portion 13 and the second core layer 20 including the second propagation portion 23 are made of silicon nitride. Also, as shown in Fig. 21, silicon has a larger effective refractive index of light than silicon nitride under the same core width condition. In Fig. 21, the solid line indicates the effective refractive index of light of silicon, and the dashed line indicates the effective refractive index of light of silicon nitride.

[0192] As described above, the increase rate of the effective refractive index of light relative to the increase rate of the core width of each of the third propagation section 32 and the fourth propagation section 42 made of silicon decreases as the core width of each of the third propagation section 32 and the fourth propagation section 42 increases. In addition, the increase rate of the effective refractive index of light relative to the increase rate of the core width of each of the first propagation section 13 and the second propagation section 23 made of silicon nitride also decreases as the core width of each of the first propagation section 13 and the second propagation section 23 increases.

[0193] 21 and 22, there are regions where the rate of increase in the effective refractive index of light relative to the rate of increase in the core width is significantly different between silicon nitride and silicon, and regions where there is almost no difference between the core widths. In Fig. 22, the solid line indicates the rate of increase in the effective refractive index of light relative to the rate of increase in the core width of silicon, and the dashed line indicates the rate of increase in the effective refractive index of light relative to the rate of increase in the core width of silicon nitride.

[0194] For example, a comparison is made between a case where the core width of the third propagation section 32 made of silicon is smaller than 1.5 μm and a case where the core width of the first propagation section 13 made of silicon nitride is smaller than 1.5 μm. The increase rate of the effective refractive index of light relative to the increase rate of the core width of the third propagation section 32 made of silicon is larger than the increase rate of the effective refractive index of light relative to the increase rate of the core width of the first propagation section 13 made of silicon nitride. Also, the increase rate of the effective refractive index of light relative to the increase rate of the core width of the fourth propagation section 42 made of silicon is larger than the increase rate of the effective refractive index of light relative to the increase rate of the core width of the second propagation section 23 made of silicon nitride. That is, there are regions in which the increase rate of the effective refractive index of light relative to the increase rate of the core width is significantly different between the third propagation section 32 and the fourth propagation section 42 made of silicon and the first propagation section 13 and the second propagation section 23 made of silicon nitride.

[0195] 21 and 22, a comparison is made between a case where the core width of the third propagation section 32 made of silicon is 1.5 μm or more and a case where the core width of the first propagation section 13 made of silicon nitride is 1.5 μm or more. The increase rate of the effective refractive index of light relative to the increase rate of the core width of the third propagation section 32 made of silicon is approximately equal to the increase rate of the effective refractive index of light relative to the increase rate of the core width of the first propagation section 13 made of silicon nitride. Also, the increase rate of the effective refractive index of light relative to the increase rate of the core width of the fourth propagation section 42 made of silicon is approximately equal to the increase rate of the effective refractive index of light relative to the increase rate of the core width of the second propagation section 23 made of silicon nitride.

[0196] Therefore, if the core widths of the first propagation section 13, the second propagation section 23, the third propagation section 32, and the fourth propagation section 42 are set in a region where the increase rate of the effective refractive index of light with respect to the increase rate of the core width is significantly different depending on the member, there is a risk of the effect of design error becoming large. For example, when the core widths of the third propagation section 32 and the first propagation section 13 are formed to be 1.4 μm, if the core widths of the third propagation section 32 and the first propagation section 13 deviate by the same manufacturing error, the difference in the effective refractive index of the light will be different. Also, when the core widths of the fourth propagation section 42 and the second propagation section 23 are formed to be 1.4 μm, if the core widths of the fourth propagation section 42 and the second propagation section 23 deviate by the same manufacturing error, the difference in the effective refractive index of the light will be different.

[0197] This causes an error in the phase difference provided by the phase adjuster 1 between the first light output from the first optical path L1 and the second light output from the second optical path L2. For this reason, when the core width is set in a region where the increase rate of the effective refractive index of light relative to the increase rate of the core width differs greatly depending on the material, it is desirable to adjust the core width depending on the material.

[0198] Here, the first propagation section 13 and the second propagation section 23 of this embodiment are set to 1.40 μm, which is a region where the increase rate of the effective refractive index of light relative to the increase rate of the core width differs greatly depending on the member. In contrast, the third propagation section 32 of this embodiment has a larger core width than the first propagation section 13 and is formed at 1.45 μm. Moreover, the fourth propagation section 42 of this embodiment has a larger core width than the second propagation section 23 and is formed at 1.45 μm.

[0199] In other words, of the first propagation section 13 and the third propagation section 32, the third propagation section 32 formed of silicon which is the side having the larger effective refractive index of light has a larger core width than the first propagation section 13 formed of silicon nitride which is the side having the smaller effective refractive index of light. Also, of the second propagation section 23 and the fourth propagation section 42, the fourth propagation section 42 formed of silicon which is the side having the larger effective refractive index of light has a larger core width than the second propagation section 23 formed of silicon nitride which is the side having the smaller effective refractive index of light.

[0200] 22, the rate of increase in the effective refractive index of light with respect to the increase in core width in the third propagation section 32 can be made closer to the rate of increase in the effective refractive index of light with respect to the increase in core width in the first propagation section 13. Also, as shown by the arrow in FIG. 22, the rate of increase in the effective refractive index of light with respect to the increase in core width in the fourth propagation section 42 can be made closer to the rate of increase in the effective refractive index of light with respect to the increase in core width in the second propagation section 23.

[0201] This makes it possible to suppress a difference in the effective refractive index between the third propagation section 32 and the first propagation section 13 even if the core widths of the third propagation section 32 and the first propagation section 13 deviate by the same manufacturing error. Also, even if the core widths of the fourth propagation section 42 and the second propagation section 23 deviate by the same manufacturing error, it is possible to suppress a difference in the effective refractive index between the fourth propagation section 42 and the second propagation section 23.

[0202] Therefore, even if an error due to a manufacturing error occurs in the phase difference that the phase adjuster 1 imparts between the first light output from the first optical path L1 and the second light output from the second optical path L2, the error can be suppressed. That is, the effect of the manufacturing error on the phase difference that the phase adjuster 1 imparts between the first light and the second light can be reduced.

[0203] (Other embodiments) Representative embodiments of the present disclosure have been described above, but the present disclosure is not limited to the above-described embodiments and can be modified in various ways, for example, as described below.

[0204] In the above embodiment, an example has been described in which the first optical path L1 and the second optical path L2 are each configured by a combination of a core layer formed of silicon nitride and a core layer formed of silicon, but the present invention is not limited to this.

[0205] For example, one of the first optical path L1 and the second optical path L2 may be composed of only a core layer made of either silicon nitride or silicon. For example, the first core layer 10, the third core layer 30, and the fifth core layer 50 may all be made of silicon nitride, or may all be made of silicon. Alternatively, the first optical path L1 may be formed by one core layer made of either silicon nitride or silicon.

[0206] The first optical path L1 and the second optical path L2 may include a core layer formed of a material other than silicon nitride and silicon. For example, the first optical path L1 and the second optical path L2 may include a core layer formed of lithium niobate, i.e., LiNbO3. In this case, the first core layer 10 may be formed of lithium niobate, the third core layer 30 may be formed of silicon nitride, and the fifth core layer 50 may be formed of silicon.

[0207] In the above-described embodiment, an example has been described in which the core widths of the first propagation section 13 and the third propagation section 32 are set to a size that allows the first light to propagate in a higher-order mode. Also, an example has been described in which the core widths of the second propagation section 23 and the fourth propagation section 42 are set to a size that allows the second light to propagate in a higher-order mode. However, the present invention is not limited to this.

[0208] For example, the first propagation section 13 and the third propagation section 32 may have a core width set to a size that allows the first light to propagate in a single mode. Also, the second propagation section 23 and the fourth propagation section 42 may have a core width set to a size that allows the second light to propagate in a single mode.

[0209] In the above embodiment, an example has been described in which the material and shape of the portion of the first optical path L1 different from the first propagation section 13 and the third propagation section 32 are the same as the material and shape of the portion of the second optical path L2 different from the second propagation section 23 and the fourth propagation section 42, but the present invention is not limited to this. For example, the material and shape of the portion of the first optical path L1 different from the first propagation section 13 and the third propagation section 32 may be different from the material and shape of the portion of the second optical path L2 different from the second propagation section 23 and the fourth propagation section 42.

[0210] In the above-described embodiment, an example was described in which the sum of the core length of the first propagation section 13 and the core length of the third propagation section 32 is equal to the sum of the core length of the second propagation section 23 and the core length of the fourth propagation section 42, but this is not limited to this.

[0211] For example, in the above embodiment, the sum of the core length of the first propagation section 13 and the core length of the third propagation section 32 may be smaller or larger than the sum of the core length of the second propagation section 23 and the core length of the fourth propagation section 42.

[0212] In the above embodiment, the size of the first direction Da of the first optical path L1 and the size of the first direction Da of the second optical path L2 are equal to each other, but the present invention is not limited to this. For example, the size of the first direction Da of the first optical path L1 may be smaller or larger than the size of the first direction Da of the second optical path L2.

[0213] In the above embodiment, the phase shifter 1 is disposed between the input-side multiplexer Mi and the output-side multiplexer Mo, but the present invention is not limited to this. For example, the phase shifter 1 may be connected to a multi-mode interference (MMI) device.

[0214] In the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential, except in cases where it is particularly expressly stated that they are essential or where they are clearly considered to be essential in principle.

[0215] In the above-described embodiments, when numerical values ​​such as the number, values, amounts, ranges, etc. of components of the embodiments are mentioned, they are not limited to the specific numbers unless it is specifically stated as required or unless it is clearly limited to a specific number in principle.

[0216] In the above-described embodiments, when referring to the shapes, positional relationships, etc. of components, etc., there is no limitation to those shapes, positional relationships, etc., unless specifically stated or in principle limited to a specific shape, positional relationship, etc.

[0217] (In view of the present disclosure) The present disclosure described above can be understood from the following viewpoints, for example.

[0218] [First viewpoint] A phase adjuster for adjusting phases of a plurality of incident light beams, A first optical path (L1) extending along a predetermined direction (Da) and through which a first light beam of the plurality of light beams propagates; a second optical path (L2) formed to extend along the predetermined direction opposite to the first optical path, through which a second light different from the first light among the plurality of light beams propagates; The first optical path and the second optical path have portions formed of materials having optical refractive indices different from each other.

[0219] [Second viewpoint] the first optical path includes a 1-1 waveguide (13) and a 1-2 waveguide (32) formed of members having optical refractive indices different from each other; The phase shifter according to the first aspect, wherein the second optical path includes a 2-1 waveguide (23) and a 2-2 waveguide (42) that have a refractive index different from at least one of the 1-1 waveguide and the 1-2 waveguide and are formed of materials having refractive indices different from each other.

[0220] [Third Perspective] When a direction in which the first optical path and the second optical path face each other is defined as a facing direction (Dc), the 1-1 waveguide is formed of the same material as the 2-1 waveguide, the facing direction has the same size as the 2-1 waveguide in the facing direction, and the size in the predetermined direction is different from that of the 2-1 waveguide, The phase shifter according to a second aspect, wherein the 1-2 waveguide is formed of the same material as the 2-2 waveguide, has the same size in the facing direction as the 2-2 waveguide in the facing direction, and has a size in the predetermined direction different from that of the 2-2 waveguide.

[0221] [Fourth viewpoint] the 1-1 waveguide and the 1-2 waveguide have a size in the opposing direction that allows the first light to propagate in a higher-order mode; The phase shifter according to a third aspect, wherein a size of the 2-1 waveguide and the 2-2 waveguide in the opposing direction is set to a size that allows the second light to propagate in a higher order mode.

[0222] [Fifth viewpoint] The phase adjuster according to a fourth aspect, wherein a member and a shape of a portion of the first optical path different from the 1-1 waveguide and the 1-2 waveguide are identical to a member and a shape of a portion of the second optical path different from the 2-1 waveguide and the 2-2 waveguide.

[0223] [Sixth viewpoint] the 1-1 waveguide has a size in the predetermined direction that is larger than a size in the predetermined direction of the 2-1 waveguide, The phase shifter according to a fifth aspect, wherein the 1-2 waveguide has a size in the predetermined direction smaller than a size in the predetermined direction of the 2-2 waveguide.

[0224] [Seventh viewpoint] The phase shifter according to a sixth aspect, wherein a sum of a size of the 1-1 waveguide in the predetermined direction and a size of the 1-2 waveguide in the predetermined direction is equal to a sum of a size of the 1-2 waveguide in the predetermined direction and a size of the 2-2 waveguide in the predetermined direction.

[0225] [Eighth viewpoint] The phase shifter according to any one of the fourth to seventh aspects, wherein a product of a size in the predetermined direction of a portion of the first optical path different from the 1-1 waveguide and the 1-2 waveguide and an effective refractive index of light is equal to a product of a size in the predetermined direction of a portion of the second optical path different from the 2-1 waveguide and the 2-2 waveguide and an effective refractive index of light.

[0226] [Ninth viewpoint] the 1-1 waveguide and the 1-2 waveguide are set so that a rate of increase in the refractive index of light relative to a rate of increase in the size in the facing direction on a side where the refractive index of light is larger approaches a rate of increase in the refractive index of light relative to a rate of increase in the size in the facing direction on a side where the refractive index of light is smaller, The phase shifter according to any one of the fourth to eighth aspects, wherein the 2-1 waveguide and the 2-2 waveguide are configured so that a rate of increase in the refractive index of light with respect to a rate of increase in the size in the facing direction on a side where the refractive index of light is larger approaches a rate of increase in the refractive index of light with respect to a rate of increase in the size in the facing direction on a side where the refractive index of light is smaller.

[0227] [10th viewpoint] The 1-1 waveguide and the 1-2 waveguide are formed such that a side of a member having a larger refractive index of light is larger in the opposing direction than a side of a member having a smaller refractive index of light, The phase shifter according to a ninth aspect, wherein the 2-1 waveguide and the 2-2 waveguide are formed so that a side of a member having a larger optical refractive index is larger in the opposing direction than a side of a member having a smaller optical refractive index.

[0228] [Eleventh viewpoint] the first optical path has a first input portion (11) to which the first light is incident and a first output portion (52) from which the first light exits, the second optical path has a second input portion (21) to which the second light is incident and a second output portion (62) from which the second light is emitted, The phase adjuster according to any one of the first to tenth aspects, wherein the first input portion, the second input portion, the first output portion, and the second output portion are formed of the same member.

[0229] [12th viewpoint] the first optical path has a first input portion (11) to which the first light is incident and a first output portion (33) from which the first light exits, the second optical path has a second input portion (21) to which the second light is incident and a second output portion (43) from which the second light is emitted, The first input portion and the second input portion are formed of the same member, The phase adjuster according to any one of the first to tenth aspects, wherein the first output section and the second output section are formed of a same material and are formed of a different material from the first input section and the second input section.

[0230] [13th viewpoint] The phase shifter according to any one of the first to twelfth aspects, wherein the first optical path and the second optical path are formed of any one of silicon, silicon nitride, and lithium niobate. [Explanation of symbols]

[0231] Da given direction L1 1st optical path L2 2nd optical path

Claims

1. A phase adjuster for adjusting phases of a plurality of incident light beams, A first optical path (L1) extending along a predetermined direction (Da) and through which a first light of the plurality of light beams propagates; a second optical path (L2) formed to extend along the predetermined direction opposite to the first optical path, through which a second light different from the first light among the plurality of light beams propagates; The first optical path and the second optical path have portions formed of materials having optical refractive indices different from each other.

2. The first optical path includes a 1-1 waveguide (13) and a 1-2 waveguide (32) formed of members having different optical refractive indices from each other, 2. The phase adjuster according to claim 1, wherein the second optical path includes a 2-1 waveguide (23) and a 2-2 waveguide (42) formed of materials having optical refractive indices different from at least one of the 1-1 waveguide and the 1-2 waveguide and different from each other in optical refractive index.

3. When a direction in which the first optical path and the second optical path face each other is defined as a facing direction (Dc), the 1-1 waveguide is formed of the same material as the 2-1 waveguide, the facing direction has the same size as the 2-1 waveguide in the facing direction, and the size in the predetermined direction is different from that of the 2-1 waveguide, 3. The phase adjuster according to claim 2, wherein the first-2 waveguide is formed of the same material as the second-2 waveguide, the first-2 waveguide has the same size in the facing direction as the second-2 waveguide in the facing direction, and the first-2 waveguide has a size in the predetermined direction different from that of the second-2 waveguide.

4. the 1-1 waveguide and the 1-2 waveguide have a size in the opposing direction that allows the first light to propagate in a higher-order mode; 4. The phase shifter according to claim 3, wherein the size of the 2-1 waveguide and the 2-2 waveguide in the opposing direction is set to a size that allows the second light to propagate in a higher-order mode.

5. 5. The phase adjuster according to claim 4, wherein a material and a shape of a portion of the first optical path different from the 1-1 waveguide and the 1-2 waveguide are the same as a material and a shape of a portion of the second optical path different from the 2-1 waveguide and the 2-2 waveguide.

6. the 1-1 waveguide has a size in the predetermined direction that is larger than a size in the predetermined direction of the 2-1 waveguide, 6. The phase shifter according to claim 5, wherein the size of the first-2 waveguide in the predetermined direction is smaller than the size of the second-2 waveguide in the predetermined direction.

7. 7. The phase adjuster according to claim 6, wherein a sum of a size of the 1-1 waveguide in the predetermined direction and a size of the 1-2 waveguide in the predetermined direction is equal to a sum of a size of the 1-2 waveguide in the predetermined direction and a size of the 2-2 waveguide in the predetermined direction.

8. 8. The phase adjuster according to claim 4, wherein a product of a size in the predetermined direction of a portion of the first optical path different from the 1-1 waveguide and the 1-2 waveguide and an effective refractive index of light is equal to a product of a size in the predetermined direction of a portion of the second optical path different from the 2-1 waveguide and the 2-2 waveguide and an effective refractive index of light.

9. the 1-1 waveguide and the 1-2 waveguide are set so that a rate of increase in the refractive index of light with respect to a rate of increase in the size in the facing direction on a side where the refractive index of light is larger approaches a rate of increase in the refractive index of light with respect to a rate of increase in the size in the facing direction on a side where the refractive index of light is smaller, 8. The phase adjuster according to claim 4, wherein the 2-1 waveguide and the 2-2 waveguide are set so that a rate of increase in the refractive index of light with respect to a rate of increase in the size in the facing direction on a side where the refractive index of light is larger approaches a rate of increase in the refractive index of light with respect to a rate of increase in the size in the facing direction on a side where the refractive index of light is smaller.

10. The 1-1 waveguide and the 1-2 waveguide are formed such that a side of a member having a larger refractive index of light is larger in the opposing direction than a side of a member having a smaller refractive index of light, 10. The phase shifter according to claim 9, wherein the 2-1 waveguide and the 2-2 waveguide are formed such that a side of a member having a larger refractive index in the opposing direction is larger than a side of a member having a smaller refractive index in the opposing direction.

11. The first optical path has a first input portion (11) to which the first light is input and a first output portion (52) from which the first light is output, The second optical path has a second input portion (21) to which the second light is incident and a second output portion (62) from which the second light is emitted, 2. The phase adjuster according to claim 1, wherein the first input portion, the second input portion, the first output portion and the second output portion are formed from the same member.

12. The first optical path has a first input portion (11) to which the first light is input and a first output portion (33) from which the first light is output, The second optical path has a second input portion (21) to which the second light is incident and a second output portion (43) from which the second light is emitted, the first input portion and the second input portion are formed of the same member, 2. The phase adjuster according to claim 1, wherein the first output section and the second output section are formed of the same material and are formed of a material different from that of the first input section and the second input section.

13. 2. The phase shifter according to claim 1, wherein the first optical path and the second optical path are formed of one of silicon, silicon nitride, and lithium niobate.

Images