Optical Integrated Circuit

Abstract

The optical integrated circuit (1) includes a waveguide (20) including a first portion (21) and a second portion (22) and configured to couple an electromagnetic wave propagating through the first portion (21) with an electromagnetic wave propagating through the second portion (22), and a nonreciprocal member (40) positioned alongside the second portion (22) in the amplitude direction of the electric field component of the electromagnetic wave. In the range where the first portion (21) and the second portion (22) are coupled, the deviation between the center of energy distribution of the electric field component of the electromagnetic wave propagating through the first portion (21) and the center of energy distribution of the electric field component of the electromagnetic wave propagating through the second portion (22) falls within a predetermined range.

Description

[Technical field]

[0001] The present disclosure relates to integrated optical circuits. [Background technology]

[0002] As described in Patent Document 1, an optical isolator is known that uses a magneto-optical material Ce:YIG as a waveguide layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2007 / 083419 Summary of the Invention

[0004] An optical integrated circuit according to an embodiment of the present disclosure includes a waveguide and a nonreciprocal member. The waveguide includes a first portion and a second portion. The waveguide is configured such that an electromagnetic wave propagating through the first portion and an electromagnetic wave propagating through the second portion are coupled together. The nonreciprocal member is positioned next to the second portion in the amplitude direction of the electric field component of the electromagnetic wave. In the range where the first portion and the second portion are coupled together, a deviation between the center of energy distribution of the electric field component of the electromagnetic wave propagating through the first portion and the center of energy distribution of the electric field component of the electromagnetic wave propagating through the second portion falls within a predetermined range. [Brief description of the drawings]

[0005] [Figure 1A] 1 is a diagram showing a configuration example of a cross section along an extension direction of a waveguide of an optical integrated circuit according to an embodiment; [Figure 1B] 1 is a diagram showing a configuration example of an optical integrated circuit according to an embodiment in a cross section perpendicular to an extending direction of a waveguide. [Diagram 2] FIG. 11 is a cross-sectional view showing a configuration of an optical integrated circuit according to a comparative example. [Diagram 3]10 is a graph showing the relationship between loss when an electromagnetic wave propagates from a first portion to a second portion of a waveguide and the height of the second portion of the waveguide. [Figure 4] 1A is a diagram showing a configuration example of an optical integrated circuit in which an insulating layer is located between a waveguide and a non-reciprocal member, in a cross section along the extending direction of the waveguide. [Diagram 5] 1 is a diagram showing a configuration example of an optical integrated circuit including an inclined portion in which the waveguide becomes higher from a first portion toward a second portion, in a cross section along the extending direction of the waveguide. [Figure 6] 1 is a diagram showing a configuration example of an optical integrated circuit in which a first portion and a second portion of a waveguide are separated from each other, in a cross section taken along the extending direction of the waveguide. [Figure 7] 1 is a diagram showing a configuration example of an optical integrated circuit including an inclined portion in which the waveguide becomes lower from a first portion to a second portion, in a cross section along the extending direction of the waveguide. [Figure 8A] 1 is a diagram showing the configuration of an optical integrated circuit according to a comparative example, which propagates an electromagnetic wave in a TE mode. [Figure 8B] 8B is a CC cross-sectional view of the optical integrated circuit of FIG. 8A. [Figure 9A] FIG. 1 is a diagram showing an example of the configuration of an optical integrated circuit according to an embodiment of the present disclosure, which propagates electromagnetic waves in a TE mode. [Figure 9B] FIG. 9B is a cross-sectional view taken along line DD of FIG. 9A. [Figure 10] FIG. 9C is a diagram showing an example of a configuration in which the end of the non-reciprocity member in the configuration of FIG. 9B is curved. [Figure 11] 13 is a diagram showing a configuration example in which the inner angle of the recess on the waveguide side is an obtuse angle. FIG. [Figure 12] 12 is a diagram showing an example of a configuration in which the end of a non-reciprocity member in the configuration of FIG. 11 is curved. FIG. [Figure 13] 1A and 1B are diagrams illustrating an example configuration in which a non-reciprocal member is inserted into a waveguide. [Figure 14] 13A and 13B are diagrams illustrating an example configuration in which the second portion protrudes on the opposite side of the non-reciprocal member. [Figure 15] FIG. 15 is a diagram showing an example of a configuration in which the ends of the second portion and the non-reciprocal member in FIG. 14 are inclined. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] (Configuration example of optical integrated circuit 1) 1A and 1B, an optical integrated circuit 1 according to an embodiment includes a substrate 50, a box layer 52, insulating layers 54 and 56, a waveguide 20, and a nonreciprocal member 40. The substrate 50 has a substrate surface 50A. The box layer 52 is located on the substrate surface 50A. The waveguide 20 is located on the box layer 52. The waveguide 20 extends in the horizontal direction of the paper, i.e., along the X-axis direction.

[0007] The insulating layer 54 is located on the box layer 52 and the waveguide 20. The insulating layer 54 has a recess 30 defined by a side surface 31 and a bottom surface 32. The recess 30 extends along the waveguide 20, i.e., along the X-axis direction. The recess 30 may be formed, for example, by etching the insulating layer 54. In FIG. 1B , a portion of the bottom surface 32 of the recess 30 includes the upper surface of the waveguide 20.

[0008] The waveguide 20 includes a first portion 21 and a second portion 22. The first portion 21 of the waveguide 20 corresponds to a portion that extends without overlapping the recess 30 of the insulating layer 54 in a plan view of the substrate 50. The second portion 22 of the waveguide 20 corresponds to a portion that extends and overlaps the recess 30 of the insulating layer 54 in a plan view of the substrate 50.

[0009] The nonreciprocal member 40 is located on the bottom surface 32 in the recess 30. That is, the nonreciprocal member 40 is in contact with the upper surface of the second portion 22 of the waveguide 20. The nonreciprocal member 40 also extends along the waveguide 20, that is, along the X-axis direction. The insulating layer 56 is located on the nonreciprocal member 40. The optical integrated circuit 1 does not necessarily need to include the insulating layer 56.

[0010] The substrate 50 may be configured to include a conductor such as a metal, a semiconductor such as silicon, glass, or a resin, etc. In this embodiment, the substrate 50 is made of silicon (Si), but is not limited to this and may be made of various other materials.

[0011] The waveguide 20 is surrounded by a box layer 52 and an insulating layer 54. The waveguide 20 is also called a core. The box layer 52 and the insulating layer 54 are also called a clad. The core and the clad may be configured to include a dielectric. The waveguide 20 is also called a dielectric line. The waveguide 20 as a core is located along the substrate surface 50A and propagates electromagnetic waves along the substrate surface 50A. In other words, the electromagnetic waves propagate through the waveguide 20 as a core in the direction in which the waveguide 20 extends.

[0012] The materials of the core and the clad are determined so that the relative dielectric constant of the core is greater than that of the clad. In other words, the materials of the core and the clad are determined so that the refractive index of the clad is smaller than that of the core. In this way, the electromagnetic wave propagating through the core can be totally reflected at the boundary with the clad. As a result, the loss of the electromagnetic wave propagating through the core can be reduced.

[0013] The dielectric constant of the core and the clad may be made larger than that of air. By making the dielectric constant of the core and the clad larger than that of air, leakage of electromagnetic waves from the optical integrated circuit 1 can be suppressed. As a result, loss due to radiation of electromagnetic waves from the optical integrated circuit 1 to the outside can be reduced.

[0014] In this embodiment, the material of the waveguide 20 as the core is silicon (Si), but is not limited to this and may be various other materials. The material of the box layer 52 and the insulating layer 54 as the clad is quartz glass or silicon oxide film (SiO2), but is not limited to this and may be various other materials. The relative dielectric constants of silicon and quartz glass are about 12 and about 2, respectively. Silicon can propagate electromagnetic waves having a near-infrared wavelength of about 1.2 μm to about 6 μm with low loss. When the waveguide 20 is made of silicon, it can propagate electromagnetic waves having a wavelength of 1.3 μm band or 1.55 μm band used in optical communication with low loss.

[0015] The nonreciprocal member 40 causes nonreciprocity in the propagation characteristics of the electromagnetic waves in the waveguide 20 located alongside the nonreciprocal member 40. Nonreciprocity is a property in which the phase shift when the electromagnetic waves propagate in a first direction in the waveguide 20 is different from the phase shift when the electromagnetic waves propagate in a second direction. For example, the first direction corresponds to the positive direction of the X-axis in FIG. 1A. In this case, the second direction corresponds to the negative direction of the X-axis in FIG. 1A.

[0016] The propagation characteristics of electromagnetic waves in the second portion 22 of the waveguide 20 where the nonreciprocal members 40 are arranged differ from the propagation characteristics of electromagnetic waves in the first portion 21 where the nonreciprocal members 40 are not arranged, in that nonreciprocity is expressed.

[0017] In this embodiment, Ce:YIG (cerium-substituted yttrium-iron-garnet) is used as the material of the nonreciprocal member 40. A transparent magnetic material such as a partially substituted YIG material such as Bi:YIG (bismuth-substituted YIG) may be used as the material of the nonreciprocal member 40. A ferromagnetic material such as FeCo, FeNi, or CoPt, or a material containing a ferromagnetic material may be used as the material of the nonreciprocal member 40. A dielectric material composited with magnetic nanoparticles, such as a nanogranular material, may be used as the material of the nonreciprocal member 40. Not limited to these, various other magnetic materials may be used as the nonreciprocal member 40. The nonreciprocal member 40 is formed by being deposited on the substrate 50 with the recess 30 formed in the insulating layer 54.

[0018] Hereinafter, an embodiment will be described in which an electromagnetic wave in TM mode propagates through the waveguide 20 illustrated in Figures 1A and 1B. The electromagnetic wave in TM mode is an electromagnetic wave in which, when the electromagnetic wave propagates along the substrate surface 50A of the substrate 50, the amplitude direction of the electric field coincides with the normal direction of the substrate surface 50A. When the electromagnetic wave in TM mode propagates in the X-axis direction in the waveguide 20 illustrated in Figures 1A and 1B, the amplitude direction of the electric field coincides with the Z-axis direction.

[0019] The intensity of the electromagnetic wave corresponds to the magnitude of the energy of the electric field component of the electromagnetic wave. Outside the waveguide 20, the intensity of the electromagnetic wave decreases the further away from the surface of the waveguide 20. The intensity of the TM mode electromagnetic wave outside the waveguide 20 decreases according to a Gaussian distribution. As a propagation characteristic of the TM mode electromagnetic wave in the waveguide 20, the mode field diameter (MFD) in the Z-axis direction, which is the amplitude direction of the electric field of the TM mode electromagnetic wave, is defined. The mode field diameter in the Z-axis direction is the value obtained by dividing the maximum intensity of the electromagnetic wave propagating through the waveguide 20 by the intensity of the electromagnetic wave, which is 1 / e 2 In other words, the mode field diameter in the Z direction is defined as the distance between two positions where the intensity of the electromagnetic wave decreases to 1 / e 2 It is defined as the length of the range that is equal to or greater than e, where e is the base of the natural logarithm, i.e., Napier's constant.

[0020] The energy of an electromagnetic wave is 1 / e 2 The mode field diameter corresponds to the length of the range in which the energy of the electromagnetic wave is effectively distributed. The range of the mode field diameter corresponds to the range in which the energy of the electromagnetic wave is effectively distributed. The range of the mode field diameter in the Z-axis direction corresponds to the range in which the energy of the electromagnetic wave propagating through the waveguide 20 is effectively distributed in the Z-axis direction.

[0021] The mode field diameter in the Z-axis direction is determined based on the dimension of the waveguide 20 in the direction along the substrate surface 50A in a cross section perpendicular to the extending direction of the waveguide 20, i.e., the width of the waveguide 20, and the dimension of the waveguide 20 in the normal direction to the substrate surface 50A of the waveguide 20, i.e., the height of the waveguide 20. The mode field diameter in the Z-axis direction is further determined based on the refractive index of the waveguide 20, the refractive index of the box layer 52 and the insulating layer 54 positioned to surround the waveguide 20, and the wavelength of the electromagnetic wave propagating through the waveguide 20.

[0022] The mode field diameter in the Z-axis direction is affected by the nonreciprocal member 40 located along the waveguide 20. Specifically, nonreciprocity appears in the propagation characteristics of the waveguide 20 when the nonreciprocal member 40 is located within the range of the mode field diameter in the Z-axis direction of the waveguide 20. In other words, nonreciprocity appears in the propagation characteristics of the waveguide 20 when the nonreciprocal member 40 is located alongside the waveguide 20 in the amplitude direction of the electric field of the electromagnetic wave, i.e., in the Z-axis direction.

[0023] Furthermore, the range of the mode field diameter in the Z-axis direction of the waveguide 20 expands to the side where the nonreciprocal member 40 is located. As the range of the mode field diameter in the Z-axis direction of the waveguide 20 expands toward the nonreciprocal member 40, the center position of the range of the mode field diameter in the Z-axis direction of the waveguide 20 moves in a direction closer to the nonreciprocal member 40. The center position of the range of the mode field diameter is also referred to as the mode center.

[0024] Here, the effect of the nonreciprocal member 40 on the position of the mode center of the waveguide 20 will be described with reference to an optical integrated circuit 9 according to a comparative example shown in FIG.

[0025] An optical integrated circuit 9 according to the comparative example is obtained by replacing the waveguide 20 in the optical integrated circuit 1 of FIG. 1A with a waveguide 90. The waveguide 90 includes a first portion 91 and a second portion 92. In a cross section perpendicular to the extending direction of the waveguide 90, the shape of the first portion 91 and the shape of the second portion 92 of the waveguide 90 are the same. The optical integrated circuit 9 includes a nonreciprocal member 40 located along the second portion 92 of the waveguide 90.

[0026] Assume that in the optical integrated circuit 9, the nonreciprocity member 40 is not positioned along the second portion 92 of the waveguide 90. In this case, the cross-sectional shapes of the first portion 91 and the second portion 92 of the waveguide 90 match, so that the propagation characteristics of the electromagnetic wave in the first portion 91 of the waveguide 90 are the same as the propagation characteristics of the electromagnetic wave in the second portion 92. In other words, the mode center of the first portion 91 of the waveguide 90 matches the mode center of the second portion 92 at the portion where the first portion 91 and the second portion 92 of the waveguide 90 are connected, that is, at the portion shown as the dashed line (A) in FIG. 2. When the propagation characteristics of the electromagnetic wave in the first portion 91 of the waveguide 90 are the same as the propagation characteristics of the electromagnetic wave in the second portion 92, no loss occurs when the electromagnetic wave propagates from the first portion 91 to the second portion 92 of the waveguide 90, or when the electromagnetic wave propagates from the second portion 92 to the first portion 91.

[0027] However, in the optical integrated circuit 9 according to the comparative example, the nonreciprocal member 40 is located along the second portion 92 of the waveguide 90. Due to the presence of the nonreciprocal member 40, the mode center of the second portion 92 of the waveguide 90 moves in a direction closer to the nonreciprocal member 40 than the mode center of the first portion 91. As a result, the mode center is shifted at the portion where the first portion 91 and the second portion 92 of the waveguide 90 are connected, that is, the portion shown by the dashed line (A) in FIG. 2. The shift between the mode center of the first portion 91 of the waveguide 90 and the mode center of the second portion 92 of the waveguide 90 increases the loss when the electromagnetic wave propagates from the first portion 91 to the second portion 92 of the waveguide 90, or the loss when the electromagnetic wave propagates from the second portion 92 to the first portion 91.

[0028] In other words, due to the shift of the mode center, the propagation characteristics of the electromagnetic wave in the first portion 91 of the waveguide 90 do not match with the propagation characteristics of the electromagnetic wave in the second portion 92. The mismatch in the propagation characteristics of the electromagnetic wave is also called a mode mismatch. Due to the mode mismatch occurring at the portion where the first portion 91 and the second portion 92 of the waveguide 90 are connected, the loss when the electromagnetic wave propagates from the first portion 91 to the second portion 92 of the waveguide 90 or the loss when the electromagnetic wave propagates from the second portion 92 to the first portion 91 becomes large.

[0029] On the other hand, in the optical integrated circuit 1 according to the present embodiment, the shape of the first portion 21 and the shape of the second portion 22 in a cross section orthogonal to the extending direction of the waveguide 20 are different. Specifically, the height of the lower surface of the first portion 21 of the waveguide 20 is the same as the height of the lower surface of the second portion 22, and the upper surface of the second portion 22 of the waveguide 20 is lower than the upper surface of the first portion 21 of the waveguide 20. In other words, when the dimension in the normal direction of the substrate surface 50A of the first portion 21 of the waveguide 20, that is, the height is represented by H1, and the dimension in the normal direction of the substrate surface 50A of the second portion 22 of the waveguide 20, that is, the height is represented by H2, H2 < H1 holds.

[0030] When the non-reciprocity member 40 is located on the side of the upper surface of the second portion 22 of the waveguide 20, that is, in the positive direction of the Z axis, the mode center of the second portion 22 moves in the direction approaching the non-reciprocity member 40, that is, in the positive direction of the Z axis. On the other hand, since the upper surface of the second portion 22 of the waveguide 20 is lower than the upper surface of the first portion 21, the mode center of the second portion 22 moves in the negative direction of the Z axis. In other words, since the center position of the second portion 22 of the waveguide 20 in the Z-axis direction is lower than the center position of the first portion 21 in the Z-axis direction, the mode center of the second portion 22 moves in the negative direction of the Z axis.

[0031] The movement direction of the mode center of the second portion 22 due to the nonreciprocal member 40 is opposite to the movement direction of the mode center of the second portion 22 due to the position of the upper surface of the second portion 22 of the waveguide 20, thereby shortening the movement distance in the Z-axis direction of the mode center of the second portion 22. The shortening of the movement distance of the mode center of the second portion 22 reduces the deviation in the Z-axis direction between the mode center of the first portion 21 of the waveguide 20 and the mode center of the second portion 22 of the waveguide 20 at the portion where the first portion 21 and the second portion 22 of the waveguide 20 are connected, i.e., the portion shown by the dashed line (A) in FIG. 1A. As a result, in the optical integrated circuit 1 of this embodiment, the loss when an electromagnetic wave propagates from the first portion 21 to the second portion 22 of the waveguide 20, or the loss when the electromagnetic wave propagates from the second portion 22 to the first portion 21, is smaller than the loss when an electromagnetic wave propagates from the first portion 91 to the second portion 92 of the waveguide 90 in the optical integrated circuit 9 of the comparative example, or the loss when the electromagnetic wave propagates from the second portion 92 to the first portion 91.

[0032] As illustrated in the graph of FIG. 3, the loss when an electromagnetic wave propagates from the first portion 21 to the second portion 22 of the waveguide 20 changes according to the change in the height (H2) of the second portion 22 of the waveguide 20. In the graph of FIG. 3, the horizontal axis represents the height (H2) of the second portion 22 of the waveguide 20. The vertical axis represents the loss when an electromagnetic wave propagates from the first portion 21 to the second portion 22 of the waveguide 20. The unit of loss is decibels (dB). The loss is expressed as a negative value. The larger the loss, the smaller the value represented.

[0033] When the height of the second portion 22 of the waveguide 20 is made lower than H1, the loss is reduced compared to the loss when the height of the second portion 22 is the same as the height (H1) of the first portion 21. The height of the second portion 22 of the waveguide 20 when the loss can be minimized is represented as Hop. When the height of the second portion 22 of the waveguide 20 is made lower than Hop, the loss is increased compared to the loss when the height of the second portion 22 is Hop.

[0034] As described above, by making the height (H2) of the second portion 22 of the waveguide 20 lower than the height (H1) of the first portion 21 of the waveguide 20, the shift of the mode center of the second portion 22 with respect to the mode center of the first portion 21 is reduced. As a result, the loss when the electromagnetic wave propagates from the first portion 21 to the second portion 22 of the waveguide 20 is reduced. Further, since the propagation characteristics of the electromagnetic wave in the waveguide 20 are symmetric, the loss when the electromagnetic wave propagates from the second portion 22 to the first portion 21 of the waveguide 20 is similarly reduced.

[0035] Also, the height (H2) of the second portion 22 of the waveguide 20 may be determined so that the loss when the height (H2) of the second portion 22 of the waveguide 20 is lowered does not become larger than the loss when H2 = H1.

[0036] In other words, the optical integrated circuit 1 is configured such that in the range where the first portion 21 and the second portion 22 of the waveguide 20 are coupled, the energy distribution of the electric field component of the electromagnetic wave propagating through the first portion 21 and the energy distribution of the electric field component of the electromagnetic wave propagating through the second portion 22 are matched. The range where the first portion 21 and the second portion 22 are coupled includes the portion where the first portion 21 and the second portion 22 are connected. The matching of the energy distributions means that the shift between the mode center in the first portion 21 and the mode center in the second portion 22 falls within a predetermined range. The predetermined range is a range in which the loss when the electromagnetic wave propagates from the first portion 21 to the second portion 22 or the loss when the electromagnetic wave propagates from the second portion 22 to the first portion 21 is smaller than the loss when the cross-sectional shapes of the first portion 21 and the second portion 22 are the same.

[0037] <When propagating an electromagnetic wave in the TE mode> The optical integrated circuit 1 according to the above-described embodiment is configured to be applicable when propagating an electromagnetic wave in the TM mode. The optical integrated circuit 1 according to the present disclosure may be configured to be applicable when propagating an electromagnetic wave in the TE mode.

[0038] An electromagnetic wave in the TE mode is an electromagnetic wave in which, when the electromagnetic wave propagates along the substrate 50, the amplitude direction of the electric field is perpendicular to the propagation direction of the electromagnetic wave and coincides with the direction along the substrate surface 50A. If an electromagnetic wave in the TE mode propagates in the X-axis direction in the waveguide 20 illustrated in FIG. 1A, the amplitude direction of the electric field coincides with the Y-axis direction.

[0039] The mode field diameter (MFD) in the Y-axis direction, which is the amplitude direction of the electric field of the TE mode electromagnetic wave, is defined as the propagation characteristic of the TE mode electromagnetic wave in the waveguide 20. The mode field diameter in the Y-axis direction is the maximum intensity of the electromagnetic wave propagating through the waveguide 20 when the intensity of the electromagnetic wave is 1 / e 2 is defined as the distance between two positions that decreases to

[0040] The mode field diameter in the Y-axis direction is affected by the nonreciprocal member 40 located along the waveguide 20. Specifically, nonreciprocity appears in the propagation characteristics of the waveguide 20 when the nonreciprocal member 40 is located within the range of the mode field diameter in the Y-axis direction of the waveguide 20. In other words, nonreciprocity appears in the propagation characteristics of the waveguide 20 when the nonreciprocal member 40 is located alongside the waveguide 20 in the amplitude direction of the electric field of the electromagnetic wave, i.e., in the Y-axis direction.

[0041] In addition, the range of the mode field diameter in the Y-axis direction of the waveguide 20 expands to the side where the nonreciprocal member 40 is located. As the range of the mode field diameter in the Y-axis direction of the waveguide 20 expands toward the nonreciprocal member 40, the mode center in the Y-axis direction of the waveguide 20 moves in a direction approaching the nonreciprocal member 40.

[0042] When the nonreciprocal member 40 is positioned alongside the second portion 22 of the waveguide 20 in the Y-axis direction, the mode center in the Y-axis direction of the second portion 22 is shifted toward the nonreciprocal member 40 relative to the mode center in the Y-axis direction of the first portion 21 of the waveguide 20. The shift in the mode center increases the loss when the electromagnetic wave propagates from the first portion 21 to the second portion 22 of the waveguide 20, or the loss when the electromagnetic wave propagates from the second portion 22 to the first portion 21.

[0043] Therefore, the second portion 22 may be configured such that the center of the second portion 22 in the Y-axis direction is shifted in a direction away from the nonreciprocity member 40. Specifically, the second portion 22 may be configured such that the dimension of the second portion 22 in the Y-axis direction, i.e., the width of the waveguide 20, narrows in a direction away from the nonreciprocity member 40. Also, the second portion 22 may be positioned shifted in the Y-axis direction with respect to the first portion 21. In this manner, the shift of the mode center of the second portion 22 from the mode center of the first portion 21 is reduced. As a result, the loss when the electromagnetic wave propagates from the first portion 21 to the second portion 22 of the waveguide 20, or the loss when the electromagnetic wave propagates from the second portion 22 to the first portion 21 is reduced.

[0044] <Summary> As described above, the optical integrated circuit 1 according to the present disclosure can reduce losses for both TM mode and TE mode electromagnetic waves when the electromagnetic waves propagate from the first portion 21 of the waveguide 20, where the nonreciprocal member 40 is not located, to the second portion 22, where the nonreciprocal member 40 is located, or when the electromagnetic waves propagate from the second portion 22 to the first portion 21.

[0045] In other words, the waveguide 20 of the optical integrated circuit 1 according to the present disclosure may be configured such that, in the range where the first portion 21 and the second portion 22 are coupled, the dimension of the second portion 22 in the amplitude direction of the electric field component of the electromagnetic wave is shorter than the dimension of the first portion 21. Furthermore, the waveguide 20 may be configured such that, in the range where the first portion 21 and the second portion 22 are coupled, the center of the second portion 22 in the amplitude direction of the electric field component of the electromagnetic wave is shifted in a direction away from the nonreciprocity member 40 with respect to the center of the first portion 21.

[0046] (Other embodiments) Other embodiments of the optical integrated circuit 1 will be described below.

[0047] <Configuration in which the insulating layer 58 is located between the waveguide 20 and the nonreciprocal member 40> As illustrated in FIG. 4, the optical integrated circuit 1 may further include an insulating layer 58 between the second portion 22 of the waveguide 20 and the non-reciprocal member 40 .

[0048] The distance between the second portion 22 of the waveguide 20 and the nonreciprocal member 40 is determined according to the thickness of the insulating layer 58. The thicker the insulating layer 58, the smaller the effect of the nonreciprocal member 40 on the second portion 22 of the waveguide 20. The thicker the insulating layer 58, the shorter the distance that the mode center of the second portion 22 of the waveguide 20 moves in the direction toward the nonreciprocal member 40. Therefore, the height (H2) of the second portion 22 of the waveguide 20 may be set appropriately according to the thickness of the insulating layer 58.

[0049] <Configuration in which the second portion 22 of the waveguide 20 includes the inclined portion 23> As illustrated in FIG. 5, the waveguide 20 may further include an inclined portion 23 connected to the first portion 21. The nonreciprocal member 40 is located not only on the second portion 22 but also on the inclined portion 23. Thus, the inclined portion 23 is included in the second portion 22. The inclined portion 23 is lower than the first portion 21 in the portion connecting to the first portion 21. The inclined portion 23 is configured to become higher as it moves away from the first portion 21. In other words, the inclined portion 23 included in the second portion 22 becomes larger in the direction approaching the nonreciprocal member 40 as it moves away from the first portion 21.

[0050] In the portion where the first portion 21 where the nonreciprocal member 40 is not located is connected to the inclined portion 23 where the nonreciprocal member 40 is located, i.e., the portion shown as dashed line (A) in Figure 5, the height (H3) of the inclined portion 23 is set so that the deviation in the Z-axis direction between the mode center of the first portion 21 of the waveguide 20 and the mode center of the inclined portion 23 of the waveguide 20 is small.

[0051] Losses when electromagnetic waves propagate through the waveguide 20 can be reduced by increasing the cross-sectional area of ​​the waveguide 20. Thus, as illustrated in Fig. 5, the waveguide 20 is configured such that the inclined portion 23 becomes higher from the portion where the inclined portion 23 is connected to the first portion 21 toward the second portion 22, whereby the cross-sectional area of ​​the second portion 22 of the waveguide 20 is increased. By increasing the cross-sectional area of ​​the second portion 22 of the waveguide 20, losses when electromagnetic waves propagate through the second portion 22 are reduced.

[0052] Also, the mode center gradually moves in the Z-axis direction in the inclined portion 23. When the mode center gradually moves in the Z-axis direction, the loss of the electromagnetic wave in TM mode is reduced more than when the mode center moves stepwise in the Z-axis direction. In other words, the smaller the amount of movement of the mode center in the Z-axis direction when the electromagnetic wave in TM mode propagates by a unit length in the X-axis direction, the less the loss of the electromagnetic wave in TM mode. In other words, by connecting the first portion 21 and the second portion 22 via the inclined portion 23, the energy distribution is easily matched.

[0053] The matching of the energy distribution in the inclined portion 23 may include that the amount by which the mode center moves along the amplitude direction of the electric field component is less than a predetermined threshold when the electromagnetic wave propagates through a unit length in the inclined portion 23. The predetermined threshold may be set according to an allowable value for loss of the electromagnetic wave.

[0054] As a result, it is possible to achieve both matching of energy distribution in a portion of the waveguide 20 where the first portion 21, where the nonreciprocal member 40 is not located, and the second portion 22, where the nonreciprocal member 40 is located, are connected, and reduction of loss when an electromagnetic wave propagates through the second portion 22. The waveguide 20 may be configured so that the height (H2) of the second portion 22 is lower than the height (H1) of the first portion 21. The waveguide 20 may also be configured so that the height (H2) of the second portion 22 is the same as the height (H1) of the first portion 21.

[0055] 6, the waveguide 20 may be configured such that the first portion 21 and the second portion 22 are spaced apart in the propagation direction of the electromagnetic wave, i.e., in the X-axis direction. That is, the waveguide 20 may be disconnected between the first portion 21 and the second portion 22. The second portion 22 includes an inclined portion 23 as an end portion closer to the first portion 21. The inclined portion 23 becomes lower as it approaches the first portion 21.

[0056] The nonreciprocal member 40 is located on the second portion 22 of the waveguide 20, and is also located between the first portion 21 and the second portion 22 of the waveguide 20. When an electromagnetic wave propagates through the nonreciprocal member 40, the refractive index of the nonreciprocal member 40 is smaller than that of the waveguide 20, and thus the mode field diameter in the nonreciprocal member 40 located at the break in the waveguide 20 becomes larger than the mode field diameter in the first portion 21 of the waveguide 20. Therefore, at the portion where the first portion 21 of the waveguide 20 and the break in the waveguide 20 are connected, that is, the portion shown by the dashed line (A) in FIG. 6, the energy distribution of the electromagnetic wave in the first portion 21 of the waveguide 20 and the energy distribution of the electromagnetic wave in the nonreciprocal member 40 located at the break in the waveguide 20 are easily matched.

[0057] At the portion where the broken portion of the waveguide 20 and the end of the inclined portion 23 of the waveguide 20 are connected, that is, at the portion shown by the broken line (B) in FIG. 6, the mode center of the nonreciprocal member 40 coincides with the mode center at the end of the inclined portion 23. The further away from the first portion 21, the higher the inclined portion 23 becomes, and the mode center gradually moves upward. The gradual movement of the mode center makes it easier for the energy distribution of the electromagnetic wave to match between the broken portion of the waveguide 20 and the inclined portion 23 of the waveguide 20. As a result, the loss when the electromagnetic wave propagates from the first portion 21 of the waveguide 20 to the second portion 22 including the inclined portion 23 of the waveguide 20 through the broken portion, or the loss when the electromagnetic wave propagates from the second portion 22 to the first portion 21 through the broken portion, is reduced.

[0058] As described above, the electromagnetic wave propagates from the first portion 21 of the waveguide 20 through the nonreciprocal member 40 located at the break, to the second portion 22. That is, the first portion 21 and the second portion 22 of the waveguide 20 are optically coupled via the nonreciprocal member 40. The break in the waveguide 20 is included in the range where the first portion 21 and the second portion 22 of the waveguide 20 are coupled.

[0059] The loss of the electromagnetic wave in the nonreciprocal member 40 is larger than the loss of the electromagnetic wave in the waveguide 20. Therefore, the shorter the disconnection portion of the waveguide 20, the smaller the loss when the electromagnetic wave propagates from the first portion 21 to the second portion 22, or the loss when the electromagnetic wave propagates from the second portion 22 to the first portion 21. The length of the disconnection portion of the waveguide 20 may be set appropriately depending on the wavelength of the electromagnetic wave, etc.

[0060] As illustrated in FIG. 7, the inclined portion 23 may be configured to have the same height as the first portion 21 at a portion connected to the first portion 21, and to become lower as it moves away from the first portion 21. In other words, the inclined portion 23 included in the second portion 22 may become smaller in a direction away from the nonreciprocal member 40 as it moves away from the first portion 21. That is, the inclined portion 23 may become thinner as it moves away from the first portion 21. Also, the nonreciprocal member 40 may become thinner toward the portion connected to the first portion 21 on the inclined portion 23. The nonreciprocal member 40 may be configured so that the thickness of the portion connected to the first portion 21 is 0. The nonreciprocal member 40 may become thinner as it moves closer to the first portion 21. Conversely, the nonreciprocal member 40 may become thicker as it moves away from the first portion 21.

[0061] In this case, at the portion where the first part 21 of the waveguide 20 is connected to the inclined part 23 of the waveguide 20, that is, the portion shown as the broken line (A) in FIG. 7, since the thickness of the non-reciprocity member 40 is 0, the mode center of the first part 21 coincides with the mode center of the inclined part 23. The thickening of the non-reciprocity member 40 moves the mode center of the waveguide 20 in a direction away from the substrate surface 50A. Therefore, as the non-reciprocity member 40 thickens away from the first part 21, the mode center of the waveguide 20 gradually changes. That is, the mode center of the waveguide 20 does not step down at the portion where the first part 21 and the inclined part 23 are connected. As a result, the loss when the electromagnetic wave propagates from the first part 21 to the second part 22 or the loss when the electromagnetic wave propagates from the second part 22 to the first part 21 is smaller than the loss in the case where the height of the first part 91 of the waveguide 90 and the height of the second part 92 do not change as in the optical integrated circuit 9 according to the comparative example shown in FIG. 2. The inclined part 23 is included in the range where the first part 21 and the second part 22 of the waveguide 20 are coupled. Also, the thinning of the inclined part 23 moves the mode center of the waveguide 20 in a direction approaching the substrate surface 50A. That is, the thinning of the inclined part 23 and the thickening of the non-reciprocity member 40 shorten the moving distance of the mode center of the waveguide 20. As a result, the loss when the electromagnetic wave propagates from the first part 21 to the second part 22 or the loss when the electromagnetic wave propagates from the second part 22 to the first part 21 is reduced.

[0062] <Configuration example for reducing the propagation loss of TE mode electromagnetic waves> In the embodiments described above, a configuration example for reducing the loss when the TM mode electromagnetic wave propagates between the non-reciprocal portion of the waveguide, that is, the first part, and the reciprocal portion, that is, the second part, has been described. Hereinafter, a configuration example for reducing the loss when the TE mode electromagnetic wave propagates between the first part and the second part of the waveguide will be described in comparison with the comparative example.

[0063] As a comparative example, an optical integrated circuit 900 that propagates electromagnetic waves in a TE mode is shown in FIGS. 8A and 8B. The optical integrated circuit 900 includes a substrate 950, a box layer 952, an insulating layer 954, a waveguide 920, and nonreciprocal members 941 and 942. The substrate 950 may be made of the same or similar material as the substrate 50. The box layer 952 may be made of the same or similar material as the box layer 52. The insulating layer 954 may be made of the same or similar material as the insulating layer 54. The waveguide 920 may be made of the same or similar material as the waveguide 20. The nonreciprocal members 941 and 942 may be made of the same or similar material as the nonreciprocal member 40.

[0064] The substrate 950 has a substrate surface 950A. The box layer 952 is located on the substrate surface 950A. The waveguide 920 is located on the box layer 952 and extends along the substrate surface 950A. In Figures 8A and 8B, the coordinate system is set so that the direction in which the waveguide 120 extends is the X-axis direction. The insulating layer 954 is located on the box layer 952 and the waveguide 920.

[0065] A recess 930 defined by side surfaces 931, 933, 934, and 935 and a bottom surface 932 is located in the insulating layer 954 and the box layer 952. The recess 930 is a rectangle with the X-axis direction as the longitudinal direction in a plan view of the substrate 950. The side surfaces 931 and 935 correspond to the long sides of the recess 930 and extend in the X-axis direction along the waveguide 920. The side surface 931 is located on the side closer to the waveguide 920. The waveguide 920 may be exposed from the insulating layer 954 at the side surface 931 or may be covered by the insulating layer 954. The side surface 935 is located on the side farther from the waveguide 920. The side surfaces 933 and 934 correspond to the short sides of the recess 930. The recess 930 may be formed by etching the insulating layer 954 and the box layer 952.

[0066] The non-reciprocal member 941 is located along a side surface 931 in the recess 930. The non-reciprocal member 942 is located along a bottom surface 932 in the recess 930. The non-reciprocal members 941 and 942 may be formed by deposition such as sputtering in the recess 930. In the deposition in the recess 930, the material of the non-reciprocal members 941 and 942 may also be deposited on the side surfaces 933, 934, or 935.

[0067] As an embodiment according to the present disclosure, an optical integrated circuit 100 that propagates an electromagnetic wave in a TE mode is shown in FIGS. 9A and 9B. The optical integrated circuit 100 includes a substrate 150, a box layer 152, an insulating layer 154, a waveguide 120, and nonreciprocal members 141 and 142. The substrate 150 may be made of the same or similar material as the substrate 50. The box layer 152 may be made of the same or similar material as the box layer 52. The insulating layer 154 may be made of the same or similar material as the insulating layer 54. The waveguide 120 may be made of the same or similar material as the waveguide 20. The nonreciprocal members 141 and 142 may be made of the same or similar material as the nonreciprocal member 40.

[0068] The substrate 150 has a substrate surface 150A. The box layer 152 is located on the substrate surface 150A. The waveguide 120 is located on the box layer 152 and extends along the substrate surface 150A. In Figures 9A and 9B, a coordinate system is set so that the direction in which the waveguide 120 extends is the X-axis direction. The insulating layer 154 is located on the box layer 152 and the waveguide 120.

[0069] A recess 130 is located in the insulating layer 154 and the box layer 152, and is defined by side surfaces 131, 133, 134, and 135 and a bottom surface 132. In a plan view of the substrate 150, the recess 130 is a quadrilateral including two parallel sides extending in the X-axis direction along the waveguide 120 and two sides different from the two parallel sides extending in the X-axis direction. The side surface 131 corresponds to one of the two sides extending in the X-axis direction that is closer to the waveguide 120. The waveguide 120 may be exposed from the insulating layer 154 at the side surface 131, or may be covered by the insulating layer 154. The side surface 135 corresponds to one of the two sides extending in the X-axis direction that is farther from the waveguide 120. The side surfaces 133 and 134 correspond to the two sides different from the two parallel sides. The side surfaces 133 and 134 intersect with the side surface 131 at an angle of less than 90 degrees in a plan view of the substrate 150. In other words, the recess 130 is configured such that the interior angles between the side surface 131 and each of the side surfaces 133 and 134 are acute angles in a plan view of the substrate 150. The recess 130 may be formed by etching the insulating layer 154 and the box layer 152.

[0070] The non-reciprocal member 141 is located along the side surface 131 in the recess 130. The non-reciprocal member 142 is located along the bottom surface 132 in the recess 130. The non-reciprocal members 141 and 142 may be formed by deposition such as sputtering in the recess 130. In the deposition in the recess 130, the material of the non-reciprocal members 141 and 142 may also be deposited on the side surface 133, 134, or 135.

[0071] In the present embodiment and the comparative example, the amplitude direction of the electric field of the TE mode electromagnetic wave propagating in the X-axis direction in the waveguides 120 and 920 coincides with the Y-axis direction. The mode field diameter (MFD) of the TE mode electromagnetic wave in the Y-axis direction is defined to be the same as the MFD of the TM mode electromagnetic wave in the Z-axis direction. In other words, the MFD of the TE mode electromagnetic wave in the Y-axis direction is calculated by dividing the MFD by the maximum intensity of the electromagnetic wave propagating in the waveguide 20 by 1 / e 2 is defined as the distance between two positions that decreases to

[0072] The nonreciprocity member is located within the range of the MFD of the TE mode electromagnetic wave, thereby realizing nonreciprocity for the TE mode electromagnetic wave. In this embodiment, the recess 130 is configured such that the nonreciprocity member 141 located along the side surface 131 is located within the range of the MFD of the TE mode electromagnetic wave propagating through the waveguide 120, and the film located along the side surface 135 is located outside the range of the MFD. In addition, the nonreciprocity member 142 located along the bottom surface 132 of the recess 130 is located outside the range of the MFD of the TE mode electromagnetic wave propagating through the waveguide 120 by being shifted in the Z-axis direction with respect to the waveguide 120. As a result, in this embodiment, the nonreciprocity member 141 realizes nonreciprocity for the TE mode electromagnetic wave propagating through the waveguide 120. On the other hand, in this embodiment, the nonreciprocity member 142 does not realise nonreciprocity for the TE mode electromagnetic wave propagating through the waveguide 120. Also in the comparative example, nonreciprocity member 941 exhibits nonreciprocity for electromagnetic waves in TE mode propagating through waveguide 920. On the other hand, nonreciprocity member 942 does not exhibit nonreciprocity for electromagnetic waves in TE mode propagating through waveguide 920.

[0073] In this embodiment, nonreciprocity is manifested in the portion of the waveguide 120 where the nonreciprocal member 141 is located along the waveguide 120. The portion where the nonreciprocal member 141 is located along the waveguide 120 is the portion where the nonreciprocal member 141 is located within the range of the MFD of the electromagnetic wave of the TE mode propagating through the waveguide 120. The waveguide 120 is divided into a portion where the nonreciprocal member 141 is located and a portion where it is not located. The portion of the waveguide 120 where the nonreciprocal member 141 is not located is referred to as the first portion 121. The portion where the nonreciprocal member 141 is located is referred to as the second portion 122. The boundary between the first portion 121 and the second portion 122 corresponds to the position of the end of the nonreciprocal member 141 in the X-axis direction, and is represented as E and F in order toward the positive direction of the X-axis. Also in the comparative example, a portion of waveguide 920 where nonreciprocal member 941 is not located is referred to as first portion 921. A portion where nonreciprocal member 941 is located is referred to as second portion 922. The boundaries between first portion 921 and second portion 922 correspond to the positions of the ends of nonreciprocal member 941 in the X-axis direction, and are represented as E and F in that order toward the positive direction of the X-axis.

[0074] In the optical integrated circuit 100 according to this embodiment, the side surfaces 133 and 134 of the recess 130 intersect with the side surface 131 at an angle of less than 90 degrees. As a result, the dimension of the nonreciprocal member 141 in the Y-axis direction gradually increases while moving from E in the positive direction of the X-axis to G, or while moving from F in the negative direction of the X-axis to H. The dimension of the nonreciprocal member 141 in the Y-axis direction is constant in the range between G and H.

[0075] As described above, the mode center is shifted in the amplitude direction of the electric field component of the TE mode electromagnetic wave, i.e., in the Y-axis direction, between the portion where the nonreciprocal member is located and the portion where the nonreciprocal member is not located, causing loss when the electromagnetic wave propagates. On the other hand, the smaller the shift of the mode center is, the smaller the loss when the electromagnetic wave propagates through the portion where the mode center is shifted is.

[0076] Furthermore, when the direction in which the electromagnetic wave in TE mode propagates, i.e., when the mode center at each position in the X-axis direction gradually moves in the Y-axis direction from first portion 121 to second portion 122 of waveguide 120, the loss of the electromagnetic wave in TE mode is reduced more than when the mode center moves in a step-like manner in the Y-axis direction. In other words, the smaller the amount of movement of the mode center in the Y-axis direction when the electromagnetic wave in TE mode propagates by a unit length in the X-axis direction, the less the loss of the electromagnetic wave in TE mode.

[0077] In the optical integrated circuit 900 according to the comparative example, the shape of the nonreciprocal member 941 in the plan view of the substrate 950 is rectangular, so that the dimension of the nonreciprocal member 941 in the Y-axis direction changes in a step-like manner at positions E and F. As a result, the mode center in the Y-axis direction of the second portion 922 moves in a step-like manner in the negative Y-axis direction relative to the mode center in the Y-axis direction of the first portion 921.

[0078] On the other hand, in the optical integrated circuit 100 according to this embodiment, the dimension of the nonreciprocal member 141 in the Y-axis direction gradually changes between E and G or between H and F. As a result, the mode center in the Y-axis direction of the second portion 122 gradually moves in the negative Y-axis direction from the mode center in the Y-axis direction of the first portion 121 while progressing from E to G or from H to F.

[0079] That is, the deviation of the mode center in the Y-axis direction when the electromagnetic wave in the TE mode propagates a unit length from the first portion 121 to the second portion 122 in the optical integrated circuit 100 according to this embodiment is smaller than the deviation of the mode center in the Y-axis direction when the electromagnetic wave in the TE mode propagates a unit length from the first portion 921 to the second portion 922 in the optical integrated circuit 900 according to the comparative example. As a result, the loss generated when the electromagnetic wave in the TE mode propagates between the first portion 121 and the second portion 122 in the optical integrated circuit 100 according to this embodiment is smaller than the loss generated in the optical integrated circuit 900 according to the comparative example.

[0080] The optical integrated circuit 100 according to this embodiment may be configured so that the amount of movement of the mode center in the Y-axis direction when the electromagnetic wave in the TE mode propagates by a unit length in the X-axis direction is less than a predetermined threshold value. The predetermined threshold value may be set according to the allowable value of loss that occurs when the electromagnetic wave in the TE mode propagates.

[0081] As illustrated in FIG. 10, the recess 130 may be configured such that the side surface 133 or 134 located at the end of the recess 130 in the X-axis direction is a curved surface that is convex in a direction away from the waveguide 120. The side surface 133 or 134 may be configured to be perpendicular to the side surface 131 at the position where the side surface 133 or 134 intersects with the side surface 131. By increasing the angle at which the side surface 133 or 134 intersects with the side surface 131, the nonreciprocal member 141 is easily formed at the position where the side surface 133 or 134 intersects with the side surface 131. In FIG. 10 as well, the end of the nonreciprocal member 141 in the X-axis direction, that is, the boundary between the first portion 121 and the second portion 122, is represented by E and F. Also, the end of the range where the dimension of the nonreciprocal member 141 in the Y-axis direction is constant is represented by G and H.

[0082] As illustrated in FIG. 11, the recess 130 may be configured so that the angle at which the side 133 or 134 intersects with the side 131 is an obtuse angle. In other words, the interior angle of the recess 130 on the waveguide 120 side may be an obtuse angle. By making the angle at which the side 133 or 134 intersects with the side 131 an obtuse angle, the nonreciprocal member 141 is easily formed at the position at which the side 133 or 134 intersects with the side 131. Also in FIG. 11, the ends of the nonreciprocal member 141 in the X-axis direction, that is, the boundary between the first portion 121 and the second portion 122, are represented by E and F. Also, the ends of the range in which the dimension of the nonreciprocal member 141 in the Y-axis direction is constant are represented by G and H. G and H correspond to the positions at which the nonreciprocal member 141 starts to move away from the waveguide 120. The nonreciprocity member 141 exhibits nonreciprocity even in the section from E to G or the section from F to H, which are away from the waveguide 120, by being located within the range of the MFD in the Y-axis direction of the TE mode electromagnetic wave propagating through the waveguide 120.

[0083] As illustrated in FIG. 12, the recess 130 may be configured such that the side surface 133 or 134 is smoothly connected to the side surface 131 in a plan view of the substrate 150. By smoothly connecting the side surface 133 or 134 to the side surface 131, the nonreciprocal member 141 is easily formed at the position where the side surface 133 or 134 intersects with the side surface 131. In addition, the side surface 133 or 134 may be a curved surface that is convex outward from the recess 130. In FIG. 12 as well, the end of the nonreciprocal member 141 in the X-axis direction, that is, the boundary between the first portion 121 and the second portion 122, is represented by E and F. In addition, the end of the range in which the dimension of the nonreciprocal member 141 in the Y-axis direction is constant is represented by G and H. G and H correspond to the positions where the nonreciprocal member 141 starts to move away from the waveguide 120. The nonreciprocity member 141 exhibits nonreciprocity even in the section from E to G or the section from F to H, which are away from the waveguide 120, by being located within the range of the MFD in the Y-axis direction of the TE mode electromagnetic wave propagating through the waveguide 120.

[0084] 10, 11, and 12, the dimension of the nonreciprocity member 141 in the Y-axis direction gradually changes between E and G or between H and F. In the section where the dimension of the nonreciprocity member 141 in the Y-axis direction gradually changes, the mode center in the Y-axis direction of the second portion 122 gradually moves in the negative Y-axis direction from the mode center in the Y-axis direction of the first portion 121. As a result, the loss generated when the electromagnetic wave in the TE mode propagates between the first portion 121 and the second portion 122 is smaller than the loss generated in the optical integrated circuit 900 according to the comparative example.

[0085] 13, the waveguide 120 may be configured such that the end in the negative Y-axis direction of the second portion 122 between E and F corresponding to the end in the X-axis direction of the nonreciprocal member 141 is located in the positive Y-axis direction further than the end in the negative Y-axis direction of the first portion 121. The waveguide 120 may be configured such that the nonreciprocal member 141 enters the waveguide 120 in the second portion 122. In this case, the dimension in the Y-axis direction of the second portion 122 is narrower than the dimension in the Y-axis direction of the first portion 121. The center in the Y-axis direction of the second portion 122 moves in the positive Y-axis direction further than the center in the Y-axis direction of the first portion 121.

[0086] Here, the dimension of first portion 121 in the Y-axis direction is represented by W1. The dimension of second portion 122 in the Y-axis direction is represented by W2. W2 is shorter than W1. The movement distance of the center of second portion 122 in the Y-axis direction relative to the center of first portion 121 in the Y-axis direction is represented by (W1-W2) / 2. Assuming that nonreciprocity member 141 does not exist, the mode center in the Y-axis direction of the TE mode electromagnetic wave propagating through second portion 122 moves in the positive Y-axis direction by (W1-W2) / 2 from the mode center in first portion 121.

[0087] The nonreciprocity member 141 is located along the second portion 122, and thus acts to move the mode center of the TE mode electromagnetic wave propagating through the second portion 122 in the negative Y-axis direction. The direction of movement of the mode center due to the action of the nonreciprocity member 141 and the direction of movement of the center of the second portion 122 in the Y-axis direction are opposite to each other. Therefore, the movement of the mode center due to the action of the nonreciprocity member 141 is cancelled by the movement of the center of the second portion 122 in the Y-axis direction. As a result, the deviation between the mode center in the first portion 121 and the mode center in the second portion 122 is reduced. By reducing the deviation between the mode center in the first portion 121 and the mode center in the second portion 122, the loss when the electromagnetic wave propagates from the first portion 21 to the second portion 22 of the waveguide 20, or the loss when the electromagnetic wave propagates from the second portion 22 to the first portion 21 is reduced.

[0088] The dimension of the non-reciprocal member 141 in the Y-axis direction between E and F and the dimension of the second portion 122 may be configured so that the deviation between the mode center in the first portion 121 and the mode center in the second portion 122 falls within a predetermined range.

[0089] 14, the waveguide 120 may be configured such that the end in the positive Y-axis direction of the second portion 122 between E and F corresponding to the ends in the X-axis direction of the nonreciprocal member 141 is located in the positive Y-axis direction further than the end in the positive Y-axis direction of the first portion 121. The waveguide 120 may be configured such that the second portion 122 protrudes in the positive Y-axis direction, i.e., to the opposite side of the nonreciprocal member 141. In this case, the dimension in the Y-axis direction of the second portion 122 is larger than the dimension in the Y-axis direction of the first portion 121. The center in the Y-axis direction of the second portion 122 moves in the positive Y-axis direction further than the center in the Y-axis direction of the first portion 121.

[0090] Here, the dimension of first portion 121 in the Y-axis direction is represented by W1. The dimension of second portion 122 in the Y-axis direction is represented by W3. W3 is longer than W1. The movement distance of the center of second portion 122 in the Y-axis direction relative to the center of first portion 121 in the Y-axis direction is represented by (W3-W1) / 2. Assuming that nonreciprocity member 141 does not exist, the mode center in the Y-axis direction of the TE mode electromagnetic wave propagating through second portion 122 moves in the positive Y-axis direction from the mode center in first portion 121 by (W3-W1) / 2.

[0091] The nonreciprocity member 141 is located along the second portion 122, and thus acts to move the mode center of the TE mode electromagnetic wave propagating through the second portion 122 in the negative Y-axis direction. The direction of movement of the mode center due to the action of the nonreciprocity member 141 and the direction of movement of the center of the second portion 122 in the Y-axis direction are opposite to each other. Therefore, the movement of the mode center due to the action of the nonreciprocity member 141 is cancelled by the movement of the center of the second portion 122 in the Y-axis direction. As a result, the deviation between the mode center in the first portion 121 and the mode center in the second portion 122 is reduced. By reducing the deviation between the mode center in the first portion 121 and the mode center in the second portion 122, the loss when the electromagnetic wave propagates from the first portion 21 to the second portion 22 of the waveguide 20, or the loss when the electromagnetic wave propagates from the second portion 22 to the first portion 21 is reduced.

[0092] The dimension of the non-reciprocal member 141 in the Y-axis direction between E and F and the dimension of the second portion 122 may be configured so that the deviation between the mode center in the first portion 121 and the mode center in the second portion 122 falls within a predetermined range.

[0093] As illustrated in FIG. 15, the optical integrated circuit 100 may be configured such that the nonreciprocal member 141 and the second portion 122 of the waveguide 120 both gradually become thicker between E and G. The optical integrated circuit 100 may also be configured such that the nonreciprocal member 141 and the second portion 122 of the waveguide 120 both gradually become thicker between F and H. That is, the optical integrated circuit 100 of FIG. 15 has the ends of the nonreciprocal member 141 and the second portion 122 of the waveguide 120 inclined in a plan view of the substrate 150 compared to the optical integrated circuit 100 of FIG. 14. The dimension of the nonreciprocal member 141 in the Y-axis direction and the dimension of the second portion 122 between G and H may be configured such that the deviation between the mode center in the first portion 121 and the mode center in the second portion 122 falls within a predetermined range.

[0094] By gradually changing the dimensions in the Y-axis direction of the nonreciprocal member 141 and the second portion 122 of the waveguide 120 between E and G or between F and H, the shift of the mode center at E or F is reduced when a positional shift in the X-axis direction occurs between the nonreciprocal member 141 and the second portion 122.

[0095] The optical integrated circuit 100 may be configured such that the dimension of the nonreciprocal member 141 in the Y-axis direction at each position in the X-axis direction is proportional to the amount of change in the dimension of the second portion 122 in the Y-axis direction in each section from E to G and in each section from F to H. This further reduces the shift of the mode center.

[0096] As described above, by propagating electromagnetic waves in TE mode using the optical integrated circuit 100 of this embodiment, the loss when the electromagnetic waves propagate from the first portion 121 of the waveguide 120, where the nonreciprocal member 141 is not located, to the second portion 122 where the nonreciprocal member 141 is located, or the loss when the electromagnetic waves propagate from the second portion 22 to the first portion 21, is reduced.

[0097] (Application example of optical integrated circuit 1) The optical integrated circuit 1 may include an element that functions as an isolator. The isolator may include at least one nonreciprocal line. The isolator may include a waveguide 20 including a second portion 22 that exhibits nonreciprocity as a nonreciprocal line. The isolator may include a reciprocal line that does not exhibit nonreciprocity. The isolator may be used in combination with a configuration that transmits electromagnetic waves. The isolator may be applied to an optical switch, an optical transceiver, or a data center. The isolator may be applied to, for example, an electromagnetic wave transmitter. The electromagnetic wave transmitter includes an isolator and a light source. The electromagnetic wave transmitter inputs an electromagnetic wave from the light source to the isolator and outputs the electromagnetic wave from the isolator to a receiver. The isolator is configured so that the transmittance of the electromagnetic wave propagating from the light source to the receiver is greater than the transmittance of the electromagnetic wave propagating from the receiver to the light source. In this way, it becomes difficult for the electromagnetic wave to be incident on the light source. As a result, the light source can be protected.

[0098] The light source may be, for example, a semiconductor laser such as a laser diode (LD) or a vertical cavity surface emitting laser (VCSEL). The light source is not limited to visible light and may be of various wavelengths. The light source may include a device for emitting electromagnetic waves. The light source may be formed together with the isolator on the substrate 50. The light source may input electromagnetic waves in TE mode or TM mode to the isolator.

[0099] The electromagnetic wave transmitter may further include a modulator and a signal input unit. The modulator modulates the electromagnetic wave by changing the intensity of the electromagnetic wave. The modulator may be located between the isolator and the receiver, not between the light source and the isolator. The modulator may pulse-modulate the electromagnetic wave, for example. The signal input unit accepts input of a signal from an external device or the like. The signal input unit may include, for example, a D / A converter. The signal input unit outputs a signal to the modulator. The modulator modulates the electromagnetic wave based on the signal acquired by the signal input unit.

[0100] The light source may include a modulator and a signal input section. In this case, the light source may output a modulated electromagnetic wave and input it to the isolator.

[0101] The electromagnetic wave transmitter may be mounted on the substrate 50. The light source may be mounted so as to be connected, via a modulator, to a branching section that branches and inputs an electromagnetic wave to at least one nonreciprocal line. The light source may be mounted so as to be connected to the branching section without a modulator. The receiver may be mounted so as to be connected to a multiplexing section that multiplexes the electromagnetic wave input from at least one nonreciprocal line without a modulator. The receiver may be mounted so as to be connected to the multiplexing section via a modulator. In this case, the modulator may be mounted so as to be connected to the multiplexing section.

[0102] The optical integrated circuit 1 may be formed by silicon photonics technology.

[0103] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications or alterations are included in the scope of the present disclosure. For example, the functions included in each component can be rearranged so as not to be logically inconsistent, and multiple components can be combined into one or divided.

[0104] In this disclosure, descriptions such as "first" and "second" are identifiers for distinguishing the configuration. Configurations distinguished by descriptions such as "first" and "second" in this disclosure may have their numbers exchanged. For example, the first part 21 may exchange the identifiers "first" and "second" with the second part 22. The exchange of identifiers is performed simultaneously. The configurations remain distinguished even after the exchange of identifiers. Identifiers may be deleted. A configuration from which an identifier has been deleted is distinguished by a symbol. Descriptions of identifiers such as "first" and "second" in this disclosure alone should not be used to interpret the order of the configurations or to justify the existence of an identifier with a smaller number.

[0105] In the present disclosure, the X-axis, Y-axis, and Z-axis are provided for convenience of explanation and may be interchanged. The configuration according to the present disclosure has been described using an orthogonal coordinate system formed by the X-axis, Y-axis, and Z-axis. The positional relationship of each configuration according to the present disclosure is not limited to an orthogonal relationship.

[0106] In one embodiment, (1) an optical integrated circuit includes a waveguide including a first portion and a second portion, configured to couple an electromagnetic wave propagating through the first portion with an electromagnetic wave propagating through the second portion, and a nonreciprocal member positioned alongside the second portion in an amplitude direction of an electric field component of the electromagnetic wave, wherein in a range where the first portion and the second portion are coupled together, a deviation between a center of energy distribution of the electric field component of the electromagnetic wave propagating through the first portion and a center of energy distribution of the electric field component of the electromagnetic wave propagating through the second portion falls within a predetermined range.

[0107] (2) In the optical integrated circuit described in (1) above, the center of the second portion in the amplitude direction of the electric field component of the electromagnetic wave may be shifted in a direction away from the nonreciprocal member relative to the center of the first portion in the amplitude direction of the electric field component of the electromagnetic wave.

[0108] (3) In the optical integrated circuit described in (1) or (2) above, in the range where the first portion and the second portion are coupled, the dimension of the second portion in the amplitude direction of the electric field component of the electromagnetic wave may be shorter than the dimension of the first portion in the amplitude direction of the electric field component of the electromagnetic wave.

[0109] (4) In the optical integrated circuit described above in (3), the second portion may become larger in a direction approaching the nonreciprocal member as it becomes farther away from the first portion.

[0110] (5) In the optical integrated circuit described above in (4), the first portion and the second portion may be positioned apart in a propagation direction of the electromagnetic wave.

[0111] (6) In the optical integrated circuit according to any one of (2) to (5) above, the nonreciprocal member may be such that the amplitude of the electric field component of the electromagnetic wave increases with increasing distance from the first portion.

[0112] (7) In the optical integrated circuit described above in (6), the second portion may become smaller in size in a direction away from the nonreciprocal member as it moves away from the first portion.

[0113] (8) The optical integrated circuit according to any one of (1) to (7) above may further include a substrate having a substrate surface, and an insulating layer located on the substrate surface. The waveguide may extend along the substrate surface. The insulating layer may have a recess surrounding the waveguide and formed on the second portion. The non-reciprocal member may be located on a bottom surface of the recess.

[0114] (9) In the optical integrated circuit described above in (8), the recess may be formed such that the second portion is in contact with the nonreciprocal member at a bottom surface of the recess.

[0115] (10) In the optical integrated circuit according to (8) or (9) above, the recess may be formed such that the insulating layer is located between the waveguide and the nonreciprocal member at the bottom surface of the recess.

[0116] (11) The optical integrated circuit according to any one of (1) to (7) above may further include a substrate having a substrate surface, and an insulating layer located on the substrate surface. The waveguide may extend along the substrate surface. The insulating layer may have a recess located surrounding the waveguide and formed along the second portion. The non-reciprocal member may be located on a side of the recess that is along the second portion.

[0117] (12) The optical integrated circuit according to any one of (1) to (11) above may be formed by silicon photonics technology. [Explanation of symbols]

[0118] 1. Optical integrated circuits 20 waveguide (21: first part, 22: second part, 23: inclined part) 30 Recess (31: side surface, 32: bottom surface) 40 Non-reciprocal Members 50 substrate (50A: substrate surface, 52: box layer, 54, 56, 58: insulating layer) 100 Optical Integrated Circuits 120 waveguide (121: 1st part, 122: 2nd part) 130 recess (131: first side, 132: bottom, 133: second side, 134: third side, 135: fourth side) 141, 142 Non-reciprocal members 150 substrate (150A: substrate surface, 152: box layer, 154: insulating layer)

Claims

1. a waveguide including a first portion and a second portion, the waveguide being configured to couple an electromagnetic wave propagating through the first portion with an electromagnetic wave propagating through the second portion; a non-reciprocal member arranged next to the second portion in an amplitude direction of the electric field component of the electromagnetic wave; Equipped with In a range where the first portion and the second portion are coupled, a dimension of the second portion in an amplitude direction of the electric field component of the electromagnetic wave is shorter than a dimension of the first portion in the amplitude direction of the electric field component of the electromagnetic wave, and the dimension of the second portion increases in a direction approaching the nonreciprocal member as it moves away from the first portion. Optical integrated circuits.

2. 2. The optical integrated circuit according to claim 1, wherein a center of the second portion in an amplitude direction of the electric field component of the electromagnetic wave is shifted in a direction away from the nonreciprocal member with respect to a center of the first portion in an amplitude direction of the electric field component of the electromagnetic wave.

3. The optical integrated circuit according to claim 1 , wherein the first portion and the second portion are spaced apart in a propagation direction of the electromagnetic wave.

4. a waveguide including a first portion and a second portion, the waveguide being configured to couple an electromagnetic wave propagating through the first portion with an electromagnetic wave propagating through the second portion; a non-reciprocal member arranged next to the second portion in an amplitude direction of the electric field component of the electromagnetic wave; Equipped with a center of the second portion in an amplitude direction of the electric field component of the electromagnetic wave is shifted in a direction away from the nonreciprocal member with respect to a center of the first portion in the amplitude direction of the electric field component of the electromagnetic wave, The non-reciprocal member has an amplitude direction of the electric field component of the electromagnetic wave that increases with increasing distance from the first portion.

5. The optical integrated circuit of claim 4 , wherein the second portion becomes smaller in a direction away from the nonreciprocal member the further away from the first portion.

6. a substrate having a substrate surface; an insulating layer located on the substrate surface; Further comprising: the waveguide extends along a surface of the substrate; the insulating layer is positioned to surround the waveguide and has a recess formed on the second portion; The non-reciprocal member is located on a bottom surface of the recess or on a side surface of the recess along the second portion.

2. The optical integrated circuit according to claim 1.

7. The optical integrated circuit according to claim 6 , wherein the recess is formed such that the second portion contacts the non-reciprocal member at a bottom surface of the recess.

8. The optical integrated circuit according to claim 6 , wherein the recess is formed such that the insulating layer is located between the waveguide and the non-reciprocal member at the bottom surface of the recess.

9. A substrate having a substrate surface; an insulating layer located on the substrate surface; Further comprising: the waveguide extends along a surface of the substrate; the insulating layer is positioned to surround the waveguide and has a recess formed on the second portion; The non-reciprocal member is located on a bottom surface of the recess or on a side surface of the recess along the second portion.

5. The optical integrated circuit according to claim 4.

10. The optical integrated circuit of claim 9, wherein the recess is formed so that the second portion contacts the non-reciprocal member at a bottom surface of the recess.

11. The optical integrated circuit of claim 9, wherein the recess is formed such that the insulating layer is positioned between the waveguide and the non-reciprocal member at the bottom surface of the recess.

12. 12. An optical integrated circuit according to any one of claims 1 to 11, which is formed by means of silicon photonics technology.

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