Isolator

Abstract

This isolator comprises a substrate (50) having a substrate surface (50A), and a reciprocal line and a non-reciprocal line (12) that extend over the substrate surface (50A) and cause at least one of the electromagnetic waves in a TE mode or the electromagnetic waves in a TM mode to propagate in the extending direction. The non-reciprocal line (12) comprises: a waveguide (20) that has a first surface (21) extending along the substrate surface (50A) and a second surface (22) extending along a surface intersecting the substrate surface (50A); a first non-reciprocal member (41) positioned along the first surface (21) of the waveguide (20); and a second non-reciprocal member (42) positioned along the second surface (22) of the waveguide (20).

Description

Isolator

[0001] The present disclosure relates to an isolator.

[0002] As described in Patent Document 1, an isolator is known in which a non-reciprocal member is positioned in line with a core in only one direction.

[0003] Japanese Patent Application Laid-Open No. 2021-21831

[0004] An isolator according to an embodiment of the present disclosure includes a substrate having a substrate surface, a reciprocal line extending on the substrate surface and propagating at least one of a TE mode electromagnetic wave and a TM mode electromagnetic wave along the extending direction, the nonreciprocal line including a waveguide having a first surface extending along the substrate surface and a second surface extending along a plane intersecting the substrate surface, a first nonreciprocal member positioned along the first surface of the waveguide, and a second nonreciprocal member positioned along the second surface of the waveguide.

[0005] 2 is a plan view showing an example of the configuration of an isolator according to an embodiment; FIG. 3 is a plan view showing an example of the configuration of a nonreciprocal line according to an embodiment; FIG. 4 is a cross-sectional view taken along the line A-A of FIG. 2; FIG. 5 is a cross-sectional view showing the width and height of a waveguide, the thickness of a nonreciprocal member, and the distance between the waveguide and the nonreciprocal member; and FIG. 6 is a plan view showing the length of the nonreciprocal member.

[0006] 1 , an isolator 10 according to one embodiment includes a substrate 50, a reciprocal line 11, a nonreciprocal line 12, a first branch 81, and a second branch 82. The reciprocal line 11 and the nonreciprocal line 12 are disposed on the substrate 50. The first branch 81 and the second branch 82 branch an electromagnetic wave and input the branched wave to the reciprocal line 11 and the nonreciprocal line 12. The first branch 81 and the second branch 82 also combine and output the electromagnetic waves output from the reciprocal line 11 and the nonreciprocal line 12. The first branch 81 and the second branch 82 may be disposed on the substrate 50 or may be disposed outside the substrate 50.

[0007] The isolator 10 is configured to transmit electromagnetic waves input to the first branch portion 81 to the second branch portion 82, and to block electromagnetic waves input to the second branch portion 82, preventing them from transmitting to the first branch portion 81. The direction in which the electromagnetic waves propagate from the first branch portion 81 to the second branch portion 82 is also referred to as the first direction. The direction in which the electromagnetic waves propagate from the second branch portion 82 to the first branch portion 81 is also referred to as the second direction. In other words, the isolator 10 allows electromagnetic waves to transmit in the first direction but does not allow them to transmit in the second direction.

[0008] (Operating Principle of Isolator 10) The isolator 10 realizes asymmetric electromagnetic wave propagation characteristics using the principle of asymmetric Mach-Zehnder interferometry. The isolator 10 is configured so that the phase difference between an electromagnetic wave propagating through the reciprocal line 11 and an electromagnetic wave propagating through the nonreciprocal line 12 is 0 degrees when propagating in a first direction and 180 degrees when propagating in a second direction, thereby transmitting the electromagnetic wave propagating in the first direction and blocking the electromagnetic wave propagating in the second direction. The isolator 10 can make the phase difference when the electromagnetic wave propagates in the first direction different from the phase difference when the electromagnetic wave propagates in the second direction by imparting nonreciprocity to the propagation characteristics of the electromagnetic waves in the nonreciprocal line 12. Nonreciprocity is a property in which the phase shift when the electromagnetic wave propagates in the first direction is different from the phase shift when the electromagnetic wave propagates in the second direction.

[0009] When electromagnetic waves propagate in a first direction, the phase difference between the electromagnetic waves propagating in the reciprocal line 11 and the electromagnetic waves propagating in the nonreciprocal line 12 is 0 degrees. Therefore, the isolator 10 needs to be configured so that the phase shift of the electromagnetic waves propagating in the first direction in the nonreciprocal line 12 matches the phase shift of the electromagnetic waves propagating in the first direction in the reciprocal line 11.

[0010] Furthermore, when electromagnetic waves propagate in the second direction, the phase difference between the electromagnetic waves propagating through the reciprocal line 11 and the electromagnetic waves propagating through the nonreciprocal line 12 is 180 degrees. Therefore, the isolator 10 must be configured so that the phase shift of the electromagnetic waves propagating through the nonreciprocal line 12 in the second direction is 180 degrees shifted relative to the phase shift of the electromagnetic waves propagating through the reciprocal line 11 in the second direction.

[0011] Here, the phase shift of the electromagnetic waves propagating in the first direction through the reciprocal line 11 matches the phase shift of the electromagnetic waves propagating in the second direction through the reciprocal line 11. Therefore, the isolator 10 needs to be configured so that the phase shift of the electromagnetic waves propagating in the second direction through the nonreciprocal line 12 is shifted by 180 degrees relative to the phase shift of the electromagnetic waves propagating in the first direction through the nonreciprocal line 12.

[0012] The phase shift of the electromagnetic waves propagating in the second direction through the nonreciprocal line 12 is 180 degrees relative to the phase shift of the electromagnetic waves propagating in the first direction through the nonreciprocal line 12. Therefore, the nonreciprocal line 12 may be configured so that the phase of the electromagnetic waves propagating in the first direction is advanced by 90 degrees and the phase of the electromagnetic waves propagating in the second direction is delayed by 90 degrees. The nonreciprocal line 12 may be configured so that the phase of the electromagnetic waves propagating in the first direction is delayed by 90 degrees and the phase of the electromagnetic waves propagating in the second direction is advanced by 90 degrees.

[0013] The isolator 10 described above may be configured so that the directions of the phase shifts of the electromagnetic waves propagating through the reciprocal line 11 and the nonreciprocal line 12 are all opposite to each other.

[0014] In the isolator 10, the reciprocal line 11 may be replaced with a first nonreciprocal line, and the nonreciprocal line 12 will be referred to as a second nonreciprocal line.

[0015] When the reciprocal line 11 is replaced with a first nonreciprocal line, the first nonreciprocal line and the second nonreciprocal line are configured such that, in a state in which nonreciprocity is not exhibited, the phase of the electromagnetic wave propagating through the second nonreciprocal line leads the phase of the electromagnetic wave propagating through the first nonreciprocal line by 90 degrees, regardless of the propagation direction of the electromagnetic wave.

[0016] The first nonreciprocal line is configured such that, in a state where nonreciprocity is exhibited, the phase of the electromagnetic wave propagating in the first direction is advanced by 45 degrees and the phase of the electromagnetic wave propagating in the second direction is delayed by 45 degrees.

[0017] The second nonreciprocal line is configured such that, when nonreciprocity is manifested, the phase of the electromagnetic wave propagating in the first direction is delayed by 45 degrees and the phase of the electromagnetic wave propagating in the second direction is advanced by 45 degrees.

[0018] By configuring the isolator 10 as described above, the phase difference between the electromagnetic wave propagating in a first direction through the first nonreciprocal line and the electromagnetic wave propagating in the first direction through the second nonreciprocal line is 0 degrees, and the phase difference between the electromagnetic wave propagating in a second direction through the first nonreciprocal line and the electromagnetic wave propagating in the second direction through the second nonreciprocal line is 180 degrees.

[0019] The isolator 10 described above may be configured so that the directions of the phase shifts of the electromagnetic waves propagating through the first nonreciprocal line and the second nonreciprocal line are all opposite to each other.

[0020] 2 and 3, the nonreciprocal line 12 includes a waveguide 20 and a nonreciprocal member 40. The waveguide 20 and the nonreciprocal member 40 are formed on a substrate 50 having a substrate surface 50A. In this embodiment, a coordinate system is set so that the substrate surface 50A is along the XY plane. The coordinate system is also set so that the waveguide 20 and the nonreciprocal member 40 extend along the X axis. The coordinate system is also set so that the waveguide 20 is located on the positive side of the Z axis with respect to the substrate surface 50A.

[0021] The substrate 50 may be configured to include a conductor such as metal, a semiconductor such as silicon, glass, or 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.

[0022] The substrate 50 includes a box layer 52 made of an insulator such as a silicon oxide film on a substrate surface 50A. The waveguide 20 is located on the box layer 52. The waveguide 20 has a first surface 21 and a second surface 22. The first surface 21 extends along the substrate surface 50A and is located on the side farther from the substrate surface 50A. The first surface 21 is located on the positive side of the Z axis of the waveguide 20. The second surface 22 extends intersecting the substrate surface 50A and the first surface 21. In this embodiment, the second surface 22 is located on the negative side of the Y axis of the waveguide 20. The second surface 22 may also be located on the positive side of the Y axis of the waveguide 20.

[0023] The waveguide 20 is surrounded by a box layer 52, an insulating layer 54, and a nonreciprocal member 40. The waveguide 20 is also referred to as a core. The box layer 52 and the insulating layer 54 are also referred to as a clad. The core and the clad may be configured to include a dielectric. The waveguide 20 is also referred to as a dielectric waveguide. The materials of the core and the clad are determined so that the relative dielectric constant of the core is greater than the relative dielectric constant 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 the refractive index of the core. In this way, electromagnetic waves propagating through the core can be totally reflected at the boundary with the clad. As a result, loss of electromagnetic waves propagating through the core can be reduced.

[0024] The dielectric constants of the core and the cladding may be greater than that of air. By making the dielectric constants of the core and the cladding greater than that of air, leakage of electromagnetic waves from the isolator 10 can be suppressed. As a result, loss due to radiation of electromagnetic waves from the isolator 10 to the outside can be reduced.

[0025] 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 cladding may be silica glass or silicon oxide film (SiO ２ ), but is not limited to this and may be various other materials. The relative dielectric constants of silicon and quartz glass are approximately 12 and approximately 2, respectively. Silicon can propagate electromagnetic waves having near-infrared wavelengths of approximately 1.2 μm to approximately 6 μm with low loss. When the waveguide 20 is made of silicon, it can propagate electromagnetic waves having wavelengths in the 1.3 μm or 1.55 μm band used in optical communications with low loss.

[0026] The nonreciprocal line 12 includes a groove 30 formed by etching an insulating layer 54. The groove 30 extends in the X-axis direction along the waveguide 20. As shown in FIG. 3 , the groove 30 is defined by side surfaces 31 and 32 and bottom surfaces 33 and 34 in a cross section viewed in the extension direction. The side surface 31 is located on the positive side of the Y-axis. The side surface 32 is located on the negative side of the Y-axis. The bottom surface 33 is located flush with the first surface 21 of the waveguide 20, but may be closer to or farther from the substrate surface 50A than the first surface 21. In other words, the bottom surface 33 may be shifted in the Z-axis direction from the first surface 21. The bottom surface 34 is located flush with the second surface 22 of the waveguide 20, but may be closer to or farther from the substrate surface 50A than the second surface 22. In other words, the position of the bottom surface 34 may be shifted in the Z-axis direction relative to the second surface 22 .

[0027] The nonreciprocal member 40 is formed by film deposition on the bottom surfaces 33 and 34 of the groove 30. As shown in FIG. 3 , the nonreciprocal member 40 may be in contact with each of the first surface 21 and the second surface 22 of the waveguide 20. The nonreciprocal member 40 may not be in contact with at least one of the first surface 21 or the second surface 22 of the waveguide 20. The nonreciprocal member 40 may be spaced apart from and face at least one of the first surface 21 and the second surface 22 of the waveguide 20. A portion of the nonreciprocal member 40 that is in contact with or faces the first surface 21 of the waveguide 20 is also referred to as a first nonreciprocal member 41. A portion of the nonreciprocal member 40 that is in contact with or faces the second surface 22 of the waveguide 20 is also referred to as a second nonreciprocal member 42.

[0028] When the nonreciprocal member 40 contacts or faces the first surface 21 of the waveguide 20 as the first nonreciprocal member 41, it is not located on the opposite side of the first surface 21. In other words, the nonreciprocal member 40 is located only on one side in the normal direction of the substrate surface 50A. Furthermore, when the nonreciprocal member 40 contacts or faces the second surface 22 of the waveguide 20 as the second nonreciprocal member 42, it is not located on the opposite side of the second surface 22. In other words, the nonreciprocal member 40 is located along the substrate surface 50A and only on one side in the direction perpendicular to the extension direction of the waveguide 20.

[0029] As described above, the nonreciprocal line 12 includes the nonreciprocal member 40 located along the waveguide 20. The nonreciprocal line 12 includes the nonreciprocal member 40, and when a magnetic field is applied, causes nonreciprocity to occur in the propagation characteristics of electromagnetic waves in the waveguide 20. Nonreciprocity is a property in which the direction of a phase shift when an electromagnetic wave propagates in a first direction is opposite to the direction of a phase shift when the electromagnetic wave propagates in a second direction. In the following description, the positive direction of the X-axis of the nonreciprocal line 12 illustrated in FIGS. 2 and 3 will be described as the first direction, and the negative direction of the X-axis as the second direction.

[0030] The magnetic field applied to the nonreciprocal line 12 is represented by B. The magnetic field (B) includes a component (B1) along the Y-axis direction, which is perpendicular to the propagation direction of the electromagnetic wave (i.e., the X-axis direction), and a component (B2) along the Z-axis direction.

[0031] 1 , the isolator 10 may further include a magnetic field application unit 70. The magnetic field application unit 70 applies a magnetic field to the nonreciprocal line 12. The magnetic field application unit 70 may include an electromagnet or a permanent magnet. The isolator 10 does not necessarily have to include the magnetic field application unit 70. When the isolator 10 does not include the magnetic field application unit 70, it may be used in combination with a device that applies a magnetic field to the nonreciprocal line 12.

[0032] 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 also 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 also be used as the material of the nonreciprocal member 40. A dielectric material composited with magnetic nanoparticles, such as a nanogranular material, may also be used as the material of the nonreciprocal member 40. The nonreciprocal member 40 is not limited to these, and various other magnetic materials may also be used.

[0033] The YIG-based nonreciprocal member 40 exhibits sufficient nonreciprocity by allowing its crystallization to progress sufficiently. The crystallization of the nonreciprocal member 40 progresses by heating the nonreciprocal member 40 to a predetermined temperature or higher. However, considering the influence on other components such as the waveguide 20 or wiring formed on the substrate 50, it is difficult to heat the entire substrate 50 to a predetermined temperature or higher during deposition of the nonreciprocal member 40. Therefore, the nonreciprocal member 40 formed in the groove 30 by deposition without heating the substrate 50 is not sufficiently crystallized and does not exhibit sufficient nonreciprocity as it is.

[0034] Therefore, in the isolator 10 according to this embodiment, the nonreciprocal member 40 may be heated by irradiation with laser light in order to crystallize the nonreciprocal member 40. As the laser light, light of a wavelength at which the nonreciprocal member 40 has a high light absorption efficiency is used. When the nonreciprocal member 40 is made of Ce:YIG, it has a high absorption efficiency for visible light. Therefore, a visible light laser may be used for heating. As described above, when the nonreciprocal member 40 is made of YIG, the nonreciprocal member 40 exhibits nonreciprocity by crystallizing.

[0035] (Conditions for manifesting nonreciprocity) In the nonreciprocal line 12, nonreciprocity manifests when certain conditions are satisfied. The conditions for manifesting nonreciprocity in the propagation characteristics of TE mode electromagnetic waves are different from the conditions for manifesting nonreciprocity in the propagation characteristics of TM mode electromagnetic waves. TE mode electromagnetic waves are electromagnetic waves in which, when the electromagnetic waves propagate along the substrate surface 50A of 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. TM mode electromagnetic waves are electromagnetic waves in which, when the electromagnetic waves propagate along the substrate surface 50A, the amplitude direction of the electric field coincides with the normal direction of the substrate surface 50A. Below, the conditions for manifesting nonreciprocity for TM mode electromagnetic waves and TE mode electromagnetic waves will be described.

[0036] <TM Mode> Conditions for nonreciprocity to appear in the propagation characteristics of TM mode electromagnetic waves in the nonreciprocal line 12 include the nonreciprocal member 40 being located either above or below the waveguide 20 when the waveguide 20 is viewed in the propagation direction of the electromagnetic waves. An electromagnetic wave propagating in TM mode has an electric field component with amplitude in the vertical direction of the waveguide 20. The vertical direction of the waveguide 20 coincides with the normal direction of the substrate surface 50A. When an electromagnetic wave in TM mode propagates through the waveguide 20, part of the energy of the electric field leaks in the vertical direction of the waveguide 20. The component of the leaked energy that is distributed inside the nonreciprocal member 40 is affected by the nonreciprocal member 40, thereby appearing nonreciprocity in the propagation characteristics of the electromagnetic wave in the waveguide 20.

[0037] 3 includes a first nonreciprocal member 41 located above the waveguide 20. By including the first nonreciprocal member 41 in the nonreciprocal line 12, the condition for the position of the nonreciprocal member 40 for nonreciprocity to appear in the propagation characteristics of TM mode electromagnetic waves in the nonreciprocal line 12 is satisfied.

[0038] The conditions under which nonreciprocity appears in the propagation characteristics of TM mode electromagnetic waves in the nonreciprocal line 12 also include the magnetic field applied to the nonreciprocal line 12 having a component in the left-right direction of the waveguide 20. The left-right direction of the waveguide 20 is perpendicular to the propagation direction of the electromagnetic waves and coincides with the direction along the substrate surface 50A.

[0039] 3, the component of the magnetic field (B) applied to the nonreciprocal line 12 in the left-right direction of the waveguide 20 is represented by B1. The left-right direction of the waveguide 20 is perpendicular to the direction in which the electromagnetic wave propagates in the waveguide 20 and corresponds to the direction along the substrate surface 50A. When the magnetic field applied to the nonreciprocal line 12 illustrated in FIG. 3 includes a component in the left-right direction of the waveguide 20, the magnetic field conditions for nonreciprocity to appear in the propagation characteristics of the TM mode electromagnetic wave in the nonreciprocal line 12 are satisfied.

[0040] Whether the phase of the electromagnetic wave advances or lags is reversed when a magnetic field component directed from left to right in the propagation direction of the electromagnetic wave is applied and when a magnetic field component directed from right to left is applied. In the nonreciprocal line 12 illustrated in FIG. 3 , when the electromagnetic wave propagates in a first direction (a direction into the page, i.e., the positive direction of the X-axis), the direction of the magnetic field applied to the waveguide 20 is rightward as viewed in the propagation direction of the electromagnetic wave. On the other hand, when the electromagnetic wave propagates in a second direction (a direction toward the front of the page, i.e., the negative direction of the X-axis), the direction of the magnetic field applied to the waveguide 20 is leftward as viewed in the propagation direction of the electromagnetic wave. In other words, when the electromagnetic wave propagates in the first direction and when the electromagnetic wave propagates in the second direction, the direction of the magnetic field applied to the waveguide 20 is reversed left to right as viewed in the propagation direction of the electromagnetic wave. Therefore, the direction of the phase shift when the electromagnetic wave propagates in the first direction is opposite to the direction of the phase shift when the electromagnetic wave propagates in the second direction, thereby achieving the function of the isolator 10.

[0041] <TE Mode> Conditions for nonreciprocity to appear in the propagation characteristics of TE mode electromagnetic waves in the nonreciprocal line 12 include the nonreciprocal member 40 being located on either the left or right side of the waveguide 20 when viewing the waveguide 20 in the propagation direction of the electromagnetic waves. An electromagnetic wave propagating in TE mode has an electric field component with amplitude in the left-right direction of the waveguide 20. The left-right direction of the waveguide 20 is perpendicular to the propagation direction of the electromagnetic waves and coincides with the direction along the substrate surface 50A. When an electromagnetic wave in TE mode propagates through the waveguide 20, part of the energy of the electric field leaks in the left-right direction of the waveguide 20. A component of the leaked energy that is distributed inside the nonreciprocal member 40 is affected by the nonreciprocal member 40, thereby appearing nonreciprocity in the propagation characteristics of the electromagnetic waves in the waveguide 20.

[0042] 3 includes a second nonreciprocal member 42 located on the right side of the waveguide 20 when viewed in the positive direction of the X-axis, which is the first direction in which electromagnetic waves propagate. By including the second nonreciprocal member 42 in the nonreciprocal line 12, the condition for the position of the nonreciprocal member 40 is satisfied, so that nonreciprocity appears in the propagation characteristics of TE mode electromagnetic waves in the nonreciprocal line 12.

[0043] The conditions under which nonreciprocity appears in the propagation characteristics of the TE mode in the nonreciprocal line 12 include that the magnetic field applied to the nonreciprocal line 12 has a component in the vertical direction of the waveguide 20. The vertical direction of the waveguide 20 coincides with the normal direction of the substrate surface 50A.

[0044] 3, of the magnetic field (B) applied to the nonreciprocal line 12, the component in the vertical direction of the waveguide 20 is represented by B2. The vertical direction of the waveguide 20 corresponds to the direction perpendicular to the substrate surface 50A. When the magnetic field applied to the nonreciprocal line 12 illustrated in FIG. 3 includes a component in the vertical direction of the waveguide 20, the magnetic field conditions for nonreciprocity to appear in the propagation characteristics of TE mode electromagnetic waves in the nonreciprocal line 12 are satisfied.

[0045] Whether the phase of the electromagnetic wave advances or delays is reversed when the nonreciprocal member 40 is located on the left side of the electromagnetic wave propagation direction and when the nonreciprocal member 40 is located on the right side. In the nonreciprocal line 12 illustrated in FIG. 3 , when the electromagnetic wave propagates in a first direction (a direction into the page, i.e., the positive direction of the X-axis), the second nonreciprocal member 42 is located on the right side of the waveguide 20 in the electromagnetic wave propagation direction. On the other hand, when the electromagnetic wave propagates in a second direction (a direction toward the page, i.e., the negative direction of the X-axis), the second nonreciprocal member 42 is located on the left side of the waveguide 20 in the electromagnetic wave propagation direction. In other words, when the electromagnetic wave propagates in the first direction and when the electromagnetic wave propagates in the second direction, the position of the second nonreciprocal member 42 as viewed in the electromagnetic wave propagation direction is reversed left and right with respect to the waveguide 20. Therefore, the direction of the phase shift when the electromagnetic wave propagates in the first direction is opposite to the direction of the phase shift when the electromagnetic wave propagates in the second direction, thereby achieving the function of the isolator 10.

[0046] 2 and 3 , in this embodiment, the nonreciprocal line 12 includes both a first nonreciprocal member 41 located above the waveguide 20 in the propagation direction of the electromagnetic waves and a second nonreciprocal member 42 located on either the right or left side of the waveguide 20 in the propagation direction of the electromagnetic waves. This satisfies the positional condition of the nonreciprocal member 40 for nonreciprocity to occur in the nonreciprocal line 12 for both TE mode electromagnetic waves and TM mode electromagnetic waves. Furthermore, the magnetic field condition for nonreciprocity to occur in the nonreciprocal line 12 is satisfied for both TE mode electromagnetic waves and TM mode electromagnetic waves by applying magnetic field components required for the TE mode electromagnetic waves and the TM mode electromagnetic waves, respectively. In other words, the nonreciprocal line 12 according to this embodiment is configured so that both the positional condition of the nonreciprocal member 40 and the magnetic field condition are satisfied.

[0047] As described above, the nonreciprocal line 12 according to this embodiment can satisfy both the positional condition of the nonreciprocal member 40 and the magnetic field condition, and therefore can exhibit nonreciprocity in the propagation characteristics regardless of whether the TE mode electromagnetic wave or the TM mode electromagnetic wave propagates through the waveguide 20. Furthermore, by including the nonreciprocal line 12 that can exhibit nonreciprocity for both the TE mode electromagnetic wave and the TM mode electromagnetic wave, the isolator 10 according to this embodiment can function to transmit electromagnetic waves propagating in a first direction and block electromagnetic waves propagating in a second direction for both the TE mode electromagnetic wave and the TM mode electromagnetic wave. In other words, the isolator 10 according to this embodiment is polarization-independent and can function to transmit electromagnetic waves propagating in a first direction and block electromagnetic waves propagating in a second direction for at least one of the TE mode electromagnetic wave and the TM mode electromagnetic wave.

[0048] As described above, in the nonreciprocal line 12 according to the present disclosure, the nonreciprocal member 40 contacts or faces both the first surface 21 and the second surface 22 of the waveguide 20. As a first comparative example, a line configured so that the nonreciprocal member 40 contacts or faces only the first surface 21 of the waveguide 20 can be considered. However, the line of the first comparative example cannot satisfy the conditions for realizing nonreciprocity in the TE mode. As a second comparative example, a line configured so that the nonreciprocal member 40 contacts or faces only the second surface 22 of the waveguide 20 can be considered. However, the line of the second comparative example cannot satisfy the conditions for realizing nonreciprocity in the TM mode. From the above, even if an isolator includes the lines of the first and second comparative examples, the isolator cannot function as a polarization-independent isolator.

[0049] The nonreciprocal line 12 according to the present disclosure can satisfy both the conditions for realizing nonreciprocity in the TE mode and the conditions for realizing nonreciprocity in the TM mode by configuring the nonreciprocal member 40 to be in contact with or facing both the first surface 21 and the second surface 22 of the waveguide 20. In other words, the isolator 10 including the nonreciprocal line 12 according to the present disclosure can function as a polarization-independent type.

[0050] (Matching the magnitude of the phase shift in the TE mode and the TM mode) As described above, nonreciprocity is a property in which the phase shift when an electromagnetic wave propagates in a first direction is different from the phase shift when the electromagnetic wave propagates in a second direction. The stronger the nonreciprocity, the larger the phase shift that occurs in the electromagnetic wave.

[0051] Here, for the isolator 10 including the reciprocal line 11 and the nonreciprocal line 12 to function, the magnitude of the phase shift between the electromagnetic waves propagating through the nonreciprocal line 12 needs to be 90 degrees. For the isolator 10 to function as a polarization-independent isolator, the magnitude of the phase shift between both the TE mode electromagnetic waves and the TM mode electromagnetic waves propagating through the nonreciprocal line 12 needs to be 90 degrees. Hereinafter, the magnitude of the phase shift that occurs when the TE mode electromagnetic waves propagate through the nonreciprocal line 12 is also referred to as the TE mode phase shift. The magnitude of the phase shift that occurs when the TM mode electromagnetic waves propagate through the nonreciprocal line 12 is also referred to as the TM mode phase shift. In other words, the magnitude of the TE mode phase shift and the TM mode phase shift both need to be 90 degrees.

[0052] However, the phase shift of the TE mode and the phase shift of the TM mode do not necessarily match. Below, an embodiment of the nonreciprocal line 12 for matching the phase shift of the TE mode and the phase shift of the TM mode will be described.

[0053] <Aspect Ratio of Waveguide 20> One factor that affects the magnitude of the phase shift is the ratio between the length of the first surface 21 and the length of the second surface 22 of the waveguide 20 when the waveguide 20 is viewed in a cross section normal to the propagation direction of the electromagnetic wave. The length of the first surface 21 of the waveguide 20 is also referred to as the left-right length of the waveguide 20 or the width of the waveguide 20. The length of the second surface 22 of the waveguide 20 is also referred to as the up-down length of the waveguide 20 or the height of the waveguide 20. As shown in FIG. 4 , the left-right length of the waveguide 20, i.e., the width, is represented by W. The up-down length of the waveguide 20, i.e., the height, is represented by H. When the waveguide 20 is viewed in a cross section normal to the propagation direction of the electromagnetic wave, the ratio of the height to the width of the waveguide 20, i.e., the value obtained by dividing the height by the width (H / W), is also referred to as the aspect ratio of the waveguide 20. The aspect ratio of the waveguide 20 affects the phase shifts of the TM mode and the TE mode, i.e., the phase shifts of both the TM mode and the TE mode change as the aspect ratio of the waveguide 20 changes.

[0054] The longer the width of the waveguide 20 is relative to its height, i.e., the smaller the aspect ratio of the waveguide 20, the more easily the electromagnetic wave energy leaks in the vertical direction of the waveguide 20. Nonreciprocity is manifested when the electromagnetic wave energy leaked in the vertical direction of the waveguide 20 is distributed inside the first nonreciprocal member 41. Therefore, the smaller the aspect ratio of the waveguide 20, the more electromagnetic wave energy is distributed inside the first nonreciprocal member 41, the stronger the nonreciprocity of the TM mode, and the larger the phase shift of the TM mode.

[0055] Furthermore, the smaller the aspect ratio of the waveguide 20, the less likely the electromagnetic wave energy is to leak in the left-right direction of the waveguide 20. Nonreciprocity is manifested by the electromagnetic wave energy leaking in the left-right direction of the waveguide 20 being distributed inside the second nonreciprocal member 42. Therefore, the smaller the aspect ratio of the waveguide 20, the less electromagnetic wave energy is distributed inside the second nonreciprocal member 42, the weaker the nonreciprocity of the TE mode, and the smaller the phase shift of the TM mode.

[0056] Conversely, the longer the height of the waveguide 20 is relative to its width, i.e., the larger the aspect ratio of the waveguide 20 is, the stronger the nonreciprocity of the TE mode becomes, resulting in a larger phase shift in the TE mode, while the weaker the nonreciprocity of the TM mode becomes, resulting in a smaller phase shift in the TM mode.

[0057] <Distance Between Waveguide 20 and Nonreciprocal Member 40> Another factor that affects the magnitude of the phase shift is the distance between the waveguide 20 and the nonreciprocal member 40. As shown in FIG. 4 , it is assumed that an insulating layer 56 is sandwiched between the first surface 21 of the waveguide 20 and the first nonreciprocal member 41. The distance between the first surface 21 of the waveguide 20 and the first nonreciprocal member 41, i.e., the thickness of the insulating layer 56, is represented by D1. It is assumed that an insulating layer 58 is sandwiched between the second surface 22 of the waveguide 20 and the second nonreciprocal member 42. The distance between the second surface 22 of the waveguide 20 and the second nonreciprocal member 42, i.e., the thickness of the insulating layer 58, is represented by D2.

[0058] The shorter the distance between the waveguide 20 and the nonreciprocal member 40, the greater the amount of energy of the electromagnetic waves leaking from the waveguide 20 that is distributed inside the nonreciprocal member 40. Nonreciprocity is manifested by the distribution of the energy of the electromagnetic waves leaking from the waveguide 20 inside the nonreciprocal member 40, so the shorter the distance between the waveguide 20 and the nonreciprocal member 40, the stronger the nonreciprocity and the greater the phase shift.

[0059] For example, the phase shift when the nonreciprocal member 40 is in contact with the waveguide 20 is larger than the phase shift when the waveguide 20 and the nonreciprocal member 40 are not in contact. When the waveguide 20 and the nonreciprocal member 40 are not in contact, the shorter the distance between the waveguide 20 and the nonreciprocal member 40, the larger the phase shift. When the nonreciprocal member 40 is in contact with the waveguide 20, the distance between the waveguide 20 and the nonreciprocal member 40 is considered to be zero. In other words, regardless of whether the nonreciprocal member 40 is in contact with the waveguide 20, the shorter the distance between the waveguide 20 and the nonreciprocal member 40, the larger the phase shift.

[0060] The nonreciprocity of the TM mode is manifested when at least a portion of the energy of the electromagnetic waves leaking in the vertical direction of the waveguide 20 is distributed inside the first nonreciprocity member 41. Therefore, the nonreciprocity of the TM mode is affected by the first nonreciprocity member 41. The shorter the distance (D1) between the first surface 21 of the waveguide 20 and the first nonreciprocity member 41, the more energy of the electromagnetic waves leaking in the vertical direction of the waveguide 20 is distributed inside the first nonreciprocity member 41, and the stronger the nonreciprocity of the TM mode becomes, resulting in a larger phase shift of the TM mode.

[0061] The nonreciprocity of the TE mode is manifested when at least a portion of the energy of the electromagnetic waves leaking in the left-right direction of the waveguide 20 is distributed inside the second nonreciprocity member 42. Therefore, the nonreciprocity of the TE mode is affected by the second nonreciprocity member 42. The shorter the distance (D2) between the second surface 22 of the waveguide 20 and the second nonreciprocity member 42, the more energy of the electromagnetic waves leaking in the left-right direction of the waveguide 20 that is distributed inside the second nonreciprocity member 42, which strengthens the nonreciprocity of the TE mode and increases the phase shift of the TE mode.

[0062] <Thickness of Nonreciprocal Member 40> Another factor that affects the magnitude of the phase shift is the thickness of the nonreciprocal member 40 as viewed from the waveguide 20. As shown in Fig. 4, the thickness of the first nonreciprocal member 41 as viewed from the first surface 21 of the waveguide 20 is represented by T1. The thickness of the second nonreciprocal member 42 as viewed from the second surface 22 of the waveguide 20 is represented by T2.

[0063] The thicker the nonreciprocal member 40 is when viewed from the waveguide 20, the greater the amount of energy of the electromagnetic waves leaking from the waveguide 20 that is distributed inside the nonreciprocal member 40. Nonreciprocity is manifested by the energy of the electromagnetic waves leaking from the waveguide 20 being distributed inside the nonreciprocal member 40, so the thicker the nonreciprocal member 40, the stronger the nonreciprocity of the electromagnetic waves and the greater the phase shift.

[0064] The thicker the first nonreciprocal member 41 is when viewed in the vertical direction of the waveguide 20, the greater the amount of energy distributed inside the first nonreciprocal member 41 of the energy of the TM mode electromagnetic waves leaking in the vertical direction of the waveguide 20. Nonreciprocity is manifested by the energy of the electromagnetic waves leaking from the waveguide 20 being distributed inside the nonreciprocal member 40, so the thicker the first nonreciprocal member 41, the stronger the nonreciprocity of the TM mode electromagnetic waves and the greater the phase shift of the TM mode.

[0065] The thicker the second nonreciprocal member 42 is when viewed in the left-right direction of the waveguide 20, the greater the amount of energy distributed inside the second nonreciprocal member 42 of the energy of the TE mode electromagnetic waves leaking in the left-right direction of the waveguide 20. Nonreciprocity is manifested by the energy of the electromagnetic waves leaking from the waveguide 20 being distributed inside the nonreciprocal member 40, so the thicker the second nonreciprocal member 42, the stronger the nonreciprocity of the TE mode electromagnetic waves and the greater the phase shift of the TM mode.

[0066] <Magnitude of magnetic field> Another factor affecting the magnitude of the phase shift is the magnitude of the magnetic field applied to the nonreciprocal line 12. The stronger the magnetic field, the stronger the nonreciprocity. As shown in FIG. 3 , the greater the magnetic field component (B1) that is perpendicular to the propagation direction of the electromagnetic wave in the waveguide 20 and along the substrate surface 50A, i.e., the first surface 21 of the waveguide 20, the stronger the nonreciprocity for the TM mode electromagnetic wave. Therefore, the greater the magnetic field component (B1), the greater the phase shift of the TM mode. Furthermore, the greater the magnetic field component (B2) that is perpendicular to the substrate surface 50A, the stronger the nonreciprocity for the TE mode electromagnetic wave. Therefore, the greater the magnetic field component (B2), the greater the phase shift of the TE mode.

[0067] As described above, the stronger the magnetic field, the stronger the nonreciprocity. On the other hand, the strength of the nonreciprocity tends to saturate. The magnetic field component (B1) may be increased to the extent that the phase shift of the TM mode is saturated. The magnetic field component (B2) may be increased to the extent that the phase shift of the TE mode is saturated.

[0068] <Summary> The aspect ratio of the waveguide 20, the distance between the waveguide 20 and the nonreciprocal member 40, the thickness of the nonreciprocal member 40, and the magnitude of the magnetic field described above are factors that can adjust the phase shift caused by the nonreciprocal member 40 when electromagnetic waves propagate through a unit length. By adjusting the factors described above, the nonreciprocal line 12 may be configured so that the phase shift caused by the first nonreciprocal member 41 when TM mode electromagnetic waves propagate through a unit length is equal to the phase shift caused by the second nonreciprocal member 42 when TE mode electromagnetic waves propagate through a unit length.

[0069] As yet another factor, the phase shift caused by the nonreciprocal member 40 when electromagnetic waves propagate through a unit length may be adjusted by arranging the first nonreciprocal member 41 so as to overlap only a portion of the first surface 21 of the waveguide 20, or by arranging the second nonreciprocal member 42 so as to overlap only a portion of the second surface 22 of the waveguide 20. The smaller the portion where the first nonreciprocal member 41 is arranged relative to the width of the first surface 21 of the waveguide 20, the smaller the phase shift caused by the first nonreciprocal member 41 when electromagnetic waves in TM mode propagate through a unit length. The smaller the portion where the second nonreciprocal member 42 is arranged relative to the height of the second surface 22 of the waveguide 20, the smaller the phase shift caused by the second nonreciprocal member 42 when electromagnetic waves in TE mode propagate through a unit length.

[0070] <Length of Nonreciprocal Member 40> Another factor that affects the magnitude of the phase shift is the length of the nonreciprocal member 40 located along the propagation direction of the electromagnetic wave in the waveguide 20. As shown in Fig. 5, the length of the first nonreciprocal member 41 located along the propagation direction of the electromagnetic wave facing the first surface 21 of the waveguide 20 is represented by L1. The length of the second nonreciprocal member 42 located along the propagation direction of the electromagnetic wave facing the second surface 22 of the waveguide 20 is represented by L2.

[0071] The phase of the electromagnetic wave shifts as it travels along the nonreciprocal member 40. Therefore, the longer the nonreciprocal member 40 located along the propagation direction of the electromagnetic wave, the greater the phase shift. The longer the first nonreciprocal member 41, the greater the phase shift in the TM mode. The longer the second nonreciprocal member 42, the greater the phase shift in the TE mode.

[0072] In this case, even if the phase shift caused by the first nonreciprocal member 41 when the TM mode electromagnetic wave propagates through a unit length is not equal to the phase shift caused by the second nonreciprocal member 42 when the TE mode electromagnetic wave propagates through a unit length, the phase shift of the TM mode electromagnetic wave and the phase shift of the TE mode electromagnetic wave in the nonreciprocal line 12 can be made equal.

[0073] <Example of Adjustment of Each Factor> As described above, the phase shift of the TM mode and the phase shift of the TE mode each change under the influence of various factors. Among the factors described above, the aspect ratio of the waveguide 20 affects both the phase shift of the TM mode and the phase shift of the TE mode, and is therefore a parameter that cannot be adjusted independently for each of the phase shifts of the TM mode and the TE mode. On the other hand, the distance between the waveguide 20 and the nonreciprocal member 40, the thickness of the nonreciprocal member 40, the length of the nonreciprocal member 40, or the magnitude of the magnetic field are parameters that can be adjusted independently for each of the phase shifts of the TM mode and the TE mode.

[0074] The nonreciprocal line 12 may be configured so that the phase shift in TM mode and the phase shift in TE mode match by adjusting various factors that affect the phase shift. By configuring the nonreciprocal line 12 so that the phase shift in TM mode and the phase shift in TE mode match, the isolator 10 including the nonreciprocal line 12 can function as a polarization-independent type. The nonreciprocal line 12 may also be configured so that the phase shift caused by the first nonreciprocal member 41 when a TM-mode electromagnetic wave propagates through a unit length is equal to the phase shift caused by the second nonreciprocal member 42 when a TE-mode electromagnetic wave propagates through a unit length. This also allows the isolator 10 including the nonreciprocal line 12 to function as a polarization-independent type.

[0075] The nonreciprocal line 12 may be configured so that the aspect ratio of the waveguide 20 is 1. In other words, the nonreciprocal line 12 may be configured so that, in a cross section normal to the extension direction of the waveguide 20, the length of the first surface 21 of the waveguide 20, i.e., the width of the waveguide 20, is equal to the length of the second surface 22 of the waveguide 20, i.e., the height of the waveguide 20. When the width and height of the waveguide 20 are equal, and other factors are the same, the phase shift of the TM mode and the phase shift of the TE mode will be equal.

[0076] As described above, the stronger the magnetic field, the stronger the nonreciprocity. On the other hand, the strength of the nonreciprocity tends to saturate. When the saturated value of the TM mode phase shift and the saturated value of the TE mode phase shift are equal, the magnetic field applied to the nonreciprocal line 12 may be increased to the extent that the phase shift of the TM mode or the TE mode is saturated. By doing so, the phase shifts of the TM mode and the TE mode hardly change with respect to the error in the magnetic field applied to the nonreciprocal line 12. As a result, the phase shifts of the TM mode and the TE mode tend to become equal.

[0077] Even if the magnetic field is not strong enough to saturate the phase shift of the TM mode or the TE mode, the magnetic field component (B1) in the direction along the substrate surface 50A and the magnetic field component (B2) in the direction perpendicular to the substrate surface 50A, as shown in Figure 3, may be made equal. In other words, the magnetic field (B) obtained by combining the magnetic field components (B1) and (B2) may be applied in a direction forming an angle of 45 degrees with respect to the substrate surface 50A. In this way, the phase shift of the TM mode and the phase shift of the TE mode become equal in the nonreciprocal line 12 configured so that the aspect ratio of the waveguide 20 is 1.

[0078] The nonreciprocal line 12 may be configured so that the aspect ratio of the waveguide 20 is a value other than 1. In other words, the nonreciprocal line 12 may be configured so that, in a cross section normal to the extension direction of the waveguide 20, the length of the first surface 21 of the waveguide 20, i.e., the width of the waveguide 20, and the length of the second surface 22 of the waveguide 20, i.e., the height of the waveguide 20, are different.

[0079] The larger the aspect ratio of the waveguide 20, the smaller the ratio of the length of the second nonreciprocal member 42 along the extension direction of the waveguide 20 to the length of the first nonreciprocal member 41 along the extension direction of the waveguide 20 may be. For example, if the height of the waveguide 20 is greater than the width of the waveguide 20, the length of the second nonreciprocal member 42 along the extension direction of the waveguide 20 may be shorter than the length of the first nonreciprocal member 41 along the extension direction of the waveguide 20. If factors other than the aspect ratio of the waveguide 20 and the length of the nonreciprocal member 40 are the same, adjusting the length of the nonreciprocal member 40 according to the aspect ratio of the waveguide 20 makes the phase shift of the TM mode and the phase shift of the TE mode generated in the nonreciprocal line 12 equal.

[0080] As the aspect ratio of the waveguide 20 increases, the ratio of the distance between the second surface 22 of the waveguide 20 and the second nonreciprocal member 42 to the distance between the first surface 21 of the waveguide 20 and the first nonreciprocal member 41 may be increased. For example, if the height of the waveguide 20 is greater than the width of the waveguide 20, the distance between the second surface 22 of the waveguide 20 and the second nonreciprocal member 42 may be increased compared to the distance between the first surface 21 of the waveguide 20 and the first nonreciprocal member 41. If factors other than the aspect ratio of the waveguide 20 and the distance between the waveguide 20 and the nonreciprocal member 40 are the same, the phase shift of the TM mode and the phase shift of the TE mode generated in the nonreciprocal line 12 are equalized by adjusting the distance between the waveguide 20 and the nonreciprocal member 40 according to the aspect ratio of the waveguide 20. Furthermore, the phase shift caused by the first nonreciprocal member 41 when an electromagnetic wave in TM mode propagates a unit length in the nonreciprocal line 12 can be equal to the phase shift caused by the second nonreciprocal member 42 when an electromagnetic wave in TE mode propagates a unit length.

[0081] As the aspect ratio of the waveguide 20 increases, the ratio of the thickness of the second nonreciprocal member 42 along the normal direction of the second surface 22 of the waveguide 20 to the thickness of the first nonreciprocal member 41 along the normal direction of the first surface 21 of the waveguide 20 may be decreased. For example, if the height of the waveguide 20 is greater than the width of the waveguide 20, the thickness of the second nonreciprocal member 42 along the normal direction of the second surface 22 of the waveguide 20 may be decreased compared to the thickness of the first nonreciprocal member 41 along the normal direction of the first surface 21 of the waveguide 20. If factors other than the aspect ratio of the waveguide 20 and the thickness of the nonreciprocal member 40 are the same, adjusting the thickness of the nonreciprocal member 40 according to the aspect ratio of the waveguide 20 makes the phase shift of the TM mode and the phase shift of the TE mode generated in the nonreciprocal line 12 equal. Furthermore, the phase shift caused by the first nonreciprocal member 41 when an electromagnetic wave in TM mode propagates a unit length in the nonreciprocal line 12 can be equal to the phase shift caused by the second nonreciprocal member 42 when an electromagnetic wave in TE mode propagates a unit length.

[0082] As the aspect ratio of the waveguide 20 increases, the ratio of the magnetic field component in a direction intersecting the substrate surface 50A, i.e., along the second surface 22 of the waveguide 20, to the magnetic field component in a direction along the substrate surface 50A, i.e., along the first surface 21 of the waveguide 20, may be reduced. For example, if the height of the waveguide 20 is greater than the width of the waveguide 20, the magnetic field component in a direction along the second surface 22 of the waveguide 20 may be reduced compared to the magnetic field component in a direction along the first surface 21 of the waveguide 20. If factors other than the aspect ratio and magnetic field component of the waveguide 20 are the same, adjusting the magnetic field component according to the aspect ratio of the waveguide 20 will equalize the phase shift of the TM mode and the phase shift of the TE mode generated in the nonreciprocal line 12. Furthermore, the phase shift caused by the first nonreciprocal member 41 when an electromagnetic wave in TM mode propagates a unit length in the nonreciprocal line 12 can be equal to the phase shift caused by the second nonreciprocal member 42 when an electromagnetic wave in TE mode propagates a unit length.

[0083] (Application Example of Isolator 10) The isolator 10 may be used in combination with a configuration for transmitting electromagnetic waves. The isolator 10 may be applied to an optical switch, an optical transceiver, or a data center. The isolator 10 may be applied to, for example, an electromagnetic wave transmitter. The electromagnetic wave transmitter includes the isolator 10 and a light source. The electromagnetic wave transmitter inputs electromagnetic waves from the light source to the isolator 10 and outputs the electromagnetic waves from the isolator 10 to a receiver. The isolator 10 is configured so that the transmittance of the electromagnetic waves propagating from the light source to the receiver is greater than the transmittance of the electromagnetic waves propagating from the receiver to the light source. In this way, it becomes difficult for electromagnetic waves to be incident on the light source. As a result, the light source can be protected.

[0084] 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 may include a device that emits electromagnetic waves of various wavelengths, not limited to visible light. The light source may be formed on the substrate 50 together with the isolator 10. The light source may input electromagnetic waves in TE mode to the isolator 10.

[0085] 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 10 and the receiver, rather than between the light source and the isolator 10. The modulator may, for example, pulse-modulate the electromagnetic wave. The signal input unit accepts input of a signal from an external device, etc. 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.

[0086] 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 10.

[0087] The electromagnetic wave transmitter may be mounted on the substrate 50. The light source may be mounted so as to be connected to the first branch 81 via a modulator. The light source may be mounted so as to be connected to the first branch 81 without a modulator. The receiver may be mounted so as to be connected to the second branch 82 without a modulator. The receiver may be mounted so as to be connected to the second branch 82 via a modulator. In this case, the modulator may be mounted so as to be connected to the second branch 82.

[0088] 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 or divided into one.

[0089] In this disclosure, descriptions such as "first" and "second" are identifiers for distinguishing the configuration. In this disclosure, the configurations distinguished by descriptions such as "first" and "second" can have their numbers exchanged. For example, the first surface 21 can exchange the identifiers "first" and "second" with the second surface 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. The descriptions of identifiers such as "first" and "second" in this disclosure should not be used solely to interpret the order of the configurations or to justify the existence of an identifier with a smaller number.

[0090] In this disclosure, the X-axis, Y-axis, and Z-axis are provided for convenience of explanation and may be interchanged. The configurations according to this disclosure have been described using an orthogonal coordinate system formed by the X-axis, Y-axis, and Z-axis. The positional relationship between the components according to this disclosure is not limited to an orthogonal relationship.

[0091] In one embodiment, (1) an isolator includes a substrate having a substrate surface, and a reciprocal line and a nonreciprocal line extending on the substrate surface and propagating at least one of a TE mode electromagnetic wave and a TM mode electromagnetic wave along the extending direction, wherein the nonreciprocal line includes a waveguide having a first surface extending along the substrate surface and a second surface extending along a plane intersecting the substrate surface, a first nonreciprocal member positioned along the first surface of the waveguide, and a second nonreciprocal member positioned along the second surface of the waveguide.

[0092] (2) In the isolator described in (1) above, in a cross section normal to the extension direction of the waveguide, an aspect ratio, which is the ratio of the length of the second surface of the waveguide to the length of the first surface of the waveguide, may be equal to 1.

[0093] (3) In the isolator described in (1) above, in a cross section normal to the extension direction of the waveguide, an aspect ratio, which is the ratio of the length of the second surface of the waveguide to the length of the first surface of the waveguide, may be a value different from 1.

[0094] (4) In the isolator described in (3) above, the larger the aspect ratio of the waveguide, the larger the ratio of the distance between the second surface of the waveguide and the second non-reciprocal member to the distance between the first surface of the waveguide and the first non-reciprocal member may be.

[0095] (5) In the isolator described in (3) or (4) above, the larger the aspect ratio of the waveguide, the smaller the ratio of the thickness of the second nonreciprocal member along the normal direction of the second surface of the waveguide to the thickness of the first nonreciprocal member along the normal direction of the first surface of the waveguide may be.

[0096] (6) In the isolator described in any one of (1) to (5) above, the phase shift caused by the first nonreciprocal member when an electromagnetic wave in TM mode propagates through a unit length may be equal to the phase shift caused by the second nonreciprocal member when an electromagnetic wave in TE mode propagates through a unit length.

[0097] (7) In the isolator described in any one of (1) to (5) above, the larger the aspect ratio of the waveguide, the smaller the ratio of the length of the second nonreciprocal member along the extension direction of the waveguide to the length of the first nonreciprocal member along the extension direction of the waveguide may be.

[0098] (8) The isolator according to any one of (1) to (5) above may further include a magnetic field application unit that applies a magnetic field to the nonreciprocal line. The magnetic field application unit may apply a magnetic field having a component in a direction perpendicular to the substrate surface when a TE mode electromagnetic wave is propagated through the nonreciprocal line, and may apply a magnetic field having a component in a direction perpendicular to the propagation direction of the electromagnetic wave in the waveguide and along the substrate surface when a TM mode electromagnetic wave is propagated through the nonreciprocal line.

[0099] (9) In the isolator described in (8) above, in a cross section normal to the extension direction of the waveguide, the larger the aspect ratio, which is the ratio of the length of the second surface of the waveguide to the length of the first surface of the waveguide, the smaller the ratio of the magnetic field component perpendicular to the propagation direction of the electromagnetic wave in the waveguide and perpendicular to the substrate surface to the magnetic field component perpendicular to the substrate surface.

[0100] (10) In the isolator described in (8) or (9) above, the phase shift caused by the first nonreciprocal member when an electromagnetic wave in TM mode propagates through a unit length may be equal to the phase shift caused by the second nonreciprocal member when an electromagnetic wave in TE mode propagates through a unit length.

[0101] (11) In the isolator described in (8) or (9) above, the larger the aspect ratio of the waveguide, the smaller the ratio of the length of the second nonreciprocal member along the extension direction of the waveguide to the length of the first nonreciprocal member along the extension direction of the waveguide may be.

[0102] (12) In the isolator according to any one of (1) to (11) above, the first nonreciprocal member and the second nonreciprocal member may contain YIG (yttrium iron garnet).

[0103] 10 Isolator 11 Reciprocal line 12 Nonreciprocal line 20 Waveguide (21: first surface, 22: second surface) 30 Groove (31, 32: side surface, 33, 34: bottom surface) 40 Nonreciprocal member (41: first nonreciprocal member, 42: second nonreciprocal member) 50 Substrate (50A: substrate surface, 52: box layer, 54, 56, 58: insulating layer) 70 Magnetic field application section 81 First branch section 82 Second branch section

Claims

1. An isolator comprising: a substrate having a substrate surface; and a reciprocal line and a nonreciprocal line extending on the substrate surface and propagating at least one of a TE mode electromagnetic wave or a TM mode electromagnetic wave along the extension direction, wherein the nonreciprocal line comprises: a waveguide having a first surface extending along the substrate surface and a second surface extending along a plane intersecting the substrate surface; a first nonreciprocal member located along the first surface of the waveguide; and a second nonreciprocal member located along the second surface of the waveguide.

2. The isolator according to claim 1, wherein in a cross section normal to the extension direction of said waveguide, an aspect ratio, which is the ratio of the length of the second surface of said waveguide to the length of the first surface of said waveguide, is equal to 1.

3. An isolator as described in claim 1, wherein in a cross section normal to the extension direction of said waveguide, an aspect ratio, which is the ratio of the length of the second surface of said waveguide to the length of the first surface of said waveguide, is a value other than 1.

4. The isolator of claim 3, wherein the greater the aspect ratio of the waveguide, the greater the ratio of the distance between the second surface of the waveguide and the second nonreciprocal member to the distance between the first surface of the waveguide and the first nonreciprocal member.

5. An isolator as described in claim 3, wherein the greater the aspect ratio of the waveguide, the smaller the ratio of the thickness of the second nonreciprocal member along the normal direction of the second surface of the waveguide to the thickness of the first nonreciprocal member along the normal direction of the first surface of the waveguide.

6. An isolator described in any one of claims 1 to 5, wherein the phase shift caused by the first nonreciprocal member when an electromagnetic wave in TM mode propagates through a unit length is equal to the phase shift caused by the second nonreciprocal member when an electromagnetic wave in TE mode propagates through a unit length.

7. An isolator as described in any one of claims 1 to 5, wherein the larger the aspect ratio of the waveguide, the smaller the ratio of the length of the second nonreciprocal member along the extension direction of the waveguide to the length of the first nonreciprocal member along the extension direction of the waveguide.

8. An isolator as claimed in any one of claims 1 to 5, further comprising a magnetic field application unit that applies a magnetic field to the nonreciprocal line, wherein the magnetic field application unit applies a magnetic field having a component in a direction intersecting the substrate surface when electromagnetic waves in TE mode are propagated through the nonreciprocal line, and applies a magnetic field having a component that intersects the propagation direction of the electromagnetic waves in the waveguide and is oriented along the substrate surface when electromagnetic waves in TM mode are propagated through the nonreciprocal line.

9. An isolator as described in claim 8, wherein, in a cross section normal to the extension direction of the waveguide, the larger the aspect ratio, which is the ratio of the length of the second side of the waveguide to the length of the first side of the waveguide, the smaller the ratio of the magnetic field component that intersects the propagation direction of the electromagnetic wave in the waveguide and that intersects the substrate surface to the magnetic field component that is in a direction along the substrate surface.

10. An isolator as described in claim 8, wherein a phase shift caused by the first nonreciprocal member when an electromagnetic wave in TM mode propagates through a unit length is equal to a phase shift caused by the second nonreciprocal member when an electromagnetic wave in TE mode propagates through a unit length.

11. The isolator of claim 8, wherein the greater the aspect ratio of the waveguide, the smaller the ratio of the length of the second nonreciprocal member along the extension direction of the waveguide to the length of the first nonreciprocal member along the extension direction of the waveguide.

12. The isolator of any one of claims 1 to 5, wherein the first nonreciprocal member and the second nonreciprocal member include YIG (yttrium iron garnet).