Nonreciprocal line, isolator, and method for manufacturing nonreciprocal line

Abstract

This non-reciprocal line is provided with a substrate having a substrate surface, a waveguide extending along the substrate surface, and a nonreciprocal member positioned so as to cover a first surface among a plurality of surfaces along the extension direction of the waveguide. The nonreciprocal line has an oxide film layer in a region facing at least the nonreciprocal member of the waveguide.

Description

Nonreciprocal line, isolator, and method for manufacturing nonreciprocal line

[0001] The present disclosure relates to a nonreciprocal line, an isolator, and a method for manufacturing the nonreciprocal line.

[0002] A technique is known for constructing a nonreciprocal line of an isolator using Ce:YIG, a material having a large magneto-optical effect and a small optical absorption coefficient (see, for example, Patent Document 1).

[0003] International Publication No. 2007 / 083419

[0004] A nonreciprocal line according to an embodiment of the present disclosure includes a substrate having a substrate surface, a waveguide, and a nonreciprocal member. The waveguide extends along the substrate surface. The nonreciprocal member is positioned to cover a first surface of a plurality of surfaces along the extension direction of the waveguide. The nonreciprocal line has an oxide film layer in at least a region of the waveguide facing the nonreciprocal member.

[0005] An isolator according to an embodiment of the present disclosure includes the nonreciprocal line.

[0006] A method for manufacturing a nonreciprocal line according to an embodiment of the present disclosure includes forming a waveguide extending along a substrate surface of a substrate, and forming a nonreciprocal member positioned to cover a first surface of a plurality of surfaces along an extension direction of the waveguide. The method for manufacturing the nonreciprocal line includes, between forming the waveguide and forming the nonreciprocal member, forming an oxide film layer on at least a region of the waveguide that will face the nonreciprocal member.

[0007] FIG. 2 is a cross-sectional view showing the configuration of a nonreciprocal line according to an embodiment; FIG. 3 is an electron microscope image showing an enlarged view of portion A of FIG. 1; FIG. 4 is a flowchart showing a method for manufacturing a nonreciprocal line; FIG. 5 is a diagram showing a schematic cross-section of a nonreciprocal line during the manufacturing process; FIG. 6 is a diagram showing a schematic cross-section of a nonreciprocal line during the manufacturing process; FIG. 7 is a diagram showing a schematic cross-section of a nonreciprocal line during the manufacturing process; FIG. 8 is a diagram showing a schematic cross-section of a nonreciprocal line during the manufacturing process; FIG. 9 is a diagram showing a schematic cross-section of a nonreciprocal line during the manufacturing process; FIG. 10 is a diagram showing a schematic configuration of an isolator according to an embodiment;

[0008] When manufacturing nonreciprocal lines, Ce:YIG (cerium-substituted yttrium iron garnet: CeY ２ Fe ５ O １２ Heating to crystallize the YIG waveguide into garnet can cause the YIG component to thermally diffuse and form an alloy with the silicon (Si) waveguide component. This alloy (silicide) has the problem of absorbing electromagnetic waves and significantly degrading light propagation efficiency. Therefore, this disclosure proposes forcibly oxidizing the surface of the Si waveguide to form a silicide barrier layer to prevent silicidation.

[0009] In this disclosure, "light" as used in a "light source" and the like is used in a broad sense to include electromagnetic waves in the ultraviolet, visible, and infrared regions. "Light" includes electromagnetic waves with wavelengths from 1 nm to 1 mm. In the following description, "light" will be referred to as electromagnetic waves where appropriate.

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The drawings used in the following description are schematic. The dimensional ratios and the like in the drawings do not necessarily correspond to the actual ones.

[0011] 1 , a nonreciprocal line 1 according to one embodiment includes a substrate 10, a box layer 20, a waveguide 30, an insulating layer 21, an oxide film layer 40, a nonreciprocal member 50, and an insulating layer 22. The box layer 20 is located on a substrate surface 10 a of the substrate 10.

[0012] The waveguide 30 is located on the box layer 20. The waveguide 30 extends in the depth direction of the page, i.e., along the Z-axis direction. Along the extension direction, the waveguide 30 has a surface (bottom surface) closer to the substrate 10, a surface (top surface) farther from the substrate 10, and two surfaces (side surfaces) sandwiched between the surface closer to the substrate 10 and the surface farther from the substrate 10. In FIG. 1 , the direction perpendicular to the substrate surface 10a is the Y-axis direction, and the direction parallel to the substrate surface 10a and perpendicular to the Z-axis direction is the X-axis direction.

[0013] In this embodiment, the insulating layer 21 is located on the box layer 20 in a portion other than the waveguide 30. In this embodiment, the insulating layer 21 is formed so that the upper surface of the insulating layer 21 is located closer to the substrate surface 10a than the upper surface of the waveguide 30. The insulating layer 21 may be formed so that the upper surface of the insulating layer 21 is flush with the upper surface of the waveguide 30.

[0014] An oxide layer 40 is formed on the top of the waveguide 30. The oxide layer 40 is formed on at least the region of the waveguide 30 facing the nonreciprocal member 50. Therefore, the oxide layer 40 is formed on the top surface of the waveguide 30 and on the regions of the side surfaces adjacent to the top surface that face the nonreciprocal member 50. The top surface of the waveguide 30 is the first surface, and the two side surfaces are the second surfaces. The oxide layer 40 on the top surface of the waveguide 30 may be configured to be thicker than the oxide layer 40 on the side surfaces.

[0015] The nonreciprocal member 50 is formed on the insulating layer 21 and the oxide film layer 40. When viewed in a plan view toward the substrate surface 10a, the nonreciprocal member 50 is positioned so as to overlap at least a portion of the waveguide 30. The nonreciprocal member 50 does not directly contact the waveguide 30.

[0016] 2 is an electron microscope image of a cross section of the nonreciprocal line 1 corresponding to part A in FIG. 1. The top of the waveguide 30 is covered with a nonreciprocal member 50. Between the waveguide 30 and the nonreciprocal member 50, there is a SiO ２ The oxide film layer 40 is formed on the lower left side of the insulating layer 21.

[0017] A further insulating layer 22 is located on top of the non-reciprocal member 50 .

[0018] The substrate 10 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 10 is made of silicon (Si), but is not limited to this and may be made of various other materials.

[0019] The waveguide 30 is surrounded by the box layer 20 and the insulating layers 21 and 22. The waveguide 30 is also referred to as a core. The box layer 20 and the insulating layers 21 and 22 are also referred to as clads. The core and clad may be configured to include a dielectric. The waveguide 30 is also referred to as a dielectric line. The waveguide 30 as a core is located along the substrate surface 10a and propagates electromagnetic waves along the substrate surface 10a. In other words, the electromagnetic waves propagate through the waveguide 30 as a core in the direction in which the waveguide 30 extends.

[0020] The materials of the core and the cladding are determined so that the relative dielectric constant of the core is greater than that of the cladding. In other words, the materials of the core and the cladding are determined so that the refractive index of the cladding 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 cladding. As a result, the loss of the electromagnetic wave propagating through the core can be reduced.

[0021] In this embodiment, the material of the waveguide 30 as the core is silicon (Si). The material of the box layer 20 and the insulating layers 21 and 22 as the cladding is silica glass or silicon oxide film (SiO ｘ ), 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 30 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.

[0022] In this embodiment, the oxide layer 40 is silicon dioxide (SiO ２ ) layer. ２ The oxide film layer 40 is formed by, for example, oxygen (O ２ The oxide layer 40 may be formed by other methods such as thermal oxidation.

[0023] The oxide film layer 40 reduces or prevents the YIG component from diffusing into the Si waveguide 30 due to thermal diffusion and alloying with Si during the heating process for garnet crystallizing the YIG that constitutes the nonreciprocal member 50. For this purpose, the thickness of the region of the oxide film layer 40 facing the nonreciprocal member 50 is preferably 5 nm or more, which is thicker than the natural oxide film that generally forms on the surface of a Si crystal. Furthermore, if the oxide film layer 40 is too thick, the distance between the waveguide 30 and the nonreciprocal member 50 increases, thereby reducing the effect of nonreciprocity. Therefore, the thickness of the oxide film layer 40 is preferably 20 nm or less.

[0024] The nonreciprocal member 50 is formed by being deposited on the insulating layer 21 and the waveguide 30 with the oxide film layer 40 formed on the waveguide 30 .

[0025] The nonreciprocal member 50 may be composed of a nonreciprocal material, such as magnetic garnet, ferrite, iron, or cobalt. In one embodiment, YIG (yttrium iron garnet) is used as the material of the nonreciprocal member 50. In this embodiment, Ce:YIG is used as the material of the nonreciprocal member 50. Ce:YIG is a material in which part of the yttrium is substituted with Ce. A transparent magnetic material such as Bi:YIG may also be used as the material of the nonreciprocal member 50. Bi:YIG is a material in which part of the yttrium is substituted with Bi. An element that substitutes part of the yttrium is also referred to as a substitution element. The substitution element is not limited to Ce or Bi. In addition to Ce or Bi, a rare earth element may also be used as the substitution element. By substituting part of the yttrium with a substitution element, the strength of the nonreciprocity exhibited by the nonreciprocal member 50 can be adjusted. Also, non-reciprocity can become strong.

[0026] YIG in which yttrium is not substituted may be used as the material of the nonreciprocal member 50. Hereinafter, YIG in which part of the yttrium is substituted with Ce, Bi, or the like, and YIG in which yttrium is not substituted will be collectively referred to simply as YIG.

[0027] YIG is a film in which yttrium, iron, and oxygen form crystals with a garnet structure, and can be formed by, for example, sputtering a target containing yttrium, iron, and oxygen in an atmosphere of a mixed gas of argon and oxygen.

[0028] <Relationship between Characteristics of Nonreciprocal Member and Nonreciprocity> When a magnetic field is applied in the X-axis direction, the waveguide 30 extending along the nonreciprocal member 50 can exhibit nonreciprocity for electromagnetic waves propagating through the waveguide 30. Nonreciprocity is a phenomenon in which, when electromagnetic waves propagate in opposite directions through the waveguide 30, the phase shift of the electromagnetic waves differs in each propagation direction. The strength of the nonreciprocity corresponds to the magnitude of the difference in the phase shift of the electromagnetic waves in each propagation direction when the electromagnetic waves propagate in opposite directions over a unit length.

[0029] The nonreciprocal member 50 causes nonreciprocity in the electromagnetic wave propagating through the waveguide 30 when the energy of the electric field of the electromagnetic wave propagating through the waveguide 30 is effectively distributed within the nonreciprocal member 50. The range in which the energy of the TM mode electromagnetic wave is effectively distributed is, for example, when the energy of the electric field component is 1 / e of the maximum energy. ２ It may be defined as a range that is equal to or greater than the range.

[0030] In the nonreciprocal line 1 illustrated in FIG. 1 , the nonreciprocal member 50 is located in the normal direction of the substrate surface 10 a as viewed from the waveguide 30. Assume that a TM-mode electromagnetic wave propagates through the waveguide 30. The TM-mode electromagnetic wave is an electromagnetic wave whose electric field amplitude direction coincides with the normal direction of the substrate surface 10 a, i.e., the Y-axis direction, when propagating through the waveguide 30 in the Z-axis direction. The electric field energy of the TM-mode electromagnetic wave is distributed in the electric field amplitude direction and decreases outside the waveguide 30 as it moves away from the top surface of the waveguide 30 in the Y-axis direction. As a result, the electric field energy of the TM-mode electromagnetic wave is effectively distributed within the nonreciprocal member 50, which is located in the Y-axis direction as viewed from the waveguide 30. Therefore, the nonreciprocal member 50 imparts nonreciprocity to the TM-mode electromagnetic wave propagating through the waveguide 30.

[0031] The nonreciprocity exhibited by the nonreciprocal component 50 is strengthened by the YIG contained in the nonreciprocal component 50. In other words, the more garnet-structure crystals the nonreciprocal component 50 contains, the stronger the nonreciprocity. The nonreciprocal component 50 is formed by depositing a nonreciprocal material on the waveguide 30 and heating the deposited nonreciprocal material to approximately 800°C to crystallize it into garnet. The oxide film layer 40 reduces or prevents the transition metal, including the ferromagnetic element contained in the nonreciprocal component 50, from thermally diffusing into the waveguide 30 and bonding with Si to form an alloy during this heating process. This alloy (silicide) absorbs electromagnetic waves. Therefore, the generation of this alloy reduces the electromagnetic wave propagation efficiency of the waveguide 30. Therefore, the oxide film layer 40 has the effect of reducing or preventing the deterioration of the electromagnetic wave propagation efficiency of the waveguide 30.

[0032] To avoid alloying of the waveguide 30, a method has been proposed in which a Ce:YIG film is separately prepared as the nonreciprocal member 50 and attached to the substrate 10 on which the waveguide 30 is formed, thereby eliminating the heating step. However, such a method is difficult to achieve in a single semiconductor process. The method of the present disclosure has the advantage that the nonreciprocal line 1 can be manufactured by a semiconductor process.

[0033] In addition, aluminum nitride (AlN) and silicon nitride (Si) are usually used as silicide barriers in semiconductor processes. ３ N ４ However, when the inventors of the present application actually conducted an investigation, they found that SiO ２ Films made of materials other than the film could not provide a sufficient effect of preventing the diffusion and alloying of the YIG component into the waveguide 30 .

[0034] As described above, according to this embodiment, the nonreciprocal line 1 has the oxide film layer 40 in at least the region of the waveguide 30 facing the nonreciprocal member 50, which reduces or prevents the YIG of the nonreciprocal member 50 from diffusing into the waveguide and forming an alloy. This reduces or prevents a decrease in the propagation efficiency of the electromagnetic wave in the nonreciprocal line 1. The effect of this embodiment is also effective when the nonreciprocal member 50 contains a ferromagnetic element other than iron. In addition to iron, the ferromagnetic element includes nickel and cobalt.

[0035] In the above embodiment, the non-reciprocal member is Ce:YIG. However, a nano-granular material can also be used as the non-reciprocal member. The nano-granular material is a material in which nano-sized magnetic particles are dispersed in an electrical insulator. The electrical insulator can be, for example, yttrium fluoride (YF ３ ) or sodium fluoride (NaF). The magnetic particles can be, for example, iron, nickel or cobalt.

[0036] In the above embodiment, the nonreciprocal line 1 is configured to propagate electromagnetic waves in TM mode. However, the nonreciprocal line 1 may be configured to propagate electromagnetic waves in TE mode. In this case, the nonreciprocal member 50 is not disposed on the top surface side of the waveguide 30 but on the side surface, i.e., the surface parallel to the YZ plane. The oxide film layer 40 is also formed in a region including the side surface of the waveguide 30 facing the nonreciprocal member 50. In this case, a magnetic field is applied in the Y-axis direction to exhibit nonreciprocity.

[0037] <Manufacturing Process of Nonreciprocal Line> Hereinafter, an example of a manufacturing method of the nonreciprocal line 1 will be described with reference to FIG. 3 and FIGS. 4A to 4F.

[0038] First, an SOI (Silicon On Insulator) substrate is prepared. The SOI substrate has a silicon oxide film (SiO ) between a silicon (Si) substrate and a surface Si layer. ２ A resist pattern is drawn on the SOI substrate, and the Si substrate 10 and the SiO ２ A Si waveguide 30 is formed on the box layer 20 (FIG. 4A, step S101).

[0039] Silicon oxide (SiO ) is deposited on the substrate 10 including the waveguide 30 by a plasma CVD (Chemical Vapor Deposition) method or the like. ｘ ) is deposited. The insulating layer 21 is deposited up to the top of the waveguide 30 ( FIG. 4B , step S102). Steps S101 and S102 form a line on the substrate 10, in which the periphery of the core of the waveguide 30 is covered with a clad of the box layer 20 and the insulating layer 21.

[0040] The area other than the area where the nonreciprocal line 1 is to be formed is masked. The area where the nonreciprocal line 1 is to be formed is masked by dry etching using SiO ｘ The upper part of the insulating layer 21 is removed and the upper part of the waveguide 30 is exposed (FIG. 4C, step S103). An organic resist is used as a mask, and CF4 is used as an etching gas. ４ and CHF ３ Fluorocarbon gases such as the above can be used.

[0041] The surface of the waveguide 30 is oxidized to form SiO ２ An oxide film layer 40 (silicide barrier layer) is formed (FIG. 4D, step S104). ２ These include plasma irradiation and immersion in a chemical with high oxidizing power. The thickness of the oxide film layer 40 that faces the nonreciprocal member 50 is adjusted to be 5 nm to 20 nm. In this embodiment, which propagates electromagnetic waves in TM mode, the oxide film layer 40 on the top surface of the waveguide 30 is made thicker than the oxide film layer 40 on the side surface. For this reason, for example, O ２ When the oxide film layer 40 is formed by plasma, O ２ The plasma is directed from above toward the upper surface of the waveguide 30 .

[0042] The nonreciprocal member 50 is deposited on the waveguide 30 and the insulating layer 21 (FIG. 4E, step S105). The nonreciprocal member 50 is deposited by, for example, sputtering a target containing yttrium, iron, and oxygen in a mixed gas atmosphere of argon and oxygen.

[0043] The non-reciprocal member 50 is heated to about 800° C. to crystallize it into garnet (step S106).

[0044] An insulating layer 22 of silicon oxide is formed on the non-reciprocal member 50 (FIG. 4F, step S107). The insulating layer 22 can be formed by any available method including sputtering and plasma CVD.

[0045] As described above, the nonreciprocal line of the present disclosure can be manufactured using a semiconductor process.

[0046] <Application to Isolator> The nonreciprocal line 1 can be applied to an isolator. An example in which the nonreciprocal line 1 is applied to an isolator will be described below.

[0047] An isolator 60 according to an embodiment of the present disclosure shown in FIG. 5 is configured on a substrate 61. The isolator 60 provides isolation for electromagnetic waves in an operating band. The "isolation function" refers to the function of transmitting electromagnetic waves traveling in the forward direction and reducing or blocking electromagnetic waves traveling in the reverse direction. The isolator 60 transmits electromagnetic waves incident on a waveguide 63 on the substrate 61 from a first end 62 through a waveguide 64 on the substrate 61 to a second end 65. The isolator 60 reduces the intensity of electromagnetic waves incident on the waveguide 64 from the second end 65 and transmits them from the waveguide 63 to the first end 62. Alternatively, the isolator 60 blocks electromagnetic waves incident on the waveguide 64 from the second end 65, preventing them from transmitting to the first end 62.

[0048] In the following description, the Y-axis direction is a direction perpendicular to the substrate surface 61a of the substrate 61 and is a direction from the substrate surface 61a toward the side where the isolator 60 is formed. The Z-axis direction is a direction along the substrate surface 61a and is a direction from the first end 62 toward the second end 65. The X-axis direction is a direction perpendicular to the Y-axis direction and the Z-axis direction.

[0049] The isolator 60 includes a Mach-Zehnder interferometer (MZI) circuit, and functions as an isolator due to the interaction between a phase difference (nonreciprocal phase difference) generated by the nonreciprocal phase shift effect of electromagnetic waves propagating through two waveguides and a phase difference (reciprocal phase difference) that is independent of the propagation direction.

[0050] The isolator 60 includes a splitter 71, a coupler 72, and a first waveguide 73 and a second waveguide 74 that connect the splitter 71 and the coupler 72, respectively. Nonreciprocal members 75 and 76 are disposed adjacent to portions of the first waveguide 73 and the second waveguide 74, respectively. The portion of the first waveguide 73 adjacent to the nonreciprocal member 75 and the portion of the second waveguide 74 adjacent to the nonreciprocal member 76 are nonreciprocal lines 77 and 78, respectively. The nonreciprocal lines 77 and 78 have the same configuration as the nonreciprocal line 1 shown in FIG. 1. As in FIG. 1, the nonreciprocal lines 77 and 78 extend in the Z-axis direction.

[0051] The splitter 71 splits the electromagnetic wave incident from the waveguide 63 into a first waveguide 73 and a second waveguide 74. A 1x2 multimode interference (MMI) optical coupler can be used as the splitter 71. The 1x2 multimode interference optical coupler can distribute the incident electromagnetic wave equally to the two waveguides. The splitter 71 is not limited to the multimode interference optical coupler, and a Y-branch circuit, a directional coupler, or the like can also be used.

[0052] The coupler 72 couples the electromagnetic waves propagating through the first waveguide 73 and the second waveguide 74 and outputs the combined waves to the waveguide 64. A 2×1 type multimode interference optical coupler can be used as the coupler 72. As with the splitter 71, the coupler 72 is not limited to a multimode interference optical coupler, and a Y-branch circuit or a directional coupler can also be used.

[0053] The first waveguide 73 and the second waveguide 74 propagate electromagnetic waves in TM mode. The first waveguide 73 and the second waveguide 74 generate a phase difference between the electromagnetic waves propagating through the two waveguides by adjusting the difference in optical path length. This phase difference is a phase difference (reciprocal phase difference) that does not depend on the propagation direction of the electromagnetic waves.

[0054] On the other hand, the nonreciprocal line 77 included in the first waveguide 73 and the nonreciprocal line 78 included in the second waveguide 74 have nonreciprocity. The propagation direction of the electromagnetic waves in the first waveguide 73 and the second waveguide 74, which is the propagation direction of the electromagnetic waves from the splitter 71 to the coupler 72, is defined as a first direction. Similarly, the propagation direction of the electromagnetic waves from the coupler 72 to the splitter 71 is defined as a second direction. In the nonreciprocal lines 77 and 78, a nonreciprocal phase shift effect occurs due to the magneto-optical effect, in which the electromagnetic waves propagating in the first direction and the electromagnetic waves propagating in the second direction have different amounts of phase change. In this embodiment, the phase shift amounts due to the nonreciprocal line 77 and the nonreciprocal line 78 are added together to form a phase difference (nonreciprocal phase difference) due to the nonreciprocal phase shift effect between the first waveguide 73 and the second waveguide 74.

[0055] 5, in this embodiment, the first waveguide 73 and the second waveguide 74 extend from the splitter 71 in the +Z-axis direction, bend in a U-shape to extend in the −Z-axis direction, and then bend again in a U-shape to extend in the +Z-axis direction toward the coupler 72. In the first waveguide 73, the nonreciprocal line 77 is provided at a position where the electromagnetic wave incident from the splitter 71 and propagating in the first direction is directed in the −Z-axis direction. In the second waveguide 74, the nonreciprocal line 78 is provided at a position where the electromagnetic wave incident from the splitter 71 and propagating in the first direction is directed in the +Z-axis direction. This arrangement makes it possible to apply a uniform magnetic field in the X-axis direction to produce a nonreciprocal phase shift effect.

[0056] The isolator 60 is adjusted so that the phases of the electromagnetic wave that is split by the splitter 71, propagates through the first waveguide 73 in a first direction, and enters the coupler 72, and the electromagnetic wave that propagates through the second waveguide 74 in the first direction and enters the coupler 72, are in phase. The isolator 60 is also adjusted so that the phases of the electromagnetic wave that is split by the coupler 72, propagates through the first waveguide 73 in a second direction, and enters the splitter 71, and the electromagnetic wave that propagates through the second waveguide 74 in the second direction and enters the splitter 71, are opposite to each other.

[0057] As an example, when an electromagnetic wave propagates in the first direction through the first waveguide 73, a phase difference (reciprocal phase difference) that is independent of the propagation direction of +90° (+π / 2) occurs with respect to the second waveguide 74. Also, when the electromagnetic wave propagates in the first direction through the first waveguide 73, a phase difference (non-reciprocal phase difference) of −90° (−π / 2) occurs with respect to the second waveguide 74 due to a non-reciprocal phase shift effect. In this case, the electromagnetic wave propagating in the first direction through the first waveguide 73 from the splitter 71 and the electromagnetic wave propagating in the second waveguide 74 become in phase with each other in the coupler 72, pass through the coupler 72, pass through the waveguide 64, and exit from the second end 65.

[0058] On the other hand, when the electromagnetic wave propagates through the first waveguide 73 in the second direction, a phase difference (non-reciprocal phase difference) of +90° (+π / 2) occurs with respect to the second waveguide 74 due to the non-reciprocal phase shift effect. Therefore, a phase difference of +180° (+π), which is the sum of the reciprocal phase difference of +90° and the non-reciprocal phase difference of +90°, occurs between the electromagnetic wave propagated through the first waveguide 73 in the second direction from the coupler 72 and the electromagnetic wave propagated through the second waveguide 74. Therefore, the electromagnetic wave branched by the coupler 72 and propagated through the first waveguide 73 and the electromagnetic wave propagated through the second waveguide 74 enter the splitter 71 as electromagnetic waves of opposite phases and cancel each other out. In this way, the electromagnetic waves incident from the second end 65 are reduced or blocked by the isolator 60, and either exit from the first end 62 with a lower intensity than the incident electromagnetic waves, or do not exit from the first end 62.

[0059] Because the isolator 60 operates as described above, it can be combined with, for example, a light source disposed on the first end 62 side. Electromagnetic waves input from the light source to the first end 62 are output from the second end 65. Electromagnetic waves such as return light that enter the isolator 60 from the second end 65 are unlikely to pass through to the first end 62. As a result, the light source is protected.

[0060] 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 61 together with the isolator 60.

[0061] 1 can be applied to the isolator 60. The nonreciprocal line 1 has better electromagnetic wave propagation efficiency than a nonreciprocal line that does not have the oxide film layer 40, and therefore can achieve high transmittance when an electromagnetic wave propagates in the forward direction of the isolator 60.

[0062] 5 is merely one example of an isolator to which the nonreciprocal line 1 can be applied. Using the nonreciprocal line 1, isolators of various configurations can be created.

[0063] 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 could 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.

[0064] In the present disclosure, descriptions such as "first" and "second" are identifiers for distinguishing the configuration. In the present disclosure, the configurations distinguished by descriptions such as "first" and "second" can have their numbers interchanged. For example, the first waveguide 73 can have its identifiers "first" and "second" interchanged with the second waveguide 74. The identifiers are interchanged simultaneously. The configurations remain distinguished even after the identifiers are interchanged. Identifiers may be deleted. A configuration from which an identifier has been deleted is distinguished by a symbol. The identifiers "first" and "second" in the present 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.

[0065] 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.

[0066] In one embodiment, (1) a nonreciprocal line includes a substrate having a substrate surface, a waveguide extending along the substrate surface, and a nonreciprocal member positioned to cover a first surface of a plurality of surfaces along the extension direction of the waveguide, and has an oxide film layer in at least a region of the waveguide facing the nonreciprocal member.

[0067] (2) In the nonreciprocal line of (1) above, the thickness of the oxide film layer in the region facing the nonreciprocal member may be 5 nm or more and 20 nm or less.

[0068] (3) In the nonreciprocal line of (1) or (2), the waveguide is made of Si, and the oxide film layer is made of SiO ２ It may be a layer.

[0069] (4) Any of the nonreciprocal lines described above in (1) to (3) may have the oxide film layer on the first surface of the waveguide and on a second surface adjacent to the first surface, and the oxide film layer on the first surface may be thicker than the oxide film layer on the second surface.

[0070] (5) In the nonreciprocal line of any one of (1) to (4) above, the nonreciprocal member may include a ferromagnetic element.

[0071] (6) In the nonreciprocal line of any one of (1) to (5) above, the nonreciprocal member may be Ce:YIG or a nanogranular material.

[0072] In one embodiment, (7) the isolator comprises any of the non-reciprocal lines described above in (1) to (6).

[0073] In one embodiment, (8) a method for manufacturing a nonreciprocal line includes forming a waveguide extending along a substrate surface of a substrate, and forming a nonreciprocal member positioned so as to cover a first surface among a plurality of surfaces along the extension direction of the waveguide, and includes forming an oxide film layer in at least a region of the waveguide that will face the nonreciprocal member between forming the waveguide and forming the nonreciprocal member.

[0074] REFERENCE SIGNS LIST 1 Nonreciprocal line 10 Substrate 20 Box layer 21 Insulating layer 22 Insulating layer 30 Waveguide 40 Oxide film layer 50 Nonreciprocal member 60 Isolator 61 Substrate 61a Substrate surface 62 First end 63 Waveguide 64 Waveguide 65 Second end 71 Splitter 72 Coupler 73 First waveguide 74 Second waveguide 75, 76 Nonreciprocal member 77, 78 Nonreciprocal line

Claims

1. A nonreciprocal line comprising: a substrate having a substrate surface; a waveguide extending along the substrate surface; and a nonreciprocal member positioned so as to cover a first surface of a plurality of surfaces along the extension direction of the waveguide, the nonreciprocal member having an oxide film layer in at least the region of the waveguide facing the nonreciprocal member.

2. The nonreciprocal line according to claim 1, wherein the thickness of the region of said oxide film layer facing said nonreciprocal member is 5 nm or more and 20 nm or less.

3. The waveguide is Si and the oxide layer is SiO ２ 3. The nonreciprocal line according to claim 1, wherein the nonreciprocal line is a layer.

4. A nonreciprocal line according to any one of claims 1 to 3, wherein the nonreciprocal line has an oxide layer on the first surface of the waveguide and on a second surface adjacent to the first surface, and the oxide layer on the first surface is thicker than the oxide layer on the second surface.

5. A nonreciprocal line according to any one of claims 1 to 4, wherein the nonreciprocal member includes a ferromagnetic element.

6. A nonreciprocal transmission line according to any one of claims 1 to 5, wherein the nonreciprocal member is Ce:YIG or a nanogranular material.

7. An isolator comprising a nonreciprocal line according to any one of claims 1 to 6.

8. A method for manufacturing a nonreciprocal line, comprising: forming a waveguide extending along a substrate surface of a substrate; and forming a nonreciprocal member positioned so as to cover a first surface of a plurality of surfaces along the extension direction of the waveguide; and, between forming the waveguide and forming the nonreciprocal member, forming an oxide film layer in at least the region of the waveguide that will face the nonreciprocal member.

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