Isolator, optical switch, optical transceiver, data center, and method for manufacturing isolator

Abstract

The isolator includes a substrate, a waveguide, an insulating layer, and a non-reciprocal member. The insulating layer has a recess. The recess is located at a position overlapping at least a portion of the waveguide. The non-reciprocal member is located in the recess. The waveguides include a first waveguide and a second waveguide. The recess includes a first recess and a second recess. The non-reciprocal members include a first non-reciprocal member located in the first recess and a second non-reciprocal member located in the second recess. A propagation direction of an electromagnetic wave in a portion of the first waveguide that overlaps the first non-reciprocal member is different from a propagation direction of an electromagnetic wave in a portion of the second waveguide that overlaps the second non-reciprocal member.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the priority of Japanese Patent Application No. 2023-90913 (filed on June 1, 2023), and the entire disclosure of this application is incorporated herein by reference. Technical Field

[0003] The present disclosure relates to an isolator, an optical switch, an optical transceiver, a data center, and a method for manufacturing the isolator. Background Art

[0004] An optical isolator using a magneto-optical material Ce:YIG as a waveguide layer is known (for example, see Patent Document 1).

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent document 1: International Publication No. 2007 / 083419. Summary of the invention

[0008] An isolator according to one embodiment of the present disclosure includes: a substrate having a substrate surface, a first waveguide and a second waveguide, an insulating layer, and a first non-reciprocal member and a second non-reciprocal member. The first waveguide and the second waveguide extend on the substrate surface and propagate electromagnetic waves in a TM mode along the extending direction. The insulating layer is located on the substrate surface and is configured to surround at least a portion of the first waveguide and the second waveguide. The insulating layer has a surface above the upper surface of the first waveguide and the second waveguide, and a first recess and a second recess. The first recess is divided by a bottom surface below the surface of the insulating layer and a side surface between the bottom surface and the surface of the insulating layer, and is located at a position overlapping with at least a portion of the first waveguide when the substrate surface is viewed from above. The second recess is divided by a bottom surface below the surface of the insulating layer and a side surface between the bottom surface and the surface of the insulating layer, and is located at a position overlapping with at least a portion of the second waveguide when the substrate surface is viewed from above. The first non-reciprocal member is located on the bottom surface of the first recess in a manner overlapping with at least a portion of the first waveguide when the substrate surface is viewed from above. The second non-reciprocal member is located on the bottom surface of the second recess so as to overlap with at least a portion of the second waveguide when the substrate surface is viewed from above. The propagation direction of the electromagnetic wave in the portion of the first waveguide that overlaps with the first non-reciprocal member when the substrate surface is viewed from above is different from the propagation direction of the electromagnetic wave in the portion of the second waveguide that overlaps with the second non-reciprocal member when the substrate surface is viewed from above.

[0009] An optical switch according to one embodiment of the present disclosure includes the isolator.

[0010] An optical transceiver according to one embodiment of the present disclosure includes the isolator and a light source optically connected to the isolator.

[0011] A data center according to an embodiment of the present disclosure communicates via a device having the isolator.

[0012] A method for manufacturing an isolator according to an embodiment of the present disclosure includes a process of forming a first waveguide and a second waveguide on a substrate for propagating electromagnetic waves in a TM mode. The method for manufacturing the isolator includes a process of forming an insulating layer on the first waveguide and the second waveguide. The method for manufacturing the isolator includes a process of forming a first recess overlapping at least a portion of the first waveguide and a second recess overlapping at least a portion of the second waveguide by etching the insulating layer. The first recess and the second recess are formed so that the propagation direction of the electromagnetic wave in the portion of the first waveguide overlapping with the first recess is different from the propagation direction of the electromagnetic wave in the portion of the second waveguide overlapping with the second recess. The method for manufacturing the isolator includes a process of forming a first non-reciprocal member on the bottom surface of the first recess and a second non-reciprocal member on the bottom surface of the second recess. The method for manufacturing the isolator includes a process of irradiating the first non-reciprocal member and the second non-reciprocal member with a laser. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a plan view showing a structural example of an isolator according to one embodiment.

[0014] Figure 2 It is a plan view showing an example of the positional relationship between the waveguide and the recessed portion.

[0015] Figure 3 yes Figure 2 AA section view.

[0016] Figure 4 It is a cross-sectional view showing a structural example in which a non-reciprocal member is in contact with the entire side surface of a recessed portion.

[0017] Figure 5 It is a cross-sectional view showing a structural example in which an insulating layer remains between the upper surface of the waveguide and the bottom surface of the recessed portion.

[0018] Figure 6 It is a cross-sectional view showing a structural example in which the bottom surface of the recessed portion is lower than the upper surface of the waveguide.

[0019] Figure 7 It is a top view showing another example of the planar shape of the recessed portion.

[0020] Figure 8 It is a plan view showing another example of the cross-sectional shape of the recessed portion.

[0021] Fig. 9 It is a plan view showing a structural example in which the extending directions of the first recessed portion and the second recessed portion are orthogonal to the direction from the first branch portion toward the second branch portion.

[0022] Fig.10 It is a plan view showing a structural example in which the extending direction of the first recessed portion intersects with the extending direction of the second recessed portion.

[0023] Fig.11 This is a plan view showing a structural example in which the waveguide is arranged in a spiral shape when a magnetic field is applied in a direction perpendicular to the direction connecting the first branch portion and the second branch portion.

[0024] Fig.12 This is a plan view showing a structural example in which the waveguide is arranged in a spiral shape when a magnetic field is applied in a direction connecting the first branch portion and the second branch portion.

[0025] Fig.13 It is a plan view showing a structural example in which the waveguide is arranged so as to be accommodated in a substantially circular laser irradiation area.

[0026] Fig.14 It is a side view showing a configuration example of irradiating laser light.

[0027] Fig.15 This is an observation example of the surface of a non-reciprocal member that is crystallized by laser irradiation.

[0028] Fig.16 This is a cross-sectional view showing an example of the relationship between the size of the crystal of the non-reciprocal member and the width of the recessed portion.

[0029] Fig.17 It is a plan view showing a structural example of an isolator further including a heater. DETAILED DESCRIPTION

[0030] When an isolator using YIG as a waveguide layer is formed on a semiconductor substrate, it is necessary to reduce the influence of YIG on the semiconductor process. According to an isolator and a method for manufacturing the same in one embodiment of the present disclosure, the influence of YIG on the semiconductor process can be reduced.

[0031] (Configuration Example of Isolator 10)

[0032] like Figure 1 As shown, the isolator 10 of one embodiment includes: a first waveguide 21, a second waveguide 22, a first recess 31, a second recess 32, a first branch portion 81, and a second branch portion 82. The isolator 10 is formed on a substrate surface 50A of a substrate 50 (see Figure 3 The first waveguide 21 and the second waveguide 22 extend on the substrate 50 in such a manner that the TM mode electromagnetic wave propagates from the first branch portion 81 to the second branch portion 82.

[0033] The extension directions of the first waveguide 21 and the second waveguide 22 are changed at least at one location. Figure 1 In the embodiment, the extension direction of the first waveguide 21 is changed at two locations of the folded portions 211 and 212. The extension direction of the second waveguide 22 is changed at two locations of the folded portions 221 and 222. The extension direction of the waveguide is reversely changed in each of the folded portions 211, 212, 221, and 222. That is, the extension direction of the waveguide is changed by 180 degrees. The angle for changing the extension direction of the waveguide is not limited to 180 degrees, but may be 90 degrees or other various angles.

[0034] When the substrate surface 50A is viewed in plan, the first recess 31 is located at a position overlapping at least a portion of the first waveguide 21. The first recess 31 may extend along the extending direction of the first waveguide 21. The first non-reciprocal member is located in the first recess 31.

[0035] When the substrate surface 50A is viewed in plan, the second recess 32 is located at a position overlapping at least a portion of the second waveguide 22. The second recess 32 may extend along the extending direction of the second waveguide 22. The second non-reciprocal member is located in the second recess 32.

[0036] <Operation principle of isolator 10>

[0037] The isolator 10 is configured to allow the electromagnetic wave in the TM mode input to the first branch portion 81 to pass through the second branch portion 82, and to allow the electromagnetic wave in the TM mode input to the second branch portion 82 to attenuate in the first branch portion 81 without passing through the first branch portion 81. The direction in which the electromagnetic wave propagates 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 wave propagates from the second branch portion 82 to the first branch portion 81 is also referred to as the second direction. That is, the isolator 10 allows the electromagnetic wave in the TM mode to pass through in the first direction, but not in the second direction.

[0038] The electromagnetic wave of the TM mode is the electromagnetic wave along the substrate surface 50A of the substrate 50 (refer to Figure 3 ) is an electromagnetic wave whose amplitude direction of the electric field is consistent with the normal direction of the substrate surface 50A when the electromagnetic wave propagates along the substrate 50. Conversely, an electromagnetic wave in the TE mode is an electromagnetic wave whose amplitude direction of the electric field is orthogonal to the propagation direction of the electromagnetic wave and is consistent with the direction along the substrate surface 50A when the electromagnetic wave propagates along the substrate 50.

[0039] The isolator 10 uses the principle of an asymmetric Mach-Zehnder interferometer to realize an asymmetric propagation characteristic of an electromagnetic wave. The isolator 10 is configured so that the phase of the electromagnetic wave that branches from the first branch portion 81 to the first waveguide 21 and the second waveguide 22 and propagates in the first direction, and the phase of the electromagnetic wave that reaches the second branch portion 82 through the first waveguide 21 and the phase of the electromagnetic wave that reaches the second branch portion 82 through the second waveguide 22 are consistent. In addition, the isolator 10 is configured so that the phase of the electromagnetic wave that branches from the second branch portion 82 to the first waveguide 21 and the second waveguide 22 and propagates in the second direction, and the phase of the electromagnetic wave that reaches the first branch portion 81 through the first waveguide 21 and the phase of the electromagnetic wave that reaches the first branch portion 81 through the second waveguide 22 are offset by 180 degrees. In this way, the isolator 10 operates in a manner that allows the electromagnetic wave to pass in the first direction but does not allow the electromagnetic wave to pass in the second direction.

[0040] The phase shift can be adjusted by the line length of the waveguide or by the effective refractive index of the waveguide. The isolator 10 is configured such that, in the absence of the first non-reciprocal member and the second non-reciprocal member, the phase of the electromagnetic wave propagating in the first waveguide 21 lags by 90 degrees compared to the phase of the electromagnetic wave propagating in the second waveguide 22, regardless of whether the electromagnetic wave propagates in the first direction or the second direction in the isolator 10. Therefore, even if only the line length or the effective refractive index of the waveguide is set, the phase shift manner of the electromagnetic wave propagating in the first direction and the phase shift manner of the electromagnetic wave propagating in the second direction will be the same.

[0041] Therefore, the isolator 10 includes a first non-reciprocal member arranged along at least a portion of the first waveguide 21 and a second non-reciprocal member arranged along at least a portion of the second waveguide 22 so that the phase shift of the electromagnetic wave propagating in the first direction and the phase shift of the electromagnetic wave propagating in the second direction in the waveguide are different. The first waveguide 21 including the first non-reciprocal member and the second waveguide 22 including the second non-reciprocal member function as non-reciprocal waveguides by application of a magnetic field.

[0042] A non-reciprocal waveguide causes the phase of a propagating electromagnetic wave to advance or lag. In the isolator 10 of the present embodiment, the non-reciprocal waveguide is configured so that the relationship between the advance and lag of the phase in the waveguide facing the propagation direction of the electromagnetic wave and to which magnetic fields from opposite directions are applied is opposite. Assume that when a magnetic field is applied from the right side of the propagation direction of the electromagnetic wave, the phase of the electromagnetic wave advances by 45 degrees, and when a magnetic field is applied from the left side of the propagation direction of the electromagnetic wave, the phase of the electromagnetic wave lags by 45 degrees. Figure 1 In the illustrated isolator 10 , a magnetic field (B) is applied in the vertical direction of the paper surface on which the isolator 10 is arranged, as indicated by arrows.

[0043] In the case where the electromagnetic wave propagates in the first direction, the propagation direction of the electromagnetic wave in the first waveguide 21 located at a position overlapping with the first non-reciprocal member in the first recess 31 is from left to right. On the other hand, the propagation direction of the electromagnetic wave in the second waveguide 22 located at a position overlapping with the second non-reciprocal member in the second recess 32 is from right to left. Among them, when the direction of the magnetic field is from bottom to top, in the first waveguide 21 located at a position overlapping with the first non-reciprocal member in the first recess 31, the magnetic field is applied from the right side of the propagation direction of the electromagnetic wave; in the second waveguide 22 located at a position overlapping with the second non-reciprocal member in the second recess 32, the magnetic field is applied from the left side of the propagation direction of the electromagnetic wave. Thus, the phase of the electromagnetic wave in the first waveguide 21 is advanced by 45 degrees. Conversely, the phase of the electromagnetic wave in the second waveguide 22 is delayed by 45 degrees. Thus, the phase of the electromagnetic wave propagating in the first direction in the first waveguide 21 is 90 degrees ahead of the phase of the electromagnetic wave propagating in the first direction in the second waveguide 22.

[0044] On the contrary, in the case where the electromagnetic wave propagates in the second direction, the propagation direction of the electromagnetic wave in the first waveguide 21 located at a position overlapping with the first non-reciprocal member in the first recess 31 is from right to left. On the other hand, the propagation direction of the electromagnetic wave in the second waveguide 22 located at a position overlapping with the second non-reciprocal member in the second recess 32 is from left to right. Among them, when the direction of the magnetic field is from bottom to top, in the first waveguide 21 located at a position overlapping with the first non-reciprocal member in the first recess 31, the magnetic field is applied from the left side of the propagation direction of the electromagnetic wave; in the second waveguide 22 located at a position overlapping with the second non-reciprocal member in the second recess 32, the magnetic field is applied from the right side of the propagation direction of the electromagnetic wave. Thus, the phase of the electromagnetic wave in the first waveguide 21 lags by 45 degrees. On the contrary, the phase of the electromagnetic wave in the second waveguide 22 leads by 45 degrees. Thus, the phase of the electromagnetic wave propagating in the first direction in the first waveguide 21 lags by 90 degrees compared with the phase of the electromagnetic wave propagating in the first direction in the second waveguide 22.

[0045] As described above, the isolator 10 is configured such that, in the absence of the first non-reciprocal member and the second non-reciprocal member, the phase of the electromagnetic wave propagating in the first direction in the first waveguide 21 lags the phase of the electromagnetic wave propagating in the first direction in the second waveguide 22 by 90 degrees.

[0046] When the electromagnetic wave propagates in the first direction, since the phase of the electromagnetic wave propagating in the first waveguide 21 is 90 degrees ahead, the phase difference between the electromagnetic wave propagating in the first waveguide 21 and the electromagnetic wave propagating in the second waveguide 22 is 0 degrees in the second branch portion 82. As a result, since the electromagnetic wave propagating in the first waveguide 21 and the electromagnetic wave propagating in the second waveguide 22 are mutually reinforced when combined in the second branch portion 82, the electromagnetic wave is transmitted in the first direction.

[0047] On the contrary, when the electromagnetic wave propagates in the second direction, since the phase of the electromagnetic wave propagating in the first waveguide 21 lags by 90 degrees, in the second branch portion 82, the phase difference between the electromagnetic wave propagating in the first waveguide 21 and the electromagnetic wave propagating in the second waveguide 22 is 180 degrees. As a result, since the electromagnetic wave propagating in the first waveguide 21 and the electromagnetic wave propagating in the second waveguide 22 weaken each other when combined in the second branch portion 82, the electromagnetic wave does not pass through in the second direction.

[0048] In other words, the isolator 10 is configured so that the propagation direction of the electromagnetic wave in the portion of the first waveguide 21 that overlaps with the first non-reciprocal member when looking down at the substrate surface 50A is different from the propagation direction of the electromagnetic wave in the portion of the second waveguide 22 that overlaps with the second non-reciprocal member when looking down at the substrate surface 50A. The isolator 10 is configured in this way so that the advance or lag of the phase of the electromagnetic wave can be different when the electromagnetic wave propagates in the first direction and when it propagates in the second direction. As a result, the isolator 10 is configured so that the electromagnetic wave propagating in the first direction is transmitted but the electromagnetic wave propagating in the second direction is not transmitted.

[0049] <Effective length>

[0050] like Figure 1 As illustrated, the first recess 31 and the second recess 32 may be configured to overlap with the first waveguide 21 and the second waveguide 22 extending in the direction from the first branch portion 81 toward the second branch portion 82. The length of the first recess 31 in the extending direction of the first waveguide 21 is represented by D1. When the first non-reciprocal member is located in the entire first recess 31, the length of the overlap between the first non-reciprocal member and the first waveguide 21 is D1. The length of the second recess 32 in the extending direction of the second waveguide 22 is represented by D2. When the second non-reciprocal member is located in the entire second recess 32, the length of the overlap between the second non-reciprocal member and the second waveguide 22 is D2.

[0051] When the non-reciprocal component 40 overlaps with the waveguide 20 in a direction orthogonal to the magnetic field B, the magnitude of the manifested non-reciprocity is determined by the distance of the overlap. Specifically, the longer the distance that the non-reciprocal component 40 overlaps with the waveguide 20 in the direction orthogonal to the magnetic field B, the greater the non-reciprocity manifested by the non-reciprocal component 40. On the other hand, when the non-reciprocal component 40 overlaps with the waveguide 20 in a direction inclined from the direction orthogonal to the magnetic field B, the magnitude of the manifested non-reciprocity is determined by the distance of the component of the overlapping distance in the direction orthogonal to the magnetic field B. That is, the distance that the non-reciprocal component 40 actually overlaps with the waveguide 20 is sometimes different from the distance that determines the magnitude of the manifested non-reciprocity. The distance that determines the magnitude of the manifested non-reciprocity is also referred to as the effective length. Figure 1 , the non-reciprocal member 40 overlaps the waveguide 20 in a direction orthogonal to the magnetic field B. Therefore, D1 is the effective length of the non-reciprocal waveguide combining the first waveguide 21 and the first non-reciprocal member. D2 is the effective length of the non-reciprocal waveguide combining the second waveguide 22 and the second non-reciprocal member.

[0052] The isolator 10 may be configured such that the effective length of the nonreciprocal waveguide combining the first waveguide 21 and the first nonreciprocal member is equal to the effective length of the nonreciprocal waveguide combining the second waveguide 22 and the second nonreciprocal member. When the recess 30 is divided into a plurality of parts, the total effective length of each part of the first recess 31 may be equal to the total effective length of each part of the second recess 32. By making the effective lengths equal, the phase is easily adjusted. As a result, the performance of the isolator 10 can be improved.

[0053] <Structural example of non-reciprocal waveguide>

[0054] Below, refer to Figure 2 as well as Figure 3 , the first waveguide 21, the first recess 31, and the first non-reciprocal member, and the second waveguide 22, the second recess 32, and the second non-reciprocal member of the isolator 10 are described. The first waveguide 21 and the second waveguide 22 are also referred to as the waveguide 20 (see Figure 2 If there is no need to distinguish the first recess 31 and the second recess 32 from each other, they are also referred to as the recess 30 (see Figure 2 If there is no need to distinguish the first non-reciprocal component and the second non-reciprocal component from each other, they are also referred to as the non-reciprocal component 40 (see Figure 2 ).

[0055] The isolator 10 is formed on a substrate 50 having a substrate surface 50A. The substrate 50 may be made of a conductor such as metal, a semiconductor such as silicon, glass, or resin. In the present embodiment, the substrate 50 is made of silicon (Si), but is not limited thereto and may be made of various other materials.

[0056] The substrate 50 has a box layer 52 on a substrate surface 50A. The box layer 52 is made of an insulator such as a silicon oxide film. The waveguide 20 is located on the box layer 52. The waveguide 20 has an upper surface 201. The upper surface 201 is located on the side opposite to the surface in contact with the box layer 52.

[0057] The substrate 50 further includes an insulating layer 54. The insulating layer 54 is disposed so as to surround at least a portion of the waveguide 20. The insulating layer 54 is made of an insulator such as a silicon oxide film.

[0058] The insulating layer 54 has a surface and a recessed portion 30 recessed relative to the surface. The recessed portion 30 can be formed by etching the insulating layer 54. The recessed portion 30 is divided by side surfaces 301, 302, 303 and 304, and a bottom surface 305. The bottom surface 305 is located on a side closer to the substrate surface 50A than the surface of the insulating layer 54, that is, at a position lower than the surface of the insulating layer 54. The side surfaces 301, 302, 303 and 304 are located between the bottom surface 305 and the surface of the insulating layer 54.

[0059] The first recess 31 is located at a position overlapping with at least a portion of the first waveguide 21. The first recess 31 may extend along the extension direction of the first waveguide 21. The second recess 32 is located at a position overlapping with at least a portion of the second waveguide 22. The second recess 32 may extend along the extension direction of the second waveguide 22. That is, the recess 30 is located at a position overlapping with at least a portion of the waveguide 20. The recess 30 may extend along the extension direction of the waveguide 20. Figure 2 , the waveguide 20 and the recess 30 extend in the X-axis direction. The side surface 301 and the side surface 302 are arranged along the X-axis direction in which the waveguide 20 extends. The side surface 303 and the side surface 304 are arranged along the Y-axis direction intersecting the direction in which the waveguide 20 extends.

[0060] The bottom surface 305 of the recess 30 is flush with the upper surface 201 of the waveguide 20. In other words, the upper surface 201 of the waveguide 20 is not covered by the insulating layer 54 and is exposed in the bottom surface 305 of the recess 30.

[0061] The non-reciprocal member 40 is arranged in contact with at least a portion of the bottom surface 305 of the recessed portion 30. The non-reciprocal member 40 may be arranged in contact with the entire bottom surface 305, or may be arranged in contact with a portion of the bottom surface 305. The non-reciprocal member 40 may also be arranged in contact with at least a portion of each of the side surfaces 301, 302, 303, and 304 connected to the bottom surface 305 of the recessed portion 30. In other words, the non-reciprocal member 40 may be in contact with the bottom surface 305 of the recessed portion 30, and may be in contact with at least a portion of the side surface 301, at least a portion of the side surface 302, at least a portion of the side surface 303, and at least a portion of the side surface 304. The non-reciprocal member 40 may also be arranged in contact with a portion of the side surfaces 301, 302, 303, and 304. That is, the non-reciprocal member 40 may not be in contact with a portion of the side surfaces 301, 302, 303, and 304. The non-reciprocal member 40 may also be located on the surface of the insulating layer 54 outside the recess 30. Figure 4 As shown, the non-reciprocal member 40 may be in contact with the entire side surface 301, the entire side surface 302, the entire side surface 303, and the entire side surface 304 of the recess 30, and may be arranged in a manner of being connected to the entire surface from the bottom surface 305 to the surface of the insulating layer 54. When the upper surface 201 of the waveguide 20 and the bottom surface 305 of the recess 30 are flush with each other, the non-reciprocal member 40 is in contact with at least a portion of the upper surface 201 of the waveguide 20. The non-reciprocal member 40 may be formed by forming a film on the recess 30.

[0062] When the substrate surface 50A is viewed from above, the recessed portion 30 may be arranged so as to overlap at least a portion of the width direction intersecting the extending direction of the waveguide 20. When the substrate surface 50A is viewed from above, the recessed portion 30 may be arranged so as to overlap a portion of the width direction of the waveguide 20. When the substrate surface 50A is viewed from above, the recessed portion 30 may be arranged so as to overlap the entire width direction of the waveguide 20.

[0063] The non-reciprocal member 40 may be located within the bottom surface 305 of the recess 30, at a position overlapping at least a portion in the width direction of the waveguide 20. The non-reciprocal member 40 may be located within the bottom surface 305 of the recess 30, at a position overlapping a portion in the width direction of the waveguide 20. The non-reciprocal member 40 may be located within the bottom surface 305 of the recess 30, at a position overlapping the entire width direction of the waveguide 20.

[0064] The non-reciprocal member 40 may be located within the bottom surface 305 of the recess 30, at a position overlapping at least a portion of the extension direction of the waveguide 20. The non-reciprocal member 40 may be located within the bottom surface 305 of the recess 30, at a position overlapping a portion of the extension direction of the waveguide 20. The non-reciprocal member 40 may be located within the bottom surface 305 of the recess 30, at a position overlapping the entire extension direction of the waveguide 20.

[0065] The waveguide 20 is surrounded by a box layer 52, an insulating layer 54 and a non-reciprocal 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 cladding. The core and the cladding may be configured to contain a dielectric. The waveguide 20 is also referred to as a dielectric line. The materials of the core and the cladding are determined so that the relative dielectric constant of the core is greater than the relative dielectric constant 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 greater than the refractive index of the core. In this way, the electromagnetic waves propagating in the core can be totally reflected at the boundary with the cladding. As a result, the loss of the electromagnetic waves propagating in the core can be reduced.

[0066] The relative dielectric constant of the core and the cladding may be greater than the relative dielectric constant of air. By making the relative dielectric constant of the core and the cladding greater than the relative dielectric constant of air, it is possible to suppress leakage of electromagnetic waves from the isolator 10. As a result, the loss caused by the electromagnetic wave radiated from the isolator 10 to the outside can be reduced.

[0067] In the present embodiment, the material of the waveguide 20 as the core is silicon (Si), but it is not limited to this, and it can also be various other materials. The material of the box layer 52 and the insulating layer 54 as the cladding is quartz glass or silicon oxide film (SiO2), but it is not limited to this, and it can also be various other materials. The relative dielectric constants of silicon and quartz glass are about 12 and about 2, respectively. Silicon can propagate electromagnetic waves with near-infrared wavelengths of about 1.2μm to about 6μm with low loss. When the waveguide 20 is composed of silicon, it can propagate electromagnetic waves with wavelengths of 1.3μm band or 1.55μm band used in optical communication with low loss.

[0068] In the present embodiment, Ce:YIG (cerium-substituted yttrium iron garnet) is used as the material of the non-reciprocal component 40. As the material of the non-reciprocal component 40, a transparent magnetic substance such as a substance in which a part of YIG is substituted, such as Bi:YIG (bismuth-substituted YIG), may be used. As the material of the non-reciprocal component 40, a ferromagnetic substance such as FeCo, FeNi or CoPt, or a substance containing a ferromagnetic substance may be used. As the material of the non-reciprocal component 40, a dielectric compounded with magnetic nanoparticles, such as a nanoparticle material, may be used. However, it is not limited thereto, and various other magnetic materials may be used as the non-reciprocal component 40.

[0069] The YIG-based nonreciprocal member 40 exhibits sufficient nonreciprocity due to sufficient crystallization. The nonreciprocal member 40 is crystallized by heating it to a predetermined temperature or higher. However, considering the influence on other structures such as waveguides and wiring formed on the substrate 50, it is difficult to heat the entire substrate 50 to a predetermined temperature or higher when the nonreciprocal member 40 is formed. Therefore, the nonreciprocal member 40 formed in the recess 30 by film formation without heating the substrate 50 is not fully crystallized, and in this state, sufficient nonreciprocity is not exhibited.

[0070] Therefore, in the isolator 10 of the present embodiment, in order to crystallize the non-reciprocal member 40, the non-reciprocal member 40 is heated by irradiating with laser. As the laser, light of a wavelength having high absorption efficiency for light of the non-reciprocal member 40 is used. When the non-reciprocal member 40 is Ce:YIG, the absorption efficiency of visible light is high. Therefore, the heating can be performed using visible light laser.

[0071] Due to optical limitations, the laser light diffuses to a limited range at the irradiation point. The irradiation range of the laser light is wider than the width of the recess 30. The area outside the non-reciprocal member 40 in the recess 30 to which the laser light is irradiated contributes less to the crystallization of the laser light. Therefore, the isolator 10 of this embodiment may also have a mask that reduces the transmittance of the laser light outside the recess 30. The mask is configured so that the transmittance of the laser light is less than the transmission threshold, or so that the reflectivity of the laser light is above the reflection threshold. As a material for the mask, for example, a metal such as aluminum can be used. As a material for the mask, it is not limited to this, and various materials can be used.

[0072] A laser absorption member may be further formed on the non-reciprocal member 40 located in the recess 30. As the absorption member, a material with high laser absorption efficiency is used. In addition, a material having absorption characteristics different from those of the non-reciprocal member 40 may be used. As the absorption member, carbon or the like with high infrared light absorption efficiency may also be used.

[0073] As described above, in the isolator 10 of the present embodiment, the non-reciprocal member 40 is heated in such a manner that the non-reciprocal member 40 hardly affects other structures of the substrate 50. In this manner, even when a material requiring a heating process is used as the non-reciprocal member 40, the influence on the semiconductor process can be reduced. In addition, the performance of the isolator 10 can be improved.

[0074] (Other Configuration Examples of Isolator 10)

[0075] The isolator 10 is not limited to the above-described embodiment, and may be configured in various other embodiments. Other configuration examples of the isolator 10 will be described below.

[0076] <Height of waveguide 20>

[0077] In the above-mentioned isolator 10, if Figure 3 As illustrated, the waveguide 20 may be arranged such that the upper surface 201 of the waveguide 20 and the bottom surface 305 of the recess 30 are flush with each other.

[0078] As other structural examples, Figure 5 As illustrated, the waveguide 20 may also be configured such that the upper surface 201 of the waveguide 20 is lower than the bottom surface 305 of the recess 30. In this case, the upper surface 201 of the waveguide 20 is covered by the insulating layer 54. Therefore, the non-reciprocal member 40 does not contact the waveguide 20. In other words, the insulating layer 54 exists between the upper surface 201 of the waveguide 20 and the non-reciprocal member 40. The thickness of the insulating layer 54 between the upper surface 201 of the waveguide 20 and the non-reciprocal member 40 is represented by T.

[0079] The non-reciprocal waveguide in the isolator 10 of the present embodiment exhibits non-reciprocity for electromagnetic waves in the TM mode. As described above, electromagnetic waves in the TM mode are electromagnetic waves in which the amplitude direction of the electric field coincides with the normal direction of the substrate surface 50A of the substrate 50 when the electromagnetic wave propagates along the substrate 50. Non-reciprocity is exhibited because the electric field component is affected by the non-reciprocal member 40. Therefore, in the cross section in the extension direction of the waveguide 20, due to the diffusion of the energy distribution of the electric field in the normal direction of the substrate surface 50A, that is, the Z-axis direction, the non-reciprocal waveguide exhibits non-reciprocity even if the non-reciprocal member 40 is separated from the waveguide 20 but still exists within a specified range.

[0080] In the present embodiment, the waveguide 20 has a rectangular cross-sectional shape. In this case, the mode field diameter in the Z-axis direction is defined as the amplitude direction of the electric field of the electromagnetic wave of the TM mode. The energy of the electric field component of the electromagnetic wave of the TM mode propagating in the waveguide 20 decreases as it is farther away from the waveguide 20 outside the waveguide 20. The energy magnitude of the electric field component of the electromagnetic wave of the TM mode outside the waveguide 20 follows a Gaussian distribution. The mode field diameter in the Z-axis direction is defined as the energy magnitude reduced to 1 / e relative to the energy magnitude of the electric field component in the upper surface 201 of the waveguide 20. 2 In other words, when the energy is 1 / e 2 In the above range, energy is efficiently distributed.

[0081] The mode field diameter in the Z-axis direction of the waveguide 20 is determined based on the length of the waveguide 20 in the width direction in a cross section orthogonal to the extension direction of the waveguide 20, the length of the waveguide 20 in the Z-axis direction, i.e., the height of the waveguide 20, the refractive index of the waveguide 20, the refractive index of the insulating layer 54, and the wavelength of the electromagnetic wave propagating in the waveguide 20.

[0082] The longer the mode field diameter in the Z-axis direction, the wider the energy distribution in the Z-axis direction of the electromagnetic wave propagating in the waveguide 20. Specifically, when the thickness (T) of the insulating layer 54 located between the upper surface 201 of the waveguide 20 and the non-reciprocal member 40 is less than 1 / 2 of the value obtained by subtracting the height in the cross section of the waveguide 20 from the mode field diameter in the Z-axis direction, the effective distribution of the energy of the electromagnetic wave propagating in the waveguide 20 affects the non-reciprocal member 40. The value of 1 / 2 of the value obtained by subtracting the height in the cross section of the waveguide 20 from the mode field diameter in the Z-axis direction is also called the thickness threshold. In other words, the thickness threshold is a value determined based on the mode field diameter of the waveguide 20 and the height of the cross section of the waveguide 20. Even when the insulating layer 54 is located between the upper surface 201 of the waveguide 20 and the non-reciprocal member 40, as long as the thickness (T) of the insulating layer 54 is below the thickness threshold, the non-reciprocal waveguide will show non-reciprocity.

[0083] As an example, the following conditions are set.

[0084] Width of waveguide 20: 400 nm

[0085] Height of waveguide 20: 220 nm

[0086] Refractive index of waveguide 20 (core): 3.45

[0087] Refractive index of insulating layer 54 (cladding): 1.53

[0088] The wavelength of the electromagnetic wave in the TM mode propagating in the waveguide 20 is 1550 nm.

[0089] In the above conditions, the mode field diameter is 800nm. The thickness threshold in the above conditions is 290nm when calculating 1 / 2 of the value (800nm-220nm) obtained by subtracting the height of the waveguide 20 from the mode field diameter. Therefore, by setting the thickness (T) of the insulating layer between the upper surface 201 of the waveguide 20 and the non-reciprocal member 40 to 290nm or less, the non-reciprocal waveguide exhibits non-reciprocity. In other words, the non-reciprocal waveguide exhibits non-reciprocity by the non-reciprocal member 40 being within the range of the mode field diameter of the waveguide 20 or the non-reciprocal member 40 being in contact with the range of the mode field diameter of the waveguide 20.

[0090] As another example, the following conditions are set.

[0091] Width of waveguide 20: 500 nm

[0092] Height of waveguide 20: 220 nm

[0093] Refractive index of waveguide 20 (core): 3.45

[0094] Refractive index of insulating layer 54 (cladding): 1.53

[0095] The wavelength of the electromagnetic wave in the TM mode propagating in the waveguide 20 is 1550 nm.

[0096] In the above conditions, the mode field diameter is 520 nm. The thickness threshold in the above conditions is 150 nm when calculating 1 / 2 of the value (520 nm - 220 nm) obtained by subtracting the height of the waveguide 20 from the mode field diameter. Therefore, by setting the thickness (T) of the insulating layer between the upper surface 201 of the waveguide 20 and the non-reciprocal member 40 to 150 nm or less, the non-reciprocal waveguide exhibits non-reciprocity.

[0097] In the case where the width and height in the cross section of the first waveguide 21 are the same as the width and height in the cross section of the second waveguide 22, the mode field diameter in the Z-axis direction in the first waveguide 21 and the mode field diameter in the Z-axis direction in the second waveguide 22 are the same value. In this case, the thickness threshold value related to the first waveguide 21 and the thickness threshold value related to the second waveguide 22 are set to the same value.

[0098] In the case where the width in the cross section of the first waveguide 21 is different from the width in the cross section of the second waveguide 22, or in the case where the height in the cross section of the first waveguide 21 is different from the height in the cross section of the second waveguide 22, the mode field diameter in the Z-axis direction in the first waveguide 21 and the mode field diameter in the Z-axis direction in the second waveguide 22 may be different values. In this case, the thickness threshold value related to the first waveguide 21 and the thickness threshold value related to the second waveguide 22 may be set to different values.

[0099] As described above, the nonreciprocal waveguide can exhibit nonreciprocity even when the nonreciprocal member 40 is not in contact with the waveguide 20. In other words, the nonreciprocal waveguide can exhibit nonreciprocity even when the upper surface 201 of the waveguide 20 is not exposed from the insulating layer 54 in the bottom surface 305 of the recess 30. Since the upper surface 201 of the waveguide 20 may not be exposed from the insulating layer 54, the upper surface 201 of the waveguide 20 is not directly exposed to the dry etching gas used to form the recess 30. As a result, the upper surface 201 of the waveguide 20 is not roughened by dry etching.

[0100] If the upper surface 201 of the waveguide 20 is damaged, even if the damage is extremely small, it will cause the loss of the electromagnetic wave propagating in the waveguide 20. In particular, since the amplitude direction of the electric field in the electromagnetic wave of the TM mode intersects with the upper surface 201 of the waveguide 20, the damage of the upper surface 201 of the waveguide 20 is likely to cause the loss of the electromagnetic wave of the TM mode. Therefore, since the upper surface 201 of the waveguide 20 does not need to be exposed from the insulating layer 54, the damage caused by dry etching will not be generated on the upper surface 201 of the waveguide 20, and as a result, the loss of the electromagnetic wave propagating in the waveguide 20 can be reduced.

[0101] In addition, as other structural examples, Figure 6 As shown, the waveguide 20 may be configured such that the upper surface 201 of the waveguide 20 is above the bottom surface 305 of the recess 30. When the insulating layer 54 is overetched under the condition that the etching rate of the insulating layer 54 is greater than the etching rate of the waveguide 20 in order to form the recess 30, the upper surface 201 of the waveguide 20 is above the bottom surface 305 of the recess 30. In this case, the upper surface 201 of the waveguide 20 is not covered by the insulating layer 54 but exposed. Therefore, the non-reciprocal member 40 is in contact with the waveguide 20.

[0102] In other words, the first recess 31 may be arranged such that the position of the bottom surface 305 of the first recess 31 in the direction perpendicular to the substrate surface 50A is lower than the position of the upper surface 201 of the first waveguide 21. The second recess 32 may be arranged such that the position of the bottom surface 305 of the second recess 32 in the direction perpendicular to the substrate surface 50A is lower than the position of the upper surface 201 of the second waveguide 22.

[0103] like Figure 6 As shown in the example, when the bottom surface 305 of the recess 30 has a step due to the protrusion of the upper surface 201 of the waveguide 20, the step may affect the crystallization of the non-reciprocal member 40. For example, when Ce:YIG is used as the non-reciprocal member 40, when Ce:YIG is crystallized by annealing, the discontinuity of the Ce:YIG film in the step may hinder the crystallization. When Ce:YIG is used as the non-reciprocal member 40, the recess 30 may be formed so that the step in the bottom surface 305 is 100 nm or less.

[0104] <Shape of concave portion 30>

[0105] like Figure 2 As shown in the example, when the substrate surface 50A is viewed from above, the recess 30 may be arranged so that the side surfaces 301 and 302 are orthogonal to the extending direction of the waveguide 20. As another structural example, Figure 7As illustrated, when the substrate surface 50A is viewed from above, the side surfaces 301 and 302 may be inclined at an angle greater than 0 degrees and less than 90 degrees relative to the direction perpendicular to the extension direction of the waveguide 20. In other words, the first recess 31 may be configured such that the side surfaces 301 and 302 located at the ends in the extension direction of the first waveguide 21 among the side surfaces 301 to 304 that divide the first recess 31 are inclined relative to the vertical plane in the extension direction of the first waveguide 21. The second recess 32 may be configured such that the side surfaces 301 and 302 located at the ends in the extension direction of the second waveguide 22 among the side surfaces 301 to 304 that divide the second recess 32 are inclined relative to the vertical plane in the extension direction of the second waveguide 22.

[0106] When the substrate surface 50A is viewed from above, since the side surfaces 301 and 302 are inclined with respect to the extension direction of the waveguide 20, the area of ​​the non-reciprocal member 40 overlapped on the waveguide 20 gradually decreases from the range overlapping with the recess 30 to the outside of the recess 30. As a result, the effective refractive index of the waveguide 20 changes more slowly from the range overlapping with the recess 30 to the outside of the recess 30, compared with the case where the side surfaces 301 and 302 are orthogonal to the extension direction of the waveguide 20.

[0107] Since the effective refractive index of the waveguide 20 changes gradually, electromagnetic waves are less likely to be reflected at the boundary between the range overlapping with the recess 30 of the waveguide 20 and the range outside the recess 30. As a result, electromagnetic wave loss in the isolator 10 can be reduced.

[0108] The recess 30 may be configured such that the side surfaces 301 and 302 are perpendicular to the substrate surface 50A in a cross section perpendicular to the substrate surface 50A. Figure 8 As illustrated, the side surfaces 301 and 302 may be inclined in a manner that expands toward the outside of the recess 30 as they move upward from the bottom surface 305 in a cross section perpendicular to the substrate surface 50A and along the extension direction of the waveguide 20. In other words, the first recess 31 may be configured such that the side surfaces 301 and 302 located at the end portions in the extension direction of the first waveguide 21 among the side surfaces 301 to 304 that divide the first recess 31 are inclined toward the outside of the first recess 31 relative to the direction perpendicular to the substrate surface 50A. The second recess 32 may be configured such that the side surfaces 301 and 302 located at the end portions in the extension direction of the second waveguide 22 among the side surfaces 301 to 304 that divide the second recess 32 are inclined toward the outside of the second recess 32 relative to the direction perpendicular to the substrate surface 50A.

[0109] The non-reciprocal member 40 is arranged on the bottom surface 305 so as to extend above the side surfaces 301 and 302 .

[0110] In the cross section of the recess 30 along the extending direction of the waveguide 20, since the side surfaces 301 and 302 are inclined so as to expand toward the outside of the recess 30, the distance from the upper surface 201 of the waveguide 20 to the non-reciprocal member 40 gradually increases. As a result, the effective refractive index of the waveguide 20 changes gradually from the range overlapping the recess 30 to the outside of the recess 30, compared with the case where the side surfaces 301 and 302 are upright with respect to the substrate surface 50A.

[0111] Since the effective refractive index of the waveguide 20 changes gradually, electromagnetic waves are less likely to be reflected at the boundary between the range overlapping with the recess 30 of the waveguide 20 and the range outside the recess 30. As a result, electromagnetic wave loss in the isolator 10 can be reduced.

[0112] <Arrangement Example of Waveguide 20 and Recess 30>

[0113] The arrangement of the waveguide 20 and the recess 30 is not limited to Figure 1 Hereinafter, other arrangement examples of the waveguide 20 and the recessed portion 30 will be described.

[0114] like Fig. 9 As shown, when a magnetic field (B) is applied along a line connecting the first branch portion 81 and the second branch portion 82, the isolator 10 can be configured such that the first recess 31 is located at a position overlapping with a portion of the first waveguide 21 extending in the up-down direction orthogonal to the magnetic field, and the second recess 32 is located at a position overlapping with a portion of the second waveguide 22 extending in the up-down direction orthogonal to the magnetic field. The first non-reciprocal member is located on the entire bottom surface 305 of the first recess 31. The second non-reciprocal member is located on the entire bottom surface 305 of the second recess 32.

[0115] Furthermore, when the electromagnetic wave propagates in the first direction from the first branch portion 81 to the second branch portion 82, the electromagnetic wave in the first waveguide 21 travels upward in the portion overlapped by the first recess 31. The electromagnetic wave in the second waveguide 22 travels downward in the portion overlapped by the second recess 32.

[0116] therefore, Fig. 9 The illustrated isolator 10 is configured so that the propagation direction of the electromagnetic wave of the first waveguide 21 at the position where the first recess 31 overlaps is different from the propagation direction of the electromagnetic wave of the second waveguide 22 at the position where the second recess 32 overlaps. As a result, Fig. 9 The isolator 10 illustrated can make the phase advance or lag different when the electromagnetic wave propagates in the first direction and when it propagates in the second direction. In addition, the isolator 10 is configured so that D1 and D2 are equal. As a result, the isolator 10 is configured to allow the electromagnetic wave propagating in the first direction to pass through but not allow the electromagnetic wave propagating in the second direction to pass through.

[0117] like Fig.10 As illustrated, when a magnetic field (B) is applied in a direction connecting the first branch portion 81 and the second branch portion 82, the isolator 10 can be configured such that the first recess 31 is located at a position overlapping with a portion of the first waveguide 21 extending in a direction inclined relative to the magnetic field, and the second recess 32 is located at a position overlapping with a portion of the second waveguide 22 extending in a direction inclined relative to the magnetic field. The first non-reciprocal member is located on the entire bottom surface 305 of the first recess 31. The second non-reciprocal member is located on the entire bottom surface 305 of the second recess 32.

[0118] In this case, the effective length of the nonreciprocal waveguide combining the first nonreciprocal member and the first waveguide 21 is the component of the distance overlapped by the first recess 31 and the first waveguide 21 in the direction orthogonal to the magnetic field, which is represented by D1. The effective length of the nonreciprocal waveguide combining the second nonreciprocal member and the second waveguide 22 is the component of the distance overlapped by the second recess 32 and the second waveguide 22 in the direction orthogonal to the magnetic field, which is represented by D2. The isolator 10 is configured so that D1 and D2 are equal. As a result, the isolator 10 is configured so that the electromagnetic wave propagating in the first direction is transmitted and the electromagnetic wave propagating in the second direction is not transmitted.

[0119] like Fig.11 as well as Fig.12 As shown, the first waveguide 21 and the second waveguide 22 may be configured in a spiral shape. The length of the first waveguide 21 from the first branch portion 81 to the second branch portion 82 is the same as the length of the second waveguide 22 .

[0120] like Fig.11 As shown, when a magnetic field (B) is applied in a direction orthogonal to the direction connecting the first branch portion 81 and the second branch portion 82, the isolator 10 can be configured so that the first recess 31 is located at a position overlapping with the portion of the first waveguide 21 extending in the left-right direction orthogonal to the magnetic field, and the second recess 32 is located at a position overlapping with the portion of the second waveguide 22 extending in the left-right direction orthogonal to the magnetic field.

[0121] like Fig.12 As shown, when a magnetic field (B) is applied along the direction connecting the first branch portion 81 and the second branch portion 82, the isolator 10 can be configured so that the first recess 31 is located at a position overlapping with the portion of the first waveguide 21 extending along the up and down directions orthogonal to the magnetic field, and the second recess 32 is located at a position overlapping with the portion of the second waveguide 22 extending along the up and down directions orthogonal to the magnetic field.

[0122] exist Fig.11 as well as Fig.12In the illustrated configuration of the waveguide 20, the isolator 10 is also configured so that D1 and D2 are equal. As a result, the isolator 10 is also configured so as to transmit electromagnetic waves propagating in the first direction but not transmit electromagnetic waves propagating in the second direction.

[0123] exist Fig.11 as well as Fig.12 In the configuration of the waveguide 20 illustrated, the recess 30 may be configured to be divided into a plurality of parts. The isolator 10 is configured so that the sum of the effective lengths in the parts of the first recess 31 is equal to the sum of the effective lengths in the parts of the second recess 32. As a result, the isolator 10 is configured to allow electromagnetic waves propagating in the first direction to pass through and not allow electromagnetic waves propagating in the second direction to pass through.

[0124] <Laser irradiation device 70>

[0125] like Fig.13 As shown, the first waveguide 21 and the second waveguide 22 can be configured to be accommodated in a substantially circular laser irradiation area LS. In this way, the laser can be effectively used to heat the non-reciprocal member 40. The first waveguide 21 and the second waveguide 22 can also be configured to be a tortuous shape including a plurality of bends so that they are accommodated in the laser irradiation area LS. In other words, the waveguide 20 can be configured to change the extension direction in a plurality of parts. In addition, other components such as electronic circuits mounted on the substrate 50 can also be arranged outside the laser irradiation area LS. In this way, laser irradiation is less likely to affect other components.

[0126] exist Fig.13 , the isolator 10 has a plurality of first recesses 31 and a plurality of second recesses 32. The effective length of each of the plurality of first recesses 31 is represented by D11 and D12. The effective length of each of the plurality of second recesses 32 is represented by D21 and D22. The first recess 31 and the second recess 32 are configured so that the sum of D11 and D12 is equal to the sum of D21 and D22. As a result, the isolator 10 is configured to allow electromagnetic waves propagating in the first direction to pass through but not allow electromagnetic waves propagating in the second direction to pass through.

[0127] like Fig.14As shown, in the isolator 10 of the present embodiment, an irradiation device 70 can be used to irradiate laser light onto the non-reciprocal member 40. The irradiation device 70 includes: a laser source 72, a lens 74, and a stage 78. The stage 78 is configured to be able to mount the substrate 50. The laser source 72 emits a laser 76. The laser 76 is converged by the lens 74. The converged laser 76 is incident on the non-reciprocal member 40 on the substrate 50 mounted on the stage 78, and heats the non-reciprocal member 40. The range of irradiation of the laser 76 on the substrate 50 is represented by LS. The stage 78 is configured to be able to control the position of the substrate 50 along the XY plane. The irradiation device 70 controls the range of irradiation of the laser 76 on the substrate 50 by controlling the position of the substrate 50 on the stage 78 and controlling the emission of the laser 76 from the laser source 72.

[0128] The laser 76 may be a pulsed laser or a continuous oscillation laser (CW oscillation laser). When the laser 76 is a pulsed laser, a large amount of energy is applied to the non-reciprocal member 40 in a short time. In this way, the temperature of the non-reciprocal member 40 rises before the heat is dissipated to the substrate 50. As a result, the non-reciprocal member 40 is effectively heated. The conditions of the pulsed laser can be set, for example, as follows.

[0129] Wavelength: 532 nanometers (nm)

[0130] Scanning speed: 100 micrometers per second (μm / s) ~ 10 millimeters per second (mm / s)

[0131] Laser irradiation range (LS) diameter: 1 to 1000 microns (μm)

[0132] Average output power: 0.1~10 watts (W)

[0133] When the substrate 50 is heated in the atmosphere, the waveguide 20 or other electronic circuits included in the substrate 50 may be oxidized. In order to prevent the components included in the substrate 50 from being oxidized, the irradiation device 70 may further include a vacuum chamber that accommodates a mounting table 78 on which the substrate 50 is mounted. The laser source 72 or the lens 74 may be accommodated in the vacuum chamber or may be disposed outside the vacuum chamber. In the case where the laser source 72 or the lens 74 is disposed outside the vacuum chamber, the vacuum chamber may include a window through which the laser light 76 is transmitted.

[0134] <Size of Crystals of the Non-reciprocal Member 40>

[0135] like Fig.15As shown, crystallization of Ce:YIG used as the non-reciprocal member 40 can be observed. The range irradiated with the laser 76 to crystallize Ce:YIG is a roughly circular range indicated by LS. In the range indicated by LS, a crystallized portion 401 where Ce:YIG is crystallized is observed. On the other hand, a non-crystalline portion 402 where Ce:YIG is not crystallized is observed outside the range indicated by LS.

[0136] The size of each crystal in the crystallized portion 401 is measured and represented by, for example, G. Fig.15 In the figure, the size of the crystal in the portion indicated as G is about 10 μm. The size of a crystal can be measured as the maximum size or the minimum size of the crystal. The size of a crystal can be measured as the diameter of a circle that approximates the shape of the crystal.

[0137] The size of each crystal in the crystallized portion 401 has a distribution. The size of most of the crystals of Ce:YIG crystals crystallized by irradiation with the laser 76 by the irradiation device 70 described above is distributed between about 5 μm and about 20 μm. The size of the crystals as a whole of the crystallized portion 401 can be calculated as a statistical value such as the average, median, or maximum value of the size of each crystal included in the crystallized portion 401.

[0138] like Fig.16 As shown, the interval between the side surface 303 and the side surface 304 dividing the width direction of the recess 30 is represented by W. The size of the crystal after the non-reciprocal member 40 located in the recess 30 is crystallized is represented by G. The recess 30 can be configured so that the width (W) of the recess 30 is longer than the size (G) of the crystal. In other words, the first recess 31 can be configured so that the length of the first recess 31 in the width direction of the first waveguide 21 is longer than the crystal size of the first non-reciprocal member. The second recess 32 can be configured so that the length of the second recess 32 in the width direction of the second waveguide 22 is longer than the crystal size of the second non-reciprocal member.

[0139] When the width of the recess 30 is shorter than the size of the crystal, the non-reciprocal member 40 is easily affected by the side surface 303 or 304 of the recess 30 during crystallization. Due to the influence of the side surface 303 or 304, the crystallization of the non-reciprocal member 40 is sometimes hindered. On the other hand, when the width of the recess 30 is longer than the size of the crystal, the non-reciprocal member 40 is less likely to be affected by the side surface 303 or 304 of the recess 30 during crystallization. As a result, the crystallization of the non-reciprocal member 40 is promoted. By promoting the crystallization of the non-reciprocal member 40, the performance of the isolator 10 can be improved.

[0140] When Ce:YIG is formed in the recess 30, in order to form a film of Ce:YIG uniformly on the bottom surface 305 of the recess 30, the recess 30 may be configured so that the ratio of the opening width of the recess 30 at the same plane height as the surface of the insulating layer 54 and the depth of the recess 30 is greater than 1. Considering that the size distribution of Ce:YIG crystals is greater than about 5 μm, the recess 30 may also be configured so that the opening width of the recess 30 is greater than 5 μm.

[0141] <Adjustment by Heaters 61 and 62>

[0142] The phase of the electromagnetic wave propagating in the waveguide also changes according to the temperature of the waveguide. In order to adjust the phase of the electromagnetic wave, the isolator 10 can also control the temperature of the waveguide. Fig.17 As shown in FIG. 1 , the isolator 10 may further include heaters 61 and 62 for controlling the temperature of a portion of each of the first waveguide 21 and the second waveguide 22. The heater 61 can control the temperature of a portion of the first waveguide 21. The heater 62 can control the temperature of a portion of the first waveguide 21. In this way, even if an error occurs in the line length of the waveguide formed on the substrate 50, the isolator 10 can compensate for the phase by temperature control. As a result, the performance of the isolator 10 can be improved.

[0143] exist Fig.17 In the embodiment, the first waveguide 21 and the second waveguide 22 are bent 180 degrees in the portion where the heaters 61 and 62 are arranged. The curvature radii of the first waveguide 21 and the second waveguide 22 may be set so that the electromagnetic wave of the TM mode passing through the portion is not radiated.

[0144] <Filter>

[0145] In the isolator 10 of the present embodiment, the non-reciprocal waveguide that combines the waveguide 20 and the non-reciprocal member 40 exhibits non-reciprocity for the electromagnetic wave of the TM mode. Therefore, since there is a portion from which the electromagnetic wave of the TE mode is removed, it is possible to prevent the electromagnetic wave of the TE mode from propagating from the second branch portion 82 to the first branch portion 81. The portion from which the electromagnetic wave of the TE mode is removed is also collectively referred to as a filter portion. As the filter portion, a directional coupler that does not couple the electromagnetic wave of the TE mode may also be used.

[0146] (Method of Manufacturing Isolator 10)

[0147] Hereinafter, an example of the steps of the method for manufacturing the isolator 10 according to the present embodiment will be described.

[0148] The waveguide 20 is formed on the box layer 52 of the substrate 50. The waveguide 20 can be formed by a combination of a film forming process and an etching process. As the film forming process, plasma CVD (Chemical Vapor Deposition) or sputtering can be performed. As the etching process, dry etching or wet etching such as RIE (Reactive Ion Etching) can be performed.

[0149] An insulating layer 54 is formed on the waveguide 20. The insulating layer 54 can be formed by plasma CVD or the like. Furthermore, a recessed portion 30 is formed on the insulating layer 54. The recessed portion 30 can be formed by dry etching.

[0150] A non-reciprocal member 40 is formed on the bottom surface 305 of the recess 30. The non-reciprocal member 40 can be formed by sputtering or the like. Furthermore, the laser is irradiated to the non-reciprocal member 40. The non-reciprocal member 40 is heated by the irradiation of the laser. By controlling the temperature of the non-reciprocal member 40 and the heating time, the degree of crystallization of the non-reciprocal member 40 can be controlled.

[0151] By executing the manufacturing method including the above-described step example, it is possible to manufacture the isolator 10. By additionally irradiating the isolator 10 after the isolator 10 is manufactured, it is possible to adjust the characteristics of the isolator 10 even after the isolator 10 is manufactured.

[0152] (Application example of the isolator 10)

[0153] The isolator 10 can be used in combination with a structure for transmitting electromagnetic waves. The isolator 10 can also be applied to an optical switch, an optical transceiver, or a data center. The isolator 10 can also be applied to an electromagnetic wave transmitter, for example. The electromagnetic wave transmitter has an isolator 10 and a light source. The electromagnetic wave transmitter inputs electromagnetic waves from the light source to the isolator 10, and outputs electromagnetic waves from the isolator 10 to the 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 is difficult for electromagnetic waves to be incident on the light source. As a result, the light source can be protected.

[0154] The light source may be, for example, a semiconductor laser such as LD (Laser Diode) or VCSEL (Vertical Cavity Surface Emitting LASER). The light source is not limited to visible light, and may also include a device that emits electromagnetic waves of various wavelengths. The light source may be formed on the substrate 50 together with the isolator 10. The light source may input electromagnetic waves in the TM mode to the isolator 10.

[0155] The electromagnetic wave transmitter may also include a modulator and a signal input unit. The modulator modulates 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 receives input of a signal from an external device or the like. The signal input unit may, for example, include 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.

[0156] The light source may be configured to include a modulator and a signal input unit. In this case, the light source may output a modulated electromagnetic wave and input it to the isolator 10 .

[0157] The electromagnetic wave transmitter may be mounted on the substrate 50. The light source may be mounted in a manner connected to the first branch portion 81 via a modulator. The light source may also be mounted in a manner connected to the first branch portion 81 without a modulator. The receiver may be mounted in a manner connected to the second branch portion 82 without a modulator. The receiver may also be mounted in a manner connected to the second branch portion 82 via a modulator. In this case, the modulator may be mounted in a manner connected to the second branch portion 82.

[0158] In the embodiments of the present disclosure, although the description is based on the drawings and embodiments, it should be noted that those skilled in the art can make various deformations or changes according to the present disclosure. Therefore, it should be noted that these deformations or changes are included in the scope of the present disclosure. For example, the functions included in each component, etc. can be reconfigured in a logically non-contradictory manner, and multiple components, etc. can be combined into one or divided.

[0159] In the present disclosure, the descriptions of "first" and "second" etc. are identifiers for distinguishing the structures. The structures distinguished by the descriptions of "first" and "second" etc. in the present disclosure can exchange the numbers in the structures. For example, the first waveguide 21 can exchange "first" and "second" as identifiers with the second waveguide 22. The identifiers are exchanged at the same time. The structures can also be distinguished after the identifiers are exchanged. The identifiers can be deleted. The structures from which the identifiers are deleted are distinguished by the figure marks. The order of the structures and the existence of small numbered identifiers cannot be interpreted solely based on the descriptions of the identifiers of "first" and "second" etc. in the present disclosure.

[0160] In the present disclosure, the X-axis, Y-axis, and Z-axis are provided for the convenience of description and can be replaced with each other. The structure of the present disclosure is described using an orthogonal coordinate system consisting of the X-axis, Y-axis, and Z-axis. The positional relationship of each structure of the present disclosure is not limited to being in an orthogonal relationship.

[0161] In one embodiment, (1) an isolator comprises: a substrate having a substrate surface; a first waveguide and a second waveguide extending on the substrate surface and causing electromagnetic waves in a TM mode to propagate along the extending direction; an insulating layer located on the substrate surface and arranged to surround at least a portion of the first waveguide and the second waveguide; and a first non-reciprocal member and a second non-reciprocal member. The insulating layer has a surface above the upper surfaces of the first waveguide and the second waveguide and a first recess and a second recess. The first recess is divided by a bottom surface below the surface of the insulating layer and a side surface between the bottom surface and the surface of the insulating layer, and is located at a position overlapping with at least a portion of the first waveguide when the substrate surface is viewed from above. The second recess is divided by a bottom surface below the surface of the insulating layer and a side surface between the bottom surface and the surface of the insulating layer, and is located at a position overlapping with at least a portion of the second waveguide when the substrate surface is viewed from above. The first non-reciprocal member is located at the bottom surface of the first recess in a manner overlapping with at least a portion of the first waveguide when the substrate surface is viewed from above. The second non-reciprocal member is located on the bottom surface of the second recess so as to overlap with at least a portion of the second waveguide when the substrate surface is viewed from above. The propagation direction of the electromagnetic wave in the portion of the first waveguide that overlaps with the first non-reciprocal member when the substrate surface is viewed from above is different from the propagation direction of the electromagnetic wave in the portion of the second waveguide that overlaps with the second non-reciprocal member when the substrate surface is viewed from above.

[0162] (2) In the isolator described in (1) above, at least a portion of an upper surface of the first waveguide may be in contact with the first non-reciprocal member. At least a portion of an upper surface of the second waveguide may be in contact with the second non-reciprocal member.

[0163] (3) In the isolator described in (1) or (2) above, the position of the bottom surface of the first recess in the direction perpendicular to the substrate surface may be lower than the position of the upper surface of the first waveguide. The position of the bottom surface of the second recess in the direction perpendicular to the substrate surface may be lower than the position of the upper surface of the second waveguide.

[0164] (4) In the isolator described in (1) above, the insulating layer may be present between the upper surface of the first waveguide and the first non-reciprocal member. The insulating layer may be present between the upper surface of the second waveguide and the second non-reciprocal member.

[0165] (5) In the isolator described in (4) above, the thickness of the insulating layer located between the upper surface of the first waveguide and the first non-reciprocal component and the thickness of the insulating layer located between the upper surface of the second waveguide and the second non-reciprocal component can be less than or equal to a value determined based on the mode field diameters of the first waveguide and the second waveguide in a direction perpendicular to the substrate surface and the heights of the first waveguide and the second waveguide in a cross section.

[0166] (6) In the isolator described in any one of (1) to (5) above, the length of the first waveguide in the first recess in the width direction may be longer than the crystal size of the first non-reciprocal member. The length of the second waveguide in the second recess in the width direction may be longer than the crystal size of the second non-reciprocal member.

[0167] (7) In the isolator described in any one of (1) to (6) above, the first non-reciprocal member and the second non-reciprocal member may include YIG (yttrium iron garnet).

[0168] (8) In the isolator described in any one of (1) to (7) above, the side surface of the side surface dividing the first recessed portion, which is located at the end of the first waveguide in the extension direction, may be inclined relative to a vertical plane perpendicular to the extension direction of the first waveguide. The side surface of the side surface dividing the second recessed portion, which is located at the end of the second waveguide in the extension direction, may be inclined relative to a vertical plane perpendicular to the extension direction of the second waveguide.

[0169] (9) In the isolator described in any one of (1) to (8) above, the side surface of the side surface dividing the first recessed portion, which is located at the end in the direction in which the first waveguide extends, may be inclined toward the outside of the first recessed portion relative to the direction perpendicular to the substrate surface. The side surface of the side surface dividing the second recessed portion, which is located at the end in the direction in which the second waveguide extends, may be inclined toward the outside of the second recessed portion relative to the direction perpendicular to the substrate surface.

[0170] (10) In the isolator described in any one of (1) to (9) above, the first waveguide and the second waveguide may be located in a substantially circular range when the substrate surface is viewed in plan.

[0171] (11) In the isolator described in any one of (1) to (10) above, a distance over which the first waveguide overlaps with the first non-reciprocal member and a distance over which the second waveguide overlaps with the second non-reciprocal member may be equal.

[0172] (12) The isolator described in any one of (1) to (11) above may further include a heater for controlling the temperature of each of the first waveguide and the second waveguide.

[0173] In one embodiment, (13) an optical switch includes the isolator described in any one of (1) to (12) above.

[0174] In one embodiment, (14) an optical transceiver includes the isolator described in any one of (1) to (12) above and a light source optically connected to the isolator.

[0175] In one embodiment, (15) data centers communicate via a device having an isolator as described in any one of (1) to (12) above.

[0176] In one embodiment, (16) a method for manufacturing an isolator comprises forming a first waveguide and a second waveguide on a substrate for propagating electromagnetic waves in a TM mode, forming an insulating layer on the first waveguide and the second waveguide, etching the insulating layer to form a first recess overlapping at least a portion of the first waveguide and a second recess overlapping at least a portion of the second waveguide, so that the propagation direction of the electromagnetic wave in the portion of the first waveguide overlapping with the first recess is different from the propagation direction of the electromagnetic wave in the portion of the second waveguide overlapping with the second recess, forming a first non-reciprocal component on the bottom surface of the first recess, forming a second non-reciprocal component on the bottom surface of the second recess, and irradiating the first non-reciprocal component and the second non-reciprocal component with laser.

[0177] Description of reference numerals:

[0178] 10: Isolator

[0179] 20: waveguide (201: upper surface, 21: first waveguide, 22: second waveguide, 211, 212, 221, 222: folded portion)

[0180] 30: Recessed portion (301, 302, 303, 304: side surface, 305: bottom surface, 31: first recessed portion, 32: second recessed portion)

[0181] 40: Non-reciprocal components

[0182] 50: substrate (50A: substrate surface, 52: box layer, 54: insulation layer)

[0183] 61, 62: Heater

[0184] 70: irradiation device (72: light source, 74: lens, 76: laser, 78: mounting table)

[0185] 81: First Branch

[0186] 82: Second Branch

[0187] LS: Laser irradiation range

Claims

1. An isolator, wherein: have: A substrate having a substrate surface; The first waveguide and the second waveguide extend on the substrate surface and allow the TM mode electromagnetic wave to propagate along the extension direction; an insulating layer located on the substrate surface and arranged to surround at least a portion of the first waveguide and the second waveguide; and a first non-reciprocal member and a second non-reciprocal member; The insulating layer has a surface above the upper surfaces of the first waveguide and the second waveguide, and a first recess and a second recess; The first recess is defined by a bottom surface below the surface of the insulating layer and a side surface between the bottom surface and the surface of the insulating layer, and is located at a position overlapping with at least a portion of the first waveguide when the substrate surface is viewed from above; The second recess is defined by a bottom surface below the surface of the insulating layer and a side surface between the bottom surface and the surface of the insulating layer, and is located at a position overlapping with at least a portion of the second waveguide when the substrate surface is viewed from above; The first non-reciprocal member is located on the bottom surface of the first recessed portion so as to overlap with at least a portion of the first waveguide when the substrate surface is viewed from above; The second non-reciprocal member is located on the bottom surface of the second recessed portion so as to overlap with at least a portion of the second waveguide when the substrate surface is viewed from above; A propagation direction of electromagnetic waves in a portion of the first waveguide overlapping with the first non-reciprocal member when the substrate surface is viewed from above is different from a propagation direction of electromagnetic waves in a portion of the second waveguide overlapping with the second non-reciprocal member when the substrate surface is viewed from above.

2. The isolator according to claim 1, wherein: at least a portion of an upper surface of the first waveguide is in contact with the first non-reciprocal member, At least a portion of an upper surface of the second waveguide is in contact with the second non-reciprocal member.

3. The isolator according to claim 1, wherein: The position of the bottom surface of the first recess in the direction perpendicular to the substrate surface is lower than the position of the upper surface of the first waveguide, The position of the bottom surface of the second recessed portion in a direction perpendicular to the substrate surface is lower than the position of the upper surface of the second waveguide.

4. The isolator according to claim 1, wherein: The insulating layer exists between the upper surface of the first waveguide and the first non-reciprocal member, The insulating layer exists between the upper surface of the second waveguide and the second non-reciprocal member.

5. The isolator according to claim 4, wherein: The thickness of the insulating layer between the upper surface of the first waveguide and the first non-reciprocal member and the thickness of the insulating layer between the upper surface of the second waveguide and the second non-reciprocal member are not more than a value determined based on the mode field diameters of the first waveguide and the second waveguide in a direction perpendicular to the substrate surface and the heights in the cross section of the first waveguide and the second waveguide.

6. The isolator according to any one of claims 1 to 5, wherein: The length of the first waveguide of the first recess in the width direction is longer than the crystal size of the first non-reciprocal member. The length of the second waveguide of the second recess in the width direction is longer than the crystal size of the second non-reciprocal member.

7. The isolator according to any one of claims 1 to 5, wherein: The first non-reciprocal member and the second non-reciprocal member include YIG (yttrium iron garnet).

8. The isolator according to any one of claims 1 to 5, wherein: A side surface that defines the first recess and is located at an end of the first waveguide in the extending direction is inclined relative to a vertical plane that is perpendicular to the extending direction of the first waveguide. Among the side surfaces defining the second recess, a side surface located at an end portion in the extending direction of the second waveguide is inclined with respect to a vertical plane perpendicular to the extending direction of the second waveguide.

9. The isolator according to any one of claims 1 to 5, wherein: A side surface that defines the first recess and is located at an end in the extending direction of the first waveguide is inclined toward the outside of the first recess relative to a direction perpendicular to the substrate surface. Among the side surfaces defining the second recess, the side surfaces located at the ends in the extending direction of the second waveguide are inclined toward the outside of the second recess with respect to the direction perpendicular to the substrate surface.

10. The isolator according to any one of claims 1 to 5, wherein: The first waveguide and the second waveguide are located in a substantially circular range when the substrate surface is viewed from above.

11. The isolator according to any one of claims 1 to 5, wherein: The distance that the first waveguide overlaps with the first non-reciprocal member is equal to the distance that the second waveguide overlaps with the second non-reciprocal member.

12. The isolator according to any one of claims 1 to 5, wherein: The invention further includes a heater for controlling the temperature of each of the first waveguide and the second waveguide.

13. An optical switch, wherein: A separator according to any one of claims 1 to 5.

14. An optical transceiver, wherein: The invention comprises the isolator according to any one of claims 1 to 5, and a light source optically connected to the isolator.

15. A data center, wherein: Communication is performed by a device having the isolator according to any one of claims 1 to 5.

16. A method for manufacturing an isolator, wherein: A first waveguide and a second waveguide are formed on the substrate to propagate electromagnetic waves in the TM mode. forming an insulating layer on the first waveguide and the second waveguide, The insulating layer is etched to form a first recessed portion overlapping at least a portion of the first waveguide and a second recessed portion overlapping at least a portion of the second waveguide, so that a propagation direction of an electromagnetic wave in a portion of the first waveguide overlapping with the first recessed portion is different from a propagation direction of an electromagnetic wave in a portion of the second waveguide overlapping with the second recessed portion. A first non-reciprocal member is formed on the bottom surface of the first recess, A second non-reciprocal member is formed on the bottom surface of the second recess, The first non-reciprocal member and the second non-reciprocal member are irradiated with laser light.

Images