Optical device, receiving apparatus, transmitting / receiving apparatus, communication system, terminal apparatus, and optical system

Abstract

To provide a highly sensitive optical device, a receiving apparatus, a transmitting / receiving apparatus, a communication system, a terminal apparatus, and an optical system.SOLUTION: An optical device according to the present invention includes a waveguide, a magnetic element, a first reflector, and a second reflector. The waveguide has a core through which light propagates and a cladding that covers the core. The first reflector is located forward in the direction of travelling of light propagating within the core. The second reflector is positioned so that light reflected by the first reflector can be radiated onto the magnetic element. The magnetic element includes a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer located between the first ferromagnetic layer and the second ferromagnetic layer. The magnetic element is irradiated with light from its side or from above.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical device, a receiving apparatus, a transmitting / receiving apparatus, a communication system, a terminal apparatus, and an optical system. [Background technology]

[0002] Photoelectric conversion elements are used for a variety of purposes.

[0003] For example, Patent Document 1 describes a receiving device that receives an optical signal using a photodiode. The photodiode is, for example, a pn junction diode that uses a semiconductor pn junction, and converts light into an electrical signal.

[0004] Furthermore, for example, a novel optical device using a magnetic element is disclosed in Patent Document 2. When the magnetic element is irradiated with light, the magnetic state changes, and the resistance value also changes. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-292107 [Patent Document 2] Japanese Patent Publication No. 2022-155468 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 2 discloses using a reflector to irradiate light from below the magnetic element, but in this case, the sensitivity of the optical device may not be sufficient.

[0007] The present invention has been made in view of the above problems, and has an object to provide a highly sensitive optical device, a receiving apparatus, a transmitting / receiving apparatus, a communication system, a terminal device, and an optical system. [Means for solving the problem]

[0008] In order to solve the above problems, the following means are provided.

[0009] The optical device according to this embodiment includes a waveguide, a magnetic element, a first reflector, and a second reflector. The waveguide has a core through which light propagates and a cladding that covers the core. The first reflector is located forward in the direction of propagation of light propagating within the core. The second reflector is positioned so that light reflected by the first reflector can be irradiated onto the magnetic element. The magnetic element includes a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer located between the first ferromagnetic layer and the second ferromagnetic layer. Light is irradiated onto the magnetic element from the side or from above. [Effects of the Invention]

[0010] The optical device, receiving apparatus, transmitting / receiving apparatus, communication system, terminal device, and optical system according to the above aspects have high sensitivity. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a perspective view of an optical device according to a first embodiment. [Figure 2] 1 is a cross-sectional view of an optical device according to a first embodiment. [Figure 3] FIG. 1 is a plan view of an optical device according to a first embodiment. [Figure 4] 2 is a cross-sectional view of the magnetic element and its vicinity in the optical device according to the first embodiment. FIG. [Figure 5] 5A to 5C are diagrams for explaining an example of operation of the magnetic element according to the first embodiment. [Figure 6] 5A to 5C are diagrams for explaining an example of operation of the magnetic element according to the first embodiment. [Figure 7] FIG. 10 is a cross-sectional view of an optical device according to a first modified example. [Figure 8] FIG. 10 is a cross-sectional view of an optical device according to a second modified example. [Figure 9]FIG. 11 is a cross-sectional view showing a first example of a connection state of a magnetic element in an optical device according to a third modified example. [Figure 10] FIG. 11 is a cross-sectional view showing a second example of the connection state of the magnetic element in the optical device according to the third modified example. [Figure 11] FIG. 1 is a schematic diagram of an optical element according to a first application example. [Figure 12] FIG. 1 is a conceptual diagram of an optical system using an optical element according to a first application example. [Figure 13] FIG. 10 is a schematic diagram of a transmitting / receiving device according to a second application example. [Figure 14] FIG. 1 is a conceptual diagram of an example of a communication system. [Figure 15] FIG. 1 is a conceptual diagram of another example of a communication system. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, the embodiments will be described in detail with reference to the drawings as appropriate. The drawings used in the following description may show characteristic portions enlarged for convenience in order to make the features easier to understand, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate changes can be made within the scope of the effects of the present invention.

[0013] The directions are defined as follows. The X direction is one direction within the plane of the surface on which the substrate extends, and the Y direction is the direction perpendicular to the X direction within the plane. For example, the X direction is the direction in which the core 11 extends near the output end of the core 11. The Z direction is the direction perpendicular to the substrate. The Z direction is an example of the stacking direction of the magnetic element 20. Hereinafter, the +Z direction may be expressed as "up" and the -Z direction as "down". The +Z direction is the direction from the core to the magnetic element. Up and down do not necessarily coincide with the direction in which gravity is applied.

[0014] "First embodiment" FIG. 1 is a perspective view of an optical device 100 according to the first embodiment. FIG. 2 is a cross-sectional view of the optical device 100 according to the first embodiment. FIG. 2 is an XZ cross section passing through the center of the core 11 in the Y direction. FIG. 3 is a plan view of the optical device 100 according to the first embodiment. The cladding 12 and the substrate 50 are omitted in FIGS. 1 and 3.

[0015] The optical device 100 includes, for example, a waveguide 10, a magnetic element 20, a terminal unit 30, a first reflector 41, a second reflector 42, and a substrate 50.

[0016] The waveguide 10, the magnetic element 20, the terminal unit 30, the first reflector 41, and the second reflector 42 are formed on a substrate 50. The substrate 50 is, for example, a semiconductor substrate, aluminum oxide, sapphire, or the like.

[0017] The waveguide 10 is a structure that forms a path along which light propagates. In this specification, light is not limited to visible light but also includes infrared light, which has a longer wavelength than visible light, and ultraviolet light, which has a shorter wavelength than visible light. The wavelength of visible light is, for example, 380 nm or more and less than 800 nm. The wavelength of infrared light is, for example, 800 nm or more and 1 mm or less. The wavelength of ultraviolet light is, for example, 200 nm or more and less than 380 nm. The light propagating through the waveguide 10 is, for example, laser light.

[0018] The waveguide 10 has, for example, a core 11 and a clad 12. The waveguide 10 totally reflects light due to the difference in refractive index between the core 11 and the clad 12. The light propagates within the core 11. A first end of the core 11 is irradiated with light from, for example, a laser diode. A second end of the core 11 faces a first reflector 41. The clad 12 covers the periphery of the core 11.

[0019] The core 11 contains, for example, lithium niobate as a main component. Some elements of the lithium niobate may be substituted with other elements. The clad 12 is, for example, SiO2, Al2O3, MgF2, La2O3, ZnO, HfO2, MgO, Y2O3, CaF2, In2O3, etc., or a mixture thereof. The materials of the core 11 and the clad 12 are not limited to this example. For example, the core 11 may be silicon or silicon oxide doped with germanium oxide, and the clad 12 may be silicon oxide. Alternatively, for example, the core 11 may be tantalum oxide (Ta2O5), and the clad 12 may be silicon oxide or aluminum oxide.

[0020] The magnetic element 20 is located within the clad 12. The magnetic element 20 may be located in the same layer as the core 11 in the Z direction, or in a different layer. The magnetic element 20 is located at a position where light that has propagated through the core 11 and been reflected by the second reflector 42 is irradiated onto the magnetic element 20 from the side or above. The magnetic element 20 is located, for example, in front of the first reflector 41 and the second reflector 42 in the traveling direction (for example, the X direction) of the light L propagating through the core 11.

[0021] The magnetic element 20 converts the state or change in state of the irradiated light into an electrical signal. The magnetic element 20 is irradiated with light having a wavelength of, for example, 400 nm or more and 1500 nm or less.

[0022] The magnetic element 20 generates a voltage when irradiated with light. When the state of the irradiated light changes, the resistance value of the magnetic element 20 in the z direction changes in response to the change in the state of the light. When the state of the light irradiated to the magnetic element 20 changes, the output voltage from the magnetic element 20 changes in response to the change in the state of the light.

[0023] 4 is a cross-sectional view of the vicinity of the magnetic element 20 of the optical device 100 according to the first embodiment. The magnetic element 20 has a stacked body 21, a first electrode 22, and a second electrode .

[0024] The first electrode 22 is located on the substrate 50 side of the laminate 21. The first electrode 22 is conductive. The first electrode 22 is made of a metal such as Cu, Al, Au, Ta, or Ti. Ta or Ti may be laminated above and below these metals. The first electrode 22 may be a laminated film of Cu and Ta, a laminated film of Ta, Cu, and Ti, or a laminated film of Ta, Cu, and TaN. The first electrode 22 may also be TiN or TaN. When the first electrode 22 contains these materials, the crystallinity of the laminate 21 is increased. The crystallinity of the laminate 21 contributes to the resistance change width of the laminate 21 in the Z direction, and therefore affects the sensitivity of the optical device 100.

[0025] The first electrode 22 is preferably a metal containing at least one element selected from the group consisting of ruthenium, molybdenum, and tungsten. The first electrode 22 may be a single layer film of ruthenium, molybdenum, or tungsten, or a laminated film having at least one layer of ruthenium, molybdenum, or tungsten. Ruthenium, molybdenum, and tungsten have high melting points (2000°C or higher) and are excellent in heat resistance. The first electrode 22 containing these elements is less likely to deteriorate even when subjected to heat treatment for crystallizing the laminate 21 or heat treatment in a semiconductor process.

[0026] The second electrode 23 faces the first electrode 22. The first electrode 22 and the second electrode 23 sandwich the stack 21 in the Z direction. The second electrode 23 is made of a conductive material. The second electrode 23 is made of a metal such as Cu, Al, or Au. The second electrode 23 may be made by stacking Ta or Ti above and below these metals. The second electrode 23 may also be made of a stacked film of Cu and Ta, a stacked film of Ta, Cu, and Ti, or a stacked film of Ta, Cu, and TaN. The second electrode 23 may also be made of TiN or TaN. When both the first electrode 22 and the second electrode 23 are not transparent to light in the used wavelength band, light is irradiated from the side of the magnetic element 20.

[0027] Furthermore, the second electrode 23 is preferably a transparent electrode that is transparent to light in the wavelength band used. The second electrode 23 preferably transmits, for example, 80% or more of the light in the wavelength band used. The second electrode 23 is, for example, an oxide such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), or indium gallium zinc oxide (IGZO). The second electrode 23 may be a metal film with a film thickness of approximately 3 nm to 10 nm. When the second electrode 23 is a transparent electrode, light can be irradiated onto the laminate 21 from above, allowing the laminate 21 to be efficiently irradiated with light.

[0028] The stack 21 is sandwiched between a first electrode 22 and a second electrode 23. The stack 21 includes, for example, a first ferromagnetic layer 1, a second ferromagnetic layer 2, and a spacer layer 3. The spacer layer 3 is located between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. The stack 21 may include other layers in addition to these. The stack 21 may include, for example, a buffer layer 4, a seed layer 5, a third ferromagnetic layer 6, a magnetic coupling layer 7, a perpendicular magnetization induction layer 8, and a cap layer 9.

[0029] The magnetic element 20 is a magnetic element including a ferromagnetic material. For example, when the spacer layer 3 is made of an insulator, the magnetic element 20 has a magnetic tunnel junction (MTJ) consisting of the first ferromagnetic layer 1, the spacer layer 3, and the second ferromagnetic layer 2. Such an element is called an MTJ element. In this case, the magnetic element 20 can exhibit a tunnel magnetoresistance (TMR) effect. When the spacer layer 3 is made of a metal, the magnetic element 20 can exhibit a giant magnetoresistance (GMR) effect. Such an element is called a GMR element. The magnetic element 20 may be called an MTJ element, a GMR element, or other names depending on the material of the spacer layer 3, but is also collectively called a magnetoresistance effect element. The resistance value in the z direction of the magnetic element 20 (resistance value when a current flows in the z direction) changes depending on the relative change between the magnetization state of the first ferromagnetic layer 1 and the magnetization state of the second ferromagnetic layer 2.

[0030] The first ferromagnetic layer 1 is a light detection layer whose magnetization state changes when irradiated with external light. The first ferromagnetic layer 1 is also called a magnetization free layer. The magnetization free layer is a layer containing a magnetic material whose magnetization state changes when a predetermined external energy is applied. The predetermined external energy is, for example, light irradiated from outside, a current flowing in the z direction of the magnetic element 20, or an external magnetic field. The magnetization state of the first ferromagnetic layer 1 changes depending on the intensity of the light irradiated to the first ferromagnetic layer 1 (light irradiated to the magnetic element 20).

[0031] The first ferromagnetic layer 1 includes a ferromagnetic material. The first ferromagnetic layer 1 includes at least one of magnetic elements such as Co, Fe, or Ni. The first ferromagnetic layer 1 may include elements such as B, Mg, Hf, or Gd in addition to the magnetic elements described above. The first ferromagnetic layer 1 may be, for example, an alloy including a magnetic element and a non-magnetic element. The first ferromagnetic layer 1 may be composed of multiple layers. The first ferromagnetic layer 1 may be, for example, a CoFeB alloy, a stacked body in which a CoFeB alloy layer is sandwiched between Fe layers, or a stacked body in which a CoFeB alloy layer is sandwiched between CoFe layers. Generally, "ferromagnetic" includes "ferrimagnetic." The first ferromagnetic layer 1 may exhibit ferrimagnetic properties. On the other hand, the first ferromagnetic layer 1 may exhibit ferromagnetic properties that are not ferrimagnetic. For example, a CoFeB alloy exhibits ferromagnetic properties that are not ferrimagnetic.

[0032] The first ferromagnetic layer 1 may be an in-plane magnetization film having an axis of easy magnetization in the in-plane direction (any direction in the xy plane) or a perpendicular magnetization film having an axis of easy magnetization in the direction perpendicular to the film plane (z direction).

[0033] The thickness of the first ferromagnetic layer 1 is, for example, 1 nm or more and 5 nm or less. The thickness of the first ferromagnetic layer 1 is preferably, for example, 1 nm or more and 2 nm or less. When the first ferromagnetic layer 1 is a perpendicular magnetization film, if the thickness of the first ferromagnetic layer 1 is thin, the effect of perpendicular magnetic anisotropy applied from the layers above and below the first ferromagnetic layer 1 is strengthened, and the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 is increased. In other words, if the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 is high, the force that causes the magnetization M1 to return to the z-direction is strengthened. On the other hand, if the thickness of the first ferromagnetic layer 1 is thick, the effect of perpendicular magnetic anisotropy applied from the layers above and below the first ferromagnetic layer 1 is relatively weakened, and the perpendicular magnetic anisotropy of the first ferromagnetic layer 1 is weakened.

[0034] As the thickness of the first ferromagnetic layer 1 decreases, its volume as a ferromagnetic material decreases, and as it increases, its volume as a ferromagnetic material increases. The responsiveness of the magnetization of the first ferromagnetic layer 1 when external energy is applied is inversely proportional to the product (KuV) of the magnetic anisotropy (Ku) and volume (V) of the first ferromagnetic layer 1. In other words, as the product of the magnetic anisotropy and volume of the first ferromagnetic layer 1 decreases, its responsiveness to light increases. From this perspective, in order to enhance its responsiveness to light, it is preferable to reduce the volume of the first ferromagnetic layer 1 after appropriately designing the magnetic anisotropy of the first ferromagnetic layer 1.

[0035] If the thickness of the first ferromagnetic layer 1 is greater than 2 nm, an insertion layer made of, for example, Mo or W may be provided within the first ferromagnetic layer 1. That is, the first ferromagnetic layer 1 may be a stack in which a ferromagnetic layer, an insertion layer, and a ferromagnetic layer are stacked in this order in the z direction. The interfacial magnetic anisotropy at the interface between the insertion layer and the ferromagnetic layer enhances the perpendicular magnetic anisotropy of the entire first ferromagnetic layer 1. The thickness of the insertion layer is, for example, 0.1 nm to 1.0 nm.

[0036] The second ferromagnetic layer 2 is a magnetization fixed layer. The magnetization fixed layer is a layer made of a magnetic material in which the state of magnetization M2 is less likely to change than the magnetization free layer when a predetermined external energy is applied. For example, the magnetization direction of the magnetization fixed layer is less likely to change than the magnetization free layer when a predetermined external energy is applied. Also, for example, the magnitude of the magnetization of the magnetization fixed layer is less likely to change than the magnetization free layer when a predetermined external energy is applied. The coercive force of the second ferromagnetic layer 2 is, for example, greater than the coercive force of the first ferromagnetic layer 1. The second ferromagnetic layer 2 has an easy axis of magnetization in the same direction as the first ferromagnetic layer 1, for example. The second ferromagnetic layer 2 may be an in-plane magnetization film or a perpendicular magnetization film.

[0037] The material constituting the second ferromagnetic layer 2 is, for example, the same as that of the first ferromagnetic layer 1. The second ferromagnetic layer 2 may be, for example, a multilayer film in which Co layers having a thickness of 0.4 nm to 1.0 nm and Pt layers having a thickness of 0.4 nm to 1.0 nm are alternately stacked several times. The second ferromagnetic layer 2 may be, for example, a laminate in which Co layers having a thickness of 0.4 nm to 1.0 nm, Mo layers having a thickness of 0.1 nm to 0.5 nm, a CoFeB alloy layers having a thickness of 0.3 nm to 1.0 nm, and Fe layers having a thickness of 0.3 nm to 1.0 nm are stacked in this order.

[0038] The magnetization M2 of the second ferromagnetic layer 2 may be magnetically coupled to M6 of the third ferromagnetic layer 6, for example, sandwiching the magnetic coupling layer 7. In this case, the combination of the second ferromagnetic layer 2, the magnetic coupling layer 7, and the third ferromagnetic layer 6 may be referred to as a magnetization fixed layer. Details of the magnetic coupling layer 7 and the third ferromagnetic layer 6 will be described later.

[0039] Figure 4 shows a bottom pin structure in which the second ferromagnetic layer 2, which is the magnetization fixed layer, is closer to the substrate 50 than the first ferromagnetic layer 1, but it may also have a top pin structure in which the second ferromagnetic layer 2, which is the magnetization fixed layer, is farther from the substrate 50 than the first ferromagnetic layer 1.

[0040] The spacer layer 3 is a layer disposed between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. The spacer layer 3 is a layer made of a conductor, an insulator, or a semiconductor, or a layer containing current-carrying points made of a conductor in an insulator. The spacer layer 3 is, for example, a non-magnetic layer. The thickness of the spacer layer 3 can be adjusted depending on the orientation directions of the magnetizations of the first ferromagnetic layer 1 and the second ferromagnetic layer 2 in the initial state, which will be described later.

[0041] When the spacer layer 3 is made of an insulating material, a material containing aluminum oxide, magnesium oxide, titanium oxide, silicon oxide, or the like can be used as the material for the spacer layer 3. These insulating materials may also contain elements such as Al, B, Si, and Mg, or magnetic elements such as Co, Fe, and Ni. A high magnetoresistance ratio can be obtained by adjusting the thickness of the spacer layer 3 so that a high TMR effect is exhibited between the first ferromagnetic layer 1 and the second ferromagnetic layer 2. To efficiently utilize the TMR effect, the thickness of the spacer layer 3 may be approximately 0.5 to 5.0 nm, or approximately 1.0 to 2.5 nm.

[0042] When the spacer layer 3 is made of a nonmagnetic conductive material, conductive materials such as Cu, Ag, Au, or Ru can be used. To efficiently utilize the GMR effect, the thickness of the spacer layer 3 may be about 0.5 to 5.0 nm, or about 2.0 to 3.0 nm.

[0043] When the spacer layer 3 is made of a non-magnetic semiconductor material, it can be made of zinc oxide, indium oxide, tin oxide, germanium oxide, gallium oxide, ITO, etc. In this case, the thickness of the spacer layer 3 may be about 1.0 to 4.0 nm.

[0044] When a layer including current-carrying points formed by a conductor in a nonmagnetic insulator is used as the spacer layer 3, the current-carrying points may be formed by a nonmagnetic conductor such as Cu, Au, or Al in a nonmagnetic insulator made of aluminum oxide or magnesium oxide. The conductor may also be made of a magnetic element such as Co, Fe, or Ni. In this case, the thickness of the spacer layer 3 may be approximately 1.0 to 2.5 nm. The current-carrying points are, for example, columnar bodies with a diameter of 1 nm to 5 nm when viewed perpendicular to the film surface.

[0045] The third ferromagnetic layer 6 is magnetically coupled to, for example, the second ferromagnetic layer 2. The magnetic coupling is, for example, antiferromagnetic coupling, and occurs due to RKKY interaction. The material constituting the third ferromagnetic layer 6 is, for example, the same as that of the first ferromagnetic layer 1.

[0046] The magnetic coupling layer 7 is located between the second ferromagnetic layer 2 and the third ferromagnetic layer 6. The magnetic coupling layer 7 is made of, for example, Ru, Ir, or the like.

[0047] The buffer layer 4 is a layer that alleviates lattice mismatch between different crystals. The buffer layer 4 is, for example, a metal containing at least one element selected from the group consisting of Ta, Ti, Zr, and Cr, or a nitride containing at least one element selected from the group consisting of Ta, Ti, Zr, and Cu. More specifically, the buffer layer 4 is, for example, Ta (element), a NiCr alloy, TaN (tantalum nitride), or CuN (copper nitride). The buffer layer 4 has a thickness of, for example, 1 nm or more and 5 nm or less. The buffer layer 4 is, for example, amorphous. The buffer layer 4 is, for example, located between the seed layer 5 and the second electrode 23 and in contact with the second electrode 23. The buffer layer 4 prevents the crystal structure of the second electrode 23 from affecting the crystal structure of the magnetic element 20.

[0048] The seed layer 5 improves the crystallinity of layers stacked on the seed layer 5. The seed layer 5 is located, for example, between the buffer layer 4 and the third ferromagnetic layer 6 and on the buffer layer 4. The seed layer 5 is made of, for example, Pt, Ru, Zr, or NiFeCr. The thickness of the seed layer 5 is, for example, 1 nm or more and 5 nm or less.

[0049] The cap layer 9 is located between the first ferromagnetic layer 1 and the first electrode 22. The cap layer 9 may include a perpendicular magnetization induction layer 8 stacked on the first ferromagnetic layer 1 and in contact with the first ferromagnetic layer 1. The cap layer 9 prevents damage to the lower layers during the process and improves the crystallinity of the lower layers during annealing.

[0050] The perpendicular magnetization induction layer 8 induces perpendicular magnetic anisotropy in the first ferromagnetic layer 1. The perpendicular magnetization induction layer 8 is made of, for example, magnesium oxide, W, Ta, or Mo. When the perpendicular magnetization induction layer 8 is made of magnesium oxide, it is preferable that the magnesium oxide has oxygen deficiency to increase conductivity. The film thickness of the perpendicular magnetization induction layer 8 is, for example, 0.5 nm or more and 5.0 nm or less.

[0051] The terminal unit 30 includes, for example, a first terminal 31, a second terminal 32, a third terminal 33, a fourth terminal 34, and a plurality of via wirings 35. The first terminal 31, the second terminal 32, the third terminal 33, and the fourth terminal 34 are exposed on the clad 12. The first terminal 31 and the fourth terminal 34 are each electrically connected to the first electrode 22 through the via wiring 35. The second terminal 32 and the third terminal 33 are each electrically connected to the second electrode 23 through the via wiring 35. A current or voltage is input to the first terminal 31, and the second terminal 32 is connected to a reference potential. A signal is output from the third terminal 33, and the fourth terminal 34 is connected to a reference potential. The first terminal 31, the second terminal 32, the third terminal 33, the fourth terminal 34, and the plurality of via wirings 35 include a conductive material.

[0052] The first reflector 41 and the second reflector 42 reflect the light output from the core 11. The first reflector 41 and the second reflector 42 are, for example, reflecting mirrors. The first reflector 41 and the second reflector 42 are, for example, located within the clad 12.

[0053] Light output from the core 11 is reflected by the first reflector 41 and the second reflector 42 in this order, and is then irradiated onto the magnetic element 20. It is preferable that light be irradiated onto the magnetic element 20 from a direction tilted at an angle of 45° or more with respect to the top surface of the magnetic element 20. In other words, it is preferable that the angle of irradiation of light onto the magnetic element 20 is a direction tilted at an angle of 45° or more with respect to the XY plane. When the second electrode 23 is a transparent electrode, the efficiency of light irradiation onto the laminate 21 can be increased by satisfying the above conditions.

[0054] The first reflector 41 is located forward in the direction of travel of light propagating through the core 11 (for example, the X direction). The height position of the first reflector 41 in the Z direction is the same as the height position of the core 11, or is higher than the core 11. When viewed from the X direction, a part of the reflecting surface of the first reflector 41 is located so as to overlap with the core 11. The height positions of the magnetic element 20 and the first reflector 41 in the Z direction may be the same, or the magnetic element 20 may be higher.

[0055] The reflecting surface 41A of the first reflector 41 is located opposite the light output end of the core 11. The reflecting surface 41A is inclined in the +X direction with respect to the YZ plane. The light output from the core 11 is reflected by the reflecting surface 41A of the first reflector 41 and bent in the Z direction. The light reflected by the first reflector 41 only needs to have a Z-directional component, and is not limited to light that travels in the Z direction.

[0056] The second reflector 42 is located in a position where it can reflect the light reflected by the first reflector 41 and irradiate the light reflected by the second reflector 42 onto the magnetic element 20. When viewed from the Z direction, the second reflector 42 may be located in a position overlapping with the first reflector 41, or may be located in the +X direction from the first reflector 41. The height position of the second reflector 42 in the Z direction is, for example, higher than the magnetic element 20.

[0057] The reflecting surface 42A of the second reflector 42 is inclined with respect to the YZ plane. Although an example in which the reflecting surface 42A is inclined in the +X direction with respect to the YZ plane is shown in Fig. 2, the reflecting surface 42A may be inclined in the -X direction with respect to the YZ plane depending on the position of the magnetic element 20. In this case, the magnetic element 20 is disposed on the core 11, and the width of the optical device 100 in the X direction can be reduced.

[0058] Next, we will explain the operation of the optical device 100. The output voltage from the optical device 100 changes with changes in the intensity of light irradiated onto the magnetic element 20. The output voltage from the optical device 100 changes as the resistance value of the magnetic element 20 in the Z direction changes.

[0059] The magnetic element 20 is irradiated with light L propagating through the waveguide 10. The light L propagates in the X direction within the waveguide 10, is reflected by the first reflector 41 and the second reflector 42, and is then irradiated with the magnetic element 20.

[0060] For example, when the intensity of light irradiated to the magnetic element 20 changes from a first intensity to a second intensity, the resistance value of the magnetic element 20 in the Z direction changes. The first intensity may be when the intensity of light irradiated to the magnetic element 20 is zero. When the resistance value of the magnetic element 20 in the Z direction changes, the output voltage from the magnetic element 20 changes.

[0061] 5 and 6 are diagrams illustrating an example of operation of the magnetic element 20 according to the first embodiment. FIG. 5 is a diagram illustrating a first mechanism of the example of operation, and FIG. 6 is a diagram illustrating a second mechanism of the example of operation. In the upper graphs of FIGS. 5 and 6, the vertical axis represents the intensity of light irradiated to the first ferromagnetic layer 1, and the horizontal axis represents time. In the lower graphs of FIGS. 5 and 6, the vertical axis represents the resistance value of the magnetic element 20 in the Z direction, and the horizontal axis represents time.

[0062] First, in a state where the first ferromagnetic layer 1 is irradiated with light of a first intensity W1 (hereinafter referred to as the initial state), the magnetization M1 of the first ferromagnetic layer 1 and the magnetization M2 of the second ferromagnetic layer 2 are antiparallel to each other, and the resistance value in the Z direction of the magnetic element 20 exhibits a second resistance value R2. Here, the case where the intensity of the light irradiated to the first ferromagnetic layer 1 is zero may be considered to be the state where light of the first intensity W1 is irradiated.

[0063] By passing a sense current Is in the Z direction of the magnetic element 20, a voltage is generated across both ends of the magnetic element 20 in the Z direction. An output voltage from the magnetic element 20 is generated between the first electrode 22 and the second electrode .

[0064] 5, it is preferable to flow the sense current Is from the second ferromagnetic layer 2 toward the first ferromagnetic layer 1. By flowing the sense current Is in this direction, a spin transfer torque acts on the magnetization M1 of the first ferromagnetic layer 1 in the opposite direction to the magnetization M2 of the second ferromagnetic layer 2, and the magnetizations M1 and M2 tend to be antiparallel to each other in the initial state.

[0065] Next, the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the first intensity W1 to the second intensity W2. For example, when a light pulse is irradiated to the magnetic element 20, the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the first intensity W1 to the second intensity W2. The light at the second intensity W2 is stronger than the light at the first intensity W1.

[0066] The second intensity W2 is greater than the first intensity W1, and the magnetization M1 of the first ferromagnetic layer 1 changes from its initial state. The state of the magnetization M1 of the first ferromagnetic layer 1 when no light is irradiated onto the first ferromagnetic layer 1 is different from the state of the magnetization M1 of the first ferromagnetic layer 1 when irradiated with light of the second intensity W2. The state of the magnetization M1 refers to, for example, the tilt angle or magnitude with respect to the Z direction.

[0067] For example, as shown in Fig. 5, when the intensity of light irradiated to the first ferromagnetic layer 1 changes from a first intensity W1 to a second intensity W2, the magnetization M1 tilts with respect to the Z direction. Also, for example, as shown in Fig. 6, when the intensity of light irradiated to the first ferromagnetic layer 1 changes from the first intensity W1 to a second intensity W2, the magnitude of the magnetization M1 decreases. For example, when the magnetization M1 of the first ferromagnetic layer 1 tilts with respect to the Z direction due to the irradiation intensity of light, the tilt angle is, for example, greater than 0° and smaller than 90°.

[0068] When the magnetization M1 of the first ferromagnetic layer 1 changes from its initial state due to irradiation of the magnetic element 20 with an optical pulse, the resistance value of the magnetic element 20 in the Z direction exhibits a first resistance value R1, and the magnitude of the output voltage from the magnetic element 20 changes from a first value to a second value. As a result, the output from the optical device 100 changes. The first resistance value R1 is smaller than the second resistance value R2. The second value is smaller than the first value. The first resistance value R1 is between the resistance value (second resistance value R2) when the magnetization M1 and the magnetization M2 are antiparallel and the resistance value when the magnetization M1 and the magnetization M2 are parallel.

[0069] In the case shown in FIG. 5, a spin transfer torque acts on the magnetization M1 of the first ferromagnetic layer 1 in the opposite direction to the magnetization M2 of the second ferromagnetic layer 2. Therefore, the magnetization M1 attempts to return to an antiparallel state with respect to the magnetization M2. When the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the second intensity to the first intensity, the magnetization M1 returns to an antiparallel state with respect to the magnetization M2. In the case shown in FIG. 6, when the intensity of the light irradiated to the first ferromagnetic layer 1 returns to the first intensity W1, the magnitude of the magnetization M1 of the first ferromagnetic layer 1 returns to its original value, and the magnetic element 20 returns to its initial state. In either case, the resistance value in the Z direction of the magnetic element 20 returns to the second resistance value R2. In other words, when the intensity of the light irradiated to the first ferromagnetic layer 1 changes from the second intensity W2 to the first intensity W1, the resistance value in the Z direction of the magnetic element 20 changes from the first resistance value R1 to the second resistance value R2.

[0070] The output voltage from the optical device 100 changes in response to changes in the intensity of light irradiated onto the magnetic element 20, and can convert changes in the intensity of the irradiated light into changes in the output voltage from the magnetic element 20. In other words, the optical device 100 can convert light into an electrical signal. For example, when the output voltage from the optical device 100 is equal to or greater than a threshold, it is processed as a first signal (e.g., "1"), and when it is less than the threshold, it is processed as a second signal (e.g., "0").

[0071] Here, the case where the magnetization M1 and the magnetization M2 are antiparallel in the initial state has been described as an example, but the magnetization M1 and the magnetization M2 may be parallel in the initial state. In this case, the resistance value in the Z direction of the magnetic element 20 increases as the state of the magnetization M1 changes (for example, as the angle change of the magnetization M1 from the initial state increases). If the initial state is one in which the magnetization M1 and the magnetization M2 are parallel, it is preferable to flow the sense current Is from the first ferromagnetic layer 1 to the second ferromagnetic layer 2. By flowing the sense current Is in this direction, a spin transfer torque acts on the magnetization M1 of the first ferromagnetic layer 1 in the same direction as the magnetization M2 of the second ferromagnetic layer 2, and the magnetization M1 and the magnetization M2 become parallel in the initial state.

[0072] Although the light irradiated onto the magnetic element 20 has two levels of intensity, namely, a first intensity and a second intensity, the intensity of the light irradiated onto the magnetic element 20 may change in multiple levels or in an analog manner. In this case, the output voltage from the magnetic element 20 changes in multiple levels or in an analog manner.

[0073] The optical device 100 according to the first embodiment can convert light irradiated onto the magnetic element 20 into an output voltage from the magnetic element 20, thereby converting the light into an electrical signal. In the optical device 100 according to the first embodiment, the magnetic element 20 is located within the cladding 12 and is packaged. Therefore, the waveguide 10 that propagates light and the magnetic element 20 that detects the light can be handled as a single component, which enables the optical device 100 to be miniaturized. Furthermore, since the waveguide 10 and the magnetic element 20 are packaged, adjustment of the optical axes of the waveguide 10 and the magnetic element 20 is not required.

[0074] Furthermore, the light propagating through the waveguide 10 is reflected by the first reflector 41 and the second reflector 42 and is irradiated onto the magnetic element 20 from the side or above the magnetic element 20. Each layer constituting the magnetic element 20 is very thin, and the crystallinity of each layer is easily affected by the underlying layer. When light is irradiated from below the magnetic element 20, the material of the first electrode 22 is limited, and it is not possible to sufficiently improve the crystallinity of the magnetic element 20. In contrast, in the optical device 100 according to this embodiment, light is irradiated from the side or above the magnetic element 20, so any material can be used for the first electrode 22. When the crystallinity of the magnetic element 20 is improved, the resistance change range (MR ratio) of the magnetic element 20 increases, and the sensitivity of the optical device 100 is improved.

[0075] Although an example of the present invention has been described above using the first embodiment as an example, the present invention is not limited to this embodiment.

[0076] For example, Fig. 7 is a cross-sectional view of an optical device 101 according to a first modified example. Fig. 7 is an XZ cross-section passing through the center of the core 11 in the Y direction. The optical device 101 shown in Fig. 7 has a waveguide 10, a magnetic element 20, a terminal unit 30, a first reflector 41, a second reflector 43, and a substrate 50. The second reflector 43 has a different shape from the second reflector 42 described above. The reflecting surface 43A of the second reflector 43 is curved. The light reflected by the reflecting surface 43A is condensed and irradiated onto the magnetic element 20.

[0077] The optical device 101 according to the first modification has the same effects as the above-described optical device 100. Furthermore, the optical device 101 can improve the efficiency of irradiating the magnetic element 20 with light by concentrating the light on the reflecting surface 43A.

[0078] For example, Fig. 8 is a cross-sectional view of an optical device 102 according to a second modified example. Fig. 8 is an XZ cross section passing through the center of the core 11 in the Y direction. The optical device 102 shown in Fig. 8 has a waveguide 10, a magnetic element 20, a terminal unit 30, a first reflector 41, a second reflector 44, and a substrate 50. The second reflector 44 has a different shape from the second reflector 42 described above.

[0079] The second reflector 44 is a meta-mirror having a meta-diffraction grating. The meta-diffraction grating is a metamaterial. The meta-diffraction grating is composed of multiple unit cells, each of which contains multiple meta-atoms. The refractive index distribution of the meta-diffraction grating can be changed by changing the shape of the unit cells. The meta-mirror exhibits high reflectivity when irradiated with light of a specified wavelength. The specified wavelength can be controlled by changing the configuration of the meta-diffraction grating.

[0080] The optical device 102 according to the second modification has the same effects as the optical device 100. Furthermore, the optical device 102 has the second reflector 44 made of a meta-mirror, which allows the wavelength of the light irradiated onto the magnetic element 20 to be controlled.

[0081] Although an example in which one magnetic element 20 is provided has been disclosed so far, a plurality of magnetic elements 20 may be provided.

[0082] Furthermore, if there are multiple magnetic elements 20, the outputs from the magnetic elements 20, which behave in the same way with respect to light, can be combined and output from the optical device. As a result, noise in the output signal of the optical device can be suppressed, and the signal-to-noise ratio of the optical device 102 can be increased.

[0083] Fig. 9 is a cross-sectional view showing a first example of a connection state of magnetic elements in an optical device according to the third modified example. As shown in Fig. 9, each of the magnetic elements 20 may be connected in series. In Fig. 9, each of the magnetic elements 20 is connected in series by a connection wiring 36. Fig. 10 is a cross-sectional view showing a second example of a connection state of magnetic elements in an optical device according to the third modified example. As shown in Fig. 10, each of the magnetic elements 20 may be connected in parallel.

[0084] Furthermore, up to this point, an example has been shown in which two reflectors (first reflector 41 and second reflector 42) are provided between the core 11 and the magnetic element 20 in the light path, but the number of reflectors between the core 11 and the magnetic element 20 may be three or more.

[0085] The optical devices according to the above-described embodiments and modifications can be used for a variety of purposes.

[0086] 11 is a schematic diagram of an optical element 200 according to a first application example. The optical element 200 shown in FIG. 11 includes a waveguide element 110 and a light source 120. The waveguide element 110 includes the above-described optical device 100 and a waveguide 111. The waveguide 111 includes an output waveguide 112 and a monitoring waveguide 113. The output waveguide 112 is a waveguide for outputting light from the light source 120 to the outside. The monitoring waveguide 113 is a waveguide for branching a portion of the light propagating through the output waveguide 112 to the optical device 100. The monitoring waveguide 113 is connected to the core 11 of the optical device 100.

[0087] Light source 120 is, for example, a laser light source. Light source 120 has, for example, a red laser 121, a green laser 122, and a blue laser 123. Light output from light source 120 propagates through output waveguide 112 and is output to the outside. A portion of the light output from light source 120 propagates through monitoring waveguide 113 and reaches optical device 100.

[0088] The optical element 200 outputs laser light to the outside while monitoring the output from the light source 120 with the optical device 100. The optical element 200 can adjust the white balance of the light output from the output waveguide 112 to the outside by adjusting the intensity of the light output from each laser.

[0089] 12 is a conceptual diagram of an optical system 300 using the optical element 200. The optical system 300 can be implemented in, for example, glasses 1000.

[0090] The optical system 300 includes the optical element 200, an optical system 310, drivers 320 and 321, and a controller 330. The optical system 310 includes, for example, a collimator lens 301, a slit 302, an ND filter 303, and an optical scanning mirror 304. The optical system 310 guides the light output from the optical element 200 to an object to be illuminated (the eye in this example). The optical scanning mirror 304 is, for example, a two-axis MEMS mirror that changes the reflection direction of the laser light in the horizontal and vertical directions. The optical system 310 is an example and is not limited to this example. The driver 320 controls the output from the light source 120 of the optical element 200. The driver 321 is a control system that drives the optical scanning mirror 304. The controller 330 controls the drivers 320 and 321.

[0091] Light L output from the light source 120 of the optical element 200 G The light propagates through the optical system 310, is reflected by the lenses of the glasses 1000, and enters the eye. Here, an example is shown in which the light is reflected by the lenses of the glasses 1000, but the light may be irradiated directly onto the eye.

[0092] Red, green, and blue light L emitted from the light source 120 G displays an image. The image can be freely controlled. The output intensities of the red laser 121, the green laser 122, and the blue laser 123 can be adjusted based on the measurement results of the output from the optical device 100 to which the visible light output from the red laser 121, the green laser 122, and the blue laser 123 is irradiated.

[0093] Using this optical system 300, an image can be projected onto the glasses 1000. Furthermore, by monitoring the intensity of the projected light with the optical device 100, the color of the image can be adjusted.

[0094] 13 is a block diagram of a transceiver 400 according to the second application example. The transceiver 400 includes a receiver 410 and a transmitter 420. The receiver 410 receives an optical signal L1, and the transmitter 420 transmits an optical signal L2.

[0095] The receiving device 410 includes, for example, a photodetector 411 and a signal processing unit 412. The photodetector 411 can be the optical device described above. In the receiving device 410, the optical device of the photodetector 411 is irradiated with, for example, an optical pulse. The optical signal L1 is composed of the optical pulse. The photodetector 411 converts the optical signal L1 into an electrical signal. The signal processing unit 412 processes the electrical signal converted by the photodetector 411. The signal processing unit 412 receives the signal included in the optical signal L1 by processing the electrical signal generated from the photodetector 411. The receiving device 410 receives the signal included in the optical signal L1 based on the output signal from the photodetector 411.

[0096] The transmitting device 420 includes, for example, a light source 421, an electric signal generating element 422, and an optical modulation element 423. The light source 421 is, for example, a laser element. The light source 421 may be located outside the transmitting device 420. The electric signal generating element 422 generates an electric signal based on transmission information. The electric signal generating element 422 may be integrated with a signal conversion element of the signal processing unit 412. The optical modulation element 423 modulates the light output from the light source 421 based on the electric signal generated by the electric signal generating element 422, and outputs an optical signal L2.

[0097] Fig. 14 is a conceptual diagram of an example of a communication system. The communication system shown in Fig. 14 has two terminal devices 500. The terminal devices 500 are, for example, smartphones, tablets, personal computers, or the like.

[0098] Each of the terminal devices 500 includes a receiving device 410 and a transmitting device 420. An optical signal transmitted from the transmitting device 420 of one terminal device 500 is received by the receiving device 410 of the other terminal device 500. The light used for transmission and reception between the terminal devices 500 is, for example, visible light. The receiving device 410 includes a light detecting device 411.

[0099] Fig. 15 is a conceptual diagram of an example of a communication system. In Fig. 14, an example is shown in which the terminal devices 500 are all smartphones, but the terminal devices 500 on the transmitting side and the receiving side may be different. For example, the terminal device 500 shown in Fig. 15 is a smartphone, and the terminal device 501 is a personal computer. [Explanation of symbols]

[0100] 1 First ferromagnetic layer 2 Second ferromagnetic layer 3 Spacer layer 4. Buffer layer 5 Seed layer 6 Third ferromagnetic layer 7 Magnetic coupling layer 8 Perpendicular magnetization induction layer 9 Cap Layer 10 Waveguide 11 cores 12 Clad 20 Magnetic elements 21 Laminate 22 1st electrode 23 2nd electrode 30 terminal units 31 1st terminal 32 2nd terminal 33 3rd terminal 34 4th terminal 35 Via wiring 36 Connection wiring 41 1st reflector 42 Second reflector 50 boards 100, 101, 102 Optical devices

Claims

1. a waveguide, a magnetic element, a first reflector, and a second reflector; the waveguide has a core through which light propagates and a clad surrounding the core, the first reflector is located in front of the core in a direction in which light propagates through the core, the second reflector is disposed at a position where the light reflected by the first reflector can be irradiated onto the magnetic element, the magnetic element comprises a first ferromagnetic layer, a second ferromagnetic layer, and a spacer layer located between the first ferromagnetic layer and the second ferromagnetic layer; An optical device in which the magnetic element is illuminated with light from the side or above.

2. The optical device according to claim 1 , wherein the magnetic element is irradiated with light from a direction inclined at an angle of 45° or more with respect to an upper surface of the magnetic element.

3. the reflecting surface of the second reflector is curved; The optical device according to claim 1 , wherein the magnetic element is irradiated with light that is reflected and concentrated by the reflecting surface.

4. the magnetic element has a first electrode and a second electrode; the second electrode is above the first electrode; 2. The optical device according to claim 1, wherein the first electrode is a metal containing at least one element selected from the group consisting of copper, aluminum, gold, tantalum, titanium, ruthenium, molybdenum, and tungsten.

5. The optical device of claim 1 , wherein the magnetic element is a plurality of magnetic elements.

6. A receiving apparatus comprising the optical device according to claim 1.

7. A transmitting / receiving device comprising the receiving device according to claim 6.

8. A communication system comprising a receiving device according to claim 6.

9. A terminal device comprising the receiving device according to claim 6.

10. An optical system comprising the optical device of claim 1 .

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