Photoelectric field enhancing element and method for manufacturing a photoelectric field enhancing element

Abstract

The present invention provides an optical electric field enhancing element capable of enhancing the electric field within a nonlinear optical material. [Solution] The optical field enhancing element comprises a cladding having a first gap extending in a first direction and having a constant gap width in a second direction perpendicular to the first direction. The optical field enhancing element comprises a first core disposed within the first gap. The optical field enhancing element comprises a second core having a width in the second direction greater than the gap width and being optically connected to the first core. The cladding is made of a material with a negative real part of its dielectric constant. The first core is made of a nonlinear optical material. The second core is made of a material having a higher refractive index than the first core. A plasmonic waveguide is defined by the first gap and the first core. A dielectric optical waveguide is defined by the second core.

Description

Technical Field

[0001] This specification relates to an optoelectronic field enhancement element and a method for manufacturing the optoelectronic field enhancement element.

Background Art

[0002] Non-Patent Document 1 discloses an optoelectronic field enhancement element capable of converting a propagation mode from a dielectric optical waveguide to a plasmonic optical waveguide. In this optoelectronic field enhancement element, a plasmonic optical waveguide is formed by a nanoscale gap formed between metal claddings. In the plasmonic optical waveguide, since light can be confined in a region smaller than the wavelength size, it becomes possible to enhance the optoelectronic field.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the technology of Non-Patent Document 1, since the inside of the gap is filled with air, a non-linear optical response does not occur. Therefore, various effects (e.g., wavelength conversion process) based on the non-linear optical response cannot be obtained.

Means for Solving the Problems

[0005] The optical field enhancing element disclosed herein comprises a cladding having a first gap extending in a first direction and having a constant gap width in a second direction orthogonal to the first direction. The optical field enhancing element comprises a first core disposed within the first gap. The optical field enhancing element comprises a second core having a width in the second direction greater than the gap width and being optically connected to the first core. The cladding is made of a material with a negative real part of its dielectric constant. The first core is made of a nonlinear optical material. The second core is made of a material having a higher refractive index than the first core. A plasmonic waveguide is defined by the first gap and the first core. A dielectric optical waveguide is defined by the second core.

[0006] According to the above configuration, the first core defining the plasmonic waveguide is made of a nonlinear optical material. This allows for the concentration of the optical electric field into the first core through mode conversion to the plasmonic waveguide, thereby enhancing the electric field within the nonlinear optical material. Since a nonlinear optical response can be generated, various effects based on this response can be obtained. [Brief explanation of the drawing]

[0007] [Figure 1] This is a top view of the photoelectric field enhancement element 1. [Figure 2] This is a partially enlarged cross-sectional view along line II-II in Figure 1. [Figure 3] This is a cross-sectional view taken along line III-III in Figure 1. [Figure 4] This is a graph of electric field strength. [Figure 5] This graph shows the relationship between the taper angle TA and the total electric field and electric field intensity. [Figure 6] This is a diagram illustrating the manufacturing method of the photoelectric field enhancement element 1. [Figure 7] This is a diagram illustrating the manufacturing method of the photoelectric field enhancement element 1. [Figure 8] This is a diagram illustrating the manufacturing method of the photoelectric field enhancement element 1. [Figure 9] This is a diagram illustrating the manufacturing method of the photoelectric field enhancement element 1. [Modes for carrying out the invention]

[0008] (Configuration of the photoelectric field enhancement element 1) Figure 1 shows a top view of the photoelectric field enhancing element 1. Note that the protective layer 14 is omitted in Figure 1 for clarity. Figure 2 shows a partially enlarged cross-sectional view along line II-II in Figure 1. Figure 2 is a cross-sectional view in the direction (x direction) across the first gap G1. Figure 3 shows a cross-sectional view along line III-III in Figure 1. Figure 3 is a cross-sectional view in the direction (y direction) along the extension of the first gap G1. The photoelectric field enhancing element 1 mainly comprises a cladding 10, a first core 11, a second core 12, an intermediate layer 13, and a protective layer 14.

[0009] The second core 12 has a flat plate shape. The second core 12 has a width W2 in the x direction. The width W2 is larger than the gap width GW1 of the first gap G1, which will be described later. The second core 12 is made of a material having a higher refractive index than the first core 11. Furthermore, the second core 12 is made of a dielectric material that has a refractive index greater than 3 and low propagation loss in the laser light wavelength band used in quantum light generation (e.g., wavelengths of 775 nm, 1550 nm). It is preferable that such a dielectric material can be deposited by methods such as sputtering, evaporation, or CVD. By depositing the film using these methods, it becomes possible to deposit the dielectric material on a microfabricated substrate. Specifically, the material for the second core 12 can be any of gallium phosphide (GaP), molybdenum sulfide (MoS2), or CVD-based silicon. In this example, the material for the second core 12 is gallium phosphide (refractive index n=3.2).

[0010] CVD-type silicon refers to a silicon layer formed by vapor phase growth. Compared to PVD-type silicon (a silicon layer formed by sputtering), CVD-type silicon has the property of lower propagation loss of propagating light. Furthermore, CVD-type silicon and PVD-type silicon can be distinguished by analyzing the presence or absence of specific gas components used in vapor phase growth.

[0011] The intermediate layer 13 is positioned in contact with the upper surface 12u of the second core 12. The intermediate layer 13 is made of a material that is transparent in the laser light wavelength band used in quantum light generation. In this embodiment, the material of the intermediate layer 13 is silicon oxide (SiO2). The thickness of the intermediate layer 13 is not particularly limited and may be, for example, several tens of nanometers.

[0012] The cladding 10 is positioned in contact with the upper surface 13u of the intermediate layer 13. That is, the cladding 10 is positioned on the upper surface 12u of the second core 12 via the intermediate layer 13. The cladding 10 has a film shape. The cladding 10 is composed of a material whose real part of dielectric constant is negative. An example of such a material is a metal with low propagation loss in the laser light wavelength band used in quantum light generation (e.g., wavelengths of 775 nm, 1550 nm). By using a metal with low propagation loss, it is possible to suppress the decrease in electric field strength when focused into a plasmonic waveguide. Examples of metals with low propagation loss include silver, gold, and aluminum. In this embodiment, silver was used. This is because silver has the lowest propagation loss among silver, gold, and aluminum.

[0013] The cladding 10 comprises a first gap G1, and second gaps G2_1 and G2_2. The first gap G1 has a constant gap width GW1 in the x direction. The first gap G1 extends in the y direction. The first gap G1 comprises an end E1 in the -y direction and an end E2 in the +y direction.

[0014] The second gaps G2_1 and G2_2 are coplanar with the first gap G1 and extend in the y-direction. The second gap G2_1 is connected to the end E1 of the first gap G1. The width in the x-direction of the second gap G2_1 at end E1 is the gap width GW1. The width in the x-direction of the second gap G2_1 at the substrate end SA1 is the gap width GW2. The gap width of the second gap G2_1 gradually increases from end E1 toward the substrate end SA1 (i.e., as it moves away in the -y-direction). In other words, the second gap G2_1 has a tapered shape that widens from gap width GW1 to GW2. The tapered shape can be various shapes. For example, the tapered shape may be a shape that widens linearly, or a shape that widens according to various curves such as a parabola or a Bézier curve.

[0015] Similarly, the second gap G2_2 is connected to the end E2 of the first gap G1. The width in the x-direction of the second gap G2_2 at end E2 is the gap width GW1. The width in the x-direction of the second gap G2_2 at the substrate end SA2 is the gap width GW2. The gap width of the second gap G2_2 gradually increases from end E2 toward the substrate end SA2 (i.e., as it moves away in the +y direction). In other words, the second gap G2_2 has a tapered shape that widens from gap width GW1 to GW2.

[0016] As shown in Figure 2, the first core 11 is located within the first gap G1. That is, the first core 11 is located within the space enclosed by the inner wall of the first gap G1 and the upper surface 12u of the second core 12. The first core 11 is also located within the second gaps G2_1 and G2_2. The upper surface 11u of the first core 11 and the upper surface 10u of the cladding 10 are located in the same plane. However, the upper surfaces 11u and 10u do not necessarily have to be located in the same plane.

[0017] The first core 11 is in contact with the second core 12 via the intermediate layer 13. The intermediate layer 13 is transparent in the laser light wavelength band used for quantum light generation. Therefore, the first core 11 and the second core 12 are in an optically connected state.

[0018] The first core 11 is made of a nonlinear optical material. In the technology of this specification, a second-order nonlinear optical material is used as the material of the first core 11. Examples of the second-order nonlinear optical material include lithium niobate (LiNbO3) and lithium tantalate (LiTaO3). In this embodiment, the second-order nonlinear optical material constituting the first core 11 is lithium niobate (refractive index n = 2.26).

[0019] The protective layer 14 is disposed in contact with the upper surface 11u and the upper surface 10u. The material and film thickness of the protective layer 14 can be in various forms. In this embodiment, the material of the protective layer 14 is silicon oxide (SiO2). Note that the protective layer 14 can be omitted.

[0020] As shown in FIG. 3, in the optoelectronic field enhancement element 1, the first gap G1 and the first core 11 define a plasmonic waveguide PW. In other words, in the first core 11, the region disposed within the first gap G1 functions as the plasmonic waveguide PW. Also, the second core 12 defines a dielectric optical waveguide DW. The entrance of the dielectric optical waveguide DW is the substrate end SA1. The exit of the dielectric optical waveguide DW is the substrate end SA2. As shown by the arrow Y1 in FIGS. 1 and 3, light can be incident from the entrance of the dielectric optical waveguide DW.

[0021] Also, the second gaps G2_1 and G2_2 define a mode conversion section that connects the dielectric optical waveguide DW and the plasmonic waveguide PW. In the mode conversion section, it is possible to convert the mode of the propagating light between the dielectric optical waveguide DW and the plasmonic waveguide PW. The mode conversion will be described later.

[0022] (Operation of the optoelectronic field enhancement element 1) Light is incident from the entrance of the dielectric optical waveguide DW (see arrow Y1). The wavelength of the incident light is at least one of the two laser light wavelength bands used in quantum light generation (e.g., wavelengths 775 nm and 1550 nm). The incident light is focused into a narrow region by the tapered shape of the second gap G2_1. Therefore, mode conversion of the propagating light occurs between the dielectric optical waveguide DW and the plasmonic waveguide PW, and the light can be confined to the plasmonic waveguide PW (see arrow Y2). This allows the optical electric field to be concentrated in the second-order nonlinear optical material (first core 11) that constitutes the plasmonic waveguide PW. Because a strong electric field can be generated in the second-order nonlinear optical material, second-order nonlinear optical effects can be significantly generated.

[0023] By generating second-order nonlinear optical effects, phenomena such as "second harmonic generation" and "spontaneous parametric downconversion" can be produced. Second harmonic generation is a phenomenon in which, when two photons of frequency ω are incident on a nonlinear optical material, the two photons combine to produce a single photon of frequency 2ω. Spontaneous parametric downconversion is a phenomenon in which, when a single photon of frequency 2ω is introduced, the single photon is split, and a pair of correlated photons of frequency ω (entangled light) is produced. In other words, quantum light such as single photons and photon pairs can be generated by the wavelength conversion process using the second-order nonlinear optical material. Furthermore, since the electric field enhancement element 1 can enhance the electric field of the second-order nonlinear optical material (first core 11), it becomes possible to generate quantum light more efficiently.

[0024] Single photons and correlated photon pairs (entangled light) generated by second-order nonlinear optical effects can be applied to quantum transformation elements and quantum cryptography. Quantum transformation elements are devices that convert visible light photons (wavelengths 400-900 nm), which are used to read and write information in quantum memory, into photons in the communication wavelength band (wavelengths around 1.3 μm or 1.5 μm), while preserving the quantum information. Quantum cryptography is a type of communication that makes eavesdropping impossible by using entangled light as a common key.

[0025] In the technology described herein, a second-order nonlinear optical material is used as the nonlinear optical material placed in the plasmonic gap (first gap G1), rather than a third-order nonlinear optical material. The reasons for this are as follows: Firstly, it can increase the efficiency of quantum light generation. That is, the nonlinearity of a third-order nonlinear optical material is weaker than that of a second-order nonlinear optical material (the nonlinear optical constant is smaller). Therefore, second-order nonlinear optical materials have a higher quantum light generation efficiency relative to incident intensity compared to third-order nonlinear optical materials. Secondly, it can generate quantum light over a wide wavelength range. Typical third-order nonlinear optical materials such as silicon and organic polymers have high losses in the visible region, making it difficult to generate and transmit quantum light in the visible region. In contrast, second-order nonlinear optical materials (e.g., lithium niobate, lithium tantalate, etc.) have no losses from the visible light to the near-infrared region, so they can generate and transmit quantum light over a wide wavelength range.

[0026] (Mode conversion by wavenumber matching) In order to concentrate the optical electric field on a second-order nonlinear optical material (first core 11) in the laser light wavelength band used in quantum light generation, it is necessary to match the wavenumbers between the dielectric optical waveguide DW and the plasmonic waveguide PW. In other words, it is necessary to bring the effective refractive index of the dielectric optical waveguide DW and the effective refractive index of the plasmonic waveguide PW closer together. By matching the wavenumbers, the efficiency of mode conversion can be increased, making it possible to concentrate the optical electric field on the second-order nonlinear optical material.

[0027] The inventors verified the conditions necessary for wavenumber matching using electromagnetic field simulations. A simulation was performed for the case where light with a wavelength of 775 nm was incident on the optical electric field enhancement element 1 from the direction of arrow Y1. In the simulation, the effective refractive index of the dielectric optical waveguide DW and the effective refractive index of the plasmonic waveguide PW were calculated. Furthermore, the optical electric field until the light propagating through the dielectric optical waveguide DW coupled to the plasmonic waveguide PW was calculated. These calculations demonstrated mode conversion through wavenumber matching.

[0028] In the first simulation condition, the refractive index of the second core 12 was set to be the same as that of the first core 11. Specifically, lithium niobate (refractive index n=2.26) was used for the second core 12, which is a dielectric optical waveguide DW, and the first core 11, which is a plasmonic waveguide PW. In this case, the effective refractive index of the dielectric optical waveguide DW was calculated to be 2.15, and the effective refractive index of the plasmonic waveguide PW was calculated to be 3.49. There was a large difference in the effective refractive index between the dielectric optical waveguide DW and the plasmonic waveguide PW, and the wavenumbers did not match between the two modes. As a result, it was found that mode conversion from the dielectric optical waveguide DW to the plasmonic waveguide PW did not occur. In other words, it was not possible to concentrate the optical electric field in the second-order nonlinear optical material (first core 11).

[0029] In the second simulation condition, the refractive index of the second core 12 was made higher than that of the first core 11, and the numerical value of the refractive index of the second core 12 was made greater than 3. Specifically, gallium phosphide (refractive index n=3.2) was used for the second core 12, which is a dielectric optical waveguide DW. Lithium niobate was used for the first core 11, which is a plasmonic waveguide PW. In this case, the effective refractive index of the dielectric optical waveguide DW was calculated to be 2.90, and the effective refractive index of the plasmonic waveguide PW was calculated to be 3.34. The effective refractive indexes of the dielectric optical waveguide DW and the plasmonic waveguide PW were close in value, and the wavenumbers could be matched between the two modes. As a result, it was found that the propagating light could be converted from the dielectric optical waveguide DW to the plasmonic waveguide PW. That is, the optical electric field could be concentrated in the second-order nonlinear optical material (first core 11).

[0030] Furthermore, the electric field strength of the plasmonic waveguide PW was calculated under the second simulation condition. The top view of Figure 4(A) shows the region where the electric field strength was calculated. The electric field strength of the plasmonic waveguide PW was calculated at the center in the width direction (x direction) and the center in the height direction (z direction). Figure 4(B) shows the graph of the electric field strength. The horizontal axis is the position in the y direction, and the vertical axis is the electric field strength. Graph De shows the electric field strength of the dielectric optical waveguide DW. Graph Pe shows the electric field strength of the plasmonic waveguide PW. As shown in region R1, it can be seen that mode conversion occurs and energy is transferred from the dielectric optical waveguide DW to the plasmonic waveguide PW. Furthermore, as shown in region R2, it can be seen that the electric field strength of the plasmonic waveguide PW can be increased by more than twice compared to the electric field strength of the dielectric optical waveguide DW.

[0031] From the above, it can be seen that by making the refractive index of the second core 12 higher than that of the first core 11, and by making the refractive index of the second core 12 greater than 3 in the laser light wavelength band used for quantum light generation, the effective refractive index of the dielectric optical waveguide DW and the effective refractive index of the plasmonic waveguide PW can be brought closer together. This enhances the interaction between the nonlinear optical material (first core 11) and light, enabling highly efficient quantum light generation.

[0032] In this embodiment, gallium phosphide is used as the material for the second core 12. The reason for this is as follows: In the laser light wavelength band used in quantum light generation, materials with a refractive index greater than 3 include, for example, amorphous silicon deposited by PVD. However, PVD-based amorphous silicon has the problem of high waveguide loss. On the other hand, amorphous gallium phosphide deposited by PVD has the characteristic of lower waveguide loss than PVD-based amorphous silicon. Therefore, by using gallium phosphide as the material for the second core 12, it is possible to reduce the waveguide loss of the dielectric optical waveguide DW.

[0033] (Taper angle TA range for Clad 10) As shown in Figure 5(A), the centerlines CL of the first gap G1 and the second gaps G2_1 and G2_2 are defined. The angle of the second gaps G2_1 and G2_2 with respect to the centerline CL is defined as the taper angle TA. The smaller the taper angle TA, the more gradually the incident light can be narrowed by the first gap G1. Therefore, the smaller the taper angle TA, the less reflection and scattering due to the discontinuity in mode conversion from photonic mode to plasmonic mode, and the higher the conversion efficiency.

[0034] Therefore, the inventors used electromagnetic field simulations to verify the optimal range of taper angle TA for mode conversion efficiency. Figure 5(B) shows the simulation results. The horizontal axis represents the taper angle TA. The vertical axis represents the total electric field intensity in the plasmonic gap (first gap G1). It can be seen that the electric field intensity of the plasmonic waveguide PW is maximum and the conversion efficiency is highest when the taper angle TA is 26° (see region R3). Furthermore, it can be seen that the slope of increase in electric field intensity due to decreasing taper angle TA saturates at approximately 28°. In other words, the angular range AR where the taper angle TA is 28° or less is the optimal range for mode conversion efficiency.

[0035] (Manufacturing method) The method for manufacturing the photoelectric field enhancement element 1 will be described with reference to Figures 6 to 9. Figures 6 to 9 are cross-sectional views of the same area as in Figure 2. First, a substrate 101 is prepared as shown in Figure 6. The substrate 101 has a structure in which a silicon layer 115, a silicon oxide film layer 114, and a second-order nonlinear optical material layer 111 are stacked. In this embodiment, the second-order nonlinear optical material layer 111 is lithium niobate (LiNbO3). The thickness of the silicon layer 115 may be, for example, 500 μm. The thickness of the silicon oxide film layer 114 may be, for example, 2 μm. The thickness of the second-order nonlinear optical material layer 111 may be, for example, 60 nm. If the initial film thickness of the second-order nonlinear optical material layer 111 is thick (e.g., 600 nm), it may be thinned to about 60 nm by physical etching (e.g., Ar etching). A commercially available LNOI substrate (Lithium Niobate On Insulator) can be used for the substrate 101.

[0036] Next, as shown in Figure 7, a resist mask 130 is deposited on the second-order nonlinear optical material layer 111 using known photolithography or electron beam lithography techniques. The resist mask 130 is a mask with apertures corresponding to the cladding 10. In other words, the regions where the first gap G1 and the second gaps G2_1 and G2_2 are formed are covered by the resist mask 130. Next, the second-order nonlinear optical material layer 111 is processed by physical etching without chemical reaction. In this example, ion milling with Ar ions was used as the physical etching. As a result, as shown in Figure 7, the second-order nonlinear optical material layer 111 in the regions corresponding to the cladding 10 is removed.

[0037] Next, as shown in Figure 8, with the resist mask 130 in place, the metal layer 110 is deposited on the upper surface of the substrate 101. In this embodiment, the metal layer 110 was made of silver. Electron beam evaporation was used as the deposition method. If the underlying film of the metal layer 110 is a film with poor adhesion to the metal layer, such as a silicon oxide film, an intermediate layer may be formed between the metal layer 110 and the underlying film to improve adhesion. For example, a transition metal layer such as titanium or chromium can be used as the intermediate layer. After that, the metal layer 110 deposited on the resist mask 130 is removed by lift-off (see arrow Y3).

[0038] Next, as shown in Figure 9, an intermediate layer 113 and a dielectric layer 112 are laminated on the upper surfaces of the metal layer 110 and the second-order nonlinear optical material layer 111. In this embodiment, the intermediate layer 113 is a silicon oxide film, and the dielectric layer 112 is gallium phosphide. Sputtering (PVD) was used as the film deposition method.

[0039] By removing the silicon layer 115 from the structure shown in Figure 9 and inverting it, the structure shown in Figure 2 is completed. That is, the dielectric layer 112 becomes the second core 12, the intermediate layer 113 becomes the intermediate layer 13, the metal layer 110 becomes the cladding 10, the second-order nonlinear optical material layer 111 becomes the first core 11, and the silicon oxide film layer 114 becomes the protective layer 14. Note that the silicon layer 115 may be left in place without being removed.

[0040] In this manufacturing method, the second-order nonlinear optical material layer 111 is processed using physical etching. This makes it possible to process the second-order nonlinear optical material layer 111 even if it is made of a material that is difficult to process by reactive ion etching (RIE). In this embodiment, after processing the second-order nonlinear optical material layer 111 which is to be placed in the first gap G1, a metal layer 110 that defines the first gap G1 is deposited. Since the metal layer 110 is not present when the second-order nonlinear optical material layer 111 is processed, the metal layer 110 is not oxidized or damaged as a result of processing the second-order nonlinear optical material layer 111. When silver is used for the metal layer 110, it is more easily oxidized than gold, so there is a significant advantage to using this manufacturing method.

[0041] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. Furthermore, the technical elements described in this specification or drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technologies illustrated in this specification or drawings can achieve multiple objectives simultaneously, and achieving even one of these objectives constitutes technical usefulness.

[0042] The following are embodiments of this technology. [Aspect 1] A cladding comprising a first gap extending in a first direction, the first gap having a constant gap width in a second direction perpendicular to the first direction, A first core located within the first gap, A second core having a width in the second direction greater than the gap width, and optically connected to the first core, Equipped with, The cladding is made of a material whose real part of the dielectric constant is negative. The first core is composed of a nonlinear optical material, The second core is composed of a material having a higher refractive index than the first core. The first gap and the first core define a plasmonic waveguide. The dielectric optical waveguide is defined by the second core. Photoelectric field enhancing element. [Aspect 2] The photoelectric field enhancing element according to embodiment 1, wherein the nonlinear optical material is a second-order nonlinear optical material. [Aspect 3] The photoelectric field enhancing element according to embodiment 2, wherein the secondary nonlinear optical material is lithium niobate or lithium tantalate. [Aspect 4] The photoelectric field enhancing element according to any one of embodiments 1 to 3, wherein the second core is made of a material whose refractive index is greater than 3 in the laser light wavelength band used for quantum light generation. [Aspect 5] The photoelectric field enhancing element according to embodiment 4, wherein the second core is one of gallium phosphide, molybdenum sulfide, or CVD-based silicon. [Aspect 6] The cladding extends in the first direction, is coplanar with the first gap, and includes a second gap connected to the first end of the first gap in the first direction. The photoelectric field enhancing element according to any one of embodiments 1-5, wherein the width of the second gap in the second direction is equal to the gap width at the end of the first gap and increases as it moves away from the end in the first direction. [Aspect 7] The photoelectric field enhancing element according to any one of embodiments 1-6, wherein the cladding is composed of silver, gold, or aluminum. [Aspect 8] The second core has a flat plate shape, The cladding has a membrane shape that is positioned on the upper surface of the second core, The photoelectric field enhancing element according to any one of embodiments 1 to 7, wherein the first core is disposed within the space enclosed by the first gap and the upper surface of the second core. [Aspect 9] The photoelectric field enhancing element further comprises an intermediate layer of transparent material positioned in contact with the upper surface of the second core. The photoelectric field enhancing element according to embodiment 8, wherein the cladding is disposed on the upper surface of the second core via the intermediate layer. [Aspect 10] A cladding comprising a first gap extending in a first direction, the first gap having a constant gap width in a second direction perpendicular to the first direction, A first core located within the first gap, A second core having a width in the second direction greater than the gap width, and optically connected to the first core, A method for manufacturing an electric field enhancing element comprising: A step of preparing a substrate having a structure in which a support layer, a silicon oxide film layer, and a second-order nonlinear optical material layer are stacked in this order, A step of forming a mask on the second-order nonlinear optical material layer having an aperture corresponding to the cladding, A step of etching the secondary nonlinear optical material layer through the mask, A step of forming a metal layer on the substrate via the mask, A removal step of lifting off the metal layer formed on the mask, The process involves forming a dielectric layer on the substrate from which the removal process has been performed, Equipped with, The cladding is formed by the aforementioned metal layer. The first core is formed by the second-order nonlinear optical material layer, The second core is formed by the dielectric layer. A method for manufacturing an electric field enhancement device. [Explanation of Symbols]

[0043] 1: Optical field enhancement element 10: Cladding 11: First core 12: Second core 13: Intermediate layer G1: First gap G2_1, G2_2: Second gap GW1: Gap width DW: Dielectric optical waveguide PW: Plasmonic waveguide

Claims

1. A cladding comprising a first gap extending in a first direction, the first gap having a constant gap width in a second direction perpendicular to the first direction, A first core located within the first gap, A second core having a width in the second direction greater than the gap width, and optically connected to the first core, Equipped with, The cladding is made of a material whose real part of the dielectric constant is negative. The first core is composed of a nonlinear optical material, The second core is made of a material having a higher refractive index than the first core. The first gap and the first core define a plasmonic waveguide. The dielectric optical waveguide is defined by the second core. Photoelectric field enhancing element.

2. The photoelectric field enhancing element according to claim 1, wherein the nonlinear optical material is a second-order nonlinear optical material.

3. The photoelectric field enhancing element according to claim 2, wherein the second-order nonlinear optical material is lithium niobate or lithium tantalate.

4. The photoelectric field enhancing element according to any one of claims 1 to 3, wherein the second core is made of a material whose refractive index is greater than 3 in the laser light wavelength band used for quantum light generation.

5. The photoelectric field enhancing element according to claim 4, wherein the second core is one of gallium phosphide, molybdenum sulfide, or CVD-based silicon.

6. The cladding extends in the first direction, is coplanar with the first gap, and includes a second gap connected to the first end of the first gap in the first direction. The photoelectric field enhancing element according to claim 1, wherein the width of the second gap in the second direction is equal to the gap width at the end of the first gap and increases as it moves away from the end in the first direction.

7. The photoelectric field enhancing element according to claim 1, wherein the cladding is composed of silver, gold, or aluminum.

8. The second core has a flat plate shape, The cladding has a membrane shape and is positioned on the upper surface of the second core. The photoelectric field enhancing element according to claim 1, wherein the first core is disposed within the space enclosed by the first gap and the upper surface of the second core.

9. The photoelectric field enhancing element further comprises an intermediate layer of transparent material positioned in contact with the upper surface of the second core. The photoelectric field enhancing element according to claim 8, wherein the cladding is disposed on the upper surface of the second core via the intermediate layer.

10. A cladding comprising a first gap extending in a first direction, the first gap having a constant gap width in a second direction perpendicular to the first direction, A first core located within the first gap, A second core having a width in the second direction greater than the gap width, and optically connected to the first core, A method for manufacturing an electric field enhancing element comprising: A step of preparing a substrate having a structure in which a support layer, a silicon oxide film layer, and a second-order nonlinear optical material layer are stacked in this order, A step of forming a mask having an aperture corresponding to the cladding on the second-order nonlinear optical material layer, A step of etching the secondary nonlinear optical material layer through the mask, A step of forming a metal layer on the substrate via the mask, A removal step of lifting off the metal layer formed on the mask, The process involves forming a dielectric layer on the substrate from which the removal process has been performed, Equipped with, The cladding is formed by the aforementioned metal layer. The first core is formed by the second-order nonlinear optical material layer, The second core is formed by the dielectric layer. A method for manufacturing an electric field enhancement device.

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