Layered optical structure based on second order nonlinear signal intensity modulation

Abstract

This invention relates to the field of nonlinear optics, and more particularly to a layered optical structure based on second-order nonlinear signal intensity modulation, comprising a prism layer, a spacer layer, a waveguide layer, a sample layer under test, and a cladding layer. Incident light is coupled into the waveguide layer via the prism layer, exciting waveguide modes within the waveguide layer under the condition of transverse wave vector matching, forming a strong local electric field that enhances the nonlinear interaction between the incident light and the sample layer under test. By optimizing the optical thickness of the spacer layer, attenuated total internal reflection of the incident light is achieved, allowing for efficient coupling of incident light energy into the waveguide modes. Simultaneously, a high-dispersion medium is used as the spacer layer, transforming the second harmonic from an evanescent wave into a propagating wave or an attenuated wave within the spacer layer, eliminating its evanescent attenuation, and enabling resonant enhancement of the second harmonic output through thickness control. This invention can significantly improve the intensity of the second harmonic and has advantages such as simple structure, ease of fabrication, and flexible material selection.

Description

Technical Field

[0001] This invention belongs to the field of nonlinear optics technology, and particularly relates to a layered optical structure based on second-order nonlinear signal intensity modulation. Background Technology

[0002] Second-order nonlinear optical effects, as core nonlinear optical processes, play a crucial role in cutting-edge technologies such as quantum light sources, electro-optic modulation, and the characterization of material crystal symmetry. With the miniaturization of integrated optoelectronics, test layers (STDs) have become highly promising nonlinear photonics platforms due to their inherently high second-order nonlinear polarizability, disregard for phase-matching limitations, and excellent on-chip heterogeneous integration capabilities. However, the atomic-level thickness of STDs limits the interaction length between light and matter, resulting in extremely weak second-harmonic conversion efficiency, which significantly restricts their application in practical devices.

[0003] To address this issue, existing technologies have proposed various enhancement strategies, such as deeply coupling the sample layer to be tested with optical microcavities, metal nanostructures, and metasurfaces, and utilizing the extremely strong local field supported by the structure to enhance the intensity of light-matter interaction.

[0004] However, the aforementioned optical micro / nano structures typically suffer from problems such as complex design, high manufacturing costs, and difficulty in fabrication. While layered optical structures offer advantages such as simple design, ease of fabrication, and low manufacturing costs, they have physical limitations in enhancing the second harmonic of the sample layer under test, making it difficult to meet the high conversion efficiency requirements of second harmonics in practical applications.

[0005] Therefore, there is an urgent need for a novel layered optical structure that can break through the theoretical limits of traditional layered optical structures and significantly enhance the second harmonic effect of the sample layer under test. Summary of the Invention

[0006] In view of this, the present invention aims to provide a layered optical structure based on second-order nonlinear signal intensity modulation, in order to solve the problems of complex design, high manufacturing cost, and difficulty in processing of existing optical micro-nano structures, while the enhancement effect of traditional layered optical structures has physical limits.

[0007] To achieve the above objectives, the technical solution created by this invention is implemented as follows: A layered optical structure based on second-order nonlinear signal intensity modulation includes a prism layer, a spacer layer, a sample under test (SUT) layer, a waveguide layer, and a cladding layer. The spacer layer, SUT layer, and waveguide layer are all located between the prism layer and the cladding layer, with the spacer layer adjacent to the prism layer and either the SUT layer or the waveguide layer adjacent to the cladding layer. The prism layer provides transverse wave vector matching for the incident light. The spacer layer adjusts the phase of the incident light to induce attenuated total internal reflection, and its refractive index is lower than that of the waveguide layer. The waveguide layer excites waveguide modes under transverse wave vector matching to generate a local electric field with an intensity higher than that of the incident light. The SUT layer performs nonlinear frequency conversion on the incident light under the influence of the locally enhanced optical field to generate a second harmonic. The cladding layer, with a refractive index lower than that of the waveguide layer, forms a refractive index difference with the waveguide layer to confine the optical field within the waveguide layer.

[0008] Furthermore, the spacer layer is made of a dispersive medium material, so that the second harmonic is a propagating wave or a decaying wave within the spacer layer, but not an evanescent wave.

[0009] Furthermore, the coating layer is a vacuum layer or a dielectric layer.

[0010] Furthermore, when the sample layer under test is located between the spacer layer and the waveguide layer, the layered optical structure is configuration A. When the incident light undergoes attenuation total internal reflection at the interface between the prism layer and the spacer layer, the following condition is satisfied:

[0011]

[0012] When the incident light is When light is polarized, we have:

[0013]

[0014]

[0015]

[0016]

[0017]

[0018] When the incident light is When light is polarized, we have:

[0019]

[0020]

[0021]

[0022]

[0023]

[0024] in,

[0025]

[0026]

[0027]

[0028] in, Represents the imaginary unit; This indicates the polarization state of the incident light. ; Indicates the thickness of the spacer layer; Indicates the thickness of the waveguide layer; The wave vector parameter represents the incident light. , This represents the horizontal component of the wave vector of the incident light within the prism layer, spacer layer, sample layer, waveguide layer, and cladding layer. , Indicates the refractive index of the prism layer. Indicates the angle of incidence of the incident light in the prism layer; Represents the speed of light in a vacuum. Indicates the angular frequency of the incident light; This represents the reflection coefficient of incident light at the interface between the prism layer and the spacer layer. This represents the reflection coefficient of incident light at the interface between the waveguide layer and the cladding layer. This represents the reflection coefficient of incident light between the lower surface of the spacer layer and the upper surface of the cladding layer; This represents the reflection coefficient of incident light between the lower surface of the spacer layer and the upper surface of the waveguide layer. This represents the reflection coefficient of incident light between the upper surface of the waveguide layer and the lower surface of the spacer layer; This represents the transmission coefficient of incident light between the lower surface of the spacer layer and the upper surface of the waveguide layer. This represents the transmission coefficient of incident light between the upper surface of the waveguide layer and the lower surface of the spacer layer. This represents the vertical component of the wave vector of the incident light within the prism layer; This represents the vertical component of the wave vector of the incident light within the cladding layer; This represents the vertical component of the wave vector of the incident light within the spacer layer; This represents the vertical component of the wave vector of the incident light within the waveguide layer; This represents the dielectric function of the prism layer; This represents the dielectric function of the cladding layer; The dielectric function of the spacer layer; This represents the dielectric function of the waveguide layer; Indicates the wavenumber of the incident light; ; This represents the linear surface conductivity of the sample layer, ignoring out-of-plane components. It represents the vacuum permittivity.

[0029] Furthermore, when the layered optical structure is configuration A, and waveguide modes are excited in the waveguide layer, the following condition is satisfied:

[0030] When the incident light is When light is polarized, we have:

[0031] When the incident light is When light is polarized, we have:

[0032] in, This represents the reflection coefficient at the interface between the spacer layer and the waveguide layer, ignoring the influence of the sample layer under test.

[0033] Furthermore, when the sample layer under test is located between the waveguide layer and the cladding layer, the layered optical structure is configuration B. When the incident light undergoes attenuation total internal reflection at the interface between the prism layer and the spacer layer, the following condition is satisfied:

[0034]

[0035] When the incident light is When light is polarized, we have:

[0036]

[0037]

[0038] When the incident light is When light is polarized, we have:

[0039]

[0040]

[0041] in,

[0042]

[0043]

[0044]

[0045] in, Represents the imaginary unit; This indicates the polarization state of the incident light. ; Indicates the thickness of the spacer layer; Indicates the thickness of the waveguide layer; The wave vector parameter represents the incident light. , This represents the horizontal component of the wave vector of the incident light within the prism layer, spacer layer, waveguide layer, sample layer, and cladding layer. , Indicates the refractive index of the prism layer. This indicates the angle of incidence of the incident light in the prism layer. This represents the angular frequency of the incident light. Represents the speed of light in a vacuum; This represents the reflection coefficient of incident light at the interface between the prism layer and the spacer layer. This represents the reflection coefficient of incident light at the interface between the spacer layer and the waveguide layer. This represents the reflection coefficient of incident light between the lower surface of the spacer layer and the upper surface of the cladding layer; This represents the reflection coefficient of incident light between the lower surface of the waveguide layer and the upper surface of the cladding layer; This represents the vertical component of the wave vector of the incident light within the prism layer; This represents the vertical component of the wave vector of the incident light within the cladding layer; This represents the vertical component of the wave vector of the incident light within the spacer layer; This represents the vertical component of the wave vector of the incident light within the waveguide layer; This represents the dielectric function of the prism layer; This represents the dielectric function of the cladding layer; The dielectric function of the spacer layer; This represents the dielectric function of the waveguide layer; Indicates the wavenumber of the incident light. .

[0046] Furthermore, when the layered optical structure is configuration B, and waveguide modes are excited in the waveguide layer, the following condition is satisfied:

[0047] When the incident light is When light is polarized, we have:

[0048]

[0049] When the incident light is When light is polarized, we have:

[0050]

[0051] in, This represents the reflection coefficient at the interface between the waveguide layer and the cladding layer, ignoring the influence of the sample layer under test.

[0052] Furthermore, the thickness of the spacer layer satisfies the resonance condition of the second harmonic within the spacer layer:

[0053] in, Represents the reflection coefficient phase angle or reflection coefficient The angle of the argument, The order of resonance is represented by an integer. The wave vector parameter representing the second harmonic; This represents the reflection coefficient between the lower surface of the spacer layer and the upper surface of the covering layer when the layered optical structure is configuration A. This represents the reflection coefficient between the lower surface of the spacer layer and the upper surface of the covering layer when the layered optical structure is configuration B.

[0054] Furthermore, the prism layer is any one of silicon carbide, titanium dioxide, and silicon nitride; the spacer layer is any one of titanium dioxide, silicon dioxide, aluminum oxide, and single-crystal hexagonal boron nitride; the waveguide layer is any one of silicon carbide, titanium dioxide, silicon nitride, lithium niobate, and zinc sulfide; and the dielectric layer is silicon dioxide or aluminum oxide.

[0055] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) This invention introduces a waveguide mode excitation mechanism and uses prism layer coupling to provide transverse wave vector matching conditions for incident light, forming a strong local electric field in the waveguide layer, which greatly enhances the interaction intensity between incident light and the sample layer under test, thereby breaking through the theoretical limit of the original layered structure enhancement factor, and can enhance the second harmonic of the sample layer under test by more than 7 orders of magnitude.

[0056] (2) The present invention uses a high dispersion medium as a spacer layer, so that the vertical component of the incident light wave vector in the spacer layer is a pure imaginary number to maintain a strong local electric field, while the vertical component of the second harmonic wave vector in the spacer layer is a real number or a complex number, thereby avoiding the second harmonic wave from being rapidly attenuated due to evanescent propagation in the spacer layer, and realizing the enhancement of the second harmonic wave.

[0057] (3) By adjusting the thickness of the spacer layer, the present invention enables the second harmonic to meet the resonance condition within the spacer layer, thereby further improving the intensity of the second harmonic.

[0058] (4) The layered optical structure proposed in this invention consists of only a prism layer, a spacer layer, a waveguide layer, a sample layer, and a cladding layer. It does not require complex nanofabrication techniques (such as electron beam lithography, focused ion beam etching, etc.) and can be prepared using standard thin film deposition, mechanical lift-off and transfer processes. It has the advantages of simple design, easy processing, and low manufacturing cost. At the same time, the structure has good material compatibility. The materials of the prism layer, spacer layer and waveguide layer can be flexibly replaced according to the working band and specific application requirements, which facilitates integration with existing on-chip photonics platforms. Attached Figure Description

[0059] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic diagram of the layered optical structure based on second-order nonlinear signal intensity modulation as described in Embodiment 1 of this invention; Figure 2 This is a schematic diagram illustrating the relationship between the structure factor and the incident angle under different waveguide modes as described in Embodiment 1 of the present invention; wherein, the vertical axis represents the structure factor. , for Both the incident light and the second harmonic are Structure factor for polarized light; x-axis represents the incident angle. Figure 3 This is a schematic diagram illustrating the relationship between the structure factor and the incident angle under different waveguide modes as described in Embodiment 2 of the present invention; wherein, the vertical axis represents the structure factor. , for The structure factor when both the incident light and the second harmonic are s-polarized; the horizontal axis represents the incident angle. Figure 4 A schematic diagram of the layered optical structure based on second-order nonlinear signal intensity modulation as described in Embodiment 3 of this invention; Figure 5This is a schematic diagram illustrating the relationship between the structure factor and the incident angle under different waveguide modes as described in Embodiment 3 of the present invention; wherein, the vertical axis represents the structure factor. , for Both the incident light and the second harmonic are Structure factor for polarized light; x-axis represents the incident angle. Figure 6 This is a schematic diagram illustrating the relationship between the structure factor and the incident angle under different waveguide modes as described in Embodiment 4 of the present invention; wherein, the vertical axis represents the structure factor. , for Both the incident light and the second harmonic are The structure factor for polarized light; the horizontal axis represents the incident angle.

[0060] Explanation of reference numerals in Example 1: prism layer 1a, cladding layer 2a, spacer layer 3a, waveguide layer 4a, sample layer under test 5a; Explanation of reference numerals in Example 3: prism layer 1b, cladding layer 2b, spacer layer 3b, waveguide layer 4b, sample layer under test 5b. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0062] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0063] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0064] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "assembly," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0065] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0066] Example 1 like Figure 1 and Figure 2 As shown, the layered optical structure based on second-order nonlinear signal intensity modulation provided in Embodiment 1 of the present invention adopts configuration A. The layered optical structure includes a prism layer 1a, a spacer layer 3a, a sample layer 5a, a waveguide layer 4a, and a cladding layer 2a stacked sequentially along the incident light propagation direction. The prism layer 1a is used to provide transverse wave vector matching conditions for the incident light. The refractive index of the spacer layer 3a is less than that of the waveguide layer 4a, and it is used to adjust the phase of the incident light so that the incident light undergoes attenuation total internal reflection. The waveguide layer 4a is used to excite waveguide modes under transverse wave vector matching to generate a local electric field with an intensity higher than that of the incident light. The sample layer 5a is used to perform nonlinear frequency conversion on the incident light under the action of the locally enhanced optical field to generate second harmonics. The cladding layer 2a is used to form a refractive index difference with the waveguide layer 4a to confine the optical field within the waveguide layer 4a. The cladding layer 2a is a vacuum layer with a refractive index of 1 or a dielectric layer with a refractive index less than that of the waveguide layer 4a.

[0067] The incident light enters the prism layer 1a at an angle greater than the critical angle for total internal reflection, exciting the waveguide mode in the waveguide layer 4a when the transverse wave vector matching condition is met. The optical field of the waveguide mode is strongly confined within the waveguide layer 4a, forming a strong local electric field in this region that is much higher than the incident light field, thereby greatly enhancing the nonlinear interaction between the incident light and the sample layer 5a under test.

[0068] When incident light undergoes attenuated total internal reflection at the interface between prism layer 1a and spacer layer 3a, the following condition is satisfied:

[0069]

[0070] When the incident light is When light is polarized, we have:

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078] When the incident light is When light is polarized, we have:

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086] in,

[0087]

[0088]

[0089]

[0090] in, Represents the imaginary unit; This indicates the polarization state of the incident light. ; This indicates the thickness of spacer layer 3a; This indicates the thickness of waveguide layer 4a; The wave vector parameter represents the incident light. , This represents the horizontal component of the wave vector of the incident light within the prism layer 1a, spacer layer 3a, sample layer 5a, waveguide layer 4a, and cladding layer 2a. , This represents the refractive index of prism layer 1a. This indicates the angle of incidence of the incident light in prism layer 1a; Represents the speed of light in a vacuum. Indicates the angular frequency of the incident light; This represents the reflection coefficient of the incident light (s-polarized light or p-polarized light) at the interface between prism layer 1a and spacer layer 3a; This represents the reflection coefficient of incident light at the interface between waveguide layer 4a and cladding layer 2a; This represents the reflection coefficient of incident light between the lower surface of spacer layer 3a and the upper surface of cladding layer 2a; This represents the reflection coefficient of incident light between the lower surface of spacer layer 3a and the upper surface of waveguide layer 4a; This represents the reflection coefficient of incident light between the upper surface of waveguide layer 4a and the lower surface of spacer layer 3a; This represents the transmission coefficient of incident light between the lower surface of spacer layer 3a and the upper surface of waveguide layer 4a. This represents the transmission coefficient of incident light between the upper surface of waveguide layer 4a and the lower surface of spacer layer 3a. This represents the vertical component of the wave vector of the incident light within prism layer 1a; This represents the vertical component of the wave vector of the incident light within the cladding layer 2a; This represents the vertical component of the wave vector of the incident light within the spacer layer 3a; This represents the vertical component of the wave vector of the incident light within waveguide layer 4a; The dielectric function of prism layer 1a is represented; The dielectric function of the cladding layer 2a is represented; The dielectric function of spacer layer 3a is represented; The dielectric function of waveguide layer 4a is represented; Indicates the wavenumber of the incident light; These represent intermediate physical parameters used to calculate the optical properties of layered optical structures. , This represents the linear surface conductivity of layer 5a of the sample under test, ignoring out-of-plane components. It represents the vacuum permittivity.

[0091] When waveguide modes are excited in waveguide layer 4a, the following condition is satisfied:

[0092] When the incident light is When light is polarized, we have:

[0093]

[0094] When the incident light is When light is polarized, we have:

[0095]

[0096] in, This represents the reflection coefficient at the interface between spacer layer 3a and waveguide layer 4a, ignoring the influence of sample layer 5a.

[0097] To quantitatively describe the enhancement effect of layered optical structures on second harmonics, a structure factor is introduced. :

[0098] in, Let be the wave vector of the incident light; The polarization state of the incident light; The local electric field strength used to reflect the fundamental frequency (incident light frequency), Used to characterize the coupling strength of second harmonic outward radiation.

[0099] for Polarized light has:

[0100]

[0101]

[0102]

[0103] for Polarized light has:

[0104]

[0105]

[0106]

[0107] in, This represents the perpendicular component of the wave vector of incident light or second harmonic in vacuum. express Transmission coefficient of polarized light at the interface between prism layer 1a and spacer layer 3a; express Transmission coefficient of polarized light at the interface between prism layer 1a and spacer layer 3a.

[0108] In traditional layered optical structures, the spacer layer 3a is often air or a low-dispersion medium. For a pure imaginary number, make The exponent term in Rapid attenuation leads to a decrease in the intensity of the second harmonic. Embodiment 1 of the present invention uses a highly dispersive medium as the spacer layer 3a to... It is a purely imaginary number (the incident light is still evanescently coupled), while By using real numbers (for propagating second harmonics) or complex numbers (for decaying second harmonics), the evanescent decay of the second harmonic within the spacer layer 3a is avoided, greatly enhancing the second harmonic. Furthermore, by adjusting the resonance of the second harmonic within the spacer layer 3a, it is possible to... This further enhances, and ultimately strengthens, the intensity of the second harmonic. The resonance of the second harmonic within spacer layer 3a can be adjusted by changing the thickness of spacer layer 3a. To achieve, to make ,in, This represents the reflection coefficient between the lower surface of spacer layer 3a and the upper surface of covering layer 2a. The angle of the argument, ; The order of resonance is represented by an integer. This represents the wave vector parameter of the second harmonic. When the thickness of the spacer layer 3a... When the resonance condition of the second harmonic is satisfied within the spacer layer 3a When the value reaches its maximum, the second harmonic radiation coupling efficiency is the highest.

[0109] Taking silicon carbide as the material for prism layer 1a and waveguide layer 4a, titanium dioxide as the material for spacer layer 3a, and molybdenum disulfide as the material for sample layer 5a as examples, the structure factor is calculated under different TE modes. The relationship between the incident angle and the incident angle.

[0110] Figure 2 Structural factors are given under different TE modes. The curves show the variation with the incident angle. Simulation results show that this layered optical structure can enhance the second harmonic intensity of molybdenum disulfide by more than seven orders of magnitude.

[0111] The working principle of the layered optical structure is as follows: Incident light is coupled through prism layer 1a and excites waveguide modes in waveguide layer 4a through transverse wave vector matching conditions. The optical field of the waveguide mode is strongly confined within waveguide layer 4a, forming a strong local electric field in this region that is much stronger than the incident light field, thereby greatly enhancing the nonlinear interaction between the incident light and the sample layer 5a. Simultaneously, a spacer layer 3a with a lower refractive index than waveguide layer 4a and appropriate dispersion characteristics is introduced. By optimizing the thickness of spacer layer 3a, attenuated total internal reflection of the incident light is achieved. Attenuated total internal reflection means that the incident light energy is completely transferred to the waveguide mode, and the reflected light intensity is close to zero, further improving the energy coupling efficiency. Based on this, by selecting a high-dispersion material as the spacer layer 3a, the incident light becomes an evanescent wave within the spacer layer 3a, while the second harmonic becomes a propagating or attenuating wave, overcoming the evanescent attenuation of the second harmonic within the spacer layer 3a in traditional layered optical structures. Furthermore, by optimizing the thickness of the spacer layer 3a, constructive resonance of the second harmonic occurs within the spacer layer 3a, significantly enhancing its outward radiation coupling efficiency. Through the synergistic effect of the above multiple mechanisms, the layered optical structure of Embodiment 1 of this invention can increase the second harmonic intensity of the sample layer under test by more than seven orders of magnitude.

[0112] Example 2 Consistent with the principle of Example 1, using silicon carbide as the prism layer 1a, titanium dioxide as the spacer layer 3a, zinc sulfide as the waveguide layer 4a, and molybdenum disulfide as the sample layer 5a, the structure factor was calculated under different TE modes. The relationship between the incident angle and the incident angle.

[0113] Figure 3 Structural factors are given under different TE modes. The curves show the variation with the incident angle. Simulation results show that this layered optical structure can enhance the second harmonic intensity of molybdenum disulfide by more than seven orders of magnitude.

[0114] Example 3 like Figure 4 and Figure 5 As shown, the layered optical structure based on second-order nonlinear signal intensity modulation provided in Embodiment 3 of the present invention adopts configuration B. The layered optical structure includes a prism layer 1b, a spacer layer 3b, a waveguide layer 4b, a sample layer 5b under test, and a cladding layer 2b stacked sequentially along the incident light propagation direction. Unlike Embodiment 1, in Embodiment 3, the sample layer 5b under test is placed between the cladding layer 2b and the waveguide layer 4b. The function of the prism layer 1b is the same as that of the prism layer 1a, the function of the spacer layer 3b is the same as that of the spacer layer 3a, the function of the waveguide layer 4b is the same as that of the waveguide layer 4a, the function of the sample layer 5b under test is the same as that of the sample layer 5a under test, and the function of the cladding layer 2b is the same as that of the cladding layer 2a.

[0115] The working principle of Example 3 is basically the same as that of Example 1. It also constructs a strong local electric field by exciting waveguide modes and achieves efficient coupling of incident light energy through attenuated total internal reflection. Simultaneously, it utilizes a high-dispersion spacer layer to eliminate the evanescent attenuation of the second harmonic and achieve resonance enhancement. The difference lies in the change in the position of the sample layer 5b under test, which leads to corresponding adjustments in the expressions for the relevant reflection and transmission coefficients.

[0116] When incident light undergoes attenuated total internal reflection at the interface between prism layer 1b and spacer layer 3b, the following condition is satisfied:

[0117]

[0118] When the incident light is When light is polarized, we have:

[0119]

[0120]

[0121]

[0122]

[0123] When the incident light is When light is polarized, we have:

[0124]

[0125]

[0126]

[0127]

[0128] in,

[0129]

[0130]

[0131]

[0132] in, Represents the imaginary unit; This indicates the polarization state of the incident light. ; This indicates the thickness of spacer layer 3b; This indicates the thickness of waveguide layer 4b; The wave vector parameter represents the incident light. , This represents the horizontal component of the wave vector of the incident light within the prism layer 1b, spacer layer 3b, waveguide layer 4b, sample layer 5b, and cladding layer 2b. , This represents the refractive index of prism layer 1b. This represents the angle of incidence of the incident light in prism layer 1b. This represents the angular frequency of the incident light. Represents the speed of light in a vacuum; This represents the reflection coefficient of incident light at the interface between prism layer 1b and spacer layer 3b; This represents the reflection coefficient of incident light at the interface between spacer layer 3b and waveguide layer 4b; This represents the reflection coefficient of incident light between the lower surface of spacer layer 3b and the upper surface of cladding layer 2b; This represents the reflection coefficient of incident light between the lower surface of waveguide layer 4b and the upper surface of cladding layer 2b. This represents the vertical component of the wave vector of the incident light within prism layer 1b; This represents the vertical component of the wave vector of the incident light within the cladding layer 2b; This represents the vertical component of the wave vector of the incident light within the spacer layer 3b; This represents the vertical component of the wave vector of the incident light within waveguide layer 4b. The dielectric function of prism layer 1b is represented; The dielectric function of the cladding layer 2b is represented. The dielectric function of spacer layer 3b is represented; The dielectric function of waveguide layer 4b is represented. Indicates the wavenumber of the incident light. .

[0133] When waveguide modes are excited in waveguide layer 4b, the following condition is satisfied:

[0134] When the incident light is When the light is polarized, then:

[0135]

[0136]

[0137] When the incident light is When the light is polarized, then:

[0138]

[0139]

[0140] in, This represents the reflection coefficient at the interface between waveguide layer 4b and cladding layer 2b, ignoring the influence of layer 5b in the sample under test.

[0141] structural factors The definition is the same as in Example 1.

[0142] for Polarized light has:

[0143]

[0144]

[0145]

[0146]

[0147]

[0148]

[0149]

[0150]

[0151]

[0152]

[0153] for Polarized light has:

[0154]

[0155]

[0156]

[0157]

[0158]

[0159]

[0160]

[0161]

[0162]

[0163]

[0164] in, express Transmission coefficient of polarized light at the interface between prism layer 1b and spacer layer 3b; express Transmission coefficient of polarized light at the interface between prism layer 1b and spacer layer 3b; express Transmission coefficient of polarized light at the interface between spacer layer 3b and waveguide layer 4b; express Transmission coefficient of polarized light at the interface between spacer layer 3b and waveguide layer 4b; express Transmission coefficient of polarized light at the interface between waveguide layer 4b and spacer layer 3b; express Transmission coefficient of polarized light at the interface between waveguide layer 4b and spacer layer 3b; express The reflection coefficient of polarized light between the lower surface of waveguide layer 4b and the upper surface of cladding layer 2b; express The reflection coefficient of polarized light between the lower surface of waveguide layer 4b and the upper surface of cladding layer 2b; express Transmission coefficient of polarized light between the lower surface of waveguide layer 4b and the upper surface of cladding layer 2b; express Transmission coefficient of polarized light between the lower surface of waveguide layer 4b and the upper surface of cladding layer 2b; express Transmission coefficient of polarized light between the upper surface of cladding layer 2b and the lower surface of waveguide layer 4b; express Transmission coefficient of polarized light between the upper surface of cladding layer 2b and the lower surface of waveguide layer 4b.

[0165] Similar to Example 1, by selecting a high-dispersion material as the spacer layer 3b and ensuring that the second harmonic satisfies the resonance condition within the spacer layer 3b, evanescent attenuation can be eliminated and the outward radiation coupling efficiency of the second harmonic can be significantly improved.

[0166] Simulations were performed using the same material system as in Example 1 (prism layer 1b and waveguide layer 4b are silicon carbide, spacer layer 3b is titanium dioxide, and sample layer 5b is molybdenum disulfide). The structure factor variation curves with incident angle under different TE modes were obtained, as shown below. Figure 5 As shown in the figure. Simulation results confirm that configuration B can also enhance the second harmonic of molybdenum disulfide by more than 7 orders of magnitude.

[0167] Example 4 Consistent with the principle of Example 3, prism layer 1b is silicon carbide, spacer layer 3b is titanium dioxide, waveguide layer 4b is zinc sulfide, and sample layer 5b is molybdenum disulfide. Simulations were performed to obtain the structure factor variation curves with incident angle under different TE modes, such as... Figure 6 As shown, it can enhance the second harmonic of molybdenum disulfide by more than 6 orders of magnitude.

[0168] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0169] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A layered optical structure based on second-order nonlinear signal intensity modulation, characterized in that, It includes a prism layer, a spacer layer, a sample layer, a waveguide layer, and a cladding layer. The spacer layer, sample layer, and waveguide layer are all located between the prism layer and the cladding layer, with the spacer layer adjacent to the prism layer and the sample layer or waveguide layer adjacent to the cladding layer. The prism layer is used to provide transverse wave vector matching conditions for the incident light; The spacer layer is used to adjust the phase of the incident light, so that the incident light undergoes attenuation and total internal reflection. The refractive index of the spacer layer is less than that of the waveguide layer. The waveguide layer is used to excite waveguide modes under transverse wave vector matching to generate a local electric field with an intensity higher than that of the incident light. The sample layer under test is used to perform nonlinear frequency conversion on the incident light under the action of a locally enhanced optical field, so as to generate a second harmonic. The refractive index of the cladding layer is lower than that of the waveguide layer, which is used to create a refractive index difference with the waveguide layer in order to confine the light field within the waveguide layer.

2. The layered optical structure based on second-order nonlinear signal intensity modulation according to claim 1, characterized in that, The spacer layer is made of a dispersive medium material, so that the second harmonic is either a propagating wave or an attenuated wave within the spacer layer.

3. The layered optical structure based on second-order nonlinear signal intensity modulation according to claim 1, characterized in that, The coating layer is either a vacuum layer or a dielectric layer.

4. The layered optical structure based on second-order nonlinear signal intensity modulation according to claim 1, characterized in that, When the sample layer under test is located between the spacer layer and the waveguide layer, the layered optical structure is configuration A. When the incident light undergoes attenuation and total internal reflection at the interface between the prism layer and the spacer layer, the following condition is satisfied: When the incident light is When light is polarized, we have: When the incident light is When light is polarized, we have: in, in, Represents the imaginary unit; This indicates the polarization state of the incident light. ; Indicates the thickness of the spacer layer; Indicates the thickness of the waveguide layer; The wave vector parameter represents the incident light. , This represents the horizontal component of the wave vector of the incident light within the prism layer, spacer layer, sample layer, waveguide layer, and cladding layer. , Indicates the refractive index of the prism layer. Indicates the angle of incidence of the incident light in the prism layer; Represents the speed of light in a vacuum. Indicates the angular frequency of the incident light; This represents the reflection coefficient of incident light at the interface between the prism layer and the spacer layer. This represents the reflection coefficient of incident light at the interface between the waveguide layer and the cladding layer. This represents the reflection coefficient of incident light between the lower surface of the spacer layer and the upper surface of the cladding layer; This represents the reflection coefficient of incident light between the lower surface of the spacer layer and the upper surface of the waveguide layer. This represents the reflection coefficient of incident light between the upper surface of the waveguide layer and the lower surface of the spacer layer; This represents the transmission coefficient of incident light between the lower surface of the spacer layer and the upper surface of the waveguide layer. This represents the transmission coefficient of incident light between the upper surface of the waveguide layer and the lower surface of the spacer layer. This represents the vertical component of the wave vector of the incident light within the prism layer; This represents the vertical component of the wave vector of the incident light within the cladding layer; This represents the vertical component of the wave vector of the incident light within the spacer layer; This represents the vertical component of the wave vector of the incident light within the waveguide layer; This represents the dielectric function of the prism layer; This represents the dielectric function of the cladding layer; The dielectric function of the spacer layer; This represents the dielectric function of the waveguide layer; Indicates the wavenumber of the incident light; ; This represents the linear surface conductivity of the sample layer, ignoring out-of-plane components. It represents the vacuum permittivity.

5. The layered optical structure based on second-order nonlinear signal intensity modulation according to claim 4, characterized in that, When the layered optical structure is configuration A, and waveguide modes are excited in the waveguide layer, the following condition is satisfied: When the incident light is When light is polarized, we have: When the incident light is When light is polarized, we have: in, This represents the reflection coefficient at the interface between the spacer layer and the waveguide layer, ignoring the influence of the sample layer under test.

6. The layered optical structure based on second-order nonlinear signal intensity modulation according to claim 1, characterized in that, When the sample layer under test is located between the waveguide layer and the cladding layer, the layered optical structure is configuration B. When the incident light undergoes attenuation and total internal reflection at the interface between the prism layer and the spacer layer, the following condition is satisfied: When the incident light is When light is polarized, we have: When the incident light is When light is polarized, we have: in, in, Represents the imaginary unit; This indicates the polarization state of the incident light. ; Indicates the thickness of the spacer layer; Indicates the thickness of the waveguide layer; The wave vector parameter represents the incident light. , This represents the horizontal component of the wave vector of the incident light within the prism layer, spacer layer, waveguide layer, sample layer, and cladding layer. , Indicates the refractive index of the prism layer. This indicates the angle of incidence of the incident light in the prism layer. This represents the angular frequency of the incident light. Represents the speed of light in a vacuum; This represents the reflection coefficient of incident light at the interface between the prism layer and the spacer layer. This represents the reflection coefficient of incident light at the interface between the spacer layer and the waveguide layer. This represents the reflection coefficient of incident light between the lower surface of the spacer layer and the upper surface of the cladding layer; This represents the reflection coefficient of incident light between the lower surface of the waveguide layer and the upper surface of the cladding layer; This represents the vertical component of the wave vector of the incident light within the prism layer; This represents the vertical component of the wave vector of the incident light within the cladding layer; This represents the vertical component of the wave vector of the incident light within the spacer layer; This represents the vertical component of the wave vector of the incident light within the waveguide layer; This represents the dielectric function of the prism layer; This represents the dielectric function of the cladding layer; The dielectric function of the spacer layer; This represents the dielectric function of the waveguide layer; This indicates the wavenumber of the incident light.

7. The layered optical structure based on second-order nonlinear signal intensity modulation according to claim 6, characterized in that, When the layered optical structure is configuration B, and waveguide modes are excited in the waveguide layer, the following condition is satisfied: When the incident light is When light is polarized, we have: When the incident light is When light is polarized, we have: in, This represents the reflection coefficient at the interface between the waveguide layer and the cladding layer, ignoring the influence of the sample layer under test.

8. The layered optical structure based on second-order nonlinear signal intensity modulation according to claim 1, characterized in that, The thickness of the spacer layer satisfies the resonance condition of the second harmonic within the spacer layer: in, Represents the reflection coefficient phase angle or reflection coefficient The angle of the argument, The order of resonance is represented by an integer. The wave vector parameter representing the second harmonic; This represents the reflection coefficient between the lower surface of the spacer layer and the upper surface of the covering layer when the layered optical structure is configuration A. This represents the reflection coefficient between the lower surface of the spacer layer and the upper surface of the covering layer when the layered optical structure is configuration B.

9. The layered optical structure based on second-order nonlinear signal intensity modulation according to claim 3, characterized in that, The prism layer is made of any one of silicon carbide, titanium dioxide, or silicon nitride; the spacer layer is made of any one of titanium dioxide, silicon dioxide, aluminum oxide, or single-crystal hexagonal boron nitride; the waveguide layer is made of any one of silicon carbide, titanium dioxide, silicon nitride, lithium niobate, or zinc sulfide; and the dielectric layer is made of silicon dioxide or aluminum oxide.

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