Terahertz wave nonlinear metal dielectric grating and application

Abstract

The invention provides a metal dielectric interlayer nonlinear waveguide and application thereof, the waveguide structure is formed by alternately stacking metal layers and dielectric layers, and the dielectric layers are located between the two metal layers. A cylindrical cavity is dug in the midpoint area of the dielectric layer to form a specific cavity structure. According to the design, through interaction of the metal layer and the dielectric layer and combination of the light field local enhancement effect of the cavity structure, the intensity of the nonlinear optical effect is remarkably improved. The waveguide structure has the advantages of being high in integration level, low in loss and high in conversion efficiency, can be widely applied to the fields of ultrafast optics, optical communication, optical sensing and the like, and provides a new solution for miniaturization and high performance of nonlinear optical devices.

Description

Technical Field

[0001] The invention belongs to the technical field of optical information processing, and specifically designs a second harmonic efficiency of a metal nonlinear medium grating. Background Art

[0002] The terahertz band, covering 0.1 to 10 THz, lies precisely between microwaves and infrared light. It can effectively probe the low-energy states and molecular vibrations of materials and is suitable for studying various nonlinear optical effects. Many materials exhibit significant nonlinear responses. This response, particularly in metals and semiconductors, can be optimized to increase the efficiency of second-harmonic generation. However, challenges remain. First, the technology for generating and detecting terahertz waves is relatively immature, especially when it comes to generating high-power, wide-bandwidth waves. Existing terahertz sources still need to be improved in terms of efficiency and stability. Second, the period, depth, and shape of the grating affect the propagation characteristics of the incident light in the grating, and improper design may lead to additional scattering and loss.

[0003] Currently, the design of metallic nonlinear dielectric gratings has resulted in second harmonic generation efficiencies that are several orders of magnitude higher than those of the underlying nonlinear dielectric materials. Achieving enhanced optical nonlinearity at the subwavelength scale offers more possibilities for manipulating light. A properly designed subwavelength metallic nonlinear dielectric grating system, comprised of alternating layers of metal and dielectric, can achieve enhanced nonlinearity while enabling ultrafast and broadband operation, which is crucial for fabricating compact, ultrafast, low-power nonlinear optical devices for optical signal processing. Nevertheless, different grating designs can change the distribution and propagation path of the incident light, helping to optimize the local intensity of the light field. By adjusting the geometry and period of the pattern, better phase matching conditions can be achieved, improving the efficiency of second harmonic generation. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art and provide a new solution for obtaining higher second harmonic efficiency by using a metal nonlinear dielectric grating.

[0005] According to a first aspect of the present invention, there is provided a metal nonlinear dielectric grating, comprising:

[0006] Metal layer;

[0007] A dielectric layer, the dielectric layer being between two metal layers of the same size, and the dielectric layer being a single unit structure;

[0008] The unit is a cylinder dug out from the center of the dielectric layer;

[0009] Light of a specific frequency in the terahertz band is used to enter the dielectric layer from the side, and simulation is started to obtain the probe signal;

[0010] Obtain the Fourier series of the probe signal, combine the electric and magnetic fields into light intensity, and then compare the two intensities to obtain the generation efficiency of the second-order harmonic.

[0011] The second-order harmonic production efficiency is adaptively encrypted, and the parameter sweep simulation is re-performed to obtain the relationship between the excitation field intensity and the second harmonic efficiency of the material.

[0012] Optionally, the metal layer is made of silver, and the thickness of the metal layer is 1.25 μm.

[0013] Optionally, the metal layer material silver is defined by a macro, ε1=-4551.87, ε2=1446.23;

[0014] Optionally, the dielectric layer is made of cadmium selenide and has a thickness of 1.25 μm.

[0015] Optionally, the dielectric layer is made of cadmium selenide with a dielectric constant of 6.0614 and material properties of second-order nonlinearity, χ2:109. -12 ;

[0016] The cylinder radius: 3 μm, height: 1.25 μm;

[0017] According to a second aspect of the present invention, a second harmonic efficiency of a metal nonlinear dielectric grating is studied, characterized in that the metal nonlinear dielectric grating as described in the first aspect is used, including the following steps:

[0018] Light of a specific frequency in the terahertz band is used to enter from the side of the dielectric layer to obtain the probe signal;

[0019] Select a steady-state period of the probe signal and use Fourier series to calculate the fourth-order harmonic. Then synthesize the electromagnetic field into power and extract the fundamental frequency and second-order harmonic. Finally, compare the two intensities to obtain the second-order harmonic production efficiency.

[0020] Adaptively encrypt the second-order harmonic production efficiency, re-parameterize the sweep simulation, and obtain the relationship between the excitation field intensity and the second harmonic efficiency of the material;

[0021] Optionally, second harmonic efficiency, including:

[0022] The ratio of the second harmonic power to the input fundamental frequency optical power under different single-frequency incident light.

[0023] A technical effect of the present invention is:

[0024] In the embodiment of the present application, firstly, compared with the traditional underlying nonlinear material, the model introduces optical nonlinear dielectric grating, which has significant advantages:

[0025] The optical properties of metallic nonlinear dielectric gratings can be accurately described by a uniform nonlinear dielectric slab. Based on such metamaterial mapping, we show that the effective optical nonlinearity in metallic dielectric gratings can be several orders of magnitude higher than that of the underlying nonlinear dielectric material; (2) they can operate in the low quality factor regime, resulting in extremely short intrinsic time responses of a few picoseconds; and (3) subwavelength nonlinear optics offers unprecedented opportunities for structural enhancement of nonlinear effects that can be modified by geometric structures.

[0026] Secondly, the second-order harmonic efficiency reflected by the unit structure of the present invention can not only ensure the stability of the probe signal to extract the steady-state period, but also predict the overall harmonic efficiency composed of repeated unit structures, saving calculation time and improving calculation efficiency.

[0027] Thirdly, the present invention further improves the second-order harmonic efficiency of materials at the subwavelength scale on the existing basis by adjusting the geometric structure of the metal nonlinear dielectric grating. Although the existing metal nonlinear grating structure has made great breakthroughs compared with the past, the present invention breaks through the limitations of the second-order harmonic efficiency of existing materials through structural adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the structure of a metal nonlinear grating according to an embodiment of the present invention;

[0029] Figure 2 Schematic diagram of a top view of a metal nonlinear grating according to an embodiment of the present invention;

[0030] Figure 3 This is a graph showing the second harmonic efficiency of a metal nonlinear grating according to an embodiment of the present invention.

[0031] In the figure: 1, dielectric layer; 2, metal layer; 3, grating structure; D, radius of the hollow cylinder; L, width of the dielectric layer. DETAILED DESCRIPTION

[0032] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that:

[0033] Unless specifically stated otherwise, the relative arrangement of components and steps, the numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0034] The embodiments of the present application will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application and are not to be construed as limiting the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0035] The terms "first" and "second" in the specification and claims of this application may explicitly or implicitly refer to one or more of the features. Throughout the description of this application, unless otherwise specified, "plurality" means two or more. Furthermore, "and / or" in the specification and claims refers to at least one of the connected entities, and the character " / " generally indicates an "or" relationship between the connected entities.

[0036] In the description of this application, it is necessary to understand that the terms "center", "longitudinal", "lateral",

[0037] The orientations or positional relationships indicated by “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc. are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0038] In the description of this application, it should be noted that, unless otherwise clearly specified and limited,

[0039] The terms "mounted," "connected," and "connected" should be interpreted broadly. For example, they can refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; and internal communication between two components. Those skilled in the art will understand the specific meanings of these terms in this application.

[0040] According to the first aspect of the present invention, see Figure 1 、 Figure 2 and Figure 3, a metal nonlinear dielectric grating is provided as an enhancement device for obtaining second-order harmonics using a single-frequency transmission metasurface. Furthermore, by influencing the interaction between the terahertz wave and the metal nonlinear dielectric grating through a specific geometric structure on the metasurface, a significant enhancement in the second-order harmonic efficiency is achieved.

[0041] Specifically, see Figure 1 The metal nonlinear dielectric grating includes a dielectric layer 1 and a metal layer 2. The dielectric layer 1 is between the metal layers 2, and a cylinder is hollowed out of the dielectric layer.

[0042] For more details, see Figure 2 , the cylinder is located in the center of the metallic nonlinear dielectric grating.

[0043] Light of a specific frequency in the terahertz band is used to enter from the side of the dielectric layer to obtain the probe signal; Figure 1 The direction of the THz beam incident is given;

[0044] Select a steady-state period of the probe signal and use Fourier series to calculate the fourth-order harmonic. Then synthesize the electromagnetic field into power and extract the fundamental frequency and second-order harmonic. Finally, compare the two intensities to obtain the second-order harmonic production efficiency.

[0045] The second-order harmonic production efficiency is adaptively encrypted and the parameter sweep simulation is re-performed to obtain the relationship between the excitation field intensity and the second-order harmonic efficiency of the material. In other words, the second-order harmonic efficiency can be obtained based on the intensity ratio of the second-order harmonic to the incident wave.

[0046] It should be noted that metal gratings can excite surface plasma fluctuations, which not only enhance the local electric field but also significantly reduce the interaction time between light and materials, further accelerating the occurrence of nonlinear effects.

[0047] In the embodiment of the present application, firstly, compared with the traditional underlying nonlinear material, the model introduces optical nonlinear dielectric grating, which has significant advantages:

[0048] (1) The optical properties of metallic nonlinear dielectric gratings can be accurately described by a uniform nonlinear dielectric slab. Based on such metamaterial mapping, we show that the effective optical nonlinearity in metallic dielectric gratings can be several orders of magnitude higher than that of the underlying nonlinear dielectric material; (2) they can operate in the low quality factor range, resulting in extremely short intrinsic time responses of a few picoseconds; and (3) subwavelength nonlinear optics offers unprecedented opportunities for structural enhancement of nonlinear effects, and these nonlinear effects can be modified by geometric structures.

[0049] Secondly, the second-order harmonic efficiency reflected by the unit structure of the present invention can not only ensure the stability of the probe signal to extract the steady-state period, but also predict the overall harmonic efficiency composed of repeated unit structures, saving calculation time and improving calculation efficiency.

[0050] Thirdly, the present invention further improves the second-order harmonic efficiency of materials at the subwavelength scale on the existing basis by adjusting the geometric structure of the metal nonlinear dielectric grating. Although the existing metal nonlinear grating structure has made great breakthroughs compared with the past, the present invention breaks through the limitations of the second-order harmonic efficiency of existing materials through structural adjustment.

[0051] In the above embodiments, the crystal structure of CdSe makes it easier to achieve phase matching, which is crucial for enhancing the efficiency of the second-order harmonic. In certain configurations, CdSe can achieve phase matching conditions, thereby maximizing the output of harmonic generation.

[0052] Optionally, the metal layer is made of silver, and the thickness of the metal layer is 1.25 μm. The material and thickness of the metal layer are relatively reasonable, which can excite surface plasma fluctuations, resulting in local electric field enhancement of the incident light, and significantly improving the efficiency of the nonlinear optical process.

[0053] Optionally, the radius of the cylinder is 3 μm, which makes the geometric structure design on the dielectric layer more reasonable. When the incident electromagnetic wave irradiates the dielectric layer, the electric field will induce nonlinear polarization of the material. Through the influence of the quadratic nonlinear term, the material will produce second harmonic light in its response.

[0054] Optionally, the second harmonic efficiency includes the ratio of the second harmonic power to the input fundamental frequency light power under different single-frequency incident lights.

[0055] In the above embodiment, the metal nonlinear dielectric grating has high second-order harmonic efficiency and can respond quickly. The present invention aims to bring breakthroughs to the fields of laser technology, communications, imaging and quantum information through innovative geometric structures.

[0056] Therefore, the present application injects a single-frequency electromagnetic wave in order to obtain the second-order harmonic efficiency intuitively and clearly, and selects multiple frequencies to find the optimal incident frequency of the metal nonlinear dielectric grating through multiple calculations.

[0057] Furthermore, the dielectric layer is made of nonlinear cadmium selenide, a typical nonlinear optical material with a high second-order nonlinear optical coefficient. This significantly improves harmonic efficiency during second harmonic generation, enhances light-light interaction, and facilitates the generation of stronger harmonic signals.

[0058] In the example of the present application, the metal layer and the surface patterned dielectric layer constitute a metal nonlinear dielectric grating. The present invention uses terahertz waves as incident beams, and the incident electromagnetic wave electric field is perpendicularly incident on the structure along the x-axis polarization direction.

[0059] According to a second aspect of the present invention, a second harmonic efficiency of a metal nonlinear dielectric grating is studied, characterized in that the metal nonlinear dielectric grating as described in the first aspect is used, including the following steps:

[0060] Light of a specific frequency in the terahertz band is used to enter from the side of the dielectric layer to obtain the probe signal;

[0061] Select a steady-state period of the probe signal and use Fourier series to calculate the fourth-order harmonic. Then synthesize the electromagnetic field into power and extract the fundamental frequency and second-order harmonic. Finally, compare the two intensities to obtain the second-order harmonic production efficiency.

[0062] Adaptively encrypt the second-order harmonic production efficiency, re-parameterize the sweep simulation, and obtain the relationship between the excitation field intensity and the second harmonic efficiency of the material;

[0063] In the above embodiment, the application design of the metal nonlinear dielectric grating is reasonable, which further improves the second-order harmonic efficiency and responds quickly on the original basis, which is crucial for compact, ultrafast, low-power nonlinear optical devices for switching and modulation, as well as all-optical information processing.

[0064] Optionally, the second harmonic efficiency includes the ratio of the second harmonic power to the input fundamental frequency light power under different single-frequency incident lights.

[0065] The metasurface sensor provided by the present application is a special photonic material composed of a specially designed periodic unit structure. These unit structures can greatly enhance the local field intensity at the subwavelength scale, thereby effectively improving the second harmonic efficiency. In the present invention, by adjusting the size and shape of the unit structure, its second harmonic efficiency can be changed, and then the geometric structure with higher second harmonic efficiency can be explored through continuous adjustment. The present invention uses a specially designed metasurface structure as the basic resonant unit. These metasurface structures are composed of a dielectric layer and are of appropriate size, making them suitable for incident waves in the terahertz band.

[0066] When a single-frequency terahertz wave is incident on a metal grating, it excites surface plasmons. This coupling significantly enhances the electric field of the terahertz wave as it approaches the metal surface. This enhanced electric field significantly strengthens the nonlinear polarization effect in the material, promoting the generation of second harmonics. The generated second harmonics are coupled and diffracted by the metal grating, with the energy propagating outward, forming a detectable signal, which can then be used to calculate the second harmonic efficiency.

[0067] Compared with non-metallic materials such as silicon, the metal nonlinear dielectric grating of the present invention has surface plasmons in the metal grating, and these plasmons can significantly enhance the localization effect of the light field. Even at relatively low incident power, a very strong electric field can be generated on the metal surface, which helps to improve the efficiency of nonlinear reactions. In addition, the design and adjustment of the geometric structure of the grating can achieve adaptive phase matching. This design can adjust the propagation direction and phase of the light wave so that the second harmonic and the fundamental frequency light wave can be effectively superimposed, thereby improving their injection efficiency. It brings possibilities for compact, ultrafast, low-power nonlinear optical devices and all-optical information processing.

[0068] It will be understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present invention, and the present invention is not limited thereto. Those skilled in the art will appreciate that various modifications and improvements can be made without departing from the spirit and substance of the present invention, and such modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A metal dielectric grating, characterized in that: include: Metal layer; A dielectric layer, the dielectric layer being between two metal layers of the same size, and the dielectric layer being a single unit structure; The unit is a cylinder dug out from the center of the dielectric layer; Light of a specific frequency in the terahertz band is used to enter the dielectric layer from the side, and simulation is started to obtain the probe signal; Obtain the Fourier series of the probe signal, combine the electric and magnetic fields into light intensity, and then compare the two intensities to obtain the generation efficiency of the second-order harmonic. The second-order harmonic production efficiency is adaptively encrypted, and the parameter sweep simulation is re-performed to obtain the relationship between the excitation field intensity and the second harmonic efficiency of the material.

2. The metal dielectric grating according to claim 1, characterized in that The metal layer is made of silver, and has a thickness of 1.25 μm.

3. The metal dielectric grating according to claim 2, characterized in that The metal layer material silver is defined by a macro, ε1 = -4551.87, ε2 = 1446.

23.

4. The metal dielectric grating according to claim 1, wherein: The dielectric layer is made of cadmium selenide and has a thickness of 1.25 μm.

5. The metal dielectric grating according to claim 4, characterized in that The dielectric layer is made of cadmium selenide with a dielectric constant of 6.0614 and material properties of second-order nonlinearity, χ2:

109. -12 .

6. The metal dielectric grating according to claim 1, wherein: The radius of the cylinder is 3 μm, and the height is 1.25 μm.

7. An application of a metal dielectric grating, characterized in that: The metal dielectric grating according to any one of claims 1 to 6 is used, comprising the following steps: S1. Use light of a specific frequency in the terahertz band to enter the dielectric layer from the side to obtain the probe signal; S2. Select a steady-state period of the probe signal and use the Fourier series to calculate the fourth-order harmonic. Then, synthesize the electromagnetic field into power and extract the fundamental frequency and second-order harmonic. Finally, compare the two intensities to obtain the second-order harmonic production efficiency. S3. Adaptively encrypt the second-order harmonic production efficiency, re-parameterize the scanning simulation, and obtain the relationship between the excitation field intensity and the second harmonic efficiency of the material.

8. The use of the metal dielectric grating according to claim 7, characterized in that: By selecting light waves of different frequencies in the terahertz band and comparing the second harmonic efficiency, the frequency at which the metal dielectric grating has the highest second harmonic efficiency is obtained.

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