Terahertz wave generator and manufacturing method

Abstract

This application relates to the field of optical communication, providing a terahertz wave generator and its fabrication method. The generator includes a substrate and a substrate-supported terahertz wave generating structure. The terahertz wave generating structure includes a first waveguide and a second waveguide made of metal. The second waveguide includes a first periodic structure and a second periodic structure. The first waveguide is disposed between the first and second periodic structures. Both the first and second periodic structures have periodically distributed notches along the direction of the first waveguide on their sides closest to the first waveguide. When a first signal light and a second signal light illuminate the cross-section of the terahertz wave generator, the first and second signal lights are frequency-differentialized to generate a terahertz wave, which propagates along the surface of the second waveguide. The terahertz wave generator provided in this application can generate terahertz waves from existing signal light, has a simple and easy-to-implement structure, and utilizes the high conversion efficiency of existing signal light, enabling the generation of more effective terahertz waves.

Description

Technical Field

[0001] This application relates to the field of optical communication technology, and in particular to a terahertz wave generator and its fabrication method. Background Technology

[0002] Terahertz waves are waves with frequencies ranging from 0.1 Hz to 10 THZ. They have applications in many different fields, such as terahertz spectroscopy, biomedical diagnostics, materials identification, and 6G high-speed communication. Across the entire spectrum, terahertz waves are the only wave that can simultaneously satisfy the ultra-wide bandwidth and high data rate of fiber optic communication, as well as the wireless transmission capabilities of microwave communication.

[0003] Because, in order to achieve further research on THz waves, there is an urgent need for an on-chip terahertz wave generation device. Summary of the Invention

[0004] This application provides a terahertz wave generator and a method for manufacturing the terahertz wave generator. The terahertz wave generator can generate terahertz waves through existing signal light conversion, and has a high conversion efficiency, enabling the generation of more effective terahertz waves.

[0005] The first aspect of this application provides a terahertz wave generator, comprising:

[0006] A substrate and at least one terahertz wave generating structure, the substrate being used to support at least one terahertz wave generating structure;

[0007] The terahertz wave generating structure includes a first waveguide and a second waveguide made of metal. The second waveguide includes at least one first periodic structure and at least one second periodic structure. The first waveguide is disposed between the first periodic structure and the second periodic structure. Both the first periodic structure and the second periodic structure have notches periodically distributed along the direction of the first waveguide on one side passing through the first waveguide.

[0008] When the first signal light and the second signal light illuminate the cross section of the terahertz wave generator, the first signal light and the second signal light propagate in the first waveguide and generate a terahertz wave after frequency difference during propagation. The terahertz wave propagates along the surface of the first periodic structure and the surface of the second periodic structure.

[0009] A second aspect of this application provides a method for preparing a terahertz wave generator, the method comprising:

[0010] Determine the first material for fabricating the first waveguide and the second material for fabricating the second waveguide;

[0011] The wavelengths of the first and second signal lights are determined based on the frequency of the terahertz waves.

[0012] The parameters of the first waveguide and the second waveguide are determined according to a first condition, wherein the difference between the first propagation constant of the first signal light and the second propagation constant of the second signal light is equal to the third propagation constant of the terahertz wave; the terahertz wave is generated by the difference frequency of the first signal light and the second signal light.

[0013] The first waveguide is fabricated on a substrate based on the first material and according to the parameters of the first waveguide;

[0014] The second waveguide is fabricated on the substrate based on the second material and according to the parameters of the second waveguide.

[0015] The technical solution provided in this application can achieve at least the following beneficial effects:

[0016] The terahertz wave generator and its fabrication method provided in this application include a substrate and at least one terahertz wave generating structure. The substrate supports the at least one terahertz wave generating structure. Each terahertz wave generating structure includes a first waveguide and a second waveguide made of metal. The second waveguide includes at least one first periodic structure and at least one second periodic structure. The first waveguide is disposed between the first and second periodic structures. Both the first and second periodic structures have periodically distributed notches along the direction of the first waveguide on their sides closest to the first waveguide. When a first signal light and a second signal light illuminate the cross-section of the terahertz wave generator, the first and second signal lights propagate in the first waveguide and generate terahertz waves by frequency difference during propagation. The terahertz waves mainly propagate along the surfaces of the first and second periodic structures facing the first waveguide. The terahertz wave generator provided in this application can generate terahertz waves based on existing signal light. It has a simple structure, is easy to implement, and utilizes the high conversion efficiency of existing signal light, enabling the generation of more effective terahertz waves. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a terahertz wave generating structure shown in an exemplary embodiment of this application;

[0018] Figure 2 This is a schematic diagram of a first periodic structure and a second periodic structure shown in an exemplary embodiment of this application;

[0019] Figure 3 This is a schematic diagram of another terahertz wave generating structure shown in an exemplary embodiment of this application;

[0020] Figure 4This is a side view of a terahertz wave generating structure shown in an exemplary embodiment of this application;

[0021] Figure 5 This is an exemplary embodiment of the present application illustrating the propagation constant and mode field distribution of a communication band;

[0022] Figure 6 This application illustrates an exemplary embodiment of the dispersion curve of a second waveguide and its corresponding mode distribution.

[0023] Figure 7(a) illustrates the relationship between terahertz wave conversion efficiency and propagation distance under phase-matching conditions in an exemplary embodiment of this application.

[0024] Figure 7(b) illustrates the variation of an overlap integral factor and effective mode area under phase-matching conditions in an exemplary embodiment of this application.

[0025] Figure 7(c) is a transmission spectrum of terahertz waves shown in an exemplary embodiment of this application;

[0026] Figure 8 This application illustrates an effective nonlinear coefficient d in an exemplary embodiment. eff E in TE1 mode z Component distribution;

[0027] Figure 9(a) illustrates another variation of the overlap integral factor and effective mode area under phase-matching conditions, as shown in an exemplary embodiment of this application.

[0028] Figure 9(b) illustrates another relationship between the terahertz wave conversion efficiency and propagation distance under phase-matching conditions, as shown in an exemplary embodiment of this application.

[0029] Figure 9(c) shows another terahertz wave transmission spectrum as illustrated in an exemplary embodiment of this application;

[0030] Figure 10 This application provides a method for preparing a terahertz wave generator.

[0031] Figure label:

[0032] 1000. Terahertz wave generator; 10. Substrate; 20. Terahertz wave generating structure; 30. Protective structure;

[0033] 101, Substrate; 102, Buffer layer; 201, First waveguide; 202, Second waveguide;

[0034] 2021, First periodic structure; 2022, Second periodic structure. Detailed Implementation

[0035] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0036] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0037] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit the application. Unless otherwise defined, the technical or scientific terms used in this application should be understood in their ordinary sense by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in this application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms "a" or "one," etc., do not indicate a quantity limitation, but rather indicate the presence of at least one. "A plurality" or "several" indicates two or more. Unless otherwise indicated, the terms "front," "rear," "lower," and / or "upper," etc., are for ease of description only and are not limited to a location or spatial orientation. The terms "comprising" or "including," etc., mean that the elements or objects preceding "comprising" or "including" encompass the elements or objects listed following "comprising" or "including" and their equivalents, and do not exclude other elements or objects. The terms "connected," "linked," etc., are not limited to physical or mechanical connections and can include electrical connections, whether direct or indirect.

[0038] Terahertz waves are waves with frequencies ranging from 0.1 Hz to 10 THZ. They have applications in many different fields, such as terahertz spectroscopy, biomedical diagnostics, materials identification, and 6G high-speed communication. Across the entire spectrum, terahertz waves are the only wave that can simultaneously satisfy the ultra-wide bandwidth and high data rate of fiber optic communication, as well as the wireless transmission capabilities of microwave communication.

[0039] However, there is currently a lack of effective THz source generation devices. Therefore, this application provides a terahertz wave generator 1000, which can generate terahertz waves by performing frequency difference generation on existing signal light, and has high conversion efficiency, and can generate more effective terahertz waves.

[0040] The structure for generating terahertz waves provided in this application will be described below.

[0041] like Figure 1 As shown, Figure 1 This is a schematic diagram of the structure of a terahertz wave generator 1000 provided in this application, wherein the terahertz wave generator 1000 includes a substrate 10 and at least one terahertz wave generating structure 20.

[0042] The substrate 10 is used to support at least one terahertz wave generating structure 20.

[0043] Continue as Figure 1 As shown, the substrate 10 includes a substrate 101 and a buffer layer 102.

[0044] The substrate 101 can be in the shape of a cuboid, cube, cylinder, prism, etc., and this application does not limit its shape. The substrate 101 can be a clean single-crystal wafer with specific crystal planes and appropriate electrical, optical, and mechanical properties, used for growing epitaxial layers to support and improve thin film properties. The material of the substrate 101 is, for example, silicon (Si). The length and width of the substrate 101 can be greater than or equal to the length or width of the buffer layer 102, and the thickness of the substrate 101 is greater than the thickness of the buffer layer 102. The thickness of the substrate 101 is generally set to be above 200 micrometers, for example, it can be set to 300 micrometers. Since the dimensions of the first and second waveguides are on the order of micrometers, they require the support of the substrate during movement. Therefore, as long as it can support other structures disposed on it, this application does not impose specific limitations on the material and thickness of the substrate 101.

[0045] A buffer layer 102 is disposed on the upper surface of the substrate 101. The buffer layer 102 can be disposed on the upper surface of the substrate 101 through manufacturing processes such as bonding or lamination; this application does not limit this. The shape of the buffer layer 102 can be a cuboid, cube, cylinder, prism, etc., and the shape of the buffer layer 102 can be the same as or different from the shape of the substrate 101. The buffer layer 102 can prevent the first signal light, the second signal light, and the terahertz wave from leaking to the substrate 101, thereby improving the conversion efficiency of the first signal light and the second signal light into terahertz waves, so as to produce more terahertz waves. The material of the buffer layer 102 can be, for example, silicon dioxide (SiO2). Since the buffer layer 102 is disposed on the substrate 101, the length and width of the buffer layer 102 can be less than or equal to the length and width of the substrate 101. Furthermore, since the buffer layer 102 is disposed between the first waveguide 201 and the substrate 101, its function is to prevent light leakage, so the thickness of the buffer layer 102 needs to be greater than the wavelength of the second signal light. It should be noted here that the wavelength of the first signal light is shorter than the wavelength of the second signal light.

[0046] For example, the substrate 10 can be provided by a commercially available manufacturer. The overall thickness and width of the substrate 10 can be determined by the terahertz wave so that the substrate 10 can better support at least one terahertz wave generating structure 20. The upper surface of the substrate 10 can be provided with one terahertz wave generating structure 20, two terahertz wave generating structures 20, three terahertz wave generating structures 20, etc., and this application does not limit this.

[0047] The substrate 10 is used to support at least one terahertz wave generating structure 20. The terahertz wave generating structure 20 is described below, continuing as follows. Figure 1 As shown, the terahertz wave generating structure 20 includes a first waveguide 201 and a second waveguide 202. The first waveguide 201 is disposed on the buffer layer 102, and the second waveguide 202 is disposed on the first waveguide 201.

[0048] The material of the first waveguide 201 can be, for example, gallium phosphide (GaP), gallium arsenide (GaAs), gallium selenide (GaSe), and lanthanides (LN). This application does not impose specific limitations on the material of the first waveguide 201, as long as the material of the first waveguide 201 satisfies the second-order nonlinear tensor χ. (2) It just needs to be non-zero.

[0049] The substrate film required for the first waveguide is deposited on the buffer layer 102, and the first waveguide is fabricated on the buffer layer 102 by waveguide etching; the second waveguide is fabricated on the buffer layer 102 by metal deposition. If the thickness of the substrate film is equal to the required cross-sectional height h of the first waveguide... eIn this case, during waveguide etching, the substrate thin film is directly etched through, and the second waveguide formed by the metal coating is directly located on the buffer layer 102; however, generally the thickness of the substrate thin film is greater than the required cross-sectional height h of the first waveguide. e So, after the substrate film is etched to form the first waveguide, a layer of substrate will remain on the buffer layer, and then the second waveguide formed by the metal coating is located directly on the remaining substrate.

[0050] During the fabrication of the first waveguide 201, if the first waveguide 201 is etched onto the upper surface of the buffer layer 102, it is often difficult to etch vertically during the etching process, resulting in protruding structures 2011 with different widths at the top and bottom. However, if the substrate of the first waveguide 201 is thin, it can also be etched into a first waveguide 201 with the same width at the top and bottom. The shape of the first waveguide 201 can be any of the following: a ridge structure, a trapezoidal structure, or a rectangular structure. After setting its parameters to preset parameters, the first waveguide 201 can achieve a propagation constant such that the difference between the propagation constant of the first signal light and the propagation constant of the second signal light is equal to the propagation constant of the terahertz wave. Therefore, after the substrate 10 is set, the parameters of the first waveguide 201 can be further set according to the preset first condition and the thickness of the substrate 10, so that the laser can etch the first waveguide 201 according to the preset parameters during laser etching. The first condition is that the difference between the first propagation constant of the first signal light and the propagation constant of the second signal light is equal to the third propagation constant of the terahertz wave. It should be noted here that the first signal light is usually referred to as the pump light, and the second signal light is usually referred to as the signal light.

[0051] The parameters of the first waveguide 201 may include the cross-sectional dimensions of the first waveguide 201. The cross-sectional dimensions of the first waveguide 201 may be obtained through simulation based on the wavelength of the first signal light, the wavelength of the second signal light, the frequency of the first signal light, the frequency of the second signal light, the frequency of the terahertz wave, the first propagation constant, the second propagation constant, and the third propagation constant.

[0052] Since the terahertz wave is generated by illuminating the cross section of the terahertz wave generator 1000 with the first and second signal lights, and the first and second signal lights propagate in the first waveguide 201 and are generated by frequency difference during propagation, the terahertz wave is obtained by converting the first and second signal lights. The expression for the conversion efficiency is:

[0053]

[0054] Among them, P p and P s These are the input powers of the first and second signal lights, P, respectively. THzThe output power of the terahertz wave is L, the waveguide length is L, Z0 and c are the impedance in vacuum and the speed of light, respectively, and ω is ω. THz and α THz These are the frequency and attenuation coefficient of the terahertz wave, respectively, d eff These are the effective nonlinear coefficients, ζ and A. eff These are the overlap integral factor and the effective mode area, respectively, and y represents the propagation distance of the terahertz wave wavelength in the waveguide.

[0055] The specific expression of the overlapping integral factor is:

[0056]

[0057] E j It is the eigenfield of terahertz waves, the first signal light, and the second signal light. It is d 33 The reduced nonlinear coefficient tensor, ω p and ω s These are the frequencies of the first and second signal lights, respectively. x, y, and z are the corresponding coordinates in the coordinate system.

[0058] The expression for the effective mode area is A. eff =(A opt1 A opt2 A THz ) 1 / 3 ,in:

[0059]

[0060] As can be seen from the above expression, to improve the conversion efficiency of the first and second signal lights into terahertz waves, the effective mode area A needs to be reduced. eff Increase the overlap integral factor ζ and select a larger nonlinear coefficient d. eff And reduce the loss α of terahertz waves. THz The difference between the first propagation constant of the first signal light and the second propagation constant of the second signal light is equal to the third propagation constant of the terahertz wave, ensuring that the first and second signal lights generate terahertz waves with maximum conversion efficiency at any position. If the difference between the first and second propagation constants of the first and second signal lights is not equal to the third propagation constant of the terahertz wave, within a certain propagation range, the energy of the terahertz wave generated by the frequency difference between the first and second signal lights will be transferred back to the first and second signal lights, thus reducing the conversion efficiency of the terahertz wave. Therefore, determining the waveguide parameters based on the first condition and the length of the substrate 10 can improve the conversion efficiency of the first and second signal lights, generating more effective terahertz waves.

[0061] For example, lithium niobate single crystal thin film (LNOI) is selected as the substrate film of the first waveguide 201. EBL (Electron Beam Lithography System) photoresist is deposited on the LNOI film, followed by photolithography and development, then LN is directly etched, and finally the photoresist is removed and cleaned to complete the processing of the first waveguide 201.

[0062] If the material of the first waveguide 201 is periodically polarized lithium niobate (PPLN), it needs to be periodically polarized after the LN waveguide etching is completed.

[0063] Furthermore, the terahertz wave generating structure 20 also includes a second waveguide 202, which includes at least one periodic structure and at least one second periodic structure 2022. The first periodic structure 2021 and the second periodic structure 2022 can be made of metals such as gold, silver, aluminum, and copper. For example, if the first periodic structure 2021 and the second periodic structure 2022 are identical, and the notch is a hollow semi-rectangular structure, such as... Figure 2 The diagram shows a first periodic structure 2021 and a second periodic structure 2022. The shapes of the first periodic structure 2021 and the second periodic structure 2022 can be the same or different, and this application does not limit this. The first periodic structure 2021 is disposed on the upper surface of the buffer layer 102, and the second periodic structure 2022 is also disposed on the upper surface of the buffer layer 102. The connection method between the first periodic structure 2021 and the buffer layer 102, and the connection method between the second periodic structure 2022 and the buffer layer 102, can be, for example, bonding, pressing, etching, etc., and is not limited here.

[0064] The first periodic structure 2021 includes a gap, and the line segment forming the gap is any one of the following: a U-shaped arc, a semi-circular arc, a three-quarter circular arc, a rectangular line segment, a T-shaped line segment, a sawtooth line segment, etc., or even an irregular curve, a broken line, etc.

[0065] The second periodic structure 2022 also includes gaps, which can be formed by any of the following line segments: U-shaped arc, semi-circular arc, three-quarter circular arc, rectangular line segment, T-shaped line segment, zigzag line segment, etc., or even irregular curves, broken lines, etc.

[0066] The first periodic structure 2021 and the second periodic structure 2022 are disposed on both sides of the first waveguide 201.

[0067] The distance between the first periodic structure 2021 and the first waveguide 201, and the distance between the second periodic structure 2022 and the first waveguide 201, are both within the range of the first distance threshold.

[0068] Therefore, the distance between the first periodic structure 2021 and the first waveguide 201 can be the same as the distance between the second periodic structure 2022 and the first waveguide 201. That is, the first waveguide 201 is located in the middle of the first periodic structure 2021 and the second periodic structure 2022, or the first periodic structure 2021 and the second periodic structure 2022 are symmetrically arranged on both sides of the first waveguide 201. This arrangement enables the generated terahertz wave to propagate on the surface of the second waveguide and maximizes the conversion efficiency between the first signal light and the second signal light.

[0069] Of course, the distance between the first periodic structure 2021 and the first waveguide 201 and the distance between the second periodic structure 2022 and the first waveguide 201 can be different, and this application does not limit this.

[0070] The first periodic structure 2021 and the second periodic structure 2022 have the aforementioned notches on their sides facing the first waveguide 201. Figure 1 and Figure 3 In the example diagram shown, the straight lines with arrows represent the first and second signal lights, and the direction of the arrows indicates the direction of transmission of the first and second signal lights towards the terahertz wave generator. That is, when terahertz waves need to be generated, the first and second signal lights will be directed towards the cross-section of the terahertz wave generator. When the first and second signal lights illuminate the cross-section of the terahertz wave generator 1000, they propagate in the first waveguide 201 and generate terahertz waves by frequency difference during propagation. The terahertz waves mainly propagate along the surfaces of the first periodic structure facing the first waveguide and the second periodic structure facing the first waveguide. Therefore, the smaller the distance between the first periodic structure 2021 and the first waveguide 201, and the smaller the distance between the second periodic structure 2022 and the first waveguide 201, the more the mode field of the terahertz waves can be compressed to the subwavelength scale, thereby improving the conversion efficiency of the first and second signal lights.

[0071] The nonlinear process in the hybrid waveguide of the second waveguide 202 and the first waveguide 201 can be described by the following equation:

[0072]

[0073] Among them, A j ,n j (j=THz,p,s) represent the normalized amplitudes and corresponding effective refractive indices of the THz wave, pump wave, and signal wave, respectively; Z0 and c represent the impedance in vacuum and the speed of light, respectively; ω THz and α THz These are the frequency and attenuation coefficient of the THz wave, respectively. effThese are the effective nonlinear coefficients, ζ and A. eff These are the overlap integral factor and the effective mode area, respectively, Δβ = β p -β s -β THz β is the phase mismatch between the three wavelengths. p Let β be the propagation constant of the first signal light. s y is the propagation constant of the second signal light, and y represents the propagation distance of the THz wavelength in the waveguide.

[0074] Therefore, when fabricating the second waveguide 202, the distances between the first periodic structure 2021 and the first waveguide 201, and between the second periodic structure 2022 and the first waveguide 201, are determined according to the aforementioned principles. This compresses the terahertz wave field distribution to a subwavelength scale, meaning the characteristic scale of the terahertz wave mode field is smaller than the wavelength of the terahertz wave. This makes the terahertz wave field distribution more concentrated, thus reducing the effective mode area and increasing the overlap integral factor, further improving the conversion efficiency of the first and second signal lights. The terahertz wave propagates in the second waveguide as a surface wave, which reduces transmission loss.

[0075] It should be noted here that, theoretically, the smaller the distance between the first periodic structure 2021 and the first waveguide 201, and the smaller the distance between the second periodic structure 2022 and the first waveguide 201, the higher the conversion efficiency. However, in order to avoid causing large losses, the distance between the first periodic structure 2021 and the second periodic structure 2022 needs to be greater than the width of the first waveguide 201 sandwiched between them, and they cannot be too close to the first waveguide 201.

[0076] Furthermore, because the terahertz wave dispersion curve of the second waveguide 202 is distributed in the form of energy bands, its characteristic is that the group velocity of the light wave tends to zero as the propagation constant increases. The group velocity approaching zero means that the localization of light in the second waveguide 202 is continuously enhanced, resulting in a band gap in the dispersion curve at the Brillouin zone boundary. The dispersion curve exhibits slow light and field enhancement effects near the Brillouin zone boundary. This localization of the light field near the Brillouin zone boundary allows for a smaller mode field in the terahertz wave, which can further reduce the nonlinear effective mode area and increase the overlap integral factor, thereby further improving the conversion efficiency.

[0077] Based on the above determination principles, the distance between the first periodic structure 2021 and the first waveguide 201, as well as the distance between the second periodic structure 2022 and the first waveguide 201, can be determined.

[0078] Then, since the parameters of the second waveguide 202 include the cross-sectional dimensions, notch dimensions, and periodic length of the notch distribution of the first periodic structure, and the cross-sectional dimensions, notch dimensions, and periodic length of the notch distribution of the second periodic structure, the specific determination steps are as follows:

[0079] 1. First, the frequency of the terahertz wave is obtained by subtracting the frequency of the first signal light from the frequency of the second signal light;

[0080] 2. Determine the wavelengths of the first and second signal lights based on the frequency of the terahertz waves;

[0081] 3. Furthermore, the difference between the first propagation constant of the first signal light in the first waveguide and the second propagation constant of the second signal light in the first waveguide is equal to the third propagation constant of the terahertz wave on the surface of the second waveguide.

[0082] 4. Input the frequencies of the first signal light, the second signal light, the terahertz wave, the wavelengths of the first and second signal lights, the etching process, the metal coating process, and the relationship between the first, second, and third propagation constants into the simulation software for simulation. Based on the simulation results, obtain the first waveguide parameters and various parameters of the second waveguide that conform to the relationship between the three propagation constants.

[0083] In addition, after the second waveguide 202 is installed, in order to protect the terahertz wave generator 1000 and extend its service life, a protective structure 30 can be installed on the upper surface of the terahertz wave generating structure 20 to protect the terahertz wave generator 1000.

[0084] The fabrication process of the terahertz wave generating structure 20 provided in this application is illustrated below by way of example:

[0085] Example 1: Figure 3 As shown, it is necessary to generate a terahertz wave with a frequency of 0.42 THz. The wavelength of the first signal light is 1684.6 nm, and the wavelength of the second signal light is 1688.6 nm. The first waveguide 201 is made of LN, and the hollow structure of the second waveguide 202 is serrated.

[0086] In order to utilize the maximum nonlinear coefficient d of LN 33 LN is selected as x-cut type, and the modes of both the first and second signal beams are TE. 00 The fundamental mode, i.e., the principal component of the electric field, is mainly along the optical axis (z-axis) of the lithium niobate crystal. In the actual fabrication process of the LN waveguide, the etching tilt angle of the first waveguide 201 is primarily determined by the fabrication process, such as... Figure 4 As shown, the etching angle here is θ, which is 60°. After the basic structure of the first waveguide 201 is determined, the propagation constant β of the terahertz wave is obtained through simulation. THz The approximate range. For example... Figure 4 Among the parameters shown, the adjustable geometric parameters for the first and second signal beams are: the width w0 of the first waveguide 201, and the etching depth h. e LN unetched thickness h LN These three geometric parameters and the propagation constant β p and β p The larger the value, the corresponding β p -β s The larger the value, the more β can be achieved within a suitable range. p -β s =β THz The parameters of the first waveguide 201 of LN that satisfy this condition are: the unetched thickness h of LN. LN The etching depth is 600nm, and the etching depth is h. e The wavelength is 300 nm, and the top width w0 of the waveguide is 1.4 μm. Below the LN layer is a SiO2 buffer layer with a thickness of 102. The thickness is 4.7 μm, and the thickness of the SiO2 protective layer on top is [not specified]. The thickness is 2μm, and the bottom layer is the Si substrate 101 with a thickness of h. Si The value is 500 μm. Simulation calculations were used to obtain the propagation constant of light waves in nonlinear dielectric thin-film waveguides and their corresponding mode field distributions under these parameters. Figure 5 ).

[0087] Figure 6 The diagram shows the terahertz wave dispersion curves and mode distributions for each dispersion pattern in the second waveguide 202. The eigenmodes corresponding to the dispersion curves with solid lines are designated TE0, and the modes corresponding to the dispersion curves with dashed lines are designated TE1. Their principal electric field components are all along the optical axis (z-direction) of LN. By adjusting... Figure 4 The parameters shown alter the z-dispersion curve of the terahertz wave. For example, keeping the period p constant, increasing the sawtooth width p2, increasing the groove depth d, decreasing the spacing g, and increasing the metal thickness h. Au It can Figure 6 The dispersion curve shifts upwards, meaning the propagation constant of the terahertz wave increases. The desired 0.42 THz modulation is achieved near the Brillouin zone boundary of the TE0 dispersion curve, with the propagation constant satisfying phase matching. This determines... Figure 4 The parameters of the metamaterial waveguide metal portion shown are determined as p = 145 μm, p1 = 40 μm, p2 = 105 μm, w = 13 μm, d = 2 μm, g = 7 μm, h Au =0.8μm. At this time, the 0.42 terahertz wave satisfies phase matching with the first signal light (1684.6nm) and the second signal light (1688.6nm).

[0088] Based on the coupled wave equations described above, it can be calculated that the conversion efficiency Γ of the terahertz wave approaches its maximum value of 1.51 × 10⁻⁶ when it propagates to 3 cm in both the first and second channels. -4 W -1 [As shown in Figure 7(a)]. The high conversion efficiency of this application is due to the large overlap integral factor and small effective mode area in the hollowed-out structural portions of the first periodic structure 2021 and the second periodic structure 2022 [as shown in Figure 7(b)]. By setting the wavelength of the first signal light to 1688.6 nm and the second signal light to vary around 1684.6 nm, a THz transmission spectrum was obtained [Figure 7(c)]. It exhibits a high conversion efficiency in the range of 0.14–0.44 THz, thus the THz transmission spectrum has broadband properties.

[0089] Example 2: Furthermore, selecting the first higher-order mode TE1 of the second waveguide 202 can also achieve efficient generation of terahertz waves. And under the condition of achieving phase matching, the distance between the first periodic structure 2021 and the first waveguide 201, and the distance between the second periodic structure 2022 and the first waveguide 201, can be further reduced. This increases the overlap integral factor and reduces the effective mode area, thus further improving the nonlinear conversion efficiency. However, because the principal component of the electric field E of TE1... z (y) is antisymmetric along the propagation direction, and the overlap integral factor ζ is also antisymmetric. To ensure that the first signal light, the second signal light, and the terahertz wave satisfy the phase-matching condition, the material of the first waveguide 201 can be selected as periodically polarized lithium niobate (PPLN). The length of the PPLN is twice that of the periodic structure of the second waveguide 202, i.e., Λ p =2p. The hybrid structure at this point is as follows: Figure 8 As shown. The effective nonlinear coefficient d after polarizing lithium niobate. eff Antisymmetric distribution:

[0090]

[0091] Multiplying by the overlap integral factor ζ ensures that the integral term in the effective mode area expression is symmetrically distributed, allowing the generated terahertz waves to accumulate continuously.

[0092] To generate a terahertz wave with a frequency of 0.42 THz, the first, second, and third propagation constants must still satisfy the first condition; thus, the wavelength of the first signal light will be 1583.2 nm, and the wavelength of the second signal light will be 1586.8 nm. Let the etching depth h of LN... eThe LN polarization period is Λ = 300 μm, the duty cycle is 0.5, and the other parameters of the LN remain the same as in Example 1. The geometric parameters of the second waveguide 202 are changed so that the desired 0.42 THz appears at the band edge of the TE1 dispersion curve and satisfies the phase matching condition. The parameters of the metallic part of the second waveguide are then determined as p = 150 μm, p1 = 25 μm, p2 = 125 μm, w = 15 μm, d = 3 μm, g = 2 μm, while the thickness remains unchanged at 800 nm. As shown in Figure 9(a), the effective mode area of ​​the sawtooth portion in the metamaterial waveguide is calculated to be reduced to 19 μm. 2 The overlap integral factor increases to 0.81. The corresponding conversion efficiency improves by an order of magnitude, reaching 1.32 × 10⁻⁶ when the terahertz wave propagates to 6 cm. -3 W -1 [Figure 9(b)]. As shown in Figure 9(c), the bandwidth of the terahertz wave transmission spectrum decreases with increasing propagation length. Here, the terahertz wave transmission spectrum does not exhibit broadband characteristics because the second dispersion curve of the terahertz wave changes faster than the first dispersion curve, and the phase mismatch increases more rapidly.

[0093] In another embodiment, such as Figure 10 As shown, this application also provides a method for fabricating a terahertz wave generator, which includes the following steps:

[0094] Step S1001: Determine the first material for fabricating the first waveguide and the second material for fabricating the second waveguide;

[0095] Step S1002: Determine the wavelength of the first signal light and the wavelength of the second signal light based on the frequency of the terahertz wave;

[0096] Step S1003: Determine the parameters of the first waveguide and the second waveguide according to the first condition. The first condition is that the difference between the first propagation constant of the first signal light and the second propagation constant of the second signal light is equal to the third propagation constant of the terahertz wave. The terahertz wave is generated by the difference frequency of the first signal light and the second signal light.

[0097] Step S1004: The first waveguide is fabricated on the substrate based on the first material and according to the parameters of the first waveguide.

[0098] Step S1005: The second waveguide is fabricated on the substrate based on the second material and according to the parameters of the second waveguide.

[0099] The preparation method has been explained in the description of the terahertz wave structure above, and will not be repeated here.

[0100] It is readily understood that, based on the several embodiments provided in this application, those skilled in the art can combine, split, or reorganize the embodiments of this application to obtain other embodiments, none of which exceed the protection scope of this application.

[0101] The above detailed embodiments further illustrate the purpose, technical solution, and beneficial effects of the embodiments of this application. It should be understood that the above are merely specific embodiments of the embodiments of this application and are not intended to limit the protection scope of the embodiments of this application. Any modifications, equivalent substitutions, improvements, etc., made on the basis of the technical solutions of the embodiments of this application should be included within the protection scope of the embodiments of this application.

Claims

1. A terahertz wave generator characterized by comprising: include: A substrate and at least one terahertz wave generating structure, the substrate being used to support at least one terahertz wave generating structure; The terahertz wave generating structure includes a first waveguide and a second waveguide made of metal. The second waveguide includes at least one first periodic structure and at least one second periodic structure. The first waveguide is disposed between the first periodic structure and the second periodic structure. Both the first periodic structure and the second periodic structure have notches periodically distributed along the direction of the first waveguide on the side closer to the first waveguide. When the first signal light and the second signal light illuminate the cross section of the terahertz wave generator, the first signal light and the second signal light propagate in the first waveguide and generate a terahertz wave after frequency difference during propagation. The terahertz wave propagates along the surface of the first periodic structure and the surface of the second periodic structure. The parameters of the first waveguide satisfy a first preset range; The parameters of the second waveguide satisfy a second preset range. The first preset range and the second preset range are used to make the propagation constant of the first signal light, the propagation constant of the second signal light, and the propagation constant of the terahertz wave satisfy phase matching; wherein, the difference between the first propagation constant of the first signal light and the second propagation constant of the second signal light is equal to the third propagation constant of the terahertz wave.

2. The terahertz wave generator according to claim 1, characterized in that, The first periodic structure and the second periodic structure are symmetrical about the first waveguide; The distance between the first periodic structure and the first waveguide and the distance between the second periodic structure and the first waveguide are both within the range of a first distance threshold, which is greater than the cross-sectional width of the first waveguide; The distance between the first periodic structure and the second periodic structure is greater than the width of the first waveguide sandwiched between them.

3. The terahertz wave generator according to claim 1, wherein The substrate includes a substrate and a buffer layer, the buffer layer being disposed on the upper surface of the substrate, and the first waveguide being disposed on the upper surface of the buffer layer. The size of the substrate is greater than or equal to the size of the buffer layer. The thickness of the buffer layer is greater than the wavelength of the second signal light.

4. The terahertz wave generator according to claim 1, wherein It also includes a protective structure disposed on the upper surface of the terahertz wave generating structure.

5. The terahertz wave generator according to claim 1, characterized in that, The parameters of the first waveguide include: the cross-sectional dimensions of the first waveguide; The parameters of the second waveguide include: the cross-sectional dimensions, notch dimensions, and periodic length of the notch distribution of the first periodic structure, and the cross-sectional dimensions, notch dimensions, and periodic length of the notch distribution of the second periodic structure.

6. A method for preparing a terahertz wave generator, characterized by comprising: The preparation method is used to prepare the terahertz wave generator according to claim 1, and the preparation method includes: Determine the first material for fabricating the first waveguide and the second material for fabricating the second waveguide; The wavelengths of the first signal light and the second signal light are determined based on the frequency of the terahertz wave, and the difference between the frequency of the first signal light and the frequency of the second signal light is equal to the frequency of the terahertz wave. The parameters of the first waveguide and the second waveguide are determined according to a first condition, wherein the difference between the first propagation constant of the first signal light and the second propagation constant of the second signal light is equal to the third propagation constant of the terahertz wave; the terahertz wave is generated by the difference frequency of the first signal light and the second signal light. The first waveguide is fabricated on a substrate based on the first material and according to the parameters of the first waveguide; The second waveguide is fabricated on the substrate based on the second material and according to the parameters of the second waveguide; The first waveguide is a periodically polarized waveguide, and the period length of the first waveguide is twice the period length of the second waveguide.

7. The production method according to claim 6, characterized by, The terahertz wave is located at the Brillouin zone boundary of the terahertz wave dispersion curve of the second waveguide.

8. The preparation method according to claim 6, characterized in that, The terahertz wave is located at the Brillouin zone boundary of the higher-order dispersion curve of the terahertz wave in the second waveguide.

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