A lithium niobate thin film fast adiabatic 3dB power splitter and a method for realizing the same

Abstract

The application discloses a lithium niobate thin film rapid adiabatic 3dB power splitter, and relates to the technical field of integrated photonics; the lithium niobate thin film rapid adiabatic 3dB power splitter comprises, from top to bottom, an upper cladding layer, an x-cut lithium niobate thin film layer, a buried oxygen layer and a silicon substrate layer; the x-cut lithium niobate layer contains a lithium niobate thin film ridge waveguide formed by etching technology; the lithium niobate thin film waveguide comprises, in sequence, an input end tapered waveguide, an input end S-bent waveguide, a rapid adiabatic mode evolution waveguide and an output end S-bent waveguide; on the basis of a traditional linear adiabatic taper, the adiabatic parameter is combined to realize nonlinear change so as to accelerate the adiabatic process, and the length of the adiabatic power splitter is reduced while the excellent characteristics of the adiabatic power splitter, such as wideband and robustness, are retained.

Description

Technical Field

[0001] This invention relates to the field of integrated photonics technology, specifically to a lithium niobate thin-film rapid thermal insulation 3dB power beam splitter. Background Technology

[0002] Integrated photonics technology provides high-performance, miniaturized, low-cost, and scalable solutions for next-generation high-speed optical communication, optical interconnects, and optical computing, with broad application prospects. Among numerous integrated photonics platforms, lithium niobate thin films, with their wide transparency window, low light absorption loss, high linear electro-optic coefficient, and second-order nonlinear coefficient, have become highly influential. 3dB power beamsplitters, as key components in the field of integrated photonics technology, can achieve 1:1 uniform beam splitting and are widely used in optical switches, modulators, optical communication, and sensor networks.

[0003] Techniques for 3dB power splitting include: directional couplers, which couple two phase-matched waveguides together, achieving uniform light distribution when the coupling length is half a beat length, and have the simplest structure [Optics Letters 48.5(2023):1264-1267]. However, due to strict phase matching conditions, they are easily affected by processing tolerances, resulting in uneven optical power distribution and limited bandwidth; multimode interference couplers, based on the self-image effect generated by light interference in multimode waveguides, can achieve uniform optical power distribution at the output end by designing the interference and phase relationship between modes in the waveguide, and have the characteristics of wide bandwidth and compactness [Optics Express 31.17(2023):27266-27273.]. However, multimode interference is prone to introducing additional optical loss, leading to a decrease in overall efficiency; and adiabatic couplers, which achieve adiabatic mode coupling by slowly changing the geometry of the optical waveguide, and have the advantages of high efficiency, large bandwidth, and high stability [Optics letters 41.13(2016):3041-3044]. However, in order to meet the thermal coupling requirements, the device length is very long, on the order of hundreds of micrometers, and the integration density is low.

[0004] Traditional adiabatic couplers typically employ linear transformation parameters, which do not require precise definition of the power transmission length. However, they must be long enough to meet adiabatic requirements and reduce energy loss caused by power coupling to other modes, resulting in lower integration density. Fast thermal adiabatic theory, building upon traditional linear adiabatic technology, uses nonlinear transformations to accelerate the adiabatic process. This reduces coupler length while retaining its superior characteristics of high bandwidth, low insertion loss, compact structure, and strong robustness. Summary of the Invention

[0005] To address the aforementioned problems in the existing technology, the present invention provides a lithium niobate thin film rapid thermal insulation 3dB power beam splitter.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A lithium niobate thin-film fast-insulation 3dB power beam splitter, viewed from top to bottom, comprises an upper cladding layer, an x-cut lithium niobate thin-film layer, a buried oxide layer, and a silicon substrate layer stacked sequentially; the x-cut lithium niobate layer contains a lithium niobate thin-film ridge waveguide formed by etching technology; the thin-film lithium niobate waveguide comprises an input-end tapered waveguide, an input-end S-bend waveguide, a fast-insulation mode evolution waveguide, and an output-end S-bend waveguide connected in sequence.

[0008] Furthermore, the input-end tapered waveguide includes parallel linear tapered waveguide a and linear tapered waveguide b, with linear tapered waveguide a located below, both having a length of L1, and a spacing of gap1 between them; the width of linear tapered waveguide b linearly changes from w0 to w2, where w0 > w2, and the width of linear tapered waveguide a linearly changes from w0 to w1, where w0 > w2. <w1。

[0009] Furthermore, the input S-bent waveguide is composed of two symmetrical third-order Bessel bend waveguides, namely input S-bent waveguide a and input S-bent waveguide b from bottom to top. Both have a length of L2 and a constant width. The spacing between them changes from gap1 to gap2, where gap1>gap2.

[0010] Furthermore, the rapid adiabatic mode evolution waveguide is a dual-waveguide system composed of two parallel rapid adiabatic mode evolution waveguides, a and b, with rapid adiabatic mode evolution waveguide a located at the bottom. Both rapid adiabatic mode evolution waveguide a and rapid adiabatic mode evolution waveguide b have a length of L3 and a spacing of gap2. The width of rapid adiabatic mode evolution waveguide a gradually changes from w1 to w1-D(w), and the width of rapid adiabatic mode evolution waveguide b gradually changes from w2 to w2+D(w), where D(w) is the spacing function and w represents the change in waveguide width. The ends of rapid adiabatic mode evolution waveguide a and rapid adiabatic mode evolution waveguide b have the same width w0.

[0011] Furthermore, the output S-bend waveguide is composed of two symmetrical third-order Bessel bend waveguides, namely output S-bend waveguide a and output S-bend waveguide b from bottom to top, with a length of L4 and a width of w0, and the spacing gradually changes from gap2 to gap3. <gap3。

[0012] Preferably, the material of the upper cladding layer is silicon dioxide or air, and the material of the buried oxide layer is silicon dioxide.

[0013] Meanwhile, this invention also discloses a method for implementing a lithium niobate thin-film rapid thermal insulation 3dB power beam splitter. The method is used to prepare the lithium niobate thin-film rapid thermal insulation 3dB power beam splitter as described in claim 5, and includes the following steps:

[0014] S1. Determine the waveguide widths w1 and w2 and the waveguide spacing gap2 in the fast adiabatic mode evolution waveguide. w0, gap1, gap3, L1, L2, and L4 are parameters for the non-mode evolution waveguide region; they only need to avoid unnecessary coupling (choosing a safe parameter if possible), therefore they do not need to be determined and optimized separately. The selection of these parameters should follow these principles: L1 should be long enough to ensure adiabatic mode transmission, while w0 needs to be consistent with the width at the end of the fast adiabatic mode evolution waveguide; L2 and L4 are obtained by defining the third-order Bessel function, with minimizing bending loss as the criterion; gap1 and gap3 are set large enough to ensure no coupling occurs between waveguides in this region.

[0015] S2. Using the Lumerical Mode Solutions numerical simulator, calculate the effective refractive index, propagation constant, electric field, and magnetic field corresponding to the symmetric and antisymmetric modes in the fast adiabatic mode evolution waveguide;

[0016] S3. Calculate the adiabatic parameters of the waveguide evolving from the fast adiabatic mode, and obtain the optimized interval function D(w) after length normalization through the fast adiabatic theory.

[0017] S4. By optimizing the interval function D(w), the fast adiabatic taper function F(z) is obtained, and the nonlinear transformation structure of the mode evolution waveguide is obtained. The transmission length L3 required to meet the 3dB power beam splitting is calculated by the Lumerical Eme Solutions numerical simulator.

[0018] The specific implementation method of S3 is as follows:

[0019] S31. The interval function D(w) adopts the linear taper function F(z) = (D f / L)z, F(z) means that w varies linearly along the propagation distance z, and the boundary condition satisfies F i =F(0)=0, the waveguide width begins to change at the initial end of the waveguide during the rapid adiabatic mode evolution, and the boundary condition satisfies F f =F(L)=(w1-w2) / 2, at the end of the waveguide in the rapid adiabatic mode evolution, the two waveguides have the same width;

[0020] S32. Adiabatic parameters are defined as follows:

[0021]

[0022] Where, β m ,β n E is the propagation constant of the eigenmodes m and n. mt and H nt , respectively, represent the transverse components of the electric and magnetic fields of the m-th and n-th eigenmodes, the integration region is the entire waveguide cross-section, and z is the propagation distance. ε is a unit vector, s is the integration plane, and ε is a minimal parameter. It is the conjugate of the transverse component of the magnetic field;

[0023] The fast adiabatic theory requires that at least one parameter in the optical waveguide system varies with the propagation distance z. Based on the fast adiabatic theory and the chain rule, D(w) is selected as the unique parameter, and the adiabatic parameter is:

[0024]

[0025] in, The integral of the electromagnetic field overlap between mode m and mode n varies with D and is independent of z; A(D) is determined by the linearly adiabatic parameter c. lin (z) Export

[0026]

[0027] D f D i Given the boundary conditions described above, the adiabatic parameters are simplified to:

[0028]

[0029] The relationship between z and D is

[0030]

[0031] S33. Integrate both sides of equation (5) and substitute the boundary condition z(D) i )=0,z(D f ) = L, thus obtaining the adiabatic parameters.

[0032]

[0033] S34. Substituting equation (6) into equation (5), we obtain the variation of the interval function D with the propagation distance z.

[0034]

[0035] S35. Substituting equation (7) into the taper function formula, we obtain the rapid adiabatic taper function F(z)=(D f / L)z FAQUAD .

[0036] The lithium niobate thin-film rapid thermal insulation 3dB power beam splitter of the present invention, compared with the prior art, has the following technical advantages:

[0037] The lithium niobate thin film fast thermally adiabatic 3dB power beam splitter proposed in this invention can excite only one of the intrinsic modes in a dual waveguide system at the input, while ensuring that the energy is not coupled to the other intrinsic mode after passing through the coupling region. The excited intrinsic mode is dominant, and the length of the coupling region that satisfies 3dB power beam splitting can be quickly determined, which is beneficial for efficient device design.

[0038] This invention proposes an optimization formula for the spacing function of a fast-absorbent 3dB power splitter. The optimization formula for the spacing function is formula (7). Using this spacing function, the corresponding taper function F(z)=(D f / L)z FAQUAD The optimal trend of waveguide width variation in the coupling region can be quickly obtained through the taper function, which can further reduce the length of the device while satisfying the adiabatic evolution conditions. Attached Figure Description

[0039] Figure 1 This is a top view of the lithium niobate thin film waveguide layer of the present invention. The two upper insets are schematic diagrams of the evolution of the mode field in the mode evolution region when light is input into a narrow waveguide, and the two lower insets are schematic diagrams of the evolution of the mode field in the mode evolution region when light is input into a wide waveguide.

[0040] Figure 2 This is a comparison diagram of the optimized spacing function of the fast adiabatic mode evolution waveguide and the optimized spacing function of the mode evolution region waveguide of the linear adiabatic power beam splitter in an embodiment of the present invention.

[0041] Figure 3 This is a comparison diagram of the adiabatic parameters of the fast adiabatic power splitter and the linear adiabatic power splitter in this embodiment of the invention.

[0042] Figure 4 This is a graph showing the relationship between waveguide length and output port transmittance in the mode evolution region of the linear adiabatic power beam splitter in an embodiment of the present invention.

[0043] Figure 5 This is a graph showing the relationship between waveguide length and output port transmittance in the mode evolution region of the fast adiabatic power beam splitter in an embodiment of the present invention.

[0044] Figure 6 This is a simulation diagram of the intrinsic mode transmission efficiency excited by the fast adiabatic power beam splitter in an embodiment of the present invention.

[0045] Figure 7 The transmission spectrum of the fast thermally adiabatic power beam splitter in this embodiment of the invention;

[0046] Figure 8 This is a simulation diagram of the electric field intensity propagation of the fast adiabatic power beam splitter in an embodiment of the present invention. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0048] See Figure 1-8 The specific embodiments of the present invention are as follows.

[0049]

Example 1

[0050] To better illustrate this embodiment, the components in the accompanying drawings may be enlarged or reduced, and do not represent the actual device dimensions. The waveguide spacing and waveguide width mentioned refer to the dimensions of the upper surface of the waveguide.

[0051] like Figure 1 The described lithium niobate thin-film fast-insulation 3dB power beam splitter, viewed from top to bottom, comprises an upper cladding layer, an X-cut lithium niobate thin-film layer, a buried oxide layer, and a silicon substrate layer stacked sequentially. The X-cut lithium niobate layer contains a lithium niobate thin-film ridge waveguide formed by etching. From left to right, the thin-film lithium niobate waveguide includes an input-end tapered waveguide, an input-end S-bend waveguide, a fast-insulation mode evolution waveguide, and an output-end S-bend waveguide connected sequentially. The upper cladding layer is made of silicon dioxide, and the buried oxide layer is also made of silicon dioxide.

[0052] When the transverse electric fundamental mode TE0 is input at the input end of waveguide a, it mainly transforms into a symmetric mode in the dual-waveguide system during the mode evolution region; when the transverse electric fundamental mode TE0 is input at the input end of waveguide b, it mainly transforms into an antisymmetric mode in the dual-waveguide system during the mode evolution region. Since phase matching is satisfied at the end of the mode evolution region, when the adiabatic change condition is met, the power is equally distributed in the two waveguides, achieving 3dB power splitting.

[0053] The input-end tapered waveguide includes parallel linear tapered waveguide a and linear tapered waveguide b, with linear tapered waveguide a located below. Both have a length of L1, and the distance between them is gap1. The width of linear tapered waveguide b linearly changes from w0 to w2, where w0 > w2. The width of linear tapered waveguide a linearly changes from w0 to w1, where w0 > w2. <w1。

[0054] The input S-bend waveguide consists of two 180° symmetrical third-order Bessel bend waveguides, namely input S-bend waveguide a and input S-bend waveguide b from bottom to top. Both have a length of L2 and a constant width. The spacing between them changes from gap1 to gap2, where gap1>gap2. In the input S-bend waveguide region, the width of waveguide a is w1 and the width of waveguide b is w2.

[0055] The rapid adiabatic mode evolution waveguide consists of a dual-waveguide system composed of two parallel rapid adiabatic mode evolution waveguides, a and b, with waveguide a located at the bottom. Both waveguides a and b have a length of L3 and a spacing of gap2. The width of waveguide a gradually changes from w1 to w1-D(w), and the width of waveguide b gradually changes from w2 to w2+D(w), where D(w) is the spacing function and w represents the change in waveguide width. The ends of both waveguides a and b have the same width w0.

[0056] The output S-bend waveguide consists of two symmetrical 180° third-order Bessel bend waveguides, namely output S-bend waveguide a and output S-bend waveguide b from bottom to top, with a length of L4 and a width of w0, and the spacing gradually changes from gap2 to gap3. <gap3。

[0057] like Figure 1 As shown, when TE0 is input from waveguide a, the eigenmode excited by the dual waveguide system is an even / symmetric mode. Initially, the mode energy is mainly concentrated in waveguide a. Since the phase matching condition is met at the end of the mode evolution region, the power is eventually evenly distributed in the two waveguides and finally output through the output waveguide.

[0058] The above-mentioned method for implementing a lithium niobate thin film fast thermal insulation 3dB power beam splitter includes:

[0059] S1. Determine the waveguide widths w1 and w2 and the waveguide spacing gap2 in the rapid adiabatic mode evolution waveguide;

[0060] S2. Using the Lumerical Mode Solutions numerical simulator, calculate the effective refractive index, propagation constant, electric field, and magnetic field corresponding to the symmetric and antisymmetric modes in the fast adiabatic mode evolution waveguide;

[0061] S3. Calculate the adiabatic parameters of the waveguide undergoing rapid adiabatic mode evolution. Using rapid adiabatic theory, obtain the optimized spacing function D(w) after length normalization. For optical evolution following a single eigenmode, the adiabatic theorem states that the adiabatic parameters must satisfy:

[0062]

[0063] Where β m ,β n E is the propagation constant of the eigenmodes m and n. mt and H nt These are the transverse components of the electric and magnetic fields of the m-th and n-th eigenmodes, respectively, and the integration region is the entire waveguide cross-section. The spacing function D adopts the linear taper function F(z) = (D... f / L)z, the boundary condition satisfies F i =F(0)=0,F f =F(L)=(w1-w2) / 2. The rapid adiabatic theory requires that at least one parameter in the optical waveguide system varies with the propagation distance z. Therefore, D is chosen as the only parameter. According to the chain rule, formula (1) becomes

[0064]

[0065] in, The integral representing the overlap of the electromagnetic fields of modes m and n varies with D and is independent of z. A(D) can be expressed by the linearly adiabatic adiabatic parameter c. lin (z) Export

[0066]

[0067] Therefore, the adiabatic conditions can be simplified to:

[0068] The relationship between z and D is

[0069] Integrate both sides of the equation and substitute the boundary condition z(D) i )=0,z(D f ) = L, thus obtaining the adiabatic parameters.

[0070] Substituting equation (6) into equation (5), we can obtain the variation of the rapid adiabatic optimization interval function D with the propagation distance z.

[0071]

[0072] Substituting equation (7) into the taper function formula, we obtain the rapid adiabatic taper function F(z) = (D f / L)z FAQUAD In all the above formulas, L represents the output waveguide length L3 in the text. L is used for ease of description.

[0073] S4. By optimizing the spacing function D(w), the fast adiabatic taper function F(z) is obtained, and the nonlinear transformation structure of the mode evolution waveguide is obtained. The transmission length L3 required to meet the 3dB power beam splitting is calculated by the Lumerical Eme Solutions numerical simulator.

[0074]

Example 2

[0075] To better illustrate this embodiment, the components in the accompanying drawings may be enlarged or reduced, and do not represent the actual device dimensions. To minimize the losses in the input and output waveguides, the input waveguide spacing gap1 and output waveguide spacing gap3 are 5.2 μm, and the input waveguide length L1 and output waveguide length L3 are 38 μm. The choice of waveguide spacing gap2 has a significant impact on the length of the mode evolution region. A smaller gap2 results in a shorter minimum coupling region that satisfies the adiabatic evolution condition. Considering that the waveguide spacing is also affected by manufacturing limitations, gap2 is set to 0.5 μm in this invention.

[0076] Using the Lumerical Mode Solutions numerical simulator, the symmetric and antisymmetric modes excited in the incident light input mode evolution region were identified, and the effective refractive index n of the two modes as parameter D changed was calculated. eff Electric field, magnetic field, and propagation constant. Based on the fast adiabatic theory, the optimal spacing function and adiabatic coefficient of the fast adiabatic power splitter are calculated, and the results are as follows: Figure 2 and Figure 3 As shown. From Figure 2 As can be seen, the adiabatic parameter c(z) of the linear adiabatic power splitter is not uniformly distributed along the length L. It is small at the beginning of the cone and gradually increases until the end. Therefore, to meet the adiabatic requirements, the length L needs to be long enough to ensure that the overall adiabatic parameter is below an acceptable value. Unlike the linear adiabatic power splitter, which exhibits a constant rate of change throughout the cone region, the fast adiabatic power splitter shows a rapid change at the beginning of the cone where c(z) is small, and a slow change at the end where c(z) is large. Strategically, dD / dz is allocated on demand, making c(z) a stable value overall. After the same length L, more energy is retained in the target mode, such as... Figure 2 and Figure 3 As shown.

[0077] By scanning the waveguide lengths of a linear adiabatic power beam splitter and a fast adiabatic power beam splitter, the transmission curves of the power beam splitters are obtained, and the results are as follows: Figure 4 and Figure 5 As shown, the length L of the 3dB coupler can be selected at the intersection of the two output curves. It can be seen from the figure that, to achieve adiabatic transmission in the mode evolution region, the linear adiabatic power coupler has a longer length. For example, at a wavelength λ = 1550 nm and an input mode at TE0, the first 3dB intersection of the linear adiabatic power splitter occurs at L = 85.9 μm, while that of the fast adiabatic power splitter is only 28.6 μm, a reduction of 66.7% in the coupling region length. This demonstrates that, under the same adiabatic conditions, the fast adiabatic theory can effectively reduce the device length.

[0078] By selecting the first 3dB intersection length of the fast adiabatic power beam splitter, a complete fast adiabatic power beam splitter is constructed, and the transmission spectrum of the entire structure is obtained. The results are as follows: Figure 6 As shown in the figure, within the wavelength range of 1500-1600nm, the conversion efficiency between the input optical mode and the output intrinsic mode exhibits high flatness and high conversion efficiency, with all conversion efficiencies exceeding 98%.

[0079] Figure 7 The simulation transmission curves of the two output ports of the fast adiabatic power splitter at wavelengths λ = 1550 nm and L3 = 28.6 μm show that the coupling ratio is within the range of 3 ± 0.55 dB throughout the entire simulation wavelength range. Figure 8 Under the same simulation conditions, the simulated electric field intensity propagation diagram clearly shows that the output light is equally divided into two output ports.

[0080] This invention is not limited to the above-described optional embodiments. Anyone can derive other products in various forms under the guidance of this invention. However, regardless of any changes made to the parameters, any technical solution that falls within the scope of the claims of this invention is protected by this invention.

Claims

1. A method for implementing a lithium niobate thin film fast adiabatic 3 dB power splitter, characterized in that, The structure of the lithium niobate thin film fast adiabatic 3dB power splitter is as follows: For the top view direction, the lithium niobate thin film fast adiabatic 3dB power splitter comprises, from top to bottom, an upper cladding layer, an x-cut lithium niobate thin film layer, a buried oxygen layer and a silicon substrate layer; the x-cut lithium niobate layer contains a lithium niobate thin film ridge waveguide formed by etching technology; the thin film lithium niobate waveguide comprises, in sequence, an input end tapered waveguide, an input end S-bent waveguide, a fast adiabatic mode evolution waveguide and an output end S-bent waveguide; The input end tapered waveguide comprises linear tapered waveguides a and b arranged in parallel, the linear tapered waveguide a is located below, the lengths of the two are L1, and the distance between the two is gap1; the width of the linear tapered waveguide b linearly changes from w0 to w2, w0>w2, and the width of the linear tapered waveguide a linearly changes from w0 to w1, w0<w1; The input end S-bent waveguide is composed of two symmetrical third-order Bessel bent waveguides, from bottom to top, the input end S-bent waveguide a and the input end S-bent waveguide b, the lengths of the two are L2, the width remains unchanged, the distance changes from gap1 to gap2, and gap1>gap2; The fast adiabatic mode evolution waveguide is composed of fast adiabatic mode evolution waveguides a and b arranged in parallel, the two waveguides satisfy the field coupling condition to form a double waveguide system; the fast adiabatic mode evolution waveguide a is located below; the lengths of the fast adiabatic mode evolution waveguides a and b are L3, and the distance between the two is gap2; the width of the fast adiabatic mode evolution waveguide a changes from w1 to w1-D(w), and the width of the fast adiabatic mode evolution waveguide b changes from w2 to w2+D(w), D(w) is a spacing function, and w is the change of the width of the waveguide; the ends of the fast adiabatic mode evolution waveguides a and b have the same width w0; The output end S-bent waveguide is composed of two symmetrical third-order Bessel bent waveguides, from bottom to top, the output end S-bent waveguide a and the output end S-bent waveguide b, the lengths of the two are L4, the widths of the two are w0, and the distance changes from gap2 to gap3, gap2<gap3; The implementation method comprises the following steps: S1. determining the waveguide widths w1 and w2 and the waveguide distance gap2 in the fast adiabatic mode evolution waveguide; S2. calculating the effective refractive index, propagation constant, electric field and magnetic field corresponding to the symmetric mode and the anti-symmetric mode in the fast adiabatic mode evolution waveguide by using a Lumerical Mode Solutions numerical simulator; S3. calculating the adiabatic parameter of the fast adiabatic mode evolution waveguide, and obtaining the optimized spacing function D(w) after length normalization by using the fast adiabatic theory; S4. obtaining the fast adiabatic taper function F(z) by using the optimized spacing function D(w), obtaining the nonlinear transformation structure of the mode evolution waveguide, and calculating the transmission length L3 required to satisfy the 3dB power splitting by using a Lumerical Eme Solutions numerical simulator.

2. The method of claim 1, wherein the lithium niobate thin film fast adiabatic 3 dB power splitter is implemented by, The S3 is specifically as follows: S31. The interval function D(w) adopts a linear taper function F(z) = (D f / L)z, the meaning of F(z) is that w is linearly changed along the direction of propagation distance z, the boundary condition satisfies F i = F(0) = 0, the waveguide width starts to change at the initial end of the fast adiabatic mode evolution waveguide, the boundary condition satisfies F f = F(L) = (w1-w2) / 2, at the end of the fast adiabatic mode evolution waveguide, the two waveguide widths are the same; S32. According to the fast adiabatic theory and the chain rule, D(w) is selected as the only parameter, and the adiabatic parameter is where represents the mode m and mode n electromagnetic field overlapping integral varies with D, and is independent of z; β m , β n is the propagation constant of eigenmodes m and n, E mt and H nt are the electric field and magnetic field transverse components of the mth and nth eigenmodes, the integral region is the entire waveguide cross section, and z is the propagation distance, is the unit vector, s is the integral plane, and ε is a small parameter, is the conjugate of the magnetic field transverse component; A(D) is derived from the adiabatic parameter c lin (z) of linear adiabatic change D f 、D i For the boundary conditions described above, the adiabatic parameter simplifies to z is related to D by S33. Integrate both sides of equation (5) and apply the boundary conditions z(D i ) = 0, z(D f ) = L to obtain the adiabatic parameter S34. Substituting formula (6) into formula (5), the change of interval function D with the propagation distance z is obtained S35. Substituting formula (7) into the taper function formula, the fast adiabatic taper function F(z) = (D f / L)z FAQUAD .

3. A lithium niobate thin film fast adiabatic 3dB power splitter prepared by the implementation method of the lithium niobate thin film fast adiabatic 3dB power splitter in any one of claims 1-2.

4. The lithium niobate thin film fast adiabatic 3 dB power splitter of claim 3, wherein, The material of the upper cladding layer is silica or air, and the material of the buried oxide layer is silica.

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