Method for manufacturing non-periodic poled lithium niobate waveguide for all-optical wavelength conversion of wavelength division multiplexed signals

Abstract

This invention discloses a method for manufacturing an aperiodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength-mode hybrid multiplexed signals. The method includes: establishing an aperiodic polarized lithium niobate waveguide model based on a superlattice thin-film lithium niobate waveguide model and a superlattice polarization direction distribution; obtaining the output amplitude functions of the signal light and idler light based on the aperiodic polarized lithium niobate waveguide model; establishing an objective function based on the output amplitude functions of the signal light and idler light; optimizing the superlattice polarization direction distribution using a simulated annealing algorithm combined with the objective function to obtain an optimal superlattice polarization direction distribution; and polarizing the superlattice thin-film lithium niobate waveguide according to the optimal superlattice polarization direction distribution to obtain the aperiodic polarized lithium niobate waveguide. This invention optimizes the superlattice polarization direction distribution of the superlattice thin-film lithium niobate waveguide, thereby obtaining an aperiodic polarized lithium niobate waveguide with excellent uniformity and wavelength conversion efficiency.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronics, and specifically relates to a method for manufacturing an aperiodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals. Background Technology

[0002] With the ever-increasing demand for information transmission, wavelength multiplexing and mode multiplexing are important ways to increase communication capacity, and wavelength converters based on wavelength and mode hybrid multiplexing signals are crucial devices for increasing the number of information transmission channels. Lithium niobate thin-film waveguide technology has driven the development of highly integrated and miniaturized all-optical wavelength converters. Wavelength converters based on lithium niobate waveguides are characterized by small size, light weight, high stability, and low required pump excitation. These advantages make them highly promising for applications in the field of optical communication.

[0003] The main existing schemes for all-optical wavelength converters based on lithium niobate waveguides for hybrid wavelength mode multiplexing signals are segmented periodically polarized lithium niobate waveguides. The main problem with this approach is that different signal modes are transmitted and interact in segments, meaning that specific signal modes only interact within specific segments. This results in low overall waveguide utilization and consequently low wavelength conversion efficiency. Furthermore, the idler light generated in the previous stage can easily interact with the pump light as the signal light in the next stage, generating crosstalk signals.

[0004] Therefore, improving waveguide utilization and wavelength conversion efficiency is of great significance and application value for the manufacture of lithium niobate wavelength conversion waveguides. Summary of the Invention

[0005] To address the problems existing in the background art, the present invention provides a method for manufacturing an aperiodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals.

[0006] The technical solution adopted in this invention is as follows:

[0007] I. A method for manufacturing an aperiodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength-mode hybrid multiplexed signals.

[0008] The manufacturing method includes the following steps:

[0009] S1) Construct a superlattice-based thin-film lithium niobate waveguide model.

[0010] Specifically, step S1 involves: using optical simulation software in a computer to obtain the structural parameters of the thin-film lithium niobate waveguide based on the effective mode field area and effective refractive index; constructing a thin-film lithium niobate waveguide model based on the obtained structural parameters; and performing superlattice processing on the thin-film lithium niobate waveguide model to obtain a superlattice thin-film lithium niobate waveguide model.

[0011] S2) Based on the superlattice thin-film lithium niobate waveguide model and the superlattice polarization direction distribution, establish an aperiodic polarized lithium niobate waveguide model, and obtain the output amplitude functions of the signal light and idler light based on the aperiodic polarized lithium niobate waveguide model.

[0012] Step S2 specifically involves:

[0013] S2.1) Based on the superlattice thin-film lithium niobate waveguide model and the superlattice polarization direction distribution, establish an aperiodic polarized lithium niobate waveguide model and construct the difference frequency process coupling wave equation of the aperiodic polarized lithium niobate waveguide model;

[0014] S2.1) For each superlattice, input the superlattice's structural parameters into the difference frequency process coupled wave equation to obtain the superlattice's optical field characteristics; obtain the boundary conditions based on the superlattice's coordinates, input the boundary conditions into the superlattice's optical field characteristics to obtain the optical field characteristics at the superlattice boundary;

[0015] S2.2) Construct the transfer matrix based on the optical field characteristics at all superlattice boundaries;

[0016] S2.3) Based on the transmission matrix and the pre-set input light field, the output light field is obtained; the two components of the output light field are the output amplitude functions of the signal light and the idler light, respectively.

[0017] In step S2, the output light field specifically refers to:

[0018]

[0019] In the formula, A represents the amplitude of the conjugate light of the signal light in the q-th superlattice. i (y N The ) represents the amplitude of the idler light in the q-th superlattice, * indicates conjugation, q represents the lattice number, N represents the total number of lattices in the waveguide, and y N Let y0 represent the Nth lattice and y0 represent the first lattice. This represents the element in the first row and first column of the transfer matrix product. This represents the element in the first row and second column of the transfer matrix product. This represents the element in the second row and first column of the transfer matrix product. M represents the element in the second row and second column of the transfer matrix product. 11 M represents the element in the first row and first column of the transmission matrix representing the optical field transmission between the first and second superlattices. 12 The first row and second column of the transfer matrix represent the optical field transmission between the first and second superlattices, M. 21M represents the element in the second row and first column of the transmission matrix representing the optical field transmission between the first and second superlattices. 22 This represents the first superlattice.

[0020] S3) Establish the objective function based on the output amplitude functions of the signal light and idler light, and use the simulated annealing algorithm to optimize the superlattice polarization direction distribution in combination with the objective function to obtain the optimal superlattice polarization direction distribution.

[0021] The process of step S3 is as follows:

[0022] S3.1) Establish the objective function based on the output amplitude functions of the signal light and the idler light;

[0023] S3.2) Set the initial temperature, temperature attenuation coefficient, and number of iterations, using the initial temperature as the simulated temperature; set multiple different target wavelengths and multiple different target modes, with each combination of target wavelength and target mode corresponding to a channel;

[0024] The target mode includes at least one of TE0 mode, TE1 mode and TE2 mode; the number of target wavelengths is 1 to 3, and the distance between the target wavelengths is a maximum of 5 μm and a minimum of 0.4 nm.

[0025] S3.3) At the simulated temperature, a superlattice polarization direction distribution is randomly generated; the wavelength conversion factor of each channel is calculated according to the superlattice polarization direction distribution d, and the wavelength conversion factor of each channel is input into the objective function to obtain the objective function value;

[0026] Wavelength conversion factor γ(λ) for each channel α,δ It can be obtained through the following formula:

[0027]

[0028] In the formula, This represents the element in the first row and second column of the transfer matrix product.

[0029] S3.4) If the objective function value is less than the optimal objective function value, then the superlattice polarization direction distribution generated in step S3.4 shall be taken as the optimal superlattice polarization direction distribution; otherwise, the superlattice polarization direction distribution generated in step S3.4 shall be taken as the optimal superlattice polarization direction distribution with the acceptance probability.

[0030] After obtaining the optimal superlattice polarization direction distribution, the objective function value corresponding to the optimal superlattice polarization direction distribution is taken as the optimal objective function value;

[0031] S3.5) Update the simulated temperature according to the temperature decay coefficient, and return to step S3.3;

[0032] S3.6) Repeat steps S3.3 to S3.5 until the simulated temperature equals the termination temperature or the preset number of iterations is reached, and output the optimal superlattice polarization direction distribution.

[0033] In step S3, the objective function is set according to the following formula:

[0034]

[0035] In the formula, γ0 represents the initial value of the guided simulated annealing algorithm, γ(λ) α,δ ) represents the channel λ α,δ The wavelength conversion factor, β represents the tuning parameter, λ α,δ This represents the channel in the α-th target wavelength and δ-th target mode, where α represents the target wavelength number and δ represents the target mode number.

[0036] S4) The superlattice-polarized thin-film lithium niobate waveguide is polarized according to the optimal superlattice polarization direction distribution to obtain an aperiodic polarized lithium niobate waveguide.

[0037] II. An aperiodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength-mode hybrid multiplexed signals obtained by the above manufacturing method

[0038] The aforementioned aperiodic polarized lithium niobate waveguide is composed of multiple superlattices of equal length, which are arranged along the signal propagation direction and have an aperiodic polarization distribution.

[0039] III. A photonic device employing the above-mentioned aperiodic polarized lithium niobate waveguide

[0040] The photonic devices include all-optical wavelength converters, etc.

[0041] The beneficial effects of this invention are:

[0042] 1. The method of the present invention utilizes a simulated annealing algorithm to optimize the superlattice polarization direction distribution of the superlattice thin-film lithium niobate waveguide, thereby obtaining an aperiodic polarized lithium niobate waveguide with excellent uniformity and wavelength conversion efficiency.

[0043] 2. The method of the present invention can increase the wavelength conversion bandwidth by increasing the distance between target wavelengths, which greatly saves the calculation time required for broadband signal amplification.

[0044] 3. The non-periodic polarized lithium niobate waveguide obtained by the method of the present invention can meet the requirements of wavelength conversion of broadband wavelength mode hybrid multiplexing signals, and has the advantages of high conversion efficiency, compact structure and lightweight. Attached Figure Description

[0045] Figure 1 This is a flowchart illustrating the method of the present invention.

[0046] Figure 2 This is a cross-sectional view of the superlattice-shaped thin-film lithium niobate waveguide model in Embodiment 1 of the present invention.

[0047] Figure 3 The average conversion efficiency and normalized variance of conversion efficiency of the non-periodic polarized lithium niobate waveguides obtained by using different superlattice lengths in Embodiment 1 of the present invention are given.

[0048] Figure 4 This is a comparison chart of the wavelength conversion efficiency of the non-periodic polarized lithium niobate waveguide and the segmented periodic polarized lithium niobate waveguide obtained in Embodiment 1 of the present invention.

[0049] Figure 5 This is a comparison chart of the wavelength conversion efficiency of the non-periodic polarized lithium niobate waveguide and the segmented periodic polarized lithium niobate waveguide obtained in Embodiment 2 of the present invention. Detailed Implementation

[0050] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0051] This invention employs a lithium niobate waveguide for all-optical wavelength mode hybrid multiplexing wavelength conversion. By effectively optimizing the superlattice polarization arrangement, an aperiodic polarized lithium niobate waveguide is obtained. Compared to traditional segmented periodically polarized lithium niobate waveguides, this aperiodic polarized lithium niobate waveguide can significantly increase the wavelength conversion efficiency of the wavelength converter.

[0052] Below, we will first further describe the meaning of some terms used in this invention:

[0053] In this invention, "all-optical wavelength mode hybrid multiplexing wavelength conversion" refers to the use of optical nonlinear effects to perform wavelength conversion on wavelength and mode hybrid multiplexing signals without converting optical signals into electrical signals for processing.

[0054] In this invention, "thin-film lithium niobate waveguide" refers to an optical waveguide structure based on thin-film lithium niobate material. Thin-film lithium niobate material can be fabricated by bonding a single-crystal lithium niobate thin film (which can be obtained by ion cutting technology, with a thickness reaching the nanometer level) onto an insulating substrate (such as silicon or silicon dioxide).

[0055] In this invention, the "superlattice-based thin-film lithium niobate waveguide model" refers to a model that considers the thin-film lithium niobate waveguide model as a model composed of N superlattices that are uniformly divided along the signal transmission direction.

[0056] In this invention, "superlattice-etched thin-film lithium niobate waveguide" refers to an unpolarized thin-film lithium niobate waveguide that has undergone lattice etching but has not yet been polarized.

[0057] In this invention, "polarization treatment" refers to applying an electrode above a superlattice-treated thin-film lithium niobate waveguide and using the electro-optic effect to reverse the polarization direction of the superlattice-treated thin-film lithium niobate waveguide.

[0058] In this invention, "superlattice polarization direction distribution" refers to the spatial arrangement of the polarization directions of all superlattices in the non-periodic polarized lithium niobate waveguide.

[0059] The first aspect of this invention provides a method for manufacturing an aperiodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength-mode mixed multiplexed signals. The method primarily utilizes a simulated annealing algorithm to optimize the polarization reversal direction arrangement of the superlattice, resulting in a waveguide structure with excellent uniformity and wavelength conversion performance. Furthermore, the method can increase the wavelength conversion bandwidth by increasing the distance between target wavelength channels.

[0060] like Figure 1 As shown, the specific steps include:

[0061] S1) Construct a superlattice-based thin-film lithium niobate waveguide model.

[0062] Optionally, the construction process of the superlattice-based thin-film lithium niobate waveguide model is as follows: In a computer, using optical simulation software, the structural parameters of the thin-film lithium niobate waveguide are obtained based on the effective mode field area and effective refractive index. Based on the obtained structural parameters, a thin-film lithium niobate waveguide model is constructed. The thin-film lithium niobate waveguide model is then subjected to superlattice processing to obtain the superlattice-based thin-film lithium niobate waveguide model.

[0063] Structural parameters typically include geometric dimensions (such as width, thickness, and length L) and material refractive index.

[0064] The superlattice treatment of the thin-film lithium niobate waveguide model refers to dividing the long-length (L) thin-film lithium niobate waveguide model into N superlattices, with all superlattices uniformly arranged along the signal transmission direction. For example, in this embodiment of the invention, the superlattice-based thin-film lithium niobate waveguide model adopts x-cut y-transmission, with the signal transmission direction in the y-direction and the polarization direction parallel to the x-direction.

[0065] The parameters for superlattice processing include the number of superlattices N, the length Δy of each superlattice, and the second-order nonlinear coefficients. In the superlattice-based thin-film lithium niobate waveguide model, the relationship between the waveguide length L, the number of superlattices N, and the length Δy of each superlattice is: L = Δy·N. The number of superlattices N should be set to an integer. The absolute value of the second-order nonlinear coefficient of each superlattice is d. 33 In practice, by selecting an appropriate superlattice length, it is possible to balance wavelength conversion efficiency and model computation time.

[0066] The optical simulation software can be Lumerical FDTD simulation software.

[0067] S2) An aperiodic polarized lithium niobate waveguide model is established based on the superlattice thin-film lithium niobate waveguide model and the superlattice polarization direction distribution. The output amplitude functions of the signal light and idler light are obtained from the aperiodic polarized lithium niobate waveguide model. In this embodiment of the invention, considering a strong pump light input, the influence of other terms is eliminated, so that the wavelength conversion efficiency is only affected by the superlattice polarization direction distribution. Therefore, by inputting the superlattice polarization direction distribution into the output light field, the output amplitudes of the signal light and idler light can be obtained. The wavelength conversion efficiency can be obtained by the following formula:

[0068] η = 20lg(γ)

[0069] In the formula, η represents the wavelength conversion efficiency and γ represents the wavelength conversion factor.

[0070] Step S2 is as follows:

[0071] S2.1) Based on the superlattice thin-film lithium niobate waveguide model and the polarization direction distribution of the superlattice, an aperiodic polarized lithium niobate waveguide model is established, and the difference frequency process coupled wave equation of the aperiodic polarized lithium niobate waveguide model is constructed; the difference frequency process coupled wave equation is used to represent the optical field variation in a single superlattice;

[0072] S2.1) For each superlattice, input the superlattice's structural parameters into the difference frequency process coupled wave equation to obtain the superlattice's optical field characteristics; obtain the boundary conditions based on the superlattice's coordinates, input the boundary conditions into the superlattice's optical field characteristics to obtain the optical field characteristics at the superlattice boundary;

[0073] In this embodiment of the invention, the boundary condition is that the amplitude of the idler light at the input end is zero, and the structural parameters of the superlattice include the effective refractive index of each wavelength and mode signal, the effective mode field area of ​​each wavelength mode signal, the lattice length, and other parameters.

[0074] S2.2) Construct a transfer matrix based on the optical field characteristics at all superlattice boundaries; the elements in the transfer matrix represent the propagation relationship of the optical field between adjacent superlattices;

[0075] S2.3) Based on the transmission matrix and the pre-set input light field, the output light field is obtained; the two components of the output light field are the output amplitude functions of the signal light and the idler light, respectively.

[0076] In step S2, the output light field is specifically as follows:

[0077]

[0078] In the formula, A represents the amplitude of the conjugate light of the signal light in the q-th superlattice. i (y N The ) represents the amplitude of the idler light in the q-th superlattice, * indicates conjugation, q represents the lattice number, N represents the total number of lattices in the waveguide, and y N Let y0 represent the Nth lattice and y0 represent the first lattice. This represents the element in the first row and first column of the transfer matrix product. This represents the element in the first row and second column of the transfer matrix product. This represents the element in the second row and first column of the transfer matrix product. M represents the element in the second row and second column of the transfer matrix product. 11 M represents the element in the first row and first column of the transmission matrix representing the optical field transmission between the first and second superlattices. 12 The first row and second column of the transfer matrix represent the optical field transmission between the first and second superlattices, M. 21 M represents the element in the second row and first column of the transmission matrix representing the optical field transmission between the first and second superlattices. 22 This represents the first superlattice.

[0079] The elements of the transmission matrix for optical field transmission between the first and second superlattices are set as follows:

[0080]

[0081] M 22 =M 11 *

[0082] M 12 =M 21 *

[0083] In the formula, M 11 M represents the element in the first row and first column of the transmission matrix representing the optical field transmission between the first and second superlattices. 12 The first row and second column of the transfer matrix represent the optical field transmission between the first and second superlattices, M. 22 M represents the element in the second row and second column of the transmission matrix representing the optical field transmission between the first and second superlattices. 21 The elements in the second row and first column of the transmission matrix represent the optical field transmission between the first and second superlattices, where e represents the phase, j represents the imaginary number, Δk represents the phase mismatch, and Δy represents the phase mismatch. q Let represent the length of the q-th superlattice, cosh denote the hyperbolic cosine function, sinh denote the hyperbolic sine function, and g(y) represent the length of the q-th superlattice. q) represents the g value of the q-th lattice.

[0084] In the above formulas, g and Γ have no physical meaning; they are merely mathematical substitutions to simplify calculations. They are set according to the following formulas:

[0085]

[0086] Δk=k p -k s -ki

[0087]

[0088] In the formula, k p Let k represent the pump light wave vector. s k represents the signal light wave vector. i The wave vector represents the idler frequency; c represents the speed of light, and ω represents the angular frequency. s ω represents the angular frequency of the signal light. i The angular frequency of the idler light is represented by n, and the effective refractive index is represented by n. s n represents the effective refractive index of the signal light. i d represents the effective refractive index of the idler frequency light. 33 A represents the second-order nonlinear coefficient of each superlattice. eff A represents the effective mode field area in the waveguide. p (0) represents the pump light amplitude at the input, A p () indicates the pump light amplitude at different locations.

[0089] The effective refractive index refers to the equivalent refractive index of light propagating in a superlattice-type thin-film lithium niobate waveguide.

[0090] S3) Establish the objective function based on the output amplitude functions of the signal light and idler light, and use the simulated annealing algorithm in combination with the objective function to optimize the superlattice polarization direction distribution to obtain the optimal superlattice polarization direction distribution.

[0091] The process of step S3 is as follows:

[0092] S3.1) Establish the objective function based on the output amplitude functions of the signal light and the idler light;

[0093] S3.2) Set the initial temperature T0, temperature attenuation coefficient ΔT, and number of iterations, using the initial temperature T0 as the simulation temperature; set multiple different target wavelengths and multiple different target modes, with each combination of target wavelength and target mode corresponding to a channel;

[0094] S3.3) At the simulated temperature, a superlattice polarization direction distribution d is randomly generated; the wavelength conversion factor γ(λ) of each channel is calculated based on the superlattice polarization direction distribution d.α,δ The wavelength conversion factor γ(λ) of each channel is used to convert the wavelength of each channel. α,δ The input is fed into the objective function to obtain the objective function value;

[0095] In step S3.3, the wavelength conversion factor γ(λ) for each channel α,δ It can be obtained through the following formula:

[0096]

[0097] In the formula, This represents the element in the first row and second column of the transfer matrix product;

[0098] S3.4) If the objective function value is less than the optimal objective function value, then the superlattice polarization direction distribution generated in step S3.4 shall be taken as the optimal superlattice polarization direction distribution; otherwise, the superlattice polarization direction distribution generated in step S3.4 shall be taken as the optimal superlattice polarization direction distribution with the acceptance probability.

[0099] After obtaining the optimal superlattice polarization direction distribution, the objective function value corresponding to the optimal superlattice polarization direction distribution is taken as the optimal objective function value;

[0100] S3.5) Update the simulated temperature according to the temperature decay coefficient, and return to step S3.3;

[0101] S3.6) Repeat steps S3.3 to S3.5 until the simulated temperature equals the termination temperature or the preset number of iterations is reached, and output the optimal superlattice polarization direction distribution.

[0102] In step S3, the objective function is set according to the following formula:

[0103]

[0104] In the formula, γ0 represents the initial value of the guided simulated annealing algorithm, γ(λ) α,δ ) represents the channel λ α,δ The wavelength conversion factor, β represents the tuning parameter, λ α,δ This represents the channel at the α-th target wavelength and the δ-th target mode, where α represents the index of the target wavelength, δ represents the index of the target mode, max represents the maximum value, and min represents the minimum value.

[0105] The smaller the objective function value E, the better the distribution of superlattice polarization directions.

[0106] Specifically, the target mode includes at least one of the TE0 mode, TE1 mode and TE2 mode.

[0107] Preferably, the number of target wavelengths is 1 to 3. The distance between the target wavelengths is a maximum of 5 μm and a minimum of 0.4 nm.

[0108] Preferably, the tuning parameter ranges from 0.1 to 10. By adjusting the value of the tuning parameter β in the objective function, the wavelength conversion factors of each channel can be balanced during the optimization process, thereby obtaining an aperiodic polarized lithium niobate waveguide with balanced mode channel wavelength conversion efficiency.

[0109] Preferably, the initial value γ0 should be selected as γ(λ). α,δ The accuracy of the optimization algorithm is 10 to 100 times that of the target algorithm.

[0110] S4) The superlattice-based thin-film lithium niobate waveguide is polarized according to the optimal superlattice polarization direction distribution to obtain an aperiodic polarized lithium niobate waveguide.

[0111] Furthermore, the method of the present invention may further include the following steps:

[0112] For multiple different superlattice lengths, the optimal superlattice polarization direction distribution corresponding to each superlattice length is obtained according to steps S1 to S3. The corresponding wavelength conversion efficiency is then calculated based on the optimal superlattice polarization direction distribution. A relationship curve is obtained by fitting the superlattice length and the corresponding wavelength conversion efficiency. The maximum lattice length of the non-periodic polarized lithium niobate waveguide that achieves high wavelength conversion efficiency is selected from the relationship curve.

[0113] Furthermore, the method of the present invention can also increase the wavelength conversion bandwidth by increasing the distance between target wavelengths, which greatly saves the calculation time required for broadband signal amplification.

[0114] A second aspect of the present invention provides an aperiodic polarized lithium niobate waveguide manufactured using the above-described method. This aperiodic polarized lithium niobate waveguide is composed of multiple superlattices of equal length, the superlattices being arranged along the signal propagation direction, and the polarization directions of the superlattices being distributed in an aperiodic manner.

[0115] Optionally, the non-periodic polarized lithium niobate waveguide may employ a ridge waveguide, including but not limited to an air cladding and a silicon dioxide substrate.

[0116] This non-periodic polarized lithium niobate waveguide enables multi-mode optical waves to interact throughout the waveguide, greatly improving the wavelength conversion efficiency of wavelength mode mixed multiplexing signals and meeting the application requirements of high-capacity all-optical communication systems.

[0117] A third aspect of the present invention provides a photonic device employing the aforementioned aperiodic polarized lithium niobate waveguide. This photonic device includes, but is not limited to, an all-optical wavelength converter.

[0118] Specific embodiments of the present invention are as follows:

[0119] Example 1

[0120] This embodiment provides a design method for an aperiodic polarized lithium niobate waveguide with all-optical wavelength conversion for wavelength mode hybrid multiplexing signals. This embodiment employs a ridge-type thin-film lithium niobate waveguide with an air cladding and a silicon dioxide substrate.

[0121] In this embodiment, the target wavelength and target mode are set according to the 50GHz wavelength division multiplexing channels CH48, CH50, and CH52 of the ITU-T G.694 standard, and the three TE modes. The target wavelengths corresponding to channels CH48, CH50, and CH52 are 1538.98nm, 1537.40nm, and 1535.82nm, respectively. The three target modes corresponding to the three TE modes are TE0, TE1, and TE2. In this case, the index α of the target mode in the objective function takes the values ​​α1, α2, or α3, corresponding to TE0, TE1, and TE2 modes, respectively. When processing the TE mode signal, the maximum second-order nonlinear coefficient d of the lithium niobate waveguide is utilized. 33 In this embodiment, lithium niobate with x-cut and y-transfer is used.

[0122] In this embodiment, the input pump light is a 100mW 775nm pump light.

[0123] This embodiment specifically includes the following steps:

[0124] S1) Construct a superlattice-based thin-film lithium niobate waveguide model. The superlattice-based thin-film lithium niobate waveguide model refers to a thin-film lithium niobate waveguide model that includes a superlattice structure.

[0125] In this embodiment, the length L of the thin-film lithium niobate waveguide is 30 mm, and the length Δy of each superlattice is [value missing]. The absolute value of the second-order nonlinear coefficient of each superlattice is d. 33 .

[0126] In this step, firstly, based on the existing process conditions, the etching parameters of the lithium niobate ridge waveguide supporting three modes are obtained using the finite difference time-domain algorithm. The thin-film lithium niobate waveguide thickness is 600 nm, and the etching depth is 300 nm. Then, the optical simulation software Lumerical FDTD is used to determine the effective mode area distribution, while ensuring a relatively small effective mode area (the effective mode areas of TE0, TE1, and TE2 are 2.193 μm). 2 2.626μm 2 3.121μm 2 Under the premise of supporting sufficient TE mode signals, the waveguide size parameters are obtained, and the resulting waveguide cross-section is as follows. Figure 2 As shown.

[0127] After constructing a thin-film lithium niobate waveguide model based on the obtained size parameters, the thin-film lithium niobate waveguide model is then subjected to superlattice processing according to the parameters of superlattice processing to obtain a superlattice thin-film lithium niobate waveguide model.

[0128] S2) Based on the superlattice thin-film lithium niobate waveguide model and the superlattice polarization direction distribution d(y q An aperiodic polarized lithium niobate waveguide model was established, and the output amplitude functions of the signal light and idler light were obtained based on the model. The output amplitude function refers to a function of the amplitude distribution of the optical field (signal light and idler light) at the output end relative to the superlattice polarization direction.

[0129] In steps S1 and S2, the thin-film lithium niobate waveguide model, the superlattice-type thin-film lithium niobate waveguide model, and the aperiodic polarized lithium niobate waveguide model all adopt mathematical models to more accurately describe the physical characteristics of the waveguide and facilitate numerical simulation and theoretical analysis.

[0130] S3) Establish the objective function based on the output amplitude functions of the signal light and idler light, and use the simulated annealing algorithm in combination with the objective function to optimize the superlattice polarization direction distribution to obtain the optimal superlattice polarization direction distribution.

[0131] The specific process is as follows:

[0132] S3.1) Establish the objective function based on the output amplitude functions of the signal light and the idler light;

[0133] S3.2) Set the initial temperature T0, the temperature decay coefficient ΔT, and the number of iterations, using the initial temperature T0 as the simulation temperature. In practice, the initial temperature T0 and the temperature decay coefficient ΔT can be determined based on empirical values ​​or preliminary experimental results, and the number of iterations can be set based on convergence conditions or preliminary experimental results.

[0134] Simultaneously, multiple different target wavelengths and multiple different target modes are set, with each combination of target wavelength and target mode corresponding to a channel. For example, when three different target wavelengths and three different target modes are set, a total of nine channels are formed.

[0135] S3.3) At the simulated temperature, a superlattice polarization direction distribution d is randomly generated; based on the superlattice polarization direction distribution d, the amplification gain G(λ) of each channel is calculated. α ), and the amplification gain G(λ) of each channel α The input is fed into the objective function to obtain the objective function value. In this embodiment, the superlattice polarization direction distribution d is a set of random positive and negative ones.

[0136] In step S3.3, each channel λ α,δ wavelength conversion factor γ(λ) α,δIt can be obtained through the following formula:

[0137]

[0138] In the formula, This represents the element in the first row and second column of the transfer matrix product.

[0139] S3.4) If the objective function value is less than the optimal objective function value, then the superlattice polarization direction distribution generated in step S3.4 is taken as the optimal superlattice polarization direction distribution; otherwise, the superlattice polarization direction distribution generated in step S3.4 is taken as the optimal superlattice polarization direction distribution with the acceptance probability; after obtaining the optimal superlattice polarization direction distribution, the objective function value corresponding to the optimal superlattice polarization direction distribution is taken as the optimal objective function value.

[0140] In practice, the acceptance probability typically decreases as the temperature decreases. In this embodiment, the acceptance probability is set as follows:

[0141] P = exp(-ΔE / T)

[0142] In the formula, P is the acceptance probability, ΔE is the difference between the current objective function value and the previous objective function value, and T is the simulated current temperature.

[0143] S3.5) Update the simulated temperature according to the temperature decay coefficient and return to step S3.3.

[0144] S3.6) Repeat steps S3.3 to S3.5 until the simulated temperature equals the termination temperature or the preset number of iterations is reached, and output the optimal superlattice polarization direction distribution.

[0145] S4) The superlattice-based thin-film lithium niobate waveguide is polarized according to the optimal superlattice polarization direction distribution to obtain an aperiodic polarized lithium niobate waveguide. The polarization treatment is usually performed using electron beam lithography (EBL).

[0146] The aperiodic polarized lithium niobate waveguide obtained in this embodiment consists of N superlattices of equal length, and the polarization directions of the superlattices are aperiodic. This waveguide supports mixed-mode multiplexing of three wavelengths (TE0, TE1, and TE2) in the communication band, as well as fundamental-mode pumped transmission of the 775nm TE mode. This waveguide can achieve wavelength conversion of three-wavelength, three-mode signals in the communication band using only a single 775nm wavelength single-mode pump.

[0147] The aperiodic polarized lithium niobate waveguide obtained in this embodiment has an input consisting of pump light and a signal light to be converted, and an output consisting of the converted signal light and idler light. This aperiodic polarized lithium niobate waveguide achieves efficient wavelength conversion.

[0148] Next, in this embodiment, the wavelength conversion effect of the obtained non-periodic polarized lithium niobate waveguide will be demonstrated through the following process:

[0149] First, using MATLAB simulations, with the input pump light intensity set to 100mW and the signal light intensity to 1mW, target wavelengths of 1538.98nm, 1537.40nm, and 1535.82nm were selected. Through this process, corresponding aperiodic polarized lithium niobate waveguides were obtained at different superlattice lengths.

[0150] For the obtained non-periodic polarized lithium niobate waveguide, the losses of the pump light and the signal light are 1 dB / cm and 0.5 dB / cm, respectively (the magnitude of the loss is independent of the superlattice length). Figure 3 The average conversion efficiency and normalized variance of conversion efficiency are shown for different superlattice lengths. It is evident that selecting a superlattice length less than 1.5 μm yields better wavelength conversion efficiency and channel uniformity. Figure 3 It is evident that the smaller the superlattice length, the higher the average conversion efficiency and the better the channel uniformity. However, at the same time, the reduction in superlattice length in the same waveguide leads to an increase in the number of superlattices, which in turn increases the computation time.

[0151] Therefore, Δy = 1.5 μm can be selected as the maximum lattice length of the non-periodic polarized lithium niobate waveguide that can achieve efficient wavelength conversion. That is, when the length Δy of each superlattice is 1.5 μm and the number of superlattices is 20,000, excellent wavelength conversion efficiency and channel equalization can be obtained while ensuring computation time.

[0152] like Figure 4 As shown, TE 0,APLN This refers to the TEO mode signal of an aperiodic polarized thin-film lithium niobate waveguide. 1,APLN This refers to the TE1 mode signal of the non-periodic polarized thin-film lithium niobate waveguide. 2,APLN This refers to the TE2 mode signal of the non-periodic polarized thin-film lithium niobate waveguide. 0,PPLN This refers to the TEO mode signal of a segmented periodically polarized thin-film lithium niobate waveguide. 1,PPLN This refers to the TE1 mode signal TE of the segmented periodically polarized thin-film lithium niobate waveguide. 2,PPLNThis refers to the TE2 mode signal of the segmented periodically polarized thin-film lithium niobate waveguide. Under the same conditions, compared with the traditional segmented periodically polarized lithium niobate waveguide with a center wavelength of 1550nm (total length is 30mm, the three segments are 12.8μm, 10μm and 7μm in length, and the polarization periods are 2.241μm, 3.332μm and 4.678μm respectively), the wavelength conversion efficiency of the non-periodic polarized lithium niobate waveguide (superlattice length is 1.5μm) obtained in this embodiment is improved from -9dB to -4.3dB.

[0153] Therefore, the method of the present invention utilizes a simulated annealing algorithm to optimize the superlattice polarization direction distribution of the superlattice thin-film lithium niobate waveguide, thereby obtaining an aperiodic polarized lithium niobate waveguide with excellent uniformity and wavelength conversion efficiency.

[0154] Example 2

[0155] Based on the method disclosed in Example 1, this embodiment provides a method for broadening the wavelength conversion bandwidth of non-periodic polarized lithium niobate waveguides for wavelength conversion of mixed-mode multiplexed signals (superlattice length is 1.5 μm).

[0156] This embodiment successfully broadens the wavelength conversion bandwidth of non-periodic polarized lithium niobate without increasing the number of target wavelengths, by increasing the distance between the target wavelengths.

[0157] The target wavelength channels used in this embodiment are 1535nm, 1540nm, and 1545nm. By increasing the distance between the target wavelengths to 5nm, an aperiodic polarized lithium niobate waveguide was obtained.

[0158] Figure 5 This is a comparison chart of the wavelength conversion bandwidth and efficiency of the non-periodic polarized lithium niobate waveguide and the segmented periodically polarized lithium niobate waveguide (total length 30mm, three segments with lengths of 12.8μm, 10μm and 7μm, and polarization periods of 2.241μm, 3.332μm and 4.678μm, respectively) obtained in this embodiment under the same conditions. Figure 5 In the middle, TE 0,APLN This refers to the TEO mode signal of an aperiodic polarized thin-film lithium niobate waveguide. 1,APLN This refers to the TE1 mode signal of the non-periodic polarized thin-film lithium niobate waveguide. 2,APLN This refers to the TE2 mode signal of the non-periodic polarized thin-film lithium niobate waveguide. 0,PPLN This refers to the TEO mode signal of a segmented periodically polarized thin-film lithium niobate waveguide. 1,PPLN This refers to the TE1 mode signal TE of the segmented periodically polarized thin-film lithium niobate waveguide. 2,PPLN This refers to the TE2 mode signal of the segmented periodically polarized thin-film lithium niobate waveguide.

[0159] Depend on Figure 5 As can be seen, the non-periodic polarized lithium niobate waveguide obtained in this embodiment has a wavelength conversion bandwidth of 32nm and a wavelength conversion efficiency of -6dB, combining a wide wavelength conversion bandwidth with high wavelength conversion efficiency.

[0160] The non-periodic polarized lithium niobate waveguides obtained in Embodiments 1 and 2 of this invention enable the three modes of light waves to interact throughout the waveguide, greatly improving the wavelength conversion efficiency of wavelength mode mixed multiplexing signals and meeting the application requirements of high-capacity all-optical communication systems.

[0161] Comparing Examples 1 and 2, it can be seen that the wavelength conversion bandwidth of the aperiodic polarized lithium niobate waveguide obtained in the examples is increased from 10 nm to 32 nm, while still maintaining high wavelength conversion efficiency. Therefore, the method of the present invention can broaden the wavelength conversion bandwidth by increasing the distance between target wavelengths without increasing the number of target wavelengths, thereby greatly reducing computation time.

[0162] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for manufacturing an aperiodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength-mode hybrid multiplexed signals, characterized in that, Includes the following steps: S1) Construct a superlattice thin-film lithium niobate waveguide model; S2) Based on the superlattice thin film lithium niobate waveguide model and the superlattice polarization direction distribution, establish an aperiodic polarized lithium niobate waveguide model, and obtain the output amplitude functions of the signal light and idler light based on the aperiodic polarized lithium niobate waveguide model; S3) Establish the objective function based on the output amplitude function of the signal light and the idler light, and use the simulated annealing algorithm to optimize the superlattice polarization direction distribution in combination with the objective function to obtain the optimal superlattice polarization direction distribution; The process of step S3 is as follows: S3.1) Establish the objective function based on the output amplitude functions of the signal light and the idler light; S3.2) Set the initial temperature, temperature attenuation coefficient, and number of iterations, using the initial temperature as the simulated temperature; set multiple different target wavelengths and multiple different target modes, with each combination of target wavelength and target mode corresponding to a channel; S3.3) At the simulated temperature, randomly generate the superlattice polarization direction distribution; based on the superlattice polarization direction distribution... Calculate the wavelength conversion factor for each channel separately, and input the wavelength conversion factor of each channel into the objective function to obtain the objective function value; S3.4) If the objective function value is less than the optimal objective function value, then the superlattice polarization direction distribution generated in step S3.4 shall be taken as the optimal superlattice polarization direction distribution; otherwise, the superlattice polarization direction distribution generated in step S3.4 shall be taken as the optimal superlattice polarization direction distribution with the acceptance probability. After obtaining the optimal superlattice polarization direction distribution, the objective function value corresponding to the optimal superlattice polarization direction distribution is taken as the optimal objective function value; S3.5) Update the simulated temperature according to the temperature decay coefficient, and return to step S3.3; S3.6) Repeat steps S3.3 to S3.5 until the simulation temperature equals the termination temperature or the preset number of iterations is reached, and output the optimal superlattice polarization direction distribution; S4) The superlattice-polarized thin-film lithium niobate waveguide is polarized according to the optimal superlattice polarization direction distribution to obtain an aperiodic polarized lithium niobate waveguide.

2. The method for manufacturing an aperiodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength-mode hybrid multiplexed signals according to claim 1, characterized in that: Specifically, step S1 involves: using optical simulation software in a computer to obtain the structural parameters of the thin-film lithium niobate waveguide based on the effective mode field area and effective refractive index; constructing a thin-film lithium niobate waveguide model based on the obtained structural parameters; and performing superlattice processing on the thin-film lithium niobate waveguide model to obtain a superlattice thin-film lithium niobate waveguide model.

3. The method for manufacturing an aperiodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength-mode hybrid multiplexed signals according to claim 1, characterized in that: Step S2 specifically involves: S2.1) Based on the superlattice thin-film lithium niobate waveguide model and the superlattice polarization direction distribution, establish an aperiodic polarized lithium niobate waveguide model and construct the difference frequency process coupling wave equation of the aperiodic polarized lithium niobate waveguide model; S2.1) For each superlattice, input the superlattice's structural parameters into the difference frequency process coupled wave equation to obtain the superlattice's optical field characteristics; obtain the boundary conditions based on the superlattice's coordinates, input the boundary conditions into the superlattice's optical field characteristics to obtain the optical field characteristics at the superlattice boundary; S2.2) Construct the transfer matrix based on the optical field characteristics at all superlattice boundaries; S2.3) Based on the transmission matrix and the pre-set input light field, the output light field is obtained; the two components of the output light field are the output amplitude functions of the signal light and the idler light, respectively.

4. The method for manufacturing an aperiodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength-mode hybrid multiplexed signals according to claim 3, characterized in that: In step S2, the output light field specifically refers to: ; ; In the formula, This represents the amplitude of the conjugate light of the signal light in the q-th superlattice. The amplitude of the idler frequency light in the q-th superlattice is represented by *, where * indicates conjugation, q represents the lattice number, and N represents the total number of lattices in the waveguide. Represents the Nth lattice. Indicates the first lattice, This represents the element in the first row and first column of the transfer matrix product. This represents the element in the first row and second column of the transfer matrix product. This represents the element in the second row and first column of the transfer matrix product. This represents the element in the second row and second column of the transfer matrix product. This represents the element in the first row and first column of the transmission matrix that represents the optical field transmission between the first and second superlattices. The first row and second column of the transfer matrix represent the optical field transmission between the first and second superlattices. This represents the element in the second row and first column of the transmission matrix that represents the optical field transmission between the first and second superlattices. This represents the first superlattice.

5. The method for manufacturing an aperiodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength-mode hybrid multiplexed signals according to claim 1, characterized in that: In step S3, the objective function is set according to the following formula: ; In the formula, This represents the initial value for guiding the simulated annealing algorithm. Indicates channel wavelength conversion factor, Indicates the tuning parameters. Indicates the first The target wavelength, the first Channels in target modes, The serial number indicating the target wavelength. Indicates the sequence number of the target pattern.

6. The method for manufacturing an aperiodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength-mode hybrid multiplexed signals according to claim 1, characterized in that: In step S3.3, the wavelength conversion factor for each channel It is obtained through the following formula: ; In the formula, This represents the element in the first row and second column of the transfer matrix product.

7. The method for manufacturing an aperiodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength-mode hybrid multiplexed signals according to claim 1, characterized in that: The target mode includes at least one of TE0 mode, TE1 mode and TE2 mode; the number of target wavelengths is 1 to 3, and the distance between the target wavelengths is a maximum of 5 μm and a minimum of 0.4 nm.

8. A non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength-mode hybrid multiplexed signals obtained by the manufacturing method described in any one of claims 1 to 7, characterized in that: The aforementioned aperiodic polarized lithium niobate waveguide is composed of multiple superlattices of equal length, which are arranged along the signal propagation direction and have an aperiodic polarization distribution.

9. A photonic device employing the non-periodic polarized lithium niobate waveguide as described in claim 8, characterized in that: This includes all-optical wavelength converters.

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