Manufacturing method of aperiodically poled lithium niobate waveguide for wavelength mode hybrid multiplexing signal all-optical wavelength conversion

Abstract

The invention discloses a manufacturing method of a non-periodically poled lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals. Comprising the following steps: establishing an aperiodically poled lithium niobate waveguide model according to a superlattice film lithium niobate waveguide model and superlattice polarization direction distribution, and obtaining output amplitude functions of signal light and idler frequency light according to the aperiodically poled lithium niobate waveguide model; establishing a target function according to the output amplitude functions of the signal light and the idler frequency light, and optimizing the superlattice polarization direction distribution by using a simulated annealing algorithm and combining the target function to obtain the optimal superlattice polarization direction distribution; and performing polarization processing on the superlattice film lithium niobate waveguide according to the optimal superlattice polarization direction distribution to obtain the aperiodically polarized lithium niobate waveguide. According to the method, the superlattice polarization direction distribution of the superlattice film lithium niobate waveguide can be optimized, so that the aperiodically poled lithium niobate waveguide with excellent balance and wavelength conversion efficiency is obtained.

Description

Technical Field

[0001] The invention belongs to the field of optoelectronics, and in particular relates to a method for manufacturing a non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals. Background Art

[0002] As the demand for information transmission increases, wavelength multiplexing and mode multiplexing are important ways to increase communication capacity, and wavelength converters based on wavelength and mode hybrid multiplexing signals are important devices for increasing the number of information transmission channels. Lithium niobate thin film waveguide technology has promoted the development of highly integrated and miniaturized all-optical wavelength converters. Wavelength converters based on lithium niobate waveguides have the characteristics of small size, light weight, high stability, and small pump excitation requirements. These advantages make it have great application prospects in the field of optical communications.

[0003] The main solution for the existing all-optical wavelength converter of wavelength mode hybrid multiplexing signal based on lithium niobate waveguide is segmented periodic polarization lithium niobate waveguide. The main problem is that for signal light of different modes, segmented transmission and interaction are adopted, and signal light of a specific mode only interacts in a specific segment. This leads to low utilization of the entire waveguide, resulting in low wavelength conversion efficiency. At the same time, since the idler light generated in the previous stage is easy to interact with the pump light as the signal light of the next segment, crosstalk signals are generated.

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

[0005] In view of the problems existing in the background technology, the present invention provides a method for manufacturing a non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals.

[0006] The technical solution adopted by the present invention is as follows:

[0007] 1. A method for manufacturing a non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals

[0008] The manufacturing method comprises the following steps:

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

[0010] The step S1 specifically comprises: using optical simulation software in a computer to obtain structural parameters of a thin-film lithium niobate waveguide according to an effective mode field area and an effective refractive index, constructing a thin-film lithium niobate waveguide model according to 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) establishing a non-periodic polarized lithium niobate waveguide model according to the superlattice thin film lithium niobate waveguide model and the superlattice polarization direction distribution, and obtaining output amplitude functions of signal light and idler light according to the non-periodic polarized lithium niobate waveguide model.

[0012] The step S2 is specifically as follows:

[0013] S2.1) establishing a non-periodic polarized lithium niobate waveguide model according to the superlattice thin film lithium niobate waveguide model and the superlattice polarization direction distribution, and constructing a difference frequency process coupled wave equation of the non-periodic polarized lithium niobate waveguide model;

[0014] S2.1) for each superlattice, inputting the structural parameters of the superlattice into the difference frequency process coupled wave equation to obtain the light field characteristics of the superlattice; obtaining boundary conditions according to the coordinates of the superlattice, inputting the boundary conditions into the light field characteristics of the superlattice, and obtaining the light field characteristics at the boundary of the superlattice;

[0015] S2.2) constructing a transmission matrix based on the light field characteristics at all superlattice boundaries;

[0016] S2.3) obtaining an output light field according to the transmission matrix and the preset input light field; 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 is specifically:

[0018]

[0019] In the formula, represents the amplitude of the conjugate light of the signal light in the qth superlattice, A i (y N ) represents the amplitude of the idler light in the qth superlattice, * represents conjugation, q represents the lattice number, N represents the total number of lattices in the waveguide, and y N represents the Nth lattice, y0 represents the first lattice, represents the first row and first column element of the product of the transfer matrices, represents the element in the first row and second column of the product of the transfer matrices, represents the element in the second row and first column of the product of the transfer matrices, represents the element in the second row and second column of the product of the transfer matrices, M 11 The element in the first row and first column of the transmission matrix representing the light field transmission from the first superlattice to the second superlattice, M 12 The element in the first row and second column of the transmission matrix representing the light field transmission from the first superlattice to the second superlattice, M 21The element in the second row and first column of the transmission matrix representing the light field transmission from the first superlattice to the second superlattice, M 22 Represents the first superlattice.

[0020] S3) establishing an objective function according to the output amplitude functions of the signal light and the idler light, optimizing the superlattice polarization direction distribution in combination with the objective function using a simulated annealing algorithm, and obtaining an optimal superlattice polarization direction distribution.

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

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

[0023] S3.2) setting the initial temperature, temperature attenuation coefficient and number of iterations, with the initial temperature being used as the simulation temperature; setting a plurality of different target wavelengths and a plurality of 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 a TE0 mode, a TE1 mode and a TE2 mode; the number of the target wavelengths is 1 to 3, and the distance between the target wavelengths is 5 μm at most and 0.4 nm at least.

[0025] S3.3) randomly generating a superlattice polarization direction distribution at a simulation temperature; calculating the wavelength conversion factor of each channel according to the superlattice polarization direction distribution d, inputting the wavelength conversion factor of each channel into an objective function, and obtaining an objective function value;

[0026] The wavelength conversion factor γ(λ α,δ ) is obtained by the following formula:

[0027]

[0028] In the formula, Represents the elements in the first row and second column of the product of the transfer matrices.

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

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

[0031] S3.5) updating the simulated temperature according to the temperature attenuation coefficient, and returning to step S3.3;

[0032] S3.6) Repeat steps S3.3 to S3.5 until the simulation temperature is equal to 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 It represents the channel of the αth target wavelength and the δth target mode, where α represents the sequence number of the target wavelength and δ represents the sequence number of the target mode.

[0036] S4) performing polarization treatment on the superlattice thin film lithium niobate waveguide according to the optimal superlattice polarization direction distribution to obtain a non-periodic polarized lithium niobate waveguide.

[0037] 2. A non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals obtained by the above manufacturing method

[0038] The non-periodic polarized lithium niobate waveguide is composed of a plurality of superlattices of equal length. The superlattices are arranged along the signal propagation direction, and the polarization direction distribution of the superlattices is a non-periodic arrangement.

[0039] 3. A photonic device using the above-mentioned non-periodic polarized lithium niobate waveguide

[0040] The photonic device includes an all-optical wavelength converter and the like.

[0041] The present invention has the following beneficial effects:

[0042] 1. The method of the present invention utilizes a simulated annealing algorithm to optimize the superlattice polarization direction distribution of a superlattice thin-film lithium niobate waveguide, thereby obtaining a non-periodic polarized lithium niobate waveguide with excellent balance 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 needs of wavelength conversion of broadband wavelength mode mixing and multiplexing signals, and has the advantages of high conversion efficiency, compact structure, and light weight. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic diagram of the process of the present invention.

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

[0047] Figure 3 The average conversion efficiency and normalized variance of conversion efficiency of the non-periodic poled lithium niobate waveguide obtained by selecting different superlattice lengths in Example 1 of the present invention.

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

[0049] Figure 5 This is a comparison chart of the wavelength conversion efficiency of the non-periodic poled lithium niobate waveguide and the segmented periodic poled lithium niobate waveguide obtained in Example 2 of the present invention. DETAILED DESCRIPTION

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

[0051] The present invention uses lithium niobate waveguides for all-optical wavelength mode mixing and multiplexing wavelength conversion, and obtains non-periodic polarized lithium niobate waveguides by effectively optimizing the polarization arrangement direction of the superlattice. Compared with the traditional segmented periodic polarized lithium niobate waveguide, this non-periodic polarized lithium niobate waveguide can significantly increase the wavelength conversion efficiency of the wavelength converter.

[0052] Below, the meanings of some terms in the present invention are further described:

[0053] In the present 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 the present invention, "thin-film lithium niobate waveguide" refers to an optical waveguide structure based on thin-film lithium niobate material. The thin-film lithium niobate material can be made by bonding a single-crystal lithium niobate thin film (which can be made by ion cutting technology and can reach a thickness of nanometers) to an insulating substrate (such as silicon or silicon dioxide).

[0055] In the present invention, the "superlattice thin film lithium niobate waveguide model" refers to a model in which the thin film lithium niobate waveguide model is regarded as a model consisting of N superlattices uniformly divided along the signal transmission direction.

[0056] In the present invention, "superlattice thin film lithium niobate waveguide" refers to an unpolarized thin film lithium niobate waveguide that has completed lattice etching but has not yet been polarized.

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

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

[0059] The first aspect of the present invention provides a method for manufacturing a non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals. The method of the present invention mainly uses a simulated annealing algorithm to optimize the polarization reversal direction arrangement of the superlattice to obtain a waveguide structure with excellent balance and wavelength conversion effect. The method of the present invention can also increase the wavelength conversion bandwidth by increasing the distance between the target wavelength channels.

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

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

[0062] Optionally, the construction process of the superlattice thin film lithium niobate waveguide model is: in a computer, using optical simulation software, obtaining the structural parameters of the thin film lithium niobate waveguide according to the effective mode field area and the effective refractive index, constructing the thin film lithium niobate waveguide model according to the obtained structural parameters, and superlattice processing is performed on the thin film lithium niobate waveguide model to obtain the superlattice thin film lithium niobate waveguide model.

[0063] Among them, structural parameters usually include geometric dimensions (such as width, thickness, length L) and material refractive index, etc.

[0064] The superlattice processing of the thin film lithium niobate waveguide model refers to: dividing the thin film lithium niobate waveguide model with a length of L into N superlattices, and all superlattices are evenly arranged along the signal transmission direction. For example, in the embodiment of the present invention, the superlattice thin film lithium niobate waveguide model adopts x-cut y transmission, the signal transmission direction is the y direction, and the polarization direction is parallel to the x direction.

[0065] The parameters of the superlattice processing include the number of superlattices N, the length Δy of each superlattice, and the second-order nonlinear coefficient. In the superlattice 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 a specific implementation, by selecting a suitable superlattice length, the wavelength conversion efficiency and the model calculation time can be balanced.

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

[0067] S2) A non-periodic polarized lithium niobate waveguide model is established based on the superlattice thin film lithium niobate waveguide model and the superlattice polarization direction distribution, and the output amplitude function of the signal light and the idler light is obtained based on the non-periodic polarized lithium niobate waveguide model. In the embodiment of the present invention, when the input pump light is considered to be a strong pump, the influence of other items is excluded so that the wavelength conversion efficiency is only affected by the superlattice polarization direction distribution, so that the output amplitude of the signal light and the idler light can be obtained by inputting the superlattice polarization direction distribution into the output light field. The wavelength conversion efficiency can be obtained by the following formula:

[0068] η=20lg(γ)

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

[0070] Step S2 is specifically as follows:

[0071] S2.1) establishing a non-periodic polarized lithium niobate waveguide model based on the superlattice thin film lithium niobate waveguide model and the superlattice polarization direction distribution, and constructing the difference frequency process coupled wave equation of the non-periodic polarized lithium niobate waveguide model; the difference frequency process coupled wave equation is used to represent the light field change in a single superlattice;

[0072] S2.1) For each superlattice, input the structural parameters of the superlattice into the difference frequency process coupled wave equation to obtain the light field characteristics of the superlattice; obtain the boundary conditions according to the coordinates of the superlattice, input the boundary conditions into the light field characteristics of the superlattice, and obtain the light field characteristics at the boundary of the superlattice;

[0073] In the embodiment of the present 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 parameters such as the effective refractive index of each wavelength and mode signal, the effective mode field area of ​​each wavelength mode signal, and the lattice length;

[0074] S2.2) constructing a transmission matrix according to the light field characteristics at all superlattice boundaries; the elements in the transmission matrix represent the propagation relationship of the light field between adjacent superlattices;

[0075] S2.3) According to the transmission matrix and the preset input light field, an 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:

[0077]

[0078] In the formula, represents the amplitude of the conjugate light of the signal light in the qth superlattice, A i (y N ) represents the amplitude of the idler light in the qth superlattice, * represents conjugation, q represents the lattice number, N represents the total number of lattices in the waveguide, and y N represents the Nth lattice, y0 represents the first lattice, represents the first row and first column element of the product of the transfer matrices, represents the element in the first row and second column of the product of the transfer matrices, represents the element in the second row and first column of the product of the transfer matrices, represents the element in the second row and second column of the product of the transfer matrices, M 11 The element in the first row and first column of the transmission matrix representing the light field transmission from the first superlattice to the second superlattice, M 12 The element in the first row and second column of the transmission matrix representing the light field transmission from the first superlattice to the second superlattice, M 21 The element in the second row and first column of the transmission matrix representing the light field transmission from the first superlattice to the second superlattice, M 22 Represents the first superlattice.

[0079] Among them, the elements of the transmission matrix of the light field transmission from the first superlattice to the second superlattice are set as:

[0080]

[0081] M 22 =M 11 *

[0082] M 12 =M 21 *

[0083] Where M 11 The element in the first row and first column of the transmission matrix representing the light field transmission from the first superlattice to the second superlattice, M 12 The element in the first row and second column of the transmission matrix representing the light field transmission from the first superlattice to the second superlattice, M 22 The element in the second row and second column of the transmission matrix representing the light field transmission from the first superlattice to the second superlattice, M 21 The element of the second row and first column of the transmission matrix representing the light field transmission from the first superlattice to the second superlattice, e represents the phase, j represents the imaginary number, Δk represents the phase mismatch, Δy q represents the length of the qth superlattice, cosh represents the hyperbolic cosine function, sinh represents the hyperbolic sine function, g(y q) represents the g value of the qth lattice.

[0084] In the above formula, g and Γ have no physical meaning, but are mathematical substitutions made to simplify the calculation. The two are set according to the following formulas:

[0085]

[0086] Δk=k p -k s -ki

[0087]

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

[0089] The effective refractive index refers to the equivalent refractive index of light when it propagates in a superlattice thin film lithium niobate waveguide.

[0090] S3) establishing an objective function according to the output amplitude functions of the signal light and the idler light, optimizing the superlattice polarization direction distribution by combining the simulated annealing algorithm with the objective function, and obtaining the optimal superlattice polarization direction distribution.

[0091] The specific process of step S3 is:

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

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

[0094] S3.3) At the simulation temperature, randomly generate the superlattice polarization direction distribution d; calculate the wavelength conversion factor γ (λα,δ ), the wavelength conversion factor γ(λ α,δ ) is input into the objective function to obtain the objective function value;

[0095] In step S3.3, the wavelength conversion factor γ(λ α,δ ) is obtained by the following formula:

[0096]

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

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

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

[0100] S3.5) updating the simulated temperature according to the temperature attenuation coefficient, and returning to step S3.3;

[0101] S3.6) Repeat steps S3.3 to S3.5 until the simulation temperature is equal to 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 Indicates the channel of the αth target wavelength and the δth target mode. α indicates the sequence number of the target wavelength, δ indicates the sequence number of the target mode, max indicates the maximum value, and min indicates the minimum value.

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

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

[0107] Preferably, the number of target wavelengths is 1 to 3. The distance between the target wavelengths is 5 μm at most and 0.4 nm at least.

[0108] Preferably, the value range of the tuning parameter is 0.1 to 10. By tuning 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 to obtain a non-periodic 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 ) to ensure the accuracy of the optimization algorithm.

[0110] S4) performing polarization treatment on the superlattice thin film lithium niobate waveguide according to the optimal superlattice polarization direction distribution to obtain a non-periodic polarized lithium niobate waveguide.

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

[0112] Under multiple different superlattice lengths, the optimal superlattice polarization direction distribution corresponding to the superlattice length is obtained according to steps S1 to S3, and then the corresponding wavelength conversion efficiency is calculated according to the optimal superlattice polarization direction distribution. The superlattice length and the corresponding wavelength conversion efficiency are fitted to obtain a relationship curve. The maximum lattice length of the non-periodic polarized lithium niobate waveguide that can achieve efficient wavelength conversion 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, thereby greatly saving the calculation time required for broadband signal amplification.

[0114] The second aspect of the present invention provides a non-periodic polarized lithium niobate waveguide manufactured by the above method. The non-periodic polarized lithium niobate waveguide is composed of multiple superlattices of equal length, the superlattices are arranged along the signal propagation direction, and the polarization direction distribution of the superlattices is non-periodic.

[0115] Optionally, the non-periodic poled lithium niobate waveguide adopts 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 light waves to interact with each other throughout the waveguide, greatly improving the wavelength conversion efficiency of wavelength mode hybrid multiplexing signals and meeting the application requirements of large-capacity all-optical communication systems.

[0117] The third aspect of the present invention provides a photonic device using the above-mentioned non-periodic polarized lithium niobate waveguide. The photonic device includes but is not limited to an all-optical wavelength converter.

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

[0119] Example 1

[0120] This embodiment provides a design method for a non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals. In this embodiment, a ridge-type thin-film lithium niobate waveguide with an air cladding and a silicon dioxide substrate is used.

[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, respectively. At this time, in the objective function, the serial number α of the target mode is α1, α2 or α3, corresponding to the TE0 mode, TE1 mode and TE2 mode, respectively. In order to utilize the maximum second-order nonlinear coefficient d of the lithium niobate waveguide when processing the TE mode signal 33 , this embodiment uses x-cut y-transduced lithium niobate.

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

[0123] This embodiment specifically includes the following steps:

[0124] S1) constructing a superlattice thin-film lithium niobate waveguide model, wherein the superlattice thin-film lithium niobate waveguide model refers to a thin-film lithium niobate waveguide model including a superlattice structure.

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

[0126] In this step, firstly, according to the existing process conditions, the finite difference time domain algorithm is used to obtain the etching parameters of the lithium niobate ridge waveguide supporting three modes. The thickness of the thin film lithium niobate waveguide is 600nm and the etching is 300nm. Then, the optical simulation software Lumerical FDTD is used to obtain the small effective mode field area (TE0, TE1, TE2 effective mode field areas are 2.193μm respectively) according to the distribution of the effective mode field area. 2 , 2.626μm 2 , 3.121μm 2 ) and can support sufficient TE mode signals, the size parameters of the waveguide are obtained, and the obtained waveguide cross section is as follows Figure 2 shown.

[0127] After constructing a thin film lithium niobate waveguide model according to the obtained size parameters, the thin film lithium niobate waveguide model is superlattice processed according to the superlattice processing parameters to obtain a superlattice thin film lithium niobate waveguide model.

[0128] S2) According to the superlattice thin film lithium niobate waveguide model and the superlattice polarization direction distribution d(y q ) establishes a non-periodic poled lithium niobate waveguide model, and obtains the output amplitude function of the signal light and the idler light according to the non-periodic poled lithium niobate waveguide model. The output amplitude function refers to the function of the amplitude distribution of the light field (signal light and idler light) at the output end and the distribution of the polarization direction of the superlattice.

[0129] In step S1 and step S2, the thin film lithium niobate waveguide model, the superlattice thin film lithium niobate waveguide model and the non-periodic poled lithium niobate waveguide model all use mathematical models to more accurately describe the physical properties of the waveguide, facilitating numerical simulation and theoretical analysis.

[0130] S3) establishing an objective function according to the output amplitude functions of the signal light and the idler light, optimizing the superlattice polarization direction distribution by combining the simulated annealing algorithm with the objective function, and obtaining the optimal superlattice polarization direction distribution.

[0131] The specific process is as follows:

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

[0133] S3.2) Setting the initial temperature T0, the temperature attenuation coefficient ΔT and the number of iterations, with the initial temperature T0 as the simulation temperature. In a specific implementation, the initial temperature T0 and the temperature attenuation coefficient ΔT can be determined based on empirical values ​​or pre-experimental results, and the number of iterations can be set based on convergence conditions or pre-experimental results.

[0134] At the same time, a plurality of different target wavelengths and a plurality of different target modes are set, and each combination of target wavelength and target mode corresponds 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 simulation temperature, randomly generate the superlattice polarization direction distribution d; calculate the amplification gain G(λ) of each channel according to the superlattice polarization direction distribution d. α ), the amplification gain G(λ α ) is input 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 The wavelength conversion factor γ(λ α,δ) is obtained by the following formula:

[0137]

[0138] In the formula, Represents the elements in the first row and second column of the product of the transfer matrices.

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

[0140] In specific implementation, the acceptance probability usually decreases as the temperature decreases. In this embodiment, the acceptance probability is set to:

[0141] P = exp(-ΔE / T)

[0142] Where 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 attenuation coefficient and return to step S3.3.

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

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

[0146] The non-periodic polarized lithium niobate waveguide obtained in this embodiment is composed of N superlattices of equal length, and the polarization direction of the superlattice is arranged non-periodically. This waveguide supports three-mode wavelength mode mixing multiplexing signals in the communication band TE0, TE1, and TE2, as well as 775nm TE mode fundamental mode pumping transmission. This waveguide only uses a single 775nm wavelength single-mode pump to realize the wavelength conversion process of three-wavelength three-mode signals in the communication band.

[0147] The input of the non-periodic poled lithium niobate waveguide obtained in this embodiment includes pump light and signal light to be converted, and the output includes converted signal light and idler light. This non-periodic poled lithium niobate waveguide realizes efficient wavelength conversion.

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

[0149] First, through MATLAB simulation, the input pump light intensity was set to 100mW, the signal light intensity was set to 1mW, and the target wavelengths were selected as 1538.98nm, 1537.40nm and 1535.82nm. Through the above process, the corresponding non-periodic polarized lithium niobate waveguides were obtained at different superlattice lengths.

[0150] For the obtained non-periodic poled lithium niobate waveguide, the losses of pump light and signal light are 1 dB / cm and 0.5 dB / cm respectively (the loss size is independent of the superlattice length). Figure 3 The average conversion efficiency and normalized variance of conversion efficiency obtained by selecting different superlattice lengths. It can be seen that when the superlattice length is less than 1.5μm, better wavelength conversion efficiency and channel balance can be obtained. Figure 3 It can be seen that the smaller the superlattice length is, the higher the average conversion efficiency is and the better the channel balance is. However, at the same time, in the same waveguide, the reduction of the superlattice length will lead to an increase in the number of superlattices, thus increasing the calculation time.

[0151] Furthermore, Δy=1.5μm can be selected as the maximum lattice length of the non-periodic poled lithium niobate waveguide that can achieve efficient wavelength conversion. That is, when the length Δy of each superlattice is 1.5μm and the number of superlattices is 20,000, it is possible to obtain excellent wavelength conversion efficiency and channel balance while ensuring the calculation time.

[0152] like Figure 4 As shown, TE 0,APLN Refers to the TE0 mode signal of the non-periodically polarized thin-film lithium niobate waveguide, TE 1,APLN Refers to the TE1 mode signal of the non-periodically polarized thin-film lithium niobate waveguide, TE 2,APLN Refers to the TE2 mode signal of the non-periodic polarized thin film lithium niobate waveguide, TE 0,PPLN Refers to the TE0 mode signal of the segmented periodically polarized thin film lithium niobate waveguide, TE 1,PPLN Refers to the TE1 mode signal TE of the segmented periodically polarized thin film lithium niobate waveguide 2,PPLNRefers to the TE2 mode signal of the segmented periodic polarized thin-film lithium niobate waveguide. Under the same conditions, compared with the traditional segmented periodic polarized lithium niobate waveguide with a central wavelength of 1550nm (the total length is 30mm, the lengths of the three segments are 12.8μm, 10μm and 7μm, 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] It can be seen that the method of the present invention optimizes the superlattice polarization direction distribution of the superlattice thin film lithium niobate waveguide by using the simulated annealing algorithm, thereby obtaining a non-periodic polarized lithium niobate waveguide with excellent balance and wavelength conversion efficiency.

[0154] Example 2

[0155] This embodiment is based on the method disclosed in Embodiment 1. The present invention provides a method for broadening the bandwidth of wavelength conversion of non-periodic polarized lithium niobate waveguides for wavelength mode mixing and multiplexing signal wavelength conversion (superlattice length is 1.5 μm).

[0156] In this embodiment, the wavelength conversion bandwidth is increased by increasing the distance between the target wavelengths without increasing the number of target wavelengths, thereby successfully broadening the wavelength conversion bandwidth of non-periodic poled lithium niobate without increasing the operation time.

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

[0158] Figure 5 This is a comparison chart of wavelength conversion bandwidth and efficiency of the non-periodic poled lithium niobate waveguide obtained in this embodiment and the segmented periodic poled lithium niobate waveguide (total length is 30 mm, three segment lengths are 12.8 μm, 10 μm and 7 μm, respectively, and polarization periods are 2.241 μm, 3.332 μm and 4.678 μm, respectively) under the same conditions. Figure 5 In TE 0,APLN Refers to the TE0 mode signal of the non-periodically polarized thin-film lithium niobate waveguide, TE 1,APLN Refers to the TE1 mode signal of the non-periodically polarized thin-film lithium niobate waveguide, TE 2,APLN Refers to the TE2 mode signal of the non-periodic polarized thin film lithium niobate waveguide, TE 0,PPLN Refers to the TE0 mode signal of the segmented periodically polarized thin film lithium niobate waveguide, TE 1,PPLN Refers to the TE1 mode signal TE of the segmented periodically polarized thin film lithium niobate waveguide 2,PPLN Refers to the TE2 mode signal of the segmented periodically polarized thin film lithium niobate waveguide.

[0159] Depend on Figure 5 It can be seen that the wavelength conversion bandwidth of the non-periodic poled lithium niobate waveguide obtained in this embodiment is 32nm, and the wavelength conversion efficiency is -6dB, which has both a wide wavelength conversion bandwidth and high wavelength conversion efficiency.

[0160] The non-periodic polarized lithium niobate waveguide obtained in Examples 1 and 2 of the present invention can enable the three modes of light waves to interact with each other in the entire waveguide, greatly improving the wavelength conversion efficiency of the wavelength mode mixing and multiplexing signal, and can meet the application requirements of large-capacity all-optical communication systems.

[0161] By comparing Example 1 with Example 2, it can be seen that the wavelength conversion bandwidth of the non-periodic poled lithium niobate waveguide obtained in Example 1 is increased from 10 nm to 32 nm, and the wavelength conversion efficiency can still be maintained at a high level. 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 the calculation time.

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

Claims

1. A method for manufacturing a non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals, characterized in that: The following steps are involved: S1) constructing a superlattice thin film lithium niobate waveguide model; S2) establishing a non-periodic polarized lithium niobate waveguide model according to the superlattice thin film lithium niobate waveguide model and the superlattice polarization direction distribution, and obtaining output amplitude functions of signal light and idler light according to the non-periodic polarized lithium niobate waveguide model; S3) establishing an objective function according to the output amplitude function of the signal light and the idler light, optimizing the superlattice polarization direction distribution in combination with the objective function by using a simulated annealing algorithm, and obtaining an optimal superlattice polarization direction distribution; S4) performing polarization treatment on the superlattice thin film lithium niobate waveguide according to the optimal superlattice polarization direction distribution to obtain a non-periodic polarized lithium niobate waveguide.

2. The method for manufacturing a non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals according to claim 1, characterized in that: The step S1 specifically comprises: using optical simulation software in a computer to obtain structural parameters of a thin-film lithium niobate waveguide according to an effective mode field area and an effective refractive index, constructing a thin-film lithium niobate waveguide model according to 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 a non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals according to claim 1, characterized in that: The step S2 is specifically as follows: S2.1) establishing a non-periodic polarized lithium niobate waveguide model according to the superlattice thin film lithium niobate waveguide model and the superlattice polarization direction distribution, and constructing a difference frequency process coupled wave equation of the non-periodic polarized lithium niobate waveguide model; S2.1) for each superlattice, inputting the structural parameters of the superlattice into the difference frequency process coupled wave equation to obtain the light field characteristics of the superlattice; obtaining boundary conditions according to the coordinates of the superlattice, inputting the boundary conditions into the light field characteristics of the superlattice, and obtaining the light field characteristics at the boundary of the superlattice; S2.2) constructing a transmission matrix based on the light field characteristics at all superlattice boundaries; S2.3) obtaining an output light field according to the transmission matrix and the preset input light field; 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 a non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals according to claim 3, characterized in that: In step S2, the output light field is specifically: In the formula, represents the amplitude of the conjugate light of the signal light in the qth superlattice, A i (y N ) represents the amplitude of the idler light in the qth superlattice, * represents conjugation, q represents the lattice number, N represents the total number of lattices in the waveguide, and y N represents the Nth lattice, y0 represents the first lattice, represents the first row and first column element of the product of the transfer matrices, represents the element in the first row and second column of the product of the transfer matrices, represents the element in the second row and first column of the product of the transfer matrices, The element in the second row and second column of the product of the transfer matrices, M 11 The element in the first row and first column of the transmission matrix representing the light field transmission from the first superlattice to the second superlattice, M 12 The element in the first row and second column of the transmission matrix representing the light field transmission from the first superlattice to the second superlattice, M 21 The element in the second row and first column of the transmission matrix representing the light field transmission from the first superlattice to the second superlattice, M 22 Represents the first superlattice.

5. The method for manufacturing a non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals according to claim 1, characterized in that: The process of step S3 is specifically as follows: S3.1) establishing an objective function based on the output amplitude functions of the signal light and the idler light; S3.2) setting the initial temperature, temperature attenuation coefficient and number of iterations, with the initial temperature being used as the simulation temperature; setting a plurality of different target wavelengths and a plurality of different target modes, with each combination of target wavelength and target mode corresponding to a channel; S3.3) randomly generating a superlattice polarization direction distribution at a simulation temperature; calculating the wavelength conversion factor of each channel according to the superlattice polarization direction distribution d, inputting the wavelength conversion factor of each channel into an objective function, and obtaining an objective function value; S3.4) if the objective function value is less than the optimal objective function value, the superlattice polarization direction distribution generated in step S3.4 is used as the optimal superlattice polarization direction distribution; otherwise, the superlattice polarization direction distribution generated in step S3.4 is used as the optimal superlattice polarization direction distribution with acceptance probability; After obtaining the optimal superlattice polarization direction distribution, the objective function value corresponding to the optimal superlattice polarization direction distribution is used as the optimal objective function value; S3.5) updating the simulated temperature according to the temperature attenuation coefficient, and returning to step S3.3; S3.6) Repeat steps S3.3 to S3.5 until the simulation temperature is equal to the termination temperature or the preset number of iterations is reached, and output the optimal superlattice polarization direction distribution.

6. The method for manufacturing a non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals according to claim 1 or 5, characterized in that: In step S3, the objective function is set according to the following formula: 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 It represents the channel of the αth target wavelength and the δth target mode, where α represents the sequence number of the target wavelength and δ represents the sequence number of the target mode.

7. The method for manufacturing a non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals according to claim 5, characterized in that: In step S3.3, the wavelength conversion factor γ(λ α,δ ) is obtained by the following formula: In the formula, Represents the elements in the first row and second column of the product of the transfer matrices.

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

9. A non-periodic polarized lithium niobate waveguide for all-optical wavelength conversion of wavelength mode hybrid multiplexing signals obtained by the manufacturing method according to any one of claims 1 to 8, characterized in that: The non-periodic polarized lithium niobate waveguide is composed of a plurality of superlattices of equal length. The superlattices are arranged along the signal propagation direction, and the polarization direction distribution of the superlattices is a non-periodic arrangement.

10. A photonic device using the non-periodic poled lithium niobate waveguide as claimed in claim 9, characterized in that: Includes all-optical wavelength converter.

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