Method for separating scattering and absorption loss spectra of thin film lithium niobate waveguide
By constructing a spatial energy attribution model and introducing an interface coupling loss term, the problem of separating and detecting scattering and absorption losses in thin-film lithium niobate waveguides under high-mode field leakage conditions was solved, and accurate detection under nonlinear coupling loss conditions was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANJING NANZHI INST OF ADVANCED OPTOELECTRONIC INTEGRATION NANJING
- Filing Date
- 2025-12-26
- Publication Date
- 2026-07-21
Smart Images
Figure CN121595515B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of waveguide detection technology, and more specifically, relates to a method for separating and detecting the scattering and absorption loss spectra of thin-film lithium niobate waveguides. Background Technology
[0002] In waveguides with a high proportion of out-of-mode leakage, the physical separability of scattering loss and absorption loss fails. Ultrathin thin-film lithium niobate (e.g., film thickness <300nm) or high refractive index difference cladding structures cause significant out-of-mode leakage into the cladding or air.
[0003] Currently, existing technical solutions typically assume that scattering loss is mainly caused by sidewall roughness and absorption loss is mainly caused by the material itself. However, under high leakage field conditions, the guided mode energy distribution often spans multiple media. Surface absorption and scattering coupling losses caused by cladding surface contamination, adsorbed moisture, and interface defects no longer satisfy a linear superposition relationship. This causes the physical decomposition premise of "total loss = scattering loss + absorption loss" to not hold in this scenario, making it difficult to guarantee the accuracy of waveguide detection under high leakage field conditions. Summary of the Invention
[0004] To address the shortcomings of existing technologies, the present invention aims to overcome the aforementioned deficiencies and propose a method for separating and detecting the scattering and absorption loss spectra of thin-film lithium niobate waveguides.
[0005] The present invention adopts the following technical solution.
[0006] The first aspect of this invention discloses a method for separating and detecting the scattering and absorption loss spectra of a thin-film lithium niobate waveguide, the method comprising: To obtain the transmission loss per unit wavelength of the thin-film lithium niobate waveguide at different wavelengths and the energy distribution ratio of each wavelength guided mode in different media, in order to determine the total transmission loss and the energy proportion of the mode field space; Based on the total transmission loss and the proportion of spatial energy in the mode field, a spatial energy attribution model is constructed. In the space energy attribution model, an interface coupling loss term is introduced, and a loss-dominant interval is established based on the interface coupling loss term. Loss spectra are extracted within the loss-dominant region, and the consistency of the loss spectra is verified by using the proportion of the mode field space energy as a weight, so as to output the scattering loss spectrum and the absorption loss spectrum.
[0007] Furthermore, obtaining the transmission loss per unit wavelength of the thin-film lithium niobate waveguide at different wavelengths and the energy distribution ratio of each wavelength guided mode in different media to determine the total transmission loss and the mode field space energy ratio includes: The thin-film lithium niobate waveguide is scanned within the target operating wavelength range, and the scanning range is discretized into multiple wavelength points to perform mode excitation on each wavelength point, thereby obtaining the input and output power of each wavelength point. The input and output power are converted into the transmittance at each wavelength point, and the transmittance is then converted into a loss spectrum per unit length by combining the effective propagation length of the waveguide.
[0008] Furthermore, the step of obtaining the transmission loss per unit wavelength of the thin-film lithium niobate waveguide at different wavelengths and the energy distribution ratio of each wavelength guided mode in different media to determine the total transmission loss and the mode field space energy ratio also includes: The energy density integral ratio of the electric field distribution of the guided mode cross section at each wavelength point is obtained, and the mode field space energy is divided into multiple spatial regions according to the energy density integral ratio, so as to determine the mode field space energy ratio corresponding to each spatial region. Align the unit length loss spectrum and mode field space energy ratio at the same wavelength point to generate a joint characterization for each wavelength point. The joint characterization is composed of the unit length loss spectrum and mode field space energy ratio at each wavelength point.
[0009] Furthermore, the construction of the spatial energy attribution model based on the total transmission loss and the proportion of spatial energy in the mode field includes: The total transmission loss is decomposed into core layer absorption loss, interface absorption loss and structural scattering loss, and the weighting factors of the core layer absorption loss, interface absorption loss and structural scattering loss are determined according to the proportion of the mode field space energy, so as to determine the spatial attribution loss term. The spatial attribution loss term is weighted according to the weighting factor, and the weighting factor of the interface absorption loss is nonlinearly adjusted in a specified scenario to obtain a characterization of total spatial attribution loss. Based on the spatial attribution total loss characterization, and by introducing a consistency residual to verify the consistency between the spatial attribution loss term and the weighting factor and the total transmission loss, the spatial energy attribution model is constructed.
[0010] Furthermore, in the spatial energy attribution model, an interface coupling loss term is introduced, and a loss-dominant interval is established based on the interface coupling loss term, including: An interface coupling loss term is introduced into the spatial energy attribution model, and a coupling weight is set for the interface coupling loss term so that the interface coupling loss term and the coupling weight are activated when the energy of the leakage field and the interface neighborhood exceeds a set threshold. Based on the interface coupling loss term and coupling weight of adjacent wavelength points, the coupling loss trend is calculated by differential slope, and the wavelength step size is normalized to obtain the normalized coupling ratio.
[0011] Furthermore, the step of introducing an interface coupling loss term into the spatial energy attribution model and establishing a loss-dominant interval based on the interface coupling loss term also includes: Based on the weighting factors of interface absorption loss, core layer absorption loss and structural scattering loss in the aforementioned space energy attribution model, the scattering weight ratio and absorption weight ratio are defined. When the scattering weight ratio and absorption weight ratio are not lower than a set threshold and the normalized coupling ratio is lower than a set threshold, the coupling loss dominant region is screened out, and the scattering loss dominant region and the absorption loss dominant region are determined. The loss-dominant region includes the coupling loss-dominant region, the scattering loss-dominant region, and the absorption loss-dominant region.
[0012] Furthermore, the step of extracting the loss spectrum within the loss-dominant region and performing a consistency check on the loss spectrum using the mode field spatial energy ratio as a weight to output the scattering loss spectrum and the absorption loss spectrum includes: Extract the scattering loss dominant region and the absorption loss dominant region from the loss dominant region, and integrate the wavelength points corresponding to the scattering loss dominant region and the absorption loss dominant region into a scattering dominant wavelength subset and an absorption dominant wavelength subset, respectively. Within the scattering loss dominant interval, the interface coupling loss term corresponding to the total transmission loss within the interval is screened out, and the corresponding scattering loss spectrum is extracted according to the weighting factor of the structural scattering loss.
[0013] Furthermore, the step of extracting the loss spectrum within the loss-dominant region and performing a consistency check on the loss spectrum using the mode field spatial energy proportion as a weight to output the scattering loss spectrum and the absorption loss spectrum also includes: Within the absorption loss dominance range, the total transmission loss of the interface absorption loss and core layer absorption loss within the range is determined, and the interface coupling loss term and the structural scattering loss term in the total transmission loss within the range are screened out to obtain the absorption loss spectrum. The structural scattering loss term is composed of the structural scattering loss and the corresponding weighting factor. Based on the weighting factors of the core layer absorption loss, interface absorption loss, and structural scattering loss, the consistency of the scattering loss spectrum and the absorption loss spectrum is checked. When the consistency deviation meets the set requirements, the scattering loss spectrum and the absorption loss spectrum are output. Otherwise, the scattering loss spectrum and the absorption loss spectrum are fine-tuned according to the weighting factors.
[0014] The second aspect of this invention discloses a device for separating and detecting the scattering and absorption loss spectra of thin-film lithium niobate waveguides, used to implement the method for separating and detecting the scattering and absorption loss spectra of thin-film lithium niobate waveguides as described in any one of the first aspects, the device comprising: The loss and energy characterization module is used to obtain the transmission loss per unit wavelength of the thin-film lithium niobate waveguide at different wavelengths and the energy distribution ratio of each wavelength guided mode in different media, so as to determine the total transmission loss and the energy ratio of the mode field space. The attribution model construction module is used to construct a spatial energy attribution model based on the total transmission loss and the proportion of spatial energy in the mode field. The dominant interval establishment module is used to introduce an interface coupling loss term into the spatial energy attribution model and establish a loss dominant interval based on the interface coupling loss term. The loss spectrum output module is used to extract the loss spectrum within the loss-dominant region and perform consistency verification on the loss spectrum using the mode field spatial energy ratio as a weight, so as to output the scattering loss spectrum and the absorption loss spectrum.
[0015] A third aspect of the present invention discloses a terminal, including a processor and a storage medium; The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method described in the first aspect.
[0016] A fourth aspect of the present invention discloses a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described in the first aspect.
[0017] The beneficial effects of the present invention are as follows: Compared with the prior art, the present invention has the following advantages: (1) This invention excites the thin-film lithium niobate waveguide in the target operating wavelength range, measures the total transmission loss per unit length of the waveguide at each wavelength, and simultaneously obtains the energy distribution ratio of the corresponding guided mode in the waveguide core, cladding and external medium, forming a joint characterization result of "total loss - spatial energy ratio" that varies with wavelength. Then, using the spatial energy ratio of the mode field as a weighting factor, the total loss is expressed as a weighted combination of three physical sources: core layer bulk absorption, interface absorption and structural scattering. This makes the loss terms no longer directly superimposed according to physical type, but attributed according to the energy ratio of the mode field in the corresponding spatial region. Under high external leakage field conditions, even if the surface absorption and scattering coupling loss caused by cladding surface contamination, adsorbed moisture and interface defects no longer satisfy the linear superposition relationship, the accuracy of waveguide detection can still be guaranteed.
[0018] (2) In the spatial attribution model, this invention introduces an interface coupling loss term for the cladding-air interface or the cladding-capping interface to characterize the impure absorption and scattering losses caused by surface adsorption, moisture, contamination layers, and interface defects. Based on the variation trend of this coupling term at different wavelengths, physical criteria for the scattering-dominant and absorption-dominant regions are established. Finally, based on the determined loss-dominant regions, the structural scattering loss spectrum is extracted within the scattering-dominant region, and the bulk absorption and interface absorption loss spectra are extracted within the absorption-dominant region. Consistency correction is performed using the mode field spatial energy weight, ultimately outputting physically self-consistent scattering and absorption loss spectra under high mode field leakage conditions, further improving the accuracy of waveguide detection under high leakage field conditions. Attached Figure Description
[0019] Figure 1 This is a schematic flowchart of the method for separating and detecting the scattering and absorption loss spectrum of thin-film lithium niobate waveguides provided by the present invention.
[0020] Figure 2 This is a schematic diagram of the structure of the thin-film lithium niobate waveguide scattering and absorption loss spectrum separation and detection device provided by the present invention. Detailed Implementation
[0021] The present application will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be construed as limiting the scope of protection of the present application.
[0022] like Figure 1 As shown in one embodiment, a method for separating and detecting the scattering and absorption loss spectra of a thin-film lithium niobate waveguide includes the following steps: Step S110: Obtain the transmission loss per unit wavelength of the thin-film lithium niobate waveguide at different wavelengths and the energy distribution ratio of each wavelength guided mode in different media, so as to determine the total transmission loss and the energy ratio of the mode field space.
[0023] In some embodiments, the method for separating and detecting the scattering and absorption loss spectra of thin-film lithium niobate waveguides provided by the present invention includes the following steps in step S110: Step S111: Perform wavelength scanning on the thin-film lithium niobate waveguide within the target operating wavelength range, and discretize the scanning range into multiple wavelength points to perform mode excitation on each wavelength point, thereby obtaining the input and output power of each wavelength point.
[0024] Step S112: Convert the input and output power into the transmittance at each wavelength point, and combine the transmittance with the effective propagation length of the waveguide to convert it into a loss spectrum per unit length.
[0025] In some embodiments, the method for separating and detecting the scattering and absorption loss spectra of thin-film lithium niobate waveguides provided by the present invention further includes the following steps in step S110: Step S113: Obtain the energy density integral ratio of the electric field distribution of the guided mode cross section at each wavelength point, and divide the mode field space energy into multiple spatial regions according to the energy density integral ratio, so as to determine the mode field space energy ratio corresponding to each spatial region.
[0026] Step S114: Align the unit length loss spectrum and mode field space energy ratio at the same wavelength point to generate a joint characterization of each wavelength point. The joint characterization is composed of the unit length loss spectrum and mode field space energy ratio at each wavelength point.
[0027] In a specific embodiment, the thin-film lithium niobate waveguide scattering and absorption loss spectrum separation detection method provided by the present invention includes steps 1 to 4: Step 1: Obtain the waveguide mode field spatial energy distribution and total loss spectrum.
[0028] Within the target operating wavelength range, the thin-film lithium niobate waveguide is mode-excited, and the total transmission loss per unit length of the waveguide is measured at each wavelength. Simultaneously, the energy distribution ratio of the corresponding guided mode in the waveguide core, cladding, and external medium is obtained, forming a joint characterization result of total loss and spatial energy proportion varying with wavelength. This includes the following sub-steps: Sub-step 1.1: Establish the input and output power acquisition chain for wavelength scanning and mode excitation.
[0029] Specifically, a wavelength scan is performed within the target operating wavelength range. The scan range is discretized into several wavelength points, and a single-mode excitation is maintained at each wavelength point (achieved in engineering through polarization control and coupling angle / position stabilization). The input power before coupling into the waveguide and the waveguide output power are recorded simultaneously. The wavelength step size needs to cover the device's operating bandwidth and reflect spectral changes. A step size of 0.05-1 nm is recommended, and 2-5 nm can be used for broadband rapid evaluation. The input power should be 0.1-10 mW to avoid noise dominance due to excessively low power and thermal effects or photorefractive interference due to excessively high power.
[0030] Sub-step 1.2: Calculate the total transmission loss spectrum per unit length from the input and output power.
[0031] Specifically, the transmittance at each wavelength is first defined as the ratio of input to output power, then converted to a loss coefficient per unit length. If using the natural logarithm, the unit is 1 / cm or 1 / m; if using decibels, the unit is dB / cm or dB / m. The waveguide length is the measured physical length or equivalent propagation length. In engineering, a test section of 0.5-5cm is commonly used to balance the measurable dynamic range and coupling stability. Therefore, the total loss spectrum per unit length is equal to the natural logarithm of the ratio of input power to output power, which is the ratio of the molecule to the effective propagation length of the waveguide. To reduce the influence of reflection or connection loss at the coupling end face, the same wavelength point can be measured repeatedly and the average value taken. It is recommended to take 3-20 measurements, with an interval of 0.5-5 seconds between each repetition.
[0032] Sub-step 1.3: Obtain the spatial energy ratio function of the guided mode in the core layer, cladding layer and external medium.
[0033] Specifically, at each wavelength, the energy density integral proportion of the cross-sectional electric field distribution of the corresponding guided mode is determined, dividing the energy into three non-overlapping spatial regions: the core region, the cladding region, and the external dielectric region (such as air or a capping layer). In engineering practice, the cross-sectional electric field distribution is obtained from a standard mode solver or equivalent measurement inversion; however, in this example, only an integrable mode field distribution is required. Therefore, the spatial energy proportion... The electric field intensity is defined using the normalized integral of the square of the electric field intensity over the region, and its expression is: ; In the formula, Represents any spatial region; For the first One wavelength point; For the first The guided mode at each wavelength point is located at the cross-sectional coordinates ( The electric field amplitude at point ( ); The energy integral domain of the entire cross section of the three spatial regions; , It is a micro-element of cross-sectional area; For any spatial region in the th The proportion of mode field energy at each wavelength point, with a value ranging from 0 to 1.
[0034] To ensure the feasibility of the project, energy normalization verification must be performed. If the deviation exceeds the limit, it indicates that there is a problem with the division of the region or the acquisition of the model field. For example, the sum of the energy proportions of the model fields in the three spatial regions should be equal to 1, and the allowable error should be controlled within ±0.02.
[0035] Sub-step 1.4 generates and outputs the joint characterization results of total loss and spatial energy ratio.
[0036] Specifically, the total loss and spatial energy percentage at the same wavelength are aligned by index to form a joint characterization result that can be directly referenced later. Simultaneously, engineering criteria are provided to confirm whether the waveguide is in a high leakage field scenario, thus ensuring specificity. The high leakage field criterion suggests using an external medium energy percentage threshold. For example, if the average mode field energy percentage of the external medium within a certain operating bandwidth exceeds a set threshold, it is considered a high leakage field waveguide. For instance, an average leakage field percentage of 0.15-0.60 within the operating bandwidth is a common high leakage field range. If the average leakage field percentage within the operating bandwidth is greater than or equal to 0.20, then the risk of linear decomposition of scattering and absorption is considered significant.
[0037] Step S120: Based on the total transmission loss and the proportion of spatial energy in the mode field, construct a spatial energy attribution model.
[0038] In some embodiments, the method for separating and detecting the scattering and absorption loss spectra of thin-film lithium niobate waveguides provided by the present invention includes the following steps in step S120: Step S121: The total transmission loss is decomposed into core layer absorption loss, interface absorption loss and structural scattering loss, and the weighting factors of core layer absorption loss, interface absorption loss and structural scattering loss are determined according to the proportion of mode field space energy, so as to determine the spatial attribution loss term.
[0039] Step S122: Attribution weighting of the spatial attribution loss term is performed according to the weighting factor, and the weighting factor of interface absorption loss is nonlinearly adjusted in the specified scenario to obtain the representation of total spatial attribution loss.
[0040] Step S123: Based on the spatial attribution total loss characterization, and by introducing consistency residual verification of the spatial attribution loss term in conjunction with the consistency of the weighting factor and the total transmission loss, a spatial energy attribution model is constructed.
[0041] In a specific embodiment, the thin-film lithium niobate waveguide scattering and absorption loss spectrum separation detection method provided by the present invention includes step 2, constructing a loss decomposition expression based on spatial energy attribution. Using the mode field spatial energy proportion obtained in step 1 as a weighting factor, the total loss is expressed as a weighted combination of three physical sources: core layer absorption, interface absorption, and structural scattering. Here, the loss terms are no longer directly superimposed according to physical type, but are attributed according to the energy proportion of the mode field in the corresponding spatial region. This includes the following sub-steps: Sub-step 2.1 defines the physical objects and symbol set of the spatial attribution term.
[0042] Specifically, the sources of loss are first spatially attributed into three categories of physical objects to avoid directly applying the linear assumption of scattering + absorption. The first category is core-layer absorption loss, attributed solely to the interior of the thin-film lithium niobate core material. The second category is interface absorption loss, attributed to energy dissipation caused by adsorption layers, water layers, contamination layers, or interface defects at the cladding-core interface and the cladding-external medium interface. The third category is structural scattering loss, attributed to radiation scattering caused by sidewall roughness, geometric undulations, etc. Then, the core-layer weight is defined as the spatial energy proportion corresponding to the core-layer absorption region. Interface absorption occurs in the interface neighborhood, requiring the determination of its corresponding energy proportion that can participate in interface loss, weighted by the cladding and external medium proportions from step 1. Structural scattering corresponds to the energy proportion that can participate in scattering in the sidewall neighborhood, obtained by multiplying the core-layer proportion by the sidewall sensitivity coefficient. The sidewall sensitivity coefficient characterizes the energy concentration of the mode near the sidewall, can be determined by waveguide geometry, and ranges from 0.2 to 1.0; a larger value indicates closer proximity to the sidewall. To ensure engineering consistency, two constant coefficients are introduced: the interface weight mapping coefficient and the scattering weight mapping coefficient. These coefficients are used to map the proportion of step 1 to the effective weights of the interface and scattering, respectively. The recommended range is 0.5-1.5, which is used to cover the engineering differences of different cladding materials and etched sidewall morphologies.
[0043] Therefore, the effective weight of interface absorption is equal to the product of the sum of the weights of the cladding region and the external medium region and the interface weight mapping coefficient, with a value range of 0-1.5; the effective weight of structural scattering is equal to the product of the core weight and the scattering weight mapping coefficient, with a value range of 0-1.5.
[0044] Sub-step 2.2: Establish the space energy weighted total loss decomposition expression and form a computable target relationship.
[0045] Specifically, at each wavelength, the total loss per unit length is expressed as a weighted sum of three types of spatially attributable loss terms. This weighted sum is not a direct addition based on physical type, but rather an attributive weighting based on the proportion of guided mode energy in the corresponding spatial region. This allows interface loss and scattering loss to coexist under high leakage field conditions without mutually negating each other; that is, the result of summing the products of the three loss coefficients and their respective effective weights.
[0046] To ensure the expression has a physically feasible boundary in engineering, constraints on the feasible range of the loss terms need to be given to avoid negative losses or unreasonable amplification. All three types of loss terms should be non-negative, and common ranges should be provided to facilitate subsequent steps in determining whether they fall within a reasonable range. In engineering, the loss terms of thin-film lithium niobate low-loss waveguides typically fall on the order of 0.001-5 per centimeter, adjusted according to device quality and waveband.
[0047] Sub-step 2.3 constructs an attribution enhancement term that correlates interface absorption with the leakage field, to avoid interface loss being misjudged as core layer absorption or scattering.
[0048] Specifically, in scenarios with high leakage fields, interface absorption is extremely sensitive to changes in the proportion of mode field energy in the external medium (leakage energy proportion). If only the linear weights of the mode field energy proportions of the cladding region and the external medium region are used, the contribution of the external medium interface is easily underestimated, thus squeezing the interface loss within a reasonable range. To address this physical attribution bias, this sub-step upgrades the effective interface weight from a linear term to a nonlinear weight that includes leakage field enhancement. This ensures that when the proportion of mode field energy in the external medium increases, the contribution of the interface term is reasonably amplified, reflecting the engineering fact that "the more energy leaks, the easier it is to be absorbed by the interface / dissipated by the contamination layer." The enhancement form uses a square term, which is convenient for engineering implementation and avoids introducing complex symbols. The expression is: ; In the formula, For enhanced interface weight; The leakage enhancement factor ranges from 0.5 to 3.0. This is the squared term of the proportion of the mode field energy of the external medium, used to increase the interface attribution weight when there is high leakage. The proportion of the mode field energy in the cladding region; This is the interface weight mapping coefficient, with a value ranging from 0.5 to 1.5.
[0049] Then, the original interface weights are replaced with the enhanced interface weights to obtain the updated spatial attribution model.
[0050] Sub-step 2.4 outputs a set of standardized spatial attribution loss decomposition expressions and provides verifiable consistency conditions.
[0051] Specifically, all the representations generated that can be directly referenced in subsequent steps are packaged and output to ensure that subsequent steps can introduce coupling terms and dominant interval criteria without additional input. To facilitate engineers in quickly determining the self-consistency of the expression on-site, a consistency residual is defined to check whether the current combination of weights and loss terms can be substituted back to obtain the total loss. This residual does not involve any algorithm; it is merely an algebraic check of the expression. In engineering, its absolute value is required not to exceed a threshold, ranging from 0.0005 to 0.05 per centimeter, adjusted according to the waveguide loss order of magnitude.
[0052] Step S130: In the spatial energy attribution model, an interface coupling loss term is introduced, and a loss-dominant interval is established based on the interface coupling loss term.
[0053] In some embodiments, the method for separating and detecting the scattering and absorption loss spectra of thin-film lithium niobate waveguides provided by the present invention includes the following steps in step S130: Step S131: Introduce an interface coupling loss term into the spatial energy attribution model and set a coupling weight for the interface coupling loss term so as to activate the interface coupling loss term and the coupling weight when the energy of the leakage field and the interface neighborhood exceeds a set threshold.
[0054] Step S132: Based on the interface coupling loss term and coupling weight of adjacent wavelength points, calculate the coupling loss trend through differential slope, and normalize the wavelength step size to obtain the normalized coupling ratio.
[0055] In some embodiments, the method for separating and detecting the scattering and absorption loss spectra of thin-film lithium niobate waveguides provided by the present invention further includes the following steps in step S130: Step S133: Based on the weighting factors of interface absorption loss, core layer absorption loss and structural scattering loss in the spatial energy attribution model, define the scattering weight ratio and absorption weight ratio.
[0056] Step S134: When the scattering weight ratio and absorption weight ratio are not lower than the set threshold and the normalized coupling ratio is lower than the set threshold, the coupling loss dominant region is screened out, and the scattering loss dominant region and the absorption loss dominant region are determined.
[0057] The loss-dominant region includes the coupling loss-dominant region, the scattering loss-dominant region, and the absorption loss-dominant region.
[0058] In a specific embodiment, the thin-film lithium niobate waveguide scattering and absorption loss spectrum separation detection method provided by the present invention includes step 3, which introduces an interface absorption-scattering coupling term and establishes a separability criterion. In the spatial attribution model of step 2, for the cladding-air interface or the cladding-capping layer interface, an interface coupling loss term is introduced to characterize the impure absorption and impure scattering losses caused by surface adsorption, moisture, contamination layers, and interface defects; and based on the changing trend of this coupling term at different wavelengths, a physical criterion for the scattering-dominant region and the absorption-dominant region is established. This includes the following sub-steps: Sub-step 3.1: Physical boundary and standard expression of interface coupling loss term.
[0059] Specifically, in high-leakage waveguides, the losses at the cladding-air interface or cladding-capping interface often possess dual properties of dissipative absorption and rough scattering triggering, meaning they should not be fully incorporated into either the interface absorption loss coefficient or the structural scattering loss coefficient. Therefore, based on the aforementioned spatial attribution model, an interface coupling loss term is introduced, with an independent coupling weight, ensuring that this term is activated only when the energy of the leaking field and the interface neighborhood is significant. In engineering, the interface coupling loss weight is defined as the product of the external medium energy percentage and the effective interface weight, calibrated with a coupling weight coefficient ranging from 0.2 to 2.0, to account for differences in capping materials, surface cleanliness, and humidity adsorption. Therefore, the final coupling term weight equals the product of the coupling weight coefficient, the leaking energy percentage, and the enhanced interface weight. Subsequently, the attribution model can be extended to a spatial attribution model incorporating the coupling term, and the interface absorption and scattering coupling loss coefficients can be determined.
[0060] To ensure that the interface absorption and scattering coupling loss coefficient has an implementable physical boundary, its value range is specified to be non-negative, and a common engineering range of 0.0005-10 per centimeter is given. When the coating layer is a polymer and has strong water absorption, the upper limit can be relaxed to 20 per centimeter, but it must be identified as the coupling-dominant region rather than the pure absorption or pure scattering region in subsequent criteria.
[0061] Sub-step 3.2: Construct the trend of coupling loss as a function of wavelength and output the spectral variation characteristics required for the separability criterion.
[0062] Specifically, to establish physical criteria for distinguishing between scattering-dominant and absorption-dominant regions, a trend quantity that does not rely on pure experience is needed. This trend quantity should characterize the increase / decrease behavior of the interface absorption and scattering coupling loss coefficient under wavelength variations and be distinguishable from the typical spectral behavior of scattering or absorption. In engineering, the trend quantity is defined using a differential slope, which is directly calculated from the coupling loss values at adjacent wavelengths. To avoid numerical incomparability due to different step sizes, the slope is normalized to the wavelength step size, expressed as: ; In the formula, For the first The wavelength slope of coupling loss at each wavelength point, in units of 1 / (cm·nm) or 1 / (cm·μm); , These are two adjacent sampling wavelength points; For the first Coupling loss coefficient at each wavelength point.
[0063] Meanwhile, to measure the relative contribution of the coupling term to the total loss, a normalized coupling ratio is defined for subsequent thresholding of the criterion. This ratio is constructed based on the ratio of the weighted contribution of the coupling term to the total loss, and numerically equals the product of the coupling loss ratio and the coupling loss coefficient, which is the ratio of the numerator to the total transmission loss, taking a value between 0 and 1. In engineering, to avoid amplification of the denominator at extremely low losses, it can be stipulated that when the total transmission loss is less than 0.001 cm, this point is not used for the ratio criterion, but instead enters the neighborhood averaging process.
[0064] Sub-step 3.3: Establish the physical criteria for the scattering-dominant region and the absorption-dominant region and output the region labeling results.
[0065] Specifically, feasible physical criteria are provided to divide the wavelength axis into at least two types of intervals: scattering-dominant intervals and absorption-dominant intervals. Simultaneously, coupling-dominant markers are retained for bands with significant interface coupling to avoid misjudgment caused by forced dichotomy. The criterion design follows two principles: First, if the coupling ratio is too large, the segment is not suitable for direct classification as pure scattering or pure absorption; second, under the premise of an acceptable coupling ratio, the relative magnitude of the enhanced interface weight and the structural scattering weight is used to determine whether scattering or absorption is more likely to dominate at that wavelength. To this end, two ratio criteria are defined: scattering weight ratio and absorption weight ratio, with corresponding set thresholds, categorized as scattering threshold, absorption threshold, and coupling threshold. The coupling threshold is used to filter out coupling-dominant intervals, with a value of 0.15-0.40. The scattering threshold and absorption threshold are used to determine scattering-dominant and absorption-dominant intervals, with values of 1.2-2.0. The scattering weight ratio is equal to the ratio of the product of the scattering weight and the scattering loss coefficient (numerator) to the product of the coupling weight and the coupling loss coefficient (denominator). The absorption weight ratio is obtained similarly.
[0066] In this embodiment, the interval marking rules are executed in the following order to ensure uniqueness: first, the coupling ratio is determined, and then scattering or absorption is determined: When the normalized coupling ratio is greater than or equal to the coupling threshold, the coupling dominance interval is determined. When the normalized coupling ratio is less than the coupling threshold and the scattering weight ratio is greater than or equal to the scattering threshold, the scattering dominance interval is determined. When the normalized coupling ratio is less than the coupling threshold and the absorption weight ratio is greater than or equal to the absorption threshold, the absorption-dominant interval is determined. When none of the above conditions are met, the current interval is determined to be a transition interval and is merged into the adjacent interval with a higher proportion in the project. The merging rule can be implemented according to the principle of continuity, but the interval merging itself does not change the above physical criterion definition.
[0067] Sub-step 3.4 performs an engineering consistency check on the interval criterion and outputs the result.
[0068] Specifically, to ensure that the introduction of coupling terms does not disrupt the consistency of the total loss back-substitution, a dedicated residual verification attribution model is defined to determine whether back-substitution reconstruction can be performed at each wavelength point. The residual threshold is set at 0.0005-0.05 per centimeter. When the number of consecutive wavelength points where the absolute value of the back-substitution residual exceeds the residual threshold exceeds a certain set number (ranging from 3 to 10 consecutive points), the physical attribution of that band is considered to be still not closed, and the entire band should be marked as coupling-dominated to avoid misjudgment triggered by occasional disturbances at a single point.
[0069] Step S140: Extract the loss spectrum within the loss-dominant region, and perform consistency verification on the loss spectrum using the proportion of mode field space energy as weight, so as to output the scattering loss spectrum and the absorption loss spectrum.
[0070] In some embodiments, the method for separating and detecting the scattering and absorption loss spectra of thin-film lithium niobate waveguides provided by the present invention includes the following steps in step S140: Step S141: Extract the scattering loss dominant region and the absorption loss dominant region from the loss dominant region, and integrate the wavelength points corresponding to the scattering loss dominant region and the absorption loss dominant region into a scattering dominant wavelength subset and an absorption dominant wavelength subset, respectively.
[0071] Step S142: Within the scattering loss dominant interval, the interface coupling loss term corresponding to the total transmission loss within the interval is screened out, and the corresponding scattering loss spectrum is extracted according to the weighting factor of the structural scattering loss.
[0072] In some embodiments, the method for separating and detecting the scattering and absorption loss spectra of thin-film lithium niobate waveguides provided by the present invention further includes the following steps in step S140: Step S143: Within the absorption loss-dominant interval, determine the total transmission loss of interface absorption loss and core layer absorption loss within the interval, and remove the interface coupling loss term and structural scattering loss term from the total transmission loss within the interval to obtain the absorption loss spectrum. The structural scattering loss term is composed of structural scattering loss and corresponding weighting factors.
[0073] Step S144: Based on the weighting factors of core layer absorption loss, interface absorption loss, and structural scattering loss, perform consistency verification on the scattering loss spectrum and absorption loss spectrum. Output the scattering loss spectrum and absorption loss spectrum when the consistency deviation meets the set requirements; otherwise, fine-tune the scattering loss spectrum and absorption loss spectrum according to the weighting factors.
[0074] In a specific embodiment, the thin-film lithium niobate waveguide scattering and absorption loss spectrum separation and detection method provided by the present invention includes step 4, which outputs the scattering and absorption loss spectra under the constraint of the dominant region. Based on the loss dominant region determined in step 3, the structural scattering loss spectrum is extracted within the scattering dominant region, and the bulk absorption and interface absorption loss spectra are extracted within the absorption dominant region. Consistency correction is performed using mode field spatial energy weighting, and finally, physically self-consistent scattering and absorption loss spectra under high mode field leakage conditions are output. This includes the following sub-steps: Sub-step 4.1: Construct an extractable wavelength subset based on the loss-dominant region markers.
[0075] Specifically, within the complete wavelength set, the wavelengths are categorized and filtered based on the values of the interval markers. If a region is marked as scattering-dominant, the corresponding wavelength point is assigned to the scattering-dominant wavelength subset, and similarly, the absorption-dominant wavelength subset is obtained. To ensure that the subsets have engineering statistical significance, if the number of consecutive wavelength points in either the scattering-dominant or absorption-dominant wavelength subset is less than a set threshold (ranging from 5 to 20, adjusted according to wavelength steps and bandwidth), the interval is considered unstable and not directly used for loss spectrum extraction.
[0076] Sub-step 4.2: Extract the structural scattering loss spectrum within the scattering-dominant region.
[0077] Specifically, within the scattering-dominant region, the contributions of interface absorption and bulk absorption are relatively small, but the coupling term may still have residual effects. Therefore, in the scattering-dominant region, the portion of the total loss contributed by the coupling term is first subtracted, and then the structural scattering loss coefficient is derived by reversing the scattering weights to obtain the initial structural scattering loss spectrum before correction. This initial spectrum is expressed as the ratio of the molecular to structural scattering weights, calculated as the difference between the total loss in the region and the weighted contribution of the coupling loss at that wavelength. To prevent numerical amplification due to excessively small weights, when the structural scattering weight is less than a set lower limit (range 0.05-0.15), the corresponding wavelength point is determined not to participate in the loss spectrum extraction process.
[0078] Sub-step 4.3: Extract the bulk absorption and interfacial absorption loss spectra within the absorption-dominant region.
[0079] Specifically, within the absorption-dominant region, the total loss mainly consists of core-layer bulk absorption and interface absorption, but the known contributions from scattering and coupling still need to be deducted. First, within the absorption-dominant region, the initially extracted structural scattering loss spectrum is mapped to the corresponding wavelength point using interpolation or extrapolation. Then, the scattering and coupling terms are subtracted from the total loss to obtain the remaining absorption-dominant loss. This remaining loss is then attributed according to the weights of the core and interface layers to obtain the initial absorption loss spectrum within the absorption-dominant region. To distinguish between bulk absorption and interface absorption, the initial absorption loss spectrum is divided into two parts according to weight ratios: the core-layer bulk absorption loss spectrum and the interface absorption loss spectrum. Furthermore, when the sum of their weights is less than 0.1, the wavelength point is not further subdivided, and only the initial absorption loss spectrum is retained as the total absorption spectrum point.
[0080] Sub-step 4.4 performs consistency correction based on the mode field space weights and outputs the final loss spectrum.
[0081] Specifically, to ensure the physical consistency of the final output scattering and absorption loss spectra across the entire wavelength range, a spatially weighted back-substitution correction is performed on the extracted original spectra. A back-substitution loss is constructed for each wavelength point and compared with the measured total loss. If systematic deviations exist, the initial structural scattering loss spectrum and initial absorption loss spectrum are fine-tuned according to the weighted proportions to ensure the back-substitution results meet consistency requirements. An allowable residual threshold is set for the presence of systematic deviations, ranging from 0.0005 to 0.05 per centimeter, until the output structural scattering loss spectrum and absorption loss spectrum do not exceed the allowable residual threshold, and the absorption loss spectrum is the sum of core volume absorption and interface absorption.
[0082] The following describes the thin-film lithium niobate waveguide scattering and absorption loss spectrum separation and detection device provided by the present invention. The thin-film lithium niobate waveguide scattering and absorption loss spectrum separation and detection device described below can be referred to in correspondence with the thin-film lithium niobate waveguide scattering and absorption loss spectrum separation and detection method described above.
[0083] like Figure 2 As shown, in one embodiment, a thin-film lithium niobate waveguide scattering and absorption loss spectrum separation and detection device includes a loss and energy characterization module, an attribution model construction module, a dominant region establishment module, and a loss spectrum output module.
[0084] The loss and energy characterization module is used to obtain the transmission loss per unit wavelength of the thin-film lithium niobate waveguide at different wavelengths and the energy distribution ratio of each wavelength guided mode in different media, so as to determine the total transmission loss and the energy ratio of the mode field space.
[0085] The attribution model building module is used to construct a spatial energy attribution model based on total transmission loss and the proportion of spatial energy in the mode field.
[0086] The dominant interval establishment module is used to introduce interface coupling loss terms into the spatial energy attribution model and establish the loss dominant interval based on the interface coupling loss terms.
[0087] The loss spectrum output module is used to extract the loss spectrum within the loss-dominant region and perform consistency verification on the loss spectrum using the proportion of energy in the mode field space as a weight, so as to output the scattering loss spectrum and the absorption loss spectrum.
[0088] The applicant of this invention has provided a detailed description of the embodiments of the invention in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above embodiments are merely preferred embodiments of the invention. The detailed description is only intended to help readers better understand the spirit of the invention and is not intended to limit the scope of protection of the invention. On the contrary, any improvements or modifications made based on the inventive spirit of the invention should fall within the scope of protection of the invention.
Claims
1. A method for separating and detecting the scattering and absorption loss spectra of a thin-film lithium niobate waveguide, characterized in that, The method includes: To determine the total transmission loss and mode field energy ratio of a thin-film lithium niobate waveguide at different wavelengths, the transmission loss per unit wavelength of the waveguide is obtained at different wavelengths. Specifically, this includes: Establish an input-output power acquisition chain for wavelength scanning and mode excitation; calculate the total transmission loss spectrum per unit length from the input and output power; obtain the spatial energy ratio function of the guided mode in the core layer, cladding layer, and external medium; form and output the joint characterization results of total loss and spatial energy ratio; Based on the total transmission loss and the proportion of spatial energy in the mode field, a spatial energy attribution model is constructed; specifically, it includes: The total transmission loss is decomposed into core layer absorption loss, interface absorption loss and structural scattering loss, and the weighting factors of the core layer absorption loss, interface absorption loss and structural scattering loss are determined according to the proportion of the mode field space energy, so as to determine the spatial attribution loss term. The spatial attribution loss term is weighted according to the weighting factor, and in the scenario of high external leakage field, the effective weight of the interface is upgraded from a linear term to a nonlinear weight that includes the enhancement of external leakage field, so that when the proportion of the mode field energy of the external medium increases, the contribution of the interface term is reasonably amplified, and the total spatial attribution loss characterization is obtained. Based on the spatial attribution total loss characterization, and by introducing consistency residual verification to check the consistency between the spatial attribution loss term and the weighting factor and the total transmission loss, the spatial energy attribution model is constructed. In the space energy attribution model, an interface coupling loss term is introduced, and a loss-dominant interval is established based on the interface coupling loss term; specifically, it includes: An interface coupling loss term is introduced into the spatial energy attribution model, and a coupling weight is set for the interface coupling loss term so that the interface coupling loss term and the coupling weight are activated when the energy of the leakage field and the interface neighborhood exceeds a set threshold. Based on the interface coupling loss term and coupling weight of adjacent wavelength points, the coupling loss trend is calculated by differential slope, and the wavelength step is normalized to obtain the normalized coupling ratio. The normalized coupling ratio is constructed based on the ratio of the weighted contribution of the coupling term to the total loss, and is numerically equal to the product of the coupling loss ratio and the coupling loss coefficient as the ratio of the numerator to the total transmission loss. Based on the weighting factors of interface absorption loss, core layer absorption loss and structural scattering loss in the aforementioned space energy attribution model, the scattering weight ratio and absorption weight ratio are defined. When the scattering weight ratio and absorption weight ratio are not lower than a set threshold and the normalized coupling ratio is lower than a set threshold, the coupling loss dominant region is screened out, and the scattering loss dominant region and the absorption loss dominant region are determined. The loss-dominant region includes the coupling loss-dominant region, the scattering loss-dominant region, and the absorption loss-dominant region. Loss spectra are extracted within the loss-dominant region, and the consistency of the loss spectra is verified by using the proportion of the mode field space energy as a weight, so as to output the scattering loss spectrum and the absorption loss spectrum.
2. The method for separating and detecting scattering and absorption loss spectra of thin-film lithium niobate waveguides according to claim 1, characterized in that, The process of obtaining the transmission loss per unit wavelength of the thin-film lithium niobate waveguide at different wavelengths and the energy distribution ratio of each wavelength guided mode in different media to determine the total transmission loss and the mode field space energy ratio includes: The thin-film lithium niobate waveguide is scanned within the target operating wavelength range, and the scanning range is discretized into multiple wavelength points to perform mode excitation on each wavelength point, thereby obtaining the input and output power of each wavelength point. The input and output power are converted into the transmittance at each wavelength point, and the transmittance is then converted into a loss spectrum per unit length by combining the effective propagation length of the waveguide.
3. The method for separating and detecting scattering and absorption loss spectra of thin-film lithium niobate waveguides according to claim 2, characterized in that, The process of obtaining the transmission loss per unit wavelength of the thin-film lithium niobate waveguide at different wavelengths and the energy distribution ratio of each wavelength guided mode in different media to determine the total transmission loss and the mode field space energy ratio also includes: The energy density integral ratio of the electric field distribution of the guided mode cross section at each wavelength point is obtained, and the mode field space energy is divided into multiple spatial regions according to the energy density integral ratio, so as to determine the mode field space energy ratio corresponding to each spatial region. Align the unit length loss spectrum and mode field space energy ratio at the same wavelength point to generate a joint characterization for each wavelength point. The joint characterization is composed of the unit length loss spectrum and mode field space energy ratio at each wavelength point.
4. The method for separating and detecting scattering and absorption loss spectra of thin-film lithium niobate waveguides according to claim 1, characterized in that, The process of extracting the loss spectrum within the loss-dominant region and performing a consistency check on the loss spectrum using the mode field spatial energy proportion as a weight to output the scattering loss spectrum and the absorption loss spectrum includes: Extract the scattering loss dominant region and the absorption loss dominant region from the loss dominant region, and integrate the wavelength points corresponding to the scattering loss dominant region and the absorption loss dominant region into a scattering dominant wavelength subset and an absorption dominant wavelength subset, respectively. Within the scattering loss dominant interval, the interface coupling loss term corresponding to the total transmission loss within the interval is screened out, and the corresponding scattering loss spectrum is extracted according to the weighting factor of the structural scattering loss.
5. The method for separating and detecting scattering and absorption loss spectra of thin-film lithium niobate waveguides according to claim 4, characterized in that, The step of extracting the loss spectrum within the loss-dominant region and performing a consistency check on the loss spectrum using the mode field spatial energy ratio as a weight to output the scattering loss spectrum and the absorption loss spectrum further includes: Within the absorption loss dominance range, the total transmission loss of the interface absorption loss and core layer absorption loss within the range is determined, and the interface coupling loss term and the structural scattering loss term in the total transmission loss within the range are screened out to obtain the absorption loss spectrum. The structural scattering loss term is composed of the structural scattering loss and the corresponding weighting factor. Based on the weighting factors of the core layer absorption loss, interface absorption loss, and structural scattering loss, the consistency of the scattering loss spectrum and the absorption loss spectrum is checked. When the consistency deviation meets the set requirements, the scattering loss spectrum and the absorption loss spectrum are output. Otherwise, the scattering loss spectrum and the absorption loss spectrum are fine-tuned according to the weighting factors.
6. A terminal, comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is configured to operate according to the instructions to perform the steps of the method according to any one of claims 1-5.
7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program implements the steps of the method according to any one of claims 1-5.