Process tolerance coupler phase compensation automatic optimization method

Abstract

The invention discloses an automatic optimization method for phase compensation of a process tolerance coupler, which comprises the following steps of: automatically calculating the phase compensation length of a PTC (Positive Temperature Coefficient) structure according to a formula, and automatically judging whether the phase compensation length meets three conditions, namely, a positive temperature coefficient (PTC) structure; according to the specific application scene of the PTC, judging whether the wavelength corresponding to the position of the minimum value of the MSE value is greater than or smaller than the central wavelength; the minimum value of the transmissivity curve is not located at the beginning and the end of the transmissivity curve; segmenting the transmissivity curve at the position of the transmissivity minimum value, respectively calculating the MSE values of the left and right sections of the transmissivity curve, and enabling the difference value of the MSE values of the left and right sections of the curve to be the minimum value; and if the phase compensation length meets the three conditions, the phase compensation length is the optimal phase compensation length. According to the method, the PTC structure with the optimal performance can be obtained through one-key optimization, and the phase compensation length can be accurate to the scale, so that the precision of a subsequent integrated optical path is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon photonics chips, and particularly to an automatic optimization method for process tolerance coupler phase compensation. Background Art

[0002] Due to its precise coupling ratio, maximally flat bandwidth, and process tolerance, and its ability to achieve low loss, low crosstalk, and large process tolerance, the process tolerance coupler (PTC) is widely used in CWDM filters. As Figure 1 shown, it is a Mach-Zehnder interferometer composed of two optical directional couplers and delay lines, that is, a standard PTC structure, which includes two directional couplers located on the left and right sides of the structure, and two arc waveguide (arc) structures in the middle, corresponding to the n-type arc and u-type arc respectively. In the figure: The phase change corresponding to the optical wave propagating in the straight waveguide with length L1 The phase change corresponding to the optical wave propagating in the straight waveguide with length L2 The phase change corresponding to the optical wave propagating in the left S-Bend The phase change corresponding to the optical wave propagating in the left curved waveguide in the middle, The phase change corresponding to the optical wave propagating in the right curved waveguide in the middle The phase change corresponding to the optical wave propagating in the right S-Bend Z: As shown in the figure, a z coordinate axis is set horizontally. z represents the general coordinate point on this coordinate axis. z = 0 represents the origin of the z coordinate axis, and z = L2 represents the point with a length of L2 in the positive direction of the coordinate axis. Thus, it can be clearly obtained that the length of the right straight waveguide is L2 - 0 = L2. Further comparison can show the meaning of L1.

[0003] d0 represents the distance between the directional couplers.

[0004] d(z): Represents the functional relationship between the longitudinal coordinate and the transverse coordinate z on the directional coupler. For example, d(L2) = d0. Its specific expression needs to change according to the selected S-bend structure. This article mainly explains the simulation optimization method, and the selection of the S-bend structure does not affect the method description.

[0005] R: The bending radius corresponding to the S-bend : Half of the angle value corresponding to the S-bend This structure is insensitive to wavelength, and applying this structure can greatly improve the stability of the output of the integrated optical circuit. The power coupling ratio S of this structure is defined as:

[0006]

[0007] Where:

[0008]

[0009] : Total input power of light wave : Output power of light wave at the transmission (Through) port : Output power of light wave at the coupling (Cross) port

[0010]

[0011]

[0012]

[0013] : Length difference between the upper and lower arc parts in the middle ; Lc(λ) is the coupling length relative to π / 2.

[0014] From the term and term in the formula for calculating S above, it can be seen that by changing the length difference between the two arc parts in the middle of the PTC structure, the regulation of the output power coupling ratio can be achieved.

[0015] In the prior art, the optimization of the phase compensation length is usually obtained by calculating the reference value of the phase compensation length using a formula, and then manually adjusting the compensation length and viewing the transmittance image to obtain a PTC structure with better performance. Figure 2 Is the enlarged image of the cross port of the PTC structure manually optimized in the prior art. Judging from the figure, the transmittance values at each wavelength are very close to the target values, which is a very good result. Figure 2In it, x represents the abscissa wavelength, and y represents the ordinate transmittance. In the figure, x = 1.261 represents the position on the figure corresponding to the wavelength value of 1261 nm. Similarly, x = 1.351 represents the position on the figure corresponding to the wavelength value of 1351 nm. The area between these two lines represents the region of interest. And y = 0.08 represents the position corresponding to the transmittance of 0.08, which is also the reference value of the current designed PTC transmittance. The purpose of drawing this straight line is to better compare the optimization results.

[0016] However, there are three drawbacks in obtaining the optimal compensation length of PTC by the manual optimization method in the prior art: First, it is necessary to manually adjust the parameters and identify them in combination with the transmittance image, which is time-consuming and laborious. The relationship between the workload W and the accuracy is: .

[0017] Second, near the optimal value of the compensation length, the similarity of the transmittance curves is very high. Due to the lack of an evaluation standard, the probability of obtaining the optimal compensation length by relying solely on visual judgment of the human eye is extremely low, making it difficult to achieve the optimal optimization. Figure 3 For the compensation lengths equal to 0.49 and 0.50 The transmittance curves corresponding to the PTC Cross ports. Although Figure 3 the shown transmittance image has a good visual sense for the human eye, but for the two cases of the compensation lengths of 0.49 and 0.50 Since the similarity of the transmittance curve results is extremely high, it is very difficult to determine which length is the optimized result.

[0018] Third, there are generally minute "protrusions" on the PTC transmittance curve, such as Figure 3 the burrs in the center of the curve in. These "protrusions" may cause false values in the optimal compensation length of PTC, but it is very difficult to eliminate these "protrusions" by the method of manual adjustment plus human eye recognition.

[0019] In view of the above problems, the present invention proposes a method for automatically obtaining the optimal compensation length of PTC. Using this method, the PTC structure with the best performance can be optimized with one key, and the compensation length can be accurately measured to the nm scale, thus greatly improving the accuracy of the subsequent integrated optical path. Summary of the Invention

[0020] In view of the above problems, the present invention proposes an automatic optimization method for process tolerance coupler phase compensation, which includes the following steps Step 1: Set the scanning range and scanning step size; Step 2: Calculate the phase compensation length, which is the minimum value of the mean square error (MSE) between the transmittance curve and the target transmittance ; Step 3: Determine whether the phase compensation length satisfies: Condition 1: According to the specific application scenario of the process tolerance coupler, determine whether the wavelength corresponding to the minimum value of the MSE is greater than or less than the central wavelength; Condition 2: The minimum value of the transmittance curve is not located at the beginning and end of the transmittance curve; Step 4: If the phase compensation length satisfies both Condition 1 and Condition 2, it can be determined that the phase compensation length calculated in Step 2 is the required phase compensation length; if the phase compensation length does not satisfy one or both of Condition 1 and Condition 2, repeat Step 1.

[0021] Preferably, in Step 3, it further includes Condition 3: Divide the transmittance curve at the position of the minimum transmittance, calculate the MSE values of the left and right transmittance curves respectively, and make the difference between the MSE values of the left and right transmittance curves the minimum; when the phase compensation length satisfies both Condition 1 and Condition 2 in Step 3, if the phase compensation length also satisfies Condition 3 at the same time, then this phase compensation length is a more optimal phase compensation length.

[0022] Preferably, the phase compensation length in Step 2 is calculated by the following formula

[0023] where, is the power coupling ratio measured at port 3 for the optical wave input at port 2 of the process tolerance coupler; is the target transmittance that the process tolerance coupler structure wants to achieve; is the full spectral wavelength of the incident optical wave of the process tolerance coupler structure; is the central wavelength of the incident optical wave of the process tolerance coupler structure; is the number of sampling points.

[0024] Preferably, Condition 1 is calculated by the following formula

[0025] where, is the power coupling ratio measured at port 3 for the optical wave input at port 2 of the process tolerance coupler; is the full spectral wavelength of the incident optical wave of the process tolerance coupler structure; is the central wavelength of the incident optical wave of the process tolerance coupler structure.

[0026] Preferably, the condition 2 is calculated by the following formula

[0027] wherein is the power coupling ratio measured at port 3 with the optical wave input at port 2 of the process tolerance coupler; is the number of sampling points.

[0028] Preferably, the condition 3 is calculated by the following formula

[0029] wherein is the power coupling ratio measured at port 3 with the optical wave input at port 2 of the process tolerance coupler; is the target transmittance that the process tolerance coupler structure aims to achieve; is the number of sampling points. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of illustrating the preferred embodiments and are not considered to be a limitation of the present invention. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings: Figure 1 is a schematic diagram of the PTC structure; Figure 2 is an enlarged view of the transmittance curve of the cross port of the PTC structure manually optimized when the phase compensation length in the prior art is equal to 0.33 ; Figure 3 is the PTC transmittance curve of the PTC cross port when the compensation lengths are equal to 0.49 and 0.5 ; Figure 4 is a schematic diagram of the PTC device ports; Figure 5 is a flowchart of the compensation length optimization calculation method of the present invention; Figure 6 is the transmittance curve of the PTC cross port when the compensation lengths obtained by using the calculation method of the present invention are equal to 0.31 , 0.33 , 0.46 , 0.49 , 0.50 respectively. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] To further illustrate the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following provides a detailed description of a waveguide crossing structure of different materials proposed according to the present invention in conjunction with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "embodiments" do not necessarily refer to the same embodiment. In addition, the specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0032] In this article, the term "and / or" is merely a description of the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B is specifically understood as: A and B can be included simultaneously, A can exist alone, or B can exist alone, and any of the above three situations can be satisfied.

[0033] According to Figure 1 the shown PTC structure, define its ports as shown in Figure 4 including Port 1, Port 2, Port 3, and Port 4. Port 2 serves as the optical wave input port, that is, corresponding to Figure 1 P in in .

[0034] According to the port definition, define the following physical parameters: : The S parameter measured at Port 3 when the optical wave is input at Port 2 : The S parameter measured at Port 4 when the optical wave is input at Port 2 : The target transmittance that the PTC structure wants to achieve : The full spectral wavelength of the incident optical wave of the PTC structure : The central wavelength of the incident optical wave of the PTC structure : The number of sampling points In order to obtain the optimal value of the compensation length of the PTC structure, it is necessary to scan the compensation length. The scanning needs to meet the following conditions:

[0035] Equation (1) finds the transmittance curve and the target transmittance The minimum value of the mean square error (MSE). Equation (2) determines the positional relationship between the wavelength corresponding to the minimum MSE value and the central wavelength (which needs to be determined according to the specific application scenario of the PTC); Equation (3) limits that the minimum value of the transmittance curve cannot be located at the beginning and end of the curve; Equation (4) divides the transmittance curve at the position of the minimum transmittance, calculates the MSE values of the left and right segments of the transmittance curve respectively, and finds the minimum value of the difference between the MSE values of the left and right segments of the transmittance curve.

[0036] Combined formula The optimal PTC compensation length can be obtained. Figure 5 shows the steps.

[0037] First, set the scanning range and scanning step size, then calculate the compensation length according to Equation (1), and then verify whether the compensation length meets the requirements through Equations (2)-(4). If the compensation length meets the limitations of Equations (2)-(4), then the compensation length is the optimal compensation length; if not, reset the scanning range and scanning step size. If the compensation length calculated by Equation (1) meets the limitations of Equations (2) and (3) but does not meet the limitation requirements of Equation (4), in this case, if higher precision is still required, reset the scanning range and scanning step size and recalculate the compensation length according to Equation (1); if the required precision is not high, then the compensation length that meets the requirements of Equations (2) and (3) can be determined as the optimal compensation length.

[0038] The following uses a specific example to illustrate. Taking the power coupling ratio S of the PTC 32 equal to 0.08 as an example, Table 1 records the calculation results of Equation when the compensation lengths are 0.31 、0.33 、0.46 、0.49 and 0.50 respectively. It can be clearly seen from Table 1 that when the compensation length is equal to 0.46 , the value calculated by Equation is the smallest, indicating that the uniformity of the PTC transmittance curve obtained at this time is the best, that is, the performance of the PTC is the best.

[0039] Table 1 Results calculated by Equation under different compensation lengths

[0040] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they know the basic creative concepts. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0041] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these changes and modifications.

Claims

1. An automatic optimization method for phase compensation of a process tolerance coupler, comprising the following steps: Step 1: Set the scanning range and scanning step size; Step 2: Calculate the phase compensation length, which is the minimum value of the mean square error between the transmittance curve and the target transmittance value; Step 3: Determine whether the phase compensation length satisfies: Condition 1: According to the specific application scenario of the process tolerance coupler, determine whether the wavelength corresponding to the minimum value of the MSE value is greater than or less than the center wavelength; Condition 2: The minimum value of the transmittance curve does not lie at the beginning and end of the transmittance curve; Step 4: If the phase compensation length satisfies both Condition 1 and Condition 2 at the same time, it can be determined that the phase compensation length calculated in Step 2 is the required phase compensation length; if the phase compensation length does not satisfy one or both of Condition 1 and Condition 2, repeat Step 1.

2. The automatic optimization method for phase compensation of a process tolerance coupler according to claim 1, characterized in that: In Step 3, it also includes Condition 3: Divide the transmittance curve at the position of the minimum transmittance value, calculate the MSE values of the left and right transmittance curves respectively, and make the difference between the MSE values of the left and right transmittance curves the minimum value; When the phase compensation length satisfies both Condition 1 and Condition 2 in Step 3 at the same time, if the phase compensation length also satisfies Condition 3 at the same time, then the phase compensation length is a more optimal phase compensation length.

3. The automatic optimization method for phase compensation of a process tolerance coupler according to claim 1, characterized in that: The phase compensation length in Step 2 is calculated by the following formula ； Among them, is the power coupling ratio obtained by measuring the optical wave input at port 2 of the process tolerance coupler and port 3; is the target transmittance that the process tolerance coupler structure wants to achieve; is the number of sampling points.

4. A method for automatically optimizing the phase compensation of a process tolerance coupler according to claim 1 or 3, characterized in that: Condition 1 is calculated by the following formula ； Among them, is the power coupling ratio measured at port 3 when optical waves are input at port 2 of the process tolerance coupler; is the full spectral wavelength of the incident light wave for the process tolerance coupler structure; is the central wavelength of the incident light wave for the process tolerance coupler structure.

5. A method for automatically optimizing the phase compensation of a process tolerance coupler according to claim 1 or 3, characterized in that: Condition 2 is calculated by the following formula ； Among them, is the power coupling ratio measured at port 3 when light waves are input at port 2 of the process tolerance coupler; is the number of sampling points.

6. The automatic optimization method for phase compensation of a process tolerance coupler according to claim 2, characterized in that: Condition 3 is calculated by the following formula ； Among them, is the power coupling ratio measured at port 3 when light waves are input at port 2 of the process tolerance coupler; is the target transmittance that the process tolerance coupler structure wants to achieve; is the number of sampling points.

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