A detection method for thin film lithium niobate waveguide etching process

Abstract

The present application provides a method for testing a thin-film lithium niobate waveguide etching process. The method comprises: preparing a sample to be tested according to a preset waveguide structure mask pattern using a thin-film lithium niobate waveguide etching process to be tested; the preset waveguide structure mask pattern includes multiple test regions, each of which is provided with a microring waveguide and a racetrack waveguide; testing the sample to be tested using a coupled optical path to obtain the quality factors of the waveguides in different test regions; fitting the microring waveguide losses in different test regions based on the quality factors; and calibrating the test results of the thin-film lithium niobate waveguide etching process to be tested based on the microring waveguide losses. In this way, the microring waveguide losses in different test regions are fitted using the quality factors of the waveguides in different test regions, and then, based on the performance of the microring waveguide losses, whether the thin-film lithium niobate waveguide etching process to be tested is accurately detected.

Description

Technical Field

[0001] The present application relates to the field of waveguide processing, and in particular to a detection method for a thin-film lithium niobate waveguide etching process. Background Art

[0002] A waveguide is a channel for light propagation in an optical device. By utilizing the principle of total reflection of light waves, the propagation of light waves can be confined to a medium at the order of the wavelength.

[0003] Lithium niobate waveguides are a type of optical waveguide. Currently, the main methods for preparing lithium niobate waveguides include titanium diffusion, proton exchange, and ion implantation. However, due to the small difference in refractive index change, these methods result in waveguide sizes that are too large, making them ineffective for on-chip integration. In recent years, due to the improvement of the preparation process of lithium niobate thin films (LNOI), people have used etching processes on the thin films to prepare lithium niobate thin film ridge waveguides with smaller linewidths. Because the light confinement ability of this waveguide is caused by the refractive index difference between the upper and lower layers and the medium on both sides and the lithium niobate, the quality of the etching process is a decisive factor in the loss of microring waveguides.

[0004] Currently, thin-film lithium niobate waveguide etching processes are typically inspected using a scanning electron microscope (SEM) to directly examine the waveguide etch morphology or an atomic force microscope (AFM) to measure the etched sidewall roughness. These measurements reveal the extent of surface defects, which in turn reflects the stability of the thin-film lithium niobate waveguide etching process. However, waveguides are affected by both surface and internal defects. Microscopes can only observe the extent of surface defects, but not internal defects. Consequently, microscopic inspection of waveguides is inaccurate, leading to inaccurate assessments of the stability of the thin-film lithium niobate waveguide etching process. Summary of the Invention

[0005] The present application provides a method for detecting a thin-film lithium niobate waveguide etching process, which can be used to solve the technical problem of inaccurate detection of the thin-film lithium niobate waveguide etching process by the existing method.

[0006] In a first aspect, the present application provides a method for detecting a thin-film lithium niobate waveguide etching process, the detection method comprising:

[0007] Preset waveguide structure mask layout;

[0008] According to the waveguide structure mask, a process sample is processed by a thin film lithium niobate waveguide etching process to prepare a sample to be tested; the sample to be tested includes a plurality of test areas, each of which is provided with a microring waveguide and a racetrack waveguide;

[0009] Testing the sample to be tested by a coupled optical path to obtain the quality factors of the microring waveguide and the racetrack waveguide in each area to be tested;

[0010] fitting the microring waveguide losses of different test areas according to the quality factors of the microring waveguide and the racetrack waveguide in each test area;

[0011] The detection result of the etching process of the thin film lithium niobate waveguide to be tested is calibrated according to the microring waveguide loss of the different areas to be tested.

[0012] In an implementation of the present application, a plurality of arrays of areas to be tested are arranged on the sample to be tested.

[0013] In an implementable manner of the present application, the waveguide structure mask pattern is preset according to the following steps:

[0014] Determining the dimensions of the microring waveguide and the racetrack waveguide in each area to be tested, and the spacing between the microring waveguide and the racetrack waveguide;

[0015] According to the size of the process sample, the number of rows and columns of the rectangular array of the plurality of test areas is preset;

[0016] The waveguide structure mask layout is made according to the sizes of the microring waveguide and the racetrack waveguide, and the number of rows and columns of the rectangular array.

[0017] In an implementation of the present application, determining the sizes of the microring waveguide and the racetrack waveguide in each area to be tested, and the spacing between the microring waveguide and the racetrack waveguide, includes:

[0018] The length of the microring waveguide in each column of the test area is set to be gradual;

[0019] The spacing between the microring waveguide and the racetrack waveguide in each row of the test area is set to be gradual.

[0020] In an implementable manner of the present application, testing the sample to be tested by a coupled optical path to obtain the quality factor of the microring waveguide and the racetrack waveguide in each area to be tested includes:

[0021] coupling light into one end of the racetrack waveguide and coupling light out from the other end of the racetrack waveguide through a coupling optical path;

[0022] Obtaining transmission spectra of different test areas of the test sample by tunable laser scanning;

[0023] reading the half-value width, the resonance wavelength and the resonance peak transmittance of the resonance peak from the transmission spectrum;

[0024] The quality factor of the racetrack waveguide in each test area is obtained according to the following formula:

[0025]

[0026] The quality factor of the microring waveguide in each test area is obtained according to the following formula:

[0027]

[0028] Among them, Q l is the quality factor of the racetrack waveguide, Q i is the quality factor of the microring waveguide, λ is the resonant wavelength, Δλ BW is the half-maximum width of the resonance peak, and T0 is the transmittance of the resonance peak.

[0029] In an implementable manner of the present application, obtaining the quality factor of the microring waveguide in each area to be measured according to the following formula includes:

[0030] When there is overcoupling between the microring waveguide and the racetrack waveguide in the test area, the quality factor of the microring waveguide is obtained according to the following formula:

[0031]

[0032] When the microring waveguide and the racetrack waveguide are undercoupled in the test area, the quality factor of the microring waveguide is obtained according to the following formula:

[0033]

[0034] Among them, Q l is the quality factor of the racetrack waveguide, Q i is the quality factor of the microring waveguide, and T0 is the resonant peak transmittance.

[0035] In an implementable manner of the present application, the overcoupling and the undercoupling are determined according to the following steps:

[0036] In the test areas in the same column, as the length of the microring waveguide gradually increases, if the resonance peak transmittance of each test area gradually decreases, then the microring waveguide and the racetrack waveguide in the test area are overcoupled; if the resonance peak transmittance gradually increases, then the microring waveguide and the racetrack waveguide in the test area are undercoupled;

[0037] In the test areas in the same row, as the spacing between the microring waveguide and the racetrack waveguide gradually increases, if the resonance peak transmittance of each test area gradually decreases, the microring waveguide and the racetrack waveguide in the test area are undercoupled; if the resonance peak transmittance gradually increases, the microring waveguide and the racetrack waveguide in the test area are overcoupled.

[0038] In an implementable manner of the present application, fitting the microring waveguide losses of different areas to be tested according to the quality factors of the microring waveguide and the racetrack waveguide in each area to be tested includes:

[0039] Obtaining a free spectrum width (FSR) according to the transmission spectrum;

[0040] According to the quality factor, the microring waveguide loss in different test areas is calculated by fitting the following formula:

[0041]

[0042] Among them, Q i is the quality factor of the microring waveguide, n g is the effective refractive index, FSR is the free spectrum width, L is the length of the microring waveguide, α is the microring waveguide loss, and λ is the resonant wavelength.

[0043] In an implementable manner of the present application, calibrating the test result of the thin film lithium niobate waveguide etching process to be tested according to the microring waveguide loss of the different test areas includes:

[0044] Obtaining an average value and a standard deviation of the microring waveguide loss according to the microring waveguide losses of the plurality of areas to be measured;

[0045] The detection result of the thin film lithium niobate waveguide etching process to be tested is calibrated according to the average value and the standard deviation.

[0046] As can be seen from the above technical solution, the present application provides a method for detecting a thin-film lithium niobate waveguide etching process, the detection method comprising: preparing a sample to be tested according to a preset waveguide structure mask pattern through a thin-film lithium niobate waveguide etching process to be tested; the preset waveguide structure mask pattern includes multiple test areas, each of which is provided with a microring waveguide and a racetrack waveguide; testing the sample to be tested through a coupled optical path to obtain the quality factor of the waveguides in different test areas; fitting the microring waveguide losses in different test areas according to the quality factor; and calibrating the detection results of the thin-film lithium niobate waveguide etching process to be tested according to the microring waveguide losses. In this way, the microring waveguide losses in different test areas are fitted by the quality factors of the waveguides in different test areas, and then, based on the average value and standard deviation of the microring waveguide losses, it is possible to detect whether the thin-film lithium niobate waveguide etching process to be tested is stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings required for use in the embodiments. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0048] Figure 1 A schematic diagram of the micro-ring waveguide loss detection principle of a thin-film lithium niobate waveguide etching process detection method provided in this application;

[0049] Figure 2 This is a flow chart of a method for detecting a thin-film lithium niobate waveguide etching process provided by this application;

[0050] Figure 3 A schematic diagram of the sample preparation process for a thin-film lithium niobate waveguide etching process detection method provided in this application;

[0051] Figure 4 A schematic diagram of a waveguide structure mask layout for a detection method of a thin-film lithium niobate waveguide etching process provided in this application;

[0052] Figure 5 A schematic diagram of a transmission spectrum of a detection method for a thin-film lithium niobate waveguide etching process provided in this application;

[0053] Figure 6 A schematic diagram of the fitted resonance peaks of a detection method for a thin-film lithium niobate waveguide etching process provided in this application;

[0054] Figure 7 These are the test results of a method for detecting a thin-film lithium niobate waveguide etching process provided in this application. DETAILED DESCRIPTION

[0055] In order to make the objectives, technical solutions and advantages of this application clearer, the implementation methods of this application will be further described in detail below with reference to the accompanying drawings.

[0056] The terms used in the following embodiments are only for the purpose of describing specific embodiments and are not intended to be limiting of the present application. As used in the specification and appended claims of this application, the singular expressions "a", "an", "said", "above", "the" and "this" are intended to also include expressions such as "one or more", unless there is a clear contrary indication in the context. It should also be understood that in the following embodiments of the present application, "at least one", "one or more" refer to one, two or more, and "a plurality" refers to two or more. The term "and / or" is used to describe the association relationship of associated objects, indicating that three relationships can exist; for example, A and / or B can represent: the existence of A alone, the existence of A and B at the same time, and the existence of B alone, where A and B can be singular or plural. The character " / " generally indicates that the related objects before and after are in an "or" relationship.

[0057] References to "one embodiment" or "some embodiments" in this specification mean that a particular feature, structure, or characteristic described in conjunction with that embodiment is included in one or more embodiments of the present application. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in yet other embodiments" appearing in various places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more but not all embodiments," unless otherwise specifically emphasized. The terms "including," "comprising," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0058] The following first introduces the micro-ring waveguide loss detection principle used in the embodiments of the present application.

[0059] See also Figure 1 , which is a schematic diagram of the micro-ring waveguide loss detection principle of a detection method for a thin-film lithium niobate waveguide etching process provided by this application;

[0060] Depend on Figure 1 It can be seen that the waveguides made by the etching process tested in this application include microring waveguides and racetrack waveguides. During use, light enters from the input port at the left end of the racetrack waveguide and is output from the output port at the right end along the arrow. At the same time, when light propagates in the racetrack waveguide, light of the resonant wavelength will couple into the microring waveguide above, causing loss. Specifically, Figure 1 In, S i is the light intensity in the racetrack waveguide before coupling between the microring and the straight waveguide; S t$I$ is the optical intensity in the racetrack waveguide after coupling between the microring and the straight waveguide; $\kappa$ is the transmission coefficient, that is, the percentage of the optical intensity that is not coupled from the racetrack waveguide to the microring waveguide; $\tau$ is the coupling coefficient, that is, the percentage of the optical intensity that is coupled from the racetrack waveguide to the microring waveguide; $A$ is the optical intensity coupled into the microring waveguide; $B$ is the optical intensity after coupling into the microring waveguide and traveling around the microring waveguide once; $R$ is the radius of the microring waveguide.

[0061] In the above process, the transfer function of light is shown in Equation (1):

[0062]

[0063] where, $\varphi$ rt is the phase; $H$ ap ($\varphi$ rt ) is the light traveling from left to right in the racetrack waveguide; $j$ is the imaginary part.

[0064] The spectrum is shown in Equations (2) to (4):

[0065]

[0066] where, $T$ ap ($\varphi$ rt ) is the transmitted optical intensity, that is, the optical intensity coupled out from the racetrack waveguide; $\alpha$ is the loss of the microring waveguide; $F$ has no special meaning; $T$ ap,min is the transmitted optical intensity corresponding to the resonant wavelength.

[0067] When light propagates in the racetrack waveguide, the light at the resonant wavelength will be coupled into the upper microring waveguide. At this time, the light transmitted from the left end to the right end in the racetrack waveguide is $\kappa$, and the light coupled into the upper microring waveguide is $\tau$. The light at the resonant wavelength is coupled into the microring waveguide and travels counterclockwise. The inherent loss of the microring waveguide is $a$.

[0068] Therefore, in the case of the existence of loss $a$, there is an absorption valley (transmission dip) at the resonant wavelength. The relationship between $\tau$ and $a$ is divided into three cases:

[0069] When $\tau = a$, at this time $T$ ap,min $= 0$, and the output signal at the resonant wavelength completely disappears. At this time, it is the critical coupling state.

[0070] When $\tau > a$, that is, the distance between the waveguide and the microring is too small, and the coupling loss is greater than the loss of light traveling around the microring once. At this time, it is the over-coupling state;

[0071] When $\tau < a$, that is, the distance between the waveguide and the microring is too large, and the coupling loss is less than the loss of light traveling around the microring once. At this time, it is the under-coupling state.

[0072] In the embodiment of the present application, the microring waveguide itself has a certain loss, and the longer the length L of the microring waveguide, the greater the microring waveguide loss, and there is a proportional relationship between L and the loss; the spacing between the microring waveguide and the racetrack waveguide is the coupling spacing, and the larger the coupling spacing, the greater the coupling loss generated when the light in the racetrack waveguide is coupled into the microring waveguide, and the two are also in a proportional relationship;

[0073] Therefore, this application uses critical coupling τ=α and a racetrack waveguide of fixed size as reference during detection (the critical coupling here is an ideal case, and critical coupling is actually impossible), and the coupling spacing and microring waveguide length are variables. In order to make τ=a hold, a coupling spacing of any size will correspond to a microring waveguide length. When the microring waveguide length is adjusted up and down, overcoupling and undercoupling are formed accordingly. In this way, different microring losses can be detected. By adjusting the coupling spacing of multiple groups of test areas at the same time, more groups of test results can be obtained. In theory, if the etching process is very stable, the microring waveguide losses in the same row are basically the same, and as the microring length in the same column increases, the measured microring waveguide losses also gradually increase. In the actual detection process, the more areas to be tested, the more accurate the results.

[0074] The embodiment of the present application discloses a method for detecting a thin-film lithium niobate waveguide etching process. The method for detecting a thin-film lithium niobate waveguide etching process disclosed in the embodiment of the present application is described in detail below with reference to the accompanying drawings.

[0075] See also Figure 2 , which is a flow chart of a detection method for a thin-film lithium niobate waveguide etching process provided by this application;

[0076] Depend on Figure 2 It can be seen that the embodiment of the present application provides a detection method for a thin-film lithium niobate waveguide etching process, which includes:

[0077] Step 101, presetting a waveguide structure mask pattern;

[0078] In the embodiment of the present application, the quality of the sample to be tested is tested to evaluate the thin film lithium niobate waveguide etching process. Therefore, a preset waveguide structure mask pattern needs to be designed first, and multiple test areas are arrayed on the sample to be tested.

[0079] It should be noted that the multiple test areas can be arranged in a regular array on the test sample, or in an irregular array on the test sample. The regular arrangement method is more convenient for the implementation of subsequent steps.

[0080] In an embodiment of the present application, the preset waveguide structure mask layout is determined according to the following steps:

[0081] Step 1011, determining the size of the microring waveguide and the racetrack waveguide in each area to be tested, and the spacing between the microring waveguide and the racetrack waveguide;

[0082] Step 1012, presetting the number of rows and columns of the rectangular array of the plurality of test areas according to the size of the process sample;

[0083] Step 1013 : making a mask layout of the waveguide structure according to the dimensions of the microring waveguide and the racetrack waveguide, and the number of rows and columns of the rectangular array.

[0084] It should be noted that, in the embodiment of the present application, the length of the microring waveguide in each column of the test area is set to be gradual; the spacing between the microring waveguide and the racetrack waveguide in each row of the test area is set to be gradual.

[0085] Step 102 , preparing a sample to be tested by etching a thin-film lithium niobate waveguide according to the waveguide structure mask pattern; the sample to be tested includes a plurality of test areas, each of which is provided with a microring waveguide and a racetrack waveguide.

[0086] See also Figure 3 , which is a schematic diagram of the sample preparation process for a detection method of a thin film lithium niobate waveguide etching process provided in this application.

[0087] Depend on Figure 3 It can be seen that this application uses a thin film lithium niobate waveguide etching process to prepare the sample to be tested:

[0088] In the embodiment of the present application, the process of etching a thin film lithium niobate waveguide to be tested according to a preset waveguide structure mask pattern to prepare a sample to be tested includes:

[0089] Step 1014, performing a smear process on a pre-prepared process sample, and using an electron beam lithography system to photolithographically form a photoresist mask structure having a plurality of test area shapes on the process sample after smearing according to the preset waveguide structure mask pattern; Figure 3 As shown, the upper left is a schematic top view of the area to be tested of the process sample after photolithography, and the upper right is a schematic side view of the area to be tested of the process sample after photolithography;

[0090] Step 1015: using an inductively coupled plasma etching system to etch a waveguide structure on the process sample, that is, forming a plurality of test areas;

[0091] Step 1016: clean the photoresist and etching residues on the waveguide structure to obtain the sample to be tested. Figure 3As shown, the lower left is a schematic top view of the area to be tested of the process sample after cleaning, and the lower right is a schematic side view of the area to be tested of the process sample after cleaning.

[0092] In the embodiments of the present application, the greater the number of microring waveguides and racetrack waveguides, the greater the number of test areas, and the more accurate the final test results. Therefore, the number of microring waveguides and racetrack waveguides can be appropriately set based on actual test capabilities and test requirements to achieve optimal test results with optimal efficiency.

[0093] Step 103, testing the sample to be tested by a coupled optical path to obtain the quality factors of the microring waveguide and the racetrack waveguide in each area to be tested;

[0094] In the embodiment of the present application, step 103 includes:

[0095] Step 301, coupling light into one end of the racetrack waveguide and coupling light out from the other end of the racetrack waveguide through a coupling optical path;

[0096] Step 302, obtaining transmission spectra of different test areas of the sample by scanning with a tunable laser;

[0097] Step 303, reading the half-value width, resonance wavelength and resonance peak transmittance of the resonance peak from the transmission spectrum;

[0098] Step 304: Obtain the quality factor of the racetrack waveguide in each test area according to the following formula:

[0099]

[0100] Step 305: Obtain the quality factor of the microring waveguide in each test area according to the following formula:

[0101]

[0102] Among them, Q l is the quality factor of the racetrack waveguide, Q i is the quality factor of the microring waveguide, λ is the resonant wavelength, Δλ BW is the half-maximum width of the resonance peak, and T0 is the transmittance of the resonance peak.

[0103] It should be noted that step 305 includes:

[0104] Step 3051: When the microring waveguide and the racetrack waveguide are overcoupled in the test area, the quality factor of the microring waveguide is obtained according to the following formula:

[0105]

[0106] Step 3052: When the microring waveguide and the racetrack waveguide in the test area are undercoupled, the quality factor of the microring waveguide is obtained according to the following formula:

[0107]

[0108] Among them, Q l is the quality factor of the racetrack waveguide, Q i is the quality factor of the microring waveguide, and T0 is the resonant peak transmittance.

[0109] In the embodiment of the present application, the overcoupling and the undercoupling are determined according to the following steps:

[0110] In the test areas in the same column, as the length of the microring waveguide gradually increases, if the resonance peak transmittance of each test area gradually decreases, then the microring waveguide and the racetrack waveguide in the test area are overcoupled; if the resonance peak transmittance gradually increases, then the microring waveguide and the racetrack waveguide in the test area are undercoupled;

[0111] In the test areas in the same row, as the spacing between the microring waveguide and the racetrack waveguide gradually increases, if the resonance peak transmittance of each test area gradually decreases, the microring waveguide and the racetrack waveguide in the test area are undercoupled; if the resonance peak transmittance gradually increases, the microring waveguide and the racetrack waveguide in the test area are overcoupled.

[0112] Step 104 : fitting the microring waveguide losses of different test areas according to the quality factors of the microring waveguide and the racetrack waveguide in each test area.

[0113] In the embodiment of the present application, step 104 includes:

[0114] Step 401, obtaining a free spectrum width FSR according to the transmission spectrum;

[0115] In the embodiment of the present application, FSR is the free spectrum width, which is defined as the distance between the resonant wavelength (λ) or frequency (ν) between two adjacent resonant peaks.

[0116] Step 402: Based on the quality factor, the microring waveguide loss of different test areas is calculated by fitting the following formula:

[0117]

[0118] Among them, Q i is the microring quality factor, n gis the effective refractive index, FSR is the free spectrum width, L is the microring length, T0 is the resonant peak transmittance, α is the microring waveguide loss, and λ is the resonant wavelength.

[0119] Step 105 , calibrating the test result of the thin film lithium niobate waveguide etching process to be tested according to the microring waveguide losses in the different test areas.

[0120] In the embodiment of the present application, step 105 includes:

[0121] Step 501, obtaining an average value and a standard deviation of the microring waveguide loss according to the microring waveguide losses of the plurality of areas to be measured;

[0122] Step 502: Calibrate the test result of the thin film lithium niobate waveguide etching process to be tested according to the average value and the standard deviation.

[0123] The following describes a thin film lithium niobate waveguide etching process provided by an embodiment of the present application through specific examples.

[0124] See also Figure 4 , which is a schematic diagram of a preset waveguide structure mask layout for a detection method of a thin-film lithium niobate waveguide etching process provided in this application.

[0125] Depend on Figure 4 It can be seen that the preset waveguide structure mask layout is determined according to steps 1011 to 1013:

[0126] The preset process sample size is 2cm*2cm, the lithium niobate film thickness is 600nm and the etching depth is 300nm.

[0127] The number of rows and columns of the area to be tested is preset to 7, wherein: Figure 4 From bottom to top, they are the 1st row to the 7th row, and from left to right, they are the 1st column to the 4th column.

[0128] The preset widths of the microring waveguide and the racetrack waveguide are both 1.4 μm.

[0129] The radius of the curved waveguide to be measured area of ​​the microring waveguide is preset to be 80 μm, and the lengths of the straight waveguides from the first row to the seventh row are 0 μm, 200 μm, 400 μm, 600 μm, 800 μm, 1000 μm and 1200 μm respectively;

[0130] The spacing between the microring waveguide and the racetrack waveguide is preset to be gradual, and from the first column to the fourth column, the spacing is 700 nm, 600 nm, 500 nm and 400 nm respectively.

[0131] In addition, the coupling mode between the racetrack waveguide and the microring waveguide is grating coupling, and the grating period is 870nm.

[0132] After completing the above steps, the sample to be tested is prepared according to the above dimensions and steps 1014 to 1016 .

[0133] See also Figure 5 , which is a transmission spectrum diagram of a detection method for a thin film lithium niobate waveguide etching process provided in this application.

[0134] Depend on Figure 5 It can be seen that the micro-ring or racetrack structure of each test area in the test sample is tested by tunable laser, using grating vertical coupling and vertical decoupling, and recording the transmission spectrum data, wherein the scanning wavelength is 1480nm-1540nm. Finally, the following is obtained: Figure 5 The transmission spectrum shown is then used to read the resonance wavelength λ and the half-peak width Δλ from the transmission spectrum. BW .

[0135] See also Figure 6 , is a schematic diagram of the fitted resonance peak of a detection method for a thin-film lithium niobate waveguide etching process provided by the present application;

[0136] By analyzing the data in the transmission spectrum, the distance between the two absorption peaks, i.e., the free spectrum width FSR, can be directly read; and the resonance peak transmittance T0 and the resonance wavelength λ can be obtained by testing the lowest point reading of the resonance peak, and the half-peak width Δλ can be obtained by fitting the resonance peak. BW The fitting results are as follows Figure 6 shown.

[0137] according to Figure 4 and Figure 6 , the method to determine undercoupling and overcoupling is:

[0138] For the same column of test areas, as the length of the straight waveguide in the microring waveguide increases, the transmittance T0 gradually decreases to indicate overcoupling, and the transmittance T0 gradually increases to indicate undercoupling;

[0139] For the same row of test areas, as the distance between the racetrack waveguide and the microring waveguide increases, the transmittance T0 gradually decreases to indicate undercoupling, and the transmittance T0 gradually increases to indicate overcoupling.

[0140] See also Figure 7 , which is the test result of a detection method for a thin film lithium niobate waveguide etching process provided in this application.

[0141] In the present application, the test results are as follows: Figure 7As shown, the bold ones are the areas to be tested with abnormal loss. The fewer the areas to be tested with abnormal loss, the more uniform the quality of the sample to be tested, that is, the better the etching process of the thin film lithium niobate waveguide to be tested. The process stability is further calibrated by calculating the average value and standard deviation.

[0142] It can be seen from the above technical solution that the present application provides a method for detecting a thin-film lithium niobate waveguide etching process, the detection method comprising: preparing a sample to be tested according to a preset waveguide structure mask pattern through a thin-film lithium niobate waveguide etching process to be tested; the preset waveguide structure mask pattern includes a plurality of areas to be tested, each area to be tested is provided with a microring waveguide and a racetrack waveguide; the sample to be tested is tested by a coupled optical path to obtain the quality factor of the waveguide in different areas to be tested; wherein, each area to be tested corresponds to a test area; the microring waveguide loss of different areas to be tested is fitted according to the quality factor; and the detection result of the thin-film lithium niobate waveguide etching process to be tested is calibrated according to the microring waveguide loss. In this way, the quality factor of the waveguide in different areas to be tested is used to fit the microring waveguide loss in different areas to be tested, and then the quality and stability of the thin-film lithium niobate waveguide etching process to be tested are calibrated based on the microring waveguide loss. The defects inside the entire wafer and lithium niobate can be detected on a large scale, thereby measuring the quality and uniformity of the thin-film lithium niobate waveguide etching process to be tested.

[0143] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein; the specification and examples are to be regarded as exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0144] It will be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings, and that various modifications and changes may be made without departing from the scope thereof; the scope of the present invention being limited only by the appended claims.

Claims

1. A method for detecting a thin film lithium niobate waveguide etching process, characterized in that: The detection method comprises: Preset waveguide structure mask layout; According to the waveguide structure mask, a process sample is processed by a thin film lithium niobate waveguide etching process to prepare a sample to be tested; the sample to be tested includes a plurality of test areas, each of which is provided with a microring waveguide and a racetrack waveguide; Testing the sample to be tested by a coupled optical path to obtain the quality factors of the microring waveguide and the racetrack waveguide in each area to be tested; The step of testing the sample to be tested by using a coupled optical path to obtain the quality factors of the microring waveguide and the racetrack waveguide in each area to be tested includes: coupling light into one end of the racetrack waveguide and coupling light out from the other end of the racetrack waveguide through a coupling optical path; Obtaining transmission spectra of different test areas of the test sample by tunable laser scanning; reading the half-value width, the resonance wavelength and the resonance peak transmittance of the resonance peak from the transmission spectrum; The quality factor of the racetrack waveguide in each test area is obtained according to the following formula: The quality factor of the microring waveguide in each test area is obtained according to the following formula: Among them, Q l is the quality factor of the racetrack waveguide, Q i is the quality factor of the microring waveguide, λ is the resonant wavelength, Δλ BW is the half-maximum width of the resonance peak, and T0 is the transmittance of the resonance peak; fitting the microring waveguide losses of different test areas according to the quality factors of the microring waveguide and the racetrack waveguide in each test area; The detection result of the etching process of the thin film lithium niobate waveguide to be tested is calibrated according to the microring waveguide loss of the different areas to be tested.

2. The method for detecting a thin film lithium niobate waveguide etching process according to claim 1, characterized in that: A plurality of test area arrays are arranged on the test sample.

3. The method for detecting a thin film lithium niobate waveguide etching process according to claim 2, characterized in that: Follow the steps below to preset the waveguide structure mask layout: Determining the dimensions of the microring waveguide and the racetrack waveguide in each area to be tested, and the spacing between the microring waveguide and the racetrack waveguide; According to the size of the process sample, the number of rows and columns of the rectangular array of the plurality of test areas is preset; The waveguide structure mask layout is made according to the sizes of the microring waveguide and the racetrack waveguide, and the number of rows and columns of the rectangular array.

4. The method for detecting a thin film lithium niobate waveguide etching process according to claim 3, wherein: The determining of the sizes of the microring waveguide and the racetrack waveguide in each area to be tested, and the spacing between the microring waveguide and the racetrack waveguide, comprises: The length of the microring waveguide in each column of the test area is set to be gradual; The spacing between the microring waveguide and the racetrack waveguide in each row of the test area is set to be gradual.

5. The method for detecting a thin film lithium niobate waveguide etching process according to claim 1, characterized in that: Obtaining the quality factor of the microring waveguide in each area to be measured according to the following formula includes: When there is overcoupling between the microring waveguide and the racetrack waveguide in the test area, the quality factor of the microring waveguide is obtained according to the following formula: When the microring waveguide and the racetrack waveguide are undercoupled in the test area, the quality factor of the microring waveguide is obtained according to the following formula: Among them, Q l is the quality factor of the racetrack waveguide, Q i is the quality factor of the microring waveguide, and T0 is the resonant peak transmittance.

6. The method for detecting a thin film lithium niobate waveguide etching process according to claim 5, characterized in that: The overcoupling and the undercoupling are determined according to the following steps: In the test areas in the same column, as the length of the microring waveguide gradually increases, if the resonance peak transmittance of each test area gradually decreases, then the microring waveguide and the racetrack waveguide in the test area are overcoupled; if the resonance peak transmittance gradually increases, then the microring waveguide and the racetrack waveguide in the test area are undercoupled; In the test areas in the same row, as the spacing between the microring waveguide and the racetrack waveguide gradually increases, if the resonance peak transmittance of each test area gradually decreases, the microring waveguide and the racetrack waveguide in the test area are undercoupled; if the resonance peak transmittance gradually increases, the microring waveguide and the racetrack waveguide in the test area are overcoupled.

7. The method for detecting a thin film lithium niobate waveguide etching process according to claim 5, characterized in that: The fitting of the microring waveguide losses of different test areas according to the quality factors of the microring waveguide and the racetrack waveguide in each test area includes: Obtaining a free spectrum width (FSR) according to the transmission spectrum; According to the quality factor, the microring waveguide loss in different test areas is calculated by fitting the following formula: Among them, Q i is the quality factor of the microring waveguide, n g is the effective refractive index, FSR is the free spectrum width, L is the length of the microring waveguide, α is the microring waveguide loss, and λ is the resonant wavelength.

8. The method for detecting a thin film lithium niobate waveguide etching process according to claim 1, characterized in that: The step of calibrating the test result of the thin film lithium niobate waveguide etching process to be tested according to the microring waveguide loss in the different test areas includes: Obtaining an average value and a standard deviation of the microring waveguide loss according to the microring waveguide losses of the plurality of areas to be measured; The detection result of the thin film lithium niobate waveguide etching process to be tested is calibrated according to the average value and the standard deviation.

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