Test apparatus, method, and test array for edge-type couplers

Abstract

The present invention provides a test apparatus, method, and test array for edge-type couplers. The test apparatus for edge-type couplers, which is placed on an optical chip, includes a loopback structure for coupling with an external optical fiber array, a cascaded test structure for testing mode-field conversion losses of TE-polarized and TM-polarized light within the chip, a polarization separation module connected to the cascaded test structure for introducing TE-polarized and TM-polarized light into the cascaded test structure and deriving it after testing, a TE diffraction grating coupling module connected to the input and output terminals of the polarization separation module for introducing and deriving TE-polarized light into the cascaded test structure, and a TM diffraction grating coupling module connected to the input and output terminals of the polarization separation module for introducing and deriving TM-polarized light into the cascaded test structure. The present invention allows for testing the coupling losses of TE-polarized and TM-polarized light, saving space within the chip and improving chip utilization efficiency.

Description

Technical Field

[0001] <Cross - reference to Related Applications> This application claims the priority of a Chinese patent application with application number 2023106103903, filed on May 26, 2023. The content of the above application is incorporated herein by reference.

[0002] The present invention relates to the field of optical technology, and particularly to a test apparatus, method, and test array for an edge coupler.

Background Art

[0003] An edge coupler (EC) is used to couple light to or output light from a photonic integrated circuit (PIC), and has the advantages of low coupling loss, a wide operating wavelength range, and the ability to simultaneously carry light in two polarization states, TE and TM. The EC is often coupled to an external optical fiber (or an optical fiber array). To obtain a better coupling effect, the mode field of the EC end face needs to match the mode field of the optical fiber. In a photonic chip, since the mode field size of a conventional waveguide is small while that of an optical fiber is large, it is necessary to provide a transition region (e.g., a wedge - shaped structure) inside the chip to convert the mode field size from small to large. Therefore, the coupling loss of the EC includes two parts: the mode field conversion loss in the transition region from the conventional waveguide (small mode field) to the EC end face (large mode field), and the light field overlap loss between the mode field of the EC end face and the mode field of the external optical fiber (i.e., the loss when the two mode fields do not ideally match).

[0004] In recent years, the use of fiber arrays (FAs) has been increasing in research and development, manufacturing testing, and mass production of products. In the manufacturing testing or R&D phase, it is necessary to construct several test structures of edge-type couplers on an optical chip to verify performance indicators such as coupling loss of the coupler. A common approach is to provide a loopback structure at the edge of the chip, including two ECs and a curved waveguide connecting them, as shown in Figure 1. The distance between the two ECs is set to be equal to the channel spacing of the FA (e.g., 250 μm), so that the chip can be connected to the FA, and the coupling loss of the ECs is tested by inputting light into or outputting light from the chip using the two channels of the FA (as shown in the direction of the arrows in Figure 1). Since the ECs can support both TE and TM polarization, it is necessary to test the coupling loss of the ECs with TE and TM polarization accordingly (represented by solid and dotted lines, respectively).

[0005] However, the coupling loss measured by this method includes the on-chip mode-field conversion loss and the light-field overlap loss with the optical fiber, i.e., the overall coupling loss of the EC. Since it is not possible to determine the individual values ​​of the on-chip mode-field conversion loss and the light-field overlap loss with the optical fiber, it is impossible to specifically analyze the cause of each part of the loss and provide sufficient and comprehensive feedback for design improvement and iteration. If the two are measured separately, additional test structures such as cascaded ECs and grating couplers (GCs) are required to measure the on-chip mode-field conversion loss, which requires more chip space. In general, it is not possible to support both TE polarization and TM polarization simultaneously with the same GC, so a test structure must be created for each polarization to test the mode-field conversion loss for TE polarization and TM polarization, respectively. Thus, since multiple test structures must be set up to complete the above functions, this approach occupies chip space, reduces test efficiency, and increases costs.

[0006] Therefore, in order to solve the problems described above in the prior art, it is necessary to provide a novel test apparatus, method, and test array for edge-type couplers. [Overview of the project]

[0007] The object of the present invention is to provide a test apparatus, method, and test array for edge-type couplers that can not only simultaneously test the coupling loss of TE polarization and TM polarization, but also measure on-chip mode-field conversion loss and light-field overlap loss, respectively, thereby saving space within the chip, improving chip utilization efficiency, and reducing costs.

[0008] To achieve the above objective, the test apparatus for edge-type couplers of the present invention is provided on an optical chip, The optical chip is provided with a loopback structure for coupling with an external optical fiber array, A cascade test structure is provided on the optical chip for testing the mode-field conversion loss within the chip for TE polarization and TM polarization. A polarization separation module connected to the cascade test structure for introducing TE polarization and TM polarization into the cascade test structure and deriving them after testing, A TE diffraction grating coupling module is connected to the input and output terminals of the polarization separation module to introduce and derive TE polarization into the cascade test structure, A TM diffraction grating coupling module is connected to the input and output terminals of the polarization separation module to introduce and derive TM polarization into the cascade test structure, The system includes a calibration module for acquiring calibration data for the TE polarization and the TM polarization.

[0009] The advantageous effects of the edge-type coupler testing apparatus described in the present invention are as follows: By setting up a polarization separation module, a TE diffraction grating coupling module, and a TM diffraction grating coupling module, TE polarization and TM polarization can be transported to a cascade test structure, respectively, for coupling testing. After passing through the polarization separation module, the TE polarization and TM polarization can be extracted, respectively, and the mode-field conversion loss of TE polarization and TM polarization within the chip can be tested in the same cascade test structure, saving space within the chip and contributing to improved testing efficiency.

[0010] Selectively, the cascade test structure includes a first curved waveguide and a group of edge-type couplers, the group of edge-type couplers includes a first edge-type coupler, a second edge-type coupler, a third edge-type coupler, and a fourth edge-type coupler, one end of the first edge-type coupler is connected to one end of the third edge-type coupler, the other end of the first edge-type coupler is connected to one end of the second edge-type coupler via the first curved waveguide, the other end of the second edge-type coupler is connected to one end of the fourth edge-type coupler, and both the other end of the third edge-type coupler and the other end of the fourth edge-type coupler are connected to the polarization separation module.

[0011] Selectively, the polarization separation module includes a first polarization splitter and a second polarization splitter, the input terminal of the first polarization splitter includes a first TE input terminal and a first TM input terminal, the output terminal of the first polarization splitter is electrically connected to the cascade test structure, the input terminal of the second polarization splitter is electrically connected to the output terminal of the cascade test structure, the output terminal of the second polarization splitter includes a first TE output terminal and a first TM output terminal, and the TE diffraction grating coupling module includes a first TE diffraction grating coupler and a second TE diffraction grating coupler. The TM diffraction grating coupling module includes a grating coupler, wherein the TM diffraction grating coupling module includes a first TM diffraction grating coupler and a second TM diffraction grating coupler, the TE polarization being input to the first TE input terminal by the first TE diffraction grating coupler, then introduced into the cascade test structure and led out to the second TE diffraction grating coupler by the first TE output terminal, and the TM polarization being input to the first TM input terminal by the first TM diffraction grating coupler, then introduced into the cascade test structure and led out to the second TM diffraction grating coupler by the first TM output terminal.

[0012] Selectively, the calibration structure includes a third polarization splitter, a fourth polarization splitter, a third TE diffraction grating coupler, a fourth TE diffraction grating coupler, a third TM diffraction grating coupler, and a fourth TM diffraction grating coupler, wherein the output terminal of the third polarization splitter is connected to the input terminal of the fourth polarization splitter via a second curved waveguide, the input terminal of the third polarization splitter includes a second TE input terminal and a second TM input terminal, and the output terminal of the fourth polarization splitter includes a second TE output terminal and a second TM output terminal, the TE polarization being introduced to the second TE input terminal by the third TE diffraction grating coupler and then sequentially passing through the third polarization splitter and the fourth polarization splitter to the fourth TE diffraction grating coupler by the second TE output terminal, and the TM polarization being introduced to the second TM input terminal by the third TM diffraction grating coupler and then sequentially passing through the third polarization splitter and the fourth polarization splitter to the fourth TM diffraction grating coupler by the second TM output terminal. The beneficial effects are as follows: By setting up a calibration structure, the losses of the GC, PS, and curved waveguide are de-embedded under both TE polarization and TM polarization conditions to extract the coupling loss of each edge coupler, and the light field overlap loss of each edge coupler is obtained according to the calculated in-chip mode field conversion loss, thereby accurately obtaining the respective values ​​of both the light field overlap loss and the in-chip mode field conversion loss, improving test efficiency, saving space in the chip, and reducing costs.

[0013] Selectively, the loopback structure includes a fifth edge coupler and a sixth edge coupler, the fifth and sixth edge couplers connected by a third curved waveguide, the optical chip is provided with a cutting lane, one end of the fifth and sixth edge couplers closer to the TE diffraction grating coupling module is located in the cutting lane, the connection point between the first and third edge couplers and the connection point between the second and fourth edge couplers are both located in the cutting lane, and the loopbacks formed between the loopback structure and the first edge coupler, the first curved waveguide, and the second edge coupler are nested. The beneficial effect is that space is saved and costs are reduced because the loopbacks formed between the loopback structure and the first edge coupler, the first curved waveguide, and the second edge coupler are nested.

[0014] Selectively, the first edge-type coupler, the second edge-type coupler, the fifth edge-type coupler, and the sixth edge-type coupler all form an angle A with the straight line on which the cutting lane is located, where 0° <A<180°である。

[0015] A first connection region is provided between the first edge-type coupler and the third edge-type coupler, a second connection region is provided between the second edge-type coupler and the fourth edge-type coupler, and the cutting lanes are provided in the first and second connection regions.

[0016] A third connection region is provided at one end of the fifth edge-type coupler closer to the cutting lane, and a fourth connection region is provided at one end of the sixth edge-type coupler closer to the cutting lane.

[0017] Selectively, either the third connection region or the fourth connection region is provided with a gap between it and the cutting lane.

[0018] Optionally, all of the first connection region, the second connection region, the third connection region, and the fourth connection region are provided in the cutting lane.

[0019] Optionally, a first etching region and a second etching region are provided in the cutting lane.

[0020] Optionally, the first etching region at least partially overlaps with the third connection region, and the second etching region at least partially overlaps with the fourth connection region.

[0021] Optionally, a gap is provided between the first etching region and the fifth edge coupler, and a gap is provided between the second etching region and the sixth edge coupler.

[0022] Optionally, the loopback structure is provided inside the cascade test structure.

[0023] Optionally, the ends of the fifth edge coupler and the ends of the sixth edge coupler are provided on different end faces of the chip.

[0024] Optionally, the number of the edge coupler groups is at least two, and the ends of the adjacent edge coupler groups are connected to each other.

[0025] Optionally, all of the first polarization splitter, the second polarization splitter, the third polarization splitter, and the fourth polarization splitter are replaced with polarization separation rotors, and all of the first TM diffraction grating coupler, the second TM diffraction grating coupler, the third TM diffraction grating coupler, and the fourth TM diffraction grating coupler are replaced with TE diffraction grating couplers.

[0026] The present invention further provides a test method for an edge coupler applicable to the above test apparatus for an edge coupler, and the test method for an edge coupler is as follows: Before chip cutting, according to the type of the initial polarization with power P0, input the initial polarization into the TE diffraction grating coupling module or the TM diffraction grating coupling module, and after testing by the cascade test structure, obtain the first polarization with power P1; input the initial polarization into the calibration structure to obtain the calibrated polarization with power P2; calculating the conversion loss of the on-chip mode field of each edge coupler in the cascade test structure based on the power P1 of the first polarization and the power P2 of the calibrated polarization.

[0027] The advantageous effects of the test method for the edge coupler of the present invention are as follows. Carry the TE polarization or TM polarization to the cascade test structure through the TE or TM grating coupling module for testing, output the corresponding first polarization, and after calibration by the subsequent calibration structure, obtain the calibrated polarization. Then, calculate the conversion loss of the on-chip mode field of each edge coupler based on the power of the first polarization and the calibrated polarization.

[0028] Optionally, the method after cutting the chip along the cutting lane, input the initial polarization into the loopback structure by the fifth edge coupler and output the third polarization with power P3 from the sixth edge coupler; calculating the coupling loss of each edge coupler in the loopback structure based on the power of the initial polarization and the power of the third polarization; further including calculating the overlap loss of the light field based on the conversion loss and coupling loss of the on-chip mode field.

[0029] The present invention further discloses a test array including a plurality of the above test devices for edge couplers, wherein a plurality of the test devices for edge couplers are arranged in an array on an optical chip, and each of the test devices for edge couplers is not exactly the same.

Brief Description of the Drawings

[0030] [Figure 1] This is a schematic diagram showing the test structure of a conventional edge-type coupler and its connection to an optical fiber array. [Figure 2] This is a schematic diagram of the test apparatus for the edge-type coupler according to the present invention. [Figure 3] This is a schematic diagram showing the structure of the edge-type coupler test apparatus according to the present invention after cutting and its connection to the optical fiber array. [Figure 4] This is a schematic diagram of the cascade test structure in the edge-type coupler test apparatus according to the present invention, when it includes 4N edge-type couplers. [Figure 5] This is a schematic diagram of the edge-type coupler in the test apparatus for the edge-type coupler according to the present invention when the edge-type coupler is tilted. [Figure 6] This is a schematic diagram of the edge-type coupler testing apparatus according to the present invention, in which a first connection region and a second connection region are provided. [Figure 7] This is a schematic diagram of the edge-type coupler testing apparatus according to the present invention, in which a third connection region and a fourth connection region are provided. [Figure 8] This is a schematic diagram showing the structure of the edge-type coupling test apparatus according to the present invention, in which the first connection area, second connection area, third connection area, and fourth connection area are all provided in the cutting lane. [Figure 9] This is a schematic diagram showing the edge-type coupler testing apparatus according to the present invention, which is provided with a first etching region and a second etching region. [Figure 10] This is a schematic diagram of the edge-type coupler test apparatus according to the present invention, in which the etching region and the connection region partially overlap. [Figure 11] This is a schematic diagram of the structure when a polarization separation rotor is used in the edge-type coupling test apparatus according to the present invention. [Figure 12] This is a schematic diagram of the loopback structure in the edge-type coupler testing apparatus according to the present invention, when it is provided inside the cascade testing structure. [Figure 13] This is a schematic diagram of the structure when the fifth edge-type coupler and the sixth edge-type coupler are arranged opposite each other in the test apparatus for edge-type couplers according to the present invention. [Figure 14] This is a flowchart of the test method for the edge-type coupler according to the present invention. [Figure 15] This is a schematic diagram of the test array according to the present invention. [Modes for carrying out the invention]

[0031] To further clarify the object, technical solution and advantages of the present invention, the technical solution in the embodiments of the present invention will be described below clearly and completely in conjunction with the drawings of the present invention. Obviously, the embodiments described are some of the embodiments of the present invention, but not all of them. All other embodiments that can be obtained by those skilled in the art without any creative effort based on the embodiments of the present invention are included within the scope of the protection of the present invention. Unless otherwise defined, technical or scientific terms used herein shall have the ordinary meanings understood by those skilled in the art in which the present invention pertains. The use of similar words such as “includes” herein means that the element or thing that appears before the word includes, without exclusion, the elements or things listed after the word and their equivalents.

[0032] Taking into consideration the problems of the prior art, an embodiment of the present invention provides a test apparatus for an edge-type coupler provided on an optical chip 10. Referring to Figure 2, The optical chip 10 is equipped with a loopback structure 20 for coupling with an external optical fiber array, A cascade test structure 30 is arranged on the optical chip 10 for testing the mode-field conversion loss within the chip for TE polarization and TM polarization. A polarization separation module 40 is connected to the cascade test structure 30 and is used to introduce and extract TE polarization and TM polarization into the cascade test structure 30, respectively. A TE diffraction grating coupling module 50 is connected to the input and output terminals of the polarization separation module 40 to introduce and derive TE polarization into the cascade test structure 30, A TM diffraction grating coupling module 60 is connected to the input and output terminals of the polarization separation module 40 to introduce and derive TM polarization into the cascade test structure 30, The system includes a calibration structure 70 for obtaining calibration data for the TE polarization and the TM polarization.

[0033] In this embodiment, TE polarization and TM polarization are tested by adding a cascade test structure 30 based on the conventional loopback structure 20. The TE diffraction grating coupling module 50 and the TM diffraction grating coupling module 60 share one cascade test structure 30 for testing, effectively reducing the space occupied inside the chip. The polarization separation module 40 introduces and derives TE polarization and TM polarization into the cascade test structure 30, respectively, for testing, thereby testing the mode-field conversion loss within the chip in two polarization states, TE and TM, and improving the testing efficiency of the chip.

[0034] In the solutions described below, the structure of the polarization separation module 40 and the calibration module 50 is described mainly only in the direction indicated by the arrows in Figure 2. Here, the so-called input can also be used as an output, and the so-called output can also be used as an input. That is, the direction of the incident and outgoing light is interchangeable and is not limited to the direction indicated by arrow 2 in the figure, so it will not be explained again here.

[0035] In some embodiments, referring again to Figure 2, the cascade test structure 30 includes a first curved waveguide 307 and a group of edge-type couplers, the group of edge-type couplers includes a first edge-type coupler 301, a second edge-type coupler 302, a third edge-type coupler 303, and a fourth edge-type coupler 304, one end of the first edge-type coupler 301 is connected to one end of the third edge-type coupler 303, the other end of the first edge-type coupler 301 is connected to one end of the second edge-type coupler 302 via the first curved waveguide 307, the other end of the second edge-type coupler 302 is connected to one end of the fourth edge-type coupler 304, and both the other end of the third edge-type coupler 303 and the other end of the fourth edge-type coupler 304 are connected to the polarization separation module 40. The polarization separation module 40 includes a first polarization splitter 401 and a second polarization splitter 402, the input terminal of the first polarization splitter 401 includes a first TE input terminal and a first TM input terminal, the output terminal of the first polarization splitter 401 is electrically connected to the cascade test structure 30, the input terminal of the second polarization splitter 402 is electrically connected to the output terminal of the cascade test structure 30, the output terminal of the second polarization splitter 402 includes a first TE output terminal and a first TM output terminal, and the TE diffraction grating coupling module 50 includes a first TE diffraction grating coupler 501 and a second TE diffraction grating coupler The TM diffraction grating coupling module 60 includes a combiner 502, and the TM diffraction grating coupling module 60 includes a first TM diffraction grating coupler 601 and a second TM diffraction grating coupler 602, wherein the TE polarization is input to the first TE input terminal via the first TE diffraction grating coupler 501, then introduced into the cascade test structure 30, and led out to the second TE diffraction grating coupler 502 by the first TE output terminal, and the TM polarization is input to the first TM input terminal via the first TM diffraction grating coupler 601, then introduced into the cascade test structure 30, and led out to the second TM diffraction grating coupler 602 by the first TM output terminal.

[0036] Furthermore, the polarization separation module 40 can separate two polarizations or combine two polarizations, and this structure is reversible, allowing it to be selected according to the actual usage scenario and needs.

[0037] In this embodiment, the calibration structure 70 is used to acquire calibration data for the TE polarization and the TM polarization, and the calibration structure 70 includes a third polarization splitter 701, a fourth polarization splitter 702, a third TE diffraction grating coupler 703, a fourth TE diffraction grating coupler 704, a third TM diffraction grating coupler 705, and a fourth TM diffraction grating coupler 706, wherein the output terminal of the third polarization splitter 701 is connected to the input terminal of the fourth polarization splitter 702 via a second curved waveguide 707, and the input terminal of the third polarization splitter 701 includes a second TE input terminal and a second TM input terminal, and the fourth polarization splitter The output terminal of the 702 includes a second TE output terminal and a second TM output terminal. The TE polarization is introduced to the second TE input terminal via the third TE diffraction grating coupler 703, then sequentially passes through the third polarization splitter 701 and the fourth polarization splitter 702 to the fourth TE diffraction grating coupler 704 via the second TE output terminal. The TM polarization is introduced to the second TM input terminal via the third TM diffraction grating coupler 705, then sequentially passes through the third polarization splitter 701 and the fourth polarization splitter 702 to the fourth TM diffraction grating coupler 706 via the second TM output terminal.

[0038] For example, the first edge coupler 301 is denoted as EC#2, the second edge coupler 302 as EC#3, the third edge coupler 303 as EC#5, the fourth edge coupler 304 as EC#6, the first polarization splitter 401 as PS#1, the second polarization splitter 402 as PS#2, the first TE diffraction grating coupler 501 as TEGC#1, the second TE diffraction grating coupler 502 as TEGC#2, and the first TM The folding grating coupler 601 is denoted as TMGC#1, the second TM diffraction grating coupler 602 as TMGC#2, the third polarization splitter 701 as PS#3, the fourth polarization splitter 702 as PS#4, the third TE diffraction grating coupler 703 as TEGC#3, the fourth TE diffraction grating coupler 704 as TEGC#4, the third TM diffraction grating coupler 705 as TMGC#3, and the fourth TM diffraction grating coupler 706 as TMGC#4. Referring to Figure 2, we will take testing TE polarization as an example. First, TE polarization with initial power P0 is input to the first TE diffraction grating coupler 501, then introduced to the first polarization splitter 401, and then sequentially passes through the third edge coupler 303, the first edge coupler 301, the second edge coupler 302, and the fourth edge coupler 304, then passes through the second polarization splitter 402, and is output via the second TE diffraction grating coupler 502, with the output optical power being P1_TE. Subsequently, TE polarization with initial power P0 is introduced to the calibration structure 70, and sequentially passes through the third TE diffraction grating coupler 703, the third polarization splitter 701, the fourth polarization splitter 702, and the fourth TE diffraction grating coupler 704, deriving an optical signal with power P2_TE, and the in-chip mode-field conversion loss for TE polarization at each edge coupler in the cascade test structure 30 is IL_1_TE = (P1_TE - P2_TE) / 4.Similarly, TM polarization with power P0 is input from the first TM diffraction grating coupler 601 to the first polarization splitter 401, and after sequentially passing through the third edge coupler 303, the first edge coupler 301, the second edge coupler 302, and the fourth edge coupler 304, it passes through the second polarization splitter 402, and then derives the optical signal with power P1_TM via the second TM diffraction grating coupler 602. TM polarization with power P0 is input to the calibration structure 70, and after sequentially passing through the third TM diffraction grating coupler 705, the third polarization splitter 701, the fourth polarization splitter 702, and the fourth TM diffraction grating coupler 706, it derives the optical signal with power P2_TM, and the in-chip mode-field conversion loss for TM polarization at each edge coupler EC in the cascade test structure 30 is IL_1_TM = (P1_TM - P2_TM) / 4. The above calculation method allows us to calculate the mode-field conversion loss within the chip of each edge-type coupler EC.

[0039] In this embodiment, the loopback structure 20 includes a fifth edge coupler 201 and a sixth edge coupler 202, the fifth edge coupler 201 and the sixth edge coupler 202 are connected by a third curved waveguide 205, the optical chip 10 is provided with a cutting lane 80, one end of the fifth edge coupler 201 and the sixth edge coupler 202 closer to the TE diffraction grating coupling module 50 is provided in the cutting lane 80, the connection position between the first edge coupler 301 and the third edge coupler 303, and the connection position between the second edge coupler 302 and the fourth edge coupler 304 are both located in the cutting lane 80, and the loopbacks formed between the loopback structure 20 and the first edge coupler 301, the first curved waveguide 307, and the second edge coupler 302 are in a nested relationship, thereby reducing chip space and cost. The optical chip 10 is provided with a loopback structure 20, which can be used to further measure the coupling loss of each edge-type coupler EC.

[0040] Illustratively, referring to Figure 3, the optical chip 10 is cut along the cutting lane 80, thereby forming a separate chip with the first edge coupler 301, third edge coupler 303, fifth edge coupler 202, and sixth edge coupler 202 located on the left side of the optical chip 10. The previously tested TE-polarized and TM-polarized signals with power P0 are then match-coupled with the optical fiber array 90 in a conventional manner and tested. Specifically, taking the TE-polarized signal with power P0 as an example, the power after the TE-polarized signal passes through the loopback structure 10 formed by the fifth edge coupler 202 and the sixth edge coupler 202 is P3_TE, the coupling loss of the edge coupler for the TE-polarized signal is IL_TE=(P3_TE-P0) / 2, and based on the calculated mode-field conversion loss IL_1_TE within the chip for the TE-polarized signal, the light field overlap loss IL_2_TE=IL_TE-IL_1_TE between the edge coupler and the optical fiber can be calculated. Similarly, if the power of the TM polarization with power P0 is P3_TM after passing through the loopback structure 10, and the coupling loss of the edge coupler with respect to the TM polarization is IL_TM=(P3_TM-P0) / 2, then based on the calculated in-chip mode-field conversion loss IL_1_TM with respect to the TM polarization, the overlap loss of the light field between the edge coupler and the optical fiber IL_2_TM=IL_TM-IL_1_TM can be calculated.

[0041] Therefore, the testing apparatus of this solution allows for the individual testing of the coupling loss of TE polarization and TM polarization, and the measurement of mode-field conversion loss within the chip and the light-field overlap loss with the optical fiber, respectively. This not only saves space within the chip but also improves utilization efficiency and reduces costs.

[0042] In the cascade test structure 30, the number of edge-type coupler groups is at least two, and the ends of adjacent edge-type coupler groups are connected to each other. Referring to Figure 4, the number of edge-type couplers is not limited to four, but may be 4N, where N is a positive integer, which facilitates the realization of cascade testing.

[0043] In some embodiments, referring to FIG. 5, the first edge coupler 301, the second edge coupler 302, the fifth edge coupler 201, and the sixth edge coupler 202 all form an angle A with the straight line where the cutting lane 80 is located, where 0° < A < 180°. By setting a certain inclination angle A, the reflection of light at the coupling end face can be reduced.

[0044] Exemplarily, the angle A = 90°, that is, the first edge coupler 301, the second edge coupler 302, the fifth edge coupler 201, and the sixth edge coupler 202 are all perpendicular to the straight line where the cutting lane 80 is located.

[0045] In some other embodiments, referring to FIG. 6, a first connection region 305 is provided between the first edge coupler 301 and the third edge coupler 303, a second connection region 306 is provided between the second edge coupler 302 and the fourth edge coupler 304, the cutting lane 80 is provided in the first connection region 305 and the second connection region 306, the waveguide widths of the first connection region 305 and the second connection region 306 are uniform, the width of the first connection region 305 is equal to the end width of the first edge coupler 301 and the end width of the third edge coupler 303, and the width of the second connection region 306 is equal to the end width of the second edge coupler 302 and the end width of the fourth edge coupler 304.

[0046] Furthermore, a gap is provided between the ends of the fifth edge coupler 201 and the sixth edge coupler 202 and the cutting lane 80, thereby protecting the edge couplers and ensuring that when cutting along the cutting lane 80, the end faces of the fifth edge coupler 201 and the sixth edge coupler 202 are not affected by end face roughness, cracks, wrinkles, burrs, etc. Therefore, the coupling loss can be normally tested after cutting.

[0047] In several other embodiments, referring to Figure 7, a third connection region 203 is provided at one end of the fifth edge-type coupler 201 closer to the cutting lane 80, and a fourth connection region 204 is provided at one end of the sixth edge-type coupler 202 closer to the cutting lane 80. Both the third connection region 203 and the fourth connection region 204 are provided with a gap between them and the cutting lane 80. By setting the third connection region 203 and the fourth connection region 204, the edge-type couplers are protected, and when cutting along the cutting lane 80, the fifth edge-type coupler 201 and the sixth edge-type coupler 202 are protected from effects such as end face roughness, cracks, wrinkles, and burrs.

[0048] In some embodiments, referring to Figure 8, the first connection region 305, the second connection region 306, the third connection region 203, and the fourth connection region 204 are all provided in the cutting lane 80, and when cutting a chip along the cutting lane 80, insufficient precision control of the cutting position does not cause cutting misalignment, preventing the width of the cut end face waveguide from becoming uncontrollable.

[0049] In some further embodiments, referring to Figure 9, the cutting lane 80 is provided with a first etching region 801 and a second etching region 802. By arranging the first etching region 801 and the second etching region 802, the influence of edge face roughness due to cutting on the edge-type couplers can be reduced, and because the edge faces are locally etched using a semiconductor etching process, the flatness of the etched edge faces is improved, and the coupling effect is enhanced. Etching is not performed between the first edge-type coupler 301 and the second edge-type coupler 302, and between the third edge-type coupler 303 and the fourth edge-type coupler 304, thereby ensuring the continuity of the cascade test structure 30, and thus the mode-field conversion test within the chip can be performed normally before cutting.

[0050] In some embodiments, a gap is provided between the first etching region 801 and the fifth edge-type coupler 201, and a gap is provided between the second etching region 802 and the sixth edge-type coupler 202, thereby avoiding damage to the ends of the loopback structure 10 due to etching.

[0051] In some further embodiments, referring to Figure 10, the first etching region 801 at least partially overlaps the third connection region 203, and the second etching region 802 at least partially overlaps the fourth connection region 204. The fact that the first etching region 801 at least partially overlaps the third connection region 203 and the second etching region 802 at least partially overlaps the fourth connection region 204 prevents insufficient precision control of the cutting position from causing cutting misalignment and making the width of the cut end face waveguide uncontrollable when cutting the chip along the cutting lane 80.

[0052] In some other embodiments, referring to Figure 11, the polarization splitters in the polarization separation module 40 can also use polarization splitter rotators (PSRs), but at the same time, the TM polarization grating couplers must be changed to TE polarization grating couplers. That is, the first polarization splitter 401, the second polarization splitter 402, the third polarization splitter 701 and the fourth polarization splitter 702 are all replaced with polarization splitter rotators, and the first TM diffraction grating coupler 601, the second TM diffraction grating coupler 602, the third TM diffraction grating coupler 705 and the fourth TM diffraction grating coupler 706 are all replaced with TE diffraction grating couplers. By changing TE polarization to TM polarization, testing of the two polarization states can be realized. For example, TE polarization is incident from TEGC#1, maintains TE polarization through PSR#1, is introduced into the cascade EC, passes through PSR#2 and is derived from TEGC#3. When TE polarization is incident from TEGC#2, it passes through PSR#1, is converted to TM polarization, passes through the cascade EC, passes through PSR#2, is converted back to TE polarization, and is derived from TEGC#4.

[0053] For example, if the incident light has power P0 and polarization state TE, enters from TEGC#1, passes through a cascade test structure of two PSRs and four edge-type couplers, is derived from TEGC#3, and the derived light power is P1_TE. With the same light source power, enters the calibration structure from TEGC#5, passes through two PSRs, is derived from TEGC#7, and the derived light power is P2_TE. The conversion loss of the on-chip mode field of each EC is IL_1_TE = (P1_TE - P2_TE) / 4. Similarly, TE polarization is incident from TEGC#2, passes through two PSRs and four EC cascade structures, and is derived from TEGC#4, with the derived light power being P1_TM. With the same light source power, it is incident from TEGC#6 into the calibration structure, passes through two PSRs, and is derived from TEGC#8, with the derived light power being P2_TM. The conversion loss of the on-chip mode field of each EC is IL_1_TM = (P1_TM - P2_TM) / 4, and the test process is essentially the same as described above, so it will not be repeated here. Here, the units of P1_TE, P2_TE, P1_TM, and P2_TM are dBm, and the units of IL_1_TE and IL_1_TM are dB.

[0054] In some embodiments, referring to Figure 12, the loopback structure 20 is located inside the cascade test structure 30. In some embodiments, the loopback structure 20 does not have to have an internal or external nesting relationship with the cascade test structure 30 and may be located in a different position (not shown).

[0055] Furthermore, referring to Figure 13, the end of the fifth edge-type coupler 201 and the end of the sixth edge-type coupler 202 are positioned opposite each other.

[0056] Furthermore, the present invention does not particularly limit the arrangement position, direction, and angle between the end faces of the fifth edge-type coupler 201 and the sixth edge-type coupler 202, so this will not be explained again here.

[0057] The test apparatus of the present invention, by arranging a TE diffraction grating coupling module, a TM diffraction grating coupling module, and a polarization separation module, propagates TE polarization and TM polarization to a cascade test structure for coupling testing, and tests the in-chip mode-field conversion loss of TE polarization and TM polarization through the cascade test structure, saving on-chip space and improving test efficiency. The nested loopback structure and rational cutting lane configuration allow for separate measurement of the respective values ​​of mode-field conversion loss and light-field overlap loss.

[0058] The present invention further discloses a test method for edge-type couplers applicable to the above-described test apparatus for edge-type couplers, and referring to Figure 14, the test method for edge-type couplers is: S1401, before cutting the chip, the power inputs the initial polarization of P0 according to the type of initial polarization into the TE diffraction grating coupling module or the TM diffraction grating coupling module, and after testing by the cascade test structure, the power acquires the first polarization of P1. S1402, a step of inputting the initial polarization into the calibration structure to obtain a calibrated polarization with power P2, S1403 includes the step of calculating the conversion loss of the on-chip mode field of each edge coupler in the cascade test structure based on the power P1 of the first polarization and the power P2 of the calibrated polarization.

[0059] Here, the conversion loss for the on-chip mode field is IL_1 = (P1 - P2) / 4.

[0060] Furthermore, the method further includes the following steps:

[0061] S1404, after cutting the chip, the initial polarization is input to the loopback structure to output a third polarization with power P3.

[0062] S1405, the coupling loss of each edge-type coupler in the loopback structure is calculated based on the power of the initial polarization and the power of the third polarization.

[0063] Here, the coupling loss is IL = (P3 - P0) / 2.

[0064] S1406, Based on the conversion loss and coupling loss of the on-chip mode field, the overlap loss of the light field is calculated.

[0065] Here, the overlap loss of the light field is IL_2 = IL - IL_1.

[0066] The process and principles of the above method correspond one-to-one with the working process of the edge-type coupling device test apparatus described above, and therefore will not be explained again here.

[0067] The present invention further discloses a test array, referring to Figure 15, which includes a plurality of the edge-type coupler test devices, wherein the plurality of edge-type coupler test devices are arranged in an array on an optical chip, and each of the edge-type coupler test devices is not exactly the same.

[0068] Some design parameters of each test device within the test array are used in the experimental design and can be set to be the same or different, and all test structures share the same cutting lane.

[0069] The integrated materials platform on which the above-described test structures are arranged includes bulk silicon, silicon-on-insulator, silicon-on-sapphire, silicon dioxide, alumina, indium phosphide, lithium niobate, and polymers. The waveguide types of the test structures include channel waveguides, ridge waveguides, slot waveguides, diffuse waveguides, and photonic crystal waveguides. The operating wavelength range of the test structures includes the visible light band, O-band, E-band, S-band, C-band, L-band, U-band, and mid-infrared band. The operating wavelengths of each test structure in the shown array may be the same or different. The application areas of the test structures include lidar, beam control, optical sensing, optical interconnects, free-space optical communications, optical storage, and optical computing. The structures of the EC include, but are not limited to, inverse tapers, stepped inverse tapers, cantilever beams, side slots, V-grooves, multiple waveguides, multilayer waveguides, and subwavelength structures. The structural designs of the PS and PSR include, but are not limited to, adiabatic couplers, bent couplers, directional couplers, Y-shaped branching, multimode interference structures, and subwavelength structures. The structural designs of the GC include, but are not limited to, linear diffraction gratings, fan-shaped curved diffraction gratings, bipolarized diffraction gratings, and multilayer material diffraction gratings. The shape of the curved waveguide includes, but is not limited to, arc shapes, linear bend shapes, Euler bend shapes, or sinusoidal shapes.

[0070] Although embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and changes can be made to these embodiments. However, it should be understood that such modifications and changes fall within the scope and spirit of the invention as defined in the claims. Furthermore, the present invention described herein is capable of other embodiments and can be carried out or realized in various ways.

Claims

1. A test apparatus for an edge-type coupler placed on an optical chip, The optical chip is provided with a loopback structure for coupling with an external optical fiber array, A cascade test structure is provided on the optical chip for testing the mode-field conversion loss within the chip for TE polarization and TM polarization. A polarization separation module connected to the cascade test structure for introducing TE polarization and TM polarization into the cascade test structure and deriving them after testing, A TE diffraction grating coupling module is connected to the input and output terminals of the polarization separation module to introduce and derive TE polarization into the cascade test structure, A TM diffraction grating coupling module is connected to the input and output terminals of the polarization separation module to introduce and derive TM polarization into the cascade test structure, A test apparatus for an edge-type coupler, comprising a calibration module for acquiring calibration data for the TE polarization and the TM polarization.

2. The cascade test structure includes a first curved waveguide and a group of edge-type couplers, the group of edge-type couplers includes a first edge-type coupler, a second edge-type coupler, a third edge-type coupler, and a fourth edge-type coupler, one end of the first edge-type coupler is connected to one end of the third edge-type coupler, the other end of the first edge-type coupler is connected to one end of the second edge-type coupler via the first curved waveguide, the other end of the second edge-type coupler is connected to one end of the fourth edge-type coupler, and the other end of the third edge-type coupler and the other end of the fourth edge-type coupler are both connected to the polarization separation module, as described in claim 1.

3. The polarization separation module includes a first polarization splitter and a second polarization splitter, the input terminal of the first polarization splitter includes a first TE input terminal and a first TM input terminal, the output terminal of the first polarization splitter is electrically connected to the cascade test structure, the input terminal of the second polarization splitter is electrically connected to the output terminal of the cascade test structure, the output terminal of the second polarization splitter includes a first TE output terminal and a first TM output terminal, the TE diffraction grating coupling module includes a first TE diffraction grating coupler and a second TE diffraction grating coupler, and the TM diffraction grating coupler The test apparatus for edge-type couplers according to claim 2, characterized in that the coupling module includes a first TM diffraction grating coupler and a second TM diffraction grating coupler, wherein the TE polarization is input to the first TE input terminal by the first TE diffraction grating coupler, then introduced into the cascade test structure and led out to the second TE diffraction grating coupler by the first TE output terminal, and the TM polarization is input to the first TM input terminal by the first TM diffraction grating coupler, then introduced into the cascade test structure and led out to the second TM diffraction grating coupler by the first TM output terminal.

4. The edge-type coupler testing apparatus according to claim 2, characterized in that the number of edge-type coupler groups is at least two, and the ends of adjacent edge-type coupler groups are connected to each other.

5. The calibration structure includes a third polarization splitter, a fourth polarization splitter, a third TE diffraction grating coupler, a fourth TE diffraction grating coupler, a third TM diffraction grating coupler, and a fourth TM diffraction grating coupler, wherein the output terminal of the third polarization splitter is connected to the input terminal of the fourth polarization splitter via a second curved waveguide, the input terminal of the third polarization splitter includes a second TE input terminal and a second TM input terminal, the output terminal of the fourth polarization splitter includes a second TE output terminal and a second TM output terminal, and the TE polarization is connected to the third TE diffraction grating. The edge-type coupler test apparatus according to claim 4, characterized in that the TM polarization is introduced to the second TE input terminal by the coupler, then sequentially passes through the third polarization splitter and the fourth polarization splitter and is led out to the fourth TE diffraction grating coupler by the second TE output terminal, and the TM polarization is introduced to the second TM input terminal by the third TM diffraction grating coupler, then sequentially passes through the third polarization splitter and the fourth polarization splitter and is led out to the fourth TM diffraction grating coupler by the second TM output terminal.

6. The edge-type coupler test apparatus according to claim 3, characterized in that the loopback structure includes a fifth edge-type coupler and a sixth edge-type coupler, the fifth edge-type coupler and the sixth edge-type coupler are connected by a third curved waveguide, the optical chip is provided with a cutting lane, one end of the fifth edge-type coupler and the sixth edge-type coupler closer to the TE diffraction grating coupling module is located in the cutting lane, the connection position of the first edge-type coupler and the third edge-type coupler, and the connection position of the second edge-type coupler and the fourth edge-type coupler are both located in the cutting lane, and the loopbacks formed between the loopback structure and the first edge-type coupler, the first curved waveguide, and the second edge-type coupler are in a nesting relationship.

7. The edge-type coupler testing apparatus according to claim 6, characterized in that the first edge-type coupler, the second edge-type coupler, the fifth edge-type coupler, and the sixth edge-type coupler all form an angle A with the straight line of the cutting lane, where 0° < A < 180°.

8. The edge-type coupler testing apparatus according to claim 6, characterized in that a first connection region is provided between the first edge-type coupler and the third edge-type coupler, a second connection region is provided between the second edge-type coupler and the fourth edge-type coupler, and the cutting lane is provided in the first connection region and the second connection region.

9. The edge-type coupler testing apparatus according to claim 8, characterized in that a third connection region is provided at one end of the fifth edge-type coupler near the cutting lane, and a fourth connection region is provided at one end of the sixth edge-type coupler near the cutting lane.

10. The edge-type coupling test apparatus according to claim 9, characterized in that a gap is provided between either the third connection region and the fourth connection region and the cutting lane.

11. The edge-type coupling test apparatus according to claim 9, characterized in that the first connection area, the second connection area, the third connection area, and the fourth connection area are all provided in the cutting lane.

12. The edge-type coupling test apparatus according to claim 9, characterized in that the cutting lane is provided with a first etching region and a second etching region.

13. The edge-type coupler testing apparatus according to claim 12, characterized in that the first etching region at least partially overlaps with the third connection region, and the second etching region at least partially overlaps with the fourth connection region.

14. The edge-type coupler testing apparatus according to claim 12, characterized in that a gap is provided between the first etching region and the fifth edge-type coupler, and a gap is provided between the second etching region and the sixth edge-type coupler.

15. The test apparatus for edge-type couplers according to claim 6, characterized in that the loopback structure is provided inside the cascade test structure.

16. The edge-type coupler testing apparatus according to claim 6, characterized in that the ends of the fifth edge-type coupler and the sixth edge-type coupler are provided on different end faces of the tip.

17. The edge-type coupler test apparatus according to claim 5, characterized in that the first polarization splitter, the second polarization splitter, the third polarization splitter, and the fourth polarization splitter are all replaced by polarization separation rotors, and the first TM diffraction grating coupler, the second TM diffraction grating coupler, the third TM diffraction grating coupler, and the fourth TM diffraction grating coupler are all replaced by TE diffraction grating couplers.

18. A test method for an edge-type coupler, applicable to the test apparatus for edge-type couplers described in claim 4, Before cutting the chip, the power inputs the initial polarization according to the type of initial polarization of P0 into a TE diffraction grating coupling module or a TM diffraction grating coupling module, tests it using the cascade test structure, and then obtains the first polarization of P1. The steps include inputting the initial polarization into the calibration structure to obtain calibrated polarization with power P2, A test method for edge-type couplers, characterized by the step of calculating the conversion loss of the on-chip mode field of each edge-type coupler in the cascade test structure based on the power P1 of the first polarization and the power P2 of the calibrated polarization.

19. The aforementioned method, After cutting the chip along the cutting lane, the initial polarization is input to the loopback structure by the fifth edge-type coupler, and the sixth edge-type coupler outputs the third polarization with power P3. A step of calculating the coupling loss of each edge-type coupler in the loopback structure based on the power of the initial polarization and the power of the third polarization, The test method for an edge-type coupler according to claim 18, further comprising the step of calculating the overlap loss of a light field based on the conversion loss and coupling loss of the on-chip mode field.

20. A test array comprising a test apparatus for an edge-type coupler according to any one of claims 1 to 17, wherein the plurality of edge-type coupler test apparatuses are arranged in an array on an optical chip, and each of the edge-type coupler test apparatuses is not exactly the same.

Images