An on-chip end-face coupler test structure

Abstract

The application relates to a kind of on-chip end face coupler test structures, which include light coupling incidence assembly and light coupling emission assembly, light coupling incidence assembly is used to transmit light from one end of the component to be measured into the component to be measured, wherein the component to be measured includes several coupler pairs cascaded along the light transmission direction, the coupler pair includes two end face couplers arranged in butt joint, and the head and tail of the two end face couplers are opposite along the light transmission direction; light coupling emission assembly is used to emit light emitted from the other end in the component to be measured. The application can eliminate the loss caused by the coupling interface mode field mismatch, so as to accurately measure the loss caused by mode conversion efficiency, so as to realize end face coupler mode conversion loss test and process problem positioning and evaluation, so as to optimize the end face coupler to obtain the end face coupler with higher coupling efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor technology, in particular to a test structure of an on-chip end-face coupler. BACKGROUND

[0002] In recent years, silicon photonics integrated circuits have rapidly emerged. As the core material of the microelectronics industry, silicon not only has excellent electrical properties, but also has low-loss optical transmission performance in the near-infrared band, making it an ideal choice for building high-efficiency optical communication components. In the manufacturing process, although the basis of silicon photonics integrated circuits is standard CMOS technology, including steps such as photolithography, thin film deposition, and etching, in order to adapt to the specific needs of photonic devices, in some cases, process parameters may need to be adjusted or additional processing steps may need to be introduced. As the interface between the silicon photonics integrated circuit and the optical fiber, laser, and other chips, the optical coupler is an important optical element in the silicon photonics integrated circuit. The end-face coupler-based horizontal coupling method and the grating coupler-based vertical coupling method are the two main optical fiber coupling methods in silicon photonics integrated circuits.

[0003] Vertical coupling allows for a larger tolerance range, reducing the need for precise alignment. It can also be implemented at any position on the chip, providing greater design flexibility. However, compared to horizontal coupling, vertical coupling involves more complex optical structure design and manufacturing processes, which may increase costs and pose long-term stability and reliability issues after packaging, requiring more testing and verification. Horizontal coupling technology is relatively mature and easy to implement multi-channel coupling, making it suitable for most silicon optical chip production solutions.

[0004] However, in the design process of the end-face coupler, the coupling efficiency of the end-face coupler depends on two key factors: first, the coupling efficiency of the optical coupling interface, i.e., the degree of mode matching between the end face and the optical fiber or laser; second, the mode conversion efficiency, i.e., whether the light can be efficiently converted into the propagation mode supported by the waveguide after entering the waveguide from the end face of the coupler, without excessive reflection or scattering loss.

[0005] During the coupling performance test of the end-face coupler, the overall performance of the coupling efficiency can be tested and evaluated by a horizontal coupling table, and the mode matching loss can be obtained by comparing the mode field size and divergence angle of the coupled optical fiber and the end-face coupler after emission, respectively. However, the loss caused by the mode conversion efficiency cannot be accurately measured. At the manufacturing process level, high-quality manufacturing processes are crucial for maintaining the consistency and accuracy of design parameters, and any process defects may reduce the mode conversion efficiency. SUMMARY

[0006] Embodiments of the present application provide an on-chip end-face coupler test structure to solve the problem of loss caused by difficulty in accurately measuring mode conversion efficiency in the related art.

[0007] Embodiments of the present application provide an on-chip end-face coupler test structure, which comprises:

[0008] a light coupling incident assembly for transmitting light from one end of a to-be-tested assembly into the to-be-tested assembly, wherein the to-be-tested assembly comprises a plurality of coupler pairs cascaded along an optical transmission direction, the coupler pair comprises two end-face couplers arranged in butt joint, and the head end and the tail end of the two end-face couplers are opposite along the optical transmission direction;

[0009] a light coupling exit assembly for emitting light exiting from the other end of the to-be-tested assembly.

[0010] In some embodiments, the light coupling incident assembly comprises a light coupling incident coupler and an incident optical waveguide, and the light coupling incident coupler is connected to the incident optical waveguide.

[0011] In some embodiments, the light coupling incident coupler is a grating coupler or an end-face coupler.

[0012] And / or, the operating wavelength band of the light coupling incident coupler comprises one or more of C band, L band, S band, O band and E band.

[0013] In some embodiments, the light coupling exit assembly comprises a light coupling exit coupler and an exit optical waveguide, and the light coupling exit coupler is connected to the exit optical waveguide.

[0014] In some embodiments, the light coupling exit coupler is a grating coupler or an end-face coupler.

[0015] And / or, the operating wavelength band of the light coupling exit coupler comprises one or more of C band, L band, S band, O band and E band.

[0016] In some embodiments, the grating coupler is a device of converging type, straight waveguide type, super surface type or photonic crystal type.

[0017] In some embodiments, the end-face coupler comprises a mode conversion waveguide and a straight waveguide for signal transmission, and one end of the mode conversion waveguide constitutes the head end of the end-face coupler, and the other end of the mode conversion waveguide is connected to one end of the straight waveguide, so that the other end of the straight waveguide constitutes the tail end of the end-face coupler.

[0018] In some embodiments, in the coupler pair, one end of the mode conversion waveguide of one end-face coupler is butt jointed to one end of the mode conversion waveguide of the other end-face coupler.

[0019] In some embodiments, in the coupler pair, one end of the straight waveguide of one of the end-face couplers is butted against one end of the straight waveguide of the other end-face coupler.

[0020] The light-coupling-injection assembly comprises an end-face coupler, and one end of the mode conversion waveguide of the end-face coupler is butted against one end of the mode conversion waveguide of the end-face coupler in the coupler pair.

[0021] The light-coupling-injection assembly comprises an end-face coupler, and one end of the mode conversion waveguide of the end-face coupler is butted against one end of the mode conversion waveguide of the end-face coupler in the coupler pair.

[0022] In some embodiments, the end-face coupler is a device of a tapered waveguide type, a graded-index type, a multi-tipped type, a curved waveguide type, a ridge waveguide type, a slot waveguide type, an inclined angle type, a sub-wavelength type, or a hybrid type.

[0023] The technical scheme provided in the present application has the following beneficial effects:

[0024] The present application can eliminate the loss caused by the coupling interface mode field mismatch, so as to accurately measure the loss caused by the mode conversion efficiency, so as to realize the end-face coupler mode conversion loss testing and process problem positioning and evaluation, so as to optimize the end-face coupler to obtain an end-face coupler with higher coupling efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical scheme in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0026] Figure 1 The schematic diagram of the on-chip end-face coupler test structure provided in an embodiment of the present application is shown in FIG. 1.

[0027] Figure 2 The schematic diagram of the on-chip end-face coupler test structure provided in an embodiment of the present application is shown in FIG. 1. Figure 1 The schematic diagram of the on-chip end-face coupler test structure provided in an embodiment of the present application is shown in FIG. 1.

[0028] Figure 3 The schematic diagram of the on-chip end-face coupler test structure provided in an embodiment of the present application is shown in FIG. 1.

[0029] Figure 4 The schematic diagram of the on-chip end-face coupler test structure provided in an embodiment of the present application is shown in FIG. 1. Figure 3 The schematic diagram of the on-chip end-face coupler test structure provided in an embodiment of the present application is shown in FIG. 1.

[0030] In the figure: 1, light coupling incident assembly; 11, light coupling incident coupler; 12, incident light waveguide; 2, light coupling emission assembly; 21, light coupling emission coupler; 22, emission light waveguide; 3, component to be tested; 4, coupler pair; 5, end face coupler; 51, mode conversion waveguide; 52, straight waveguide. DETAILED DESCRIPTION

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will be combined with the accompanying drawings for the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0032] Referring to Figure 1 , Figure 2 , Figure 3 and Figure 4 , the embodiments of the present application provide an on-chip end face coupler test structure, which comprises a light coupling incident assembly 1 and a light coupling emission assembly 2, and the light coupling incident assembly 1 and the light coupling emission assembly 2 are arranged at intervals along an optical transmission direction to form a placement area of a component to be tested 3 between the two.

[0033] The component to be tested 3 comprises a plurality of coupler pairs 4 cascaded along the optical transmission direction, and each coupler pair 4 comprises two end face couplers 5 arranged in abutment, and the two end face couplers 5 are opposite in head-to-tail along the optical transmission direction.

[0034] The light coupling incident assembly 1 is used for transmitting light from one end of the component to be tested 3 into the component to be tested 3.

[0035] The light coupling emission assembly 2 is used for emitting light out of the other end of the component to be tested 3.

[0036] The principle of the present application is as follows:

[0037] The end face coupler 5 generally comprises a mode conversion waveguide 51 and a straight waveguide 52 for signal transmission, and one end of the mode conversion waveguide 51 constitutes a head end of the end face coupler 5, and the other end of the mode conversion waveguide 51 is connected to one end of the straight waveguide 52, so that the other end of the straight waveguide 52 constitutes a tail end of the end face coupler 5, and for the convenience of understanding, the two ends are marked with letters A and B, as shown in Figure 1As shown, the width of the mode conversion waveguide 51 gradually increases or decreases along the light transmission direction, so that the width of one end of the mode conversion waveguide 51 is different from that of the other end, such as the smaller width end is the head end A, and the larger width end is connected with the straight waveguide 52, so that the end of the straight waveguide 52 far away from the head end A is the tail end B.

[0038] Since the head and tail of the two end face couplers 5 are opposite, the order of the head and tail of one end face coupler 5 in the coupling device pair 4 along the light transmission direction is A→B, and the order of the head and tail of the other end face coupler 5 is B→A.

[0039] If the light first enters the straight waveguide 52 of the first end face coupler 5 of the measured component 3 through the light coupling incidence assembly 1, that is, enters from the tail end B of the first end face coupler 5, as shown in Figure 1 As shown, when the transmitted light passes through the first end face coupler 5, based on the design principle of the end face coupler, the mode field of the light field is transmitted to the head end A of the first end face coupler 5 under the action of the waveguide. Since the head and tail of the two end face couplers 5 are opposite, the head end A of the second end face coupler 5 is connected with the head end A of the first end face coupler 5, so the mode field of the head end A of the second end face coupler 5 is exactly the same as that of the head end A of the first end face coupler 5, and no loss is introduced due to the mode field mismatch of the coupling interface, only the mode conversion loss in the transmission process exists, so the total loss can be measured. Referring to Figure 2 As shown, before or after the test of the measured component 3, the light coupling incidence assembly 1 and the light coupling emission assembly 2 are directly connected, the test structure body loss caused by the light coupling incidence assembly 1 and the light coupling emission assembly 2 can be obtained, and the mode conversion loss of the measured component 3 can be obtained by deducting the test structure body loss from the total loss.

[0040] If the light first enters the mode conversion waveguide 51 of the first end face coupler 5 of the measured component 3 through the light coupling incidence assembly 1, that is, enters from the head end A of the first end face coupler 5, as shown in Figure 3As shown, when the transmitted light passes through the first end-face coupler 5, based on the design principle of the end-face coupler, under the action of the waveguide, the mode field of the light field is transmitted to the tail end B of the first end-face coupler 5 of the first coupler pair 4, and then is transmitted to the head end A of the second end-face coupler 5 of the first coupler pair 4. Since the head end and the tail end of the two end-face couplers 5 are opposite, the head end A of the first end-face coupler 5 of the second coupler pair 4 is butted with the head end A of the second end-face coupler 5 of the first coupler pair 4, so the mode field of the head end A of the first end-face coupler 5 of the second coupler pair 4 is completely the same as the mode field of the head end A of the second end-face coupler 5 of the first coupler pair 4, and no loss is introduced due to the mode field mismatch of the coupling interface, only the mode conversion loss in the transmission process exists, and thus the total loss can be measured. Referring to Figure 4 As shown, before or after the test on the to-be-tested component 3 is completed, the light coupling into the component 1 and the light coupling out of the component 2 are directly connected, the test structure body loss caused by the light coupling into the component 1 and the light coupling out of the component 2 can be obtained, and the mode conversion loss of the to-be-tested component 3 can be obtained by subtracting the test structure body loss from the total loss.

[0041] Therefore, the application can actually eliminate the loss introduced due to the mode field mismatch of the coupling interface, so that the loss caused by the mode conversion efficiency can be accurately measured, and the mode conversion loss test of the end-face coupler, the positioning and evaluation of the process problem, and the optimization of the end-face coupler to obtain the end-face coupler with higher coupling efficiency can be realized.

[0042] Specifically, at the manufacturing process level, since the mode conversion waveguide has relatively high requirements on the minimum line width and the waveguide sidewall roughness of the process, the loss is different under different process line widths and sidewall roughnesses, so the process quality can be evaluated through the test structure. Secondly, the consistency between wafers and wafer batches can be evaluated through the mode conversion efficiency result of the test structure, so as to feedback and adjust the manufacturing process and chip device design.

[0043] It should be noted that when the test is performed, the light emitted by the light source passes through the polarization controller and is coupled into the light coupling component 1 through the coupling optical fiber, and then is transmitted to the to-be-tested component 3. After being transmitted through the to-be-tested component 3, the light is coupled out of the light coupling component 2 to another out-coupling optical fiber, and then is transmitted to the optical power meter through the out-coupling optical fiber for measurement.

[0044] The to-be-tested component 3 in the application can include one, two, three or more large numbers of coupler pairs 4, so as to realize wafer-level or chip-level batch testing to evaluate the mode conversion loss of the end-face coupler.

[0045] It can be seen that the test structure provided by the application not only helps engineers to more accurately locate the process limit of the end-coupler, but also effectively identifies specific process defects that may cause performance degradation, and can systematically analyze and quantify the performance changes in each manufacturing batch. Through in-depth analysis of the test data, it is possible to better distinguish the key factors affecting the coupling efficiency, such as modal mismatch, material property differences, and slight deviations in the manufacturing process. At the same time, based on these test results, the R&D team can adjust and optimize the design parameters and manufacturing processes, such as improving the waveguide structure design, selecting a more suitable material combination, or optimizing the etching and deposition steps. This not only helps to reduce the uncertainty caused by process fluctuations, but also significantly improves the overall performance and reliability of the end-coupling device, enabling higher overall coupling efficiency and ensuring that each produced end-coupler meets the expected optical performance standards, thereby supporting the widespread application of silicon photonics integrated circuits in high-speed communication, sensing, and other advanced application fields.

[0046] It can be understood that the end-coupler 5 is a device of a tapered waveguide type, a graded-index type, a multi-tipped type, a curved waveguide type, a ridge waveguide type, a slot waveguide type, an inclined angle type, a sub-wavelength type, or a hybrid type.

[0047] Referring to Figure 1 , Figure 2 , Figure 3 and Figure 4 , as a preferred embodiment, the light-coupling incidence assembly 1 includes a light-coupling incidence coupler 11 and an incidence light waveguide 12, and the light-coupling incidence coupler 11 is connected to the incidence light waveguide 12.

[0048] The light-coupling incidence coupler 11 is a grating coupler or an end-coupler. If an end-coupler is used, the end-coupler can have the same structure as the end-coupler 5 in the to-be-tested assembly 3, or can have other existing end-couplers that are not the same. Regardless of whether the same structure as the end-coupler 5 in the to-be-tested assembly 3 is used, calibration will be performed at the end, thereby eliminating the influence of the light-coupling incidence assembly 1. The grating coupler is a device of a converging type, a straight waveguide type, a metasurface type, or a photonic crystal type.

[0049] The operating wavelength band of the light-coupling incidence coupler 11 includes one or more of a C band, an L band, an S band, an O band, and an E band.

[0050] Referring to Figure 1 , Figure 2 , Figure 3 and Figure 4As shown, as a preferred embodiment, the light coupling exit assembly 2 comprises a light coupling exit coupler 21 and an exit light waveguide 22, and the light coupling exit coupler 21 is connected with the exit light waveguide 22.

[0051] The light coupling exit coupler 21 is a grating coupler or an end face coupler; the grating coupler is a device of converging type, straight waveguide type, super surface type or photonic crystal type.

[0052] The working waveband of the light coupling exit coupler 21 comprises one or several of C waveband, L waveband, S waveband, O waveband and E waveband.

[0053] As described above, the head and tail ends of the two end face couplers 5 in the coupler pair 4 are opposite, and the connection mode of the component to be tested 3 comprises the following modes:

[0054] Connection mode one: refer to Figure 1 As shown, for the coupler pair 4, the head end A of the two end face couplers 5 is butted; for the adjacent two coupler pairs 4, the tail end B in the end face coupler 5 of one coupler pair 4 is butted with the tail end B in the end face coupler 5 of the other coupler pair 4.

[0055] For the connection mode one, at this time, the light coupling entry assembly 1 comprises a light coupling entry coupler 11 and an entry light waveguide 12, and one end of the entry light waveguide 12 is butted with the tail end B of the first end face coupler 5 of the component to be tested 3; the light coupling exit assembly 2 comprises a light coupling exit coupler 21 and an exit light waveguide 22, and one end of the exit light waveguide 22 is butted with the tail end B of the last end face coupler 5 of the component to be tested 3.

[0056] If at this time the component to be tested 3 contains N coupler pairs 4, as Figure 1 , the total loss measured is Q1, as Figure 2 , the test structure body loss measured is Q2, then the mode conversion loss Q of each end face coupler 5 is as follows:

[0057]

[0058] Connection mode two: refer to Figure 3 As shown, for the coupler pair 4, the tail end B of the two end face couplers 5 is butted; for the adjacent two coupler pairs 4, the head end A in the end face coupler 5 of one coupler pair 4 is butted with the head end A in the end face coupler 5 of the other coupler pair 4.

[0059] For the second connection mode, the light coupling incidence assembly 1 needs to add an end face coupler 5 in addition to the light coupling incidence coupler 11 and the incidence light waveguide 12, the head end A of the end face coupler 5 is butted against the head end A of the first end face coupler 5 of the to-be-tested assembly 3; the light coupling incidence assembly 2 needs to add an end face coupler 5 in addition to the light coupling incidence coupler 21 and the incidence light waveguide 22, the head end A of the end face coupler 5 is butted against the head end A of the last end face coupler 5 of the to-be-tested assembly 3.

[0060] If the to-be-tested assembly 3 contains N coupler pairs 4 at this time, as shown in Figure 3 , the total loss measured is Q1, as shown in Figure 4 , the test structure body loss measured is Q2, then the mode conversion loss Q of each end face coupler 5 is as follows:

[0061]

[0062] It can be understood that for the above-mentioned second connection mode, the end face couplers 5 added in the light coupling incidence assembly 1 and the light coupling incidence assembly 2 can be common end face couplers 5, that is, for different to-be-tested assemblies 3, the common end face couplers 5 can be used.

[0063] It can be understood that for the above-mentioned second connection mode, since the number N of the coupler pairs 4 can be very large when batch testing is performed, at this time, two end face couplers 5 can be directly extracted from the original to-be-tested assembly 3 and allocated to the light coupling incidence assembly 1 and the light coupling incidence assembly 2, and the remaining coupler pairs 4 are used as the actual to-be-tested assembly 3 for measurement, at this time, the mode conversion loss Q calculation formula is as follows:

[0064]

[0065] Wherein, N is the to-be-tested assembly 3 containing N coupler pairs 4, as shown in Figure 3 , the total loss measured is Q1, as shown in Figure 4 , the test structure body loss measured is Q2.

[0066] The reason why this processing mode of the second connection mode can be adopted is that when the two end face couplers 5 are butted into the coupler pairs 4, no recognition is needed, whether the head end is butted against the head end or the tail end is butted against the tail end, the test structure provided by the present application can be used for testing, which plays a foolproof design, because: since the mode conversion loss Q is an average value, and the number N can be very large, the loss of one coupler pair 4 (N-1) will not have too much influence, and the result accuracy can be guaranteed.

[0067] In the description of the present application, it should be noted that the terms "upper", "lower", and the like are used for indicating the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. Unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting" should be interpreted broadly, for example, can be fixed connection, can also be detachable connection, or integral connection; can be mechanical connection, can also be electrical connection; can be directly connected, can also be indirectly connected through an intermediate medium, can be internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0068] It should be noted that in the present application, relational terms such as "first" and "second" and the like are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitations, the element defined by the statement "including a" does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0069] The above is only a specific embodiment of the present application, which enables those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied herein.

Claims

1. An on-chip end-coupler test structure, characterized by, It is used for measuring the loss caused by mode conversion efficiency, which includes: The light coupling incident assembly (1) is used for transmitting light from one end of the to-be-tested assembly (3) into the to-be-tested assembly (3), wherein the to-be-tested assembly (3) includes a plurality of coupler pairs (4) cascaded along the light transmission direction, the coupler pair (4) includes two end-face couplers (5) arranged in butt joint, and the head and tail ends of the two end-face couplers (5) are opposite along the light transmission direction; The light coupling exit assembly (2) is used for emitting light out of the other end of the to-be-tested assembly (3); The light coupling incident assembly (1) includes a light coupling incident coupler (11) and an incident light waveguide (12), and the light coupling incident coupler (11) is connected with the incident light waveguide (12); The light coupling exit assembly (2) includes a light coupling exit coupler (21) and an exit light waveguide (22), and the light coupling exit coupler (21) is connected with the exit light waveguide (22); The end-face coupler (5) includes a mode conversion waveguide (51) and a straight waveguide (52) for signal transmission, and one end of the mode conversion waveguide (51) constitutes the head end of the end-face coupler (5), and the other end is connected to one end of the straight waveguide (52), so that the other end of the straight waveguide (52) constitutes the tail end of the end-face coupler (5); In the coupler pair (4), one end of the mode conversion waveguide (51) of one of the end-face couplers (5) is butted with one end of the mode conversion waveguide (51) of the other end-face coupler (5).

2. The on-chip end-face coupler test structure according to claim 1, wherein: The light coupling incident coupler (11) is a grating coupler or an end-face coupler; And / or, the operating waveband of the light coupling incident coupler (11) includes one or more of C waveband, L waveband, S waveband, O waveband and E waveband.

3. The on-chip end-face coupler test structure according to claim 1, wherein: The light coupling exit coupler (21) is a grating coupler or an end-face coupler; And / or, the operating waveband of the light coupling exit coupler (21) includes one or more of C waveband, L waveband, S waveband, O waveband and E waveband.

4. The on-chip end-face coupler test structure according to claim 2 or 3, wherein: The grating coupler is a device of converging type, straight waveguide type, super surface type or photonic crystal type.

5. The on-chip end-face coupler test structure according to claim 1, wherein: In the coupler pair (4), one end of the straight waveguide (52) of one of the end-face couplers (5) is butted with one end of the straight waveguide (52) of the other end-face coupler (5); The light coupling incident assembly (1) includes an end-face coupler (5), and one end of the mode conversion waveguide (51) of the end-face coupler (5) is butted with one end of the mode conversion waveguide (51) of the end-face coupler (5) in the coupler pair (4). The light coupling exit assembly (2) comprises an end face coupler (5), and one end of a mode conversion waveguide (51) of the end face coupler (5) is butted against one end of a mode conversion waveguide (51) of the end face coupler (5) in the coupler pair (4).

6. The on-chip end face coupler test structure of claim 1, wherein: The end face coupler (5) is a device of a tapered waveguide type, a graded index type, a multi-tip type, a curved waveguide type, a ridge waveguide type, a slot waveguide type, an inclination angle type, a sub-wavelength type, or a hybrid type.

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