Multistage end face coupler for interconnection of optical fiber and on-chip photonic integrated device

Abstract

The invention relates to the technical field of micro-nano optoelectronic devices, in particular to a multistage end face coupler for interconnection of an optical fiber and an on-chip photonic integrated device, which comprises a 3 * 2 multi-mode interference coupler, a connecting single-mode waveguide and a 2 * 1 multi-mode interference coupler, the 3 * 2 multi-mode interference coupler comprises three input conical waveguides, a first multi-mode waveguide and a dual-output conical waveguide which are connected in sequence; the 2 * 1 multi-mode interference coupler comprises a double-input conical waveguide, a second multi-mode waveguide, a single-output conical waveguide and a single-mode waveguide which are connected in sequence; the middle input conical waveguide and the side input conical waveguide are symmetrically distributed about the optical axis, the first multimode waveguide and the second multimode waveguide comprise interference areas and transition areas, and the width of the transition areas is narrowed in the light propagation direction; the transmission loss of the end face coupler can be reduced, the alignment tolerance is increased, and the processing difficulty is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of micro-nano optoelectronic devices, and in particular to a multi-stage end-face coupler used for interconnecting an optical fiber with an on-chip photonic integrated device. Background Art

[0002] Since on-chip laser technology is not yet mature, optical coupling between optical fibers and integrated optical waveguide structures is a necessary input and output interface for photonic integrated circuits. Efficient coupling of optical signals plays a vital role in many applications such as optical interconnection, optical switching, and integrated quantum optics.

[0003] However, there are many kinds of losses when the traditional single-mode optical fiber and the on-chip waveguide structure are directly coupled, including Fresnel reflection loss caused by the difference in the end face refractive index or the existence of an air gap, the alignment error loss caused by the horizontal or vertical offset during docking, the mode field mismatch loss between the optical fiber and the waveguide end face, and the transmission loss introduced by the end face coupler. For Fresnel reflection loss, the commonly used technology is to use a refractive index matching liquid to replace the air gap at the connection between the optical fiber and the waveguide. For the alignment error loss, it is often evaluated by the 3dB or 1dB tolerance of the coupling structure. For SMF-28 optical fiber, the core material is often doped SiO2, while the cladding is pure SiO2, so the refractive index difference between the core and the cladding is small. In contrast, in order to realize small-sized, low-loss, and highly constrained waveguide devices, on-chip passive waveguide devices often use materials with a larger refractive index such as Si and Si3N4 as the core layer, while the cladding is still pure SiO2, so the refractive index difference between the core and the cladding is large, and the light field distribution is more concentrated. Due to the different effective refractive index between the end face of the optical fiber and the on-chip waveguide device, there is a large difference in the light field distribution.

[0004] At present, a variety of coupling structures have been studied, mainly single-layer end-face coupling, vertical coupling based on grating structure, and 3D coupling based on multi-layer structure or thickness variation structure. Compared with end-face coupling, vertical coupling has lower coupling efficiency and often requires additional reflection layers to solve the problem of substrate leakage; while 3D structure requires more complex process flow, and has high processing difficulty and complexity. Therefore, it is of great significance to achieve efficient coupling of light by designing a single-layer end-face coupling type coupling structure. Summary of the invention

[0005] In view of the above problems, the present invention provides a multi-stage end face coupler for interconnecting optical fibers with on-chip photonic integrated devices, which solves the technical problems of long coupling length, small alignment tolerance, low coupling efficiency and great processing difficulty of end face couplers in the prior art.

[0006] The present invention provides a multi-stage end-face coupler for interconnecting an optical fiber with an on-chip photonic integrated device, comprising a 3×2 multimode interference coupler, a connecting single-mode waveguide 6 and a 2×1 multimode interference coupler;

[0007] The 3×2 multimode interference coupler comprises two side input tapered waveguides 1, a middle input tapered waveguide 2, a first multimode waveguide and a dual output tapered waveguide 5, wherein the output ends of the side input tapered waveguide 1 and the middle input tapered waveguide 2 are both connected to the input end of the first multimode waveguide, and the output end of the first multimode waveguide is connected to the input end of the dual output tapered waveguide 5;

[0008] The 2×1 multimode interference coupler includes a dual-input tapered waveguide 7, a second multimode waveguide, a single output tapered waveguide 10 and a single-mode waveguide 11. The dual-output tapered waveguide 5 is connected to the input end of the dual-input tapered waveguide 7 through a connecting single-mode waveguide 6, the output end of the dual-input tapered waveguide 7 is connected to the input end of the second multimode waveguide, and the output end of the second multimode waveguide is connected to the input end of the single-mode waveguide 11 through the single output tapered waveguide 10.

[0009] Preferably, the center line of the middle input tapered waveguide 2 is arranged along the optical axis direction of the multi-stage end face coupler, and the center lines of the two side input tapered waveguides 1 are symmetrically distributed with the optical axis as the symmetry axis; the widths of the side input tapered waveguide 1 and the middle input tapered waveguide 2 both widen linearly from the input end to the output end; the center line of the side input tapered waveguide 1 is offset from the input end to the output end in a direction away from the optical axis.

[0010] Preferably, the first multimode waveguide comprises a first multimode waveguide interference region 3 and a first multimode waveguide transition region 4, and the light inputted by the side input tapered waveguide 1 and the middle input tapered waveguide 2 interferes in the first multimode waveguide interference region 3, and is connected to the dual output tapered waveguide 5 through the first multimode waveguide transition region 4; the width of the first multimode waveguide interference region 3 remains unchanged along the light propagation direction, the width of the first multimode waveguide transition region 4 narrows along the light propagation direction, and the width of the output end is consistent with the input width of the dual output tapered waveguide 5;

[0011] The second multimode waveguide includes a second multimode waveguide interference region 8 and a second multimode waveguide transition region 9. The light input by the dual-input tapered waveguide 7 interferes in the second multimode waveguide interference region 8, passes through the second multimode waveguide transition region 9, and is output to the single output tapered waveguide 10; the width of the second multimode waveguide interference region 8 remains unchanged along the light propagation direction, the width of the second multimode waveguide transition region 9 narrows along the light propagation direction, and the output end width is consistent with the width of the single output tapered waveguide 10.

[0012] Preferably, the width of the side input tapered waveguide 1 and the middle input tapered waveguide 2 ranges from 90nm to 120nm, the spacing between the side input tapered waveguide 1 and the middle input tapered waveguide 2 ranges from 0.8μm to 1.2μm, and the output end widths of the side input tapered waveguide 1 and the middle input tapered waveguide 2 are consistent; the length of the side input tapered waveguide 1 and the middle input tapered waveguide 2 along the light propagation direction ranges from 30μm to 50μm.

[0013] Preferably, the width of the first multimode waveguide interference region 3 ranges from 6 μm to 20 μm, and the width variation profile curves of the first multimode waveguide transition region 4 and the second multimode waveguide transition region 9 are function curves of power function, exponential function or trigonometric function.

[0014] Preferably, the dual-output tapered waveguide 5 includes two tapered waveguides symmetrically distributed with the optical axis of the multi-stage end face coupler as the symmetry axis, the widths of the two tapered waveguides of the dual-output tapered waveguide 5 are linearly narrowed along the light propagation direction, the output end of the dual-output tapered waveguide 5 is connected to the connected single-mode waveguide 6, the output end width of the dual-output tapered waveguide 5 is consistent with the width of the connected single-mode waveguide 6, the input end width of the dual-output tapered waveguide 5 ranges from 1.4μm to 2μm, the length of the dual-output tapered waveguide 5 along the light propagation direction is 10μm, and the length of the connected single-mode waveguide 6 along the light propagation direction is 10μm.

[0015] Preferably, the dual-input tapered waveguide 7 includes two tapered waveguides symmetrically distributed with the optical axis of the multi-stage end face coupler as the symmetry axis, the input end widths of the two tapered waveguides of the dual-input tapered waveguide 7 are consistent with the width of the connected single-mode waveguide 6, and the widths both widen linearly along the light propagation direction; the output end width of the dual-input tapered waveguide 7 ranges from 0.8μm to 1.2μm, and the length of the dual-input tapered waveguide 7 along the light propagation direction is 10μm.

[0016] Preferably, the width of the single output tapered waveguide 10 narrows linearly along the light propagation direction, the input end width of the single output tapered waveguide 10 is consistent with the output end width of the dual input tapered waveguide 7, and the output end of the single output tapered waveguide 10 is connected to the single mode waveguide 11, and the width is consistent with the single mode waveguide 11.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects:

[0018] (1) Compared with the existing end-face coupler structure, the present invention creatively cascades two multimode waveguides and adopts a three-taper input end, which can not only meet the mode spot size matching of the optical fiber-waveguide end face, but also reduce the transmission loss of light in the coupler.

[0019] (2) The overall thickness of the present invention remains unchanged, and the device design is performed only on a single-layer structure, which is a symmetrical structure and can avoid the complexity and uncertainty of the process of a multi-layer structure.

[0020] (3) The end face coupler device proposed in the present invention is based on the principle of multi-mode interference coupler, has a small size, and a length of only about 150 μm, which can reduce the size of the device and provide more allowable area for subsequent effective devices.

[0021] (4) The present invention adopts a three-taper input end structure, which can reduce the effective refractive index of the end face mode, expand the waveguide mode area, achieve mode field matching, and increase the alignment tolerance. The side taper center offset structure is designed to prevent the problem of high processing difficulty caused by the narrow spacing of the wide end structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings are only for the purpose of illustrating particular embodiments and are not to be construed as limiting the invention.

[0023] Figure 1 This is a schematic top view of the end face coupler structure provided by the present invention.

[0024] Figure 2 This is a 3D schematic diagram of the end face coupler structure provided by the present invention.

[0025] Figure 3 An internal light field transmission diagram of one solution of the end face coupler provided by the present invention.

[0026] Figure 4 This is the mode field distribution diagram of the three input ends of the end coupler provided by the present invention.

[0027] Figure numerals: 1-side input tapered waveguide, 2-middle input tapered waveguide, 3-first multimode waveguide interference region, 4-first multimode waveguide transition region, 5-dual output tapered waveguide, 6-connected single-mode waveguide, 7-dual input tapered waveguide, 8-second multimode waveguide interference region, 9-second multimode waveguide transition region, 10-single output tapered waveguide, 11-single-mode waveguide, 12-single-mode optical fiber. DETAILED DESCRIPTION

[0028] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. In addition, the present invention can also be implemented in other ways different from those described herein, and therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0029] In order to illustrate the effectiveness of the method proposed by the present invention, the above technical solution of the present invention is described in detail below through a specific embodiment. Figure 1 , Figure 2 As shown, a multi-stage end-face coupler for interconnecting optical fiber with on-chip photonic integrated devices is disclosed, including a 3×2 multimode interference coupler (Multimode Interference, MMI) and a 2×1 multimode interference coupler. The 3×2 multimode interference coupler includes two side input tapered waveguides 1, a middle input tapered waveguide 2, a first multimode waveguide and a dual output tapered waveguide 5. The output ends of the side input tapered waveguide 1 and the middle input tapered waveguide 2 are both connected to the input end of the first multimode waveguide, and the output end of the first multimode waveguide is connected to the input end of the dual output tapered waveguide 5. The 2×1 multimode interference coupler includes a connected single-mode waveguide 6, a dual input tapered waveguide 7, a second multimode waveguide, a single output tapered waveguide 10 and a single-mode waveguide 11. The dual output tapered waveguide 5 is connected to the input end of the dual input tapered waveguide 7 through the connected single-mode waveguide 6, the output end of the dual input tapered waveguide 7 is connected to the input end of the second multimode waveguide, and the output end of the second multimode waveguide is connected to the input end of the single-mode waveguide 11 through the single output tapered waveguide 10.

[0030] The thickness of the overall structure of the multi-level end-face coupler for interconnecting optical fibers with on-chip photonic integrated devices provided by the present invention is consistent with the thickness of a single-mode waveguide. Taking the Si3N4 waveguide of 850nm wavelength light as an example, when the thickness of the single-mode waveguide is 300nm, the width single-mode condition is calculated to be 500nm by the finite difference eigenmode method (FDE), that is, when the width of the single-mode waveguide is 500nm, it can be ensured that it only supports fundamental mode transmission at a wavelength of 850nm.

[0031] In some embodiments, the three input ends formed by the two side input tapered waveguides 1 and the middle input tapered waveguide 2 of the present invention are symmetrically distributed as a whole. Specifically, the center line of the middle input tapered waveguide 2 is arranged along the optical axis direction of the multi-stage end face coupler, and the center lines of the two side input tapered waveguides 1 are symmetrically distributed with the optical axis as the symmetry axis. The widths of the side input tapered waveguide 1 and the middle input tapered waveguide 2 are linearly widened from the input end to the output end. The center line of the side input tapered waveguide 1 is offset from the input end to the output end in a direction away from the optical axis. Through this structure, the three input ends of the present invention can avoid the additional loss caused by the process due to the narrow distance of the wide end of the three-taper waveguide.

[0032] The width and spacing of the side input tapered waveguide 1 and the middle input tapered waveguide 2 of the present invention determine the mode overlap integral (Overlap) with the optical fiber coupling end face. Taking coupling with an 850nm single-mode optical fiber with a mode field diameter (MFD) of 2.5μm as an example, the width of the side input tapered waveguide 1 and the middle input tapered waveguide 2 ranges from 90nm to 120nm, and the spacing ranges from 0.8μm to 1.2μm, wherein the width of the middle waveguide can be slightly wider than that of the side waveguide, for example, about 10nm wide. The end face mode field diagram is shown in Figure 4, at which time the Overlap reaches about 93%. Its length ranges from 30μm to 50μm.

[0033] In some embodiments, the output end widths of the two side input tapered waveguides 1 and the middle input tapered waveguide 2 are consistent, and the output end widths of the side input tapered waveguide 1 and the middle input tapered waveguide 2 are determined by the size of the interference enhancement region in the first multimode waveguide. In a multimode waveguide with a fixed width, the interference behavior of the same input mode in the waveguide at the same wavelength is fixed, so the position of the output end of the side input tapered waveguide 1 is consistent with the side position of the output end of the 1×3MMI beam splitter at the same width, and the calculated output end spacing of the 1×3MMI beam splitter under the same width and wavelength conditions is the output end spacing of the side input tapered waveguide 1 and the middle input tapered waveguide 2.

[0034] In some embodiments, the first multimode waveguide includes a first multimode waveguide interference region 3 and a first multimode waveguide transition region 4. The width of the first multimode waveguide interference region 3 is constant along the light propagation direction. Light input from the three input ends interferes in the first multimode waveguide interference region 3 and is transmitted to the dual-output tapered waveguide 5 through the first multimode waveguide transition region 4. The width of the first multimode waveguide transition region 4 gradually narrows along the light propagation direction, and the width at the narrow end is the same as the outer width of the dual-output tapered waveguide 5. In this way, light loss caused by light exiting the output end face of the multimode waveguide can be prevented.

[0035] The width range of the first multimode waveguide interference zone 3 of the present invention is 6μm-20μm. The width of the multimode waveguide interference zone will affect the input tapered waveguide center offset position and the length of the multimode waveguide. The wider the width, the longer the length required for the multimode waveguide, and the larger the corresponding device size. If the width is too narrow, the output end spacing will be too close, increasing the process difficulty. Therefore, it is necessary to balance the device size and the output end spacing. The width change profile of the first multimode waveguide transition zone 4 of the present invention can be set to a variety of function curves, such as power functions, exponential functions, trigonometric functions, etc. Taking the power function with an exponent of m as an example, the range of m is 0-1. When m is 0, the width change profile of the transition zone is a horizontal line that continues the multimode waveguide. When m is 1, the shape of the transition zone is a connection between the first multimode waveguide and the dual output tapered waveguide 6. Figure 3 : The optical field transmission diagram of the transition region of the first multimode waveguide and the second multimode waveguide when the m values ​​are 0.7 and 1 respectively.

[0036] In some embodiments, the dual-output tapered waveguide 5 is identical and symmetrically distributed along the optical axis. The widths of the two tapered waveguides of the dual-output tapered waveguide 5 are linearly narrowed along the light propagation direction. The output end of the dual-output tapered waveguide 5 is connected to the connected single-mode waveguide 6. The width of the input end of the dual-output tapered waveguide 5 is determined by the size of the interference enhancement region in the first multimode waveguide, and the width of the output end is consistent with the width of the connected single-mode waveguide 6. Through this structure, the light output can be efficiently guided, and the transmission loss can be reduced through single-mode waveguide transmission.

[0037] The input end width of the dual-output tapered waveguide 5 of the present invention is determined by the size of the interference enhancement region in the first multimode waveguide. Taking the multimode waveguide width of 8 μm as an example, the input end width of the dual-output tapered waveguide 5 ranges from 1.4 μm to 2 μm. The narrow end is connected to the single-mode waveguide and has the same width as the single-mode waveguide. Its length ranges from about 10 μm.

[0038] In some embodiments, the size of the connecting single-mode waveguide 6 is specially designed to only meet the fundamental mode transmission, and the transmission loss can be effectively reduced by avoiding high-order mode crosstalk. The length of the connecting single-mode waveguide 6 is about 10 μm.

[0039] In some embodiments, the dual-input tapered waveguide 7 is composed of two identical tapered waveguides, the input end widths of the two tapered waveguides of the dual-input tapered waveguide 7 are consistent with the widths of the connected single-mode waveguide 6, and the widths are linearly widened along the light propagation direction. The output end width of the dual-input tapered waveguide 7 is determined by the size of the interference enhancement region in the second multimode waveguide, ranging from 0.8 μm to 1.2 μm, and the length range is about 10 μm.

[0040] In some embodiments, the second multimode waveguide includes a second multimode waveguide interference region 8 and a second multimode waveguide transition region 9. The width of the second multimode waveguide interference region 8 along the light propagation direction remains unchanged. The light input by the dual-input tapered waveguide 7 interferes in the second multimode waveguide interference region 8, passes through the second multimode waveguide transition region 9, and is output to the single output tapered waveguide 10. The width of the second multimode waveguide transition region 9 along the light propagation direction gradually narrows, and the width of the narrow end is the same as the width of the single output tapered waveguide 10. In this way, the light loss caused by direct emission from the output end face of the second multimode waveguide can be prevented. The width of the second multimode waveguide interference region 8 is determined by the optimized 1×2 MMI beam splitter multimode waveguide width that satisfies the same spacing between the output waveguides and the dual-input tapered waveguides 8.

[0041] In some embodiments, the width of the single-output tapered waveguide 10 is linearly narrowed along the light propagation direction, the input end width of the single-output tapered waveguide 10 is consistent with the output end width of the dual-input tapered waveguide 7, and the output end of the single-output tapered waveguide 10 is connected to the single-mode waveguide 11, and the width is the same as the single-mode waveguide 11 for subsequent light transmission.

[0042] It should be understood that the linear tapered waveguides involved in the present invention, including: the transition forms of the side input tapered waveguide 1, the middle input tapered waveguide 2, the dual output tapered waveguide 5, the dual input tapered waveguide 7 and the single output tapered waveguide 10 can be optimized into quadratic, exponential, trigonometric and other forms.

[0043] The implementation scheme of the multi-stage end coupler for interconnecting optical fiber and on-chip photonic integrated device provided by the present invention has an optimal transmittance of about 85%, a horizontal 3dB alignment tolerance of about 3.1μm, and a vertical 3dB alignment tolerance of about 2.6μm. At the same time, the overall device size is about 150μm, which greatly reduces the device size compared to the length of about 700μm of the single-cone end coupler under the same conditions. It can be seen that through the cascade structure of two multi-mode interference couplers, combined with the three-tip inverted cone structure, high coupling efficiency, large alignment tolerance and small size can be achieved, providing support for realizing efficient optical coupling between optical fiber and photonic integrated chip.

[0044] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0045] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0046] In the present invention, the terms "first", "second", "third", "fourth" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance. The term "plurality" refers to two or more, unless otherwise clearly defined.

[0047] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A multi-stage end coupler for interconnecting an optical fiber with an on-chip photonic integrated device, characterized in that: It includes a 3×2 multimode interference coupler, a connecting single-mode waveguide (6) and a 2×1 multimode interference coupler; The 3×2 multimode interference coupler comprises two side input tapered waveguides (1), a middle input tapered waveguide (2), a first multimode waveguide and a dual output tapered waveguide (5), wherein the output ends of the side input tapered waveguide (1) and the middle input tapered waveguide (2) are both connected to the input end of the first multimode waveguide, and the output end of the first multimode waveguide is connected to the input end of the dual output tapered waveguide (5); The 2×1 multimode interference coupler comprises a dual-input tapered waveguide (7), a second multimode waveguide, a single-output tapered waveguide (10) and a single-mode waveguide (11); the dual-output tapered waveguide (5) is connected to the input end of the dual-input tapered waveguide (7) via a connecting single-mode waveguide (6); the output end of the dual-input tapered waveguide (7) is connected to the input end of the second multimode waveguide; and the output end of the second multimode waveguide is connected to the input end of the single-mode waveguide (11) via the single-output tapered waveguide (10).

2. The multi-stage end coupler for interconnecting an optical fiber and an on-chip photonic integrated device according to claim 1, characterized in that: The center line of the middle input tapered waveguide (2) is arranged along the optical axis direction of the multi-stage end face coupler, and the center lines of the two side input tapered waveguides (1) are symmetrically distributed with the optical axis as the symmetry axis; the widths of the side input tapered waveguide (1) and the middle input tapered waveguide (2) both linearly widen from the input end to the output end; and the center line of the side input tapered waveguide (1) deviates from the input end to the output end in a direction away from the optical axis.

3. The multi-stage end coupler for interconnecting an optical fiber and an on-chip photonic integrated device according to claim 2, characterized in that: The first multimode waveguide comprises a first multimode waveguide interference region (3) and a first multimode waveguide transition region (4); light input from the side input tapered waveguide (1) and the middle input tapered waveguide (2) interferes in the first multimode waveguide interference region (3) and is connected to the dual output tapered waveguide (5) through the first multimode waveguide transition region (4); the width of the first multimode waveguide interference region (3) remains unchanged along the light propagation direction, the width of the first multimode waveguide transition region (4) narrows along the light propagation direction, and the output end width is consistent with the input end width of the dual output tapered waveguide (5); The second multimode waveguide comprises a second multimode waveguide interference region (8) and a second multimode waveguide transition region (9); light input from the dual-input tapered waveguide (7) interferes in the second multimode waveguide interference region (8), passes through the second multimode waveguide transition region (9), and is output to the single output tapered waveguide (10); the width of the second multimode waveguide interference region (8) remains unchanged along the light propagation direction, the width of the second multimode waveguide transition region (9) narrows along the light propagation direction, and the width of the output end is consistent with the width of the single output tapered waveguide (10).

4. The multi-stage end coupler for interconnecting an optical fiber and an on-chip photonic integrated device according to claim 3, characterized in that: The width of the side input tapered waveguide (1) and the middle input tapered waveguide (2) ranges from 90 nm to 120 nm, the spacing between the side input tapered waveguide (1) and the middle input tapered waveguide (2) ranges from 0.8 μm to 1.2 μm, the output end widths of the side input tapered waveguide (1) and the middle input tapered waveguide (2) are consistent; the length of the side input tapered waveguide (1) and the middle input tapered waveguide (2) along the light propagation direction ranges from 30 μm to 50 μm.

5. The multi-stage end coupler for interconnecting an optical fiber and an on-chip photonic integrated device according to claim 4, characterized in that: The width of the first multimode waveguide interference region (3) ranges from 6 μm to 20 μm, and the width variation profile curves of the first multimode waveguide transition region (4) and the second multimode waveguide transition region (9) are function curves of a power function, an exponential function or a trigonometric function.

6. The multi-stage end coupler for interconnecting an optical fiber and an on-chip photonic integrated device according to claim 5, characterized in that: The dual-output tapered waveguide (5) comprises two tapered waveguides symmetrically distributed with the optical axis of the multi-stage end face coupler as the symmetry axis, the widths of the two tapered waveguides of the dual-output tapered waveguide (5) both linearly narrow along the light propagation direction, the output end of the dual-output tapered waveguide (5) is connected to the connected single-mode waveguide (6), the output end width of the dual-output tapered waveguide (5) is consistent with the width of the connected single-mode waveguide (6), the input end width of the dual-output tapered waveguide (5) ranges from 1.4 μm to 2 μm, the length of the dual-output tapered waveguide (5) along the light propagation direction is 10 μm, and the length of the connected single-mode waveguide (6) along the light propagation direction is 10 μm.

7. The multi-stage end coupler for interconnecting an optical fiber and an on-chip photonic integrated device according to claim 6, characterized in that: The dual-input tapered waveguide (7) comprises two tapered waveguides symmetrically distributed with the optical axis of the multi-stage end face coupler as the symmetry axis; the input end widths of the two tapered waveguides of the dual-input tapered waveguide (7) are consistent with the width of the connected single-mode waveguide (6), and the widths both linearly widen along the light propagation direction; the output end width of the dual-input tapered waveguide (7) ranges from 0.8 μm to 1.2 μm, and the length of the dual-input tapered waveguide (7) along the light propagation direction is 10 μm.

8. The multi-stage end coupler for interconnecting an optical fiber and an on-chip photonic integrated device according to claim 7, characterized in that: The width of the single-output tapered waveguide (10) narrows linearly along the light propagation direction, the input end width of the single-output tapered waveguide (10) is consistent with the output end width of the dual-input tapered waveguide (7), and the output end of the single-output tapered waveguide (10) is connected to the single-mode waveguide (11), and the width is consistent with the single-mode waveguide (11).

Images