An optical fiber-waveguide coupler and a manufacturing method thereof

Abstract

The present invention provides an optical fiber - waveguide coupler and a manufacturing method thereof. By fusing a first multimode optical fiber with a high - refractive - index optical fiber to form a gradient structure with specific dimensions, the mode - conversion loss is effectively reduced. At the same time, through the groove technology, the tapered high - refractive - index optical fiber is fixed on the SOI substrate, realizing high - precision alignment and adiabatic coupling between the high - refractive - index optical fiber and the tapered waveguide, significantly improving the coupling efficiency and bandwidth. At a working wavelength of 1550 nm, the simulated coupling efficiency of the optical fiber - waveguide coupler of the present invention is as high as 99.4%, and the - 1dB bandwidth is about 220 nm. The manufacturing process of the optical fiber - waveguide coupler of the present invention is simple, with low cost, without the need for expensive 3D printing technology or waveguide suspension design, having excellent structural stability, being insensitive to position changes, and being able to resist mechanical vibration, and is suitable for low - temperature working environments.

Description

Technical Field

[0001] The present invention belongs to the technical field of optoelectronics and relates to an optical fiber-waveguide coupler and a manufacturing method thereof. Background Art

[0002] Optical fiber-chip coupling technology is crucial for ensuring the efficient and stable operation of optical quantum devices such as superconducting nanowire single-photon detectors, cryogenic electro-optic modulators, and single-photon sources. These devices usually need to work under low-temperature (<40K) or even extremely low-temperature (<0.3K) conditions to ensure their optimal performance. However, the existing optical fiber-chip coupling technology still faces some challenges. For example, the coupling efficiency of grating coupling is usually lower than 30%, the bandwidth is less than 10 nanometers, and complex process steps are required to improve the coupling efficiency. While end-face coupling can achieve a coupling efficiency of more than 80% and a bandwidth of more than 100 nanometers, the choice of coupling position is relatively restricted. More critically, in a low-temperature environment, due to the thermal expansion and contraction of materials and packaging devices, both of these coupling methods may cause alignment offsets, thus significantly reducing the coupling efficiency.

[0003] Although the adiabatic coupling method can reduce the impact of thermal expansion and contraction on the coupling efficiency to a certain extent, affected by factors such as substrate optical field leakage, it usually requires a waveguide suspension design or the use of 3D printing technology to manufacture high-refractive-index optical coupling microstructures. However, the suspended waveguide design not only increases the process complexity but also easily causes collapse due to the instability of its structure, posing challenges to subsequent processes such as ultrasonic cleaning and dicing. On the other hand, the high cost of 3D printing equipment and the additional optical loss caused by the surface roughness of the printed structure also make it difficult to achieve a coupling efficiency close to 100%.

[0004] Therefore, how to improve the optical fiber-chip coupling efficiency, enhance the structural stability, simplify the processing technology, reduce the cost, and ensure the stable operation of the device in a low-temperature environment and other issues have become an important technical problem that needs to be solved urgently.

[0005] It should be noted that the above introduction of the technical background is only for the convenience of clearly and completely explaining the technical solutions of the present application and facilitating the understanding of those skilled in the art. It cannot be considered that the above technical solutions are well-known to those skilled in the art just because these solutions are described in the background art part of the present application. Summary of the Invention

[0006] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide an optical fiber-waveguide coupler and a manufacturing method thereof, which are used to solve the problems of low optical fiber-chip coupling efficiency, low structural stability, complex process, and high cost in the prior art.

[0007] To achieve the above and other related objectives, the present invention provides a method for fabricating an optical fiber-waveguide coupler, comprising the following steps:

[0008] Provide an SOI substrate, which includes a silicon substrate, a buried oxide layer, and a top silicon layer stacked in sequence from bottom to top;

[0009] Pattern the top silicon layer to obtain a waveguide layer, which includes a tapered waveguide;

[0010] Form a groove in the silicon substrate, with at least one groove located in front of the initial end of the tapered waveguide and spaced a preset distance from the tapered waveguide;

[0011] Provide a first multimode optical fiber and a high refractive index optical fiber, where the refractive index of the high refractive index optical fiber is greater than that of the buried oxide layer;

[0012] Align and fuse one end of the first multimode optical fiber with one end of the high refractive index optical fiber, and perform a tapering process on a preset section of the fused high refractive index optical fiber to obtain a tapered section, where the diameter of the tapered section is smaller than that of the non-tapered section of the high refractive index optical fiber, and the connection between the tapered section and the non-tapered section forms a tapered transition section;

[0013] Fix the tapered section on the upper surface of the tapered waveguide, suspend the tapered transition section above the groove, and fix at least a part of the non-tapered section on the inner wall of the groove.

[0014] Optionally, the method of fusing the high refractive index optical fiber with the first multimode optical fiber includes resistance wire heating fusion and discharge fusion.

[0015] Optionally, the groove includes a V-shaped groove, and the center line of the V-shaped groove, the center line of the tapered waveguide, and the center line of the high refractive index optical fiber coincide in the orthographic projection on the silicon substrate.

[0016] Optionally, the tapered section is fixed on the SOI substrate by an ultraviolet curable adhesive, and the refractive index range of the ultraviolet curable adhesive is 1.1 to 1.7.

[0017] Optionally, the method further includes the following steps:

[0018] Provide a second multimode optical fiber, align and fuse one end of the second multimode optical fiber with the other end of the high refractive index optical fiber, and the second multimode optical fiber serves as a test interface for facilitating connection to an optical fiber test device.

[0019] The present invention also provides an optical fiber-waveguide coupler, comprising:

[0020] A silicon substrate, a buried oxide layer, and a waveguide layer stacked in sequence from bottom to top, where the waveguide layer includes a tapered waveguide;

[0021] A groove, located in the silicon substrate, at least one of the grooves being in front of the initial end of the tapered waveguide and spaced a preset distance from the tapered waveguide;

[0022] A high refractive index optical fiber, the refractive index of the high refractive index optical fiber being greater than that of the buried oxide layer. The high refractive index optical fiber includes a non-tapered section, a tapered transition section, and a tapered section. The diameter of the tapered section is smaller than that of the non-tapered section, and the junction between the tapered section and the non-tapered section forms the tapered transition section. Among them, the tapered section is fixed on the upper surface of the tapered waveguide, the tapered transition section is suspended above the groove, and at least a part of the non-tapered section is fixed on the inner wall of the groove;

[0023] A first multimode optical fiber, one end of the first multimode optical fiber being butt-fused with one end of the high refractive index optical fiber.

[0024] Optionally, the groove includes a V-shaped groove, and the orthographic projections of the center line of the V-shaped groove, the center line of the tapered waveguide, and the center line of the high refractive index optical fiber on the silicon substrate coincide.

[0025] Optionally, further comprising:

[0026] A second multimode optical fiber, one end of the second multimode optical fiber being butt-fused with the other end of the high refractive index optical fiber. The second multimode optical fiber serves as a test interface for facilitating connection to an optical fiber test device.

[0027] Optionally, the length range of the tapered transition section is 200 - 250 microns, and the diameter range of the tapered section is 2 - 3 microns.

[0028] Optionally, the length range of the tapered waveguide is 100 - 300 microns, the width range of the initial end of the tapered waveguide is 160 - 250 nanometers, and the width range of the termination end of the tapered waveguide is 470 - 530 nanometers.

[0029] As described above, the fiber-waveguide coupler and its manufacturing method of the present invention form a gradient structure with specific dimensions by splicing a first multimode fiber and a high refractive index fiber, effectively reducing the mode conversion loss. At the same time, through the groove technology, the tapered high refractive index fiber is fixed on the SOI substrate, realizing the high-precision alignment and adiabatic coupling between the high refractive index fiber and the tapered waveguide, and significantly improving the coupling efficiency and bandwidth. At a wavelength of 1550 nm, the simulated coupling efficiency of this fiber-waveguide coupler is as high as 99.4%, and the -1dB bandwidth is about 220 nm. The manufacturing process of the fiber-waveguide coupler of the present invention is simple and low-cost, without the need for expensive 3D printing technology or waveguide suspension design, has excellent structural stability, is insensitive to position changes, and can resist mechanical vibration. In addition, the fiber-waveguide coupler of the present invention can operate stably in a low-temperature environment of 2.3K, has good low-temperature performance, and is suitable for optical coupling applications in low-temperature environments, such as being used in cooperation with devices such as waveguide-type superconducting single-photon detectors and low-temperature quantum dots. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The process flow diagram showing the manufacturing method of the fiber-waveguide coupler of the present invention.

[0031] Figure 2 The schematic structural diagram of the SOI substrate provided in the manufacturing method of the fiber-waveguide coupler of the present invention.

[0032] Figure 3 The schematic diagram of the structure obtained after forming a waveguide layer including a tapered waveguide in the manufacturing method of the fiber-waveguide coupler of the present invention.

[0033] Figure 4 The top view showing the formation of a waveguide layer having a tapered waveguide, a first straight waveguide, a bent waveguide, and a second straight waveguide connected in sequence in an example of the manufacturing method of the fiber-waveguide coupler of the present invention.

[0034] Figure 5 The schematic diagram of the structure obtained after forming a groove in the silicon substrate in the manufacturing method of the fiber-waveguide coupler of the present invention.

[0035] Figure 6 The schematic diagram of the structure obtained after aligning and splicing one end of the first multimode fiber with one end of the high refractive index fiber in the manufacturing method of the fiber-waveguide coupler of the present invention.

[0036] Figure 7 The schematic diagram of the structure obtained after tapering a preset section of the high refractive index fiber in the manufacturing method of the fiber-waveguide coupler of the present invention.

[0037] Figure 8Shown is a schematic cross-sectional structure diagram of the fiber-optic waveguide coupler fabricated according to the present invention.

[0038] Figure 9 Shown as Figure 8 A detailed enlarged view of the cross-sectional structure of the fiber-optic waveguide coupler.

[0039] Figure 10(a) shows a schematic diagram of the vertical offset between the tapered section of the high-index fiber and the tapered waveguide in the method for fabricating the fiber-optic waveguide coupler of the present invention.

[0040] Figure 10(b) shows the influence of the vertical offset between the tapered section of the high-index fiber and the tapered waveguide on the coupling efficiency in the method for fabricating the fiber-optic waveguide coupler of the present invention.

[0041] Figure 11(a) shows a schematic diagram of the horizontal offset of the projection of the center line of the high-index fiber and the center line of the tapered waveguide on the silicon substrate in the method for fabricating the fiber-optic waveguide coupler of the present invention.

[0042] Figure 11(b) shows the influence of the horizontal offset of the projection of the center line of the high-index fiber and the center line of the tapered waveguide on the coupling efficiency on the silicon substrate in the method for fabricating the fiber-optic waveguide coupler of the present invention.

[0043] Figure 12(a) shows a schematic structural diagram of the radius of the tapered section of the high-index fiber in the method for fabricating the fiber-optic waveguide coupler of the present invention.

[0044] Figure 12(b) shows the influence of the radius of the tapered section of the high-index fiber on the coupling efficiency in the method for fabricating the fiber-optic waveguide coupler of the present invention.

[0045] Figure 13 Shown is the influence of the refractive index range of the ultraviolet curable adhesive on the coupling efficiency in the method for fabricating the fiber-optic waveguide coupler of the present invention.

[0046] Figure 14(a) shows a schematic cross-sectional view of the V-groove for placing the untapered section of the high-index fiber in the method for fabricating the fiber-optic waveguide coupler of the present invention.

[0047] Figure 14(b) shows a schematic cross-sectional view of the tapered section of the high-index fiber located on the waveguide layer in the method for fabricating the fiber-optic waveguide coupler of the present invention.

[0048] Figure 15 Shown is a schematic diagram of the test device for the fiber-optic waveguide coupler of the present invention.

[0049] Figure 16(a) shows a schematic diagram of the mode field distribution of the fiber-optic waveguide coupler of the present invention simulated by simulation.

[0050] Figure 16(b) shows a schematic diagram of the mode field distribution corresponding to different positions of the fiber-waveguide coupler of the present invention in simulation.

[0051] Figure 17 Figure showing the transmission efficiency of the fiber-waveguide coupler of the present invention in simulation.

[0052] Description of component labels

[0053] 101 Silicon substrate

[0054] 102 Buried oxide layer

[0055] 103 Top silicon layer

[0056] 104 Waveguide layer

[0057] 1041 Tapered waveguide

[0058] 1042 First straight waveguide

[0059] 1043 Bending waveguide

[0060] 1044 Second straight waveguide

[0061] 105 Groove

[0062] 106 First multimode fiber

[0063] 107 High-index fiber

[0064] 1071 Untapered section

[0065] 1072 Tapered transition section

[0066] 1073 Tapered section

[0067] 108 Fusion joint

[0068] 109 Grating coupler

[0069] 110 Second multimode fiber

[0070] 111 Light source

[0071] 112 First power meter

[0072] 113 Second power meter

[0073] Steps S1 to S6 Detailed implementation manners

[0074] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand the other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0075] Please refer to Figures 1 to 17 . It should be noted that the diagrams provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner. Therefore, only the components related to the present invention are shown in the diagrams, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0076] Embodiment 1

[0077] This embodiment provides a method for manufacturing an optical fiber - waveguide coupler. Please refer to Figure 1 , which shows the process flow chart of this method, including the following steps:

[0078] S1: Provide a SOI substrate, where the SOI substrate includes a silicon substrate, a buried oxide layer, and a top silicon layer stacked in sequence from bottom to top;

[0079] S2: Pattern the top silicon layer to obtain a waveguide layer, and the waveguide layer includes a tapered waveguide;

[0080] S3: Form a groove in the silicon substrate, and at least one of the grooves is located in front of the initial end of the tapered waveguide and is spaced from the tapered waveguide by a preset distance;

[0081] S4: Provide a first multimode optical fiber and a high - refractive - index optical fiber, and the refractive index of the high - refractive - index optical fiber is greater than the refractive index of the buried oxide layer;

[0082] S5: Align and fuse one end of the first multimode optical fiber with one end of the high - refractive - index optical fiber, and perform a tapering process on a preset section of the fused high - refractive - index optical fiber to obtain a tapered section. The diameter of the tapered section is smaller than the diameter of the non - tapered section of the high - refractive - index optical fiber, and the connection between the tapered section and the non - tapered section forms a tapered transition section;

[0083] S6: Fix the tapered section on the upper surface of the tapered waveguide, suspend the tapered transition section above the groove, and fix at least a part of the non - tapered section on the inner wall of the groove.

[0084] First, please refer to Figure 2, perform the step S1: Provide a SOI substrate, which includes a silicon substrate 101, a buried oxide layer 102, and a top silicon layer 103 stacked in sequence from bottom to top.

[0085] As an example, the method for forming the buried oxide layer 102 includes an oxidation method, an ion implantation method, or other suitable methods, and the material of the buried oxide layer 102 includes silicon oxide or other suitable materials. In this embodiment, silicon oxide material is used as the buried oxide layer 102.

[0086] Please refer to again Figure 3 , perform the step S2: Pattern the top silicon layer 103 to obtain a waveguide layer 104, and the waveguide layer 104 includes a tapered waveguide 1041.

[0087] Specifically, use photolithography and dry etching processes to pattern the top silicon layer 103 to obtain the waveguide layer 104.

[0088] As an example, please refer to Figure 3 and Figure 4 , the length L1 of the tapered waveguide 1041 ranges from 100 to 300 microns, the width W1 of the initial end of the tapered waveguide 1041 ranges from 160 to 250 nanometers, the width W2 of the termination end of the tapered waveguide 1041 ranges from 470 to 530 nanometers, and the height H wg of the tapered waveguide 1041 ranges from 190 to 250 nanometers to meet high-efficiency fiber-waveguide adiabatic coupling. Preferably, the width W1 of the initial end of the tapered waveguide 1041 is 200 nanometers, the width W2 of the termination end of the tapered waveguide 1041 is 500 nanometers, and the height H wg of the tapered waveguide 1041 is 220 nanometers to meet single TE mode transmission.

[0089] In an example, the waveguide layer 104 further includes a first straight waveguide 1042, a bent waveguide 1043, and a second straight waveguide 1044 connected in sequence, and the first straight waveguide 1042 is connected to the termination end of the tapered waveguide 1041.

[0090] Specifically, the waveguide layer 104 includes a tapered waveguide 1041, a first straight waveguide 1042, a bent waveguide 1043, and a second straight waveguide 1044 that are connected in sequence. The width W3 of the first straight waveguide 1042 is the same as the width W2 of the termination end of the tapered waveguide 1041 to match the tapered waveguide 1041. The bent waveguide 1043 is an S-shaped structure, and the waveguide of the S-shaped structure is composed of two identical arcs connected end to end. In this embodiment, the radius of the arc is greater than 30 microns to avoid bending loss and the influence of the evanescent field of the optical fiber. The value range of the central angle of the arc is 0° to 90° (including the end values). In this embodiment, it is preferably to use an arc with a central angle of 90° to form the S-shaped waveguide, but it is not limited thereto. In addition, in this embodiment, the length L2 of the first straight waveguide 1042 and the length L3 of the second straight waveguide 1044 can be selected according to actual needs and are not limited herein.

[0091] Please refer to again Figure 5 , perform the step S3: form a groove 105 in the silicon substrate 101, and at least one groove 105 is located in front of the initial end of the tapered waveguide 1041 and is spaced apart from the tapered waveguide 1041 by a preset distance.

[0092] Specifically, in this example, one groove 105 is provided at each of the initial end and the termination end of the tapered waveguide 1041, and the two grooves 105 are spaced apart from the tapered waveguide 1041 by a preset distance.

[0093] As an example, the method for forming the groove 105 includes mechanical cutting, photolithography and etching, or other suitable methods.

[0094] Please refer to again Figure 6 , perform the step S4: provide a first multimode optical fiber 106 and a high refractive index optical fiber 107, and the refractive index of the high refractive index optical fiber 107 is greater than the refractive index of the buried oxide layer 102.

[0095] Specifically, the refractive index of the high refractive index optical fiber 107 is greater than 1.5, which helps to effectively confine light inside the waveguide and reduce the leakage of light to the substrate.

[0096] As an example, the first multimode optical fiber 106 includes a multimode quartz optical fiber, and the high refractive index optical fiber 107 includes a sapphire optical fiber or a germanium dioxide optical fiber.

[0097] Please continue to refer to Figure 6 and Figure 7, perform the step S5: Align and fuse one end of the first multimode optical fiber 106 with one end of the high-refractive-index optical fiber 107, and perform a tapering process on a preset section of the fused high-refractive-index optical fiber 107 to obtain a tapered section 1073. The diameter of the tapered section 1073 is smaller than the diameter of the untapered section 1071 of the high-refractive-index optical fiber 107, and the connection between the tapered section 1073 and the untapered section 1071 forms a tapered transition section 1072.

[0098] Specifically, as Figure 6 shown, the fusion point 108 (i.e., the part where the optical fiber end faces contact and fuse) of the high-refractive-index optical fiber 107 and the first multimode optical fiber 106 includes a tapered structure, and the length L s of the tapered structure ranges from 40 to 100 micrometers. By controlling the structure and shape of the fusion point 108, the fusion quality is ensured, and the influence of fusion on the mode field loss during the mode conversion process is reduced.

[0099] As an example, the fusion method of the high-refractive-index optical fiber 107 and the first multimode optical fiber 106 includes resistance wire heating fusion and discharge fusion.

[0100] Specifically, in one embodiment, a multimode quartz optical fiber is used as the first multimode optical fiber 106, and a sapphire optical fiber is used as the high-refractive-index optical fiber 107. A discharge fusion operation is performed by a Fujikura 88s type or other types of fusion equipment. The diameter range of the sapphire optical fiber is 60 to 100 micrometers to ensure the mode field matching with the multimode quartz optical fiber. Since the melting point of the sapphire optical fiber is higher than the glass transition temperature of the multimode quartz optical fiber, during discharge fusion, the discharge point should be appropriately offset from the fusion point 108, that is, located on the sapphire optical fiber side, to avoid damaging the multimode quartz optical fiber. Specifically, the distance L offset by which the discharge point is offset from the fusion point ranges from 20 to 100 micrometers to ensure the best fusion effect.

[0101] Specifically, in another embodiment, a multimode quartz optical fiber is used as the first multimode optical fiber 106, and a germanium dioxide optical fiber is used as the high-refractive-index optical fiber 107. The diameter range of the germanium dioxide optical fiber is 125 to 200 micrometers. Since the glass transition temperature of the germanium dioxide optical fiber is relatively low (340 °C), it is difficult to precisely control the fusion temperature using traditional low-discharge fusion. Therefore, a low-power heating method is required, that is, fusion is achieved by resistance wire heating. During the fusion process, an annular resistance wire surrounds the multimode quartz optical fiber to ensure that the heating point is appropriately offset from the fusion point 108. The distance L offsetThe range of is controlled within 1 to 3 mm, and the range of heating power is set within 2 to 3 W. This parameter setting can ensure that the multimode quartz optical fiber will not soften and sag due to overheating, and can also ensure that the germanium dioxide optical fiber reaches the required softening state. Subsequently, by moving the germanium dioxide optical fiber close to the multimode quartz optical fiber, when the two are close, the germanium dioxide optical fiber thermally expands and is bonded and fused with the multimode optical fiber.

[0102] As an example, the method for manufacturing the optical fiber-waveguide coupler of this embodiment further includes the following steps:

[0103] A second multimode optical fiber 110 is provided, and one end of the second multimode optical fiber 110 is aligned and fused with the other end of the high refractive index optical fiber 107. The second multimode optical fiber 110 serves as a test interface to facilitate connection with optical fiber testing equipment (not shown).

[0104] As an example, Figure 7 As shown, the diameter D1 of the tapered section 1073 is in the range of 2 to 3 microns to meet the adiabatic coupling of the optical fiber and the waveguide. The initial diameter of the tapered gradual section 1072 is determined by the selected high refractive index optical fiber 107. The length L of the tapered gradual section 1072 is taper The range is 200 to 250 microns to avoid mode conversion and light loss caused by too fast reduction in fiber diameter, ensuring effective transmission and coupling of optical signals.

[0105] Please see again Figure 8 and Figure 9 , execute step S6: fix the tapered section 1073 to the upper surface of the tapered waveguide 1041 , the tapered gradient section is suspended above the groove 105 , and at least a portion of the un-tapered section 1071 is fixed to the inner wall of the groove 105 .

[0106] Specifically, Figure 8 and Figure 9 As shown, the tapered section 1073 is fixed to the upper surface of the tapered waveguide 1041 and optically coupled with the tapered waveguide 1041 by bonding, and the tapered gradient section 1072 is suspended above the groove 105, effectively avoiding direct contact with the SOI substrate to cause mode loss.

[0107] Specifically, Figure 10(a) and 10(b)As shown, when the tapered section 1073 is directly attached to the tapered waveguide 1041, the highest coupling efficiency can be achieved. To ensure that the coupling loss does not exceed -1 dB, the range of the vertical offset ΔZ between the tapered waveguide 1041 and the tapered section 1073 should be controlled within 0 to 0.13 micrometers. In this embodiment, the tapered waveguide 1041 is directly attached to the tapered section 1073, and the vertical offset ΔZ is 0 micrometers.

[0108] Specifically, as Figure 11(a) and 11(b) shown, to ensure that the coupling loss does not exceed -3 dB, the range of the horizontal offset ΔX between the center line of the high refractive index optical fiber 107 and the center line of the tapered waveguide 1041 in the positive projection on the silicon substrate 101 is 0 to 0.05 micrometers. In this embodiment, the center line of the refractive index optical fiber coincides with the center line of the tapered waveguide 1041 in the positive projection on the silicon substrate 101, and the horizontal offset ΔX is 0 micrometers.

[0109] As an example, the range of the radius R1 of the tapered section 1073 is 1 to 1.5 micrometers. As Figure 12(a) and 12(b) shown, when the radius R1 of the tapered section 1073 is 2 micrometers, the coupling loss is still less than 1 dB. In this embodiment, the radius R1 of the tapered section 1073 is preferably 1.5 micrometers.

[0110] As an example, the tapered section 1073 is fixed to the SOI substrate by an ultraviolet curable adhesive, and the refractive index range of the ultraviolet curable adhesive is 1.1 to 1.7. Preferably, the refractive index range of the ultraviolet curable adhesive is 1.1 to 1.5. As Figure 13 shown, within this refractive index range, a low coupling loss can be maintained, effectively reducing the leakage of the mode field energy to the external environment due to too high refractive index of the external environment of the optical fiber, thereby avoiding the reduction of the coupling efficiency.

[0111] As an example, the groove 105 includes a V-groove, and the center line of the V-groove, the center line of the tapered waveguide 1041, and the center line of the high refractive index optical fiber 107 coincide in the positive projection on the silicon substrate 101 to achieve high-precision coupling alignment between the high refractive index optical fiber 107 and the tapered waveguide 1041.

[0112] Specifically, as Figure 14(a) and 14(b) shown, the depth of the V-groove is H v , and the width of the V-groove is W v, the apex angle of the V-groove is 2θ, where the value range of the apex angle 2θ of the V-groove is 30° to 150°. In this embodiment, the depth of the V-groove is determined by the diameter of the high-index fiber 107 to ensure that the fiber centers of the untapered section 1071 and the tapered section 1073 are aligned in height. Specifically, the radius of the untapered section 1071 is R, the radius of the tapered section 1073 is R1, the depth H of the V-groove v and the width W of the V-groove v satisfy the following relationship:

[0113]

[0114] Thus, an optical fiber-waveguide coupler is fabricated, and the optical fiber-waveguide coupler can operate at room temperature or low temperature (2.3K).

[0115] To evaluate the performance of the obtained optical fiber-waveguide coupler, a test device as Figure 15 shown is used to test the performance of the obtained optical fiber-waveguide coupler. The test device includes a light source 111 that emits a 1550-nm wavelength, a first power meter 112, and a second power meter 113. Among them, the light source 111 is connected to the other end of the first multimode fiber 106 to provide the optical signal required for testing. The first power meter 112 is connected to the structure of the waveguide layer 104 to measure the optical power after coupling. The second power meter 113 is connected to the other end of the second multimode fiber 110 and is used to measure the remaining optical power after coupling.

[0116] Specifically, as Figure 15As shown, the waveguide layer 104 includes a tapered waveguide 1041, a first straight waveguide 1042, a bent waveguide 1043, and a second straight waveguide 1044 connected in sequence. The tapered waveguide 1041 adiabatically couples light from the tapered section 1073 of the high-refractive-index optical fiber 107 into the waveguide layer 104. The light passes through the tapered waveguide 1041, the first straight waveguide 1042, and the bent waveguide 1043 and reaches the second straight waveguide 1044. The other end of the second straight waveguide 1044 is connected to a grating coupler 109, and the grating coupler 109 is precisely aligned through a standard optical fiber. Through the first power meter 112, the coupling efficiency of the fiber-waveguide coupler can be measured (i.e., the ratio of the optical power coupled into the waveguide layer 104 to the total optical power input into the first multimode optical fiber 106). At the same time, through the second multimode optical fiber 110 and the second power meter 113, the remaining output optical power after coupling can be tested (i.e., the optical power that is not coupled into the waveguide layer 104 but transmitted along the second multimode optical fiber 110) to evaluate the performance and possible losses of the fiber-waveguide coupler and ensure that the coupling efficiency of the fiber-waveguide coupler meets the design requirements.

[0117] To further verify the accuracy of the test device and the performance of the fiber-coupler, we simulated the mode field distribution and transmission characteristics of the fiber-waveguide coupler through simulation software. The simulation results are as Figure 16(a) and 16(b) shown. Figure 16(a) shows that as the transmission distance increases, the width of the tapered waveguide 1041 gradually increases, and the process of light adiabatically coupling from the tapered section 1073 of the high-refractive-index optical fiber 107 into the tapered waveguide 1041. Figure 16(b) shows the schematic diagrams of the mode field distributions corresponding to different positions ①②③④, reflecting different stages of the coupling between the high-refractive-index optical fiber 107 and the tapered waveguide 1041. As the transmission distance increases, the coupling efficiency of the fiber-waveguide coupler gradually increases. When the transmission distance reaches 275 micrometers, the coupling efficiency reaches a maximum value of 99.4%.

[0118] In addition, the simulation also provides information about the transmission bandwidth, as Figure 17 shown. The fiber-waveguide coupler has the highest coupling efficiency of 99.4% at a wavelength of 1550 nanometers. Moreover, the adoption of the adiabatic coupling design enables the -1dB bandwidth of the fiber-waveguide coupler to reach approximately 220 nanometers.

[0119] The manufacturing method of the fiber-optic waveguide coupler in this embodiment has a simple technological process. By splicing the first multimode fiber with a high-refractive-index fiber to form a gradient structure with specific dimensions, the mode conversion loss is effectively reduced, and efficient optical coupling is achieved. In addition, through the groove, the high-refractive-index fiber with different diameter segments after tapering treatment is accurately fixed on the SOI substrate, ensuring high-precision alignment and adiabatic coupling between the high-refractive-index fiber and the tapered waveguide. This not only effectively avoids the leakage of the optical field of the fiber to the substrate during the optical coupling process, but also improves the coupling efficiency and bandwidth of the fiber-optic waveguide coupler, expands the application of the fiber-optic waveguide coupler in a low-temperature environment, reduces the process cost, and improves the stability of the structure.

[0120] Embodiment 2

[0121] In this embodiment, an optical fiber-waveguide coupler is provided. The coupler can be fabricated by using the fabrication method described in Embodiment 1 or other suitable fabrication methods. Please refer to Figure 8 , which shows a schematic cross-sectional structure diagram of the fiber-optic waveguide coupler fabricated in this embodiment, including a silicon substrate 101, a buried oxide layer 102, and a waveguide layer 104 stacked in sequence from bottom to top, and including a groove 105, a high-refractive-index fiber 107, and a first multimode fiber 106. Among them, the waveguide layer 104 includes a tapered waveguide 1041; the groove 105 is located in the silicon substrate 101, and at least one groove 105 is located in front of the initial end of the tapered waveguide 1041 and is spaced a preset distance from the tapered waveguide 1041; the refractive index of the high-refractive-index fiber 107 is greater than that of the buried oxide layer 102. The high-refractive-index fiber 107 includes a non-tapered section 1071, a tapered gradient section 1072, and a tapered section 1073. The diameter of the tapered section 1073 is smaller than that of the non-tapered section 1071, and the connection between the tapered section 1073 and the non-tapered section 1071 constitutes the tapered gradient section 1072. Among them, the tapered section 1073 is fixed on the upper surface of the tapered waveguide 1041, the tapered gradient section is suspended above the groove 105, and at least a part of the non-tapered section 1071 is fixed on the inner wall of the groove 105; one end of the first multimode fiber 106 is aligned and spliced with one end of the high-refractive-index fiber 107.

[0122] As an example, the material of the buried oxide layer 102 includes silicon oxide or other suitable materials, and the material of the waveguide layer 104 includes silicon or other suitable materials. In this embodiment, silicon oxide material is used as the buried oxide layer 102, and silicon material is used as the waveguide layer 104.

[0123] As an example, the groove 105 includes a V-shaped groove. The center line of the V-shaped groove, the center line of the tapered waveguide 1041, and the center line of the high refractive index optical fiber 107 coincide in the orthographic projection on the silicon substrate 101, so as to achieve high-precision coupling alignment between the high refractive index optical fiber 107 and the tapered waveguide 1041.

[0124] Specifically, the range of the horizontal offset ΔX between the center line of the high refractive index optical fiber 107 and the center line of the tapered waveguide 1041 in the orthographic projection on the silicon substrate 101 is 0 to 0.05 micrometers. In this embodiment, the center line of the refractive index optical fiber coincides with the center line of the tapered waveguide 1041 in the orthographic projection on the silicon substrate 101, and the horizontal offset ΔX is 0 micrometers.

[0125] Specifically, one groove 105 is provided at each of the initial end and the termination end of the tapered waveguide 1041, and the two grooves 105 are spaced apart from the tapered waveguide 1041 by a preset distance.

[0126] As an example, the length L1 of the tapered waveguide 1041 ranges from 100 to 300 micrometers, the width W1 of the initial end of the tapered waveguide 1041 ranges from 160 to 250 nanometers, the width W2 of the termination end of the tapered waveguide 1041 ranges from 470 to 530 nanometers, and the height H of the tapered waveguide 1041 wg ranges from 190 to 250 nanometers to meet the requirements of high-efficiency fiber-waveguide adiabatic coupling. Preferably, the width W1 of the initial end of the tapered waveguide 1041 is 200 nanometers, the width W2 of the termination end of the tapered waveguide 1041 is 500 nanometers, and the height H of the tapered waveguide 1041 wg is 220 nanometers to meet the requirements of single TE mode transmission.

[0127] In one example, the waveguide layer 104 further includes a first straight waveguide 1042, a bent waveguide 1043, and a second straight waveguide 1044 that are connected in sequence, and the first straight waveguide 1042 is connected to the termination end of the tapered waveguide 1041.

[0128] Specifically, the width W3 of the first straight waveguide 1042 is the same as the width W2 of the termination end of the tapered waveguide 1041 to match the tapered waveguide 1041. The bent waveguide 1043 is an S-shaped structure, and the waveguide of the S-shaped structure is composed of two identical arcs connected end to end. In this embodiment, the radius of the arc is greater than 30 micrometers to avoid bending loss and the influence of the evanescent field of the optical fiber. The value range of the central angle of the arc is 0° to 90° (including the end values). In this embodiment, the S-shaped waveguide formed by an arc with a central angle of 90° is preferably selected, but it is not limited thereto. In addition, in this embodiment, the length L2 of the first straight waveguide 1042 and the length L3 of the second straight waveguide 1044 can be selected according to actual needs and are not limited herein.

[0129] As an example, the first multimode optical fiber 106 includes a multimode quartz optical fiber, and the high refractive index optical fiber 107 includes a sapphire optical fiber or a germanium dioxide optical fiber.

[0130] As an example, the fusion joint 108 between the high refractive index optical fiber 107 and the first multimode optical fiber 106 includes a tapered structure, and the length L s of which ranges from 40 to 100 micrometers. By controlling the structure and shape of the fusion joint 108, the fusion splicing quality is ensured, and the influence of the fusion splicing on the mode field loss during the mode conversion process is reduced.

[0131] As an example, the length L taper of the tapered transition section 1072 ranges from 200 to 250 micrometers to avoid mode conversion and optical loss caused by the too rapid reduction of the optical fiber diameter, ensure the effective transmission and coupling of the optical signal, and the initial diameter of the tapered transition section 1072 is determined by the selected high refractive index optical fiber 107. The diameter D1 of the tapered section 1073 ranges from 2 to 3 micrometers to meet the adiabatic coupling of the optical fiber - waveguide.

[0132] As an example, the vertical offset ΔZ between the tapered waveguide 1041 and the tapered section 1073 ranges from 0 to 0.13 micrometers. In this embodiment, the tapered waveguide 1041 is directly attached to the tapered section 1073, and the vertical offset ΔZ is 0 micrometers to achieve the highest coupling efficiency.

[0133] As an example, the radius R1 of the tapered section 1073 ranges from 1 to 1.5 micrometers. In this embodiment, the radius R1 of the tapered section 1073 is preferably 1.5 micrometers.

[0134] As an example, the tapered section 1073 is fixed to the SOI substrate by an ultraviolet curable adhesive, and the refractive index range of the ultraviolet curable adhesive is 1.1 to 1.7. Preferably, the refractive index range of the ultraviolet curable adhesive is 1.1 to 1.5. Within this refractive index range, a lower coupling loss can be maintained, effectively reducing the leakage of the mode field energy to the external environment caused by too high refractive index of the external environment of the optical fiber, thereby avoiding the reduction of the coupling efficiency.

[0135] As an example, the fiber-waveguide coupler further includes a second multimode optical fiber 110. One end of the second multimode optical fiber 110 is aligned and fusion spliced with the other end of the high refractive index optical fiber 107. The second multimode optical fiber 110 serves as a test interface for facilitating the connection of optical fiber test equipment.

[0136] Specifically, the fiber-waveguide coupler can operate at room temperature or low temperature (2.3K).

[0137] Specifically, the simulated coupling efficiency of the fiber-waveguide coupler at a wavelength of 1550 nm reaches 99.4%, and the -1dB bandwidth reaches about 220 nm.

[0138] For the fiber-waveguide coupler of this embodiment, the high refractive index optical fiber that is fusion spliced with the first multimode optical fiber and subjected to tapering treatment is precisely fixed to the SOI substrate through a groove, realizing high-precision alignment with the tapered waveguide. Further, the tapered section of the high refractive index optical fiber is in close contact with the tapered waveguide for optical coupling, ensuring adiabatic coupling transmission of light and significantly improving the coupling efficiency. At a wavelength of 1550 nm, the simulated coupling efficiency of this fiber-waveguide coupler is as high as 99.4%, and the -1dB bandwidth is about 220 nm, showing excellent broadband performance. In addition, this fiber-waveguide coupler is simple to manufacture and has a low cost, and has the characteristics of insensitivity to position and less influence by mechanical vibration, ensuring the reliability and stability in practical applications. Moreover, this fiber-waveguide coupler can operate stably in a low-temperature environment of 2.3K and has good low-temperature performance.

[0139] In summary, the fiber-waveguide coupler and its manufacturing method of the present invention form a gradient structure with specific dimensions by fusing the first multimode fiber with a high refractive index fiber, effectively reducing the mode conversion loss. At the same time, the tapered high refractive index fiber is fixed on the SOI substrate through the groove technology, realizing the high-precision alignment and adiabatic coupling between the high refractive index fiber and the tapered waveguide, significantly improving the coupling efficiency and bandwidth. At a wavelength of 1550 nm, the simulated coupling efficiency of the fiber-waveguide coupler of the present invention is as high as 99.4%, and the -1dB bandwidth is about 220 nm. The manufacturing process of the fiber-waveguide coupler of the present invention is simple and low-cost, without the need for expensive 3D printing technology or waveguide suspension design, has excellent structural stability, is insensitive to position changes, and can resist mechanical vibration. In addition, the fiber-waveguide coupler of the present invention can operate stably in a low-temperature environment of 2.3K, has good low-temperature performance, and is suitable for optical coupling applications in low-temperature environments, such as being used in cooperation with devices such as waveguide-type superconducting single-photon detectors and low-temperature quantum dots. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0140] The above embodiments are only illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A manufacturing method of an optical fiber - waveguide coupler, characterized in that Including the following steps: Providing a SOI substrate, which includes a silicon substrate, a buried oxide layer, and a top silicon layer stacked in sequence from bottom to top; Patterning the top silicon layer to obtain a waveguide layer, and the waveguide layer includes a tapered waveguide; Forming a groove in the silicon substrate, and at least one of the grooves is located in front of the initial end of the tapered waveguide and is spaced a preset distance from the tapered waveguide; Providing a first multimode optical fiber and a high refractive index optical fiber, and the refractive index of the high refractive index optical fiber is greater than the refractive index of the buried oxide layer; Aligning and fusion splicing one end of the first multimode optical fiber with one end of the high refractive index optical fiber, and performing a tapering process on a preset section of the fused high refractive index optical fiber to obtain a tapered section, the diameter of the tapered section is smaller than the diameter of the untapered section of the high refractive index optical fiber, the connection between the tapered section and the untapered section constitutes a tapered transition section, the length range of the tapered transition section is 200 - 250 microns, the diameter range of the tapered section is 2 - 3 microns, and the fusion splicing point of the high refractive index optical fiber and the first multimode optical fiber includes a tapered structure, the length range of the tapered structure is 40 - 100 microns; Fixing the tapered section on the upper surface of the tapered waveguide, suspending the tapered transition section above the groove, and fixing at least a part of the untapered section on the inner wall of the groove; 2. The manufacturing method of the optical fiber-waveguide coupler according to claim 1, wherein: The fusion splicing method of the high refractive index optical fiber and the first multimode optical fiber includes resistance wire heating fusion splicing and discharge fusion splicing; 3. The manufacturing method of the optical fiber-waveguide coupler according to claim 1, characterized in that: The groove includes a V-shaped groove, and the center line of the V-shaped groove, the center line of the tapered waveguide, and the center line of the high refractive index optical fiber coincide in the orthographic projection on the silicon substrate; 4. The manufacturing method of the optical fiber-waveguide coupler according to claim 1, characterized in that: The tapered section is fixed on the SOI substrate through an ultraviolet curable adhesive, and the refractive index range of the ultraviolet curable adhesive is 1.1 - 1.7; 5. The manufacturing method of the optical fiber-waveguide coupler according to claim 1, wherein Further including the following steps: Providing a second multimode optical fiber, aligning and fusion splicing one end of the second multimode optical fiber with the other end of the high refractive index optical fiber, and the second multimode optical fiber serves as a test interface for facilitating connection to an optical fiber test device; 6. An optical fiber-waveguide coupler, characterized in that, Including: A silicon substrate, a buried oxide layer, and a waveguide layer stacked in sequence from bottom to top, and the waveguide layer includes a tapered waveguide; A groove located in the silicon substrate, and at least one of the grooves is located in front of the initial end of the tapered waveguide and is spaced a preset distance from the tapered waveguide; A high refractive index optical fiber, the refractive index of the high refractive index optical fiber is greater than the refractive index of the buried oxide layer, the high refractive index optical fiber includes an untapered section, a tapered transition section, and a tapered section, the diameter of the tapered section is smaller than the diameter of the untapered section, the connection between the tapered section and the untapered section constitutes a tapered transition section, the length range of the tapered transition section is 200 - 250 microns, the diameter range of the tapered section is 2 - 3 microns, wherein the tapered section is fixed on the upper surface of the tapered waveguide, the tapered transition section is suspended above the groove, and at least a part of the untapered section is fixed on the inner wall of the groove; A first multimode optical fiber, one end of the first multimode optical fiber is aligned and fusion spliced with one end of the high refractive index optical fiber, a fusion splicing point of the high refractive index optical fiber and the first multimode optical fiber includes a tapered structure, and a length range of the tapered structure is 40 to 100 micrometers.

7. The optical fiber-waveguide coupler according to claim 6, wherein: The groove includes a V-shaped groove, and a positive projection on the silicon substrate of a center line of the V-shaped groove, a center line of the tapered waveguide, and a center line of the high refractive index optical fiber coincide.

8. The optical fiber - waveguide coupler according to claim 6, characterized in that, Further included: A second multimode optical fiber, one end of the second multimode optical fiber is aligned and fusion spliced with the other end of the high refractive index optical fiber, and the second multimode optical fiber serves as a test interface to facilitate connection of an optical fiber test device.

9. The optical fiber - waveguide coupler according to claim 6, characterized in that: A length range of the tapered waveguide is 100 to 300 micrometers, a width range of an initial end of the tapered waveguide is 160 to 250 nanometers, and a width range of a termination end of the tapered waveguide is 470 to 530 nanometers.

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