An end coupler suitable for large-size single-mode optical fiber and a preparation method thereof

Abstract

The invention discloses an end face coupler suitable for large-size single-mode optical fiber and a preparation method thereof, wherein a first refractive index layer covers a substrate; a second refractive index layer extends along a first direction, one end of which is located at a second end face and has a "convex"-shaped cross section, and the other end covers a part of the first refractive index layer and has a trapezoidal or rectangular cross section, and the thickness of the second refractive index layer gradually increases along the direction from the first end face to the second end face; a third refractive index layer extends from the first end face to the second end face; the third refractive index layer includes two continuous sections, the first section structure covers a part of the first refractive index layer and has a gradually increasing width, and the second section structure covers a strip region and a ridge region of the second refractive index layer; a fourth refractive index layer covers the third refractive index layer; light is gradually coupled from the fourth refractive index layer and the third refractive index layer into the second refractive index layer for transmission, and is suitable for energy coupling between large-size single-mode optical fiber and on-chip optical waveguide, and has high coupling conversion efficiency and low alignment accuracy requirements.

Description

Technical Field

[0001] The embodiments of the present invention relate to the technical field of end couplers, and in particular to an end coupler suitable for large-size single-mode optical fibers and a preparation method thereof. Background Art

[0002] Currently, the two commonly used methods of coupling light to the chip are end-face coupling and grating coupling. Compared with grating coupling, end-face coupling has the advantages of large working bandwidth, high coupling efficiency, polarization insensitivity and easy packaging.

[0003] However, the end couplers reported at this stage still have some problems, such as small mode field area and low coupling efficiency for large-sized ordinary single-mode optical fibers. How to improve the coupling efficiency of large-sized single-mode optical fibers is a technical problem that needs to be solved urgently. In addition, the end couplers reported have complex preparation processes, which are not conducive to batch preparation; small preparation tolerances, and high requirements for the precision of the preparation process. Summary of the invention

[0004] The present invention provides an end face coupler suitable for large-size single-mode optical fiber and a preparation method thereof. The end face coupler is suitable for light beam coupling between an optical chip and a large-size single-mode optical fiber and has a high coupling conversion efficiency.

[0005] In a first aspect, the present application provides an end coupler suitable for a large-size single-mode optical fiber, comprising a substrate, a first refractive index layer, a second refractive index layer, a third refractive index layer and a fourth refractive index layer arranged in sequence; the end coupler comprises a first end face and a second end face;

[0006] The first refractive index layer covers the substrate;

[0007] The second refractive index layer extends along the first direction, one end of which is located at the second end face and is a ridge-shaped region with a "convex"-shaped cross section; the other end covers part of the first refractive index layer and is a strip-shaped region with a trapezoidal or rectangular cross section, and the thickness of the second refractive index layer gradually increases along the first direction; wherein the first direction is the direction from the first end face to the second end face;

[0008] The third refractive index layer extends from the first end surface to the second end surface; the third refractive index layer includes two continuous sections, the first section structure covers a portion of the first refractive index layer, and the second section structure covers the stripe region and the ridge region of the second refractive index layer; along the first direction, the width of the first section structure gradually increases;

[0009] The fourth refractive index layer covers the third refractive index layer;

[0010] The refractive index of the first refractive index layer is n1, the refractive index of the second refractive index layer is n2, the refractive index of the third refractive index layer is n3, and the refractive index of the fourth refractive index layer is n4;

[0011] n1<n4<n3<n2.

[0012] Optionally, the thickness of the stripe-shaped region and the ridge-shaped region of the second refractive index layer ranges from 0 nm to 1 μm; the width of the top of the stripe-shaped region and the ridge-shaped region of the second refractive index layer ranges from 0.1 μm to 2 μm.

[0013] Optionally, the width of the first section structure is W1, and the width of the second section structure is W2, wherein 0.1 μm≤W1≤W2≤4 μm.

[0014] Optionally, along the first direction, the width of the second section structure remains unchanged or gradually increases.

[0015] Optionally, along the first direction, the length of the first section structure is L1, and the length of the second section structure is L2, wherein the value range of L1 is 100 μm~2000 μm, and the value range of L2 is 100 μm~2000 μm.

[0016] Optionally, the thickness of the third refractive index layer ranges from 0.05 μm to 1 μm.

[0017] Optionally, the fourth refractive index layer has a width ranging from 10 μm to 20 μm, and a thickness ranging from 6 μm to 20 μm.

[0018] Optionally, the thickness of the first refractive index layer is at least 1 μm.

[0019] Based on the same inventive concept, in a second aspect, the present application further provides a method for preparing an end face coupler suitable for a large-size single-mode optical fiber, which is used to prepare the end face coupler provided in the first aspect, wherein the end face coupler comprises a first end face and a second end face; the preparation method comprises:

[0020] providing a substrate;

[0021] preparing a first refractive index layer on one side of the substrate;

[0022] A second refractive index layer is prepared on the surface of the first refractive index layer away from the substrate; the second refractive index layer extends along the first direction, one end of which is located at the second end face, is a ridge-shaped region, and has a "convex"-shaped cross section; the other end covers part of the first refractive index layer, is a strip-shaped region, and has a trapezoidal or rectangular cross section; the thickness of the second refractive index layer gradually increases along the first direction; wherein the first direction is the direction from the first end face to the second end face;

[0023] From the first end face to the second end face, a third refractive index layer is prepared on the surface of the stripe-shaped region and the ridge-shaped region of the second refractive index layer and part of the first refractive index layer; the third refractive index layer includes two continuous sections, the first section structure covers part of the first refractive index layer and the width gradually increases, and the second section structure covers the stripe-shaped region and the ridge-shaped region of the second refractive index layer; along the first direction, the width of the first section waveguide gradually increases;

[0024] Preparing a fourth refractive index layer on a surface of the third refractive index layer away from the substrate;

[0025] The refractive index of the first refractive index layer is n1, the refractive index of the second refractive index layer is n2, the refractive index of the third refractive index layer is n3, and the refractive index of the fourth refractive index layer is n4;

[0026] n1<n4<n3<n2.

[0027] In summary, the end face coupler suitable for large-size single-mode optical fiber provided in the present application improves the coupling efficiency of the optical fiber to the fourth and third refractive index layers by setting the fourth refractive index layer to cover the third refractive index layer; the width of the first section structure of the third refractive index layer is gradually increased, thereby improving the coupling conversion efficiency of light from the fourth refractive index layer to the third refractive index layer; the second section structure of the third refractive index layer is set to cover the second refractive index layer, and the second refractive index layer extends in the direction from the first end face to the second end face and the thickness gradually increases, which is conducive to the gradual coupling of light from the third refractive index layer into the second refractive index layer for transmission; by reasonably setting the structural dimensions of each refractive index layer to match the energy coupling between the large-size single-mode optical fiber and the on-chip optical waveguide, a higher coupling conversion efficiency and a lower alignment accuracy requirement are obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic structural diagram of an end coupler applicable to large-size single-mode optical fibers provided in the present application;

[0029] Figure 2 yes Figure 1 A side cross-sectional view of an end coupler for large-size single-mode optical fibers provided in;

[0030] Figure 3 yes Figure 1The top view of the end coupler provided in the figure and the cross-sectional views of the optical fiber at the CS1 section, CS2 section, CS3 section, CS4 section, CS5 section, and CS6 section and their corresponding mode field diagrams;

[0031] Figure 4 The test diagram of mode field overlap between silica and optical fiber of different sizes;

[0032] Figure 5 The test diagram of mode field overlap between silicon oxynitride and optical fiber of different sizes;

[0033] Figure 6 Schematic diagram of the change of coupling efficiency from silicon dioxide to silicon oxynitride in TE0 mode with interaction length;

[0034] Figure 7 is the interaction field diagram between silicon dioxide and silicon oxynitride;

[0035] Figure 8 Schematic diagram of the change of coupling efficiency from silicon oxynitride to lithium niobate in TE0 mode with interaction length;

[0036] Fig. 9 This is the interaction field diagram from silicon oxynitride to lithium niobate;

[0037] Fig.10 The effect of fiber center offset on coupling loss;

[0038] Fig.11 The effect of fabrication deviation of silicon dioxide waveguide and silicon oxynitride waveguide under different boundary conditions on coupling loss;

[0039] Fig.12 The device bandwidth of the end coupler provided for this application;

[0040] Fig.13 It is a schematic diagram of the preparation process of the end coupler suitable for large-size single-mode optical fiber provided by the present application;

[0041] Fig.14 It is a schematic diagram of a method for preparing an end coupler suitable for large-size single-mode optical fiber provided in the present application. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below in conjunction with the accompanying drawings and examples. It is understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings. It is obvious to those skilled in the art that various modifications and changes can be made in the present invention without departing from the spirit or scope of the present invention. Therefore, the present invention is intended to cover modifications and changes of the present invention that fall within the scope of the corresponding claims (technical solutions claimed for protection) and their equivalents. It should be noted that the implementation methods provided in the embodiments of the present invention can be combined with each other without contradiction.

[0043] The present invention proposes an end face coupler in view of one or more of the above problems existing in the prior art. Figure 1 It is a schematic structural diagram of an end coupler applicable to large-size single-mode optical fibers provided in the present application; Figure 2 yes Figure 1 A side cross-sectional view of an end coupler for large-size single-mode optical fibers provided in; Figure 3 yes Figure 1 The top view of the end coupler provided in the figure and the cross-sectional views of the optical fiber at the CS1 section, CS2 section, CS3 section, CS4 section, CS5 section, and CS6 section and their corresponding mode field diagrams. Figure 1-Figure 3 As shown, in order to solve the problem that the end face coupler of the traditional optical waveguide structure cannot meet the coupling requirements of the large mode field diameter optical fiber, the embodiment of the present application provides an end face coupler suitable for large-size single-mode optical fiber, including a substrate 10, a first refractive index layer 20, a second refractive index layer 30, a third refractive index layer 40 and a fourth refractive index layer 50 arranged in sequence; the refractive index of the first refractive index layer 20 is n1, the refractive index of the second refractive index layer 30 is n2, the refractive index of the third refractive index layer 40 is n3, and the refractive index of the fourth refractive index layer 50 is n4, n1<n4<n3<n2.

[0044] The end face coupler includes a first end face M1 and a second end face M2; the first refractive index layer 20 covers the substrate 10; the second refractive index layer 30 is located on the side of the first refractive index layer 20 away from the substrate 10, extends along the first direction (X direction in the figure) and the thickness gradually increases, one end of which is located on the second end face M2, is a ridge region 32, and has a "convex" cross section; the other end covers part of the first refractive index layer 20, is a strip region 31, and has a trapezoidal or rectangular cross section; wherein the first direction X is the direction from the first end face M1 to the second end face M2. The third refractive index layer 40 extends from the first end face M1 to the second end face M2; the third refractive index layer 40 includes two continuous sections, the first section structure 41 covers part of the first refractive index layer 20, the width gradually increases, and the second section structure 42 covers the strip region 31 and the ridge region 32 of the second refractive index layer 30; the fourth refractive index layer 50 covers the third refractive index layer 40.

[0045] At present, for the 1550 nm band, single-mode optical fibers with a mode field diameter of 9 μm to 11 μm are generally referred to as large mode field diameter optical fibers, i.e., large-size single-mode optical fibers. As an example, the present application embodiment takes the preparation of an end coupler of a single-mode optical fiber with an operating wavelength of 1550 nm, a numerical aperture NA of 0.14, a mode field diameter of (10.4±0.5) μm, and a cladding diameter of 125 μm as an example for explanation.

[0046] For example, refer to Figure 1~Figure 2 As shown, the substrate 10 can be made of Si material, the first refractive index layer 20 is made of silicon dioxide (SiO2), and the refractive index n1 ranges from 1.43 to 1.45; the second refractive index layer 30 is made of lithium niobate waveguide (LN), and the refractive index n2 ranges from 2.20 to 2.22; the third refractive index layer 40 is made of silicon oxynitride waveguide (SiON), and the refractive index n3 ranges from 1.5 to 1.7; the fourth refractive index layer 50 is made of silicon dioxide (SiO2), and the refractive index n4 ranges from 1.46 to 1.48, wherein n2>n3>n4>n1.

[0047] Among them, lithium niobate film is a performance-rich optical platform with excellent properties such as high birefringence efficiency, high second-order nonlinear coefficient, high electro-optic coefficient, and wide light transmission window, and has been widely used in the field of optical communications. This embodiment of the application takes lithium niobate material as an example and proposes a low-loss end coupler suitable for large-size single-mode optical fibers.

[0048] Specifically, refer to Figure 1~Figure 3As shown, the end coupler has a first end face M1 and a second end face M2. The shape of the cross section of the end coupler can be "convex" or other types, as long as it matches the size of the optical fiber output end. The embodiment of the present application does not impose any specific restrictions. The optical fiber output end can be coupled and docked with the first end face M1. The light beam is coupled by the end coupler and output from the second end face M2. The coupling process of the light beam is as follows:

[0049] First stage coupling: The light beam is coupled to the silicon oxynitride layer via an optical fiber.

[0050] Exemplarily, the third refractive index layer 40 is a transition material, and a silicon oxynitride structure with a thickness of 0.4 μm, a width of 0.7 μm, and a refractive index n3 of 1.62 can be used. The fourth refractive index layer 50 is an outer covering material, and a silicon dioxide SiO2 with a thickness of 12 μm and a width of 15 μm can be used. The refractive index n4 of silicon dioxide SiO2 is selected to be less than the refractive index n3 of silicon oxynitride SiON. The combination of silicon oxynitride SiON and silicon dioxide SiO2 can well bind light, and the overall refractive index is close to the core of the optical fiber. Its mode volume is close to the mode volume corresponding to a single-mode optical fiber with a core diameter of (10.4±0.5) μm and a cladding diameter of 125 μm, and the light emitted from the optical fiber can be effectively coupled from the fourth refractive index layer 50 to the third refractive index layer 40.

[0051] Furthermore, if Figure 2 As shown, along the X direction in the figure, the third refractive index layer 40 is composed of a continuous first section structure 41 and a second section structure 42. The first section structure 41 interacts with part of the first refractive index layer 20 and the fourth refractive index layer 50. Since n2>n3>n4>n1, the light beam is confined to the first section structure 41 with a high refractive index for transmission; the second section structure 42 interacts with the strip area 31 and the ridge area 32 of the second refractive index layer 30, and the light beam is coupled from the second section structure 42 to the strip area 31 and the ridge area 32 of the second refractive index layer 30 with a high refractive index.

[0052] Furthermore, combined with Figure 3As shown, the width W1 of the first section structure 41 in the second direction (i.e., the y direction) in the figure is gradually designed; along the X direction in the figure, the width W1 of the first section structure 41 in the y direction in the figure is set to gradually increase, and the width W2 of the second section structure 42 in the y direction in the figure can remain unchanged or also gradually increase. For example, the width W2 of the second section structure 42 is set to 1.5 μm, and the width W1 of the first section structure 41 in the y direction in the figure gradually widens from 0.7 μm to the same as the width W2 (1.5 μm) of the second section structure 42. By gradually setting the width W1 of the first section structure 41, the TE0 (transverse mode) and TM0 (longitudinal mode) modes in the optical fiber can be coupled to the waveguide fundamental mode corresponding to the refractive index structure (silicon oxynitride SiON). Among them, the gradient length L1 of the first section structure 41 can be 1000 μm.

[0053] Second stage coupling: The beam is coupled from the silicon oxynitride layer to the lithium niobate layer

[0054] Specific, combined Figure 2 and Figure 3 As shown, the second refractive index layer 30 is composed of a strip region 31 and a ridge region 32, and its material can be a lithium niobate waveguide (LN). The second refractive index layer 30 can also include a coupling plate layer 33, which is a part of the ridge region 32. Figure 3 The planar layer structure shown in the figure is used to connect the first refractive index layer 20 and fix the stripe region 31 and the ridge region 32 of the second refractive index layer 30. The stripe region 31 and the ridge region 32 of the second refractive index layer 30 extend along the X direction in the figure, one end of which is located at the second end surface M2, and the other end covers a part of the first refractive index layer 20; Figure 2As shown, along the X direction in the figure, the width of the strip region 31 and the ridge region 32 of the second refractive index layer 30 in the y direction in the figure is set to remain unchanged, and the thickness h1 of the strip region 31 and the ridge region 32 of the second refractive index layer 30 in the Z direction in the figure is gradually increased. The overlapping slope region P of the strip region 31 and the ridge region 32 of the second refractive index layer 30 and the second section structure 42 is an interaction region, and the third refractive index layer 40 and the second refractive index layer 30 (lithium niobate waveguide) perform energy transfer at the slope. By gradually changing the thickness design of the strip region 31 and the ridge region 32 (lithium niobate waveguide LN) of the second refractive index layer 30, the requirements for the etching accuracy of the photolithography machine can be reduced, and the complexity of the preparation can be reduced; at the same time, by adjusting the thickness h1 of the strip region 31 and the ridge region 32 (lithium niobate waveguide LN) of the second refractive index layer 30, the interaction slope length of the strip region 31 and the ridge region 32 of the second refractive index layer 30 and the second section structure 42 can be controlled. For example, the silicon oxynitride SiON in contact with lithium niobate LN is set to have a width of 1.5 μm in the y direction in the figure and a thickness of 0.4 μm in the z direction in the figure; the lithium niobate waveguide in the contacting part is gradually thinned from a thickness of 600 nm to 0-100 nm, and the width in the y direction in the figure is 0.6 μm or gradually increased, and the length L2 of the gradient part is 700 μm. By gradually designing the thickness of the strip region 31 and the ridge region 32 of the second refractive index layer 30, the mode volume in the lithium niobate waveguide can be increased, so that it matches the mode in the silicon oxynitride waveguide, and the light field in the silicon oxynitride waveguide is efficiently coupled to the lithium niobate waveguide.

[0055] Specifically, taking the TE0 fundamental mode as an example, the TE0 mode in the optical fiber is coupled to the third refractive index layer 40 (silicon oxynitride layer) with a similar mode spot size, and then the third refractive index layer 40 exchanges energy with the second refractive index layer 30 (lithium niobate layer) with a gradient thickness. Figure 4 and Figure 5 As shown, multiple cross sections (CS) of the end coupler and the beam mode field distribution at the cross section (CS) are cut. After testing and analysis, it can be obtained that the end coupler provided by the embodiment of the present application has a single-ended coupling loss of 0.70 dB for the fundamental mode TE0 of the lithium niobate waveguide and a single-ended coupling loss of 1.5 dB for TM0, thereby having a high end coupling efficiency. Among them, the CS1 section to the CS6 section can be the equidistant sections of the end coupler in the X direction, the CS1 section is the first end face M1 of the end coupler, and the CS6 section is the second end face M2 of the end coupler.

[0056] It should be noted that the widths of all refractive index layers in the embodiments of the present application can meet the photolithography machine preparation conditions commonly used in the industry, thereby greatly reducing the cost and time of preparation.

[0057] In some embodiments, Figure 2 As shown, the thickness h2 of the third refractive index layer 40 ranges from 0.05 μm to 1 μm.

[0058] Figure 4 The test diagram of mode field overlap between silica and optical fiber of different sizes; Figure 5 The figure is a test chart of the mode field overlap between silicon oxynitride and optical fiber of different sizes.

[0059] For example, continue to refer to Figure 1-Figure 3 As shown, the fourth refractive index layer 50 is made of silicon dioxide SiO2, the third refractive index layer 40 is made of silicon oxynitride SiON, and the TE0 mode field overlap is selected as the optimal value, referring to Figure 4 As shown, the fourth refractive index layer 50 is set to have a width scanning range of 10 μm to 18 μm in the y direction and a thickness scanning range of 8 μm to 16 μm in the z direction. Preferably, the optimal values ​​of the silicon dioxide SiO2 parameters are a thickness of 12 μm and a width of 15 μm.

[0060] Reference Figure 5 As shown, the influence of the width and thickness of the third refractive index layer 40 (silicon oxynitride layer) on the mode field overlap can be further explored. The width scanning range of the third refractive index layer 40 in the y direction is set to 0.5 μm~1 μm, and the thickness scanning range is set to 0.1 μm~0.6 μm. Figure 5 As shown in the figure, when the size of the silicon oxynitride structure is smaller, the mode field overlap between it and the optical fiber is higher, but it also means that less light is confined to the silicon oxynitride SiON structure. Tests have found that when too little light is confined to the silicon oxynitride structure, even if the interaction length L1 between silicon dioxide SiO2 and silicon oxynitride SiON is very long, it is difficult to ensure efficient mode conversion between the two. Therefore, the size of the silicon oxynitride SiON needs to be reasonably selected.

[0061] Optional, combined Figure 3 As shown, the width of the first section structure 41 is set to W1, and the width of the second section structure is set to W2, wherein 0.1 μm≤W1≤W2≤2 μm. Within this range, the width of the third refractive index layer 40 has a good limiting effect on the light field.

[0062] Optional, continue to refer to Figure 3 As shown, along the first direction X, the width W2 of the second section structure 42 remains unchanged or gradually increases.

[0063] Optional, continue to refer to Figure 3As shown, along the first direction X, the length of the first section structure 41 is L1, and the length of the second section structure 42 is L2, wherein the value range of L1 is 100 μm ~ 2000 μm, and the value range of L2 is 100 μm ~ 2000 μm. Optionally, the length L1 of the first section structure 41 is set to be in the range of 100 μm ~ 2000 μm, and the length L2 of the second section structure 42 is set to be in the range of 100 μm ~ 2000 μm. Within this range, the first section structure 41 (silicon oxynitride SiON) and the fourth refractive index layer 50 (silicon dioxide SiO2) have a higher energy conversion efficiency.

[0064] Optional, continue to refer to Figure 2 and Figure 3 As shown, the third refractive index layer 40 may further include a third section structure 43 connected to the second section structure 42. The width and thickness of the third section structure 43 may remain unchanged, and its length L3 may be set as required.

[0065] Figure 6 Schematic diagram of the change of coupling efficiency from silicon dioxide to silicon oxynitride in TE0 mode with the interaction length L1; Figure 7 is the interaction field diagram between silicon dioxide and silicon oxynitride; Figure 6 The horizontal axis is the interaction length (Length) between silicon dioxide and silicon oxynitride, unit: micrometer (μm), and the vertical axis is the coupling efficiency (Transmission, T); Figure 7 Figure (a) is a top view of TE0 mode coupling. Figure 7 Figure (b) shows the side view of TE0 mode coupling. Figure 1-Figure 3 , Figure 6 As shown, in order to ensure that the light in the silicon dioxide SiO2 is fully coupled to the silicon oxynitride SiON during the transition from the width W1 of the first section structure 41 to the width W2 of the second section structure 42, the starting width W1 of the first section structure 41 can be set to 0.7 μm, the tail width W2 to 1.5 μm, and the height to 400 nm. The interaction length between the first section structure 41 (silicon oxynitride SiON) and the fourth refractive index layer 50 (silicon dioxide SiO2) is L1. Figure 6 As shown in the figure, when the interaction length L1 between silicon oxynitride SiON and silicon dioxide SiO2 is 1000 μm or more, a conversion efficiency of 99% can be effectively achieved. Figure 7 As shown in FIG. 1 , when the interaction length L1 between silicon oxynitride SiON and silicon dioxide SiO2 is 1000 μm or more, the energy of TE0 in silicon dioxide SiO2 is almost completely transferred to silicon oxynitride SiON, with a high coupling conversion efficiency.

[0066] It should be noted that the coupling condition of the TM0 fundamental mode is similar to that of TE0 and will not be shown in detail here.

[0067] Furthermore, the mode field of the interaction portion between the silicon oxynitride SiON layer and the lithium niobate LN layer is similar to that of the optical fiber and the silicon oxynitride SiON layer. When the size parameters of the third refractive index layer 40 and the fourth refractive index layer 50 are determined, in order to further ensure efficient mode conversion between the third refractive index layer 40 and the second refractive index waveguide 30, it is necessary to further reasonably select the slope length L2 of the strip region 31 and the ridge region 32 (lithium niobate LN) of the second refractive index layer 30.

[0068] Optionally, the thickness of the stripe region 31 and the ridge region 32 of the second refractive index layer 30 is set to be in the range of 0-1 μm; the width of the top of the stripe region 31 and the ridge region 32 of the second refractive index layer 30 is in the range of 0.1 μm-2 μm.

[0069] Among them, refer to Figure 3 As shown, the contact length between the stripe region 31 and the ridge region 32 (lithium niobate LN) of the second refractive index layer 30 and the second segment structure 42 (silicon oxynitride SiON) of the third refractive index layer 40 is defined as the interaction length L2.

[0070] Figure 8 Schematic diagram of the change of coupling efficiency from silicon oxynitride to lithium niobate in TE0 mode with interaction length; Fig. 9 is the interaction field diagram from silicon oxynitride to lithium niobate; where, Figure 8 The middle horizontal axis is the interaction length (Length) between silicon oxynitride and lithium niobate, unit: micrometer (μm), and the vertical axis is the coupling efficiency (Transmission, T); Fig. 9 (a) is a top view of TE0 mode coupling, and (b) is a side view of TE0 mode coupling. Figure 1-Figure 3 and Figure 8 As shown, when the slope length L2 of lithium niobate LN is at least 700 μm, the TE0 mode of the strip region 31 and the ridge region 32 (lithium niobate LN) of the second refractive index layer 30 and the second segment structure 42 can achieve a coupling conversion efficiency of more than 98.75%. Figure 8 As shown, when the interaction length L2 between the strip region 31 and the ridge region 32 (lithium niobate LN) of the second refractive index layer 30 and the second segment structure 42 (silicon oxynitride SiON) is 700 μm or more, the energy of TE0 in the silicon oxynitride SiON is almost completely transferred to the lithium niobate LN, with a high coupling conversion efficiency.

[0071] In addition, in order to further ensure efficient coupling between the optical fiber and the third refractive index layer 40, it is necessary to further reasonably select the center offset of the core relative to the silicon oxynitride SiON, thereby reducing the influence of the core center offset on the coupling loss.

[0072] Optional, continue to refer to Figure 1-Figure 3 As shown, the fourth refractive index layer 50 is set to have a width ranging from 10 μm to 20 μm and a thickness ranging from 6 μm to 20 μm.

[0073] Fig.10 The effect of fiber center offset on coupling loss; Fig.11 The effect of the preparation deviation of silicon dioxide structure and silicon oxynitride structure under different boundary conditions on the coupling loss. Fig.10 The horizontal axis is the offset between the core center of the optical fiber and the optimal position of the first end face coupling efficiency (fiber offset), unit: micron (μm), and the vertical axis is the coupling loss (Loss), unit: dB. Fig.11 In the figure (a), the horizontal axis is the SiO2 offset. Fig.11 In the figure (b), the horizontal axis is the SiON layer preparation deviation (SiON offset).

[0074] Exemplary, reference Figure 1-Figure 3 , Fig.10 and Fig.11 As shown, taking the coupling efficiency of optical fiber and 12 μm *15 μm (on the yz plane) silicon oxynitride SiO2 structure as an example, Fig.10 As shown, by using the end face coupler provided in the embodiment of the present application, the influence of the optical fiber center offset on the coupling loss is small; Fig.11 As shown in Figure (a), when the silicon dioxide SiO2 structure is within the preparation deviation range of ±5μm, the end face coupler has only 4 dB loss as a whole, indicating that the preparation deviation of the silicon dioxide SiO2 structure has little effect on the overall loss of the device when using the end face coupler provided in the embodiment of the present application; Fig.11 As shown in Figure (b), when the silicon oxynitride SiON structure is within the preparation deviation range of ±1 μm, the overall loss fluctuation of the end coupler does not exceed 0.1 dB, indicating that the preparation deviation of the silicon oxynitride SiON structure has little effect on the overall loss of the device.

[0075] Fig.12 The device bandwidth of the end coupler provided in this application. Fig.12 In the figure, the horizontal axis is wavelength (Wavelength), unit: nanometer (nm); the vertical axis is coupling efficiency (Transmission, T). Fig.12As shown, when the wavelength is in the range of 1370 nm to 1600 nm, the coupling efficiency of the TE0 and TM0 modes is more than 90%, indicating that the end face coupler provided by the embodiment of the present application has a larger bandwidth as a whole.

[0076] In some embodiments, continue to refer to Figure 1-Figure 3 As shown, the thickness of the first refractive index layer 20 is at least 2 μm, which can prevent the light beam from being coupled into the substrate 10 through the first refractive index layer 20 .

[0077] In some embodiments, continue to refer to Figure 1-Figure 3 As shown, the first refractive index layer 20 and the fourth refractive index layer 50 can both be made of silicon dioxide SiO2 using different preparation processes, and the refractive index n1 of the first refractive index layer 20 is less than the refractive index n4 of the fourth refractive index layer 50 .

[0078] Based on the same inventive concept, the embodiment of the present application further provides a method for preparing an end coupler suitable for large-size single-mode optical fiber, which is used to prepare the end coupler provided in the above embodiment. Fig.13 It is a schematic diagram of the preparation process of the end coupler suitable for large-size single-mode optical fiber provided by the present application; Fig.14 Schematic diagram of the preparation method of the end coupler for large-size single-mode optical fiber provided by the present application. Fig.13 and Fig.14 As shown, the end face coupler includes a first end face M1 and a second end face M2. The preparation method of the end face coupler applicable to a large-size single-mode optical fiber provided in the embodiment of the present application includes:

[0079] S101. Provide a substrate.

[0080] S102, preparing a first refractive index layer on one side of the substrate.

[0081] Specifically, refer to Fig.13 As shown in FIG. 1 (a), a silicon wafer Si is used as a substrate 10, and a first refractive index layer 20 is prepared on the substrate 10. The first refractive index layer 20 is made of silicon dioxide SiO2.

[0082] S103, preparing a second refractive index layer on a surface of the first refractive index layer away from the substrate.

[0083] For details, please refer to Fig.13 As shown in FIG. 2 (a), a second refractive index structure layer 30' is formed on the surface of the first refractive index layer 20 away from the substrate 10, and the second refractive index structure layer 30' is made of lithium niobate LN; Fig.13 As shown in Figure (b), lithium niobate LN is partially removed to form a slope; Fig.13As shown in FIG. (c), lithium niobate LN is etched to form a strip region 31 and a ridge region 32 of the second refractive index layer 30, the strip region 31 and the ridge region 32 of the second refractive index layer 30 extend along the first direction X, one end of which is located at the second end surface M2, and the other end covers a portion of the first refractive index layer 20; Figure 2 As shown, along the X direction in the figure, the widths of the stripe-shaped regions 31 and the ridge-shaped regions 32 of the second refractive index layer 30 may remain unchanged or gradually increase, and the thickness h1 thereof may gradually increase.

[0084] S104, preparing a third refractive index layer on the stripe-shaped region and ridge-shaped region of the second refractive index layer and a portion of the surface of the first refractive index layer from the first end face to the second end face.

[0085] Specifically, refer to Fig.13 As shown in the middle (d) figure, along the X direction in the figure, the third refractive index layer 40 is prepared from the first end surface M1 to the second end surface M2 of the substrate 10. The third refractive index layer 40 uses silicon oxynitride SiON, and the third refractive index layer 40 is composed of a continuous first section structure 41 and a second section structure 42. Among them, the first section structure 41 covers part of the first refractive index layer 20, and the second section structure 42 covers the strip area 31 and the ridge area 32 of the second refractive index layer 30; along the first direction, the width of the first section structure 41 gradually increases, and the width of the second section structure 42 can remain unchanged or increase or decrease.

[0086] S105, preparing a fourth refractive index layer on a surface of the third refractive index layer away from the substrate.

[0087] Specifically, refer to Fig.13 As shown in Figure (e), a fourth refractive index layer 50 is prepared on the surface of the third refractive index layer 40 away from the substrate 10. The fourth refractive index layer 50 is made of silicon dioxide SiO2. In order to match optical fibers of different sizes, in some embodiments, the silicon dioxide SiO2 can be partially etched to form an end face coupler with a "convex" cross-sectional shape, so that its cross-sectional size matches the mode field diameter of the single-mode optical fiber.

[0088] The end coupler is prepared.

[0089] The refractive index of the first refractive index layer is n1, the refractive index of the second refractive index layer 30 is n2, the refractive index of the third refractive index layer 40 is n3, and the refractive index of the fourth refractive index layer 50 is n4.

[0090] n1<n4<n3<n2.

[0091] In summary, the method for preparing the end face coupler of a large-size single-mode optical fiber provided in the embodiment of the present application not only has a high coupling effect, but also has the advantages of a simple preparation process and can be prepared in batches; small preparation tolerance and low requirements on the precision of the preparation process.

[0092] It should be noted that the drawings and embodiments of the present disclosure are only used to exemplify the preparation of end couplers of high-refractive index material lithium niobate, and are not used to limit the protection scope of the present disclosure. In other embodiments, when the refractive index of the material satisfies n1<n4<n3<n2, the material parameter setting protection scope of the above embodiments may also be applied.

[0093] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, combinations and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. An end coupler suitable for large-size single-mode optical fibers, characterized in that: It includes a substrate, a first refractive index layer, a second refractive index layer, a third refractive index layer and a fourth refractive index layer arranged in sequence; the end face coupler includes a first end face and a second end face; The first refractive index layer covers the substrate; The second refractive index layer extends along the first direction, one end of which is located at the second end face and is a ridge-shaped region with a "convex"-shaped cross section; the other end covers part of the first refractive index layer and is a strip-shaped region with a trapezoidal or rectangular cross section, and the thickness of the second refractive index layer gradually increases along the first direction; wherein the first direction is the direction from the first end face to the second end face; the second refractive index layer also includes a coupling plate layer, which is a part of the ridge-shaped region and is a planar layer structure, used to connect the first refractive index layer and fix the strip region and the ridge-shaped region of the second refractive index layer; The third refractive index layer extends from the first end surface to the second end surface; the third refractive index layer includes two continuous sections, the first section structure covers a portion of the first refractive index layer, and the second section structure covers the stripe region and the ridge region of the second refractive index layer; along the first direction, the width of the first section structure gradually increases; The fourth refractive index layer covers the third refractive index layer; The refractive index of the first refractive index layer is n1, the refractive index of the second refractive index layer is n2, the refractive index of the third refractive index layer is n3, and the refractive index of the fourth refractive index layer is n4; n1<n4<n3<n2; The thickness of the stripe region and the ridge region of the second refractive index layer ranges from 0 nm to 1 μm; the width of the top of the stripe region and the ridge region of the second refractive index layer ranges from 0.1 μm to 2 μm; The width of the first section structure is W1, and the width of the second section structure is W2, wherein 0.1 μm≤W1≤W2≤4 μm; along the first direction, the width of the second section structure is constant or gradually increases; along the first direction, the length of the first section structure is L1, and the length of the second section structure is L2, wherein the value range of L1 is 100 μm~2000 μm, and the value range of L2 is 100 μm~2000 μm; The thickness of the third refractive index layer ranges from 0.05 μm to 1 μm.

2. The end coupler according to claim 1, characterized in that: The fourth refractive index layer has a width ranging from 10 μm to 20 μm and a thickness ranging from 6 μm to 20 μm.

3. The end coupler according to claim 1, characterized in that: The thickness of the first refractive index layer is at least 1 μm.

4. A method for preparing an end coupler suitable for large-size single-mode optical fiber, for preparing the end coupler according to any one of claims 1 to 3, wherein the end coupler comprises a first end face and a second end face; characterized in that: The preparation method comprises: providing a substrate; preparing a first refractive index layer on one side of the substrate; A second refractive index layer is prepared on the surface of the first refractive index layer away from the substrate; the second refractive index layer extends along the first direction, one end of which is located at the second end face and is a ridge-shaped region with a "convex"-shaped cross section; the other end covers part of the first refractive index layer and is a strip-shaped region with a trapezoidal or rectangular cross section; the thickness of the second refractive index layer gradually increases along the first direction; wherein the first direction is the direction from the first end face to the second end face; the second refractive index layer also includes a coupling flat layer, which is a part of the ridge-shaped region and is a planar layer structure, used to connect the first refractive index layer and fix the strip region and the ridge-shaped region of the second refractive index layer; From the first end face to the second end face, a third refractive index layer is prepared on the surface of the stripe-shaped region and the ridge-shaped region of the second refractive index layer and part of the first refractive index layer; the third refractive index layer includes two continuous sections, the first section structure covers part of the first refractive index layer and the width gradually increases, and the second section structure covers the stripe-shaped region and the ridge-shaped region of the second refractive index layer; along the first direction, the width of the first section structure gradually increases; Preparing a fourth refractive index layer on a surface of the third refractive index layer away from the substrate; The refractive index of the first refractive index layer is n1, the refractive index of the second refractive index layer is n2, the refractive index of the third refractive index layer is n3, and the refractive index of the fourth refractive index layer is n4; n1<n4<n3<n2.

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