A lithium niobate end face coupler, optical chip and optical quantum computer

Abstract

The utility model relates to a lithium niobate end face coupler, including substrate: the lower cladding layer, covering layer are sequentially equipped from below to above on the substrate, the upper end of lower cladding layer is sequentially equipped with first flat plate structure and first waveguide structure from below to above, and first waveguide structure is located the upside of bottom layer first flat plate structure, and first flat plate structure and first waveguide structure are located in covering layer, and first flat plate structure includes first flat plate layer and the second waveguide structure located the upside of first flat plate layer, wherein, the thickness of first flat plate layer is 1nm 30nm, and the thickness of first flat plate layer is less than the thickness of second waveguide structure, the utility model discloses a lithium niobate end face coupler adds first flat plate layer, significantly reduces the coupling loss of thin film lithium niobate end face coupler, is favorable to the mass production of lithium niobate end face coupler.

Description

Technical Field

[0001] This utility model relates to the field of optical device technology, specifically to a lithium niobate end-face coupler, an optical chip, and an optical quantum computer. Background Technology

[0002] Lithium niobate (LiNbO3), as an important optoelectronic functional material, possesses irreplaceable application value in the field of photonics due to its unique electro-optic, acousto-optic, and nonlinear optical properties, as well as its wide transparency window. However, the coupling efficiency between lithium niobate end-face couplers and optical fibers remains one of the important factors limiting its development.

[0003] Currently, optical coupling technologies for thin-film lithium niobate are mainly divided into two categories: surface grating coupling and end-face coupling. Surface grating coupling achieves vertical coupling of the optical field by etching periodic structures on the waveguide surface, but it has inherent defects such as narrow operating bandwidth, strong polarization dependence, and low coupling efficiency. On the other hand, end-face coupling technology expands the mode field area by adjusting the waveguide size (such as tapered waveguide width or height) to match the fiber mode field, which can effectively compensate for the shortcomings of surface grating coupling and is also more convenient for subsequent chip packaging.

[0004] However, existing end-face coupler technology still faces significant challenges. On the one hand, the etching process for lithium niobate requires extremely high precision. Due to the limited maturity of current etching technology, significant deviations between the waveguide linewidth or height and the design values ​​are common in actual processing (e.g., waveguide sidewall tilt angles limiting minimum linewidth and inaccurate mode refractive index control). This results in higher losses in the actual end-face coupler than expected, leading to low yields in mass production. On the other hand, end-face couplers have stringent requirements for refractive index matching of the cladding material (such as SiO2). The refractive index of the cladding SiO2 must be strictly controlled to approach the refractive index of the buried oxide layer (BOX layer) SiO2; otherwise, it is difficult to form a near-circular spot on the end face, leading to a significant increase in losses. Especially for large-spot end-face couplers, the difficulty of controlling the aforementioned refractive index matching is further increased, severely limiting their adaptability for large-scale production.

[0005] In summary, existing lithium niobate end-face coupler technology has significant shortcomings in terms of processing tolerance and cladding material refractive index compatibility. There is an urgent need for a new end-face coupling structure design that can reduce the dependence on etching precision and relax the cladding refractive index matching requirements, so as to reduce the coupling loss of the end-face coupler and promote the industrialization of lithium niobate end-face couplers. Utility Model Content

[0006] To address the aforementioned problems, this invention provides a lithium niobate end-face coupler. By adding a first flat plate layer, this invention significantly reduces the coupling loss of thin-film lithium niobate end-face couplers, which is beneficial for the large-scale production of lithium niobate end-face couplers.

[0007] To achieve the above objectives, the technical solution adopted by this utility model is as follows:

[0008] The first aspect of this utility model provides a lithium niobate end-face coupler, including a substrate:

[0009] The substrate is provided with a lower cladding layer and a cover layer from bottom to top. The upper end of the lower cladding layer is provided with a first flat plate structure and a first waveguide structure from bottom to top. The first waveguide structure is located directly above the bottom first flat plate structure. The first flat plate structure and the first waveguide structure are located within the cover layer. The first flat plate structure includes a first flat plate layer and a second waveguide structure located directly above the first flat plate layer.

[0010] The thickness of the first plate layer is 1nm-30nm, which is less than the thickness of the second waveguide structure.

[0011] In one example, the lower surface of the first waveguide structure is connected to the upper surface of the second waveguide structure, and the first planar layer and the second waveguide structure are an integral structure that is not fully etched.

[0012] In one example, the second waveguide structure gradually widens from the fiber coupling end to the wafer connection end, and the narrower end face of the second waveguide structure is the first end face, the cross-sectional shape of the first end face is trapezoidal.

[0013] In one example, the upper width of the first end face is 50nm-500nm, and the lower width of the first end face is 200nm-800nm.

[0014] In one example, the first waveguide structure gradually widens from the fiber coupling end to the wafer connection end, and the narrower end face of the first waveguide structure is the second end face, the cross-sectional shape of the second end face is trapezoidal.

[0015] In one example, the upper width of the second end face is 100nm-300nm, and the lower width of the second end face is 300nm-600nm.

[0016] In one example, the lower cladding layer is made of SiO2 material; the capping layer is made of SiO2 material; the substrate is an SOI wafer Si substrate; the first planar structure is made of LiNbO3 material; and the first waveguide structure is made of LiNbO3 material.

[0017] In one example, the thickness of the second waveguide structure is 100nm-300nm.

[0018] In one example, the thickness of the first waveguide structure gradually increases from the fiber coupling end to the wafer connection end, with the thickness of the thinner end of the first waveguide structure being 150nm-300nm and the thickness of the thicker end being 300nm-600nm.

[0019] The second aspect of this utility model provides an optical chip in which the lithium niobate end-face coupler described in the first aspect of this utility model is placed at the input port and / or output port of the optical chip for coupling a laser source or optical fiber, thereby realizing the transmission of optical signals between the optical chip and an external optical path.

[0020] The third aspect of this utility model provides an optical quantum computer, including the lithium niobate end-face coupler described in the first aspect of this utility model, for photon coupling in the optical quantum computer;

[0021] The photonic coupling includes photonic coupling from a single-photon source to a quantum circuit, photonic coupling within the quantum circuit, and photonic coupling from the quantum circuit to a single-photon detector.

[0022] By employing the above technical solution, this utility model has at least the following advantages compared with the prior art:

[0023] This utility model discloses a lithium niobate end-face coupler. By adding an incompletely etched lithium niobate planar layer (first planar layer) to the end-face coupler, the dependence on the etching process precision of lithium niobate is effectively reduced. This significantly reduces the impact of etching deviation on the light spot, avoids loss problems caused by waveguide size deviation, improves the processing yield of the end-face coupler, and provides process tolerance support for large-scale manufacturing. Moreover, the design of the first planar layer relaxes the strict matching requirements of the SiO2 cladding refractive index. Even if there is a certain deviation between the refractive index of the SiO2 cladding and the SiO2BOX layer, the end-face light spot can still be guaranteed to be nearly circular. This effectively solves the problem of high coupling loss caused by poor cladding material compatibility, greatly improves the process compatibility of the end-face coupler, and is more suitable for the needs of large-scale production.

[0024] In summary, by adding a first flat plate layer, this utility model balances the tolerance of processing technology with the compatibility of cladding materials, and significantly reduces the coupling loss of the thin-film lithium niobate end-face coupler, which is beneficial for the large-scale production of lithium niobate end-face couplers.

[0025] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0026] Figure 1 The figure shown is a cross-sectional structural schematic diagram of the lithium niobate end-face coupler of this utility model.

[0027] Figure 2 The figure shown is a three-dimensional structural schematic diagram of the lithium niobate end-face coupler of this utility model.

[0028] Figure 3 The figure shown is a partially enlarged three-dimensional structural diagram of the lithium niobate end-face coupler of this utility model.

[0029] Figure 4 The image shown is a cross-sectional SEM image of the fiber coupling end of a lithium niobate end-face coupler provided in an embodiment of this utility model.

[0030] Figure 5 The image shows the light intensity distribution of a lithium niobate end-face coupler coupled to an optical fiber according to an embodiment of this invention. Figure 1 .

[0031] Figure 6 The image shows the light intensity distribution of a lithium niobate end-face coupler coupled to an optical fiber according to an embodiment of this invention. Figure 2 .

[0032] Figure 7 The image shows the light intensity distribution of a lithium niobate end-face coupler coupled to an optical fiber according to an embodiment of this invention. Figure 3 .

[0033] Figure 8 The diagram shows the workflow of the optical quantum computer of this invention.

[0034] Explanation of reference numerals in the attached figures:

[0035] Substrate 1, lower cladding layer 2, capping layer 3, first planar structure 4, first waveguide structure 5, first planar layer 41, second waveguide structure 42. Detailed Implementation

[0036] The specific embodiments of this utility model are described in detail below. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the utility model. In this document, unless otherwise specified, the data range includes endpoints.

[0037] The terminology used in this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms “a,” “the,” and “the” used in this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0038] It should be understood that although the terms first, second, third, etc., may be used to describe various structures in this invention, these structures should not be limited to these terms. These terms are only used to distinguish structures of the same type from each other. For example, without departing from the scope of this invention, a first structure may also be referred to as a second structure, and similarly, a second structure may also be referred to as a first structure.

[0039] This utility model provides a lithium niobate end-face coupler, see [link to relevant documentation]. Figures 1-4 The substrate includes a substrate 1. From bottom to top, a lower cladding layer 2 and a capping layer 3 are sequentially disposed on the substrate 1. From bottom to top, a first planar structure 4 and a first waveguide structure 5 are sequentially disposed on the upper end of the lower cladding layer 2. The first waveguide structure 5 is located directly above the bottom first planar structure 4. The first planar structure 4 and the first waveguide structure 5 are located within the capping layer 3. The first planar structure 4 includes a first planar layer 41 and a second waveguide structure 42 located directly above the first planar layer 41. The thickness of the first planar layer 41 is 1 nm to 30 nm. (For example, 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm or 30nm), the thickness of the first planar layer 41 is less than the thickness of the second waveguide structure 42.

[0040] This invention relates to a lithium niobate end-face coupler. By adding an incompletely etched lithium niobate planar layer (first planar layer) to the end-face coupler, the influence of etching deviation or cladding refractive index mismatch on the spot size can be significantly reduced. This avoids the increased loss caused by abnormal spot size due to large differences in the width of the lithium niobate tip waveguide caused by immature lithium niobate etching technology. Furthermore, by adding the first planar layer to the end-face coupler, the spot shape can be changed from irregular to near-circular, avoiding the increased loss caused by the mismatch between the spot shape of the end-face coupler and the fiber spot shape. In addition, the design of this first planar layer relaxes the strict matching requirement of the SiO2 cladding refractive index, allowing the SiO2 cladding (i.e., the capping layer) refractive index to match the SiO2 BOX layer (i.e., the lower cladding, where BOX stands for "Silicon Dioxide Buried") refractive index. Even with a certain deviation in the "OxideLayer" (i.e., the buried oxide layer of silicon dioxide), the end face spot can still be nearly circular, effectively solving the problem of high coupling loss caused by poor compatibility of cladding materials, greatly improving the process compatibility of the end face coupler, and making it more suitable for large-scale production needs.

[0041] Furthermore, by controlling the thickness of the first planar layer to be 1nm-30nm and less than the thickness of the second waveguide structure, this invention effectively balances the effect of the lithium niobate planar layer thickness on the beam size, avoiding the problem that excessive thickness leads to further beam shrinkage and incompatibility with the optical fiber. At the same time, the thickness difference between the first planar layer and the second waveguide structure optimizes the overall structure, ensuring precise control of the beam size by the end-face coupler, thereby improving coupling efficiency and process stability, and avoiding increased loss due to the difficulty of etching process and the high refractive index requirement of the cladding SiO2.

[0042] In one instance, such as Figures 1-2 As shown, the lower surface of the first waveguide structure 5 is connected to the upper surface of the second waveguide structure 42, and as... Figures 3-4As shown, the first planar layer 41 and the second waveguide structure 42 are an integrated structure with incomplete etching. By designing the first planar layer and the second waveguide structure as an integrated structure with incomplete etching, the waveguide mode will not change abruptly when light propagates in the structure, reducing light loss during transmission. It should be noted that "integrated structure" means that the first planar layer 41 and the second waveguide structure 42 are not two independently processed and spliced ​​components, but are formed by processing the same raw material (lithium niobate) as a whole. The two are completely continuous in material composition, without any artificial splicing interface, and are essentially different parts of the same substrate; "incomplete etching" means that during the preparation of the first planar layer 41 and the second waveguide structure 42, an etching process was used to remove excess material around the target area of ​​the raw material that was to be retained, but the etching depth did not penetrate the entire thickness of the raw material. That is, the first planar structure of this invention is a lithium niobate material with an integrated structure of the first planar layer 41 and the second waveguide structure 42, which is retained by incomplete etching of the raw material.

[0043] In one instance, such as Figure 2 As shown, the second waveguide structure 42 gradually widens from the fiber coupling end to the wafer connection end, and the narrower end face of the second waveguide structure 42 is the first end face, as shown in the figure. Figures 3-4 As shown, the cross-sectional shape of the first end face is trapezoidal.

[0044] Furthermore, in one example, the upper width of the first end face is 50nm-500nm, and the lower width of the first end face is 200nm-800nm. It should be noted that the cross-sectional shape of the first end face is trapezoidal. The "upper width" and "lower width" refer to the two parallel sides of the trapezoid (i.e., the "base" of the trapezoid). Therefore, the upper width of the first end face refers to the length of the upper parallel side in the cross-section of the trapezoid, and the lower width of the first end face refers to the length of the lower parallel side in the cross-section of the trapezoid. In this invention, the first end face of the second waveguide structure is the fiber coupling end, and the fiber coupling end is configured as a trapezoidal structure.

[0045] In one instance, such as Figure 2 As shown, the first waveguide structure 5 gradually widens from the fiber coupling end towards the wafer connection end. The narrower end face of the first waveguide structure 5 is the second end face, and the cross-sectional shape of the second end face is trapezoidal. The first waveguide structure acts as a light confinement mechanism, trapping light around the waveguide and preventing light spot dispersion. Further, in one example, the upper width of the second end face is 100nm-300nm, and the lower width of the second end face is 300nm-600nm.

[0046] In this invention, the fiber coupling end refers to the end face coupled to the optical fiber, and the wafer connection end refers to the waveguide structure end face connecting to other devices inside the wafer. Figure 1 In the diagram, the left surface of the end coupler is the fiber optic coupling end surface, and the right surface of the end coupler is the wafer connection end surface.

[0047] In one instance, such as Figure 2 As shown, the thickness of the first waveguide structure gradually increases from the fiber coupling end to the wafer connection end. The thickness of the thinner end face of the first waveguide structure is 150nm-300nm, and the thickness of the thicker end face is 300nm-600nm. The different thicknesses of the two end faces of the first waveguide structure are mainly determined by the thickness of the first planar structure and the design parameters required for the end face coupler structure.

[0048] In one example, the lower cladding layer is made of SiO2 material; the capping layer is made of SiO2 material; the substrate is an SOI wafer Si substrate; the first planar structure is made of LiNbO3 material; and the first waveguide structure is made of LiNbO3 material.

[0049] In one example, the thickness of the second waveguide structure is 100nm-300nm.

[0050] In one instance, such as Figure 1 As shown, the lower surface of the first flat plate layer 41 is connected to the upper surface of the lower cladding layer 2.

[0051] In one instance, such as Figure 1 As shown, the lower surface of the cover layer 3 is connected to the upper surface of the lower cover layer 2.

[0052] In one instance, such as Figure 1 As shown, the lower surface of the lower cladding layer 2 is connected to the upper surface of the substrate 1.

[0053] The working principle of this novel end-face coupler is based on its multi-layer structure design, which controls the mode of the optical field. A lower cladding layer and a capping layer are sequentially arranged on the substrate. Above the lower cladding layer, a first plate structure (including a first plate layer and a second waveguide structure) cooperates with the first waveguide structure. The presence of the first plate layer (with a thickness limited to 1nm-30nm and less than the thickness of the second waveguide structure) allows for precise adjustment of the mode size during optical field propagation. Specifically, when light enters from the wafer connection end, initially, most of the light is confined in the first waveguide structure. As the first waveguide structure gradually narrows until it ends, the light transfers from the first waveguide structure to the second waveguide structure and the first plate layer. Then, as the width of the second waveguide structure gradually decreases, the light gradually escapes from the second waveguide structure and the first plate layer, forming a circular spot. When the second waveguide structure is at its thinnest, the circular spot becomes large enough to couple with the optical fiber. When light is incident from the optical fiber to the end coupler, the first waveguide structure and the first planar layer work together. Through the linear control characteristic of the planar layer thickness on the mode spot (the mode spot expands appropriately when the thickness increases, avoiding excessive thickness that would cause the light spot to shrink), the optical field mode spot in the waveguide gradually matches the optical fiber mode field. At the same time, the incompletely etched first planar layer can effectively buffer the influence of etching process deviations (such as the waveguide width or height not matching the design value) on the light spot. Through the optical field constraint effect of the planar layer, even if there is a deviation between the refractive index of the cladding SiO2 and the BOX layer, the near-circular shape of the end face light spot can still be maintained, thereby reducing coupling loss and achieving efficient and stable coupling between the lithium niobate chip and the optical fiber.

[0054] The second aspect of this invention provides an optical chip in which the lithium niobate end-face coupler described in the first aspect of this invention is placed at the input port and / or output port of the optical chip for coupling a laser source or optical fiber, thereby enabling the transmission of optical signals between the optical chip and an external optical path.

[0055] A third aspect of this invention provides an optical quantum computer, such as... Figure 8 As shown, the lithium niobate end-face coupler described in the first aspect of this utility model is used for photon coupling in an optical quantum computer.

[0056] Photon coupling includes photon coupling from a single photon source to a quantum circuit, photon coupling within a quantum circuit, and photon coupling from a quantum circuit to a single photon detector.

[0057] It should be noted that photon coupling from a single-photon source to a quantum circuit refers to the efficient transmission of photons emitted by a single-photon source in a quantum computer to subsequent quantum circuits. If a laser or similar source is used as the single-photon source, and the laser chip emits light from its end face, the lithium niobate end face coupler of this invention can be used to couple its emission end face to the fiber end face, allowing the laser to be transmitted along the fiber to the other end, and then enter the passive waveguide on the chip through a vertical fiber coupler, thereby coupling the photons generated by the single-photon source into the quantum computing system; photon coupling within the quantum circuit.

[0058] It should be noted that photon coupling inside the optical quantum circuit refers to the fact that the optical quantum circuit is a key component for realizing optical quantum algorithms, and is usually composed of multiple waveguides, beam splitters and other optical elements. The lithium niobate end-face coupler of this invention can be used to connect different waveguide segments in the optical quantum circuit, or to connect the waveguide to the external optical fiber, to efficiently couple the input photons into the optical quantum circuit and ensure low loss when the photons are transmitted in the circuit.

[0059] It should be noted that photon coupling from the quantum circuit to the single-photon detector refers to coupling the photons processed in the quantum circuit to subsequent components such as the single-photon detector. The single-photon detector can be used to detect the results of quantum computing. The lithium niobate end-face coupler of this invention can couple the photons output from the quantum circuit to the single-photon detector, realizing the conversion of photon signals to electrical signals, thereby completing the reading of the calculation results of the quantum computer.

[0060] The present invention will be described in detail below through embodiments. The embodiments described herein are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0061] Example 1

[0062] The structural design of the lithium niobate end-face coupler is shown below:

[0063] Substrate 1: Silicon substrate (500 μm thick);

[0064] Lower cladding layer 2: SiO2BOX layer (thickness 4.7μm, refractive index 1.443);

[0065] First planar structure 4: First planar layer 41 (lithium niobate, 15nm thick), second waveguide structure 42 (lithium niobate, 285nm thick, with a trapezoidal first end face, a top width of 200nm, and a bottom width of 430nm);

[0066] First waveguide structure 5: Lithium niobate graded waveguide (the end face width of the wafer connection end is 0.9μm and the thickness is 300nm. The end face of the fiber coupling end (i.e. the second end face) is trapezoidal, with a width of 200nm on the top side and 430nm on the bottom side. The thickness of the thinner end face is 230nm and the thickness of the thicker end face is 450nm. It is located directly above the second waveguide structure 42).

[0067] Covering layer 3: SiO2 layer (thickness 200μm, refractive index 1.455).

[0068] Test methods and conditions: Incident light wavelength 1550nm, fiber type UHNA4, mode field diameter 3.3μm; 1) Coupling loss between the above fiber and the chip equipped with the lithium niobate end-face coupler of this embodiment, in dB / facet; 2) Directly use a mode spot tester to test the mode spot size and shape of the lithium niobate end-face coupler of this embodiment, as well as its matching degree with the fiber mode field, in %.

[0069] The test results of this embodiment are as follows: coupling loss is -1 dB / facet, matching degree with fiber mode field is 90%, and the spot shape is nearly circular. Figure 5 As shown.

[0070] Comparative Example 1

[0071] The structural design of the lithium niobate end-face coupler is shown below:

[0072] The parameters of substrate 1, lower cladding layer 2, capping layer 3, and first waveguide structure 5 are the same as in embodiment 1; the only difference is that the first flat plate structure 4 does not include the first flat plate layer 41, and the second waveguide structure 42 is directly disposed on the surface of the lower cladding layer 2.

[0073] The test methods and conditions are the same as in Example 1. The test results of this comparative example are as follows: coupling loss is -2 dB / facet, matching degree with fiber mode field is 80%, spot shape is nearly elliptical, and the spot area is too large. Figure 6 As shown.

[0074] Comparative Example 2

[0075] The structural design of the lithium niobate end-face coupler is shown below:

[0076] The parameters of substrate 1, lower cladding layer 2, capping layer 3, and first waveguide structure 5 are the same as in Example 1; the only difference is that the first planar layer 41 (lithium niobate, 35nm thick) is the same.

[0077] The test methods and conditions are the same as in Example 1. The test results of this comparative example are as follows: the coupling loss is -3 dB / facet, the matching degree with the fiber mode field is 70%, the spot shape is regular, but the spot area is too small. Figure 7 As shown.

[0078] In addition, it should be noted that, Figures 5-7 The horizontal axis represents the position in the y-direction, and the unit is micrometers (microns); the vertical axis represents the position in the z-direction, and the unit is also micrometers (microns).

[0079] Compared to Example 1, Comparative Example 1 lacks a first flat plate layer, which significantly affects the size of the light spot at the cross-section. Figure 6 As shown, the light spot shape is nearly elliptical, and the spot area is too large. Embodiment 1 of this utility model avoids the increased loss caused by abnormal spot size due to the large difference in waveguide width at the tip of lithium niobate caused by the immature etching technology of lithium niobate. It also avoids the abnormal spot size and shape that can occur when the refractive index of the SiO2 capping layer is difficult to adjust to be close to the refractive index of the SiO2 in the lithium niobate wafer BOX layer. Figure 5 As shown, the light spot shape of Embodiment 1 of this utility model is nearly circular, with low coupling loss and a higher degree of matching with the fiber mode field.

[0080] Compared to Example 1, Comparative Example 2 has an excessively thick first flat layer, which results in a regular light spot shape but a small light spot area. Figure 7 As shown. In Embodiment 1 of this utility model, by setting an appropriate thickness of the first flat plate layer, the shape of the light spot can be further adjusted from an irregular shape to a near-circular shape, and the area of ​​the light spot is appropriate. This avoids the problem of increased loss caused by the mismatch between the shape of the light spot of the end face coupler and the shape of the optical fiber light spot, resulting in lower coupling loss and higher matching degree with the optical fiber mode field of this utility model's lithium niobate end face coupler.

[0081] This invention adds a first plate layer to the lithium niobate end coupler and limits its thickness to 1nm-30nm, which is less than the thickness of the second waveguide structure. At the same time, the first waveguide structure is designed to be located directly above the first plate layer and is an integrated structure that is not completely etched, combined with a waveguide design with a gradient trapezoidal cross section. Its beneficial effects are as follows: By setting the first planar layer, the dependence on the etching process precision of lithium niobate is effectively reduced, the impact of etching deviations (such as waveguide width or height not matching the design value) on the light spot is reduced, and the processing yield of the end-face coupler is improved; at the same time, the requirement for strict matching of the refractive index of the cladding SiO2 is relaxed. Even if there is a deviation between the refractive index of the cladding SiO2 and the BOX layer, the near-circular shape of the end-face light spot can still be maintained, avoiding increased loss due to the mismatch between the light spot shape and the fiber; in addition, by limiting the thickness range of the first planar layer and its relationship with the thickness of the second waveguide structure, the control effect of the planar layer thickness on the mode spot size is balanced (the mode spot expands appropriately when the thickness increases, avoiding excessive thickness that leads to a shrinking light spot), achieving precise matching between the optical field mode spot in the waveguide and the fiber mode field, significantly reducing coupling loss, and improving the process compatibility and large-scale production adaptability of the end-face coupler.

[0082] The preferred embodiments of this utility model have been described in detail above; however, this utility model is not limited thereto. Within the scope of the technical concept of this utility model, various simple modifications can be made to the technical solution of this utility model, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed by this utility model and are all within the protection scope of this utility model.

Claims

1. A lithium niobate end-coupler, characterized by, Including substrate, The substrate is provided with a lower cladding layer and a cover layer from bottom to top. The upper end of the lower cladding layer is provided with a first flat plate structure and a first waveguide structure from bottom to top. The first waveguide structure is located directly above the bottom first flat plate structure. The first flat plate structure and the first waveguide structure are located within the cover layer. The first flat plate structure includes a first flat plate layer and a second waveguide structure located directly above the first flat plate layer. The thickness of the first plate layer is 1nm-30nm, which is less than the thickness of the second waveguide structure.

2. The lithium niobate end-coupler of claim 1, wherein, The lower surface of the first waveguide structure is connected to the upper surface of the second waveguide structure, and the first planar layer and the second waveguide structure are an integral structure that is not completely etched.

3. The lithium niobate end-coupler of claim 1, wherein, The second waveguide structure gradually widens from the fiber coupling end to the wafer connection end, and the narrower end face of the second waveguide structure is the first end face, and the cross-sectional shape of the first end face is trapezoidal.

4. The lithium niobate end-coupler of claim 3, wherein, The upper width of the first end face is 50nm-500nm, and the lower width of the first end face is 200nm-800nm.

5. The lithium niobate end-coupler of claim 1, wherein, The first waveguide structure gradually widens from the fiber coupling end to the wafer connection end, and the narrower end face of the first waveguide structure is the second end face, the cross-sectional shape of the second end face is trapezoidal.

6. The lithium niobate end-coupler of claim 5, wherein, The upper width of the second end face is 100nm-300nm, and the lower width of the second end face is 300nm-600nm.

7. The lithium niobate end-coupler of claim 1, wherein, The lower cladding layer is made of SiO2 material; the capping layer is made of SiO2 material; the substrate is an SOI wafer Si substrate; the first planar structure is made of LiNbO3 material; and the first waveguide structure is made of LiNbO3 material.

8. The lithium niobate end-coupler of claim 1, wherein, The thickness of the second waveguide structure is 100nm-300nm; And / or, the thickness of the first waveguide structure gradually increases from the fiber coupling end to the wafer connection end, the thickness of the thinner end of the first waveguide structure is 150nm-300nm, and the thickness of the thicker end of the first waveguide structure is 300nm-600nm.

9. An optical chip, characterized in that, A lithium niobate end-face coupler as described in any one of claims 1-8 is placed at the input port and / or output port of the optical chip to couple a laser source or optical fiber, thereby enabling the transmission of optical signals between the optical chip and an external optical path.

10. A photonic quantum computer, characterized by Including the lithium niobate end-face coupler according to any one of claims 1-8, for photon coupling in the optical quantum computer; The photonic coupling includes photonic coupling from a single-photon source to a quantum circuit, photonic coupling within the quantum circuit, and photonic coupling from the quantum circuit to a single-photon detector.

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