Bent waveguide structure

Abstract

The application relates to a curved waveguide structure, comprising: a curved waveguide segment, the curved waveguide segment having an inner profile and an outer profile; the curved waveguide segment is curved to one side where the inner profile is located; an auxiliary waveguide segment is arranged on the inner side of the inner profile and extends along a curved direction; the curved direction is the extension direction of the inner profile; wherein a cladding is filled between the curved waveguide segment and the auxiliary waveguide segment; the material refractive index of the auxiliary waveguide segment is greater than the material refractive index of the cladding. The curved waveguide structure can reduce the transmission loss of the curved waveguide structure without increasing the size of the curved waveguide.

Description

Technical Field

[0001] This application relates to the field of optical waveguide technology, and in particular to a bent waveguide structure. Background Technology

[0002] In optical waveguide technology, curved waveguides are a common structure for connecting different functional units on optical chips, primarily used to change the transmission direction of optical signals. As optical chips evolve towards miniaturization and high integration, curved waveguides are typically designed to be more compact to save chip area. However, this results in a smaller bending radius. When optical signals propagate in such curved waveguides, the bending causes the mode field to shift outwards, leading to some mode energy escaping the waveguide and generating bending radiation loss, thus increasing the transmission loss. Therefore, achieving a balance between compact structure and low transmission loss in curved waveguides has become a pressing technical challenge. Summary of the Invention

[0003] Based on this, this application provides a curved waveguide structure that can reduce the transmission loss of the curved waveguide structure without increasing the size of the curved waveguide, thereby facilitating the compact design of the curved waveguide structure.

[0004] On one hand, this application provides a curved waveguide structure, including: a curved waveguide segment having an inner contour and an outer contour; the curved waveguide segment bends toward the side where the inner contour is located; an auxiliary waveguide segment disposed inside the inner contour and extending along the bending direction; the bending direction is the extension direction of the inner contour; wherein, a cladding layer is filled between the curved waveguide segment and the auxiliary waveguide segment; the refractive index of the material of the auxiliary waveguide segment is greater than the refractive index of the material of the cladding layer.

[0005] Optionally, the radial spacing between the outer edge of the auxiliary waveguide segment and the inner contour is a constant value; the outer edge of the auxiliary waveguide segment is the edge of the auxiliary waveguide segment closest to the inner contour; the radial spacing is the distance between the outer edge of the auxiliary waveguide segment and the inner contour in the radial direction; the radial direction is perpendicular to the bending direction.

[0006] Optionally, the curvature of both the inner and outer contours gradually increases and then gradually decreases along the bending direction; the radial distance between the inner and outer contours gradually increases and then gradually decreases along the bending direction; and the curvature of the inner contour, the curvature of the outer contour, and the radial distance between the inner and outer contours reach their maximum values ​​at the same position.

[0007] Optionally, the radial spacing between the outer edge and inner contour of the auxiliary waveguide segment falls between 0.15 micrometers and 1 micrometer.

[0008] Optionally, the refractive index of the auxiliary waveguide section is less than or equal to the refractive index of the curved waveguide section.

[0009] Optionally, the radial width of the auxiliary waveguide segment is a constant value; the radial width is the distance between the inner edge and the outer edge of the auxiliary waveguide segment in the radial direction.

[0010] Optionally, the radial width of the auxiliary waveguide segment is greater than or equal to 0.1 micrometers.

[0011] Optionally, the auxiliary waveguide segment consists of multiple sub-waveguide segments spaced apart along the bending direction.

[0012] Optionally, the multiple sub-waveguide segments include: an input tapered segment; the input tapered segment is located at one end of the auxiliary waveguide segment near the input end of the curved waveguide segment; in the input tapered segment, the radial width of the input tapered segment gradually increases along the optical transmission direction; and an output tapered segment; the output tapered segment is located at one end of the auxiliary waveguide segment near the output end of the curved waveguide segment; in the output tapered segment, the radial width of the output tapered segment gradually decreases along the optical transmission direction.

[0013] Optionally, the curved waveguide structure further includes: an input straight waveguide section, located at the input end of the curved waveguide section and tangentially connected to the curved waveguide section; and an output straight waveguide section, located at the output end of the curved waveguide section and tangentially connected to the curved waveguide section.

[0014] In several embodiments of this application, an auxiliary waveguide segment is provided inside the inner contour of the curved waveguide segment, and the refractive index of the auxiliary waveguide segment is greater than that of the cladding material. This allows the auxiliary waveguide segment to increase the equivalent refractive index of the curved waveguide segment in the curved inner region, thereby causing the mode field to shift towards the inner contour side and enhancing local constraint, reducing bending radiation loss. This reduces the transmission loss of the curved waveguide structure without increasing the size of the curved waveguide, which is beneficial for the compact design of the curved waveguide structure. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a bent waveguide structure according to an embodiment of this application;

[0016] Figure 2 for Figure 1 A magnified view of part A in the image;

[0017] Figure 3 This is a transmission spectrum of a bent waveguide structure according to an embodiment of this application;

[0018] Figure 4 This is a schematic diagram of a bent waveguide structure according to another embodiment of this application;

[0019] Figure 5 This is a schematic diagram of a curved waveguide structure according to another embodiment of this application.

[0020] Figure label:

[0021] 100 / 200 / 300, Bending waveguide structure; 110, Bending waveguide segment; 111, Inner contour; 112, Outer contour; 120, Auxiliary waveguide segment; 121, Inner edge; 122, Outer edge; 130, Cladding; 140, Input straight waveguide segment; 150, Output straight waveguide segment; G, Radial spacing; W, Radial width of auxiliary waveguide segment; θ, Bending angle; FW, Bending direction; FJ, Radial direction. Detailed Implementation

[0022] To make the technical solution and beneficial effects of this application more apparent and understandable, a detailed description is provided below by listing specific embodiments. The accompanying drawings are not necessarily drawn to scale, and local features may be enlarged or reduced to more clearly show the details of the local features; unless otherwise defined, the technical and scientific terms used herein have the same meanings as those in the technical field to which this application pertains.

[0023] refer to Figure 1 and Figure 2 Some embodiments of this application provide a curved waveguide structure 100. The curved waveguide structure 100 includes a curved waveguide segment 110, an auxiliary waveguide segment 120, and a cladding 130.

[0024] The curved waveguide segment 110 has an inner contour 111 and an outer contour 112. The curved waveguide segment 110 bends towards the side containing the inner contour 111. The auxiliary waveguide segment 120 is located inside the inner contour 111 and extends along the bending direction FW. The bending direction FW is the extension direction of the inner contour 111. A cladding layer 130 fills the space between the curved waveguide segment 110 and the auxiliary waveguide segment 120. The refractive index of the material of the auxiliary waveguide segment 120 is greater than that of the material of the cladding layer 130.

[0025] It is understandable that, such as Figure 1 As shown, the inner contour 111 of the curved waveguide segment 110 refers to the boundary line near the bending center within the waveguide plane of the optical chip, while the outer contour 112 refers to the boundary line away from the bending center. Furthermore, in this application, the bending direction FW can be determined based on the tangent direction of the inner contour 111 at a certain position, and the radial direction FJ refers to the direction perpendicular to the bending direction FW. It is understood that... Figure 1 The bending direction FW and radial direction FJ shown are the directions of the inner contour 111 at the position shown in the figure. As the inner contour 111 extends, its bending direction FW and radial direction FJ will also change accordingly.

[0026] The aforementioned curved waveguide structure 100, by providing an auxiliary waveguide section 120 inside the inner contour 111 of the curved waveguide section 110, and the refractive index of the material of the auxiliary waveguide section 120 being greater than that of the cladding 130, enables the auxiliary waveguide section 120 to increase the equivalent refractive index of the curved waveguide section 110 in the curved inner region, thereby causing the mode field to shift towards the inner contour 111 and enhancing local constraint, reducing bending radiation loss. Thus, the transmission loss of the curved waveguide structure 100 can be reduced without increasing the size of the curved waveguide, which is beneficial for the compact design of the curved waveguide structure 100.

[0027] Furthermore, in the aforementioned curved waveguide structure 100, the auxiliary waveguide segment 120 and the curved waveguide segment 110 are independently configured solid structures, with a cladding 130 filling the space between them. This allows the configuration of the auxiliary waveguide segment 120 to be independent of the structure of the curved waveguide segment 110. Parameters such as the radial distance G between the outer edge 122 and the inner contour 111 of the auxiliary waveguide segment 120, and the radial width W of the auxiliary waveguide segment 120, can be set independently, without being bound to the parameters of the inner contour 111 and outer contour 112 of the curved waveguide segment 110. In actual design, designers can adjust the parameters of the auxiliary waveguide segment 120 according to different bending angles θ, bending radii, and material plateaus to adjust the equivalent refractive index distribution and coupling strength on the inner side of the bend, and confirm the optimal combination through electromagnetic simulation. Therefore, the curved waveguide structure 100 offers high flexibility and design freedom.

[0028] It should be noted that in the above-mentioned curved waveguide structure 100, the material of the auxiliary waveguide section 120 can be selected from various materials with a refractive index greater than that of the cladding material 130, so that the auxiliary waveguide section 120 can improve the equivalent refractive index of the curved waveguide section 110 in the curved inner region.

[0029] Optionally, the refractive index of the auxiliary waveguide section 120 can be set to be less than or equal to the refractive index of the bent waveguide section 110. This setting ensures that the optical transmission capability of the auxiliary waveguide section 120 is not excessive, thereby reducing the risk of introducing additional losses or higher-order modes, and thus reducing transmission loss. As a specific example, when the cladding 130 is made of silicon dioxide and the bent waveguide section 110 is made of silicon, the auxiliary waveguide section 120 can also be made of silicon.

[0030] It should be noted that the curved waveguide structure 100 of this application is not limited to silicon waveguide platforms, but can also be set on various planar waveguide platforms such as silicon nitride and thin-film lithium niobate.

[0031] In some embodiments, the radial distance G between the outer edge 122 of the auxiliary waveguide segment 120 and the inner contour 111 is a constant value. The outer edge 122 of the auxiliary waveguide segment 120 is the edge of the auxiliary waveguide segment 120 closest to the inner contour 111. The radial distance G is the distance between the outer edge 122 of the auxiliary waveguide segment 120 and the inner contour 111 in the radial direction FJ. The radial direction FJ is perpendicular to the bending direction FW.

[0032] In the aforementioned curved waveguide structure 100, the radial distance G between the outer edge 122 and the inner contour 111 of the auxiliary waveguide section 120 is a constant value. This ensures that the effect of the auxiliary waveguide section 120 on improving the equivalent refractive index on the inner side of the bend remains consistent along the bending direction FW, allowing the mode field to change smoothly within the curved waveguide section 110 without generating additional mode disturbances due to changes in the radial distance G. This further reduces the transmission loss of the curved waveguide structure 100.

[0033] It is understood that the radial spacing G in this application is not limited to a constant value; in other embodiments, the radial spacing G may also be set to a gradual value.

[0034] In some embodiments, reference Figure 1 and Figure 2 The curvature of both the inner contour 111 and the outer contour 112 gradually increases and then gradually decreases along the bending direction FW; the radial distance between the inner contour 111 and the outer contour 112 gradually increases and then gradually decreases along the bending direction FW. The curvature of the inner contour 111, the curvature of the outer contour 112, and the radial distance between the inner contour 111 and the outer contour 112 reach their maximum values ​​at the same position.

[0035] Specifically, in the aforementioned curved waveguide structure 100, the curvature of the inner contour 111 and the outer contour 112 in the curved waveguide segment 110 gradually increases and then gradually decreases along the bending direction FW. This allows the curvature of the inner and outer contours of the curved waveguide segment 110 to change slowly along the bending direction FW, so that the mode field can gradually adapt to the change in the waveguide direction during transmission, thereby reducing mode mismatch loss.

[0036] Furthermore, due to the larger curvature at the middle position of the curved waveguide segment 110, the mode field tends to shift outwards towards the bend. Therefore, in the aforementioned curved waveguide structure 100, the radial spacing between the inner contour 111 and the outer contour 112 is also set to gradually increase and then gradually decrease along the bending direction FW, that is, the radial width of the curved waveguide segment 110 gradually increases from both ends towards the middle. This results in a larger radial width of the curved waveguide segment 110 at the middle position, providing stronger lateral constraint on the mode field, thereby accommodating mode field shift and suppressing bending radiation loss.

[0037] Furthermore, in the aforementioned curved waveguide structure 100, the curvature of the inner contour 111, the curvature of the outer contour 112, and the radial distance between the inner contour 111 and the outer contour 112 reach their maximum values ​​at the same location. This makes the widest position of the curved waveguide segment 110 correspond to the position with the largest curvature, thereby more effectively suppressing bending radiation loss.

[0038] Optional, see reference Figure 2 The radial distance G between the outer edge 122 and the inner contour 111 of the auxiliary waveguide section 120 falls between 0.15 micrometers and 1 micrometer.

[0039] Specifically, when the radial spacing G is too large, the evanescent field coupling strength between the auxiliary waveguide section 120 and the curved waveguide section 110 is weak, making it difficult to effectively suppress the bending radiation loss. Therefore, setting the radial spacing G between the outer edge 122 and the inner contour 111 of the auxiliary waveguide section 120 to less than or equal to 1 micrometer can make the suppression effect of the auxiliary waveguide section 120 more obvious, thereby reducing the transmission loss of the curved waveguide structure 100.

[0040] Furthermore, when the radial spacing G is too small, the processing accuracy requirements of the auxiliary waveguide section 120 will increase significantly, and the processing yield will decrease substantially, which is not conducive to mass production. Therefore, setting the radial spacing G to 0.15 micrometers to 1 micrometer can simplify the manufacturing process of the bent waveguide structure 100, thereby reducing mass production costs.

[0041] In some embodiments, reference Figure 1 and Figure 2 The radial width W of the auxiliary waveguide section 120 is a constant value. The radial width W is the distance between the inner edge 121 and the outer edge 122 of the auxiliary waveguide section 120 in the radial direction FJ. This makes the effect of the auxiliary waveguide section 120 on improving the equivalent refractive index on the inner side of the bend more uniform, thereby further reducing the mode perturbation introduced by the change in the cross-section of the auxiliary waveguide section 120 itself, and thus reducing the transmission loss of the bend waveguide structure 100.

[0042] As a concrete example, in Figure 1 In the curved waveguide structure 100 shown, the bending design radius R of the curved waveguide segment 110 is 25 micrometers, the bending angle θ is set to 82°, and the nominal widths of the input straight waveguide segment 140 and the output straight waveguide segment 150 are 0.9 micrometers. The outer contour 112 and inner contour 111 of the curved waveguide segment 110 are both generated using parametric smooth curves, with the inner contour 111 parameter being 0.050 and the outer contour 112 parameter being 0.190. The radial width W of the auxiliary waveguide segment 120 is 0.1 micrometers, and the radial distance G between the outer edge 122 and the inner contour 111 of the auxiliary waveguide segment 120 is 0.169 micrometers. When simulation tests are performed under these conditions, the transmission spectrum of the curved waveguide structure 100 is as follows: Figure 3 As shown, by Figure 3 It can be seen that when the light wavelength is below 1360nm, the transmission loss of the bent waveguide structure 100 is less than 0.03dB, which is at a low level.

[0043] It is understood that the radial width W of the auxiliary waveguide segment 120 in this application is not limited to a constant value. For example, some embodiments of this application also provide another curved waveguide structure 200, which differs from the aforementioned curved waveguide structure 100 in that... Figure 4 In the curved waveguide structure 200 shown, the auxiliary waveguide section 120 is set as a whole fan-shaped structure, and the auxiliary waveguide section 120 can also achieve the function of reducing transmission loss.

[0044] Optional, see reference Figure 2 The radial width W of the auxiliary waveguide section 120 is greater than or equal to 0.1 micrometers. This simplifies the fabrication process of the auxiliary waveguide section 120, thereby reducing the manufacturing cost of the curved waveguide structure 100.

[0045] Optionally, the auxiliary waveguide segment 120 consists of multiple sub-waveguide segments (not shown) arranged at FW intervals along the bending direction.

[0046] Specifically, the structure of the auxiliary waveguide section 120 is not limited to Figure 1 The structure shown is a continuously extending structure. In some other embodiments, the auxiliary waveguide section 120 can also be constructed by arranging multiple sub-waveguide segments at intervals, wherein the outer edges of the multiple sub-waveguide segments constitute the outer edge 122 of the auxiliary waveguide section 120. In this case, the auxiliary waveguide section 120 can still achieve the effect of suppressing bending radiation loss. Moreover, the equivalent refractive index of the multiple sub-waveguide segments can be adjusted by parameters such as the width and gap of each sub-waveguide segment, thereby making the adjustment of the equivalent refractive index of the auxiliary waveguide section 120 more flexible.

[0047] In some embodiments, the plurality of sub-waveguide segments include an input tapered segment and an output tapered segment. The input tapered segment is located at one end of the auxiliary waveguide segment 120 near the input end of the curved waveguide segment 110. In the input tapered segment, the radial width gradually increases along the optical transmission direction. The output tapered segment is located at one end of the auxiliary waveguide segment 120 near the output end of the curved waveguide segment 110. In the output tapered segment, the radial width gradually decreases along the optical transmission direction.

[0048] Specifically, when the auxiliary waveguide section 120 is composed of multiple sub-waveguide sections, an input tapered section and an output tapered section can be respectively provided at both ends of the auxiliary waveguide section 120. The radial width of the input tapered section gradually increases along the optical transmission direction, while the radial width of the output tapered section gradually decreases along the optical transmission direction. The advantage of this arrangement is that it allows the modulation of the mode field by the auxiliary waveguide section 120 to have a gradual transition at both ends, thereby avoiding mode abrupt changes caused by the sudden appearance or disappearance of the auxiliary waveguide section 120 at its ends, thus reducing mode mismatch loss.

[0049] In some embodiments, reference Figure 1 The curved waveguide structure 100 further includes: an input straight waveguide section 140, disposed at the input end of the curved waveguide section 110 and tangentially connected to the curved waveguide section 110; and an output straight waveguide section 150, disposed at the output end of the curved waveguide section 110 and tangentially connected to the curved waveguide section 110.

[0050] Specifically, the input straight waveguide section 140 and the input end of the curved waveguide section 110 are tangentially connected. This ensures that there is no abrupt change in direction at the junction of the input straight waveguide section 140 and the curved waveguide section 110, achieving a continuous transition. As a result, when the mode field enters the curved waveguide section 110 from the input straight waveguide section 140, it can smoothly adapt to the change in waveguide direction, thereby reducing the mode mismatch loss and reflection loss caused by the change in direction, and thus reducing the transmission loss of the curved waveguide structure 100.

[0051] Similarly, the output straight waveguide section 150 and the output end of the curved waveguide section 110 are tangentially connected, which prevents the output straight waveguide section 150 and the curved waveguide section 110 from having a sudden change in direction at the junction, thus achieving a continuous transition and reducing the transmission loss of the curved waveguide structure 100.

[0052] It should be noted that, Figure 1 In the bent waveguide structure 100 shown, the bending angle θ is 82°. This angle setting is exemplary. The bending angle θ of the bent waveguide structure 100 of this application can also be set to other angles, which can be determined according to the requirements of changes in the optical transmission direction. For example, in Figure 5 In the bent waveguide structure 300 shown, the bending angle is set to 180°. In addition, the bending radius of the bent waveguide structure 100 can be adjusted according to the material, operating wavelength and process design rules of the bent waveguide section 110.

[0053] Furthermore, it should be noted that the waveguide widths of the input straight waveguide section 140 and the output straight waveguide section 150 in this application can be set according to actual application requirements. For example, when using a silicon nitride optical waveguide for optical transmission, the waveguide widths of the input straight waveguide section 140 and the output straight waveguide section 150 can be set to 3 micrometers to support wide waveguide single-mode transmission.

[0054] In this application, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "height," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the purpose of simplifying the description of this application and do not indicate that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. In other words, they should not be construed as limitations on this application.

[0055] In this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating the relative importance of the indicated features or the number of indicated technical features. Therefore, a feature specified as "first" or "second" may explicitly include at least one of those features. In this application, "multiple" means at least two, such as two, three, etc.; "several" means at least one, such as one, two, three, etc., unless otherwise explicitly specified.

[0056] In this application, unless otherwise expressly defined, the terms "installation," "connection," "linking," "fixing," "setting," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can also refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0057] In this application, unless otherwise expressly defined, the terms "above," "on top of," "over," "above," "below," "below," "below," or "below" for "first feature over second feature" can refer to the first and second features being in direct contact, or to the first and second features being in indirect contact through an intermediate medium. Furthermore, "above," "over," and "below" for "first feature over second feature" can mean the first feature is directly above or diagonally above the second feature, or simply indicates that the horizontal height of the first feature is higher than the horizontal height of the second feature. Similarly, "below," "below," and "below" for "first feature over second feature" can mean the first feature is directly below or diagonally below the second feature, or simply indicates that the horizontal height of the first feature is lower than the horizontal height of the second feature.

[0058] It should be understood that the above embodiments are exemplary and are not intended to include all possible embodiments covered by the claims. Various modifications and changes can be made to the above embodiments without departing from the scope of this disclosure. Similarly, the various technical features of the above embodiments can be arbitrarily combined to form other embodiments of this application that may not be explicitly described. Therefore, the above embodiments only illustrate several embodiments of this application and do not limit the scope of protection of this patent application.

Claims

1. A curved waveguide structure, characterized in that, include: A curved waveguide segment having an inner contour and an outer contour; the curved waveguide segment bends toward the side containing the inner contour. An auxiliary waveguide segment is disposed inside the inner contour and extends along the bending direction; the bending direction is the extension direction of the inner contour. The curved waveguide segment and the auxiliary waveguide segment are filled with a cladding; the refractive index of the auxiliary waveguide segment is greater than that of the cladding.

2. The curved waveguide structure according to claim 1, characterized in that, The radial distance between the outer edge of the auxiliary waveguide segment and the inner contour is a constant value; the outer edge of the auxiliary waveguide segment is the side edge of the auxiliary waveguide segment closest to the inner contour; the radial distance is the distance between the outer edge of the auxiliary waveguide segment and the inner contour in the radial direction; the radial direction is perpendicular to the bending direction.

3. The curved waveguide structure according to claim 1, characterized in that, The curvature of the inner contour and the curvature of the outer contour both gradually increase and then gradually decrease along the bending direction; the radial distance between the inner contour and the outer contour gradually increases and then gradually decreases along the bending direction; the curvature of the inner contour, the curvature of the outer contour, and the radial distance between the inner contour and the outer contour reach their maximum values ​​at the same position.

4. The curved waveguide structure according to claim 1, characterized in that, The radial distance between the outer edge of the auxiliary waveguide segment and the inner contour falls between 0.15 micrometers and 1 micrometer.

5. The curved waveguide structure according to claim 1, characterized in that, The refractive index of the material in the auxiliary waveguide section is less than or equal to the refractive index of the material in the curved waveguide section.

6. The curved waveguide structure according to claim 1, characterized in that, The radial width of the auxiliary waveguide segment is a constant value; the radial width is the distance between the inner edge and the outer edge of the auxiliary waveguide segment in the radial direction.

7. The curved waveguide structure according to claim 1, characterized in that, The radial width of the auxiliary waveguide segment is greater than or equal to 0.1 micrometers.

8. The curved waveguide structure according to any one of claims 1-7, characterized in that, The auxiliary waveguide segment is composed of multiple sub-waveguide segments arranged at intervals along the bending direction.

9. The curved waveguide structure according to claim 8, characterized in that, The plurality of sub-waveguide segments include: An input tapered section is located at one end of the auxiliary waveguide section near the input end of the curved waveguide section; in the input tapered section, the radial width of the input tapered section gradually increases along the optical transmission direction. The output tapered section is located at one end of the auxiliary waveguide section near the output end of the curved waveguide section; in the output tapered section, the radial width of the output tapered section gradually decreases along the optical transmission direction.

10. The curved waveguide structure according to any one of claims 1-7, characterized in that, Also includes: An input straight waveguide segment is located at the input end of the curved waveguide segment and is tangentially connected to the curved waveguide segment; An output straight waveguide section is located at the output end of the curved waveguide section and is tangentially connected to the curved waveguide section.

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