Waveguide crossing device made of different materials and used for silicon optical chip

Abstract

The invention discloses a waveguide crossing device made of different materials and used for a silicon optical chip, which comprises an upper layer waveguide and a lower layer waveguide which are crossed with each other, and is characterized in that the lower layer waveguide sequentially comprises a first width fixed section, a first width transition section, a second width fixed section, a second width transition section and a third width fixed section; the first width transition section and the second width transition section are of a linear transition trapezoidal structure, and the width of the first width transition section is gradually reduced from the second width fixed section until the width of the first width transition section is the same as that of the second width fixed section; and the width of the second width transition section is gradually increased from the second width fixed section until the width of the second width transition section is the same as that of the third width fixed section. By means of the waveguide cross structure design, low transmission loss and low reflection of the silicon-based waveguide and low crosstalk between the silicon-based waveguide and the silicon nitride waveguide are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon photonics chips, and particularly to a waveguide crossing device made of different materials for silicon photonics chips. Background Art

[0002] With the development of technology, the device density of silicon photonics chips is continuously increasing. And due to the requirements of functions, performance, etc., different materials are involved in the devices. Therefore, on silicon photonics chips, the cross structure between waveguides is inevitable. In chip design, as the main device, the silicon-based waveguide must have very low loss (about 0.01 dB) and very low light wave reflection (< -26 dB) when the transmitted light wave passes through the cross structure, so as not to cause device degradation and increase the overall insertion loss of the silicon photonics chip.

[0003] Figure 1 Figures (a)-1 and (b) show typical waveguide crossing structures on existing mass-produced silicon photonics chips. Since the vertical distance between waveguides is very close, generally only about 80 - 90 nm, crosstalk will occur between waveguides, which will inevitably affect the waveguide performance on the silicon photonics chip, mainly causing high loss and high reflection when the light wave passes through the waveguide crossing structure. If the device structure requires, and when it is unavoidable and the number of waveguide crossings must be many, then due to high loss and high reflection, the silicon-based chip will basically be unusable. At the same time, due to the waveguide manufacturing process on the silicon-based chip, compared with the silicon nitride-based waveguide, its waveguide loss is several times higher. Therefore, the silicon-based waveguide has a lower tolerance for loss.

[0004] There is a need to design a waveguide structure with lower loss to meet the requirements of the device. Summary of the Invention

[0005] In view of the above problems, the present invention provides a waveguide crossing device made of different materials for silicon photonics chips, which includes an upper waveguide and a lower waveguide that cross each other. The lower waveguide successively includes a first width fixed section, a first width tapered section, a second width fixed section, a second width tapered section, and a third width fixed section. The first width tapered section and the second width tapered section are in a linear tapered trapezoidal structure. The width of the first width tapered section gradually decreases from the second width fixed section until its width is the same as that of the second width fixed section. The width of the second width tapered section gradually increases from the second width fixed section until its width is the same as that of the third width fixed section.

[0006] Preferably, the widths of the first width fixed section and the third width fixed section are the same.

[0007] ​Preferably, the width at the widest part of the first width-varying section is the same as the width of the first width-fixed section; the width at the widest part of the second width-varying section is the same as the width of the third width-fixed section.

[0008] Preferably, the first width-varying section and the second width-varying section have the same length.

[0009] Preferably, the lengths of the first width-varying section and the second width-varying section are 50 µm - 500 µm.

[0010] Preferably, the second width-fixed section is located below the upper waveguide, and its length is the same as the width of the upper waveguide.

[0011] Preferably, the width of the second width-fixed section is 300 nm.

[0012] Preferably, the width of the upper waveguide is 700 nm - 800 nm.

[0013] Preferably, the widths of the first width-fixed section and the second width-fixed section are 400 nm - 500 nm.

[0014] Preferably, the upper waveguide is a silicon nitride waveguide, and the lower waveguide is a silicon-based waveguide. Description of the Drawings

[0015] By reading the following detailed description of the preferred embodiments, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings: Figure 1 Figures (a)-1(b) are structural diagrams of a double-layer waveguide crossing device in the prior art, where Figure 1 Figure (a) shows the structural relationship of the double-layer waveguide, Figure 1 Figure (b) shows the distance between the upper and lower layers of the double-layer waveguide; Figures 2(a)-2(b) are schematic structural diagrams of the double-layer waveguide crossing device of the present invention, where Figure 2(a) is the overall structural diagram and Figure 2(b) is the structural diagram of the lower waveguide; Figure 3 Figures (a)-3(d) are Figure 1 loss results of the simulation calculation of the double-layer waveguide crossing device shown, where Figure 3 Figure (a) is the optical wave transmission path of the waveguide device, Figure 3 Figure (b) is the loss of the optical wave of the device from port 1 to port 2, Figure 3 Figure (c) is the reflection of the optical wave of the device from port 1 to port 1, Figure 3 Figure (d) is the crosstalk of the optical wave of the device from port 1 to port 3 or 4; Figure 4 (a)-(c) are the loss results of the simulation calculation of the exemplary structure of the double-layer waveguide crossing device of the present invention shown in Figure 2; Figure 4 (a) is the loss of the optical wave of the device from port 1 to port 2, Figure 4 (b) is the reflection of the optical wave of the device from port 1 to port 1, Figure 4 (c) is the crosstalk of the optical wave of the device from port 1 to port 3 or 4; Figure 5 (a)-(b) are the loss results of the simulation calculation of two other exemplary structures of the double-layer waveguide crossing device of the present invention, where Figure 5 (a) is the loss when the width of the second width-fixed section 1-3 is 200 nm, Figure 5 (b) is the loss when the width of the second width-fixed section 1-3 is 400 nm. Detailed implementation manners

[0016] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following provides a detailed description of a waveguide crossing structure of different materials proposed according to the present invention in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. In addition, the specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0017] The term "and / or" in this article is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B is specifically understood as: it can include both A and B at the same time, A can exist alone, or B can exist alone, and it can have any one of the above three situations.

[0018] As shown in Figures 2(a) and 2(b), a waveguide crossing device of different materials applied to a silicon photonic chip proposed by the present invention includes an upper waveguide 1 and a lower waveguide 2 that cross each other. The vertical distance between the upper waveguide 1 and the lower waveguide 2 is preferably 80 nm - 90 nm. The material of the upper waveguide is preferably silicon nitride, and the material of the lower waveguide is preferably a silicon-based material. As Figure 1 shown in (a)-(b), the loss of the two-layer crossed waveguide structure device in the prior art is large, and the upper and lower waveguides are both designed with the same width. The present invention creatively designs the crossed waveguide structure and designs the lower waveguide 1 as a tapered structure.

[0019] As shown in FIGS. 2(a)-2(b), the upper waveguide 1 and the lower waveguide 2 are spaced apart by a certain distance. The lower waveguide 1 sequentially includes a first width-fixed section 1-1, a first width-gradual section 1-2, a second width-fixed section 1-3, a second width-gradual section 1-4, and a third width-fixed section 1-5. The widths of the first width-fixed section 1-1 and the third width-fixed section 1-5 are designed to be the same, and the widths at the widest points of the first width-gradual section 1-2 and the second width-gradual section 1-4 are the same as those of the first and third width-fixed sections 1-1 and 1-5, and this width is preferably 400 nm - 500 nm. The first width-gradual section 1-2 and the second width-gradual section 1-4 are in a linear-gradual trapezoidal structure, and their lengths are preferably the same, and their lengths are preferably 50 µm - 500 µm. The width of the first width-gradual section 1-2 gradually decreases from the second width-fixed section 1-1 until its width is the same as that of the second width-fixed section 1-3; the width of the second width-gradual section 1-4 gradually increases from the second width-fixed section 1-3 until its width is the same as that of the third width-fixed section 1-5. The second width-fixed section 1-3 is located below the upper waveguide 2, and its length is the same as the width of the upper waveguide 2. The width of the upper waveguide 2 is 700 nm - 800 nm. The width of the second width-fixed section 1-3 is not the narrower the better, and is preferably 300 nm; if the width of this section is designed to be narrower or wider, it will cause an increase in loss, which is contrary to the design of the present invention.

[0020] The thickness of the lower waveguide 1 is preferably 210 nm - 220 nm, and the thickness of the upper waveguide 2 is preferably 200 - 500 nm.

[0021] Through the above structural design, low transmission loss, low reflection in the silicon-based waveguide, and low crosstalk with the silicon nitride waveguide are achieved.

[0022] Figure 3 (a)-(d) are Figure 1 the loss calculation results obtained from the simulation design of the existing cross-structured waveguide shown in FIGS. (a)-(b). Figure 1 In the example of (b), the distance between the upper and lower waveguides is 80 nm, the width of the upper waveguide (silicon nitride waveguide) is 700 nm, and the width of the lower waveguide (silicon-based waveguide) is 400 nm. It can be seen from the calculation of the simulation design that Figure 1 the typical cross structure of the prior art shown in FIGS. (a)-(b) has a loss as high as 0.04 dB and an optical wave reflection as high as 21.5 dB, as Figure 3 shown in FIGS. (b)-(c). As Figure 3 shown in (d), the crosstalk between different waveguides can be ignored.

[0023] Figure 4(a) - 4(c) are the loss calculation results obtained from the simulation design of the cross-structured waveguide of the present invention shown in Fig. 2(a) - 2(b). Figure 4 For the waveguide structures of (a) - 4(c), the distance between the upper and lower waveguides is the same as that in Figure 1 (b), which is also 80 nm. The width of the upper waveguide (silicon nitride waveguide) is 700 nm. The widths of the first fixed section 1-1 and the third fixed section 1-5 of the lower waveguide (silicon-based waveguide) are 400 nm, and the width of the second fixed section 1-3 is 300 nm. The lengths of the first and second width tapered sections 1-2 and 1-4 are 50 µm. It can be seen from the figure that through the waveguide cross structure designed by the present invention, its loss is reduced to 0.01 dB, as shown in Figure 4 (a), fully meeting the requirements for the loss of the cross-structured waveguide; as shown in Figure 4 (b), the optical wave reflection is reduced to -38 dB. The crosstalk suppression between different waveguides is 57 dB, as shown in Figure 4 (c), and its performance is better.

[0024] Figure 5 (a) - 5(b) show the simulation calculation results when the width of the second width fixed section 1-3 is 200 nm and 400 nm under the condition that other structures and dimensions are the same as those of the embodiment in Fig. 2(a) - 2(b). It can be seen from the calculation results that the losses reach 0.8 dB and 0.85 dB respectively, and the losses are too large to meet the requirements of waveguide design.

[0025] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they learn the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments as well as all changes and modifications falling within the scope of the present invention.

[0026] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A waveguide crossing device of different materials for a silicon photonic chip, comprising an upper waveguide and a lower waveguide crossing each other, characterized in that: The lower waveguide includes a first fixed width section, a first width gradient section, a second fixed width section, a second width gradient section, and a third fixed width section in sequence; the first width gradient section and the second width gradient section are in a linear gradient trapezoidal structure, and the width of the first width gradient section gradually decreases from the second fixed width section until its width is the same as that of the second fixed width section; the width of the second width gradient section gradually increases from the second fixed width section until its width is the same as that of the third fixed width section.

2. The waveguide intersection device of different materials for silicon photonic chip according to claim 1, characterized in that: The first fixed width section and the third fixed width section have the same width.

3. The waveguide intersection device of different materials for silicon photonic chip according to claim 1, characterized in that: The width of the first width gradient section at its widest point is the same as the width of the first width fixed section, and the width of the second width gradient section at its widest point is the same as the width of the third width fixed section.

4. The waveguide intersection device of different materials for silicon photonic chip according to claim 1, characterized in that: The first width gradient section and the second width gradient section have the same length.

5. The waveguide intersection device of different materials used in silicon photonic chips according to claim 4, characterized in that: The lengths of the first width gradient section and the second width gradient section are 50 μm-500 μm.

6. The waveguide intersection device of different materials for silicon photonic chip according to claim 1, characterized in that: The second fixed width section is located below the upper waveguide, and the length of the second fixed width section is the same as the width of the upper waveguide.

7. The waveguide intersection device of different materials for silicon photonic chip according to claim 1, characterized in that: The width of the second fixed-width segment is 300 nm.

8. The waveguide intersection device of different materials for silicon photonic chip according to claim 1, characterized in that: The width of the upper waveguide is 700nm-800nm.

9. The waveguide intersection device of different materials for silicon photonic chip according to claim 1, characterized in that: The widths of the first fixed-width segment and the second fixed-width segment are 400 nm-500 nm.

10. The waveguide intersection device of different materials for silicon photonic chip according to claim 1, characterized in that: The upper waveguide is a silicon nitride waveguide, and the lower waveguide is a silicon-based waveguide.

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