A silicon-based multimode converter based on Bezier curve profile

Abstract

The present invention discloses a silicon-based multimode mode converter based on a Bezier curve profile. The converter comprises, from bottom to top, a silicon substrate, a buried oxide layer, a silicon waveguide layer, and a silicon dioxide upper cladding layer. The buried oxide layer is grown on the surface of the silicon substrate, the silicon waveguide layer is grown on the surface of the buried oxide layer, and the silicon dioxide upper cladding layer covers the upper surfaces of the buried oxide layer and the silicon waveguide layer. This invention significantly reduces the size of the mode converter, reduces reflection loss, increases operating bandwidth, and eases manufacturing difficulty.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated optics, and in particular to a silicon-based multi-mode converter based on a Bezier curve profile. Background Art

[0002] With the rapid development of artificial intelligence, integrated photonic circuits (PICs) have gained widespread attention and application. To further expand the capacity of optical communication systems, mode division multiplexing (MDM) technology has become a key research focus in the field of optical communications in recent decades. MDM leverages the differences in optical waveguide modes to achieve parallel transmission of different modes, significantly increasing the system's transmission capacity. In particular, in the field of silicon-based photonics, MDM technology has gradually transitioned from theoretical to practical application, paving a new path for high-speed, high-capacity optical communication systems.

[0003] The core of mode division multiplexing technology lies in achieving efficient modulation, demodulation, and conversion of different optical waveguide modes. This requires the design of a series of key components, including mode multiplexers, mode converters, mode filters, and mode demultiplexers. Mode converters enable efficient conversion between different optical modes, ensuring that signals can switch freely between them. Silicon-based photonics platforms, due to their superior integration and compatibility, can achieve conversion and control of multiple optical modes on the same platform. This makes silicon-based mode converters extremely promising for high-speed optical communications.

[0004] In recent years, optical mode converters have made considerable progress. Traditional mode converters are implemented using complex optical components such as multilayer mirrors, prisms, and fiber bundles, which have limitations in terms of integration and cost. With the rise of silicon-based photonics, a variety of efficient mode converter designs have been proposed based on different waveguide structures, such as directional couplers, multimode interference couplers, and subwavelength gratings. However, they all suffer from narrow bandwidth, large size, and single functionality. Therefore, higher integration, higher performance, and smaller size mode converters are an inevitable requirement for future development.

[0005] Based on this background, it is necessary to design a silicon-based multimode mode converter based on Bezier curve profile, which can realize the conversion of multiple modes on a single device, realize a multifunctional, high-performance mode converter, and ensure compact size. Summary of the Invention

[0006] Purpose of the invention: The present invention provides a silicon-based multimode mode converter based on a Bezier curve profile, which can significantly reduce the size of the mode converter, reduce reflection loss, increase the operating bandwidth, and reduce manufacturing difficulty.

[0007] Technical solution: The silicon-based multimode mode converter based on a Bezier curve profile described in the present invention includes: from bottom to top, a silicon-based substrate, a buried oxide layer, a silicon waveguide layer, and a silicon dioxide upper cladding layer; wherein the buried oxide layer is grown on the surface of the silicon-based substrate, the silicon waveguide layer is grown on the surface of the buried oxide layer, and the silicon dioxide upper cladding layer covers the upper surfaces of the buried oxide layer and the silicon waveguide layer.

[0008] Furthermore, the silicon waveguide layer is provided with an intermediate conversion functional area, which is, in order from left to right, an input waveguide, a left Bezier curve contour gradient waveguide, a middle rectangular waveguide, a right Bezier curve contour gradient waveguide, and an output waveguide.

[0009] Furthermore, the width of the Bezier curve gradient waveguide on the left starts to gradually change from the right side of the input waveguide, gradually widening to the same width as the middle rectangular waveguide, and the gradient trajectory is defined by the Bezier function. The width of the Bezier curve gradient waveguide on the right starts to gradually change from the right side of the middle rectangular waveguide, gradually narrowing to the same width as the output waveguide.

[0010] Furthermore, the upper and lower sides of the left Bezier curve contour gradient waveguide and the right Bezier curve contour gradient waveguide are uniquely determined by the coordinate parameters of the control points corresponding to the cubic Bezier curves.

[0011] Furthermore, the left-side Bezier curve contour gradient waveguide, the middle rectangular waveguide, and the right-side Bezier curve contour gradient waveguide in the middle conversion function area are composed of multiple identical periodic units arranged symmetrically on the left and right. The materials of each periodic unit are random, and each periodic unit is filled with silicon or silicon dioxide. The two filling methods are represented by 1 and 0, respectively. The performance of the device under the two filling materials of the first periodic unit is calculated, and the periodic unit corresponding to the higher quality factor is retained through the quality factor definition. The same optimization is continued for the next periodic unit until the calculation of the last periodic unit is completed, completing a round of optimization. The optimization is repeated, and when the quality factor reaches the threshold or no longer increases, the optimization ends, and the optimized structure is obtained.

[0012] Furthermore, the function of the intermediate conversion functional area is to convert the TE0 mode of the input waveguide into the TE0 mode of the output waveguide; convert the TE1 mode of the input waveguide into the TE2 mode of the output waveguide; and convert the TE2 mode of the input waveguide into the TE1 mode of the output waveguide.

[0013] Furthermore, the width of the input waveguide and the output waveguide is 1.0-1.3 μm, and the height is 220 nm.

[0014] Furthermore, the length of the left Bezier curve gradient waveguide and the right Bezier curve gradient waveguide is 1.4-1.8 μm, and the height is 220 nm, and the length of the middle rectangular waveguide is 1.6-2.0 μm, the width is 1.8-2.0 μm, and the height is 220 nm.

[0015] Furthermore, the etching radius of the periodic unit is 50 nm, and the etching height is 220 nm.

[0016] Furthermore, the silicon-based substrate is a silicon wafer of standard size, the buried oxide layer is made of silicon dioxide material and is thermally grown on the silicon-based substrate, with a thickness of 2 to 3 μm, and the material of the upper cladding layer is also silicon dioxide.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) Large working bandwidth: the device can operate in the bandwidth range of 1400-1600nm, covering the important S, C and part of the E, L bands of optical communication; (2) Small structural size: through the optimized combination of Bezier curve profile and direct binary algorithm, the size of the device is less than 4.8μm×1.8μm; (3) The device is rich in functions: the conversion from TE0 mode to TE0, the conversion from TE1 mode to TE2, and the conversion from TE2 mode to TE1 can be realized on a single device; (4) Low manufacturing difficulty: the present invention only uses a single-layer silicon waveguide and only needs to be manufactured through one etching under the complementary metal oxide semiconductor (CMOS) process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the structure of the silicon-based multi-mode converter of the present invention.

[0019] Figure 2 FIG. 4 is a side view of the silicon-based multi-mode converter of the present invention.

[0020] Figure 3 This is a distribution diagram of electric field components of the silicon-based multimode mode converter of the present invention that realizes conversion from TE0 mode to TE0, conversion from TE1 mode to TE2, and conversion from TE2 mode to TE1 at an operating wavelength of 1.55 μm.

[0021] Figure 4 This is a bandwidth diagram of the silicon-based multimode mode converter of the present invention that realizes conversion from TE0 mode to TE0, conversion from TE1 mode to TE2, and conversion from TE2 mode to TE1 within the 1400nm-1600nm band.

[0022] Among them, 1. Input waveguide; 2. Bezier curve contour gradient waveguide on the left; 3. Middle rectangular waveguide; 4. Bezier curve contour gradient waveguide on the right; 5. Bezier curve; 6. Periodic unit; 7. Output waveguide; 8. Silicon dioxide upper cladding layer; 9. Silicon-based substrate; 10. Buried oxide layer; 11. Silicon waveguide layer. DETAILED DESCRIPTION

[0023] like Figure 1 and Figure 2 As shown, a silicon-based multimode mode converter based on a Bezier curve profile comprises, from bottom to top, a silicon substrate, a buried oxide layer, a silicon waveguide layer, and a silicon dioxide upper cladding layer. The buried oxide layer is grown on the surface of the silicon substrate, the silicon waveguide layer is grown on the surface of the buried oxide layer, and the silicon dioxide upper cladding layer covers the upper surfaces of the buried oxide layer and the silicon waveguide layer.

[0024] The intermediate conversion functional area is located in the silicon waveguide layer, including an output waveguide, a Bezier curve gradient waveguide on the left, a middle rectangular waveguide, a Bezier curve gradient waveguide on the right, and an output waveguide.

[0025] The width of the Bezier curve gradient waveguide on the left starts from the right side of the input waveguide and gradually widens to the same width as the middle rectangular waveguide. The gradient trajectory is defined by the Bezier function. The width of the Bezier curve gradient waveguide on the right starts from the right side of the middle rectangular waveguide and gradually narrows to the same width as the output waveguide.

[0026] The upper and lower sides of the left and right Bezier curve gradient waveguides are uniquely determined by the coordinate parameters of the control points corresponding to the cubic Bezier curves. The cubic Bezier curve is confirmed by four coordinate points. The first and second coordinate points of the left upper Bezier curve coincide with the horizontal and vertical coordinates of the upper vertex of the input waveguide. The fourth coordinate point coincides with the coordinates of the upper vertex on the left side of the middle rectangular waveguide. The abscissa of the third coordinate point is consistent with the abscissa of the upper vertex of the input waveguide, and the ordinate is half the sum of the ordinates of the upper vertex of the input waveguide and the upper vertex on the left side of the middle rectangular waveguide. The first and second coordinate points of the left lower Bezier curve coincide with the horizontal and vertical coordinates of the lower vertex of the input waveguide. The fourth coordinate point coincides with the coordinates of the lower vertex on the left side of the middle rectangular waveguide. The abscissa of the third coordinate point is consistent with the abscissa of the lower vertex of the input waveguide, and the ordinate is half the sum of the ordinates of the lower vertex of the input waveguide and the lower vertex on the left side of the middle rectangular waveguide.

[0027] The first and second coordinate points of the upper right Bezier curve coincide with the horizontal and vertical coordinates of the upper vertex of the output waveguide, the fourth coordinate point coincides with the coordinate of the upper right vertex of the middle rectangular waveguide, the third coordinate point has the same horizontal coordinate as the upper vertex of the output waveguide, and the vertical coordinate is half the sum of the vertical coordinates of the upper vertex of the output waveguide and the upper vertex on the left side of the middle rectangular waveguide. The first and second coordinate points of the lower right Bezier curve coincide with the horizontal and vertical coordinates of the lower vertex of the output waveguide, the fourth coordinate point coincides with the coordinate of the lower right vertex of the middle rectangular waveguide, the third coordinate point has the same horizontal coordinate as the lower vertex of the output waveguide, and the vertical coordinate is half the sum of the vertical coordinates of the lower vertex of the output waveguide and the lower vertex on the right side of the middle rectangular waveguide.

[0028] The intermediate conversion function area is composed of multiple identical periodic units arranged symmetrically on the left and right. The materials of each periodic unit are random. Each periodic unit is filled with silicon or silicon dioxide, and the two filling methods are represented by 1 and 0 respectively. The performance of the device of the first periodic unit under the two filling materials is calculated. The quality factor is defined and the periodic unit corresponding to the higher quality factor is retained. The same optimization is continued for the next periodic unit until the calculation of the last periodic unit is completed, completing a round of optimization. The optimization is repeated. When the quality factor reaches the threshold or no longer increases, the optimization ends and the optimized structure is obtained.

[0029] The function of the intermediate conversion functional area is to convert the TE0 mode of the input waveguide into the TE0 mode of the output waveguide; convert the TE1 mode of the input waveguide into the TE2 mode of the output waveguide; and convert the TE2 mode of the input waveguide into the TE1 mode of the output waveguide.

[0030] Some dimensions meet the following conditions: the width of the input waveguide and the output waveguide are both 1.0~1.3μm, and the height is 220nm; the length of the Bezier curve gradient waveguide on the left and the Bezier curve gradient waveguide on the right are 1.4~1.8μm, and the height is 220nm; the length of the middle rectangular waveguide is 1.6~2.0μm, the width is 1.8~2.0μm, and the height is 220nm; the etching radius of the periodic unit is 50nm, and the etching height is 220nm.

[0031] The silicon-based substrate is a silicon wafer of standard size. The buried oxide layer uses silicon dioxide material and is thermally grown on the silicon-based substrate. Its thickness is 2 to 3 μm. The material of the upper cladding layer is also silicon dioxide.

[0032] Figure 3 The electric field component distribution diagram of the silicon-based multimode mode converter of the present invention realizing the conversion from TE0 mode to TE0, the conversion from TE1 mode to TE2, and the conversion from TE2 mode to TE1 at the working wavelength of 1.55 μm is given.

[0033] Figure 4 The bandwidth diagram of the silicon-based multimode mode converter of the present invention for realizing conversion from TE0 mode to TE0, conversion from TE1 mode to TE2, and conversion from TE2 mode to TE1 is given.

[0034] In summary, this invention proposes a silicon-based multimode mode converter based on a Bezier curve profile, which offers advantages such as small size, wide bandwidth, and multiple functions. This mode converter can be designed and optimized using inverse design algorithms, including direct binary search, and the designed device has good versatility in the optoelectronics field. The application value of this invention lies in the development of a universal, high-performance, and compact mode converter, which can expand the application of mode division multiplexing technology in optical communication systems and promote the miniaturization, integration, and high-performance of optical interconnect systems.

Claims

1. A silicon-based multi-mode converter based on Bezier curve profile, characterized in that: include: From bottom to top, there are a silicon-based substrate (9), a buried oxide layer (10), a silicon waveguide layer (11), and a silicon dioxide upper cladding layer (8); wherein, the buried oxide layer (10) is grown on the surface of the silicon-based substrate (9), the silicon waveguide layer (11) is grown on the surface of the buried oxide layer (10), and the silicon dioxide upper cladding layer (8) covers the upper surfaces of the buried oxide layer (10) and the silicon waveguide layer (11); the silicon waveguide layer (11) is provided with an intermediate conversion functional area, which is sequentially arranged from left to right, including an input waveguide (1), a left Bezier curve contour gradient waveguide (2), a middle rectangular waveguide (3), a right Bezier curve contour gradient waveguide (4), and an output waveguide (7); the left Bezier curve contour gradient waveguide in the intermediate conversion functional area is a rectangular waveguide (3), a right Bezier curve contour gradient waveguide (4), and a right Bezier curve contour gradient waveguide (7); The contour gradient waveguide (2), the middle rectangular waveguide (3), and the right Bezier curve contour gradient waveguide (4) are composed of multiple identical periodic units (6) arranged symmetrically on the left and right. The materials of each periodic unit are random. Each periodic unit is filled with silicon or silicon dioxide, and the two filling methods are represented by 1 and 0 respectively; the performance of the device of the first periodic unit under the two filling materials is calculated, and the periodic unit corresponding to the higher quality factor is retained through the definition of quality factor; the same optimization is continued for the next periodic unit until the calculation of the last periodic unit is completed, which completes a round of optimization; the optimization is repeated, and when the quality factor reaches a threshold or no longer increases, the optimization ends, and the optimized structure is obtained.

2. The silicon-based multi-mode converter based on Bezier curve profile according to claim 1, characterized in that: The width of the Bezier curve gradient waveguide (2) on the left gradually changes from the right side of the input waveguide (1) and gradually widens to the same width as the middle rectangular waveguide (3), and the gradient trajectory is defined by the Bezier function. The width of the Bezier curve gradient waveguide (4) on the right gradually changes from the right side of the middle rectangular waveguide (3) and gradually narrows to the same width as the output waveguide (7).

3. The silicon-based multi-mode converter based on Bezier curve profile according to claim 1, wherein: The upper and lower sides of the left Bezier curve contour gradient waveguide (2) and the right Bezier curve contour gradient waveguide (4) are uniquely determined by the coordinate parameters of the control points corresponding to the cubic Bezier curve (5).

4. The silicon-based multi-mode converter based on Bezier curve profile according to claim 1, wherein: The function of the intermediate conversion functional area is to convert the TE0 mode of the input waveguide into the TE0 mode of the output waveguide; convert the TE1 mode of the input waveguide into the TE2 mode of the output waveguide; and convert the TE2 mode of the input waveguide into the TE1 mode of the output waveguide.

5. The silicon-based multi-mode converter based on Bezier curve profile according to claim 1, wherein: The width of the input waveguide (1) and the output waveguide (7) is 1.0 to 1.3 μm, and the height is 220 nm.

6. The silicon-based multi-mode converter based on Bezier curve profile according to claim 1, characterized in that: The length of the left Bezier curve profile gradient waveguide (2) and the right Bezier curve profile gradient waveguide (4) is 1.4-1.8 μm, and the height is 220 nm. The length of the middle rectangular waveguide (3) is 1.6-2.0 μm, the width is 1.8-2.0 μm, and the height is 220 nm.

7. The silicon-based multi-mode converter based on Bezier curve profile according to claim 1, characterized in that: The etching radius of the periodic unit (6) is 50 nm, and the etching height is 220 nm.

8. The silicon-based multi-mode converter based on Bezier curve profile according to claim 1, wherein: The silicon-based substrate (9) is a silicon crystal of standard size. The buried oxide layer is made of silicon dioxide and is thermally grown on the silicon-based substrate. The thickness of the buried oxide layer is 2 to 3 μm. The material of the upper cladding layer is also silicon dioxide.

Images