Optical power divider based on sub-wavelength grating enhanced conical ultrathin waveguide and preparation method thereof
By designing an optical power divider for a subwavelength grating-enhanced tapered waveguide on an ultrathin silicon waveguide platform, the problem of insufficient manufacturing tolerance in existing technologies has been solved, achieving low-loss, wide-bandwidth, and high-integration optical power distribution, which is suitable for next-generation silicon-based photonic integrated circuits.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHUHAI YIHONG COMM ENG CO LTD
- Filing Date
- 2026-03-19
- Publication Date
- 2026-05-12
AI Technical Summary
Existing optical power dividers on ultrathin silicon waveguide platforms suffer from insufficient manufacturing tolerance and difficulty in simultaneously achieving low loss, wide spectral bandwidth, and high integration, thus failing to meet the development needs of next-generation high-integration, high-robustness, and low-loss silicon-based photonic integrated chips.
An optical power divider design based on subwavelength grating-enhanced tapered ultrathin waveguides was adopted. By integrating subwavelength gratings in the coupling regions of three tapered waveguides, mode field overlap was improved. The optical power divider was fabricated by combining electron beam lithography and reactive plasma etching methods, achieving 50:50 optical power distribution and a wide bandwidth in an ultra-compact size.
Achieving insertion loss of less than 0.38 dB in the 1400–1700 nm wavelength range, with large manufacturing tolerance and small relative wavelength deviation, it can achieve arbitrary splitting ratios, enriching the diversity of power dividers for ultrathin silicon waveguides and providing a scalable solution for high-tolerance silicon photonic integrated circuits.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of optical communication device technology, and in particular to an optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide and its fabrication method. Background Technology
[0002] With the rapid development of data-intensive technologies such as 5G communication, artificial intelligence, and quantum computing, traditional electronic interconnects face problems such as limited bandwidth and low energy efficiency. Photonic integrated circuits (PICs) have become the preferred solution due to their ultra-high bandwidth and low latency. Among them, silicon-based photonics has become the mainstream integration platform due to its compatibility with CMOS processes, high refractive index contrast, and scalability. Conventional 220 nm thick silicon waveguides have shortcomings in evanescent field utilization and process tolerance, prompting the rise of silicon photonic platforms based on ultrathin waveguide architectures. Ultrathin silicon waveguides can be less than 100 nm thick, which can significantly reduce TE mode sidewall effects and transmission losses, making them suitable for optical switching, signal processing, and other scenarios. Their large waveguide top optical field extension ratio makes them suitable for gas and biochemical sensing. At the same time, ultrathin silicon / low-dimensional material heterostructures can enhance light-matter interactions, enabling the miniaturization of active devices and improving signal integrity and energy efficiency.
[0003] On the other hand, optical power dividers, as core components of on-chip signal processing and quantum integrated circuits, have been implemented in various ways. Regarding on-chip optical power divider research, in 2012, Sheng Zhen et al. from the Chinese Academy of Sciences proposed a 1×2 multimode interference (MMI) power divider, which exhibits an insertion loss (IL) of less than 0.1 dB in the wavelength range of 1530 nm to 1570 nm [IEEE Photonics Journal, 2012, 4(6): 2272-2277.]. In 2015, Lukas Chrostowski et al. from the University of British Columbia, Canada, proposed an asymmetric waveguide-assisted 2×2 directional coupler to achieve arbitrary power distribution, with an insertion loss of less than 1 dB and a spectral bandwidth of 75 nm [Optics Express, 2015, 23(3): 3795]. In 2016, Efstratios Skafidas et al. from the University of Melbourne, Australia, proposed a power divider based on adiabatic tapered waveguides. This divider uses three tapered waveguides to achieve adiabatic coupling and splitting of optical signals, achieving an insertion loss of less than 0.19 dB in the 1530 nm–1600 nm wavelength range. In 2018, Zhao Jia et al. from Shandong University used a multimode tapered branched waveguide as a Y-branch to achieve 50:50 power distribution, improving the power uniformity of the two output ports by 4 dB and achieving an insertion loss of less than 0.6 dB [Optik, 2019, 180: 866-872]. All of these optical power dividers are based on traditional thick silicon waveguide architectures, which suffer from insufficient process robustness and difficulty in simultaneously achieving low loss, wide spectral bandwidth, and high integration.
[0004] Regarding patents, in 2018, Liu Yong et al. of Jiangsu Haiwan Semiconductor Technology Co., Ltd. disclosed a multi-path Y-type optical power divider chip based on planar optical waveguides (Chinese Utility Model Patent: CN209117907U), which can realize multi-path power distribution and reduce insertion loss and process difficulty; in 2022, Wang Xibin et al. of Jilin University disclosed a few-mode optical power divider based on MMI optical waveguide structure (Chinese Invention Patent: CN114153027A), which uses organic polymers as waveguide materials, can realize multi-mode power distribution, has low cost and is suitable for mass production; in 2022, Subramaniam of GlobalFoundries (USA) Integrated Circuit Technology Co., Ltd. Krishnamursi et al. disclosed an optical power splitter containing three tapered waveguide cores (Chinese Invention Patent: CN115524787A), which achieves a customized splitting ratio by adjusting the overlap distance. Based on existing technologies, Y-type branch splitters have a simple structure but limited operating bandwidth; multimode interference devices rely on self-imaging effects and suffer from drawbacks such as large size and poor output power uniformity; directional couplers can adjust the splitting ratio through structural parameters but exhibit significant wavelength sensitivity; and while adiabatic couplers offer advantages such as wide bandwidth and short coupling length, the size of the tapered tip and waveguide gap is too narrow, resulting in low tolerance for manufacturing errors.
[0005] Therefore, improving the manufacturing tolerance and optimizing the overall performance of optical power dividers is of great significance. However, the research and application of high-performance optical power dividers for ultra-thin silicon waveguide platforms are still relatively scarce, which cannot meet the development needs of the next generation of highly integrated, robust, and low-loss silicon-based photonic integrated chips.
[0006] Therefore, existing technologies still need to be improved and developed. Summary of the Invention
[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide an optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide and its fabrication method, aiming to enrich the diversity of power dividers for ultrathin silicon waveguides and provide more options for the application of optical power dividers.
[0008] The technical solution of the present invention is as follows: In a first aspect, the present invention provides an optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide, wherein the optical power divider is a silicon-on-insulator with a top silicon layer having a preset pattern, the thickness of the top silicon layer being 70 nm, and the top silicon layer with the preset pattern comprising an input straight waveguide, a first coupling region, a second coupling region, and an output waveguide connected sequentially along the optical transmission direction; The first coupling region contains staggered input tapered waveguides, a first output tapered waveguide, and a second output tapered waveguide. The first and second output tapered waveguides are located on both sides of the input tapered waveguide. The input tapered waveguide is tapered along the optical transmission direction, and the first and second output tapered waveguides are tapered in the opposite direction of the optical transmission direction. The first coupling region is also filled with a first subwavelength grating. The second coupling region includes a first output straight waveguide and a second output straight waveguide arranged in parallel, and a second subwavelength grating distributed between the first output straight waveguide and the second output straight waveguide. The first output straight waveguide is connected to the first output tapered waveguide, and the second output straight waveguide is connected to the second output tapered waveguide. The first and second subwavelength gratings are both arranged perpendicularly along the light transmission direction, and the first and second subwavelength gratings have the same period and fill factor.
[0009] Optionally, the input tapered waveguide, the first output tapered waveguide, and the second output tapered waveguide have the same tapered structure, with a tip width of 100 nm and a bottom width of 800 nm.
[0010] Optionally, the first coupling region is an axisymmetric or non-axisymmetric structure, and the second coupling region is an axisymmetric structure, wherein the axis of symmetry of the axisymmetric structure is parallel to the optical transmission direction.
[0011] Optionally, when the first coupling region is an axisymmetric structure, the spacing between two adjacent tapered waveguides in the input tapered waveguide, the first output tapered waveguide, and the second output tapered waveguide is 100~150 nm.
[0012] Optionally, when the first coupling region is a non-axisymmetric structure, the distance between the input tapered waveguide and the first output tapered waveguide is 0.1~2.1. m, the distance between the input tapered waveguide and the second output tapered waveguide is 100 nm; Alternatively, when the first coupling region is a non-axisymmetric structure, the distance between the input tapered waveguide and the first output tapered waveguide is 100 nm, and the distance between the input tapered waveguide and the second output tapered waveguide is 100 nm.
[0013] Optionally, the fill factor of the first subwavelength grating and the second subwavelength grating is 0.43~0.52; and / or, The periods of the first and second subwavelength gratings are 200 nm; and / or, The first subwavelength grating has 19 or 23 periods, and the second subwavelength grating has 6 periods.
[0014] Optionally, the output waveguide includes a first output waveguide and a second output waveguide, the first output waveguide and the second output waveguide are respectively connected to the first output straight waveguide and the second output straight waveguide, and there is a preset distance between the first output waveguide and the second output waveguide.
[0015] Optionally, the output waveguide is an axisymmetric structure, and the axis of symmetry of the axisymmetric structure is parallel to the optical transmission direction; The first output waveguide includes a first output curved waveguide and a third output straight waveguide connected sequentially along the optical transmission direction; The second output waveguide includes a second output curved waveguide and a fourth output straight waveguide connected sequentially along the optical transmission direction; Both the first and second output curved waveguides have Bezier curves in shape.
[0016] Optionally, the output waveguide is an axisymmetric structure, with the axis of symmetry parallel to the optical transmission direction. The first output waveguide includes a fifth straight output waveguide, a first curved output waveguide, and a third straight output waveguide connected sequentially along the optical transmission direction. The second output waveguide includes a sixth straight output waveguide, a second curved output waveguide, and a fourth straight output waveguide connected sequentially along the optical transmission direction. The first curved output waveguide and the second curved output waveguide are both Bézier curves. or, The output waveguide has an axisymmetric structure, with the axis of symmetry parallel to the optical transmission direction. The first output waveguide is composed of a fifth straight output waveguide, and the second output waveguide is composed of a sixth straight output waveguide.
[0017] A second aspect of the present invention provides a method for fabricating an optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide as described above, comprising the following steps: The optical power divider is fabricated by etching the top silicon layer using silicon-on-insulator (SiO2) as the material and by employing electron beam lithography and reactive plasma etching methods.
[0018] Beneficial Effects: This invention improves mode field overlap by integrating subwavelength gratings in the coupling regions of three tapered waveguides, enabling an optical power divider to achieve 50:50 optical power distribution in an ultra-compact size (4.9 μm × 1.85 μm) within a wavelength range of 1400–1700 nm, with an insertion loss of <0.38 dB and a wide bandwidth. Furthermore, the optical power divider based on subwavelength grating-enhanced tapered ultrathin waveguides provided by this invention also exhibits large manufacturing tolerances and small relative wavelength deviations. Moreover, by adjusting the waveguide offset, the optical power divider can achieve arbitrary splitting ratios. Therefore, this invention enriches the diversity of power dividers based on ultrathin silicon waveguides, providing more options for optical power divider applications, while offering a scalable solution for developing high-tolerance silicon photonic integrated circuits.
[0019] In this invention, the fabrication of devices on silicon on an ultrathin insulator results in less energy distributed on the waveguide sidewalls of the ultrathin waveguide, which reduces scattering losses caused by sidewall roughness. The weak light confinement capability of the ultrathin waveguide leads to a high evanescent field intensity, enhancing the interaction between the waveguide and the environment, and thus improving device performance. Attached Figure Description
[0020] Figure 1This is a schematic diagram of the structure of an optical power divider in one embodiment of the present invention.
[0021] Figure 2 This is a schematic diagram of the structure of an optical power divider in another embodiment of the present invention.
[0022] Figure 3 for Figure 1 or Figure 2 A magnified view of the optical power divider.
[0023] Figure 4 (a) is a partial structural diagram of the optical power divider in another embodiment of the present invention, and (b) is a partial structural diagram of the optical power divider in yet another embodiment of the present invention.
[0024] Figure 5 The figure shows the three-dimensional FDTD simulation results of the 3-dB optical power divider in Example 1. (a) shows the three-dimensional FDTD simulation results of IL in the wavelength range of 1400~1700 nm for different f values, and (b) shows the three-dimensional FDTD simulation results of IL as G changes.
[0025] Figure 6 The following is a three-dimensional FDTD simulation result of the optical power divider in Example 2, in which the first subwavelength grating is extended downward along the y-axis by a distance L1. Among them, (a) is the result of the output port transmittance changing with L1 at a wavelength of 1550 nm, (b) is the result of the output port IL changing with L1 at a wavelength of 1550 nm, and (c) is the result of the transmittance and IL of the optical power divider with a splitting ratio of 30:70 in the wavelength range of 1500-1600 nm.
[0026] Figure 7 The graph shows the wavelength correlation deviation results for different L1 optical power dividers in the wavelength range of 1500~1600 nm.
[0027] Figure 8 The following are three-dimensional FDTD simulation results of the optical power divider when the upper optical path is extended upward along the y-axis by a distance L2 in Example 2. Among them, (a) is the result of the output port transmittance changing with L2 at a wavelength of 1550 nm, (b) is the result of the output port IL changing with L2 at a wavelength of 1550 nm, and (c) is the result of the transmittance and IL of the optical power divider with a splitting ratio of 10:90 in the wavelength range of 1500~1600 nm.
[0028] Figure 9 The graph shows the wavelength correlation deviation results for different L2 optical power dividers in the wavelength range of 1500~1600 nm.
[0029] Figure 10(a) is the SEM image of the 3-dB optical power divider prepared in Example 3, (b) is the IL result of the 3-dB optical power divider prepared in Example 3 in the wavelength range of 1500~1600 nm, and (c) is the IO result of the 3-dB optical power divider prepared in Example 3 in the wavelength range of 1500~1600 nm.
[0030] Figure 11 (a) is a magnified SEM image of a portion of the 3-dB optical power divider prepared in Example 3, and (b) is a result of the coupling efficiency.
[0031] Figure 12 In the image, (a) is the SEM image of the MZI device, and (b) is the normalized transmission spectrum of the MZI device.
[0032] The labels in the attached diagram: 1. Input straight waveguide; 2. First coupling region; 21. Input tapered waveguide; 22. First output tapered waveguide; 23. Second output tapered waveguide; 24. First subwavelength grating; 3. Second coupling region; 31. First output straight waveguide; 32. Second output straight waveguide; 33. Second subwavelength grating; 4. Output waveguide; 41. First output waveguide; 411. First output curved waveguide; 412. Third output straight waveguide; 413. Fifth output straight waveguide; 42. Second output waveguide; 421. Second output curved waveguide; 422. Fourth output straight waveguide; 423. Sixth output straight waveguide. Detailed Implementation
[0033] This invention provides an optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide and its fabrication method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
[0035] The terms used in this document, such as “vertical,” “horizontal,” “up,” “down,” “left,” “right,” and similar expressions, are for illustrative purposes only and do not represent the only possible implementation.
[0036] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.
[0037] If the embodiments of the present invention involve descriptions such as "first" or "second", such descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.
[0038] This invention provides an optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide. The optical power divider is a silicon-on-insulator (SOI) with a pre-defined pattern on a top silicon layer (70 nm thick). (It is known in the art that SOI is composed of a substrate silicon layer, a buried oxide layer, and a top silicon layer stacked sequentially from bottom to top. This invention obtains the optical power divider by etching the top silicon layer to form the pre-defined pattern.) Figures 1 to 4 As shown, the top silicon layer with a preset pattern includes an input straight waveguide 1, a first coupling region 2, a second coupling region 3, and an output waveguide 4 connected sequentially along the optical transmission direction; The first coupling region 2 contains staggered input tapered waveguides 21, first output tapered waveguides 22, and second output tapered waveguides 23. In a direction perpendicular to the optical transmission direction, the first output tapered waveguides 22 and 23 are located on either side of the input tapered waveguide 21. The input tapered waveguide 21 is tapered along the optical transmission direction (i.e., the narrower tip of the input tapered waveguide is downstream of the optical transmission direction, and the wider bottom is upstream of the optical transmission direction). The first output tapered waveguides 22 and 23 are both tapered in the opposite direction of the optical transmission direction (i.e., the wider bottom of the first output tapered waveguide and the narrower tip is upstream of the optical transmission direction). The first coupling region is also filled with a first subwavelength grating 24. The second coupling region 3 includes a first output straight waveguide 31 and a second output straight waveguide 32 arranged in parallel (i.e., both the first output straight waveguide and the second output straight waveguide are parallel to the optical transmission direction) and a second subwavelength grating 33 distributed between the first output straight waveguide 31 and the second output straight waveguide 32. The first and second subwavelength gratings are both arranged perpendicularly along the light transmission direction, and the first and second subwavelength gratings have the same period and fill factor.
[0039] This invention improves mode field overlap by integrating subwavelength gratings in the coupling regions of three tapered waveguides, enabling an optical power divider to achieve 50:50 optical power distribution in an ultra-compact size (4.9 μm × 1.85 μm) and achieve an insertion loss of <0.38 dB in the 1400–1700 nm wavelength range. Furthermore, the optical power divider based on subwavelength grating-enhanced tapered ultrathin waveguides provided by this invention also exhibits large manufacturing tolerances and small relative wavelength deviations. Furthermore, by adjusting the waveguide offset, the optical power divider can have any splitting ratio (e.g., (10~90):(10:90), specifically 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, etc.). Therefore, this invention enriches the diversity of power dividers for ultrathin silicon waveguides, provides more choices for the application of optical power dividers, and provides a scalable solution for the development of high-tolerance silicon photonic integrated circuits, thus promoting the development of ultrathin silicon photonics in next-generation high-density, high-efficiency optoelectronic systems.
[0040] In this embodiment, the device is fabricated on an ultrathin insulator (top silicon layer thickness is 70 nm). The ultrathin waveguide has less energy distributed on its sidewalls, which reduces scattering loss caused by sidewall roughness. The ultrathin waveguide has weak light confinement, resulting in a high evanescent field intensity, which enhances the interaction between the waveguide and the environment, thus improving device performance.
[0041] In some embodiments, the input tapered waveguide, the first output tapered waveguide, and the second output tapered waveguide have the same tapered structure, and the size of the tapered structure can be set according to actual needs. For example, Figure 1 , Figure 2 and Figure 3 As shown, the thickness of the cone structure is 70 nm, and the width of the tip of the cone structure is W. t The width of the cone structure is 100 nm, and the bottom width W is 800 nm to meet the single-mode condition.
[0042] In some implementations, the first coupling region is an axisymmetric structure (e.g., Figure 1 , Figure 2 and Figure 3 (as shown) or non-axisymmetric structures (such as) Figure 4 As shown in the figure, the second coupling region is an axisymmetric structure, and the axis of symmetry of the axisymmetric structure is parallel to the optical transmission direction.
[0043] When both the first and second coupling regions are axisymmetric structures, the distance between the three tapered waveguides is smaller, enabling simultaneous mode conversion and optical field coupling, and achieving a better 50:50 beam splitting.
[0044] In some implementations, when the first coupling region is an axisymmetric structure, such as Figure 3 As shown, in the input tapered waveguide, the first output tapered waveguide and the second output tapered waveguide, the spacing G between two adjacent tapered waveguides is 100 ~ 150 nm, for example, it can be 100 nm, 110 nm, 120 nm, 130 nm, 140 nm or 150 nm, etc.
[0045] In some implementations, when the first coupling region is a non-axisymmetric structure, such as Figure 4 As shown in (a), the spacing G between two adjacent tapered waveguides in the input tapered waveguide, the first output tapered waveguide, and the second output tapered waveguide is 100 nm.
[0046] In some implementations, when the first coupling region is a non-axisymmetric structure, such as Figure 4 As shown in (b), the distance between the input tapered waveguide and the first output tapered waveguide is 0.1~2.1 μm, and the distance between the input tapered waveguide and the second output tapered waveguide is 100 nm.
[0047] In some implementations, such as Figure 3 As shown, the fill factor of the first subwavelength grating and the second subwavelength grating is 0.43~0.52 (for example, it can be 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, 0.51 or 0.52, etc.).
[0048] In some implementations, such as Figure 3 As shown, the period P of the first subwavelength grating and the second subwavelength grating is 200 nm, the number of periods n1 of the first subwavelength grating is 19 or 23, and the number of periods n2 of the second subwavelength grating is 6.
[0049] In some implementations, such as Figure 1 As shown, the output waveguide includes a first output waveguide 41 and a second output waveguide 42. The first and second output waveguides are respectively connected to the first and second straight output waveguides, and there is a preset distance between them. In this embodiment, having a preset distance between the first and second output waveguides can reduce crosstalk between the output waveguides, improve the spectral purity of the signal, and also improve the process tolerance.
[0050] In some implementations, such as Figure 1 As shown, the output waveguide has an axisymmetric structure, and the axis of symmetry of the axisymmetric structure is parallel to the optical transmission direction; The first output waveguide 41 includes a first output curved waveguide 411 and a third output straight waveguide 412 connected sequentially along the optical transmission direction; The second output waveguide 42 includes a second output curved waveguide 421 and a fourth output straight waveguide 422 connected sequentially along the optical transmission direction; Both the first and second output curved waveguides have Bezier curves in shape.
[0051] In addition, such as Figure 1 As shown, the first output waveguide 41 may further include a fifth output straight waveguide 413, which may or may not be provided as needed. When the fifth output straight waveguide is not provided, the first output curved waveguide 411 is directly connected to the first output straight waveguide 31. When the fifth output straight waveguide is provided, the fifth output straight waveguide 413 is connected to the first output straight waveguide 31, the first output curved waveguide 411 is connected to the fifth output straight waveguide 413, and the third output straight waveguide 412 is connected to the first output curved waveguide 411.
[0052] The second output waveguide 42 may further include a sixth output straight waveguide 423, which may or may not be provided as needed. When the sixth output straight waveguide 423 is not provided, the second output curved waveguide 421 is directly connected to the second output straight waveguide 32. When the sixth output straight waveguide is provided, the sixth output straight waveguide 423 is connected to the second output straight waveguide 32, the second output curved waveguide 421 is connected to the sixth output straight waveguide 423, and the third output straight waveguide 412 is connected to the second output curved waveguide 421.
[0053] Of course, such as Figure 2 As shown, the first output waveguide 41 may also include only the fifth output straight waveguide 413, and the second output waveguide 42 may also include only the sixth output straight waveguide 423 (i.e., without the first output curved waveguide, the third output straight waveguide, the second output curved waveguide, and the fourth output straight waveguide). The fifth output straight waveguide 413 is connected to the first output straight waveguide 31, and the sixth output straight waveguide 423 is connected to the second output straight waveguide 32.
[0054] In some embodiments, the optical power divider completes a power distribution region with a length of 4.9 μm along the optical transmission direction.
[0055] In some specific embodiments, the size of the power distribution area completed by the optical power divider along the optical transmission direction is 1.85 μm × 4.9 μm.
[0056] This invention also provides a method for fabricating an optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide as described above, comprising the following steps: The optical power divider is fabricated by etching the top silicon layer using silicon-on-insulator (SiO2) as the material and by employing electron beam lithography and reactive plasma etching methods.
[0057] In this embodiment, the device is fabricated based on ultrathin silicon-on-insulator (SSI) with a top silicon layer thickness of 70 nm. The lateral dimensions of the ultrathin waveguide must be increased to near the micrometer scale, which significantly reduces the requirements for the fabrication process. Ultrathin waveguides have less energy distributed on their sidewalls, resulting in reduced scattering loss due to sidewall roughness. Many waveguide devices operate by utilizing the interaction between the waveguide's evanescent field and the environment. Ultrathin waveguides have weak light confinement, leading to a high evanescent field intensity, which enhances the interaction between the waveguide and the environment, thus improving device performance. Therefore, compared to commercially available thick waveguides (waveguide thickness of 220–500 nm), ultrathin waveguides offer advantages in fabrication, signal transmission, and sensing.
[0058] The present invention will be further described below through specific embodiments.
[0059] In the following embodiments, the thickness of the top silicon layer in the ultrathin silicon-on-insulator (SOI) wafer (or ultrathin silicon-on-insulator wafer, which includes a top silicon layer, a buried oxide layer and a substrate silicon layer stacked sequentially from top to bottom) is 70 nm, the thickness of the buried oxide layer (composed of silicon dioxide) is 2 μm, and the thickness of the substrate silicon layer is 725 μm.
[0060] Example 1: Design of a 3-dB Optical Power Divider In this embodiment, a 3-dB optical power splitter is used. The optical power splitter is an ultrathin silicon-on-insulator with a preset pattern on the top silicon layer, such as... Figure 2 and Figure 3 As shown, the top silicon layer with a preset pattern has an axisymmetric structure. The axis of symmetry of the axisymmetric structure is parallel to the optical transmission direction. The top silicon layer with a preset pattern includes an input straight waveguide 1, a first coupling region 2, a second coupling region 3 and an output waveguide connected sequentially along the optical transmission direction. The output waveguide is composed of a fifth output straight waveguide 413 and a sixth output straight waveguide 423 arranged in parallel.
[0061] The first coupling region 2 contains staggered input tapered waveguides 21, first output tapered waveguides 22, and second output tapered waveguides 23. In a direction perpendicular to the optical transmission direction, the first output tapered waveguides 22 and second output tapered waveguides 23 are located on both sides of the input tapered waveguides 21. The input tapered waveguides are tapered along the optical transmission direction, and the first and second output tapered waveguides are tapered in the opposite direction to the optical transmission direction. The first coupling region is also filled with a first subwavelength grating 24. The second coupling region 3 includes a first output straight waveguide 31 and a second output straight waveguide 32 arranged in parallel, and a second subwavelength grating 33 distributed between the first output straight waveguide 31 and the second output straight waveguide 32. The first output straight waveguide 31 is connected to the first output tapered waveguide 22, and the second output straight waveguide 32 is connected to the second output tapered waveguide 23. The fifth output straight waveguide 413 is connected to the first output straight waveguide 31, and the sixth output straight waveguide 423 is connected to the second output straight waveguide 32. The first subwavelength grating and the second subwavelength grating are both arranged perpendicularly along the light transmission direction, and the first subwavelength grating and the second subwavelength grating have the same period and fill factor; The input tapered waveguide 21, the first output tapered waveguide 22, and the second output tapered waveguide 23 have the same tapered structure, and the tip width of the tapered structure is denoted as W. t The width of the bottom end of the cone-shaped structure is denoted as W; The width of the first coupling region is denoted as W. s (i.e., the width perpendicular to the optical transmission direction), in the first coupling region, the distance between two adjacent tapered waveguides is denoted as G, the period of the first subwavelength grating is denoted as P (period along the optical transmission direction), the fill factor of the first subwavelength grating is denoted as f, and the number of periods of the first subwavelength grating is denoted as n1; the period of the second subwavelength grating is the same as the period of the first subwavelength grating, also denoted as P (period along the optical transmission direction), the fill factor of the second subwavelength grating is the same as the fill factor of the first subwavelength grating, also denoted as f, and the number of periods of the second subwavelength grating is n2.
[0062] The length of the input straight waveguide along the optical transmission direction is 5. m, the lengths of the fifth and sixth output straight waveguides are 5. m; W t=100 nm, W=800 nm (i.e., increasing from a linear tapered width of 100 nm at the tip to a width of 800 nm at the bottom to satisfy the single-mode condition), G=100 nm, P=200 nm (considering the resolution of nanofabrication, in the first coupling region, the distance G between two adjacent tapered waveguides is set to 100 nm, and the period P of the subwavelength grating is chosen to be 200 nm).
[0063] This embodiment uses the finite-difference time-domain (FDTD) simulation method to optimize the device structure. First, the particle swarm optimization (PSO) algorithm is used to simultaneously optimize the parameters f, Ws, n1, and n2 to minimize the insertion loss (IL) at a wavelength of 1550 nm. The formula for calculating IL is shown in Equation (1).
[0064] (1) Among them, P up P down For the two output waveguide optical powers (in this embodiment, P) up P corresponds to the optical path where the fifth output straight waveguide is located. down (corresponding to the optical path where the sixth output straight waveguide is located), P in This is the input waveguide optical power.
[0065] To improve computational efficiency, a rapid preliminary optimization was performed using 2.5-dimensional variational FDTD (varFDTD), yielding f=0.5 and W. S =1.8 μm, n1=17, n2=9.
[0066] Then, a three-dimensional FDTD scan was used to further minimize the IL at a wavelength of 1550 nm. The optimal values for each parameter were: f=0.43, Ws=1.64 μm, n1=19, and n2=6. These optimizations resulted in an IL of less than 0.11 dB at 1550 nm with a device length of 4.9 μm.
[0067] To evaluate manufacturing tolerance, the effects of different values of f and G on the IL value were calculated based on the optimal value (only the values of f and G were varied, while other parameters remained constant). The results are as follows: Figure 5 As shown. By Figure 5 As shown in (a), as f changes from 0.43 to 0.52, the IL of the device at 1550 nm wavelength is <0.14 dB, and the IL of the device in the wavelength range of 1400~1700 nm is <0.38 dB. Figure 5 As shown in (b), when G changes from 100 to 150 nm, the IL of the device at a wavelength of 1550 nm increases only slightly by 0.03 dB, proving that the design of the 3-dB optical power divider has good manufacturing tolerance.
[0068] In this embodiment, the preferred values for each parameter of the 3-dB optical power divider are determined as follows: f = 0.43~0.52 (more preferably, f = 0.43), G = 100~150 nm (more preferably, G = 100 nm), W s =1.64 μm, n1=19, n2=6, P=200 nm, W t =100 nm, W=800 nm, the length of the input straight waveguide is 5 μm, and the lengths of the first and second output straight waveguides are 1.2 μm. The lengths of the fifth and sixth output straight waveguides are 5 μm.
[0069] Example 2: Design of a power divider with arbitrary splitting ratio To address the wavelength dependence of the evanescent field, this embodiment breaks the symmetry of the 3-dB power divider in Embodiment 1, specifically as follows: Figure 4 As shown in (a), G=100 nm, f=0.5, n1=23, W s0 =1.2 μm (W s0 =W+2×W t +2×G=800 nm+2×100 nm+2×100 nm =1.2 μm, the remaining parameters are the same as the final optimized parameters in Example 1, i.e., n2=6, P=200 nm, W t =100 nm, W=800 nm, the length of the input straight waveguide is 5 μm, and the lengths of the first and second output straight waveguides are 1.2 μm. m, the lengths of the fifth and sixth output straight waveguides are 5 μm, and the first subwavelength grating extends downward along the y-axis by a length L1. Increasing n1 can lengthen the coupling length between the tapered waveguides, enabling more efficient optical coupling to the output waveguides and reducing insertion loss (improving optical coupling efficiency).
[0070] Then a three-dimensional FDTD simulation was performed, and the results are as follows: Figure 6 As shown. By Figure 6 From (a) and (b), we can see that as L1 increases, the lower port (P) down Transmission initially increases with increasing L1, gradually saturating when L1 increases to 1 μm. When L1 is in the range of 0.0~1.0 μm, a splitting ratio of 50:50~30:70 is achieved at a wavelength of 1550 nm (the splitting ratio reaches 30:70 when L1=1 μm), and IL is less than 0.17 dB.
[0071] The transmittance and IL results of the optical power divider with a splitting ratio of 30:70 (L1=1 μm) are as follows: Figure 6As shown in (c), the IL is <0.18 dB in the wavelength range of 1500~1600 nm. The wavelength correlation deviation of the optical power divider with a splitting ratio of 30:70 is <1.9% in the 1500~1600 nm wavelength range (the wavelength correlation deviation of optical power dividers with different L1 values is less than 2.8%, such as...). Figure 7 (As shown).
[0072] To obtain a spectrophotometric ratio of 30:70 to 10:90, such as Figure 4 As shown in (b), the optical path (P) of the optical power divider with a splitting ratio of 30:70 is connected. up The entire structure is shifted upwards along the y-axis by L2, while keeping other parameters constant (i.e., G=100 nm, n2= 6, P=200 nm, W...). t = 100 nm, W = 800 nm, L1 = 1 μm, f = 0.5, n1 = 23, the length of the input straight waveguide is 5 μm, and the lengths of the first and second output straight waveguides are 1.2 μm. The lengths of the fifth and sixth output straight waveguides are 5 μm.
[0073] Then a three-dimensional FDTD simulation was performed, and the results are as follows: Figure 8 As shown. By Figure 8 As shown in (a) and (b), when L2 is in the range of 0.0~2.0 μm, a splitting ratio of 30:70~10:90 is achieved at a wavelength of 1550 nm, and IL is less than 0.6 dB.
[0074] The IL results for the optical power divider with a splitting ratio of 10:90 (L2=0.8 μm) are as follows: Figure 8 As shown in (c), its IL < 0.37 dB in the 1500–1600 nm wavelength range. The wavelength correlation deviation of the optical power divider with a splitting ratio of 10:90 in the 1500–1600 nm wavelength range is < 1.7% (the wavelength correlation deviation of the optical power divider with different L2 values is less than 2%, such as...). Figure 9 (As shown).
[0075] The above results demonstrate that the subwavelength grating-enhanced tapered ultrathin waveguide optical power divider can achieve any power splitting ratio.
[0076] Example 3: Fabrication of a 3-dB Optical Power Divider Based on the 3-dB optical power divider obtained in Example 1 (such as...) Figure 2 The preferred values for each parameter (as shown) are f=0.43, G=100 nm, W s =1.64 μm, n1=19, n2=6, P=200 nm (where the width of the silicon strip is 86 nm), Wt =100 nm, W=800 nm, the lengths of the first and second output straight waveguides are 1.2 μm. Fabrication is as follows: Figure 1 The device shown differs from the 3-dB optical power divider in Example 1 only in the structure of the output waveguide and the length of the input waveguide. Figure 1 As shown, in this embodiment, the output waveguide includes a first output waveguide 41 and a second output waveguide 42. The first output waveguide 41 includes a fifth straight output waveguide 413, a first curved output waveguide 411, and a third straight output waveguide 412 connected sequentially along the optical transmission direction, and the fifth straight output waveguide 413 is connected to the first straight output waveguide 411. The second output waveguide 42 includes a sixth straight output waveguide 423, a second curved output waveguide 421, and a fourth straight output waveguide 422 connected sequentially along the optical transmission direction, and the sixth straight output waveguide 423 is connected to the second straight output waveguide 422. The first curved output waveguide and the second curved output waveguide are both Bézier curves. The length L of the first curved output waveguide and the second curved output waveguide along the optical transmission direction is 110 μm (this ensures that the loss mainly comes from the coupling region). The distance D between the first straight output waveguide and the second straight output waveguide is 25 μm.
[0077] The length of the input straight waveguide is 20 μm, the lengths of the fifth and sixth output straight waveguides are 4 μm, and the lengths of the third and fourth output straight waveguides are 20 μm.
[0078] The fabrication process primarily utilizes electron beam lithography (EBL) and reactive ion etching (RIE) methods, and includes the following steps: (1) Silicon wafer cleaning: The ultrathin SOI wafer is immersed in acetone, isopropanol and deionized water in sequence for ultrasonic vibration. Finally, nitrogen gas is used to blow away the water droplets on the surface of the ultrathin SOI wafer and a hot plate is used to dry it.
[0079] (2) Spin coating of photoresist: Place the silicon wafer on a spin coater and fix it under vacuum. Apply positive photoresist AR-P6200.09 while it is stationary. Then set the spin coater speed to spin coat. After spin coating, place it on a hot plate and bake at 150 degrees Celsius for 1 minute to remove the solvent.
[0080] (3) Electron beam lithography: The photoresist is exposed according to the design pattern using an electron beam lithography machine.
[0081] (4) Development: The exposed ultrathin SOI wafer is sequentially immersed in developer (AR600-546) for 1 minute and fixer (AR600-60) for 30 seconds to dissolve the photoresist in the exposed area and form the required photoresist mask pattern.
[0082] (5) Etching: Anisotropic dry etching is performed in a reactive plasma etching machine using a mixture of SF6 (sulfur hexafluoride) and CHF3 (trifluoromethane) gas to remove the part of the top silicon layer in the ultrathin SOI wafer that is not protected by photoresist (i.e., the desired pattern is formed on the top silicon layer), and the designed pattern is transferred to the ultrathin SOI wafer.
[0083] (6) Photoresist removal: First, use acetone immersion to remove the photoresist on the wafer, and then use a plasma cleaner to clean the wafer surface.
[0084] SEM image of the prepared 3-dB optical power divider is shown below. Figure 10 As shown in (a) of the figure, the right-hand image is an enlarged view of the area bounded by the left-hand image. It can be seen that the number of periods of the first subwavelength grating is n1=19, the number of periods of the second subwavelength grating is n2=6, and the width of the silicon strip in one period of the subwavelength grating is 86 nm.
[0085] The inter-laser voltage (IL) of devices in the 1500–1600 nm wavelength range was measured using a tunable laser and a power meter. The results are as follows: Figure 10 As shown in (b) above, the IL value of the prepared 3-dB power divider is 0.17 to 0.38 dB in the wavelength range of 1500 to 1600 nm.
[0086] The output port imbalance (IO) of the prepared 3-dB optical power divider was tested, and the results are as follows: Figure 10 As shown in (c), the IO value is 0.2 to 0.33 dB in the wavelength range of 1500 to 1600 nm.
[0087] The formula for calculating IO is shown in equation (2).
[0088]
[0089] In this embodiment, a subwavelength grating coupler is used to couple the light in the optical fiber to the waveguide, such as... Figure 11 As shown, fiber-to-waveguide optical coupling is performed at the input and output ports using a subwavelength grating coupler, which has a peak coupling efficiency of -6.8 dB at a wavelength of 1542 nm and a bandwidth of ~38 nm 1 dB.
[0090] Furthermore, in this embodiment, the 3-dB optical power splitter prepared above is used as a beam splitter / combiner to construct an asymmetric Mach-Zehnder interferometer (MZI): the upper arm uses a 20 μm radius curved waveguide instead of a straight waveguide. Figure 12 In (a) of the diagram, the geometric structure produces an optical path difference. Figure 12 (b) shows the normalized transmission spectrum of MZI, with a minimum extinction ratio of 27.0 dB at 1501.3 nm and a maximum extinction ratio of 37.1 dB at 1572.5 nm, and a free spectral range of ~18.1 nm. This confirms that the subwavelength grating tuned tapered waveguide distributor has efficient beam splitting / combining capabilities.
[0091] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.
Claims
1. An optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide, characterized in that, The optical power divider is silicon-on-insulator with a preset pattern on the top silicon layer. The thickness of the top silicon layer is 70 nm. The top silicon layer with the preset pattern includes an input straight waveguide, a first coupling region, a second coupling region, and an output waveguide connected sequentially along the optical transmission direction. The first coupling region contains staggered input tapered waveguides, a first output tapered waveguide, and a second output tapered waveguide. The first and second output tapered waveguides are located on both sides of the input tapered waveguide. The input tapered waveguide is tapered along the optical transmission direction, and the first and second output tapered waveguides are tapered in the opposite direction of the optical transmission direction. The first coupling region is also filled with a first subwavelength grating. The second coupling region includes a first output straight waveguide and a second output straight waveguide arranged in parallel, and a second subwavelength grating distributed between the first output straight waveguide and the second output straight waveguide. The first output straight waveguide is connected to the first output tapered waveguide, and the second output straight waveguide is connected to the second output tapered waveguide. The first and second subwavelength gratings are both arranged perpendicularly along the light transmission direction, and the first and second subwavelength gratings have the same period and fill factor.
2. The optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide according to claim 1, characterized in that, The input tapered waveguide, the first output tapered waveguide, and the second output tapered waveguide have the same tapered structure, with a tip width of 100 nm and a bottom width of 800 nm.
3. The optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide according to claim 1, characterized in that, The first coupling region is an axisymmetric or non-axisymmetric structure, and the second coupling region is an axisymmetric structure, wherein the axis of symmetry of the axisymmetric structure is parallel to the optical transmission direction.
4. The optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide according to claim 3, characterized in that, When the first coupling region is an axisymmetric structure, the spacing between two adjacent tapered waveguides in the input tapered waveguide, the first output tapered waveguide, and the second output tapered waveguide is 100~150 nm.
5. The optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide according to claim 3, characterized in that, When the first coupling region is a non-axisymmetric structure, the distance between the input tapered waveguide and the first output tapered waveguide is 0.1~2.1 μm, and the distance between the input tapered waveguide and the second output tapered waveguide is 100 nm; Alternatively, when the first coupling region is a non-axisymmetric structure, the distance between the input tapered waveguide and the first output tapered waveguide is 100 nm, and the distance between the input tapered waveguide and the second output tapered waveguide is 100 nm.
6. The optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide according to claim 1, characterized in that, The fill factor of the first subwavelength grating and the second subwavelength grating is 0.43~0.52; and / or, The periods of the first and second subwavelength gratings are 200 nm; and / or, The first subwavelength grating has 19 or 23 periods, and the second subwavelength grating has 6 periods.
7. The optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide according to claim 1, characterized in that, The output waveguide includes a first output waveguide and a second output waveguide, which are respectively connected to the first output straight waveguide and the second output straight waveguide, and there is a preset distance between the first output waveguide and the second output waveguide.
8. The optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide according to claim 7, characterized in that, The output waveguide has an axisymmetric structure, and the axis of symmetry of the axisymmetric structure is parallel to the optical transmission direction. The first output waveguide includes a first output curved waveguide and a third output straight waveguide connected sequentially along the optical transmission direction; The second output waveguide includes a second output curved waveguide and a fourth output straight waveguide connected sequentially along the optical transmission direction; Both the first and second output curved waveguides have Bezier curves in shape.
9. The optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide according to claim 7, characterized in that, The output waveguide is an axisymmetric structure, with the axis of symmetry parallel to the optical transmission direction. The first output waveguide includes a fifth straight output waveguide, a first curved output waveguide, and a third straight output waveguide connected sequentially along the optical transmission direction. The second output waveguide includes a sixth straight output waveguide, a second curved output waveguide, and a fourth straight output waveguide connected sequentially along the optical transmission direction. The first curved output waveguide and the second curved output waveguide are both Bézier curves. or, The output waveguide has an axisymmetric structure, with the axis of symmetry parallel to the optical transmission direction. The first output waveguide is composed of a fifth straight output waveguide, and the second output waveguide is composed of a sixth straight output waveguide.
10. A method for fabricating an optical power divider based on a subwavelength grating-enhanced tapered ultrathin waveguide as described in any one of claims 1-9, characterized in that, Includes the following steps: The optical power divider is fabricated by etching the top silicon layer using silicon-on-insulator (SiO2) as the material and by employing electron beam lithography and reactive plasma etching methods.