Silicon-based compact mode converter using bricked subwavelength grating

Lu Meng-Jia; Yun Bin-Feng

doi:10.7498/aps.72.20230673

Abstract

Facing the increasing capacity requirements of on-chip optical interconnects, mode division multiplexing technology (MDM), which fully uses the different spatial eigenmodes at the same wavelength as independent channels to transmit optical signals, has attracted tremendous interest. Mode-order converter that can convert the fundamental mode into high-order mode is a key component in MDM system. However, it is still very challenging to achieve compact mode-order converters with high performances. Subwavelength grating (SWG) can be equivalent to homogenous material, which has the prominent advantages such as controlling over birefringence, dispersion and anisotropy, thus making photonic devices possess high performance. Wheras the conventional SWG only needs single-etch step, but the implementation of SWG structure usually requires a fabrication resolution on the order of 100 nm and below, which is difficult for current wafer-scale fabrication technology. The anisotropic response of SWG can be further engineered by introducing bricked topology structure, providing an additional degree of freedom in the design. Meanwhile, the requirement for fabrication resolution can also be reduced (> 100 nm). In this work, we experimentally demonstrate compact TE₀-TE₁ mode-order converter and TE₀-TE₂ mode-order converter by using a bricked subwavelength grating (BSWG) based on a silicon-on-insulator (SOI) with the BSWG having a minimum feature size of 145 nm. In the proposed mode-order converter, a quasi-TE₀ mode is generated in the BSWG region, which can be regarded as an effective bridge between the two TE modes to be converted. Flexible mode conversion can be realized by only choosing appropriate structural parameters for specific mode transitions between input/output modes and the quasi-TE₀ mode. By combining three-dimensional (3D) finite difference time domain (FDTD) and particle swarm optimization (PSO) method, TE₀-TE₁ mode-order converter and TE₀-TE₂ mode-order converter are optimally designed. They can convert TE₀ mode into TE₁ and TE₂ mode with conversion length of 9.39 µm and 11.27 µm, respectively. The simulation results show that the insertion loss of < 1 dB and crosstalk of < –15 dB are achieved for both TE₀-TE₁ mode-order converter and TE₀-TE₂ mode-order converter, their corresponding working bandwidths being 128 nm (1511–1639 nm) and 126 nm (1527–1653 nm), respectively. The measurement results indicate that insertion loss and crosstalk are, respectively, less than 2.5 dB and –10 dB in a bandwidth of 68 nm (1512–1580 nm, limited by the laser tuning range and grating coupler).

Keywords:

Authors and contacts

Advanced Photonics Center, Southeast University, Nanjing 210096, China

Corresponding author: Yun Bin-Feng, ybf@seu.edu.cn

Funds: Project supported by the National Natural Science Foundation of China (Grant No. 62171118)

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References

[1]	Luo L W, Ophir N, Chen C P, Gabrielli L H, Poitras C B, Bergmen K, and Lipson M 2014 Nat. Commun. 5 3069 Google Scholar
[2]	Li C L, Liu D J, and Dai D X 2019 Nanophotonics 8 227 Google Scholar
[3]	Hsu Y, Chuang C Y, Wu X R, Chen G H, Hsu C W, Chang Y C, Chow C W, Chen J, Lai Y C, Yeh C H, Tsang H K 2018 IEEE Photonics Technol. L. 30 1052 Google Scholar
[4]	Li H Q, Wang P J, Yang T J, Dai T, Wang G C, Li S Q, Chen W W, Yang J Y 2018 Opt. Laser Technol. 100 7 Google Scholar
[5]	Pan T H and Tseng S Y 2015 Opt. Express 23 10405 Google Scholar
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[8]	Gabrielli L H, Liu D, Johnson S G, Lipson M 2012 Nat. Commun. 3 1217 Google Scholar
[9]	Xu H N, Shi Y C 2018 Laser Photonics Rev. 12 1700240 Google Scholar
[10]	Chang W J, Lu L L Z, Ren X S, Lu L H, Cheng M F, Liu D M, Zhang M M 2018 IEEE Photonics J. 10 4501008 Google Scholar
[11]	Garcia-Rodriguez D, Corral J L, Griol A, Llorente R 2017 Opt. Lett. 42 1221 Google Scholar
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[19]	Wu F, Liu T T, Long Y, Xiao S Y, Chen G Y 2023 Phys. Rev. B 107 165428 Google Scholar
[20]	Mia M B, Jaidye N, Ahmed I, Ahmed S Z, Kim S 2023 Opt. Express 31 4140 Google Scholar
[21]	He Y, Zhang Y, Zhu Q M, An S, Cao R Y, Guo X H, Qiu C Y, Su Y K 2018 J. Lightwave Technol. 36 5746 Google Scholar
[22]	González-Andrade D, Gonzalo Wanguemert-Perez J, Velasco A V, Ortega-Monux A, Herrero-Bermello A, Molina-Fernandez I, Halir R, Cheben P 2018 IEEE Photonics J. 10 2201010 Google Scholar
[23]	González-Andrade D, Dias A, Wanguemert-Perez J G, Ortega-Monux A, Molina-Fernandez I, Halir R, Cheben P, Velasco A V 2020 Opt. Laser Technol. 129 106297 Google Scholar
[24]	Cheng Z, Wang J, Yang Z Y, Zhu L N, Yang Y Q, Huang Y Q, Ren X M 2019 Opt. Express 27 34434 Google Scholar
[25]	Wang H W, Zhang Y, He Y, Zhu Q M, Sun L, Su Y K 2019 Adv. Opt. Mater. 7 1801191 Google Scholar
[26]	Sun L, Hu R, Zhang Z H, He Y, Su Y K 2021 IEEE J. Sel. Top. Quant. 27 8100308 Google Scholar
[27]	Luque-González J M, Ortega-Moñux A, Halir R, Schmid J H, Cheben P, Molina-Fernández I, Wangüemert-Pérez J G 2021 Laser Photonics Rev. 15 2000478 Google Scholar
[28]	Lu M J, Deng C Y, Sun Y, Wang D Y, Huang L, Liu P C, Lin D D, Cheng W, Hu G H, Lin T, Yun B F, Cui Y P 2022 Opt. Express 30 24655 Google Scholar
[29]	Luque-González J M, Herrero-Bermello A, Ortega-Moux A, Sánchez-Rodríguez M, Velasco A V, Schmid J H, Cheben P, Molina-Fernández I, Halir R. 2020 Opt. Lett. 45 3398 Google Scholar
[30]	Yao R K, Li H X, Zhang B H, Chen W W, Wang P J, Dai S X, Liu Y X, Li J, Li Y, Fu Q, Dai T G, Yu H, Yang J Y, Pavesi L 2021 J. Lightwave Technol. 39 6253 Google Scholar
[31]	Mao S Q, Hu J Z, Zhang H Y, Jiang W F 2022 IEEE J. Quantum Elect. 58 8400106 Google Scholar

Cited By

图 1 (a) 模式转换器方案的结构示意图; (b), (c) BSWG的部分放大图与SEM图

Figure 1. (a) Schematic of the mode converter; (b), (c) part enlarged view and SEM image of the BSWG.

DownLoad: Full-Size Img PowerPoint

图 2 器件优化过程流程图

Figure 2. Flow chart of the optimization process.

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图 3 (a) TE₀-TE₁模式转换器的透射光谱; (b) TE₀-TE₂模式转换器的透射光谱

Figure 3. (a) Transmission spectra for the TE₀-TE₁ mode converter; (b) transmission spectra for the TE₀-TE₂ mode converter.

DownLoad: Full-Size Img PowerPoint

图 4 (a) 带有TE GC的直波导显微图; (b) TE GC的SEM图; (c) 不同光纤角度下TE耦合光栅的传输光谱

Figure 4. (a) Microscope image of the reference straight waveguide with TE-type grating couplers; (b) SEM image of TE-type grating coupler; (c) transmission spectra of TE-type grating couplers under different fiber angles.

DownLoad: Full-Size Img PowerPoint

图 5 (a), (c) TE₀-TE₁模式转换器的测试方案显微图; (b), (d) TE₀-TE₂模式转换器的测试方案显微图以及TE₁-TE₃模式复用器的SEM图

Figure 5. (a), (c) Microscope images of the measure schemes for TE₀-TE₁ mode converter; (b), (d) microscope images of the measure schemes for TE₀-TE₂ mode converter and SEM images of TE₁-TE₃ multiplexer.

DownLoad: Full-Size Img PowerPoint

图 6 TE₀-TE₁模式转换器(a)和TE₀-TE₂模式转换器(b)的SEM图及其放大的伪彩图

Figure 6. SEM images and corresponding pseudocolor SEM images of TE₀-TE₁ mode converter (a) and TE₀-TE₂ mode converter (b).

DownLoad: Full-Size Img PowerPoint

图 7 模式转换器的插损和串扰的测试链路图

Figure 7. Experimental setup for measuring the insertion loss and crosstalk of mode converter.

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图 8 测试得到的器件传输谱　(a) TE₀-TE₁模式转换器; (b) TE₀-TE₂模式转换器

Figure 8. Measured transmission spectra: (a) TE₀-TE₁ mode converter; (b) TE₀-TE₂ mode converter.

DownLoad: Full-Size Img PowerPoint

表 1 模式转换器的优化设计参数

Table 1. Optimized design parameters for the mode converter.

模式转换功能 W_MMI/μm W_O/μm W_T2/μm W_D/μm L_T1/μm L_T2/μm L_c/μm $ \overline {\Delta z} $

TE₀-TE₁ 2.10 0.9 0.229 0 3.00 3.2 3.19 0.16
TE₀-TE₂ 2.67 1.4 0.350 0.373 3.21 4.0 4.06 0.14

DownLoad: CSV

表 2 模式(解)复用器的详细参数

Table 2. Detail parameters for the mode (de) multiplexer.

模式(解)
复用器总线波导
的宽度/μm 接入波导
宽度/μm 间隔/nm 耦合长度/μm

TE1 0.835 0.4 200 15.5
TE2 1.29 0.406 200 21.3
TE3 1.63 0.38 200 18

DownLoad: CSV

[1]	Luo L W, Ophir N, Chen C P, Gabrielli L H, Poitras C B, Bergmen K, and Lipson M 2014 Nat. Commun. 5 3069 Google Scholar
[2]	Li C L, Liu D J, and Dai D X 2019 Nanophotonics 8 227 Google Scholar
[3]	Hsu Y, Chuang C Y, Wu X R, Chen G H, Hsu C W, Chang Y C, Chow C W, Chen J, Lai Y C, Yeh C H, Tsang H K 2018 IEEE Photonics Technol. L. 30 1052 Google Scholar
[4]	Li H Q, Wang P J, Yang T J, Dai T, Wang G C, Li S Q, Chen W W, Yang J Y 2018 Opt. Laser Technol. 100 7 Google Scholar
[5]	Pan T H and Tseng S Y 2015 Opt. Express 23 10405 Google Scholar
[6]	Xu Y, Liu L P, Hu X, Dong Y, Zhang B, Ni Y 2022 Opt. Laser Technol. 151 108028 Google Scholar
[7]	Ohana D, Levy U 2014 Opt. Express 22 27617 Google Scholar
[8]	Gabrielli L H, Liu D, Johnson S G, Lipson M 2012 Nat. Commun. 3 1217 Google Scholar
[9]	Xu H N, Shi Y C 2018 Laser Photonics Rev. 12 1700240 Google Scholar
[10]	Chang W J, Lu L L Z, Ren X S, Lu L H, Cheng M F, Liu D M, Zhang M M 2018 IEEE Photonics J. 10 4501008 Google Scholar
[11]	Garcia-Rodriguez D, Corral J L, Griol A, Llorente R 2017 Opt. Lett. 42 1221 Google Scholar
[12]	Chen W W, Wang P J, Yang J Y 2014 IEEE Photonics Technol. L. 26 2043 Google Scholar
[13]	Oner B B, Ustun K, Kurt H, Okyay A K, Turhan-Sayan G 2015 Opt. Express 23 3186 Google Scholar
[14]	Chack D, Hassan S, Qasim M 2020 Appl. Opt. 59 3652 Google Scholar
[15]	Liu L P, Xu Y, Wen L, Dong Y, Zhang B, Ni Y 2019 Appl. Optics 58 9075 Google Scholar
[16]	Cheben P, Halir R, Schmid J H, Atwater H A, Smith D R 2018 Nature 560 565 Google Scholar
[17]	Luque-González J M, Sánchez-Postigo A, Hadij-ElHouati A, Ortega-Moñux A, Wangüemert-Pérez J G, Schmid J H, Cheben P, Molina-Fernández I, Halir R, 2021 Nanophotonics 10 2765 Google Scholar
[18]	Yu Z J, Xu H N, Liu D J, Li H, Shi Y C, Dai D X 2022 J. Lightwave Technol. 40 1784 Google Scholar
[19]	Wu F, Liu T T, Long Y, Xiao S Y, Chen G Y 2023 Phys. Rev. B 107 165428 Google Scholar
[20]	Mia M B, Jaidye N, Ahmed I, Ahmed S Z, Kim S 2023 Opt. Express 31 4140 Google Scholar
[21]	He Y, Zhang Y, Zhu Q M, An S, Cao R Y, Guo X H, Qiu C Y, Su Y K 2018 J. Lightwave Technol. 36 5746 Google Scholar
[22]	González-Andrade D, Gonzalo Wanguemert-Perez J, Velasco A V, Ortega-Monux A, Herrero-Bermello A, Molina-Fernandez I, Halir R, Cheben P 2018 IEEE Photonics J. 10 2201010 Google Scholar
[23]	González-Andrade D, Dias A, Wanguemert-Perez J G, Ortega-Monux A, Molina-Fernandez I, Halir R, Cheben P, Velasco A V 2020 Opt. Laser Technol. 129 106297 Google Scholar
[24]	Cheng Z, Wang J, Yang Z Y, Zhu L N, Yang Y Q, Huang Y Q, Ren X M 2019 Opt. Express 27 34434 Google Scholar
[25]	Wang H W, Zhang Y, He Y, Zhu Q M, Sun L, Su Y K 2019 Adv. Opt. Mater. 7 1801191 Google Scholar
[26]	Sun L, Hu R, Zhang Z H, He Y, Su Y K 2021 IEEE J. Sel. Top. Quant. 27 8100308 Google Scholar
[27]	Luque-González J M, Ortega-Moñux A, Halir R, Schmid J H, Cheben P, Molina-Fernández I, Wangüemert-Pérez J G 2021 Laser Photonics Rev. 15 2000478 Google Scholar
[28]	Lu M J, Deng C Y, Sun Y, Wang D Y, Huang L, Liu P C, Lin D D, Cheng W, Hu G H, Lin T, Yun B F, Cui Y P 2022 Opt. Express 30 24655 Google Scholar
[29]	Luque-González J M, Herrero-Bermello A, Ortega-Moux A, Sánchez-Rodríguez M, Velasco A V, Schmid J H, Cheben P, Molina-Fernández I, Halir R. 2020 Opt. Lett. 45 3398 Google Scholar
[30]	Yao R K, Li H X, Zhang B H, Chen W W, Wang P J, Dai S X, Liu Y X, Li J, Li Y, Fu Q, Dai T G, Yu H, Yang J Y, Pavesi L 2021 J. Lightwave Technol. 39 6253 Google Scholar
[31]	Mao S Q, Hu J Z, Zhang H Y, Jiang W F 2022 IEEE J. Quantum Elect. 58 8400106 Google Scholar

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