Inverse Designed Vertical Grating Coupler on Thin‑Film Lithium Niobate (Invited)

Chengkai Jiang; Kaiyan Pan; Xinyu Zhang; Qi Qin; Xiaopeng Hu; Shining Zhu

doi:10.3788/CJL250951

Chinese Journal of Lasers, Volume. 52, Issue 18, 1803029(2025)

Inverse Designed Vertical Grating Coupler on Thin‑Film Lithium Niobate (Invited)

Chengkai Jiang¹, Kaiyan Pan¹, Xinyu Zhang², Qi Qin^3,4、**, Xiaopeng Hu^1、*, and Shining Zhu^1,2

Author Affiliations

¹College of Engineering and Applied Sciences, Nanjing University, Nanjing 210093, Jiangsu , China

²School of Physics, Nanjing University, Nanjing 210093, Jiangsu , China

³College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, Guangdong , China

⁴Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area, Shenzhen 518045, Guangdong , China

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Figures & Tables(8)

Fig. 1. Schematic diagram of vertical grating coupler structure based on inverse design

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Fig. 2. Simulated cross-sectional electric field distribution of vertical grating coupler

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Fig. 3. Influence of vertical grating coupler structure parameters on coupling efficiency. (a) Width offset versus coupling efficiency; (b) etching depth versus coupling efficiency; (c) incident angle of optical fiber versus coupling efficiency; (d) fiber location versus coupling efficiency

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Fig. 4. SEM images of vertical grating coupler. (a) Overall view; (b)(c) local zoom

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Fig. 5. Schematic diagram of fiber-chip vertical coupling system

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Fig. 6. Coupling efficiency versus working wavelength

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Table 1. Parameters of vertical grating coupler optimized by inverse design
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Table 1. Parameters of vertical grating coupler optimized by inverse design
j 1 2 3 4 5 6 7 8 9 10
w_j /nm 464 467 730 406 320 382 687 357 400 459
t_j /nm 370 320 320 320 488 437 456 474 395 345
j 11 12 13 14 15 16 17 18 19 20
w_j /nm 457 450 476 476 479 487 452 396 413 407
t_j /nm 403 372 350 349 341 346 417 441 450 465

Table 2. Comparison of performance of grating couplers on TFLN

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Table 2. Comparison of performance of grating couplers on TFLN

Reference	Thickness of LN /nm	Structure	Measured coupling efficiency /dB	θ /（°）	Year
［22］	400	Bottom reflector	-3.5	8	2019
［21］	410	Uniform	-7.0	8	2019
［10］	600	Uniform	-6.3	10	2021
［19］	700	Non-uniform	-3.8	6	2024
［23］	400	Non-uniform	-3.37	2.5	2024
This work	500	Non-uniform	-4.3	0	2025

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Chengkai Jiang, Kaiyan Pan, Xinyu Zhang, Qi Qin, Xiaopeng Hu, Shining Zhu. Inverse Designed Vertical Grating Coupler on Thin‑Film Lithium Niobate (Invited)[J]. Chinese Journal of Lasers, 2025, 52(18): 1803029

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