[1] R. Marchetti, C. Lacava, L. Carroll, K. Gradkowski, P. Minzioni. Coupling strategies for silicon photonics integrated chips. Photon. Res., 7, 201-239(2019).

[2] L. Cheng, S. Mao, Z. Li, Y. Han, H. Y. Fu. Grating couplers on silicon photonics: design principles, emerging trends and practical issues. Micromachines, 11, 666(2020).

[3] X. Mu, S. Wu, L. Cheng, H. Y. Fu. Edge couplers in silicon photonic integrated circuits: a review. Appl. Sci., 10, 1538(2020).

[4] F. Van Laere, G. Roelkens, M. Ayre, J. Schrauwen, D. Taillaert, D. Van Thourhout, T. F. Krauss, R. Baets. Compact and highly efficient grating couplers between optical fiber and nanophotonic waveguides. J. Lightwave Technol., 25, 151-156(2007).

[5] S. K. Selvaraja, D. Vermeulen, M. Schaekers, E. Sleeckx, W. Bogaerts, G. Roelkens, P. Dumon, D. Van Thourhout, R. Baets. Highly efficient grating coupler between optical fiber and silicon photonic circuit. Conference on Lasers and Electo-Optics/International Quantumm Electronics Conference, CTuC6(2009).

[6] W. S. Zaoui, A. Kunze, W. Vogel, M. Berroth, J. Butschke, F. Letzkus, J. Burghartz. Bridging the gap between optical fibers and silicon photonic integrated circuits. Opt. Express, 22, 1277-1286(2014).

[7] Y. Ding, C. Peucheret, H. Ou, K. Yvind. Fully etched apodized grating coupler on the SOI platform with −0.58 dB coupling efficiency. Opt. Lett., 39, 5348-5350(2014).

[8] J. Hong, A. M. Spring, F. Qiu, S. Yokoyama. A high efficiency silicon nitride waveguide grating coupler with a multilayer bottom reflector. Sci. Rep., 9, 12988(2019).

[9] N. Hoppe, W. S. Zaoui, L. Rathgeber, Y. Wang, R. H. Klenk, W. Vogel, M. Kaschel, S. L. Portalupi, J. Burghartz, M. Berroth. Ultra-efficient silicon-on-insulator grating couplers with backside metal mirrors. IEEE J. Sel. Top. Quantum Electron., 26, 8200206(2019).

[10] D. Taillaert, P. Bienstman, R. Baets. Compact efficient broadband grating coupler for silicon-on-insulator waveguides. Opt. Lett., 29, 2749-2751(2004).

[11] Z. Zhang, X. Chen, Q. Cheng, A. Z. Khokhar, X. Yan, B. Huang, H. Chen, H. Liu, H. Li, D. J. Thomson, G. T. Reed. High-efficiency apodized bidirectional grating coupler for perfectly vertical coupling. Opt. Lett., 44, 5081-5084(2019).

[12] X. Chen, C. Li, C. K. Y. Fung, S. M. G. Lo, H. K. Tsang. Apodized waveguide grating couplers for efficient coupling to optical fibers. IEEE Photon. Technol. Lett., 22, 1156-1158(2010).

[13] L. He, Y. Liu, C. Galland, A. E. J. Lim, G. Q. Lo, T. Baehr-Jones, M. Hochberg. A high-efficiency nonuniform grating coupler realized with 248-nm optical lithography. IEEE Photon. Technol. Lett., 25, 1358-1361(2013).

[14] A. Bozzola, L. Carroll, D. Gerace, I. Cristiani, L. C. Andreani. Optimising apodized grating couplers in a pure SOI platform to −0.5 dB coupling efficiency. Opt. Express, 23, 16289-16304(2015).

[15] R. Marchetti, C. Lacava, A. Khokhar, X. Chen, I. Cristiani, D. J. Richardson, G. T. Reed, P. Petropoulos, P. Minzioni. High-efficiency grating-couplers: demonstration of a new design strategy. Sci. Rep., 7, 16670(2017).

[16] Z. Zhang, X. Chen, Q. Cheng, A. Z. Khokhar, Z. Zhang, X. Yan, B. Huang, H. Chen, H. Liu, H. Li, D. J. Thomson. Two-dimensional apodized grating coupler for polarization-independent and surface-normal optical coupling. J. Lightwave Technol., 38, 4037-4044(2020).

[17] C. Chang, Y. Hsu, H. Kuo, Y. Lai. Subwavelength apodized grating coupler for silicon photonics waveguide coupling. Opto-Electronics and Communications Conference, 1-3(2020).

[18] Z. Zhang, K. Zhang, Q. Cheng, M. Li, T. Liu, B. Huang, Z. Zhang, H. Liu, H. Li, P. Niu, H. Chen. High-efficiency two-dimensional perfectly vertical grating coupler with ultra-low polarization dependent loss and large fibre misalignment tolerance. IEEE J. Quantum Electron., 57, 8400407(2021).

[19] M. Fan, M. A. Popović, F. X. Kärtner. High directivity, vertical fiber-to-chip coupler with anisotropically radiating grating teeth. Conference on Lasers and Electro-Optics (CLEO), CTuDD3(2007).

[20] Y. Tang, Z. Wang, L. Wosinski, U. Westergren, S. He. Highly efficient nonuniform grating coupler for silicon-on-insulator nanophotonic circuits. Opt. Lett., 35, 1290-1292(2010).

[21] C. Alonso-Ramos, P. Cheben, A. Ortega-Moñux, J. H. Schmid, D.-X. Xu, I. Molina-Fernández. Fiber-chip grating coupler based on interleaved trenches with directionality exceeding 95%. Opt. Lett., 39, 5351-5354(2014).

[22] D. Benedikovic, C. Alonso-Ramos, P. Cheben, J. H. Schmid, S. Wang, D.-X. Xu, J. Lapointe, S. Janz, R. Halir, A. Ortega-Moñux, J. G. Wangüemert-Pérez, I. Molina-Fernández, J.-M. Fédéli, L. Vivien, M. Dado. High-directionality fiber-chip grating coupler with interleaved trenches and subwavelength index-matching structure. Opt. Lett., 40, 4190-4193(2015).

[23] D. Benedikovic, C. Alonso-Ramos, D. Pérez-Galacho, S. Guerber, V. Vakarin, G. Marcaud, X. Le Roux, E. Cassan, D. Marris-Morini, P. Cheben, F. Boeuf, C. Baudot, L. Vivien. L-shaped fiber-chip grating couplers with high directionality and low reflectivity fabricated with deep-UV lithography. Opt. Lett., 42, 3439-3442(2017).

[24] L. Cheng, X. Mu, S. Wu, X. Tu, H. Y. Fu. Perfectly vertical grating coupler for O and C-band. Frontiers in Optics + Laser Science APS/DLS, JW4A.57.S(2019).

[25] S. Khajavi, D. Melati, P. Cheben, J. H. Schmid, Q. Liu, D. X. Xu, N. Y. Winnie. Compact and highly-efficient broadband surface grating antenna on a silicon platform. Opt. Express, 29, 7003-7014(2021).

[26] T. W. Ang, G. T. Reed, A. Vonsovici, A. G. Evans, P. R. Routley, M. R. Josey. Highly efficient unibond silicon-on-insulator blazed grating couplers. Appl. Phys. Lett., 77, 4214-4216(2000).

[27] B. Wang, J. Jiang, G. P. Nordin. Embedded slanted grating for vertical coupling between fibers and silicon-on-insulator planar waveguides. IEEE Photon. Technol. Lett., 17, 1884-1886(2005).

[28] J. Schrauwen, F. Van Laere, D. Van Thourhout, R. Baets. Focused-ion-beam fabrication of slanted grating couplers in silicon-on-insulator waveguides. IEEE Photon. Technol. Lett., 19, 816-818(2007).

[29] L. Yu, L. Liu, Z. Zhou, X. Wang. High efficiency binary blazed grating coupler for perfectly-vertical and near-vertical coupling in chip level optical interconnections. Opt. Commun., 355, 161-166(2015).

[30] G. Roelkens, D. Van Thourhout, R. Baets. High efficiency silicon-on-insulator grating coupler based on a poly-silicon overlay. Opt. Express, 14, 11622-11630(2006).

[31] D. Vermeulen, S. Selvaraja, P. Verheyen, G. Lepage, W. Bogaerts, P. Absil, D. Van Thourhout, G. Roelkens. High-efficiency fiber-to-chip grating couplers realized using an advanced CMOS-compatible silicon-on-insulator platform. Opt. Express, 18, 18278-18283(2010).

[32] S. Yang, Y. Zhang, T. Baehr-Jones, M. Hochberg. High efficiency germanium-assisted grating coupler. Opt. Express, 22, 30607-30612(2014).

[33] J. C. Mak, W. D. Sacher, H. Ying, X. Luo, P. G. Q. Lo, J. K. Poon. Multi-layer silicon nitride-on-silicon polarization-independent grating couplers. Opt. Express, 26, 30623-30633(2018).

[34] A. Michaels, E. Yablonovitch. Inverse design of near unity efficiency perfectly vertical grating couplers. Opt. Express, 26, 4766-4779(2018).

[35] S. Hooten, R. G. Beausoleil, T. Van Vaerenbergh. Inverse design of grating couplers using the policy gradient method from reinforcement learning. Nanophotonics, 10, 3843-3856(2021).

[36] X. Tu, W. Xie, Z. Chen, M. F. Ge, T. Huang, C. Song, H. Y. Fu. Analysis of deep neural network models for inverse design of silicon photonic grating coupler. J. Lightwave Technol., 39, 2790-2799(2021).

[37] M. K. Dezfouli, Y. Grinberg, D. Melati, J. H. Schmid, P. Cheben, S. Janz, D. X. Xu. Design of fully apodized and perfectly vertical surface grating couplers using machine learning optimization. Proc. SPIE, 11689, 116890J(2021).

[38] X. Wen, K. Wu, Q. Song. Design of a barcode-like waveguide nanostructure for efficient chip-fiber coupling. Photon. Res., 4, 209-213(2016).

[39] X. Chen, C. Li, H. K. Tsang. Fabrication-tolerant waveguide chirped grating coupler for coupling to a perfectly vertical optical fiber. IEEE Photon. Technol. Lett., 20, 1914-1916(2008).

[40] L. Liu, J. Zhang, C. Zhang, S. Wang, C. Jin, Y. Chen, K. Chen, T. Xiang, Y. Shi. Silicon waveguide grating coupler for perfectly vertical fiber based on a tilted membrane structure. Opt. Lett., 41, 820-823(2016).

[41] L. Cheng, S. Mao, X. Tu, H. Y. Fu. Dual-wavelength-band grating coupler on 220-nm silicon-on-insulator with high numerical aperture fiber placed perfectly vertically. J. Lightwave Technol., 39, 5902-5909(2021).

[42] X. Zhou, H. K. Tsang. Optimized shift-pattern overlay for high coupling efficiency waveguide grating couplers. Opt. Lett., 47, 3968-3971(2022).

[43] M. K. Dezfouli, Y. Grinberg, D. Melati, P. Cheben, J. H. Schmid, A. Sánchez-Postigo, A. Ortega-Moñux, G. Wangüemert-Pérez, R. Cheriton, S. Janz, D.-X. Xu. Perfectly vertical surface grating couplers using subwavelength engineering for increased feature sizes. Opt. Lett., 45, 3701-3704(2020).

[44] D. Melati, Y. Grinberg, M. K. Dezfouli, S. Janz, P. Cheben, J. H. Schmid, A. Sánchez-Postigo, D.-X. Xu. Mapping the global design space of nanophotonic components using machine learning pattern recognition. Nat. Commun., 10, 4775(2019).

[45] Lumerical Solutions,. Lumerical Solutions. http://www.lumerical.com/products/

[46] F. Olyslager. Electromagnetic Waveguides and Transmission Lines Monographs in Electrical and Electronic Engineering(1999).

[47] F. Van Laere, T. Claes, J. Schrauwen, S. Scheerlinck, W. Bogaerts, D. Taillaert, L. O’Faolain, D. Van Thourhout, R. Baets. Compact focusing grating couplers for silicon-on-insulator integrated circuits. IEEE Photon. Technol. Lett., 19, 1919-1921(2007).

[48] A. Y. Piggott, J. Petykiewicz, L. Su, J. Vučković. Fabrication-constrained nanophotonic inverse design. Sci. Rep., 7, 1786(2017).

[49] A. M. Hammond, R. M. Camacho. Designing integrated photonic devices using artificial neural networks. Opt. Express, 27, 29620-29638(2019).

[50] S. So, Y. Yang, T. Lee, J. Rho. On-demand design of spectrally sensitive multiband absorbers using an artificial neural network. Photon. Res., 9, B153-B158(2021).