High-efficiency spot-size converter for thin-film lithium niobate modulators

Yi Liu; Wei Chen; Yuhao Zhang; Keqi Cao; Yu Liu; Ming Li; Ninghua Zhu

doi:10.1117/12.2647519

23 January 2023 High-efficiency spot-size converter for thin-film lithium niobate modulators

Yi Liu, Wei Chen, Yuhao Zhang, Keqi Cao, Yu Liu, Ming Li, Ninghua Zhu

Proceedings Volume 12556, AOPC 2022: Optoelectronics and Nanophotonics; 125560Q (2023) https://doi.org/10.1117/12.2647519
Event: Applied Optics and Photonics China 2022 (AOPC2022), 2022, Beijing, China

Abstract

Lithium niobate on insulator (LNOI) electro-optic modulator has broad application prospects in rapidly developing largecapacity and high-density coherent optical communication systems, due to its small size, ultra-high bandwidth and low voltage. However, the high coupling loss currently limits its practical application. In this paper, in order to realize efficient coupling property, we propose a high-coupling-efficiency bilayer inverse tapered spot-size converter (SSC) that can be integrated with an LNOI modulator. The spot-size converter consists of three parts: a double-layer inverse tapered waveguide in LNOI, a straight LNOI-based waveguide and a SiON waveguide. We mainly consider end-surface coupling efficiency, abrupt loss and transmission efficiency. The simulation results show that the total coupling efficiency of the chip to the lensed fiber with a mode-spot diameter of 3.2 µm can achieve to 97.51%/96.3% for TE/TM light at a wavelength of 1550 nm. The coupler shows high coupling efficiency and good polarization independence. The 3dB alignment tolerance between fiber and coupler is estimated as ±1.4 μm/±1.4 μm in X/Z direction for TE light, and ±1.45 μm/±1.3 μm in X/Z direction for TM light. Our coupler shows relatively large alignment tolerances that makes the optical packaging of the LNOI modulator more reliable. The proposed high-efficiency spot-size converter in this work is of great significance for realizing the practical application of LNOI modulators.

Citation Download Citation

Yi Liu, Wei Chen, Yuhao Zhang, Keqi Cao, Yu Liu, Ming Li, and Ninghua Zhu "High-efficiency spot-size converter for thin-film lithium niobate modulators", Proc. SPIE 12556, AOPC 2022: Optoelectronics and Nanophotonics, 125560Q (23 January 2023); https://doi.org/10.1117/12.2647519

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KEYWORDS

Waveguides

Modulators

Tolerancing

Lithium niobate

Refractive index

Thin films

Waveguide modes

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