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Electro-optic tunable grating-assisted optical waveguide directional coupler in lithium niobate

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Abstract

In this paper, a high-performance electro-optical tunable grating-assisted directional coupler (GADC) is proposed and demonstrated experimentally. Our proposed GADC consists of a two-mode waveguide (TMW) and a single-mode waveguide (SMW) formed with lithium niobate (LN). By introducing a long-period waveguide grating into the side-wall of the TMW to compensate for the phase mismatch of the fundamental modes of the SMW and TMW, the fundamental modes of the two waveguides can be coupled efficiently each other at a specific wavelength. Furthermore, push–pull electrode structure is introduced to achieve the electro-optic (EO) tuning function featuring high speed, low driving voltage, and large tuning range. The best LN GADC we fabricated on x-cut LN substrate using annealing proton exchange process shows a high isolation of ~ 34 dB at 1532.9 nm wavelength, quite large EO tuning efficiency of 1.195 nm/V (1526.4–1549.1 nm) or 1.736 nm/V (1576.1–1602.2 nm), and a thermo-optic tuning efficiency of 0.128 nm/°C (22–60 °C). Our proposed LN GADC can find applications in the fields of high-speed tunable wavelength filtering, mode filtering, and EO modulation.

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Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the corresponding authors upon reasonable request.

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Acknowledgements

This research was supported by the grants from the National Natural Science Foundation of China (NSFC) (Grant Nos. 62075027, U20A20165), the Key R&D Program of Sichuan Province (Grant No. 2020YFSY0003), and the Key Technology R&D Program of Shenzhen (Grant No. JSGG20210802154413040).

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  1. School of Optoelectronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu, 611731, China

    Jun Hui Li & Kai Xin Chen

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JL and KC wrote the main manuscript text and prepared all figures. Both reviewed the manuscript.

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Correspondence to Kai Xin Chen.

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Li, J.H., Chen, K.X. Electro-optic tunable grating-assisted optical waveguide directional coupler in lithium niobate. Appl. Phys. B 129, 39 (2023). https://doi.org/10.1007/s00340-023-07986-0

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