Abstract

We have proposed a polarization-independent directional coupler (DC) by using sections with optimal coupling strength designs on the lithium-niobate-on-insulator platform. With this design, arbitrary polarization-independent coupling ratio ranging from 0% to 100% can be achieved by tuning the length of the identical coupling region. The DC exhibits ultralow excess losses (${\lt} {0.1}\;{\rm{dB}}$) and polarization-dependent losses (${\lt}{0.05}\;{\rm{dB}}$ for the complete coupling) over a bandwidth of 100 nm. Moreover, the proposed DC is compact in size, simple in structure, and easy to fabricate.

© 2020 Optical Society of America

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