Photonic Metamaterial‐Inspired Polarization Manipulating Devices on Etchless Thin Film Lithium Niobate Platform

Photonic metamaterials interact with light at the micro–nano scale, enabling unprecedented optical manipulation capabilities, which play a key role in nonlinear optics, spin optics, negative index, and zero index materials. Recently, thin‐film lithium niobate on insulator (LNOI) has emerged as a promising platform for integrated photonics due to its unique material properties, including an excellent electro–optic effect, wide transparency window, and low waveguide losses. Metamaterial structures are promising for constructing novel integrated photonic circuit building blocks on LNOI as they can provide advantageous circuit functionality. In this work, as a proof of concept, high‐performance polarization manipulating devices including polarization splitter rotator (PSR), polarization rotator (PR), and polarizer are demonstrated using photonic metamaterials on the etchless LNOI platform by introducing a silicon nitride layer on the top of LNOI wafer as the loading material. In this way, full advantage of lithium niobate (LN) can be taken to achieve various high‐performance integrated photonic devices, while avoiding the etching of LN and simplifying the fabrication process greatly, which can bring bright prospects for achieving large‐scale lithium niobate integrated photonic circuits. High‐performance polarization manipulating devices including polarization splitter rotator, polarization rotator, and polarizer using photonic metamaterials are proposed and experimentally demonstrated in silicon nitride‐loaded lithium niobate on insulator. The metamaterials are used to control the coupling state of different polarizations, provide asymmetry in the vertical direction, and reduce the radiation loss at discontinuous interfaces.