A Long‐Period Grating Formed by Residual Stress on Thin‐Film Lithium Niobate With Efficient Electro‐Optic and Thermo‐Optic Tuning

ABSTRACT We propose and demonstrate a long‐period waveguide grating with tunable resonant wavelength and contrast based on hybrid polymer and thin‐film lithium niobate platform. The grating is formed in the polymer cladding through stress‐induced refractive index modulation, achieved by a periodic metal structure on the cladding. This metal structure also acts as a heater for thermo‐optic (TO) tuning and an electrode for electro‐optic (EO) tuning. Thanks to the bidirectional index change provided by the EO effect, the device allows either red or blue shift of the resonant wavelength and control of the resonant contrast. The fabricated device exhibits a resonant contrast of 12.38 (19.65) dB at 1553.43 (1542.68) nm for the x ( z ) polarization, with EO tuning efficiencies of 20.2 (25.1) pm/V. Further annealing experiments reveal that its operation can switch from a stress‐dominated to a more linear, EO‐dominated regime. Consequently, applying +60 V increases the contrast from 24.18 to 31.86 dB, whereas −60 V completely suppresses the resonance; meanwhile, the EO tuning efficiency rises to 28.5 pm/V. Additionally, the grating achieves a maximum TO tuning efficiency of 18.6 pm/mW. Our proposed grating can be employed to implement tunable photonic devices in optical communications and information processing systems.