High-Frequency and High-Linearity Lithium Niobate Electro-optic Modulator

Thin-film lithium niobate has attracted extensive attention for microwave photonics because of its properties of large electro-optical coefficients, low optical loss, and excellent scalability. However, the linearity of electro-optic modulators especially in high-frequency regions becomes one of the bottlenecks for developing large-dynamic-range microwave photonics applications. Here, we propose and demonstrate a high-frequency and high-linearity electro-optic modulator based on a Fabry-Perot cavity-assisted Mach-Zehnder interferometer. The Fabry-Perot cavity consisting of asymmetric Bragg gratings works like a microring cavity but has large modulation efficiency because of avoiding bent waveguides. Spurious-free dynamic ranges of similar to 118.47, 108.75, and 97.92 dB<middle dot>Hz(4/5) are experimentally measured under modulation signals of 1, 10, and 20 GHz, respectively. Compared with a conventional Mach-Zehnder interferometer electro-optic modulator, improvements of nearly 20, 17, and 10 dB at modulation frequencies of 1, 10, and 20 GHz are realized, respectively. Therefore, the demonstrated high-frequency and high-linearity electro-optic modulation will find many microwave photonics applications such as filters, beam forming, and optoelectronic oscillations.