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 ∼118.47, 108.75, and 97.92 dB·Hz4/5 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.