  Integrated lithium niobate (LN) photonics is a promising platform for future
chip-scale microwave photonics systems owing to its unique electro-optic
properties, low optical loss and excellent scalability. A key enabler for such
systems is a highly linear electro-optic modulator that could faithfully covert
analog electrical signals into optical signals. In this work, we demonstrate a
monolithic integrated LN modulator with an ultrahigh spurious-free dynamic
range (SFDR) of 120.04 dB Hz4/5 at 1 GHz, using a ring-assisted Mach-Zehnder
interferometer configuration. The excellent synergy between the intrinsically
linear electro-optic response of LN and an optimized linearization strategy
allows us to fully suppress the cubic terms of third-order intermodulation
distortions (IMD3) without active feedback controls, leading to ~ 20 dB
improvement over previous results in the thin-film LN platform. Our
ultra-high-linearity LN modulators could become a core building block for
future large-scale functional microwave photonic integrated circuits, by
further integration with other high-performance components like low-loss delay
lines, tunable filters and phase shifters available on the LN platform.
