Lithium Niobate (LN) does not exist in the natural world and is a purely artificial inorganic material. It is composed of lithium, niobium, and oxygen. People usually refer to LN as a distorted perovskite type of crystal. LN has many unique features, such as a wide operational wavelength window, electro-optic (Pockels) effect, nonlinear optical polarizability, acousto-optic (AO) effect, rare earth doping possibility, pyroelectric effect, etc. These effects are helpful for various applications, especially in photonics devices.
One of the unique features of lithium niobate is its high electro-optic (EO) coefficient, which makes it a good material of choice for an EO modulator. For example, bulk LN-based modulators with high speeds and superior linearity are valuable for typical fiber-optic communication systems.
Even though researchers have developed thin-film LN (TFLN) modulators with speeds up to 100Gb/s NRZ, it is possible to improve the speed further by shortening the Mach–Zehnder interferometer (MZI) arm length or using more advanced modulation schemes.
There are many performance metrics to characterize a modulator. It is usually challenging to achieve all the best metrics simultaneously. There is a lot of space to optimize the overall performance or enhance one specific metric to adapt these devices to different application scenarios. The strong EO effect of LN can realize high-performance modulators and benefit other areas where EO modulation shows advantages, such as the EO frequency comb.