Abstract
Recently, integrated photonics has attracted considerable interest owing to its wide application in optical communication and quantum technologies. Among the numerous photonic materials, lithium niobate film on insulator (LNOI) has become a promising photonic platform owing to its electro-optic and nonlinear optical properties along with ultralow-loss and high-confinement nanophotonic lithium niobate waveguides fabricated by the complementary metal–oxide–semiconductor (CMOS)-compatible microstructure engineering of LNOI. Furthermore, ferroelectric domain engineering in combination with nanophotonic waveguides on LNOI is gradually accelerating the development of integrated nonlinear photonics, which will play an important role in quantum technologies because of its ability to be integrated with the generation, processing, and auxiliary detection of the quantum states of light. Herein, we review the recent progress in CMOS-compatible microstructure engineering and domain engineering of LNOI for integrated lithium niobate photonics involving photonic modulation and nonlinear photonics. We believe that the great progress in integrated photonics on LNOI will lead to a new generation of techniques. Thus, there remains an urgent need for efficient methods for the preparation of LNOI that are suitable for large-scale and low-cost manufacturing of integrated photonic devices and systems.
Highlights
In contemporary society, the demand for highbandwidth optical communication, including for mobile high-definition video streaming, autonomous vehicle applications, remote surgery, telepresence applications, and interactive 3D virtual reality gaming, is sharp increasing[1–5]
The electro-optical modulator is the key component in optical fiber communication, which modulates the light signal for loading information through electricity
Optical modulation is realized by a voltage-induced refractive index change, which can be described by the change in the ellipsoid of the refraction index influenced by an external electric field as Δβij 1⁄4 γijk Ek þ hijklEk El þ 1⁄4, where Δβij is the variation in the dielectric impermeability under the external electric field (E), γijk is the linear electro-optic coefficient or Pockels coefficient, and hijkl is the quadratic electro-optic coefficient or Kerr coefficient
Summary
Ferroelectric domain engineering of LN crystals has been extended from 1D to 2D and 3D, which was comprehensively reviewed in reference[9]. Most integrated photonic circuits have been built on four key platforms: indium phosphide[24,25], silicon-oninsulator (SOI)[26–28], silicon nitride[25,29], and LN30,31. The selection of a material platform is based on the functionality of the optical components in the circuit, a low propagation loss, and industry-compatible fabrication processes[18]. The compatibility of silicon integrated circuit manufacturing is the main reason for the development of silicon photonics[32]. On-chip generation and manipulation of entangled photons based on annealed proton exchanged waveguide circuits integrated on a zcut PPLN crystal was demonstrated[36]. Nanophotonic LN waveguides with a larger refractive index contrast and a smaller optical mode size have emerged as a branch of integrated lithium niobate photonics[37–40], LN was perceived as a difficultto-etch material.
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