Abstract
Abstract Lithium niobate (LiNbO3) on insulator (LNOI) is a promising material platform for integrated photonics due to single crystal LiNbO3 film’s wide transparent window, high refractive index, and high second-order nonlinearity. Based on LNOI, the fast-developing ridge-waveguide fabrication techniques enabled various structures, devices, systems, and applications. We review the basic structures including waveguides, cavities, periodically poled LiNbO3, and couplers, along with their fabrication methods and optical properties. Treating those basic structures as building blocks, we review several integrated devices including electro-optic modulators, nonlinear optical devices, and optical frequency combs with each device’s operating mechanism, design principle and methodology, and performance metrics. Starting from these integrated devices, we review how integrated LNOI devices boost the performance of LiNbO3’s traditional applications in optical communications and data center, integrated microwave photonics, and quantum optics. Beyond those traditional applications, we also review integrated LNOI devices’ novel applications in metrology including ranging system and frequency comb spectroscopy. Finally, we envision integrated LNOI photonics’ potential in revolutionizing nonlinear and quantum optics, optical computing and signal processing, and devices in ultraviolet, visible, and mid-infrared regimes. Beyond this outlook, we discuss the challenges in integrated LNOI photonics and the potential solutions.
Highlights
Lithium niobate (LiNbO3, LN) is one of the most popular materials for electro-optic devices and nonlinear optical devices in the fast-growing field of integrated photonics [1]
This review focuses on the new physics, new methods, and new applications that LN on insulator (LNOI) and ridge structures bring to the field of integrated LN photonics
In addition to the applications we have reviewed, we envision integrated LNOI devices’ potential applications in high-performance nonlinear and quantum optics; devices in UV, visible, and mid-IR regimes; and optical computing and signal processing
Summary
Lithium niobate (LiNbO3, LN) is one of the most popular materials for electro-optic devices and nonlinear optical devices in the fast-growing field of integrated photonics [1]. As the development of metal-diffusing processes, titanium diffusion stood out and became the most commonly used one due to the fact that titanium diffusion can provide a relatively high refractive index contrast (~0.04) and a small effective diffusion depth (~1.6 μm) [8,9,10,11] Another traditional method for nanostructuring LN is proton exchange, which can achieve similar structure and performance as those provided by titanium diffusion [12,13,14]. Compared with titanium diffusion and proton exchange, ridge structure brings a high degree of flexibility to the fabrication of LN nanostructures Such flexibility enables fabricating waveguide on the submicrometer scale, and allows fabricating various structures, such as microring, periodically poled LN (PPLN) [40], and photonic crystal [41]. This section discusses the challenges in integrated LN photonics and the potential solutions
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