Integrated photonics on thin-film lithium niobate (2102.11956v1)

Abstract: Lithium niobate (LN), an outstanding and versatile material, has influenced our daily life for decades: from enabling high-speed optical communications that form the backbone of the Internet to realizing radio-frequency filtering used in our cell phones. This half-century-old material is currently embracing a revolution in thin-film LN integrated photonics. The success of manufacturing wafer-scale, high-quality, thin films of LN on insulator (LNOI), accompanied with breakthroughs in nanofabrication techniques, have made high-performance integrated nanophotonic components possible. With rapid development in the past few years, some of these thin-film LN devices, such as optical modulators and nonlinear wavelength converters, have already outperformed their legacy counterparts realized in bulk LN crystals. Furthermore, the nanophotonic integration enabled ultra-low-loss resonators in LN, which unlocked many novel applications such as optical frequency combs and quantum transducers. In this Review, we cover -- from basic principles to the state of the art -- the diverse aspects of integrated thin-film LN photonics, including the materials, basic passive components, and various active devices based on electro-optics, all-optical nonlinearities, and acousto-optics. We also identify challenges that this platform is currently facing and point out future opportunities. The field of integrated LNOI photonics is advancing rapidly and poised to make critical impacts on a broad range of applications in communication, signal processing, and quantum information.

• The paper demonstrates that ion slicing and wafer-bonding techniques enable high-quality LNOI wafers for compact photonic circuits.
• The paper highlights enhanced electro-optic modulators that achieve over 100 GHz bandwidth with CMOS compatibility.
• The paper shows that advanced periodic poling and dispersion engineering boost nonlinear efficiencies for quantum optics and telecommunications.

Overview of Integrated Photonics on Thin-Film Lithium Niobate

The paper extensively reviews advancements and challenges in integrated photonics utilizing thin-film lithium niobate (LN) technology. LN, with its high electro-optic and nonlinear-optic coefficients, long-standing application history, and compatibility with various optical frequencies, has been a critical material for photonic technologies. This review covers the basics of LN material properties, nanofabrication techniques, potential integrated applications, and current developments, providing a comprehensive snapshot of this rapidly evolving field.

Materials and Fabrication

The ability to create high-quality lithium niobate on insulator (LNOI) wafers has significantly propelled the integration of LN into photonic circuits. The paper discusses how ion slicing and wafer-bonding techniques have been instrumental in producing these wafers, essential for realizing compact, high-performance photonic components ranging from waveguides to resonators. This development has facilitated the fabrication of low-loss optical waveguides, cavity structures, and various active and passive photonic elements, which are crucial for integrated optics.

Electro-Optics

The application of LN's electro-optic properties in modulators is a significant focus. The research highlights the enhancement achieved in thin-film LN modulators, which offer bandwidths over 100 GHz and operate at CMOS-compatible voltages. These modulators excel in optical communications, significantly outperforming traditional bulk LN devices in terms of size, power efficiency, and bandwidth. These advances pave the way for smoother integration of optical and electronic systems for high-speed data processing.

Nonlinear Optics

Thin-film LN also considerably impacts nonlinear optics, offering record-high efficiencies in frequency conversion processes, such as second-harmonic generation (SHG) and optical parametric oscillation (OPO). The paper underscores how innovations in periodic poling techniques and dispersion engineering can tailor the nonlinear responses of LN devices. These capabilities are vital for developing sources for quantum optics applications and broadband frequency combs, which have become indispensable tools in precision measurement and telecommunications.

Quantum and Hybrid Integration

Another critical area explored is the integration potential of LN with other material platforms, notably silicon photonics. The combination can leverage the advantages of both worlds: the mature fabrication processes of silicon and the superior optical properties of LN. Moreover, LN's role in advancing quantum photonics through efficient nonlinear processes and hybrid integration with quantum emitters and detectors is discussed, signifying its substantial potential in enabling scalable quantum information processing circuits.

Challenges and Future Outlook

Although LN exhibits promising traits for integrated photonics, several challenges exist. These include issues related to charge carrier effects, photorefraction under high optical powers, and the complexity of precise wafer-scale LN processing. The paper suggests that overcoming these hurdles will require continued progress in nanofabrication techniques, material enhancements, and innovative device designs.

In conclusion, the research on thin-film lithium niobate presents a compelling case for its expansive role in the future of photonic integration. Its use is set to extend across telecommunications, quantum technologies, and integrated optics, marking a transition into versatile and multifunctional optical systems. The paper recommends exploring further material improvements and hybrid integration strategies to fully leverage LN's capabilities in next-generation photonic applications. The synergy of industrial and academic efforts will be crucial in driving future developments in this domain.