Di Zhu, Linbo Shao, Mengjie Yu, Rebecca Cheng, Boris Desiatov, C. J. Xin, Yaowen Hu, Jeffrey Holzgrafe, Soumya Ghosh, Amirhassan Shams-Ansari, Eric Puma, Neil Sinclair, Christian Reimer, Mian Zhang, and Marko Lončar
Di Zhu,1,*
Linbo Shao,1
Mengjie Yu,1
Rebecca Cheng,1
Boris Desiatov,1
C. J. Xin,1
Yaowen Hu,1
Jeffrey Holzgrafe,1
Soumya Ghosh,1
Amirhassan Shams-Ansari,1
Eric Puma,1
Neil Sinclair,1,2
Christian Reimer,3
Mian Zhang,3
and Marko Lončar1,4
1John A. Paulson School of Engineering and Applied Sciences, Harvard University, 29 Oxford Street, Cambridge, Massachusetts 02138, USA
2Division of Physics, Mathematics and Astronomy, and Alliance for Quantum Technologies (AQT), California Institute of Technology, 1200 E. California Boulevard, Pasadena, California 91125, USA
3HyperLight Corporation, 501 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
Di Zhu, Linbo Shao, Mengjie Yu, Rebecca Cheng, Boris Desiatov, C. J. Xin, Yaowen Hu, Jeffrey Holzgrafe, Soumya Ghosh, Amirhassan Shams-Ansari, Eric Puma, Neil Sinclair, Christian Reimer, Mian Zhang, and Marko Lončar, "Integrated photonics on thin-film lithium niobate," Adv. Opt. Photon. 13, 242-352 (2021)
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 successes of manufacturing wafer-scale, high-quality thin films of LN-on-insulator (LNOI) and 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 has enabled ultra-low-loss resonators in LN, which has 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.
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From a variety of sources and some data may be incomplete. Discrepancies exist in the literature due to material composition, physical form, and growth method/condition.
Linear optical refractive indices are given at 1550 nm, with $o/e$ denoting ordinary/extraordinary axis.
Table 2.
State-of-the-Art -Factors of Some Representative Optical Cavities in the Thin-Film LN Platform, Noted by Their Cavity Type and Fabrication Method
MZM, Mach–Zehnder modulator; PM, phase modulator; IQ modulator, in-phase/quadrature modulator; MIM, Michelson interferometer modulator. ${V_\pi}$ and ${V_\pi} \cdot L$ refer to low-frequency (near-DC) values, and those for PMs are divided by 2 to match MZMs. All modulators were measured near 1550 nm.
Segmented CPW electrode.
Measured 1.8 dB EO roll-off at 50 GHz; extrapolated 3 dB EO bandwidth to be ${\sim}{{175}}\;{\rm{GHz}}$.
Not traveling wave.
Estimated from electrical bandwidth; measurement up to 500 GHz without significant roll-off from index mismatch.
Estimated based on Ref. [227].
Limited by measurement instrument; extrapolated to ${\gt}\;{{200}}\;{\rm{GHz}}$.
Estimated from calculation.
Table 4.
Representative Resonant EO Modulators Based on Thin-Film LN
From a variety of sources and some data may be incomplete. Discrepancies exist in the literature due to material composition, physical form, and growth method/condition.
Linear optical refractive indices are given at 1550 nm, with $o/e$ denoting ordinary/extraordinary axis.
Table 2.
State-of-the-Art -Factors of Some Representative Optical Cavities in the Thin-Film LN Platform, Noted by Their Cavity Type and Fabrication Method
MZM, Mach–Zehnder modulator; PM, phase modulator; IQ modulator, in-phase/quadrature modulator; MIM, Michelson interferometer modulator. ${V_\pi}$ and ${V_\pi} \cdot L$ refer to low-frequency (near-DC) values, and those for PMs are divided by 2 to match MZMs. All modulators were measured near 1550 nm.
Segmented CPW electrode.
Measured 1.8 dB EO roll-off at 50 GHz; extrapolated 3 dB EO bandwidth to be ${\sim}{{175}}\;{\rm{GHz}}$.
Not traveling wave.
Estimated from electrical bandwidth; measurement up to 500 GHz without significant roll-off from index mismatch.
Estimated based on Ref. [227].
Limited by measurement instrument; extrapolated to ${\gt}\;{{200}}\;{\rm{GHz}}$.
Estimated from calculation.
Table 4.
Representative Resonant EO Modulators Based on Thin-Film LN