• Churaev, Mikhail
• Wang, Rui Ning
• Snigirev, Viacheslav
• Kippenberg, T. J.
• Tan, Zelin
• Bereyhi, Mohammadjafar
• Kuznetsov, Nikolai
• Siddharth, Anat
• Lihachev, Grigory
• Riemensberger, Johann
• Li, Zihan

Abstract

<jats:title>Abstract</jats:title><jats:p>Photonic integrated circuits are indispensable for data transmission within modern datacenters and pervade into multiple application spheres traditionally limited for bulk optics, such as LiDAR and biosensing<jats:sup>1</jats:sup>. New applications and higher performance are enabled by the diversification of optical waveguide materials past silicon-on-insulator. Of particular interest are ferroelectrics such as Lithium Niobate, which exhibit a large electro-optical Pockels effect enabling ultrafast and efficient modulation, but are difficult to process via dry etching<jats:sup>2</jats:sup>. For this reason, etching tightly confining waveguides - routinely achieved in silicon or silicon nitride - has not been possible. Diamond-like carbon (DLC) was discovered in the 1950s <jats:sup>3</jats:sup> and is a material that exhibits an amorphous phase, excellent hardness, and the ability to be deposited in nano-metric thin films. Its use today is pervasive, ranging from applications for hard disk surfaces <jats:sup>4</jats:sup> and medical devices <jats:sup>5</jats:sup> to low friction coatings for automotive components <jats:sup>6</jats:sup>. It has excellent thermal, mechanical, and electrical properties, making it an ideal protective coating. Here we demonstrate that DLC is also a superior material for the manufacturing of next-generation photonic integrated circuits based on ferroelectrics, specifically Lithium Niobate on insulator (LNOI). Using DLC as a hard mask, we demonstrate the fabrication of deeply etched, tightly confining, low loss photonic integrated circuits with losses as low as 4 dB/m and Q-factor as high as 10 · 10<jats:sup>6</jats:sup>. In contrast to widely employed ridge waveguides <jats:sup>7,8</jats:sup>, this approach benefits from a more than 1 order of magnitude higher area integration density while maintaining efficient electro-optical modulation, low loss, and offering a route for efficient optical fiber interfaces. As a proof of concept, we demonstrate a frequency agile hybrid integrated III-V Lithium Niobate based laser with sub-kHz linewidth and tuning rate of 0.7 Peta-Hertz per second with excellent linearity and CMOS-compatible driving voltage. Our approach can herald a new generation of high density ferroelectric photonic integrated circuits, in particular for applications in coherent laser based ranging <jats:sup>9</jats:sup> and beamforming <jats:sup>10</jats:sup>, optical communications <jats:sup>7</jats:sup>, and classical <jats:sup>11</jats:sup> and quantum computing networks <jats:sup>12</jats:sup>.</jats:p>

Topics

• density
• impedance spectroscopy
• surface
• amorphous
• Carbon
• phase
• thin film
• nitride
• hardness
• Silicon
• Lithium
• dry etching