Fabrication of lithium niobate metasurfaces via a combination of FIB and ICP-RIE

Chunyan Jin; Wei Wu; Lei Cao; Bofeng Gao; Jiaxin Chen; Wei Cai; Mengxin Ren; Jingjun Xu

doi:10.3788/COL202220.113602

Abstract

Lithium niobate (LN) metasurfaces have emerged as a new platform for manipulating electromagnetic waves. Here, we report a fabrication technique for LN nano-grating metasurfaces by combining focused ion beam (FIB) milling with inductively coupled plasma reactive ion etching (ICP-RIE). Steep sidewalls with angles larger than 80° are achieved. Sharp quasi-bound states in the continuum are observed from our metasurfaces. The measured transmission spectra show good agreement with the numerical simulations, confirming the high quality of the fabricated metasurfaces. Our technique can be applied to fabricate the LN metasurfaces with sharp resonances for various applications in optical communications, on-chip photonics, laser physics, sensing, and so on.

Lithium niobate ( ${LiNbO}_{3}$ , LN) is a key crystal material in photonics, which has comprehensive functional properties, such as optical harmonic generation, electro-optic, acousto-optic, and photorefractive properties^[1,2]. Particularly, thin-film LN on insulator (LNOI) has emerged in recent years as a new feasible platform for various integrated LN photonic applications, such as microcavity frequency comb^[3–5], waveguiding modulators^[6–12], ultracompact quantum light sources^[13,14], and on-chip spectrometers^[15]. Furthermore, as a typical artificial nano-structured material, the metasurfaces that are formed by engineered subwavelength building blocks known as meta-atoms have demonstrated the ability to control optical waves with unprecedented flexibility, providing a new promising solution for shrinking optical devices down to subwavelength dimensions. In the recent years, studies of LN metasurfaces have captured a growing interest, and various intriguing optical phenomena have been demonstrated, including structural color^[16], engineerable second harmonic generation^[17–21], enhanced electro-optic modulations^[22–24], and generation of entangled photon pairs^[25].