Ultraviolet optomechanical crystal cavities with ultrasmall modal mass and high optomechanical coupling rate.

Wen Zhou,Bingqing Zhu,Xiankai Sun,Jingwen Ma,Hon Ki Tsang,Zejie Yu

doi:10.1038/srep37134

Abstract

Optomechanical crystal (OMC) cavities which exploit the simultaneous photonic and phononic bandgaps in periodic nanostructures have been utilized to colocalize, couple, and transduce optical and mechanical resonances for nonlinear interactions and precision measurements. The development of near-infrared OMC cavities has difficulty in maintaining a high optomechanical coupling rate when scaling to smaller mechanical modal mass because of the reduction of the spatial overlap between the optical and mechanical modes. Here, we explore OMC nanobeam cavities in gallium nitride operating at the ultraviolet wavelengths to overcome this problem. With a novel optimization strategy, we have successfully designed an OMC cavity, with a size of 3.83 × 0.17 × 0.13 μm3 and the mechanical modal mass of 22.83 fg, which possesses an optical mode resonating at the wavelength of 393.03 nm and the fundamental mechanical mode vibrating at 14.97 GHz. The radiation-limited optical Q factor, mechanical Q factor, and optomechanical coupling rate are 2.26 × 107, 1.30 × 104, and 1.26 MHz, respectively. Our design and optimization approach can also serve as the general guidelines for future development of OMC cavities with improved device performance.

Highlights

Other wide-bandgap semiconductors, the prominent advantage of gallium nitride (GaN) is its bandedge emission covering the ultraviolet regime[27] for integrating optomechanics and optoelectronics[28] in a single device
We may refer to one side of the hole array as an “Optomechanical crystal (OMC) mirror”, whose reflection loss directly determines the intrinsic optical and mechanical Q factors
We aim at designing an OMC nanobeam cavity with the optical resonant wavelength around 400.00 nm, the mechanical modal mass around 20.00 fg, and the optomechanical coupling rate greater than 1.00 MHz. This is achievable through device downscaling and optimization in the entire parameter space, but we find it quite resource-demanding and time-consuming to find an OMC cavity with decent Q factors and optomechanical coupling rate simultaneously

Summary

Introduction

Other wide-bandgap semiconductors, the prominent advantage of GaN is its bandedge emission covering the ultraviolet regime[27] for integrating optomechanics and optoelectronics[28] in a single device. Composition, and doping technologies[29] have led to high-power laser diodes[30] and high-responsivity photodetectors[31,32] based on InGaN/GaN multi-quantum-well structures. It has been employed for the realization of passive photonic integrated circuits[33], ring resonators[34], and two-dimensional photonic crystal cavities[35,36]. In contrast to the previous implicit optimization methods[8,16,18], our approach provides a step-by-step guideline and is advantageous to fine tuning of the overall device performance, which applies to other wide-bandgap semiconductor platforms with similar refractive indices

Methods

Results

Conclusion