High-Q nanobeam cavities on a silicon nitride platform enabled by slow light

Jiahao Zhan,Israel De Leon,Zeinab Jafari,Mario Dagenais,Sylvain Veilleux

doi:10.1063/5.0007279

Jiahao Zhan, Israel De Leon + Show 3 more

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https://doi.org/10.1063/5.0007279

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Abstract

Silicon nitride integrated photonic devices benefit from a wide working spectral range covering the visible and near-infrared spectra, which in turn enables important applications in bio-photonics, optical communications, and sensing. High-quality factor optical resonators are essential photonic devices for such applications. However, implementing such resonators on a silicon nitride platform is quite challenging due to the low refractive index contrast attainable with this material. Here, we demonstrate that silicon nitride photonic cavities comprising a slow-light waveguide bounded by mirrors can in principle exhibit quality factors in the order of several millions despite a relatively low refractive index contrast. We show that the energy stored in such a slow-light cavity exhibits a cubic dependence on the cavity length, which can enable extremely large quality factors with modest-length cavities. We present the design and experimental characterization of silicon nitride slow-light nanobeam-type cavities. Two sets of nanobeam cavities were fabricated to experimentally verify the cubic dependence of the Q factor on the cavity length. The highest measured Q factor in our devices is 4.42 × 105, which is limited by fabrication imperfections.

Highlights

IntroductionMost silicon nitride (SiN) nanobeam cavity designs to date have resorted to using suspended (air-cladded) architectures, reporting measured Q factors in the range of 104–105.15–17 the increased Q factors come at the cost of a more complex fabrication process and structural fragility
We report the design and experimental characterization of high-Q non-suspended nanobeam cavities fabricated on a 300-nm-thick silicon nitride (SiN) platform
The structures consist of 1D slow-light photonic crystal waveguides of various lengths bounded by Bragg mirrors

Summary

Introduction

Most SiN nanobeam cavity designs to date have resorted to using suspended (air-cladded) architectures, reporting measured Q factors in the range of 104–105.15–17 the increased Q factors come at the cost of a more complex fabrication process and structural fragility. A recent effort to tackle this problem has reported an encapsulated SiN nanobeam cavity design with theoretical and measured Q factors of ∼105 and 7000, respectively.. A recent effort to tackle this problem has reported an encapsulated SiN nanobeam cavity design with theoretical and measured Q factors of ∼105 and 7000, respectively.12 While this represents important progress, more work is still required to achieve Q factors comparable to those of suspended SiN or silicon nanobeam cavities while maintaining the device’s ease of fabrication and structural robustness A recent effort to tackle this problem has reported an encapsulated SiN nanobeam cavity design with theoretical and measured Q factors of ∼105 and 7000, respectively. While this represents important progress, more work is still required to achieve Q factors comparable to those of suspended SiN or silicon nanobeam cavities while maintaining the device’s ease of fabrication and structural robustness

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