par Acharyya, Nirmalendu ;Kozyreff, Gregory
Référence Proceedings of SPIE - The International Society for Optical Engineering, 11364, 1136413
Publication Publié, 2020-04-02
Article révisé par les pairs
Résumé : With the advent of silicon and silicon nitride (Si3N4) whispering gallery mode (WGM) resonators, a high quality factor Q (> 1E6) can be achieved. These high Q cavities provide an ideal platform to study light-matter interactions. However, such high Q can only be achieved when the cavity radius is large compared to the operating wavelength. In small circular cavities, the bending losses, originating from the change in the direction of propagation of light, dominate. This radiation of energy from the cavity cannot be eliminated by improving the fabrication techniques and material quality. This is the biggest hurdle in reducing size of the WGM cavities, which is crucial for their efficient use as ultra-sensitive biosensors, sources of nonlinear effects and quantum optical sources. In all these application, a large Q/V ratio is essential to improve the performance. Here, we propose a new design in which a silicon nitride cavity of small radius (R ≤ 2µm) is encircled by one or more external shells. We show that by optimally choosing the thicknesses and the radii of the external shells, there can be dramatic reduction of the radiation of light from the inner cavity. In fact, Q as high as > 1E6 (only found in bare cavities of larger radii) can be obtained. The external shells, being ultra-thin cannot guide light and hence the mode is trapped in the inner cavity. Thus, the quality factor can be significantly enhanced keeping the small mode volume. Owing to the improved Q/V, applications in ultra-sensitive biosensing and the study of nonlinear effects is viable such unusually small cavities. Additionally, the proposed design can be fabricated with the existing state-of-the-art technology.

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