Abstract

Optical microcavities are attractive with the generation of whispering gallery mode (WGM), while the high-Q cavity contains numerous degenerate WGMs with varying orbital angular momenta, which can result in instability of laser oscillation. The incorporation of gratings with higher-order Bragg diffraction patterns is often utilized in conjunction with microcavities to enhance coupling efficiency between incident light and WGMs, and to break degeneracy. Although such functional microcavities are commonly fabricated via top-down methods such as pho-tolithography as one-off pieces, utilizing bottom-up methods such as microdispensing is preferable when orienting towards photonic integrated circuits. However, the conventional dispensing method is quite difficult to make the functional microcavity because the grating period used in visible light or optical telecommunication wavelength bands becomes smaller than 1 µm that is almost the smallest size of microdispensed structure [1]. To meet this size constraint, nanodispensing technology is proposed in recent years, which utilizes the precision of force-controlled positioning in atomic force microscopy (AFM) in conjunction with the versatility of fluidics, thereby enabling the creation of functional and topographical features on a submicrometer scale [2]. In this work, we surmount the obstacle of the 1 µm size constraint by demonstrating the fabrication of second order diffraction grating patterns on Si₃N₄ optical microring (n = 2.04 at 1550 nm) via the utilization of nanodispensing technique.

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